Side Chain Crosslinked Anion Exchange Membrane for Acid Concentration by Electrodialysis

Electrodialysis (ED) technology for waste acid treatment has high economic efficiency and environmentally friendly advantages. The primary limitation of ED in the retrieval of low-concentration spent acids lies in the leakage of hydrogen ions through anion exchange membranes (AEMs) due to its extremely small size and high mobility. To address this issue, a series of AEMs named QPAB-x (x = 3, 5, 7, 10) were designed for acid concentration in ED process by increasing the membrane densities through in situ crosslinking in this study. The successful synthesis of polymers was confirmed through ¹H nuclear magnetic resonance hydrogen (¹H NMR) spectroscopy and Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. Furthermore, ATR-FTIR spectroscopy showed that the higher the side chain content, the higher the crosslinking degree of the membranes. X-ray photoelectron spectroscopy (XPS) was employed to characterize the effects of aqueous and acidic environments on QPAB membranes. The performance disparities between QPAB-x membranes in acidic and aqueous environments were examined separately. Subsequently, the influence of crosslinking degree on the acid-blocking capability of the membranes was thoroughly investigated by conducting ED acid-concentration experiments to monitor the hydrogen ions concentration process and determine the current efficiency and energy consumption of the QPAB-x membranes. Our experimental results demonstrated that QPAB-x membranes with higher cross-linking degrees have lower water content, especially the QPAB-10 membrane with an IEC of approximately 1.5 mmol g^–1 and a remarkably low water content of around 10%. This leads to a reduced H⁺ transfer number and excellent acid-blocking properties. Additionally, compared to commercial membrane A2, using the QPAB-10 membrane in the ED process resulted in a higher final H⁺ concentration in the concentrated chamber. Consequently, these synthesized membranes exhibit considerable promise in the field of ED acid recovery.