Proton-blocking tadpole-type anion exchange membranes for acid recovery by electrodialysis

Abstract

Three kinds of long-side-chain-modified tadpole-type anion exchange membranes (AEMs) named QPEK-DMODAs with microphase separated structures designed for electrodialysis (ED) acid recovery were fabricated from N,N-dimethyloctadecylamine (DMODA) as quaternization agent and poly(arylene ether ketone) (PEK) as skeleton, which is the copolymer of 2,2′,6,6′-tetramethyl biphenol (TMBP) and 4,4′-difluorobenzophenone (DFBP). QPEK-DMODAs were characterized systematically including basic structures and properties, ED recovery performance of H2SO4 solutions without or with metal impurities, and corrosive acid stability. The well-defined microphase separation structure of QPEK-DMODA-3 is formed by the suitable distribution of tadpole ionic groups at the highest IEC of 2.09 mmol g−1. The aggregate structure offers the membrane competent mechanical stability, ion conductivity and permselectivity, as well as low energy consumption and water transport ratio at the ED process. QPEK-DMODA-3 exhibits higher current efficiency (54.58 %) and recovery H+ concentration (1.74 M) than those of QPEK-DMODA-1, QPEK-DMODA-2 and commercial AMX with comparable energy consumption to that of AMX under the ED conditions of Fe2+ absence. Moreover, the Fe2+ removal rate (88.74 %) and ion selectivity (S = 57.32) of QPEK-DMODA-3 are remarkably higher than those of AMX (67.10 % and 17.32) without the scarce of recovery efficiencies in the ED recovery tests of 0.50 M H2SO4 solution containing 0.10 M of Fe2+. The combination of the comparable tolerance to strong acid to that of AMX and the confirmed good ED recovery performances declares a strong potential of tadpole-type QPEK-DMODA-3 in waste acid recovery by electrodialysis.