Liquefied petroleum gas desulfurization by HTBN/PAN composite membrane

Liquefied Petroleum Gas Desulfurization by HTBN/PANComposite Membrane

Jian Chen, Jinxun Chen, Jiding Li, Xiaolong Han, Xia Zhan, Cuixian Chen

Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

Received 27 May 2009; accepted 22 January 2010DOI 10.1002/app.32145Published online 13 April 2010 in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: Hydroxyl-terminated polybutadiene/acry-lonitrile (HTBN) polymer material was selected for deepdesulfurization of liquefied petroleum gas (LPG) accordingto the solubility parameter method, and then crosslinkedHTBN membranes were prepared, in which asymmetricpolyacrylonitrile (PAN) membranes prepared with phaseinversion method acted as the microporous supportinglayer in the flat-plate composite membrane. The differentfunction compositions of composite membranes were char-acterized by reflection FTIR in order to investigate thecrosslinking reaction. The surface and section of compositemembranes were investigated by scanning electron micro-scope (SEM). The composite membranes prepared in thisstudy were used in LPG for deep desulfurization. Effectsof amount of HTBN and operation pressure on the desul-

furization efficiency of LPG were investigated experimen-tally. Experiment results demonstrated that with themembrane having a HTBN layer of 11 lm, permeabilityparameter of methyl mercaptan came to 17,002 Barrer andthat of hydrocarbon came to 504 Barrer at 30 wt % ofHTBN and 0.25 MPa, which showed that the membraneused to desulfurization in LPG can achieve high-removalefficiency. These results demonstrated that the membraneseparation method could be significant in practical appli-cation for deep desulfurization of LPG. VC 2010 Wiley Periodi-cals, Inc. J Appl Polym Sci 117: 2472–2479, 2010

Key words: HTBN; PAN; desulfurization; liquefiedpetroleum gas; membranes

INTRODUCTION

Liquefied petroleum gas (LPG) is the main house-hold fuels in many cities all over the world, espe-cially in China. However, sulfur present in LPGresults in SOx air pollution, which is directly respon-sible for acid rain. Ultra-deep removal of sulfur fromtransportation fuels, particularly from LPG, hasbecome very important in petroleum refining indus-try worldwide. The need for cleaner burning fuels

has resulted in continuous worldwide efforts toreduce the sulfur levels in LPG. The reduction ofLPG sulfur has been considered to be an importantmeans for improving air quality.1–3

A number of solutions, such as Merox process,4,5

have been suggested to reduce sulfur in LPG, butnone of them have been proven to be ideal. Tradi-tionally, hydrotreating process is the most effectivetechnology used for removal of organic sulfurs pres-ent in industry. However, this technology suffersfrom the high investment and operating costs. Itshould be important to find advanced technology toremove the organic sulfur present in gasoline.Membrane separation technology, compared with

traditional separation technology, such as distilla-tion, molecular sieve, extraction, has many advan-tages: (1) High separation efficiency, (2) low energyconsumption, (3) simple operation, and so on.6,7

Kong and coworkers applied crosslinked polyethyl-ene glycol (PEG) membranes in sulfur removal fromfluid catalytic-cracking (FCC) gasoline, and theresults indicated that sulfur enrichment factor cameto 4.83 as flux was 0.64 kg/m2h.8–10 In our previouswork,11–14 polydimethylsiloxane (PDMS)/polyacrylo-nitrile (PAN) composite membranes were studiedand applied for pervaporative desulfurization formodel gasoline. However, deep desulfurization ofLPG was scarcely investigated by membrane

Correspondence to: J. Li ([email protected]).Contract grant sponsor: Major State Basic Research

Program of China; contract grant number: 2009CB623404.Contract grant sponsor: National Natural Science

Foundation of China; contract grant numbers: 20736003,20906056.

Contract grant sponsor: National High TechnologyResearch and Development Program of China; contractgrant numbers: 2007AA06Z317, 2008EG111021.

Contract grant sponsor: Foundation of Ministry ofEducation of China; contract grant number: 20070003130.

Contract grant sponsor: Foundation of the State KeyLaboratory of Chemical Engineering; contract grantnumber: SKL-ChE-08A01.

Contract grant sponsor: Postdoctor Science Foundationof China; contract grant number: 023201069.

