Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

A set of high-pressure view apparatus was designed for determining the critical properties of chemicals. In order to check the reliability of the apparatus, the critical temperatures (Tc) and critical pressures (Pc) of pure n-heptane, cyclohexane, methanol, ethanol, 1-propanol, methyl tert-butyl ether (MTBE), and binary mixture n-hexane + ethanol were measured. The experimental data were in good agreement with the literature data, which proves the reliability of the apparatus used in the work. The critical temperatures and critical pressures of five binary mixtures containing gasoline additive (MTBE+ n-heptane, MTBE + cyclohexane, MTBE + methanol, MTBE + ethanol, MTBE + 1-propanol) were measured using the high-pressure view cell with visual observation.The critical temperatures and critical pressures for the five binary mixtures were all reported for the first time. In addition, the critical temperatures and critical pressures of the binary mixture n-heptane + cyclohexane (two of main components in gasoline) were also measured. All the critical lines for the mixtures studied are continuous which connect the critical points of the two pure components, indicating their phase diagrams belong to type I proposed by Scott and van Konynenburg. The critical points of these systems were calculated by the Peng-Robinson equation of state with the Wong-Sandler mixing rule.This model could calculate the critical properties of the mixtures well with the binary interaction parameter kij obtained by fitting the experimental critical data. And the experimental data were all fitted well with Redlich-Kister equation. The maximum average absolute deviations were 0.06% for critical temperatures and 0.35% for critical pressures.