Extension of the COSMO-RS-PDHS model to the prediction of activity coefficients in concentrated {water-electrolyte} and {water-polyol} solutions

• COSMO-RS-PDHS allows to predict γi in {water-salt} or {water-polyol} solutions.
• It combines COSMO-RS, the Pitzer-Debye-Hückel model and a chemical solvation model.
• The variable hydration of the species is taken into account in this study.
• A new set of COSMO-radii is proposed in this study for un-parameterized elements.
• COSMO-RS-PDHS satisfactorily predicts activity coefficients and water activities.

Recently, we have introduced the COSMO-RS-PDHS model, i.e. a new tool to predict activities and activity coefficients of electrolytes in binary {water-electrolyte} systems. However, the fixed hydration assumption used in this early stage of the development of model, limits its range of validity (from 0 to 6 molal). The present study aims at overcoming this limitation through the development of a new chemical model that handles the successive hydration reactions of the chemical species. Using the COSMO-RS values of chemical potentials of hydrated species, the equilibrium constants of these successive hydration reactions are predicted. The resulting model accurately predicts water activities and activity coefficients of electrolytes in concentrated solutions (up to 20 molal). COSMO-RS-PDHS is finally used to predict water activities in several {water-polyol} systems. The predicted activity coefficients and water activity results are in very good agreement with experimental data, even by using the default COSMO-radii (if available like in {water-LiCl}, {water-NaCl} or {water-polyol} solutions), as well as by using our proposed set of COSMO-radii which enables to predict activity coefficients in the {water-KCl} mixture where the potassium is not yet included in the parameterized set of COSMO-radii in the current state of art of COSMO-RS.