CO2/C2H6 separation using solubility selective membranes

Ethane can be a major component of natural gas, and it forms a maximum pressure azeotrope with carbon dioxide, which can hinder carbon dioxide removal if distillation is used. This paper describes a solubility selective membrane material for this separation. A crosslinked poly(ethylene oxide) [PEO] material [XLPEO] was prepared from a prepolymer solution containing 71 wt.% poly(ethylene glycol) methyl ether acrylate [PEGMEA] monomer and 29 wt.% poly(ethylene glycol) diacrylate [PEGDA] crosslinker, and it exhibits high carbon dioxide permeability and high carbon dioxide/ethane selectivity. For example, at 253 K and 10 atm total feed fugacity, the CO2/C2H6 selectivity for a 45 mol% CO2 and 55 mol% C2H6 gas mixture is approximately 12, and the CO2 permeability is 83 Barrers. The performance of the membrane material for breaking the CO2/C2H6 azeotrope was simulated using a computer model. XLPEO was found to be effective in breaking the azeotrope. At a feed composition of 45 mol% CO2 and 55 mol% C2H6, 85% ethane recovery could be achieved at an ethane purity of 78% for a single stage membrane separation operating at 253 K and 11.3 atm total pressure. Experimental sorption, pure gas diffusion and permeability, and mixed gas permeation data for CO2 and C2H6 in this polymer are presented at temperatures ranging from 253 to 308 K.