Cation exchange hybrid membranes prepared from PVA and multisilicon copolymer for application in alkali recovery

Cation exchange multisilicon copolymer with a long main chain and many branched chains as well as high content of cation exchange and Si(OR)3 groups has been developed from sodium allylsulfonate (SAS) and vinyltrimethoxysilane (VTMS). The corresponding PVA/SiO2 cation exchange hybrid membranes have been prepared via the sol–gel process of the copolymer with poly(vinyl alcohol) (PVA). The hybrid membranes have the water uptake (WR) 84–106%, ion exchange capacity (IEC) 0.14–0.45 mmol/g, initial decomposition temperature (IDT) 225–233 °C and tensile strength (TS) 23.9–44.0 MPa. They are stable in 1 M NaOH solution with a linear expansion ratio (LER) of 17.7–18.3% and a weight loss percent of 4.3–5.5% for 30 days. The diffusion dialysis (DD) process for the alkali mixture indicates that the dialysis coefficients of NaOH (UOH) are around 0.0065–0.0086 m/h and the separation factors (S) are in the range of 24.4–51.6 for the NaOH/Na2WO4 system and 13.9–9.6 for the NaOH/NaAlO2 system. Hence, the hybrid membranes can be potentially applied in the DD process for the alkali recovery.