Application of a stochastic method to the solution of the phase stability problem: cubic equations of state

Abstract

Phase equilibrium calculations and phase stability analysis are of fundamental importance in various chemical engineering applications, such as azeotropic and three-phase distillation, supercritical extraction, petroleum and reservoir engineering, etc. Phase stability is often tested using the tangent plane criterion, and a practical implementation of this criterion is to minimise the tangent plane distance function (TPDF), defined as the vertical distance between the molar Gibbs energy surface and the tangent plane for given phase composition. In the present work, we use a modified TPDF and an equation of state as the thermodynamic model. We advocate a stochastic sampling and clustering method to locate the minima of the TPDF and compare its reliability with some of the most promising global optimisation methods. Our method is user-friendly and not computationally demanding regarding the number of function evaluations, and CPU time.