Thermodynamics of mixtures containing a fluorinated benzene and a hydrocarbon

Abstract Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor ( S CC ( 0 ) ) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. The H m E values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on C pm E of solutions involving n-alkanes, or on H m E of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative C pm E values of these systems. It is shown that structural effects can contribute largely to H m E . This is investigated in terms of the excess molar internal energy at constant volume, U V m E , whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of H m E and U V m E with the fluorohydrocarbons is different. H m E values change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while U V m E changes in the order: 1,4-C6H4F2 > C6H6 ≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative H m E values. The application of the S CC ( 0 ) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.