Siloxane-urethane membranes for removal of volatile organic solvents by pervaporation

Aqueous dispersions of siloxane-urethane copolymers (polysiloxaneurethanes) containing 0-49% of siloxane moieties were synthesized by the modified prepolymer-ionomer method. The properties of the dispersions were determined. Dense membranes were prepared from those dispersions by crosslinking with a multifunctional aziridine derivative. The structure of the obtained membranes was investigated by FTIR, solid state C-13 NMR, Si-29 NMR and DSC. Prepared membranes were tested in vacuum pervaporation of the following water-organic mixtures: water-tertbutyl methyl ether (1.8% wt. MTBE) and water-butyl acetate (0.25% wt. BuAc) at a temperature of 313 K. It was found that pervaporation properties of the polysiloxaneurethane membranes depended on the content of siloxane moieties. The best separation and transport properties were observed for the membrane containing 49% of siloxane groups. For this membrane separation factor cc was equal to 750 and 13 70 for water-MTBE and water-BuAc mixtures, respectively. The ratio of organic to water partial molar fluxes (J(org)/J(water)) was 2.8 and 0.5, respectively. This membrane was highly hydrophobic, thus the measured flux of pure water was about half of that for the membrane with a lower content of siloxane moieties.