Effect of entrainers and of solute size and polarity in supercritical fluid solutions

Although supercritical extraction has been widely publicized as a novel separation technique of great versatility, it now appears that its applications will be in a number of specialized situations, each characterized by a rather specific set of requirements. To develop such applications, one requires a rather thorough understanding of the chemistry and physics of the supercritical fluid state at the molecular level. New experimental data are presented for the solubility of several solid solutes and solute mixtures in entrainer-doped supercritical fluid carbon dioxide. These results, along with others from the literature, are used to demonstrate the effects of solute size (appreciable) and solute polarity (small) in pure supercritical fluids. Solvent effects appear to be far more important than solute structure, and polar and hydrogen-bonding entrainers exhibit large effects on both solute loading and selectivity. Thus, it appears that entrainers can be used to tailor supercritical fluid solvents for specific applications.