Microwave synthesis of high performance FAU-type zeolite membranes

Journal of Membrane Science 337 (2009) 47–54

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Microwave synthesis of high performance FAU-type zeolite membranes:Optimization,characterization and pervaporation dehydration of alcohols

Guangqi Zhu a ,b ,Yanshuo Li a ,Han Zhou a ,b ,Jie Liu a ,Weishen Yang a ,?

a State Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,457Zhongshan Road,Dalian 116023,China b

Graduate School of Chinese Academy of Sciences,Beijing 100049,China

a r t i c l e i n f o Article history:

Received 29November 2008

Received in revised form 10March 2009Accepted 20March 2009

Available online 28 March 2009Keywords:

FAU-type zeolite membrane In situ synthesis Microwave heating

Taguchi experimental design Pervaporation

a b s t r a c t

High performance FAU-type zeolite membranes were synthesized by the “in situ aging-microwave synthe-sis”(AM)method in a clear solution with the molar composition of 70Na 2O:1Al 2O 3:20SiO 2:2000H 2O.The AM method couples in situ aging at relatively low temperature and fast crystallization under microwave heating (MH).To achieve the optimization of the synthesis parameters,the in situ aging and MH tem-peratures,as well as the probable ranges of the corresponding times were ?rstly determined by means of investigating their effects on the crystal structures and morphologies of the zeolite layers.Then the Taguchi experimental design was employed to further optimize the in situ aging and MH times of the two-stage synthesis.The as-synthesized zeolite membranes showed high pervaporation performance for the dehydration of ethanol and isopropanol aqueous solutions.Only pure water was detected in the permeate before the water content decreased to ca.9%for water/ethanol mixtures and ca.6%for water/isopropanol mixtures,respectively.

? 2009 Elsevier B.V. All rights reserved.

1.Introduction

Zeolite-based ?lms and membranes are important functional materials in the nanotechnology era with versatile applications.Many efforts have been made on developing high performance zeo-lite membranes,while hydrothermal treatment in air ovens is still the main synthesis technique.In the late 1980s,microwave heating (MH)was introduced to the synthesis of zeolites [1].Compared with conventional heating (CH)in air ovens,MH can greatly shorten the synthesis time and produce zeolites with high purity and narrow particle size distribution [2].These advantages inspire researchers to prepare zeolite membranes with high performance in a short time.Up to date,several types of zeolite membranes have been synthesized under MH,and the progress of microwave synthesis of zeolite membranes was summarized in a recent review [3].

In most cases,MH was employed to promote the secondary growth of the zeolite seeded layers,whereas few zeolite mem-branes were in situ synthesized under MH with satisfactory separation performance [4].Recently,our group developed an ef?-cient method named “in situ aging-microwave synthesis”(AM)to synthesize LTA-type zeolite membranes [5–7].With a relatively short crystallization time,the thermal and density gradients in the clear synthesis solution were eliminated,and thus long tubular

?Corresponding author.Tel.:+8641184379073;fax:+8641184694447.E-mail address:yangws@https://www.360docs.net/doc/189179621.html, (W.Yang).URL:https://www.360docs.net/doc/189179621.html,/(W.Yang).LTA-type zeolite membranes were successfully synthesized,which showed excellent performance in the pervaporation dehydration of organic solvents [8].The AM method couples two successive steps,i.e.in situ aging at relatively low temperature and fast crystallization under MH.It was concluded that an amorphous gel layer containing plenty of pre-nuclei was ?rst formed on the support surface after in situ aging.These pre-nuclei rapidly and simultaneously devel-oped into crystal nuclei under MH,and then the crystals grew by means of propagation through the gel network and conjoined with each other.In this way,a dense zeolite layer was obtained after the two-stage synthesis without the aid of arti?cial seeding [6].

