Journal of Industrial and Engineering Chemistry 18 (2012) 604–610

A novel membrane on pervaporation performance for dehydrationof Caprolactam solution

Qin Li, Ping Yu *, Yanwen Lin, Tianrong Zhu, Yunbai Luo

College of Chemistry and Molecule Science, Wuhan University, Wuhan 430072, PR China

A R T I C L E I N F O

Article history:

Received 23 December 2010

Accepted 22 March 2011

Available online 7 November 2011

Keywords:

Konjac glucomannan

e-Caprolactam

Cross-linking

Pervaporation

A B S T R A C T

Konjac glucomannan (KGM) is a kind of polysaccharide with wide applications, except in pervaporation

(PV). This article focuses on the new function of KGM and simultaneously improving a new dehydration

process for e-Caprolactam (CPL). KGM was cross-linked with glutaraldehyde (GA) at proportions of 0.3,

0.5, and 0.7 wt%. Cross-linked membranes were characterized by scanning electron microscope, Fourier

transform-infrared, and X-ray diffraction to assess the membranes of morphology, intermolecular

interactions, and observe the effects of cross-linking on crystallinity, respectively. Cross-linked KGM as

the active layer of the composite membranes has the net matrix structure, and many characteristics

improved compared with pure KGM. Data showed that KGM cross-linked with GA displayed good

swelling and PV performance, and the composite membranes had superior separation performances in

dehydrating the CPL solution. The highest separation factor could reach 3531. The study provided a new

way for both KGM application and CPL dehydration.

� 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at SciVerse ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

1. Introduction

The application of polymers has become more widespread withthe development of industry worldwide. Most industrial polymersnow are obtained by chemical synthesis, be decomposed slowly innature [1]. Polymer materials with high-value applications thatdegrade under natural conditions have become the focus of thepolymer application industry in recent years. Scientists havegradually committed themselves to research on natural macro-molecular material [2,3], in hopes of alleviating the petroleumcrisis and environmental problems.

Konjac glucomannan (KGM), a polysaccharide, is extracted fromthe tuber of Amorphohallus Konjac, K Koch. It consists of b-1,4-linked D-mannose and D-glucose units with a molar ratio of 1.6:1 [4–6] and a low degree of acetyl groups at the side chain C-6 position. Itis a natural polymer with excellent biocompatibility, biodegradabil-ity, and hydrophilicity [7,8]. It can be easily prepared into variousderivatives due to the activity of hydroxyl groups. Various modifiedforms of KGM have been shown as novel medicine [9], environmen-tally benign emulsifier [10], and drug carriers [11].

Pervaporation (PV) is an effective, energy-efficient alternativeand eco-friendly clean technology used to separate azeotropic,close-boiling, isomeric, or heat-sensitive liquid mixtures in the

* Corresponding author. Tel.: +86 27 68772263; fax: +86 27 68776726.

E-mail address: yuping@whu.edu.cn (P. Yu).

1226-086X/$ – see front matter � 2011 The Korean Society of Industrial and Engineer

doi:10.1016/j.jiec.2011.11.039

chemical industry [12–14]. For e-Caprolactam (CPL) purification,traditional separation techniques, such as thin-film distillation,crystallization, and melt crystallization by suspension, have manydisadvantages, especially low heat transfer coefficient, a largeamount of middle pressure steam consumption, and coagulationfrom steam containing considerable CPL. Therefore, we introducedPV into CPL purification. We previously used a variety ofmembranes, such as modified PVA [15] and chitosan–PVA blendingcomposite membranes [16], used in a CPL-water system on PV[17,18]. Many studies report the properties of modified KGMmembranes on food and packaging industries [19,20]. However,the application of KGM as a material in PV has not been reported.With its good hydrophilic nature, KGM in PV for a CPL-watersystem may be an excellent film-forming separate material.However, the difficulty in using natural polymer is due to lowdurability, especially poor water resistance.

