Solubility of H2S in 1-(2-hydroxyethyl)-3-methylimidazolium ionic liquids with different anions

The solubility of hydrogen sulfide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([HOemim]+)-based ionic liquids (ILs) containing different anions, viz. hexafluorophosphate ([PF6]−), trifluoromethanesulfonate ([OTf]−), and bis-(trifluoromethyl)sulfonylimide ([Tf2N]−) at temperatures ranging from 303.15 to 353.15 K and pressures of up to about 1.8 MPa was measured by a volumetric based static apparatus. The solubility data were correlated using two models: (1) the Krichevsky–Kasarnovsky equation and (2) the extended Henryʹs law combined with the Pitzerʹs virial expansion for the excess Gibbs energy. Henryʹs law constants (at zero pressure) in mole-fraction and molality scales were obtained at different temperatures by means of these two models. Using the solubility data, the partial molar thermodynamic functions of solution, i.e. Gibbs energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of H2S is greater than that of CO2 in the corresponding ILs studied in this work and that the solubility of both gases increases as the number of trifluoromethyl (–CF3) groups in the anion increases, i.e. the solubility behavior of both gases follows the order [HOemim][Tf2N] ≥ [HOemim][OTf] > [HOemim][PF6] > [HOemim][BF4].