Calculation of vapour-liquid equilibria in mixed solvent/salt systems using an extended UNIQUAC equation

Abstract

A new method for the correlation and prediction of salt effects on VLE is proposed. The model combines a term of the Debye-Hückel type with a modified UNIQUAC equation with concentration-dependent parameters. The model parameters are ion-specific, and no ternary parameters are required. Application of the model to alcohol-water/salt mixtures has shown that the change in vapour phase composition on addition of salt to the liquid phase can be represented with good accuracy. Fifty-four ternary data sets were correlated with a total mean of the absolute deviation in the vapour phase mole fraction of 0.012. Deviations in calculated pressures or temperatures may, however, be rather high, especially at high salt concentrations. The maximum salt concentration for the included data points in the database is 10 mol/kg for 1:1 salts and 6.5 mol/kg for 2:1 salts.