Detailed Calculation of Complex Fluid Phase Equilibrium Sections for Ternary Systems

Abstract

Phase equilibrium diagrams of fluid phases in ternary systems can have a high complexity. In this work, a strategy and calculation methods for the computation of complete sections of ternary fluid phase equilibrium surfaces is proposed. To illustrate the methodology, we present computed results for the fluid phase equilibrium of an isothermal section for the ternary highly non-ideal system CO2+H2O+2-propanol(IPA), as described by a given model and given set of values of the model parameters. The calculation method is based on the prior identification of (univariant) key points (KPs) of the ternary isotherm. From such KPs, it is possible to build the different equilibrium lines that constitute the ternary isothermal diagram, with the help of a numerical continuation method. The results show a high level of complexity including a number of three-phase loci, critical loci, and ternary critical endpoints, together with a ternary four-phase equilibrium point.