Sorption behavior and separation performance of novel facilitated transport membranes for CO2/CH4 mixtures

A water-soluble copolymeric membrane material containing tertiary amine and carboxyl groups for CO2 facilitated transport has been synthesized by radical polymerization of DMAEMA(2-N,N-dimethyl aminoethyl methacrylate)-AA(acrylic acid). The composition the copolymer was determined by elemental analysis, the intrinsic viscosity [h] of the copolymer was determined with an Ubbelohde viscometer. The composite membranes were prepared by casting solution of poly(2-N,N-dimethyl aminoethyl methacrylate-co-acrylic acid sodium) on the various support layer. The copolymeric membranes were crosslinked by heat treatment at 120°C. The effects of the molecular weight and carrier (tertiary amine and carboxyl groups) content of the copolymer, the support layer of the composite membrane, CO2 content in CO2/CH4 mixed gas, on the membranes separation performance were investigated. The result shows that the CO2/CH4 selectivity of the composite membrane increased but the CO2 permeation rate decreased with increasing molecular weight of the copolymer, both the CO2/CH4 selectivity of and the CO2 permeation rate had a maximum against the carrier (tertiary amine and carboxyl groups) content of the copolymer. The permeation performance of the composite membrane for CO2/CH4 mixed gas was not as good as those obtained with pure CO2 and CH4 gas because of the coupling effects between CO2 and CH4.

A series of copolymers of different molecular weights and various carrier contents were prepared by common radical polymerization method. The increase in molecular weight for copolymer resulted in a slight decrease in permeation for CO2 but a major decrease for CH4, hence driving a remarkable increase in selectivity. This was explained by the restricted mobility in higher molecular weight membranes. Both CO2 and selectivity of CO2 over CH4 have a maximum against the carrier content. This was because the various monomer ratios led to the variation of not only facilitated transport but also d-spacing and crystallinity. The material and pore diameter of the support membrane affected the composite membrane performance. The permeation performance of the gas mixtures are not as good as those obtained with pure gas because of the coupling effects between CO2 and CH4. Further investigation of the CO2 facilitated transport mechanism and the humidity degree influence on the fixed carrier membranes is necessary.