Thermodynamics of mixtures of nonspherical molecules. III. Fluid phase equilibria and critical loci

Abstract

The influence of strong dipolar and quadrupolar forces on the fluid phase diagram of binary mixtures is investigated, using the Padé approximant to the free energy proposed by Stell, Rasaiah, and Narang for pure fluids. This approximant is known to give good results for such model fluids in the liquid phase, and is shown here to give quite good results for gases also. Using a Lennard‐Jones mixture as the reference system, a study is made of the effect of dipolar and quadrupolar forces on (a) the vapor–liquid equilibrium surfaces, (b) the vapor–liquid critical loci, (c) the azeotropic lines, (d) the liquid–liquid equilibrium curves, and (e) the liquid–liquid critical loci. The model systems exhibit almost all of the major classes of binary fluid phase diagrams that have been observed experimentally.