FAU-type zeolite as well as LTA-type belongs to low-silicon zeo-lites.FAU-type zeolite membrane can be used for the dehydration of organic solvents and the separation of organic mixtures [9].The sep-aration factor of FAU-type zeolite membrane is inferior compared with LTA-type for dehydration,especially in low water content,whereas the permeation ?ux is higher [10,11]probably due to its larger pore size.Thus it suits to the dehydration of the feeds rela-tively rich in water.Previous synthesis methods usually involve a seeding process to induce the formation of FAU-type zeolite in the subsequent hydrothermal treatment.Instead of CH,Kita et al.[12]and Weh et al.[13,14]employed MH for the secondary growth of the FAU-type zeolite seed layers in gel solutions.In this paper,we applied the AM method to the synthesis of FAU-type zeolite mem-branes in a clear solution.The effects of the synthesis parameters on the crystal structures and morphologies of the zeolite layers were ?rst investigated in detail.Then Taguchi experimental design,one of the most effective and time-saving methods for the studies involv-

0376-7388/$–see front matter ? 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.memsci.2009.03.026

48G.Zhu et al./Journal of Membrane Science 337 (2009) 47–54

ing multiple factors [15],was used to optimize the in situ aging and MH times.The as-synthesized zeolite membranes were pure FAU phase and showed excellent pervaporation performance towards the alcohol aqueous solutions.2.Experimental

2.1.Membrane synthesis

FAU-type zeolite membrane was prepared on the surface of porous ?-Al 2O 3tubes (homemade,12mm outside diameter,9mm inside diameter,75mm length and ca.1?m pore size).The syn-thesis procedure is illustrated in Fig.1.The synthesis solution was prepared by dissolving aluminium foil (≥99.99%)into sodium hydroxide (>99.6%)solution,and then adding silica sol (SiO 2ca.31%,Na 2O ≤0.2%,Zhejiang Yuda Chemical)into the solution.After stirring at room temperature for 8h,a clear and homo-geneous solution was obtained,with the molar composition of 70Na 2O:1Al 2O 3:20SiO 2:2000H 2O.About 90ml synthesis solution was poured into a Te?on autoclave,where a support tube was placed vertically.The autoclave was ?rst put in an air oven at 333K for a period (in situ aging),and then heated in a customized microwave oven.The synthesis solution was quickly heated up to 363K with the full power 1400W and then held that temperature for typically 20min with a low power.After the synthesis,the mem-branes were taken out,thoroughly washed with deionized water and dried at 333K overnight.The same synthesis procedure was repeated for the second stage synthesis.2.2.Membrane characterization

Crystal structures of the membranes were identi?ed by the X-ray diffraction patterns (XRD,Rigaku D/MAX 2500/PC,Cu K ?radiation,operating at 40kV and 200mA).The XRD patterns were processed with MDI Jade 5.0.

Morphologies and thicknesses of the membranes were observed by the scanning electron microscopy (SEM,Quanta 200FEG,FEI Company,operating at 30kV).The compositional analyses were performed by the energy-dispersive X-ray spectrometry (EDX,EDAX Inc.,operating at 30kV).To avoid the interference from the support,the Si/Na molar ratio was used as a direct indication of the corresponding Si/Al molar ratio of each zeolite membrane [16].

Pervaporation measurements towards ethanol (≥99.7%,Tian-jin Kermel Chemical)and isopropanol (≥99.7%,Tianjin Kermel Chemical)aqueous solutions were carried out at 338K.The

effec-Fig.1.Schematic illustration of the AM synthesis procedure.

tive membrane area was 24cm 2.The apparatus and experimental details were described elsewhere [17].Water contents of the feed and permeate were determined by GC (HP 5890).3.Results and discussion

3.1.Effect of AM synthesis parameters

In this study,there were four main synthesis parameters,i.e.the temperatures and times performed during in situ aging and MH.For simpli?cation,the zeolite membranes synthesized with different procedures will be coded as A T 1t 1M T 2t 2,where T 1and t 1represent the in situ aging temperature (K)and time (h),while T 2and t 2the MH temperature (K)and time (min),respectively.We ?rstly investi-gated the effects of the synthesis parameters on the structures and morphologies of the zeolite layers,aiming to con?ne their ranges preparatory to the Taguchi experimental design.

3.1.1.In situ aging temperature and time

In situ aging proved to be a necessary process for the AM synthesis of LTA-zeolite membranes so as to overcome the nucleation-related bottleneck and increase the nucleation density on the support [5].In this study,it was also found that no zeolite peaks were present in the XRD patterns (not provided here)of the samples obtained by direct MH,or MH after ex situ aging,i.e.the synthesis solution was aged solely and the support tubes were put in before MH [5].

