High pressure phase behavior modeling of asymmetric Methane + n-Alkane binary systems with the RKPR EOS

GALDO, M.V.; GOMEZ, M.J.; MILANESIO, J. M.; CISMONDI DUARTE, M.

Conferencia; 13th International Conference on Properties and Phase Equilibria for Products and Process Design (PPEPPD 2013); 2013

It is well established that the phase behavior of mixtures between hydrocarbons which do not differ much in size is easy to correlate or even predict with equations of state and classic quadratic mixing rules. Nevertheless, the complexity and difficulty of correlation increase as the asymmetry and therefore the immiscibility of the system increase. In particular, the binary mixtures of Methane with higher n-alkanes exhibit phase behavior of type V from C6 on, and probably of type III for higher carbon numbers like 20 and 30, although the solidification of the paraffin prevents from experimentally studying the complete critical lines. These very asymmetric hydrocarbon mixtures not only present an interesting academic challenge for their modeling, but they are becoming more important technologically, since the world oil reserves are becoming heavier in average. The RKPR EOS was developed in recent years in order to consider asymmetric systems and allow for a good representation of densities for different types of compounds while maintaining the relative simplicity of cubic equations of state. In this work the RKPR EOS is applied for the first time for the correlation of phase behavior in the series of binary systems Methane + n-Alkane. In addition to the use of attractive and repulsive interaction parameters with quadratic mixing rules, the role of the extra degree of freedom that the RKPR model offers for setting the pure compound parameters was also examined. A new table of RKPR pure compound parameters was defined for n-Alkanes. A comparative study was made with the Peng-Robinson EOS, based on following the same optimization procedure for interaction parameters.