47 International Journal of Water Research 2015; 5(2): 47-57

ISSN 2348 – 2710

Original Article

Synthesis and Characterization of Poly (methyl methacrylate-g–starch)

Composite Cation Exchange Membrane for the Electrolysis of Sodium Chloride

Savita Dixita, Sandhya Palb and S.N.Yadevc

a,b, Maulana Azad National Institute of Technology Bhopal c Central Institute of Plastic Engineering and Technology, Chennai (Tamilnadau), India

Corresponding Author: Dr. Savita Dixit

Tel: +91-755-4051653

Email: savitadixit1@yahoo.com

Fax: +91-755- 2670562

Received 14 August 2015; accepted 27 October 2015 Abstract

We have reported the preparation and characterization of poly (mma-g-starch) cation exchange membrane used for the

electrodialysis of sodium chloride solution. The syrup of polymers was synthesized by means of free radical

polymerization of methyl methacrylate using benzoyl peroxide and azo-bisisobutyronitrile (AIBN) as initiators and

dimethylaniline (DMA) as an accelerator in a water medium. Copolymers were synthesized through free radical

polymerization of starch derivatives in methyl methacrylate (MMA). The syrup is casted on a wet porous clay support to

prepare a non-interpenetrating graft membrane. The composite membrane is modified by using gas phase nitration,

followed by amination with hydrazine hydrate, and further reaction with dichloroethane and potassium hexa fluoro

phosphate to introduce hexa fluoro phosphate Chloride (KPF6Cl-) charges on its surface. The modification effect was

studied with FTIR, AFM, SEM, water uptake capacity, contact angle, and the ion exchange capacity measurement. The

experimental results of the electrodialysis of sodium chloride were reported and presented in the terms of current efficiency

and energy consumption for NaOH production. The effect of different operating parameters like salt concentration, current

density, and circulation rates on the current efficiency has been investigated. Prepared membrane has an ion exchange

capacity of 0.794 meq./g which is near to that of the commercially available Nafion-117 membrane having an ion

exchange 0.9 meq./g capacity and the current efficiency for the electro dialysis process of sodium sulfat has more than 90%

and specific energy consumption of 0.1kW/Mol at 2N concentration of the salt at 1000A/m2. The prepared grafted

membrane used for electro dialysis of sodium chloride has a current efficiency of 94.5% and a power consumption of about

0.1032 kW/mol at the same concentration of salt and at a current density of 254 A/m2.

.

© 2015 Universal Research Publications. All rights reserved

Key words Polymethyl Methacrylate, Starch, sodium chloride, membrane, electro dialysis.

1. Introduction

The development of biotechnology and chemical in the

expanded area depends on reliable green technology for the

downstream processes which incorporate purification,

separation and isolation of the molecules [1-4]. Electro

property based membrane separation process involving ion

exchange membranes are not only part of electro chemistry,

but also involve in the different field like separation

techniques i.e. elect dialysis (ED), electro-electro dialysis

and electrode ionization [5, 6]. The most popular industrial

application of ED is the production of drinking water from

brackish water and sea water. This process is widely used

for the purification by demineralization of solutions of

widely varying industrial fluids encountered in the food,

pharmaceutical and chemical industries [7, 8]. In view of

this, development of strong and cost effective cation and

anion exchange membrane with good psychochemical and

electrochemical properties is the highly desired for the

desalination process1.

In Chlor-alkali electrolysis an aqueous solution of sodium

chloride is decomposed electrolytically by direct current,

producing chlorine at the anode, hydrogen as a cathode and

sodium hydroxide solution in the catalyst chamber. Earlier

it was carried either in a mercury cell or in a diaphragm

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48 International Journal of Water Research 2015; 5(2): 47-57

cell. The former utilizes mercury as the cathode for the

electrolytic reaction, as well as for absorbing sodium ions

as mercury amalgam, which is next reacted with deionised

water to produce the caustic soda solution, also only a

small fraction of salt is decomposed per pass through the

cell [9]. This process produces high purity NaOH at high

concentration (50-52 weight %), but causes poisonous

mercury pollution. The diaphragm cell process utilizes

asbestos, to separate caustic soda and chlorine produced

during the electrolysis. This process suffers from low

current efficiency (30-40%) and produces weak cell liquor,

containing 12-14 weight% NaOH [10]. A new type of cells,

membrane cells have now replaced both the mercury and

diaphragm cells [11]. A typical membrane electrolytic cell

consists of two compartments separated by a cation

permeable membrane. Concentrated brine flows through

anode compartment where chlorine gas is produced. The

cathode compartment has NaOH solution (typical

concentration values of 23-35 wt. %) where the hydrogen

evolution takes place with simultaneous production of the

OH¯ ions. The sodium ions diffuse through the membrane

from the anode compartment to cathode compartment to

form NaOH.

