pervaporation separation of isopropanol-water mixtures through crosslinked chitosan membranes

Journal of Membrane Science 262 (2005) 91–99

Pervaporation separation of isopropanol/water mixtures throughcrosslinked chitosan membranes�

D. Anjali Devia, B. Smithab, S. Sridharb, T.M. Aminabhavia,∗a Membrane Separations Division, Center of Excellence in Polymer Science, Karnatak University, Dharwad 580 003, Karnataka, India

b Membrane Separations Group, Chemical Engineering Division, Indian Institute of Chemical Technology, Hyderabad 500 007, Andhra Pradesh, India

Received 16 August 2004; received in revised form 23 March 2005; accepted 26 March 2005Available online 17 May 2005

Abstract

Chitosan membrane having 84% degree of deacetylation was crosslinked with toluene-2,4-diisocyanate and tested for the dehydration ofisopropanol by the pervaporation method. Pure and crosslinked membranes were characterized by Fourier transform infrared spectroscopyand wide angle X-ray diffraction to study the intermolecular interactions and crystallinity, respectively. Dynamic mechanical thermal analyseswere undertaken to assess the thermal and mechanical stabilities of the membranes. Sorption studies were performed in water, isopropanola anism. Them of 472 anda ess andp©

K

1

dotstrtDpse

f

mix-sily.

nkedand

ctiv-use

hy-intoom-henA

dhydein-

ughervedplexves-

0d

s well as different composition feed mixtures to understand the polymer–liquid interactions and pervaporation separation mechembrane appears to have a good potential for breaking the aqueous azeotrope of 87.5 wt.% isopropanol with a high selectivitysubstantial water flux of 0.39 kg/m2 h 10�m. The influence of operating parameters such as feed composition, membrane thickn

ermeate pressure on membrane performance like flux and selectivity was investigated.2005 Elsevier B.V. All rights reserved.

eywords:Pervaporation; Isopropanol/water azeotrope; Chitosan membrane; TDI

. Introduction

Pervaporation (PV) has been widely used for the dehy-ration of aqueous–organic mixtures[1–3]. Chitosan (CS)r poly(d-glucosamine), a natural biopolymer, obtained by

he deacetylation of chitin, has many inherent characteristicsuch as hydrophilicity, biocompatibility, antibacterial proper-ies, and a remarkable affinity for many substances[2]. Manyeports are available in the earlier literature on the PV separa-ion of water–alcohol mixtures using CS membranes[3–11].etailed description of the preparation of acetic acid com-lex, carboxymethyl, cyanoethyl, amidoxime, carboxyethyl,ulfonated and phosphorylated CS membranes are givenlsewhere[5,6]. Chitosan has many biomedical applications

� This article is CEPS Communication #51.∗ Corresponding author. Tel.: +91 836 2771275;

ax: +91 836 2771275.E-mail address:[email protected] (T.M. Aminabhavi).

[12–15], but in dehydration studies on aqueous–organictures, its hydroxyl and amino groups can be modified ea

Chitosan swells in water and hence, it can be crossliby a suitable agent to improve its mechanical strengthselectivity during PV experiments. The separation seleity for water–alcohol mixture for CS itself is not high becaits free amine form is water insoluble. Since CS has bothdroxyl and amine groups, it can be modified chemicallymany forms. Glutaraldehyde (GA) has been the most cmonly used crosslinking agent that forms Schiff base wreacted with CS[13]. Reports on the PV performance of Gcrosslinked CS membranes[14] show higher selectivity anpermeation flux than those of glyoxal and terephthalaldecrosslinked membranes, which results in higher flexibilityduced by GA to the polymeric chain. Mochizuki et al.[16]studied the PV separation of water-ethanol mixtures throCS membranes neutralized by various acids and obshigh selectivity to water. They treated acetic acid commembranes in NaOH solution to make CS neutral and in

376-7388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
oi:10.1016/j.memsci.2005.03.051

92 D. Anjali Devi et al. / Journal of Membrane Science 262 (2005) 91–99

tigated the effect of metal species such as cobalt on selectivity.Divalent ions including SO42− were effective for increasingthe selectivity[17]. Dense CS membranes that are ionicallycrosslinked by sulfuric acid showed the highest selectivitywith lower permeation rates.