Fig.2shows the XRD patterns of the zeolite layers obtained with different in situ aging times at 323and 333K.Intense peaks of FAU-type zeolite appeared in the XRD pattern of A 3238M 36320(Fig.2a).The membrane was not pure phase,however,as the peaks at 2?=7.2?,10.2?,12.5?,etc.were assigned to LTA phase.The for-mation of LTA-type zeolite was probably due to the high content of sodium hydroxide in the clear synthesis solution [17].

Prolonging

Fig.2.XRD patterns of FAU-type zeolite layers:(a)A 3238M 36320;(b)A 32324M 36320;(c)A 3338M 36320;(d)A 3334M 36320;(e)A 3338;(f)A 33312.

G.Zhu et al./Journal of Membrane Science337 (2009) 47–54

49

Fig.3.SEM images of A3338:(a)top view and(b)cross-section.

in situ aging time at323K,though the peaks of LTA phase gradually weakened,they were still appreciable even after24h(Fig.2b).

In contrast,A3338M36320consisted of a pure FAU phase zeolite layer revealed by the XRD pattern(Fig.2c).Previously we reported that the optimal in situ aging temperature for the CH synthesis of FAU-type zeolite membranes was323K[17].In this case,since the Si/Al ratio of the synthesis solution was doubled,the higher in situ aging temperature,i.e.333K,was supposed to suppress LTA phase effectively by means of accelerating the dissolution of colloidal sil-ica and the rearrangement of aluminosilicate species[17].There was a tiny LTA peak at2?=7.2?in the XRD pattern of A3334M36320 (Fig.2d).Therefore,4h of in situ aging was not long enough to thoroughly suppress LTA phase.On the other hand,it should be no longer than12h,when considerable FAU peaks appeared in

the Fig.4.SEM images of FAU-type zeolite membranes:(a)top view of A3338M35820;(b)top view;(c)cross-section of A3338M36320;(d)top view of A3338M36820.

50G.Zhu et al./Journal of Membrane Science337 (2009) 47–54

XRD pattern before MH,indicating a signi?cant growth of FAU-type zeolite(Fig.2f).

Fig.3a shows that the support surface was covered by a continu-ous gel layer embedded with a great many spherical grains after8h in situ aging at333K.In the magni?ed image,these uniform grains (ca.300–400nm)turned out to be the aggregates of hundreds of nano-crystallites.The gel layer was ca.2?m in thickness(Fig.3b), with a Si/Al ratio of0.8.In the corresponding XRD pattern(Fig.2e), the appreciable and wide peak at2?=6.1?revealed the existence of FAU phase,i.e.the crystallites aforementioned.Therefore,it was concluded that the nucleation event took place during in situ aging and primary zeolite crystallites commenced forming in the matrix of the gel layer.

3.1.2.Microwave heating temperature

Fig.4shows the SEM images of the membranes synthesized with 20min of MH at358,363and368K after in situ aging.A3338M35820 (Fig.4a)and A3338M36320(Fig.4b)presented similar morphol-ogy of the zeolite layers,which was compact and composed of uniform crystals.Nevertheless,the crystals of A3338M36320were well-shaped with more obvious faces.It seemed that the crystal-lization process under MH was more complete in20min at363K than358K.The thickness of A3338M36320zeolite layer was ca.4?m (Fig.4c).

The morphology of A3338M36820was quite different,as shown in Fig.4d.A lot of rough particles were present in the zeolite layer with visible cracks.In the XRD pattern,a distinct peak arose

at Fig.5.I F/S vs.the MH time at363K.A3338M36320was selected for the second stage synthesis.

2?=12.2?,which was assigned to the(101)peak of P-type zeolite. As a consequence,the rough particles were believed to be P-type zeolite[17,18].P-type zeolite is a common impurity phase when synthesizing FAU-type zeolite,especially under the conditions of high synthesis temperature or long synthesis time.The

existence Fig.6.SEM images of the top views of(a)A3338M36310,(b)A3338M36330and(c)A3338M36360,as well as(d)XRD patterns of A3338M36330and A3338M36360.

G.Zhu et al./Journal of Membrane Science337 (2009) 47–5451

of P-type zeolite would weaken the compactness of FAU-type zeo-lite layers owing to the cubic-to-tetragonal phase transformation under a dry atmosphere or at elevated temperatures.To avoid impu-rity phases and save synthesis time,MH was performed at363K in the following investigation.

