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, δ H , may be used to predict its dissolution in liquids. The usual definition of δ H involves Δ v H , 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 δ H (CO 2 , T ). The appreciable polarizability of CO 2 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 δ H (scCO 2 , T , P ) is a useful quantity to know. The large discrepancies between the reported quantities for δ H (CO 2 , T ) are analyzed and discussed.