Natural gas purification using supported ionic liquid membrane

Abstract 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 (CO 2 ), methane (CH 4 ), ethane (C 2 H 6 ) and propane (C 3 H 8 ) were tested through the SILM at a trans-membrane pressure of 0.7 MPa and temperature of 313 K. 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 CO 2 /CH 4 ideal permselectivity was calculated. Mixed gas permeability and permselectivity for the binary mixture of CO 2 /CH 4 (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 CO 2 absorptive capacity and ideal solubility selectivity for CO 2 /CH 4 ( S =9.69), the incorporation of this IL in a SILM is less promising for the removal of CO 2 from natural gas streams, because the permselectivity for CO 2 /CH 4 is low.