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 CH₄ 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/N₂ 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 cm³(STP) cm^?2 s^?1 cmHg^?1] and a CO₂/N₂ selectivity of 58.9 were obtained for the CO₂/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.