THE MHV2 MODEL - A UNIFAC-BASED EQUATION OF STATE MODEL FOR VAPOR LIQUID AND LIQUID LIQUID EQUILIBRIA OF MIXTURES WITH STRONG ELECTROLYTES

MHV2 is a group contribution equation of state based on the modified Huron-Vidal mixing rule. It combines the Soave-Redlich-Kwong (SRK) equation of state with a model for the excess Gibbs energy, the modified UNIFAC model. For the MHV2 model a new approach is presented which can be used for mixtures containing strong electrolytes. The salt is considered as a single component (solvated salt molecules) and not as dissociated into ionic species, whereby the number of parameters is significantly reduced. Only short-range interactions are taken into account, and the symmetric reference state is used for all species. Therefore, standard thermodynamic calculations can be performed by assuming the presence of salt in all the equilibrium phases. It is shown that, although MHV2 is based on the group contribution concept, it represents vapor-liquid equilibria (VLE) for mixed-solvent salt mixtures with an accuracy similar to that obtained with the molecular extended UNIQUAC model. Modified UNIFAC interaction parameters between solvent groups and the salts NaCl, KCl, CaCl2, CuCl2, NiCl2, HgCl2, SrCl2, NaBr, KBr, KNO3, CaNO3, Ba(NO3)2, Sr(NO3)2, NaF, NaI, and KI are given. The ability of MHV2 to predict liquid-liquid equilibria (LLE) for mixed-solvent salt mixtures is also discussed.