Journal ofAppliedPolymerScience,Vol. 117, 2472–2479 (2010)VC 2010 Wiley Periodicals, Inc.

technology in detail, whereas gas membrane separa-tion was more difficult and sulfur in gas was ardu-ous to remove.

In this study, based on solubility parameter analy-sis, HTBN polymer material was selected for deepdesulfurization of LPG. HTBN, new membrane ma-terial, has not been extensively investigated for theseparation of various mixtures.15 Moreover, micro-porous PAN ultrafiltration membranes were used assupporting layer of the composite membranes,whereas PAN and HTBN both have ACN bond sotheir interface could cement closely. Subsequently,HTBN/PAN composite membranes were preparedand used to LPG system. The influences of concen-tration of HTBN and operation pressure on the sepa-ration performance of the membranes were investi-gated experimentally in order to obtain morepractical membrane preparation condition for thescale up of membrane separation technology, whichis the most important point for practical application.

EXPERIMENTAL

Materials

The hydroxyl-terminated polybutadiene/acrylonitrileliquid rubber (HTBN), as shown in Figure 1, withmolar mass of 2.96 � 103, polydispersity index of1.77 and hydroxyl group value of 0.5672 mmol/g,available from Qilong Chemical Industry Co. PANpowder was obtained from Shanghai PetrochemicalCompany, which contained 6% methyl methacrylate(MMA) and 0.3% 2 methyl-2-propene-1-sulfonate asco-monomers (Mw¼ 75,000). N-methyl pyrrolidone(NMP) was obtained from Beijing Yili Fine Chemi-cals Co., Beijing, China. Toluene diisocyanate (TDI),a 80/20 mixture of 2,4 and 2,6 isomers supplied byChengdu Union Chemical Reagent Research Insti-tute, analytically pure (AP), was purified by vacuumdistillation (8.638 � 103 Pa, 148�C). Toluene anddibutyltin dilaurate (DBTL) were purchased fromTianjin Chemical Company of China for the prepara-tion of HTBN membrane. All the chemicals used inthe experiments were of analytical grade and wereused without any further purification.

Membrane preparation

Supporting PAN UF membranes preparation

PAN was used as a membrane material after beingdried in vacuum at 150�C for 6 h. 20 wt % of PANwas dissolved in NMP at 80�C by stirring for 12 hand then the casting solution was filtrated to get ridof impurity. To remove air bubbles, the casting solu-tion was kept at room temperature for 24 h undervacuum. After degassing, the casting solution wascast on a polyester nonwoven fabric with a scraper

of 150 lm thickness. The nascent membrane wasdried for 10 s at 25�C. Then, it was immersed intoDI water at 25�C. After the immersion, the precipi-tated membranes were washed for 12 h to removeresidues of solvent mixtures from the membranes.

Composite membranes preparation

HTBN, crosslinking agent TDI, and catalyst DBTLwere dissolved in toluene at room temperature. Af-ter being degassed under vacuum, the solution wascast onto the PAN membrane with a scraper of 20lm thickness. The membrane was first vulcanizedunder room temperature to evaporate the solvent,and then introduced into a vacuum oven to com-plete crosslinking. Controlling the HTBN concentra-tion or the coating amount could produce mem-branes with variable top layer thickness. Thethickness of the top skin layer could be determinedby means of scanning electron microscope (SEM)photographs.16 All experiments, in this study, wereperformed with the same membrane operationprocedure.

Membrane characterization

Scanning electronic microscopy

To investigate the membrane structure, SEM charac-terization of the prepared membranes had been car-ried out. For this purpose, the membrane sampleswere fractured under liquid nitrogen and thencoated with Au/Pd under vacuum conditions. Thecross-section and surface membrane morphologieswere taken by scanning electronic microscopy (JSM-7401F SEM).

Fourier transform infrared spectra–attenuated totalreflection (FTIR–ATR)

Information about the presence of specific functionalgroups of the prepared membrane surfaces wasobtained by a Nicolet IR 560 spectrometer with hori-zontal ATR accessory equipped with a ZnSe crystal.For evaluation, a total of 32 scans were performed ata resolution of 4 cm�1 at temperature of 25�C. Mean-while, FTIR spectra were recorded within the rangeof 4000–400 cm�1. The software from Nicolet wasused to record the spectra and for the selection ofthe corresponding backgrounds.

Figure 1 The chemical structure of HTBN.

