Preparation of heterogeneous bipolar membranes and their performance evaluation for the regeneration of acid and alkali

Abstract

A cost effective bipolar membrane has been prepared by the solution casting method for the hydrolysis of inorganic and organic salts using a bipolar electrodialysis technique. Two types of heterogeneous–heterogeneous composite bipolar membranes (BPM) have been prepared. The first one is prepared by the dispersion of cation exchange resin powder in polystyrene solution and cast on a commercially available anion exchange membrane. The second type of BPM has been prepared by the dispersion of anion exchange resin powder in polystyrene solution and then cast on a commercially available cation exchange membrane. Both the BPMs have been prepared without using the interfacial layer required for water splitting. Both the BPMs exhibited low ionic resistance, moderate to high water uptake, high ion-exchange capacity, high ionic conductivity, appropriate stability and high water splitting efficiency during the bipolar electrodialysis process. Water splitting efficiency of the prepared BPMs was also tested in a four compartment bipolar electrodialysis cell for converting sodium chloride and sodium formate/sodium acetate into their corresponding acids and sodium hydroxide. During hydrolysis of 0.5 M sodium chloride 87–90% current efficiency and 5.23–3.78 kW h kg⁻¹ power consumption values were observed for the two different types of BPMs. Similarly, during hydrolysis of 0.5 M sodium formate 92–94% current efficiency and 4.25–3.85 kW h kg⁻¹ power consumption values were observed for both types of BPMs. The performance of BPMs slightly reduced during hydrolysis of 0.5 M sodium acetate solution due to the slower ionization of sodium acetate. The performance of the BPMs is comparable with commercial BPMs.

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Introduction

A bipolar membrane (BPM) is a composite membrane consisting of a cation exchange layer (CL) and anion exchange layer (AL) joined together.¹ Sometimes an interfacial hydrophilic layer is kept in contact with CL and AL. The role of the hydrophilic interface is to split water molecules into protons (H⁺) and hydroxide ions (OH⁻) with an applied potential.² The generated H⁺ and OH⁻ ions migrate towards the cathode and anode, respectively. The AL and CL of BPM allow the selective transportation of H⁺ and OH⁻.³ BPMs are widely used for the generation of acid and alkali from the hydrolysis of salts.⁴ A BPM should have high selectivity, low voltage drop, high stability in acid, base and high mechanical property.⁵ The simplest bipolar electrodialysis stack (BPED) consists of a three component system containing a BPM, a cation exchange membrane (CEM) and an anion exchange membrane (AEM). BPED has also been used for the preparation of organic acids and fine chemicals.^6–8 BPMs have been prepared by pasting CEM and AEM together using heat and pressure or by using an adhesive that binds the CEM and AEM.^9,10 BPM has also been prepared from a single sheet of polymeric material containing both negative charge and quaternary ammonium moiety at the opposite sides.¹¹ Among all the above mentioned methods, the casting method is very simple and cost effective. BPM prepared by solution casting method exhibits good mechanical strength, high limiting current density and low membrane resistance.¹² Most of the AL is prepared from polysulfone by chloromethylation reaction using chloromethyl methyl ether followed by amination with trimethyl amine.^13,14 Chloromethyl ether is a hazardous chemical and hence it is advisable to prepare AL by avoiding chloromethylation reaction.¹⁵ Thus it is desirable to prepare AL of BPM by alternate route. Cost effective BPM preparation was reported by dispersing polystyrene/divinyl based cation and anion exchange resin powder separately in polyvinyl chloride solution followed by drying of one layer casting on another layer solution.^16,17 The BPM prepared by above technique suffers stability as the layers are easily separated in water and hence could not be used for practical application. BPM has been prepared by casting sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) solution on cross-linked AEM Prepared from benzylic bromination of PPO followed by quaternization and cross-linking with diamine.^18,19 Heterogeneous–homogeneous composite BPM was prepared first by preparing AL from dispersion of anion exchange resin powder solution in polyether sulfone (PES) followed by drying. Next CL layer (which was prepared from sulfonated PES) was cast on AL.²⁰ Cost of commercially available BPM is very high because of the incompatibility of CL and AL which results delamination of each layer. The main challenging in the preparation of BPM is the adhesion between CL and AL. Therefore, our aim was to prepare BPM by adhering AL or CL (which were prepared by dispersion of anion/cation exchange resin powder) with the use of suitable stabilizer upon casting on commercial CEM/commercial AEM. This process will reduce the cost of BPM compare to commercial BPM.

