Highly permselective tadpole-type ionic anion exchange membranes for electrodialysis desalination

Abstract

A series of tadpole-type ionic ionomers PPO-DMODAs with long alkyl side chains designed for electrodialysis (ED) desalination were synthesized successfully from dimethyloctadecylamine (DMODA) and brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO). The series of AEMs display stably low water uptakes ranging from 6.2% to 15.1% and high dimensional stabilities with swelling rations of 1.9%–4.8% at temperatures of 25 °C–60 °C. The nano-phase separated tadpole-type ionic structures ensure that the PPO-DMODAs membranes show excellent permselectivities with values above 94.6% and outstanding ED performances in the mostly reported desalination system of NaCl aqueous solutions. Especially, PPO-DMODA-3 surpasses commercial membrane TWEDA1 in ED competitions and ED-stability matches with current efficiency (η) of 88.7%, salt flux (J) of 80.61 mg m−2 s−1, energy consumption (EC) of per kg of NaCl of 2.56 kWh kg−1 and η retentions of the repeated runs higher than 97% of that of the origin run. Moreover, PPO-DMODA-3 membrane obtained from the ethanol solution exhibits stable aggregate structure and ED performances comparable to those of the PPO-DMODA-3 membranes cast with NMP and TCE solutions. Good solubility of PPO-DMODAs in ethanol offers an environmentally friendly green method to fabricate ED AEMs. In consideration of the advantages of low cost, simple synthesis process and green membrane casting technology, PPO-DMODA-3 membrane has a strong potential for ED-desalination application.