Abstract

The mixing rules proposed by Kwak and Mansoori for the Peng-Robinson equation of state have been modified to describe vapor-liquid equilibrium in mixtures that contain supercritical CO2. Data in the literature for nine binary liquid-vapor systems containing supercritical CO2 are used for testing the modified models. The systems studied were binary mixtures containing carbon dioxide with lauric acid, palmitic acid, oleic acid, linoleic acid, 1-octanol, 1-decanol, 2-methyl-1-pentanol, ?-pinene, and limonene. The modifications studied included the introduction of a nonquadratic mixing rule proposed by one of the authors and a different interaction parameter for the volume constant of the equation of state. Compared to results in the literature, the Kwak-Mansoori combining rules and the proposed empirical modifications give lower deviations in correlating the solute concentration in the vapor phase, the most important variable for the design of supercritical extraction processes. Contrary to arguments found in the literature, it is also demonstrated that a severe test for an equation of state and its mixing rules is the correlation of the solute concentration in vapor-liquid mixtures. © 2004 American Institute of Chemical Engineers.