Enthalpies, excess volumes, and specific heats of critical and supercritical binary mixtures

A scaling-law crossover thermodynamic model is applied to caloric properties of five binary mixtures, carbon dioxide + ethane, ethane + propane, n-pentane + benzene, n-pentane + acetone, and ammonia + water. Enthalpy increments, excess enthalpies, excess volumes, and specific heats are calculated on the phase boundaries and in the near-critical and supercritical one-phase regions, and calculated values agree well with experimental data. The method requires as input the mixture excess critical compressibility factor, as obtained from critical loci, which in this approach are determined from modified Leung-Griffiths correlations. The only additional variables needed are the acentric factors of the pure components and a few fitting parameters which describe the unknown thermodynamic energies along the critical locus and which are not needed for the phase boundary and supercritical properties in pressure-temperature-density space.