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 [PF ₆]^- 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.