Dehydrofluorination of 1, 1, 1-Trifluoroethane Catalyzed by Metal Fluorides

Abstract

CH₃CF₃ a by-product of the process preparing CH₂=CF₂ from CH₃CCl₃ or CH₂=CCl₂, is fairly stable and not easily dehydrofluorinated by pyrolysis. The objects of this paper are to find effective metal fluoride catalysts, and to elcidate their activities for dehydrofluorination.
Experiment has been carried out by a flow reactor in the absence or presence of various metal fluorides, and the acidities of these fluorides has been determined by the normal butyl amine titration method.
The results obtained are as follows:
1) The dehydrofluorination in the absence of catalyst at temperatures higher than 750°C is of the first order kinetics and the reaction rate constant k is given by
k =1.63 × 10¹⁰ exp (-53800/RT)
2) As in the dehydrofluorination of CH₃CHF₂ which was reported by us previously, (synthesized) AlF₃, FeF₃, MgF₂ are acive for dehydrifluorination at lower temperature as 530°C, while (commercial) AlF₃, CaF₂, SrF₂, BaF₂, ZnF₂, CdF₂, MnF₂, SnF₂ are inactive. All the catalytically active fluorides have some acidity, while inactive fluorides have none, and hence the acidity appears to be oirrelated with the catalytical activity.
3) Basic aluminum fluoride has been found active and the most stable. The dehydrofluorination reaction catalyzed by this catalyst has been proved to be surface reaction controlling, and the activation energy is 28.3 kcal/mol.