Gas separations using non-hexafluorophosphate [PF6]− anion supported ionic liquid membranes

Previously, we reported on using Room temperature ionic liquids (RTILs) in place of traditional solvents for supported liquid membranes to take advantage of their unique properties. This previous work used RTILs with the hexafluorophosphate [PF6]− anion. However, the [PF6]− anion in the presence of water can break down into HF. In the current work, we studied RTIL-membranes made from the following water stable anions: bis(trifluoromethanesulfonyl)amide [Tf2N]−, trifluoromethanesulfone [CF3SO3]−, chloride [Cl]−, and dicyanamide [dca]−. We report CO2 permeabilities of 350 barrers (for [Cl]−) to 1000 barrers (for [Tf2N]−) combined with CO2/N2 ideal selectivities of 15 (for [Cl]−) to 61 (for [dca]−). Note that these permeability/selectivities place RTIL-membranes above the upper-bound in a CO2/N2 Robeson plot of representative polymers. The CO2/CH4 ideal selectivities range from 4 (for [Cl]−) to 20 (for [dca]−), thereby placing the [dca]-membrane above the upper-bound for the CO2/CH4 Robeson plot.