Supported room temperature ionic liquid membranes for CO2/CH4 separation

Room temperature ionic liquids (RTILs) are organic salts which are liquid at or around room temperature. These compounds exhibit many outstanding physical properties such as great thermal stability and no measurable vapor pressure. In this work supported ionic liquid membranes (SILMs) were prepared by impregnating pores of α-alumina inorganic supports with various ionic liquids. In addition to membranes prepared with pure RTILs we were able to synthesize membranes with RTIL mixtures using 1-aminopyridinium iodide dissolved in 1-butyl-4-methylpyridinium tetrafluoroborate or methyltrioctylammonium bis(trifluoromethylsulfonyl)imide. This combination of an RTIL with an organic salt containing an amine group dramatically improved the membrane separation properties. The SILMs displayed CO2 permeance on the order of 5 × 10−10 to 5 × 10−9 mol m−2 s−1 Pa−1 combined with CO2/CH4 selectivity of 5–30. Although these values are comparable with the current systems for CO2 purification, CO2 permeance is still rather low for these compounds.