The gas sweetening process requires an efficient solvent with strong absorption capability to capture acid gases from flue gas. Absorption can be strong by a chemical formation (as "chemical" absorption) or simple with no chemical reactions (as "physical" absorption). The purpose of the present study was to compare the CO2 solubility of the chemically absorbing ionic liquid, 1-butyl-3-methylimidazohum acetate ([Bmim][Ac]), with the physically absorbing ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), as a function of temperature at (298.15 to 318.15) K for pressure up to 50 bar. In addition, the CO2 solubility for binary mixtures containing 75% [Bmim][Ac] + 25% [Bmim][BF4], 50% [Bmim][Ac] + 50% [Bmim][BF4] and 25% [Bmim][Ac] + 75% [Bmim][BF4] are measured over the same temperature range. Henry's law constants are reported for the solubility of CO2 in the studied pure and mixed ionic liquids. Furthermore, the density of mixed ionic liquids is experimentally measured in T = 298.15 K, 308.15 K, and 318.15 K. Finally, the partial molar thermodynamic functions of solvation containing Gibbs free energy, enthalpy, and entropy are evaluated based on the variation of Henry's law constants (as a representative of solubility) with temperature.