Excess Gibbs energies of the ternary system ethanol+ N, N-dimethylformamide+cyclohexane at 298.15 K

Abstract

Vapour–liquid equilibrium (VLE) for the ternary system ethanol (EtOH)+ N, N-dimethylformamide (DMF)+cyclohexane (Cy) and for the relevant binary mixtures containing DMF have been determined at 298.15 K by headspace gas chromatographic analysis of the vapour phase directly withdrawn from an equilibrium apparatus. Measurements of liquid–liquid equilibria in both binary DMF+Cy and ternary mixtures have been also carried out. The binary VLE data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. Excess Gibbs energies G E as well as activity coefficients γ i of components have been obtained and briefly discussed. While EtOH+DMF behaves almost ideally with slightly negative G E-values, both EtOH+Cy and DMF+Cy exhibit large positive deviations. The G Es of the ternary system are positive with the exception of a narrow region in dilute Cy. The excess entropy and the temperature dependence of G E and γ i have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity. The predictions by different equations of the effect of temperature on the mutual solubilities of DMF and Cy as well as on the binodal curve of EtOH+DMF+Cy have been compared with experiment.