Influence of quaternary ammonium moieties on poly(phenylene oxide) based anion exchange membranes for acid reclamation by diffusion dialysis

Disposal of acidic effluent pose significant environmental challenges. To mitigate this challenge, acid reclamation from the effluent offers a sustainable solution. Therefore, membrane-based separation processes such as diffusion dialysis (DD) have proven practical approach for acid reclamation. Here, we report a designed synthesis of anion exchange membrane (AEMs) from brominated poly(phenylene oxide) followed by quaternization with four various quaternary ammonium (QA) moieties. These QA groups are aliphatic, cyclic aliphatic, aromatic, and bicyclic. The fabricated membrane’s structural, morphological, and thermo-mechanical stabilities were illustrated through ¹H NMR, FT-IR spectroscopy, SEM, AFM, UTM and TGA analysis. Among the prepared membranes, AEM-4 exhibited outstanding electrochemical traits: water uptake (27 %), ion exchange capacity (1.1 meq g⁻¹), and conductivity (9.8 mS cm⁻¹). The acid reclamation of fabricated membranes was evaluated in a lab-scale setup, focusing on proton diffusion coefficient (U_H⁺) and separation factor. AEM-4 membrane demonstrated superior proton diffusion coefficient (17.3 × 10⁻³ m h⁻¹) and separation factor (54.4) in acid effluents (HCl/FeCl₂), surpassing AEM-1, AEM-2, and AEM-3 by ∼1.3, ∼1.2 and ∼1.0 times, respectively. This study investigated the impact of these QA groups on AEM properties, aiming to identify the optimal QA group for synthesizing AEMs for DD application.