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

The Extended UNIQUAC model has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures. It is an electrolyte model f ormed by combining the original UNIQUAC model, the Debye-Huckel 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 ther mal 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 so lubility 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 pr esence of several ions (Na+, K+, NH4+, Cl-, NO3-, SO42-, CO2- and HCO3-) sh ows that the Extended UNIQUAC model is able to give an accurate description of VLE and SLE in ternary add quaternary mixtures, using the name set of b inary interaction parameters. The capability of the model to predict accura tely the phase behaviour of methanol-water-three salts systems is illustrat ed. (C) 2000 Elsevier Science Ltd. All rights reserved.