LPG DESULFURIZATION BY HTBN/PAN COMPOSITE 2473

Journal of Applied Polymer Science DOI 10.1002/app

Separation experiments

Separation experiment apparatus used in this study isshown in Figure 2. The membrane was positioned inthe stainless-steel permeation cell, and the effectivesurface area of the membrane in contact with the feedmixture in this cell was 34.1 cm2. The feed LPG wascontinuously circulated from a feed tank to theupstream side of the membrane in the cell at thedesired temperature, and the feed temperature wasmonitored with a digital thermometer. After a steadystate was obtained (about 1 h after start-up), masstransfer equilibrium was stable, whereas the vacuumin the downstream side of the apparatus was main-tained at about 200 Pa using a vacuum pump. Thecompositions of the feed solution and permeationwere analyzed by gas chromatography (Chengdu,WDL-94). The results were reproducible and theerrors inherent in the measurements were less than2%. The permeation flux (J) of the membrane was cal-culated using the expression

J ¼ Q

A� t(1)

where Q (cm3, STP) is the total volume of permea-tion collected through the effective area of mem-

brane (A, cm2) during time (t, s) after the state hasbeen reached.Given that the gaseous mixture on both the feed

and permeate side is ideal, the fugacity differencecan be approximately equal to the partial pressuredifference. The gas permeability of i component wasdetermined by the following equation:

Pi ¼ Qi � l

Dfi � Affi Qi � l

DPi � A(2)

where Pi is the gas permeability of i component, Bar-rer (1 Barrer ¼ 10�10 cm3 (STP) cm/cm2 s cmHg), Qi

is the permeation flow rate of i component (cm3

(STP)/s), l is the membrane thickness (cm) deter-mined by micrometer, Dfi and DPi are the fugacityand pressure difference of i component betweenfeed and permeate sides (cmHg), respectively, and Ais the effective membrane area (cm2).Then the selectivity a of a membrane in a binary

system is obtained as:

a ¼ PA

PB(3)

TABLE IProperties of the Main Components in the LPG18

Components Methyl mercaptan Propane Propylene Isobutane Isobutene

Boiling point (�C) 5.9 �42.1 �47.7 �11.8 �6.8Bond length (A) CAS 1.82 C¼¼C 1.34 C¼¼C 1.34

CAC 1.54 CAC 1.54SAH 1.33 CAC 1.54 CAC 1.54

CAH 1.10 CAH 1.10CAH 1.10 CAH 1.10 CAH 1.10

Solubility parameter d(J1/2/cm3/2) 17.7 11.8 13.2 14.1 13.6Mole fraction in LPG 400 ppm 30.8% 40.5% 14.7% 10.8%

Figure 2 Scheme of the experimental apparatus.

2474 CHEN ET AL.


where PA and PB are the gas permeability of A andB gasses, respectively.

THEORY

Solubility parameter

Solubility parameter (d) was proposed first by Hilde-brand and Scott,17 which defined it as the squareroot of cohesive energy for unit volume molecule.The solubility parameter, which depends on chemi-cal and physical structure of material, is importantto characterize the interaction intensity among sim-ple liquids and closer solubility parameter results inhigher attraction for permeation components inmembrane phase. The closer the solubility parame-ters between two substances, the better for their mu-tual solubility. The d value of certain substance canbe represented by its three components: Dispersionforce (dd), polarity force (dp), and hydrogen bondforce (dh). The relation is expressed as

d2 ¼ d2d þ d2p þ d2h (4)

In this study, the group contribution method forpredicting solubility parameter18 was adopted andthe formula was given by eq. (5):

d ¼ Ecoh

V

� �12

¼P

i EiPi Vi

� �12

(5)

where Ei and Vi are internal energy and molecularvolume for each structural group, respectively.

Method of membrane material selection bysolubility parameter theory

Solubility parameter is effective to characterize theinteraction intensity between solvent and membrane,so it is an important way for membrane materials

selection. Whether or not the membrane can fulfillits separation goal depends on the relative permea-tion capability of the membrane to components. Thecloser the solubility parameters between permeationcomponent and membrane, the better for their mu-tual solubility and their separation performance. Insummary, it is a feasible way to evaluate the selec-tivity of the membrane by estimating the interactionbetween polymer and solvent molecule.19

To a ternary system, including component A, com-ponent B, and membrane, the component which hascloser solubility parameter with membrane shouldexert strong dissolution performance. That is to say,higher attraction results in the increased solubilityfor permeation components in the membrane. So thepreferential dissolution of component A with com-ponent B in the membrane can be estimated by the

Figure 3 The cross-section morphology of the HTBN/PAN composite membrane.

