Automated generation of isoplethic phase diagrams for fluid binary systems from equations of state

Abstract

High pressure phase behavior of mixtures is of major importance in the analysis and development of applications of supercritical fluids, as well as in the study of reservoir fluids, among many diverse applications. Different classes of phase diagrams of fluid mixtures are useful to understand mixing/demixing processes, to explore conditions at which such processes occur and to study the influence of temperature and pressure on solubility values. This work presents and illustrates in detail an algorithm for the automated generation of complete fluid phase envelopes at specified composition, for binary mixtures. The algorithm is based on the location of singular points at the set system composition, before starting off the building of the phase envelope. Such singular points include vapor-liquid critical points, liquid-liquid critical points and liquid-liquid-vapor points. The algorithm also finds the segments of computed liquid-liquid-vapor lines that must be included in the phase diagram to more completely characterize the phase behavior at the set global composition. The models used in this work are of the equation of state (EoS) type. The variety for the observed qualitative behavior of computed isopleths is wide, giving place to a proposed classification of 18 different arrangements of isopleth points and segments, or cases, plus some sub-cases.