A COMPARISON OF THERMODYNAMIC MODELS FOR VLE DATA IN ELECTROLYTE SYSTEMS

Multiple-solvent electrolyte systems are important in the distillation of binary and multicomponent mixtures in the presence of one or more electrolytes. The phase equilibria is normally at constant pressure and the temperature covers the bubble-point temperature range of the mixture. Results for single-solvent, single-electrolyte systems are often at 298 K, which is considerably lower than the usual bubble-point temperatures in distillation. W. Mock et al. (1986) present phase equilibria for mixed-solvent electrolyte systems based on the NRTL method and identified as the NRTLE method. The model takes into account solvent-solvent, ion-solvent, and ion-ion interactions. The two basic assumptions are that the local composition of cations around a central cation is zero, and that the distribution of cations and anions around a central molecule leaves the net local ionic charge as zero. It was found that the contribution due to the extended Debye-Huckel term was small and could be eliminated.