The use of entrainers in modifying the solubility of phenanthrene and benzoic acid in supercritical carbon dioxide and ethane

Abstract

The solubilities of phenanthrene and benzoic acid were measured in supercritical carbon dioxide and ethane entrained with a small amount of benzene, acetone, methylene chloride or cyclohexane. Most of the experiments involved measuring the solubility of the solute as a function of entrainer composition, but some isocratic solubility data over a pressure range 100–300 bar was also obtained. It was found that the solubilities of both solutes increased with increasing amount of entrainer present in the supercritical gas, but that the specific entrainer used made little difference. Two elementary theoretical models of the entrained solvent were evaluated with the result that the data were better explained by considering the entrainer as a second solvent mixture rather than as a modifier of the supercritical fluid density. The solubilities of naphthalene and benzoic acid were also measured in a supercritical gas mixture containing 6.2 mol% ethane in carbon dioxide. In both cases the observed solubilities fell at an intermediate value between the known solubilities of the solutes in the pure supercritical solvents. Again, the addition of the second component to the gas appeared to behave as a chemical modifier of the solvent power of the fluid rather than only as a modifier of the solvent's P V T properties.