This paper aims to modify KGM to improve the mechanicalproperties [21], water solubility, and separative duty of a CPLsolution with a cross-linking agent. The morphological structure,thermal stability, and mechanical properties of the modified filmcharacterization were assessed using infrared (IR), wide-angle X-ray diffraction (WAXRD), derivative thermogravimetric curve(DTG), scanning electron microscope (SEM), and swelling test.The relationship between the structure and the physicochemicalproperties was discussed. In addition, this paper aims to determinewhether KGM modified film would have the desired separativeduty for a CPL solution.

ing Chemistry. Published by Elsevier B.V. All rights reserved.

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610 605

2. Experiment

2.1. Materials

CPL (industrial grade) was supplied by Baling Petrochemical Co.Ltd. (SINOPEC, China), while KGM was purchased from QiangsenKonjac Corp., Wuhan, China. The content of glucomannan is above95%. The viscosity is 10 Pa S in 1 wt% concentration. Glutaralde-hyde (GA, 25 wt% in water) was purchased from Guoyao ChemicalsCo., Ltd. (Sichuan, China). Other chemicals were of reagent gradeand used without further purification.

Porous ultrafiltration membrane of polyacrylonitrile (PAN)(cut-off MW 5 � 104) was supplied by the Development Centerof Water Treatment Technology (China). Deionized water wasused in preparing the aqueous feed solutions for the PVexperiments.

2.2. Preparation of cross-linked composite membranes

KGM was dissolved in deionized water to prepare a concentra-tion of 1 wt% solution. A series amount (0.3, 0.5, and 0.7 wt% of thesolute) of the cross-linking agent (GA) was added, and the reactionlasted for 24 h. The resulting homogenous solution was used forthe sequent process after degassing.

The coated membranes, hydrolyzed PAN microporous mem-branes, were prepared by immersing PAN ultrafiltration mem-brane in 5 wt% NaOH aqueous solution at 50 8C for 1 h, washedthoroughly with deionized water until neutral, immersed in 1 NHCl aqueous solution for 20 min, and then washed with water untilneutral [22]. Then, the prepared solution was cast on the porousPAN substrate membranes held on a glass plate. The compositemembranes in the gelatination state were allowed to evaporateslowly in a dust-free atmosphere until dry at ambient temperature.Finally, the composite membranes were treated in an air-circulating oven to effect thermal cross-linking structure. Thecross-linked membranes in different GA mass ratios (0.3%, 0.5%,and 0.7%) were designated as KGM-1, KGM-2, and KGM-3,respectively.

2.3. Swelling experiments

Equilibrium swelling experiments on active layer of allmembranes were performed in feed mixtures of CPL/water withcompositions ranging from 30 to 70 wt% water at 40 8C. Themasses of dry membranes were first determined and wereequilibrated by soaking in different compositions of feedmixture in a sealed vessel for 48 h. The absorbed membraneswere taken out and wiped off the surface solution with tissuepaper carefully, weighed it as Ws. All experiments wereperformed at least three times and the results were averaged.The percentage degree of swelling (S) was calculated by thefollowing equation:

S ð%Þ ¼ ðWs � WdÞWd

� 100 (1)

where Wd and Ws are the weights of the dry and swollenmembranes, respectively.

2.4. Characterization

2.4.1. Fourier transform-infrared (FT-IR) spectroscopy

The cross-linking reaction of KGM with GA was confirmedthrough FT-IR. The FT-IR spectra of various composite mem-branes were scanned using a Nicolet AVATAR 360 FT-IRspectrometer.

2.4.2. Scanning electron microscopy (SEM)

The morphologies of the KGM composite membranes wereobserved with SEM (FEI Quanta 200, Holland). All specimens werecoated with a conductive layer of sputtered gold.

2.4.3. X-ray diffraction (XRD) analysis

XRD measurements were analyzed using a Shimadzu XRD-6000(Japan) diffractometer equipped with graphite monochromatizedCu Ka radiation (l = 1.54060 A) at 40 kV and 30 mA with a scanrate of 48/min. The angle of diffraction was changed from 58 to 458to identify any changes in the crystal structure.

