pervaporation separation of water + isopropanol mixtures using novel

Journal of Membrane Science 260 (2005) 142155

Pervaporation separation of water + isopropnanocomposite membranes of poly(vinyl aB. V .N. R

ence, Kemical

arch 22005

Abstract

Novel nanocomposite polymeric membranes containing nanosized (30100 nm) polyaniline (PANI) particles dispersed in poly(vinyl alco-hol) (PVA) were prepared and used in the pervaporation separation of waterisopropanol feed mixtures ranging from 10 to 50 mass% of waterat 30 C. Of the three nanocomposite membranes prepared, the membrane containing 40:60 surface atomic concentration ratio of PANI:PVAproduced the highest selectivity of 564 compared to a value of 77 observed for the plain PVA membrane. Flux of the nanocomposite mem-branes was lower than those observed for the plain PVA membrane, but selectivity improved considerably. Membranes were characterizedby differentspectroscopyfeed mixtureto the acid-daddition, moTemperatureof PANI parthis study co 2005 Else

Keywords: N

1. Introdu

Dehydratechniquesuccesses o

cated withis possiblethe azeotropolymeric

This pape# 57. Correspon

fax: +91 836E-mail ad

0376-7388/$doi:10.1016/jial scanning calorimetry, dynamic mechanical thermal analyzer, X-ray photoelectron spectroscopy, Fourier transform infraredand scanning electron microscopy. The highest selectivity with the lowest flux was observed for 10 mass% water containing

. Flux increased with increasing amount of water in the feed, but selectivity decreased considerably. These results were attributedoped PANI particles in the PVA membrane as a result of change in the micromorphology of the nanocomposite membranes. Inlar mass between cross-links and fractional free volume of the membranes are responsible for the varying membrane performance.effect on permeability was investigated for 10 mass% water containing feed with the membrane containing higher concentration

ticles, the presence of which could be responsible for varied effect of water permeation through the membrane. Membranes ofuld remove as much as 98% of water from the feed.vier B.V. All rights reserved.

anocomposite membrane; Polyaniline; Poly(vinyl alcohol); Diffusion; Pervaporation

ction

tion of isopropanol by pervaporation (PV)has been widely studied [13]. One of the keyf PV is that, if suitable membranes can be fabri-

high permeability and good selectivity to water, itto achieve an excellent separation, particularly atpic composition. However, more number of novelmembranes are needed for a successful operation

r is Center of Excellence in Polymer Science Communication

ding author. Tel.: +91 836 2215372/2778279;2771275/747884.dress: [email protected] (T.M. Aminabhavi).

of the process in view of the fact that PV is environmentallycleaner than the conventional distillation; moreover, theprocess is energy intensive. Literature search indicatesthat poly(vinyl alcohol), PVA, has been the widely usedmembrane in the PV separation of waterorganic mixtures[36], but due to the presence of hydrophilic groups inPVA, the chain induces excessive swelling during PV.Therefore, attempts have been made to modify the structureof PVA by cross-linking, blending, grafting, etc. [36]. Inthe course of our investigations, we realized that one ofthe means to control membrane swelling is to incorporatenanosized inorganic particles in the polymer matrix [79].Polymers have also been reinforced with the nanosizedcellulose whiskers by using the solgel techniques [10,11].The method involves dissolving the preformed polymer

see front matter 2005 Elsevier B.V. All rights reserved..memsci.2005.03.037ijaya Kumar Naidu a, Malladi Sairam a, K.V.Sa Membrane Separations Division, Center of Excellence in Polymer Sci

b Organic Coatings and Polymers Division, Indian Institute of ChReceived 21 October 2004; received in revised form 13 M

Available online 3 Mayanol mixtures using novellcohol) and polyanilineaju b, Tejraj M. Aminabhavi a,

arnatak University, Dharwad 580003, IndiaTechnology, Hyderabad 500007, India

005; accepted 14 March 2005

B. Vijaya Kumar Naidu et al. / Journal of Membrane Science 260 (2005) 142155 143

in solgel precursor solutions, simultaneous formation oforganic and inorganic phases through the synchronouspolymerization of the organic monomer and the solgelprecursorstions involincorporati

Severalas membrabeen reporline (PANIfor its highin the sizePANI has tdoping/unding force fgens in thereadily puswould induing in varycal changedifferent chPANI is hy[19,20]. Heover the orgadvantagesbranes conmatrix.

In an efand to incrhybrid nanoaniline in thwas introdupolymerizatrix, a nanphase extenanocompothe nanopaPANI nanopared are cconsist of ananoscale dpossess imbrane swelmembranesferent amoThe membcalorimetry(DMTA), Xtransform itron microsbranes wasfor the wat50 mass%PV performture (i.e., 1ent tempera

2. Experimental

2.1. Materials

borata moleicals,

Mumr colo, hydrlfate

R gradbai, In

avingatorythe n

Prepabranes

lymeshed rdifferred inH of

is mixddedolaras sti

ndeda clea

PANGA bontaibranedistillcompoilined PVApreparer.

