Manufacture of tetrafluoroethane - a recent chapter of catalytic fluorine chemistry

Abstract

1,1,1,2-Tetrafluoroethane (R 134a) is the favourite substitute for CFC 12 in refrigeration and air conditioning technology, having no ozone depletion potential and a reduced greenhouse warming effect. Due to high economical and environmental demands, the elaboration of a catalytic reaction as a manufacturing process represents a recent challenge in industrial fluorine chemistry. Starting with chlorinated C 2-compounds several reaction pathways leading to R 134a are possible. The results of our investigation favour a gas phase reaction of trichloroethylene and HF on a special Cr/Mg-catalyst affording selectively tetrafluoroethane. ▪ The efficiency of the chloro-fluoro-exchange in R 133a is determined by the thermodynamic equilibrium and by side reactions. Being a slightly endothermic reaction at higher temperatures, conversion of R 133a increases while selectivity for the desired R 134a decreases. Optimized conditions have to take in account numerous factors including chemical and technical requirements. Recycling of the unreacted intermediate R 133a as well as quantitative consumption of the HF-reagent are important features of the process avoiding environmental strain.