Prediction of vapor-liquid equilibria of binary-solvent electrolytes

An iterative method is presented that is used to predict vapor-liquid equilibria (VLE) of single-salt multisolvent electrolytes of the form solvent-cosolvent-salt. A local composition model (LCM) and an electrolyte model based on the exponential modification of the Mean Spherical Approximation (EXP-MSA) are combined with traditional phase equilibria relations to estimate the pressures and compositions of a vapor phase in equilibrium with a binary-solvent electrolyte. In addition, a pseudo-solvent model is used to obtain a variety of averaged liquid phase electrolyte properties. For our initial model system, methanol-water-LiCl, the above method accurately predicts the salt effects upon vapor composition for dilute to moderate salt concentrations up to 20 mol% LiCl, and yields good approximations of vapor pressure depression for LiCl up to 14 mol%. Three electrolyte systems are investigated: water-ethylene glycol-LiBr, ammonia-water-LiBr, and methanol-water-LiCl.