The advantage in using cation selective lies in the selected

transport of cation (Na+) and reduced transport of anion,

thus giving higher current efficiency and low chloride

concentration in the NaOH compartment. In addition, a

higher concentration of alkali can be used which means

lower resistance of the cell and a low voltage across the cell

leading lower electrical power requirements [12] (Figure 1

and reaction1).

Electrolysis of NaCl at anode:

2Cl- Cl2 + 2e-

Electrolysis of water at Cathode:

2H2O +2e- H2 +2OH-

Overall Reaction:

2NaCl +2H2O Cl2 +H2 +2NaOH (1)

Cation exchange membranes were the first of the

electrically charged membranes, which were

commercialized and put into extensive industrial

applications. They allow only cation to pass through them.

Therefore, 90% of all planned Chlor-alkali industry

expansion is in ion exchange membrane cell processes. The

type of functional groups found on the cation exchange

membranes are usually sulfonic acid, carboxylic acid or

phosphoric acid groups etc. Polymers used for these types

of membranes are polystyrene, polyphosphazene, PS-DVB,

PVDF [13-15], etc.

The major commercially used membranes are Nafion®

(DuPont), Aciplex (Asahi chemicals) and Fleming (Asahi

glass). These membranes are very expensive and get

denatured at high

working temperatures (>1000C). Cation exchange

membranes have been developed in the literature based on

synthetic polymers like Polysulfone [16], Polyether sulfone

[17], Polyether ether ketone [18], Poly (styrene-co-divinyl

benzene) [19], and natural and synthetic blend polymer

like, Poly (methylmethacrylate-g-starch) [20-22]

Polyaniline-g-starch [23] and poly (vinyl alcohol/Chitosan)

[24] etc. Among all these membranes, Poly

(methylmethacrylate -g- starch) based membranes have

been stated to be the best for use in electro dialysis [25, 26]

because of this blend material is environmental benign

(biodegradable), nontoxic and biocompatible. The cross-

linked membranes Poly (mma-g-starch) have reactive sites

for fictionalization reactions like nitration,

chloromethylataion, and sulfonation, etc. Cation exchange

membranes based on Poly (mma-g-starch) have been

obtained by blending of Poly methylmethacrylate (mma)

and starch, followed by nitration using sodium nitrite with

sulfuric acid in the presence of ferrous sulfate. Therefore,

there is a need to develop chemically and thermally stable,

highly selective, biodegradable, inexpensive and easy to

manufacture ion exchange membranes [27].

In this way, we have prepared ceramic supported poly

(mma-g-starch) based cation exchange membrane modified

using a multi step process, low temperature reaction with

different chemical for the modification process on the

surface. The membrane prepared has a high charge density

of functional groups on its surface and has been

characterized using SEM, AFM, and FTIR, ion exchange

capacity, current voltage characteristics, contact angle

measurements and water content. Further, this has been

used for the electrolysis of sodium chloride and the

efficient membrane has been investigated in terms of

current efficiency and power requirements. We have also

studied the effect of various parameters like, salt

concentrations, current density and flow rates on the

membrane performance.

