HP Labs Technical Reports

A Hydration Model of Aqueous Solutions of Inorganic Electrolytes at High Temperature and Pressure

Leibovitz, Jacques



Abstract: The classical model of electrolytic solutions fails to explain the correlations of Styrikhovich, of Martynova and of Marshall. An expanded version which includes the hydration processes inherent in solubilization and ionic dissociation processes was shown to be internally inconsistent. A new hydration model of aqueous solutions of inorganic electrolytes at high temperature and pressure, based on a novel interpretation of ionic dissociation at high temperature and pressure, is proposed. The model yields a unifying treatment of electrolytic solutions at high temperature and pressure valid over the whole range of electrolytes from the weakest to the strongest, in liquid and vapor phases as well as in cases where the solvent is diluted with an inert fluid.

The proposed model accounts for the correlations of Styrikhovich, of Martynova and of Marshall, and shows that these correlations are particular cases of the more general relations derived from that model by rigorous thermodynamic reasoning. The proposed model also predicts the gradual conversion of electrolytes in aqueous solutions into non-electrolytes as the water density is decreased, whether by dilution with an inert solvent or by pressure reduction (at supercritical conditions), consistent with observed trends. The power of the model for practical applications is demonstrated by working out an example of interest to the electrical power industry. The results predict an observed trend not understood before.

In principle, the model is not restricted to applications at infinite dilution. It is therefore of practical importance to determine the range of concentrations at which the model still applies.

This report has been superceded by HPL-94-51.

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