Measuring and modelling the absorption and volumetric properties of CO2 and H2S in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate

Abstract

The absorption capacity of the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) for the single gases carbon dioxide and hydrogen sulfide was measured at temperatures from (298 to 353) K and pressures up to about 2.0 MPa. The corresponding molar volumes of CO2/H2S-saturated liquid phase were also measured in the above temperature and pressure ranges. At the same temperature and pressure, the solubility of hydrogen sulfide in [C2mim][BF4], expressed on the molality scale, is more than three times that of CO2. 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 for dissolution of the gases in that particular ionic liquid. The partial molar volume at infinite dilution for CO2/H2S + [C2mim][BF4] mixtures was estimated from the measured molar volumes. The new experimental data were correlated by using two models: (a) a model comprised of the extended Henry’s law and Pitzer’s virial expansion for the excess Gibbs energy, and (b) a generic Redlich-Kwong (GRK) type of cubic equation of state. Both models adequately good correlate the experimental data; however, the first model shows a slightly higher correlative accuracy than the second one. The selectivity of [C2mim][BF4] to separate CO2 and H2S is also discussed on the basis of correlation results.