Chara

. Foues-IR s

branesct 4100040

. X-rae corembadzu

r sup[11]. Recent trends using PV membrane separa-ve the development of composite membranes byng zeolites as the reinforcing fillers [1214].investigations utilizing the conjugated polymersnes to separate various liquid mixtures have alsoted in the literature [1518]. Interest in polyani-) as a material for membrane separations stemsselectivity toward liquids since most liquids areregime of 0.21 nm. Another advantage is that

he ability to be tailored after its synthesis throughoping processes. Since there is a tremendous driv-or adding protonic dopants to the imine nitro-

PANI backbone [18], the polymer chains arehed apart by the incoming dopants. Thus, dopingce morphological changes in the polymer result-ing permselectivities. Besides such morphologi-s, the undoped and doped forms of PANI exhibitaracteristics. For instance, the undoped form ofdrophobic, while the doped form is hydrophilicnce, doped PANI preferentially permeates wateranics, such as isopropanol. The above-mentionedare considered to search for novel mem-

taining PANI nanoparticles dispersed in the PVA

fort to minimize the swelling of PVA membraneease water selectivity, we have developed a novelcomposite membrane by in situ polymerization ofe PVA matrix in acidic media. Aniline monomerced into the PVA matrix and by carrying in sitution outside the mesopores of the polymer ma-ocomposite structure was formed. The organicnds along the channels to the openings in thesite structure due to strong interactions betweenrticle formed and the continuously polymerizedparticles. Polymeric nanocomposites thus pre-

alled hybrid nanocomposite membranes, whichn organic polymer matrix in which PANI in theimension is dispersed. These membranes shouldproved barrier properties by controlling mem-ling. In the present paper, three nanocomposite

were prepared by polymerizing aniline in dif-unts to obtain the PVAPANI nanocomposites.ranes were characterized by differential scanning

(DSC), dynamic mechanical thermal analyzer-ray photoelectron spectroscopy (XPS), Fourier

nfrared spectroscopy (FT-IR) and scanning elec-copy (SEM). The PV performance of these mem-studied at 30 C in terms of flux and selectivity

erisopropanol feed mixtures ranging from 10 toof water. Finally, the temperature dependence onance was investigated for the selected feed mix-

0 mass% water containing feed mixture) at differ-tures (40 and 50 C).

LawithChemcals,ambe(GA)persuof AMumter hlaborusing

2.2.mem

PopublithreeprepaThe pTo thwas a

equimture wsuspeontoPVAwithture cMemwithnano

of anII anwas

mann

2.3.

2.3.1studi

FTmem

Impaof 40

2.3.2Th

and m(Shimpoweory reagent grade PVA (87% degree of hydrolysis)cular weight 125,000 was procured from s.d. FineMumbai, India. AR grade aniline (Loba Chemi-

bai, India) was vacuum distilled and stored in anred bottle under cold conditions. Glutaraldehydeochloric acid, acetone, isopropanol, ammoniumand all other chemicals used in this work weree samples, purchased from s.d. Fine Chemicals,dia. These were used as received. Deionized wa-

a conductivity of 20S/cm was produced in thefrom the Permionics pilot plant (Vadodara, India)anofiltration membrane module.

ration of PVAPANI nanocomposite

rization of aniline in PVA was carried out as per theeport [21] to obtain the nanocomposite. To prepareent nanocomposites, a 3 mass% solution of PVAwater, 0.6, 0.9 or 1.2 mL of aniline were added.

the solution was adjusted to 1 by adding dil. HCl.ture, an aqueous solution of ammonium persulfateat 5 C under constant stirring by maintaining theratio of aniline to ammonium persulfate. The mix-rred for 4 h to obtain the colloidal PANI particlesin PVA. This reaction mixture was then pouredn glass plate to cast the membranes. The dried

I nanocomposite membranes were cross-linkedy dipping them in 200 mL aqueous acetone mix-ning 1 mL of GA and 1 mL of con. HCl for 12 h.s were removed from the bath, washed three timesed water and dried in an oven at 40 C for 4 h. Thesite membranes prepared with 0.6, 0.9 or 1.2 mLwere designated as PVAPANI-I, PVAPANI-PANI-III, respectively. Plain PVA membrane

ed by using 3 mass% PVA solution in a similar

cterization

rier transform infrared (FT-IR) spectroscopic

pectra of the pure aniline, PVA and PVAPANIin KBr pellets were recorded on a Nicolet, Model(Milwaukee, WI, USA) in the wavelength region0 cm1.

y photoelectron spectral (XPS) studiese level XPS spectra of polyaniline salts and basesranes were recorded using KRATOS AXIS 165) with Mg K X-ray source 253.6 eV. The X-rayply was operated at 75 W and 5 mA. Pressure

144 B. Vijaya Kumar Naidu et al. / Journal of Membrane Science 260 (2005) 142155

in the analysis chamber during scans was kept below108 Torr and the peak area ratios for various elements werecorrected by the experimentally determined instrumentalfactors. Thwas decomGaussian liAll fitting pwidths andfor each sroutine.

2.3.3. Dynstudies

Dynamilus, tan ) oPVAPANusing DMTa tensile ming rate of 3and uncrosinvestigate

2.3.4. DiffDSC th

linked mem(Model DSbetween 25nitrogen at

2.3.5. ScanScannin

nanocompoelectron mtechnique.directly sub

2.3.6. PartZeta ave

nanocomposizer, Mode

2.4. Swelli

DynamiPVAPANperformedan electronBD-53, Tulished earldisk-shapethe anhydrabout 48 h bmeasureme

ance (Mod0.01 mg.

