Liquid–liquid equilibrium of (perfluoroalkane + alkane) binary mixtures

Despite the structural similarity between perfluoroalkanes (PFCs) and alkanes (HCs), mixtures containing these two classes of compounds present large deviations from Raoultʹs law and extended immiscibility regions. The study of these mixtures is of great interest for both practical applications and testing or improving theories of mixtures as well as for the general understanding of solute–solvent interactions. In this work, new liquid–liquid equilibrium (LLE) data for mixtures of perfluoro-n-octane and linear alkanes from C6 to C9 are presented. Data were measured at atmospheric pressure by turbidimetry and at pressures up to 150 MPa using a laser light scattering technique. The binary liquid–liquid equilibrium data were correlated using relations derived from renormalization group (RG) theory and the Modified UNIFAC with temperature dependent interaction parameters. The soft-SAFT equation of state (EoS) was also used, with parameters taken from vapour–liquid equilibrium (VLE) data to study their transferability to liquid–liquid equilibrium data. It is shown that using those parameters soft-SAFT can provide a good description of the data measured far from the critical point at atmospheric pressure and a correct dependence of the critical temperature up to 150 MPa if the size interaction parameter is also considered.