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

TASSIN, N.G.; ZUÑIGA, S.; YANES, 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 Ethane with higher n-alkanes exhibit liquid-liquid-vapor equilibrium and a discontinue liquid-vapor critical line, which implies phase behavior of type V or IV, from C18 on. These very asymmetric hydrocarbon mixtures not only present and interesting academic challenge for their modeling, but they are also 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 Ethane + 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 comparative study was made with the Peng-Robinson EOS, based on following the same optimization procedure for interaction parameters.