2. Experimental

2.1. Materials

Analytical grade calcium carbonate, benzoyl peroxide

(BPO), azo-bis-isobutyronitrile (AIBN) is procured from

S.D. Fine Chemicals (Bombay, India). Analytical grade

tetraethylorthosilicate (TEOS), Dimethylaniline (DMA),

Sodium nitrite, Ferrous Sulfate, hydrazine hydrate,

imidizole, di-chloroethane, Potassium hexa Fluoro

phosphate, Sodium chloride, sodium hydroxide, polyvinyl

alcohol, di-sodium hydrogen phosphate, hydrochloric acid,

toluene, methanol and fused calcium chloride are obtained

from Qualigens, Bombay. Methylmethacrylate (MMA)

kaolin, ball clay, pyrophallite, calcium carbonate, feldspar,

quartz and starch are obtained from Loba (India). Before

polymerization, MMA is first washed with 5% NaOH

solution and then vacuum distilled to remove all the

49 International Journal of Water Research 2015; 5(2): 47-57

inhibitors. The AIBN and BPO are recrystallized in

methanol before being used as initiators for

methylmethacrylate (MMA) polymerization reaction. All

the other chemicals are used as received.

2.2 Preparation of Membrane assembly

The method of preparing a membrane assembly is given in

Figure 2 and consists of steps, such as preparation of

support, synthesis of polymer syrup, the casting of

membrane over the support and finally modifying the

membrane to chemically bind the ionic liquid moiety with

it. Clay

mixture

Mixing

Casting

Drying 24 hrs

Room

Temperature

SupDrying 24 hrs

1000CSup

Drying 24 hrs

2500CSup

9000C

SupTEOSSup10000C

Sup

Membrane

CastingNitrationNO2

Amination

NH2

CH2CH2Cl2N

CH2CH2Cl

CH2CH2Cl

Imidazole

N

CH2CH2

CH2CH2

KPF6

PSN

CH2CH2

CH2CH2

PS

PS PS

PS N

N N

Cl-

N

Cl-

NN

NN

Cl-

+

+

Cl-KPF6

KPF6

++

PS

+

Sup

Sup= Support

PS= polymer syrup Figure 2. Preparation of Membrane assembly (included

clay support preparation, polymer synthesis, polymer

casting in support and chemical modification of

membrane). In this Figure, Sup = Support and PS =

Polymer syrup

2.3 Preparation of clay supports

The composite membrane prepared in this work consists of

a clay support and a polymer film deposited on its surface.

The clay support must have pores that are connected

continuously from the feed stream to permeate stream,

otherwise no permeation through the support is possible.

The clay support provides mechanical, chemical and

thermal stability to the membrane. Ceramic support is

prepared by mixing of clays of kaolin, ball clay, red mud,

calcium carbonate, fly ash, and quartz in water according to

the reference [19, 26]. Whereas we replaced the feldspar

and pyrophyllite of the some industrial waste materials like

red mud and fly ash [28]. Firstly the all clay materials are

mixed well to give a thick paste which is used to cast the

support into a flat disk over a gypsum plate. During casting,

care is taken to ensure that no air gaps are present in it and

is spread into a metal ring of a desired dimension.

Firebricks are placed over the supports to ensure a uniform

drying on both surfaces.

Then, they are dried at different temperatures (1000C,

2500C and 9000C) so as to impart sufficient mechanical

strength. The supports are polished on a silicon abrasive

paper to get the final smooth clay discs of 2-3 mm

thickness and a diameter of 65mm. The supports are

washed and dried at 1000C overnight, and then dipped in a

solution of the TEOS solution (tetraethyl orthosilicate, 49

ml mixed with 1ml 35% HCl and 6.5ml water in the molar

ratio of 1:0.04:2). Than the supports are calcined at 10000C

for a period of 3-4 h in a furnace and after this, the supports

are again washed with water and dried [29].

2.4. Synthesis of polymer syrup

Methyl methacrylate polymerized using a dual initiator

system (BPO and AIBN) in the presence of DMA

(dimethylaniline) to get a homogeneous viscous polymer

solution. A typical procedure to prepare PMMA was

followed which involved placing 20 ml of MMA, 0.15 g

(0.75%) of BPO (benzoyl peroxide) and 0.1082 g of ABIN

(azo-bisisobutyronitrile) in 100 ml of water and 0.5 g of

PVA (poly vinyl alcohol) and 5 g of di-sodium hydrogen

phosphate in a 250 ml flask and the solution was stirred for

1h at 800C to complete the polymerization of monomer

[30]. Thick PMMA syrup collects by the separating funnel.

Starch (5% 1.23g) dissolves in Dimethyl sulphoxide

solution. Then after PMMA slurry and starch salutation

mix with each other and sonicate at least two hours in

sonicater [22, 31]. Assumed structure of the Pmma-g-starch

polymer given in Figure 3.

