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国际工程科技发展战略高端论坛 InternationalTop levelForumonEngineering ScienceandTechnologyDevelopmentStrategy 膜技术在水和气体净化中 的应用 MO JISHU ZAISHUIHE QITIJINGHUA ZHONG DE YINGYONG MEMBRANETECHNOLOGYFORGAS ANDLIQUIDSEPARATIONSAND PURIFICATIONS

膜技术在水和气体净化中 的应用...工程院编著.--北京:高等教育出版社,2014.10 (国际工程科技发展战略高端论坛) ISBN978-7-04-041258-1

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书书书

国际工程科技发展战略高端论坛InternationalTop-levelForumonEngineeringScienceandTechnologyDevelopmentStrategy

膜技术在水和气体净化中

的应用MOJISHUZAISHUIHEQITIJINGHUAZHONGDEYINGYONG

MEMBRANETECHNOLOGYFORGASANDLIQUIDSEPARATIONSANDPURIFICATIONS

内容提要

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膜技术在水和气体净化中的应用 :汉英对照 /中国工程院编著. -- 北京 :高等教育出版社,2014.10

(国际工程科技发展战略高端论坛)

ISBN978-7-04-041258-1

Ⅰ.①膜… Ⅱ.①中… Ⅲ.①薄膜技术 -应用 -净水 -汉、英②薄膜技术 -应用 -空气净化 -汉、英 Ⅳ.①TU991.2②X51

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编辑委员会

主 任曹湘洪

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黎念之 高从!

目  录

第一部分 综述

膜技术在水和气体净化中的应用国际高端论坛综述  3!!!!!!!!!!!!!!

第二部分 参会专家名单

参会专家名单  23!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

第三部分 主题报告及报告人简介

MembraneEngineeringforanInnovativeProcessEngineering EnricoDrioli,etal. 27!!!

SurveyontheDevelopmentofMembraneScienceandTechnologyinChina

WanqinJin,etal. 48!!!!!!!!!!!!!!!!!!!!!!!!!!

MembranesandWater—RecentDevelopments TonyFane,etal. 58!!!!!!!!!!

饮用水安全问题与膜法水处理技术进展 侯立安 等 70!!!!!!!!!!!!!!

纳滤膜法处理和回收废水中低浓度全氟辛酸铵 万印华 等 83!!!!!!!!!!!

LargeScaleGasandVaporSeparationsUsingMembranes—APragmaticPerspective

WilliamJ.Koros 96!!!!!!!!!!!!!!!!!!!!!!!!!!!

PreparationandApplicationofZeoliteMembranesinPervaporation XuehongGu 132!!!

Nanoparticles(andNanotubes)inMembranesforLiquidandGasSeparations:ABriefOverview

KamaleshK.Sirkar 139!!!!!!!!!!!!!!!!!!!!!!!!!

StudyandApplicationofCO2SeparationMembranes YimingCao,etal. 163!!!!!!

AntiproteinfoulingStrategyinMicrofiltrationandUltrafiltrationMembranes:AMinireview

Focusingon“Graftingfrom”PolymerizationofZwitterions XiaolinWang,etal. 183!!

InvestigationsandApplicationsofNewTypeIonExchangeMembranes T.W.Xu,etal. 206!!

后记  215!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

书书书

第一部分

综  述

膜技术在水和气体净化中的应用国际高端论坛综述

一、引  言

2013年10月16-17日,由中国工程院主办的“膜技术在水和气体净化中的

应用”国际高端论坛在中国科学院过程工程研究所举行。中国工程院院士高从

!

、侯立安、曹湘洪参加论坛,来自海外以及全国相关科研院所及高校的 160多名

代表参加了这一膜技术领域的高端盛会。

本次论坛特邀了美国工程院院士 NormanLi、美国膜材料协会主席及美国工

程院院士 WilliamJ.Koros、欧洲膜材料协会主席 EnricoDrioli等在膜技术研究领

域有影响力的知名专家学者到会作主旨报告,以膜技术在水和气体净化中的应用

为主题,重点就膜过程、膜材料、膜应用等研究领域的最新进展进行专题报告。欧

洲膜材料协会主席 EnricoDrioli和新加坡膜技术中心教授 TonyFane针对新型膜

过程,如膜蒸馏、正渗透、膜乳化、膜冷凝、膜结晶等的最新研究进展进行了深入讲

解;美国工程院院士 WilliamJ.Koros针对气体分离膜材料和气体分离膜应用等进

行了全面介绍。

与会中外专家学者就膜技术在污水回用领域的应用、海水淡化采用膜技术的

经济性、气体膜在石化领域的应用以及未来膜技术的发展趋势等问题进行了深入

研讨。

膜技术在水和气体净化领域的应用是全球的发展趋势。各种耦合技术,如反

渗透与正渗透耦合以降低能耗和产水成本、反渗透与膜蒸馏技术的耦合以实现零

排放为目标将是未来膜技术在污水回用领域的发展趋势。未来对膜过程的研究

主要是如何降低膜过程的能耗。

二、报告内容

(一)膜过程———创新的过程工程

1膜技术在过程强化中的应用

目前,膜工程对各个领域的影响不断增加。海水和苦咸水脱盐、工业水的回

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

用、废水处理、气体分离、膜生物反应器(MBR)、人工合成有机物工业均为膜过程

成功的典型案例。其他膜过程,如 MBR被认为是最可行的技术。膜成功应用的

动力在很大程度上源自膜的基本特性,如节能、环境影响小、无化学试剂及易于自

动化等。这与过程强化战略紧密相关。

目前,全球所面临的关键问题是如何维持工业的稳定增长,过程强化是可行

的解决方案,膜在过程强化中起到重要作用。它具有替代传统能量强化技术的潜

力,实现特种组分的选择性和高效传递,提高反应过程性能。在膜的运行系统中,

反渗透(RO)膜系统的脱盐效率是热法的 10倍;MBR的紧凑程度是传统淤泥法

的5倍多;燃料电池与 RO单元组合的效率是热法的16倍。

海水脱盐所用膜的产能为430亿t/d,占整个脱盐市场的63%,脱盐市场不断

增长,其中海水反渗透脱盐将占到反渗透脱盐技术的80%。

2绿色、环境友好的溶剂/稀释剂

在过去的30年中,聚偏氟乙烯(PVDF)作为制备膜的合适材料,已广泛用于

制备 MF/UF膜。PVDF膜的制备方法为相转化法。相转化包括非溶剂诱导相转

化(NIPS)和热致相分离(TIPS)。近年来,通常采用 TIPS法制备 PVDF膜。

在用 TIPS法制备 PVDF膜的过程中,稀释剂非常重要,其影响 PVDF膜的形

态、结构和性能。在高温下用 TIPS法制备膜的合适稀释剂,应该与聚合物有相容

性、具低挥发性和良好的热稳定性。另外,稀释剂相对分子质量较低、低毒及环境

友好。EnricoDrioli教授在报告中总结了 1990—2012年相关文献用 TIPS法制备

膜的稀释剂,如邻苯二甲酸酯、邻苯二甲酸二辛酯(DOP)、人造的酞酸二丁酯、二

苯(甲)酮、碳酸二苯酯等。

意大利国家研究理事会膜技术研究所的 EnricoDrioli教授带领他的课题组用

广泛接触食物类聚合物(聚乳酸)的增塑剂乙酰基柠檬酸三丁酯(ATBC)作为制

备 PVDF的稀释剂。ATBC为水性和油性聚合的增塑剂,这些聚合物包括丙烯酸、

甲基丙烯酸等聚合物体系。与 DOP相比,制备硝酸纤维素薄膜时,它有许多改

进,如低毒、寿命长。

3膜技术发展的新型膜过程

膜蒸馏:膜技术与蒸馏过程相结合的膜分离过程,它以疏水微孔膜为介质,在

膜两侧蒸气压差的作用下,料液中挥发性组分以蒸气形式透过膜孔,从而实现分

离的目的。膜蒸馏的优势有:理论上的 100%截留率;占地面积小、结构紧凑、建

设费用低;操作温度低、可利用废热、操作压力低,设备投资少,过程更安全、更容

易操作等。

膜结晶:由膜蒸馏发展而来。与传统结晶技术相比,膜结晶的优势主要有:传

膜技术在水和气体净化中的应用国际高端论坛综述

质面积大、诱导周期短、能够优化控制过饱和程度、异相成核的表面效应、由于聚

合物膜表面导致成核自由能的降低、可控制低过饱和程度下的晶体成长速率、可

控制晶型、晶体尺寸均一、晶体尺寸分布窄。膜结晶过程主要用于生产催化剂晶

体以及无机、有机或生物材料的结晶,用于耐溶剂结晶过程、选择性的多晶形物结

晶等。

膜乳化:膜乳化技术是1988年由日本科学家提出的新型乳化方法,该法是在

一定的压力下,将分散相通过微孔膜分散到连续相中,其显著特点是乳状液液滴

大小主要由微孔膜孔径来控制而呈单分散性。与传统乳化技术相比,膜乳化的优

势有:能耗低、制备条件温和、可形成单分散胶团/微粒、胶团/微粒尺寸和形状均

匀、通过改变膜孔尺寸和操作条件可以调控胶团/微粒的大小等。膜乳化作为一

种新型的乳状液制备技术,可以制备各种类型粒径的单分散乳状液。膜乳化过程

在食品乳状液、药物控释系统、单分散微球(囊)的制备等诸多领域有着广泛的应

用前景。

膜冷凝:作为一种清洁的单元操作,膜冷凝可以作为废气的一种预处理手段,

如作为 CO2废气进入另一个膜单元之前的预处理手段。与致密膜相比,膜冷凝操

作压力低;与常规冷凝相比,膜冷凝没有腐蚀现象。

目前,耦合膜过程优势明显,其中,FO-RO耦合脱盐过程备受关注,该过程

的分离原理是,待处理废水经过适当预处理后,泵入 FO单元的进料液侧,将经过

适当预处理的海水泵入 FO单元的驱动液侧,通过 FO膜,进料液侧待处理废水中

的水通过 FO膜进入到驱动液侧的海水中,进料液侧的废水被浓缩,而海水被不

断稀释,被稀释后的海水再泵入反渗透系统进行处理,通过 RO,获得产品水和 RO

浓水。该过程的技术目标是实现电耗低于 25kW·h/m3,主要通过三方面实现:

① 将水回收率再提高30%;② 浓水再减少30%;③ 产水的价格实现06美元/t。

该耦合过程的研究重点主要集中在:① FO-RO耦合过程的研究(包括原理、系

统设计、系统结构等);② 新型 FO/RO膜材料的研究;③ 污染控制技术研究;④

预处理技术研究。

此外,MD/PRO耦合脱盐过程也是一个研究热点,常规海水脱盐系统的回收

率小于 40% ~50%,通过这一耦合过程,可以处理反渗透海水淡化后的高含盐

水,可将高含盐水排放量减少到30%,能量回收 5W/m2,实现水和能量资源的高

效利用。

目前,GE正在开展采用膜蒸馏技术浓缩高盐度废水(TDS150~230g/L)项

目,膜蒸馏过程中没有膜性能的下降和膜结垢现象,目前 GE正在寻找合适的试

验地点,预计2014年膜蒸馏有可能会实现商业化模式运行。

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

4未来努力方向

为了适应主体和环境的变化,开发一系列新的、不同性能的膜。巧妙的质量/

热传递规律;对危险环境(如军事、极限运动、空间站等)的自我维护及适应性;抗

污染性、可冲洗性及自清洁性;对有害液体、辐射热、紫外及化学和生物试剂有更

高的防护性;膜保护层的自修复;在极端环境和运行条件中具有更好的力学性能

和耐化学性;膜用于长距离通信、数据存储和检测的传感器;开发预测材料的性能

的模型。

(二)中国膜科学技术发展的概况

1膜技术在中国的发展历史

中国膜技术始于20世纪50年代,在90年代后期得到迅速发展,90年代 RO/

NF膜技术已经由实验室研究转向中试化研究,此时开始进行气体分离膜方面的

研发,对于氮气、氢气的分离已取得较好的效果,还有一些专家进行了渗透蒸发、

膜蒸馏、膜反应器等方面的研究,从 2000年到目前,膜科技在中国取得了显著进

步,出现了一些新的膜材料(PVDF、PES、PP等)、制备方法(NIPS、TIPS等)、新的

膜过程(MD/MBR)等。

2中国膜科学技术的现状

最近几年,膜分离技术的发展得到了国家相关部门的高度重视,国家重点基

础研究计划(“973”、“863”)和国家自然科学基金项目均对膜研究给予专项资金

支持,从而使得我国的膜分离技术取得很好的成就。目前,中国膜研究机构及公

司有1000多家,约有300多家公司可以生产膜,如膜天、赛诺等;研发成果也已经

在工业处理、海水淡化等领域得到应用。

3典型膜技术

(1)MF/UF

主要介绍了两种材质的膜,即 PVDF和 PVC,PVC膜由于具有优良的化学稳

定性、成本低,且具有较高的性能,被广泛应用,此膜材料主要采用 NIPS方法进行

制备。台湾高雄自来水厂采用海南立癉公司生产的 PVC超滤膜建成亚洲最大的

超滤自来水生产厂,规模达到30m3/d。结合膜天公司采用 TIPS法生产的 PVDF

超滤膜,介绍了 TIPS膜制备方法的发展。TIPS膜制备方法的关键是选择合适的

溶液完成 PVDF膜的液液分离。

(2)NF/RO

由均苯三酰氯与芳香二胺通过界面聚合形成聚酰胺复合膜是目前海水淡化

反渗透膜的主要制备方法。我国长春应用化学研究所自行设计制备的基于联苯

膜技术在水和气体净化中的应用国际高端论坛综述

四酰氯(BTEC)、联苯三酰氯(BTRC)、芳香三胺(TAM)等新型单体的新的聚酰胺

膜材料,突破了由均苯三酰氯(TMC)与芳香二胺制备反渗透复合膜的限制,研究

结果表明基于三胺单体的反渗透复合膜,TMC膜比 MPD膜水通量提高近 30%,

为进一步优化成膜工艺制备提供可产业化的新型反渗透复合膜奠定基础。目前

我国生产的反渗透膜元件达到国外先进水平,市场的占有率也在逐步增长,初步

具备与国际抗衡的水平。

(3)气体分离膜

已应用于气体分离领域的高分子材料有 PDMS,PI,PMP,PPO,PT等,中国科

学院大连化学物理研究所与中海油合作,将膜分离技术用于低品位天然气中回收

甲烷、轻质油及液化气,总投资近500万,年处理量为 1360万 Nm3,解决了单井气

田气源不稳定、CO2含量高(80%以上)等技术难点。

(4)其他一些典型的膜材料

A沸石分子筛膜

沸石分子筛膜是将沸石制备成厚度为微米级的薄膜,实现分子的分离,重点

介绍了 NaA型和 MFI型沸石膜。国内不少大学都在研究沸石膜的制备,不过目

前尚未有工业应用实例,到目前为止,仅日本某企业在 20世纪 90年代成功建成

并投产了一套 NaA沸石膜的工业装置,该装置用于醇/水分离。

B金属膜

金属膜具有良好的塑形、韧性和强度以及对环境和物料的适应性,因此得到

关注。主要是钯膜、多孔 Ti-Al、Fe-Al复合膜等。

4在中国膜技术发展趋势及其面临的挑战

国家“十二五”计划将重点扶持膜科技发展,膜产值到2015年要达到1000亿

元,所以中国膜技术发展空间很大,极具潜力。

提到膜科技发展基础研究方面的三个问题:

1)如何通过环境与分离性能关系提升膜过程的工艺设计水平;

2)如何通过分离性能与材料结构关系将膜过程的设计从工艺设计推进到微

观结构的设计;

3)在应用过程中膜的浓差极化。

(三)膜和水的发展现状

目前新加坡获取淡水资源的途径主要有以下三方面:雨水收集、海水淡化和

废水回收。其中,雨水收集系统主要处理的是地表水资源,采用微滤膜(MF)和超

滤膜(UF)过滤技术;海水淡化采用的是反渗透(RO)脱盐技术,过滤成本较大;工

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

业和生活废水的回收采用反渗透或是纳滤技术(NF)过滤二级处理水,以节约成

本。这三种水处理技术均是通过膜技术来实现。膜技术已经成为新加坡获取淡

水资源的中坚力量。从 TonyFane教授提供的数据可以看到,2010年新加坡通过

海水淡化技术为其国内提供了 10%的水资源,而 2060年这一数字将提高到

30%;另外,在2010年新加坡通过废水回收技术为其国内提供了 30%的水资源,

而2060年这一数字将提高到50%。现在,每天通过膜技术处理的水量已经达到

了1Mt,对于新加坡如此小的国土面积,这样的处理能力可谓相当可观。

1新型膜和膜过程

(1)反渗透

反渗透(RO)技术是目前海水淡化工厂最常采用的工艺。近年来建造的海水

淡化工厂规模越来越大。更多的处理量要求意味着更大的膜组件,对膜通量的要

求也更高,这些方向也是膜科学中心的研究热点。目前提高膜通量的一种研究方

向是在膜片中添加带有孔道的纳米物质,比如碳纳米管、沸石、石墨筛等无机材

料。另外一种是根据仿生学原理,在反渗透薄膜中添加水通道蛋白,这种方法对

膜通量性能的提高非常明显,从而减少水处理工厂的能源浪费。但是由于浓差极

化(CP)的影响,膜片通量的提高并不意味着膜组件通量的提高。为了降低浓差

极化的影响,需要改进膜组件的设计,比如对导流网的重新设计、膜组件之间连接

方式的改进等。

(2)正渗透

正渗透(FO)的低能耗和能量回收优势,使其成为一个热点问题,它是一种依

靠渗透压驱动的膜分离过程,即水通过选择性半透膜从较高水化学势区域(低渗

透压侧)自发地扩散到较低水化学势区域(高渗透压侧)的过程。正渗透过程的

驱动力是驱动液与原料液的渗透压差,不需要外加压力作为驱动力。与反渗透过

程相比,正渗透具有如下优点:膜污染较轻、无需外加压力、能耗低、回收率高、浓

水排放量少、污染小、环境友好。在 FO过程中,膜是一个关键因素。近来,SMTC

已经制备出用于 FO过程的平板膜和中空纤维膜。

(3)膜蒸馏

膜蒸馏(MD)凭借其高水回收率、高脱盐率而备受关注,它能处理反渗透不

能处理的高盐水,并且可利用工业废热。膜蒸馏是采用微孔疏水膜,以膜两侧蒸

汽压差为驱动力的一种新型膜分离过程。它可以算是迄今为止脱盐效率最高的

膜技术。膜蒸馏所用的膜为不被待处理溶液润湿的疏水微孔膜,即只有蒸汽能够

进入膜孔,液体不能透过膜孔。用于膜蒸馏过程的膜需要有强疏水性和高孔隙

率,目前 SMTC已开发了超疏水膜蒸馏膜的制备技术。

膜技术在水和气体净化中的应用国际高端论坛综述

(4)延迟渗透

将正渗透膜稍微改进,就可用于延迟渗透(PRO)膜过程。PRO过程可以根

据盐梯度产生能量,如根据海水/河水的含盐量梯度,用于海水/河水处理。近来,

SMTC已经制备出用于 PRO过程的平板膜和中空纤维膜。

(5)膜蒸馏结晶

膜蒸馏结晶(MDC)是由膜蒸馏演变而来,对于经过反渗透海水淡化后的浓

水以及其他的浓缩盐类,可以通过膜蒸馏结晶处理来分别回收水分和盐类固体。

膜蒸馏结晶过程的两个难点是需要将结晶过程控制在膜组件外部结晶,并且需要

优化整个过程的能量利用。过程的权衡以及优化控制可以采用 Aspen模拟软件

模型模拟。

(6)新型膜生物反应器(MBRS)

SMTC在常规膜生物反应器的基础上,正在致力于开发新型膜生物反应器,

如膜蒸馏生物反应器(MDBR)和正渗透生物反应器(FOBR)。MDBR和 FOBR均

是具有高截留率的膜生物反应器(HRMBR),它们采用特种膜,都可以在ORT>>

HRT下运行,为难降解物质的处理提供充分时间。这两种膜生物反应器的优势

是都可以利用低温热、产水水质更好。HRMBR的特点是盐类可以大量累积,这

样就需要适盐菌。此外,MDBR也需要最低能耐 55℃的嗜热菌。MBR也改进为

流化床厌氧膜生物反应器,流化床厌氧膜生物反应器的优势是污染少、沼气量小。

另外,萃取膜生物反应器可用于进料废水里有机溶剂的萃取过程。接下来几年

内,MBR+RO将成为污水处理回用的发展趋势。

2未来的展望

膜法污水回用是全球的发展趋势,膜法污水回用过程中,RO仍是主导,但是

在反渗透膜、膜组件以及操作模式上尚需改进和提高。FO和 MD凭借其能量再

生优势,在水回用方面的作用越来越突出。

未来对膜过程的研究主要是如何降低膜过程的能耗。未来的主要研究方向

主要集中在:① 低能量消耗的预处理工艺;② 高通量反渗透膜的制备;③ 耦合工

艺,如 FO-RO-PRO的发展;④ 新型污染控制技术的开发;⑤ 厌氧工艺的使用;

⑥ 苦咸水浓缩。上述问题的解决,可有效提高膜技术在水回用领域的优势。

(四)我国饮用水安全及膜法水处理应用现状

1饮用水安全概述

世界卫生组织(WHO)调查资料显示,全世界约 80%的疾病和 50%的癌症与

饮用不洁的水有关。当今,中国工业高速发展,人民享受经济发展的成果,然而,

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

我国的环境日益成为最重要的问题,特别是水资源安全。没有安全的水资源社会

的可持续发展无法实现。在中国,饮用水安全包括两个方面:一个是在特定时间

和区域因为大雨从而导致洪水泛滥;另一个是由于污染或干旱导致水资源短缺。

在过去的20年里,中国的洪水灾害不断增加,如何使用雨水作为饮用水,特

别是在雨期,是一个热点问题。在干旱地区,地下水是最重要的饮用水来源,但一

些二价离子如砷和溴等将造成严重的健康危害,需要除去这些有害物质。在中国

的东部和南部,虽然有很多河流和湖泊,但水污染很严重,污水处理和减少排放被

认为是保护水资源的两个有用的方法。

2饮用水安全面临的挑战

1)我国水资源总体现状堪忧:① 水资源匮乏;② 水资源分布不均;③ 地下

水水质恶化;④ 湖泊水质堪忧。

2)污染物种类多元化:① 悬浮物污染;② 氮磷有机物污染;③ 重金属污染;

④ 酸碱污染;⑤ 难降解有机物污染;⑥ 放射性物质污染;⑦ 热污染;⑧ 特种污

染物。

3)传统净水工艺面临新挑战:① 新污染物不断出现,污染日趋复杂,饮用水

呈现污染物复合、污染过程复合以及污染效应复合的复合污染特征;② 《生活饮

用水卫生标准》(GB5749—2006)全面实施,指标由35项增加到106项;③ 传统水

处理工艺以去除水中悬浮物、胶体颗粒物为主,对小尺寸污染物,去除能力有限。

3膜法水处理技术的发展及应用现状

基于上述现状和需求,许多膜技术用于水处理以保证饮用水的安全。在中

国,超滤过程被安装在超过数百个水处理厂中。例如,从 2009年起,10000m3/d

的超滤膜组件装置在太湖运行,50000m3/d的超滤装置在佛山市设计并建成。

反渗透是另一种用于脱盐的膜技术,但水处理的成本较高,在中国很少有水厂使

用。一些有机物不能被超滤脱除,反渗透可以将所有离子脱除,而纳滤可以脱除

大多数有机物和二价离子,其通量高于反渗透。因此,纳滤过程被用于制备饮用

水,一些小型的水厂也在北京、杭州等城市建成。将来,膜技术会更多的应用在非

饮用水供应和污水处理过程中,如果一些非技术因素可以被消除,如膜技术处理

的水允许进入管网系统,将缓解中国的水压力。

针对不同尺寸的污染物,可以使用不同类型的膜分离技术,特别适合于解决

当前我国饮用水污染物多元化的难题。膜法处理饮用水的热点问题主要包括:

① 增强膜的抗污染能力,延长使用寿命;② 膜法处理饮用水时,有益离子的保留

问题;③ 基于膜过程的组合工艺设计及应用。

由于饮用水中可能含有多种污染物,单一的膜法处理饮用水可能难以完全保

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膜技术在水和气体净化中的应用国际高端论坛综述

证水的安全性,组合工艺处理法仍是饮用水处理的常用方式,膜组合工艺应用的

实例———天津杨柳青水厂膜处理示范工程、曹妃甸 RO海水淡化示范工程、太阳

能动力膜过程系统、美国远途救援净水系统等。

4研究展望与建议

(1)新型膜工艺流程设计与优化

研发先进的膜处理组合工艺,优化协同不同工艺、方法,探索联合净化方法,

实现多种技术优势互补。

(2)膜与组件及过程的研发

① 研发抗污染、抗氧化、高通量、机械强度高、寿命长、价格低廉的新型膜材

料,如沸石分子筛、杂化材料、纳米材料、仿生材料、抑菌材料等;② 研发新型大单

元膜组件及新型膜组件组合方式,推动膜用于水净化及深度处理过程;③ 研究水

在膜内的传输机制和离子的截留机制等分离机制,反馈膜材料的设计。

(3)非传统水源的综合利用

非传统水资源的开发利用主要包括雨水利用、污水资源化及“海水开源”三

方面,传统水资源和非传统水资源的耦合互补利用,有利于解决饮用水供水矛盾。

(4)加快推进制度建设

加快推进制度建设包括用水总量控制制度、用水效率控制制度、水功能区限

制纳污制度、管理责任与考核制度等。

(5)建设膜产业科技强国

我国膜产业虽已进入了快速增长期,但与国际水平相比尚有较大差距,高性

能膜材料、膜组件等仍需进口,因此需要加大政策扶持力度、提升自主创新能力、

深化国际交流合作、加强人才队伍和平台建设。

(五)大型气体分离膜

膜技术在气体分离纯化领域中得以应用。论坛重点介绍了以膜技术作为主

要手段,实现高回报、高效分离的技术实例,其中包括天然气中高浓度酸性气体的

去除;膜诱导吸附法脱除烟道气中二氧化碳;丙烯和丙烷这两种难分离气体的分

离;以及页岩气中脱水工艺这一极有意义的研究方向。通过几个大规模使用膜技

术的实例来说明膜技术的成果,阐述气体膜应用未来的展望。

1膜的发展过程

20世纪60年代以来,以超滤和微滤为代表的第一代膜过程。多孔结构膜如

超滤和微滤的应用奠定了膜过程在工业领域应用的重要基础。

第二代膜过程催生的反渗透工艺,于 20世纪 60和 70年代开始兴起。反渗

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

透设施能源效率比蒸馏过程提高一个数量级。如今,其提供着 100亿 gal/d的淡

水,大约占据全球海水淡化市场份额的 60%(其市场份额还在提升,并将逐渐取

代热法)。之后,这些更先进的第二代膜可以区分自由水和水合的阳离子和阴离

子,在埃米级别的分子尺度上是实现分离。其能够识别的特征尺寸大约 6?,也

就是说可以截留大于该尺寸的所有物质。

第三代膜产品是在70年代曾一度被忽视的气体分离膜技术。然而现在第三

代膜的应用也已非常广阔:① 超过95%的钻井平台所用氮气;② 5% ~15%的分

离埃米及大小的气体物质(018~05?);③ 脱除天然气中的 CO2等工艺都是以

第三代膜为核心技术的。

第四代必须大幅度地提高膜性能,实现在高能耗的能源、化工、食品和纯水领

域的大规模应用。其关键就要突破聚合物的扩散极限并实现全分子尺寸上的高

效膜分离,需要考虑在第四代膜中添加更高效的先进材料,如沸石、陶瓷、金属和

金属有机骨架材料(MOF)。

2能源、环保、制造业领域的应用

膜分离工程作为能源的解决方案,通过提供更高的能量利用率和回收率缓解

能源紧张的局面。作为一个能源密集型产业,在上游实现化学能的高效利用和回

收,能够使化工产业将风险最小化、效益最大化。

(1)天然气净化领域

天然气净化领域中先进的膜的应用:① 管道中甲烷气运输前的预处理;② 降

低在甲烷气中掺杂二氧化碳时造成的气体燃烧值的降低。这一领域应用的主要

问题是:膜的溶胀和塑化现象,乙酸纤维素膜对 CH4和 CO2的渗透性增加,CO2/

CH4选择性下降。如何避免溶胀和塑化现象,或者在该过程后成功地恢复膜的性

能是一个必须解决的问题。

(2)乙烯、丙烯以及乙烷、丙烷的分离

传统化工中,这样的过程是典型的能源密集型产业。其原因是,分离纯化过

程需化学状态的转变,其相变热和热驱动力巨大,需要消耗极大能量。化工厂区

2/3的面积和80%的能量在这一过程中消耗。然而利用膜技术进行分离,无需化

学状态的转变(气相与液相的转变),也就减少了分离过程的相变热和热驱动的

消耗,其节能效果十分客观。

3高性能材料在气体分离膜中的添加与应用

(1)高性能碳材料在气体分离膜中的添加与应用

碳分子筛(CMS)可以有效提高调整 CO2/CH4的分离系数。芳香族聚合物复

杂的聚合途径以及如何在这个过程中掺入 CMS以提高膜的性能,是一个非常有

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膜技术在水和气体净化中的应用国际高端论坛综述

前景的课题。CMS具有“超薄”的杂化石墨烯片状材质。

碳分子筛(CMS)可以调整 CO2/CH4结合性能,从而获得不同的分离效果。

当前,从线性芳香族聚合物中均匀添加 CMS仍然是较复杂的过程。它包含的关

键控制因素有:制膜料与 CMS的分散;热解温度;“放热”;热解气的释放。

(2)MOF(金属 -有机骨架)材料在气体分离膜中的添加

MOF材料是一个非常新颖的分子级别的框架结构,其具有极大的比表面积

和规整的结构,被成功地用于聚合物混合动力汽车的发电中,不需要分散和裂解,

就可以制备纳米复合中空纤维膜。其制成的具有01μmol/LZIF-8聚合物的混

合涂料涂覆或功能层使膜的性能产生了质的飞跃。其可控的结构也能够使膜材

料获得对不同分子的高选择渗透性。能够提供克服聚合物扩散上限的能力。扩

散选择性达到更高的标准(其实例就是实现丙烯/丙烷分离)。

总之,新的大型气体膜过程已经得到广泛应用。例如,天然气中的 CO2/CH4分离的应用;更先进的 N2/CH4和(N2+CO2)/CH4案例需要碳分子筛的添加与应

用;石化工业 “下游”的分离,如丙烯/丙烷的分离。但仍然期待出现潜在的主要

的节能应用和竞争优势应用领域。先进制膜材料的研发和膜结构形态的控制至

关重要,同时制造出高比表面体积的膜组件,提供相应的生产实用设备,也是重要

的技术关键。

(六)渗透汽化用沸石分子筛膜的制备和应用

沸石分子筛膜是由沸石分子筛颗粒在多孔支撑体上紧密堆积而成的一层薄

膜,利用其规则的分子筛孔道结构可实现物质分子水平的分离。亲水性的 NaA

型分子筛渗透汽化膜具有规则的孔道结构,孔径为 042nm,大于水的分子直径

029nm,而小于绝大多数有机溶剂的分子直径,且其本身具有极强的亲水性,因

而特别适合于有机溶剂脱水。

基于亲水沸石膜的渗透汽化(蒸汽渗透)分离被认为是一个经济有效的从有

机溶剂中脱水的技术,研究人员做了大量工作以改善膜性能、降低设备成本。报

告展示了课题组最近在制备沸石膜和在工业有机溶剂脱水方面的应用情况。

1)擦涂和浸渍相结合的引晶方法,可制备重现性好、高品质的 NaA型沸石

膜;纳米尺寸的球磨晶种也被用于诱导制备 NaA型沸石膜,这可显著降低合成时

间;使用二甲基二甲氧基硅烷(DMDS)作为硅烷前体,通过水解反应可进行分子

筛膜晶间孔道的修补。

2)采用晶种擦涂和浸渍相结合的晶种涂覆方式用于分子筛膜合成。先将支

撑体用砂纸打磨后烘干,采用晶种糊状物擦涂支撑体表面,以消除支撑体表面可

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能存在的缺陷,再用提拉浸渍法预涂晶种,最后采用水热合成法合成 NaA分子筛

膜,所合成的 NaA分子筛膜表面连续致密、分离性能优良、重复性好,适合规模化

生产。

3)采用球磨机对具有较大粒径的 NaA分子筛颗粒进行破碎,获得纳米级分

子筛颗粒作为晶种,然后在载体表面涂覆一层晶种层,采用水热合成法诱导制备

NaA分子筛膜。所合成的 NaA分子筛膜同时具有高的分离性能和渗透通量,合

成周期短、成膜重复性高,适合规模化放大生产。

4)分子筛膜晶间孔道的修补方法:利用分子筛膜侧室的有机硅烷修饰液,通

过晶间孔道与滞留在孔道上的水发生水解反应,产生 SiO2基团,进而有效减小分

子筛膜晶间孔道。本方法修饰后的分子筛膜的分离选择性可得到显著增加,成品

率高、重复性好。

目前,项目与江苏九天高科有限公司合作,建成了一条年产 10000m2、长

800mm的单通道膜的生产线。很多基于 NaA型沸石膜的工业脱水过程的工作

已经开展。为稳定运行,进料要求控制 pH值在 65~85,已建成的甲醇、乙醇、

异丙醇、乙腈等溶剂的工业脱水装置超过10个,这些溶剂可被脱水至水含量低于

01%(质量分数)。

此外,在制备中空纤维分子筛膜也进行了广泛研究,经测定 NaA型中空纤维

结构的沸石膜具有超过9kg/(m2·h)的高渗透通量,表现出良好耐酸性的 T型

中空纤维沸石膜也已制备完成,可用于 pH4条件下丙醛溶液的脱水。开发出了

中空纤维沸石膜组件。

(七)纳滤处理和回收废水中低浓度持久性污染物全氟辛酸铵

近年来,全氟辛酸铵(APFO)作为一种稳定性强的有机污染物,越来越引起全

世界的关注。由于 APFO分子链中较强的 C—F以及其良好的水溶性,很难通过

物理和化学方法降解,因而该有机污染物将长期存在于环境中,对环境造成污染。

报告主要介绍了纳滤膜 NF90和 NF270对 APFO的脱除以及浓缩回收情况,以及

在大生产过程中通过纳滤装置完成对工业废水中 APFO的浓缩再利用。

1)通过合适的纳滤膜实现废水中 APFO的回收和脱除。NF90对 APFO的脱

出率达到了99%,高于 NF270对 APFO的脱出率(92%),因此选择 NF90纳滤膜

处理含有 APFO的工业废水最合适。

2)通过 NF90纳滤膜,在适当的工艺条件下,可以完成 APFO的浓缩,从而得

到高浓度的 APFO。

3)通过 NF90纳滤膜可以从生产含氟聚合物产生的废水中,处理以及回收

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膜技术在水和气体净化中的应用国际高端论坛综述

APFO,其回收率达到99%以上,因而大幅度地降低了 APFO的排放,解决了其环

境污染问题。

4)一套每天处理200m3具有较低含量 APFO废水的纳滤装置已经成功投入

生产,该体系能够在生产 PVDF的工厂中完成废水中 APFO的回收以及浓缩再

利用。

从实验室小试实验,选择了合适的纳滤膜,经过完善工艺,最终在工厂建立了

纳滤水处理装置,完成了其对 APFO的浓缩。降低了工业废水中 APFO对环境的

污染,而且浓缩的 APFO可以进行回收再利用。不但产生经济效益,还具有一定

的环境效益。

(八)纳米粒子膜在液体和气体分离中应用的回顾

在膜中加入小颗粒用于分离最早出现在1965年由通用电气制备的包含硅颗

粒的硅橡胶膜。含有无机颗粒、沸石晶体的混合基质膜(MMM)在 20世纪 80年

代开始出现,并对新型吸收剂的发展产生了影响。高纵横比薄片的出现又进一步

促进了膜的发展,这些研究往往针对气体分离。随后出现的碳纳米管引起了人们

对碳纳米管 -聚合物混合基质膜的研究兴趣,加入合成的碳纳米管或改性的碳纳

米管,液体分离膜的性能受到显著影响。此外,还有许多有关碳纳米管或碳纳米

管/沸石杂化膜用于反渗透膜、纳滤膜领域的研究,其中包括在膜中加入包括石墨

薄片、金属有机骨架在内的纳米粒子制备出耐溶剂的纳滤膜。报告主要从以下三

个方面对纳米粒子膜在液体和气体分离中的研究进行了回顾:① 混合基质膜在

气体分离中的研究;② 混合基质膜在液体分离中的研究;③ 混合基质膜在渗透汽

化中的研究。

1混合基质膜在气体分离中的研究

首先以 He和甲烷气体为例,介绍了其在 25℃,在硅橡胶、天然橡胶、低密度

聚乙烯、高密度聚乙烯等聚合物中的传输、溶解、选择性等特征,从基于最小的沸

石界面的各种气体的动力学筛分直径,到提出气体分离膜的理论机制,介绍了混

合基质膜用于气体分离的研究起源,最后以橡胶和玻璃态聚合物膜分离 H2/N2气

体的渗透性和选择性之间的“upper-bound”上限 Robeson关系(1991年)为例,阐

明了渗透性和选择性之间互为制约的关系。对于气体和液体分离来说,传统有机

聚合物膜的渗透性和选择性存在 trade-off效应,很难同时提高,与之相比,混合

基质膜能够突破 trade-off效应的制约,使得渗透性和选择性同时提高,并兼具有

机高分子材料和无机材料的优点。然后列举了早期有关混合物基质膜的相关

研究。

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膜技术在水和气体净化中的应用

混合基质膜中填充的添加剂有沸石纳米晶体、气相二氧化硅、纳米二氧化硅、

碳分子筛、单壁碳纳米管、石墨薄片、石墨烯、枝状大分子。以填充沸石晶体为例,

认为制备气体混合基质膜面临以下挑战:① 在沸石相和有机膜相之间的界面相

容性成为造成膜的选择性损失的一个主要问题,尤其是玻璃态聚合物;② 膜皮层

厚度低(小于等于50nm),需要至少10层填充材料获得一个渗透阈值,并要求沸

石晶体有甚少的团聚;③ 含有尖锐晶体的纺丝溶液可能会破坏或损伤纺丝模具

表面,导致中空纤维膜表面出现缺陷;④ 膜组件制备时填充的固相物影响了膜的

刚性。

2混合基质膜在液体分离中的研究

作为第二相,用于混合基质膜中的材料有沸石晶体(制备薄层纳米复合膜)、

硅纳米颗粒、硅纳米凝胶(可避免纳米颗粒的团聚)、TiO2纳米颗粒、银纳米颗粒、

多壁碳纳米管(MWCNT)、单壁碳纳米管(SWCNT)、金属有机骨架(MOF)、水通

道蛋白、Noria超级分子(充当固体质子载体)。

Jeong等2007年介绍了采用界面聚合法分别制备RO薄层纳米复合膜(TFN)

和薄层复合膜(TFC)的结构,区别是 TFN膜聚酰胺功能层中含有纳米粒子。US

专利(020/0062156A)提出了在功能层上添加纳米颗粒的四种方法来制备 RO膜,

分别为:① 将纳米颗粒添加到水相;② 将纳米颗粒添加到有机相;③ 将纳米颗粒

添加到有机相和水相;④ 将纳米颗粒添加到含有水溶液的水相中。MaryL.Lind

等2009年试验研究了沸石晶体尺寸对沸石 -聚酰胺反渗透纳米复合膜的纯水通

量和 NaCl脱盐率的影响。Mary等对沸石 -聚酰胺纳米复合膜用于正渗透进行

了改进,对膜的渗透系数、盐截留率、盐渗透系数等性能进行了研究。另一个材料

是有机金属骨架(MOF),Sorribas等 2013年发现,与相同截留率时的 TFC膜相

比,MOF-TFN膜渗透能力得到大大提高。

报告还介绍了采用 CNT制备选择性分离膜的两种方法:一种是通过化学气

相沉积(CVD)法制作整齐排列的 CNT基膜;另一种为在聚合基体中或预先存在

的膜孔中分散/引入改性的 CNT。这种 CNT基混合膜可用于 UF,选择性地截留

20kDa和100kDa的分子质量。这种膜的水通量可达传统 UF膜的 5~6倍。利

用这种膜作为基体,采用界面聚合法制备了含有 CNT的聚酰胺 FO膜。制备的

FO膜通量提高3倍,盐透过率降低了 3倍。更高的通量也对控制浓差极化提出

更高的要求。

Roy等2011年对 CNT在膜分离中的应用进行了研究报道,通过采用多孔膜

作为基体,在水相溶液中加入 CNT制备亲水性 PP-CNT膜、亲水性 PES-CNT

膜,认为 CNT基混合膜有非常好的应用前景。

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总之,采用界面聚合法制备随机排列的碳纳米管 -薄层复合膜相对容易;为

了提高溶质截留率,必须提高表面功能层的密度,如果目的是 RO脱盐,那么功能

层聚合物的特点、水簇的特点则非常关键;采用CVD法制备垂直排列的CNT混合

基质膜既困难又昂贵;垂直排列的 CNT混合基质膜可控制溶剂通量和溶质分离。

3混合基质膜在渗透汽化中的研究

Vane等2008年研究了混合基质膜用于乙醇/水的渗透汽化分离,通过在硅

橡胶上负载65%(质量分数)的沸石 ZSM-5(疏水的),制备的 ZSM-5/硅橡胶混

合基质膜,在50℃时分离含有5%(质量分数)的乙醇水溶液,乙醇/水的分离系数

最高为30。Lin等2013年报道了采用制备的 PTFPMS/沸石4A(亲水的)混合基

质膜用于分离乙醇/水溶液,乙醇/水的分离系数高达 115。渗透通量高达

2321012kmol·m/(m2·s·kPa),是 PTFPMS膜的6倍。

用于液体分离的含有纳米晶体的混合基质膜正在被商品化。现有改进主要

对溶剂通量有所提高,而对溶质截留率没有影响。在 FO和 UF方面,碳纳米管混

合基质膜和碳纳米管支撑膜取得一定的进展。除化学气相沉积法,还需要研究更

简便的制备碳纳米管垂直排列膜的方法。用于气体分离的混合基质膜还没有实

现商品化,距离商品化的实现还有很艰难的路要走。

(九)CO2分离用膜的研制和应用

CO2分离主要包括烟道气和天然气中 CO2的分离去除,它直接与人类在新世

纪面临的环境和能源两个关键问题相关,CO2是温室气体的重要组成部分,需要

从烟道气中分离去除 CO2以减少温室效应;天然气中含有 CO2和 H2S等酸性气

体,这些酸性气体会腐蚀运输管道,因此必须控制其含量以提升天然气的品质。

报告主要从三个方面进行了介绍。

1聚酰亚胺材料的合成及中空纤维膜的制备

1)开发了几种新型聚酰亚胺材料的合成方法,显示了较好的 CO2渗透性和

分离能力,已进行了20kg规模的聚酰亚胺生产过程的实施。

为调节膜的选择性、提高抗塑化性,使所制备的膜兼具好的气体渗透性和选

择性,向膜材料的主链 6FDA-mPDA中添加 PEO成分,使共聚物既包含软段成

分,又有硬段成分。

2)经过优化具有较好膜孔结构形态的、高 CO2通量和满意分离效果的中空

纤维膜及工业规模的膜组件已经制备出来,一旦条件具备就可以进行真实工况条

件下的运行。

中国科学院大连化学物理研究所成功地设计了包括高效气/液分离、多级预

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过滤和膜组件装配成串联或并联模式的组合分离过程,借助化工软件的优化使整

套膜设备在最佳状态下将 CO2从天然气中分离出来,该套设备已在 2006年年底

投入运营。

2MOF/聚酰亚胺混合膜

无机/有机杂化膜是膜技术的重要研究领域,合成了两种可控颗粒尺寸的

MOF(金属有机骨架,是由含氧、氮等的多齿有机配体与过渡金属离子自组装而成

的配位聚合物)材料,实验证明,以聚酰亚胺作为基膜材料、添加 MOF后可在没有

明显的选择性损失情况下提高气体的渗透性、具有良好膜孔形态的中空纤维杂化

膜的制备正在进行中。

目前用已合成的两种 MOF即 Micro-ZIF-8和 Micro-CuBTC作为添加剂

所制备的无缺陷的混合基质膜的气体选择性几乎没有变化,而渗透性均高于麦克

斯韦模型(Maxwellmodel)的结果,其中 Micro-ZIF-8还要高于 Micro-CuBTC。

3PTFE多孔膜吸收过程

PTFE是具有非常好的化学稳定性和机械强度的聚合物膜材料,中国科学院

大连化学物理研究所开发了具有自主知识产权的、孔结构可控的 PTFE中空纤维

生产线,设计开发了用于从天然气中去除 CO2的膜接触器,目前与一家国际公司

合作的膜接触器系统正在安装调试,将在2013年年底试运行。

(十)新型通用离子交换膜的研究和实践

1阴离子交换膜研究进展

对于膜的性能,主要通过膜的选择性、渗透性和稳定性三方面来考察。其面

临的主要问题是:① 如何避免使用有害的材料———氯甲基甲醚(CME)?② 如何

单独控制离子交换容量(IEC)和水含量(WC)?③ 如何使得制备的膜具有全面

性?④ 如何提高膜的稳定性?

以上问题的解决方案包括使用溴化来替代氯甲基化以避免使用 CME,同时

通过控制溴化比例和溴化度来控制离子交换容量和水含量。采用定量设计,如氨

基化,使得采用同种聚合物制备不同用途的离子交换膜成为可能。利用仿生交联

剂制备具有高强度和良好热稳定性的有机 -无机杂化膜。

2离子化单体的离子交换膜研究进展

离子交换膜在燃料电池中得到广泛应用,这种应用也对离子交换膜提出了多

种性能上的要求,如高的 H+/OH-导率、低的燃料融合性、优良的机械强度以及

长期稳定性等。

研究人员从 Nafion膜材料的结构中得到启发,选择侧链型离子化芳香族聚合

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膜技术在水和气体净化中的应用国际高端论坛综述

物作为制备离子交换膜的材料,而侧链型离子化芳香族聚合物又可以通过芳香族

聚合物后接枝离子化侧基和离子化侧基单体聚合两种方式得到,从而可以精确控

制离子化基团的位置和含量。例如,直接酰化聚酮或者先对离子化的单体进行酰

化后再进行聚合都是立足于此研究思路。

3以离子交换膜为基础的膜过程的发展及应用

目前离子交换膜的应用主要集中在生物医药、水处理以及石化领域三大方

面。生物医药的应用主要包括:氨基丁酸、药物氨基酸、赖氨酸以及发酵有机酸的

处理方面;水处理的应用主要包括:电镀废水、丁腈橡胶废水等废水处理方面;石

化领域的应用主要用于脱硫剂再生以及石化废水处理方面。

目前,中国科技大学的新型离子交换膜已经开始商业化生产,并被用于有机

酸生产、净化分离等领域。

三、交流与讨论

与会中外专家学者就膜技术在污水回用领域的应用、在海水淡化领域的应用

成本、气体膜在石化领域的应用以及未来膜技术的发展趋势等问题进行了深入的

交流与讨论。

膜技术在水和空气净化领域的应用是全球的发展趋势。在膜法污水回用以

及海水淡化过程中,RO膜仍是主导。在 RO膜片的研发方面仍是以聚酰胺薄层

复合膜的改性为主,最新的技术包括已经商业化的采用纳米沸石分子筛粒子改性

以提高膜片的水通量以及采用仿生学原理在反渗透薄膜中添加水通道蛋白以提

高膜的水通量;在膜组件方面的开发趋势是不断追求膜组件的大型化以提高产水

效率;在整个脱盐工艺流程的设计上更加注重水和能源的综合利用,各种耦合技

术,如反渗透与正渗透耦合以降低能耗和产水成本、反渗透与膜蒸馏技术的耦合

以实现零排放为目标,将是未来的发展趋势。

针对海水淡化领域的膜技术成本问题,与会专家认为目前海水淡化成本已有

大幅度下降,但因材料成本上升,所以总体上海水淡化成本降低了一些,但是短期

内很难有大幅降低或突破。海水淡化的两大技术主要是蒸馏和反渗透,目前的

海水淡化应用以反渗透为主,新加坡第一座海水淡化工厂———新泉海水淡化

厂,是目前全球最大型的采用反渗透技术的海水淡化厂,海水淡化成本在 07

美元左右。未来的发展趋势是将蒸馏和反渗透技术结合起来,可大大降低海水

淡化的成本,3年后每立方米海水淡化的成本将从目前的约 70美分降到 50

美分。

气体分离膜在天然气净化领域,乙烯、丙烯以及乙烷、丙烷的分离回收领域得

91

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

到了广泛应用,但先进制膜材料的研发和膜结构形态的控制至关重要,同时制造

出高比表面体积的膜组件、提供相应的生产实用设备,也是重要的技术关键。未

来对膜过程的研究主要是如何降低膜过程的能耗。

02

第二部分

参会专家名单

参会专家名单

曹湘洪 中国工程院院士

黎念之 美国工程院院士

高从!