In the present work, we are reporting an alternate method for the preparation of heterogeneous–heterogeneous BPM by (i) dispersing anion exchange resin powder in polystyrene solution and cast on commercial CEM and (ii) dispersing cation exchange resin powder in polystyrene solution and cast on commercial AEM followed by evaporation of solvent by drying. Both the processes produced efficient BPM. The water splitting efficiency of the prepared BPMs was studied for the hydrolysis of sodium chloride, sodium sulfate, sodium acetate, and sodium formate into their corresponding acids and base during the BPED process at different applied potential.

Experimental

Materials

Polystyrene (PSt) received from National Chemicals. All other reagents such as ethylene dichloride (EDC), toluene, sodium chloride (NaCl), sodium formate (HCOONa), sodium acetate (CH₃COONa), sodium sulphate (Na₂SO₄), and sulphuric acid (H₂SO₄) of AR grade obtained from S.D. Fine Chemicals, India, were used without further purification. Anion-exchange resin powder (3.4 meq. g⁻¹ ion-exchange capacity) and cation exchange resin powder (3.5 meq. g⁻¹ ion-exchange capacity) were supplied by ion-exchange India.

Preparation of BPM

10 g of PSt was dissolved in the mixture of EDC (30 mL) and toluene (45 mL) under stirring at 60 °C for 4 h until homogeneous solution is prepared. Next, 10 g anion exchange resin powder was added into the polymer solution and mixture was kept at 60 °C for 5 h. This mixture was caste on commercial CEM and kept at room temperature for 24 h for complete drying. Similarly, the other type of BPM was prepared by dispersing the cation exchange resin powder in PSt solution (prepared in mixture of EDC and toluene) and cast on commercial AEM.

Characterization of BPM

FT-IR and optical microscope analysis

FT-IR spectra of the CL and AL were recorded with FTIR (Perkin Elmer Instrument) at room temperature from 4000 to 600 cm⁻¹. The samples were grinded with KBr and pellets were then made for the analysis. Optical microscope images of prepared BPMs were carried out by keeping the membrane pieces underneath of a Leica S8AP0 microscope and the images were taken with a camera (Leica DFC295).

Water uptake

Water uptake capacity of the membranes was determined by keeping the membranes in distilled water for 24 h at room temperature. Membrane weight (W_wet) was taken after wiping the water drops from membrane surfaces using tissue paper. Weight of dry membranes (W_dry) was also measured after drying for 12 h at 70 °C.

Ion exchange capacity (IEC) of the membrane layers (both CL and AL) were determined using reported procedure.^21,22

Ionic conductivity (K^m) of the membranes

Ionic conductivity measurements of AEM, CEM, AL, CL and BPM were determined after equilibrating the samples in 0.1 N NaCl solutions for 24 h. For the measurement the membranes are sandwiched between two square piece graphite electrodes (1.0 cm²). Ionic conductivity (K^m) of the membranes was calculated using membrane resistance from equation:^21,22

K^m = L/RA (2)

where L (cm) is the distance between the electrodes used to measure the potential, R (ohm) is the resistance of the membrane, and A is the surface area of the membrane (cm²).

Transport number of the membranes

The transport number (t) of AEM, CEM, AL and CL was determined by EMF method. The membrane potential (E_m) was determined in a two compartment cell made of acrylic sheet of effective membrane area 9.0 cm² using NaCl in the two compartments of concentrations 0.1 M and 0.01 M respectively. Pieces of AEM, CEM, AL and CL were separately placed in the above cell. Two platinum electrodes were connected through the two ends of the membrane by salt bridge. The potential developed across the membrane was measured by connecting two platinum electrodes with a multimeter (MECO KM 857). t value was calculated from the following equation:^21,22where R is the gas constant, F is the Faraday constant, T is the absolute temperature (298 K), C₁ and C₂ are the concentration of NaCl solution.

