Alkylated Imidazole Moieties in a Cross-Linked Anion Exchange Membrane Facilitate Acid Recovery with High Purity
Rakhi Mondal, Sandip Pal, Uma Chatterjee
Abstract
An anion exchange membrane (AEM) is applied for acid recovery through the diffusion dialysis (DD) process. However, a specially designed AEM is required to achieve a high dialysis coefficient of acid (UH+) and separation factor (S). The design of our membrane for acid recovery and metal ion separation is based on the optimization of water swelling, structural stabilization (cross-linking), and introduction of cationic moieties where the delocalization of charge in a ring system (imidazole) is possible. Based on the above design, herein, preparation of a cross-linked AEM using a poly(acrylonitrile)-co-poly(vinyl imidazole) copolymer for the separation of metal ions and acid (HCl) is reported. The AEMs have been prepared by quaternization of the copolymer followed by cross-linking. The effect of a quaternizing agent (alkyl chain length) and copolymer composition on the performance of the membranes has been evaluated. The membrane (AEM2-Bu-2) prepared by the quaternization of the copolymer (AN/VIm = 75:25 mol/mol) with 1-bromobutane followed by cross-linking exhibits the highest acid recovery performance with a UH+ of 0.047 m/h and S value of 130 during the separation of the 1 M HCl + 0.18 M FeCl2 mixture. The quaternized imidazole ring provides stabilization of the cationic charge, which enhances the performance of the membrane. This work provides an insight to design a high-performance AEM for acid recovery through the DD process.