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.