Figure 3. Assumed structure of Pmma-g-starch polymer22

2.4. Membrane Preparation

2.4.1 Composite membrane casting

The support is placed over wet polyurethane foam and a

thin, uniform layer of syrup of approximately 2g is applied

on the surface and is allowed to dry over it for 30 min. The

significance of wet polyurethane foam is that whenever

membrane is cast over wet ceramic support, the polymer

does not pierce inside the pores. The polymer film is

allowed to dry in the atmosphere for 6 h so that the

untreated monomer gets evaporated. The polymer

composite membrane, thus formed is then kept in an oven

for cross linking at 700C for four hours.

2.4.2. Chemical modification of PMMA-g -starch

membrane The steps are involved to modify the membrane to make

the charge on the surface and hydrophilic in nature. Surface

modification of the composite membrane is carried out to

introduce fixed negative charges (KPF6Cl-) on its surface.

The steps of modifications of the membrane are as follows.

The nitration is carried out in a glass reactor, which has a

stainless steel lid. It has a rubber septum in the center for

50 International Journal of Water Research 2015; 5(2): 47-57

creating the vacuum inside the reactor and injecting the

gases with the help of a needle. In this work, NOx is

produced in a 1.5 liter two neck flask by reacting sodium

nitrite (10 g) with sulfuric acid (25 ml) in the presence of

ferrous sulfate (5 g). The reactor is then filled with 500 ml

of NOx (a mixture of NO and NO2) gases and kept at 800C

for 3 hrs for nitrating the Poly (mma-g-starch) clay

composite membrane [32-34] (reaction 2).

2NaNO2 + H2SO4 Na2SO4 + 2HNO2

3HNO2 H2O + HNO3 +2NO

FeSO4 +NO (Fe NO) SO4

2NO+O2 2NO2 (2)

The nitrated polystyrene clay composite membrane is

aminated by using 50% hydrazine hydrate/water mixture at

500C for two hours in a water bath. The aminated clay

composite membrane, thus prepared is modified with 1% 1,

2 dichloroethane solution in methanol at 500C for 45 min. It

is then modified with 2% imidazole solution in water at

500C for 45 min. Finally, the imidazole membrane is

modified with 2% hexa Fluoro phosphate solution in water

at 500C for 45 min.

3. Membrane characterization

3.1. FT-IR The chemical structure and the chemical modification of

unmodified and modified membranes were investigated by

using bruker FT-IR (Vertex-70) spectrometer in the range

of 500–4000 cm−1. The spectra are obtained by making a

pellet of 1mg powder of crushed polymer films as samples

and 200 mg of IR spectroscopic grade KBr pellets.

3.2. Scanning electron microscopy (SEM)

The Scanning electron microscope (Joel-JSM (Model 840

A) is used to view the structural morphology and

asymmetric nature of the graft clay-composite membrane.

The membrane samples are dipped in liquid nitrogen and

sputtered with gold to a thickness of approximately 150 Å

to create a conducting surface, before being analyzed. This

analysis has been carried out for both unmodified and

modified membranes to observe the changes in structural

morphology of the surfaces upon chemical modification.

3.3. Atomic Force Microscopy (AFM) The Atomic force microscope is the advanced

characterization tool which has been applied extensively

for studying ultra-filtration and nano filtration membranes.

AFM have eliminated the tedious process of sample

preparation as it can image non-conducting samples and is

used to determine the average pore size and surface

roughness of the membrane. All the samples were scanned

using Molecular Imaging (MI), USA made AFM

equipment in Acoustic AC (AAC) mode. A sharp

cantilever tip scans the surface of the membrane and

generates a line profile of the surface. This line profile is

used to find the pore sizes, pore size distribution and also

the surface roughness.

3.4. Contact angle measurement

The contact angle made by water on the unmodified and

modified PS membranes is measured by using Rame`-Hart

Inc. (RHI) made Goniometer (model 100-00-230). The

measurement of the contact angle helps in the estimation of

the extent of the hydrophilic nature of the membrane.