Current–voltage (i–v) curves for BPM in different electrolytes solution during hydrolysis

The current–voltage curves of BPM-1 and BPM-2 were measured for the hydrolysis of inorganic and organic salts in an in-house made small BPED unit of effective area 80 cm². The housing was made from rigid polyvinyl alcohol sheet. Precious titanium oxide based electrodes was used as anode and stainless steel was used as cathode. Four pieces of prepared BPMs, AEM (IONSEP-HC-A) and CEM (IONSEP-HC-C) were packed in the unit. AC-DC rectifier (Aplab, India) was used as a power supply. The BPED unit consists of four compartments. Different salt solutions (500 mL) of concentration 0.5 M and 500 mL water were circulated in three compartments (compartments 2, 3 and 4) at flow rate 5 L h⁻¹. Sodium sulphate (500 mL, 0.1 M) was circulated in the electrode wash compartment (compartment 1 and 6) at a flow rate 3 L h⁻¹. With the progress of reaction, alkali and acids were produced in compartments 3 and 4 and concentration of salt solution was reduced in compartments 2 and 5. Scheme 1 describes the configuration of membrane arrangement in BPED stacks. The current change throughout the experiment was recorded. The concentration of generated alkali and acid in compartments 3 and 4 was determined by standard titration method.²³

Scheme 1 Schematic representation of membrane arrangement in BPED unit.

The performances of the prepared membranes are analyzed in terms of current efficiency and energy consumption calculated by the following equations;^21,22

Power consumption (W in kW h kg⁻¹) during BPED process is defined as the amount of energy needed during hydrolysis of one kg salt. W has been calculated using the following equation:^21,22

where V is the applied voltage; I is the current (A); dt is the total time (h) of water splitting process; and w is the weight of salt (kg) removed.

The current efficiency (CE) is defined as the fraction of the current transported by the specific ion and has been calculated using the following equation:

where F is the Faraday constant (26.8 A h mol⁻¹); w is amount of salt removed (g), M is the molecular weight of salt used, N is the number of cell pairs (4 pairs), Q is the amount of electricity passed (A h).

Results and discussions

Preparation and characterization of bipolar membrane

Two types of bipolar membranes have been prepared by casting of AL on commercial CEM (designated as BPM-1) and CL on commercial AEM (designated as BPM-2) respectively.^14,15 Our main objective was to prepare BPM by adhering CL and AL. First, different polymeric stabilizers such as polyvinyl chloride, polysulfone and polycarbonate were tried as the stabilizer for the dispersion of cation/anion exchange resin powder. Next, this dispersed solution was caste on commercial AEM or CEM and kept in an oven at 50 °C for drying. After drying, delamination of layers occurred when polyvinyl chloride, polysulfone and polycarbonate were used as stabilizer. This is due to the lack of adhesion between stabilizer, dispersed resin powder and commercial heterogeneous AEM/CEM. Next, polystyrene was used as a stabilizer for the dispersion of cation/anion exchange resin powder. The dispersion in polystyrene was almost homogeneous due to the compatibility between polystyrene and polystyrene/polydivinyl benzene based cation and anion exchange resin power which arise due to strong hydrophobic interaction between polystyrene from the stabilizer and polystyrene from functional resin component. This AL/CL layer was then cast on commercial CEM/AEM which after drying shows the strong bonding between each layer. This may be due to the polystyrene part which anchors as connector between Al/CL layer and heterogeneous commercial AEM/CEM.^24,25 Hence; the BPMs prepared using dispersion of cation/anion exchange resin powder in polystyrene and casting upon commercial CEM/AEM exhibited required electrochemical properties for water splitting. Fig. 1 shows the FT-IR spectra of CL and AL.

Fig. 1 Curves (1) and (2) represent FT-IR spectra of CL and AL respectively.

The bands appeared at 3432 cm⁻¹, 2920 cm⁻¹ and 2850 cm⁻¹ in curve (1), are assigned to the stretching vibrations of OH of SO₃H, C–H bonds of aromatic and aliphatic protons of polystyrene moiety. The bands also appeared at 1170 cm⁻¹ and 1037 cm⁻¹ are assigned to the stretching vibrations for S=O and O=S=O respectively.²⁶ On the other hand, the absorption bands appeared at 703 cm⁻¹, 1486 cm⁻¹, 1600 cm⁻¹, 2920 cm⁻¹, 3028 cm⁻¹ and 3425 cm⁻¹ in curve (2), corresponds to C–Cl of chloromethylated resin part which was not fully quaternized and mixed with the quaternary aminated resin, aliphatic –CH₃, –CH₂, –CH and aromatic –CH, –NH, respectively.²⁷

Fig. 2 shows the optical microscopic images of the BPM-1 and BPM-2. The optical images revealed that the adhesion between CL/AL and AEM/CEM in case of BPM-1 and BPM-2 is appropriate and the adhesion junction (two layered structure) is appeared in the images.

