A Combined Experimental and PC-SAFT Modeling Investigation on the High-Pressure Density of Ionic Liquids with CO ₂

In this study, the density of four binary mixtures of ionic liquids (ILs) with carbon dioxide (CO2) was measured at high pressure by using a vibrating-tube densimeter. The ionic liquids triethylsulfonium bis(trifluoromethylsulfonyl) imide [S222][(CF3SO2)2N], 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide [C3C1C1Im][(CF3SO2)2N], 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl) imide [C3C1pyr][(CF3SO2)2N], and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide [C4C1C1Im][(CF3SO2)2N] were selected because of their different cations and the common anion. Measurements were performed at a pressure range of P = (10.0 to 70.0) MPa, temperatures from 303.15 to 313.15 K, and CO2 mole fractions from 0.2 to 0.7. From these results, the excess molar volume was calculated and presented negative values under almost all composition range, indicating a volume contraction behavior, despite the small values. Finally, the experimental density results were used to estimate the parameters of a Tammann–Tait-type equation and PC-SAFT equation of state. In addition, the regressed parameters were used to obtain the isothermal compressibility kT.