Modelling the phase behaviour and excess properties of alkane + perfluoroalkane binary mixtures with the SAFT–VR approach

The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subcritical conditions have been studied using the SAFT–VR equation of state. In previous work [C. McCabe, A. Galindo, A. Gil-Villegas, G. Jackson, Predicting the high-pressure phase equilibria of binary mixtures of perfluoro-n-alkanes plus n-alkanes using the SAFT–VR approach, J. Phys. Chem. B 102 (1998) 8060–8069] the SAFT–VR equation was successfully used to predict the phase behaviour of binary mixtures of low molecular weight n-perfluoroalkanes + n-alkanes. A transferable binary interaction parameter was proposed which enabled the accurate prediction of the critical lines for all the systems studied. In this work we focus on the low pressure liquid–liquid immiscibility displayed by binary mixtures of longer chains (C5C8). New transferable binary interaction parameters for these mixtures are proposed, based on the reproduction of the UCST and excess volumes for the n-hexane + n-perfluorohexane system. With these parameters, predictions are then made for the vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE) and excess volumes of other binary mixtures without any additional fitting to experimental data. The resulting predictions from the SAFT–VR equation are in good agreement with the available experimental data.