DISQUAC predictions on thermodynamic properties of ternary and higher multicomponent mixtures: I. Results for total pressure measurements at isothermal conditions of ternary systems

Abstract

The ability of DISQUAC to represent vapor-liquid equilibria, VLE, particularly pressures for sets of ( x 1, x 2) values at a given temperature, of ternary mixtures is investigated. Results are obtained using binary interaction parameters only, that is, ternary interactions are neglected. At this end, a set of 39 ternary systems and of 98 related binaries is analyzed. The ternary mixtures treated are of widely different classes. They may be formed by only hydrocarbons; by one or two polar, but not self-associated, compounds and hydrocarbons; or by one or two alcohols and organic solvents, such as hydrocarbons, CCl 4 or polar components. Deviations for ternary and binary systems are similar. The mean relative standard deviation in pressure is 0.020 for the former, and 0.017 for the latter. This means that good predictions on VLE of ternary mixtures can be obtained, taking into account binary interactions only. Moreover, DISQUAC results are practically independent of the system considered, and are valid over a wide range of temperature. Poorer predictions are obtained for those solutions with a binary showing a miscibility gap. It is also noteworthy that, in most of the cases, the interaction parameters needed are already available in the literature. Only for a few binary systems considered, the VLE data are correlated to obtain interchange coefficients which are later used to predict VLE of the related ternary. For the binary mixtures, DISQUAC predicts correctly: the coordinates of azeotropes and excess Gibbs energies, G E. A comparison between DISQUAC results and those obtained using different association models is also presented. DISQUAC and the UNIQUAC association theory yield similar predictions for ternary systems containing two alcohols and one n-alkane.