Two-phase constant phase fraction lines in binary isopleths: Computation method utilizing liquid-liquid-vapor information and resulting analysis

Abstract

In this work, a criterion is proposed, for binary systems, for detecting the segments, of already calculated liquid-liquid-vapor (LLV) equilibrium lines, which should be part of the heterogeneous region of a yet to be computed isopleth of set global composition z. This criterion is based on a system of equations corresponding to mass conservation constraints. Through the application of this criterion, it is also possible to automatically detect the LLV points that will be located on the phase envelope of the isopleth, i.e., the double saturation points. On the other hand, at specified z and specified phase mole fraction Φx of a given “x” phase, a two-phase line of constant Φx becomes defined. Such line will be made of one or more segments. Each segment has one or more origin/termination points (endpoints). The present criterion also identifies, of such endpoints, those of the LLV type. The detected endpoints are used by an algorithm, proposed also in this work, for computing two-phase constant phase mole fraction lines or segments for binary systems. The proposed methodology is here illustrated for the CO2 (1) + n-tetradecane (2) binary system. The obtained results suggest the existence of complex phase behavior patterns in the heterogeneous regions of the isopleths, depending on the set global composition. The presence of critical points significantly contributes to the mentioned complexity.