Materials Chemistry and Physics 94 (2005) 288–291

Preparation of a novel polysulfone/polyethylene oxide/siliconerubber multilayer composite membrane for

hydrogen–nitrogen separation

Zhen Yea,b,∗, Yong Chenb, Hui Li b,Gaohong Heb,c, Maicun Denga,b

a Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR Chinab Tianbang National Engineering Research Centre of Membrane Technology, Dalian 116023, PR China

c Dalian University of Technology, School of Chemical Engineering, Dalian 116012, PR China

Received 24 January 2005; received in revised form 14 April 2005; accepted 2 May 2005

Abstract

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A novel polysulfone/polyethylene oxide/silicone rubber (PSf/PEO/SR) multilayer composite membrane was fabricated by doubolysulfone substrate membrane with polyethylene oxide and silicone rubber. Gas permeation experiments were performed a◦C forydrogen and nitrogen. PSf/PEO/SR membrane displayed high and steady performance for H2/N2: permeances of H2 and N2 of 49.51 and.601 GPU, respectively, and H2/N2 ideal separation factor of 82.3. It was explained that layer interfaces due to the introduction of PEOs the permselective media and are responsible for the higher H2/N2 ideal separation factor which has exceeded the intrinsic permselecf the three polymers used in this study.2005 Elsevier B.V. All rights reserved.

eywords: Multilayer membrane; Polysulfone; Polyethylene oxide; Hydrogen

. Introduction

In the early 1980s, Henis and Tripodi[1,2] developedomposite membrane for gas separation with acceptableermeability and high permselectivity and established theHenis resistance model” approach to the membrane. Henisesistance composite membrane found commercial applica-ions of membrane separation technology in H2 recoverynd purification processes. Henis resistance model in which

he mass transport through the membrane was described innalogue to an electric circuit has been used as the basis

or gas membrane separation process because it was usefuln analyzing the resistance components and the membraneermselectivity. Thereafter other models such as Wheatstone-ridge model[3], improved Henis resistance model[4], and

∗ Corresponding author. Tel.: +86 411 84379192; fax: +86 411 84677947.E-mail address: yezhen@dicp.ac.cn (Z. Ye).

Series RC circuit model[5] were also brought forwardmodify and complement the Henis resistance model.

Henis resistance composite membrane generally coof two layers: top coating layer made by a nonselecand highly permeable material and porous asymmetricstrate with a dense skin layer. The coating layer isto plug the pores in the skin layer of the substrate,the substrate made of permselective polymer is responfor the membrane separation. However, multilayer comite membrane usually has three layers and can be diinto two types based on the membrane configuration: (stive layer)/(gutter layer)/(support substrate)[6,7] and (sealing or protective layer)/(selective layer)/(support subst[8–10]. Polymers such as polyacrylonitrile (PAN)[7], poly(4-vinylpyridine) (PVP)[8] and cellulose nitrate (CN)[9] havebeen used as selective layer material to prepare multcomposite membrane.

In this paper we report a novel polysulfone/polyethyloxide/silicone rubber multilayer composite membrane (

254-0584/$ – see front matter © 2005 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2005.05.001

Z. Ye et al. / Materials Chemistry and Physics 94 (2005) 288–291 289

PEO/SR)[11]. The membrane structure and separation mech-anisms for H2/N2 are discussed.

2. Experimental

2.1. Membrane preparation

Polysulfone (PSf) hollow fibers with asymmetric structurewere spun by a dry-wet spinning procedure[12] on a labora-tory spinning apparatus. A spinning solution of 35 wt.% PSf(UDEL® P-3500) in complex solvents was used. After wash-ing and drying, fibers of typical dimensions (450/150�m,o.d/i.d.) were obtained. Bundles of 50 fibers each with alength of 25 cm were sealed at one end, while the shell sideof the other end was glued onto an aluminum holder usingepoxy resin.

PSf/PEO/SR multilayer membrane was prepared by suc-cessively coating the bundles with polyethylene oxide (PEO,Aldrich Catalog No.: 37,277-3,Mw = 4× 105) and siliconerubber (SR, Sylgard® 184) solutions. Hollow fiber bundleswere firstly immersed into 0.1 wt.% PEO/water coating solu-tion for 30 min and desiccated at room temperature for 24 h.PEO-coated membrane was then dip-coated with a 3 wt.%SR/pentane coating solution for 8 min with applying vacuuminside the fibers. Silane coupling agent KH-550 was addedt sivef ranew ameS f/SRm ,a tor int

2

ssurec eateflp eancea ge

J

w(

Fig. 1. Cross-sectional TEM micrograph of PSf/PEO/SR multilayer com-posite hollow fiber membrane.

(cm3 s−1), A the effective area of the membrane (cm2),pf − pp the pressure difference between the feed and the per-meate (cmHg), andT the operation temperature (K).

3. Results and discussion

3.1. Membrane morphology

Cross-sectional morphology of PSf/PEO/SR membranewas determined by transmission electron micrograph (TEM)and the image was displayed inFig. 1. Three layers andtwo obvious interfaces indicated by two straight lines areobserved. TEM image demonstrates that PEO and SR havebeen coated on the PSf hollow fiber substrate and the multi-layer composite membrane has been successfully prepared.

3.2. Gas permeation performance

Pure gas permeation results of PSf/PEO/SR and PSf/SRmembranes are listed inTable 1. PSf/PEO/SR membrane hasan H2 permeance of 49.51 GPU while that of PSf/SR mem-brane is 41.50 GPU. Meanwhile, the H2/N2 ideal separationfactor of the membrane (defined as the ratio of their puregas permeances,JH /JN ) has nearly increase of 30% from6 rme-a

TP mbran

Averag

J 49.51J 0.601J 82.3

a

o the PEO and SR coating solution to improve the adheorces of different polymers. PSf/SR composite membas also prepared by coating the bundles with the sR coating solution and methods. PSf/PEO/SR and PSembranes were stored for at least 48 h at 30◦C before usend the PSf/PEO/SR membrane was stored in a desicca

he course of termly stability testing.

