Gas-solid equilibrium in mixtures containing supercritical CO2 using a modified regular solution model

A model that includes an equation of state and an excess Gibbs free energy model is proposed and applied to the correlation of phase equilibria in gas + solid systems containing supercritical carbon dioxide. A modified "regular solution" model for the excess Gibbs free energy that considers nonpolar, polar, and hydrogen-bonding contributions and a generalized three constant equation of state is proposed. The mixing rule derived for the model includes a concentration-dependent interaction parameter and an interaction parameter into one of the volume constants of the equation of state. Literature data for nine binary gas + solid systems containing supercritical carbon dioxide are used for testing the proposed model. The systems studied were binary mixtures containing carbon dioxide as solvent with 2,3-dimethylnaphthalene, 2,6-dimethylnaphthalene, caffeine, cholesterol, anthracene, naphthalene, phenanthrene, pyrene, and benzoic acid. The proposed model correlates the solute concentration in the gas phase better than several other models presented in the literature that use the same number of interaction parameters.