Isopropanol, a widely used solvent in chemical and phar-maceutical industries, is known to form an azeotrope withwater, a characteristic that creates difficulties in its recov-ery by the conventional distillation[18]. The application ofPV as a means to achieve dehydration of solvents has re-ceived a widespread attention from chemical, petrochemicaland pharmaceutical industries. However, the recent technol-ogy improvements have led to a rapid commercialization ofseveral novel membranes that are economical, safe and cleanto be used in the separation of azeotropic and close by boil-ing liquid mixtures by the PV technique[19]. Considerableliterature on the successful dehydration of isopropanol byPV is available.Table 1gives a comparison of PV perfor-mance data of other membranes used in PV separation ofisopropanol–water mixtures[20–24]. It is realized that per-formance of pure CS membrane is not satisfactory due tolarger free volume between the molecular chains. The mem-brane properties of CS can be improved by blending withother polymers[25] or by incorporating a high selectivityzeolite into the membrane[26]. In an effort to investigatethe effect of crosslinked structure on the PV performance ofC -2,4-d ranei s arec

2

2

ies> i, In-d wasr izedw ra-t

2

stinga S in2 teredt wasc knessa fol-l tedt ofs ed byu ropso und

to be the optimum reaction time, but higher concentrationsof TDI produced brittle membranes. The crosslinked mem-branes were washed with acetone and finally vacuum driedfor a period of 12 h. The dried films were utilized in PVexperiments. The stability of the membrane was analyzedby bending the membrane before and after PV studies. Theexperiment performed for the duration of 3 months duringwhich the membrane was found to be stable. After this period,the membrane was bent to ensure its mechanical stability andit was noted that despite bending completely the membranedid not break. Hence, the membrane durability and stabilityappears to be reasonably good[27].

2.3. Membrane characterization

2.3.1. FT-IR studiesPure and crosslinked CS membranes were scanned in

the range 400–4000 cm−1 wave numbers using Nicolet-740,Perkin-Elmer-283B FT-IR spectrophotometer.

2.3.2. Ion exchange capacity (IEC)To determine the total number of interacting groups

present in the membranes, unmodified and crosslinked chi-tosan of similar weight were soaked in 50 mL of 0.01 Msodium hydroxide solution for 12 h at ambient temperature.T lfu-r lorica tantw on

I

o

I

w eu-t l-f es, 5r ounto sedf

2sed

t d CSi sg asv s-t inter-s

2stor-

a -s at a

S membrane, we have used for the first time, tolueneiisocyanate (TDI) as a crosslinking agent and the memb

s used in the PV dehydration of isopropanol. The resultompared with existing membranes.

. Experimental

.1. Materials

Isopropanol, glacial acetic acid and TDI of purit99.9% were purchased from Loba Chemicals, Mumbaia. Chitosan (flakes) of 84% degree of deacetylationeceived as a gift sample from the local market. Deionater of conductivity 20�S/cm was generated in the labo

ory itself.

.2. Membrane preparation

Chitosan membranes were prepared by solution cand solvent evaporation method. The 3 wt.% solution of C% (v/v) aqueous acetic acid was prepared, stirred and fil

o remove the undissolved matter. A bubble-free solutionast on a clean glass plate/petridish to the desired thicnd dried in atmospheric conditions at room temperature

owed by vacuum drying for a period of 5 h at the elevaemperature (50◦C) in an oven to remove the last tracesolvent. The membranes thus prepared were crosslinksing TDI in a hexane bath containing two to three df dibutyl tin dilaureate as a catalyst. Nearly 6 h were fo

hen, 10 mL of solution was titrated against 0.005 M suic acid. The sample was regenerated with 1 M hydrochcid, washed free of acid with water and dried to conseight. The IEC was calculated according to the equati