2.4.4. Thermal analyses

Thermal gravimetric analysis was conducted with SETSYS 16instrument (France) under a nitrogen atmosphere with a flowcapacity of 50 ml/min. The scan was carried out at a heating rate of10 8C/min from 20 8C to 600 8C. The sample weight was about 5–10 mg and analyzed using an a-Al2O3 crucible.

2.4.5. PV experiments

The tested membrane was allowed to equilibrate for about 1–2 h at the corresponding temperature before performing the PVexperiment with fixed compositions of the feed mixture. Afterestablishing a steady state, the permeate vapor was collected in atrap immersed in the liquid nitrogen jar on the downstream side atfixed intervals. The feed mixtures varied from 30 to 70 wt%; CPLand PV experiments were conducted in the range of 40–60 8C [16].Pervaporation unit is the same as it used in reference [15,16].

From the PV data, the separation performance of membraneswas assessed in terms of flux (J) and separation factor (a). Thesewere calculated using the following equations, respectively:

a ¼ yw=yCPL

xw=xCPL(2)

J ¼W

At(3)

where in Eq. (2), xw, yw are the mole fraction of water in the feedand permeate, and xCPL, yCPL are the mole fraction of CPL in the feedand permeate; in Eq. (3), W (g), A (m2) and t (h) are the weights ofpermeates, effective membrane area, and time, respectively.

3. Results and discussion

3.1. Membrane characterization

3.1.1. FT-IR analysis

The IR spectrum of KGM (Fig. 1a) shows that the typicalabsorption band of KGM [19]. The absorption band at 896 cm�1 isattributed to the glucose unit of KGM, while the absorption bandsat 875 and 809 cm�1 are vibrations of the mannose unit in KGM.Compared with pure KGM, the absorption band of the stretching of–OH groups in cross-linked membranes were narrower and theabsorption frequency shifts to a lower wave number. This suggeststhat the interaction between cross-linking agent and KGM reducedthe number of–OH groups, which is also seen in the change of thepeak at 1635 cm�1, indicating that cross-linking reaction reducedthe number of hydrogen bonds. FT-IR results confirmed the cross-linking in the polymers.

3.1.2. SEM analysis

Fig. 2 shows the SEM micrographs of the cross-sectionmorphology for KGM film. The multilayer structure of themembrane was observed clearly: an active layer and a supportedporous layer similar to the membrane studied by Zhang et al.[15,18]. The surface of the active layer was smooth and compact

Fig. 1. FT-IR spectra of pure and crosslinked KGM membranes with different GA

contents. Fig. 3. X-ray diffraction pattern of (a) pure KGM; (b) KGM-1; (c) KGM-2 and (d)

KGM-3.

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610606

without any cracks. The thickness was less than 10 mm, and theentire section was homogenized. The aperture of the porous layerwas also arranged regularly, which benefits the permeable of themembranes and improves the flux [15].

3.1.3. XRD analysis

Fig. 3 shows the XRD patterns of pure KGM, KGM-1, KGM-2, andKGM-3. The diffraction pattern showed only weak and broadprominent peaks. All samples studied exhibited hump-like diffusepeaks within the 2u range of 10–258. The pattern of pure KGM(Fig. 3a) showed a broad peak at about 2u = 158 [23]. Generally, thissuggests that pure KGM films were highly amorphous with lowcrystallinity. The lack of stereo-regularity along the backbone ofKGM molecules could account for the low crystallinity becauseKGM is a copolymer of mannose and glucose with a random andoccasional occurrence of acetyl groups at the saccharide unitsalong the molecule. Different from the pattern of pure KGM, thepatterns of KGM-1, KGM-2, and KGM-3 had weaker peaks.Generally, the cross-linking composites disturbed the KGM fromcrystallization, resulting in decreasing crystallinity. The structureof the polymer was significant prior to water penetration throughthe membrane on PV. This is because the decrease in crystallinityreduced diffusion resistance and increased free volume, helping toimprove the penetration flux of each component [24]. The X-rayresult agreed with the FT-IR result.