3.5. Water uptake capacity Water uptake capacity calculated by according to the

ASTM standards. Water uptake measurement was

performed by dipping the dried membranes (dried at 150

°C for 1 hour) in distilled water for 24 hours at room

temperature. The membranes were taken out, wiped with

blotting paper and then weighed. The water uptake capacity

of the membrane was calculated by using the following

equation:

Water Uptake (%) = Wwet -Wdry*100/Wdry (3)

3.6. Cation Exchange Capacity (CEC)

The cation exchange capacity is an important

electrochemical property of an ion exchange membrane and

is a measure of no. of fixed charges per unit weight of dry

membrane. In order to determine CEC, the modified film

was first immersed in distilled water for a period of 24 h

and then in 1M HCl aqueous solution for another 24 h to

convert it to H+ forms. The film was then washed with

distilled water to remove excess acid. The film was finally

equilibrated with 0.5N NaOH aqueous solution for 24 h and

the cation exchange capacity was determined from the

reduction in alkalinity by back titration. The cation

exchange capacity (CEC) was calculated from the

following equation [19, 35].

CEC = (N1-N2) *V/W (4)

Where, where, N1 is the normality of NaOH before

equilibration, N2 is the normality of NaOH after

equilibration; V is the volume of NaOH taken for titration

and W is the weight of modified poly (mma-g-starch) film.

3.7. Current-Voltage characteristics

The current-voltage curve, which is an important

characterization technique to determine the limiting current

density of a membrane, was found out by using a test cell

as shown in Figure 4. This cell consists of two

compartments arranged between Platinum anode and SS

cathode with membrane in the canter. Before the actual

experiment, both the compartments were filled with 1N salt

solution and circulated using peristaltic pumps for two

hours to reach an equilibrium state. Then the current-

voltage curve was obtained by slowly increasing the current

across the membrane in small intervals and noting the cell

voltage after waiting for the current to reach a steady value

[19, 36].

Figure 4. Cell arrangement for measuring the potential

drop across the membrane

51 International Journal of Water Research 2015; 5(2): 47-57

3.8. Experimental set up for electrolysis

The experimental setup used for Electro dialysis using the

membrane is shown in Figure 5. which consists of two

detachable compartments, each having a volume of 75 ml

with the provision for fixing a membrane between the

compartments. The inlets are connected to peristaltic

pumps for the continuous flow of the electrolyte solutions.

The two electrodes used, namely the cathode are made of

Stainless steel and the anode is made of Platinum wires.

The two solutions anolyte (NaCl) and catholyte (water) are

circulated through two 1 litre glass reservoirs using

peristaltic pumps. The solutions are continuously stirred

with magnetic stirrers and the power is supplied using

constant DC power source (0–32V 10 A). A potential

difference is applied across the electrodes and a constant

current density through the membrane is maintained [19].

Samples of catholyte are taken for every 30 min time

interval and the concentrations of NaOH produced are

measured volumetrically by the titration method. Each

electro dialysis run typically carried out for 90 min under

the different operating conditions like salt concentration,

current density and flow rate. For the determination of the

total energy consumption in the electro dialysis process, the

voltage should be approximately constant between two

consecutive readings. The current efficiency (%) and the

energy consumption (kWh/mol NaOH produced) are

determined by the following formulae:

Where ΔC is the change in concentration of NaOH (mol/l)

in time Δt seconds, v is the volume of catholyte solution in

liters, I is the current in amperes, F is the Faraday constant,

VAvg is the average cell voltage for each electrolysis run,

and ΔN is the moles of NaOH produced during the

electrolysis run for time t.

Figure 5. Schematic diagram of the experimental setup for

the electrolysis of sodium chloride

4. Result and Discussion

4.1 FT-IR

The FTIR spectra of the unmodified and modified

membranes are given (in the range of 4000-500cm-1). Fig.