EC = B − P × MNaOH × 5

m(1)

r

EC = B − P × (MH2SO4 × 2) × 5

m(2)

hereB is the amount of 0.005 M sulfuric acid used to nralize unmodified chitosan,P is the amount of 0.005 M suuric acid used to neutralize the crosslinked membranepresents the factor corresponding to the ratio of the amf NaOH taken to dissolve the polymer to the amount u

or titration, andm is the sample mass in g.

.3.3. XRD analysisA Siemens D 5000 powder X-ray diffractometer was u

o assess the solid-state morphology of the crosslinken a powder form. The X-rays of 1.5406̊A wavelength waenerated by a Cu K� source. The angle of diffraction waried from 0◦ to 65◦ to identify the change in the cryal structure and intermolecular distances between theegmental chains after crosslinking.

.3.4. Thermal analysis by DMTAThe dynamic mechanical properties of CS specimen (

ge and loss moduli, tanδ) were measured by DMTA 1V intrument (Rheometric Scientific, USA) in tensile mode

D. Anjali Devi et al. / Journal of Membrane Science 262 (2005) 91–99 93

Table 1Comparison of the pervaporation performance of the present crosslinked chitosan membrane with the literature data for water–isopropanol mixtures

Membrane Temperature(◦C)

Thickness(�m)

Water in feed(wt.%)

Flux (kg/m2 h) Normalizedflux (×10�m)

Selectivity Reference

Chitosan/TDI 30 50 8.4 0.079 0.39 472 Present workPASA 20 30 0.003 0.008 3686 [20]PASA-bromo propane 30 10 0.004 0.013 ∞PASA-bromooctane 30 0.009 0.026 111PASA-(1-bromo-2-

phenylethane)30 0.006 0.019 ∞

PASA-methylbromoacetate

30 0.008 0.024 ∞

PASA-ethylbromoacetate 30 0.003 0.010 ∞PVA crosslinked with

glutaraldehyde30 – 10 0.194 – 116 [21]

PVA crosslinked withcitric acid

30 – 05 0.095 – 741

Composite membrane ofNaAlg and chitosan

60 45 10 0.554 2.493 2010 [22]

NaAlg 30 – 10 0.058 – 411 [23]NaAlg/GG-g-pAAm – 10 0.062 – 796NaAlg/GG-g-pAAm – 10 0.043 – 891NaAlg/PVA (75:25) – 0.025 – 195 [24]NaAlg/PVA (50:50) – 0.034 – 119NaAlg/PVA (25:75) – 0.039 – 91

PASA: poly(amide sulfonamide); PVA: poly(vinyl alcohol); NaAlg: sodium alginate; GG: guar-gum; AA: acrylamide.

frequency of 10 or 1.0 Hz at the heating rate of 3◦C/min to de-termine the viscoelastic behavior of the crosslinked and pureCS membranes in nitrogen atmosphere over the temperaturerange 35–200◦C.

2.3.5. Sorption studiesWeighed samples of cross-linked chitosan films (3 cm di-

ameter) were soaked in pure water and isopropanol as wellas binary mixtures of different compositions. The films weretaken out at different soaking time intervals and weighed im-mediately after carefully wiping out the excess liquid to deter-mine the amount of liquid sorbed by the film at that particulartime duration,t. The process was repeated until the films at-tained steady state as indicated by a constant weight after acertain period of soaking time. The degree of swelling wascalculated from the equation:

degree of swelling= Ms

Md(3)

whereMs is the mass of the swollen polymer in g andMdis the mass of the dry polymer in g. The % sorption wascalculated from the equation

% sorption=(

Ms − Md

Md

)× 100 (4)

2

20 mL

b tedm Hgi mbly

(Fig. 1b) was approximately 20 cm2. The experimentalprocedure is described in detail elsewhere[28]. Permeatesamples were collected after a period of 8–10 h. Tests werecarried out at room temperature (30± 2◦C) and repeatedtwice using fresh feed solution to check reproducibility. Thecollected permeates were weighed after allowing them toattain room temperature in a Sartorius electronic balance(accuracy, 10−4 g) to determine the flux. Feed as well aspermeate mixtures were analyzed by gas chromatography(Nucon, Model 5765) to evaluate the membrane selectivity.

