Correlation and prediction of solubility of low vapor pressure solids in supercritical fluids

Abstract

Binary solubility data of hydrocarbon solids in supercritical fluids were correlated using the compressed gas model. Data included in the analysis were for solubilities of binary mixtures of napthalene, 2,3- and 2,6-dimethylnapthalene, benzoic acid, phenanthrene, anthracene and pyrene in both ethylene and carbon dioxide, and of napthalene, phenanthrene and anthracene in ethane. Two equations of state--the Peng-Robinson equation and the Lee-Kesler equation with Plocker, Knapp and Prausnitz mixing rules--were tested in conjunction with the compressed gas model, permitting a direct comparison of the two equations of state. The sensitivity of the model to changes in the parameters was analyzed for each equation of state.

Prediction of the solubility data of five binary mixtures was attempted. The mixtures were hexamethyl benzene and fluorene in both ethylene and carbon dioxide, and diphenylamine in carbon dioxide. The binary attraction parameter (or"unlike pair energy parameter") of the Peng-Robinson equation was correlated with the heat of vaporization of the solid. The binary interaction parameter of Plocker, Knapp and Prausnitz (1978) mixing rules was correlated as they suggested for high-pressure vapor-liquid-equilibria. The most accurate predictions were obtained using the Lee-Kesler equation with Plocker, Knapp and Prausnitz mixing rules. Predictions of the solubilities of hexamethyl benzene and fluorene in carbon dioxide were accurate to within 30 percent error; results for hexamethyl benzene in ethylene were accurate to within 50 percent error; and results for fluorene in ethylene and diphenylamine in carbon dioxide were inaccurate.