Fig. 2 Optical micrograph images of (a) BPM-1 and (b) BPM-2 respectively.

Physical and electrochemical properties of CL, AL and BPM

The physicochemical and electrochemical properties of ionic layers (AL, CL) and composite BPMs (BPM-1 and BPM-2) are presented in Table 1. The membranes exhibited reasonable water uptake, high IEC and high K^m at room temperature. The water uptake of BPM-1 and BPM-2 is higher than individual water uptake of CEM, AL, CM and AEM. The BPM is prepared by casting of AL/CL on CEM/AEM. As all the layers contain charge and hydrophilic in nature, the final water uptake of BPM becomes higher than individual layer.

Table 1 Physicochemical and electrochemical properties of AEM, CEM, AL, CL, BPM-1 and BPM-2

Type of layer	Water uptake (%)	IEC	Thickness (mm)	K^m (mS cm^−1)	t
CEM	40	2.2	0.42	3.24	0.92
AL	24.4	2.61	0.32	3.20	0.89
BPM-1	52	—	1.006	3.29	—
AEM	40	2.0	0.42	3.23	0.92
CL	23.4	2.37	0.26	2.16	0.91
BPM-2	55	—	1.087	3.48	—

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Fig. 3a and b shows the variation in K^m with NaCl concentration for AEM, CL, BPM-1, CEM, AL and BPM-2. The K^m values increased with the concentration of NaCl due to increase of concentration of exchangeable ions (Na⁺ or Cl⁻) for all types of membranes.^21,22 BPM-1 and BPM-2 exhibited low K^m in compare with CL and AL. This may be attributed to the higher charge density of BPMs.²⁰

Fig. 3 Conductivity vs. NaCl concentration plots of (a) CEM, AL and BPM-1 and (b) AEM, CL and BPM-2 respectively.

Determination of limiting current density of bipolar membranes

The limiting current density of BPM-1 and BPM-2 was determined using 4 pieces of each type of membranes (AEM, CEM and BPM-1/BPM-2) in BPED unit using 0.5 M Na₂SO₄, 0.5 M NaCl, 0.5 M CH₃COONa and 0.5 M HCOONa respectively. The voltage was varied from 1–20 volt per cell pair. Fig. 4a and b shows variation of current density with applied potential for BPM-1 and BPM-2 respectively.

Fig. 4 Current density vs. applied potential plots of (a) BPM-1 and (b) BPM-2 using 0.5 M Na₂SO₄, 0.5 M NaCl, 0.5 M CH₃COONa and 0.5 M HCOONa respectively.

It is observed from Fig. 4a and b that up to 8 volt per cell pair applied potential the current density does not linearly increase with the applied potential. The resistance of the membrane increases due to depletion of ions at the interface region of BPMs. After applied voltage 10 volt per cell pair water splitting started and hence the transportation of ions (H⁺ and OH⁻) through the BPM started and hence current density increases linearly with the applied potential. Therefore, BPED experiments can be carried out at applied potential 8 volt per cell pair and above.

Effect of applied potential on the salt conversion

BPED experiments to hydrolyse 0.5 M Na₂SO₄ solutions into H₂SO₄ and NaOH using BPM-1 were carried out under varying applied potentials (8–15 volt per cell pair). Fig. 5 shows the variation of current density with time at different applied potential. The final concentration of produced acid and alkali, W and % CE values obtained as determined from Fig. 5 has been presented in Table 2.

Fig. 5 Current density vs. time plots for BPM-1 using 0.5 M Na₂SO₄ at different applied potential.

Table 2 BPED results obtained during hydrolysis of 0.5 M Na₂SO₄ at different applied potential using BPM-1

Applied potential (volt per cell pair)	H2SO4 (M)	NaOH (M)	W (kW h kg^−1)	CE (%)
8	0.14	0.40	6.54	23
10	0.17	0.46	7.49	25
12	0.20	0.44	8.98	25
15	0.19	0.48	9.80	29

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The performance of BPM-1 increases with the increase of applied potential (volt per cell pair). The final concentration of produced acid and alkali was similar with BPM-1 at applied potential 10 and 12 volt per cell pair. The W value obtained at applied potential 12 volt per cell pair was higher than obtained with applied potential 10 volt per cell pair, whereas CE value was same for both the applied potential.