 中国工程院院士

金万勤 南京工业大学,教授

侯立安 中国人民解放军第二炮兵部队工程设计研究所,中国工程院院士

王晓琳 清华大学,教授

顾学红 南京工业大学,教授

曹义鸣 中国科学院大连化学物理研究所,教授

徐铜文 中国科学技术大学,教授

万印华 中国科学院过程工程研究所,教授

汪 勇 南京工业大学,教授

姜忠义 天津大学,教授

王乃鑫 北京工业大学,教授

EnricoDrioli 意大利国家研究理事会膜技术研究所,教授

TonyFane 新加坡膜技术中心,教授

WilliamJKoros 美国佐治亚理工学院工程学院,美国工程院院士

KamaleshKSirkar 美国新泽西理工学院,教授

32

第三部分

主题报告及报告人简介

MembraneEngineeringforanInnovativeProcessEngineering

EnricoDrioli1,2,3,4,etal.

1InstituteonMembraneTechnology,NationalResearchCouncilof

Italy,ITM-CNR,c/oUniversityofCalabria,viaP.Buccicubo17/

C,Rende(CS)Italy

2DepartmentofChemicalEngineeringandMaterials,Universityof

Calabria,viaP.Bucci,Rende(CS)

3WCUEnergyDepartment,HanyangUniversity,Seoul,Korea

4CenterofExcellenceinDesalinationTechnology,KingAbdulaziz

University,SaudiArabia

Abstract:Ourmodernsocietyhastosolveand overcomevarioussevere

problemsformaintainingandincreasingthequalityofourlives,suchas:

globalwaterstress,energyproduction,environmentalpollution,CO2capture,

etc.Processintensification in processengineering,new advanced smart

materialsandmolecularengineeringarealldisciplineswhichmightcontribute

tofindsolutions.MembraneEngineeringiscoveringallaspectsofprocess

engineering,frommolecularseparationtochemicaltransformations(membrane

reactors),tomassandenergytransferbetweendifferentphases(membrane

contactors).

Inthelastyears,theimpactofmembraneoperationsinvariousareashas

grownfast.Seawaterandbrackishwaterdesalination,industrialwaterreuse,

wastewatertreatment,gasesseparations,membrane bioreactors,hybrid

artificialorgansandagroindustry(suchasdairyindustry,juicesandwine

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

productions,etc.)aretypicalexamplesofmembraneengineeringsuccess.

Themotivationforthissuccessisinlargepartrelatedtotheirbasicproperties

interm ofenergy consumption,low environmentalimpacts,no use of

chemicals,easytoautomatization,etc.Alltheseaspectsareverywellrelated

tothestrategyofProcessIntensification.

Integratedmembraneoperationsare also growing in interestand in

industrialutilization.Integrated membraneoperationsmightbeconsidered

todayinvariousproductionlines,basedintheutilizationofexistingmembrane

systemsfromthedownstreamprocessingtothefinalproductformulations.

Thisworkcriticallyreviewsthecurrentstatusandemergingapplicationsof

(integrated)membraneoperationswithaspecialfocusonwater,energyand

rawmaterialsproduction.

1 Introduction

The growing population along with industrialization and development

causedsevereissueswhichhavetobefacedtoensureandimprovetheliving

standardofthefuturegenerations.Inparticular,thelackoffreshwaterandthe

growingneedofenergyandrawmaterialsarecurrentproblemswhichhaveto

beaddressed toensuretheprogressofthefuturesociety.Tomeetthe

requirementsofsustainabledevelopment,theProcessIntensification(PI)

strategycanbeused.Itentailsto:① maximizetheeffectivenessofintraand

intermolecularevents;② giveeachmoleculethesameprocessingexperience;

③ optimizethedrivingforcesateveryscaleandmaximizethespecificsurface

areatowhichtheseforcesapply;④ maximizethesynergisticeffectsfrom

partialprocesses[1,2].Membraneengineeringisatechnologyinwhichallthe

requirementsofPIcanberealized[1,3] duetoitsintrinsiccharacteristicsof

advancedmolecularseparation,improvedefficiency,easeofoperationand

scaleup,andaptitudetointegratedifferentbutcomplementarymembrane

operations.Membrane engineering, including pressure driven membrane

operations,membranecontactors,gasseparation,fuelcellapplicationsetc.,

bringschemicalengineering toanew and highlyimproved level.Today

membraneprocesseshaveinseveralcasesleftbehind theconventional

chemicalunitoperations.Membranebioreactors(MBR)inmunicipalwater

82

treatments,pressuredrivenmembraneoperationsandintegratedmembrane

systemsinseawaterand brackishwaterdesalinationaresomeimportant

examples where conventionalplants have been turned into membrane

processesduetotheirhighenergeticefficiency,compactness,extraordinary

levelofphysicaldisinfectionandreducedsludgeproduction.

Membrane engineering with its various operations can address the

growingproblemsnotonlyofwaterstressbutalsoofmineraldepletionand

energyconsumptions.

Potablewatershortageisoneofthemostseriousproblem forfuture

generations.Ithasbeenestimatedthat,intheyear2000,31billonpeople

livedundermoderatewaterstressand26billionwereexposedtohighlevels

ofwaterstress[4].Accesstofreshandcleanwaterisstronglylinkedtothe

healthofthepopulation[5],thereforeinmanydeveloping countrieswater

resourcesarethemainrequisitefortheimprovementofthelivingstandards.

Moreover,waterresourcesarenotonlyconsumedindomesticactivitiesbut

also in agriculture, industrialand touristic uses thus influencing food

productionandindustrialgrowth.Waterstressispredictedtoincreaseinthe

futureyears.Thesameishappeninginenergyconsumption.Thelattergrew

rapidlyinthelastdecadesandisprojectedtoincreasefurtherinthefollowing

years(Fig.1)[6].Asaconsequence,efficienttechnologiesabletominimize

energyintensity(ie., energy consumption perunitGDP)have been

developedandwillbefurtherresearchedinfuture(Fig.1).

Inthelastdecadesmineraldeficiencyisalsobecomingquitecommonall

overtheworld.Forexample,thedemandforlithiumhasalreadydoubledover

thepastdecadeanditisexpectedtomorethandoubleoverthenext10years

(Fig.2).Lithiumgrowingconsumptionwaslargelydrivenfromitsuseinsmall

formatlithiumion battery(ie.,rechargeable batteriesused in consumer

devicessuchascellphones,laptops,digitalcamerasandhandheldpower

tools).Futureincreaseinlithiumdemandisexpectedtocomefromcontinued

growthinthesmallformatlithiumionbattery,aswellasnewdemandfromthe

largeformatlithiumionbatteryusedinapplicationssuchasthehybrid,plug

inhybridandfullelectricvehicle-aswellasforbatteryapplicationswithinthe

utilitygridstorageindustry.Untilnowlithium hasbeenmainlyrecoveredfrom

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Fig.1 Outlookofenergyconsumption(leftaxis)andenergyintensity

(rightaxis)(adaptedfrom[6])

mineralsintheminingindustryorfromhighcontentlithiumwaterssuchassalt

lakebrines.Themaindrawbacksofthelithium productionprocessesarethe

lowlithiumgradesandrecoveryfactors,thecomplicationsinhavingavailable

newproductionsitesorinenlargingtheexistingsaltlakebrinesareas(in

particularbecausetheyareassociatedwithhighlevelofpollution[7]).

Fig.2 Lithiumdemandforecast(http://www.globalprofitsalert.com/globalinvestment

news/kelleydamiani/anelementforlithiumbatteriessettoflourish117211)

Anotherexampleofmineraldepletioncanbefoundintheincreasing

uraniumdemand(asenergysource)whichhasalreadyexceededtheglobal

03

production[8]andwhichareprojectedtoincreasefrom61500tonsin1997to

75000tonsin2020(Fig.3).

Fig.3 Worlduraniumproductionanddemand

(http://moneyformoney.wordpress.com/tag/cco/)

Membraneengineeringofferscomprehensiveprospectstothesolutionof

futurewater,energyandrawmaterialsdemands.

Thisworkgivesacriticalevaluationofthecurrentstatusandemerging

applicationsofmembraneoperations,withaspecialfocusonwater/energy/

mineralproductionfromsaltywaters.Ithighlightssomeofthelatestadvances

inmembraneprocessesandprovidesalookatthemajorchallengesforfurther

developmentofmembranetechnology.

2 Membraneoperationsforwater,energyandrawmaterialsproductionfromsaltywaters

Theimportanceofpotablewater,cleanenergyand sustainableraw

materialsourcesisevidentconsideringthedrawbacksofwatershortage,fossil

fuelsemissionsandfiniteresourcesdepletion.Analternativesourceofwater,

energyandmaterialsissaltywater.Membraneengineeringhasalreadyshown

itspotentialitiesin waterdesalination where,today,the mostparticular

accomplishmentofmembranetechnologyisthereplacementofconventional

distillationmethodologiesforfreshwaterproduction(suchasconventional

multistageflash(MSF)andmultieffectdesalination(MED))withmembrane

baseddesalinationprocesses(mainlyreverseosmosis(RO)).

Forwhatconcernscleanenergy,itcanbeproducedbysalinitygradient

13

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

power(SGP).SGPisbasedonthechemicalpotentialdifferencebetween

concentratedanddilutesaltsolutions.Theconversionoftheosmoticenergyof

saltsolutions into mechanicalorelectricalenergy can be realized by

osmoticallydrivenmembraneoperationssuchasforward osmosis(FO),

pressureretardedosmosis(PRO)andreverseelectrodialysis(RED).

Saltwaterscanbeexploitedalsofortheproductionofthoserawmaterials

currentlyin strong demand and dangerous depletion trough membrane

distillation(MD)andmembranecrystallization(MCr).

21 Potablewaterproductionthroughmembraneprocesses

Membranetechnologyistodayrecognizedasthedominanttechnologyfor

waterdesalinationbecausethermaloptionsareapproximately10timesless

energyefficient[9] and itisexpected to furtherconsolidate in future its

leadershipthroughthedesignofintegratedmembraneprocesses.

Theglobalinstalleddesalinationcapacityaroundtheworldis652million

m3/dandmembraneinstallationsaccountforaround60% ofthedesalination

markettodayandhavebeenforecastedtoincreaseto80% in201690% of

membranedesalinationinstallationsuseRO technologywhosecapacityis

increasingrapidly.Onlyincountrieswithabundantoilreserves,thermalMSF

andMEDplantsarebuilt.ThegrowingnumberofROdesalinationplantsisin

largepartduetoseveraladvancesintechnologythatoccurredduringthe

1990s,whichinclude:

newlowenergyROmembraneswithimprovedsaltrejectionandlower

price,

highefficiencypumpsandmotors,

moreefficientenergyrecoverydevices(ERDs).

TheprogressesinSWROdesalinationcausedadecreasinginthecostof

the reclaimed waterfrom membrane plants and an increasing use of

membranetechnologyforwaterdesalination.

Currently,RO desalinationplantswithcapacitiesofmorethan500000

m3/dareinoperation[10,11]andthegoalofreachingacapacityofmegatons

perdayisnowemerging.ExamplescanbefoundintheMegatonprojectin

Japanand intheSEAHERO projectinSouthKorea[12-14].However,the

23

massivecapacityincrementalsopromotessomeseriousconcernssuchasthe

disposaloftheproducedbrine.Otheraspectsthatneedimprovementsfora

furtherspreading ofmembranebased desalination systemsare the cost

reductionandtheimprovementofwaterquantityandquality.Alltheseissues

canbeaddressedinanintegratedapproachinwhichdifferentmembrane

operationscanbeused intheRO pretreatmentand posttreatment.For

example,intheRO pretreatmentsomeotherpressuredrivenmembrane

processescan be utilized as an interesting alternative to conventional

processes(i.e.,chemicalsandmechanicalfiltrationunits).Inparticular,MF

(a lowpressure membrane process forthe removalofcolloidaland

suspendedmicrometersizeparticles),UF(anotherlowpressuremembrane

processtypicallyusedtoretainmacromolecules,colloids,andsoluteswith

molecularweightsgreaterthanfew thousand)and NF(a high pressure

membraneprocessfortheremovalofturbidity,microorganisms,hardness,

andmostpartofmultivalentions)are becoming standard and efficient

pretreatmentoptionsforseaandbrackishwaterdesalination.

Forwastewatertreatment,MF/UF pretreatmenttechnology can also

efficientlyreducethehighlyfoulingnatureofthefeed.

Otherbenefitsarisingfrom theutilizationofpressuredrivenmembrane

processesinthepretreatmentstepsarethepossibilitytohandlealarge

variationinraw waterquality,thesmallerfootprintandtheopportunityto

increaseROfluxandwaterrecovery.Proofofthebenefitsintheadoptionof

membraneoverconventionalpretreatmentistheirrecentproliferation.

Anotherpretreatmentoption to reduce naturalorganic matteristhe

utilizationofamembranebioreactor(MBR).Thishasagreatpotentialto

providedisinfectedeffluentsofhighquality,especiallysuitableforreuseand

recyclinginwastewatertreatmentorforROpretreatmentinseaandbrackish

waterdesalination[19].UseofanMBR asRO pretreatmentisalsobeing

investigatedintheMEDINAresearchproject(http://medina.unical.it).

Asitwillbedescribedinthefollowingsections,alsothedangerous

effectsofthe brine discharged from the RO desalination plantson the

environmentcanbeminimizedthroughanintegratedsystem inwhichthe

desalinationprocessisredesignedintroducingmembraneoperationsalsoin

33

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

theRO posttreatmenttransformingthetraditionalbrinedisposalcostina

potentialnewprofitablemarket.Inparticular,① membranedistillation(MD)

andmembrane crystallization(MCr)can be utilized forproducing solid

materialsofhighqualityandcontrolledproperties(asspecificpolymorphof

salts),② pressureretardedosmosis(PRO)andreverseelectrodialysis(RED)

canbeusedtogenerateenergyfromRObrine.

Otherexamplesofintegratedmembranebasedprocessesfordesalination

aretheabovementionedMEGATONandSEAHEROprojects.Inthefirstpartof

theprojectstheemphasishasmainlybeenonincreasingthedesalination

capacity.However,inthesecondpartoftheprojectsthebrinedisposalissues

andtheenergyconsumptionsareaddressed.Hybridsystemswithmembrane

distillation(MD)andpressureretardedosmosis(PRO)unitsareproposedfor

theminimizationoftheenvironmentalimpactofthebrine,therecoveryof

energy(seesection25)andtheextractionofvaluableresourcesfrom the

brine.Moreover,theSEAHEROproject(http://www.seahero.org/eng/)has

suggestedahybridsystem forwardosmosis/reverseosmosisforincreasing

therecoveryfactorby30% andherebyreducingthebrinevolumeinthesame

extend.Thishybriddesalinationprocesscanminimizetheenergyconsumption

tolessthan25kW·h/m3andwaterpriceto06$/t.

22 Membranecontactorsinwatertreatmentandwaterpurification

Membrane contactors(MCs)are systems utilizing a hydrophobic

membranewithappropriateporestructureasafixedinterfacebetweentwo

differentphaseswithoutdispersingonephaseintoanother.Intheseprocesses

themembranedoesnotactasaselectivebarrierbutrathersustainsthe

interfaces.The separation processisbased on the principlesofphase

equilibrium.

With respectto conventionalsystems, MCs have some important

advantagessuchashighinterfacialareapervolumeunit,low operating

temperaturesandpressure,highrejection,modulardesign,easyscaleup,

less membrane fouling and low sensitivity to concentration polarization

phenomenon.Drawbacksarerelatedtothepresenceofanadditionalmass

transportresistance(themembraneitself)andtotheratherlimitedrangeofthe

43

operatingpressuresbelow thebreakthroughthreshold.Theperformanceof

MCsstronglydependsonthepropertiesofthemembranesused.Ingeneral,a

highhydrophobicity(foraqueousapplications)isrequiredtopreventwetting

andmixingbetweenthedifferentphasesincontact;elevatedpermeability

leadstohighfluxes;highchemicalandthermalstabilityarenecessaryto

improvethemembraneresistancetochemicalattackanditsresistanceto

degradationanddecomposition.

MDandMCraretwoexamplesofMCsthatcanbeusedformitigatingthe

impactofconcentratesontheenvironmentandfortherecoveryofthevaluable

containedcomponents.

1)Membranedistillation(MD)isamembraneprocesswhichcombines

bothmembranetechnologyandevaporationprocessinginoneunit.Itinvolves

thetransportofwatervaporthroughtheporesofhydrophobicmembranesvia

a partialpressure difference across the membrane.With respectto

conventionaldesalinationtechnologiessuchasmultistageflashdistillationand

RO(techniquesinvolvinghighthermalenergyandhighoperatingpressure

respectively,finallyresultinginexcessiveoperatingcosts),MD offersthe

attractivenessofoperationatatmospherepressureandlowtemperatures(30~

90℃),withthetheoreticalabilitytoachieve100% saltrejection.Moreover,

MDisnotlimitedbyconcentrationpolarizationphenomenaasitisthecasein

RO.Previouswork[15] showedthatnoconcentrationpolarisationoccurswith

membranedistillationatconcentrationsupto300g/L.Arelativelysmallflux

declineisobservedwhenconcentrationandviscosityincrease,butthisisonly

duetothermodynamiceffects:whenthesaltconcentrationincreases,the

activitycoefficientismodifiedandthiscanexplainthewaterfluxdecrease.

However,thisfluxdeclineislowincomparisonwiththeoneobserved(ofabout

70% oftheinitialflux)withRO,whichisduetobothosmoticpressureand

concentrationpolarisation.

2) Membranecrystallization(MCr) is conceived as an alternative

technologyforproducingcrystalsandpurewaterfromsupersaturedsolutions;

theuseofthemembranedistillationtechniqueintheconcentrationofasolution

bysolventremovalinthevaporphaseisutilizedinthisapplication.

MCrisabletopromotecrystalsnucleationandgrowthinawellcontrolled

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

pathway,startingfromundersaturatedsolutions.Inamembranecrystallizerthe

membranematrixactsasaselectivegateforsolventevaporation,modulating

thefinaldegreeandtherateforthegenerationofthesupersaturation.Hence,

thepossibilitytoactonthetransmembraneflowrate,bychangingthedriving

forceoftheprocess,allowstomodulatethefinalpropertiesofthecrystals

producedbothintermsofstructure(polymorphism)andmorphology(habit,

shape,size,andsizedistribution).Theexperimentalevidencesthatcanbe

foundinseveralpublishedarticles[16-18]validatetheeffectivenessofMCrasan

advancedmethodforperformingwellbehavedcrystallizationprocesses.

MDandMCrarebothefficienttoolstoimproveseawaterdesalination

processes:

1)integrationofaMDunittoprocessROretentatecould① increasethe

amountofrecoveredwaterand② reducetheamountofdischargedbrine;

2)integrationofaMCrunittoprocessROretentatecould① enhancethe

waterrecoveryfactor,② minimizethedischargedbrineand③ produce

valuablecrystallineproducts.

ThestudiescarriedoutbyDrioliandcoworkers[16,20,21]showedthatthe

introductionofaMCrunitonNFandRO retentatestreamsofanintegrated

membranebaseddesalinationsystem constitutedbyMF/NF/RO increases

plantrecoveryfactorso much to reach928%.Moreover,ithasbeen

experimentallyshownthatthepresenceoforganiccompound(i.e.,humic

acid)intheretentateinhibitscrystalsgrowthrate[22].Thisprovedthenecessity

tooptimizetheNF/RO pretreatmentsteps,inordernotonlytoreducethe

NF/ROmembranefoulingbutalsotocontrolthecrystallizationkineticsthatare

linkedwiththenatureandtheamountoftheforeignspeciesexistinginthe

highlyconcentratedbrinesemergingfromtheNFandROstages.

InsomestudiesonMCr[23]arapiddecreaseintransmembranefluxhas

beenobservedduetocrystaldepositiononthemembranewhichreducedthe

membranepermeability.Thisproblemcanbeminimizedthrougharightdesign

oftheprocessandapropercontroloftheoperativeconditions.Withrespectto

the bestcontrolofoperative conditions, temperature polarization is an

importantfactordepressing the driving force and hereby the process

performance.Alietal.[24] exploredtheeffectoftemperaturepolarizationon

63

membranedistillationperformancebymeansofaspeciallydesignedcell.In

particular,acellwithsixteensensorslocatedatspecificlocationswithinits

bodywasbuilttomeasurethebulkandmembranesurfacetemperatureson

bothfeed and permeate sides.Theyfound thattemperature polarization

phenomenondecreaseswithincreasingthefeedflowrate,anddecreasingthe

feedinlettemperatureandconcentration.Moreover,theyprovedthatsolution

concentrationhasverylessroleinfluxreductionascomparedtothermal

polarizationatlow feed concentration,whereasthefluxreductiondueto

concentrationbecomesimportantathighfeedconcentrationwhereacoupling

ofheatandmasstransferexists.

Finally,theadditionaladvantageofmembranedistillationandmembrane

crystallizationoflowworkingtemperatureprovidesthepossibilitiestoutilize

wasteheatorothersustainableenergyresources(suchasgeothermalorsolar

energy).

23 Membranedistillationapplications

Eventhoughmembranedistillationwaspatentedinthe1960s[25],itishas

notbeencommercializedbecauseofthesuccessofcompetingtechnologies.

Howeverinthelastfewyears,MDhasemergedwithnumerouscommercially

devicesandnovelapplicationsbesidesdesalination.

AnincreasingindustrialapplicationforMDisthetreatmentofwastewater

resulting from the textile industry, including the purification of dye

solutions[26,27].Membrane distillation has also found applications in

metallurgicalprocessesforwhichnoothermembranebasedsystemsapply.

Someapplicationsincludeconcentratingwasteacid,causticandsaltsolutions

withconcentrationsashighas1mol/L[28].

AnovelapplicationforMD hasbeenproposedbyCathetal.[29] who

incorporatedMDintoacombineddirectosmosis/osmoticdistillation(DO/OD)

processtotreathygieneandmetabolicwastewater.

MDhasbeenalsoexploredinfoodindustryforjuiceapplications(for

example,fortheconcentrationoffruitjuicesattemperatureslowerthanother

thermalmethods for the preservation of the organoleptic traits and

flavours[30,31])ortoincreasethealcoholicpotentialofthemust[30]ortorecover

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

ethyl2,4decadienoate(i.e.,themainpeararomacompoundfromasolution

containinganethanolwatermixture)[32].

The separation ofmethanolwatermixtures and ofbenzenetoluene

mixturesareothernovelapplicationsforMD[33].

DespitethepotentialforMDinalltheabovedescribedsystems,itswide

commercialimplementationhasnotyettakenplace.However,therecent

concernsemergingfrom greenhousegasemissionsandenergyconsumption

havepromptedtheindustrialworldtoconsidertheuseofrenewableenergyas

akeyfactorfornewtechnologiesthatarebeingdeveloped.Thisaspectcanbe

particularlyexploitedinwatertreatmentsystemswhereobtainedwatersare

frequentlywarm and theirthermalenergycanbeused todrivetheMD

separationprocess.Therefore,theMD treatmentofwastebrinestreams

becomessustainableandusefultoenlargeexistingwatersuppliesorreduce

brinedisposalvolumes.Anexamplecanbefoundinthewastewaterproduced

byoilandgasindustryreferredasoilfieldwaterorproducedwater.Produced

waterleavingtheoilandgasproductionprocessisingeneralatahigh

temperature making the treatmentwith membrane distillation ideal[34,35].

Nevertheless,volatilecomponentscontainingintheproducedwater,suchas

smallorganicmoleculesanddissolvedgasesmightbetransportedacrossthe

membrane,causingcontaminationofthepermeate[35].Differentpolyvinylidene

fluoride(PVDF)andpolypropylene(PP)hollowfibermembranesweretested

indirectcontactMDfordesaltingrealhighsalineoilfieldproduced[36]andthe

analysisofthecollectedpermeatesindicatedthatsaltrejectionfactorsgreater

than99% and totalcarbonrejectionhigherthan90% canbeachieved.

Alkhudhirietal.[37]havetestedairgapmembranedistillationforthetreatment

ofproducedwater.Theyfoundthatsaltandorganicrejectionareashighas

9999% and986%,respectively.

24 Membranecondenserforwatercapturing

Anothernovelmembranecontactorapplicationwiththevisionofwater

separationandrecoveryfrom industrialgaseouswastesteamsismembrane

condenser[38-40].Inthismembranetechnology,hydrophobicmembranesare

utilizedforwatercondensationand recoveryintheretentatesideofthe

83

membranemodule,whereasthedehydrated stream isrecovered onthe

permeateside ofthe membrane.Experimentshave been carried outto

evaluatethemembranemoduleperformanceintermsofamountofrecovered

water, in function ofvarious operating parameters(ie., membrane

characteristics,temperature,pressureandrelativehumidityoftheinletflue

gas).Theexperimentalresultswerevalidatedthroughthesimulationanalysis

oftheprocess.Theachievedresultsindicatethathighamount(>20%)ofthe

watervaporinitiallycontainedinthefluegasstreamcanberecoveredasliquid

withverylowΔT(<5℃)betweeninletfluegasandmembranemodule.

Thewaterobtainedbycondensationassistedbymembranesrepresentsa

newandpromisingsourceofwater.Membranecondenser,moreover,might

beconsideredofinterestinvariousgasstreamstreatments,withmembraneas

an appropriate pretreatmentfor dehumidification or reduction of ion

concentration.

25 Membranetechnologyforenergyproduction

Membraneengineering iscontributing in a positive waynotonlyto

minimizewatershortageandrawmaterialsdepletion,butitalsoprovidesthe

possibilitytoproduceenergyfrom cleanandsustainablesources.Attention

towardsgreenenergyresources,suchassolarorwind,isgrowingandmore

andmoretheseenergysourcesarebeingimplementednotonlyinindustries

butalsoforhouseholdconsumption.However,mostoftheseenergysources

are dependentupon weatherconditions and frequently notapplicable

continuously.A sustainableform ofenergysourceindependentfrom solar

radiationorwind poweristhesalinitygradientenergy,also called blue

energy.Thelatteristheenergythatcanbeobtainedfrommixingwaterstreams

withdifferentsaltconcentrations.Blueenergyisavailablewherefreshwater

streamsflowintotheseaoritcanbemadeavailablefromnaturalorindustrial

saltbrines.

Ingeneral,alltechniquescurrentlyavailableforsaltywatertreatment

couldbeusedtogeneratepowerfromsalinitygradientswhenoperatedinthe

reversed mode,such as:pressureretarded osmosis(PRO)and reverse

electrodialysis(RED).

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

PROisanosmoticallydrivenmembraneprocessthatusesamembraneto

separatetwosolutionswithdifferentsalinity(forexamplefreshwaterand

seawater).Ifhydrostaticpressureisappliedtotheconcentratedsolution,the

watertransportwillbepartlyretarded,whichresultsinapressurizationofthe

volumeoftransportedwater.Thispressurizedvolumecanbeusedtogenerate

electricalpowerinaturbine.

InRED aconcentratedsolution(eg,seawater)andadilutesolution

(eg,riverwater)flow throughastackofalternating cationand anion

exchangemembranes(CEMsandAEMs)betweenacathodeandananode.

Thechemicalpotentialdifferencebetweenthetwosolutionsinducesavoltage

overeachmembrane(membranepotential),andthetotalpotentialofthe

system isthesum ofthepotentialdifferencesoverallmembranes.The

chemicalpotentialdifferenceactivatesiontransportthroughthemembranes

fromtheconcentratedsolutiontothedilutesolution.Thepotentialdifference

overtheelectrodescanbeusedtogenerateelectricalpowerwhenanexternal

loadorenergyconsumerisconnectedtothecircuit.

PROandREDhavetheirownfieldofapplication:PROseemstobemore

adapttogeneratepowerfromconcentratedsalinebrinesbecauseofthehigher

powerdensitycombinedwithhigherenergyrecovery.Forthesamereason,

REDseemstobemoreattractiveforpowergenerationusingseawaterand

riverwater[41].

Althoughthesalinitygradientpowerwasrecognizedmorethan50years

ago,manyresearchanddevelopmentissues,especiallythoserelatedto

membranepropertiesandcosts,stillneedtoberesolvedbeforePRO and

RED are available forlargescale commercialapplication.However, a

reconsiderationofthese membrane processes is worthwhile due to the

decliningmembranecosts,totheincreasingpricesoffossilfuelsandtothe

possibilitytoredesigndesalinationplantsforwaterandenergyproductionvia

theintegration ofRO(asdesalination technology)and RED(asenergy

productiontechnology).

AhybridREDsystemusinghighlyconcentratedsolutionsrecoveredfrom

aseawaterdesalinationplant(based onRO orevaporation)and further

concentratedbysolarevaporation,andseawater(orbrackishwater)asthe

04

dilutesolution,hasbeenproposedbyBrouns[42].Modelsimulationsofthis

system indicate thatthe developmentofthin membranes with specific

characteristicsintermsofresistivityandpermselectivityinanadequateRED

stackdesignisnecessaryforproducingahighREDoutput.AFP7European

funded project “Reverse Electrodialysis Alternative Power Production

(acronym:REAPower)”launchedin2010isutilizingREDforenergyproduction

fromthebrineofthedesalinationplants.Thevisionoftheprojectistogaina

poweroutputof536 kW/m3 bymixing brineand seawater.Bythisan

expectedpowerdensityof215W/m2 canbeobtained[43].Furthermore,

extensiveresearchisdevotedtomaterialsandcomponentdevelopmentforthe

commercializationofthisparticularprocedure.

Postetal.[41] estimatedthattheglobalenergyoutputfrom estuariesis

26×1012W,whichisapproximately20% ofthepresentworldwideenergy

demand.Skilhagen[44]estimatedthatthecostofenergyfromosmoticpoweris

50~100 /(MW·h),whichiscomparableandcompetitivewithothernew

renewableenergysourcessuchaswaveandwind[44].

ANorwegiancompanycurrentlycommercializingPROisStatkraft.Thefirst

prototypewasoperationalin2009[44]andanagreementhasbeensignedwith

IDEtechnologiesforthedesignandconstructionofa2MWpilotplant[45,46].In

thenext,aplantof25MW willberealized[47,48].Iftheenergyoutputfrom all

Norwegiansalinitygradientsources(around12TW·h/a)willberecovered,

10% oftheNorwegianpowerconsumptionwillbesaved[49].

3 Membranematerialsformembranecontactorapplications

Membranedevelopmentisanessentialkeyfactorforthecommercialization

ofmembrane operations.An example has been the developmentofthe

asymmetriccelluloseacetatemembraneforreverseosmosis(RO)whichmade

ROdesalinationacommercialopportunityinthe1960s.Untilnowmembrane

improvementhas mainly been focused on making the membrane more

hydrophilicforthe needs ofpressure driven membrane operations.The

developmentofnovelpolymericmembranesisnowevolvingfortheuseinthe

new membraneoperationssuchasmembranedistillationand membrane

crystallization.Inthepast,membranedistillationhasbeenmainlycarriedout

14

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

withcommercialmembranesproperlymanufacturedformicrofiltration,however

researchactivitiesonpreparationofmembranesspecificdevelopedforMDare

emerging rapidly[50].Fluoropolymers(such asPVDF,PTFE and ECTFE)

providethepossibilitytomanufacturehydrophobicmembraneswithsuperior

thermalstability,improvedchemicalresistanceandlowsurfacetension[51].

PVDF is widely used forcontactorapplications because ofthe easy

processabilitywithphaseseparationmethodsalongwithgoodhydrophobicity

andchemicalresistance[51].SeveralPVDFmembraneshavebeenpreparedby

changingtheprocessingconditions,suchasadditives,solvents,airgab,

borefluidsetc.[52].Thepreparedmembraneshaveshowngoodperformance

both in direct contact membrane distillation and vacuum membrane

distillation[52].Superiorhydrophobicmembranescanbeobtainedbycoating

thePVDFmembraneswithegHYFLONinordertoimprovethemechanical

resistance,themicrostructureandtheliquidentrypressure[53].

Recentapproachesarealsoconsideringtheperformanceofmicroporous

hydrophobic/hydrophiliccompositemembrane,withatophydrophobicthin

layerresponsibleforthemasstransport,andahydrophilicsublayerableto

reducetheconductiveheatlossthroughthewholemembranematrix[50].

Although membrane operations are highly affiliated with sustainable

development,inthemembranepreparationproceduressometoxicsolvents

areused.In orderto ensure the overallsustainabilityofthe membrane

technology,frommembrane/modulefabricationtoendproductutilization,Cui

etal.haveinvestigatedanenvironmentalfriendlysolvent,acetyltributylcitrate

(ATBC),forthepreparationofPVDFmembranes[54].Thissolventcanalsobe

usedinmedicalapplication,beverageindustry,toys,etc.Thecarriedout

study indicated that the prepared PVDF membranes exhibited good

mechanicalproperties,promisingforwatertreatmentapplications.

4 Conclusions

Highwaterstress,increasingenergyconsumptionsandmineraldepletion

areallalreadycriticalissues.Processengineeringisoneofthedisciplines

moreinvolvedinthetechnologicalinnovationsnecessarytofacethesestrongly

interconnectedproblems.Asamatteroffact,waterisalsoneededforenergy

24

generation(eg.,coolingcomponent);energyisalsoneededindesalination

andforrawmaterialproduction(especiallyinminingwherelargeamountof

energyandwaterarenecessary).

Recently,process engineering has suggested the logic ofProcess

Intensification(PI)toresolvetheseproblems.Membranetechnology,whose

basicaspectssatisfytherequirementsofthePIstrategy,canrepresenta

problemsolverwithintercorrelatedsolutions.Inthelastyearsmembranes

operationshave been alreadyassigned a keyrole in waterreclamation

schemesthatareaimed athigherwaterqualityreuseapplications(ie.,

reverseosmosisisconsideredoneofthemostpromisingtechnologiesfor

desalting salty waters).Moreover, the traditionalmembrane separation

operations(eg., MF, UF, NF, RO), widely used in many different

applications,aretodaycombinedwithnewmembranesystemssuchasMD,

MCr,PRORED.Atpresent,redesignofimportantindustrialproductioncycles

bycombining various membrane operations suitable forseparation and

conversionunits,andthusrealizinghighlyintegratedmembraneprocesses,is

anattractive opportunitybecause ofthe synergistic effectsthatcan be

attained.

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EnricoDrioli  hasbeenDirectoroftheInstituteon

MembraneTechnologyoftheNationalResearchCouncil

(ITMCNR),Italy,since1993.HeistodayHonorary

FoundingDirectoroftheITMCNR,EmeritusProfessorat

theUniversityofCalabria,DistinguishedChairProfessor

attheHanyangUniversityinKorea,DistinguishedAdjunct

ProfessorattheKingAbdulazizUniversityinSaudiArabia.

HereceivedhisDoctor’sdegreeinUniversityofNaples,

Italyin1965.DrioliwasaprofessorofChemistryandElectrochemistryattheSchoolof

EngineeringinUniversityofNaples,Italy,aswellasattheSchoolofEngineeringin

64

UniversityofCalabria,Italy.

DrioliwasPresidentoftheEuropeanSocietyofMembraneScienceandTechnology

(1982-1998)andChairmanoftheWorkingPartyonMembranesoftheEuropean

FederationofChemicalEngineering(since1985).Hehasreceivedanumberof

honorarydegreesandawardsincludingthe1999HonoraryFoundingPresidentofthe

EuropeanMembraneSocietyandhonorarymemberoftheA.V.TopchievInstituteof

PetrochemicalSynthesisattheRussianAcademyofSciences,Moscow.Honorary

ProfessorChinaNorthwestUniversityinXi’an,Shaanxi.Hewasapatronmemberof

theIndianMembraneSocietyandaMemberoftheAdvisorBoardoftheUNESCO

CenteronMembraneScienceandTechnologyattheNewSouthWalesUniversity,

Australia,etc.HeisservingtodayalsoascoordinatoroftheEuropeanErasmus

DoctorateSchoolinMembraneEngineering(EUDIME).

74

SurveyontheDevelopmentofMembraneScienceandTechnologyinChina

WanqinJin,etal.

NanjingTechUniversity,Nanjing,China

Researchonmembraneandmembraneprocesseswasstartedfrom1950s

inChina.In1958,themembraneresearchinChinawasstartedinInstituteof

Chemistry.The firstmembrane wasion exchange membranesbased on

PVA[1].In1965,exploringresearchonreverseosmosis(RO)membraneswas

begun.ThisworkwaspioneeredbyProf.GaoinOceanUniversityofChina.

FirstROmembraneiscelluloseacetate(CA)membrane.Thisworklaidagood

foundationfortheprogressofmembranescienceandtechnologyinChina.In

1970s,Chinesemembraneenteredthedevelopingstage.Themembranesand

relatedmodulesaremostdeveloped,suchaselectrodialysis(ED),RO,

ultrafiltration(UF)andmicrofiltration(MF).In1980s,membranetechnologies

steppedintoapplicationstage,andalsosomenewmembraneprocesseswere

developed.Water treatments by membrane technology were putinto

application,suchasseawaterdesalination,purewaterproduction,purification

andconcentrationofvariousliquids;andsomeofapplicationswereinlarge

scale.Meanwhile,gasseparation(GS)membranesdevelopedveryquickly.

ThemembraneprocessesforoxygenenrichmentandseparationofN2/H2enteredpilotperiod.Studiesonpervaporation(PV),membranedistillation

(MD),inorganicmembranes(IM)andmembranereactors(MR)werealso

carriedout.In1990s,membraneresearchgotintoarapiddevelopingperiod.

Variousmembraneandmembranesprocesseswereinvestigatedextensively.

Especially,preparationofinorganicmembraneentered commercialization,

andinorganicmembraneswereapplied inchemicalindustry.Inaddition,

membraneapplicationinbioengineeringwaslaunched.Fromthebeginningof

thiscentury,Chinesemembraneresearchersmadeagreatprogress.Inthe

84

aspectofmembranepreparation,manynew typesofmembranematerials

werestudied,suchasRO TFC membrane,PVDFmembranepreparedby

TIPS,zeolite membranesforpervaporation.In the aspectofmembrane

processes,MD processinpilotscaleforseawaterdesalinationandMBR

processinlargescaleforwaterreusewerecarriedout.Somenewmembranes

andnewmembraneprocessesarebeinginvestigated.

Atpresent,thereareover100membraneresearchteamsinChinaand

theyarelocatedinChineseuniversitiesandresearchinstitutes.Amongthem,

about30researchgroupscontributeimportantworktomembraneresearchof

China.Infact,intheseyearsthedevelopmentofmembranetechnologyina

largeextentbenefitedfrom theChinesegovernment’sstrongsupport.One

importantfinancialsupportformostresearchersisfrom NationalNatural

ScienceFoundationofChina(NSFC).Anotherveryimportantfinancialsupport

isfromtheMinistryofScienceandTechnologyofChina.Therearethreemain

typesofsupportsfrom it.Oneisnationalbasicresearchprogram,named

“973”,whichisthebiggestgranttosupportfundamentalresearchinChina.

Thesecondprogramis“863”plan,anditpromoteslab’stechnologytopilot

orcommercialscale.Thethirdprogram istheNationalKeyTechnologyR&D

Program,andthisprogram supportsthepilottechnologytoindustrialscale.

From2003tonow,wearegrantedtwophases“973”plan,andobtained

about60millionRMB.The“973”plangreatlypromotedthefundamental

studiesofmembranescienceandtechnologyinChina.Underofthegreat

supportfromChinesegovernment,Chinesemembraneresearchmadeagreat

progress.ThenumberoftheChinesepatentsinmembranefieldincreasesyear

byyear, and more and more papers aboutmembrane research were

publishedbyChineseresearchers.Furthermore,alargemembranemarkethas

beenformedinChinabecausetheforeignmembranecompaniesenteredand

Chinaitselfhas a lotofenterprises.There are nearly1000 membrane

companies,andamongthem over300aremembranemanufacturers.Some

bigmembranemanufacturershaveplayedasignificantroleinmembrane

productionand membraneprocessesinChina.Theyshortenthegap of

membranetechnologybetweenChinaandsomeadvancedcountriesinsome

membranes.

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

MF/UFmembranesarethebiggestmembraneproductioninChina.Asfor

preparingporouspolymerMF/UFmembranes,therearetwomainmethods,

NIPSandTIPS.Generally,theMF/UFmembranesviaNIPSmethodhavebig

fingerlikepore,buttheirporesizesarenotuniform.ThemembranesviaTIPS

haveuniform poresizeandgoodmechanicalstrength.Apatentedtechnique

fromZhejiangUniversitypreparedlowcostandhighperformanceofcapillary

PVC(polyvinylchloride)blendingmembranes[2].Themembranescanbeused

forultrafiltrationornanofiltrationprocesses.OneofthebiggestUFmembrane

manufacturersisLitreeCompany.Itcanproduce3millionm2PVCmembranes

peryear,andhaveover500000residentialcustomers.Forexamples,thePVC

membraneswereappliedforwatertreatmentatKaohsiungofTaiwanwith

capacityof300thousandtonperday,andmembranesbasedwatersystem

provideddirectdrinkingwaterforvisitorsfrom 260countriesforShanghai

WorldEXPO2010.ThePVCmembranesarealsoappliedformunicipalwater

treatment.

ThePVDFhollowfibermembraneshavebeenwidelyappliedindifferent

areas.Thismostusedfieldisthemembranebioreactor(MBR)system based

onthemembrane.PVDFmembranescanbepreparedbyTIPSmethod.The

keypointofTIPSmethodforPVDFmembranesistoselectasuitablediluentto

undergothe liquidliquid phase separation with PVDF polymer.Tsinghua

Universityhassuccessfullydeveloped a seriesofdiluentswith different

polarities to broad the liquidliquid phase separation region forPVDF

membranes[3].TheyobtainedsuitablediluentssuchasDPKandDPCandgot

bicontinousmicrostructureofPVDFmembranes.Furthermore,theyrecently

haverealizedtheindustrialproductionofPDVFmembranesviaTIPSbyScinor

Corporation with the yield of300 thousand m2 peryear.Some PVDF

membraneshavebeenappliedinwatertreatment,forexampleinSolarand

Steelindustry,withthecapacityof30thousandtonsperday.

DuringtheapplicationofMF/UFmembranesinwatertreatment,oneof

thecriticalproblemsisthemembranefouling.Forexample,intheMBR

system,thereisalwaysformationofbiofoulingfilmonthemembranesurface,

resultinginreducedseparationperformanceandshortlifetimeofmembranes.

Inordertoimprovethehydrophilicityandantifoulingpropertiesoftheporous

05

membranes,aseriesofsurfacemodificationsofpolymermembranes,suchas

polymergrafting,plasmatreatment,copolymerizationand macromolecule

immobilizationhavedevelopedbyZhejiangUniversity[4-6].Thesedeveloped

approachesareveryeffectivetoavoidbiofouling.

Recently,ROmembraneshavebeenmadedramaticprogressinChina.

Severalnew monomersforRO membraneswithhighfluxand antifouling

propertieshavedeveloped[7,8].Theseworkmadetheperformanceofdomestic

RO membranesclosertotheworldadvancedproducts.RO manufacturer

VontronCompanyincreasedtheChineseROmarketshare.Theapplicationof

ROmembranesinChinamainlyincludesdrinkingwaterproduction,purewater

industryanddesalinationofseawater.Takewaterdesalinationforexample,the

numbersofROequipmentwithcapacityover100tonperdayareabout40.

Forpervaporationprocess,therearemanygroupsfocusedonpolymeric

membranesin China.Groupcontribution method calculating the solubility

parametersofthemembranematerialsandthecomponentsofthetarget

separation system has been developed by Tsinghua University[9].They

obtainedaseriesofhighperformancepervaporationmembrane,including

PVAandPDMS.ThePVApervaporationmembranehasbeencommercialized.

OneofthetypicalPVAapplicationsofpervaporationmembranesinChinaisfor

solventdehydration.Untilnow,thereareover60solventdehydrationplants

usingPVAmembranesinChina,suchasforethanol,isopropanolsystem

dehydration.

From1980s,themainmembranematerialsdevelopedinChinaforgas

separationarePDMS,PI,PMP,PPOandPTMSP.Theapplicationsofthese

membranesareover26provincesanddistrictsinChina.Theapplyingfields

covermanygasrelated industries.Oneofthewidestapplicationsofgas

separationmembranesishydrogenrecoveryandpurification.Theapplication

fieldsincludesynthesisammoniaprocess,methanolproduction,andrefinery

gas.Furthermore,gasseparationmembranesarealsoapplied forVOCs

recovery,such asapplication in gasstation,olefin purge gasand oil

productionprocess.InordertoobtainCO2gasseparationmembrane,several

groupsdevotedtodevelopseveralnew membranematerialsforCO2 gas

separation.Forexample,DalianInstituteofChemicalPhysicsand Tianjin

15

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Universityrecently have developed many kinds ofhigh performance gas

separationmembranematerialswithgoodantiplasticizationandantioxidizability

properties,suchascrosslinkedpolyimide,multipermselectivematerialsand

novelfixedcarriermembranematerials[10-12].

Chinahastheworldbiggestchlorinealkaliindustrywiththecapacityof35

milliontonperyear.Developingdomesticionexchangemembranesarecritical

forChineseresearchers.In2010,DongyueGroupsuccessfullydevelopedthe

productionlineofdomesticperfluorinatedionexchangemembranes,andthey

appliedinchlorinealkaliplantswiththecapacityof10thousandtonsperyear.

Anotherkindofionexchangemembraneisbipolarionexchangemembranes.

Domestic bipolarion exchange membranes have been developed by

UniversityofScienceandTechnologyofChinaandrealizedtheirindustrial

production and application[13].Forexample, the bipolarion exchange

membranescanbeappliedforacidrecoveryfrom aluminum foilproduction

feeds.Thetreatmentamountoffeedacidicsolutionsreached59thousandm3

peryear.

Besidesorganicmembranes,therearemanyinstitutionsinChinadevoted

totheresearchofinorganicmembranes,andtheyaremainlylocatedinthe

eastern coastalcities.Among them, the research group from Nanjing

UniversityofTechnologyisthebiggest,whichisledbyProf.NanpingXu.From

1990 to now, inorganic membranes have a greatdevelopmentand

impressivelyfrom thelaboratorytothemarket.Thereareseveralimportant

milestones.ThemostimportantmilepostisProf.Xu’sGroupmadetheceramic

membranetechnologyfromthelaboratorytothemarketin1997.

Ceramicmicrofiltrationand ultrafiltrationmembraneshavebeenlarge

scaleproducedandappliedformorethantenyearsinChina.Atpresent,

commercializedMFandUFceramicmembranesaremainalumina,zirconia

andtitania.JiangsuJiuwuHighTechCo.,Ltd.isthebiggestmanufacturerfor

ceramicmembranesinChina.Itsuppliestubularandmultichannelmembrane

elements.UFceramicmembraneswereusedtodealwiththewastewatersuch

asbanknoteprintingwastewaterandrollingemulsion.Whenthemembrane

technologyusedinbanknoteprintingwastewater,itcanreuseofthetreated

waterandrecoveryofvalueddyes.Steelfactorycanproducelargeamountof

25

oilwateremulsion.WhenweusedtheZrO2 membrane,therejectionofoil

reached999%,andrecoveryofwaterlargerthan90%.Thisprocessis

runningforover10 years.Thetechniqueisused inmorethan20 steel

factories.Oneimportantapplicationofporousceramicmembranesisinthe

biotechnologyindustries,suchasforinosinerefinement.Comparedwiththe

traditionaltechnology, ceramic membrane technology improves inosine

recoveryfrom85% tomorethan90%,reducestheconsumptionofacidand

base,reduces70% wastewateranddecreases60% ofCODinwastewater.

