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, N-2, and CH4 pure gases and their binary mixtures. The results show that the CO2 transport obeyed the facilitated transport mechanism, whereas N-2 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 x 10(-6) cm(3)(STP) cm(-2) s(-1) cmHg(-1)] and a CO2/N-2 selectivity of 58.9 were obtained for the CO2/N-2 mixture. The heat treatment was used to improve the CO2/N-2 selectivity. At an applied pressure of 0.8-0.92 MPa, the membrane heat-treated under 100 degrees C possessed a CO2 permeance of 82 GPU and a CO2/N-2 selectivity of 60.4, whereas the non-heat-treated membrane exhibited a CO2 permeance of 111 GPU and a CO2/N-2 selectivity of 45. After heat treatment, the CO2/N-2 selectivity increased obviously, whereas the CO2 permeance decreased. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40043.