Phase equilibria in binary mixtures of propane and phenanthrene: Measurements and modeling
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abstract
Systems consisting of a volatile solvent composed of small molecules, such as propane, and a solute consisting of low volatile, complex molecules, such as poly-aromatic compounds, are known to show complex phase behavior. Multiphase fluid behavior may occur as well as the occurrence of a solid phase, which further increases the complexity of the phase diagrams. The present work focuses on binary mixtures consisting of propane + phenanthrene. This system shows type III phase behavior in the classification of Scott andVan Konynenburg. Various two-phase and three-phase equilibria were measured experimentally, including equilbria in the presence of solid phenanthrene. Based on the course of the various three-phase equilibriaan estimation could be made for the location of thequadruple point solid phenanthrene-liquid-liquid-vapor. A Group Contribution Equation of State (GC-EoS)developed by Skjold-Jrgensen was applied to reproduce the experimental datapoints. Phenanthrene was considered as a single groupfor which pure group parameters had to be determined by fitting phenanthrene vapor pressure data. Interaction parametersbetween phenanthrene and the CH 3 and CH 2groups in propane were fitted to propane-phenanthrenebubble point data. The GC-EoS was applied tocalculate vapor and liquid phase fugacities which wererequired in the phase equilibria calculations. The fugacity of pure solid phenanthrene was related to the fugacity of the pure subcooled liquid using changes in Gibbs free energy and a thermodynamic cycle which proceeds from the subcooled liquid to the solid state and passes through the triple point. Good agreement between experimental and calculated phase equilibrium data was obtained with the GC-EoS.
