[10] Preparation of Inner-side Tubular Zeolite NaA Membranes in a Continuous Flow System

7/27/2019 [10] Preparation of Inner-side Tubular Zeolite NaA Membranes in a Continuous Flow System

1/10

Available online at www.sciencedirect.com

Separation and Purification Technology 59 (2008) 141150

Preparation of inner-side tubular zeolite NaA membranesin a continuous flow system

Marc Pera-Titus 1, Marta Bausach 1, Joan Llorens , Fidel Cunill

Chemical Engineering Department, University of Barcelona, 08028 Barcelona, Spain

Received 21 February 2007; received in revised form 30 May 2007; accepted 31 May 2007

Abstract

Zeolite NaA membranes were synthesized on the inner side of porous titania (rutile) asymmetric tubular supports in a flow system where the

synthesis gel was circulated through the support with flow rates in the range 1.54 mL min1

by the action of gravity. The syntheses were carriedout hydrothermally at 358 K for 67 h either with or without previous brush-seeding of the supports. The membranes (1020m in thickness)

showed great ability to dehydrate ethanol/water mixtures (92:8, w/w) by pervaporation with selectivities and fluxes, respectively, up to 8500 and

1.2kgm2 h1 at 323 K. The role of intercrystalline defects in the pervaporation performance of the synthesized membranes was also investigated.

2007 Elsevier B.V. All rights reserved.

Keywords: Zeolite membrane; Continuous synthesis; Pervaporation; Alcohol dehydration; Intercrystalline pathways

1. Introduction

The research field on zeolite membranes has gained increas-

ing attention in the last two decades in both materials science

and chemical engineering owing to their potential applicationsas membrane separators, catalytic membrane reactors, selec-

tive sensors and components in micro-electronic devices [15].

In particular, a great deal of studies have been devoted to the

preparation of hydrophilic zeolite membranes for dehydrating

azeotropic and close-boiling liquid mixtures by pervaporation

[611]. Among these zeolites, zeolite NaA has been the target of

many investigationsdue to itshigh Al/Si ratio andsmallpore size

(4.1 A). Under non-acidic conditions, zeolite NaA membranes

offer the double advantage of high selectivity towards water sep-

aration (>10,000) and high water fluxes. These attributes make

them attractive for dehydrating solvents at industrial level [12].

Among the different synthetic strategies reported in the lit-

erature for zeolite membrane synthesis [1319], zeolite NaA

membranes have been conventionally prepared by hydrother-

mal synthesis onto a porous support in one or several batch

Corresponding author. Tel.: +34 934034872; fax: +34 934021291.

E-mail addresses: [email protected](M. Pera-Titus),

[email protected] (J. Llorens).1 Present address: Institut de Recherches sur la Catalyse et lEnvironnement

de Lyon (IRCELYON), UMR5256, CNRS/Universite Claude Bernard, Lyon 1,

France.

cycles, either in situ or with a preliminary seeding step (i.e.

secondary growth method). The seeding of the support helps

improving the quality and reproducibility of the zeolite layers by

decoupling the nucleation and crystal growth steps [20,21]. By

carefully controlling the seed layer coating the support throughthe use of a convenient technique (e.g. cross-flow filtration [22]

or vacuum seeding [23]), the synthesized membranes show an

improved separation performance and a preferential crystalline

orientation. Table 1 shows a detailed survey of the most relevant

seeding and hydrothermal synthesis conditions together with

the available lab-scale techniques for zeolite NaA membrane

preparation.

Regarding the methods presented in Table 1, most of the stud-

ies have been devoted to preparing zeolite films on flat supports

or onto the outer surface of tubular supports. In the special case

of inner-side tubular membranes, more suitable for developing

full-size industrial modules, gel renewal constitutes an effec-

tive strategy to partially overcome nutrient depletion due to the

restricted accessibility of the synthesis solution to the lumen of

the support. We have recently reported the batch preparation of

high quality inner-side zeolite NaA membranes on -alumina

under a low-g centrifugal field [26], which creates an axial flow

that renews the synthesis solution in contact with the membrane.

In order to reduce the number of synthesis cycles, we have

also addressed the preparation of inner-side zeolite NaA mem-

branes using a semi-continuous synthesis system [24]. This

technique, earlier conceived by Pina et al. [25] for outer-side

1383-5866/$ see front matter 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.seppur.2007.05.038
mailto:[email protected]:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_11/dx.doi.org/10.1016/j.seppur.2007.05.038http://localhost/var/www/apps/conversion/tmp/scratch_11/dx.doi.org/10.1016/j.seppur.2007.05.038mailto:[email protected]:[email protected]


2/10

142 M. Pera-Titus et al. / Separation and Purification Technology 59 (2008) 141150

Nomenclature

a activity

A parameters in the Antoine equation for vapor sat-

uration pressure (K1)

