Supported liquid membranes have been prepared by impregnation of commercial porous polymer films with the ionic liquid 1-n-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. The ionic liquid has been characterized, and the membranes have been tested to determine performance in the selective separation of CO2 from He. Experiments were conducted in a constant pressure system, and pure gas permeability/selectivity data are reported. Membranes prepared with polysulfone supports have been found to be stable to 125 degrees C. The CO2 permeability of the membranes increases from 744 to 1200 barter as the temperature increases from 37 to 125 degrees C. The CO2/He selectivity decreased from 8.7 to 3.1 over the same temperature range. (c) 2007 Elsevier B.V. All rights reserved.