2.5. Pervaporation experiments

The procedure used in PV experiments was describedr [25,ht oferatuthermtainedbai, Ibraneure. Ars werxperimrisopht of pompos

andof re

embraion flu

W

At(PA

1, FA isr in peeight,A (takindepunde

ion to

esults

Synthe

ispersresenc) [27carbo

lose (Hondu

est thems ofheir el2,33].rocessus appromaged poures hases,

to sepe N(1s) spectrum, after background subtractions,posed into suitable components consisting of ane shape with a Lorentzian broadening function.arameters including the number of components,intensities were freely adjustable and determinedpectrum with an iterative least squares fitting

amic mechanical thermal analysis (DMTA)

c mechanical properties (storage and loss modu-f the plain PVA, uncross-linked and cross-linked

I nanocomposite membranes were measured byA IV instrument (Rheometric Scientific, USA) inode at a frequency of 10 or 1.0 Hz and at the heat-C/min. Viscoelastic behavior of the cross-linked

s-linked membranes in nitrogen atmosphere wasd in the temperature range of 30200 C.

erential scanning calorimetric (DSC) studiesermograms of all the uncross-linked and cross-branes were recorded using Rheometric ScientificCSP), UK. The DSC thermograms were recordedand 400 C at the heating rate of 10 C/min under

mosphere.

ning electron microscopic (SEM) studiesg electron micrographs of the PVAPANIsite membranes were recorded using a Joel

icroscope at 10 kV following the gold sputteringThe prepared nanocomposite membranes werejected to SEM analysis.

icle size measurementrage diameter of the PANI particles in PVAPANIsite dispersions was measured by using a Zeta-l 3000HS, Malvern, UK.

ng experiments

c and equilibrium swelling experiments onI nanocomposite and plain PVA membranes werein waterisopropanol mixtures at 30 0.5 C inically controlled incubator (WTB Binder, Modelttilgen, Germany) as per the procedures pub-ier [2224]. Circularly cut (diameter = 2.5 cm)d membranes were stored in a desiccator overous calcium chloride maintained at 30 C forefore performing the swelling experiments. Massnts were taken on a digital Mettler microbal-el AE 240, Greifensee, Switzerland) sensitive to

earlieWeigTempby amainMummem

mixtvapoPV ewateweigate cindexgraph

Mmeat

J =

=

Herewatethe warea,

threetakenposit

3. R

3.1.

Dthe p(PVP[28],celluetc. Csuggof filand t[21,3the pvarioelectjugatmixtof cused26]. The effective membrane area was 32.43 cm2.the feed mixture taken in the PV cell was 50 g.re of the feed mixture was maintained constantostatic water jacket. Downstream pressure wasbelow 10 Torr using a vacuum pump (Toshniwal,ndia). Before the actual experiment, the testwas equilibrated for about 2 h with the feedfter establishment of a steady state, permeatee collected in traps immersed in liquid nitrogen.ents were performed with the feed mixture of

ropanol taken in different compositions. Theermeate collected in the trap was noted and perme-ition was determined by measuring the refractiveby comparing it with the previously establishedfractive index versus mixture composition.ne performance was studied by calculating per-x, J and selectivity, using the equations:

(1)

PA

)(1 FAFA

)(2)

mass% of water in the feed and PA is mass% ofrmeate. The flux (kg/m2 h) was calculated fromW (kg) of liquids permeated, effective membraneen in m2) and measurement time, t (h). At leastendent measurements of flux and selectivity werer the same conditions of temperature and feed com-confirm the steady-state permeation.

and discussion

sis of nanocomposite membranes

ion polymerization of aniline can be carried out ine of steric stabilizers like poly(vinyl pyrrolidone)], PVA [27], hydroxy propyl cellulose (HPC)xy methyl cellulose (CMC) [29], hydroxy ethylEC) [30], poly(vinyl methyl ether) (PVME) [31],

ctivity, particle size and morphology data wouldconductive nature and stabilization. PreparationPANI with various insulating polymer matrices

ectrical, mechanical properties have been reportedThese studies indicated that one could enhance

ibility of PANI and utilize its conductive nature inlications such as electrostatic discharge (ESD),

netic induction (EMI), etc. Studies utilizing con-lymers as membranes to separate ions and liquidave also been reported [3436], but in majoritypristine conducting polymer membranes werearate gaseous or liquid mixtures. In the present


investigation, PVAPANI nanocomposite membranes wereused for the PV separation of waterisopropanol feedmixtures. To the best of our knowledge, this is the first kindof study on such membranes in PV applications dealing withthe separation of waterisopropanol mixtures.

3.2. FT-IR analysis

FT-IR spectrum of aniline, plain PVA and PVAPANInanocomposite membrane is displayed in Fig. 1. For PVA, thepeaks at 2912, 1324 and 843 and 1084 cm1 are attributed toC H stretching, C H bending and C O stretching, respec-tively. A broad high absorption peak observed at 3445 cm1is due to O H stretching frequencies of PVA. The band at1727 cm1 is attributed to the carbonyl functional groupsdue to residual acetate groups remaining after the manufac-ture of PVA from the hydrolysis of poly(vinyl acetate) oroxidation during manufacturing and processing. Vibrationalbands observed for PANI are in accordance with the earlierliterature reports [37]. These bands for PANI could be ex-plained on the basis of normal modes of aniline and benzene.A broad band in the region 34153460 cm1 is assigned tothe N H stretching vibration. Bands at 2915 and 2850 cm1are assigned to vibrations associated with the N H moiety inC6H4NH2C6H4 group or sum frequency. Bands at 1565 and1490 cm1 are due to quinonoid ring (Q) and or benzenoidring (B). The bands at 1370 and 1300 cm1 are assigned to

Fig. 1. FT-IRposite membr

C N stretching vibration in QBQ and QBC, QBB, BBQ,while a band at 1240 cm1 is due to C N stretching vibra-tion of the aromatic amine. In the region of 10201170 cm1,the aromatic C H in-plane-bending modes are observed. ForPANI, a strong band appears at 1140 cm1 due to electronicband or a vibrational band of nitrogen quinone. A band at705 cm1 is assigned to the ring C C bending vibration,while that at 590 cm1 is due to the ring in plane deformation.The C H out-of-plane bending mode has been used as a keyto identify the type of substituted benzene. For PANI, thismode was observed as a single band at 825 cm1, which wasin the range 800860 cm1 as reported for 1,4-substitutedbenzene. P1140 and 5matrix.