Si (0) MS surface diffusivity of water at zero coverage

(m2 s1)ESw activation energy of water diffusion (kJ mol

1)

ESw,eff effective activation energy of water diffusion

defined by Eq. (2) (kJmol1)

KSw adsorption constant of water (Pa1)

thickness of the zeolite layer (m)

M molecular weight (kg mol1)

NSw surface flux of water (kg m2 s1)

P0w saturation vapor pressure of water (Pa)

R constant of gases (8.314 Pa m3 mol1 K1)

SWG seeding weight gain (mg cm2)

T temperature (K)

xw molar fraction of water in the liquid feedXw weight fraction of water in the liquid feed

Yw weight fraction of water in the vapor permeate

Greek symbols

H0w adsorption enthalpy of water on zeolite NaA

(kJ mol1)

S density of zeolite NaA (1900 kg m3)

zeolite NaA membrane synthesis, allows pulse-renewal of the

synthesis solution in an autoclave at periodic intervals by the

action of a set of electro-pneumatic valves. Layer formation canbe controlled by adjusting the gel renewal rate (i.e. the rate at

which fresh gel is introduced into and used gel removed out

of the autoclave). The membranes with the best pervaporation

performance are those prepared with gel renewal rates lying

in the range 1/41/7 min1 (i.e. introduction of fresh gel every

47 min). These membranes give selectivities and fluxes up to

16,000 and 0.6kg m2 h1, respectively, for the separation of

92:8 (w/w) ethanol/water mixtures at 323 K.

Despite the benefits of the semi-continuous synthesis sys-

tem in terms of layer growth control, this technique presents

some drawbacks regarding large-scale implementation. First, it

involves the synthesis of membranes in an autoclave filled with

a volume of 155 mL of synthesis gel that surrounds the tube(95% of total volume), but which itself is not employed in

the synthesis of inner-side layers, thus contributing negatively

to the economy of the process. A second shortcoming is related

to the periodical pulse-renewal of the gel in the lumen of the

support, which might sweep away the zeolite seeds and remove

the amorphous gel layer covering the support surface during

the synthesis. Finally, two semi-continuous synthesis cycles are

often required to ensure good PV performance.

To overcome all the above stated limitations, an alternative

method for gel renewal can focus on using a flow system where

the gel is continuously circulated in the lumen of the tubes.

However, only a few studies dealing with the synthesis of inner-

side tubular zeolite membranes by inducing a forced flow have

been reported in theliterature.In this way, Richter et al.[34] have

reported the synthesis of ZSM-5 membranes on the inner side

of-alumina tubes and capillaries at 423K for 72 h by pumping

the synthesis gel in the lumen of the supports at a flow rate in the

range 414 mL min1 (0.25 cm min1). Culfaz et al. [35] have

also prepared good quality MFI-type zeolite membranes on -

alumina tubular supports at 355368 K for 7276 h in one to

three cycles with a circulation of the synthesis gel by the action

of a peristaltic pump at a flow rate of 648 mL min1.

To our knowledge, the use of a flow system for zeolite NaA

membrane synthesis has only been reported by Yamazaki and

Tsutsumi [36] on flat supports, but has not already been reported

for inner-side tubular configurations. Accordingly, this study is

aimed at the hydrothermal synthesis of inner-side zeolite NaA

membranes in a continuous flow system where the synthesis gel

is flown by the action of gravity. The technique is promising for

scaling up the synthesis process and for zeolite NaA synthesis

in multi-channel tubes and capillaries.

2. Experimental

The zeolite NaA membranes were prepared by in situ and

seeded hydrothermal synthesison the inner-sideof tubular asym-

metric supports of 8 mm i.d. and 10 mm o.d. (TAMI, France).

At the innermost part of these supports there was a 0.8m pore-

size titania (rutile) layer of approximately 40m in thickness.

Before the synthesis, the tubes were subjected to enameling at

both ends with a commercial glaze (Duncan AN 313 Antique

Blue) and a home-made glaze, both resistant to strong alkali,

leaving an effective permeation length of approximately 5 cm

and inner area of 12.6 cm

2

. The glazed tubes were dried at roomtemperature for a few minutes and then heated to 1173 K for

15 min with a heating ramp of 1 K min1.

2.1. Seeding of the supports

Prior to secondary growth synthesis, the inner surface of the

tubular supports was brush-seeded with A-type zeolite crys-

tals (2m) supplied by IQE (Industrias Qumicas del Ebro,

Zaragoza, Spain). To this end, zeolite NaA crystals were pow-

dered on a thin test-tube brush capable of penetrating the lumen

of the supports. Then the inner side of the supports was seeded

by rotating the zeolite-loaded brush along the tube axis. The

zeolite layer coating the support after the seeding was measuredin terms of seeding weight gain (SWG) [mg of seeds cm2 of

surface area].

