Superior diffusion dialysis anion exchange membranes from miscible polyether sulfone – poly(vinyl pyrrolidone-co-styrene) blends

Abstract

Diffusion dialysis is a promising method for the recovery of titania waste acid due to its low energy consumption and ease of operation. However, the current commercial anion exchange membranes (AEMs) suffer from low acid permeability coefficient and high cost. To address this issue, the development of high-performance AEMs is crucial for the successful recovery of titania waste acid by diffusion dialysis. Previous studies [Journal of Membrane Science, 2022, 662, 120980] have shown that the dense polyether sulfone - poly(vinyl pyrrolidone) (PES-PVP) blend membranes can be converted into AEMs through the protonation reaction of the O atoms in pyrrolidone with H+ in sulfuric acid solution. This process enables the efficient separation of sulfuric acid from ferrous sulfate. The acid permeability coefficient of the blend membrane is influenced by the content and molecular weight of PVP. Higher content and molecular weight of PVP result in a greater acid permeability coefficient of the membranes. It is observed that due to the water solubility of PVP, the amount of PVP added to the blend membranes cannot exceed 60%, however this would restrict further improvement in the acid permeability coefficient of the membranes. Additionally, there is a concern regarding the long-term stability of the membranes as the PVP may get washed out from the membranes. To this, P(VP-co-St) copolymers with a certain hydrophobicity are synthesized through free radical copolymerization of hydrophilic monomer N-vinylpyrrolidone (VP) and hydrophobic monomer styrene (St). PES-P(VP-co-St) dense membranes are then prepared by mixing the P(VP-co-St) copolymers with PES. The objective of this study is to investigate the effects of P(VP-co-St) molecular weight, VP content, and composition of the casting solution on the physicochemical properties, mass transfer properties, and stability of the blend AEMs. The results show that homogeneous dense membranes can be prepared by completely mixing PES with P(VP-co-St) copolymers with 87–90 wt% VP content and 100–150 kDa molecular weight. The permeability coefficients of H2SO4 (PH2SO4) and FeSO4 (PFeSO4) increase with the VP content in the membrane phase. The ion exchange capacity of the PES-P(VP-co-St)-1# AEM varies in the range of 0.32–0.81 mmol/g dry membrane. For the PES-P(VP-co-St) blend membranes, synthesized by blending P(VP-co-St) with 90 wt% VP content with PES at a mass ratio of 7:3 (VP content of 61 wt% in the membranes), the PH2SO4, PFeSO4, and selectivity coefficient of the membranes are 692 × 10−9 m2/h, 5.8 × 10−9 m2/h, and 119, respectively. The PH2SO4 of the PES-P(VP-co-St) AEM is much higher than that of the commercial AEM Tianwei DF-120 while maintaining high selectivity. This study successfully develops AEMs with high performance in diffusion dialysis through a convenient method by blending P(VP-co-St) copolymers with PES.