Extended UNIQUAC model for correlation and prediction of vapour–liquid–solid equilibria in aqueous salt systems containing non-electrolytes. Part A. Methanol–water–salt systems

Abstract

The Extended UNIQUAC model has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures. It is an electrolyte model formed by combining the original UNIQUAC model, the Debye–Hückel law and the Soave–Redlich–Kwong equation of state. In this work the model is extended to aqueous salt systems containing non-electrolytes in order to demonstrate its ability in representing solid–liquid–vapour (SLV) equilibrium and thermal property data for these strongly non-ideal systems. The model requires only pure component and binary temperature-dependent interaction parameters. The calculations are based on an extensive database consisting of salt solubility data in pure and mixed solvents, VLE data for solvent mixtures and mixed solvent–electrolyte systems and thermal properties for mixed solvent solutions. Application of the model to the methanol–water system in the presence of several ions (Na +, K +, NH 4 +, Cl −, NO 3 −, SO 4 2−, CO 3 2− and HCO 3 −) shows that the Extended UNIQUAC model is able to give an accurate description of VLE and SLE in ternary and quaternary mixtures, using the same set of binary interaction parameters. The capability of the model to predict accurately the phase behaviour of methanol–water–three salts systems is illustrated.