2.2. Hydrothermal syntheses

The hydrothermal syntheses were carried out in one cycle

for periods of 37 h at atmospheric pressure in the tempera-

ture range 353363 K with a cloudy synthesis gel of molar

composition 1.0 Al2O3:1.8 SiO2:3.9 Na2O:270 H2O. The gel

was prepared using two aluminate and silicate precursor solu-

tions according to the procedure reported previously [22]. The

aluminate solution was prepared by dissolving the appropri-


3/10

M. Pera-Titus et al. / Separation and Purification Technology 59 (2 008) 1411 50 143

Table1

ConditionsforzeoliteNaAmembranepreparationbyhydrothermalsynthesis

Reactorconfiguration

Compositionofthesynthesissolution

(Al2O3:SiO2:

Na2O:H2O:templates)

T(K)

Tim

e(h)/cycles

Support

Seedingtechnique

Seedsize(m)

References

Semi-continuous(AC)

(1/41/16min1)

1:1.8:3.9:273

363373

5/12

-Al2O3innertube

Brushseeding;C-Ffiltration

2

[24]

Semi-continuous(AC)

(1/131/25min1)

1:1.8:3.9:273

363

5/1

-Al2O3outertube

Rubbing

1

[25]

Centrifugalfield(VS)

(100rpm)

1:2:2:120400

363373

3/24

-Al2O3innertube

C-Ffiltration

2,4

[22]

Centrifugalfield(VS)

(5202520rpm)

1:1.8:3.6:270

373

3/23

-Al2O3innertube

Brushseeding

1

[26]

Dynamic(AC)(75rpm)

1:5:55.1:1004

.7

323

48/1

ZrO2/Csheet

[8]

Static(VS)

1:5:50:1000

333

24/1

-Al2O3outertube

C-Ffiltration

0.33.0

[22]

1:2:3:200

363

24/1

Hollowfiber

[27]

1:2:3:200

363

16

24/13

-Al2O3disk

Dipcoating

1

[28]

1:4.4:41.9:833.3

353

4/1

TiO2disk

UV(32W)

[29]

1:5:50:1000

363

16

/1

-Al2O3disk

Dipcoating

1

[30]

1:2:2:120

373

3.5/1

Mullite,-Al2O3outertubes

1

[9]

Static(VSwithdistiller)

1:2:2:80144

353373

36

/1

-Al2O3outertube

Rubbing;Dipcoating

200mesh

[6]

Static(VS-MW

2450MHz)

1:2:3:200

363

54

0min/1

-Al2O3disk

Rubbing

NA

[31]

1:5:50:1000

363

15min/1

Rubbing

NA

[32]

Static(AC)

1:9:80:5000

353

5/1

-Al2O3disk

Rubbing;Dipcoating

0.7

[33]

Notation:Autoclave(AC);vesselopentoatmosphere(VS).

Fig. 1. Scheme of the continuous flow system used for inner-side zeolite NaA

membrane synthesis.

ate amount of sodium aluminate powder supplied by Aldrich

(Al2O3 = 53 wt.%, Na2O=43wt.%, Fe2O3 = 4 wt.%) in deion-

ized water at 343 K under vigorous stirring in a closed flask. The

silicate solution was prepared by dissolving a sodium silicate

solution supplied by Aldrich (SiO2 =27wt.%,NaOH=14wt.%)

in the remaining water under stirring. The silicate solution was

added in three consecutive steps to the aluminate solution under

vigorous stirring and the temperature was kept to 343 K.

The scheme of the experimental set-up used for inner-side

zeolite NaA membrane synthesis is depicted in Fig. 1. In general

terms, the support, with the outer surface wrapped with Teflon

tape to avoid crystal deposition, was placed inside a moduleimmersed in a temperature-controlled oilbath.The gelwas flown

through the lumen of the tube by the action of gravity from a

reservoir (2 L) preheated at 323 K and kept under mild stirring

to a discharge vessel. A thermocouple positioned in the lumen

of the tube was used to monitor any temperature fluctuation

with gel introduction. In this work, the gel flow rate was fixed

at a value in the range 1.54 mL min1 for all the synthesized

membranes, which is expected not to sweep away the growing

zeolite layer on the support inner surface. Thegel flow rate could

be regulated by means of the height difference between the level

of the gel in the reservoir and that at the outlet of the system.

