Predicting LLE in mixed-solvent electrolyte systems by an electrolyte EOS

International audience; This work extends the previously published aqueous electrolyte equation of state (AEEOS) to predict liquid-liquid equilibria (LLE) of mixed-solvent electrolyte systems. Interaction parameters between ions and organic solvents, and cations and anions were determined by fitting the experimental vapor-pressure data of binary methanol + halide electrolyte mixtures, and then correlated to the cationic Stokes and anionic Pauling diameters. The focus is on the ionic standard/reference state and the standard Gibbs energy for transferring salts from one solvent to another. The methods applied to predict LLE of several ternary water + organic solvent + salt system are to select: 1. the hypothetical ideal gas at unit mol fraction, the system temperature, and 1 bar as the ionic standard state; 2. the infinite dilution in the solvent mixture as the ionic reference state, whose activity coefficients were converted to those at the infinite dilution in pure water by the ionic standard Gibbs energy of transfer. The predicted LLE results agree well with the measured data without any adjusted parameters in fitting the ternary experimental data. The extended AEEOS is comparable to the model of Zerres and Prausnitz, but the latter requires two adjusted parameters in fitting the ternary experimental data for each ternary system.