Obtainement of pentafluoroethane from dichlorotetrafluoroethane - Note I

Gaseous fluorination with hydrogen fluoride at atmospheric pressure of the two isomers CClF₂-CClF₂ and CF₃-CCl₂F was continuously carried out on a chromic oxide based catalyst. The fluorinated derivative, obtained at a selectivity higher than 90%, was pentafluorochloroethane. Hexafluoroethane and an isomeric mixture of trichlorotrifluoroethanes were obtained as byproducts. The latter were recycled to fluorination together with unconverted C₂Cl₂F₄. Both conversion of C₂Cl₂F₄ and selectivity to C₂ClF₅ were affected by temperature, contact time and molar ratio of the reagents.The catalytic activity of chromic oxide was adversely affected by small amounts of water in the hydrogen fluoride. A difference in reactivity between the two isomers CF₃-CCl₂F and CClF₂-CClF₂ was also observed.It was also observed that the byproduction of C₂Cl₃F₃ was due to the disproportionating activity of obromic oxide versus C₂Cl₂F₄.