The height difference was progressivelyincreasedfrom an initialvalue of10 cm, in the beginning of thesynthesis to compensate

the reduction of the gel level in the reservoir. At the end of the

synthesis, the as-synthesized membranes were removed from

the module, washed with boiling water for 1 h and dried in an

oven at 373 overnight under vacuum (


4/10


zeolite layer. The dehydration performance of the as-synthesized

membranes was first studied by vacuum PV for the separation of

a 92:8 (w/w) ethanol/water mixture at 323 K with the permeate

pressure kept


5/10


Fig. 2. XRD patterns of zeolite NaA layers grown onto the inner

surface of seeded and unseeded tubular supports (T= 358 K; synthe-

sis time= 67 h; gel flow rate= 1.54 mLmin

1

). (a) Membrane ZA02,SWG=0.11mgcm2; (b) membrane ZA04, SWG = 0.13 mgcm2; (c) mem-

brane ZA07, SWG= 0 mgcm2. The asterisk shows the location of rutile peaks

from the support.

secondary growth method shows higher and more definite peaks

than that of membrane ZA07 prepared by in situ hydrothermal

synthesis.Accordingly, the seeding of the support appears to pro-

vide more crystalline layersdue to a more uniform andcontrolled

growth of the zeolitic material.

Fig. 3 shows some SEM micrographs of membranes ZA02,

ZA04 and ZA07. The inspection of the top view micrographs

of these membranes (see Fig. 3a1c1) reveals in all cases the

presence of well-intergrown layers constituted by a randomlyoriented distribution of cubic and truncated-side cubic crys-

tals. In good keeping with the XRD patterns plotted in Fig. 2,

the differences in surface morphology observed for membrane

ZA07 (Fig. 3a1) compared to membranes ZA02 and ZA04

(Fig. 3a1b1) might be attributed to the presence of amorphous

material on the layer. Fig. 3a2c2 show that the membranes con-

sist of three layers: (1) synthesized zeolite layer, (2) intermediate

titania layer and (3) bulk support constituted by large crystals

that generates a macroporous array of7m mean pore size.

In all cases, the thickness of the zeolite layer lies in the range

1020m and increases with the synthesis time. The seeding of

the support does not seem to exert an effect on layer thickness,

in agreement to what is observed when preparing membranes inthe semi-continuous system.

3.3. PV performance of the as-synthesized membranes

The results of the PV tests carried out on the as-synthesized

membranes towards the dehydration of ethanol/water mixtures

are summarized in Table 3. For comparison, Table 3 also includes

some reported data concerning the PV performance of some

membranes synthesized under a centrifugal field and in a semi-

continuous system. As can be seen, in the optimal synthesis

conditions, a continuous flow system provides membranes with

excellent selectivities and high total fluxes. A stability test car-

Table 3

PV performance of the membranes prepared in the continuous flow system in

comparison with those reported in our previous literature

Membrane Synthesis technique PV resultsa

Selectivity

(W/E)

NT (kg m2 h1)

ZA01

Continuous flow system

51 0.93ZA03 1091 0.76

ZA04 495 1.16

ZA05 8538 0.89

ZA08 160 0.72

ZA09 76 0.97

ZA10bSemi-continuous system

2444 0.48

ZA11b 1050 0.48

ZA12cCentrifugal field

502 0.62

ZA13c 294 0.32

ZA14 Batch synthesis 1.50

a PV conditions: feed pressure, 13bar; feed water fraction, 89wt.%; T,

323 K; permeate pressure, 13mbar.

b From ref. [15]renewal rate: (at a) 1/7min1; (at b) 1/4min1; (at c) twosynthesis cycles; -Al2O3 support.

c From ref. [17]rotational speed, 100rpm; (at c) three synthesis cycles;

-Al2O3 support.

ried out for membrane ZA05 (see Fig. 4) reveals that this

membrane preserves its PV performance for at least 100 h of

continuous operation.

It should be noted that the fluxes for the membranes prepared

in this work are ca. twice the value that can be obtained for

membranes synthesized under a centrifugal force field and in a

semi-continuous synthesis system (see Table 3). This result is

consistent with the reduction up to half of the layer thickness forthe membranes prepared in a continuous flow system compared

to those prepared with the other two aforementioned techniques.

In addition, these fluxes are as high as the best values reported

in the literature for the PV separation of ethanol/water mixtures

using both flat and inner-/outer-side zeolite NaA membranes

at the same temperature and feed composition (see Table 4 for

comparison) and are comparable with those that can be obtained

with commercial zeolite NaA membranes [41,42].

Fig.5 showsacorrelationbetweentheN2 permeanceand both

the total flux and water/ethanol selectivity for the membranes

listed in Table 2. As expected, the water/ethanol selectivity is

reduced with the N2 permeance, while the total flux across the

membrane shows the opposite trend. The membranes are onlyable to separate ethanol/water mixtures efficiently when their

N2 permeance is


6/10


Fig. 3. SEM micrographs of tri-layered membranes ZA02, ZA04 and ZA07 grown on asymmetric TiO2 supports. Top views, a1c1; cross-sections, a2c2. Synthesis

conditions as in Fig. 2.

number of gel pulses in the lumen of the support using the semi-

continuous system seems to make it more difficult to prevent the

membranes from defect formation, thus requiring thicker layers

to achieve a similar PV performance.