3.1.3.Microwave heating time

Fig.5shows the intensity ratio of FAU(111)peak and the sup-port peak at2?=25.5?(I F/S)vs.the MH time,which re?ects the growth of FAU-type zeolite on the support.For the?rst stage syn-thesis,the I F/S value ascended rapidly during the initial20min, indicating a fast growth of FAU-type zeolite.A slight increase con-tinued until ca.50min.Since the nucleation of FAU-type zeolite occurred during in situ aging,the pro?le of I F/S before50min could be regarded as the S-shape crystal growth curve without the induc-tion period.Our previous studies revealed that the crystallization process of LTA-zeolite membranes under MH could be divided into two steps,i.e.a fast growth by propagation and densi?cation and a limited growth controlled by the solution-mediated growth mechanism.The optimal MH time to synthesize high performance LTA-type zeolite membranes coincided with the in?exion of the two steps[6].In this case,the in?exion MH time was around20min.

For the second stage synthesis of A3338M36320,I F/S exhibited a sharp increase in the initial5min of MH and reached the maximum around20min.The SEM image(Fig.4b)con?rms that a complete layer of FAU-type zeolite crystals formed on the support after the ?rst stage synthesis.These crystals reacted as“seeds”in the second stage synthesis and promoted the nucleation in the gel phase.In consequence,more and maturer FAU crystallites formed after in situ aging,which made the following crystallization under MH proceed faster than that of the?rst stage synthesis[5].I F/S began to descend after20min,also earlier than that of the?rst stage synthesis.The decrease of I F/S was probably brought by phase transformation to P-type zeolite,which would be discussed in the following sections.

Fig.6a–c shows the SEM images of membrane A3338M36310, A3338M36330and A3338M36360.The zeolite layer of A3338M36310 consisted of uniform crystals(ca.300–400nm),which could be traced back to the grains formed after in situ aging.Nano-crystallites that composed the grains were hardly discriminable,whereas a lot of voids were present between crystals,indicating that the merging process was limited within individual grains at this stage(Fig.6a). After20min,the zeolite layer became much denser(Fig.4b).Some groups of crystals in close proximity fused together,followed by the bridging of the gaps between them.Since the crystals were getting crowded,they exerted on each other and consequently developed notches at their perimeters,which engendered the morphology of crystal faces.The crystals grew larger after30min of MH,develop-ing obvious crystal faces.However,a few rough particles as shown in the inserted image of Fig.6b embedded in the zeolite layer,which were supposed to be primary P-type zeolite.It signi?ed the begin-ning of phase transformation.In the XRD patterns,no appreciable P-type zeolite peak arose at2?=12.2?until60min(Fig.6d),when considerable P-type zeolite particles spread over the zeolite layer (Fig.6c).The Si/Al ratio of the zeolite membrane increased to

ca.

Fig.7.SEM images of(a)the top view and(b)cross-section of A3338M36320–A3338M36320and(c)the top view of A3338M36320–A3338M36330,as well as(d)XRD patterns of A3338M36320–A3338M36320and A3338M36320–A3338M36330.

52G.Zhu et al./Journal of Membrane Science337 (2009) 47–54

Table1

Factors and levels for L9(34)orthogonal array.

Factors1st At(h)1st Mt(min)2nd At(h)2nd Mt(min)

Level1615615

Level2820820

Level310251025

1.5after the initial MH with full power and kept almost changeless thereafter.

Fig.7shows the SEM images of membrane A3338M36320–A3338M36320and A3338M36320–A3338M36330(the former AM stands for the?rst stage synthesis procedure and the latter the second stage).For A3338M36320–A3338M36320,the zeolite crystals were tightly knit with each other and some fused together to form larger crystals(Fig.7a).No visible defects were present in the zeo-lite layer.The layer thickness increased appreciably to about5?m (Fig.7b).After further MH for30min,considerable P-type zeolite crystals again appeared in the zeolite layer(Fig.7c),which was con?rmed by XRD shown in Fig.7d.Apparently,the phase transfor-mation was accelerated as the crystallization process was facilitated at the second stage MH.The obvious peak at2?=12.2?indicated that a great deal of P-type zeolite formed in this period,which led to the destruction of the zeolite layers and thus a decrease of I F/S. Therefore,the second stage MH time should be restricted within 30min.EDX characterization showed no distinct change of the Si/Al ratio during the second stage MH,which was around1.5.

