Density, Viscosity, and CO₂ Solubility in the Ionic Liquid Mixtures of [bmim][PF₆] and [bmim][TFSA] at 313.15 K

The density and viscosity of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]­[PF₆]), 1-butyl-3-methylimidazolium bis­(trifluoromethanesulfonyl)­amide ([bmim]­[TFSA]), and their mixtures were measured at 313.15 K and at atmospheric pressure. Furthermore, the CO₂ solubilities and the CO₂-saturated densities of [bmim]­[PF₆], [bmim]­[TFSA], and their mixtures were determined at 313.15 K and pressures up to 8.5 MPa using a volume-variable high-pressure apparatus. The ionic liquid mixtures were prepared at the mole fractions of [bmim]­[PF₆] of 0.25, 0.50, and 0.75. The CO₂ solubilities in both the mole fraction and molarity scales increased with the composition of [bmim]­[TFSA], and the pressure-mole fraction curves showed a typical behavior for the physical absorption. The CO₂-saturated density of the ionic liquid phase decreased with increasing the composition of [bmim]­[PF₆] and the pressure. Excess volumetric properties were calculated from the pressure–volume–mole fraction relations.