3.4. Effect of feed composition and temperature on the PV

performance: role of intercrystalline domains

Fig. 6 plots the effect of the feed composition on the total

flux and water/ethanol selectivity at low feed water fractions

(210 wt.%) for membrane ZA05 prepared in a continuous flow

system and for membranes ZA11ZA13 prepared using either

a semi-continuous synthesis system or in the presence of a cen-

trifugal field (see Table 3). As can be seen in Fig. 6a, the total

flux shows a linear increase with the water composition or water

activity in the feed for all the membranes, as expected on the

basis of the strong hydrophilic character of zeolite NaA. Given

the trends shown in Fig. 6a, the surface diffusivities of water at

zero coverage can be calculated using an adsorptiondiffusion

model based on the MaxwellStefan diffusion theory as was


7/10


Table 4

PV performance of zeolite NaA membranes towards dehydration of ethanol/water mixtures

Thickness (m) Support Water in feed (wt.%) T(K) Selectivity (W/E) Flux (kg m2 h1) Reference

1020 TiO2 tube (i) 10 323 8500 0.81.0 This study

30 -Al2O3 tube (i) 8 323 600 0.50 [22]

2030 -Al2O3 tube (i) 8 323 >10000 0.50 [24]

10 -Al2O3 tube (o) 10 398 3600 3.80 [25]

7 -Al2O3 tube (i) 9 366 130 2.50 [26]NA ZrO2/C sheet 10 323343 9001000 0.160.18 [8]

3.5 TiO2 disk 5 318 >10000 0.86 [29]

10 Mullite tube (o) 10 323 >10000 0.77 [9]

30 -Al2O3 tube (o) 10 323 1700 0.79 [6]

4 -Al2O3 disk 10 303 10000 1.00 [33]

NA Mullite tube (o) 5 298 >10000 0.68 [37]

30 Mullite tube (o) 10 333 1000 1.20 [7]

5 SS tube (o) 10 313 180 0.079 [38]

7 -Al2O3 disk 10 298 3000 0.072 [39]

10 -Al2O3 disk 10 333 >10000 0.57 [19]

56 -Al2O3 tube (i) 5 323 >10000 1.50 [40]

Notation: Outer tube (o); inner tube (i); not available (NA).

Fig. 4. Water/EtOH (W/E), selectivity () and flux () as a function of time

for membrane ZA05. PV conditions as in Table 3.

outlined in a previous work[43]

Sw(0) =NSTYwZA

SqMMwKSwaw,LP0w

(1)

where the activity coefficients have been estimated by the

UNIFAC method [44] and a value of 104 Pa1 has been

considered for the adsorption constant of water, KSw. In thepresent calculations, the contribution of the support to the over-

all mass transfer has been omitted, since it has been found

to be


8/10


Fig. 6. Evolution of (a) total flux and (b) water/ethanol selectivity with water feed composition for membranes: (a) ZA5 (), (b) ZA11 (), (c) ZA12 () and (d)

ZA13 (). PV conditions as in Table 3. The straight and dashed lines refer to the trends observed for membrane ZA5 and for the set of membranes ZA11ZA13,

respectively.

the basis of their lower water/ethanol selectivities compared to

those of membrane ZA05.

Fig. 7 shows the effect of temperature on the water flux

and selectivity for the set of membranes ZA03, ZA05, ZA11

and ZA12. As expected, an Arrhenius trend of the water flux

with temperature is observed for all the tested membranes (see

Fig. 7a), with effective activation energies lying in the range

3340 kJmol1. These values agree, within the limits of the

experimental error, with those reported by Kondo et al. [9] (see

Table 5). Taking into account all the contributions to water mass

transfer in the PV process according to an adsorptiondiffusion

model [43], the effective activation energy of water includes the

following contributions:

ESw,eff= ESw +H

w + RA (2)

where Ew is the activation energy for water surface diffusion,

Hw the adsorption enthalpy of water on zeolite NaA andparameter A belongs to the Antoine equation that accounts for

the evolution of saturation vapor pressure with the temperature

(A =5300K1 for water in the temperature range 293363 K).

Taking a value of43kJ mol1 for the adsorption enthalpy

of water [43], the computed activation energy of water found

in this study approaches the effective activation energy val-

ues (note that RA = 44.06 kJ mol1Hw =43kJmol1!!).

Therefore, the activation energy of water diffusion falls into the

interval 3340 kJ mol1, which compares well with the value

reported by Zhu et al. [45] from the separation of water/N2mixtures using zeolite NaA membranes.

