The simultaneous correlation of liquid−liquid (LL), liquid−solid (LS), and LLS equilibrium data for four water + organic solvent (alcohol or acetone) + inorganic salt (NaCl) ternary systems at 25 °C has been carried out. First, the NRTL equation was used to formulate the excess Gibbs energy (G E), assuming nondissociation of the dissolved salt in the liquid phase. Afterward, a modification of the NRTL equation taking into account the ionic behavior of the solid (electrolyte-NRTL) was introduced into the simultaneous correlation of the equilibrium regions for the same systems. The binary parameters and the comparison of the experimental and calculated equilibrium data obtained with both the molecular and electrolyte models are presented in this work. The stability analysis based on the Gibbs energy function of mixing, together with the common tangent criteria have been used to validate the parameters calculated.

5Closed miscibility gaps in ternary liquid mixtures, at constant temperature and pressure, are obtained if phase separations occur only in the ternary region, whilst all binary mixtures involved in the system are completely miscible. This type of behaviour, although not very frequent, has been observed for a certain number of systems. Nevertheless, we have found no information about the applicability of the common activity coefficient models, as NRTL and UNIQUAC, for these types of ternary systems. Moreover, any of the island type systems published in the most common liquid-liquid equilibrium data collections, are correlated with any model. In this paper, the applicability of the NRTL equation to model the LLE of island type systems is assessed using topological concepts related to the Gibbs stability test. A first attempt to correlate experimental LLE data for two island type ternary systems is also presented.

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The condensed phase equilibrium behavior of water + organic solvent + salt systems, when different hydrates are formed in the solid phase, increases the number of equilibrium zones, substantially complicating the simultaneous correlation of the equilibrium data in all the existing regions. In this paper, a procedure to perform the correlation of this type of system is presented in great detail, using, as an example, the water + 1-butanol + LiCl ternary system, where the salt appears in two forms:  anhydrous and monohydrated (LiCl·H2O). To this end, the non-random two-liquid (NRTL) model for the excess Gibbs energy (G E) has been implemented, because the assumption of an electrolytic character for the solution in the liquid phase, despite being potentially more correct physically, does not give more flexibility to the G E function, as was discussed in a previous work. The common tangent plane criterion is used as an equilibrium condition to determine the equilibrium compositions in all the regions. The results obtained show the limitations of the NRTL equation to model this type of system, as a consequence of its lack of flexibility, in terms of the topological concepts that are related to the Gibbs energy of mixing (G M) function and the tangent plane criterion.

Equilibrium data for type 3 ternary systems comprising a liquid-liquid-liquid equilibrium region (LLLE tie-triangle) are not frequently correlated, as is evidenced by a lack of studies in the literature. In the present paper, a robust algorithm to calculate or correlate equilibrium data for this type of system is proposed. This algorithm is based on geometric aspects related to the Gibbs energy of mixing (g M ) and possesses some interesting advantages that are discussed in the text. The methodology put forward is applied to correlate the equilibrium data of three type 3 ternary systems. The NRTL model is used to define g M , and the common tangent plane criterion to define the equilibrium condition for the calculations. The lack in flexibility of the NRTL equation to model these systems is discussed.