Unifac prediction of vapor—liquid equilibria in mixed solvent—salt systems

Abstract

The Sander model for correlation and prediction of salt effects on vapor—liquid equilibria (VLE) of mixed solvents combines a term of the Debye—Hückel type with a modified UNIQUAC equation with concentration dependent parameters. In this work the UNIQUAC equation has been substituted by the original UNIFAC group-contribution model with concentration independent group interaction para-meters. Group interaction parameters have been estimated between ions (Li +, Na +, K +, Ca 2+, Ba 2+, Sr 2+, Cu 2+, Ni 2+, Hg 2+, F −, Cl −, Br −, J −, NO 3 − and CH 3COO −), and solvent groups (CH 2, OH, CH 3OH, H 2O, CH 3CO), while previously published group interaction parameters between solvent groups have been maintained. It is shwon that the proposed model represents VLE for solvent—water—salt mixtures with an expected average accuracy of the total pressure around 9% and of the vapor-phase mole fractions around 4%. Since it is a predictive group-contribution method it has a much broader range of applicability than the Sander model.