Regarding the evolution of the water/ethanol selectivity with

the temperature at low water fractions and in the tempera-

ture range 303363 K (see Fig. 7b), a maximum appears to be

observed at 325 K for the best quality membranes, namely

membranes ZA03 and ZA05 prepared in the continuous flow

system. However, for membranes ZA11 and ZA13, a posi-

tive trend of the selectivity with the temperature seems to be

observed. In agreement with the above stated considerations

dealing with the role of intercrystalline domains, the discrepancy

between both trends might be ascribed to the higher contribution

of large defects in the latter membranes. For these membranes,

when operated at low feed water fractions, a temperature raise

might enhance water diffusion acrossthe zeolite layer, thus com-

pensating to a certain extent the preferential mass transfer of

ethanol through large defects and therefore giving rise to anincrease in the membrane selectivity.

More insight into the effect of large intercrystalline pores in

the PV performance in zeolite NaA membranes can be gained

by comparing their ability towards dehydration of short- and

long-chain primary alcohols. Fig. 8 plots the evolution of the

total flux and selectivity towards water separation of membrane

ZA13 with the length of chain of the primary alcohol in the

liquid mixture at low water fractions (2.5 and 4.5 mol%) and at

323 K. As can be seen, while the total flux appears to be only

Fig. 7. Evolution of (a) total flux and (b) water/ethanol selectivity with temperature for membranes: (a) ZA3 (), (c) ZA5 (), (b) ZA11 () and (d) ZA13 (). PV

conditions as in Table 3. The straight and dashed lines refer to the trends observed for membranes ZA3 and ZA5 and for membranes ZA11ZA13, respectively.


9/10


Table 5

Effective activation energies of water flux across zeolite NaA membranes

Membrane Synthesis technique Xw range (wt.%) Trange (K) Ew,eff (kJmol1)a Reference

ZA03Continuous flow system

4.34.7

303363

34 1 This study

ZA05 3.94.2 39 2 This study

ZA11 Semi-continuous 2.559.0 40 4 This study

ZA13 Centrifugal field 4.85.2 33 3 This study

Zeolite NaA (outer-side) Static batch 10100313353

35 [9]

Zeolite NaA (flat) Static batch 10 5152 [7]

a Typical error for a probability level of 95%.

Fig. 8. Evolution of (a) total flux and (b) water/alcohol selectivity with the number of carbon atoms in the alcohol for membrane ZA13. Feed composition: ( )

xw = 2.5mol% and () xw = 4.5 mol%. Other PV conditions as in Table 4. The straight lines refer to the trends observed.

slightly affected by the length of chain of the alcohol, except for

methanol, whose molecule ressembles more to that of water, the

selectivity becomes strongly promoted. As has been outlined by

Okamoto et al. [6] when studying the performance of zeolite

NaA membranes towards the dehydration of methanol, ethanol,

acetone and DMF mixtures, the selectivity of the membranes is

promoted as the ability of the solvent to adsorb on zeolite NaAis reduced. Moreover, despite the presence of a certain number

of large defects in the zeolite layer, their contribution to mass

transfer is compensated by that within zeolite pores due to their

stronger hydrophilic character, which favors the adsorption of

smaller molecules.

4. Conclusions

A continuous flow system has been presented in this work

that allows the synthesis of good quality zeolite NaA mem-

branes on the inner-side of tubular ceramic supports. Compared

to other reported methods for inner-side zeolite NaA membranesynthesis (i.e. semi-continuous and centrifugal force field), this

technique is economically advantageous, since only the gel fill-

ing the lumen of the support is refreshed along the synthesis.

Taking into account that this technique can be easy to scaled-up,

it constitutes a promising option for inner-side zeolite mem-

brane synthesis at large scale and for zeolite NaA synthesis in

multichannel tubes and capillaries. The selectivities and fluxes

of the membranes prepared using this technique approach the

best values reported in the literature for inner-side zeolite NaA

membranes. This latter aspect is especially promising in terms

of membrane area economy. Notwithstanding the presence of a

large number of defects, zeolite NaA membranes can be used

confidently in PV applications that involve dehydration of heavy

non-adsorbing species, like 1-butanol and 1-pentanol.

Acknowledgements

The authors would like to express their gratitude to the Span-

ish Ministry of Education and Science for financial support(projects PPQ2000-0467-P4-02 and CTQ2005-08346-C02-01).

The comments of Dr. Sylvain Miachon have been very useful in

the preparation of this paper.

References

[1] E.E. McLeary, J.C. Jansen, F. Kapteijn, Zeolite based films, membranes

and membrane reactors: progress and prospects, Microporous Mesoporous

Mater. 90 (2006) 198.

[2] J. Coronas,J. Santamaria, Theuse of zeolite films insmall-scaleand micro-

scale applications, Chem. Eng. Sci. 59 (2004) 4879.