3.3. X-ray

XPS is agree of conbinding enecan be identhe atomicvarious intneutral andthe properlused to chadopant ratiship [384position ofthe present

charaus forace atoduced

compoin th

itrogecenterAPAn in Feak caine, ant inof niN(1s

nic rad

1ANI raPANI fi

e

PANI-IPANI-IIPANI-IIspectra of plain PANI, plain PVA and PVAPANI-II nanocom-ane.

were

vario(surfthe renano

paredN

are

I, PVshowgen pto impresekindslutingcatio

TablePVA/PPVA

Sampl

PVAPVAPVAeaks corresponding to PANI observed at 2850,90 cm1 confirm the presence of PANI in the PVA

photoelectron spectroscopic (XPS) analysis

powerful tool, which characterizes the doping de-ducting polyaniline [37]. From the characteristicrgies of the photoelectron, the elements involvedtified and peak intensity can be directly related toconcentration in the sample surface. In addition,rinsic redox states of PANI as well as differentpositive nitrogen species can be quantified from

y curve fitted N(1s) core level spectrum. XPS wasracterize PANI salts and its blends to determine theo and to explain the structureproperty relation-0]. It was also used to examine the surface com-sterically stabilized polypyrrole colloids [41]. Inwork, PVAPANI films and their respective saltscterized by XPS to find the nitrogen content andms of nitrogen (see Fig. 2). The PVA/PANI ratiomic concentration ratio) was determined based onatomic concentration of nitrogen in PVAPANI

site membranes with that of pristine PANI pre-e absence of PVA under similar conditions.n peaks in XPS spectrum of PVAPANI filmsed at 400, 402 and 402 eV for PVAPANI-NI-II and PVAPANI-III films, respectively as

ig. 2. According to the published report [37], nitro-n be deconvoluted into four peaks correspondingmine and the positively charged nitrogen atomsthe PANI backbone. In the present study, threetrogens (see Table 1) were observed on deconvo-) peak of nitrogen, which corresponds to amine,ical and cationic nitrogen atoms, respectively.

tio and deconvolution results of N (1s) XPS spectra oflms

PVA/PANI (surface atomicconcentration ratio)

Deconvoluted N(1s)binding energy (eV)

0.78 400.9, 402.0, 402.80.73 401.1, 401.8, 402.8

I 0.52 400.5, 401.3, 402.4


Fig. 2. Deconbranes (a) PVAposite membr

3.4. DSC/D

DMTAoccurringand frequewas scanne

then at theSamples ofto 300 C.uncross-lin

membranes were measured at a frequency of 1 Hz. The plotsof loss tangent (tan ) versus temperature in C are dis-

d in Fig. 3(a)(c) respectively, for the uncross-linked,-linked PVAPANI, plain PVA and cross-linked PVAbranes. For PVA, three mechanical dispersions wereted above 50 C [43]. A relatively sharp peak inith a maximum at 70 C is assigned to the primaryrsion (a) associated with the glass transition of theer. In this transition temperature region, dynamic

lus, E decreases markedly from the frozen modulus,ating that the micro-Brownian motions of the mainchains become conspicuous in the amorphous regions.presence of the secondary dispersion ( ) due to theplayecross

mem

reporE wdispepolymmoduindicPVAThevoluted N(ls) spectra of PVAPANI nanocomposite mem-PANI-I, (b) PVAPANI-II and (c) PVAPANI-III nanocom-

anes.

MTA analyses

provides a sensitive test of physical changesin polymers over a wide range of temperaturency [42]. In the present study, first frequencyd on the specimen at ambient temperature andselected frequency, temperature was scanned.

this study were analyzed from room temperatureDynamic mechanical properties of the plain PVA,ked and cross-linked PVAPANI nanocomposite

a

local relaxbroad shousample givrelaxation

The tanPANIPVAin the ranaround 50peak appeachain relaxrelaxationnanocompomembrane.Table 2) ofing temperTm of thenanocompoPVA, suggeafter introd

StoragePVA, crosPVAPANlus measurstorage moPVA and Pwhich laterthe plain PVing PANI, i

3.5. SEM a

SEM mmembranes

Table 2Melting onsedifferent mem

Membrane

PVAPVAPANI-IPVAPANI-IIPVAPANI-IIation mode of the PVA main chains appear as alder ranging from 0 to 30 C in the E curve. Thees another dispersion signal above 100 C due toin the PVA crystalline phase. curves of the uncross-linked and cross-linkednanocomposite membranes showed two peaks

ge 5570 and 100145 C, respectively. Peaks70 C are due to the Tg of PVA. The secondring around 100145 C is the peak, due toation in the crystalline phase of PVA. This was more prominent in the PANI-introducedsite membranes compared to the plain PVASimultaneously, the DSC analysis (see Fig. 4 andthe cross-linked PVA showed a decrease in melt-ature, Tm after cross-linking with GA, whereas

uncross-linked and cross-linked PVAPANIsite membranes increased compared to the plainsting a more ordered arrangement of PVA chainsucing PANI particles in the matrix.

