Thermodynamic Equilibria Modeling of Ternary Systems of Solid Organics in Compressed Carbon Dioxide

Carbon dioxide as a compressed gas is a non-polar molecule, thus it is not a particularly good solvent for polar organic compounds. Therefore, a polar cosolvent is usually recommended for enhancing the solubility power of compressed gas for polar organic compounds. Moreover, accurate prediction of compressed gas behavior in mixtures is highly required, besides the experimental assessments of the influence of key operating parameters. Many authors have used equations of state combined with mixing rules to develop mathematical models for the determination of solubilities of systems composed of a solute, a solvent, and a cosolvent. In this work, the Stryjek and Vera modified Peng-Robinson equation of state (PRSV EoS) with the van der Waals mixing rules were used to formulate a mathematical model for the solubility of solids in supercritical fluids with cosolvents, i.e., in ternary systems. All three binary interaction parameters involved were determined for different ternary systems for which experimental data were available; these parameters were used to calculate the solubilities for those systems. Results obtained showed that the model fitted very well the experimental data for all the systems studied.