[3] J. Coronas, J. Santamaria, State-of-the-art in zeolite membrane reactors,

Top. Catal. 29 (2004) 29.[4] T.C. Bowen, R.D. Noble, J.L. Falconer, Fundamentals and applications of

pervaporation through zeolite membranes, J. Membr. Sci. 245 (2004) 1.

[5] J. Caro, M. Noack, P. Kolsch, R. Schafer, Zeolite membranesstate of

their development and perspectives, Microporous Mesoporous Mater. 38

(2000) 3.

[6] K. Okamoto,H. Kita, K. Horii,K. Tanaka,Zeolite NaAmembranes:prepa-

ration, single-gas permeation, and pervaporation and vapor permeation of

water/organic liquid mixtures, Ind. Eng. Chem. Res. 40 (2001) 163.

[7] D. Shah, K. Kissick, A. Ghorpade, R. Hannah, D. Bhattacharyya, Pervapo-

ration of pharmaceutical waste streams and synthetic mixtures using water

selective membranes, J. Membr. Sci. 179 (2000) 185.

[8] J.J. Jafar, P.M. Budd, Separation of alcohol/water mixtures by pervapora-

tion through zeolite A membranes, Microporous Mater. 12 (1997) 305.

[9] M. Kondo, M. Komori, H. Kita, K. Okamoto, Tubular-type pervaporation

module with zeolite NaA membrane, J. Membr. Sci. 133 (1997) 133.


10/10


[10] X. Li, E. Kikuchi, M. Matsukata, Separation of wateracetic acid mixtures

by pervaporation using a thin mordenite membrane, Sep. Purif. Technol.

32 (2003) 199.

[11] S. Li, V.A. Tuan, J.L. Falconer, R.D. Noble, Pervaporation of water/THF

mixtures using zeolite membranes, Ind. Eng. Chem. Res. 40 (2001) 1952.

[12] Y. Morigami, M. Kondo,J. Abe,H. Kita,K.I. Okamoto,The firstlarge-scale

pervaporationplantusingtubular-typemodulewith zeolite NaAmembrane,

Sep. Purif. Technol. 25 (2001) 251.

[13] H. Lee, P.K. Dutta, Synthesisof free standing chabazitefilms, MicroporousMesoporous Mater. 38 (2000) 151.

[14] S. Alfaro, M. Arruebo, J. Coronas, M. Menendez, J. Santamaria, Prepa-

ration of MFI type tubular membranes by steam-assisted crystallization,

Microporous Mesoporous Mater. 50 (2001) 195.

[15] Z.-L. Cheng, Preparation of NaA zeolite membrane with highpermeability

by using a modified VPT method, Chem. Lett. 35 (2006) 1056.

[16] K. Aoki, K. Kusakabe, S. Morooka, Gas permeation properties of A-type

zeolite membrane formed on porous substrate by hydrothermal synthesis,

AIChE J. 46 (2000) 221.

[17] A. Huang, W. Yang, Electrophoretic technique for hydrothermal synthesis

of NaA zeolite membranes on porous-Al2O3 supports, Mater. Res. Bull.

42 (2007) 657.

[18] A. Navajas, R. Mallada, C. Tellez, J. Coronas, M. Menendez, J. Santa-

maria, The use of post-synthetic treatments to improve the pervaporation

performance of mordenite membranes, J. Membr. Sci. 270 (2006) 32.[19] Y. Li, H. Chen, J. Liu, W. Yang, Microwave synthesis of LTA zeolite

membranes without seeding, J. Membr. Sci. 277 (2006) 230.

[20] L.C. Boudreau, J.A. Kuck, M. Tsapatsis, Deposition of oriented zeolite A

films: in situ and secondary growth, J. Membr. Sci. 152 (1999) 41.

[21] J. Bronic, B. Sobunic, M. Skreblin, Investigationof the influenceof seeding

on the crystallization of zeolite A in the membrane-type reactor, Microp-

orous Mesoporous Mater. 28 (1) (1999) 73.

[22] M. Pera-Titus, J. Llorens, F. Cunill, R. Mallada, J. Santamaria, Preparation

of zeolite NaA membranes on the inner side of tubular supports by means

of a controlled seeding technique, Catal. Today 104 (2005) 281.

[23] A. Huang, Y.S. Lin, W. Yang, Synthesis and properties of A-type zeolite

membranes by secondary growth method with vacuum seeding, J. Membr.

Sci. 245 (2004) 41.

[24] M. Pera-Titus, R. Mallada, J. Llorens, F. Cunill, J. Santamaria, Prepara-

tion of inner-side tubular zeolite NaA membranes in a semi-continuous

synthesis system, J. Membr. Sci. 278 (2006) 401.

[25] M.P. Pina, M. Arruebo, M. Felipe, F. Fleta, M.P. Bernal, J. Coronas, M.

Menendez, J. Santamaria, A semi-continuous method for the synthesis of

NaA zeolite membranes on tubular supports, J. Membr. Sci. 244 (2004)

141.

