Natural gas purification using supported ionic liquid membrane

This paper examines the possibility of the application of a supported ionic liquid membrane (SILM) for natural gas purification. The ionic liquid (IL) 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([emim][FAP]) was impregnated successfully in the γ-alumina layer of a tubular porous asymmetric membrane. The pure gas permeability of natural gas components, such as carbon dioxide (CO₂), methane (CH₄), ethane (C₂H₆) and propane (C₃H₈) were tested through the SILM at a trans-membrane pressure of 0.7MPa and temperature of 313K. The following trend of pure gas permeability was observed for the SILM in this study: P_CO2>P_CH4>P_C2H6>P_C3H8. Moreover, the CO₂/CH₄ ideal permselectivity was calculated. Mixed gas permeability and permselectivity for the binary mixture of CO₂/CH₄ (50/50%, v/v) was also measured. The mixed gas permselectivity (α=1.15) was found to be much lower than the ideal permselectivity (α=3.12). The performance of the SILM was significantly affected by the presence of water, which is also generally present in natural gas. Even though [emim][FAP] is an excellent alternative absorbent with high CO₂ absorptive capacity and ideal solubility selectivity for CO₂/CH₄ (S=9.69), the incorporation of this IL in a SILM is less promising for the removal of CO₂ from natural gas streams, because the permselectivity for CO₂/CH₄ is low.