A thermodynamic correlation of gas solubilities

Low-pressure solubility data have been correlated for eleven gases in nine solvents over a wide temperature range by considering the dissolution process in two steps. First the gas is condensed isothermally to a hypothetical liquid at 1 atm. pressure, and then this hypothetical liquid is dissolved in the solvent. The free energy of the first step depends only on the properties of the solute, which in the case of nonpolar gases can be adequately described by the theorem of corresponding states. The second step depends on the properties of both solute and solvent and, in the case of nonpolar systems, can be described by the theory of regular solutions. The correlation depends on three solute parameters: the solubility parameter, the molar volume, and the fugacity of the hypothetical liquid; the last of these has been plotted as a generalized function for the reduced temperature range of 0.7 to 3.2. A separate plot is given for hydrogen. These parameters may be used to make good estimates of low-pressure gas solubilities (or K values) in nonpolar solvents over a wide range of temperature. A semiempirical method for correlating the solubilities of gases in polar solvents is also described and illustrated for several cases. Since the correlation presented in this paper covers a wide temperature range, it is possible to make estimates of the heats of solution of gases in liquids. These may be useful in enthalpyblance calculations as required in certain phase-separation operations.