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 li quid-liquid phase diagrams related to binary mixtures of CFC-lubricating oi l for which miscibility gaps of UCST, LOST and hourglass type are present. Some liquid-liquid equilibrium measurements have been carried out for the f luorinated compounds R134a, R125, R143a, and R32 in mixtures with polyester -based lubricating oils (PES), pentaerythritol tetraheptanoate (PTE) and tr imethylolpropane 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 t he basis of the results obtained in fitting binary systems, a predictive ap proach 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. (C) 2000 Elsevier Science S.A. All rights reserved.