Enhanced Alkali Recovery and Desalination by Cation Exchange Membranes Utilizing Dry Wet Phase Inversion Technique: Impact of Co-ions, Osmotic, and Electro-Osmotic Phenomena

Cation exchange membranes (CEMs) are widely used for water desalination, as well as for the separation and concentration of alkali by electrodialysis (ED). The economic viability of the process depends on the electrochemical properties of the CEM. Sulfonated poly(ether ether ketone) (SPEEK) has been chosen to fabricate the CEM using the dry wet phase inversion (DWPI) technique. DWPI requires less polymer material and time, providing good mechanical strength due to the fabric support. DWPI can be a better alternative for crafting efficient dense membranes than solvent evaporation. Representative SPK/dd-PI/2 membrane prepared using a mixed solvent system of N, N dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (VDMF/VDMSO = 60:40) on both sides of the fabric exhibits superior desalination performance with a power consumption of 0.92 kW h kg–1 and a current efficiency of >95% at an applied potential of 6 V using ED. It also shows better alkali recovery performance separately by diffusion dialysis (DD) (18.6%) and ED (79.2%). The alkali recovery performance was further enhanced to 94.6% by the hybrid DD-ED process. The counterionic transport phenomenon of Na+ and the co-ionic transport of Cl– and OH– have been studied. The osmosis and electro-osmosis during the ED-based ion separation have also been investigated and compared with a commercial IONSEP-HC-C membrane and CEM prepared by a solvent evaporation technique from the SPEEK polymer.