Becauseofchemicalresistanceandthermalstability,ceramicmembranescan

beappliedinchemicalindustry.Oneexampleisporousceramicmembrane

reactor.Themembranereactortechnologycanbeusedinheterogeneous

catalyticreaction,whichcancouplethecatalyticreactionwiththemembrane

separationin one process and realize the productand catalystinsuit

separation.Itcan be applied in the production ofimportantmedicine

intermediatepaminophenolandchemicalintermediatecyclohexanoneoxime.

Ceramicmicrofiltrationmembranesweresuccessfullyemployedtoremoveultrafine

catalysts from the reacted slurry.The recovered catalysts were recycled

continuouslybacktothereactorandreusedinthenextbatchofreaction.

Inthelastdecade,zeolitemembraneshaveattractedmuchattention

becauseoftheirpotentialapplicationsasselectiveseparationmembranes,

catalyticmembranereactor,chemicalsensorsandmicroelectronics.Mostwork

ofthisfieldhasfocusedonthesynthesisandapplicationsofNaAandMFI

zeolitemembranes.ForpreparingNaAzeolitemembrane,thewipinganddip

coatingmethodwasappliedtoseedsupporttolowtheinfluenceofdefectof

mulliteandraisethepermeationflux[14].What’smore,usingpolymerNaA

zeolitecompositehollowfiberassupportofNaAmembranes,PVdehydration

resultsshowsthatthefluxincreasesto93kg/(m2·h)andseparationfactor

isstilllargerthan10000[15].MFIzeolitemembranepreparedonYSZhollow

fiberssupportshowshigheralcoholseparationperformancefromalcohol/H2O

systemsthantheotherinorganicsupportedMFImembrane.NaAmembranes

havebeenlargescaleproducedbyNanjingUniversityofTechnologyand

industrialappliedforisopropanol,methanol,andethanoldehydration.

Mixedionicelectronicconducting(MIEC)materialsarewidelyinvestigated

35

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

inChinasince1990s.ThechallengesofMIECaredevelopingnewmembrane

materialswithhighoxygenpermeabilityand highchemicalstability,new

methodsforthepreparationofmaterialsandmembranesandnew dense

membranereactors.ManykindsofMIECmaterialshavebeendevelopedin

recentyears.Forpreparationofasymmetricmixedconducting membrane,

especiallyofsupportedtubularmembrane,acombinationofspinspraying

andcosinteringmethodhasbeendeveloped.Itprovidesanewpathforthe

preparationofasymmetrictubularmembrane.Thissimpleandcosteffective

fabricationtechniquecanbereadilyusedformassproduction.Ontheaspect

oftheapplicationsofMIECmembranes,theycanbeusedforpartialoxidation

ofmethane(POM),CO2decompositioncoupledwithPOM,watersplittingand

NOdecompositionetc.

Porousmetalsareofgreatinterestasapotentialengineeringmaterialin

variousindustrialfieldsbecauseoftheiruniquepropertiessuchastheirimpact

energy absorption capacity, theirgas and liquid permeability, thermal

conductivity,andelectricalinsulatingproperties.PorousTi-Al&Fe-Alalloys

membraneshavebeenpreparedbyCentralSouthUniversity.Themembranes

havebeenappliedforproductionofTiCl4andZnSO4.

Inthepastdecade,newmembranematerialsandmembraneshavealso

agreatdevelopmentinChina.Variousbioinspiredsmartgatingmembranesof

thermoresponsive,pHresponsive,glucoseresponsive,molecularrecognizable

havebeensuccessfullydevelopedbySichuanUniversity[16-18].Forexample,a

positivelyK+ -responsivemembranewithfunctionalgatesdrivenbyhost

guestmolecularrecognition is prepared by grafting poly(NIPAMco

AAB15C5)copolymerchainsintheporesofporousnylon6membranes[19].

Thegraftedgatesinthemembraneporescouldspontaneouslyswitchfrom

“closed”stateto“open”statebyrecognizingK+ionsintheenvironmentand

viceversa.ThepositivelyK+ -responsivegatingactionofthemembraneis

rapid,reversible,andreproducible.

Membraneswithhighlyuniform poresizeareimportantinvariousfields.

ZhejiangUniversityreported thepreparationand performanceofordered

membranestemplated bybreath figures,and the pore diameterofthe

membraneisonthemicrometerscale[20].Theordered membranes(pore

45

diameterof3μm)fabricatedattwophaseinterfacesenableahighresolution

and energysaving separation process.Nanjing University ofTechnology

prepareduniform membranescharacterizedbyeasilyaccessible,continuous

nanoporesystemswithwelldefined,uniform poresizesbynondestructive

replicationofnanoporouspolymericmembraneswithlikewisebicontinuous

morphologies[21].Thenanoporouspolymericmembranesconsistedofrecoverable

asymmetricBCPsandweregeneratedbyselectivelyswellingtheminority

componentofthe BCP accompanied by reconstruction ofthe domains

consistingoftheglassymajoritycomponent[22].

Metalorganicframeworksareconstructedfrom metalionsorionclusters

actingas“joints”andtheorganicligands(imidazolatesforZIF)as“linkers”

toproducetheporouscoordinationpolymerwiththehighlyregularstructure.

Thismaterialhasmanyadvantageswithhighsurfaceareas,tailormade

pores, designable structures, preferentialadsorption.Because of the

advantages,MOFhasbeenregardedasanewtypeofmembranematerial.

ThefirstMOF(HKUST-1)membranewaspreparedoncoppernetviainsitu

hydrothermalgrowth,whichshowsexcellentH2 separationperformance[23].

TheMOFbasedmixedmatrixmembrane(ZIF-8/PMPS)wassynthesized.It

showsaverypromisingperformanceforrecoveringbioalcoholsfrom dilute

aqueoussolution[24].Nanjing UniversityofTechnologydeveloped afacile

reactiveseedingmethodforthepreparationofcontinuousMOFmembranes,in

whichtheporoussupportactedastheinorganicsourcereactingwiththe

organicprecursortogrow aseeding layer[25].Theasprepared MIL-53

membraneshowshighselectivityfordehydrationoftheazeotropeofethyl

acetate(EAC)aqueoussolutionbypervaporation.Anewgenerationofachiral

separationmembranecomposedofhomochiralZn2(bdc)(llac)(dmf)(Zn-

BLD)wassuccessfullyfabricatedonaporouszincoxidesubstratebya

reactiveseedingtechnique[26].Aneevalueof330% forRmethylphenyl

sulfoxide(MPS)overS-MPSwasobtainedatthefeedconcentrationof5

mmol/L.Inaddition,stepbystepseedingmethodwasdevelopedtoprepare

HKUST-1(knownasCu3(btc)2)membranesonporousαaluminasupports.

Recently,inordertopromotethedevelopmentofmembranematerials

industry,“12thfiveyearplan”(2011-2015)inmembranefieldhaslistedthe

55

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

“membranematerialswithhighperformance”asmajorprojectbytheMinistry

ofScience and Technology ofChina.The key directions include water

treatment,gasseparation,specialmembranesand new membranesand

membraneprocesses.Theseresearcheswillprovidetheoryfoundationof

designandpreparationforapplicationorientedmembranematerials.

Insummary,membranescienceandtechnologyhasbeenmadegreat

progresssince1990sinChina.Next,muchattentionshouldbepaidtothe

researchthroughtheeffortsofourselves,andtheinternationalexchangeand

cooperation.ThedevelopmentofmembranescienceandtechnologyinChina

hasbeeninternationallyrecognized.Chineseresearchersarebeingexpected

tomakeagreatercontributiontothedevelopmentofmembranescienceand

technologyinnearfuture.

References

[1] ZhuXCh.HuaxueTongbao,1958,10:606.(inChinese)

[2] XuYY,WangJN,LiuF,etal.Patent:CN200810062570.8.(inChinese)

[3] LinYK,TangYH,MaHY,etal.JApplPolymSci,2009,114:1523.

[4] WangC,WuJ,XuZhK.MacromolRapidCommun,2010,31:1078.

[5] YangYF,HuHQ,LiY,etal.JMembrSci,2011,376:132.

[6] WangC,RenPF,HuangXJ,etal.ChemCommun,2011,47:3930.

[7] WangHF,LiL,ZhangXS,etal.JMembrSci,2010,353:78.

[8] XuJ,FengXSh,GaoCJ.JMembrSci,2011,370:116.

[9] GmehlingJ,LohmannJ,JakobA,etal.IndEngChemRes,1998,37:4876.

[10] YuXW,WangZh,WeiZhH,etal.JMembrSci,2010,362:265.

[11] LiShCh,WangZh,YuXW,etal.AdvMater,2012,24:3196.

[12] WangMM,WangZh,WangJX,etal.EnergyEnvironSci,2011,4:3955.

[13] WangAL,PengShCh,WuYH,etal.JMembrSci,2010,365:269.

[14] LiuYM,YangZhZh,YuCL,etal.MicroporMesoporMater,2011,143:348.

[15] WangZhB,GeQQ,ShaoJ,etal.JAmChemSoc,2009,131:6910.

[16] ChuLY,LiY,ZhuJH,etal.AngewChemIntEd,2005,44:2124.

[17] QuJB,ChuLY,YangM,etal.AdvFunctMater,2006,16:1865.

[18] MeiY,ChuLY,WangHD,etal.AdvFunctMater,2008,18:652.

[19] LiuZh,LuoF,JuXJ,etal.AdvFunctMater,2012,22:2742.

[20] DingShJ,ZhangDY,ChenJS,etal.JAmChemSoc,2012,134:95.

[21] WangY,LiFB.AdvMater,2011,23:2134.

[22] WangY,HeChCh,XingW H,etal.AdvMater,2010,22:2068.

65

[23] GuoHL,ZhuGSh,HewittIJ,etal.JAmChemSoc,2009,131:1646.

[24] LiuXL,LiYSh,ZhuGQ,etal.AngewChemIntEd,2011,50:10636.

[25] HuYX,DongXL,NanJP,etal.ChemCommun,2011,47:737.

[26] WangW J,DongXL,NanJP,etal.ChemCommun,2012,48:7022.

Prof.WanqinJin isaprofessorofChemicalEngineering

atNanjingUniversityofTechnology,andtheDeputy

directoroftheStateKeylaboratoryofMaterialsoriented

ChemicalEngineering,China.HereceivedhisPh.D.from

NanjingUniversityofTechnologyin1999.Hewasa

researchassociateatInstituteofMaterialsResearch&

EngineeringofSingapore(2001),anAlexandervon

HumboldtResearchFellow(2001-2013),andvisiting

professorsatArizonaStateUniversity(2007)andHiroshimaUniversity(2011,JSPS

invitationfellowship).Hecurrentlyresearchesonmixedconductingmembranesfor

oxygen separation and catalytic membrane reactor, organic/ceramic composite

membranesforpervaporation,andbiosensors,andhaspublishedover160international

refereedjournalpapersandheld15patents.HeisnowontheEditorialBoardsof

JournalofMembraneScience,JournalofNanomaterialsandChineseJournalof

ChemicalEngineering,andisacouncilmemberofAseanianMembraneSociety.

75

MembranesandWater—RecentDevelopments

TonyFane1,2,3,etal.

1SingaporeMembraneTechnologyCentre(SMTC),Singapore

2NanyangEnvironment&WaterResearchInstitute(NEWRI),

Singapore

3SchoolofCivil&EnvironmentalEngineering,Nanyang

TechnologicalUniversity(NTU),Singapore

Fig.1 Themembranesandwaterdomain

1 Introduction

Membranetechnologyisplayinganincreasinglyimportantroleinthewater

industry.Thisincludesmembranesforsurfacewatertreatment,fordesalination

(bothbrackishandseawater),forwastetreatmentinbioreactorsandfor

water reclamation and reuse (seeFig.1). The available membrane

technologiesrangefrom lowpressuremicroporousmembranes(MFandUF)

tohigherpressuremembranes(NFandRO),aswellaselectrodialysisandthe

emergingtechniquesofforwardosmosis(FO)andmembranedistillation(MD).

85

Recentdevelopmentshavefocusedonnovelmembranesandoperationsand

assessingnovelprocesses.Thedrivershavebeenimprovedefficiencyand

energyissues,inresponsetotheneedtoreduceGHG emissions.Inthis

presentationthestatusofmembranesandwaterisreviewed.Inaddition,

examplesare provided bythe developmentofmembrane technologyin

SingaporeandresearchattheSingaporeMembraneTechnologyCentre.

2 Singapore&SMTC

Singaporeisaworldleaderintheapplicationofmembranetechnologyto

watersupply.Currentlymorethan12megatonsperdayofwaterpassthrough

membranesinSingapore.Thiscomprisesabout274MLd(millionliterperday)

surface watertreatment,455 MLd desalination and 500 MLd NeWater

reclamation.Notsurprisinglythismembranedependentenvironmentsupports

R&Dinmembranetechnology.Arecentreport(Lux(2013))highlightsthe

successofthisapproachwiththetop2universitiesbeingfromSingapore.The

researchintheSMTCreflectsmanyofSingapore’sprioritiesandthelatest

trendsinmembranesandwater.

TheSingaporeMembraneTechnologyCentrewasestablishedinearly

2008withtheprimaryobjectivetodofundamentalandappliedresearchin

membranetechnologyforenvironmentandwaterindustries.TheSMTC has

morethan40projectsinthethematicareas:

-waterproduction,

-waterreclamation,

-membranebioreactors,

-energyissues,

-sensorsandmonitoring,

-membranesforspecialneeds.

Underlyingobjectivesaretoimproveefficiencyandreduceenergyusage

inmembranesinwater.Therearemajoreffortsin(i)novelmembranes,(ii)

moduledesignandoperation,(iii)foulinganditscontrol,(iv)noveland

improvedmembraneapplications.Thefollowinghighlightsouractivities.

3 Novelmembranes

1)Reverseosmosis.Althoughdesalinationisconstrainedbyminimum

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

energyandosmoticpressureconsiderationsthereisthepotentialtoreduce

seawaterdesalination energy by 25% to 30% with superpermeability

membranes.Asaresultthereisanongoingquestforsuchmembranes.One

approachmaybebiomimeticmembranes,incorporatingaquaporinswhichare

naturalproteinbasedwaterchannelswithhighwaterandlowsaltpermeability.

Aquaporinscanbecombinedwithliposomestoform sphericalvesicles,and

wehaveshownthatthesecanbeincorporatedintothinfilmcomposite(TFC)

membranes(Zhaoetal.,2012)withfluxesenhancedby50% ormore.Both

flatsheetandhollowfibrecompositesarepossible.

2)LowpressureNF.SeveralmethodshavebeenevaluatedtoproduceNF

membranescapableofwatersoftening atmodestpressures(≤ 2 bar).

Methodsincludelayerbylayerdepositionofpolyelectrolytesandduallayer

hollowfibres.Usingthelatterprocessmembraneshavebeenpreparedwith

waterpermeabilitiesof15lmh/bar(L/(m2·h·bar),1bar=105 Pa)and

rejectionsofmonoanddivalentionsofabout10% and >90% respectively.

Numerousapplicationsofthesemembranesareenvisaged.

3)Forwardosmosis(FO).FO isahottopicduetoitspotentialforlow

energyprocessingorinenergyrecovery(seebelow).SMTChasproduced

bothflatsheetand hollow fibremembraneswithoutstanding properties.

MembranestructureisakeyissuewitharequiredROlikeskinlayerandathin

andhighlyporoussupportlayer.WecanproduceTFChollowfibremembranes

withhighwaterpermeabilityandlowsalttransmission(Chou,2010).Adual

skinhollow fibrehasbeenpreparedtohelpcontrolinternalfoulingofthe

membrane.AdevelopmentofourFOmembraneisverysuitableforPressure

RetardedOsmosis(PRO,seebelow).

4)Membranedistillation(MD).MDhastheattractionthatitcanprocess

saltywatertohighrecoveriesandextractwaterfrom SWRO brine.Itisalso

amenabletouseofwasteheatwithlowGHGemissions.MDmembranesneed

tobehydrophobicandhighlyporous,andwehavedevelopedtechniquesto

increasecontactanglesintothesuperhydrophobicrange(Liaoetal.,2013).

ThispropertyallowsMDoperationwithoutwettingoutandlossofseparation.

WeareusingMDmembranesinMDcrystallizationandtheMDbioreactor(see

below).

06

4 Modules,hydrodynamics,systems

Advancesinmembranesneedtobematchedtoenhancedtechniquesto

controlconcentrationpolarizationand fouling.SMTC hasbeen examining

variousstrategiestoenhancepolarizationcontrol.

1)Vibrations.Vibrationscanbereadilyappliedtosubmergedhollow

fibres,bothaxiallyandlaterally,tocontrolpolarizationandfouling.Wehave

observedbetterenhancementwithlateralmovementandasmalldegreeof

fibrelooseness(Lietal.,2013).Theoreticalanalysissuggestsimproved

controlforsmalldiameterfibres(Zamanietal.,2013).Itismorechallenging

toapplyvibrationstoRO modules.Howeverwehaveshownthatrotational

vibrationsofaspiralwound modulecansignificantlydelaytheonsetof

scaling.

2)Bubbling.Althoughbubblingiswidelyusedforpolarizationandfouling

controlinMBRsthereisaneedforoptimization(Xiaetal.,2013).Thebenefit

oftwophaseflowhasalsobeendemonstratedinahollowfibreMDmodule

wherebubblinghasimprovedshellsideflowdistributionandincreasedfluxby

over100%(Chenetal.,2013).

3)ROcascadedesign.Therearenovelwaystomodifypolarizationand

osmoticeffectsinRO.InanRO processplanttherearecombinationsof

membranemodulesandpressurevesselsinmultistagecascades.SMTChas

developednovelarrangementsbasedonthe‘refluxrecycle’conceptfamiliar

tochemicalengineering.Asanexample,ouranalysisshowsthattheprocess

canbeoperatedatlowerpressures,orcanachievehigherrecovery(75%)at

thetypicalpressurefor50% recoveryoperation(Chongetal.,2013).

5 Operationalandfoulingissues

Foulingisasignificantsourceofinefficiencyinallmembraneprocesses.

SMTChasbeeninvestigatingfoulingacrossthespectrum from lowpressure

pretreatment,RO, MBRs, MD and FO applications.One ofthe most

challengingissuesisbiofouling.

1)BiofoulinginRO.Usingwellcontrolledfeedandoperatingconditions

wehaveshownhow biofoulinginRO ismitigatedbyflux,crossflow,the

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

presenceofspacers,nutrientleveletc(Suwarnoetal.,2012).Therateof

foulingcorrelateswiththeestimatedconcentrationofnutrientatthemembrane

surface.Confocalmicroscopyofautopsiedsamplesrevealsthedevelopmentof

thebiofilm components.Anovelbiomimicrystrategyisbeingevaluatedthat

usesNOdonorstotriggerbiofilmdispersion,withencouragingresults(Barnes

etal.,2013).

2) Biofouling in MD.The MD bioreactor(see below) experiences

biofoulingthatmanifestsasafoulingresistance.Inadditionthebiofilm also

influencesthemagnitudeofthevapourpressureinMD throughtheKelvin

effect(Gohetal.,2013).Interestinglythebiofoulingappearstoprotectthe

membranefromearlywettingout.

6 Applicationsandprocesses

Thefollowingdescribesexamplesofnovelmembraneapplicationsinthe

waterdomain.

1) Pressure retarded osmosis(PRO).PRO provides a means of

generatingpowerfrom salinitygradients,suchasseawater/riverwateror

SWRObrine/NeWaterbrine.ThemosteffectivePROmembranesaremodified

FOmembranesthatcanmaximisetheosmoticpressuredifference.SMTChas

developedbothflatsheetandhollow fibrePRO membranes(Chouetal.,

2012);ourmostrecentmembranescanachieve20W/m2at15barandthisis

competitivewithanyotherreportedPROmembranes.Therearealsonewflow

sheetoptionsinvolvingthecombinationofPROwithRO.Energysavingsand

increasedwaterrecoveryarefeasible.

2)Forwardosmosisdraw solutes.SomeapplicationsofFO cantake

advantageofavailabledraw solutes,asinthePRO exampleabove.Other

applicationsmaybecomefeasibleifaneffectivedrawsoluteisdeveloped.The

requirementisfora materialwith high osmotic pressure thatisreadily

regenerated.OneapproachbeingdevelopedatSMTCistheuseofthermo

sensitivehydrogels(Caietal.,2013).

3)MDcrystallization(MDC).SeawaterRObrine,andotherconcentrated

saltscanbeprocessedbyMDCtorecoverwaterandsolids.Thechallengeis

controlofthecrystallizationprocessexternaltotheMDmoduleandalsoto

26

optimisetheenergyusageoftheprocess.Thetradeoffbetweenmembrane

areaandenergyusagehasbeenanalysedbyanAspenbasedmodel(Guan

etal.,2012).

4)Novelmembranebioreactors(MBRs).Inadditiontoacomprehensive

studyofconventionalMBRs,includingfouling(Zhangetal.,2006),SMTCis

developingarangeofnovelMBRs.TheMDBR(Phattaranawiketal.,2008)

andtheFOMBR(Yapetal.,2012)are‘highretention’(HR)MBRsusing

membranesthatallowoperationwithORT>>HRT,providingtimefortreatment

ofrecalcitrants.BothMBRshavethepotentialtouselowgradeheatandto

producehighqualitywater.A featureofthe HRMBRsisthatsaltsalso

accumulate.Thismeansthathalophilicbiomassisrequired;theMDBRalso

needsthermophilesforoperationatca55℃.AdditionalMBR applications

involvetheFluidizedBedAnaerobicMBRforlowfoulingandbiogasproduction

andtheExtractiveMBRwithorganic(membrane)extractionintoabioreactor

fororganicsindifficultfeedwaters(salty,pHextremes).

5)Membranesforspecialneeds.Watersupplyisusuallyjeopardisedafter

tsunamiorearthquakeevents.SMTChasaninterestinmembranesforthese

situations,aswellasinthirdworldwatersupply.Wehaveproposedadecision

toolforemergencywatersupplytechnologies(Looetal.,2012)andhave

developedan‘integralmembrane’basedoncryogelsthatcanachievegood

waterrecoveryfromturbidstreams(Looetal.,2013).

6) Life cycle assessment(LCA).Decision tools are usefulin the

identificationofpreferredprocessoptions.ThewidelyusedLCAtechniquehas

onlyrecentlybeenusedformembranetechnologyapplications.SMTC has

appliedLCAtoassesstheecotoxicimpactofbrinedischargetheimproved

approach(Zhouetal.,2013)reducesrelianceonchemicalanalysisand

ecotoxicologytests.

7 Sensorsandmonitoring

Theefficiencyofmembraneprocessescanbeimproved byeffective

monitoringtoprovideearlywarningofproblems.SMTC isevaluating and

developinganumberofsensorsforlowpressureandhighpressuremembrane

processes.

36

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

1)Integritysensor(IS).Thisdevicecandetectchangesinpermeate

qualityfromalowpressuremembraneduetomembraneorfibredamage.The

ISrespondstosmallchangesintransmembranepressurewhenasample

passesovertheIS‘collection’membrane(Krantzetal.,2011),andcan

detect1damagedfibrein105fibres.TheISiscommercializedbyastartup

company(MINTP/L).

2)Ultrasonictimedomainreflectometry(UTDR).TheUTDRhasbeen

usedforseveralyearstodetectmembranefouling.SMTChasextendedthe

UTDRapplicabilitytodetectionofcolloidalandbiofouling.Thelatterisa

particularlychallengeasbiofilmshavesimilaracousticimpedancetowaterand

thishasbeenovercomeusinganacousticenhancementtechnique(Simetal.,

2013).Applicationinvolvesa‘canarycell’conceptwhereasidestream

passesthroughaflatsheetsimulator(operatingatsimilarconditionstothe

plant)withaUTDRdetector.Thecanarycellsignalpreemptstheproblemson

theplant,providinganearlywarning.

3)Electricalimpedancespectrometry(EIS).Thecanarycellcanalsobe

fittedwithEISdetectors.Usingelectrodesinthefeedandpermeatestreams

theEISusesawiderangeofAC frequenciesanddetectstheimpedance

spectrathatcanthenbeinterpretedintermsoffoulinglayers.SMTC,in

collaborationwithInphazePtyLtd.,hasshownthatEISsignalsprovidea

‘fingerprint’associatedwithdifferenttypesoffoulant(Simetal.,2013).

8 Futureprospects

Fig.1depictsthevariousmembraneactivitiesinwaterandrelatedpower

andbrineissues.Therewillinevitablyberenewedeffortstoreducenetpower

consumptioninthemembranesandwaterdomain.Inthissectionwespeculate

ontrendsforfuturedevelopments.

(1)Desalination

Currentstateoftheartmembranedesalinationdemandsabout30to

35kW·h/m3waterproduced.Ofthisabout25kW·h/m3isusedforthe

membraneprocessesofpretreatment(ca03 kW· h/m3) and reverse

osmosis(ca22kW·h/m3),asdepictedinFig.2TheROstage,including

energyrecovery,typicallyoperatesatabout2xtheminimum energyof

46

separation(106kW·h/m3at50% recoveryfor35g/Lseawater(Elimelech

andPhilip,2011)).Therearesomeopportunitiestoreducethemembrane

processenergydemandfordesalinationandthesearesummarizedatthe

bottomofFig.2Firstlythepretreatment,toreduceturbidityandassimiliable

organiccarbon,couldpotentiallybeachievedinabiologicallystabilized,

gravitydriven,UFprocess(similartoPeterVarbanetsetal.,2010).The

energydemandforthiscouldbenegligiblysmall.ForROthenextgeneration

ofsuperpermeabilitymembranes,configuredinamultistagecascade,could

potentiallyshave30% offtheROenergydemandgivingavaluearound15

kW·h/m3(Fig.2).FinallytheosmoticpowerembeddedintheRObrinecould

berecoveredbyPRO,ifalowsalinitystreamisavailable,toyieldupto03

kW· h/m3 brine.Thelowersalinitystream could beconcentratefrom a

wastewaterreclamationplant.A spinofffrom thisPRO stagewouldbea

diluted seawaterbrine fordischarge.Overallthe energy formembrane

desalinationcoulddropfromabout25toavalueintherange15to12kW·

h/m3.Thiswouldrepresentasignificantdropof40% to50% indesalination

energydemand.Thetradeoffwouldbealargerfootprintforpretreatmentand

forthePROprocess,andadditionalcapitalcostforthePRO.

Fig.2 Membranedesalinationandenergydemand

(2)OtherFOopportunities

DirectdesalinationbyFO islimited bytheavailabilityofasuitable

‘engineered’drawsolutionthatisreadilyregenerated;thedevelopmentof

suchadrawsoluteisalongterm challenge.HoweverFO canbeattractive

whenhighsalinitystreamsareavailable.Twoexamplescouldhaveapplication

56

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

intheshortterm,asfollows:

1)Seawaterpretreatment.Inthiscaseseawaterprovidesthedrawand

impairedwater(lowsalinitywastewater)isthedilutingstream.Thisapproach

deliverslowerosmoticpressurefeedtoRO,withpotentialenergysavings(Sim

etal.,2013a).Thetradeoffisaproductwaterderivedpartiallyfrom waste

water.

2)Fertigation.Inthisprocessthedrawsolutionisaconcentratedfertilizer

andthedilutionwatercould bebrackishground water.TheFO process

providesameansofgroundwaterdesalinationwithmodestenergydemand

(Phuntsoetal.,2011).

(3)MDopportunities

TheattractionsofMD,namelyprocessingathighsalinityandtheabilityto

usewasteheat(asalowGHGoption),providesignificantincentivesformore

applicationsofthis technology.Ofinterestare opportunities to increase

seawaterrecoverybybrineprocessing,possiblycombinedwithrecoveryof

valuableminerals,and acoupled processwithFO,whereMD achieves

regeneration ofdraw solute.In addition MD is being considered for

concentrationof‘producedwater’,forexampleinaprocesscombiningMD

withvapourcompression(globenewswire,2013).

(4)AnaerobicMBRs

Energy,asbiogas,frommunicipalwastewatershouldhaveabigfuture.

ThemembranebioreactorhaspotentialbenefitsinprovidingcontrolofSRT,

somecontrolofORT,andyieldingahighqualitywater.Howevermembrane

foulingmaybeanissue.TheanaerobicfluidizedbedMBRappearstocontrol

foulingatmodestenergydemandwithoutgasscouring(Kim etal.,2011).

SMTCishelpingtooptimizethisapproachwithKoreanandUSpartners.

AnotheroptionforfutureAnMBRsmaybetheuseofvibratingmembranes(Li

etal.,2013).

(5)Foulingmonitors

DevelopmentsatSMTC pointtotheuseofnovelsensorstodetect

incipientfoulinginmembraneplant,allowingforcorrectiveaction.Costbenefit

analysisshouldbeabletoconfirm thesuitabilityinagivenapplication.The

noninvasivedetectionmethodsbasedonvariouselectromagneticandoptical

66

propertiescanbeincorporated into‘canarycells’located inaprocess

sidestreamtomonitorthe‘stateoftheprocess’(Sim etal.,2012),orin

sensorsmeasuringthe‘state(foulingpropensity)ofthefeed’.Fig.3depicts

theapproachthatcouldusetelemetriccommunicationofdata.

Fig.3 SensorsforfoulingcontrolinRO

9 Conclusions

Membranesarevitaltowatersupply.Reflectingglobalinterests,research

attheSMTC coversthespectrum ofmembranewateractivities,from non

salinetosalinetowastewater.There are manyopportunitiesto increase

efficiencyandreducenetenergyrequirements.

References

BarnesR,etal.2013.Biofouling,29(2):203-212.

CaiY,etal.2013.WaterResearch,47(11):3773-3781.

ChenG,etal.2013.Desalination,308:47-55.

ChongTH,etal.2013.(inpreparation)

ChouS,etal.2010.Desalination,261(3):365-372.

ChouS,etal.2012.JMembSci,385:25-33.

ElimelechM,PhilipW A.2011.Science,333:712-717.

GohS,etal.2013.JMembSci,438:140-152.

globenewswire.com/news.release/2013/09/23….GEandmemsys.

GuanG,etal.2012.IEChemRes,5(41):13405.

76

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

KimJH,etal.2011.ES&T,45:576-581.

KrantzW,etal.2011.Desalination,283:117-122.

LiaoY,etal.2013.JMembSci,440:77-87.

LiTetal.2013.JMembSci,427:230-239.

LooSL,etal.2012.WaterRes,46(10):3125-3151.

LooSL,etal.2013.SoftMatter,9(1):224-234.

LuxReport.2013.Top Academics and Institutions in WaterResearch,2013.MINT P/L.www.

mintmembranes.com.

PeterVarbanetsM,etal.2010.WaterRes,44:3607-3616.

PhattaranawikJ,etal.2008.Desal,223:386-395.

SimV,etal.2012.IDAJournal,4(3):36-48.

SimV,etal.2013.JMembSci,428:24-37.

SimV,etal.2013a.Membranes(openaccess),3(3):98-125.

SimL,etal.2013.JMembSci,443:45-53.

SuwarnoR,etal.2012.JMembSci,405:219-232.

XiaL,etal.2013.WaterRes,47(11):3762-3772.

YapW,etal.2012.BioresTechnol,122:217-222.

ZhangJ,etal.2006.JMembSci,284:54-66.

ZhaoY,etal.2012.JMembSci,423:422-428.

ZhouJ,etal.2013.Desalination,308:233-241.

TonyFane  isachemicalengineerfrom Imperial

College,London,whohasworkedonmembranessince

1973.Hiscurrentinterestsareinmembranesappliedto

environmentalapplicationsandthewatercycle,witha

focusonsustainabilityaspectsofmembranetechnology,

includingdesalinationandreuse.Heisaformerdirectorof

the UNESCO Centre for Membrane Science and

TechnologyattheUniversityofNewSouthWalesand

HeadofChemicalEngineeringatUNSW.Since2002hehasdirectedmembrane

researchinSingaporeasTemasekProfessor(2002-2006)atNanyangTechnological

University,and since2008 asFoundingDirectoroftheSingaporeMembrane

TechnologyCentre(SMTC)atNTU.HeisnowDirectorMentoratSMTC.TheSMTChas

agroupofover85researchersdedicatedtofundamentalandappliedresearchinto

86

membranesforthewatercycle.HeisontheAdvisoryBoardoftheJournalofMembrane

Science(formereditorfrom1992to2005)andEditorialBoardofDesalination.Heisa

FellowoftheAcademyofTechnologicalScience&EngineeringandthePatronofthe

MembraneSocietyofAustralasia.

96

饮用水安全问题与膜法水处理技术进展

侯立安1,2 等

1浙江大学化学工程与生物工程学系,杭州

2西安高技术研究所,西安

摘要:针对日益严重的水源污染和水资源短缺问题,研发高效的饮用水净化

技术是亟待解决的民生问题之一。膜分离技术因其高效、低耗等优点在饮用水安

全保障方面备受关注。本文针对饮用水安全面临的难题和挑战,介绍了膜法饮用

水净化技术的发展沿革,论述了膜组合工艺在饮用水安全保障方面的应用现状,

对未来膜法饮用水净化技术的发展提出了建议。

关键词:膜技术;水处理;饮用水;安全

一、引  言

饮用水安全问题主要包括两个方面:饮用水资源短缺和饮用水质保障。其

中,饮用水质量直接关乎人类健康,因而受到人们的广泛关注。随着工业和经济

的发展以及城镇化速度的加快,饮用水污染问题已呈日益恶化的趋势。世界卫生

组织(WHO)调查资料显示,目前水中已见报道的污染物高达 2221种,其中供人

们饮用的自来水中可能含有近750种对人体有害的物质,全世界已发现的约80%

的疾病和50%的癌症与饮用不洁净的水有关[1]。

由于中国近年来经济的快速发展,环境问题日益显著,一些地区的饮用水源

受到污染。另外,突发性的非传统安全事件对饮用水安全同样造成一定威胁。因

此,开发实用的饮用水净化和应急技术,构建完善的安全保障体系具有重大意义。

近年来,膜技术在分离纯化方面表现出的明显优势使其在饮用水安全保障方

面得到了很好的应用[2,3],相对于传统的水处理技术,膜分离技术净化饮用水更

为绿色、高效。

07

饮用水安全问题与膜法水处理技术进展

二、饮用水安全面临的挑战

(一)中国饮用水资源总体现状堪忧

中国的饮用水面临着淡水资源匮乏,水资源分布不均,地下水质恶化与过度

开发,湖泊水量与水质急剧降低等诸多安全问题。而且中国 80%的饮用水净化

方法还停留在传统的混凝、沉淀、过滤、消毒四步工艺,而传统的净化工艺已难以

应对近年水体中越来越多的有机污染物,使得安全合格的饮用水更难得到保障。

(二)污染物种类多元化

由于中国工农业发展较为迅速,产业发展模式不够完善,造成环境污染比较

严重,从而导致饮用水源呈现复合污染趋势,大大增加了饮用水处理的难度和成

本。常见的饮用水污染种类及其危害见表1。

表1 饮用水污染类型及危害

污染类型 危害

悬浮物污染 水体变得浑浊,吸附有毒物质、重金属、农药等

氮磷有机物污染 为水中微生物生长提供营养,导致水体微生物污染

重金属污染 重金属使蛋白质变性,对人、畜有直接的生理毒性

酸碱污染 饮用水 pH值的过高或过低,都影响人的体液环境

难降解有机物污染 难以生物降解,容易在生物体内累积

放射性物质污染 导致生物畸变、破坏生物的基因结构及致癌等

热污染 水温升高使水中某些毒物的毒性升高

特种污染物含有各类病毒、细菌、寄生虫等病原微生物,流入水体会传播各种疾病;生

物毒剂或化学毒剂破坏人体内的新陈代谢过程

(三)传统净水工艺面临新挑战

尽管中国饮用水安全保障力度持续加大,法律法规和标准体系日益健全,饮

用水安全状况得到显著改善。但由于中国经济发展方式尚未得到根本改变,加之

受全球气候变化和工业化、城镇化快速推进的影响,饮用水安全形势仍然不容乐

观:相当部分的淡水资源难以直接饮用,需要初级或深度处理,以华北地区地下水

为例,可直接饮用的仅占222%,需要专门处理的高达 5655%[4]。另外,污染问

题日益突出,新污染物不断出现,污染日趋复杂,饮用水呈现污染物复合、污染过

17

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

程复合以及污染效应复合的复合污染特征。而传统水处理工艺以去除水中悬浮

物、胶体颗粒物为主,对小尺度污染物去除能力有限,因此,严格的水质标准和严

重的污染问题直接挑战着传统净水工艺,使之面临巨大的挑战,膜法水处理技术

被认为是保障饮用水安全的重要方法之一。

三、膜法饮用水净化技术的发展及应用现状

(一)膜法饮用水净化技术的发展沿革

针对日益复杂的饮用水安全问题,越来越多的研究者将目光投向膜技术。20

世纪末研究者开始尝试将微滤(MF)技术应用于饮用水净化研究,并于 2005年在

美国康涅狄格州的 FoxwoodsCasino厂采用调节 pH值后加曝气预氧化和压力式

柱状微滤膜工艺,饮用水净化处理的效果均良好[6]。随着对 MF净水工艺研究的

深入,发现 MF产水不够洁净,分离尺度更小的超滤(UF)过程的用于饮用水净化

处理,研究发现,UF的产水较 MF更为纯净,对常规的自然水源,经 UF处理后便

可达到饮用水安全标准,典型案例是对美国明尼苏达州规模为 26万 m3/d的

Minneapolis净水厂进行改造:原工艺为投加石灰软化—铁盐混凝—沉淀—滤池过

滤,改造后的过程则采用压力式柱状超滤膜替换滤池,产水水质得到明显提高[6]。

随着膜法饮用水净化技术的发展,发现对于盐度较高或小分子有机物较多的

水源,UF往往难以奏效,特别是 UF对 TOC、CODMn、UV254的去除率偏低[7]。于是

开始尝试将纳滤(NF)和反渗透(RO)技术应用于饮用水净化处理,发现 RO和 NF

具有非常良好的有机物和盐去除性能[8]。Gaid等[9]对法国 Mery-Sur-Oise水厂

NF工艺做了详细的研究,结果表明该工艺对有机物有着很好的去除效果:对溶解性

有机碳(DOC)平均去除率为60%,对农药莠去津(Atrazine)和西玛津(Simazine)去

除率达90%以上,出水中残留的微污染物绝大部分低于分析检测限度。

近年来,随着部分地区饮用水源呈现复合污染的趋势,以及对膜法饮用水净

化技术研究的不断深入,逐渐形成了以膜技术为核心的组合工艺,并将饮用水净

化从常规处理逐步推向以膜组合工艺为主的深度处理。

(二)膜组合工艺在饮用水安全保障中的应用进展

由于饮用水中可能含有多种污染物,单一的膜法饮用水净化过程往往难以保

证水质安全。膜组合技术将多个分离过程相结合,可以发挥不同过程的分离特

点,达到处理复杂污染的效果,是饮用水深度处理的常用方式。膜集成工艺通常

包括图1所示的三个主要部分:预处理、主处理及精处理。其中,预处理工艺主要

27

饮用水安全问题与膜法水处理技术进展

用于去除原水中的胶体、颗粒物、细菌等,一般选择去污因数低、适用范围广的处

理技术,如絮凝沉淀、吸附、过滤、超滤、微滤等;主处理工艺主要使用能大幅降低

原水中重金属、放射性元素和有机物的技术,如蒸发、纳滤、反渗透等;精处理工

艺:选择能够深度去除水中污染物的工艺,如离子交换等。

图1 膜组合工艺流程示意图

1膜过程与其他技术的组合工艺应用进展

机械过滤是最简单的预处理工艺,将机械过滤的产水加药杀菌后进入膜系统

构成组合工艺,可以大幅度提高产水水质。典型的应用实例是如图 2所示基于此

组合工艺的天津杨柳青水厂,该膜组合工艺处理示范工程建成于 2008年 5月,以

微污染的滦河原水为水源,系统产水规模为 5000m3/d,总产水率为 98%,运行结

果表明[10]:出水浊度主要集中在007~008NTU,除浊效果理想;粒径大于2μm

的颗粒数稳定在10个/mL以下,大大提高了去除两虫的保障率;常规工艺出水和

膜出水的耗氧量接近,都满足标准要求,但总体趋势膜出水更好;另外,与传统工

艺相比,膜工艺的加氯量和三氯化铁投加量较少,对铁、亚硝酸盐、细菌、藻类等水

质指标的去除效果更好。

图2 天津杨柳青水厂膜处理示范工程流程示意图

混凝是饮用水处理过程中最常用的工艺之一,直接将混凝与微滤(MF)或超

滤(UF)组合的工艺较为简单,但混凝过程对膜的影响颇有争议,一些学者认为金

属离子与水中的天然有机物发生结合之后,容易在膜表面沉积,从而加重膜的污

染[11]。因此,简单地絮凝与膜组合工艺较少被采用。

活性炭吸附可以有效地去除水中大部分低浓度有机物和色度,20世纪 70年

代后期开始被应用于饮用水处理,但对有机物等的去除不够彻底,并且活性炭中

容易滋 生 微 生 物,因 此 活 性 炭 吸 附 后 再 经 膜 处 理 可 以 确 保 水 质 安 全。

Tomaszewska等[12]将 UF和活性炭吸附相耦合,该组合工艺对色度、腐殖酸、酚的

37

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

去除率分别为96%、89%、97%。另外,也有人发现使用活性炭和 UF的组合工艺

对合成有机物(SOC)、嗅和味的去除效果均有很大的改善[13]。Tsujimoto[14]则对

颗粒活性炭(GAC)吸附与 UF组合工艺进行研究,发现 GAC的吸附作用和生物

酶解作用,可以有效提高水中有机物的去除率、提高出水水质、降低膜污染。

臭氧具有非常良好的灭菌效果,Tanaka等[15]进行了臭氧预氧化和 UF组合的

工艺探究,他们发现臭氧可以将水中的有机物分解成不易污染膜的小分子物质,

既提高产水安全性,又降低膜污染。

2多膜过程组合工艺应用进展

不同类型的膜孔径尺度差异较大,可用于去除不同尺度的污染物,该特点特

别适合解决饮用水污染物多元化的难题。因此,多膜组合工艺成为目前饮用水深

度处理的重要研究和应用方向。在多膜过程组合工艺中,设计者常将 MF或 UF

作为系统预处理部分,而将纳滤和反渗透作为主处理工艺。最常用的工艺为利用

MF去除大颗粒或者藻类,UF去除细菌和浊度,纳滤和反渗透则用于去除盐分和

有机物。

多膜组合工艺最典型的代表为海水淡化过程。根据膜的孔径大小 MF膜可

用于去除藻类,因此,早期或部分水质较好的海水淡化过程中,MF被作为 RO的

预处理过程并简化系统工艺。例如,2005年建成的世界上最大的以色列 Ashkelon

海水淡化厂主要设施由五个部分组成,其中,最核心部分即由 MF和 RO过程组

成,作为最终预处理的 MF产水进入 RO脱盐,整个产水能力达到 33万 m3/d。然

而,很多地区海水浊度较高,直接使用 MF很难奏效,又有设计者开发出连续 MF

为代表的新型 MF技术,并被广泛使用,它们可以更好地降低水体中胶体颗粒和

细菌数量,产水水质更为优异[16]。

由于 RO膜表面为致密的分离薄层,对进水的 SDI等有较高的要求,MF并不

能完全保证 RO的进水要求。UF作为 RO的预处理技术是近期发展起来的很有潜

力的膜工艺,特别适合于高浊度海水原水:UF出水 SDI值一般为02~1,浊度在1

NTU以下,且水质非常稳定,基本不受原水水质变化的影响。例如,中国首个自主

设计并由国内企业总承包的最大膜法海水淡化工程于2011年在河北曹妃甸建成投

产[17],日产淡水5万 m3,该工程便是采用“气浮 -UF-RO”的联合工艺(图3)。

图3 曹妃甸多膜组合海水淡化工艺流程图

47

饮用水安全问题与膜法水处理技术进展

多膜组合工艺不仅能有效地保障饮用水水质,而且还具有非常好的操作灵活

性,可以根据水质的不同调节所使用到的膜过程,因而特别适合水质动态变化的

地区使用。例如,周志军等[18,19]利用 UF和 RO组合工艺建立了一个海岛饮用水

处理示范装置,该装置可以根据沿海池塘水在季节变换时产生的淡咸水交替的问

题,控制单独使用 UF或者组合工艺,既保证供水质量,也降低了运行成本。类似

地,印度Dasari等[20]最近在安得拉邦Prakasam建立了一个UF和低压RO的组合工

艺示范装置用于处理地表和地下水,并进行了经济性评价,发现地表水需要采用组

合工艺进行处理,水回收率达到60%;而地下水采用 UF装置处理后即可达到饮用

标准,水回收率为80%,因此,从经济性考虑针对不同水源应采用相应的处理工艺。

合理的组合工艺设计还可以获得高产水回收率。例如,将低压 RO与 UF组

合,UF的浓缩水作为低压 RO进水,则可大幅度减少浓水的排放,提高系统产水

效率。陈欢林等[21,22]以钱塘江潮汐咸水为研究对象,将超滤、纳滤和反渗透三膜

过程组合用于处理周期性变化的潮汐水。其中,超滤作为整个系统的核心工艺,

在淡水期作为主产水单元;纳滤则在咸水期使用,可以除去咸水中的大部分盐;低

压 RO作为最后一个环节,用于UF和NF的浓水脱盐,进一步回收淡水,在保证产

水达标的情况下,整个系统的回收率可达90% ~95%。

表5列出了几种典型的膜组合工艺用于处理饮用水的结果,从表中可以看

出,以膜过程为主的组合工艺在饮用水安全保障方面效果非常明显。

表5 针对不同处理对象的膜集成工艺对比

膜集成工艺 处理对象 处理结果 参考文献

UF+RO 地表水(印度) 去除几乎所有的盐分和有机物,水回收率达到60%以上 [20]

UF+NF+RO 钱塘江水 去除水体盐分、有机物,大大提高系统水回收率 [21,22]

MF+RO 地下水 产水达到国家饮用水标准,口感大大改善 [23]

混凝 +MF+RO低浊度

海水产水达到国家饮用水标准 [24]

UF+RO高浊度

海水

CODMn、总硬度、Cl-的去除率分别达到了 95%、

98%、97%以上,脱盐率也达到97%[25]

MF+RO高污染海水

(西西里岛)产水达标,多年来运行稳定,耐生物污染 [26]

NF-RO 海水 降低操作压力,提高回收率 [27]

UF+RO波斯湾海水

(阿联酋)产水效果好,回收率高 [28]

MF+RO地中海海水

(以色列)

产水达标,产水量大,是世界最大的海水淡化工厂

之一[29]

57

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

3新能源膜组合工艺研究进展

反渗透和纳滤等均属于压力驱动膜过程,产水过程需要克服渗透压,能耗相

对较高,因此开发利用太阳能、风能和核能等新能源的膜组合工艺具有重要的

意义。

辽宁红沿河核电站利用核能驱动,采用 UF+RO组合工艺建立了中国首个核

电海水淡化项目,出水水质达到生产和直接饮用的标准[30]。

太阳能是最可再生能源,邵卫云等[19]在舟山岛建立的以雨水为水源、以太阳

能为动力的屋顶接水与超滤供水组合示范系统,是膜组合工艺的崭新形式。另

外,为了弥补阴雨天太阳能无法工作的不足,还开发了如图 4(b)所示的太阳能加

风能发电系统,为膜过程提供能源,大大提高了紧急电力保证度,供水能力可达到

15m3/d。

图4 太阳能动力屋顶接水供水系统示范和太阳能加风能发电系统

El-Shaarawi等[31]搭建了一个太阳能光伏泵驱动海水淡化反渗透组合系统,

并建立了一个数学模型来描述不同操作参数、地区和天气条件下太阳能 -RO系

统海水淡化的性能和投资成本,模拟结果对建立独立的小型太阳能驱动 RO海水

淡化具有重要的参考意义。

4膜法应急供水组合工艺研究进展

当发生强降雨等较大自然灾害时,供水系统容易受到水源污染、管道破裂、污

水渗漏等损害,水中各种有机物、重金属、微生物等严重超标,使得水源中各组分

异常复杂、水质变差,严重影响饮用水安全。采用常规的饮用水制备工艺来处理

雨水,难以保证产水水质,结合应急供水的特征,对雨洪等进行适当的预处理后,

使其满足 RO等膜技术的要求,经低压 RO处理后即可获得符合国家标准的饮

用水。

根据已有的研究工作,基于 UF和低压 RO膜过程的双膜组合工艺可以在雨

67

饮用水安全问题与膜法水处理技术进展

洪应急供水安全中发挥重要的作用[32]。针对多变、污染的水源,经双膜处理后的

产水水质稳定、达标。除此之外,膜集成应急净水装置还具有适合多途径运输、多

方位组装、复杂的环境和气候,可长短期切换运行等特点。

王世昌等[33]报道了国际上近几年才开发出的膜法紧急供水淡化与净化系统

(图5),装置主要技术包括 UF或 UF+RO,装置易于运送与安装。该系统可适应

于高浊度水、海水、核污染水、生物与化学污染水等。该装置具有除浊能力强,可

从3000NTU除到05NTU,可除重金属铅、钙、汞、砷等,产水稳定,不易堵塞,快

速净化(只需3~5s)等优点。

图5 美国开发的远途救援净水系统

随着核能的开发和国际形势日趋复杂,发生放射性污染的可能性正在逐渐增

大,一旦发生日本福岛核电站泄漏等类似紧急状况,高性能的应急供水装置就显

得非常重要。据报道采用以纳滤为核心技术的特殊污染水处理膜组合系统,可将

比活度为5488Bq/L的原水净化成比活度为 03289Bq/L的净水(表 4),对放射

性核素的去除率大于9999%[2,34,35]。

表4 特殊污染水处理膜组合系统对放射性物质的去除

核素 水比活度/(Bq/L) 出水比活度/(Bq/L)

铯 -137 794 0069

钚 -239 120 00179

锆 -95 1640 <0095

铌 -95 2470 <0065

钌 -103 464 <0082

合计 5488 03289

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

四、膜法饮用水安全保障的展望与建议

(一)未来膜法饮用水安全保障的研究重点

随着膜法饮用水净化技术发展逐渐成熟,以及水安全问题的日趋严峻,对膜

法饮用水安全保障体系也提出了更高的要求,因此,可以预见以下几个方面可能

会成为膜法饮用水安全保障的研究重点。① 耐污染膜与工艺的开发:膜法饮用

水净化的成本较传统工艺偏高,延长膜的使用寿命可以适当降低制水成本,所以

深入开展膜污染机制研究,开发耐污染膜和基于“临界污染点”设计抗污染的工

艺显得尤为重要;② 膜法处理饮用水时,有益离子的保留问题:尽管可以通过膜

组合工艺得到水质非常稳定的去离子纯净水,但纯净水作为长期饮用水源是否健

康一直是个有争议的话题,大多数研究者认为,选择性地保留一部分有益离子是

非常有必要的,如何充分发挥分离膜的选择性,有效或选择性地保留有益离子将

成为未来的研究方向之一;③ 反渗透浓海水的处理:随着海水淡化产能的增加,

排放到近海的浓海水量逐渐增加,对环境造成了严重的污染,浓海水中含有大量

有价值的物质,同时高盐水也具有高的化学能,利用正渗透、反电渗析等技术进行

盐差发电可能会成为未来的一个研究热点。

(二)膜法饮用水安全保障发展建议

膜法水处理技术是目前最有效的饮用水安全保障手段,其去除效率与膜的类

型、进水水质、运行条件等因素息息相关,在实际应用中,应针对不同的水质和运

行条件来研发最适合的膜处理组合工艺,实现多种技术优势互补;同时还需继续

研发新型的膜材料与膜组件,如具备抗污染、抗氧化、高通量、机械强度高、寿命

长、价格低廉的新型膜材料,以及新型大单元膜组件和新型膜组件组合方式,推动

膜用于水净化和深度处理过程;此外,由于目前膜技术应用方面的研究较多,膜分

离机制方面的研究还不够系统,还不能科学合理地解析膜的分离过程,对工程实

践也缺乏指导作用,因此探讨膜分离过程的解析表达是膜科学研究的重点之一。

利用好雨水与海水这类非传统饮用水源,同样可以有效地缓解用水供水矛

盾,对雨水资源进行收集、储存和净化后可以直接利用;而以海水为原水,通过海

水脱盐处理生产淡水,将在中国饮用水供应中发挥越来越大的作用。鉴于膜法饮

用水净化技术的优势,应加快推进膜法处理饮用水的管网准入制度建设。

87

饮用水安全问题与膜法水处理技术进展

五、结  语

饮用水安全是保障社会发展、维护公众健康的关键物质基础,而膜技术是水

处理领域的新技术,随着国家政策扶持力度的不断加大,膜分离技术的创新发展,

相信未来膜技术在水安全保障领域的应用将更广阔。

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[32] 赵海洋,周志军,张林,等.双膜法集成技术保障城市雨洪应急供水的可行性研究.中国市政工程,

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14-16.