2.4.2. Flux and selectivityIn pervaporation, flux,Jof a given species, say faster per-

meating component,i of a binary liquid mixture comprisingof i (water) andj (isopropanol) is given by

Ji = Wi

At(5)

HereWi represents the mass of water in permeate (kg),Ais the membrane area (m2) and t represents the permeationtime (h). In the present study, even though different mem-brane thicknesses were utilized, the flux has been normalizedand reported for the thickness of 10�m for the effect of feedcomposition and effect of permeate pressure. Membrane se-lectivity, α is the ratio of permeability coefficients of water tot tivec

α

wt

.4. Pervaporation experiments

.4.1. Influence of operating conditionsPervaporation experiments were carried out on a 10

atch level instrument with an indigenously construcanifold (Fig. 1a) operated at a vacuum as low as 0.05 mm

n the permeate line. Membrane area in the PV cell asse

hat of isopropanol, which is calculated from their respeconcentrations in feed and permeate as given below,

= y(1 − x)

x(1 − y)(6)

herey is the permeate weight content of water (%) andx ishe feed weight content of water (%).


Fig. 1. Schematics of laboratory pervaporation unit.

2.5. Analytical procedure

Feed and permeate samples were analyzed using a Nu-con Gas Chromatograph (GC Model 5765) installed withthermal conductivity detector (TCD) and packed columnof 10% DEGS on 80/100 Supelco port of 1/8 in. i.d. and2 m length. The oven temperature was maintained at 70◦C(isothermal), while the injector and detector temperatureswere maintained at 150◦C each. The sample injection sizewas 1�L and pure hydrogen was used as a carrier gas at apressure of 1 kg/cm2. The GC response was calibrated for thisparticular column and conditions with known compositionsof isopropanol–water mixtures. Calibration factors were fedinto the software to obtain the correct analysis for unknownsamples.

3. Results and discussion

Chitosan membrane was chosen for the PV stud-ies of isopropanol–water mixtures on the basis of theclose proximity of its Hansen’s solubility parameter value

(43.04 J1/2/cm3/2) [29] to that of water (47.9 J1/2/cm3/2) [30]as well as other useful features, such as hydrophilicity, goodmechanical strength and chemical resistance.Scheme 1rep-resents the crosslinking reaction between amino groups ofchitosan with the isocyanate group of TDI, resulting in theformation of urea linkage. This is possible because the aminogroup of chitosan is a stronger nucleophile than its hydroxylgroup. During the crosslinking reaction, the amino group ofchitosan interacts with the carbonyl group of TDI, resultingin the formation of urea linkages. An estimation of the num-ber of groups present before and after crosslinking gives anidea of the extent of crosslinking.

3.1. Membrane characterization

3.1.1. Ion exchange capacity (IEC)The amount of residual amine and hydroxyl groups present

after crosslinking was estimated from the IEC studies. Itwas noted that unmodified chitosan showed an IEC of0.42 mequiv./g, whereas the crosslinked polymer exhibitedan IEC of 0.2 mequiv./g. The IEC is equivalent to the totalnumber of free amino groups (considering the fact that amino


Scheme 1. Crosslinking reaction of chitosan with 2,4-toluylene diisocya-nate.

groups are more interactive than hydroxyl groups), R-NH2present in the membrane which decreased upon crosslink-ing [31]. This shows that almost 50% of the amine groupspresent in the unmodified chitosan have now formed thecrosslinks with TDI.Scheme 1represents the crosslinkingreaction occurring between chitosan and TDI. The occur-rence of crosslinking is proved by IEC and FT-IR studies.Hence, TDI will establish a linkage with chitosan throughurea formation as confirmed by FT-IR (Fig. 2). To the best ofour knowledge, it is the first kind of study wherein TDI is em-ployed as a crosslinking agent and the membrane could with-stand the solvent environment and PV condition employed inthis study.

