Alkaline stable thermal responsive cross-linked anion exchange membrane for the recovery of NaOH by electrodialysis

Abstract

We report synthesis of acrylonitrile-vinylimidazole copolymer (PVACN) as novel cross-linking agent, for the fabrication of highly conducting stable and thermal responsive cross-linked polysulfone based anion exchange membrane (AEM) for the recovery caustic soda from industrial waste by electrodialysis. Reported cross-linker (PVACN) showed synergised properties aliphatic carbon chain and grafted ionic groups, while structural features of cross-linked AEM impart conductive and stable nature. Cross-linked architecture of the AEM also formed tight and dense structure. Reported PSCr (cross-linked polysulfone) AEMs possessed imidazolium quaternized groups to avoid Hoffmann elimination reaction (E2), while relatively less number of OH− attacking sites also showed membrane stability under alkaline medium. Suitable optimized PSCr/3 AEM exhibited 1.21 meq g−1 ion-exchange capacity (IEC), 5.5 × 10−2 S/cm ionic conductivity along with 21.7% swelling ratio, and assessed to be highly suitable for alkali recovery by electrodialysis. Electrodialytic recovery of NaOH was performed by increasing the concentrations about 5-times, while about 80% of treated water was also recovered as spin-off. Electro-dialyzer showed 1.33 kWh/kg energy consumption, 75.7% current efficiency at 35 °C, which were significantly improved with increase in feed temperature. Reported AEM provides sustainable and feasible alternative for applying ED for alkali separation/recovery from the industrial waste water.