CO2 solubility in and physical properties for ionic liquid mixtures of 1-butyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide

The densities, viscosities, and electrical conductivities for ionic liquid mixtures composed of 1-butyl-3-methylimidazolium acetate, [BMIM][AcO] and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [BMIM][Tf2N] at different compositions have been measured over the temperature range (298-363) K. The solubilities of CO2 have also been determined in the [BMIM][AcO]-[BMIM][Tf2N] mixtures at atmospheric pressure and over the temperature range (283-333) K. The viscosity for the mixtures remarkably increases with increasing concentration of [BMIM][AcO] at a given temperature, whereas the conductivity strongly decreases. In Walden plots, the data points for the [BMIM][AcO]-[BMIM][Tf2N] mixtures lie between the two lines for the neat ILs. At fixed concentrations or temperatures, the Walden plots give straight lines. The excess quantities have been obtained for molar volume, viscosity and molar conductivity. The excess molar volume is positive and less dependent of temperature, whilst the excess viscosity and molar conductivity are all negative and very sensitive to temperature. The solubility of CO2 in the mixtures at atmospheric pressure was almost proportional to the concentration of [BMIM][AcO], indicating that the chemical absorption of CO2 takes place stoichiometrically in not only [BMIM][AcO] but also in the [BMIM][AcO]-[BMIM][Tf2N] mixtures. The decrease in viscosity and the increases in density and electrical conductivity observed for the CO2-saturated [BMIM][AcO]-[BMIM][Tf2N] mixtures were discussed in terms of the reaction mechanism.