The effects of multi-functional groups from PVA and ternary multisilicon copolymer on diffusion dialysis

• Ternary multisilicon copolymers containing –COOH and –SO3Na groups are prepared.
• Membranes with controllable multi-functional groups are developed.
• The membranes have high dialysis coefficients of NaOH (0.013–0.021 m/h).
• Coupling effects can be formed for the transport of both Na+ and OH− ions.

Ternary multisilicon copolymers are prepared from copolymerization of acrylic acid, sodium styrene sulfonate and γ-methacryloxypropyl trimethoxy silane, from which functional groups of –Si(OCH3)3, –COOH and –SO3Na are obtained respectively. The acidic –COOH groups may induce gel during copolymerization, and thus sufficient solvent needs to be used. The –Si(OCH3)3 groups can crosslink with polyvinyl alcohol (PVA) to yield cation exchange hybrid membranes.The membranes have the ion exchange capacity of 1.01–2.26 mmol/g, water uptake of 39.1–59.7%, swelling degrees of 108–339% in 65 °C water after 192 h, and swelling degrees of 254–344% in 65 °C alkaline solution after 60 h. Membrane with proper ratios of multi-functional groups can sorb 1.4 mol/L NaOH in 1.0 mol/L NaOH solution. The membranes are used in diffusion dialysis (DD) process for alkali recovery from NaOH/Na2WO4 solution. The dialysis coefficients of NaOH (UOH) are in the range of 0.013–0.021 m/h at room temperature, with the separation factors of 15–23. The high UOH values indicate the superiority of multi-functional groups. The –OH, –COOH and –SO3Na groups from PVA and multisilicon copolymer chains may have coupling effects on the transport of both Na+ and OH− ions.