08

饮用水安全问题与膜法水处理技术进展

StatusofPotableWaterSecurityandProgressofMembraneWaterTreatmentProcesses

Li’anHou1,2,etal.

1DepartmentofChemicalandBiologicalEngineering,Zhejiang

University,Hangzhou,China

2InstituteofXi’anHighTechResearch,Xi’an,China

Abstract:As to the increasingly serious waterpollution and shortage,

developingeffectiveprocesstoassurethesecurityofpotablewaterisoneof

theurgentlivelihoodissues.Membranebasedwatertreatmenthasattracted

attentionandbeenstudiedtopurifydrinkingwaterduetoitshighefficiency

andlowconsumption.Inthispaper,thedifficultyandchallengeofthesafetyin

thepotablewaterhavebeenintroduced,andthedevelopinghistoryofthe

membraneprocessforpotablewatertreatmenthasbeenpresented.The

applicationprogressofmembraneintegratedprocessforassuringthesecurity

ofpotablewaterhasbeenreviewed.Finally,severalsuggestionsarelistedfor

thedevelopmentofmembranebasedwatertreatmentinpotablewatersupply.

Keywords:membraneprocess;watertreatment;potablewater;safety

18

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Li’anHou istheexpertonenvironmentalengineering

andAcademicianofChineseAcademyofEngineering.He

isfromXuzhou,JiangsuProvince.Heisthedoctorof

engineering, the professorand doctoralsupervisor.

Moreover,heistheadvancedexpertconnecteddirectly

withcentralauthorities,theVicepresidentofChina

SocietyforFuturesStudies,theconsultantofChinese

SocietyofEnvironmentalSciences,theVicechairmanof

ManMachineEnvironmentSystem EngineeringCommitteeofSystemsEngineering

SocietyofChina,theVicechairmanofExpertCommitteeoftheMembraneIndustry

AssociationofChinaandthevicechairmanofBeijingAssociationofInventions,etc.

AcademicianLi’anHouhasbeendevotinghimselftotheresearchonenvironmental

engineeringforseveraldecades.Heputforwardfirstlyandsuccessfullydevelopedwater

treatmentandairpurificationtechnologyandaseriesofequipmentcorrespondingly.He

mademanybreakthroughs,significantcontributionsandcreativeachievementsfor

discoveringandestablishingthepollutionpreventionandcontrolsystem.Inaddition,he

wonNationalAwardforScienceandTechnologyProgressforfivetimesandProvincial

AwardforProgressinScienceandTechnologyfortwentythreetimes.Besideit,hewon

twentytwonationalpatentsandpublishedthreemonographs.Hepublishedmorethan

150academicpapers.In1996,heachievedtheGovernmentSpecificAllowance.In

2001,hewonthe“Truthfromfacts”OutstandingYouthAwardofChina.In2005,he

achievedtheInventionandEntrepreneurshipPrizefirstly.In2010,hewasawardedthe

titleof“advancedworker”nationalpopularsciencework.

28

纳滤膜法处理和回收废水中低浓度全氟辛酸铵

万印华 等

中国科学院过程工程研究所生化工程国家重点实验室,北京

摘要:采用纳滤膜考察了从废水中回收全氟辛酸铵的可行性,先用全氟辛酸

铵模拟溶液考察了纳滤膜 NF270和 NF90对全氟辛酸铵的截留效果,在全氟辛酸

铵浓度为100mg/L时,纳滤膜 NF270的截留率为920%,而纳滤膜 NF90的截留

率大于990%。选用 NF90进一步考察了操作条件对纳滤膜回收全氟辛酸铵效

果的影响,在过膜通量为 664L/(m2·h)、搅拌速度为 2400r/min、温度为 25℃

时可以将起始浓度为10000mg/L的全氟辛酸铵浓缩至 117073mg/L,浓缩结束

时跨膜压力为149bar,表明采用纳滤膜能够从废水中回收全氟辛酸铵。在小试

实验工作的基础上,对该工艺进行了工业化放大,设计建造了一套日处理量为

200t废水的全氟辛酸铵回收装置,在某聚偏氟乙烯生产企业中用于处理和回收

废水中低浓度全氟辛酸铵,取得了良好的效果。

关键词:纳滤;全氟辛酸铵;废水处理;回收

一、引  言

全氟辛酸(perfluorooctanoicacid,PFOA)是一种有机全氟化合物(perfluorinated

chemicals,PFCS),在自然界中并不是天然存在,是由人工合成的物质,其制造和使

用历史已经超过60年[1]。全氟辛酸较碳氢链表面活性剂具有更低的表面张力,

润湿性能更好,具有良好的热稳定性以及化学稳定性,应用范围非常广泛。在含

氟聚合物生产中,全氟辛酸的铵盐还被用作乳化剂,用于乳液法含氟聚合物的聚

合反应中,生产的聚合物主要有聚四氟乙烯、聚偏氟乙烯、聚全氟乙丙烯等,全氟

辛酸铵用于含氟聚合物的生产已经有50多年的历史。与其他典型的持久性有机

污染物不同,全氟辛酸的水溶性较好,不易吸附至固体表面,排放到自然界中的全

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氟辛酸都会迁移至水体中,且在迁移过程中不易被土壤、活性污泥吸附,非常容易

在水体中累积。由于碳氟键的稳定性,全氟辛酸不易被降解,在不同国家和地区

的地表水、地下水、海洋,甚至是自来水中都能检测到全氟辛酸的存在[2,3],在人

迹罕至的偏远区域,也能在自然环境中检测到全氟辛酸的存在[4]。全氟辛酸在生

物体内和环境中不易降解,会在生物食物链和环境中累积,在人体内的半衰期在

35年左右[5],其对健康和环境的危害逐渐为众多研究所证实。因此,水体中的

全氟辛酸污染急需引起重视。

工业废水排放被认为是全氟辛酸排放至自然界中的主要途径之一,许多文献

报道生活在排放源附近的居民体内的全氟辛酸浓度较高[6,7]。由于全氟辛酸化

学稳定性非常好,传统的污水处理工艺无法将其从水体中去除干净,需要采用如

光化学降解法[8]、超声降解法[9]等方法才能将其部分降解,一般采用吸附[10]、絮

凝[11]等方法将其从水体中去除。但由于全氟辛酸生产成本较高、价格非常昂贵,

如果能够从废水中回收利用,还可取得显著的经济效益。目前,从废水中回收全

氟辛酸铵的工艺主要有蒸馏浓缩法、泡沫分离法、离子交换法等方法,但都存在着

回收效率低、成本高、造成二次污染等问题。纳滤膜的分离性能独特,尤其对低相

对分子质量的有机物截留率高,用于处理含有低浓度有机物废水效果良好,可用

做从废水中回收全氟辛酸。本研究采用纳滤膜回收废水中的低浓度全氟辛酸铵,

并在实验研究的基础上在某化工厂进行了工业化运行,取得了良好效果,可为含

有低浓度全氟辛酸铵废水的处理工艺提供一种新的方法。

二、实  验

(一)实验材料

本实验考察了两种纳滤膜对全氟辛酸铵的浓缩效果,这两种纳滤膜分别是

NF270和 NF90,根据各制造厂商提供的资料以及实验测定的数据,这两种纳滤膜

的基本性能参数如表1所示。

表1 实验用膜的基本性能参数

性能参数 NF270 NF90

膜材料 聚酰胺 聚酰胺

截留分子质量(MWCO)/Da 200 150

纯水透过系数(25℃)/[L/(m2·h·bar)] 15.6 10.1

NaCl稳定脱盐率/% 85~95

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纳滤膜法处理和回收废水中低浓度全氟辛酸铵

续表

性能参数 NF270 NF90

MgSO4稳定脱盐率/% >97 >97

CaCl2稳定脱盐率/% 40~60

最高操作温度/℃ 45 45

最高操作压力/bar 41 41

连续运行 pH范围 3~10 3~10

短时清洗 pH范围 1~11 1~11

最大给水污染指数(SDI) 5 5

  脱盐率测试条件:500mg/LCaCl2,70psi(4.8bar),25℃;2000mg/LMgSO4,70psi(4.8bar),25℃;2000mg/LNaCl,70

psi(4.8bar),25℃。

实验所用全氟辛酸铵(ammoniumperfluorooctanoate,APFO)由日本东洋纺化

学生产,纯度大于980%,购于北京百灵威化学技术有限公司。溶液均用去离子

水配制,所有溶液在进行纳滤实验前先经过045μm的微滤膜预过滤。

(二)实验装置

纳滤实验装置如图1所示,带磁力搅拌的终端膜过滤装置为实验室自制,容

积为130mL,有效膜面积为452×10-4m2。实验操作温度保持在 25℃,所有的

实验都在恒定通量(constantpermeateflux)条件下操作。纳滤实验装置(图 1)主

要由高压泵、进样柱(50mL)和进样阀、带磁力搅拌的终端膜过滤装置、压力传感

器及采集系统组成。在测试膜片纯水通量时,将进样阀切换至“load”状态,这时

料液槽中的纯水直接进入膜过滤装置。在浓缩实验时,先将进样阀切换至“load”

状态,将所需要的料液注入进样柱中,然后将门切换至“injection”状态,这时,进入

纳滤实验装置的是进样柱中的溶液。所用进样阀和进样环与高压活塞泵配套,最

高能承受40bar的压力。

(三)分析方法及仪器

全氟辛酸铵溶液的浓度采用紫外分光光度计在 210nm处测定,所用仪器为

上海精密仪器厂 UV757CRT分光光度计。但紫外分光光度法在测定浓度小于

50mg/L的全氟辛酸铵溶液时偏差较大,不能用于定量。

参照文献[12],低浓度的全氟辛酸铵采用高效液相色谱和质谱联用测定,但

操作条件与文献[12]有些不同。实验所用设备由美国 Agilent公司 HPLC1100和

美国 ThermoFisher公司 LCQDecaXP电喷雾质谱组成,色谱柱为 ZorbaxSBC18

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图1 带进样装置的纳滤实验装置示意图

1料液槽;2高压泵;3压力传感器;4带磁力搅拌的终端膜过滤装置;5磁力搅拌器;

6渗透液收集槽;7计算机数据采集系统;8进样阀和进样柱

(150mm×21mmid,5μm);流动相 A:水(含 01% TFA),B:乙腈(含 01%

TFA);梯度:0~13min,B:30% ~90%,13~20min,B:90%,20~25min,B:90%

~30%,25~30min,B:30%;流速:02mL/min,进样量为50μL。

质谱条件:ESI电喷雾离子源,喷雾电压为 45kV,加热电压为 25V,离子导

入电压(skimmer电压)为20V,离子传输毛细管温度为300℃,采用负离子监测模

式。

(四)实验步骤及理论部分

1实验步骤

实验用膜在使用前先在去离子水中浸泡过夜,在进行纳滤实验前用去离子水

在20bar下压实 30min以上,待纯水通量稳定后再使用。实验采用浓缩操作模

式,不断将料液由进料柱注入搅拌槽中,恒定过膜通量,检测并记录过膜压力,收

集透过液,待达到一定的浓缩倍数后停止实验,收集浓缩液,分别测定透过液及浓

缩液的全氟辛酸铵含量。

2计算方法

溶质的截留率用表观截留率(Robs)来表示,其计算公式为

Robs = 1-CpC( )b

×100%

式中,Cp为透过液中溶质的浓度,mg/L;Cb为截留液侧溶质的浓度,mg/L。

由于实验采用终端过滤,截留液侧溶质的浓度是变化的,其浓度由下式计算:

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纳滤膜法处理和回收废水中低浓度全氟辛酸铵

  

式中,Cb为截留液侧溶质的浓度,mg/L;Cb0为截留液侧溶质的初始浓度,mg/L;Cp为透过液中溶质的浓度,mg/L;V0为搅拌槽的容积;VP为渗透液的体积。

溶液浓缩倍数(volumereductionrate,VRR)用下式计算:

VRR=V0+VPV0

式中,V0为起始料液的体积;VP为浓缩液的体积,在本实验中,浓缩液的体积是恒

定不变的,即为130mL。

三、实验结果及分析

(一)纳滤膜的评测与筛选

1纳滤膜的纯水通量测定

膜的纯水通量是膜性能的一个基本参数,与膜的孔径大小及孔隙率相关,在

一定程度上与膜的截留率相关。在不同通量下测定膜的跨膜压力,考察其跨膜压

力随过膜通量的变化情况,可以确定膜的稳定性。由图2所示,NF270和 NF90这

两种的纳滤膜的跨膜压力随着过膜通量的增加而不断增加,且线性较好,表明在

实验操作条件下,这两种膜的透水性能均非常稳定。

图2 两种纳滤膜的跨膜压力随过膜通量的变化情况

在相同的过膜通量条件下,NF270的跨膜压力要比 NF90的小,根据公式 J=

Lp·Δp(J为透过通量,Δp为压差)可以计算两种膜的纯水透过系数,NF270和

NF90在25℃时的平均膜纯水透过系数分别为 101L/(m2·h·bar)和 156L/

(m2·h·bar),NF270的纯水通量要比 NF90大50%左右。

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2两种纳滤膜对低浓度全氟辛酸铵的截留浓缩效果对比

将浓度为100mg/L的全氟辛酸铵溶液注入搅拌槽中,分别用 NF270膜和

NF90膜对其进行浓缩,通量为1327L/(m2·h),搅拌速度为 600r/min,温度为

25℃,每浓缩一倍时(透过 13mL)收集透过液,记录跨膜压力,透过 143mL后停

止浓缩(图3)。

图3 浓缩过程中跨膜压力(TMP)和浓缩液侧全氟辛酸铵浓度随时间的变化:

(a)NF90;(b)NF270

在浓缩过程中,NF90的起始跨膜压力约为 12bar,要比 NF270的起始压力

83bar高,但都与这两种膜在相同通量时过纯水的跨膜压力相似,说明在全氟辛

酸铵浓度较低时,对膜的影响较小。随着浓缩的进行,NF90的跨膜压力上升明

显,当浓缩12倍时,NF90的跨膜压力达到 206bar,这时浓缩液侧的全氟辛酸铵

浓度为1178mg/L。而 NF270膜在浓缩过程中跨膜压力上升并不明显,在浓缩 12

倍时,NF270的跨膜压力为92bar,这时浓缩液侧全氟辛酸铵的浓度为1105mg/L。

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纳滤膜法处理和回收废水中低浓度全氟辛酸铵

这表明 NF90对 PFOA的截留率要高于 NF270,由图 4可知,NF90在全氟辛酸铵

浓度较低时,膜的截留率接近100%,而 NF270的截留率在最低时仅有92%左右,

但会随着截留液侧全氟辛酸铵浓度的升高而不断升高。虽然 NF90的跨膜压力

要比 NF270高些,但在处理低浓度全氟辛酸铵时的截留率更高,所以更加适合用

于含有低浓度全氟辛酸铵废水的处理。

图4 浓缩过程中透过液中全氟辛酸铵浓度以及膜表观截留率随截留液侧浓度的变化:

(a)NF90;(b)NF270

(二)纳滤膜操作条件对全氟辛酸铵回收效果的影响

在纳滤膜的使用过程中,膜的操作条件,如膜面流速、过膜通量、温度等对膜

的分离、浓缩效果也会产生较大的影响。而过膜通量是其中较为关键的参数,增

加过膜通量可以提高膜的处理效率,也可以增加膜的截留率,但是过高的膜通量

会加剧膜表面的浓差极化,导致跨膜压力的升高,浓差极化导致的膜表面溶质浓

度的升高还会导致膜表观截留率的下降以及透过液中溶质浓度的升高。

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将10000mg/L的全氟辛酸铵溶液注入搅拌槽中,用 NF90膜对其进行浓缩,

搅拌速度为 2400r/min,考察不同通量 664L/(m2·h)、1327L/(m2·h)、

1997L/(m2·h)对浓缩效果的影响,温度为 25℃,每浓缩一倍时(透过 13mL)

收集透过液,记录跨膜压力。

在过膜通量为1997L/(m2·h)时,起始的跨膜压力即为284bar,后迅速上

升至 373bar,只能浓缩三倍。降低过膜通量能降低跨膜压力,在过膜通量为

664L/(m2·h)时起始跨膜压力为 87bar,至浓缩 12倍时,跨膜压力也只有

149bar,还能继续浓缩(图5)。

图5 不同过膜通量下跨膜压力随浓缩倍数的变化

从图6中可以看出,在较低的过膜通量时,透过液中的全氟辛酸铵浓度要高,

提高过膜通量可以降低透过液中全氟辛酸铵的含量,这是由于增加过膜通量,提

高了水的过膜速度,而水要比溶质更易透过膜,因此透过液中的溶质浓度会降低。

但将过膜通量提高至一定程度时,会加剧浓差极化,导致膜表面的溶质浓度大大

高于本体液中的浓度,透过液中溶质浓度升高,膜表观截留率降低。

图6 不同过膜通量下透过液中全氟辛酸铵浓度随浓缩倍数的变化

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纳滤膜法处理和回收废水中低浓度全氟辛酸铵

在较低的过膜通量条件下,由于膜表面的浓差极化现象并不严重,可以将全

氟辛酸铵溶液浓缩到较高的浓度,在过膜通量为664L/(m2·h)时,可以将起始

浓度为10000mg/L的全氟辛酸铵浓缩至 117073mg/L(图 7),而跨膜压力也只

有149bar,浓缩效果较好。

图7 不同过膜通量下所能浓缩到的最高的全氟辛酸铵浓度

四、工业化应用及效益

实验研究表明,纳滤膜能够用于浓缩废水中低浓度的全氟辛酸铵,可将废水

中浓度为100mg/L的全氟辛酸铵浓缩至 100000mg/L以上,得到的浓缩液可以

重新用于生产过程中,经过处理后的水也可以用于其他生产工艺中,在进行废水

处理的同时实现了有用物质的回收,具有明显的经济和环境效益。因此,进一步

将纳滤膜法处理低浓度全氟辛酸铵废水工艺进行工业化应用,实施单位是一家生

产聚偏氟乙烯聚合物的企业,排放的废水中不仅含有全氟辛酸铵,还有残留的聚

合物。根据工厂的实际工况,工业化设计时在纳滤系统前面设计了一套超滤系

统,用于废水的澄清,澄清后的废水再用纳滤膜浓缩全氟辛酸铵。

(一)设计概要

系统设计处理含低浓度全氟辛酸铵废水能力为 200t/d,按照每天工作 20h、

2h清洗设备、2h机动设计,设备设计废水处理能力为 10t/h。由于废水中的全

氟辛酸铵含量较低,约为100mg/L,如需将其回用,需要尽可能将其浓缩,设计将

废水浓缩100倍以上,且处理后的废水中含氟化合物含量低于10mg/L,满足国家

相关排放标准。

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(二)工艺流程

为了保证废水水量能够持续供应且废水水质的稳定,将含氟树脂生产过程中

产生的废水统一收集起来放入原水储罐中,由于废水中含有较多的残留树脂,首

先采用超滤系统将废水中的悬浮树脂去除,澄清后的废水放入超滤缓冲罐中,再

用纳滤系统对澄清后的废水进行浓缩,浓缩液进入浓缩液储罐中,透过液一部分

进入系统清洗用水储罐中(CIP系统),一部分回用至其他工艺,具体的工艺流程

如图8所示。

图8 全氟辛酸铵回收系统工艺流程示意图

该系统主要由超滤预处理系统、纳滤浓缩系统和控制系统组成,超滤和纳滤

系统通过控制系统都能实现远程和现场控制。

(三)经济效益

投入实际运行的全膜法回收废水中全氟辛酸铵示范工程的废水处理量为

10t/h,系统可以回收废水中 99%以上的全氟辛酸铵,系统已经在某氟化工企业

正常运行4年多,每天可以回收全氟辛酸20kg左右,平均每年可以回收 6t左右

的全氟辛酸,按照全氟辛酸每吨售价 120万元左右,每年回收的全氟辛酸价值达

到720万元左右,运行成本(包括电费、耗材、设备折旧、人工等)约86万元/年,具

有明显的经济和社会效益。

纳滤膜法回收全氟辛酸铵具有能耗低、操作简单、易于放大、不需要任何辅助

设备、不产生二次污染等优点。废水中的全氟辛酸铵的回收率在 99%以上,经过

处理后的废水中含氟化物浓度低于 10mg/L,完全满足国家相关排放标准,且该

方法对类似的含低浓度氟化物废水具有通用性,具有很高的经济和环保效益。

五、结  论

1)小试实验表明,在合适的操作条件下,纳滤膜可以将废水中浓度为

29

纳滤膜法处理和回收废水中低浓度全氟辛酸铵

100mg/L左右的全氟辛酸铵浓缩 100倍以上,对全氟辛酸铵的截留率始终

保持在 990%以上,得到的浓缩液可以回收并用于生产过程中,经过处理的

废水也能重复利用。因此,采用纳滤膜技术可以实现全氟辛酸铵废水的零

排放。

2)根据聚偏氟乙烯生产废水的排放情况,建立了超滤预处理,回收废水中的

全氟辛酸铵工艺。该工艺能够将废水中的全氟辛酸铵回收 990%以上,具有明

显的经济和环境效益。

参考文献

[1] PostGB,CohnPD,CooperKR.Perfluorooctanoicacid(PFOA),anemergingdrinkingwatercontaminant:A

criticalreviewofrecentliterature.EnvironmentalResearch,2012,116:93-117.

[2] KimSK,etal.OccurrenceofperfluorooctanoateandperfluorooctanesulfonateintheKoreanwatersystem:

Implicationtowaterintakeexposure.EnvironmentalPollution,2011,159(5):1167-1173.

[3] MakYL,etal.PerfluorinatedcompoundsintapwaterfromChinaandseveralothercountries.Environmental

Science&Technology,2009,43(13):4824-4829.

[4] PrevedourosK,etal.Sources,fateand transportofperfluorocarboxylates.EnvironmentalScience&

Technology,2006,40(1):32-44.

[5] HanX,etal.Renaleliminationofperfluorocarboxylates(PFCAs).ChemicalResearchinToxicology,2012,25

(1):35-46.

[6] SteenlandK,etal.associationofperfluorooctanoicacid(PFOA)andperfluorooctanesulfonate(PFOS)withuric

acidamongadultswithelevatedcommunityexposuretoPFOA.EnvironmentalHealthPerspectives,2010,118

(2):229-233.

[7] SteenlandK,etal.Associationofperfluorooctanoicacidandperfluorooctanesulfonatewithserumlipidsamong

adultslivingnearachemicalplant.AmericanJournalofEpidemiology,2009,170(10):1268-1278.

[8] HoriH,etal.Decompositionofenvironmentallypersistentperfluorooctanoicacidinwaterbyphotochemical

approaches.EnvironmentalScience&Technology,2004,38(22):6118-6124.

[9] ChengJ,etal.Sonochemicaldegradationofperfluorooctanesulfonate(PFOS)andperfluorooctanoate(PFOA)in

landfillgroundwater:Environmentalmatrixeffects.EnvironmentalScience& Technology,2008,42(21):

8057-8063.

[10] Rattanaoudom R,VisvanathanC.RemovalofPFOA byhybridmembranefiltrationusingPAC and

hydrotalcite.DesalinationandWaterTreatment,2011,32(1-3):262-270.

[11] DengSB,etal.Removalofperfluorooctanoatefromsurfacewaterbypolyaluminiumchloridecoagulation.

WaterResearch,2011,45(4):1774-1780.

[12] LiJG,etal.Developmentofextractionmethodsfortheanalysisofperfluorinatedcompoundsinhumanhair

andnailbyhighperformanceliquidchromatographytandemmassspectrometry.JournalofChromatography

A,2012,1219:54-60.

39

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

TreatmentandRecoveryofLowConcentrationPersistentOrganicPollutantofAmmoniumPerfluorooctanoatefromWastewaterbyNanofiltration

YinhuaWan,etal.

StateKeyLaboratoryofBiochemicalEngineering,Instituteof

ProcessEngineering,ChineseAcademyofSciences,

Beijing,China

Abstract:The feasibility of recovery of low concentration ammonium

perfluorooctanoate(APFO)from wastewaterwasstudied.Twonanofiltration

membranes,i.e.,NF270 and NF90,weretested withanAPFO model

solution.TherejectionofAPFOfortheNF270was92.0%,andfortheNF90

was"

99.0%atafeedconcentrationof100mg/LAPFO.Theeffectsof

operatingconditionswerealsoexamined.Withincreasingmembraneflux,the

concentrationfactorandAPFOrejectiondecreased.Atastirredspeedof2400

r/min,amembranefluxof66.4L/(m2·h),theconcentrationofAPFO of

117073mg/L was obtained with the NF90 membrane and the final

transmembranepressurewas14.9bar.Basedontheresults,ananofiltration

systemwiththetreatingcapacityof200t/dlowconcentrationAPFOcontaining

wastewaterwasbuiltup and successfullyputinto operation in a PVDF

productionplant.

Keywords: nanofiltration; ammonium perfluorooctanoate; wastewater

treatment;recovery

49

纳滤膜法处理和回收废水中低浓度全氟辛酸铵

Dr. Yinhua Wan  is professor ofBiochemical

EngineeringandViceDirectorsofStateKeyLaboratoryof

BiochemicalEngineering, and NationalEngineering

ResearchCentreforBiotechnology(Beijing)atInstitute

ofProcessEngineering,ChineseAcademyofSciences.

HeisalsocurrentlyservingasViceSecretaryGeneralof

ChineseSocietyofBiotechnology.ProfessorWanjoined

theInstituteofProcessEngineering,ChineseAcademyof

SciencesinDecember2004,afterworkingasanAcademicVisitorandpostdocat

OxfordUniversityformorethan6years.Prof.Wan’sresearchinterestmainlyfocuses

on membrane separation technology and itsapplicationsin biotechnology and

wastewatertreatment.

59

LargeScaleGasandVaporSeparationsUsingMembranes—APragmaticPerspective

WilliamJ.Koros

SchoolofChemical&BiomolecularEngineering,Collegeof

Engineering,GeorgiaInstituteofTechnology,Atlanta,Georgia,USA

Abstract:Largescaleseparationandpurificationprocessesareintegralparts

ofcommodityproductioncomplexes.Whilereactorscorrectlyreceiveagreat

dealofattention,roughly40% oftheenergyconsumptioninthechemicaland

refiningandpetrochemicalindustriesisassociatedwithseparationprocesses.

Mostcurrentlargescaleseparationprocesseshavebeendevelopedwitha

focusonefficacy,ratherthanaconcernaboutenergyefficiency,perse.Gas

andvaporseparationprocessesareparticularlyenergyintensiveandoffer

highpayoffopportunities to reduce both energy consumption and CO2emissionsin commodity production processes. Recentdevelopments in

membranematerialshavesetthestagefortheemergenceofanewgeneration

ofmuchmoreenergyefficientgasandvaporseparations;however,identifying

newmaterialsisonlyanecessaryfirststep.Inadvancedseparationdevices

suchasmembranes,modulemanufacturing,ratherthanspecialmaterialsper

seareusuallythelimitingcostfactor.Thisfactcanhelpguidepragmatic

considerationofstrategiestoenabletheemergenceofanewgenerationof

membranesto reduce energyintensitywithin upstream naturalgasand

downstreamchemicalprocessingindustries.Beginningwithahighlevelview,

elementsofsuchastrategyaredevelopedinthispaperandusedtodefinea

pathto the nextgeneration ofsuccessfulmembrane processesforgas

separations.Specificexamplesofthisstrategyandimplementationpathsare

providedtooutlinehowtheapproachcanbeimplementedwithmutualbenefit

toindustryandsociety.

69

1 Introduction

Largescaleseparationandpurificationprocessestransform low value

resourcesintomoreusefulfuels,basicchemicals,foodandcleanwater;

however,they also consume a greatdealofenergy. Growing global

population,increasedcompetitionfornaturalresourcesandthedesirefor

betterworldwide standards ofliving willintensify demands upon such

processes.Thesetrendswillplaceaburdenonavailableenergyresources

andleadtolargeincreasesincarbondioxideemissionsundera“businessas

usual”scenario.Approachesthatminimizeenergyintensivethermallydriven

separationscanallowasmuchasanorderofmagnitudereductioninenergy

intensityperunitofproductpurified[1,2].Whilealreadywidelyusedinwater

purification,advancedmembraneapproachescannotyetbeappliedwidely,

duetothelackofmembranessuitableforaggressivenonaqueousfeeds.

Recentdevelopments in membrane materials and formation approaches

providetoolstoextendthelowenergyintensityseparationrevolutionbeyond

watertoincludeabroaderspectrum oflargescalefeeds[3-18].Thispaper

focusesonspecificnewmaterialsfrom thisgroupofmaterialswitharealistic

potentialto enable economicalgasand selected vaporseparations.An

importantaspectofthefocusinthispaperistheneedtobeabletoform

economicallargescalemodulesbasedonthepreferredmaterials.Toprovide

context,Iwillbrieflyconsiderabroaderframework,includingallmembrane

separations,andthenfocusonthespecialchallengesassociatedwithgasand

vaporcases.

In2005,IparticipatedinaNationalResearchCouncilworkshopentitled

“SustainabilityintheChemicalIndustry:GrandChallengesandResearch

Needs”[19],andthereportfrom theworkshopprovidesusefulinsightsand

guidance,evenin2013[20].Iparticipatedinasessionintheworkshopentitled

“ReducingtheEnergyIntensityoftheChemicalProcessIndustry”,which

focusedonthehighenergyintensityofthechemicalandalliedindustry.

ImprovementinenergyefficientseparationprocesseswasakeytopicthatI

focusedoninthatsession,andIhavecontinuedtopursuethisactivelysince

thattime.Indeed,thepresentpaperprovidesanupdateonsomeofthe

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

importantdevelopmentsthathaveoccurredsincethetimeoftheworkshop.

JeffSiirola,whoatthetimewasaseniorresearcheratEastmanChemical

Company,notedpointsthatarestillvalidtoday,despitethemuchmore

optimisticpictureregardingthelikelyavailabilityofhydrocarbonresources—

especiallynaturalgas.Dr.Siirolanoted that80 percentofallchemical

manufacturingenergyisassociatedwiththeprocessingofmaterialsderived

from methane,ethane,propane,andaromatics[21].TherebirthoftheUS

chemicalprocessindustryhasbeenlargelydrivenbyavailabilityoflowercost

naturalgas and naturalgas liquids related to the socalled shale gas

revolution[22].ThereductioninenergycostsintheUnitedStateshasgiventhe

U.S.afavorableworldwidepositionthatisexpectedtobemaintainedfor

decades.Despitethisadvantage,withacknowledgedincreasesintheglobal

longterm demandforenergyandhydrocarbonresources,lowerprocessing

energyintensityremainsatleastasimportantin2013asitwasin2005.World

populationgrowthto9~10billionpeople(1.6×)isexpectedoverthenext

severaldecades.Moreover,growingdemandindevelopingcountrieswith

alreadylargepopulationswilldrivechemicalindustryoutputmuchbeyondthe

1.6Xfoldgrowthinpopulationgrowth—perhapsbyasmuchas5fold[23].

Shorttermeconomicsfavorrapiddeployment,withenergyefficiencyand

environmentalsustainabilitygivensecondarystatus.Eveniflocalgovernment

regulationsencourageadoptionofenvironmentallybeneficialapproachessuch

asmembranes,globalcompetitionmayfavoralowercost,lesssustainable

processoption.Despitethishurdle,ifdonewisely,technologyenabledenergy

efficiencycanbeatruly“noregrets”opportunityforfarsightedindustrial

adopterstogainlongterm competitiveadvantagesaswellasbeinggood

globalcitizens.

Ausefulbenchmarktoguidethinkingwithregardtoseparationissuesis

thewellstudiedUScasewheretheindustrialsectorisresponsiblefor33% of

totalenergyconsumption.Over40% oftheenergyconsumptioninthemassive

chemicalandrefiningandpetrochemicalindustryisconsumedbyseparation

processes[24].Thescaling0.4×0.33=0.132suggeststhatover13% oftotal

energyconsumptionisassociatedwithseparationoperations.Theimplications

ofa“businessasusual”scalingtoaccommodatetheprojected5Xincreasein

89

globalcommodities correspond to the equivalentof66% ofallenergy

consumedinallsectorsoftoday’sglobaleconomy.Sincethebulkofsuch

energywillcomefrom hydrocarbonsourcesformanyyears,thisenergy

burdenwouldbringwithitasimilarincreaseinCO2 emissions.Fortunately,

membranesoffera viable option to address this challenge to control

manufacturing energycostsand CO2 emissions.Neverthelessmembrane

technologymustbeintroducedbeforeinstallationofenergyinefficientthermally

intensive processes, since once such energy inefficientprocesses are

installed,theirlong(30~50years)liveswillrequireregulatoryinterventionto

forcetheirreplacement.

Toillustratethisissue,oneneedstoonlyconsiderproductionoffresh

waterbydesaltingbrackishandseawaterbrines.Currentlymorethan9billion

gallonsperdayworldwidedesalting capacityexists,and roughlyhalfis

membranebased,whilehalfisthermallydriven(e.g.,multieffectandflash

evaporators)[1].Modernreverseosmosis(RO)desaltingtechnologycontinues

toclaimanincreasingfractionoftheevergrowingmarket;however,despite

RO’smorethan10Xhigherenergyefficiency,oldthermalplantswithfully

depreciatedcapitalequipmentremaininuse.A similarsituationcanbe

envisionedinchemicalprocessingindustriesifscaleuptohandlethe5×

capacityexpansionisdonebyconventionalthermallyintensiveapproaches.

Indeed,energyefficientalternativesmustbedevelopedsoonfornonaqueous

feedstoavoidbuildinginlongterm inefficientprocessesasthechemical

processingindustriesmakecapacityexpansions.

Tohavealargeimpact,largescaleprocessesmustbethefocusto

enablesignificantreductionsinenergyuse(andCO2emissions).Moreover,

whilemanynetdrivingforcescanbeimposedtodrivepermeationbetween

upstream and downstream membrane faces, transmembrane pressure

differencesareeconomicalandsimpletoapply.Sincelargescalepressure

drivengasandvaporseparationsarelargepayofftargetsforwhichscience

andtechnologyarestillunderdevelopment,theyarethemainfocusofthis

paper.

Continuoussteadystatemembraneoperationsofalltypesinvolvefeed,

permeate,andnonpermeatestreams.TheseparationofapermeatedAfroma

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

second,rejectedBcomponentischaracterizedbythesocalled“separation

factor”,giveninEq.(1),whichshowstherelativemembraneenrichmentA

vs.B:

SF=

CompositionofAdownstream( )CompositionofBdownstreamCompositionofAupstream( )CompositionofBupstream

(1)

SincetheSFisa“ratioofratios”,anymeasureofcomposition(mole

fraction,massfraction,concentration,etc.,)canbeusedinEq.(1)aslong

asoneconsistentlyusesthesamemeasureforbothupstreamanddownstream

phasesincontactwiththemembrane.Locallywithinamodule,theratioof

compositionsleavingthedownstream faceofamembraneequalstheratioof

thetransmembrane fluxes ofA vs.B.Since fluxes are determined by

transmembranedrivingforcesandresistancesactingoneachcomponent,the

ratioofthefeedcompositioninthedenominatornormalizestheSFtoprovidea

measureofefficiencythatisideallyindependentofthefeedcomposition.

Minimizationofmembraneresistancerequiresminimizingeffectivemembrane

thickness withoutintroducing defects, and requires “micromorphology

control”,whichisatopicthatimpactsvirtuallyallmembraneapplications.

2 Hydrodynamicsieving(MF&UF)separations—generation1membranes

Practicalmicrofiltration(MF)andultrafiltration(UF)liquidseparation

membranesrelyuponaporousmembranetofilterparticlesormacromolecules

(B)suspendedinalowmolecularweightfeedfluid(A).WhileporesinMF

membranesarelargerthaninUFmembranes,inbothcasestransmembrane

pressuredifferencesmotivatethesuspendingfluid(usuallywater)topass

throughmicroscopicallyobservablepermanentporesinthemembrane.The

fluidflowdragssuspendedparticlesandmacrosolutestothesurfaceofthe

membranewheretheyarerejectedduetotheirexcessivesizerelativetothe

membranepores.Thisprocessconcentrates“B”componentsintheupstream

nonpermeatestream.Ontheotherhandessentiallypurelowmolecularweight

“A”ispresentinthedownstream permeateiftheporesizedistribution

preventsany“B”frompassageacrossthemembrane(i.e.,SF→∞).

001

Concentratingliquid feedsrepresentsmajorenergycostsforpaints,

foods,andmanywasterecyclestreams.Ofteninsuchcases,MFandUFcan

enablelargeenergysavingscomparedtoevaporationapproaches[1].Evenif

thermalenergyinputisneededinafinalfinishingstep,usingmembranesin

primaryconcentrationstepscanprovidelargeoverallprocessingcostsavings.

3 Transitionfromporoustonanoporousornonporousselectivelayersgeneration2membranes

AsshowninFig.1,whenpermeatedandrejectedcomponentsapproach

micromoleculardimensions(<20?)hydrodynamicsievingforcesnolonger

areadequatetoperform thesubtlesizeandshapediscriminationrequired.

Progressingfromnanofiltration(NF)toreverseosmosis(RO)togasseparation

(GS)involvesfinerandfinersizediscriminationbetweenpermeatedand

rejectedentities.Forgasseparations,infact,onlyfractionsofanangstromare

involved,andinallofthesecases,intermolecularforcesarethedominant

determinantsoftheresistanceactingoneachpenetrant.

Fig.1 Sizespectrumofpermeateandthecontrollingmechanismoftransport[19]

Forallmicromolecularly selective NF, RO and GS processes, a

thermodynamic“partitioning”alsoaffectsthefluxexpressionandmustbe

consideredtodescribetheprocessintermsofexternalphaseconditions.

Specifically,asocalled“partitioncoefficient”,Ki,istypicallydefinedas:

Ki=[CompositionofComponentiinmembrane][CompositionofComponentiinexternalphase]

(2)

SinceKiisexpressedasaratio,anyconsistentmeasureofcompositionin

themembraneandexternalphasesmaybeusedinEq.(2).WhenKi>1,the

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

membraneactsasa“concentrator”toattractcomponentifrom theexternal

phasetothemembranesurfacefortransmembranemovement.Entropicas

wellasenthalpiceffectscanbeatplay,andthebalanceofthesecancause

eitherahigherorlowerconcentrationofagivensoluteinsidethemembrane

relativetotheexternalphase.Ifthetendencytoenterthemembraneis

negligible,thepartitioncoefficientapproacheszero,i.e.,Ki→0.

Combined sizediscriminating and thermodynamicpartitioning permits

adjustmentoftherelativecompositionsofdifferentsmallmoleculesorions

havingtransmembranechemicalpotentialdifferencesbetweenthemembrane

upstreamanddownstreamfaces.Theratiooftheeffectiveresistanceactingon

Bvs.thatactingonAinthemembranespecifiesthemembranespecificability

toseparatethisABpair.Themembranethicknesscancelsfrom theratio,so

thekeyratioofresistancesactingoncomponentBvs.Aiscomprisedofa

productofpartitioningandmobilityratiofactors.Formostmembranes,the

mobilityratiocanbeapproximatedasDA/DB,theratiooftheaveragediffusion

coefficientsforcomponentA vs.B within the membrane phase.In this

commoncase,thereforetheeffectiveidealmembraneselectivity,αAB,isgiven

byEq.(3):

αAB =[DA][DB]

[KA][KB]

(3)

Inprinciple,“mobilityselectivity”,DA/DB,and“partitioningselectivity”,

KA/KB,canbetunedtodevelopadvancedmaterialsforanysmallmolecule

separationusinganytypeofmolecularlyselectivemembranematerial.RO

purification ofpotable waterfrom brine relies upon both “partitioning

selectivity”and“mobilityselectivity”contributionsfrom Eq.(3).Practical

optimizationofthemembranematerialandstructuresforaqueousreverse

osmosishasoccurredforseveraldecadesandhasresultedinveryefficient

high performance systems[25-27]. On the other hand, nonaqueous

nanofiltrationcasesinvolvingtheabilitytoseparateorganicstreamsremaina

highlychallengingandstillemergingarea[3-5].“Pervaporation”isavariantof

reverseosmosisthatusesalowpressureliquidfeedwithavaporpermeate

undervacuum.Sincepervaporationinvolvespermeationandevaporationofa

portionofthefeeditrequiressignificantthermalenergyinput,andbecause

201

reverseosmosiseliminatesthisrequirement,itbecamethefavoredprocessfor

waterdesalination. This willprobably be the case fororganic stream

separationsaswell.

Economicalmanufacturingofmoduleswithhighsurfaceareaisneededto

enablepracticallargescalemembranesystems.Thisbasicfactisclearfrom

Eq.(4),whereproductivity(e.g.,tonsperday,etc.)isrepresentedasthe

productofafluxandarea.

Productivity=[Flux]·[Area]=[Δμ(Chem,Potential)][Resistance]

·[Area] (4)

Practicallimitsexiston reducing membrane thicknessin economical

manufacturingprocesses,butrequiredΔμcanbeminimizedbymaximizingthe

contactarea across which transportoccurs. The ability to configure

membranestomaximizethethermodynamicseparationefficiencytoavalue

approachingthefreeenergyofdemixingdistinguishthemfromlessadvanced

separation approaches. Ofcourse, creating high contactsurface area

modulesrequiresbalancingcapitalcostwithoperatingcostadvantages,so

thereisacriticalneedtocreatelow costbuteffectivehighsurfacearea

devices.Indeed,whilespecialmaterialsarecriticaltoachievetheseparations

needed,itismodulemanufacturing,ratherthanspecialtymaterialsthatis

usuallythelimiting costfactor.Thisfactmakesdeviceengineering and

fabricationmoreimportantinalladvancedlowenergyintensiveprocessesby

comparisontoconventionalthermallydriven bulkseparations.In reverse

osmosis,ultrathinfilminterfaciallypolymerizedpolyamide(<500?)selective

layersprovidesufficientlyhighfluxestoallowtheuseofspiralwoundmodules,

whichprovideareasupto400m2/m3,tobeviable.Thesituationisarguably

differentforgasseparationswherefluxesarelower,leadingtolowermodule

productivitiesthaninliquidsystems.

4 Gasandvaporseparations—generation3membranes

Membranebasedapplicationsforremovaloforganicvaporsfrom gas

streamsandeventheseparationofpermanentgases(e.g.,O2vs.N2,CO2vs.CH4,H2vs.CH4)arecommercialrealities,andaresometimesreferredto

asGen3 membranes[1-2].Organicvaporremovalfrom permanentgases

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

typicallyreliesuponrubberypolymers.ThepartitioningterminEq.(3)always

favorsthemorecondensablevapormolecule,butinrubberypolymerslike

siliconerubber,thediffusioncoefficientratiofavorsthesmallergaslessthanit

wouldbeinahighlyrigidglassypolymer.Membranesforcaptureandrecycle

of volatiles from polyolefin storage bins (eg., polyvinyl chloride,

polyethylene,polypropylene)andforremovalofnaturalgasliquidsfrom fuel

gas use this principle favoring sorption and permeation ofthe more

condensableorganiccomponentusingrubberymembranes[27-29].

