Solid-Supercritical Fluid Equilibrium: Experimental and Theoretical Studies of Partial Molar Volumes and Solubilities

Abstract

Solvent-solute interactions present in a supercritical mixture were indirectly observed by measuring both the solubilities and partial molar volumes of relatively simple organic solids dissolved in the fluid phase between 12-70(DEGREES)C and 50-450 Bar. Results of solubility experiments for naphthalene dissolved in supercritical ethane and anthracene, phenanthrene and triphenylmethane in both ethane and carbon dioxide indicated strong and highly nonideal solvent-solute interactions. Observed solubilities were a factor of 10('3)-10('8) of that predicted using only the ideal gas law. The data were used to develop a simple, semi-empirical solid-super-critical fluid solubility correlation which requires only one correlated temperature independent pure component parameter for both the solute and solvent.

Partial molar volume experiments for naphthalene, tetrabromomethane and camphor dissolved at infinite dilution in supercritical ethylene and carbon dioxide are presented using a new experimental technique based on density measurements following constant temperature and pressure dilution. Large negative solute partial molar volumes (-1000 to -20,000 cc/mole) were always observed for compressible supercritical fluid mixtures which may indicate that the solvent clusters around the solute at infinite dilution. Solubility and partial molar volume data were used together to show that the original Redlich-Kwong, Soave and Peng-Robinson equations may need quite different interaction parameters to correlate solubility and partial molar volume data.