Properties of the liquid-liquid coexistence curves with several critical points

Abstract

The thermodynamic analysis of the coexistence curves with any number of critical points in binary mixtures at constant pressure was carried out in the framework of the regular-mixing theory. We proposed a universal temperature dependence of the general energy interaction parameter both for one and for several critical points. An evolution of multicritical point coexistence curves was analyzed and a unified consideration of the boundaries of liquid-liquid and vapor-liquid equilibria was fulfilled. As a result, new properties of the multicritical point coexistence curves were derived and new phase transitions were theoretically predicted. The relationships between conjugate phase separation temperatures were applied to calculate a pressure dependence of mutual solubility of the 2-butanol/water mixtures as a system with three critical points. Moreover, the generalized reduced temperature for the systems with several critical points was introduced to compare scaling and regular-mixing approaches to the quantitative description of the published experimental data on coexistence curves with two critical points.