Pure- and mixed-gas carbon dioxide/ethane permeability and diffusivity in a cross-linked poly(ethylene oxide) copolymer

Pure and mixed-gas CO₂ and C₂H₆ permeability coefficients in a cross-linked poly(ethylene oxide) copolymer were measured at temperatures ranging from -20 to +35°C. The polymer was prepared by photopolymerization of a solution containing 70wt% poly(ethylene glycol) methyl ether acrylate (PEGMEA) and 30wt% poly(ethylene glycol) diacrylate (PEGDA). Four different gas mixtures (10, 25, 50 and 70mol% CO₂) were considered at feed pressures up to 20atm. Carbon dioxide permeability was not changed by the presence of ethane at T≥25°C, but it increased with increasing ethane content at lower temperatures. Ethane permeability, in contrast, increased significantly in the presence of carbon dioxide compared to its pure-gas value, an effect whose extent increased with decreasing temperature. Permeability data were combined with pure- and mixed-gas sorption isotherms to calculate pure and mixed-gas effective diffusion coefficients of each gas. For carbon dioxide, there was no significant dependence of the diffusion coefficient on ethane concentration in the feed. On the other hand, the diffusion coefficients of both ethane and carbon dioxide increased with increasing concentration of carbon dioxide in the polymer. A simplified free volume model with two adjustable parameters for each gas was able to correlate the effects of temperature and penetrant concentration on gas permeability, with an average prediction error lower than 8%.