TABLE IISolubility Parameters of Typical Polymeric Membrane Materials

Membrane material dM (J1/2/cm3/2) DdA (J1/2/cm3/2) DdB (J1/2/cm3/2) DdA/DdB

Polyacrylonitrile (PAN) 26.61 13.41 8.91 1.51Polysulfone (PS) 21.36 8.16 3.66 2.23Polytetrafluoroethylene (PTFE) 13.99 0.79 3.71 0.26Polyimide (PI) 32.30 19.10 14.60 1.31Polydimethylsiloxane (PDMS) 21.01 7.81 3.31 2.36Polyurethane (PU) 20.98 7.78 3.28 2.37Polyvinylpyrrolidone (PVP) 20.56 7.36 2.86 2.57Cellulose acetate (CA) 20.06 11.86 7.36 1.61Polystyrene (PS) 18.50 5.30 0.80 6.63Polyvinylbutyral (PVB) 23.12 9.92 5.42 1.83Poly(vinyl chloride) (PVC) 26.49 13.29 8.79 1.51Poly(ethylene glycol) (PEG) 20.10 6.90 2.40 2.88Polypropylene (PP) 21.93 8.73 4.23 2.06Cellulose triacetate (CTA) 24.60 11.40 6.90 1.65HTBN 17.80 4.60 0.10 46.00Poly(vinyl acetate) (PVAC) 23.10 9.90 5.40 1.83



solubility parameter theory with the quantity DdADdB

byeq. (6).

DdADdB

¼ dA � dMj jdB � dMj j (6)

RESULTS AND DISCUSSION

Results of preliminary membranematerial selection

Real LPG is a rather complex mixture composed ofalkanes and olefins ranging from C3 to C5, and themain components in the LPG is propylene. Typical or-ganic sulfur compounds in LPG is mercaptan, espe-cially methyl mercaptan. To determine preliminarymembrane material, propylene was selected to standfor LPG, whereas methyl mercaptan was chosen asthe representative organic sulfur. That is, the mem-brane materials to be selected should permeatemethyl mercaptan (component B) and prohibit pro-pylene (component A). By calculation and query, thesolubility parameters of various polymeric membranematerials were obtained, as shown in Table I.18

From Table II, the DdA/DdB values of HTBN andpolystyrene (PS) membrane material were far largerthan that of others. Considering above analysis,HTBN and PS may have better dissolution and per-meation performance to sulfur species. Furthermore,HTBN is a rubber polymer and, therefore, can offerhigh free volume for the diffusion of the permeatemolecules. Consequently, HTBN was determined asthe promising membrane material for LPGdesulfurization.

SEM photographs of membranes

SEM permits imaging cross-section and surfacemembrane morphologies. The cross-section morphol-

ogy of the HTBN/PAN membrane was shown inFigure 3. As demonstrated in the SEM photographs,there was a clear boundary between the HTBN toplayer and the PAN support layer. Meanwhile, thecross-sectional structure of the HTBN/PAN compos-ite membrane consisted of an ultrathin-skin layerand a porous finger-like structure. Moreover, thethickness of the HTBN top layer was determined tobe about 11 lm from the SEM photograph by thescale tab.16 The surface morphologies of the PANmembrane and HTBN/PAN composite membranewere shown in Figure 4(a,b), respectively. Whencompared Figure 4(a) with Figure 4(b), the originallyporous surface of the PAN substrate was covered bya flat featureless HTBN layer, and the surface of theHTBN/PAN composite is dense and there is no pin-hole or crack. Moreover, the top composite mem-brane layer, functioning as the basis of selectivity,had a nonporous and tight structure, which is im-portant for the practical application.