[26] F. Tiscareno-Lechuga, C. Tellez, M. Menendez, J. Santamaria, A novel

device for preparing zeolite-A membranes under a centrifugal force field,

J. Membr. Sci. 212 (2003) 135.

[27] X. Xu,Y. Bao, C. Song, W. Yang, J. Liu, L. Lin, Synthesis, characterization

and single gas permeation properties of NaA zeolite membranes, J. Membr.

Sci. 249 (2005) 51.

[28] X. Xu, W. Yang, J. Liu, L. Lin, N. Stroh, H. Brunner, Synthesis of NaA

zeolite membrane on a ceramic hollow fiber, J. Membr. Sci. 229 (2004) 81.

[29] A.W.C. Van den Berg, L. Gora, J.C. Jansen, M. Makkee, T. Maschmeyer,

Zeolite A membranes synthesized on a UV-irradiated TiO2 coated metal

support: the high pervaporation performance, J. Membr. Sci. 224 (2003)

29.

[30] X. Xu, W. Yang, J. Liu, L. Lin, Synthesis of NaA zeolite membranes from

clear solution, Microporous Mesoporous Mater. 43 (2001) 299.

[31] X. Xu, W. Yang, J. Liu, L. Lin, Synthesis of NaA zeolite membrane by

microwave heating, Sep. Purif. Technol. 25 (2001) 241.

[32] Y. Han, H. Ma, S. Qiu, F. Xiao, Preparation of zeolite A membranes bymicrowave heating, Microporous Mesoporous Mater. 30 (1999) 321.

[33] I. Kumakiri, T. Yamaguchi, S.I. Nakao, Preparation of zeolite A and fau-

jasite membranes from a clear solution, Ind. Eng. Chem. Res. 38 (1999)

4682.

[34] H. Richter, I. Voight, P. Fischer, P. Puhlfur, Preparation of zeolite mem-

branes on the inner surface of ceramic tubes and capillaries, Sep. Purif.

Technol. 32 (2003) 133.

[35] P.Z. Culfaz, A. Culfaz, H. Kalipcilar, Preparation of MFI type zeolite

membranes in a flow system with circulation of the synthesis solution,

Microporous Mesoporous Mater. 92 (2006) 134.

[36] S. Yamazaki, K. Tsutsumi, Synthesis of A-type zeolite membrane using a

plateheaterand its formationmechanism,MicroporousMesoporousMater.

37 (2000) 67.

[37] M. Kazemimoghadam, A. Pak, T. Mohammadi, Dehydration of

water/1,1-dimethylhydrazinemixtures by zeolite membranes,MicroporousMesoporous Mater. 70 (2004) 127.

[38] S.M. Holmes, M. Schmitt, R.J. Markert, J.O. Plaisted, P.N. Forrest, P.N.

Sharratt, A.A. Garforth, C.S. Cundy, J. Dwyer, Zeolite A membranes for

use in alcohol/water separations. Part I. Experimental investigation, Chem.

Eng. Res. Des. 78 (2000) 1084.

[39] C.M. Braunbarth, L.C. Boudreau, M. Tsapatsis, Synthesis of ETS-4/TiO2compositemembranes and their pervaporationperformance,J. Membr.Sci.

174 (2000) 31.

[40] H. Ahn, H. Lee, S.B. Lee, Y. Lee, Pervaporation of an aqueous ethanol

solution through hydrophilic zeolite membranes, Desalination 193 (2006)

244.

[41] V. van Hoof, C. Dotremont, A. Buekenhoudt, Performance of Mitsui NaA

type zeolite membranes for the dehydration of organic solvents in com-

parison with commercial polymeric pervaporation membranes, Sep. Purif.

Technol. 48 (2006) 304.

[42] A. Urtiaga, E.D. Gorri, C. Casado, I. Ortiz, Pervaporative dehydration of

industrial solvents using a zeolite NaA commercial membrane, Sep. Purif.

Technol. 32 (2003) 207.

[43] M. Pera-Titus, J. Llorens, J. Tejero, F. Cunill, Description of the dehydra-

tion pervaporation performance of A-type zeolite membranes: a modeling

approach based on the MaxwellStefan theory, Catal. Today 118 (2006)

73.

[44] R.C. Reid, J.M. Prausnitz, B.E. Poling, The Properties of Gases and Liq-

uids, fourth ed., McGraw-Hill, New York, 1987.

[45] W. Zhu, L. Gora, A.W.C. Van den Berg, F. Kapteijn, J.C. Jansen, J.A.

Moulijn, Water vapour separation from permanent gases by a zeolite-4A

membrane, J. Membr. Sci. 253 (2005) 57.

Documents

[10] Preparation of Inner-side Tubular Zeolite NaA Membranes in a Continuous Flow System