New correlations for prediction of high-pressure phase equilibria of n-alkane mixtures with the RKPR EoS: Back from the use of l ij (Repulsive) interaction parameters

Abstract

After detecting some inadequate predictions of volumetric properties and solid-liquid equilibria with the RKPR Equation of State coupled to previously correlated parameters (Cismondi Duarte, M.; et al. Fluid Phase Equilib. 2015, 403, 49-59), we analyzed the causes and concluded that the problems were related to the predominant role of the lij repulsive interaction parameter on those correlations. With the aim of proposing a model able to describe in a correct and consistent way the phase and volumetric behavior of the n-alkane-n-alkane binary mixtures, including the more asymmetric ones, here we made a turn back from our previous parameter correlations. Leaving behind the use of lij parameters, which combined with the arithmetic average combining rule transforms the quadratic into a linear mixing rule for the covolume, we developed in this work for PR and RKPR EoS new correlations of the kij attractive parameters with temperature dependence for the homologous series of binary mixtures formed by methane, ethane, propane, n-butane, or n-pentane with heavier normal alkanes, adopting zero values when both carbon numbers are equal to or higher than six. This also involved a new parametrization of pure n-alkanes for the RKPR EoS and new volume shift correlations for both models. The results show a very good predictive power for the phase behavior of n-alkane binary systems, with RKPR showing a much better performance than that of PR in the case of the more asymmetric systems, and a correct description of volumetric properties.