Measurement and correlation of critical properties for binary mixtures and ternary mixtures containing gasoline additives

The critical properties of three binary mixtures and three ternary mixtures containing gasoline additives (including methanol + 1-propanol, heptane + ethanol, heptane + 1-propanol, methanol + 1-propanol + heptane, methanol + 1-propanol + methyl tert-butyl ether (MTBE), and ethanol + heptane + MTBE) were determined by a high-pressure cell. All the critical lines of binary mixtures belong to the type I described by Scott and van Konynenburg. The system of methanol + 1-propanol showed little non-ideal behavior due to their similar molecular structures. The heptane + ethanol and heptane + 1-propanol systems showed visible non-ideal behavior for their great differences in molecular structure. The Peng-Robinson equation of state combined with the Wong-Sandler mixing rule (PR-WS) was applied to correlate the critical properties of binary mixtures. The critical points of the three ternary mixtures were predicted by the PR-WS model with the binary interaction parameters using the procedure proposed by Heidemann and Khalil. The predicted critical temperatures were in good agreement with the experimental values, while the predicted critical pressures differed from the measured values. The experimental values of binary mixtures were fitted well with the Redlich-Kister equation. The critical properties of ternary mixtures were correlated with the Cibulka's equation, and the critical surfaces were plotted using the Cibulka's equations.