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New experimental results are presented for the solubility of carbon dioxide in the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) for temperatures from (293 to 393) K and pressures up to about 9.7 MPa. Solubility pressures are correlated by means of the extended Henry's law.

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A model for the Gibbs excess energy of mixed-solvent (chemical-reacting) electrolyte systems is presented. The activities of solvent and solute species are calculated by applying a new extension of Pitzer's equation for the excess Gibbs energy of aqueous electrolyte solutions, which allows for solvent mixtures. The capability of the new model to simultaneously describe such properties as, e.g., the mean ionic activity coefficient and the solubility of a salt (for example, sodium chloride) in a binary solvent mixture (for example, methanol + water), as well as the influence of that salt on the vapor-liquid equilibrium of that binary solvent mixture, is tested. The new model gives an explanation for the "salting-out" and "salting-in" effects resulting, e.g., from the addition of a salt to a liquid mixture of volatile solvents. The new model can also be applied to describe the gas solubility in mixed solvents in the presence of electrolytes. The capability of the new model to describe the solubility of a single gas in a binary solvent mixture is tested by dealing with the solubility of carbon dioxide in aqueous solutions of methanol over the whole range of solvent composition, i.e., from pure water to pure methanol.

A high-pressure view-cell technique based on the synthetic method was used to determine the solubility of carbon dioxide in the ionic liquid 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][CH 3 SO 4 ]). The temperature ranged from 293.2 K to 413.1 K, the pressure and the carbon dioxide molality reached up to ∼10 MPa and ∼3.3 mol of CO 2 ‚(kg of [bmim][CH 3 SO 4 ]) -1 , respectively. The (extended) Henry's law was successfully applied to correlate the solubility pressures. The final results for the Henry's constant (at zero pressure) of carbon dioxide in [bmim][CH 3 SO 4 ] (on the molality scale) are correlated within the estimated uncertainty (( 1.3 %) by ln(k H,CO 2 (0) /MPa) ) 7.2738 -1775/(T/K) -0.002033(T/K). Furthermore, some small corrections were applied to the experimental results for the solubility of carbon dioxide in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) reported in previous work. The corrected values for the Henry's constant of carbon dioxide in [bmim][PF 6 ] only slightly and systematically deviate (by about -2 % at given temperature) from the values reported previously.