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Phase behavior of systems composed by supercritical carbon dioxide and ethanol is of great interest, especially in the processes involving supercritical extraction in which ethanol is used as a cosolvent. The development of an apparatus, which is able to perform the measurements of vapor-liquid equilibrium (VLE) at high pressure using a combination of the visual and the acoustic methods, was successful and was proven to be suited for determining the isothermal VLE data of this system. The acoustic method, based on the variation of the amplitude of an ultra-sound signal passing through a mixture during a phase transition, was applied to investigate the phase equilibria of the system carbon dioxide + ethanol at temperatures ranging from 298.2 K to 323.2 K and pressures from 3.0 MPa to 9.0 MPa. The VLE data were correlated with Peng-Robinson equation of state combined with two different mixing rules and the SAFT equations of state as well. The compositions calculated with the models are in good agreement with the experimental data for the isotherms evaluated.

Density measurements of the n-heptane + n-dodecane binary mixture were performed with a vibrating tube densitometer in the temperature range of (293.15 to 363.15) K and pressure up to 70 MPa at six different n-heptane mole fractions: x 1 = 0, 0.1999, 0.3991, 0.5999, 0.7998, and 1. Densities of the CO2 + n-heptane + n-dodecane ternary mixtures were also measured at the same temperature and pressure ranges for two different isopleths: CO2 (0.4904) + n-heptane (0.2548) + n-dodecane (0.2548), and CO2 (0.7425) + n-heptane (0.1288) + n-dodecane (0.1288). The obtained experimental data were correlated by a polynomial model and by a Tait-based equation. Density values for pure n-heptane and n-dodecane were found to be in agreement with literature data within approximately 0.3%. The isothermal compressibility and thermal expansion values of these mixtures were obtained by differentiation from the models as a function of pressure and temperature. Analysis of these properties pointed out that the polynomial model provided more accurate results related to derived properties. The excess volume of the mixtures was also determined. In general, they are negative, but they become positive for binary mixtures in the heptane-rich region as well as at higher pressures for ternary mixtures.

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