Supercritical fluid extraction of solids.: Statistical thermodynamic approach

To study the effect of non-sphericity of solvent and solute molecules on the main characteristics of supercritical fluid extraction we consider the fourth-order virial expansion in which the individual virial coefficients (and cross terms) were determined from the formula proposed recently for the Kihara generalized pair potential. The Kihara four-step square-well potential was assumed; its form makes it possible to write analytic expressions for the considered virial coefficients and, consequently, for the main thermodynamic functions-the residual chemical potential of solute and total pressure. The method is applied to determine the dependence of the mole fraction of solute on temperature or pressure in the binary systems carbon dioxide-naphthalene and ethylene-naphthalene and the effect of the cosolvent on the solute concentration in the system ethylene-naphthalene-acetone at 308 K. Fair agreement with the simulation and experimental data was found.