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_vH, 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(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 δ_H(scCO₂,T,P) is a useful quantity to know. The large discrepancies between the reported quantities for δ_H(CO₂,T) are analyzed and discussed.