Isomerization reaction of 1,1,2,2-tetrafluorethan on fluorinated chromia: A consideration of the adsorption behavior on the catalyst

Adsorption of HF is a crucial step in the course of heterogeneously catalyzed reaction of chlorocarbons with gaseous HF. Hence, the adsorption equilibrium of HF and haloalkanes involved in the isomerization reaction of 1,1,2,2-tetrafluoroethane into 1,1,1,2 tetrafluoroethane on the catalyst surface has been studied in detail. By evaluation of the measured reaction data using the partial differential equation of isomerization expanded for variant orders to take into account influence of the adsorption the reaction order of HF was found to be zero in all stages, that of trifluoroethylene decreases from 1 to 0.5 for the reaction to 1,1,1,2 tetrafluoroethane, all others remain essentially one. Based on experimentally determined adsorption isotherms, the cell theory of adsorption allowed the extrapolative calculation of the adsorption isotherms for both isomers of tetrafluoroethane, trifluoroethylene and HF for a wide range of temperature. The formation of a pre-adsorption layer of HF at the chromia surface is in agreement with the reaction order (0) for HF. From these results, conclusions were drawn regarding the reaction mechanism of the isomerization reaction of 1,1,2,2 tetrafluoroethane.