(31c) Thermodynamic Properties of Simple and Multicomponent Electrolytes in Mixed Solvent System to Extreme Temperatures and Pressures

The thermodynamic properties of electrolyte solutions at high temperatures and pressures are of theoretical and significant economic importance in mineral, oil and other industries. Despite an increase in recent years of the experimental data available on the thermodynamic properties of aqueous electrolytes at high temperatures and pressures, the corresponding data for other solvents, especially mixed solvents at high temperatures are sparse. Prediction of mineral scaling and corrosion at conditions of high temperature, pressure, and concentration is essential for safe and successful operation of ultra-deepwater oil and gas production processes. For example, during production from a gas/oil well a large quantity of ethane 1, 2 diol (MEG) is used to prevent gas hydrate formation.  Due to environmental and economic concerns, MEG is often recovered via a thermal vacuum distillation process. This hydrate inhibitor adversely enhances scale formation, however, the impact of temperature and concentration on mineral scale formation during inhibitor regeneration is largely unknown.  The solubility data in aqueous/MEG mixed solvent systems are needed to evaluate the impact of high temperature on mineral scale formation in hydrate inhibitor/brine solutions.  Also, from a theoretical standpoint, the infinite miscibility of a cosolvent such as MEG with water provides an opportunity to study the transfer properties of an electrolyte between two solvents over the entire composition range. Although the semiempirical models developed in aqueous solutions can in principle be extended to include mixed solvents, this extension is not possible (especially at higher temperatures) due to the scarcity of the experimental data necessary for estimation of the characteristic model parameters. In the literature, there are some semiempirical models for mixed solvents near 298.15 K; however, the extensions of these models to higher temperatures, again, are limited by the lack of availability of the required input data. Because of these limitations, a new approach is needed that requires as input a very limited set of data that are either available or can be obtained/estimated with the least amount of effort. Here we present a model for predicting the thermodynamic properties of simple and multicomponent electrolytes in mixed solvent systems to extreme temperatures and pressures from data at 298.15 K together with available auxiliary literature data.