Fig. 2. The cross-section morphology of the crosslinked KGM membrane.

3.1.4. Thermal analysis

Thermal stability analysis of polymer material is helpful inselecting materials with the best properties for specific use. Fig. 4shows the DTG thermograms of pure KGM and cross-linked KGMfilms. Pure KGM showed a one-stage degradation process withinthe range of 200–400 8C. This could be attributed to thedisintegration of macromolecule chains of KGM. Compared withpure KGM film, the peak corresponding to the decompositiontemperature of cross-linked films moved to the high temperaturezone; along with the increasing ratio of cross-linking agent in thefilms, the peak was also moving to the higher temperature region.This is because the reaction between the compounds withaldehyde groups and the compounds with hydroxyl groups formedthe aldehyde complex ring compounds and ether compounds,which have better thermal stability [15]. Compared with the pureand cross-linked PVA membranes used in the same system, thestability of KGM membranes is stronger.

3.2. PV characteristics

3.2.1. Swelling experiments

Sorption mechanism is an important factor for membraneswelling in the PV process, together with the diffusion, controls thetransport of permeating molecules under the chemical potentialgradient. This section determines the influences of sorption in PVperformance. To study the effects of cross-linking agent ratio onmembrane swelling, the percentage degree of swelling was plottedwith respect to different mass percentages of CPL from 30% to 70%in the feed at 40 8C, as shown in Fig. 5.

Fig. 4. DTG thermograms of (a) pure KGM; (b) KGM-1; (c) KGM-2 and (d) KGM-3.

Fig. 5. Degree of swelling for crosslinked KGM membrane at 40 8C.

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610 607

The degree of swelling of the membrane increased when theCPL content in the solution decreased because all membranes werehighly hydrophilic and increased the strong interaction betweenwater molecules and the membrane containing –OH groups [25].

An increase in the proportion of cross-linking agents fordifferent membranes decreased the swelling degree of cross-linked KGM membranes due to the strengthened cross-linkingreaction with KGM and GA. More cross-linking reactions formedmore cross-linked bonds, so that the activity of molecular chainsreduced step by step, increasing the mechanical strength of themembranes but reducing the hydrophilic characteristic [18]. Thismeans water molecules were absorbed more preferentially thanCPL and hence would diffuse more easily through the membranes.

3.2.2. Effect of operating temperature

The PV process is temperature dependent [26,27], as both fluxand separation factor are influenced by a change in temperature.The stability of cross-linked membranes at high temperatures isalso worth studying. We chose the KGM-2 membrane and thecondition of 50 wt% of CPL in feed to study temperature effects, andthe resulting values are presented in Fig. 6.

Fig. 6. Effect of the operating temperature on the pervaporation performances for KGM-2

CPL aqueous solution.

The operating temperature range was chosen from 40 8C to60 8C [28]. Under the condition studied, water and the CPL flux ofKGM-2 membrane were 267 and 0.229 g/(m2 h), respectively,whereas at 50 8C and 60 8C, the data were 384.1, 0.394, and 558.2,and 0.756 g/(m2 h), respectively. The total flux and separationfactor (Fig. 6b) were 267.2 and 1298, g/(m2 h), respectively,whereas at 50 8C and 60 8C, the data were 384.5, 1085, and 559, and821 g/(m2 h), respectively. As shown in Fig. 6a, this could beattributed to the increase in feed temperature making the partialfluxes increase, and this phenomenon may be traditionallyexplained by the increase in frequency and amplitude of thethermally induced polymer chain. The other source of this behaviorwas the change in penetrant diffusivities [29] and the expansion ofthe free volume [30]. Increasing temperature brings about highermolecular diffusivity [31,32]. The partial fluxes increased follow-ing an increase in temperature, while the separation factordecreased synchronously (Fig. 6b). This is because high tempera-ture not only decreased the intermolecular interaction betweenpermeants, but also decreased within the membrane material,increasing the free –OH groups on the membrane [24]. These areresponsible for dominating the plasticizing effect on the mem-brane due to greater swelling. Therefore, the permeation of

in terms of (a) water and CPL flux and (b) total flux and separation factor at 50 wt%

Table 1The chemical and physical characteristics of water and CPL.