Ontheotherhand,mostgasseparationsofonepermanentgasfrom

anotherpermanentgasrelyprimarilyuponmobilityselectivity,basedonsize

differencesleadingtopreferredpermeationofthesmallerpenetrant.Evenfor

thesecases,however,thecondensablenatureofCO2 alsohelpspromote

highseparationfactorsrelativetomoresupercriticalgaseslikeN2andeven

CH4[30,31].An early successfulmajor application of gas separation

membranesinlargescaleseparationsinvolvedCO2 removalfrom CH4 in

naturalgas[28].The abilityto incrementallyadd installed capacityisa

particularlyattractive aspectofmembranebased processesthatallows

expenditures only as needed.Cellulose acetate (CA) hollow fiber

membranesarethemostcommonlyusedmaterialsforcurrentCO2/CH4separationsinvolvingmoderateCO2contents.Sincetheinitialdeploymentof

membranesattheSACROCfacility,theunithasbeenexpandedfrom only

70MMscfd(millionsofstandardcubicfeetperday,1scf=0.0283168m3)

toover600MMscfdcurrently.

The technology to create ultrathin skins via reactive interfacial

polymerization,whichisthedominantparadigm foraqueousRO,proved

impracticalfordrygasseparations.Nevertheless,theroughly10Xhigher

surfacetovolumeoffibermodulesvs.spiralwoundmodulesstillenables

commerciallyviablemoduleproductivityforgasseparation[1,19,27,32].These

Gen3fibersaremoresophisticatedthanearlierreverseosmosisfibersand

havethinnerselectivelayersthatcanbe“caulked”torepairnanoscopic

defects,allowingthemtoapproachthicknessesofthereactivelyformedGen2

reverseosmosislayers.Inaddition,advancedGen3fiberswerespunas

compositestructurescomprisingmorecostlybutmoreselectivethinsheath

401

layers[34].Suchmembranes,with~250μm diameters,yieldedeconomically

productivehighsurfacetovolumeratiomodulessuitableforseparationofeven

relativelylow sorbing gaspenetrants,e.g.O2 and N2.Fig.2 givesa

schematicrepresentationofthehollowfiberapproachwithhighlightsregarding

theadvantagesitofferedtoenablesuccessinGen3applications.

Fig.2  Gen3hollow fiberasymmetricmembranemodulesexceed

capabilitiesofspiralwoundflatsheetmoduletechnologythathasmuch

lowermodulesurfacetovolumeratios[27,33-34]

5 Generation4—highlychallenginggas&vaporseparationcases

Tosignificantlyimpactglobalenergyuse,awidespectrumofseparations

mustbe addressed effectively,and itisstrategicallywise to selectan

approachcapableofoptimizingperformancevs.costacrossthelargescale

energyintensive molecularseparations spectrum. Hollow fibers are key

elementsinsuchastrategy.Inaddition,appropriatecandidate“advanced

materials”shouldbeselectedtoenableevolutionaryadvancementofthe

technologybasewithoutdisruptivechangesintheexisting manufacturing

paradigm.

Gen3gasseparationssuchasO2removalfrom airorCO2removalfrom

naturalgasusingglassypolymerswereamajortechnicalstepbeyondGen2

liquidseparationsandevenvaporgasseparations.Indeed,sizeandshape

discriminationsupto10timesfinerinpercentagesizedifferencebetween

permeatedandrejectedcomponentscomparedtothoseinROwereachieved

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

inGen3(2).AtlowCO2partialpressures,wheremembranematrixswelling

islow,continuedrefinementinintrinsicsizeandshapediscriminationisan

adequatestrategy.Unfortunately,thetendencyforsupercriticalCO2toswell

andsoftenrigidmatricesoftypicalpolymersusedformoderateCO2 partial

pressureGen-3feedspresentsnewchallenges.Indeed,naturalgasfeeds

containing40mol% -50mol% CO2athighpressures(800~1000psia,1psia

=1lb/in2=6895kPa)representthedemandingconditionstypicalofthose

that“Gen4”systemsmustface.Suchfeedscannotbeaddressedrealistically

byGen1toGen3membranetypesmentionedabove.

Fig.3  Upstream (production)anddownstream (crackingandrefining)

involveseparationsthatcanbenefitfromGen4membraneprocessestoreduce

   processenergyintensityandCO2footprints

Fig.3illustratestypicalGen4challenges.Beginningatthehighupstream

pressureproductionwellhead,removalofcontaminants(generallyCO2 and

sometimesH2S)[35]occurstomaketheproducedgassuitablefortransfertoa

downstream facility. Atthe downstream site, many energy intensive

separationsoccur.Insuchadownstream facility,separationofC2 andC3olefinsfrom paraffinsaremajorenergyintensiveactivitiesandareusefulto

considerforillustrativepurposes.Ideally,CO2removalfrom rawnaturalgas

canevenenablereinjectionatthewellsitewithmultiplebenefitstoprovide

enhancedproductionbymaintainingreservoirpressureandreducesviscosities

ofcoproduced associated crude oil,ratherthan causing environmental

impactsduetoatmosphericventing.Naturalgasconsumptioncomprises

roughly25trillionscf/aintheU.S.and116trillionscf/a(2.5billiont/a),

worldwide[35].Moreover,naturalgasisoneofthefastestgrowingenergyand

feedstocksources,becauseitisabundantandrelativelycleanerthanliquid

fossilfuelsorcoal.Carbondioxide,asthemostabundantcontaminant,can

601

exceed50mol% insomenaturalgasfeeds,withCO2 contentsabove70%

beingcommoninenhancedoilrecoveryapplications[1].Thesefactsmakethe

CO2/CH2pairanespeciallyimportantseparationtarget.Althoughmembranes

intrinsicallyofferthemostefficientseparationsoption,improvedmaterials,

beyondthoseinGen3casesareneededtoenabletheirbroaduseinthis

application[6-19,32,36-60].

Downstreamprocessingofhydrocarbons,especiallynaphthaandnatural

gasliquids,transformsthesefeedstocksintoanarrayofcomponentsinhuge

crackingfurnaces.SubsequentseparationofvaluableC2andC3olefinsfrom

thecomplexmixtureleavingthecrackingunitsarethemostenergyintensive

partofsuchprocesses.In2010globalethyleneproductioncapacitywas145

milliontons[61].Cryogenicdistillation,performedat-25℃ and320psig

(1psig=6895kPa)inacolumncontainingover100trays,iscurrentlythe

highlyenergyintensiveapproachthatdominatesethylene/ethaneseparations.

Propyleneisalsoacruciallyimportantfeedstockforpolymersanddiverse

derivativesformanufacturingvaluablechemicals,andthepropylenepropane

splittercancontain200trays.Typically,theseunitsarecapacitylimitedwith

upto7% annualgrowthandademandof77milliontonsin2010[62].

Intrinsically highly selective advanced materials, such as zeolites,

ceramics,metalsandmetalorganicframeworkmaterials,havenotyetbeen

economicallyscalabletolargemodules.Indeed,forming suchadvanced

materialsthatofferhigherselectivityperformancecurrentlyrequiresaradically

differentmanufacturingparadigm from thatwhichhasledtohighsurfaceto

volumeGen1 toGen3 modules.Thissimplefactrepresentsthemajor

practicalhurdletousingtheseadvancedmaterialstoaddressGen4needs.

Ontheotherhand,theevolutionaryfiberbasedpathnotedinFig.4appears

likelytoenabledevelopmentofincreasinglysophisticatedmaterialsbeyond

Gen3polymersinordertocreatemembraneswithperformanceandcost

combinationsthatmeetmany challenging separation requirements noted

earlier.

Thefirststep onthispathtopracticalGen4 materialsbeginswith

crosslinkedpolymerstoovercomeswellinginducedperformancelosses.The

possible nextstep involves hybrid materials, comprising polymerwith

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Fig.4 (a)selectivity-permeabilitytradeoffperformancerelationshipbetweenadvanced

materialsandpolymersthatcanbeprocessedintoasymmetrichollow fibersusingthe

approachshowninFig.2;(b)advantagesofpolymer-derivedroutestoadvanced

materialsvs.otheradvancedmaterialswithsimilarperformanceoptionsbutwhichrequire

   morecostlyprocessingtoscale-upfromlabtolargecommercialscalemodules

embedded inorganic ormetalorganic framework nanoparticles to use

advantagesofhardtoprocesspureadvanced materialswhilemaintaining

processingsimplicityofpolymerfiberspinning.Finally,themostevolved

form—comprising carbon molecular sieve (CMS) materials—offers

extraordinarycapabilitieslikeotheradvancedmaterialsbutwithonlyasingle

pyrolysisstepusingprecursorsderivedfrom Gen3typepolymerfibers[1].

Thisincreasinglysophisticated familyofmaterialsoffersthe potentialto

addressallbutthehighesttemperature,mostoxidizingfeeds.Thisfamilyalso

addressesmostimportantlargescaleseparationneedsofinteresttoboth

currentandalternativefeedstockprocesses.Aworkablestrategytoimplement

thisvisionwillbeillustratednextbyconsiderationofsomespecificcases.

Clearly,forthemostchallenging(e.g.,hightemperatureoxidizingfeeds)

zeolite,metaland advanced ceramicmaterialswillstillbeneeded[16,18].

Thesecasestrulyrepresenta“fifthgeneration” vision,whichmustbe

pursued;however,itseemswisetofirstfocusonthefourthgenerationtopics

notedhere.Indeed,lessonslearnedindevelopingcosteffectivemodules

fromfourthgenerationmaterialsarelikelytobehelpfulinultimatelyidentifying

economicalapproachestosuchfifthgenerationmaterials.

801

6 Upstreamseparationexamples:aggressivenaturalgaspurification

Covalentlycrosslinkingmembranestopreventplasticizationinaggressive

feedshaveprimarilyfocusedonalreadyrigidpolyimidebackbonematerials

withtypicalglasstransitionsofteningpointsapproaching300-400℃.Clearly,

manyapproachestostabilizationcanbeenvisioned,butwhicheveroneis

consideredshouldbeextendabletoasymmetrichollowfiberstructurestohave

apracticalimpact.Oneapproachinthisregardreliesuponoptimizingadiol

crosslinkingagentattachedtoafreeacidofthepolymerinsolution[36,37].Such

monoesterifiedpolymerscanbesolutioncast(orspunintofibers)followedby

heatingtoonly220℃ tocompletethetransesterificationcrosslinkingreaction

shownbelow.ThemethodisadaptableandHOROHcanbemanypossible

linkers;however,propanedioloffersagoodbalanceofmechanicaland

transportproperties.

Fig.5 Esterificationbasedcrosslinkingtoachievestabilizedhighperformance

polymersforadvancedsizeselectivemembranematerials[36]

The copolyimide structure shown in Fig6 has an intrinsically high

permselectivitybasedonitrigidsizedandshapediscriminatingmatrix.The

presenceofthemonoesterifiedunitalsoprovidestheabilitytobespunintoa

highproductivityasymmetricstructuresthatcanbesubsequentlycrosslinked.

Thiscrosslinkingstabilizesthematerialagainstswellinginduced selectivity

losses,eveninanasymmetrichollowfiberform.Theintrinsicperformanceof

thismaterialfallsclosetotheupperboundlineselectivitypermeabilitytradeoff

linedefinedin1991[39],andlaterextendedin2008[40].Forconvenience,this

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structurebasedona3∶2ratioofdiaminomesityleneanddiaminobenzoicacid

with6FDA dianhydride is referred to as PDMC (eg., propane diol

monoesterified crosslinked polymide); howevermany variations on this

structurecouldbeused[60].ThePDMCintrinsicpermeabilityandselectivityare

somewhathigherthanthatofCAevenforlow feedpressuresofa50∶50

mixture.More importantly,however,PDMC,maintainsa high CO2/CH4selectivityof~ 45 atveryhighfeed pressuresof50∶50 mixtures.By

comparisontotheaboveCAcase,forroughlyevery45CO2moleculesthat

permeate,only1CH4 permeatestobereinjected,whichisroughlyonlya

22% productlosscomparedtothe1/8or12.5% lossinthecaseofCA.This

excellentperformanceisindicatedbytheessentiallyunchangedselectivityand

permeabilityfortheopenredpointvs.thesolidredpointatlowandhighfeed

pressures,respectivelyinFig.6.Notonlyisthemembraneperformance

attractive,butalsotheprocessshowninFig.2andFig.6toachievethis

performanceisattractive,requiringminimalchangesvs.Gen3materialsto

form a fully asymmetric crosslinked membrane. By tuning the dope

compositionandspinningconditions,monoesterifiedcopolymerwithatleast

onediolpertwocarboxylicacidscanbespunasanasymmetricfiberviathe

approachesusedforsimplenoncrosslinkablefibersinFig.2.Thefibersare

thensolventexchanged topreventcapillaryforceinduced porecollapse

duringdrying.However,unlikeasimpleGen3materiallikecelluloseacetate

(CA),crosslinkingcanbeachievedusingthepropanediolsidechains.To

achievethiscrosslinking,byperformingthefinaldryingstageatanoptimized

highertemperature,intersegmentalcrosslinkingandrigidificationoccurswhile

thedesired asymmetryismaintained.Indeed,thefinalmembraneadds

virtuallynonew processing stepsand iseffectivelyan“evolved Gen3”

material,illustratingatrulyeconomicalGen4membrane.

Analternativeapproachtostabilizationagainstpenetrantinducedswelling

eliminatestheneedfortheestercrosslinkinginFig.5&Fig.6.Thisapproach,

termedDRIC,Decarboxylation,RadicalInducedCrosslinking,canbeuseful

forevenmoreaggressivefeedsforwhichtheestercrosslinkingapproachmay

be compromised by hydrolysis. Both the estercrosslinked, and DRIC

materialsmaintaintheirhighselectivityinthepresenceofrealisticaggressive

011

Fig.6 Gen4crosslinkedmembranesforhighCO2contentnaturalgascleanup

feeds.Other(Gen3)materialswithoutsomeadditionalstabilizationmaylie

onorneartheupperperformanceboundundermildfeedconditions(say<50

psiCO2partialpressure),butloseselectivitybadlywhenexposedtoactual

aggressiveswellingfeeds.TheDRICpolyimidewasderivedfrom thesame

precursorasthatinFig.6,butinthefreeacidform,withoutpropanediol

monoesterification.Thisfreeacidform canbetransformedtoacrosslinked,

CO2plasticizationresistantmaterialbysimpleheatingbelow Tg,toinduce

decarboxylation,radicalinduced crosslinking DRIC stabilization[63,64].The

reactionproceedsviaadianhydrideintermediate,whichistypicallyformed

around150-200℃ incarboxylicacid containing polymers[65-72].IR data

suggestslikelycrosslinkingsites,notedinFig.7.

Fig.7 Crosslinkingfordecarboxylation/radicalinducedcrosslinking(DRIC)

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Acomplexpathwaywithmultiplepossibleintermediatesispossibleduring

heatingabove220℃,butthefinalresultsleadstocrosslinkingsimilartothat

notedintherelated workbyEskay[70-72].A keystep inthecrosslinking

appearstoinvolveformationofanhydridemoietiesfromDABAcontainingunits

onneighboringchainsegments.Subsequentcreationoffreeradicalsonthe

formerlyconnected phenylrings(thatare on the DABA groupsin the

polyimides)canthenoccuratsufficientlyhightemperature.Themostlikely

crosslinkingsiteisthecombinationofneighboringfreeradicalscreatedonthe

phenylringsformerlypartoftheanhydride,whichrecombinetoform a

biphenyllinkage.Nevertheless,allthreepotentialsitesillustratedinFig.7are

viablestabilizinglinkages.Thefreeradicaldecompositionoftheanhydride

doesnotoccurefficientlyuntiltemperaturerisesabove220℃,andothersites

may require highertemperatures. In any case, largescale backbone

decompositiondoesnotbegintooccuruntilmuchhighertemperaturesnear

450-470℃[63-64].LikethePDMC material,theDRIC materialmaintains

selectivityunderaggressiveconditionsnotedinFig.6.

Similarly,socalled“thermallyrearranged”(TR)and otherstabilized

polymerderived samples noted earlier[6-15,32,36-59] can maintain attractive

selectivitypropertiesinthepresenceofswellingfeeds.Infact,however,few

potentiallystablespinnablepolymericmaterialshaveactuallybeentestedas

asymmetricmembranesunderextremeconditionsabove50atm(1atm =

101325×105Pa)withhighCO2contentsnotedinFig.6forthePDMC(and

DRIC)materials.Also,asnotedearlier,whilepurezeolitemembranesshow

durabilityunderaggressiveconditionslikethosenotedinFig.6,costhas

hinderedtheirlargescaleuse.Forallpolymerbasedmaterials,somedegree

ofcrosslinking islikelytoberequired tomaintainperformancenearthe

spinnablepolymerupperboundtradeofflinesnotedinFig.4.Thisreality

makesthehighpayoffGen4topicofswellingstabilizedasymmetrichollow

fibermembranesanactiveareaofdevelopment.

Hybridmaterials—astep beyond “simple” crosslinked materials:The

progressioninperformance“evolution”suggestedinFig.4indicatesthatan

obviousstep beyond crosslinking stabilizationinvolvestheuseofhybrid

materials[38]. Hybrid combinations of polymers with high separation

211

performancematerials,whichareexpensiveaspuremembranematerials,

offeropportunitiesbeyondthoseofevenrigidcrosslinkedpolymerssuchas

PDMCorotherspinnablestabilizedpolymers.Tobeeconomical,thismay

requirenanocompositespinning ofdopestoform compositesheathcore

fibers.Suchaddedcomplexitymaymakeittemptingtobypasstheneedfor

hybridmaterialsandtoproceeddirectlytocarbonmolecularsievematerials

notedinFig.4.Anotheraspectofthisissuewillbediscussedlaterinthe

contextofaspecializedolefinparaffindownstream separationapplication,

whereonlyCMSappearstobefundamentallyandeconomicallyworkable.For

naturalgas,ZIF(zeoliticimidazolateframeworks)andothermetalorganic

framework“inserts”[73-86] appearviable to boostCO2/CH4 selectivityof

stabilizedspinnablematriceslikethosenotedintheprecedingsection.In

fact,however,anadditionalissuecomplicatessuchhybridsthatrelyupon

coordinatingmetalionstomakethe“inserts”.Specifically,reactivitywith

H2S[87],whichsometimesaccompaniesCO2asacontaminantinnaturalgas,

limitstheavailable“insert”choices.TheuseofH2Sstablezeolitesinsteadof

ZIFs can eliminate H2S stability concerns; however, additionalsurface

functionalization is required to promote compatibility between the totally

inorganicdispersedparticlesandthecontinuousorganicmatrix(79,81).In

suchcases,whicharenotsorare,themorerobustcarbonmatrixoffers

advantages.Therefore,duetospacelimitationsinthispaper,althoughthe

hybridapproachoffersapotentiallyattractiveoption,itwillnotbediscussed

furtherhereinthecontextofupstreamseparations.Instead,theadvantagein

takingthestepfromapurelyGen3materialtoCMSwillbeillustratedforthe

CO2/CH4gaspairwithoutpassagethrough“hybrid”materials.

Extensiontocarbonmolecularsieve(CMS)membranesforaggressiveCO2/

CH4separations:Thespecialpropertiesofcarbonmolecularsievesresultfrom

theirhighlyrigidmatrices,whichmakethem alimitingcaseforpolymer

derivedmembranematerials[88-110].Theabilitytousedifferencesinpenetrant

configurationalentropy[90]intheactivatedstateofsubtlydifferentpenetrants

providesanadditionaltoolforengineeringmobilityselectivityinEq.(3).Use

oftheconfigurationalentropyfactorintheactivatedstateistypicallynot

availablewithevenrigidpolymersthatcanbeformedintoasymmetricfibers,

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duetosegmentalmotionswithinthematrix.Thesemotionsareeffectively

absentinCMS,zeolitesandceramics.Thisadditionalfeatureallowsoneto

extendmobilityselectivitycapabilitiesincaseswheretheshape,ratherthan

onlythenominalLennardJonestumblingdiameterdifferbetweentwosimilar

moleculeslikepropyleneandpropaneorethyleneandethane.Untilrecently,

CMSmaterialsweretoodifficulttofabricatereproduciblyandeconomicallyto

makeintohighperformancehollow fibermembranesforthelargescale

applicationsdiscussedinFig.3.Recentworkhasrevealedpracticalwaysto

workwiththesematerialsinactualasymmetricfiberforms.Despitethese

encouragingdevelopments,workisneededtobetterdefinestructureproperty

relationships.TranslatingpropertiesofprecursorstoultimateCMSproperties

createdunderdifferentpyrolyticprocessing atmospheresstillhave many

elementsofartaswellasscience.TheunderstandingoftheinterestingCMS

classofmaterialsisinasimilarlyemergingstatetothatwhichrigidglassy

polymerswereinwhenGen3membranesbegantobepursued several

decades ago. At that time, rigid glassy polymers provided large

improvementsoversimplerubberypolymerswithonlylowmobilityselectivities.

Similarly,CMSmaterialsappearlikelytoenablethenextstepinmobility

selectivitytobeachievedbeyondrigidglassypolymersusingtheadded

configurationalentropycontrolaffordedbytheirintrinsicnatures.

CMSmembranescanbeformedbythermaldecompositionofpolymer

precursors,resultinginalmostpurecarbonmaterials,inmanycasesabove

90% carbon[90-92].Dependingupontheprecursor,pyrolysistendstoform

cokeorchar.Coketendstoformgraphiteatatemperatureabove2473K,but

charremainsinanamorphousstructure.Suchamorphouscharrichmaterials

arebelievedtohaveahighlyaromaticstructurecomprisedofdisorderedsp2

hybridizedcarbonsheetswithanglesofdisorientationofseveraldegreesas

illustratedinFig.8(a)and(b)[88,93].Thestructurecanbeenvisionedto

compriseroughlyparallellayersofcondensedhexagonalringswithnothree

dimensionalcrystallineorder.Poresareformed from packing imperfections

betweenregionsinthematerial,andtheporestructureinCMSmembranesis

describedas“slitlike”withan“idealized”structureillustratedinFig.8(c).

ThisporestructurecanbefurtherrepresentedasshowninFig.8(d)withan

411

idealizedbimodalporedistribution.Thisdistributionconsistsof“micropores”of

6-20?connectedbysmallersocalled“ultramicropores”[94-96].Thecombination

ofultramicroporesandmicroporesprovidesthemolecularsievingfunctionand

highpermeabilitycharacteristicoftheseunusualmaterials.Thedisordered

structureofthecarbonmaterialisdifferentfrom zeolites,whichhavea

uniform, welldefined set of pores. Despite the distribution of the

ultramicropores,CMS materials offerthe importantadvantage offacile

formationofhighlyselectivedefectfreemembranesusefulingasseparation

applications.Moreover,despitetheirhighmoduliandrigidity,CMShollow

fibermembranes(unlikethickerdenseCMSfilms)areremarkablyflexible.

The basis for this valuable macroscopic flexibility is not completely

understood,butmayreflecttheabilityofthenoncrystallinearrayofgraphene

likesheetstoslidepasteachotherduringdeformations.

Fig.8 Idealizedstructuresofglassycarbonsandanidealizedporesizedistribution

ofcarbonmolecularsievematerialsrepresentingmicroporesandultramicropores

Structures ofCMS membranes have been investigated by many

researchersusingtraditionaltechniques,suchasXraydiffraction(XRD),

transmissionelectronmicroscopy(TEM),andadsorption[89,97,98].Unfortunately,

theamorphousnatureofCMS,makesitdifficulttodeterminethedetailed

structure,especiallytheultramicroporenaturethatgovernsthemolecular

sievingprocess.WhenXRDisperformed,broadpeaksareobserveddueto

theamorphousstructureofCMS,therebycomplicatingestimationofactual

porestructure[97].HighresolutionTEMresultsarealsoinconclusiveduetothe

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amorphousstructure,andpossibleporesofthematerialaredifficulttotruly

define.Chen,Loo,Wang,andDoconductedanargonadsorptionisothermto

obtainaporesizedistributionofCMSmembranes,butcouldnotusefully

analyzetheselectiveultramicroporeregion.Similarly,SteelandKorosand

CampoandMendesconcludedthattheporesizedistributionderivedfromCO2adsorptionequilibrium wasinadequatetoexplainCMSporestructuresthatare

responsibleformolecularsieving[97,99].Despitethesedifficulties,theimportanceof

theseunusualCMSstructures,namelytheapplicableultramicroporedistribution,

canbeprobedbyusingvariousgasmoleculesasprobes(99).

Asin the case ofpolymers,transportthrough CMS membranesis

modeledbythesorptiondiffusionselectivitymechanism representedinEq.

(3).EveninCMSmaterials,gasmoleculessorbintothemembraneatthe

upstream,diffuseundertheinfluenceofachemicalpotentialgradient,andfinally

desorbfromthemembraneatthedownstream.ForCMSmaterials,thediffusion

coefficient,Di,inCMSmembranesisanevenstrongerfunctionofpenetratesize

vs.glassyandrubberypolymers.Asaresult,CMSmembraneenablemolecular

sievingdiscriminationbetweensimilarlysizeandshapepenetrants.Thesorption

coefficient,equaltotheconcentrationofgassorbeddividedbythepenetrant

partialpressureatequilibrium,dependsuponthecondensabilityofthegas

penetrantanditsinteractionswiththemembranematerial.

Thepolymerprecursor,6FDA/BPDADAM,hasastructuresomewhat

relatedtothatofthecrosslinkablepolyimidenoted inFig.6,butisnot

crosslinkable,sinceitlackstheDABArepeatunit.Ratherthanrelyingupon

thesingle6FDAdianhydrideandtwodifferentdiaminesinthecopolymer,

6FDA/BPDADAM,usesthesingleDAMdiamineandtwodifferentdianhydride

units selected to balance backbone packing disruption and rigidity.

Specifically,50% ofthehighlypackingdisruptive6FDAisreplacedbythe

highlypackableBPDAdianhydrideasshowninFig.9.

Fig.9 6FDA/BPDA-DAM polyimideprecursorforcarbonmolecularsieve

611

Apyrolysistemperatureof550℃ witha2hsoaktimeatof550℃ canbe

usedwith30ppmO2inargonpyrolysisatmosphereusingapyrolysissystem

likethatshowninFig.10withabilitytomonitoroxygenconcentrationduring

pyrolysisstudies;however,thesimplestcasecorrespondingtoultrahighpurity

argonalsoisattractivewherelargerultramicroporesareneeded(99).

Fig.10 PyrolysissystemwithO2monitoringcapabilityduringpyrolysis

Fig.11comparesperformanceat35℃,includingcelluloseacetate(CA),

whichwasdiscussedinFig.6.AsshownagaininFig.11,theCO2/CH4selectivityoftheCAfallsdramaticallyfrom around40at10psitoabout8at

800psiafora50∶50CO2∶CH4feed,soatthehighpressure,alossof1CH4occursforevery8CO2’spermeated,ie.,12.5% CH4lossoccurs.Thislost

CH4iseitherwastefullyventedorreinjectedintothereservoirwiththeCO2permeatestream,whereitissubsequentlyunrecoverableinitsdilutedform.

ThestablePDMC andDRIC decarboxylatedmaterialsshow selectivitiesof

roughly45and28at800psia,and2.5% and3.6% CH4loss,respectively—

verylargeimprovementsvs.CA.

Fig.11 Comparisonat35℃ ofPDMC&DRICvs.celluloseacetate(CA)&

6FDA/BPDA-DAM CMS(550℃ with30ppmO2doping)

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Even more impressive, however, the CMS membrane shows an

intrinsicallyhigherselectivityofroughly65withapermeabilityof2500Barrersin

the50∶50CO2∶CH4feed.Inthiscaseonly1CH4forevery65CO2’spermeated

islost,i.e.,1.5%,representingavaluableimprovementoverboththestateof

theartCAandevenoverthePDMCandDRICpolymers.Theopenandclosed

circlesat1atm and800psiaarevirtuallythesamefortheCMS.The

significanceof3.6% lossinthecaseoftheDRICsamplevs.1.5% lossfor

theCMSsampleinthecaseofatypicallargefield(500×106scfperday)

illustratespossibleimpactsofimprovements.Forinstance,fora50∶50feedof

500×106scfd,2.1% losspreventionsavingsinCH4resourceequals0.02×

05×500×106scfd =5×106scfd,correspondingtoroughly5×109BTU/d,

whichisequivalentto62.4MW—alargeamountofenergy!The2500Barrer

CO2permeabilityoftheCMSvs.thestateoftheartDRICpolymerwith250

BarrersCO2permeabilityfor800psiafeedof50∶50CO2∶CH4mixtureisalso

significant(note the log scale on permeability in Fig11). The more

permeableCMSwillreducemodulesizeifequivalentthicknessselectivelayers

canbecreatedfortheCMSvs.DRIC membranes.Thehigherselectivity

PDMCmaterialcanenablelessCH4 productlossvs.theDRIC material;

however,moremoduleswouldberequiredforthelowerpermeabilityofthe

PDMC.Ontheotherhand,forthesameselectivelayerthicknessforCMS,

PDMC and DRIC materials,lessCH4 lossand fewermoduleswould be

requiredusingCMS.RecentworkhassuccessfullyformedasymmetricCMS

fiberswith similar,butstillthicker,selective layerscompared to those

achievablewithPDMCandDRIC.Recentadvancestosuppresscollapseof

theasymmetric supportlayerabove the polymerglass transition have,

however,beenreported[100,101],sotheCMStechnologyisverypromising.

7 Downstreamseparationsexamples:olefinparaffinseparationmembranes

As noted earlier, ethylene and propylene are importantsynthetic

chemicalsinthepetrochemicalindustrybutareintrinsicallydifficulttoseparate

duetothesimilarphysicalpropertiesofsaturated/unsaturatedhydrocarbons.

A1993reviewnotedtheenergyuseforolefin/paraffinseparationstobe1.2×

811

1014BTU/a[102]andbasedonaconservative4.5% globalgrowthoverthis

period[61],this translates to 1.9 ×1014 BTU/a currently. Conventional

technologytoseparateolefin/paraffinmixturesisenergyintensivedistillation,

andisperformedatelevatedpressuresintraditionalmultitrayfractionators.

The large energy costcreates an incentive foralternative technology.

Considerableresearchindicatesthepotentialofmembranesintheolefin/

paraffinseparationarena,butthispotentialhasnotyetbeenrealizedinactual

large scale processes. Capacity expansions ofexisting thermallydriven

separationunitsareidealwaystointroducemembranesintolargescaleuse

while minimizing risks and building familiarity with this relatively new

technology.Thisapproachleveragesexistinginvestmentswithouttheneedto

build entirely new thermallydriven separation units. Within an existing

integratedplant,valuablecompoundsinavaporfeedstreamcurrentlysentto

anotherthermallydrivenseparationunitcouldbemembranefractionatedinto

highervalueproductswithminimalexpenseandsignificantenergysavings.

Fig.12 ConventionalseparationofC2andC3mixtures

integratedwithpossiblemembraneunits[108,111]

DebottleneckingofC2andC3Splitters:Fig.12illustratesthisapplicationof

advancedofmembranesunits.Dependingupontheseparationcharacteristics

of the membrane material, this approach could allow a significant

debottleneckingoftheC2andC3splitters.Conventionalpolymermaterialsare

limitedbytheperformanceupperboundbetweenproductivityandselectivity

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tradeoff[103]suchasthatillustratedschematicallyinFig.4—especiallyunder

theaggressiveswelling conditionsofsuchunderaggressivehydrocarbon

feeds.Moreover,while,facilitatedmembranesofferhighselectivity,theyare

morecomplexthantraditionalmembranesandhavebeenunderdevelopment

fordecades[104,105].PurelyinorganicandMetalOrganicFramework(MOF)

membraneswithrigidporestructure,occupytheregioninFig.4abovethe

upperbound;however,expensivefabricationcostandtheirbrittlenatures

havehinderedtheiruseinsuchlargescaleapplications.Recentworkinvolving

“hybrids”based onspecialityMOFsand selected polymermatriceshas

shownpromisefortheC3 olefinsvs.paraffinseparationsinFig.12[106].

Moreover,sincesuchhybridscanstillbeprocessedusingtheapproach

showninFig.2foreconomicalfiberformation,hybridsmaybeattractivefor

suchdebottlenecking applicationslikethoseinFig.12.A morecomplex

spinneretisrequiredtoproduceasheathcorestructure,butavoidanceofthe

additionalCMSpyrolysisstepformembraneformationmakesthisapproach

attractive.

InrecentpapersfabricationofMatrimid derivedCMSmembranesfor

bothethylene/ethaneandpropane/propyleneseparationweredescribed[107-109].

ThetranslationofsuperiorCMSdensefilm propertiesintoasymmetrichollow

fibermembrane is a challenging step in asymmetric CMS hollow fiber

membraneformation.Substructurecollapseofthesupportingwallwasfound

tooccurinMatrimid polymerfiberduringintenseheattreatments.Sucha

porouswallcollapseresultsinincreasedeffectiveseparationlayerthickness

andreducedpermeance.Recentdevelopmentsbasedonsimpleprecursor

treatmentpriortopyrolysisovercomethisporouswallcollapseissue,providing

apath to form CMS hollow fiberswith high productivityand selectivity

membranes[100-101]. In fact, by tuning properties ofCMS membranes

discussedfortheCO2/CH4case,optimizedCMSmembranesusefulforolefin

paraffinmembraneapplicationsinFig.12canalsobecreated.Thesame

pyrolysistemperature(550℃)usedfortheCO2/CH4 applicationiseffective

theolefinparaffinpairs;however,fortheselargerpenetrants,apureargon

pyrolysisatmospherewasuseful,ratherthanthe30ppmO2inargonpyrolysis

atmosphereusedfortheCO2/CH4 pair[100,107-111].Theslitlikeporestructure

021

created in thiscase,providesa unique combination ofultramicropores

(responsible formolecularsieving) and micropores (responsible for

sorption),thatareidealforolefinparaffinseparations[96,99,107-111].Moreover,

sinceCMSmembranesareproducedviacontrolledpyrolysisofasymmetric

hollow fiber polymer precursors, they provide high performance and

economicalscalabilitycomparedtostandardinorganicmembranesandmetal

organicmembranes.

8 Olefinsselectivemembranesforolefin/paraffinseparations

BesidestheapplicationinFig.12,CMSmembranesappeartobesuited

foranevenmoreadvancedapplicationillustratedinFig.13[108,111]basedona

mixed olefinsparaffinsselective membrane.Thisnew conceptisa step

beyondtheconceptinFig.12involvingseparateC2 olefinparaffinandC3olefinparaffindebottleneckingmembranes,andfocusesonthedeethanizer

showninFig.13asdiscussedbyXuetal.[108].Polymericmembranecannot

dothisseparation,butthedatainTable1show thattheCMSmembrane

discussedforthebinaryseparationsinFig.12isalsousefulforthisdeethanizer

debottleneckingcase.

Table1 Olefin/paraffintransportpropertiesforhollowfibermembranes[108]

CMS

Precursor

(P/l)

C2H4

(P/l)

C2H6

(P/l)

C3H6

(P/l)

C3H8

αC2H4

/C2H6

αC3H6

/C3H8

αC3H6

/C2H6

αC2H4

/C3H6

6FDA/

BPDADAM15.9 4 17.5 0.85 3.9 20.5 4.38 0.91

  PermeanceunitisGPU;35℃ testingtemperature,puregasC2H4andC2H6testedat100psia,puregasC3H6andC3H8were

testedat50psiaforCMSderivedfromFig.9precursorpyrolyzedat550℃ underUHPArgon.

Besidespurecomponents,Xuetal.alsotestedatypicalrealisticmixed

gas,typicalofadeethanizerfeed,andshowedthatitcanbeseparatedusing

suchaCMSmembrane.Thegasmixturemostlycontainstwoand three

carbonatomshydrocarbons(C2’sandC3’s),andwastestedat25℃ and60

psig.ThefeedandpermeatecompositionslistedinTable2demonstrate

enrichmentinolefins(ethyleneandpropylene)tomorethan91%,while7.2%

ethaneandonly0.7% propanewasretainedinthepermeatestream.

121

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Table2 Feedandpermeatecompositionsofamixedgaspermeationtestusingthedeethanizer

feedasfeedmixturetoaCMSmembranewithsimilarpropertiestothatusedtoproducethepure

gasbinaryseparationsinTable1

Gas Feed/(mol%) Permeate/(mol%)

C2H4 54.4 75.3

C3H6 14.8 16

C2H6 17.1 7.2

C3H8 13.5 0.7

Otherhydrocarbons 0.2 0.8

  

Fig.13 Hybridprocessofoneolefinsselectivemembraneunitandtwodistillation

columns

DE=deethanizer,andC2=aconventionalC2splitter

TheXuetal.studyindicatestheviabilityoftheolefinsselectivemembrane

formixed carbon numberolefin/paraffin separations and suggests the

possibility of the high payoff debottlenecking opportunity shown in

Fig.13[108,111].Clearly,themembranewithperformanceinTable1&Table2

canalsoconcentrateolefins(ethyleneandpropylene)inthepermeatestream

whilepropanewillbeconcentratedintheretentatestreamwithsomeethanein

bothpermeateandretentatestream.Thepropaneandethaneintheretentate

canbe returned to a crackerwith two usefulproducts (ethylene and

propylene) being simultaneously enriched in the process. The ternary

221

permeatestream(ethylene,propyleneandminorethane)canbeseparated

easily.Aftersuchanolefinsselectivemembrane,anexisting deethanizer

couldremovebothC2sfrom propylenewithlowerheatduty,sincepropane

andsomeethanearealreadyremovedbythemembraneunit.A second

distillationcolumn,essentiallyaC2 splittercouldthenseparateethyleneand

ethane,butwith increased capacityhaving advantagesbeyond the de

bottleneckingstrategyinFig.12.

Xuetal. also note thateven the use ofotherhigh performance

microporousmaterials(zeolites,metalorganicframeworks(MOFs)),such

anolefinsselectivemembranehasnotbeenreportedpreviously[108].Infact,

forapureZIF8membranetransportpropertiesofethylene,ethane,propylene

andpropane[112]show a permeance orderof:(P/l)C2H4 > (P/l)C2H6 >

(P/l)C3H6 >(P/l)C3H8.Clearly,whilesuchamembranecanseparateC2’sfrom

C3’s,itisunabletoseparateolefinsfrom paraffinstoenabletheabove

flowsheet.Zeolites(andzeoliteslikematerials)with2dimensionalporesable

tolimitpenetrantconfigurationalentropyinthediffusiontransitionstatelikethe

CMSmembranesreportedbyXuetal.,mayalsobeattractiveforolefin/paraffin

separations;however,theporesinCMSmaterialaremoreeasilyoptimized.

EthylenehasasignificantadvantageoverethaneinCMSmembranes,

duetodifferencesinconstraintsonthedegreesoffreedom intheactivated

state[90,109,110].Acombinationofsuchaneffectforpropylene,coupledwithits

highercriticaltemperature(andhencehighersorption)vs.ethaneislikelythe

causeofthefavorablepropyleneethaneselectivity.Insuchacase,besides

thedebottleneckingnotedinFig.12,reconfiguringthecurrentethyleneplant

maysavesignificantcapitalcosts,operationalenergyaswellasreduce

processfootprintandCO2 emissions.Whilefurtherprocessintegrationand

materialswillbe needed,the example showsthe exciting opportunities

availablewiththeadvancedCMStypemembraneplatform.

9 Summaryandconclusions

Largescale membranebased gas and vaporseparation processes

presentbothchallengesandopportunitiesforCO2 emissionreductionsand

energy efficiency improvements. Combined needs formore advanced

321

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

materials and economical manufacturing approaches can be best

accommodatedusingapolymerderivedasymmetrichollowfibertechnology

platform.Introducingincreasinglysophisticatedmembraneswithperformance

and costto meetspecific needsbeyond those currentlyavailable isa

pragmatic evolutionary strategy thatminimizes risks and maximizes the

likelihoodofacceptancebyindustry.Theincreasinglysophisticatedfamilyof

polymerderivedmaterialsencompassesconventionalpolymers,crosslinked

polymers,polymerinorganic hybrids and carbon molecularsieves. This

strategyallowsaddressingallbutthehighesttemperature,mostoxidizing

feeds,andwillpotentiallyevenprovideaframeworkforultimatelycreating

economicalmembranessuitableforthesetypesoffeeds.

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031

William J.Koros istheRobertoGoizuetaChairand

GeorgiaResearchAllianceEminentScholarinMembranes

attheGeorgiaInstituteofTechnology.In1977hejoined

thefacultyattheNorthCarolinaStateUniversity,andin

1984hemovedtoTheUniversityofTexasatAustinwhere

heservedasChairmanofChemicalEngineeringfrom1993

to1997.HejoinedtheSchoolofChemicalEngineeringat

GeorgiaInstituteofTechnologyin2001.Heservedasthe

EditorinChiefoftheJournalofMembraneSciencefrom1991-2008.Dr.Koroshas

publishedover350articlesandholds14USPatentsonmembranes,barriermaterials

andsorbents.HewasrecognizedbytheAIChEInstituteAwardforExcellencein

IndustrialGasesTechnologyin1995andtheAIChESeparationDivision’sClarence

GerholdAwardin1999.HewaselectedtotheUSNationalAcademyofEngineeringin

2000andnamedaFellowoftheAIChEandtheAAASin2002and2003,respectively.

In2008,Dr.KorosreceivedtheAlanMichaelsAwardforInnovationinMembrane

ScienceandTechnologyfromtheNorthAmericanMembraneSociety.Hereceivedthe

WilliamH.WalkerAwardforExcellencein2010andwasthe63rdInstituteLecturer

fortheAIChEin2011.Dr.Korosisoneof12KAUSTInvestigatorsselectedworldwide

tohelplaunchtheKingAbdullahUniversityofScienceandTechnologyinSaudiArabia

focusedonsolvingkeyproblemsfacingmankind.

131

PreparationandApplicationofZeoliteMembranesinPervaporation

XuehongGu

NanjingUniversityofTechnology,Nanjing,China

Goodafternoon,ladiesandgentleman.Itismyhonortobehereto

presentourrecentwork.ThetopicformytalkisPreparationandApplicationof

ZeoliteMembranesinPervaporation.MynameisXuehongGufrom Nanjing

UniversityofTechnology.

Thispresentationincludesfourparts.First,Iwouldliketomakeabrief

introductiononthezeolitemembrane.Then,Iwilltalkaboutoureffortson

membranesynthesisforimprovingseparationperformance.Andthen,Iwill

alsotellsomeapplicationofzeolitemembranes,especially,someindustrial

applicationcasesindehydrationoforganicsbyNaAzeolitemembranes.

Withthedevelopmentofmembraneseparation,separationobjectshave

beenmovingfrombigsizetosmallsize.Fortheporousmembranes,wehave

microfiltrationforvirusandsmallparticlesseparation,ultrafiltrationforprotein

andmacromoleculeseparation,nanofiltrationcouldbeusedforoligosaccharides

andmultivalention separation.Butwhataboutthe separation forsmall

molecules?Here,Iamgoingtotalkaboutzeolitemembranes.

Zeoliteisakindofcrystallinealuminosilicate.Thecrystalshavewell

definedmicroporeswithasizeoflessthan1nm.Ifwepackzeoliteparticles

closelyontheporoussubstrate,thenthezeolitelayercanbeused for

molecularseparationbasedonzeoliticpores.Theseparationisbasedon

molecularexclusion oradsorptiondiffusion. This membrane shows high

thermochemicalstabilityandmechanicalstrength.

ThereareseveraltypesofzeolitemembraneslikeNaAandMFI.Those

couldbeused fordifferentseparationsystemsdepending ontheirpore

structureandsurfaceproperty.Theapplicationsincludedorganicdehydration,

231

organic/organicseparationand gasmixtureseparation.Therearesome

typicalseparationsystemssuchasdehydrationoforganics,xyleneseparation,

hydrogenseparationandCO2separation.

Ifwelookatfigureforpublicationsinthepast10years,wecanseethe

publicationnumberhasbeenincreasingyearbyyear.Thismeansthatzeolite

membraneshavereceivedmoreattention.Manyresearchgroupshavebeen

donealotofresearchworkonzeolitemembranes,butthereareverylimited

companiestobeabletoprovidecommercialproducts.Theapplicationsare

onlyrelatedtodehydrationoforganics.Thissuggeststhatitisdifficultto

industrializezeolitemembranesforpracticalapplications.Themainreasonfor

thatconcernsthereproducibilityoflargescalepreparation,membranestability

inindustrialsystemsandfabricationcosts.

Howtoimproveseparationperformanceforzeolitemembranes?Since

zeolitemembranelayersaresupportedbyporoussubstrate,thesubstrate

surfacewouldhaveimportanteffectonthegrowthofzeolitelayer.Also,

becausethisismulticrystallinestructure,intercrystallineporesornonzeolitic

poresembedded inthelayerwillaffecttheseparationperformance.To

addressthoseissues,weproposesomestrategiesforzeolitemembrane

preparation,likeimprovingsubstratesurface,reducingseedsizeandhealing

nonzeoliticpores.

IwillshowyouthepreparationofNaAzeolitemembrane.Thismembrane

ishighlyhydrophilicandhasporesizeof4.2?.Themembranecanbeused

fordehydrationoforganic.Thistypeofmembraneispreparedbysecondary

growthmethod.Generally,useddipcoatingasseedingmethod.Substrate

wasfirstcoatedwithseedsandthenfurtherputintosynthesissolutionfor

hydrothermalcrystallization.

Werealizedthatthesurfacemorphologyhadaveryimportanteffecton

membranequality.Ifthesubstratesurfacehaspinholes,thendefectswould

begeneratedinthezeolitelayer.Wetriedtousesandpapertotreatsubstrate

surface.Thesurfaceroughnessimprovedbuttherearesomedentsorcaves

onthat.Whenusingdipcoatingmethodasseedingapproach,wefound

thosemembranesshowedlowreproducibility.Forindustrialproductions,itis

unavoidabletohavedefectsordentsonsubstratesurface.Sohowcanwedo

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膜技术在水和气体净化中的应用

withthat?

Here,weproposedacombinedseedingapproach.First,weusedseed

pastetorub thesubstratesurface.Thiscould mend somedefectsand

improvesubstratesurfaces.Afterthisoperation,wefollowedbydipcoating

methodtoprovideauniform seedlayer.Wethenusedtheseededsubstrate

formembranesynthesis.

Itwasinteresting tofind thatveryhighreproducibilityformembrane

synthesis.Ifyoulookatthetable,wecanfindthatallfivemembraneshad

highseparationperformance.Compared withdipcoating orrubbing,the

combinedmethodshowedbetterperformance.Thisapproachcouldbeused

forlargescaleproductionofzeolitemembrane.Theresultalsosuggestedthat

thesurfacemicrostructureofsubstratehasanimportanteffectonthezeolite

membranequality.

Ontheotherhand,wetriedtoreducetheparticlesizeofNaAzeolite

seedsbyballmillingtreatment.Aftertreatfor3h,theparticlescouldreduce

from2μmto0.3μm.Thetreatmentcangeneratelatticedefectsontheball

milledparticles.Itisinterestingtofindwhenweusetheballmilledseedto

induceNaAzeolitemembrane,thesynthesistimecouldbereducedlargely

from3.5htwiceto4honce.

IfwelookattheSEM images,wecanfindtheballmilledseedscoating

couldprovideaveryuniformzeolitelayer.Alsotheasformedzeolitelayerwas

denserthanthelayerwhenwesynthesizeditat100℃ for4h.Thesmall

particlesizeandlatticedefectscouldacceleratecrystallization.

Dowe have posttreatmentto improve membrane performance after

membranesynthesis?Here,we proposed a simply method forhealing

nonzeoliticporesbyhydrolysisofsilane.WeusedDMDSsilane,whichhas

kineticdiameterlargerthanzeoliticpores.Thissilanewasintroducedintoone

sideofzeolitemembrane.TheothersidewassweptbyDIwater.Thesilane

encounterswithwaterinthedefects.Thus,hydrolysisofsilanewouldoccurto

generateamorphousSiO2inthedefects.

