Effect of Peng−Robinson Binary Interaction Parameters on the Predicted Multiphase Behavior of Selected Binary Systems

The ability of the Peng−Robinson equation of state (PR EOS) to calculate the high-pressure, multiphase behavior of select binary systems has been examined using K- and L-points (also referred to as critical end points) in phase space as key landmarks and adjusting the attractive term binary interaction parameter (δ 12 ). The ethane + ethanol system showed a transition from type II behavior to type III behavior as δ 12 increased, but the type V phase behavior exhibited experimentally could not be calculated with any value of δ 12 . The equation of state incorrectly calculated type V phase behavior for the methane + n -pentane system, which experimentally shows type I behavior. The type V behavior of the methane + n -hexane system was qualitatively calculated with δ 12 = 0.014 giving the best fit to the experimental L-point while the type V behavior of the methane + n -heptane system was calculated, but the three-phase line failed to extend below the experimental four-phase point temperature and pressure (which experimentally masks the L-point). The propane + fluorene and propane + anthracene binaries showed type V behavior with a three-phase line extending below the experimental four-phase point pressure and temperature with δ 12 = −0.05 and δ 12 = 0.01, respectively. Calculations with the propane + triphenylmethane binary showed that a constant binary interaction parameter could not produce a three-phase line extending below the four-phase point, suggesting a limitation of the PR EOS to model this system’s multiphase fluid−solid behavior.