Measurement and thermodynamic modeling of solid–liquid–gas equilibrium of some organic compounds in the presence of CO2

Solid–liquid–gas (SLG) phase equilibrium measurements have been performed in a view cell apparatus, using the “first melting point” method. SLG data are presented for five binary mixtures of CO2 with naphthalene, phenanthrene, benzoic acid, palmitic acid and stearic acid. The experimental data are correlated with the cubic Peng–Robinson EoS coupled with the conventional van der Waals one fluid mixing rules. Two different approaches for the calculation of the solid phase fugacity are examined. In the first the solid vapor pressure is used as the reference solid fugacity and in the second the so-called subcooled liquid reference state is used. The comparison of the two approaches indicates that the latter gives much better results than the former. Finally, the recently developed Universal-Mixing-Rule Peng–Robinson-Unifac (UMR-PRU) model is applied for the prediction of the SLG equilbrium curves of the CO2/naphthalene and CO2/phenanthrene systems, yielding satisfactory results, especially when coupled with the subcooled liquid reference state approach.