(380e) Phase Equilibria In Binary Mixtures of Propane and Phenanthrene: Measurements and Modeling

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 and
Van Konynenburg¹. 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 equilibria
an estimation could be made for the location of the
quadruple point solid phenanthrene-liquid-liquid-vapor.

A
Group Contribution Equation of State (GC-EoS)
developed by Skjold-Jørgensen^2,3 was applied to reproduce the experimental data
points. Phenanthrene was considered as a single group
for which pure group parameters had to be determined by fitting phenanthrene vapor pressure data. Interaction parameters
between phenanthrene and the CH₃ and CH₂
groups in propane were fitted to propane-phenanthrene
bubble point data. The GC-EoS was applied to
calculate vapor and liquid phase fugacities which were
required 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.  

References

[1]  P.N. Van Konynenburg, R.L.
Scott, Philosophical Transactions of the Royal Society, (1980), 298, 495-540.

[2]  S. Skjold-Jørgensen, Fluid Phase Equilibria,
(1984), 16, 317-351.

[3]  S. Skjold-Jørgensen, Industrial and Engineering Chemistry
Research, (1988), 27, 110-118.