Calculation of tri-critical points

Abstract

Procedures are presented for calculating higher order critical points in thermodynamic models. The procedures arise from an analysis of the Gibbs tangent plane criterion for phase stability. New methods are proposed for evaluating the functions that must be zero at critical points and the ease with which these functional evaluations can be carried out is the major element in permitting calculation of higher order critical points in mixtures of any number of components. Comparison is made between experimental data and tri-critical points for ternary mixtures as calculated with the Peng-Robinson and SRK equations.