Thermodynamics of mixtures containing a very strongly polar compound. Part I. Experimental phase equilibria (solid–liquid and liquid–liquid) for sulfolane + alkan-1-ols systems. Analysis of some mixtures including sulfolane in terms of disquac

Abstract

Equilibrium temperatures for liquid–liquid and solid–liquid transitions of systems containing sulfolane and propan-1-ol, butan-1-ol, octan-1-ol or tetradecan-1-ol were measured by a dynamic method. From butan-1-ol, the mixtures show an upper critical solution temperature, which increases with the length of the alcohol. It may attributed to a decreasing of the effective dipole moment of the alkan-1-ol which markedly decreases the interactions between unlike molecules. The coexistence curves become shifted to the high molar fractions of sulfolane in solutions with longer alkan-1-ols, probably due to size effects. Binary systems of sulfolane with cycloalkanes, n-alkanes, benzene or toluene, CCl₄ or alkan-1-ols were analyzed in terms of a purely physical model, DISQUAC. The corresponding interaction parameters are reported. DISQUAC represents fairly well, over a rather wide range of temperature, a complete set of thermodynamic properties: liquid–liquid equilibria, LLE, solid–liquid equilibria, SLE, vapor–liquid equilibria, VLE, molar excess Gibbs energies, G^E, molar excess enthalpies, H^E and natural logarithms of activity coefficients at infinite dilution, ln γ_i^∞. Deviations observed for LLE are typical for mean field theories as calculations are developed assuming that thermodynamic properties close to the critical points are analytical. Experimental data show that sulfolane may play the role of an almost inert diluent, because of the steric hindrance of its globular nature.