Direct enthalpy measurements were carried out for the methanol-benzene system as a function of composition, temperature (250° to 500°F.), and pressure (30 to 1,400 lb./sq. in. abs.). From these data pressure-enthalpy diagrams were prepared to show the enthalpy and entropy above a reference state of saturated liquid at 77°F. Similar results were obtained for a single binary system of methanol and n-hexane and a single ternary mixture.

The conventional generalized correlations were not satisfactory for predicting vapor-phase enthalpies for mixtures involving methanol. A new method requiring a knowledge of the heat of dimerization, the equilibrium constant for the reaction, and the interaction constant, is proposed for such polar-nonpolar systems based upon association of the polar component.

The most striking feature of the data for mixtures was the large heat of mixing in the vapor phase for the systems containing methanol. The same type of equation found suitable for the heat of mixing in the vapor phase was applicable to the liquid data.

From the enthalpy data across the two-phase region, it was possible to predict a limited amount of information on the compositions of the liquid and vapor phases in equilibrium. An azeotrope exists in the methanol-benzene system, which at 325°F. contains 75 mole % methanol.