6a depicts the FT–IR spectra of Pmma-g-starch

(unmodified membrane). It is confirmed that all the two

spectra are similar except for a few changes in the spectra

of the composites. The features that is similar to identify

the presence of PMMA in all of them. The characteristic

vibration bands of PMMA appear at 1722 n (C=O) and

1600 n (C–O). The bands at 3329 and 2925 cm–1

correspond to the C–H stretching of the methyl group

(CH3) while the bands at 1304 and 1481 cm–1 are

associated with C–H symmetric and asymmetric stretching

modes, respectively [30]. The band at 3025n represents the

O-H stretching of starch. The 1246 cm–1 band is assigned to

torsion of the methylene group (CH2) and the 1170 cm–1

band corresponds to the vibration of the ester group C–O,

while C–C stretching bands are at 1073 and 888 cm–1. The

FTIR analysis has been carried out to confirm the presence

of nitrate, amine, dichloroethane, imidazole and KPF6

functional groups on the modified membranes. Fig. 6b

shows an additional peak at 1588 cm-1 for NO2 group. The

spectra of aminated show no extra peak for the amine

group, but all the NO2 groups disappear confirming the

amination of the membrane. Imidazole group shows peaks

at 2780 cm-1. The spectra of KPF6 membrane in show no

extra peak, but all the imidazole groups disappear

confirming the Poly (mma-g-starch) membrane modified

with KPF6.

0.5

0.6

0.7

0.8

0.9

1

1.1

400100016002200280034004000

Wavelength(cm-1)Tr

ansm

ittan

ce

Figure 6a. Unmodified spectra of poly (mma-g-starch)

0

0.2

0.4

0.6

0.8

1

1.2

400100016002200280034004000

Wavelength(cm-1)

Tran

smitt

ance

Figure 6b. Modified spectra of poly (mma-g-starch)

4.2. Scanning electron microscopy (SEM) The membrane samples were dipped in liquid nitrogen and

covered with gold to a thickness of approximately 150 Å to

create a conducting surface, before being analyzed.

52 International Journal of Water Research 2015; 5(2): 47-57

This analysis has been carried out for both unmodified and

modified membranes to observe the changes in structural

morphology of the surfaces upon chemical modification.

The SEM pictures of the unmodified and modified

membranes are shown in Figure.7a and Fig.7b. In Fig.7a, a

smooth layer of unmodified membrane at 15K

magnification is clearly visible with agglomerate particles

of polymer running across the surface. These particles on

higher magnifications show a cleavage due to evaporation

of untreated monomers, The SEM picture of the modified

membrane is shown in Fig.7b at the same magnification of

Fig.7a.

The modified membrane indicates that the cracks are not

continuous. Different chemical modification process

overcoat the graft membrane and filled the cracks of the

surface. There are some pores also present in surface. The

pore size of the membrane is confirmed by AFM analysis.

The image 7c is the cross section image of membrane with

ceramic support. In this image, the dense part depicts the

ceramic material with some agglomerated particles that

show the silica particles of tetraethyl-orthosilicate. Another

cross section view is the polymer layer, which is coated

layer by layer on ceramic support. The polymer has not

impregnated in the ceramic support it is clearly visible in

this image.

Figure 7a. SEM picture of unmodified membrane

Figure7b. SEM picture of modified membrane

Figure7c. SEM picture of modified membrane

53 International Journal of Water Research 2015; 5(2): 47-57

4.3. Atomic Force Microscopy (AFM)

The AFM images of the unmodified and modified

membranes are shown in Fig. 8a and Fig. 8b. The dark

regions in the image are the probable pores and the bright

regions are the peaks on the membrane surface. The

average pore size of the membrane was found to be around

40-60 nm from the line profiles of the different regions.

Figure 8a. AFM image of unmodified membrane

Figure 8b. AFM image of modified membrane

4.4. Contact angle measurement The contact angle made by the water on the unmodified and

modified membranes was determined following the

procedure given in section 3.4. The average angle measured

is 820 on the unmodified membrane and of the modified

membranes, 750 of nitrated membrane, 580 on aminated

membrane, 520 on 1, 2 dichloroethane membrane, 460 on

imidazole membrane and 420 on KPF6 membrane. The

decrease in the contact angle indicates that the graft

membrane was becoming hydrophilic in nature of chemical

modification.