.2. Gas permeation test

The membrane was potted into a stainless steel preell for pure gas permeation measurement and the permows from the open end were measured at 30◦C with theermeate side set at atmospheric pressure. Gas permcross the membrane,J, was obtained using the followinquation:

= Q

A(pf − pp)× 273

T(1)

hereJ is the gas permeance in GPU (1 GPU = 10−6 cm3

STP) cm−2 s−1 cmHg−1), Q the flux per unit of time

able 1ure gas permeation properties through PSf/PEO/SR and PSf/SR me

PSf/PEO/SR

1a 2a 3a

H2 (GPU) 49.35 49.11 50.08

N2 (GPU) 0.596 0.602 0.606

H2/JN2 82.8 81.6 82.6

Feed pressure (Gauge): 5 atm.

2 2

3.8 to 82.3. PSf/PEO/SR membranes show better petion performance than PSf/SR membranes.

es at 30◦C

PSf/SR

e 4a 5a 6a Average

41.38 41.41 41.72 41.500.649 0.646 0.656 0.650

63.8 64.1 63.6 63.8

290 Z. Ye et al. / Materials Chemistry and Physics 94 (2005) 288–291

Fig. 2. Stability measurements of PSf/PEO/SR membrane permeation prop-erties (Sample 3#).

Stability of PSf/PEO/SR membrane permeation propertieswas tested every 15 days for 2 months at 30◦C, and the resultsare shown inFig. 2. There was a slight decrease in H2 perme-ance and increase in ideal separation factorJH2/JN2 whichreached 85.0 two months later. Such membrane is applicablein H2 purification and recovery in refinery tail gas, ammoniaproduction and syngas composition adjustment process.

The intrinsic permeation properties of H2 and N2 in PSf,SR and PEO materials are listed inTable 2. As shown inTable 2, each of the ideal separation factors of the three

Table 2The intrinsic permeability coefficients of polymeric materials for H2 and N2

used in this study and the ideal separation factorPH2/PN2

Materials T (◦C) PH2 (Barrerb) PH2/PN2 Reference

PSf 35 5–200 25.0–75.0 [13]SR 35 500–3000 1.5–3.0 [13]PEOa 35 1.8 7.2 [14]

a Mw = 1× 106.b 1 Barrer = 10−10 cm3 (STP) cm cm−2 s−1 cmHg−1.

polymers for H2/N2 separation is less than 81.9, which isthe average ideal separation factor of PSf/PEO/SR mem-brane during 2-month termly measurements. According tothe aforementioned resistance model, ideal separation factorof a composite membrane must be lower than the intrinsicselectivity of the most permselective polymer which is usedto form the membrane. The intrinsic H2/N2 permselectivitiesof PSf is normally regarded as in the scope of 72–80, how-ever, differences between PSf/PEO/SR membrane and otherreported multilayer composite membranes are that none ofthe three layers of PSf/PEO/SR membrane is responsible forthe higher ideal separation factor. As a result, neither of fore-going (selective layer)/(gutter layer)/(support substrate) or(sealing or protective layer)/(selective layer)/(support sub-strate) multilayer membrane structures is accordance withthree layers of PSf/PEO/SR membrane. In this case, thecontributing permselective media should be attributed tothe two layer interfaces due to the introduction of PEOlayer.

Compared with PSf/SR membrane, the permeance of “fastgas” H2 becomes higher and that of “slow gas” N2 becomeslower in PSf/PEO/SR membrane. The chemical and physi-cal properties of the layer interface region may result in thechange tendencies of H2 and N2 permeances in PSf/PEO/SRmembrane.

The interfacial affinity will affect the membrane perfor-m hilicp too layerb rfacev PSfs others ean-wi thei har-am es inH y.

4

hol-l ncef Hp Rm -t ru firstr morep s onm tionm ffectso para-t

ance. Generally speaking, PSf is a kind of hydropolymer compared with hydrophobic SR. It is difficultbtain a PSf/SR membrane with integrated SR coatingecause it is hard to spread hydrophobic SR on PSf suery well. In contrast, hydrophilic PEO spread better onurface, and the transient PEO layer may offer a smourface for SR coating in PSf/PEO/SR membrane. Mhile, the degradation and aggregation of PEO[15] and the

nteraction of the polymers are involved in the forming ofnterfaces. Currently, an in-depth study on the structural ccteristic of the membrane interfaces, the H2/N2 separationechanism and the application of these novel membran2 membrane separation is in progress in our laborator

. Conclusion

In summary, novel PSf/PEO/SR multilayer compositeow fiber membrane not only provided high performaor H2/N2 separation but also shows a good stability in2ermeation. Ideal H2/N2 separation factor of PSf/PEO/Sembrane has exceeded the intrinsic H2/N2 permselectivi

ies of PSf which is the most H2/N2 permselective polymesed in this study, and to our best knowledge, it is theeport that three less permselective polymers can form aermselective composite membrane. For future studieultilayer composite membrane a focus on the formaechanism of the membrane layer interfaces and the ef the layer interfaces on the composite membrane pre

ion should be taken into account.

Z. Ye et al. / Materials Chemistry and Physics 94 (2005) 288–291 291

Acknowledgements

Special thanks are due to Ms. ZHANG Guihua, Mr.WANG Yuting and Ms. DOU Hong for their help in gas per-meation experiments.

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