Double cross-linking PVA-SiO2 hybrid membranes for alkali recovery

The NH2 group from APTEOS can enhance membrane homogeneity, thermal stability and flexibility due to its compatibility with PVA-OH groups. The membranes have high selectivity (62-101) but low permeability in diffusion dialysis process for separating NaOH/Na2WO4 solution. Single type of Si(OCH3) groups produces large silica particles (1.5-5μm), which reduce membrane stability but enhance permeability. The membrane has low strength and flexibility, and high swelling degrees in 65 °C water (373-408%) and weight loss percentage in 65 °C NaOH solution (25.8-28.7%). The permeability can reach up to 0.0076-0.0092 m/h but the selectivity is only 23.7-25.0 at 20-40 °C. The combination of Si(OCH3) and Si(OC2H5) groups (TEOS and MPS) can obtain high strength and flexibility (20.3 MPa, 571%), acceptable swelling degrees (232-279%) and balanced permeability and selectivity (0.0043-0.0071 m/h, 45-110). Hence, double cross-linking agents can be combined to prepare optimized neutral membranes for diffusion dialysis.