Improving the functionality of a nanofiltration membrane device

comprising the precursor is processed to trans-form it into a membrane that has a desired prop-erty. Including a thermoplastic precursor as adesired component, which itself is less thermo-plastic, permits separate pieces of the membraneto be joined by welding or other thermal process-es relying on the melting characteristics of thecomponents to achieve a bond. The inventionalso encompasses fabricating a reinforced ion-conducting membrane by melting and mixing anon-ion-conducting precursor to an ion-con-ducting polymer with an essentially inert poly-mer. The composite material is then processed totransform the non-ion-conducting polymer intothe ion-conducting form. The mixing of the pre-cursor and the inert polymer may also beachieved by co-precipitating a solution of theprecursor and a suspension of the inert polymer;impregnating the precursor onto the walls of thepores of a porous, essentially inert polymer. Itmay also be achieved by filling the pores of aporous, inert polymer with a solution compris-ing a non-ion-conducting precursor to an ion-conducting polymer, and evacuating the solventto substantially fill the pores of the porous,essentially inert polymer with the precursor. Alsopossible is melting the precursor, filling the poresof a porous inert polymer with the melted pre-cursor and cooling the precursor to form anessentially pore-free composite membrane. Patent number: US 6495209 Inventor: A.J. CisarPublication date: 17 December 2002

Hollow-fibre membrane oxygenator Assignee: Terumo Kabushiki Kaisha, JapanA hollow-fibre membrane oxygenator (externalblood circulation type) has been developed. Ithas a housing that contains numerous poroushollow-fibre membranes for gas transfer. In theoxygenator, blood flows along the outer side ofthe hollow-fibre membranes, whereas oxygen-containing gas flows along their inner side. Anouter surface or outer layer of the hollow-fibremembrane (acting as the blood-contacting por-tion) is coated with synthetic polymer mainlyformed of alkoxyalkyl(meta)acrylate containinga C(1–4)alkoxy group and a C(1–4)alkyl group.An intermediate layer and inner layer of the

hollow-fibre membranes contain substantiallyno synthetic polymer. Patent number: US 6495101 Inventors: K. Yokoyama, T. Anzai, A. Okumura,Y. Kasori Publication date: 17 December 2002

Polysulphone/polyether sulphoneand polyethylene membraneAssignee: Kalsep Ltd, UKA membrane that can be used in membrane fil-tration processes, and which has a reduced ten-dency to fouling has been invented. It contains apolysulphone or a polyether sulphone and apolyethylene oxide/polypropylene oxide substi-tuted diamine, and can be made by a phaseinversion process in the presence of pore modify-ing agents (such as an alcohol, glycerol or glycol)to create a membrane that has a pore size rangeof 0.1 µm to 1 µm. It is also hydrophilic. Patent number: US 6495043 Inventor: M.L. HeijnenPublication date: 17 December 2002

Controlling multiple oxidizer feed-streamsApplicant: US Filter Corp, USAThis invention involves a method and apparatusfor controlling and optimizing the feed of two ormore oxidizers to an aqueous stream, therebyproviding a synergistic effect. The combined useof amperometric sensor technology (with theamperometric sensor technology employing agas-permeable membrane) provides definitivecontrol of each oxidizer feed streamPatent number: WO 02/101372Inventor: R. Martin Publication date: 19 December 2002

Wastewater treatment during phosphatizationApplicant: Henkel Kommanditgesellschaft aufAktien, GermanyThe invention relates to a method for treatingan overflow of a phosphatization bath, or rins-ing water after phosphatization, with a phos-phatizing solution containing 3–50 g/L phos-phate ions and 0.2–3 g/L zinc ions. Thephosphatization bath overflow or rinsing flow

undergoes membrane filtration and the reten-tate of the membrane filtration can be circulat-ed in a retentate circuit. The invention is char-acterized in that either a reagent is added to thephosphatization bath overflow, rinsing water orretentate circuit, prior to membrane filtration(in order to delay the blocking up of mem-brane). In this case, the reagent is chosen from0.01–5 g/L of a complexing agent for heavymetals, or an acid, whereby the quantity is suchthat the pH value of the rinsing water falls tobetween 0.5 and 2.5. It is also characterized bythe fact that membrane filtration is interruptedat selected intervals and the membrane is treat-ed with an aqueous solution of an acid whichhas a pH value of between 0 and 1.8.Patent number: WO 02/101115Inventors: J.-W. Brouwer, P. Kuhm, I. PeirowPublication date: 19 December 2002

Syngas production using an oxygentransport membraneApplicant: Praxair Technology Inc, USA, andBP Corp North America Inc, USAA method of producing a crude syngas productstream, or a syngas product stream by furtherprocessing of the crude syngas product stream,is described. Both the crude and syngas productstream comprise carbon monoxide and hydro-gen. The crude syngas product stream addition-ally comprises carbon dioxide and moisture. Inaccordance with the method, methane in a feedstream is converted into the hydrogen and car-bon monoxide in at least two stages to form acrude syngas stream. An initial stage has an oxy-gen transport membrane reactor that uses a cat-alyst to promote carbon dioxide or steammethane reforming. Since the conversion isshared between two stages, the oxygen trans-port membrane reactor can be operated at a suf-ficiently low temperature to avoid ceramicmembrane deterioration caused by the creepeffect. A subsequent stage can be operated at ahigher temperature with more favourable equi-librium conditions to complete the conversionof the methane.Patent number: WO 02/100773Inventors: R. Prasad, J. Schwartz, E.T. Robinson,C.F. Gottzmann Publication date: 19 December 2002

PATENTS

11Membrane Technology January 2003

Improving the functionality of ananofiltration membrane device Assignee: Eastman Kodak Co, USAThis invention relates to a method of improvingthe functionality of a membrane that is used ina nanofiltration (NF) device. In particular, itcovers a device designed for the treatment ofwastewater that is generated by the processwhich is used to develop films and photographs.

