PVA/SiO2 anion exchange hybrid membranes from multisilicon copolymers with two types of molecular weights

Multisilicon copolymer has a long main chain and many branched chains, with plenty of ion-exchange (N+(CH3)3Cl−) and Si(OCH3)3 groups. Multisilicon copolymer with the low molecular weight (Mr of 795) is difficult to gel, while that with the high molecular weight (Mr of 4152) has two gelation times. One is the “pseudo gelation” within 0.03–2.5 days, and the other is within 14–48 days. The two types of multisilicon copolymers are crosslinked with polyvinyl alcohol (PVA) to prepare anion exchange hybrid membranes. Membranes from the low molecular weight copolymer have lower water uptakes (WR, 62–87%), ion exchange capacities (IECs, 0.6–0.9 mmol/g), thermal stability (223–239 °C) and mechanical strength (7–12 MPa, 42–97%). Membranes from the high molecular weight copolymer are homogeneous, transparent and colourless. They have higher WR of 195–464%, IECs of 1.0–1.5 mmol/g, short-term thermal stability of 244–247 °C, mechanical strength (15–23 MPa, 122–208%) and organic solvent resistance. All the membranes can be potentially applied in diffusion dialysis (DD) process for recovery of CH3COOH and HCl. The dialysis coefficients of CH3COOH (UCH3COOH) can reach up to 0.009 m/h, and the dialysis coefficients of HCl (UH) are in the range of 0.01–0.043 m/h with the separation factors of 22–39 (0.01–0.029 m/h and 28–39 for the low molecular weight, and 0.024–0.043 m/h and 22–26 for the high molecular weight), superior to those of commercial DF-120 membrane (0.009 m/h, 18.5).