FTIR photographs of membranes

The attenuated total reflection Fourier transforminfrared spectroscopy is a commonly used methodto characterize the chemical structure of the sur-face.20 The ATR technique enables the identificationof specific molecules and groups located within 100nm from the surface layer. To obtain detailed infor-mation about the structural changes of HTBN/PANmembranes resulting from crosslinking modification,FTIR spectra of the surface of HTBN/PAN mem-branes were recorded in Figure 5 using the ATRtechnique. From Figure 5, peaks at 2911 cm�1 and2238 cm�1 were assigned to CAH stretching andACN stretching, respectively. As for the strength ofthe ACN peak, PAN [from Fig. 5(a)] was strongerthan HTBN [from Fig. 5(b)]. The reason was that

Figure 4 The surface morphology of the HTBN/PAN composite membrane.

2476 CHEN ET AL.


PAN contained more ACN group than HTBN andHTBN was crosslinked by ACN bond, which led tothe spectra of the crosslinked membranes displayingevidently weakened absorbance signals of ACN.These changes were the evidences of crosslinkingreaction of hydroxyl-terminated HTBN with TDIunder dibutyltin dilaurate catalysis. Different cross-linking agent content HTBN/PAN membranes wereshown as Figure 6(a–d). From Figure 6(a–d), 3288cm�1 (NAH stretching) strengthened and 2238 cm�1

(ACN stretching) weakened with the crosslinkingagent content increased as more ACN reacted withAOH of HTBN to form a crosslinked polymer. Fur-thermore, 2264 cm�1 (AN¼¼C¼¼O antisymmetricstretching in TDI of crosslinking agent) evidentlyindicated that crosslinking affected the structure ofHTBN/PAN membranes because the chemical con-

nection occurred between macromolecules and retic-ular spatial structure formed.

Effect of trans-membrane pressure (TMP) on flux

Figure 7 illustrated the effect of pressure differenceon total flux at different HTBN content. In the sameHTBN content, it can be observed clearly that per-meation flux increased significantly with the rise ofpressure difference from 0.25 to 0.4 MPa, which wasconsistent with common rule.21 Furthermore, at thesame pressure difference, as shown in Figure 7, thetotal flux increased with the increasing of HTBNcontent. The separation performance is dominatedby the sorption and diffusion characteristics of theindividual components. This result implied that,when the HTBN content increased, more HTBN

Figure 7 Effect of pressure difference on the total flux ofHTBN/PAN composite membrane at 22�C. [Color figurecan be viewed in the online issue, which is available atwww.interscience.wiley.com.]

Figure 8 Effect of pressure difference on the permeabilityparameter of methyl mercaptan at 22�C. [Color figure canbe viewed in the online issue, which is available atwww.interscience.wiley.com.]

Figure 6 FTIR spectra of different crosslinking agent con-tent HTBN/PAN membranes: (a) 2 wt %, (b) 4 wt %, (c) 6wt %, and (d) 8 wt %. [Color figure can be viewed in theonline issue, which is available at www.interscience.wiley.com.]

Figure 5 FTIR spectra of HTBN/PAN composite mem-branes: (a) PAN and (b) HTBN/PAN. [Color figure can beviewed in the online issue, which is available atwww.interscience.wiley.com.]



chains occurred crosslinking reaction from FTIRphotographs of membranes. Thereby, the top HTBNlayer, functioning as the basis of permselectivity,brought out more porous network stereostructurebecause HTBN materials belong to rubber category.In a word, with the HTBN content increased, thefree volume of HTBN membrane increased, whichled to the total flux increased. In a word, theincrease in total flux was due to the increase of themobility of individual permeating molecules causedboth by the pressure and by the enhanced mobilityof the polymer segments.

Effect of pressure difference on permeability

The effect of pressure difference on the permeabilityparameter of methyl mercaptan and hydrocarbonwas depicted in Figures 8 and 9, respectively. FromFigures 8 and 9, it can be found that permeability ofmethyl mercaptan was larger than that of hydrocar-bon at the same pressure difference and same HTBNcontent, which was attributed to the fact that methylmercaptan permeates more easily than hydrocarbonat the same condition. It can also explained by thedata of Table II. In addition, permeability of methylmercaptan decreased and permeability of hydrocar-bon increased with pressure difference increasing atthe same HTBN content. When the pressure differ-ence increased, an extensive swelling of the mem-brane occurred due to the strong affinity of methylmercaptan to the membrane. It is well-known that aremarkable swelling of polymer membranes leads toan opened membrane structure and consequently anenhancement of the permeating in the polymermembranes. Although methyl mercaptan had moreprivilege than other organic species to penetrate themembrane, methyl mercaptan content in LPG was

very low (ppm scale) and hydrocarbon was abso-lutely preponderant. Therefore, increasing pressuredifference resulted in more hydrocarbons permeat-ing in the polymer membranes, which made againstmethyl mercaptan permeability. In conclusion, per-meability parameter of methyl mercaptan came to17,002 Barrer and that of hydrocarbon came to 504Barrer at 30 wt % of HTBN and 0.25 MPa, whichshowed that the membrane used to desulfurizationin LPG can achieve high removal efficiency.