3.1.2. FT-IR studiesFig. 2 shows the FT-IR spectra of the pure and the

crosslinked CS membrane. The spectrum of crosslinked CSfilm shows peaks in the range 700–850 cm−1, indicating thepresence of benzene ring. Reduced number of peaks in therange of 1000–1200 cm−1 compared to the spectra of pureCS is due to the vibration of CO bond formed by the ure-thane linkage. The peak observed at 1640 cm−1 shows thepresence of urea. The spectra of pure CS shows a broad peakat wavenumbers 1570–1655 cm−1, which indicates the pres-ence of amide I and II. The wavenumber 2833 cm−1 cor-r xylg st anda 2,4-d

Fig. 2. FT-IR spectra of (a) unmodified chitosan membrane and (b)crosslinked chitosan membrane.

3.1.3. XRD studiesFrom the spectra obtained for pure and crosslinked CS

shown inFig. 3, it is observed that XRD patterns of bothpure and crosslinked CS membranes appear to be semicrys-talline. The broad peaks observed in the XRD pattern around10◦ of 2θ indicate the average intermolecular distance of theamorphous part and relatively sharp semicrystalline peaksare centered at around 20◦ of 2θ. From these observations, itcan be concluded that the average intermolecular distancesin CS and crosslinked CS are the same. It can be seen that

Fig. 3. XRD spectra of (a) unmodified chitosan membrane and (b)crosslinked chitosan membrane.

esponds to CH2 stretching, whereas that of free hydroroup is observed at 3450 cm−1. FT-IR analysis confirm

he crosslinking of chitosan by the reaction of hydroxylmine groups of CS with the carbonyl group of toluene-iisocyanate.


Fig. 4. DMTA tracings of (a) unmodified chitosan membrane and (b)crosslinked chitosan membrane.

there are two distinct bands with their maxima at 2θ = 7–9◦and 2θ at 20◦, which are related to two types of crystals:crystal 1 and crystal 2[32]. Crystal 1, which correspondsto the peak at 9◦ is responsible for the separation, sinceit comprises functional groups likeNH2 and OH andhas undergone significant change after crosslinking. A re-duction in the effectived-spacing value from 12.07̊A forpure CS to 7.8̊A for the crosslinked CS gives a clear pic-ture of the shrinkage in cell size or inter-segmental spac-ing, which would improve the selective permeation of CSmembrane.

3.1.4. Thermal analysisThermal properties of the pure and crosslinked CS

membranes were examined by DMTA. It was of partic-ular interest to estimate how the thermal transition ofCS varied with crosslinking. DMTA tracings of CS andits crosslinked structure are shown inFig. 4a and b,which reveal that pure CS has a glass transition temper-ature,Tg at 112.6◦C, which gets enhanced to 176.65◦Cfor the crosslinked membrane, indicating that crosslink-ing with TDI might have caused a reduction in segmentalmobility.

3.1.5. Swelling characteristicsSwelling data of the crosslinked CS membrane in

isopropanol–water mixtures of different compositions arepresented inTable 2. The % sorption computed from Eq.(4) in the feed composition at the azeotropic concentrationcontaining 12.5 wt.% of water was found to be low i.e., 15,but sorption increased steadily with an increase in water com-position, which indicates that CS membrane interacts exten-sively with water and is capable of selective absorption andpermeation of water molecules to bring about the separation.However, absorption of a large amount of water at high feedwater concentrations could cause the membrane to swell ex-cessively leading to a decrease in membrane selectivity.

