Binary and Ternary Phase Behavior of α-Pinene, β-Pinene, and Supercritical Ethene

High-pressure isothermal vapor−liquid equilibria have been measured for binary and ternary systems containing α-pinene, β-pinene, and supercritical ethene, at 288.15 K, 298.15 K, 308.15 K and pressures between 4 MPa and 8 MPa. Experimental results were obtained in an apparatus based on the synthetic method where the main feature is a variable-volume high-pressure cell with a glass window, making it possible to observe the phase behavior. A rod attached to the movable piston allowed the estimation of the density of the phase under study. Results show that the solubilities of both pinenes in supercritical ethene are very similar. The resulting binary pressure−temperature diagrams are of type I, according to the classification of Scott−van Konynenburg. The ternary systems are also of type I, according to the classification of McHugh−Krukonis. Three-phase liquid−liquid−gas regions are likely to exist in these systems but were not observed due to limitations in the apparatus used. To model the experimental results, we used the Peng−Robinson equation of state with van der Waals one-fluid mixing rules and Panagiotopoulos−Reid combining rules, which involves two binary interaction parameters to be determined from regression of experimental data. Deviations between experimental and calculated pressures were always less than 0.8%. Experimental vapor and liquid densities were compared with those generated by this equation. Ternary phase behavior was predicted using only binary interaction parameters retrieved from each binary system, resulting in mole fraction deviations less than 5% for the liquid phase and 3% for the vapor phase.