Effect of types of inorganic salt on BPED performance

The hydrolysis of inorganic salts for e.g. 0.5 M Na₂SO₄ and 0.5 M NaCl were also studied using BPM-1 and BPM-2 at an applied potential 10 volt per cell pair. Fig. 6a and b shows the current density vs. time plots obtained with BPM-1 and BPM-2 during hydrolysis of 0.5 M Na₂SO₄ and 0.5 M NaCl. The results obtained from Fig. 6a and b in terms of concentration of generated acid and alkali, W and CE have been presented in Table 3. At constant applied potential, current density initially increased, attaining the maximum value and then again further decreased with time. The voltage drop across the membrane depends on solution resistance as well as Donnan and diffusion potentials at solution–membrane interfaces. At the beginning of the experiments, deionized water was passed through compartments 3 and 4, which increases the resistance of the membrane. The concentration of produced alkali in compartment 3 and concentration of produced acid in compartment 4 increased under constant applied potential gradient, due to water splitting (OH⁻ and H⁺) at the interfacial zone of a BPM. As a result, electrical resistance in compartments 3 and 4 rapidly decreased with time, which results an increase in current density under applied constant potential.²⁰

Fig. 6 Current density vs. time plots for (a) BPM 1 and (b) BPM-2 during hydrolysis of 0.5 M Na₂SO₄ and 0.5 M NaCl at 10 volt per cell pair applied potential.

Table 3 BPED results obtained during hydrolysis of 0.5 M Na₂SO₄ and 0.5 M NaCl, using BPM-1 and BPM-2 at 10 volt per cell pair applied potential

Type of bipolar membrane	Type of salt	Concentration of acid (M)	Concentration of alkali (M)	W (kW h kg^−1)	CE (%)
BPM-1	Na2SO4	0.12	0.45	7.49	25
BPM-1	NaCl	0.18	0.50	5.23	87
BPM-2	Na2SO4	0.19	0.48	5.87	33
BPM-2	NaCl	0.20	0.50	3.78	90

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It has been observed that the concentration of produced alkali is higher than the concentration of produced acid when hydrolysis of 0.5 M Na₂SO₄ and 0.5 M NaCl was carried out using BPM-1 and BPM-2. This is due to the lower transport number of SO₄²⁻ and Cl⁻ than OH⁻.²⁸ OH⁻ exhibits anomalously high mobility in aqueous solutions due to solvation.²⁹ Hence, the transport number of ions follows the trend t_SO4²⁻ < t_Cl⁻ < t_OH⁻. Hence the value of W increases and CE decreases during hydrolysis of Na₂SO₄ using both BPM-1 and BPM-2 whereas in case of hydrolysis of 0.5 M NaCl, the W value decreases and CE value increases for both BPM-1 and BPM-2. The W value obtained with BPM-2 was lower than that of BPM-1 during hydrolysis of both the inorganic salts. Hence, the performance of BPM-2 is higher than BPM-1.

Effect of types of organic salt on BPED performance

At an applied potential 10 volt per cell pair the hydrolysis of organic salts such as 0.5 M CH₃COONa and 0.5 M HCOONa were also carried out using BPM-1 and BPM-2. Fig. 7a and b shows the variation of current density with time during hydrolysis of 0.5 M CH₃COONa and 0.5 M HCOONa using BPM-1 and BPM-2. Table 4 shows the concentration of produced NaOH and respective acid, W and CE values obtained during hydrolysis of organic salts using BPM-1 and BPM-2.

Fig. 7 Current density vs. time plots for (a) BPM 1 and (b) BPM-2 during hydrolysis of 0.5 M CH₃COONa and 0.5 M HCOONa at 10 volt per cell pair applied potential.

Table 4 BPED results obtained during hydrolysis 0.5 M CH₃COONa and 0.5 M HCOONa using BPM-1 and BPM-2 at 10 volt per cell pair applied potential

Type of bipolar membrane	Type of salt	Concentration of acid (M)	Concentration of alkali (M)	W (kW h kg^−1)	CE (%)
BPM-1	CH3COONa	0.29	0.28	4.38	75
BPM-1	HCOONa	0.39	0.37	4.25	92
BPM-2	CH3COONa	0.29	0.23	4.24	77
BPM-2	HCOONa	0.41	0.33	3.85	94

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Table 4 indicates that conversion of RCOONa to corresponding acid and alkali and CE were decreased, while W value increased with the increase in the carbon chain length of organic salt. These results can also be explained by ion transport and water splitting effect at the BPM. The dissociation of RCOONa to corresponding cation and anion reduces with the increase in the carbon number in the organic acid (RCOO⁻). With the application of potential, H⁺ produced from the splitting of water at the interface of BPM combines with the RCOO⁻ from organic salt and produces acid. The transport number of HCOO⁻ > CH₃COO⁻ and hence the conversion of RCOONa to RCOOH decreases with increasing carbon number in the organic salt.²⁰ The performance of BPM-2 is better than BPM-1 during hydrolysis of all types of organic salts.

