Proton blockage membrane with tertiary amine groups for concentration of sulfonic acid in electrodialysis

Abstract

The weak base of tertiary amine groups was introduced into poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) anion exchange membranes (AEMs) by Cu(I)-catalyzed “click chemistry” in order to fabricate proton blockage membranes for sulfonic acid concentration in electrodialysis (ED). The degree of functionalization has been confirmed quantitatively by 1H NMR spectroscopy. Fourier transform infrared spectroscopy (FTIR) was also used to confirm the functional groups in the membranes matrix. The prepared proton blockage membrane with tertiary ammonium groups showed lesser swelling and water uptake ratios than the typical AEMs with strong organic base of quaternary ammonium groups. It is believed that the strong organic base of quaternary ammonium has a stronger hydration effect on water than that of tertiary amine groups. Interestingly, the concentration limitation of membranes with tertiary amine groups was higher than that of the membrane with quaternary ammonium groups, indicative of the proton blocking capabilities of the AEMs as a result of the weak base introduced into the matrix. Moreover, it was found that the concentration limitation of tertiary amine based AEMs was also influenced by the weight-based ion exchange capacities (IECw), essentially the water uptake and swelling ratios of the membranes. The highest concentration limitation of AEMs with tertiary ammonium groups for H+ was 3.02 mmol/L with IECw value of 1.67 mmol/g, which is slightly higher than the 3.00 mol/L reported for the commercial AEM (Neosepta ACM). Therefore, AEMs containing weak base groups are potential candidates for proton blockage membrane for acid recovery applications by ED process.