THERMODYNAMICS OF ELECTROLYTE SOLUTIONS: THE ISOACTIVE SOLUTION THEORY (OSMOTIC COEFFICIENTS, ACTIVITY, MIXED-SOLVENT)

Aqueous and non-aqueous multi-component electrolyte solutions are present in many industrial chemical processes. Prediction of the operating characteristics of such processes requires calculation of the equilibrium thermodynamic properties of the electrolyte components, based on experimental data and supplemented by theories and correlations. These methods must be widely applicable in order to handle the wide ranges of operating conditions which are demanded by most processes. Present models are specific; as a result, the focus is mainly on electrolytes in a particular solvent medium. In the most cases the medium is water. In this thesis, a new model, the isoactive (ISAC) solution theory is proposed, developed and implemented. Ternary or higher order phase equilibria are estimated in terms of thermodynamic properties of the constituent binaries. The procedure is based upon the idea of utilizing binary solutions, rather than pure components or hypothetical solutions, as the standard state. Furthermore, the ternary and constituent binaries are at constant solvent chemical potential. Binary information on non-idealities, such as size and orientation effects, solute-solute and solute-solvent interactions, is incorporated to the model, a priori. Thus, only ternary and higher order effects on activity coefficients are neglected. Such choice of reference state eliminates the requirement that all components be liquids in the pure state at the temperature and pressure of the mixture. Consequently, the isoactive solution theory applies equally well to solutions of strong aqueous electrolytes, vapor-liquid equilibria (VLE) of mixed-solvent electrolytes and VLE of non-electrolyte solutions. Predictions and comparison of the ISAC model with existing models in each category demonstrate that the proposed approach is broad, accurate and comparable to the best of them