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Phase equilibria data for the system formed by clove oil + CO 2 were measured at pressures from 58.3 to 108.1 bar and temperatures of 303.2, 313.2, and 328.2 K. The phase equilibrium experiments (cloud points) were performed using a high-pressure variable-volume view cell. The phase transitions were visually recorded as bubble or dew points. The clove oil used in the present work was extracted with carbon dioxide at 150 bar and 298.2 K, and it consisted of a mixture of the following mass fractions: eugenol (75.5%), β-caryophyllene (12.1%), eugenol acetate (11.0%), and R-humulene (1.40%). Liquid-liquid-vapor equilibria were observed at 303.2 and 308.2 K, and liquid-vapor equilibria were observed at 313.2, 318.2, and 328.2 K. The phase equilibria data were modeled assuming the system to be a pseudobinary system. The Peng-Robinson equation of state with the quadratic mixing rule was used. The experimental data were fitted using the simulated annealing minimization method. Two different procedures were employed: (i) the phase stability was calculated using the Helmholtz free energy and the interval analysis, and (ii) the phase equilibrium was calculated using the Gibbs free energy, which was solved with the simulated annealing method. The model described quantitatively the experimental data.

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-The tangent plane criterion has become important for a correct solution evaluation phase and chemical of equilibrium problem. This method, applicable to single and multiphase systems, is mainly used for a single equation of state modeling all phases involved. The present work is mainly concerned with the application of interval analysis methods for global energy minimization in high-pressure phase stability problems. Two approaches are applied: (i) the Gibbs free energy global minimization under conditions of constant temperature and pressure and (ii) the Helmholtz free energy density global minimization under conditions of constant temperature and volume. Five case studies, one ternary and four binary systems, are analyzed in connection with the Peng-Robinson equation of state (PREOS) model. Five more case studies, for the CO 2 + trans-2-hexen-1-ol system at high pressures, are used to compare different methods of phase equilibrium calculation with the approach using interval analysis. Finally, a complex system, clove oil + CO 2 , is analyzed. The results indicate that the interval analysis method is robust and reliable for all the problems studied.