Ifwe used permporometry to examine the He permeance through

nonzeoliticpores,wecanfindthatthepermeanceforthemodifiedmembrane

droppedlargely.After1hmodificationonMFIzeolitemembrane,theHe

431

permeancethroughnonzeoliticporesdecreasedbyabout62%.

ThismethodhasbeenusedtohealthedefectsofMFIzeolitemembranes.

Lookingatthistable,theoriginalMFImembranehasaseparationfactorof23

forseparationofxylenemixture,after1hmodification,theseparationfactor

couldincreaseto5.5.After2hmodification,thiscouldbe10.8.However,

thepermeationfluxdecreaseverylimitedly.Thismethodcanbeusedfor

healingnonzeoliticporesofNaAzeolitemembranes.After3hmodification,

theseparationfactorincreasedfrom51to1103.

Thezeolitemembranehasshowedgreatpotentialapplicationsinmolecule

separation.Howtofurtherexpandtheapplications?Thekeypointistoreduce

theinvestmentcosts.Soitisnecessarytoimprovemembraneflux.Zeolite

membraneincludestwolayersmembrane,layerandsubstrate.Whenwe

reducedthesubstratethickness,wefoundthatsignificantimprovementin

permeationfluxwasobtained.Thelargeeffectfromsubstratewasrelatedwith

PVoperation.Thelow operationpressureonthesubstratesideleadedto

severemeanfreepatchfordiffusingmolecule.Sothesubstratewallwould

havestrongereffectonmoleculartransfer.

Weusedamodeltodescribethediffusionprocessofpurewaterthrough

membrane.Formembranelayer,weusedFicklawtodescribeadsorption

diffusionmechanism.Onthesubstrate,weused Knudsendiffusionand

viscousflowtodescribeit.

Thisiscalculatedpermeationfluxthroughmembrane.Wecanseethatthe

permeationfluxwasaffectedbythepressureonpermeationside.Atlow

permeationpressure,thesubstratethicknessshowedobviouseffectonthe

permeationflux.Whenreducingthethickness,thepermeationfluxincreased

significantly.

Toobtain high flux,we can develop hollow fibersupported zeolite

membrane.The reduce thicknesswallcan improve flux.Moreover,the

membranehassmallouterdiameter,whichcouldimprovepackingdensity

significantly.

WefirstpreparedAl2O3hollowfibersbyspinningmethod.Thefiberhas

about1.8mm inouterdiameter,about0.5mm inthickness,whichismuch

lowerthantheceramictubesusedrightnowforindustry.Thisfiberhasfinger

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likestructure,whichishelpfultoreducethetransportresistance.

WeusedthefiberstosynthesizeNaAmembranes.Twoseedingmethods

including dipcoating and vacuum seeding were used for membrane

synthesis.Consideringlargescaleproduction,vacuumseedingmethodwould

bepreferred.Theachievedmembraneshowedhighpermeationfluxof2-3

timesthantubularmembranes.

Toimproveacidresistance,wealsopreparedTtypezeolitemembrane

onYSZ hollow fibers. This membrane has been successfully used for

dehydrationofethanolwithpHvalueof3.Whenwecomparedthepermeation

fluxofmethanol,ethanolandisopropanol,wecouldfindthepermeationflux

following the sequence ofArrheniusplots.We also obtained veryhigh

permeationfluxforIPA,whichreached7.36kg/(m2·h).

Afterhaving those hollow fiber structured membranes, we have

constructedmembranemoduleswith0.1and0.2m2.Wehavetestedthe

membranemodulesforseparationof80wt.% ethanolsolution.Themembrane

showedhighseparationefficiencyforethanoldehydration.

Consideringwithpracticalapplication,wealsodeveloped4-channels

Al2O3hollowfiber.Thefiberhasprovidedmuchhigherstrengththansingle

channelone.WesynthesizedNaAzeolitemembranesontheoutersurfaceof

hollowfibers.Veryhighpermeationfluxof>10kg/(m2·h)wasachieved.

Theseparationfactorwashigherthan10000.Thisisduetothespecialpore

structure for4- channelhollow fibers with fingerlike structure. This

configurationmightbeabletouseforpracticalindustrialapplication.

Basedonabovesynthesisapproaches,wehaveproducedtubularNaA

zeolitemembranesinlargescale.Wecareaboutthepracticalapplications.

ThechallengeforNaAmembranesinpracticalapplicationisstability.After

investigation,werealizedthatthemembranewasnotsuitableforoperatein

acidsystem.Also,itcouldnotbeoperatedinalkalinesystem andhaving

cations.Besides,themembranewasnotgoodforhighwatercontent.Sowe

proposedapretreatmentforthefeedbeforemembraneseparation.Thefeed

solutionshouldbecontrolledneutralandlowconductivityinadvance.

Thisisourfirstplantforrecoveryofwasteisopropanolfrom85% to98%.

Thewasteisopropanolcomesfrom productionlineofcephalosporin.After

631

production,thewasteisopropanolwasgenerated,whichcontainedsomesalts

andalkali.TheoriginalmethodfordehydrationusedNaOH extraction.We

usedmembraneseparationplanttoreplacethat.Thecapacityforthisplantis

5000t/a.Thetotalmembraneareaisabout70m2.Thishasshortenedthe

processsteps.Thisequipmenthasbeenrunningforover3years.

Wemade a technicaland economic comparison among membrane

process,alkalidehydrationandadsorption.Wecanseethatthemembrane

processdemandedveryfewvaporconsumption.Furthermore,itonlyneeded

1peopletohandletheautomaticsystem.Thetreatmentcostcouldbesaved

by65% -75% bythemembraneapproach.

HereisanotherapplicationcaseforproductionofIPA,whichisobtained

byacetonehydrogenation.Thereactantfrom reactiontowermainlyincludes

IPA,acetoneandwater.Themixturewasfedtoadistillationtower.The

productfrombottomisintroducedtoanothertowerforfurtherrectification.The

topgeneratesternaryazeotropeincludingacetone,IPAandwater.Wehave

usedNaAmembranesfordehydrationandreturntothefeedforreaction.This

system canimproveacetoneconversionandobtainhighproductivity.The

systemhasacapacityof1500t/a.

ThethirdapplicationcaseIam goingtointroduceistherecoveryof

ethanol.Thissolventhasbeenusedforpharmaceuticalproduction.Thisis

requiredtodehydratefrom90wt.% to99.5wt.%.Theoriginalmethodused

extractiondistillation by salts.This consumed much energy also cause

pollutionandcorrosion.Theplantwasestablishedinpharmaceuticalcompany

inlastyear,andhasacapacityofabout1500t/aandamembranearea

of42m2.

ThefourthapplicationcaseIwouldliketointroduceisalsoaboutrecovery

ofisopropanol.Theoriginalseparationmethodusedrotatingpackedbedplus

NaOHextraction.Inthiscase,weusedNaAzeolitemembraneseparationto

replacethat,whichhasacapacityof3000t/aandamembraneareaof

56m2.

Now,wehaveestablishedabout20plantsforindustrialsolventdehydration,

the separation systems concerning methanol, ethanol, isopropanoland

butanone.

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Since2007,wehavestartedresearchworkonzeolitemembranesfor

severalyears. In 2011, we established a company forpromoting the

technology,whichhasaNaAzeolitemembraneproductioncapacityof10000

m2/a.

Finally,Iwouldlikethegovernmentforthefinancialsupports.Ithankmy

teamfortheirhardwork.Thanksforyourattention.

Dr. Xuehong Gu  isa professorofChemical

EngineeringatNanjingUniversityofTechnology.Heis

alsothedeputydirectorofNationalSpecialSeparation

MembraneEngineeringandTechnologyResearchCenter.

HegothisBS(1997)andPhD(2006)atCollegeof

ChemistryandChemicalEngineering,NanjingUniversity

ofTechnology.DuringApr.2003andJan.2007,hedid

postdoctoralresearchatNewMexicoInstituteofMining

andTechnologyandUniversityofCincinnatisuccessively.Hebecameaprofessorof

NanjingUniversityofTechnologysinceFeb.2007.Hisresearchworkisfocusedon

preparationofzeolitemembranesandcatalyticmembranereactions,whichconcerns

energyrelatedandenvironmentalapplications.Hehaspublishedmorethan30SCI

indexedarticlesandfiled17Chineseinventionpatents.Hereceived5Scienceand

TechnologyAwardsfromJiangsuProvince(FirstLevel2004),ChinesePetroleumand

ChemicalIndustryAssociation(FirstLevel2007andFirstLevel2012)andChinese

MinistryofEducation(SecondLevel2011andSecondLevel2012).Hewasawarded

ExcellentYoungInvestigatorFundbyNationalNaturalScienceFoundationofChina,

OutstandingYoungInvestigatorFundbyJiangsuProvince,SixTalentPeakofJiangsu

Province,YoungScientificandTechnologicalTalentofJiangsu“333project”and

HightechEntrepreneurof“Nanjing321Strategy”.Heisinchargeofabout18

foundationprojectssponsoredbyNational“973”Program,“863”Program,National

NaturalScienceFoundationofChina,JiangsuProvincialScienceandTechnology

Department,etc.

831

Nanoparticles(andNanotubes)inMembranesforLiquidandGasSeparations:ABriefOverview

KamaleshK.Sirkar

Dept.ofChemical,BiologicalandPharmaceuticalEngineering,

NewJerseyInstituteofTechnology,Newark,USA

Abstract:Theearliestknownexampleofverysmallparticlesinpolymeric

membranesusedforseparationofgaseousmixturesappearedin1965when

thinflatsiliconerubbermembranescontainingsilicaparticlesweredeveloped

for commercial applicationsMixedmatrix membranes where inorganic

nanoparticles,zeolitenanocrystalsetc.areincorporatedinapolymermatrix

startedappearinginearlytolateeighties.Abriefoverviewofsuchresearch

directedtoward overcoming theRobeson(1991)limitisprovided.High

aspectratioflakesfacilitateddevelopmentofbarriermembranes.Influenced

bygasseparationinvestigationsofsuchmixedmatrixmembranes,efforts

wereinitiatedinlaterhalfof2000-2010toexploreliquidseparationsthrough

mixedmatrixmembranesofpolymernanoparticles/nanocrystals.Emergence

ofcarbonnanotubesduringthisverytimegeneratedaninterestincarbon

nanotube(CNT)basedmembraneswheretheliquidflowedthroughtheinner

core ofCNTs.Substantialinterestwas generated as wellin polymeric

membraneswhoseliquidphaseseparationperformancecouldbesubstantially

influencedbyincorporationofCNTsormodifiedCNTsasaninclusionphase.

TherehavebeenanumberofinvestigationsinCNTbasedorzeolitecontaining

polymericmembranesinreverseosmosis(RO),forwardosmosis(FO)and

nanofiltration(NF) including solventresistantNF.A varietyofinclusions

includingmetalorganicframework(MOF)basednanoparticlesinapolymer

matrixhavebeenstudied.Thesedevelopmentswillbebrieflyidentifiedand

theperformancesofsuchmembraneswillbereviewed.

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膜技术在水和气体净化中的应用

1 Introduction

Syntheticnonbiologicalmembranes can be made from a variety of

materialsincludingpolymers,ceramics,metalsandmetallicalloys.Inaddition

membranescanbemadeofhybrid materialssuchasorganicinorganic,

ceramicmetallic,polymericbiologicaletc.Furthergelsaswellasliquidscan

servesuccessfullyasmembranes.Membranesincommercialusearein

generalpolymericinnaturealthoughceramicmembranesarealsousedbut

much less often; metallic systems are being developed especially for

hydrogenseparation.Foranintroductiontovariousmembranetechnologies,

seeHo and Sirkar(2001).Foradvanced membrane technologiesand

applications,seeLietal.(2008).

Thefeedmixtureforseparationmaybeingasphaseorliquidphase.Gas

phaseseparationsofinterestincludegasmixtures,gasvapormixturesand

vaporvapormixtures.Liquidphaseseparationsystemsarebroaderinthat

molecular mixtures, moleculemacromolecule mixtures, macromolecule

macromoleculemixtures,particlesuspensionsandtheirvariouscombinations

areinvolved.Foralongtimethedistinguishingcharacteristicofthepolymeric

membranesinoverwhelmingcommercialuseforbothtypesoffeedphases

wasthatonlypolymerswereinvolved.

Thispaperwillprovidealimitedoverviewofdevelopmentsinmixedmatrix

membranesforliquidseparationsaswellasgasseparations.Inamixed

matrixmembrane,thematrixisusuallypolymericinnature;butitcancontain

solidinorganic inclusions,organic inclusionsoreven liquids.Historically

mixedmatrixmembraneswerefirstintroducedforgasseparation.Abrieflist

ofinclusionsusedtothatendisasfollows:zeolitenanocrystals,fumedsilica

(13nm),silicananopowder(10nm or30nm),carbonmolecularsieve

(CMS) particles(submicron to2 μm),single wallcarbon nanotubes

(SWCNTs),activatedcarbon,graphiteflakes,graphene,TiO2,polyethylene

glycols(PEGs),polyamidoamine(PAMAM)dendrimers,otheraminesetc.

Mixedmatrixmembranes forliquid separations were introduced recently

(around2007);theinclusionsofinteresttherearezeolitenanocrystals,

SWCNTs,multiplewallcarbonnanotubes(MWCNTs),silicananoparticles,

041

TiO2nanoparticlesetc.

Inview oftheextensiveliteratureonmembranegasseparationusing

mixed matrix membranes, itis appropriate to begin the treatmentby

identifyingmajorcharacteristicsofmembranegasseparation.Thiswillprovide

ausefulbackgroundforthisareaofevolvingmembranetechnology.Wewill

providefirstaverybriefintroductiontomembranegasseparationandthen

discussimportantdevelopmentalaspectsandproblemsvisàvismixedmatrix

membranes.We willthen focus on mixedmatrix membranes forliquid

separations.Forarecentreview ofthestateoftheartinmembranegas

separationtill2008,seeBernardoetal.(2009).AchapterbyLiuetal.

(2008)providesacomprehensiveaccountoftheprogressinmixedmatrix

membranesforgasseparationtill2007.

2 Basisformixedmatrixmembranesforgasseparation

Forseparationofgasmixturesthroughapolymericmembrane,itiswell

knownthattheselectivityofaspeciesAoveranotherspeciesBintermsofa

separationfactorαABisgivenby

αAB =QAMQBM

= DAMD( )BM

SAMS( )BM

(1)

Heretheratio(DAM/DBM)iscalledthediffusivityselectivitywhereDAMidentifiesforexample,thediffusioncoefficientofspeciesAinthemembrane

M.Theratio(SAM/SBM)iscalledthesolubilityselectivitywithSAMrepresenting

thesolubilityofspeciesAinthemembrane.Forgasseparationthroughglassy

polymers, diffusivity selectivity dominates; forgas separation through

rubberypolymersusuallysolubilityselectivityisfarmoreimportant.Diffusivity

selectivityisdeterminedprimarilybythediametersofthegasmoleculesof

thetwo species,dA and dB,visàvisthe chain gap openingsin the

polymer.

Formostpolymers,thediffusivityselectivityisproportionaltoexp(-fm{dAn-dBn})wherethevalueofthepowernforrotationallyhinderedstiffchain

polymersis2;thevalueofnforflexiblerubberypolymersis1.Asaresult,

whenthediametersofthetwospeciestobeseparatedaresomewhatfarapart

asforexampleinthecaseofH2(0.289nm)versusCH4(0.38nm)orCO

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(0.376nm) the selectivityachieved in commercialized glassypolymeric

membraneswithn=2variesbetween30and250(ZolandzandFleming,

2001).Thisrangeiseconomicallyquitegood.Althoughtherecanbebetter

membranesintermsofselectivity,improvementsinotherpropertiesareof

primaryinterest.Contrastthissituationwiththatwhenthespeciesdimensions

arenotfarapartasforexampleinthecaseofairseparation(O2(0.346nm)

andN2(0.364nm))ornaturalgasprocessing(CO2(0.33nm)andCH4(0.38nm)).Hereoneneedstoachieveahigherselectivityforeachsystem.

Forexample,theobservedselectivityforO2-N2system forglassypolymers

rangesbetween3-7(ZolandzandFleming,2001),whilethatforCO2-CH4systemrangesbetween5and30(ZolandzandFleming,2001).Thereare

otherfactorswhichleadtofurtherreductionsintheselectivity;forexamplein

naturalgasprocessing,highCO2partialpressureplasticizesglassypolymeric

membranesleadingtoasignificantreductioninCO2-CH4selectivityfrom30-

40to15-20orlower.

Onthebasisofalargeamountofliteraturedataonpermeabilityvs.

selectivityofawidevarietyofpolymericmembranesforgasseparation,

Robeson(1991)hadconcludedthatthereisanupperboundinthecurveof

selectivityvs.permeabilityforanybinarygasmixture.Thisstudyessentially

postulatedthatthereisanintrinsicupperlimittohowhighcantheselectivity

beforagivenvalueofthepermeability(ofthemorepermeablespecies;e.

g.,O2 inO2-N2 system).Thehigherthepermeability,theloweristhe

selectivity.Aphenomenologicalbasisforsuchabehaviorhasbeenprovided

byFreeman(1999).Sinceverylowpermeabilityisalsonotacceptable,this

postulatedupperlimittendedtosuggestthatalternatestrategiesareneededif

amembraneistohavehighpermeabilityaswellashighselectivityingas/

vaporseparationapplications.

Inthefieldofnonpolymericmaterials,inorganicmolecularsieves,suchas

zeolite4Acrystals,haveanO2-N2selectivityofaround37at25℃.Although

thepermeabilityofO2 throughthismolecularsieveisalow 0.77barrer

comparedto,say,1.3barrerthroughaglassypolyimide(PI)filmofinterest,

itsveryhigh selectivityoughtto increase the selectivityofa glassyPI

membrane(whichhasaselectivityof7.2at25℃)ifthezeolitecrystalscould

241

beincorporatedinaPIfilm withoutasubstantialreductioninpermeability.

MahajanandKoros(2000)illustratedthispossibilitybyplottingthecalculated

valueofthepermeabilityofsuchamixedmatrixmembraneagainsttheO2-N2selectivityforvariousloadingsofthezeolite.Asthezeoliteloadingincreased

beyond40% theselectivitywentbeyondtheRobesonupperlimitforthegiven

valueofpermeability.

Itisusefultopointoutthebasicrelationshipsthatgovernthepermeability

ofamixedmatrixmembranebasedonpolymericblends(Robeson,2010).

Themixedmatrixmembranemaybecomposedofamiscibleoranimmiscible

polymerblend.Focusnow onimmisciblepolymerblends(notethatmost

mixedmatrixmembranesaremadeofdisparatephasesalmostinvariably

immiscible,e.g.,zeoliteinapolymer;thereforesurfacecompatibilizationmay

beneeded).Letthepermeabilitycoefficientsoftheimmiscibleblendandthe

polymercomponents1 and 2 presentin volume fractionsofφ1 andφ2respectivelyarePb,P1,andP2 respectively.Thesepermeabilitycoefficients

arerelatedbyeither

Pb =φ1P1+φ2P2 (2)

foraparallelmodel,or

Pb =P1P2/(φ1P2+φ2P1) (3)

foraseriesmodel.Theparallelmodelprovidesanupperboundwhereasthe

seriesmodelprovidesalowerbound.

Amodelfrequentlyusedwithmixedmatrixmembranesforgasseparation

involvesMaxwell’sequation(Maxwell,1873)fortheeffectivepermeability

Peffofthemixedmatrixmembranecontainingdispersionofspheresofone

material(subscriptd)inacontinuousormatrixphase(subscriptm)

Peff=Pm{[Pd+2Pm -2φd(Pm -Pd)]/[Pd+2Pm +φd(Pm -Pd)]} (4)

Whenthedispersedphaseisnonporous,i.e.,Pd iszero,therelationgets

simplifiedto

Peff=Pm{(1-φd)/[1+(φd/2)]} (5)

Thisrelation shows thatnonporous dispersed phase willlead to lower

permeabilitythroughthemixedmatrixmembrane.Earlieritwaspointedout

thatMahajanandKoros(2000)hadcalculatedthepermeabilityofamixed

matrixmembraneofzeolite4AinPIandthepermeabilitycoefficientexceeded

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theRobeson(1991)upperlimitwhenthezeoliteloadingwentbeyond40%;

theyhademployedEq.(4)withappropriatepermeabilitiesforthetwophases,

thematrixandthezeolite.

3 Mixedmatrixmembranesforgasseparation:examples

Letusrecognizeattheoutsetthatthedispersedphaseinthepolymeric

matrixcanbeasolidoraliquidwhichcanbeanoligomer.Intermsofsolid

fillers,theearliestcommercialexamplewasthatof33%(massfraction)silica

particlesinflatandthinsiliconerubbermembranesmanufacturedbyGeneral

Electric(Robb,1965).Itisnotknownwhetherthesesilicaparticleswere

nanoparticles ornot. Oxygen permeabilities in dimethylsiloxane films

decreased from 700 Barrerto400 Barrerwhensilicamassfractionwas

increasedfrom0to60%.Robb(1965)indicatingthatthepermeabilitydidnot

decreaseasmuchastheparallelmodel(Eq.(2))wouldsuggest;however

Maxwell’sEq.(4)doespredictthisvalue.Therewasasignificantamountof

researchgoing oninvestigating variouspermeation/transportpropertiesin

studiesondiffusioninpolymerscontainingavarietyoffillers(seeBarrer,

1968);thesefillersweregenerallyinert.Forpolymermembranescontaining

adsorptivefillers,PaulandKemp(1973)carriedouttimelagstudieswhereas

KempandPaul(1974)carriedoutgassorptionstudies.

Thenextearlieststudyofgasseparationusingamixedmatrixmembrane

appearedinaUOPpatent(Kulprathipanjaetal.,1988;thereareseveral

otherUSPatentsissuedtoUOPinthisgeneralareaaround1988)using

silicalitezeoliteincelluloseacetate(CA)membranesforCO2/H2separation.

NormallyadenseCAmembraneisselectiveforH2overCO2;thezeolitemade

itaCO2selectivemembrane.Sincethenaconsiderableamountofresearch

hasbeencarried outwithavarietyofmixedmatrixmembranesforgas

separation.Awholerangeofglassypolymershasbeenusedjustasavariety

ofadsorbentsandmolecularsieveswereexplored;ashortlistofglassy

polymers includes brominated polyphenylene oxide, cellulose acetate,

perfluoropolymer Teflon AF2400, polyetherimide, various polyimides,

polyethersulfone,poly(4methyl2pentyne)(PMP),polymersofintrinsic

microporosity(PIM),polysulfoneetc.SeeLiuetal.(2008)foranextensive

441

listofearlierreferences.Thesestudiespointedoutcertaincommonfeatures.

1)Theremustbegoodinterfacialadhesion/compatibilitybetweenthe

matrixphaseandthefiller/nanoparticlebeingused;otherwisevoidsatthe

matrixfillerinterfacewillallownonselectivegasmixturetransportthroughthese

corridors.Interfacialcompatibilizationisthereforepracticedoften.

2)Insemicrystallinepolymersitisknownthatintheregionattheinterface

betweentheamorphouspolymerandthecrystallineregion,polymerchainsare

somewhatmoreimmobilizedthaninthebulkoftheamorphousregionleading

tolowerpermeability.Thefillerinthepolymermatrixphaseplaysasimilarrole

asthecrystallineregionsinasemicrystallinepolymer.

3)Nanosizednonporoussilicaparticleswhichtendtoform aggregates

introducedisruptioninpolymerpackingdensityandcreateadditionalfree

volume/void space which leads to increased permeability butreduced

selectivityforsystemsbasedonsmallgasmoleculessuchasO2-N2 etc.

Howeverformorecondensablegases,oneobserveshigherselectivityatthe

sametime.

4)Accidentalpluggingoftheallimportantporesinthezeoliteorother

adsorbentshastobeavoided.

5) The fillershould be a nanoparticle.Since the skin thicknessof

commercialgasseparationmembranesareintherangeof50-100nm and

sinceitisnecessarytohaveapercolationthresholdviaasufficientdensityof

nanoparticles,thenanoparticledimensionsshouldpreferablybeintherange

ofnomorethan5-20nm.

Wewillnow identifybrieflytheperformancesofselectedmixedmatrix

membranes forgas separation to highlightspecific behavioralaspects

mentionedabove.Toavoidthepossibilityofvoidsatthepolymercrystal

interfaceduetotheextremerigidityofaPImatrixoriginallyselectedforitshigh

O2-N2selectivity,MahajanandKoros(2000)usedaflexiblepolymersuchas

polyvinylacetate(PVAc)withzeolitessuchasanaluminosilicatetypezeolite

4A.ItisknownthatPVAchasaffinitiesforaluminaandthereforeforthe

aluminosilicatezeolite.TheyobservedasignificantenhancementinO2-N2selectivityfromthevalueof5.9ofpurePVAcwithunchangedorslightlylower

permeabilitiesat15% zeoliteloading;at40% zeoliteloading,theselectivity

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膜技术在水和气体净化中的应用

wentuptoahighof9.7-10.4butthepermeabilitieswerereducedbyalmost

40% duetoinhibitionofchainmobilitynearthecrystalsurface.Pecharetal.

(2006)adoptedanalternatestrategy.ZeoliteLcrystalswhosesurfaceswere

functionalizedwithaminogroupswhichcouldlinkcovalentlywithcarboxylic

acidgroupsonapolyimidebackboneweredispersedinaPImatrixtoensure

the absence ofinterfacialvoids; there was a slightenhancementin

permeabilitiesbutnosubstantialenhancementinselectivity(Pecharetal.,

2006).Furtherwith the aminofunctionalsilane coupling used,sorption

capacitiesofthezeolitesweresubstantiallyreduced.

Carbonmolecularsieveswhenincorporatedinrigidglassypolymerssuch

aspolyimide(Matrimid) and polyetherimide(Ultem) yielded enhanced

selectivitiesaswellasincreasedspeciespermeabilities(Vuetal.,2003)in

bothO2-N2andCO2-CH4systems.Activatedcarbonincorporatedinglassy

acrylonitrilebutadienestyrene(ABS)ledtobothincreasedselectivityand

permeability(Ansonetal.,2004).Anothercarbonbasedfiller,crystalline

graphiteflake,(particlesizerange,1-15μm)yielded(Pengetal.,2007)

considerable enhancements in a slightly different problem namely,

pervaporationseparation ofbenzenecyclohexane mixture via a polyvinyl

alcoholmembranecontainingagraphiteloadingthatvariedfrom0to10%.For

1μmparticlesat6% loading,thepermeationfluxwasenhanced4foldandthe

benzenecyclohexaneselectivitywasincreased6times.Theenhancementin

benzenepermeabilityisexplained primarilybythechanged freevolume

characteristicsofthePVAgraphitemembrane.

Merkeletal.(2002)studiedtheeffectoffumedsilica(TS530,particle

size~11-13nm)contentonnbutanepermeabilityandnbutane/methane

selectivityofglassypoly(4methyl2pentyne)(PMP)at25℃ usingmixtures

composedof98%(molefraction)methaneand2%(molefraction)nbutane

atafeedpressureof11.2atmandapermeatepressureof1atm.Theyfound

thatnbutanepermeabilityincreasedabout5timesandtheselectivitywentup

about2timesasonegoesfrompurePMPto40%(massfraction)fumedsilica.

BydisruptingthepackingofrigidbulkyPMPchains,fumedsilicananoparticles

apparentlyincreasesaccessiblefreevolumeinthepolymermatrixwithout

introducingcavitieslargeenoughtopromoteweaklyselectiveornonselective

641

freephaseflow mechanisms(e.g.,KnudsenorPoiseuilletransport).This

increaseinfreevolumeaugmentsdiffusivity,weakensthesizesievingnatureof

PMP, factors thatincrease both permeability and reverse selectivity by

increasing the solubility of the condensable C3+ hydrocarbons over

noncondensableonessuchas,methaneinthatthelargermoleculepermeates

faster.

Thechanged performanceishighlydependentonthenatureofthe

polymeranditsinteractionwiththesilicananoparticlesandtheirtendencyto

form aggregates/agglomerates.Silica nanoparticlesof10 nm size were

incorporated in the glassypolymerbrominated poly(2,6diphenyl1,4

phenyleneoxide(BPPOdp))(Congetal.,2007);theresultingmembranes

wereflexibleandachievedaCO2 permeabilityof436barrerat23% silica

loadingwithoutaffectingthepermselectivityofthesystemsCO2/N2andCO2/

CH4.TheCO2permeabilitywasmuchhigherthanthatofthestraightpolymer

namely,78barrer.Theenhancedpermeabilityisascribedtothedevelopment

ofnanogaps around the silica nanoparticles whose surface was not

compatibilized.Suchnanogapswilldisappearifthesilicananoparticlesurface

iscompatibilized.Ahnetal.(2010)studiedmixedmatrixmembranebehavior

usingthefumedsilicananoparticles(usedbyMerkeletal.,2002)dispersed

inapolymerofintrinsicmicroporosity(PIM1).Theyobservedconsiderable

enhancementofindividualgaspermeabilityasthesilicavolumefractionwas

increased.Thismaybeduetopolymerchaindisruptionornanovoidsforming

atthe particlematrix interface.However,the selectivity decreased with

increasedsilicananoparticleloading.Itappearedthattheobserveddecrease

inselectivityinO2-N2systemwithincreasedO2permeabilitywasfollowingthe

directionalprofileofRobeson(1991)upperboundlimit.

Itthereforeappearsthatperformanceofamixedmatrixsystem ingas

separationwillbeverysystemdependent.Inamixedmatrixsystemcontaining

imperviousnanoparticles,thereprobablywillbepermeabilityenhancementof

anindividualgasunlessthereisaperfectlycompatibilizedinterfacebetween

thematrixandthenanoparticleandthereisnochaindisruption.Itismorethan

likelythattherewillbepermeabilityenhancementforindividualgas/vapor

speciesduetochaindisruptionordevelopmentofnanogaps.Ontheother

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膜技术在水和气体净化中的应用

hand,withimperviousnanoparticles,theselectivitymayremainthesameor

bereducedunlessthereissignificantdisruptionofthechainpackingandthere

isconsiderabledifferencebetweenthespeciesincondensability.However

wherepermeablenanoparticlesareinvolveditisoftenpossibletoenhance

boththesystemselectivityandindividualspeciespermeability.Poreplugging

of permeable nanoparticles/zeolites/activated carbon will reduce the

performance.Specificinteractionsbetweenthepermeatinggas/vaporspecies

andthenanoparticleareespeciallyusefulforenhancingbothpermeabilityand

selectivity.

Thereisanotherkind ofsolid nanoparticle/fillerwhich introducesa

differentdimension because of their shape/aspect ratio. When thin

impermeableflakesareusedwithalargeaspectratiobetweentheirlengthand

thethickness,thepermeationpathlengthisconsiderablyincreasedleadingto

reducedpermeability.Suchmembranesarequiteusefulasapermeation

barrier.Iftheflakebecomespermeabletoonlyoneofthespeciesthenthe

enhancementinselectivityaswellaspermeabilitybecomesconsiderable.As

theflakeaspectratioincreasesbeyond15,amixedmatrixmembranewitha

selectively permeable flake achieves an extraordinary enhancementin

selectivityclosetothatoftheflakeselectivity(Cussler,1990).Thisisin

contrasttosphericalinclusions.Graphicalillustrationsofflakes(visàvisthe

aspectratio and the exfoliation issue), nanoparticles, zeolites etc. in

membranesforgasseparationareavailableinSirkar(2008).

Mixedmatrixmembraneshavealsobeenpreparedwithinclusionsofsmall

molecularweightcompounds,oligomers,polymersetc.yieldingmembranes

withhighlyenhancedperformances.Liuetal.(2008)illustrateconsiderable

earlierresearchonliquidpolymermixedmatrixmembranesespeciallyinvolving

polyethyleneglycol(PEG).Herewepointoutanexampleofanaminebased

polymerincorporatedinapolyvinylalcoholpoly(siloxane)matrixtoseparate

CO2fromH2.ModeratelyhinderedpolyNisopropylallylamine(MW,120000-

200000)wasincorporated asafixedsiteCO2carrieralong withmobile

carriersinthepolymermatrixwhichprimarilyservedasthemediumtoprovide

thedispersedamines(ZhaoandHo,2013).Suchamembraneprovideda

CO2/H2selectivitygreaterthan90andCO2/N2selectivityhigherthan150at

841

120℃ fromafeedattwoatmospheresinthepresenceofconsiderablewater

vapor.ConsultZhaoandHo(2013)foradditionalreferencesonsimilar/

relatedmixedmatrixmembranes.

Oligomericaminesareofspecialrelevanceinmixedmatrixmembranesfor

enhancedand selective CO2 transport.Pure polyamidoamine (PAMAM)

dendrimerofgenerationzerowasfoundbyKovvalietal.(2000,2001)to

haveexceptionallyhighselectivityforCO2overavarietyofgasspeciessuch

asN2,O2 etc.aslongasthereisconsiderablemoistureinthefeedgas

environment.TheRITEGroupinJapanhasexploitedthisfeaturetodevelop

highlyefficientmembranesforCO2 capturefrom fluegas.Taniguchietal.

(2008)incorporatedPAMAMdendrimersofvariousgenerations(e.g.,0,1,

3,5)inanUVcrosslinkedPEG membranematrixforCO2N2 separation;

generallyGen0performedthebest.However,theoverallselectivitieswere

quitehighandrangedbetween200and500forallmembranesinvestigated.

Thereisanotherdimensiontothepracticalrealizationofmixedmatrix

membranesforgasseparation.Onecommonformofcommercialmembranes

ishollow fibers;generallytheyhaveeitheracompositeoranasymmetric

structurewiththeselectivelayerbeingverythin.Liuetal.(2008)have

providedausefuldescriptionofvariousconsiderationsinthefabricationof

suchhollow fibers.Specifically,fabrication ofa duallayermixed matrix

membranewiththethinlayerontheoutsidecontainingthedispersedphase

hasbeentreated.Someofthechallengesforachievingsuchalayerusing

molecularsievesare:Reducingaggregationlevelofthemolecularsieves;

reproducibilityissue;interactionofthepolymerand themolecularsieve;

interactionbetweenhardcrystallinesievesandthediesurfaceetc.Softernon

aggregatingnanoscaledispersedphaseentitiesarelikelytoreducesomeof

theseproblems.

4 Mixedmatrixmembranesforliquidseparation:introduction

Eversincethefirstdescriptionofcarbonnanotubes(CNTs)byIjimain

Nature(1991),explorationofitsusefulnessinavarietyofapplicationshas

expandedexponentially.Theparticulartopicofinteresthereismolecular

transportleading to highlyselective separationsfrom liquid solutionsfor

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膜技术在水和气体净化中的应用

reverseosmosis(RO),forwardosmosis(FO),nanofiltration(NF)and

ultrafiltration(UF).TheearliestexamplewasprovidedbyHoltetal.(2006)

whoprovideddatawhereindoublewallcarbonnanotubes(DWCNTs)with

diametersoflessthan2nm serveaspores(inanimpermeablematrix)

throughwhichwaterwastransportedatratesthreeordersofmagnitudefaster

thanthosesuggestedbycontinuum models.Moleculardynamicssimulations

suggestalsosuchfasttransportasindicatedinHoltetal.Observedgasflow

ratesthroughsuchCNTsalsoindicatedanorderofmagnitudehighertransport

ratethanthatpredictedbyKnudsendiffusion.

Holtetal.(2006)didnotachievedesalinationsincetheDWCNTshad

muchlargerinnercorediameterstobeabletorejectsalt.However,this

particulardevelopmentalongwithexperimentsonenhancedgasseparationby

usingzeolitesinapolymermatrixopened thepossibilitiesforachieving

improveddesalinationperformanceviaamixedmatrixdesalinationmembrane.

Theworkhorseofmostdesalinationmembranesisaninterfaciallypolymerized

(IP) ultrathin polyamide membrane on a porouspolysulfone membrane

support.Suchmembranesareoftenidentifiedasathinfilmcomposite(TFC).

Jeong etal. (2007) created a socalled nanocomposite desalination

membranebyhavingNaAzeolitenanoparticlesdispersedinthe50-250nm

thickinterfaciallypolymerizedfilmonaporouspolysulfonesupport.

Zeolitenanoparticlesweredispersed(0.004%-0.4%,m/V)inthe

organicphasesolutioncontainingtrimesoylchloride(TMC)inhexane;this

solutionreactedwitha2% aqueoussolutionofmphenylenediamine(MPD)

soaking the porous polysulfone supportmembrane to form the ultrathin

polyamidemembraneforROontheporoussupport(Jeongetal.,2007).At

thehighestnanoparticleloading,purewaterpermeabilitywasnearlydouble

thatofregularpolyamidefilmswithequivalentNaClrejections.Sincethe

interfacialpolymerizationtakesplaceintheorganicphaseforthemonomers

used, the zeolite nanocrystals introduced in the hexane phase were

incorporatedinthethinpolymerizedfilm.Notethatzeolitemembranesbased

ononlyNaAzeoliteshadbeendevelopedalreadyforhighlyselectivewater

removalbypervaporationfrom asolutionofethanolwater(Kondoetal.,

1997,2010).Thezeolitecrystalsareexpectedtopassonlywaterselectively

051

thoroughitssubnanoporesandenhancewaterpermeabilityoftheIPbased

membranewithoutcompromisingsaltrejectioncapabilitiesunlessnanogaps

arecreatedattheinterfacebetweenthecrystalandthepolyamidematrix.

Notefurtherthatlargersizenanocrystalscouldtraversethewholethicknessof

theinterfaciallypolymerizedskinifitisquitethin.Suchamembranewas

identifiedasathinfilmnanocomposite(TFN).

Atthisstage,twoalternateroutesappearedinthesearchforbetterliquid

phaseseparationmembranes:Incorporatezeolitesorotherwaterselective

molecularsievesormicroporoussolidsintheIPfilmandcreateamixedmatrix

membrane;ordevelopcarbonnanotubebasedmembranes.Itisusefulto

criticallyevaluatethestatusofCNTbasedmembranesfollowingwhatRoyet

al.(2011)wrote.Holtetal.(2006)developedaverticallyalignedarrayof

DWNTsonasiliconchipbyamanystepprocessincludingacombinationof

chemicalvapordeposition,ionmillingandreactiveionetchingendingupwith

amembranecontainingCNTsopenatbothends.Themembranehoweverhad

alowCNTbasedporosityofonlyaround0.5%.Thisprocedureformembrane

fabricationisdemanding.TheCNTbasedmembranesinMajumderetal.

(2005)requireademandingfabricationprocedureaswelleventhoughthe

rateofwaterpermeationthroughtheinnercoreoftheCNTswas4to5orders

ofmagnitudehigherthanthosepredictedbyconventionalfluidflowtheory.Yu

etal.(2009)preparedaverticallyalignedCNTmembranehavingahighCNT

based porosity of21% via solventevaporation and collapsing ofCVD

synthesisbasedarrayofCNTs.Gaspermeatedatahighratethroughthe

interstitialporesaswellastheinnercoreoftheCNTs;theydemonstrated

nanofiltrationof3.2nm goldnanoparticlesaswell.Thisstructurewouldlimit

thesmallerdimensionsofsolutesthatcanberejectedduetothedimensionsof

theinterstitialopenings.AbriefreviewofCNTbasedmembranesisavailable

inLpezLorenteetal.(2010).

Wewillquote now whatRoyetal.(2011) opined on thistopic.

“FabricationofmembranesbasedontransportthroughtheinnercoreofCNTs

is very demanding. Large scale inexpensive fabrication ofCNTbased

membranesneedstobecarriedoutonareadilyscalableplatform which

shouldbeeasilyimplementedinapolymermatrixleadingtoacompactand

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膜技术在水和气体净化中的应用

economicalmembranedevice.Polymermatrixitselfwhichcanbenonporous,

mesoporousormicroporous,mayhaveconsiderablesolventfluxandsolute

selectivity.Infact,polymericmembranescanachieveselectivitybetweentwo

species/macromolecules/particlesoveranextremelywiderangeofmolecular

weightsandspecies/particlesizes.Speciesdiscriminationoversuchabroad

rangeofmolecularweights/sizesetc.islikelytobedifficultatthistimefor

CNTinnercorebasedseparationprocessessincetheinnercoredimensionsof

CNTsareavailableonlyinparticularsizesandarenotinfinitelyvariablewiththe

currentsynthesiscapabilities.”

Onthebasisofsuchconstraints,Royetal.(2011)pursuedadifferent

strategywhichreliedonutilizingtheinteractionorlackofinteractionbetween

theexternalsurfaceofthecarbonnanotubeandthepolymermatrixinthe

contextoffabricationofsolventresistantnanofiltration(SRNF)membranesto

startwith.From gasseparationresearchonmixedmatrixmembranesitis

knownthatananoparticledispersedinthepolymermatrixmaycreatean

interfacialregion with enhanced gas permeability due eitherto lack of

interfacialbondingleadingtonanogapsorlocaldisturbancetothematrixchain

packingaroundit.SincethesolutestobeseparatedinSRNFhavemolecular

weightsbetween200-1000dalton,onecouldassumethatnanogapsof

smallerdimensionswillrejectsuchsolutes;yetthesolventtransportratewould

beconsiderableenhancedthroughsuchnanogaps.

Interfacialpolymerization(IP)wasutilizedtofabricatesolventresistant

nanofiltrationmembranesofpolyamidecontainingapolymerCNTcomposite

onporoushydrophilizedpolypropylenesubstrate(Royetal.,2011).Inthis

nanocomposite membrane, the IPgenerated polyamide provides the

selectivityandthenanogapsbetweentheexternalsurfacesoftheMWCNTs

externallyfunctionalizedwithhydrophilic/hydrophobicgroupsandthematrix

polymerenhancesolventfluxbyalmostanorderofmagnitude.Membranes

achievehighrejectionsofsolutesbrilliantblueR(826,MW)andSafraninO

(351,MW)from theirmethanolandaqueoussolutions.Inthefabrication

procedure,MWCNTsaredispersedinoneofthemonomercontainingphases.

TheoutsidesurfacesofMWCNTswererapidlyfunctionalized earlierwith

hydrophilic (-COOH) groups orhydrophobic groups via microwave

251

treatment(Wangetal.,2006);thosewithhydrophilicgroupsaregenerally

dispersedinmonomercontainingaqueoussolutionandthosewithhydrophobic

groupsaregenerallydispersedinmonomercontainingorganicsolventpriorto

fabricatingIPbasedmembranes.Otherwisesurfactantsareused.

TheMWCNTlevelsusedinmakingthesemembraneswereintherangeof

0.01% -0.06%(massfraction).OneCNTcanpotentiallyprovidethroughits

interfacewiththepolymermatrixacontinuoustransportcorridorfromoneend

oftheCNTtotheotherthuseliminatingtheneedforasubstantialCNTvolume

fractiontoachieveapercolationthreshold.ThisisparticularlyvalidinIPbased

membraneswhoseskinthicknessesareoftheorderof100nm whereasCNT

lengthswereatleastintherangeof1toafewmicrometers.Itisnotknown

clearlywhetherinthepresentcasemicrowavetreatmentopeneduptheCNTor

not.Supposeitdid.Thenonehastocontendwiththepossibilityofthetest

solutesenteringaMWCNTmouthatthefeedsolutioninterface(ifthemouthis

opentothefeedsolutionandnotburiedinsidethepolymerizedskin)andgo

easilytotheotherendoftheIPfilm.Thiswouldbeaverylargesourceof

leakageoftestsolutesunlesstheotherendoftheMWCNTdidnotopenup.

FurthertheopeninteriordimensionoftheMWCNTs(30nm)wasquitelarge.

Itwasobservedinsteadthatthesoluterejectionsofthemembranesformed

werenotaffectedwhethertherewasMWCNTsornot.Iftheinteriorsurfaceof

theMWCNTswerefunctionalizedbymicrowaves,thesolventfluxwouldbe

reducedsubstantially;furtherthesolutefluxwillincreaseleadingtolower

soluterejection.

Ifoneweretothinkofdesalinationusingtheinnercoreofthesinglewall

CNT,otherconsiderationscomein.TheionicradiusofNa+ andCl- are

1.16? and 1.81 ? respectively(Burgess,1988).The kinetic sieving

diameterofwaterinzeolitesis ~2.7?(Breck,1974).Itisknownfor

polymericseawaterreverseosmosismembranesthatwatermoleculecluster

sizesexceeding4innumberaretheminimum neededtotransportsaltions

throughapolymericmembrane(StrathmannandMichaels,1977).Itisclear

thenthattheinternaltubediameterinsinglewallcarbonnanotubes(SWCNTs)

(~4-5?)willnotprovidesuchanopeningforthewaterclusteraroundasalt

ionthusallowingonlywatermoleculestogothroughSWNTs.Howeveronehas

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膜技术在水和气体净化中的应用

tohaveonlySWCNTswithopenmouthstotakecareofthismechanism.

Withouta highly controlled chemicalvapor deposition (CVD)based

fabricationprocedureandadditionalsteps,suchascenarioisdifficultto

achieve;ifachieveditislikelytobequitecostlyandchallengingtoscaleup.

5 MixedmatrixmembranesforliquidseparationsinRO,FOandNF:examples

Wewillfirstconsiderexamplesofthinfilmcomposites(TFCs)preparedby

interfacialpolymerization with nanoparticles(that are not nanotubes)

incorporatedinthepolymerizedfilm:theTFNs.Thenanoparticlesincorporated

wereasfollows:zeolitecrystals,silica,silver,TiO2,silicasols(toavoid

agglomeration ofsilica nanoparticles),metalorganic framework (MOF),

aquaporin etc. Ofthese silvernanoparticles were introduced to provide

antibacterialproperty.Fourstudiesusingzeolitecrystalsarerelevant.Threeare

from UCLA,Los Angeles,CA (USA):Jeong etal.(2007) (already

considered),Lindetal.(2009),Lindetal.(2010).Thelatestoneisfrom

Singapore:Maetal.(2012).

Lindetal.(2009)employedLindetypeAzeolitecrystalsintheNaAform

havingthefollowingdimensions:97nm,212nm,286nm;0.2% (m/V)

crystals were dispersed in the organic phase priorto polymerization.

RejectionsofNaCl,MgSO4 and PEG 200 (3.5 ? radius) bytheTFN

membraneswerestudiedandfoundtobequiteclosetoorslightlylessthan

thatoftheTFC membranewithoutthenanoparticles.TheTFN membranes

werefoundtobesomewhatmorepermeableandmorenegativelychargedand

thickerthanaregularTFCmembrane.TFNmembraneshavingsmallersize

zeolite crystalsproduced higherfluxes;the authorscould notconclude

whetheritwasduetoanincreasedamountofnanochannels.Preferential

interactionbetweenthepolymerizedfilm andthenanocrystalincludinglower

extentofcrosslinkingislikely.Lindetal.(2010)demonstratedNaClrejection

levelscomparabletocommercialseawaterdesalinationROmembranes(~

99.4%)withTFNmembranescontaining0.2% zeolitesintheorganicphase

andafewposttreatments;thefluxlevelswerealsocomparable.Ingeneral,

thesaltrejectionlevelswereslightlylowerforotherTFNmembraneswithwater

451

fluxessomewhathigher.Ma etal(2012) employed conventionalTFC

formulationforaninterfaciallypolymerizedpolyamidemembranewith40-150

nmNaAzeoliteparticlesdispersedintheorganicphaseatloadingsbetween

0.02to0.4(m/V,%).Theloadingof0.1% yieldedthebestFOperformance

withawaterpermeability80% higherthanthebaselineTFCmembranebuta

somewhatlowersaltrejection.Thesurfacesofthemembraneswererougher

thanthebaselinemembranes.

Afew remarkstocharacterizesomeobservationsinthesepublications

follow:

1)zeolitenanocrystalsweredispersedintheorganicphasepriortoIP;

2)TFN membraneshadhighchargedensity(muchmorenegatively

chargedthanthebasePAmembrane)andexhibitedsuperhydrophilicity;

3)porefilled(templatingagentnotremovedafterhydrothermalsynthesis)

zeolitefluxwaslessthanporeopenzeoliteflux;

4)smallerzeolitesproducedgreaterpermeabilityenhancements;

5)TFN membranepermeabilityofwaterisgenerallyhigherthanthe

correspondingTFCmembrane;

6)higherzeoliteloadingreduceswaterpermeabilitydueprobablytoa

thickerPAlayer;theloadinglevelfoundusefulisaround0.1-0.2(m/V,%);

7)thesaltrejectionvirtuallyneverexceeded thecorresponding TFC

membraneandisusuallymarginallyorsignificantlylower.

