Proton blockage PVDF-co-HFP-based anion exchange membrane for sulfuric acid recovery in electrodialysis

Recovery of sulfuric acid from industrial wastewater via electrodialysis (ED) has become a hot topic recently. Since the commercially used anion exchange membranes (AEM) generally lead to the severe proton leakage during ED process, the efficiency of the acid recovery was seriously affected. In this work, a series of proton blockage cross-linking AEM has been prepared by modifying poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) with 1-vinylimidazole, followed by crosslinking with 1,4-dibromobutane. Our investigation demonstrates that the as-prepared PVDF-co-HFP-based AEM has the observable asymmetric structure on the two sides of the AEM with a smooth and dense surface and a rough and porous surface. The asymmetric structure and the hydrophobicity of the fluorinated backbone of AEM render the improved proton blocking performance, and the increased electrical efficiency and reduced energy consumption of acid recovery. For example, the optimized AEM (AEM-0.5) exhibits the acid concentration with the values of cH+ = 2.04 M (initial proton concentration: 1.0 M) in concentrate cell during 12 h-ED process at current density of 20 mA cm−2 and low energy consumption of 1.75 kw·h·kg−1 relative to the commercial NEOSEPTA® AHA and proton blockage ACM AEM. It is believed that this study can provide a guideline for designing advanced proton blocking AEMs.