Thermodynamics of mixtures with strongly negative deviations from Raoult's law. Part 3. Application of the DISQUAC model to mixtures of triethylamine with alkanols. Comparison with Dortmund UNIFAC and ERAS results

Abstract

Binary mixtures of triethylamine (TEA) and alkanols have been investigated in the framework of DISQUAC. The systems are built by three contacts: aliphatic–hydroxyl, aliphatic–nitrogen, and hydroxyl–nitrogen. The corresponding interaction parameters are reported and discussed. The former are avalilable in the literature but were modified (particularly the third dispersive (DIS) and quasichemical (QUAC) interchange coefficients) for sec- and tert-alkanols + n-alkanes using recent data on excess heat capacities at constant pressure (CEP) for systems of these alkanols with n-heptane. The interaction parameters for aliphatic-nitrogen contacts are purely dispersive. The structure dependence of the DIS and QUAC interchange coefficients of the hydroxyl-nitrogen contacts in 1-alkanols + TEA systems is similar to that found in other solutions previously investigated. The QUAC interchange coefficients remain constant from ethanol and are also valid for 2-alkanols and tert-butanol. Methanol behaves differently. A short discussion in terms of effective dipole moments is also included. DISQUAC represents well the thermodynamic properties examined: vapor-liquid equilibria (VLE), molar excess Gibbs energies (GE) and molar excess enthalpies (HE). DISQUAC provides better results than the Dortmund version of UNIFAC using the published geometrical and interaction parameters. ERAS parameters for 1-alkanols + TEA systems are also reported. Interactions between unlike molecules are stronger for solutions with methanol or ethanol. DISQUAC improves ERAS results on HE, while both models give similar results for GE. However, ERAS needs an specific parameter, with unknown temperature-dependence, to describe properly GE. The main advantage of ERAS is its ability to provide information on VE. Its main limitation is that can be only applied to those systems where association is expected. DISQUAC, a purely physical model, can be applied to any type of binary mixture, as it is followed from this and previous studies.Key words: theory, liquids, associated, thermodynamics, group contributions.