Effect of pressure difference on separation factor

From Figure 10, separation factor of methyl mercap-tan decreased with the increase of pressure differ-ence at the same HTBN content. That is to say, thepermselectivity of methyl mercaptan decreased withincreasing pressure gradient. In general, the permse-lectivity of gas separation through polymer mem-branes is the product of the ratio between the solu-bility of permeants into polymer membranes (thesolubility selectivity) and the ratio between the diffu-sivity of permeants in polymer membranes (the dif-fusivity selectivity), according to the solution–diffu-sion theory. Thereby, the permselectivity for theLPG mixtures through the membrane depends onboth solubility and diffusivity. First, the methyl mer-captan molecules that have a higher affinity for themembranes than the hydrocarbon molecules arepreferentially sorbed into the membrane in the sorp-tion process. Then, the diffusivity of these moleculesin the internal membrane is significantly dependenton the molecular size and shape.14 In this case,increasing pressure difference led to a higher perme-ation rate and a lower separation factor as the vol-ume of ASA is bigger than that of ACA.

Figure 10 Effect of pressure difference on separation fac-tor of HTBN/PAN composite membrane at 22�C. [Colorfigure can be viewed in the online issue, which is availableat www.interscience.wiley.com.]

Figure 9 Effect of pressure difference on the permeabilityparameter of hydrocarbon at 22�C. [Color figure can beviewed in the online issue, which is available atwww.interscience.wiley.com.]

2478 CHEN ET AL.


Especially, exorbitant addition of crosslinkingagent brought about lower flux and membrane in-tensity decrease for solubility restricted to crosslink-ing agent and above results were unfavorable forpractical application. For this reason, at the range of15–25 wt % of HTBN, separation factor almostdecreased with HTBN content increasing at thesame pressure difference. Furthermore, separationfactor had a point of transition at 30 wt % of HTBNcontent. That is, up to the 30 wt % of the HTBN,separation factor exerted higher level. It could beexplained that the hydrocarbon penetrated very dif-ficultly when the interchain free volume of HTBNmembrane decreased at a definite degree. In conclu-sion, separation factor came to 33.7 at 30 wt % ofHTBN and 0.25 MPa, which was more practical andefficient for the scale up of membrane technology.

CONCLUSIONS

Selection membrane material is important funda-mental research for LPG desulfurization by mem-brane process. In this research, solubility parametersof LPG main components and typical polymericmembrane materials were calculated and given out.For methyl mercaptan, which is the primary contentin sulfur species, solubility parameter was about17.7 J1/2/cm3/2, whereas about 11–14 J1/2/cm3/2 formost other hydrocarbon species in LPG. The distinctdifference in solubility parameters between themwas just the key to fulfill the desulfurization. By thesolubility parameter theory and membrane prepara-tion experiments, HTBN was determined as thepromising membrane material for LPG deepdesulfurization.

Simultaneously, HTBN/PAN composite mem-branes were prepared based on the selected mem-brane material. The effects of the membrane prepa-ration conditions, such as HTBN content, and theoperation conditions, such as pressure difference onthe gas separation properties were investigated. Ex-perimental results indicated that permeability ofmethyl mercaptan was evidently higher than thepermeabilities of other hydrocarbons. Permeationflux increased significantly with the rise of pressure

difference from 0.25 to 0.4 MPa, and the relationshipbetween total flux and pressure difference was lin-ear. In addition, permeability of methyl mercaptandecreased and permeability of hydrocarbonincreased with pressure difference increasing at thesame HTBN content. Separation factor of methylmercaptan decreased with the increase of pressuredifference. Therefore, HTBN/PAN membrane wasproved to be an efficient alternative route for the re-moval of sulfur impurities out of LPG, which hadthe potential for becoming practical application.

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Liquefied petroleum gas desulfurization by HTBN/PAN composite membrane