3.2. Influence of operating conditions

It is well known that separation characteristics of a mem-brane depend upon the interaction between solvent to be sep-arated and the membrane matrix. Hydrophilic membrane likeCS can develop hydrogen bond interaction with water lead-ing to preferential sorption and diffusion of water through thebarrier membrane[33]. The influence of feed composition,membrane thickness and permeate pressure on membraneperformance has been examined in detail.

3.2.1. Effect of feed compositionrties

w g them ium.T withT ingo tingp branet .E cedaT ilicC ism[ Sm over,t lef genb nesoi wn ah velyn ingt ivityd feeds ell aso ane.T aterc feedm witha ncedfl as a

The influence of feed concentration on PV propeas studied. Experiments were carried out after soakinembrane for 12 h in the feed mixture to ensure equilibrhe PV performance of chitosan membrane crosslinkedDI was studied for various feed compositions comprisf 4.415–39.672 wt.% water, while keeping other operaarameters such as permeate pressure and mem

hickness constant at 2 mmHg and 50�m, respectivelyxpectedly, a rise in feed concentration of water produn increase in water flux from 0.28 to 1.24 kg/m2 h (seeable 2and Fig. 5). Mass transport through a hydrophS membrane occurs by solution–diffusion mechan

34]. As shown inScheme 1, the structure of crosslinked Cembrane has polar urethane and urea linkages. More

he residual OH and NH2 groups will also be availabor the interaction with water molecules through hydroonding. In addition to sorption data of the membrabtained for the binary feed mixtures presented inTable 2,

t was found that the crosslinked CS membrane has shoigh degree of sorption in pure water (121%), but relatiegligible sorption in pure isopropanol (0.05%). Accord

o the solution–diffusion mechanism, membrane selectepends on the partition of two components between theolution and the upstream layer of the membrane as wn the difference of their diffusivities across the membrhe preferential affinity of the membrane towards wauses swelling, which allows a rapid permeation ofolecules. The extent of sorption correspondingly risesn increase in feed water concentration resulting in enhaux. However, increased swelling of the membrane h


Table 2Effect of feed composition on separation performance of the crosslinked chitosan membrane (permeate pressure 2 mmHg; membrane thickness 50�m)

Feed composition % Sorption in membrane Permeate composition Selectivity,α = y(1−x)x(1−y) Normalized flux (kg/m2 h)

Water (x) Isopropanol (1− x) Water (y) Isopropanol (1− y)

4.415 95.585 5.4 96.02 3.98 523.33 0.288.385 91.615 6.6 97.73 2.27 472.00 0.39

10.633 89.367 15.55 98.08 1.92 429.25 0.4516.262 73.105 25.0 98.49 1.51 336.27 0.6128.581 71.419 27.9 98.70 1.3 190.31 0.9439.672 60.328 31.2 88.89 11.11 12.25 1.24

negative impact on membrane selectivity since the swollenand plasticized upstream membrane layer allows someof the isopropanol molecules to escape into the permeateside along with water molecules, indicating a drop inselectivity from 523.33 to 12.25 as seen inFig. 5. It is worthmentioning that the membrane showed promising results fordehydrating feeds containing 5–28% water. Selectivity,α

is good for residual water concentrations below 28%. Thus,azeotropic composition (87.5 wt.%) of isopropanol waseasily broken down by PV process. About 97.73% of waterwas obtained in permeate with a selectivity of 472 and a fluxof 0.39 kg/m2 h. The results of this work show comparablefluxes and selectivities with respect to other membranes ascompared inTable 1for dehydrating isopropanol.

