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We observed that the mutual diffusion coefficients of benzene in supercritical carbon dioxide exhibited a maximum at pressures above the critical pressure of the mixture, and a strong concentration dependence near the critical point. These surprising experimental results can be explained by replacing the concentration gradient of diffusion with a chemical potential gradient as suggested from irreversible thermodynamics. Then, it can be understood that diffusion coefficients have a maximum value at the critical point of a mixture. The Peng−Robinson equation of state was used to illustrate these relationships.

A thermodynamic theory of phase separation in mixtures possessing LCST is presented which incorporates (1) chemical equilibrium theory to account for cross association between solute and solvent, (2) Flory-Huggins theory for the difference of molecular volumes, and (3) NRTL equation for the interaction between molecules. The theoretical predictions of binodal curves over a wide temperature range are in good agreement with experimental findings in some binary aqueous solutions. The model can also reproduce the flat coexistence curves near the consolute points.

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Isothermal vapor-liquid equilibria for 21 fluorocarbon + alcohol systems ranging from 283 to 313 K at atmospheric pressure were measured. The solubility of fluorocarbons into alcohols decreases with increase in temperature and is on the order of a thousand times greater than that of water. The solubility of fluorocarbons derived from ethane in methanol increases as the number of hydrogen atoms in a molecule increases. From the experimental data, Henry's law constants of dichlorodifluoromethane (CCl 2 F 2 , CFC12), chlorodifluoromethane (CHClF 2 , HCFC22), difluoromethane (CH 2 F 2 , HFC32), chloropentafluoroethane (C 2 ClF 5 , CFC115), pentafluoroethane (C 2 HF 5 , HFC125), 1,1,1,2-tetrafluoroethane (CH 2 FCF 3 , HFC134a), and 1,1-difluoroethane (CH 3 CHF 2 , HFC152a) in methanol, ethanol, and 2-propanol were obtained. The values were correlated as a function of temperature with the Valentiner equation.