Thermodynamics of mixtures containing a very strongly polar compound. 11. 1-Alkanol+alkanenitrile systems

Abstract

1-Alkanol + alkanenitrile systems have been studied by means of the DISQUAC, ERAS and UNIFAC (Dortmund) models. DISQUAC and ERAS parameters for the alkanol/nitrile interactions are reported. DISQUAC describes a whole set of thermodynamic properties: phase equilibria, vapour-liquid (VLE), liquid-liquid (LLE) and solid-liquid (SLE) equilibria, molar excess functions, Gibbs energies,G_m^E, and enthalpies, H_m^E, and partial excess molar enthalpies at infinite dilution, H_mi^(E,∞) using the same set of interaction parameters for each solution. The dependence on the molecular structure of the interaction parameters is similar to that observed in other previous applications to mixtures formed by 1-alkanols and a strongly polar compound, in such way that the quasichemical interchange coefficients can be kept constant from 1-propanol. However, methanol and ethanol solutions behave differently. From the analysis of experimental data for H_m^E, TS_m^E (=H_m^E-G_m^E), and molar excess volumes, V_m^E, it is concluded that the studied systems are characterized by dipolar interactions and strong structural effects. The former are more relevant in acetonitrile solutions. Association effects are more important in butanenitrile mixtures. DISQUAC improvesH_m^Eresults from the ERAS model. ERAS results onH_m^E for systems containing acetonitrile are also improved by UNIFAC. This remarks the importance of dipolar interactions in the investigated mixtures. ERAS describes the variation of V_m^E(x_1=0.5) with the 1-alkanol size for mixtures with a given nitrile, but the concentration dependence of this excess function is poorly represented.