Studiesconductedearlieraswellassubsequenttotheabovementioned

studies utilized othernanoparticles. The polyamide thin film composite

membranesobtainedbyincorporatingTiO2nanoparticles(Kwaketal.,2001;

Leeetal.,2008),silvernanoparticles(Lee etal.,2007) displayed

nanofiltrationbehaviornamely,highsolventflux,highrejectionsofsaltssuch

asMgSO4containingdivalentionsandlowrejectionsofNaCl.Thisbehavior

suggestedthatnanogapscreatedbetweenthenanoparticleinclusionandthe

polyamidemembraneareresponsiblefortheobservedbehavioreventhough

the membranes developed had some antifouling/antibacterialproperties.

Resultsofincorporationofsilicananoparticleswerestudiedbyquiteafew

investigatorswithvariableresults.

1)Jadavetal.(2009)employed3nmand16nmsilicananoparticlesin

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膜技术在水和气体净化中的应用

the TFN membrane ofpolyamide; they could achieve brackish water

desalinationbutnofurtherindicatingthatsomenanogapswereactingas

defects.

2)Huetal.(2013)employedininterfacialpolymerization2,2′bis(1

hydroxyl1trifluoromethyl2,2,2trifluoroethyl)4,4′methylenedianiline(BHTTM)

intheaqueousphaseand trimesoylchlorideintheorganicphaseona

polyethersulfonesupportmembrane with a silica solintroduced into the

aqueousphase;01% silicaconcentrationwasfoundtobeoptimal.The

membranesperformedasNFmembraneswithamaximumof94% rejectionof

Na2SO4.

3)Inanearlierstudy,Huetal(2012)employedpiperazineasthe

aqueousphase monomerformaking a TFC polyamide membrane with

aqueoussilicasolintheaqueousphaseandobtainedaNFmembranewith

97.4% rejectionofNa2SO4.

We willnow summarize results ofmembranes employing carbon

nanotubes(CNTs)inavarietyofwaysbeyondwhatwasdonebyRoyetal.

(2011).TheprocessesofintereststudiedareNFandFO;theCNTsused

were generally functionalized MWCNTs. Goh etal. (2013) fabricated

polyamideimide(PAI)hollowfibers,functionalizedMWCNTswithcarboxylic

acidgroups,immobilizedthesefunctionalizedMWCNTsonthehollow fiber

outsidesurfacebyvacuum filtrationandthenthissurfacewaschemically

crosslinkedwithpolyethyleneimine(PEI)todevelopapositivelychargedNF

membrane. The membranes had a pure water permeability of

4.48L/(m2·h·bar)andaMgCl2rejectionof87.8% at1barindicatinga

44% waterpermeability enhancementforsimilarsolute rejection.These

membranes exhibited almostsimilarenhancementin waterflux without

compromisingsolutefluxinaFOprocesswith0.5mol/LMgCl2asthedraw

solutionanddeionizedwaterasfeed.Shenetal(2013)employedpiperazine

andtrimesoylchloridebasedinterfacialpolymerizationonaporouspolysulfone

substratewhereintheorganicphasecontained MWCNTswhosesurfaces

having-COOHand-OHgroupsintroducedearlierbyacidtreatmentwere

graftedwithpolymethylmethacrylate.ThisTFNmembranewithhydrophobized

CNTsurfaceshowed99% Na2SO4rejectionwitha2000ppm feedsolutionat

651

1MPaanda62% enhancedwaterfluxoverthecorrespondingTFCmembrane

inNF.Additionalresultsfromstudieshavingvariationsofthesamethemeare

availableinthefollowingpublications.

InWuetal.(2013),MWCNTswithfunctionalizedcarboxylicgroupsused

at0.5mg/mLintheaqueoussolutionwithtriethanolamineaswellassome

surfactantsand TMC onaporouspolysulfonesupportmembraneyielded

doublethewaterpermeabilityofthefilm withouttheMWCNTs;howeverthe

rejectionofNa2SO4 didnotgobeyond85%.Daraeietal.(2013)grafted

polyacrylic acid on the MWCNTs and prepared nanocomposite

polyethersulfonebased nanofiltration membrane with high waterflux and

improvedrejectionandantifoulingproperties.Zhaoetal.(2014)improved

theperformanceofpolyamidebasedRO membranewithoutsacrificingsalt

rejectionbyincorporatingMWCNTsmodifiedtoimprovetheirdispersivity;

increasedMWCNTloadingincreasedthewaterfluxwithsoluterejectionslowly

decreasing.

Otherinclusionshavebeenusedbesidesthosementionedabove.An

exampleisprovidedbySorribasetal.(2013)whereMOFswereintroducedin

anIPbasedpolyamidelayerwhichledto2-6timessolventpermeation

enhancementsforgreaterthan 90% rejections ofstyrene oligomers of

molecularweightslargerthan295insolventssuchasmethanolandTHF.

A numberofcorporationsare beginning to exploitsuch membrane

technologiesemployingzeolitesorCNTs.PoriferaInc.(Hayward,CA,USA)

isemployingalignedCNTbasedmembranesforultrafiltrationandclaimingto

haveachieved5-6 timeshigherwaterfluxwithsimilarMW cutoffthan

conventionalUFmembranes.PoriferaInc.claimstohavemade300millimeter

wafersofsuchmembranes.PoriferaInc.isalsoexploringotherapplicationsof

alignedCNTmembranes.NanoH2O Inc.isanotherCaliforniacompany(El

Segundo, CA, USA) preparing spiralwound membrane modules for

desalinationusingthinfilmcompositemembranesinwhichnanomaterialshave

beenintroducedintotheselectivelayer.SuchTFNmembranesareclaimedto

have50% -100% increaseinwaterpermeabilitywithrespecttothebaseTFC

membranes.Largemembraneunitshavebeenmanufacturedforcommercial

applications.

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Afewconclusionsareprovidednowalongwithafewsuggestions.

1)IPbasedrandomlyplacedCNTTFCmembranesarerelativelyeasyto

fabricate.

2)Toimprovesoluterejectionthedensityofsurfacefunctionalization

probablyneedstogoup;thenatureofthefunctionalizingpolymer,itswater

clusteringpropertyetc.areofgreatimportanceifRO desalinationisthe

objective.

3) Verticallyaligned CNTbased membranes obtained via CVD are

difficult/costlytofabricate.

4)VerticallyalignedCNTbasedmembranesallowtheIDofCNTtocontrol

solventfluxandsoluteseparation.

5)FacilefabricationofverticallyalignedCNTbasedmembranewillyield

highsolventfluxandappropriatesoluterejection.

6)AppropriatelypurifiedCNTsareofgreatusetoachievethisgoal.

However,thecostoffabricatingsuchmembraneswithasufficientdensity

ofCNTshavingappropriateinternaldiametersforparticularseparationsis

likelytobehigh;costcomparisonwithrelativelyinexpensivepolymerbased

membranesisinevitable.Concurrentlyradicalenhancementofsolventfluxwill

bringinitswakehighconcentrationpolarizationonthefeedside.Novelfluid

managementtechniqueswillbeneededtocontrolsuchalevelofpolarization.

TheliquidseparationprocessesdiscussedsofarinvolvedRO,FO,NF

andUF.Mixedmatrixmembraneshavealsobeenusedforpervaporationas

mentionedalready(Pengetal.,2007).Theearlieststudyonpervaporation

wasdonebyHennepeetal.(1987)usingalcoholselectivesilicalitedispersed

inasiliconerubbermatrixforseparationfrom analcoholwatersolution.

Hydrophiliczeolite4Aparticleswereincorporatedinpoly(dimethylsiloxane)

(PDMS)andpoly(trifluoropropylmethylsiloxane)(PTFPMS)membranes;the

lattermembranesyieldedwaterethanolpermselectivitiesashighas11.5and

waterpermeabilities6timeshigherthanunfilledPTFPMSmembranes(Linet

al.,2013).ThislaststudyfromLeeVanegroupispartofaseriesofstudies

usingbothhydrophilicaswellashydrophobiczeolitesinrubberymembranes

forpervaporationbasedseparationofalcoholwatersolutions.

Inmixedmatrixmembranesforgasseparation,wehadindicatedearlier

851

thatmembranes having selectively permeable flakes could achieve an

extraordinaryenhancementintheselectivityandpermeationofthespecies

selectively permeating through the flake. In hydrogenbased proton

conducting fuelcells,the permeation rate ofa proton in a humidified

environmentwas enhanced considerably by having a nanocomposite

membraneofthefollowingtype.Inanionomermembraneofsay,sulfonated

polyetherketone,lamellarzirconium phosphatesweredispersed;theseflakes

havehighprotonconductivityleadingtoenhancedprotonconductivityinthe

membranealong withenhancementinotherpropertiessuchasreduced

swelling,increasedmechanicalresistanceetc.(Albertietal.,2003).

Asingasseparationwheredistinctmolecularentities/polymerssuch

aspolymericamineswereaddedtothepolymericmatrixtoenhancethe

permeationofselectedgasspecies,similarlyintheperformanceofproton

conductingfuelcellssupramoleculeshavebeenimpregnatedinNafionto

enhanceitsprotonconductivityamong othersathighertemperatures.

Photocurablehyperbranched(HB)polyesterterminatedwithfunctional

carboxylicacidgroups,namelyHBPEAcCOOH,wasincorporatedinthe

ionicdomainsofNafiontoenhancetheprotonconductivity(Kyuand

Nazir,2013).

6 Summary

The conceptofusing mixedmatrix membranes fora variety of

problemsingasseparationaswellasliquidseparationsisquiteattractive.

Considerable enhancements in membrane performance have been

demonstrated in a variety ofgas separations. In liquid separations

enhancementinsoluterejectionwasgenerallyelusive;howeversignificant

enhancementofsolventfluxe.g.,waterfluxhasbeendemonstrated.

Individualsystemcharacteristicsarecrucialindeterminingenhancementor

deterioration in performance in mixedmatrix membranes containing

nanocrystals,nanoparticles,CNTsetc.Concurrently,significantattention

hastobepaidtothefollowingareas:matrixinclusioninterface,selective

membranefabricationproblems,cost,scaleup.

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

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MembraneHandbook.Boston:Springer.

161

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膜技术在水和气体净化中的应用

Kamalesh K. Sirkar, PhD,  is a Distinguished

ProfessorofChemicalEngineeringandtheFoundation

ProfessorinMembraneSeparationsatNewJerseyInstitute

ofTechnology (NJIT). Sirkaris an internationally

renownedexpertinmembraneseparationtechnologies.He

istheinventorofthecommercializedmembranebased

solventextractiontechnologyforwhichHoechstCelanese

receivedHonorableMention in the1991 Kirkpatrick

Award.Hehaspioneeredamongothersthenotionofmicroporousmembranesas

membranecontactorsoftwoimmisciblefluidphasesaswellasthecontainedliquid

membrane.

SirkarwasaprofessorofChemicalEngineeringatIIT,KanpuraswellasatStevens

InstituteofTechnology.Hehasreceivedanumberofhonorarydegreesandawards

includingthe2005AIChEInstituteAwardforExcellenceinIndustrialGasesTechnology

andthe2008ClarenceGerholdAwardoftheSeparationsDivisionofAIChE.

HeistheEditorinChiefofthejournal,CurrentOpinioninChemicalEngineering.

HewasalsotheeditoroftheElsevierSeriesinMembraneScienceandTechnology

during2005-2011.HeservedasanAssociateEditorofSeparationScienceand

Technologyduring2005-2011.Heisserving/hasservedasamemberoftheeditorial

boardsofJ. MembraneScience, I&EC Research, and Separation Scienceand

Technology.SirkarisacoeditorofthewidelyusedMembraneHandbook.Hehas

authored174refereedpublications,19bookchapters,29USpatentsandover300

presentations.HewasthePresidentoftheNorthAmericanMembraneSocietyduring

1998-1999andaDirectoroftheSeparationsDivisionofAIChEduring1993-1996.

HeisaFellowofAAAS.

261

StudyandApplicationofCO2SeparationMembranes

YimingCao,etal.

DalianInstituteofChemicalPhysics,ChineseAcademyof

Sciences,Dalian,China

1 Introduction

CO2separations,mainlyfromfluegastoreducewarmhouseeffectsand

raw naturalgas to upgrade its quality, are directly related with both

environmentandenergythathavebeenthoughtastwokeyissueshuman

beingwillfaceinthenewcentury.ThusstudyofCO2captureandstoragehas

attractedworldwideinterests.Currentlysolventabsorptionisstillthemost

successfulandwidelyappliedmethodforCO2 removal,whileusuallythis

processneedshighcapitalinvestment;regenerationofsolventalsorequires

hightemperatureleadingtolargeenergyconsumption.Comparedwithsolvent

absorption,separationofCO2 from amixturebymembranetechnologyhas

obviousadvantagese.g.:simpleprocess,easytoscaleup,nophase

change(lowenergycost)andenvironmentfriendly.Wehavebeenfocusing

onCO2 separationmembraneresearchforlong timeand currentlythree

researchdirectionsarebeingexploredinthisarea:polyimidesynthesisand

membranefabrication,MOFscontainingmixedmatrixmembranefabrication

andmembraneabsorptionwithPTFEmembranecontactor.

2 Polyimidesynthesisandhollowfiberfabrication[1]

2.1 Polyimidesynthesisandintrinsicgasseparationproperty

Polyimidesare rigid,owning highmelting pointplusglasstransition

temperature,andthermallystablepolymersobtainedbypolycondensation

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

reactionsofdianhydrideswithdiamines.Theinterestingaspectofthiskind

materialsisthattheirseparationpropertiescanbetailoredbyusingdifferent

combinationsofdianhydridesand diamines.A series ofpolyimide with

differentgasseparationpropertyhavebeensynthesizedinourlab.Among

themanovelcopolyimide(CPI)ofODPATMPDA/DAThasobtainedmore

attention because ofits excellentseparation performance forCO2/CH4separation:itownsanintrinsicCO2permeabilityof10.82barrer(1barrer=

1×10-10cm3(STP)·cm/(cm2·s·cmHg))withidealselectivitiesof45.5

overN2and48.6overCH4whentestedatroomtemperatureand0.30MPa.

Atpresenttime20kgsynthesisscalehasbeensuccessfullyrealizedasshown

inFig.1.

Fig.1 LargescalePIsynthesissetup(20kg/batch)

2.2 ODPATMPDA/DATcopolyimidehollowfibermembranefabrication

Inbrief,certainamountofdried CPIand dehydrated Nmethyl2

pyrrolidone (NMP) were mixed with little ethanolas a nonsolvent

additive.CPIwasdissolvedcompletelyunderN2protectionat60℃.Gas

bubblesinthepolymersolutionwereeliminated undervacuum before

spinning.Anascentfiberwasextrudedthroughaspinneretandentereda

tapwatercoagulantbathbeforeanairgap ofcertaindistance.The

spinningratewascontrolledbygearpumpandtheflowrateofborefluid

wascontrolledwithasyringepump.SEM observationrevealedthatthe

461

prepared hollow fiber membrane possessed a typicalasymmetric

morphologyofgasseparationmembraneasshowninFig.2.

Fig.2 SEM picturesofpreparedPIHFM:(a)crosssection;(b)innersurface

section;(c)outersurface;(d)innersurface;(e)partofcrosssection;(f)outer

partofcrosssection

2.3 Gasseparationperformanceevaluation

2.3.1 Puregastest

Permeationrates ofpure gases including N2, CH4 and CO2 were

measuredwithpreparedPIHFMatroomtemperatureand0.3MPa.Thetest

resultsarelistedinTable1.PreparedPIHFM hadaCO2permeationrateas

highas39.4GPU(1GPU =1×106cm3(STP)/(cm2·s·cmHg))withan

idealselectivityof44.7overN2and47.3overCH4.Itisnotcommonthatsuch

ahighperformancefibercouldbeachieveddirectlywithoutanyfurthercoating

step.Theresultsproved thatPIsynthesized inourlab notonlyhasan

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

excellentgasseparationperformancebutalsocanbeeasilyfabricatedina

formofdefectfreeHFM.

Table1 PuregaspermeationperformanceofPIHFM

Fiber

properties

P/l(GPU)

N2

P/l(GPU)

CH4

P/l(GPU)

CO2

Selectivity

CO2/N2

Selectivity

CO2/CH4

Value 0.88 0.83 39.4 44.7 47.3

  2.3.2 Plasticizationpressuretest

PlasticizationmeanswhenmembraneisfacingextremelyhighCO2partial

pressure,largeamountofCO2willdissolveinmembranematerialthusleadto

asharpincreaseofgaspermeance.AsshowninFig.3,CO2 permeance

underdifferentpressurewasmeasuredandtheresultsshowedthatwithinlow

pressurerangefrom0.30MPato2.25MPa,CO2permeanceinCPIHFMwas

relativelystable(around40-50GPU).Continuedpressureincreaseledtoa

sharpCO2permeanceincreasetoabout103GPUat3.45MPa.Whentested

at5.1MPa,wesawanextremelyhighCO2permeanceof370GPUthatmeant

thecurrentlymeasuredCPIHFMwasalmostcompletelyplasticized.Basedon

testresultsitcouldbedeterminedthatCPIHFMpreparedinthisworkownsa

plasticizationpointof2.25MPa.ThismeansitcanbesafelyusedwithCO2partialpressurenothigherthan2.25MPa.

Fig.3 PlasticizationphenomenainpreparedCPIHFM

2.3.3 Gasmixturepressureinfluence

InthissectiongasmixtureofCO2/N2(50%/50%)permeationinprepared

661

CPIHFM wasinvestigatedunderdifferentpressure.Thedetailedresultsare

presentedinFig.4.

Fig.4  PressureinfluencewithCO2/N2(50%/50%)mixtureasfeedgas

(roomtemperature):(a)gaspermeance;(b)gaspercentageandcalculated

separationfactorofCO2/N2

InformationofgaspermeanceispresentedinFig.4(a).Forgasmixture

permeance,asmallfluctuationfrom10GPUto13GPUcouldbeseenwithin

thetestedfeedpressurefrom0.5MPato6.6MPa.GCanalysisenablesus

findingouttheexactcompositionofpermeate.PartialpermeanceofN2 was

interesting:inthepressurerangeof0.5MPato4.5MPa,itownedarelatively

stablepermeancearound0.50GPUto0.75GPU;furtherfeedgaspressure

increaseledtoasharpincreaseofN2 permeancetoaround2GPU.We

believethesharpN2 permeanceincreaserevealedthatfiberswerefacing

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

plasticizationproblem becauseCO2 partialpressureunderthispressurehas

exceededitsplasticizationpoint.Fig.4(b)suppliestheinformationofgas

compositioninpermeateandthecalculatedseparationfactorofCO2/N2.Itis

clearlyseenthatunderfeedpressureupto4.5MPa,feedpressureincrease

slightlyfacilitatedCPIHFM’sseparationperformance.CO2 percentagein

permeateshowedanincreasefrom93.3% to951%.Unfortunatelycontinued

gasmixturepressureincreasebroughtasharpdecreaseofCO2percentagein

permeate,namely,from85.1% of5.0MPato77.4% of6.6MPacausedby

plasticizationasexplainedabove.Interm ofcalculatedseparationfactorof

CO2/N2,beforeplasticizationtheCPIHFM showedaseparationfactorinthe

rangeof19-26;andplasticizationterriblydegradedtheseparationfactorof

CO2/N2toaslowas5.9-6.9thatwasmaintainedduringthesecondtime

test.

2.3.4 Operationtemperatureinfluence

Gaspermeationinpolymericmembranescanbeperfectlydescribedby

solutiondiffusionmechanism andgaspermeationinpolymericmembranewill

beinfluencedgreatlybytheoperationtemperature.Inthissectioneffectof

operationtemperatureongasseparationperformanceofpreparedCPIHFM

wasinvestigatedandtheresultsarepresentedinFig.5.GasmixtureofCO2/

N2(50%/50%)wasusedasthesample.Testswerecarriedoutwithafeed

pressure3.0MPaandtemperaturerangeappliedwasfrom20to80℃.

From Fig.5(a) itis clearly seen thattemperature enhanced gas

permeationinpreparedCPIHFM obviously.Wesaw analmostlineargas

mixturepermeance increase with testtemperatures. In terms ofpartial

permeanceforCO2 andN2,bothshowedobviousincreasewithoperation

temperaturebutdefinitelyCO2 madeadominantcontribution.Similarasthe

trade offeffectbetween gas permeability and selectivity forpolymeric

membranes, though temperature increase facilitated gas permeance,

unfortunatelyatthesametimeitobviouslychangedthegascompositionof

permeateinanundesired wayasshowninFig.5(b).At20℃,CO2concentrationinpermeatewasashighas95.5%;andcontinuedtemperature

increaseto40℃ and 60℃ broughtrelativelylowerCO2 percentagesin

permeateas94.4% and 92.5% respectively;atthe highestoperation

861

temperatureof80℃,CO2percentageinpermeatedroppedto89.7% thatwas

muchlowerthan95.5% of20℃.Interm ofcalculatedseparationfactor,we

sawobviousselectivitydegradationwithtemperatureincrease.Whatshouldbe

pointedouthere isthatthe prepared CPIHFM could withstand severe

operationtemperatureashighas80℃.Thiscould beconcluded asan

additionaladvantageofourinhousesynthesizedODPATMPDA/DATCPI.

Fig.5 TesttemperatureinfluencewithCO2/N2(50%/50%)mixture

asfeedgas(3.0MPa):(a)gaspermeance;(b)gaspercentageand

calculatedseparationfactorofCO2/N2

2.3.5 Releasedgasflowrateinfluence

InthissectiongasmixtureofCO2/CH4(10%/90%)wasusedassample

andallmeasurementswerecarriedoutatroomtemperaturewithafixedfeed

pressureof3.0MPa.TestresultsareshowninFigure6.Interm ofgas

mixturepermeanceasshowninFig.6(a),higherreleasedflowrateobviously

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

facilitatedgaspermeationinCPIHFM.Whenreleasedgasflowrateincreased

from0.24to1.91cm3(STP)/s(1.37to8.33timesofthecorresponding

permeateflowrate),gasmixturepermeanceincreasedfrom1.3to1.7GPU.

FurtherobservationfoundthatCO2 permeanceincreaseplayedanabsolute

dominatingrolefortotalgaspermeanceincrease.Ontheotherside,asshown

inFig.6(b),withinthesamereleasedgasflowrateincreaserange,CH4percentageinreleasedgasdecreasedfrom 99.5% to94.6%;andCO2percentageinpermeateincreasedfrom44.8% to60.6% obviously.Intermof

CO2recovery,wesawasharpdecreasefrom98.4% to57.3% byincreasing

thereleasedgasflowrate.Whatshouldbespeciallymentionedisthat4times

ofpermeateflowratecouldbereleasedfromshellsideasnaturalgasproduct

withCO2percentagestilllessthan2% meetingstrictpipelinespecifications.

Fig.6 ReleasedgasflowrateinfluencewithCO2/CH4(10%/90%)mixture

asfeedgas(roomtemperature,3.0MPa):(a)gaspermeance;(b)gas

percentageandCO2recovery

071

GasmixturetestresultsprovedthatthepreparedODPATMPDA/DATCPI

HFMshowedpromisingapplicationpotentialforCO2 separationfrom natural

gasandwillbeabletocompetewithcurrentlyappliedcommercialhollowfiber

membranesifitcangeneratestableseparationperformanceafterlongduration

operationthatwillbecarriedoutinourcontinuedresearch.

2.3.6 Additionalinformation

In2006 we successfully designed and developed a setup ofCO2separationfromnaturalgasbymembranetechnologyasshowninFig.7.Ithas

atreatingcapacityof40000Nm3/dandlocatedinHualianoilcellofFushan

OilField.Thissetuphasbeensteadilyrunningforseveralyearssincethenwith

satisfiedseparationperformance.

Fig.7 SetupofCO2separationfromnaturalgasbymembranetechnologydevelopedbyDICP

3 MOFscontainingmixedmatrixmembranefabrication[2]

3.1 Briefintroduction

Organicpolymeristhedominantmaterialofcommercialgasmembranes

usedinindustry.However,thefurtherapplicationsoforganicmembranesare

restrictedbyRobesonupperbound.Therefore,theinorganicmembranes

suchaszeolite,carbon,andsilicamembranes,havereceivedmoreattentions

inrecentyears.Buttherearestillsomeproblemsfortheindustrialapplication

oftheinorganicmembranes,includingfragility,surfacedefects,complex

preparationprocess,highcost,andlow fillingdensity.Consequently,the

mixedmatrixmembranes(MMMs),asanewtypeofmembranes,whichare

preparedbyaddinginorganicparticlesintothepolymericmatrix,combinethe

advantagesoforganicmembranesandinorganicmembranes,andhavethe

potentialtoshoweasyoperabilityaswellasgoodgasseparationproperty,

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

hasgrownup tobeaveryimportantresearcharea.MOFs,whichare

inorganicorganichybridmaterialscomposedofmetalsandorganicligands,

havelargesurfaceareas,tunableporesizes,and strong adsorptionfor

specialgases,thusareidealadditivesforMMMs.

3.2 MOFssynthesisandproperty

MOFsofCu3(BTC)2wassynthesizedbyamodifiedsynthesisprocess.Its

SEMpictureandmoleculestructureareshowninFig.8.

Fig.8 SEM picture(a)andmoleculestructure(b)ofCu3(BTC)2

Continuedcharacterizationbynitrogensorptiondesorptionisothermrevealed

thatithasaBETsurfaceareaof1439cm2/gandporevolumeof0.612cm3/g,

andpossessesadecompositiontemperaturehigherthan300℃.

3.3 Mixedmatrixmembranefabricationandgasseparationperformance

Cu3(BTC)2andUltem 1000polymerweredehydratedat110℃ for24h

beforemembranefabrication.TheCu3(BTC)2 powderwasdispersedinto

DMAcwithmechanicalagitationtoobtainfinesolution.Ultem 1000polymer

wasdissolvedinDMActoformhomogeneoussolution.TheCu3(BTC)2/Ultem1000mixedsolutionwascastontoacleanglasssubstrateandheatedto

volatilizethesolvent.Theformedmembraneswerepeeledfromtheglassand

furtherdriedinvacuumovenatthetemperaturerangeof80-190℃.Thepure

polymermembranewasfabricatedaccordingtothesimilarprocess.TheSEM

pictureoffabricatedmixedmatrixmembrane(with20wt% MOFsloading)is

showninFig.9anditsgasseparationperformancemeasuredat35℃ and3.5

atm arepresentedinFig.10.From crosssectionSEM imagesoftheC/U

MMMsitcanbeseenthatCu3(BTC)2 did notaggregateand disperse

271

uniformlythroughoutthepolymermatrix.TheCu3(BTC)2particleswerewetted

quitewellbythepolymerandnointerfacialdefectisfoundaroundtheCu3(BTC)2particles.Intermofgasseparationperformance,C/UMMMsshowed

muchhighergaspermeabilitythanpurepolymericmembraneandatthesame

timegasselectivitywasalmostremainingunchanged.

Fig.9 SEM pictureoffabricatedmixedmatrixmembrane

Fig.10 Gasseparationperformanceoffabricatedmixedmatrixmembrane

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膜技术在水和气体净化中的应用

Fig.11 CO2,O2permeabilitiesandidealselectivities((a)CO2/N2

andCO2/CH4,and(b)O2/N2)ofpureUltem1000membraneand

C/UMMMswithdifferentloadingsat35℃ and0.35MPa

3.4 MOFsloadinginfluence

InthissectioninfluenceofMOFsloadingongasseparationperformance

wascarriedout.Fig.11(a)showstheseparationpropertiesofpureUltem1000

membraneandC/UMMMsforCO2/N2andCO2/CH4.TheCO2permeabilityof

theC/U MMMsincreased astheCu3(BTC)2 loading increased,and the

selectivityoftheC/UMMMsforCO2/N2andCO2/CH4increasedorremained

comparedwiththepureUltem1000membrane,whentheCu3(BTC)2loading

oftheC/UMMMswasnomorethan30%(massfraction).Itcanbeconcluded

thattheCu3(BTC)2particleswerewettedwellbythepolymerandtherewasno

nonselectiveinterfacialdefectintheC/UMMMs.Whentheloadingincreasedto

35%(massfraction),theCO2permeabilityexhibitedanobviousincrease:the

permeabilityofCO2increasedby262% comparedwiththepureUltem 1000

471

membrane,whiletheselectivityforCO2/N2wasunchangedandforCO2/CH4decreasedslightly(about10%).TheseparationpropertyforO2/N2(Fig.11

(b))wasalsoimprovedastheCu3(BTC)2 wasadded,theO2 permeability

increasedwithslightdecreaseoftheO2/N2selectivity.

Inbriefconclusion ithas been proven thatwith polyimide as base

membranematerialtheadditionofMOFscangreatlyenhanceitsgaspermeation

performancewithoutanyobviousselectivityloss.Currentlyattemptstofabricate

ahollowfiberhybridmembranewithoptimizedmorphologyandenhancedgas

separationperformancearebeingcarriedout.

4 MembraneabsorptionwithPTFEmembranecontactor[3]

4.1 Briefintroduction

Recentlyresearchoncombinationofmembranewithothertraditional

separationmethodsisattractingmoreattentionsandamongthem membrane

absorptionhassteppedoutasapromisingtechnology.Membraneabsorption

hasadvantages ofhigh selectivity and large CO2 absorption capacity.

Comparedwithtraditionalabsorptiontower,itpossessesextraadvantagesin

caseofoffshoreapplicationbecauseofitsmuchcompactedsetupandbetter

operationflexibility.AtypicalsketchformembraneabsorptionisgiveninFig.

12.Flowingfeedgasandabsorbentwasseparatedbyporoushollowfiber

membranesinacontactor.Whatshouldbepointedoutisthatmicroporesof

hollowfibermustbeoccupied byfeed gasotherwiseifitwaswetted gas

absorptioncapabilityofmembraneabsorptionsystemwillbedeterioratedterribly.

Fig.12 Membraneabsorptionsystemsketch

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

4.2 PTFEhollowfibermembranefabricationandmorphology

Inordertoavoid microporewetting,aproperchoiceofmembrane

materialandcarefulmanipulationofporousmorphologyareveryimportant.In

otherwords,themethodsforbreakthroughpressureimprovementmainly

includeincreasingmaterialhydrophobicity,reducingporesizeandselecting

absorbentwith largersurface tension.PTFE isa superiorpolymerwith

excellentchemicalstabilityand mechanicalstrength.With a novelself

developedandpatentedfabricationprocess,PTFEhollow fibermembrane

withfinelycontrolled porousstructurehasbeensuccessfullyprepared as

showninFig.13.Themembranehasanaverageporediameteraround0.1-

0.4μmandporosityashighas60%.

Fig.13 SEM pictureofPTFEhollowfibermembrane

4.3 Membranecontactortestandevaluation

AsimplemembraneabsorptiontestsystemsketchispresentedinFig.14.

Ingeneral,feedgasmixturewithcertainpressurewasintroducedtotubeor

shellsideofmembranecontactor,andabsorbentwascounterflowingonthe

othersidewithalittlebithigherpressureforbubblingavoidance.Gasand

absorbentcontactedwitheachotherattheoutersurfaceofmicroporesand

CO2 ingasmixturewasselectivelyabsorbed.Anexactlycontrolled gas

releaseflowratewasmaintainedatfeedsidethatwasthepurifiedproductgas

withmuchlowerCO2percentage.Gasmixturecompositionwasanalyzedby

GC.CO2/CH4(10%/90%)mixturewasusedasfeedgas.

671

Fig.14 Membraneabsorptiontestsystem

4.3.1 InfluenceoffeedpressureandMDEAconcentrationinabsorbent

InthissectioninfluenceoffeedpressureandMDEA concentrationin

absorbentwassystematicallyinvestigatedandtheresultsarepresentedin

Fig.15.Alltestswerecarriedoutatroomtemperaturewithafeedgasflowrate

of0.8L/minandabsorbentflowrateof0.1kg/min.

From Fig.15 itcanbeclearlyseenthatoperationpressurebrought

obviouslydifferenteffecttoCO2removalefficiency.Thestartinglowpressure

wasanexceptionsinceatthispointallCO2removalefficiencywasquitelow

whenwaterand MDEA solution were applied as absorbent. Continued

pressureincreasedidnotshowtoomuchinfluenceforthesetwoabsorbents.

MEAsolutionpresentedahighestCO2removalefficiencyof82% whenrunning

at1MPa.Interm ofMDEAconcentrationinfluence,theresultsshowedthat

0.5mol/LMDEAsolutionpossessedrelativelybetterCO2 removalefficiency

than0.1mol/LMDEAsolution.Thiscanbeeasilyexplainedsincehigher

MDEAinsolutionmeansmoreavailablereactantforCO2absorption.

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Fig.15 InfluenceoffeedpressureandMDEAconcentrationinabsorbent

4.3.2 Influenceofoperationmode

Fig.16 Influenceoffeedoperationmode

Inthissectiontwodifferentoperationmodes(feedgaswaskepteitheron

shellsideortubeside)wereappliedtofindoutiftherewasanychangeof

absorptioneffect.Absorbentof0.5mol/LMDEAsolutionwasselectedand

otheroperationconditionswereexactlysameasabove.Theresultsare

presentedinFig.16andgenerallyspeakinggasintubesidebroughtabetter

871

CO2removalefficiency.Webelieveaproperexplanationofthephenomena

mustconsidertheconfigurationofmembranecontactorincludingfiberpacking

density,shellsideflowingdistributiondesign,etc.Westronglybelievea

higherCO2removalefficiencymeansabetterCO2contactingopportunitywith

absorbentinthecontactor,inotherwords,lessdeadvolumeonfeedgas

side.

4.3.3 Influenceoffeedgasandabsorbentflowrate

Inthissectionadetailedinvestigationoffeedgasandabsorbentflowrate

influencewascarriedoutatroomtemperatureand1MPa.Feedgasflowrate

of08 L/min wasmaintained during absorbentflowrate effecttestand

absorbentflowrateof0.1kg/minwasmaintainedduringfeedgasflowrate

effecttest.TheresultsareshowninFig.17.

Firstwenoticedthatamongallthreeabsorbentsapplied,purewater

showedthepoorestabsorptioncapabilityand0.1mol/LMEAsolutionbrought

abestabsorptioneffect.Gasflowrateincreaseobviouslyenhancedtheoverall

CO2fluxsincehigherfeedgasflowratemeansgascompositionintubeside

willhaveahigherCO2concentrationthusbroughtmoreabsorptionandhigher

flux.Unfortunatelythetradeoffeffectbetweenreleasedgasflowrateand

separationperformancedeterminedthathigherfeedgasflowrateinevitablyled

toadecreaseofCO2 removalefficiency.Comparedwithit,anincreaseof

absorbentflowrateincreasebroughtpositiveeffecttobothoverallCO2fluxand

CO2 removalefficiency. This should be quite reasonable since higher

absorbentflowrateonshellsidemeansliquidatthissidecouldbereplaced

morequicklythusabsorbentcouldbemuch“fresher”andpossessbetterCO2absorptioncapability.Thisiswhyweseeenhancedeffectsonbothterms.

Whatshouldbepointedouthereisthatadrawbackoflargerliquidflowratewill

bemoreenergyconsumptioninordertodrivethishighlyviscousliquidflowing

onshellside.

4.4 Additionalinformationofpilotsystem

Aswecanseefrom allabovetestPTFEmembranecontactorforCO2

removalfrom raw naturalgashasbeensystematicallyinvestigatedandthe

resultsarequiteencouraging.Currentlycooperatedwithaforeigncompany,a

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Fig.17 Influenceoffeedgasflowrateandliquidabsorbentflowrate

pilotmembranecontactorsystem isbeingassembledwhichwillbetested

abroadsooninthisyear.ThedetailedsetupispresentedinFig.18.

081

Fig.18 ApilotsetupofPTFEmembranecontactorsystem

Inthispaperwebrieflyintroduced ourresearchinthefield ofCO2separationandstoragebymembranerelatedtechnology,andthreeareas

were mainly mentioned, namely polyimide synthesis and membrane

fabrication,mixedmatrixmembranepreparationandmembraneabsorption

process.Thoughmixed matrixmembraneisstillatastageofscientific

exploration,theothertwo,from thepointofourview basedonresearch

progress,westronglybelievetheirpracticalapplicationcouldbesuccessfully

realized.

References

[1] JieXM,DuanCJ,WangL,etal.Fabricationofanasymmetric4,4′oxydiphthalicanhydride2,

4,6trimethyl1,3phenylenediamine/2,6diaminotoluenecopolyimidehollowfibermembraneand

itsperformanceforCO2separation.IndEngChemRes,2014,53(11):44424452.

[2] DuanCJ,KangG D,LiuD D,etal.Enhancedgasseparationpropertiesofmetalorganic

frameworks/polyetherimidemixedmatrixmembranes.JournalofAppliedPolymerScience,Article

firstpublishedonline:16APR,2014,DOI:10.1002/app.40719.

[3] HuaCG,KangG D,JiaJX,etal.PhysicalabsorptionofCO2 usingpolyvinylidenefluoride

membranecontactorathighpressureandmathematicalsimulation.ChemicalJournalofChinese

Universities,2013,34(4):906912.

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膜技术在水和气体净化中的应用

  Prof.YimingCao LeaderofMembraneTechnology

Group,Dalian NationalLaboratory forClean Energy

(DNL),DalianInstituteofChemicalPhysics(DICP),

ChineseAcademyofSciences(CAS).

Prof.Caoismemberofseveralmembranerelated

organizationsinChinasuchasMembraneIndustrySociety

Expert Committee, National Separation Membrane

Standardization Technical Committee, and National

ScientificKeyProjectExpertCommittee.Heisalsoservingaseditorforjournalsof

WatertreatmenttechnologyandMembranescienceandtechnology.

ResearchesinhisgrouparemainlyfocusingonCO2 separationfieldsincluding

synthesisofpolymericmembranematerials(especiallypolyimide)forCO2separation;

membraneabsorptionprocessfortheremovalofCO2fromlowqualitynaturalgaswith

porousPTFEhollowfibermembrane;MOFs/polyimidehybridmembranepreparation

forCO2removal.Hisgroupisalsoactiveintheresearchofliquidtreatmentmembranes

suchasMF,NF,etc.

Asprimeinvestigator,Prof.Caohassuccessfullycompletedmanynationaland

internationalcollaborative projects in membrane research area. His research

achievements,especiallyinCO2 separationarea,haveattractedwideattentionand

broughthimseveralimportantprizesinmembraneresearchfieldofChina.

281

AntiproteinfoulingStrategyinMicrofiltrationandUltrafiltrationMembranes:AMinireviewFocusingon“Graftingfrom”PolymerizationofZwitterions

XiaolinWang,etal.

BeijingKeyLaboratoryofMembraneMaterialsandEngineering,

DepartmentofChemicalEngineering,TsinghuaUniversity,Beijing,

China

Abstract:Theproteinfoulingonthemembranethatisregardedasthefirststep

ofmembranefoulinglimitsthewideapplicationofmembranetechnologies,

suchasmicrofiltration(MF)andultrafiltration(UF).Zwitterionicmaterials

form thehydrationlayerbyelectrostaticinteractionand hydrogenbond,

contributing to the stable antiproteinfouling property. “grafting from”

polymerizationthatthezwitterionicmonomerscanbepolymerizedusingan

initiationreactiononthemembranesurfacehasbeenregardedasasimple,

useful,andversatileapproachtotheantifoulingmodificationofmembrane.

Thisstrategyprovidescontrollableintroductionofgraftchainswithahigh

densityandalongterm chemicalstabilityassuredbycovalentattachmentof

graftchains.Thisarticlepresentsaminireview ofrecentprogressonthe

graftingpolymerizationofzwitterionicmonomersfrom thesurfaceofpolymer

membrane,including the introduction ofzwitterionsand the methodsof

graftingpolymerizations.Variousapproachessuchasfreeradicalgrafting

polymerization, photoinduced grafting polymerization, plasmainduced

graftingpolymerizationandcombinedmethodswerecomparedonuniformity

and grafting amountofzwitterionic polymer, relative flux ofmodified

membrane,simplicityandenvironmentpollutionofoperation,andcostof

technique.

381

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Keywords:antiproteinfouling strategy; MF/UF membrane; grafting

polymerization;zwitterion

1 Introduction

Ithasbeenacknowledgedthatmembraneseparationhaslow energy

consumption, ease of continuous operation and environmentalfriendly

characteristics,andisatechnologyofsignificantnote,notonlyforwastewater

treatmentbutalsoforagrofoodandbiomedicalmarkets[1-8].Microfiltration

(MF)andultrafiltration(UF)arethepressuredrivenmembraneprocessesto

retain macromolecules orhigh molecularweightcompounds, excluding

bacteriaand viruses[9],whichhavebeenextensivelyused inmembrane

technology[10,11].However,themaindrawbackofthistechnologyismembrane

fouling,whichoftenlimitsitswideapplicationsthroughouttheworld[10,12].

Studiesonfoulingofmembraneshaveshownthatproteinadsorptionon

membranesurfaceshasbeenrecognizedastheinitialstepofmembrane

foulinginnumerouspracticalapplications,followedbyplateletadhesionor

bacterialbiofilm formation[5,11,13,14].Itresultsindeteriorationofmembrane

performance[15].Thus,proteinadsorptionisoneofthemostimportant

phenomenaindeterminationofthebiocompatibilityofmembrane[16].In

general,proteinsadsorbontoasurfaceofmembranewithinafewminutes

whenthemembranecontactsproteincontainingliquidssuchasblood,

plasma,andbiomedicalwastewater,etc[16].Oneofthecrucialfactors

impacting protein adsorption is the surface property ofmembranes

becauseitdeterminestheinteractionbetweenaproteinmoleculeandthe

membrane materials which plays an importantrole in the extentof

membranefouling[11,15].Therefore,theprimarytargetforinhibiting or

preventingproteinadsorptionistodevelopsuperlowfoulingorantifouling

surfaces[11,14,17,18].

MostofthecommercialmembranesforMF/UFprocessesaremadefrom

hydrophobicpolymersduetothehighthermal,chemicalandmechanical

stability[15,19-22].However,becauseofthehighhydrophobicity,thesematerials

arepronetoadsorptionofprotein[23,24].Theconstructionofahydrophilic

481

surfacehasbeenbelievedtoreduceproteinadsorptioneffectively[16],dueto

thefactthatthehydrophilicsurfaceattractssomuchwaterthatadsorptionof

proteinsisreducedandevenprevented[15].Therefore,surfacemodificationof

membraneswithhydrophilicorawatersolublepolymerchainhastobe

investigated[16].Inthepastdecades,apromisingzwitterionicnonfouling

material has been found[25,26]. The materials containing zwitterionic

phosphorylcholine(PC)headgroupshavebecometherepresentativesto

createnonbiofoulingsurfacesfrom1990s,butPCbasedmonomers,suchas

2methacryloyloxyethylphosphorylcholine(MPC),aremoisturesensitiveand

noteasyto be synthesized[27].Recently,sulfobetaine having a kind of

zwitterionicmaterialwith a similarstructure ofPC has been proved a

biocompatiblematerialwithanexcellentproteinadsorptionresistantproperty.

Sulfobetainesurfacesarecapableofbindingasignificantamountofwater

moleculesbecauseoftheformationofahydrationlayerviaelectrostatic

interactionand hydrogenbond[28].Therefore,sulfobetainecanlead toa

strongrepulsiveforcetoproteinatspecificseparationdistancesandmakethe

proteincontactwiththesurfaceinareversemannerwithoutasignificant

conformationchange[27,29,30].

During the past5 years,researchershave confirmed the abilityof

sulfobetainecoatingsonthesurfacesofvariouspolymerMF/UFmembranesto

resistprotein adsorption and then significantly retard bacterialbiofilm

formation[4-6,27,29,31-34].Amongthesurfacemodificationtechniquesdeveloped

todate,“graftingfrom”polymerization(monomersarepolymerizedusingan

initiationreactiononthesurface)hasemergedasasimple,useful,and

versatileapproachduetothecontrollableintroductionofgraftchainswitha

highdensityandexactlocalizationtothesurfacewithoutaffectingthebulk

properties,andthelongterm chemicalstabilitywhichisassuredbycovalent

attachmentofgraftchains[15,23,35].

Inthispaper,asthenovelmodifiedmaterials,zwitterionicmaterialssuch

asphosphobetaine,sulfobetaineand carboxybetaine,willbefocused to

enhancetheantiproteinfoulingperformanceofMF/UFmembrane.Illustrative

examplesofgrafting polymerizationofzwitterionfrom theformed MF/UF

membranewillbediscussed.Althoughmorethanonemembraneparameteris

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

influencedontheperformanceofMF/UFmembrane,whichnotallmaybe

advantageous,wewillmainlyfocusondecreaseinproteinadsorptionofMF/

UFmembranes.Themethodsarecomparedandratedontheirapplicabilityfor

surfacemodificationofMF/UFmembranes.

2 Zwitterionsandtheirproperty

2.1 Zwitterions

Zwitterions,whichbearbothanionicandcationicgroupsinthesame

monomerunit,haveprovedpromisingmaterialsforseparationmembranes[36].

Thetypicalanionicgroupforzwitterionisquaternaryammomiumgroup,while

thecationicgroupsincludethesulfonic,carboxylicandphosphoricgroups.In

thepast20years,zwitterionssuchasphosphobetaineandsulfobetaineare

widelyappliedinmodificationofpolymermembranes,whichnotonlyfacilitate

thewatertransportthroughthemembranes,butalsoimprovetheirantifouling

properties[37,38].Themonomersofphosphobetaineandsulfobetaine,suchas

2methacryloyloxyethylphosphorylcholine(MPC)andsulfobetainemethacrylate

(SBMA),respectively,havethesimilarstructure,asshowninFig.1.

Fig.1 Chemicalstructuralformulaofzwitterionsusedintheantifouling

modificationofpolymermembranesurface:(a)2methacryloyloxyethyl

phosphorylcholine(MPC);(b)sulfobetainemethacrylate(SBMA)

Itisregardedthatthebiomembranesurfaceisthebestsurfacefor

smooth interaction with proteins and cells[19]. In 1972, Singerand

Nicolson[39]proposedamodelofthestructureofabiomembrane,whichis

wellknown as the fluidmosaic model. According to this model,

681

phospholipidsareasymmetryandarrangedinabilayerstructure.The

negatively charged phospholipids such as phosphatidylserine are

predominantlyontheinner,cytoplasmicsideofthemembrane,whereas

theneutral, zwitterionic MPC lipidssuch asphosphatidylcholinesare

locatedintheouterleaflet.TheMPCsurfaceprovidesaninertsurfacefor

biologicalreactionsofproteinstooccursmoothlyonthemembrane[19].It

providesthatphosphobetainewithMPC headgroupsisnaturallyprotein

resistantintheoutsidelayerofcellmembranes[40].However,theMPCis

moisturesensitiveandnoteasytosynthesizeandhandle,whichlimitsits

applicationinpracticalfields[41,42].

Poly(sulfobetaine)isreported toexhibitazwitterionicstructureand

wholeneutralelectricity similarto thatofpoly(phosphobetaine)based

materials[11,30],whichresultsinthesimilarproteinresistant.Ithasaverysmall

disturbingeffectonthestructureofthehydrogenbondingnetworkofwater

moleculesindilutesolutionsbecauseoftheintraandintertetherproximity

betweentheoppositelychargedgroups[42,43].Sulfobetainemonomeriseasierto

synthesizeandhandlebutSBMApolymerswerethoughttobelessfoulingresistant

thanPCpolymers[44].Inthepast10years,preparationandcharacterizationof

sulfobetainepolymershavebeenextensivelystudied[11,27,29,30,33,38,45-48].Additionally,

zwitterionic polymers based on carboxybetaine monomer units not only

demonstratethegoodresistancetononspecificproteinadsorptionandshort

termbacterialadhesionbutalsohasabundantfunctionalgroupsconvenientfor

theimmobilizationofligands[49,50].Ithasbeenfoundthatzwitterionsinthe

sulfobetainepolymersremainintheirdiionicform overabroaderpHrange

thanthecarboxybetainepolymers[43,49,50-53].