modulus (E) versus temperature plots fors-linked PVA, cross-linked and uncross-linkedI films are shown in Fig. 5. The storage modu-es the stiffness of the polymer. A sharp decrease indulus was observed for the plain PVA, cross-linkedVAPANI films in the glass transition region,reached a plateau. However, storage modulus ofA (1.23 107 Pa) has increased after incorporat-

ndicating an increase in the rigidity of PVA chains.

nalysis

icrographs of the PVAPANI nanocompositeare displayed in Fig. 6. The micrograph

t temperatures and molar mass between cross-links (Mc) ofbranes

Melting onset (C) Mc 104 (kg/mol)Uncross-linked Cross-linked

175 143 886196.1 193.0 285196.6 195.7 115

I 194.0 199.0 15


confirmedmatrix. Spconcentratianiline (PVagglomeratFig. 3. tan curves of (a) uncross-linked PVAPANI, (b) cross-linked PVAPANI,

the uniform distribution of PANI particles in PVAherical PANI particles were observed at a loweron of aniline, whereas at higher concentration ofAPANI-III), PANI particles were found to beed.

3.6. Partic

Numberparticles inFig. 7. Zet

Fig. 4. DSC thermograms of (a) uncross-linked and (b) crand (c) plain and cross-linked PVA membranes.

le size analysis

average size distribution histograms of PANIall the three nancomposites are displayed in

a average diameter of the PANI particles in the

oss-linked membranes.


PVA matrithough ze900 nm fornumber ofdiameter ra

3.7. Molar

Molar mtrix is impoin the presein the literaIn the absenone could cthe moduluelasticity [4

Mc = e

where isthe benzenFig. 5. E curves of (a) uncross-linked PVAPANI, (b) cross-linked PVAPANI, a

x increased with increasing aniline content. Eventa average diameter ranged between 700 and

all the three nanocomposites prepared, a largeparticles were found to be present in the lowernge i.e., 30100 nm.

mass between cross-links

ass, Mc between the cross-links in a polymer ma-rtant to know the dimensional stability of the filmsnce of liquids. This parameter was widely studiedture for both wet and dry polymer films [44,45].ce of solubility parameter values of the polymers,alculate Mc from the DMTA measurements usings values following the kinetic theory of rubber6,47] as

(3)

the density of the film (kg/m3), measured bye displacement method, e =E/3RT (where E is

modulus asal gas conues of Mcmembrane,membranesvalue thatfor the plaiite membrasetup of thto the pervtion 3.10).of PANI pto decreaseMc = 15 1pared.

3.8. Free v

Molecuis influenceas a result ond (c) plain and cross-linked PVA membranes.

t a temperature above Tg) and R is the univer-stant (8.314 107 cal/mol deg). Calculated val-are also given in Table 2. For the plain PVAMc = 886 104 kg/mol, the highest among all the. For PVAPANI-I, the Mc = 285 104 kg/mol, a

is almost three-times smaller than that observedn PVA. Such a decrease in Mc of the nanocompos-ne could indicate changes in the morphological

e membranes. These changes are directly relatedaporation performance (to be discussed in Sec-It can be seen that with an increasing amount

articles in the PVA matrix, the Mc values tendconsiderably. Thus, for the PVAPANI-III, the04 kg/mol, the smallest of all the membranes pre-

olume

lar transport through dense polymeric membranesd by the presence of free volume [48], which arisesf voids created due to poor chain packing during


Fig. 6. SEMPVAPANI-II

the membrchain segmfor the fastfree volum

FFV = Vsp

where Vsp ioccupied b

V0 = 1.3V

Here Vw is the van der Waals volume estimated from thegroup contribution method [49]. Within a given family ofpolymers, penetrant diffusivity and permeability can be cor-

d with FFV [50]. The FFV results presented in Table 3ase with increasing amount of PANI in the matrix. Thisase in free volume space in the nanocomposite mem-s with increasing PANI particles could be the result

orphological changes occurring during the fabricatione membranes and/or while carrying out polymeriza-eaction of aniline in acidic media. Thus, the increaseddoping could have induced higher free volume spacesn these matrices. However, for the plain PVA membrane,was lmaderelateincreincrebraneof mof thtion racidwithiFFVtionsmicrographs of (a) PVAPANI-I, (b) PVAPANI-II, and (c)I nanocomposite membranes.

ane cross-linking process. If the space betweenents is large, then more free channels are availableer movement of liquid molecules. The fractionale (FFV) of the membrane was calculated by using: V0Vsp

(4)

s polymer bulk specific volume and V0 is volumey the polymer chains calculated as [49]:

W (5)

membranessilica.

3.9. Swelli

Dynamiobtained inpresented ikinetics is crelation tostudy, sweincreasingto the incredecreasingswelling wthe natureplain PVA30 min, whit took 40longer timeswelling isstudied bycross-linkinaddition, frmolecules cation effectFor instancbranes sweof the nanto the combefore) thawater.

Table 3Fractional fredata for differ

Plain PVA

0.5798

0.114owest. These results follow the general observa-by Merkel et al. [8] for the nanocomposite blendprepared from poly(4-methyl-2-pentyne)/fumed

ng results

c swelling results of the membranes at 30 C10 mass% water containing feed mixture are

n Fig. 8 and also included in Table 3. Swellingontrolled by the diffusion of solvent molecules inthe polymer chain relaxation [51]. In the presentlling increased slightly, but systematically withamount of PANI in the matrix; this could be dueased void spaces for these membranes with theMc values. The time required to attain equilibriumas not identical, since it varied depending uponof the membrane material. For instance, with themembrane, swelling reached equilibrium withinile for PVAPANI nanocomposite membranes,

min. However, experiments were continued forto ensure complete equilibration. Thus, polymerinversely related to chain morphology as can bethe Mc data. For instance, a matrix with higherg will exhibit lower swelling and vice versa. Inee volume and nature of the penetrating liquidould exert an influence on swelling. TheTg (relax-s) of the polymers has shown an effect on swelling.e, with increasing Tg of the nanocomposite mem-lling increased. Therefore, the PV performanceocomposite membrane can be explained as duebined effects of several parameters (discussed

t are equally important in the selective transport of

e volume of the membranes along with equilibrium swellingent membranes at 10 mass% of water in the feed at 30 C

PVAPANI-I PVAPANI-II PVAPANI-III

Fractional free volume0.5809 0.5815 0.5831

Equilibrium swelling (g)0.074 0.080 0.084


VAPANI-II, and (c) PVAPANI-III nanocomposites.

