(398r) Thermodynamic Modeling of the HCl–H?O Binary System Using the Association Electrolyte Non-Random Two Liquids Framework

Hydrochloric acid (HCl) is classified as a strong acid, and its aqueous solution serves as one of the most extensively utilized electrolytes across various industrial applications. It is widely employed in metal purification processes, the regeneration of ion exchange resins, and numerous environmental and geochemical systems. In parallel with experimental investigations, considerable efforts have been dedicated to the thermodynamic modeling of the HCl–H₂O binary system. These modeling approaches are generally categorized into two primary frameworks: equation-of-state (EOS)-based models and activity coefficient-based models.

In the present study, a thermodynamic model for the HCl–H₂O system is formulated within the framework of the Association Electrolyte Nonrandom Two-Liquid (AeNRTL) activity coefficient model. The model explicitly accounts for the partial dissociation of HCl into hydrogen (H⁺) and chloride (Cl⁻) ions, thereby capturing the true ionic speciation in solution. The model parameters—obtained via regression of comprehensive experimental thermodynamic data—include binary interaction parameters for both molecular and ionic species, as well as equilibrium constants associated with the dissociation reaction.

The developed model demonstrates high accuracy in predicting phase equilibria and other thermodynamic properties over the entire composition range, from pure water to pure HCl, and across a wide temperature range. AeNRTL Model predictions exhibit excellent concordance with available experimental data, affirming its reliability and robustness for describing the thermodynamic behavior of the HCl–H₂O binary system.