Solubility of CO2 and H2S in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

Abstract

The solubility of carbon dioxide and hydrogen sulfide gases in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C2mim][OTf]) was measured at temperatures from (303.15–353.15) K and pressures up to about 3.0 MPa. The Henry's law constants were determined from the new experimental data, which in turn were used to derive the change of some thermodynamic functions of dissolution of the gases in that particular ionic liquid. The new experimental data were correlated by a combination of the extended Henry's law and Pitzer's model for the excess Gibbs energy. The average relative percent deviation (ARD%) of correlated molality values from experimental data are within experimental uncertainties, which indicate quite good correlative accuracy of the Pitzer's model for the systems under investigation. Results show that at the same temperature and pressure, the solubility of H2S in [C2mim][OTf], expressed on the molality scale, is more than four times that of CO2. Comparison of the obtained experimental data indicates that the solubility of H2S, expressed on the molality scale, in [C2mim][OTf] is much more than its magnitude in the high-capacity ionic liquids 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([C2mim][eFAP]) and 1-ethyl-3-methylimidazolium bis(trifluoromethyl) sulfonylimide ([C2mim][Tf2N]). For example the molality of H2S at 303.15 K and 2.0 MPa is 2.5 times and 1.3 times that of [C2mim][eFAP] and [C2mim][Tf2N], respectively. Solubility of CO2 in the ionic liquids follows the order [C2mim][OTf] < [C2mim][Tf2N] < [C2mim][eFAP]. Compared with other ionic liquids, [C2mim][OTf] could potentially be used for separation of CO2 and H2S gases from each other.