4.5. Water uptake capacity

The swelling behavior, not only investigated mechanical

properties and dimensional stability of the membrane, it

also influences its ability of ion selectivity and electrical

resistance. The swelling behavior of the membrane is

investigated in terms of the water content and it is

determined for the modified composite membrane reported

in this work. As per the procedure given in section 3.5, the

modified and unmodified film was first immersed in

distilled for a period of 24 h and then dried at 600C for 5

hours until a constant weight is obtained [19]. The

unmodified poly (mma-g-starch) membrane denote the

hydrophobic nature and thus shows only 22.8% water

uptake, whereas the modified membrane has hydrophilic

chloride functional groups on its surface and so its water

uptake capacity is found to be 29.5%. In the comparison of

unmodified and modified membranes, the commercially

available Nafion-117 membrane showing more

hydrophobic nature with 14% water absorption capacity.

The modified membranes have a high water uptake

capacity, but secure dimensional stability because the

membranes have been cross-linked during preparation and

absorption of water take place at the sites of functional

groups.

4.6. Cation exchange capacity (CEC)

The cation exchange capacity of the modified film was

determined using the procedure given in the section 3.6.

This procedure is taken by ASTM standards.

The cation exchange capacity of the modified poly (mma-

g-starch) films has been determined from the reduction in

alkalinity by back titration to be 0.0.784 meq./g, according

to the procedure given by ASTM standards.. The cation

exchange capacity of Poly (mma-g-starch) membrane is

0.784 meq./g and commercially available Nafion-117

membrane having 0.9 meq./g. This is amongst the most

commonly used cation exchange membranes. The prepared

membrane can be successfully replaced the Nafion

membrane [37, 38].

4.7. Current voltage characteristics (I-V curve)

The current-voltage characteristic curve is used to

determine the limiting current density of the prepared poly

(mma-g-starch) cation exchange membrane. The I-V curve

is obtained by using the membrane in the electro dialysis

set-up and following the procedure given in the

section 3.7. The curves are shown in Figure 9a and 9b. It

can be seen from the I-V curve, there is first a linear

segment and then followed by another very steep linear

segment. The point at which current shows the steady state

behaviour (not fluctuation) with respect of voltage that

54 International Journal of Water Research 2015; 5(2): 47-57

Fig. 9a and 9b, I–V characteristics of poly (mma-g-starch) cation exchange membranes

segment defines the minimum current density. The first

point where there is a change in the slope of the curve

corresponds to the limiting current density and is found to

be 515 A/m2 at 0.5N and 405 A/m2 at 1N for our

membrane. These values are compared very well with the

values reported in the literature [39].

5. Effect of operating conditions on membrane

performance

The suitability of developed cation exchange membrane for

the electro-membrane applications was assessed in terms of

current efficiency and energy consumption for the salt

removal experimental condition. The current efficiency is a

measure as a fraction of current carried by sodium ions

through the cation exchange membrane. The salt

concentration current density and flow rates are the main

parameters, which affect the current efficiency and energy

requirement.

During the experiments to determine the influence of one

parameter the other variables are kept in standard

conditions of 1N NaCl, 254 A/m2 of current density, and

circulation rate of 99 ml/min. The current efficiency and

power consumption at the base condition are 91.5% and

0.1215 kWh/mol NaOH production. According to literature

[40], we can easily notice prepayerd membrane shows

highest current efficiency and low energy consumption

with respect of Nafion membrane.

The overall performance of the cation exchange membrane

(CEM) including the current efficiency, cell voltage

(average values), sodium ion transport number and energy

consumption over a period of 90 min is given in Table1.

5.1 Effect of current density on current efficiency and

power consumption

The effect of current density is shown in Table1. Figure 10

shows the effect of current density over the current

efficiency at standard conditions. It is observed that there is

a slight increase in current efficiency up to 254 A/M2 and

further decreases at higher current densities. The same was

reported earlier by Tzanetakis et al [40] where it has been

indicated that the electro dialysis at higher current densities

might have been performed above the limiting current. So

when operated above the limiting current density, the

concentration polarization will come into picture reducing

55 International Journal of Water Research 2015; 5(2): 47-57

Figure 10. Variation of current efficiency of CEM with time at different current densities (salt concentration = 1N, flow

rate = 66 ml/min, temperature = 25 ◦C).