3.2.Optimization of the in situ aging and MH times

Previous investigations con?rmed the in situ aging and MH tem-peratures,as well as the probable ranges of the in situ aging and MH times.Further optimization of the in situ aging and MH times of the two-stage synthesis was carried out through the Taguchi experi-mental design.The orthogonal array of L9(34)was employed,and the factors and levels are listed in Table1.We selected6,8and10h for in situ aging time(At),while15,20and25min for MH time (Mt),respectively.The interactions between the four factors were ignored.

The experimental layout and the pervaporation performance of the as-synthesized zeolite membranes towards a water/ethanol (10/90,w/w)mixture at338K are presented in Table2.The water content in the permeate(W p)was taken as the measured response. The average response for each factor was computed at each level and labelled as K ij,where i represents a factor and j a level.From the average responses,the range(R=K max?K min)of each factor was cal-culated,where K

max and K min were the maximum and minimum for each factor.It was noted that all the membranes were highly water-selective with W p beyond94.6%.Besides,no ethanol was detected Fig.8.K ij vs.three levels of1st in situ aging time,1st MH time,2nd in situ aging time and2nd MH time.

in the permeate for three membranes.This proved the feasibility of the AM method and previous analyses of the effects of synthesis parameters.Fig.8plots K ij vs.three levels of each factor.Based on the aforementioned results,the following conclusions could be made: (1)The optimal values of1st in situ aging,1st MH,2nd in situ aging

and2nd MH times were10h,20min(coinciding with the in?ex-ion of the two crystallization steps),8h and20min,respectively.

(2)1st MH time,with the maximal R,was considered to be the most

in?uential factor of the four.

(3)Though the average response increased with1st in situ aging

time,the membranes synthesized with less in situ aging time

(i.e.Membrane2)also showed high performance as long as the

other three factors were optimal,indicating that1st in situ aging time was less in?uential.

A supplemental experiment was carried out to validate the reproducibility of the AM method and the effect of1st in situ aging time.The pervaporation performance of the membranes synthe-sized with the optimal synthesis parameters except1st in situ aging time was shown in Table3.All the W p of zeolite membranes reached 100%though1st in situ aging time varied from6to10h.The aver-age?ux,however,decrease slightly with1st in situ aging time,from 1.72to1.59kg m?2h?1.In consequence,high performance FAU-type zeolite membranes could be synthesized by the AM method with high reproducibility.

3.3.Pervaporation dehydration of alcohols

Fig.9shows the pervaporation performance of the as-synthesized FAU-type zeolite membrane(Membrane10)towards

Table2

Experimental layout and the pervaporation performance of the as-synthesized zeolite membranes towards a water/ethanol(10/90,w/w)mixture at338K.

No.Experimental plan Pervaporation performance

1st At(h)1st Mt(min)2nd At(h)2nd Mt(min)W p(wt.%)Flux(kg m?2h?1)

161561594.6 1.66 2620820100a 1.70 3625102595.5 1.76 481582596.0 1.74 58201015100 1.62 682562097.3 1.68 71015102097.5 1.66 81020625100 1.62 9102581599.2 1.64

K i196.796.097.397.9

K i297.810098.498.3

K i398.997.397.797.2

R 2.2 4.0 1.1 1.1

G.Zhu et al./Journal of Membrane Science 337 (2009) 47–54

53

Table 3

Pervaporation performance of FAU-type zeolite membranes synthesized with dif-ferent 1st in situ aging time towards a water/ethanol (10/90,w/w)mixture at 338K.

No.1st At (h)W p (wt.%)Flux (kg m ?2h ?1)Average

?ux (kg m ?2h ?1)106100 1.70116100 1.74 1.72

126100 1.71138100 1.65148100 1.62 1.63

158100 1.611610100 1.591710100 1.62 1.59

18

10

100

1.56

Fig.9.Pervaporation performance of Membrane 10towards (a)water/ethanol and (b)water/isopropanol mixtures at 338K.

Fig.10.Pervaporation performance of FAU-type zeolite membranes in situ synthe-sized under CH towards (a)water/ethanol and (b)water/isopropanol mixtures at 338K.

ethanol and isopropanol aqueous solutions at 338K.For the water/ethanol mixtures (Fig.9a),W p was 100%initially,presented a slow decline when the water content in the feed (W f )varied from 9.1%to 2.2%,and ?nally dropped to ca.30%when W f was 0.45%.The permeation ?ux of water decreased almost linearly from 1.72to 0.047kg m ?2h ?1,while the permeation ?ux of ethanol gradually increased to 0.11kg m ?2h ?1.For the water/isopropanol mixtures (Fig.9b),the membrane behaved even better.W p was or close to 100%until W f decreased to 4.8%,after when W p declined slowly with the decrease of W f .The permeation ?ux of water presented a similarly linear decrease nevertheless it was larger than that of water/ethanol mixtures.Only a small amount of isopropanol was detected in the permeate when W f decreased to 0.7%.

