Development of a thermodynamic model of aqueous solution suited for foods and biological media. Part A: Prediction of activity coefficients in aqueous mixtures containing electrolytes

In food and biological processes, aqueous complexes cover a wide diversity of species and the presence of several phases. The modelling of such processes must take into account these specificities, which require a generalization of the existing thermodynamic models of aqueous solutions. The chemical potential (the molar Gibbs free energy) of a given compound is an important variable to characterize the physical-chemical properties at equilibrium. Its value depends on two parameters: the Gibbs free energy of formation and the activity coefficient. Both are linked to a chosen reference state. Then, the main thermodynamic modelling task consists in the prediction and/or the collection of formation properties data and in the development of a predictive model of activity coefficients. This work introduces a new prediction tool of activity coefficients of electrolytes in {water-salt} systems. This tool is based on an extension of the COSMO-RS method towards the representation of the thermodynamic equilibrium properties of charged species. For this purpose, the long-range interactions between ions are taken in account by a Pitzer-Debye-Huckel term. The resulting model called “COSMO-RS-PDHS” is then fully predictive.