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 (SCC(0)) formalism. DISQUAC interaction parameters SCC (0) 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 excess molar enthalpy (HmE) 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 excess molar isobaric heat capacity (CpmE) of solutions involving n-alkanes, or on HmE 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 CpmE values of these systems. It is shown that structural effects can contribute largely to HmE. This is investigated in terms of the excess molar internal energy at constant volume, UVmE , whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of HmE and UVmE with the fluorohydrocarbons is different. HmE valuesn change in the sequence C6F6 > 1,4-C6H4F2> C6H6 > C6H5F, while UVmE 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 HmE values. The application of the SCC(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.