3.10. Perv

Noveltyfirst time,were prepof waterisvaried depthe polymePANI partithough somalso presenduring polnanocompoplain PVA

Fig. 8. Plotsing isopropanPVAPANI-II

aldine oxidation state by the oxidative polymerizationiline in an acidic medium, hence the PANI particlesrsed in the PVA matrix were in the acid-doped form.esulting doped films were dark green in color. Flux andtivity data are displayed in Figs. 9 and 10, respectively,

4oration

of waFig. 7. Number average particle size distribution of (a) PVAPANI-I, (b) P

aporation results

of the present investigation is that, for thePANI-doped PVA nanocomposite membranes

ared and used to study their PV performanceopropanol feed mixtures. The PV performance

ending upon the amount of aniline dispersed forrization to occur in the PVA matrix. The dispersedcles were in the size range of 30100 nm, even

e smaller number of particles > 100 nm weret depending upon the amount of aniline used

emer

of andispeThe rselec

TablePervap

Mass%

Feedymerization. The PV results of the PVAPANIsite membranes are compared in Table 4 with themembrane. Since PANI was synthesized in the

of swelling vs. time at 10 mass% of water in water contain-ol mixtures. Symbols: () pure PVA, () PVAPANI-I, ()and () PVAPANI-III nanocomposite membranes.

1020304050

1020304050

1020304050

1020304050data of water + isopropanol mixtures at 30 C

ter in Water flux (kg/m2 h) SelectivityPermeate

PVA

89.57 0.095 77.388.2 0.216 29.987.62 0.320 16.585.43 0.366 8.884.63 0.398 5.5

PVAPANI-I67.44 0.035 18.678.38 0.068 14.581.04 0.091 1086.38 0.116 9.589.02 0.156 8.1

PVAPANI-II98.28 0.061 514.387.97 0.090 29.363.02 0.084 4.080.73 0.127 6.387.13 0.194 6.8

PVAPANI-III98.43 0.069 564.292.56 0.221 49.884.82 0.243 13.071.75 0.219 3.867.8 0.218 2.1


Fig. 9. Water flux vs. mass% of water in feed mixture at 30 C. Symbolshave the same meanings as in Fig. 8.

for the ranwater washydrophilic0.398 kg/mmixture cointeractionleading to aConverselyas small amixture. Tfrom the plbut the perwater, sincPVAPANin the permwater-contaPVA membPVAPAN

Fig. 10. Selechave the same

water was removed in the permeate for the feed containing10 mass% water. This could be due to an increased flux ofwater, since the higher amount of PANI present in the dopedstate of thefrom the fe

In caseflux varieddecreasedan increasiflux of thewith increaPVA matrixPANI partihydrophilicof a rigid pmatrix couThis effectlower selecto PVAPApermeabili

o the rc memsmalle memasingase, se memermeacompodecreaesserx, moh woubranes0 massbranesction

d PANtivityge of feed compositions investigated. Flux ofhigher for the plain PVA membrane due to its

nature. The increase in flux from 0.095 to2 h with increasing water content of the feeduld be explained as due to higher hydrophilics between water molecules and that of the PVA,n increase in the swelling of the PVA membrane., selectivity to water decreased from 77.3 tos 5.5 with increasing water content of the feedhe concentration of permeate (water) obtainedain PVA membrane was about 90 mass% of watermeability of isopropanol was much smaller thane water is more polar than isopropanol. In case ofI-I nanocomposite membrane, the amount of watereate is higher (i.e., 89.02 mass%) for 50 mass%ining feed (a reverse trend to that of the plainrane). On the other hand, with PVAPANI-II and

I-III nanocomposite membranes, 98.43 mass% of

due tscopiveryof thincredecrein ththe pnano

withthe lmatriwhicmem

for 1mem

interadopeselectivity vs. mass% of water in feed mixture at 30 C. Symbolsmeanings as in Fig. 8.

due to thewater. Whibut in the psuch as in cmight be b

Overall,water is liklogical chavariabilityits composthe morphoAs the watof the diffuto be blockpermselectdoping in tsteady-statPVA matrix could absorb higher amount of watered containing large quantities of water.of PVAPANI-I nanocomposite membrane, thefrom 0.035 to 0.156 kg/m2 h, while the selectivityfrom 18.6 to 8.1 for the feed mixture containingng amount of water ca. from 10 to 50 mass%. The