Many manufacturing or processing methodsproduce wastewater which, on the one hand, can-not be conveyed directly to the drains because of

its composition, while, on the other hand, it con-tains precious substances whose recovery and reusemay have economic advantages. A good example isthe photograph processing industry, whereexposed photographic film and paper go throughseveral treatment baths, after which chemicalsmust be removed from the finished products.

It is common to use systems for treating andrecycling the wastewater – in particular NFdevices. NF is a technique used for the selectiveseparation of salts and organic compounds insolution. NF membranes usually allow the

passage of molecules whose molecular weight isbetween 200 daltons and 1000 daltons.However, multivalent ionized salts and non-ion-ized organic compounds with molar mass morethan 1000 daltons are mostly retained.

It has been noticed that the retention rate ofmembranes is not optimal during treatment;that is, a not insignificant amount of substancesto be filtered is found in the permeate. Thisproblem is especially important in NF systemsthat are used discontinuously to treat differentbatches of solution.

The main object of this invention is to pro-vide a method for improving the functionalityof an NF membrane so as to optimize its reten-tion rate. Although it aims to improve NFmembranes that are used in the photographicindustry, the method can be used in any NF sys-tem for treating any type of effluent, and, inparticular, effluents that have a relatively highsaline concentration.

Figure 1 shows the schematic layout of anNF device. It comprises a tank (10) in whichis found the solution to be filtered and recy-cled. The device also comprises an NF mod-ule (20), containing a membrane (21)through which the solution to be treated iscirculated. The solution circulates in a set ofpipes (30). The tank is fed with the solutionby a first pipe (31) coming from the treat-ment bath. A second pipe (32) enables thesolution contained in the tank to be taken tothe NF module (20). A pump (40) enables

the solution to be conveyed through thispipe, and its flow rate to be regulated throughthe NF module. A third pipe (33) is providedto take the retentate into the tank, while afourth (34) is used to clear the permeate fromthe device so as to recycle it in the treatmentbath (not shown). This pipe is used in pro-duction mode, i.e. when the solution con-tained in the tank is treated.

Furthermore, the device comprises a fifthpipe (35) in which the permeate is taken to thetank. This pipe is only used when the device isin what is referred to as initialization mode. Athree-way valve (50) enables switching betweenthe two use modes (initialization and the pro-duction modes).

In the example which follows, washingwater from a seasoned stabilization bath is col-lected in the tank (10) through pipe (31).When the tank is full, the pump is run and thetwo modes are operated.

In this way, 10 L of the stabilization fluid arefiltered using the NF module equipped with anNF45 Filmtec membrane (with an area 2.21m2). The feed rate of the module is 600 L/h,with a mean pressure of 30 bar. The bath com-prises: thiosulphate, 13 308 mg/L; sulphate,9921 mg/L; silver, 920 mg/L; iron, 2650 mg/L;chemical oxygen demand (COD), 33 440mg/L; and total organic carbon (TOC), 8100mg/L.

The permeate was sampled at various outputsof recycled water – the output being defined byEquation 1.

R = (permeate volume/initial volume of solution to be treated) × 100 (1)

Table 1 groups together the analysis of the con-centration of the various chemical compoundscontained in the permeate for a permeate out-put of 70%.

The first column shows the concentration ofthe chemical compounds present in the perme-ate when the NF device is used directly in pro-duction mode, without initialization phase. Thesecond column shows the concentration of thechemical compounds present in the permeatewhen the device is used with an initializationphase before the production mode. In the sec-ond case, the initialization phase lasts about fiveminutes. In both cases, the concentration of thecontaminating chemical compounds in a tank ismeasured in which the permeate coming fromthe pipe (34) is recovered when the volume ofpermeate collected is 70% of the initial volumeto be treated.

Table 2 groups together the analysis of theconcentration of the various chemical com-pounds contained in the permeate for a perme-ate output of 90%. The first column shows theconcentration of the chemical compounds pre-sent in the permeate when the NF device is useddirectly in production mode, without initializa-tion phase. The concentration is then measured.The second column shows the concentration ofthe chemical compounds present in the perme-ate when the NF device is used with an initial-ization phase.

In the second case, the initialization phaselasts about five minutes. In both cases, theconcentration of the contaminating chemicalcompounds in a tank is measured in which thepermeate coming from the pipe (34) is recov-ered when the volume of permeate collected is90% of the initial volume to be treated.

These examples show that when an initializa-tion phase is used in the NF process, the con-centration of filtered chemical compounds,which are found in the permeate, decreases sig-nificantly. In this way, the functionality of theNF membrane is improved.

Patent number: US 6492098 Inventor: D.J. Martin Publication date: 10 December 2002

PATENTS

12Membrane Technology January 2003

31

10

3240

33 2021

5035

34

30

Figure 1. A device which enables the use of the nanofiltration (NF) module, which is detailed inpatent US 6492098. The use of an initialization phase in the NF process improves the functionalityof the membrane.

Table 1. Concentration in thepermeate for a 70% permeate output.

Concentration (mg/L)

Without init. With init.phase phase

(invention)

Thiosulfate 1536 820

Sulfate 674 435

Silver 44 22

Iron 35 6.3

COD 8170 5840

TOC 2260 1650

Table 2. Concentration in thepermeate for a 90% permeate output.

Concentration (mg/L)

Without init. With init.phase phase

(invention)

Thiosulfate 3739 1923

Sulfate 1272 678

Silver 115 51

Iron 60 15

COD 9100 8110

TOC 2425 2190