Solid-Liquid Phase Equilibria of Organic Compounds Under High Pressures

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Solid-liquid phase equilibria of the binary mixtures of organic compounds have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel newly designed. The uncertainties in the measurements of temperature, pressure and composition are within 0.1 K, 0.5 MPa and 0.001 mole fraction, respectively.1 Systems investigated(1) simple eutectic systems : benzene + cyclohexane, benzene + 2-methyl-2-propanol(2) systems with formation of intermolecular compounds : carbon tetrachloride + benzene, carbon tetrachloride + p-xylene(3) partial solid solution system : -methylnaphthalene + -methylnaphthalene(4) complete solid solution system : chlorobenzene + bromobenzene2 Apparatus and experimental proceduresThe measurements were performed in a high-pressure vessel with a couple of optical windows. The sample liquid of a known composition was introduced in the equilibrium vessel, which was immersed in a liquid bath thermostatically controlled within 0.05 K, and was compressed gradually. The phase transition and solid-liquid coexistence were observed visually.3 Experimental results and discussionThe freezing temperature at a constant composition increases monotonously with increasing pressure in all cases of phase diagrams. The eutectic temperature shifts to higher temperature, and the eutectic composition shifts to richer composition of the component whose pressure coefficient of freezing temperature is larger. In the systems forming intermolecular compounds, it is found that the congruent melting point turns to the incongruent melting point, and that one compound disappears under high pressure. The solid-liquid coexistence curve can be correlated satisfactorily by an equation newly proposed for all systems.