PANI incorporated PVA membranes increasedsing concentration of PANI nanoparticles in thefor the obvious reason that more the number of

cles present in the PVA matrix, higher will be thehydrophilic interactions. Since PANI is moreolymer than PVA and hence, its presence in the

ld help to reduce the overall membrane swelling.could further be compensated by the observedtivity of PVAPANI-I nanocomposite comparedNI-II and PVAPANI-III. High variability in the

ty of water for the doped PANI (Table 4) may beelatively large effect that differences in the micro-

brane morphology have on the permeability ofmolecule such as water. See for e.g., theMc values

branes presented in Table 2, wherein with anamount of PANI in the PVA matrix, the Mc valuesuggesting the morphological changes occurringbranes. These Mc data have a direct effect on

tion flux data of water. For instance, in case ofsite membranes, the flux increased systematicallysing Mc, which is reasonable to assume that with

number of chain entanglements in the polymerre number of diffusional pathways are available,ld explain the increased flux of the PVAPANI. Thus, the optimum selectivity values observed% water containing feed mixture for all the three

could be the result of increased preferentials of water (compared to isopropanol) with theI-incorporated films. However, the decrease in

at higher amounts of water in the feed could bepreferential escape of isopropanol along with

le waters size (0.28 nm) gives it a high diffusivity,resence of higher amount of PANI nanoparticles,ase of PVAPANI-III, the PVA membrane pores

locked leading to a lower selectivity to water.the level of doping interaction between PANI andely to be sensitive to the microscopic morpho-nge of the film, which may account for the highin the permselectivity of water due to variations ofition in the feed. As doping takes place over time,logy properties of the membrane could change.

er molecules accumulate in the membrane, somesion pathways through the membrane are likelyed off or become smaller. When this happens,

ivity of the membrane begins to decline untilhe film stabilizes and permselectivity reaches thee value. Thus, the decline in selectivity at higher


compositions of water in the feed is likely due to swellingas well as doping effects that take place in the membraneover the course of the PV experiment. Additionally, thedopant leaching could also play a role in affecting thepermselectivity of water/isopropanol feeds. Large variationsin selectivity of the doped PANI-containing PVA membranescould be due to highly sensitive dopant leaching effects[52]. These effects may be caused by the greater role thatsolubility selectivity plays on the overall permselectivity ofwaterisopropanol in the HCl-doped PANI particles. Sincethe solubility of waterisopropanol feeds plays a greaterrole in the permselectivity, a slight difference in the extentof dopant leaching from the HCl-doped PANI-containingmembranes will have much greater effect on the selectiv-ity of this matrix than those mixtures where the overallpermselectivity is dominated by the diffusive selectivity[53].

In the present study, PVAPANI-II and PVAPANI-III nanoco98 mass% oThis is becdoped formthe separatall membracase of dop(chemicalwater is semuch greatnature of thto providewater transSee for e.gTable 3, win the matrin permeatmeation inyet the sorpto describemembranethus impormembranes

Fig. 11. Comparison of vapor liquid equilibrium curve (), with PV data ()for water (l)-isopropanol (2) mixtures at 30 C for PVAPANI-III membrane.

procbeenlationtropicse ofrity inefore,lationPV haanocom

d forr selecure (1ed. Figis alwthe c

compoed co

e, resue PV

brane-basedeparating waterisopropanol mixtures. Compared to

Table 5Comparison o e data on PVA-based membranes for water + isopropanol mixtures at30 C

Membrane Flux (kg/m2 h) Selectivity ReferencePVAPANI-II 0.069 564 Present workNaAlg/PVA ( 0.025 195 [4]NaAlg/PVA ( 0.034 119NaAlg/PVA ( 0.039 91PVA + KA 0.179 410 [55]PVA + NaA 0.183 328PVA + CaA 0.190 233PVA + NaX 0.216 133PVA cross-lin 0.194 116 [56]PVA cross-lin 0.095 741

PVA: poly(vin aX: zeolites.mposite membranes were able to extract almostf water from the 10 mass% water containing feed.

ause when the PANI particles are present in their, these will induce hydrophilicity as a result of

ed charges. Thus, the ionic character of the over-ne could facilitate the transport of water. In theed PANI, both diffusion (size effect) and sorptioninteraction effect) appear to favor water so thatlectively transported through the membranes to aer extent. Additionally, due to the water-adsorptivee PANI particles, their presence could also helpthe free diffusion channels to give an increasedport along the void channels of the membrane.., the fractional free volume data presented inhich increase with increasing contents of PANIix. These data follow the same trends of increaseion flux. However, the exact mechanism of per-PV is quite complicated at the molecular level,tiondiffusion concept has been widely acceptedthe PV performance. The microchanges in the

morphology (i.e., in terms of FFV, Mc and Tg) aretant to explain the molecular transport across the.

InhasdistilAzeothe uimpuTherdistilwithIII nsuitebettemixtstudicurve

at allnano

the fephas

Thmem

PVAfor s

f PV performance of the present nanocomposite membranes with literatur

Mass% of water in feed

I 1075:25) 1050:50) 1025:75) 10

20

ked with glutaraldehyde 10ked with citric acid 5

yl alcohol); PANI: polyaniline; NaAlg: sodium alginate; KA, NaA, CaA, Ness engineering, the purification of isopropanoltraditionally achieved through the azeotropicwherein, benzene is used as an entrainer.distillation is a energy-consuming process and

entrainer like benzene could cause an unwantedthe final product as well as the side streams.

