Thermodynamic Modelling of Electrolyte Solutions

Electrolyte solutions are encountered in many industrial applications. In the oil and gas industry, electrolytes are present in acid gas capture processes (CO ₂ , H ₂ S) by chemical absorption or in hydrocarbon systems in the presence of brine. Electrolyte solutions are also present in water treatment units and desalination processes, in hydrometallurgy and in fertilizer production. Electrolytes play a key role in corrosion problems, and are used in energy production and storage systems such as batteries, supercapacitors, electrolyzers and fuel cells, hydrogen storage in salt cavities, as well as in refrigeration and humidity control systems.

Knowledge of the thermochemical properties of electrolytes is essential for plant sizing: for example, the sizing of absorption and desorption columns in the carbon dioxide capture process is directly linked to the chemical equilibria and thermodynamic properties of solutions containing ionic species. The solubility of the gas in an aqueous solution, as well as the water content in the vapour phase, are also linked to the salt content of this solution. Salt solubility and crystallization rates are also directly related to the activity coefficients of the ions in solution, and crystallizer sizing requires in-depth knowledge of these properties. The aim of this article is to define the thermodynamic properties commonly used for electrolyte solutions, and to present the main models available for calculating properties over a wide temperature and salt concentration range. We also present a few examples of industrial applications.