Solubility Parameter of Carbon Dioxide—An Enigma

The solubility of gaseous carbon dioxide in a variety of solvents has been extensively studied, the solute interacting with most solvents via dispersion forces. Hence, its Hildebrand solubility parameter, δH, may be used to predict its dissolution in liquids. The usual definition of δH involves ΔvH, the molar enthalpy of vaporization, strictly applicable to liquids. This expression is inapplicable for carbon dioxide, being a gas at the temperatures of technical interest (298 ≤ T/K ≤ 333), and various indirect methods have been employed for the determination of δH(CO2,T). The appreciable polarizability of CO2 and its ability to accept hydrogen bonds from suitable donor solvents prompted the determination of its Hansen solubility parameters. Finally, supercritical carbon dioxide has been extensively used as a solvent so that its δH(scCO2,T,P) is a useful quantity to know. The large discrepancies between the reported quantities for δH(CO2,T) are analyzed and discussed.