ANALYSIS OF EXCESS FREE-ENERGY BASED EQUATIONS OF STATE MODELS

A comparison is made of the capabilities of various equation of state (EOS) + excess free energy (G(ex)) models in representing the activity -coefficient models they incorporate. Such EOS models need to reproduc e the excess Gibbs free energy behavior of the activity-coefficient mo dels as closely as possible in order to represent low-pressure vapor-l iquid equilibrium behavior of complex mixtures accurately, and also to make accurate the vapor-liquid predictions at higher temperatures and pressures using only low-pressure information. It is demonstrated tha t the EOS models that use the excess Helmholtz free energy instead of the excess Gibbs free energy, and that combine the EOS with activity-c oefficient models at the infinite pressure limit, are successful for c alculations of the type just described.