Table 1. Overall performance of the cation exchange membrane (CEM)

S.No Flow

rate(ml/min)

Current

Density

(A/m2)

Time

(min)

Conc. Of

Nacl(N)

Cell

Voltage

(V)

Current

Efficiency

(%)

Na+

Transport

number

Energy

Consu-

mption

(KWh/mol)

1 33 127 30 0.5 5.9 85.3 0.853 0.8324

2 66 254 60 0.5 5.8 87.6 0.876 0.6485

3 99 509 90 0.5 8.2 80.8 0.808 0.8142

4 33 127 30 1.0 5.1 88.6 0.886 0.1523

5 66 254 90 1.0 4.7 91.5 0.915 0.1215

6 99 509 60 1.0 5.2 88.1 0.881 0.1589

7 33 127 30 2.0 4.9 89.4 0.894 0.1469

8 66 254 60 2.0 6.2 86.8 0.868 0.7458

9 99 254 90 2.0 4.4 94.5 0.945 0.1032

the current efficiency. At lower current density, i.e. At 127

A/M2, there is a decrease in power consumption, but

efficiency is low.

In the standard conditions of 2N NaCl, 254 A/m2 and at a

circulation rate of 99 ml/min, the current efficiency is

found to be 94.5% and the energy consumption of 0.1032

kWh/mol of NaOH produced.

5.2. Effect of salt (anolyte) concentration on current

efficiency and power consumption

The effect of salt concentration on current efficiency,

power consumption is shown in Table 4. In Figure 11, the

effect of the salt concentrations over the current efficiency

has been found that the current efficiency was increasing

with an increase in salt concentration and this behavior is

perfect agreement with what reported in the literature [41].

Thus, because of the higher current efficiency, it would be

ideal to operate the electro dialysis process at higher

concentrations, but this also has an associated disadvantage

with it as discussed now. It was noticed that when the

experiments were run at very high concentrations, fouling

of the membrane takes place. This reduces the current

efficiency and increases the energy consumption. So, 0.5N,

1N and 2N concentrations of NaCl were used to study their

effect on the current efficiency. The power consumption

also followed a similar trend like the Current efficiency. At

higher concentrations of NaCl up to 2N, there is a decrease

in power consumption, but eventually increased as the

concentration is increased further.

Figure 11. Variation of current efficiency of CEM with

time at different salt concentrations (current density = 254

A/m2, flow rate = 66 ml/min, temperature = 250C).

56 International Journal of Water Research 2015; 5(2): 47-57

5.3. Effect of circulation rate on current efficiency and

power consumption

The effect on the circulation rates of the catholyte and

anolyte on current efficiency for CEM is shown in Figure

12. If the circulation rate increase then the current

efficiency will be increased, this is proved by the Figure.12.

This may have been due to the transport behaviour

associated with gas evolution is not the rate limiting step in

the narrow cell channel at the low flow rates. The current

efficiency is slightly high at lower flow rates, which can be

explained because of the good mass transport behavior

associated with the gas evolution in the narrow cell

channel. The trend of power consumption is also following

the same trend as the current efficiency. With increased

circulation rates up to 66 ml/min, the power consumption

decreased and then again increased further with higher flow

rate of 99 ml/min [41, 6].

6. Conclusion

An ultra-filtration, cross linked poly (mma-g-starch) clay

composite membrane has been successfully prepared by

chemically modifying by step by step process. Prior to the

membrane casting, the support was dipped in TEOS

(tetraethoxysilane) and was found to withstand longer runs

of experimentations without collapsing. The cation

exchange membrane, thus prepared was characterized by

scanning electron microscopy (SEM), FTIR spectroscopy,

water content, contact angle measurement, atomic force

microscopy (AFM) and cation exchange capacity. Finally

membrane has been tested for at least for four months and

we could get similar results within 6% of variation of that

reported here. The effect of operating parameters (current

density, circulation rate and salt concentration) on the

performance of the membrane has been studied. The

current efficiency of the membrane is found to decrease

slightly for higher current densities, and increased with an

increase in salt concentration and flow rates. In the standard

conditions of 2N NaCl, 254 A/m2 and at a circulation rate

of 99 ml/min, the current efficiency is found to be 94.5%

and the energy consumption of 0.1032 kWh/mol of NaOH

produced. The current efficiency, increased with an

increase in flow rate and salt concentration, but decreased

slightly with an increase in current density. Recent

advances in the development of cation-exchange membrane

may encourage the suitability of these membranes for

different types of electro-membrane applications.

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Source of support: Nil; Conflict of interest: None declared