Thermochemistry of Solutions of Alkanes in Binary Mixtures: Azeotropes

This work is devoted to the study of azeotropes by the method of solvation thermodynamics. In the present work the thermochemistry of alkane solutions in binary mixtures was studied. The infinite dilution solution enthalpies ofn-hexane,n-octane, andn-dodecane in binary mixtures were measured at 298.15 K. Alkanes were used as solutes since they are not capable of specific interactions with solvents. It should be noted that the differences in the solution of alkanes in a series of solvents are caused by differences in the interactions between the solvent molecules. Binary mixtures (benzene-cyclohexane) and (n-hexane-acetone) at different molar ratios, including the compositions corresponding to azeotropes, were used. The composition of both azeotropes obtained by distillation was determined by means of densimetry, and was found to be in good agreement with published data. The compositions of chosen azeotropes insignificantly change with temperature. The excess solution enthalpies ofn-alkanes in binary solvents were calculated. It was found that the extremum value of the excess solution enthalpy corresponds to their azeotrope composition.