Preparation of vinyl amine-co-vinyl alcohol/polysulfone composite membranes and their carbon dioxide facilitated transport properties

A vinyl amine-vinyl alcohol copolymer (VAm-VOH) was synthesized through free-radical polymerization, basic hydrolysis in methanol, acidic hydrolysis in water, and an anion-exchange process. In the copolymer, the primary amino groups on the VAm segment acted as the carrier for CO₂-facilitated transport, and the vinyl alcohol segment was used to reduce the crystallinity and increase the gas permeance. VAm-VOH/polysulfone (PS) composite membranes for CO₂ separation were prepared with the VAm-VOH copolymer as a selective layer and PS ultrafiltration membrane as a support. The membrane gas permselectivity was investigated with CO₂, N₂, and CH ₄ pure gases and their binary mixtures. The results show that the CO₂ transport obeyed the facilitated transport mechanism, whereas N₂ and CH₄ followed the solution-diffusion mechanism. The increase in the VAm fraction in the copolymer resulted in a carrier content increase, a crystallinity increase, and intermolecular hydrogen-bond formation. Because of these factors, the CO₂ permeance and CO₂/N ₂ selectivity had maxima with the VAm fraction. At an optimum applied pressure of 0.14 MPa and at an optimum VAm fraction of 54.8%, the highest CO₂ permeance of 189.4 GPU [1 GPU = 1 × 10^-6 cm ³(STP) cm^-2 s^-1 cmHg^-1] and a CO₂/N₂ selectivity of 58.9 were obtained for the CO ₂/N₂ mixture. The heat treatment was used to improve the CO₂/N₂ selectivity. At an applied pressure of 0.8-0.92 MPa, the membrane heat-treated under 100°C possessed a CO₂ permeance of 82 GPU and a CO₂/N₂ selectivity of 60.4, whereas the non-heat-treated membrane exhibited a CO₂ permeance of 111 GPU and a CO₂/N₂ selectivity of 45. After heat treatment, the CO₂/N₂ selectivity increased obviously, whereas the CO₂ permeance decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40043.