Symmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model

The electrolyte nonrandom two-liquid (eNRTL) model is reformulated as a symmetric activity coefficient model with the reference states chosen to be pure liquids for solvents and pure fused salts for electrolytes. These reference states are consistently used in the local interaction term, represented by a reformulated NRTL expression, and the long-range interaction term, represented by an extended symmetric Pitzer−Debye−Hückel expression. Retaining the local electroneutrality and like-ion repulsion hypotheses, the new symmetric electrolyte NRTL model yields simpler activity coefficient expressions for both molecular and ionic species. The utility of the model is demonstrated with vapor−liquid equilibrium, liquid−liquid equilibrium, and solid−liquid equilibria of several mixed solvent electrolyte systems.