Molecular formula Molecular weight State of normal temperature Dipole moment (debye) Melting point, 8C

Water H2O 18.02 Liquid 1.85 0

CPL NH(CH2)5CO 113.18 Solid 3.88 68–70

Table 2Activation energy data of KGM-1, KGM-2 and KGM-3 in pervaporation at (a) 60 wt%

and (b) 70 wt% CPL aqueous solution.

Feed

concentration

Membrane

type

DEa activation energy

(kJ/mol)

Et Ew ECPL

60 wt% KGM-1 26.42 26.41 41.33

KGM-2 27.88 27.86 47.47

KGM-3 29.20 29.17 48.30

70 wt% KGM-1 28.90 28.88 36.25

KGM-2 31.06 31.03 52.99

KGM-3 32.33 32.30 56.30

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610608

diffusing molecules and the associated molecules through themembrane becomes easier, leading to an increase in totalpermeation flux while suppressing the separation factor. Increas-ing feed temperature increased the vapor pressure in the feedcompartment, but the vapor pressure at the permeate side was notaffected. These resulted in an increase in driving force withincreasing temperature. The morphological structures of thepolymer network highly influenced the free volume in the matrixand eventually affected the solubility and diffusivity of feedcomponents through the membranes [14] (Table 1).

Compared with PVA membranes [17], KGM membranes cross-linked with 0.5 wt% GA have lower flux and higher separationfactor under the same condition due to fewer active groups of unitmass and denser network structure.

Temperature-dependent flux data were fitted to the Arrheniusrelationship to estimate the activation parameters. The apparentactivation energy (DEa) of water and CPL permeates through theKGM-1, KGM-2, and KGM-3 membranes with 70% CPL concentra-tions were calculated based on the Arrhenius formula as shown inFig. 7. The results are summarized in Table 2. The Arrheniusrelationship is expressed in Eq. (4):

J ¼ J0 exp�Ep

RT

� �(4)

where J, g/(m2 h) is permeation flux; Ep, kJ/mol is the activationenergy for permeation; J0 g/(m2 h) is the permeation rate constant;R, kJ/(mol K) is the molar gas constant; and T, K is the temperaturein Kelvin.

Et is the activation energy for total permeation values, for KGM-1, KGM-2, and KGM-3 membranes at 60 wt% CPL content werefound to be 26.42, 27.88, and 29.20 kJ mol/1, respectively. Ew is theactivation energy for water permeation values, for KGM-1, KGM-2,and KGM-3 membranes were 26.41, 27.86, and 29.17 kJ mol/1,respectively. The activation energies of total and water permea-tions were very close for the three membranes in this study. Thissuggests that water flux has control over total flux. In addition, theactivation energy for CPL permeation is higher than that for waterpermeation. This implies that water consumes less energy forpermeation and has higher permeability than CPL. This suggeststhat a higher separation factor needs lower energy.

