Non-ideal mixing behaviour of (0.5C 2H 6 + 0.5C 3H 6) II. Excess properties and their representation by equations of state

Abstract

Excess heat capacities at constant pressure, excess enthalpies, excess entropies, and excess Gibbs functions of (0.5C 2H 6 + 0.5C 3H 6) were determined from precise measurements of the heat capacity and the Joule-Thomson coefficient of the mixture and of its components obtained in previous investigations by flow calorimetry. The investigated range of state includes the critical point of propene and extends to about twice the critical density. Since the components are similar in size, shape, and chemical nature, the deviations from ideal mixing are generally small. Large excess heat capacities, enthalpies, and entropies are observed only in the vicinity of the critical point of propene, whereas the excess Gibbs function is small even in this range of state. The residual and excess thermodynamic properties of the mixture are compared with the results from different equations of state. Generally, the best results are obtained with Starling's modification of the Benedict-Webb-Rubin equation and with the extension of the Lee-Kesler procedure by Plöcker, Knapp, and Prausnitz. However, even for this mixture of non-polar components of similar shape and size, the deviations between calculated and experimental results are, for the most part, markedly larger than the experimental uncertainties.