2.2 Resistancetoproteinadsorption

Ostuni[54]findthatthesurfacesresistingtheadsorptionofproteinsexhibit

fourmolecularlevelcharacteristics:① hydrophilic;② withhydrogenbond

acceptors;③ withouthydrogenbonddonors;④ overallelectricalneutrality,

whichprovesthehypothesisthattheinteractionofthesurfacewithwaterisof

greatimportancetotheresistancetoadsorptionofproteins[54,55].Zwitterionic

polymerformsahydrationlayerviaelectrostaticinteractionsanddoesnot

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

significantly disturb the Hbonded network structure of the water

molecules[42,55].Itisexpected thatzwitterionsarecapableofbinding a

significantamountofwatermoleculesandform ahydrationlayernearthe

surfacewhichformsaphysicalandenergeticbarriertopreventtheadsorption

ofprotein[17].Theamountoffreewatermolecularandthechangeinstructure

ofproteinmolecularnearthesurfaceofzwitterionicpolymerrepresentitswater

binding capacity,whichplaysanessentialroleintheresistanceagainst

adsorptionofproteins[56].Besides,the resistance ofpoly(zwitterionic)

materialstoproteinadsorptionistightlycorrelatedwiththeuniformityofcharge

distributionandthechargeneutralityoftwooppositechargemoieties[17,25].By

using both molecular mechanics and molecular dynamics simulation

techniques,itcanbefoundthatbalancedcharge,minimizeddipoleandclose

packing density are the key factors for the nonfouling behavior of

zwitterions[42,55].

Adsorptionofproteinsconsistsoftwoparts:theformationofaninterface

between the surface and the protein with release ofwaterand the

reorganizationofproteinonadsorption[54].Thestructureofzwitterionicchains

willimpacttheinteractionamongprotein,waterandzwitterionicgroups.The

increaseinthealkylgroupsofzwitterionicchainsmayforcestheanionicand

cationicmoietiesfurtherapart,whichisfavorabletothehydrationandthe

counteractionofelectrostrictioneffect[43,57].Additionally,thehighgrafting

amountand long chainlengthofMPC polymercontributetoadramatic

reductioninproteinadsorption[58].However,lotsofresearchersfoundthatthe

hydrationandhydrophilicityofzwitterionicpolymershowa“sudden”change

ratherthanaslowincreasewithincreasingthicknessorgraftingamount[59].It

wasfoundthatthethinnerpolySBMAbrushes(<50nm)showahydrophilic

surface,whilethickerbrushes(>100nm)haveamoreorlesslinearincrease

inhydrophobicitywithincreasingbrushthickness[57].Ontheotherhand,the

shorterpolySBMA brushesmaynotform coatingsdenseenoughtoresist

proteinadsorptionwhereasthelongerpolymerbrushesshowashighprotein

adsorption,whichresultsinaminimalvalueofproteinadsorptionat62nmin

filmthicknessofpolySBMA[58].Allofthesemaybeattributedtothereversible

selfassociationinzwitterionicpolymers,includingnonassociation,interchain

881

association(betweenzwitterionicgroupsonthesamechains),andintrachain

association(betweenneighboringpolymerchains)[57,59],asshowninFig.2.

Forthethinnerpoly(zwitterion)brushes,thestericfactorsrelatedtothe

polymerbackboneandthehydratedchargedgroupshindertheformationof

ionpairs[57].Thereisnonassociationinzwitterionicpolymer,whichmakesthe

polymerhydrophilicand swollen.Increaseinthethicknessofzwitterionic

chainsresultsintheenhancementofresistancetoproteinadsorption.Forthe

thickerpoly(zwitterion)brushes,theprobabilityofionpairingeventsorself

associationbecomeshigher,whichleadstoanincreaseinpolymervolume

fractionand adecreaseindielectricconstant.Thus,theselfassociation

becomesmorefavorableandleadstoasupercollapsedstate[60].Undersuch

condition,the hydrophilic groups like sulfonate groups and quaternary

ammonium groupsmayhideinsidethecollapsedchainsandthepolymer

showshydrophobicproperty.Therefore,zwitterionicpolymerhasawettability

transitionoccurringatprecisethicknesses,belowwhichallbrushesshowed

thesamehydrophiliccharacterandabovewhichthebrushesweremoreor

lessequallyhydrophobic[59].

Fig.2 Differentconformationalstatesofpolymersinbrushesrangingfrom

fullyhydrated,nonassociatedchainstocollapsedchainswithinterchainand

intrachainassociations

3 GraftingpolymerizationofzwitterionsfromMF/UFmembrane

Surfacemodificationhasbeenconsideredausefulmethodtoimprovethe

antifouling performance of membrane without destroying the bulk

properties[61].Amongvariousmethods,graftingpolymerizationisregardedas

oneofthemostpromisingmethodstomodifythemembranesurfacethrough

the covalentbonding interaction between the grafted chains and the

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国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

membrane[20].Tointroducethezwitterionicpolymeronthemembranesurface

viagraftingpolymerization,both“graftingto”and“graftingfrom”approaches

canbeemployed.Theformerinvolvestetheringofzwitterionicpolymerchains

ontosurfacesbyoneend,whichallowsaprecisecontrolofgraftedchain

structurebutisdifficulttoobtaindensepolymerchains[23,62].Comparedtothe

former,thelatterismorewidelyusedforsurfacemodificationofdifferentkinds

ofmembranes,whichshowsahighergratingefficiencyduetothelesssteric

hindranceofdiffusingsmallmonomerscomparedtopolymerchains[23].For

thesurfacemodificationwithzwitterions,“graftingfrom”hasmuchmore

choicesto controlthe grafting degree, chain lengths and structure of

zwitterionicpolymerthroughvarying differentinitiating means,zwitterionic

monomer,concentration,temperature,polymerizationtimeandotherreaction

conditions[20].

Theprocessof“graftingfrom”polymerizationconsistsoftwosteps:①

attachmentofinitiatorsontosurfaces;②polymergrowthfrominitiatorsites[62].

Accordingtotheversatileinitiating means,thegrafting polymerizationof

zwitterionicmonomerfrom thesurfaceofmembranecanbecategorizedas

freeradicalgraftingpolymerization,photoinducedgraftingpolymerization,

plasmainducedgraftingpolymerization,andcombinedmethods.Allversatile

methodstomodifytheantiproteinfoulingperformanceofMF/UFmembranein

thelast3yearsarelistedinTable1.

3.1 Freeradicalgraftingpolymerization

3.1.1 “Living”/controlledgraftingpolymerization

Recently,“living”/controlledgraftingpolymerizationhasbeenusedto

graftzwitterionicpolymeronamembranesurface[64].Thismethodshowsthe

easeofpolymerizationwithoutthestrictreactionconditionrequiredforionic

polymerizations such as complete absence ofwater. Itcombines the

advantageoflivingionicpolymerizationforabettercontrolandtheversatilityof

freeradicalpolymerization[20,70]. The developmentof“living”/controlled

graftingpolymerizationinaqueoussystemshasenableditsapplicationinthe

surfacegraftingonthemembranedirectlyusingwaterbornesystem asthe

reactionmedium[20].

091

书书书

Table1 Graftingpolymerizationofzwitterionsfrommembranetoenhancetheirantifoulingperformanceinthelast3years

Methods

Nascent

membrane

Zwitterionic

monomer

Graftingamount

/(μg/cm2)

Contact

angle/(°)

Purewater

flux/[L/(m2·h)]

Protein/bio

system

Fluxrecoveryratio/

proteinadsorption

Freeradical

grafting

polymerization

PESflatmem

brane[63]

MCP

82.90±237(Nas

cent)

46.43±1.93(Modi

fied)

after3s

156.3(Nascent)

107.8(Modified)

at0.1MPa

1.0mg/mL

ofBSA

60.6%(Nascent)

87.0%(Modified)

(Fluxrecoveryratio)

PSfflatmem

brane[64]

SBMA

≈1800

≈75(Nascent)

≈30(Modified)

0.02012(Nascent)

0.04672(Modified)

at1mmHg

1.0mg/mL

ofBSA

42.37%(Nascent)

98.01%(Modified)

(Fluxrecoveryratio)

PVDFflatmem

brane[33]

SBMA

608

90(Nascent)

59(Modified)

≈130(Nascent)

≈115(Modified)

at0.25MPa

1.0mg/mL

ofBSA

47.6%(Nascent)

85.1%(Modified)

(Fluxrecoveryratio)

PVDFhollowfi

bermembrane[5]

MPDSAHa;

SBMA

247

338

75.9(Nascent)

15(Modified)

40(Modified)

after100s

1592(Nascent)

1482(Modified)

1365(Modified)

at0.1MPa

1.0mg/mL

ofBSA

52.0%(Nascent)

93.4%(Modified)

92.8%(Modified)

(Fluxrecoveryratio)

PVDFhollowfi

bermembrane[6]MPDSAH

513

875±21 (Nascent)

22.1±2.0(Modi

fied)

after5.5s

1592(Nascent)

1319(Modified)

at0.1MPa

1.0mg/mL

ofBSA

52.0%(Nascent)

97.8%(Modified)

(Fluxrecoveryratio)

191

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

书书书

Continued

Methods

Nascent

membrane

Zwitterionic

monomer

Graftingamount

/(μg/cm2)

Contact

angle/(°)

Purewater

flux/[L/(m2·h)]

Protein/bio

system

Fluxrecoveryratio/

proteinadsorption

Freeradical

grafting

polymerization

Cellulose

flat

membrane[62]

CBMA

-20(Modified)

-BSA

≈58μg/cm2(Nas

cent)

≈05μg/cm2(Modi

fied)

(Proteinadsorption)

Cellulose

flat

membrane[14]

SBMA;

MCP

47.64±140(Nas

cent)

21.7±186(Modi

fied)

20.3±133(Modi

fied)

-Plateletpoor

plasma

1.8μg/cm2(Nascent)

<1μg/cm2(Modified)

<1μg/cm2(Modified)

(Proteinadsorption)

Cellulose

flat

membrane[32]

SBMA

≈80%

(polymeriza

tiondegree)

≈620(Nascent)

≈100(Modified)

at0.02MPa

1.0mg/mL

ofBSA

>90%(Modified)

(Fluxrecoveryratio)

PUflatmem

brane[61]

SBMA

≈4%

(Grafting

de

gree)

60±2(Nascent)

33±2(Modified)

-Human

venousblood

13.5(Nascent)

35.6(Modified)

(Thrombintime,TT)

PETbflatmem

brane[65]

SBMA

3-40

-35467(Modified)

at0.1MPa

0.1g/Lof

IgG

018

μg/cm2(Modi

fied)

(Proteinadsorption)

291

书书书

Continued

Methods

Nascent

membrane

Zwitterionic

monomer

Graftingamount

/(μg/cm2)

Contact

angle/(°)

Purewater

flux/[L/(m2·h)]

Protein/bio

system

Fluxrecoveryratio/

proteinadsorption

Photoinitiated

grafting

polymerization

PEShollowfiber

membrane[46]

SBMA;

MPC

≈1700μg/

cm2≈1670

μg/cm2

≈90(Nascent)

≈40(Modified)

≈30(Modified)

≈550(Nascent)

≈350(Modified)

≈400(Modified)

at0.1MPa

106cells/mL

ofPseudo

monasputida

≈0.4(Nascent)

≈0.8(Modified)

≈0.9(Modified)

(Fluxrecoveryratio)

Woven

PPfi

ber[66]

TM∶SAc

(1∶1)

≈12.5%

(Grafting

de

gree)

106(Nascent)

27(Modified)

≈6100g/(m2·h)

(Nascent)

≈5300g/(m2·h)

(Modified)

at0.1MPa

1.0g/Lof

BSA;

1.0g/Lof

Lyz

91.4%(Modified)

90.2%(Modified)

(Fluxrecoveryratio)

PPflatmem

brane[27]

SBMA

≈440

145±4(Nascent)

≈20(Modified)

after5s

1091(Nascent)

5250(Modified)

at0.5MPa

1.0g/Lof

BSA;

10g/L

of

Lyz

40%(Nascent)

97%(Modified)

81%(Modified)

(Fluxrecoveryratio)

Plasmainduced

grafting

polymerization

PVDFflatmem

brane[29]

SBMA

≈900

105(Nascent)

≈30(Modified)

1.0g/Lof

humanfibrin

ogen

100%(Nascent)

10%(Modified)

(Proteinadsorption)

391

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

书书书

Continued

Methods

Nascent

membrane

Zwitterionic

monomer

Graftingamount

/(μg/cm2)

Contact

angle/(°)

Purewater

flux/[L/(m2·h)]

Protein/bio

system

Fluxrecoveryratio/

proteinadsorption

Plasmainduced

grafting

polymerization

ePTFEdflat

membrane[68]

SBMA

850

≈120(Nascent)

≈25(Modified)

-plateletpoor

plasma

100%(Nascent)

20%(Modified)

(Relativeproteinad

sorption )

PPfibrous

membrane[69]

SBMA

≈2400(at

mospheric

plasmatreat

ment)

0(Nascent)

135(Modified)

fordiiodomethane

1.0g/Lof

humanfibrin

oge

100%(Nascent)

<10%(Modified)

(Relativeproteinad

sorption)

Combined

methods

PPnonwoven

membrane (Plas

ma+UV)

[48]

MPDSAH

327.7μg/cm2

123(Nascent)

≈20(Modified)

after3s

11370(Nascent)

9799(Modified)

at0.1MPa

1.0g/Lof

BSA

30%(Nascent)

90%(Modified)

(Fluxrecoveryratio)

WovenPPfiber

(UV

+AT

RP)[11]

SBMA

≈17%

(Grafting

de

gree)

106(Nascent)

≈20(Modified)

≈6.0kg/(m2·h)

(Nascent)

≈5.6kg/(m2·h)

(Modified)

at0.1MPa

1.0g/Lof

BSA

46.5%(Nascent)

91.6%(Modified)

(Fluxrecoveryratio)

  a 3(methacryloylamino)propyldimethyl(3sulfopropyl)ammoniumhydroxide(MPDSAH).

b poly(ethyleneterephthalate)(PET).

c [2(methacryloyloxy)ethyl]trimethylammoniumchloride(TM);3sulfopropylmethacrylatepotassiumsalt(SA).

d Expandedpoly(tetrafluoroethylene)(ePTFE).

491

Theatom transferradicalpolymerization(ATRP)processdevelopedby

Prof.KrzysztofMatyjaszewskiin1994,whichiswellknownasonekindof

“living”/controlledgraftingpolymerizationforitsversatilitytomonomers,mild

polymerizationconditions,toleranceinimpurities,andtheabilitytosynthesize

welldefinedpolymersinacontrolledmanner[5,6,11,62].Inrecentyears,surface

initiatedatomtransferradicalpolymerization(SIATRP)ismostwidelyusedto

graftzwitterionicchainsorbrushesonthemembranesurface[20].Thismethod

isabletodesignandtailorthegraftdensity,chainlengthandchemical

compositionofzwitterionicpolymeronmembranesurface,asaresult,the

morphologyand propertiesofthemembranesurfacecanbetuned[14,64].

Moreover,comparedwiththeconventionalradicalpolymerization,SIATRP

can produce more uniform and smooth poly(zwitterion) surface on

membrane, which is of great significance for the antiproteinfouling

performanceduringtheMForUFprocess[20].Itiscrucialtochoosethe

suitablesolventforthepoly(zwitterion)graftingonmembranesurface[20]:① it

shouldpromotethesuccessfulcontrolledpolymerizationofgraftedzwitterionic

chains;② itshouldmaintaintheintegrityofmembranebulkwithoutdamageor

dissociation;③ itshouldbeenvironmentalfriendly.

Inourpreviousworks[5],SIATRPwasusedtopreparehydrophilicPVDF

hollow fibermembranewithimproved antiproteinfouling performance,in

whichthegraftingamountofpoly(sulfobetaine)waswellcontrolled.Liuet

al.[14]preparedthreekindsofpoly(zwitterion)graftedcellulosemembranes

viaSIATRP.Allthezwitterionicmonomerswerepolymerizedfromtheinitiator

immobilizedcellulosemembranesurfacesinamixturesolventofwaterand

methanolusingCuBrandbipyridineascatalysts.Theirstudyconfirmedthat

thepoly(sulfobetaine)modifiedmembranesurfacewasaseffectiveasthe

poly(phosphobetaine)modifiedmembranesurfaceforresistingadsorptionof

proteinandadhesionofplatelet.YangandUlbricht’swork[65]demonstrated

that polySBMA could be grafted from tracketched poly (ethylene

terephthalate)(PET)membranesurfaceviaSIATRP.Thegraftingprocess

waswellcontrolledbyadjustingtheATRPconditionsandalinearincreaseof

degreeofgraftingcouldbeachieved.Theresultantmembranewaspotential

membraneadsorberforproteinpurification.

591

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

Fortheinertmembraneslackingactivegroups(suchasfluoropolymer

andpolypropylenemembranes),thesurfacemodificationusingSIATRPoften

involvesorganicsolventsandmultistepstrategies[71].ActivatorRegenerated

byElectronTransferATRP(ARGETATRP),anewATRPinitiatingsystem,is

developedtofacilitatesolutionandemulsionATRPinaqueousmedia[72].This

processcantolerateexcessreducingagentsothatCu(II)canbereducedto

Cu(I)rapidlyinthepolymerizationsystem andthencatalyticpolymerization

ATRPmonomer[73].Thus,thereactioncanbeconductedinthepresenceof

limited amounts ofair[62]. Forexample, water/methanoland CuBr/Bpy

complexcouldbeusedasthesolventandcatalyst,respectivelytograftthe

poly(sulfobetaine)from thesurfaceofPVDFBrmembrane[5].Inaqueous

media,thestructureofthecatalyticspeciesisamonocationiccomplex[Cu

(I)(Bpy)2]+ withahalidecounterion.Theioniccatalystspeciesinaqueous

mediaareactiveenough,asaresult,theadditionofwaterinthesolventwill

increasethepolymerizationrate[11].Yuan’sgroup[62]performedthegrafting

polymerizationofcarboxybetainebrushfrom cellulosemembraneviaARGET

ATRP.Theresultsshowedthatthegraftedcellulosemembranehadimproved

resistancetononspecificproteinadsorptionandplateletadhesion,aswellas

reducedhemolysisrate.

3.1.2 Physisorbedfreeradicalgraftingpolymerization

Azoandperoxideinitiators,suchasazobisisobutyrylnitrile(AIBN),are

adoptedasasourceofradicalsforgraftingpolymerizationofvinylandacrylic

monomersonthesurfaceofpolymermembranesincetheyareabletoattach

topolymericmembraneandtobedecomposedintoradicalsatmoderate

temperature[33,74].Huetal.[75]proposedaphysisorbedfreeradicalgrafting

techniquetocreateradicalsonpolymersurfaceandthenreactwithhydrophilic

polymers.Usingthistechnique,thesulfobetainemonomerscanbecovalently

attachedontoboththesurfaceandtheinsideofmembrane,andthegrafting

polymerizationcan be carried outwithoutlimitation ofmore complicated

proceduressuchashighenergyreactorsorintenselightsources.PolySBMA

wasfirstlygraftedfrom thesurfaceofPVDFmembraneviaphysisorbedfree

radicalgraftingtechniqueandthewatercontactangledecreasedfrom59°to

17°within120swasachievedatthesurfaceofmembranewith608μg/cm2of

691

graftingamount[33].

3.1.3 Redoxgraftpolymerization

Surfacemodificationbyredoxgraftpolymerizationusingcerium ion

(Ce(IV))asinitiatorisanotherwellknownmethodforthepolymerization

ofzwitterionicmonomer[63].Thisprocesscanbeperformedatmoderate

temperatureandwillmakethesidereactionminimized,thus,theCe(IV)

induced grafting polymerization has a minimalextentofungrafted

homopolymerandahighgraftingefficiencyofinitiator[6,77,78].Duringthe

graftcopolymerization,theCe(IV)isreducedtocerousion(Ce(III)),

andfreeradicalsitesarecreatedonthemembranesurface.Theradical

sitesinitiate graftcopolymerization ofthe vinylgroup in zwitterionic

monomerswhicharepresentinthereactionsolution.

Ourprecedingwork[4,6]preparedahighlyhydrophilicandantiprotein

foulingPVDFhollow fibermembranewithagood stabilityviaATRP of

HEMA and subsequent Ce(IV)induced grafting polymerization of

MPDSAH.Thevalueofcontactangledroppedto22.1°andtheamountof

proteinadsorptionalmostequaledzeroasthegraftingamountreached

513μg/cm2.ThemodifiedPVDFmembranehadsignificantlyreducedthe

extentofproteinfoulingandmostofthefoulingwasreversible.Shenand

Lin[78]graftedpoly(sulfobetaine)onthecellulosemembranesurfaceusing

cericammonium nitrate(CAN)asinitiator.Liu’s[63]studyreportedonthe

graftingpolymerizationofzwitterionicmonomer,MPC,onthemembrane

surfacebyredoxgraftpolymerizationusingthesameinitiator(i.e.CAN),

whichonlyrequired one step reaction and avoided the complexand

unfavorablepretreatmentprocessandhydroxylatedtreatment.Allother

propertiesofthemodifiedmembranearelistedinTable1.

3.2 Photoinducedgraftingpolymerization

Photo(UV)induced“graftingfrom”polymerizationmethodisanother

commontechniqueforantifoulingmodificationofmembranesurfacedueto

thelow investmentcost,mild reaction conditions, simple and versatile

operation[27,46,79].Thisprocessoccursatthemembraneskinandeffectively

improvesthesurfaceperformancesofthemembranewithoutaffectingthebulk

791

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

propertiesbecauseoftherelativelylowenergyofUVsource[47].Thegrafting

amountand permeate performance ofthe modified membrane can be

controlledconvenientlyinUVinducedgraftingprocess[67,80].

Forthemembranemadefrom thephotosensitivebasepolymer(photo

reactivesidegrouporpartofpolymerbackbone),thisapproachinvolvesthe

directgeneration offree radicalsfrom the membrane surface underUV

irradiation[23,79].PESisoneoftheintrinsicphotoreactivepolymers,withwhich

thehollowfibermembranepreparedcanbemodifiedbyphotograftingofMPC

andSBMAtoimprovetheantibiofoulingproperties[46].

Forthe membranes with less electroactive property, such as PP

membraneandPVDFmembrane,initiatingradicalsitesshouldbegenerated

atthemembranesurfacebytheintroductionofphotosensitivegroupsasa

resultofthe reaction ofa photo initiatorwith the membrane underUV

irradiation[23].Benzophenon(BP)anditsderivativesareusuallyneededfor

the initiation ofthe UVassisted grafting polymerization ofzwitterionic

monomersatthesurfaceofsuchmembranes[20,23].Inthiscase,BP is

decomposedtostarterradicalsthatthen transferto the membrane and

abstracthydrogenatom from surroundingchemicalspecies,contributingto

thegenerationofinitiatingradicals[20,23].BPcanbecoatedontothemembrane

surfacebyadsorptionmethodwhichcouldminimizethehomopolymerization

ofmonomerandenhancethegraftingefficiency[20,81].ComparedwithPVDF

membrane,UVinduced grafting polymerization is more suitable forPP

membraneduetothepresenceofactivetertiaryhydrogeninPP[27].ThePP

microporousmembrane can be highly hydrophilized by the UVinduced

graftingofpolySBMA,thegrafting amountand theresistancetoprotein

adsorption can be optimized through altering SBMA concentration, BP

concentrationandUVtime[27].Allotherpropertiesofthemodifiedmembrane

arelistedinTable1.

3.3 Plasmainducedgraftingpolymerization

To increase the hydrophilicity in orderto obtain the lowfouling

membranesurface,treatmentusingplasmahasbeenextensivelystudied

overthelasttwodecadestoanchorthezwitterionicgraftchainsonthe

891

surface ofmembrane efficiently[20,23,68]. Surface zwitterionization by

plasmainducedgraftingpolymerizationiseasytooperateandespecially

suitable forbiomedicalmembrane modification in the dry and clean

process[69].Ithasbeenreportedthatlowtemperatureplasmainduced

graftinghasbeenperformedtoimprovethepermeatefluxandantifouling

performanceofMFandUFmembranes[82].

Plasmainducedgraftingofpoly(zwitterion)chainsonthemembrane

surfaceincludestwomainprocesses:① destructionofapolymersupportby

plasmaactivating(generationofradicals);② depositionofanewzwitterionic

layeronthemembranesurfacebyzwitterionicpolymerization[23].Theycanbe

balancedbyaltering thekindsofplasmagasand theapplied process

parameters.Thus,thegraftingamountandthelengthofzwitterionicchains

canbecontrolledbybothplasmaparameters,suchaspressure,power,

sampledisposition,treatmenttime,andpolymerizationconditions,suchas

monomerconcentration,kind ofsolvent,grafting time,asaresult,the

thicknessofthepoly(zwitterionic)layercanbecontrolleduptotheangstrom

levels[20,23].Moreover,thedynamicplasmaflownotonlypresentsalonger

glowdistancethanthestaticplasmabutalsoproduceslargerquantityof

peroxideson the membrane, and even excites the second membrane

layer[82].Recently,Lee’s[69]andChang’s[29]groupsemployedatmospheric

plasmainduced surface copolymerization method to prepare polySBMA

grafted PP and PVDF membranes. The results suggested that the

hemocompatiblenatureofgraftedpolySBMAbycontrollinggraftingamountvia

atmospheric plasma treatmentgives a greatpotentialin the surface

zwitterionizationofhydrophobicmembranesforuseinhumanwholeblood.All

otherpropertiesofthemodifiedmembranearelistedinTable1.

Althoughplasmainducedsurfacezwitterionizationprovideshighergrafting

yieldandshortermodificationtimethansurfacegraftingviaATRP,ithasa

relativelyhighcostoftheoperationbecauseoftherequirementofavacuum

system[20,29,69].Additionally,plasmatreatmentusuallyresultsinthechemical

degradationofgrafted poly(zwitterion) due to the high energyofion

bombardment[29].

991

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

3.4 Combinedmethods

Recently,combinedtechniqueswerepresentedforgraftingpolymerization

ofzwitterionicmonomeronmembranesurface.ATRPwasusuallycombinedwith

initiatorimmobilizationasthepretreatmentthroughusingchemicaltreatment[5]

andUV[11,47,83].Forexample,thepoly(SBMA)canbetetheredontothesurface

ofPPflatmembranethroughacombinedmethodofUVinducedsurfacegraft

polymerizationfollowedbyATRPtoensurethehighdensityandcontrollable

structureofthepoly(SBMA)chains.Theresultsdemonstratedthegoodanti

proteinfoulingperformanceofmodifiedPPmembrane[11].Inaddition,O2plasmapretreatmentcombiningwithUVinducedgraftpolymerizationcanbe

usedtoachievethegraftingpolymerizationofMPDSAHonthePPnonwoven

fabricmembrane.Themodifiedmembraneexhibitedhighfluxrecoveryratio

andexcellentantifoulingstabilityduringthemicrofiltrationprocessofBSA

solution[48].Allotherpropertiesofthe modified membrane are listed in

Table1.

3.5 Comparisonofdifferentgraftingpolymerizations

Table2presentsacomparisonbetweenthefourgraftingpolymerizations.

Hereweonlyattempttogiveageneralimpressionaccordingtothepresented

resultsin literature,because one method may be influenced by many

parameterssimultaneously.Freeradicalgraftingpolymerizationmayleadto

undesirable surface changes and contamination due to the multistep

strategies,whichresultsinarelativelylowuniformityofpoly(zwitterionic)layer

onthemembranesurface.Thegraftingpolymerizationinducedbyphotoor

plasmaprobablyprovidessimpleoperationandgoodmembranesmoothness,

butitshigh costsofequipmentleadsto the drawbacksforlargescale

application.Combinationofthedifferentgraftingtechniquesiscomplexin

regardtocostandenvironmentproblems.However,itoftencontributesto

high grafting amount and multifunctions of poly(zwitterionic)grafted

membrane. In addition, mostofthe grafting polymerization methods

experiencedthereductionofpurewaterfluxduetotheporeplugging.Since

allofthegraftingpolymerizationmethodscanbeemployedtograftzwitterionic

002

polymeronthemembranesurfacetoimprovethehydrophilicityandfouling

resistancetoproteins,wecanmakeupthefluxreductionbyotherways,such

astheincreaseinoperationalpressureandtemperature,ornotconsiderit

furtherwhentherequirementallows.

Table2 Advantagesanddisadvantagesofmodificationmethods

Methods UniformityGrafting

amount

Relative

fluxSimplicity

Environment

pollutionCost

Freeradical

graftingpolymerizationLow Low Low Common Common Low

Photoinduced

graftingpolymerizationCommon Low Low High Low High

Plasmainduced

graftingpolymerizationHigh High Low High Low High

Combinedmethods Common High High Low Common High

  

4 Conclusionsandprospects

ProteinfoulingisofgreatimportanceforthemembranefoulingofMF/UF

process,whichisthefirststepofmembranefoulinginitiatingthefollowing

platelet adhesion, bacterial biofilm formation and other biofouling

phenomenon.Therefore,the growth ofantiproteinfouling materials and

associated membrane modification(graftingpolymerization) is critically

significant,especiallyforbiomedicalapplication.Zwitterionicmaterialsthat

possessthemaximum polarityform thehydrationlayerthroughelectrostatic

interaction(e.g.solvationofion)andhydrogenbond,resultinginthesuper

highhydrophilicityand superstableantiproteinfouling property.Withthe

understandingofantiproteinfoulingmechanismandthegraftingpolymerization

principleofzwitteriononthemembranesurface,futureresearchdirection

couldfocusonthedevelopmentofnovelzwitterionicmonomersthatpossess

morefunctionalgroupsandcombinedgraftingpolymerizationmethodsthat

renderthezwitterionicpolymermoreefficientanddurableonthemembrane

surfacetomeetchallengeoftheexcellentmembraneuniformityandlongterm

102

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

stableperformance.Basedonthese,thecostontechniquesandoperations

shouldbereducedappropriatelybydesigningtheoptimalmeanstosynthesize

zwitterionicmonomersandcompletegraftingpolymerizationsonthemembrane

surface.Inshort,thepoly(zwitterion)graftedmembranewouldbeofgreat

interestintheantiproteinfoulingstrategiesinMF/UFmembrane,whichhelps

toexpandthemembraneapplicationinthefieldsofagrofood,biomedicine

andotherbiofiltrationprocess.

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XiaolinWang isaprofessorofDepartmentofChemical

EngineeringandtheDirectorofBeijingKeyLaboratoryfor

Membrane Materials and Engineering at Tsinghua

University.ProfessorWangreceivedB.Eng.(1983)and

M.Eng.(1986)degreeinchemicalengineeringfrom

NanjingInstituteofChemicalTechnology,China,andhe

receivedDr.Eng.(1995)degreeinchemicalengineering

fromtheUniversityofTokyo,Japan.ProfessorWanghas

beenengagedinmembranetechnologyandelectrochemistryforabout20years.His

researchhastouchedmanyaspectssuchastransportphenomenainchargedporous

membranes,watertreatmentand productseparation with membraneprocesses,

fabricationofnanoporouspolymericmembranesbythermallyinducedphaseseparation

method,aswellasdevelopmentofelectrochemicalmaterialsandprocesses.Professor

Wanghaspublishedmorethan200papersandtakenoutmorethan10patents.Heisa

402

subeditorofMembraneScienceandTechnology(inChinese)from2004,astanding

editorofWaterTreatmentTechnology(inChinese)from2006,astandingcommitteeof

theSocietyofSeawaterDesalinationandWaterReuseinChinafrom2006,avicedean

oftheMembraneEngineeringandApplicationCommitteesubjectedtoChinaMembrane

IndustryAssociationfrom2006,thesecretarygeneralofBeijingMembraneSocietyfrom

2005,thecouncilmemberofAseanianMembraneSocietyfrom 2004.Hewasa

chairmanofthe3thConferencesofAseanianMembraneSocietyin2006,Beijing.

502

InvestigationsandApplicationsofNewTypeIonExchangeMembranes

T.W.Xu,etal.

LabofFunctionalMembrane,DepartmentofChemistry,University

ofScienceandTechnologyofChina,Hefei,China

Abstract:Thedevelopmentofsyntheticionexchangemembrane(electro

membrane)reportedbyJudaandMcRaein1950stimulatedbothcommercial

and academic interestin such membranes and the related processes.

Nowadays,synthetic ion exchange membraneshave been improved by

variousmethodsandhavemanypracticaluses.Theprocessesbasedon

electromembranessuch asdiffusion dialysis,conventionalelectrodialysis

(CED),electrodialysiswithbipolarmembranes(EDBM),etc.,canrealize

somenewsynthesisprocessestoachievethemaximalutilizationofresources

andpollutionprevention.Theycanalsobeflexiblycoupledwithmanyother

technologiesandobtainabetterfunctionbymeansoftechnologicalsymbiosis

andcanrealizeclosingloopswheninputtingwastematerialsasthefeedstock

andcarryingoutproduction,resourceregenerationandeffluenttreatmentat

thesametime.Inthisreport,preparationofnovelionexchangemembranes

andtheirnewapplicationswillbedescribed.Specifically,anewplatform,

polyacylationofionizedmonomers,forionexchangemembranespreparation

willbeintroducedindetail.Followingthisapproach,alibraryofSCTSAPsis

underconstruction by designing a variety ofionized monomers and

comonomersasbuildingblocksinordertotunethestructuresoftheside

chainsandmainchainsofSCTSAPs,respectively.

Keywords:ionexchange membranes; electrodialysis; diffusion dialysis;

ionizedmonomers;polyacylation;sidechains;mainchains

602

1 Introduction

Ionexchangemembranes(IEMs)areanewbranchofpolymers,which

havebeenusedasabulkplatformforprocessingandproductionofmaterials,

chemicalsandenergy.Thedevelopmentofsyntheticionexchangemembrane

(electromembrane)reportedbyJudaandMcRaein1950stimulatedboth

commercialand academic interestin such membranes and the related

processes[1].Nowadays,thesyntheticionexchangemembraneshavebeen

improvedbyvariousmethodsandhavemanypracticaluses[2-3].TheIEMsare

usuallypreparedfrom monomersorpolymersthatareavailabletointroduce

ionicgroupsintothefinalformedmembrane.Preparationofionexchange

membranesstartingwithmonomersbypolymerizationorpolycondensation

requiresthatatleastoneofthesemonomersmustcontainacationicoran

anionicmoiety.ThemostsignificantandthelargestscaleappliedIEMsarethe

perfluorinatedmembranesused inthechloralkaliproductionand energy

storage orconversion system (fuelcell). Even though perfluorinated

membraneshaveexcellentmechanicalandthermalstability,thehighpriceof

theperfluorinatedmaterialandmanyweaknessessuchasahighdegreeof

swellingandapoorpermselectivityinperfluorinatedmembraneshavedirected

theattentionofpreparing membranesfrom nofluorinematerial,suchas

hydrocarbonPE,polypropylene(PP),poly(vinylidenefluoride)(PVDF),

polyetherketone(PEK),polyethersulfone(PES),polyetherketone(PEK),

poly(phenylene sulfide) (PPS), PPO (polypropylene oxide), PBI

(polybenzimidazole),etc[4-5].Thankstotheoutstandingchemical/thermal

stability and interesting acid/base amphoteric characteristic of the

benzimidazolering,sulfonatedbenzimidazolecontainingpolymers(SBIPs)as

promising candidate materials forIEMs have been attracting extensive

attention.Meantime,stimulatedbythedevelopmentofnew ionexchange

membraneswithbetterselectivity,lowerelectricalresistance,andimproved

thermal, chemical, and mechanical properties, many ionexchange

membranesbasedprocessessuchaselectrodialysis(ED),electrodialysis

withbipolarmembranes(EDBM),electrodeionization(EDI),diffusiondialysis

(DD),Donnandialysis,reverseelectrodialysis(RED),etc.havebeenwidely

702

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

usedinmanyprocesses,suchaswaterdesalination,cleaningproductionor

separation,resourcesrecycling,powergeneration,andsensitiveelectrode

preparation[6].ThestudywillgiveabriefintroductionoftheIEMspreparedby

polyacylationofionizedmonomersandsomenewapplicationsofionexchange

membranesbasedprocesses.

2 Preparationofionexchangemembranebypolyacylationofionizedmonomers

Byreferring the structuremorphologyofthe Nafion membranes,we

developedanew routeforpreparingIEMsfrom sidechaintypesulfonated

aromaticpolymers(SCTSAPs)[7-8].Thesenew polymersincludearobust

aromaticmainchaintogiveahighmechanicalandchemicalstabilityand

pendantsulfonic acid groupslinked to the mainchain to give a good

electrochemicalproperty. A schematic preparing route ofthese novel

membraneswasillustratedinFig.1.Atfirst,4,4′oxydibenzoicacid(ODBA),

4phenoxybenzoicacid(POBA),3,3′,4,4′tetraaminobiphenyl(TABP),

disodium2,2′di(sulfopropyloxy)biphenyl(SBP)andEaton’sreagentwere

mixedandpolymerizedtogetSPEKEBIpolymer.Then,theSPEKEBIpolymer

wasdissolvedinNmethylpyrrolidone(NMP)togetadilutesolution;the

obtainedsolutionwascasted onaflatglassplateand dried togetthe

membrane.Thepreparedmembranesexhibitedprotonconductivityhigher

thanNafionwhilemaintaining alow swellratio.Thissuggeststhatthese

membranesarecompetitivealternativestoNafionmembranesforfuelcell

process. Interestingly, the membranes were prepared by a direct

polyacylationofionizedmonomers.Themainadvantagesofthispreparing

routecan be summarized in two points.Atfirst,the functionalgroups

(sulfonatedgroups)wereintroducedtothemonomersbeforepolymerization

reaction.Theadvantageofpresulfonation(sulfonationbeforepolymerisation)

comparedwithpostsulfonation(sulfonationafterpolymerisation)isthatthis

givesanaccuratecontrolofthenumberandpositionofthesulfonategroupby

directly using sidechainsulfonated aromatic monomers. Since the few

reportedsidechainsulfonatedaromaticmonomerswereusuallyprepared

underharshconditionswithacomplicatedreactionprocess.Incontrast,

802

Fig.1 (a)schematicillustrationoftheconceptof“onepotacylation/heterocyclization

copolycondensation”;(b)syntheticroutetoSPEKEBI[8]

wepresentonepotsynthesisofdisodium2,2′di(sulfopropyloxy)biphenyl

(SBP) as a novelsidechainsulfonated aromatic monomer and its

polyacylationasafacileandversatileapproachtoSCTSAPsforthefirsttime.

TheintroductionofSBPgroupensuresthattherehasenoughnumberofacidic

sulfonategroupsonone polymerchain.Furthermore,the polymerization

reactionswereconductedbyapolyacylationprocess.Bytaketheadvantage

ofacylationreactionbetweencarboxylicacidandelectronricharenegroupsin

acidiccondition(P2O5/polyphosphoricacid,P2O5/CH3SO3H,etc),aseriousof

sidechainsulfonatedaromaticmembranescanbeprepared.Thepreparation

routeisasimple,higheffectiveprocess,sincethereactionwastakesplaceina

902

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

“onepot”waytocombinethesyntheticadvantageofionizedmonomersfor

polyacylationandthestructuraladvantageofaromaticheterocycles.Considering

therichlibraryofpossibleionizedmonomers,polyacylationofionizedmonomers

opensanewdimensionforthepreparationofionexchangemembranes.

3 Newapplicationsofionexchangemembranes

In addition to the membrane preparation research, we contributes

significantlytotheindustrialapplicationoftheED basedtechnologiesfor

cleanerproduction/separation assummarized in Fig.2.These industrial

explorationsincludetheseparationofbioproductsfrom byproducts(organic

acidsseparationfrom fermentationbroths,γaminobutyricacid (GABA)

separation from NH4Cl, etc), high salinity wastewater treatment

(tetramethylammonium hydroxide (TMAH) recovery from developer

wastewater,nitrile butadiene rubberwastewatertreatment,pichlorohydrin

wastewatertreatment,electroplatingwastewatertreatment,etc).

Fig.2 Theapplicationofionexchangemembranesbasedprocess

Forexample, a complicated, laborconsuming, and environmental

hazardousprocesswasneededintheconventionalproductionofthegluconic

acid(Fig.2). When bipolarmembrane (BPM) is introduced to this

preparationroute,thewatersplitting H+ ionscanbeused toacidifythe

gluconatesalt;whichthewatersplittingOH- ionscanbeusedastheraw

materialforreaction.Inthisway,fivesteps(inthecolorboxesoftheFig.3)

canbereduced.Thisimprovedrouteisnotonlyenergysavingbutalso

012

environmentfriendly.ApilotBPMEDsetupwasestablishedforgluconicacid

productioninZhangshu,JiangxiProvince,China.Theconversionrateof

gluconatewashigherthan95.6% withcurrentefficiencyof71.5%.

Fig.3 Theconventionalroutefortheproductionofgluconicacid(graysquaremeans

thesestepscanbereducedbyusingtheEDBM technology,EDBM,electrodialysis

withbipolarmembranes)[6]

TMAHisthemostcommonlyuseddeveloperinduringthemanufacturing

ofsemiconductorsandphotoelectricindustries.Alargeamountofwastewater

containingTMAHandisgenerated.Consideringthehighlyalkalinityandtoxic

propertyoftheTMAH,thetreatmentofTMAHcontaineddeveloperwastewater

isatoughanddifficultproblem.Theconventionalavailabletechnologiessuch

asbiologicaldegradation,chemicaloxidative,andadsorptionusuallyhave

lowefficiencyandhighprocesscostfordeveloperwastewatertreatment.In

practical,theprocesscostfortreatingdeveloperwastewaterinChinaisas

highas~200 $/t.Byconsideringthemaincharacteristicsofdeveloper

wastewater,TMAHcanbeseparatedfrom thechelatingorganicagentsand

surfactantbytheintroductionofanelectrodialysisprocess.Therefore,the

electrodialysistechniquewasemployedfortherecoveringandconcentratingof

TMAHfrom developerwastewater[9].Theeffectofcurrentdensityonthe

112

国际工程科技发展战略高端论坛

膜技术在水和气体净化中的应用

recoveryprocesswasinvestigatedbyconsideringthestabilityofmembranes

andprocesscost.Resultsindicatedthattheoptimalcurrentdensitywas

chosenat30mA/cm2.TMAHcanbeconcentratedintherangeof7.45% -

833%.Theusedmembranesintheexperimentswerestableandsuitablefor

thiswastewatertreatment.The totalprocesscostwasestimated to be

36.4$/twithoutconsideringtheprofitoftherecoveredTMAH.Naturally,

electrodialysisisa costeffective and environmentfriendlytechnologyfor

treatingdeveloperwastewater.

4 Conclusions

Ion exchange membranes and related processes have attracted

multidisciplinaryattentionsandalsofoundavarietyofapplicationssuchas

waterdesalination,cleaningproductionorseparation,resourcesrecycling,

powergeneration,andsensitiveelectrodepreparation.Inthisstudy,the

“onepot”polyacylationofionizedmonomershasbeenproposedforthe

synthesisofsidechaintypesulfonatedmembranes.Thepreparationstreategy

achieve the quantitative design ofmembranes combine the synthetic

advantageofionizedmonomersforpolyacylationandthestructuraladvantage

ofaromaticheterocycles.Someexamplesforthenew applicationsofion

exchangemembranesforbioproductsseparationandwastewatertreatment

werealsobrieflyintroduced.

References

[1] JudaW,McRaeW A.Coherentionexchangegelsandmembranes.JAm Chem Soc,1950,

72:1044.

[2] XuTW.Ionexchangemembranes:Stateoftheirdevelopmentandperspective(review).J

MembrSci,2005,263(1-2):1-29.

[3] LeongJX,DaudW RW,GhasemiM,etal.Ionexchangemembranesasseparatorsinmicrobial

fuelcellsforbioenergyconversion:Acomprehensivereview.Renewable&SustainableEnergy

Reviews,2013,28:575-587.

[4] KoterS,PiotrowskiP,KerresJ.Comparativeinvestigationsofionexchangemembranes.J

MembrSci,1999,153:8390.

[5] RikukawaM,SanuiK.Protonconductingpolymerelectrolytemembranesbasedonhydrocarbon

polymers.ProgressinPolymerScience,2000,25(10):1463-1502.

[6] XuTW,HuangC H.Electrodialysisbasedseparationtechnologies:A criticalreview.AIChE

212

Journal,2008,54(12):3147-3159.

[7] ZhangZH,WuL,VarcoeJ,etal.Aromaticpolyelectrolytesviapolyacylationofprequarternized

monomersforalkalinefuelcells.JMaterChemA,2013,1:2595.

[8] ZhangZH,XuTW.Onepotacylation/benzimidazolizationcopolymerizationapproachtoside

chaintypeprotonconductivemembranes.JMembrSci,2013,446:121-124.

[9] WangYM,Zhang Z H,Jiang C X,etal.Electrodialysis process forthe recycling and

concentratingoftetramethylammoniumhydroxide(TMAH)fromphotoresistdeveloperwastewater.

IndEngChemRes,2013,52(51):18356-18361.

T.W.Xu isaProfessorofTheUniversityofScience

andTechnologyofChina.HereceivedhisBachelor’s

degreein1989andmaster’sdegreein1992fromHefei

UniversityofTechnology,China.HereceivedhisPh.D.

ofChemicalEngineeringin1995fromTianjinUniversity,

ChinaandPostPh.D.ofPolymerSciencein1997from

NankaiUniversity,China.Prof.XuhadbeenVisiting

ScientistofUniversityofTokyoandTokyoInstituteof

Technologyduring2000-2001.HehadbeenVisitingProfessorofGwangjuInstituteof

ScienceandTechnology,Koreaduring2006-2008.ProfessorXuhasguided42

doctoralstudents,33graduatestudentsandpostdoctoral6untilnow.Hehadpublished

morethan230SCIindexarticlesandapplicationsforinventionpatents42(23

License).ProfessorXuwasselected“NewCenturyExcellentTalents”ofMinistryof

educationChinain2004andawardedOutstandingYouthFoundationofChinain2010.

ProfessorXuservesasexecution/guesteditorandeditorialboardof8kindsofSCI/EI

internationaljournals,andservesasmonographeditorofthreeinternationalenglish

book.

312

后  记

科学技术是第一生产力。纵观历史,人类文明的每一次进步都是由重大的科

学发现与技术革命所引领和支撑的。进入 21世纪,科学技术日益成为经济社会

发展的主要驱动力。我们国家的发展必须以科学发展为主题,以加快转变经济发

展方式为主线。而实现科学发展、加快转变经济发展方式,最根本的是要依靠科

技的力量,最关键的是要大幅提高自主创新能力,要推动我国经济社会发展尽快

走上创新驱动的轨道。党的十八大报告指出,科技创新是提高社会生产力和综合

国力的重要支撑,必须摆在国家发展全局的核心位置,要实施“创新驱动发展战

略”。

面对未来发展的重任,中国工程院将进一步发挥院士作用,邀请世界顶级专

家参与,共同以国际视野和战略思维开展学术交流与研讨,为国家战略决策提供

科学思想和系统方案,以科学咨询支持科学决策,以科学决策引领科学发展。

只有高瞻远瞩,才能统筹协调、突出重点地建设好国家创新体系。工程院历

来高度重视中长期工程科技发展战略研究,通过对未来 20年及至更长远的工程

科技发展前景进行展望与规划,做好顶层设计,推动我国经济社会发展尽快走上

创新驱动的轨道。

自2011年起,中国工程院开始举办一系列国际工程科技发展战略高端论坛,

旨在为相关领域的中外顶级专家搭建高水平高层次的国际交流平台,通过开展宏

观性、战略性、前瞻性的研究,进一步认识和把握工程科技发展的客观规律,从而

更好地引领未来工程科技的发展。

中国工程院学术与出版委员会将国际工程科技发展战略高端论坛的报告汇

编出版。仅以此编之作聚百家之智,汇学术前沿之观点,为人类工程科技发展贡

献一份力量。

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