Binary Vapour-Liquid Equilibria of Some Fluorochemical-Hydrocarbon Systems

This study involves the experimental determination of phase equilibria data for fluorochemical-hydrocarbon mixtures in order to: (a) investigate alternative refrigerants and refrigerant mixtures, and (b) extend the use of fluorochemicals as potential solvents to separation processes. The Montreal Protocol (1987) and subsequent amendments prohibit the use of ChloroFluoroCarbons (CFCs) and HydroChloroFluoroCarbons (HCFCs). There is therefore a need for new working fluids with thermodynamic properties that are comparable or better than those of CFCs and HCFCs (viz. toxicity, insulating ability, flammability, stability and cost), but with lower ozone depletion and global warming potential. These alternative refrigerants include fluorinated olefins, fluorinated oxygenates (e.g. fluoro-ethers and fluoro-epoxides), and their mixtures with hydrocarbons. Historically, fluorochemicals have not been extensively investigated as extraction agents in chemical separation processes; however their physical properties and solvating abilities suggest that they are suitable candidates. A prerequisite for the design and optimisation of separation processes is a reliable knowledge of the phase equilibrium behaviour. Moreover, accurate thermophysical properties are required to evaluate the performance of refrigeration cycles and determine the optimum composition of new working fluids. The alternative fluorinated systems which can be used for both refrigeration and separation applications have not been extensively studied in literature. Consequently, predictive thermodynamic models such as PSRK are not capable of describing such systems. To this end, measurement of binary vapour-liquid equilibria data for a fluorinated olefin (Hexafluoropropylene), and a fluoro-epoxide (Hexafluoropropylene Oxide) with alkanes and alkenes, have been undertaken at the Thermodynamics Research Unit (Durban, South Africa), and the CEP-TEP laboratory (Fontainebleau, France). All experimental measurements were performed on equipment based on the “static-analytic” method, equipped with a micro-capillary ROLSITM sampler. The experimental data will be used to fit interaction parameters for two new groups in the PSRK group contribution model, (CF2=CF-), illustrated by Hexafluoropropylene, and (CF-O-CF2), illustrated by Hexafluoropropylene Oxide.