Fig. 7. Temperature dependence of (a) water and CPL flux and

3.2.3. Effect of feed composition

Flux and separation factor results are displayed in Fig. 8. Fig. 8ashows the effect of feed composition on total permeation flux vs.concentrations of 30–70 wt% CPL in feed at 45 8C for KGM-1, KGM-2, and KGM-3 membranes [17]. The flux of KGM-1 increased from234 to 530 g/(m2 h) for feeds containing 30–70 wt% CPL, whichwere 214–447 g/(m2 h and 180–402 g/(m2 h for KGM-2 and KGM-3, respectively. The superiority of flux for KGM-1 was obvious. Thetotal permeation flux increased for all membranes with increasingmass percentage of water in the feed. This behavior is consistentwith previous reports on dehydrating an aqueous organic mixturethrough hydrophilic polymeric membranes [24,33–35]. Suchresults are due to the preferential absorption of water moleculesbecause of hydrophilic–hydrophilic interactions that correspondwith the swelling experiment of the membranes. At a higherconcentration of water in the feed, the membranes swelled greatly.The separation factor decreased gradually at a higher concentra-tion of water in the feed for each membrane, irrespective of theamount of GA in the membrane matrix (Fig. 8b). The trend is thesame as in Ref. [18]; in comparison, KGM membranes have theadvantage in terms of the separation factor.

From KGM-3 to KGM-1, total flux increased gradually withdecreased cross-linking agent content in the membranes. Itconfirmed the explanation on the effects of GA composition thathigher GA in membranes formed a denser network structure. Theresults show that both total flux and separation factor changed inthe law with the feed change.

(b) total flux for 60 wt% and 70 wt% CPL concentration.

Fig. 8. Total flux and separation factor vs. wt% of CPL in the feed for KGM-1, KGM-2 and KGM-3 membranes at 45 8C.

Fig. 9. Effect of GA mass ratio on pervaporation characteristics of KGM membranes for 50 wt% CPL in feed at 40–60 8C: (a) separation factor and (b) total permeation flux.

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610 609

3.2.4. Effect of cross-linking agent content

Fig. 9 shows the effect of the cross-linking agent content in KGMcomposite membranes on PV properties. The total permeation fluxdecreased with increasing cross-linking agent content, and theseparation factor was in reverse. The decrease in permeation fluxdepended on the variation in free volume in the membrane. Anincrease in the cross-linking agent increases the cross-linkingdensity of polymer film and makes the membrane structuredenser. Thus, the available free volume is smaller, making itdifficult for the permeants to pass through the membrane andreducing the total permeation flux.

Previous studies have indicated that the hydrophilic–hydro-phobic nature of membranes affect the separation factor. Anincrease in cross-linking agent content decreases the hydrophilicnature of membranes because more hydrophilic group, –OH,

reacted with the cross-linking agent to form ether. Thus, theseparation factor increased with more cross-linking agents. Thisagrees with reports for GA cross-linked poly (vinyl alcohol)membrane and poly(vinyl alcohol)/chitosan membrane [17,18].

4. Conclusions

Cross-linked KGM composite membranes were prepared and aPV dehydration experiment was conducted. The introduction of across-linking agent, GA, changed the structure of the KGMmolecule, and then affected the PV performance of the KGMcomposite membranes. FT-IR spectra and XRD curves showed thechanges in structure, while SEM displayed the morphology of thecomposite membranes. The reaction of GA and KGM decreased themembranes’ hydrophilicity, increased tolerance to both water and

Q. Li et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 604–610610

CPL, and improved the thermal stability of membranes. Allmembranes could work under the condition of 60 8C and 70 wt%CPL in feed. With decreasing cross-linking agent content, thepermeation flux increased with a drop in separation factor. Theincrease in temperature and feed water concentration increasedthe total flux and decreased the separation factor. Swelling resultsfollowed the same trends. Meanwhile, the application of cross-linked KGM composite membranes in CPL/water system on PV wassuccessful. The largest total permeation flux for CPL/water systemcould reach 1678 g/(m2 h) while maintaining a significantseparation factor of 247.

References

[1] R.A. Gross, B. Kalra, Science 297 (2002) 803.[2] M. Darder, P. Aranda, E. Ruiz-Hitzky, Adv. Mater. 19 (2007) 1309.[3] A.K. Mohanfty, M. Misra, L.T. Drza, J. Polym. Environ. 10 (2002) 19.[4] B. Li, B.J. Xie, J. Appl. Polym. Sci. 93 (6) (2004) 2775.[5] K. Ogawa, Agric. Biol. Chem. 55 (1991) 2105.[6] G. Zhou, Y. Li, L. Zhang, et al. Mater. Res. A 83A (2007) 931.[7] C.B. Xiao, S.J. Gao, L.N. Zhang, Macromol. Sci. A 38 (1) (2001) 33.[8] C.B. Xiao, Y.S. Lu, L.N. Zhang, J. Appl. Polym. Sci. 81 (4) (2001) 882.[9] X. Gan, Patent CN 99116531 (2000).

