Comparison of Gamma G excess mixing rules for multi-phase equilibria in some ternary systems

The excess Gibbs free energy mixing rules for cubic equations of state proposed by Heidemann and Kokal, Dahl and Michelsen and Wong and Sandler are compared. The equations of state such as the Peng-Robinson or SRK equations contain the pure component behavior and vapor non-ideality. The G excess mixing rules, therefore, should principally modify the properties of the mixed dense phases (i.e., the liquids) so as to match the G excess model being incorporated. The basis for the comparisons in this paper is the relative success of the mixing rules in reproducing the phase behavior in some ternary systems that is given by the G excess models (not necessarily the original data since the G excess models available in the DECHEMA compilation are not always effective in correlating the data). The particular systems examined all show two or more liquid phases, perhaps in equilibrium with a vapor, since liquid phase behavior is the focus.