Effect of pressure on the solid-liquid phase equilibria of binary organic systems

Solid-liquid phase equilibria of the binary mixtures of the organic liquids have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel. The systems investigated are as follows: (1) simple eutectic systems-benzene + cyclohexane system and benzene + 2-methyl-2-propanol system; (2) eutectic systems with formation of intermolecular compounds — carbon tetrachloride + p-xylene system and carbon tetrachloride + benzene system; (3) partial solid solution system--methylnaphthalene + -methylnaphthalene system; and (4) complete solid solution system-chlorobenzene + bromobenzene system. The uncertainties of the measurements of temperature, pressure and composition are within ±0.1 K, ± 0.5 MPa, and ±0.001 mole fraction, respectively. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The eutectic mixture becomes richer in the component whose temperature coefficient of the freezing pressure is larger and the eutectic temperature rises monotonously with increasing pressure in the eutectic systems. The pressure-temperature-composition relation of the solid-liquid phase equilibria can be expressed satisfactorily by an equation newly proposed.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.