[10] Z.G. Chen, M.H. Zong, G.J. Li, Process Biochem. 41 (2006) 1514.[11] J. Du, R. Sun, S. Zhang, L.F. Zhang, C.D. Xiong, Y.X. Peng, Biopolymers 78 (2005) 1.[12] D.J. Upadhyay, N.V. Bhat, J. Membr. Sci. 255 (2005) 181.[13] F.R. Chen, H.F. Chen, J. Membr. Sci. 109 (1996) 247.

[14] A.S. Ariyaskul, R.Y.M. Huang, P.L. Douglas, R. Pal, X. Feng, P. Chen, L. Liu, J. Membr.Sci. 280 (2006) 815.

[15] L. Zhang, P. Yu, Y.B. Luo, J. Appl. Polym. Sci. 103 (2007) 4005.[16] Q. Li, P. Yu, T.R. Zhu, L. Zhang, Q. Li, Y.B. Luo, Desalination 16 (2010) 304.[17] L. Zhang, P. Yu, Y.B. Luo, Sep. Purif. Technol. 52 (2006) 77.[18] L. Zhang, P. Yu, Y.B. Luo, J. Membr. Sci. 306 (2007) 93.[19] C.G. Xu, X.G. Luo, X.Y. Lin, X.R. Zhuo, L.L. Liang, Polymer 50 (2009) 3698.[20] L.H. Cheng, A. Abd Karim, M.H. Norziah, C.C. Seow, Food Res. Int. 35 (2002) 829.[21] C.B. Xiao, H.J. Liu, S.J. Gao, L. Zhang, J. Macromol. Sci. Pure Appl. Chem. 37 (2000)

1009.[22] X.P. Wang, J. Membr. Sci. 170 (2000) 71.[23] Z. Xu, B.J. Xie, Eur. Food Res. Technol. 223 (1) (2006) 132.[24] M.C. Burshe, S.B. Sawant, J.B. Joshi, V.G. Pangarkar, Sep. Purif. Technol. 12 (2)

(1997) 145.[25] S.S. Kulkarni, S.M. Tambe, A.A. Kittur, M.Y. Kariduraganavar, J. Appl. Polym. Sci. 99

(2006) 1380.[26] L.K. Pandey, C. Saxena, V. Dubey, J. Membr. Sci. 227 (2003) 173.[27] M.C. Bursche, S.B. Sawant, J.B. Joshi, V.G. Pangarkar, Sep. Purif. Technol. 13 (1998)

47.[28] P. Kanti, K. Srigowri, J. Madhuri, B. Smitha, S. Sridhar, Sep. Purif. Technol. 40 (2004)

259.[29] X.S. Feng, R.Y.M. Huang, J. Membr. Sci. 116 (1996) 67.[30] H. Fujita, A. Kishimoto, K.M. Matsumoto, Trans. Faraday Soc. 56 (1960) 424.[31] E.L. Cussler, J. Membr. Sci. 52 (1990) 275.[32] W.L. McCabe, J.C. Smith, P. Harriott, Unit Operations of Chemical Engineering, 7th

ed., McGraw-Hill, New York, 2004.[33] H.M. Guan, T.S. Chung, Z. Huang, M.L. Chung, S. Kulprathipanja, J. Membr. Sci. 268

(2006) 113.[34] S.M. Ahn, J.W. Ha, J.H. Kim, Y.T. Lee, S.B. Lee, J. Membr. Sci. 247 (2005) 51.[35] C.H. Lee, W.H. Hong, J. Membr. Sci. 135 (1997) 187.