Comparison of W and CE (%) of BPM-1 and BPM-2 with commercial BPM

The suitability of the prepared BPM-1 and BPM-2 for BPED process was determined by comparing the W and CE value with commercial BPM and literature reported BPMs during hydrolysis of different salts.^20,30–32 The results have been summarized in Table 5.

Table 5 Comparison of W and CE% value obtained with developed BPMs and literature reported BPMs during BPED process using different salts

Types of BPM	W (kW h kg^−1)	CE (%)	Reference
a Commercial BPM used for the production of tartaric acid from its sodium salt.b Commercial BPM used for the production of p-toluene sulfonic acid from its sodium salt.c Commercial BPM used for the hydrolysis of HCOONa.d Heterogeneous–homogeneous composite BPM used for the hydrolysis of HCOONa.e Developed BPM used for the hydrolysis of HCOONa.
FT-BP (FuMA-Tech GmbH, Germany)^a	12–16	92	29
BP-1 (Tokuyama Soda, Japan)^b	4.1	30	30
BP-1 (Neosepta, Japan)^c	4.3–16.6	72	31
Composite BPM^d	4.73	71.4	20
BPM-1^e	4.25	92	This work
BPM-2^e	3.85	94	This work

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It is observed from Table 5 that the performance of BPM-1 and BPM-2 are comparable in terms of low W value and high CE values with respect to commercial BPMs or literature reported BPMs during hydrolysis of different salts by BPED technique. The prepared BPMs (both BPM-1 and BPM-2) shows better performance during hydrolysis of 0.5 M HCOONa than the reported BPMs.²⁰

Conclusions

We have prepared heterogeneous–heterogeneous BPM from the combination of CL/commercial AEM and AL/commercial CEM. The resulting BPMs showed required mechanical stability and electro-chemical properties for use in bipolar electrodialysis process. Cation layer, anion layer and bipolar membranes were separately prepared and their properties were evaluated. Both the BPMs were used to study the hydrolysis of inorganic and organic salts into their corresponding acid and alkali by bipolar electrodialysis technique. In case of BPM-1.87% CE and 5.23 kW h kg⁻¹ W value were observed whereas for BPM-2, 90% CE with 3.78 kW h kg⁻¹ W values were observed during hydrolysis of 0.5 M NaCl solution. During the hydrolysis of 0.5 M HCOONa, 92% CE and 4.25 kW h kg⁻¹ W values were observed with BPM-1, whereas for BPM-2, 94% CE with 3.85 kW h kg⁻¹ W values were observed. The performance of BPM-1 and BPM-2 was similar during hydrolysis of 0.5 M HCOONa. However, efficiency of the process was slightly reduced (low CE, high W vales achieved) during the hydrolysis of 0.5 M CH₃COONa under similar experimental conditions. Relatively low dissociation of CH₃COONa compared to HCOONa was responsible for the variation in performance in terms of W and CE values. Moreover, as the electrochemical properties of BPM-1 and BPM-2 are reasonably good, high CE, low W values were obtained during hydrolysis of NaCl and HCOONa into their corresponding acid and base by BPED process. The results are comparable with the commercially available BPMs. The performance of the BPMs in BPED unit in terms of high CE and low W value during hydrolysis of salt may be increased by increasing the number of cell pairs or by increasing the effective membrane area of the unit which directly influence the water splitting potential. These results can be a basis of the preparation of BPM, by using proper stabilizer for the dispersion of anion/cation exchange resin powder followed by casting the solution on CEM/AEM for hydrolysis of inorganic and organic salts by bipolar electrodialysis technique.

Acknowledgements

CSIR-CSMCRI registration number 57/2015. We thank the centralised analytical facility of CSIR-CSMCRI for analytical support. We acknowledge CSIR-CSMCRI projects (OLP 0078 and CSC0104) for financial support. Vaibhavee Bhadja acknowledges CSC0104 for providing fellowship.

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