PV technique could be a better alternate to simple. Hybrid processes combining simple distillationve also been recommended [54]. The PVAPANI-

posite membrane of this study would be well-further detailed investigations, since it exhibitedtivity at the azeotropic composition of the feed

2.5 mass% of water) than the other membranes. 11 displays such a dependence wherein, the PVays higher than the vaporliquid equilibrium lineompositions, demonstrating that PVAPANI-IIIsite membrane selectively permeate water at all

mpositions and that the membrane acts as a thirdlting in the effective separation of water.performance of PVAPANI-III nanocompositeis compared in Table 5 with all the othermembranes published in the literature [4,55,56]


our earlier results [4] on sodium alginate/PVA blend mem-branes, the present nanocomposite membranes could offeran improved flux and better selectivity to water. The plainPVA membrane cross-linked with glutaraldehyde developedby Burshe et al. [56] had a selectivity of 116 with a fluxof 0.194 kg/m2 h for the separation of waterisopropanolmixture. On the other hand, 5 mass% water-containingfeed mixture of waterisopropanol had a selectivity of 741,when the plain PVA was cross-linked with citric acid [56].Comparing with the PVA membranes incorporated withKA, NaA, CaA and NaX type zeolites [55], which gavean improved flux with reasonable selectivites ranging from410 to 133present PVmuch supe

3.11. Temp

Anotherliquids throperature ofpermeationpermeate ffeed mixturin Table 6.is observedwith an appfurther incflux, but noincrease indue to anAdditionalthe type prefree volumincreased pwith the oin permeatactivation e

JP = JP0 ewhere JP ithe universThe estimin case o(EP = 79.48indicate thenergy barr

Table 6Pervaporationtemperatures

Temperature (

304050

4. Conclusions

The present study addresses the development of novelnanocompopersed witthe pervapranging inSEM micof polyanimatrix. Theglutaraldehspectra. M

ater abol) m

PANate wositiormanc0 C)

e acidx. Ho-linksporta

owled

ofessothe

R), Grf thison (U01/CPer Sc

rence

.S. Totinate aeparatio

embr.. Cha.A. Asan/hyembr.

.M. Amorationembran

5 (2005.D. Ku

ohol) mormami09140.A. Kitabhavig ZSMolym. Sat 20 mass% water containing feed mixture, theAPANI-III nanocomposite membranes gave

rior values (see Table 5).

erature-dependent permeation rate

method of increasing the permeation rates ofugh a membrane module is by increasing the tem-the permeating solution. Temperature-dependentrate, selectivity and mass% of water in the

or 10 mass% water and 90 mass% isopropanole through the PVAPANI-III membrane are givenA two-fold increase in the permeation rate (flux)upon raising the temperature from 30 to 40 C,

reciable loss in selectivity from 564 to 181. Uponreasing the temperature to 50 C, an increase int a drastic decrease in selectivity is observed. Theflux over the studied temperature range is likelyincreased diffusion rate of the feed molecules.ly, in the complex nanocomposite membrane ofpared in this study, slight changes in the fractional

e with increasing temperature could result in theirermeation flux. These observations are consistentbserved systematic decrease in mass% of watere with increasing temperature. The Arrheniusnergy,EP for the PV process was computed using:

xp(EP/RT ) (6)s permeation flux, JP0 the Arrhenius constant, Ral gas constant, and T the temperature in Kelvin.ated EP values for PVAPANI-III membranef water (EP = 16.18 kJ/mol) and isopropanolkJ/mol) for waterisopropanol feed mixtures

e easy energy required to cross the potentialier in the activated state during the flow process.

data of PVAPANI-III nanocomposite membrane at differentfor 10 mass% water containing feed mixtureC) Water flux

(kg/m2 h)Mass% of waterin permeate

Selectivity

0.069 98.43 564.20.144 95.26 180.90.158 92.87 117.2

to walcohPVAseparcompperfoand 5of thmatricross

are im

Ackn

Prthank(CSIport omissi41/20Polym

Refe

[1] Ugs

M[2] A

WtoM

[3] Tpm

9[4] M

c

f4

[5] AininPsite membranes of poly(vinyl alcohol) dis-h the doped polyaniline nanoparticles used fororation separation of waterisopropanol feedscomposition from 10 to 50 mass% of water.

rographs confirmed the uniform distributionline nanoparticles in the poly(vinyl alcohol)solution-cast membranes were cross-linked with

yde as confirmed by Fourier transform infraredembranes could exhibit an increased selectivityout five-folds compared to the plain poly(vinyl

embrane at the expense of reduced water flux. TheI-III nanocomposite membrane could successfullyaterisopropanol feed mixture at the azeotropicn compared to simple distillation. The membranee was also studied at higher temperatures (40

. The results of this study were explained in termsdoping effects of the PANI particles in the PVAwever, the parameters like molar mass between, fractional free volume and extent of swellingnt to explain the pervaporation results.

gements

r T.M. Aminabhavi and Dr. B.V.K. Naidu (RA)Council of Scientific and Industrial Researchant No. 80(0042)/02/EMR-II for a financial sup-study. Authors thank the University Grants Com-GC), New Delhi, India for a major funding (F1-P-II) to establish the Center of Excellence inience.

s

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Pervaporation separation of water+isopropanol mixtures using novel nanocomposite membranes of poly(vinyl alcohol) and polyanilineIntroductionExperimentalMaterialsPreparation of PVA-PANI nanocomposite membranesCharacterizationFourier transform infrared (FT-IR) spectroscopic studiesX-ray photoelectron spectral (XPS) studiesDynamic mechanical thermal analysis (DMTA) studiesDifferential scanning calorimetric (DSC) studiesScanning electron microscopic (SEM) studiesParticle size measurement

Swelling experimentsPervaporation experiments

Results and discussionSynthesis of nanocomposite membranesFT-IR analysisX-ray photoelectron spectroscopic (XPS) analysisDSC/DMTA analysesSEM analysisParticle size analysisMolar mass between cross-linksFree volumeSwelling resultsPervaporation resultsTemperature-dependent permeation rate

ConclusionsAcknowledgementsReferences

pervaporation separation of water + isopropanol mixtures using novel

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