Abstract
Dense PES (polyether sulfone) - PVP (polyvinyl pyrrolidone) blend membranes are proposed to recover titania waste acid by diffusion dialysis. These dense membranes can simply be prepared by the solution casting method, and the spontaneous quaternization of the N and O atoms in pyrrolidone with H+ in sulfuric acid solution turns them into effective anion exchange membranes very suitable for the fractionation of sulfuric acid/sulfate. In this work, the influence of the PVP molecular weight (K30 and K90), the composition of the casting solution and the concentration of sulfuric acid in the post-treatment step on the physicochemical properties and mass transfer performance of the membranes are systematically investigated. It is found that the content of absorbed sulfuric acid in the dense membranes increases with the increasing PVP content (20–60 wt%) in the membranes, after the equilibration in 2.68 M H2SO4. The content of H+ in blend membranes with PVP K30 (K30 series) is 0–5.73 mmol/(g dry membrane), while that in the membranes with PVP K90 (K90 series) is 0–5.34 mmol/(g dry membrane). The permeability coefficients of H2SO4 and FeSO4 in the K30 and the K90 series membranes also increase gradually, ranging from 0–200 × 10−9 m2/h and 0–8.81 × 10−9 m2/h, respectively. The largest selectivity coefficient of H2SO4/FeSO4 can reach 1800. The permeability coefficients of H2SO4 and FeSO4 also increase gradually with the increase of the solution acid concentration, and the selectivity remains excellent. These PES-PVP dense membranes show very good chemical stability, the permeability coefficients of H2SO4 and FeSO4 for a blend membrane with 55 wt% PVP K30 remain unchanged in a 2.68 M H2SO4 solution for 337 days. This study would provide valuable guidance for the application of these PES-PVP blend anion exchange membranes in the recovery of titania waste acid by diffusion dialysis.
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