Equation of state for solutions of electrolytes in mixed solvents

Abstract

Based on molecular theory, an equation of state (EOS) is derived for a mixture containing electrolytes in a mixed solvent. Calculations are performed for the ternary system watermethanollithium bromide. The equation of state follows from an expression for the Helmholtz energy; parameters are fitted to vapor-pressure, density, and osmotic-coefficient data between −10 and 120 °C from infinite dilution to 15 mol% salt. For the binary systems, deviations in vapor pressure are ∼ 2–4%. When applied to the ternary system, using only binary parameters, the EOS predicts vapor pressures with a mean deviation of 6% and vapor compositions with a mean deviation of < 1.5 mol%. The EOS presented here may be useful for calculating vaporliquid equilibria for electrolyte systems at high pressures.