Fig.10shows the corresponding pervaporation performance of FAU-type zeolite membranes in situ synthesized by CH [17].For the

Table 4

Pervaporation performance of FAU-type zeolite membranes towards a water/ethanol (10%)mixture.Zeolite (Si/Al)

T (K)

Pervaporation performances Membrane performances

Ref.

Flux (kg m ?2h ?1)

Separation factor H 2O permeance (10?6mol m ?2s ?1Pa ?1)H 2O/EtOH selectivity (1.5)

338 1.7010,000a

2.4010,000This study NaX (1.3)338 1.48380 2.04470[17]NaX (1.3)348 1.91170 1.65210[12]NaY (2.1)348 1.59130 1.35140NaY

348 3.9109 3.1124[19](1.4–1.6)348 4.0300 3.6360[18]NaY 3489.11908.0228[20]NaY

3489.9

190

8.8

231

[11]

a

Beyond the detection limit of GC.

54G.Zhu et al./Journal of Membrane Science337 (2009) 47–54

water/ethanol mixtures(Fig.10a),the decrease of W p was much faster,and the permeation?ux of ethanol exceeded that of water after W f was lower than ca.2%.For the water/isopropanol mix-tures(Fig.10b),W p was100%initially,and then decreased gradually to39.5%as W f decreased to0.80%.By contrast,the correspond-ing W p of Membrane10was beyond80%at the similar W f.The permeation?ux of water decreased rapidly when W f was in the range of6–3%,probably owing to the incremental permeation of isopropanol which blocked the passage of water.

Apparently,the dehydration performance of Membrane10was preferable,especially when W f was of a low value.It could be thus concluded that the non-zeolitic pores were much fewer in the zeolite membranes synthesized by the AM method than those synthesized by CH.For comparison,Table4lists the pervaporation performance of the main FAU-type zeolite membranes reported so far.Membrane10shows overwhelming preponderance in both the separation factor and the water/ethanol selectivity,indicating that a great improvement has been achieved in the synthesis of FAU-type zeolite membrane.The relatively low water permeance compared with the data given by Sato et al.[11,18,20]probably remains with the difference in support type:Sato et https://www.360docs.net/doc/189179621.html,ed asymmetric porous ?-Al2O3support,which was of low permeation resistance.

4.Conclusions

In situ microwave synthesis of high-quality FAU-type zeolite membranes were achieved by the AM method in a clear solution. In situ aging was indispensable as it suppressed the formation of LTA phase and facilitated the nucleation of FAU-type zeolite.The following crystallization process under MH was found to be iden-tical with that of LTA-type zeolite membrane.A rapid growth by propagation through the gel network took place at?rst,parallel-ing with the agglomeration and densi?cation of the crystallites formed after in situ aging and the elimination of the voids.Then the crystallization slowed down,controlled by the solution-mediated growth mechanism which led to the well-shaped zeolite crystals. Afterwards,P-type zeolite came into being and weakened the com-pactness of zeolite layers.Based on the characterization of the formation process,the optimization of the synthesis parameters were readily achieved through the Taguchi experimental design.1st MH time seemed to be the most in?uential factor,with the opti-mal value coinciding with the in?exion of the two crystallization steps.The AM method was ef?cient and reproducible to prepare pure-phase FAU-type zeolite membranes,which exhibited prefer-able water-selectivity in the pervaporation dehydration of ethanol and isopropanol.Only pure water could be detected in the perme-ate before the water content decreased to ca.9%for water/ethanol mixtures and ca.6%for water/isopropanol mixtures.Furthermore, it also proved effective in the scale-up production.We have suc-cessfully synthesized high performance tubular FAU-type zeolite membranes with the length of85cm recently.Acknowledgments

This work was supported by National Science Fund for Distin-guished Young Scholars(20725313)and the Ministry of Science and Technology of China(Grant No.2005CB221403).

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