Solubility of carbon dioxide and ethane in three ionic liquids based on the bis{(trifluoromethyl)sulfonyl}imide anion

The objective of this work was to study the influence of changing the cation of the ionic liquid (IL) on gas solubility. For this purpose, the low-pressure solubility of carbon dioxide and of ethane in three ILs based on the bis{(trifluoromethyl)sulfonyl}imide anion ([NTf₂]^-) was determined experimentally. Solubility data is reported for 1-ethyl-3-methylimidazolium ([C₁C₂Im]⁺), 1-butyl-1-methylpyrrolidinium ([C₁C₄pyrr]⁺) and propylcholinium ([N_1132-OH]⁺) bis{(trifluoromethyl)sulfonyl}imide ILs between 300 and 345 K. These data are precise to within ±1% and accurate to within ±5%. In these ILs, carbon dioxide (mole fraction solubility between 1 and 3 × 10^-2, molarity between 0.03 and 0.1 mol L^-1) is one order of magnitude more soluble than ethane. The effect of changing the cation is small but significant. Changing the cation has a similar effect on both gases even if the differences are more pronounced in the case of ethane with the order of solubility [C₁C₄pyrr][NTf₂] > [C₁C₂Im][NTf₂] > [N_1132-OH][NTf₂]. For all the systems, the solubility decreases with temperature corresponding to exothermic processes of solvation and negative enthalpies and entropies of solvation were calculated. The properties of solvation of the two gases in [C₁C₄pyrr][NTf₂] do not vary significantly with temperature while important variations are depicted for both gases in [C₁C₂Im][NTf₂].