COMBINED EXCESS FREE-ENERGY MODELS AND EQUATIONS OF STATE

An approach is presented for introducing excess free energy models into mixing rules for cubic equations of state where the "standard state" for the mixing process is zero pressure. The formalism permits insertion into the mixing rules parameters in excess free energy models that were obtained from correlating low pressure data using separate liquid phase and vapor phase models without any loss in the character off the correlation. The resulting equation of state model can contain the vapor pressure, vapor phase non-idealities and liquid phase information otherwise contained in separate models. A proposal is made for extrapolation to include possibly near-critical and super-critical components. Examples of three-phase and azeotropic systems are discussed. © 1990.