VAPOR-LIQUID-EQUILIBRIUM OF PURE FLUIDS FROM A SIMPLE THERMODYNAMIC PERTURBATION-THEORY

We derive a perturbation theory for linear and nonlinear molecules int eracting through the Kihara potential. This theory may be considered a s a simplified version of more elaborated treatments previously propos ed for this model. An advantage of the new formulation is that express ions for Helmholtz free energy, pressure, and entropy are analytical s o that vapor-liquid determination becomes an easy task. Vapor-liquid e quilibria obtained from the theory showed fair agreement with simulati on results of the model. Moreover, we compared theoretical predictions of coexistence densities and vapor pressures with experimental result s for ethane, carbon dioxide, and benzene. Good agreement was found in al the cases over a broad range of temperatures. The presented treatm ent combines the simplicity required in chemical engineering applicati ons with well-defined approximations on a statistical thermodynamic tr eatment.