CATALYTIC GAS-PHASE FLUORINATION OF 1,1,1-TRIFLUORO-2 CHLOROETHANE OVER CHROMIUM(III) OXIDE - PREPARATION OF HYDROFLUOROALKANES

The transformation of CF3CH2Cl over bulk chromium(III) oxide, fluorinated or not, leads mainly to the fluorination product CF3CH2F and to the alkene CF2=CHCl. In the presence of HF, CF3CH2F is the main product. In absence of HF this product is also obtained with HF formed in the elimination reaction of CF3CH2Cl to CF2=CHCl. At the same time a part of HF is used for the fluorination of chromium oxide. The XPS analysis of fluorinated catalysts with HF gives surface fluorine atomic contents which correspond to a F/Cr ratio of 0.36. A survey of the effect of partial pressures of HF and of CF3CH2Cl shows a zero order for HF and a 0.6 order for CF3CH2Cl. The fluorination reaction could occur on a partially fluorinated chromium(III) oxide involving HF oligomer species previously postulated by Rowley et al. [L. Rowley, J. Thomson, G. Webb and J.M. Winfield, Appl. Catal. A, 79 (1991) 89-103].