Description of the liquid–liquid equilibrium in binary and multicomponent CFC/lubricating oil mixtures by means of an extended Flory–Huggins model

An extended Flory–Huggins model has been developed and used to interpret liquid–liquid phase diagrams related to binary mixtures of CFC–lubricating oil for which miscibility gaps of UCST, LCST and hourglass type are present. Some liquid–liquid equilibrium measurements have been carried out for the fluorinated compounds R134a, R125, R143a, and R32 in mixtures with polyester-based lubricating oils (PES), pentaerythritol tetraheptanoate (PTE) and trimethylolpropane triheptanoate (TTE). The extended Flory–Huggins model has been applied in the simultaneous description of the liquid–liquid and vapor–liquid phase equilibrium using the same set of adjustable parameters. On the basis of the results obtained in fitting binary systems, a predictive approach has been developed for the description of a miscibility gap related to a mixture formed by two or more halogenated compounds with a lubricating oil.