Global phase behaviour in methane plus n-alkanes binary mixtures

Abstract

The methane plus linear alkanes series is one of the simpler and most common type of mixtures presented in the industry and its accurate representation is paramount because of the diversity of its applications. From a theoretical perspective, its structural simplicity due to the low degree of synergy and the absence of short-range dispersive forces suggests that a good model should represent these systems with acceptable accuracy. Based on these ideas and the relatively regular behaviour of n-alkanes, these systems have become particularly suitable for trial calculation in convoluted models, in order to verify their capabilities in both quantitative and qualitative predictions. In this contribution, the soft-SAFT equation of state is used for the construction of the serial prediction domain global phase diagram (spd-GPD) of the methane plus linear alkanes series. The main goal is to address the capability of the equation of state to predict the global behaviour of the binary mixtures until methane plus n-decane, with special emphasis in accurately reproducing the mechanism and topology of mixtures. All systems shown here are predicted with quantitative accuracy, including a complete description of their taxonomy. The information obtained from the equation of state allows the validation of some predictions of the spd-GPD in the absence of experimental data. Following this analysis, the double retrograde behaviour lies between the methane plus propane and methane plus n-butane systems, while the tricritical transition of the series is found between the methane plus n-pentane and methane plus n-hexane mixtures. Also, the presence of the molar density inversion phenomenon is predicted to begin between the methane plus n-hexane and methane plus n-heptane systems, while no signals of mass density inversions are found on these mixtures.