Stable cycloaliphatic quaternary ammonium-tethered anion exchange membranes for electrodialysis

In this work, we have investigated a series of anion exchange membranes (AEMs) based on brominated poly(2,6-dimethyl-1,6-phenylene oxide) (BPPO) tethered with three saturated heterocyclic quaternary ammonium groups (QAs) of 1-methylpyrrolidine (MPY), N-methylpiperidine (MPRD), and 4-methylmorpholine (MMPH) for electrodialysis (ED) applications, respectively, along with BPPO with trimethylamine (TMA) and Neosepta AMX made for comparison. Our investigations demonstrate that the optimized BPPO-MPRD, having an ion exchange capacity of 1.67 mmol g−1, is highly stable in aqueous KOH (1 mol L−1) with ion exchange capacity retention ratio of 85.1% and hydroxide conductivity retention ratio of 80.3% at 60 °C for over 15 days, relative to other heterocyclic amine decorated AEMs. In ED application process, BPPO-MPRD shows the NaCl removel ratio of 98.8% and energy consumption of 12.58 kWh kg−1, outperforming the Neosepta AMX (97.4% & 15.76 kWh kg−1). The results demonstrate that the as-prepared BPPO-MPRD AEM can be applied in ED.