3.2.2. Effect of membrane thicknessThe effect of membrane thickness on water flux and

selectivity were evaluated at constant feed composition(azeotropic) and permeate pressure (2 mmHg) by castingmembranes of thickness ranging from 25 to 125�m. With anincrease in membrane thickness, a gradual reduction in fluxfrom 0.265 to 0.032 kg/m2 h can be clearly evidenced fromFig. 6. Even though the availability of polar groups enhances

F e ofc ep

with an increase in membrane thickness, the flux decreasessince diffusion of feed is retarded due to increased resistanceto mass transfer. The permeate concentration of water variedfrom 88.89 to 96.02 wt.%, which means that selectivity hasincreased from 12.2 to 523.3. In the PV experiment, upstreamlayer of the membrane is swollen and plasticized due to sorp-tion of feed liquid thus, allowing the unrestricted transportof feed components. In contrast, the downstream layer is vir-tually dry due to continuous evacuation in the permeate sideand therefore, this layer forms the restrictive barrier, whichallows only the interacting and smaller size molecules such aswater to pass through. It is expected that the thickness of thedry layer would increase with an increase in the overall mem-brane thickness, thereby resulting in an improved selectivityas observed in the present case.

3.2.3. Effect of permeate pressureThe effect of permeate pressure on membrane perfor-

mance of the crosslinked chitosan membranes was studied inthe range 0.5–20 mmHg at a constant membrane thickness of50�m. As the permeate pressure decreases, the driving forcefor diffusing molecules decreases, resulting in higher perme-ate rates.Fig. 7exhibits a considerable increase in flux from0.06 to 0.58 kg/m2 h. Similarly, selectivity decreased from745 to 22. With the increasing permeate pressures, diffusiono the

F ce ofc rmeatep

ig. 5. Effect of feed composition on pervaporation performancrosslinked chitosan membranes (membrane thickness 50�m, permeatressure 1 mmHg).

f the feed molecules through the membrane, which is

ig. 6. Influence of membrane thickness on pervaporation performanrosslinked chitosan membranes (feed composition: azeotropic, peressure: 2 mmHg).


Fig. 7. Effect of downstream pressure on pervaporation performance ofcrosslinked chitosan membrane (feed composition: azeotropic, membranethickness: 50�m).

rate-determining step, becomes slow whereas, high vacuumexerts a larger driving force. Under lower vacuum conditions,the volatility of feed components governs the separation se-lectivity of the membrane. Isopropanol, being more volatilethan water, permeates competitively, thus lowering theselectivity.

4. Conclusions

Hydrophilic pervaporation of this study has shown animmense potential as a viable technique for the dehydra-tion of isopropanol. Toluene diisocyanate-crosslinked chi-tosan membrane, used for the first time in the literature,could easily break the azeotrope of isopropanol–water mix-ture, indicating that the membrane acts as a third phase andselectively allows water molecules to pass through due topreferential affinity. TDI appears to be a useful and novelcrosslinking agent by rendering chitosan highly selectiveto water without compromising heavily on the flux. Char-acterization of the membranes by FT-IR and XRD con-firmed the crosslinking of chitosan. The XRD results ofthe crosslinked chitosan showed a reduction in the effec-tive d-spacing value, which is an indication of shrinkagein the cell size, which would in turn, improve the selec-t didn me-c feedw oundt ex-t in-c singm d thes eatep lec-t fec-

tively combined with distillation to constitute an economicalhybrid process to achieve the desired purity levels of iso-propanol.

Acknowledgments

Dr. T.M. Aminabhavi and Miss Anjali Devi thank theUniversity Grants Commission, New Delhi (Grant No.F1-41/2001/CPP-II) for a financial support to establishthe Center of Excellence in Polymer Science (CEPS). Dr.K.V.S.N. Raju, Organic Coatings and Polymers Division forDMTA analyses. Ms. C.L. Kalpana and Ms. G. Dhanuja,Membrane Separations Groups, IICT, are thanked fortheir assistance. The help from Mr. Saibabu of DesignDivision for tracing work is gratefully acknowledged. Dr.M. Ramakrishna, Head, Membrane Separations Group,deserves thanks for his support and encouragement. Thiswork represents a collaborative research under the MoUbetween IICT, Hyderabad and CEPS, Dharwad.

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