Saturation Point and Phase Envelope Calculation for Reactive Systems Based on the RAND Formulation

Abstract The equilibrium calculation of a reactive mixture under the phase-fraction specification, including saturation point calculation and phase envelope calculation, is desirable for the relevant process analysis and simulation. We developed the saturation RAND formulation and the corresponding algorithms for these phase-fraction specification problems. Two types of phase fraction were distinguished: the component-based one and the element-based one, which led to different constraint equations in the formulation. We further introduced element-based partition coefficients to cross the critical point of a reactive mixture in the phase envelope construction. In addition, the general formulation for reactive mixtures can be reduced and used for calculating simpler non-reactive mixtures. We illustrated the robustness and efficiency of our algorithms using four examples: Pxy diagrams for CO2-NaCl brine, a solid–liquid Tx diagram for MgCl2-water, a PT phase envelope for a reactive mixture with the alkene hydration reaction, and a PT phase envelope for a non-reactive hydrocarbon mixture.