Thermodynamics of mixtures with strongly negative deviation from Raoult's law Part 1Application of the DISQUAC model to mixtures of alkan-1-ols and propanal or linear alkanones and trichloromethane

Abstract

Thermodynamic properties: vapour–liquid equilibria (VLE), molar excess Gibbs energies, G^E, molar excess enthalpies, H^E, or the mole fraction structure factors, S_cc(0), of systems containing alkan-1-ols and propanal, or linear alkanones and CHCl₃, i.e. strongly associated mixtures which show compound formation, are studied in the framework of the DISQUAC (dispersive quasichemical) model. Interaction parameters for the contacts OH–CO (in propanal) and Cl (in CHCl₃)–CO (in alkanones) are reported. For alkan-1-ol–propanal systems, DISQUAC gives better results for VLE than other models previously applied, such as lattice fluid(LF), lattice fluid associated solution (LFAS), extended real associated solution (ERAS), or the universal quasichemical (UNIQUAC) association theory. For H^E, only the latter improves results meaningfully but DISQUAC gives good agreement for S_cc(0). It is shown that heterocoordination is an esssential characteristic of this class of systems. For linear alkanones with CHCl₃, DISQUAC consistently describes G^E and H^E. Only the symmetry of the G^E curve of the propan-2-one–CHCl₃ mixtures is not entirely satisfactory. The calculated S_cc(0) also shows that heterocoordination plays an important role in these mixtures. As a trend, heterocoordination seems to be represented by large and negative enthalpic parameters for the selected contacts.

The ability of DISQUAC to predict VLE and H^E for the complex ternary systems propan-2-one–butan-2-one–CHCl₃ and methanol–propan-2-one–CHCl₃ is examined. Previously, the highly non-ideal mixture methanol–CHCl₃ was studied with the necessity for interaction parameters for the OH–Cl contact. DISQUAC accurately describes the VLE of this system, and reproduces reasonably the S-shaped H^E. S_cc(0) shows that this system is characterized by homocoordination. For the ternary mixtures considered, DISQUAC yields good results for VLE at different temperatures but H^E values are only qualitative.