Abstract
The catalytic gas phase reaction between CF3CClCH2 with HF yielding CF3CFCH2 was investigated regarding the reaction pathways involved. Different from the reaction under liquid phase (homogenous) conditions, in heterogeneous phase CF3CClCH2 does not add HF forming the saturated intermediate CF3CFClCH3 but undergoes direct Cl/F exchange at the starting olefin molecule resulting directly in the formation of CF3CFCH2. This might be caused mainly by the fact that under heterogeneous gas phase conditions higher temperatures are needed as compared to liquid phase conditions thus suppressing the formation of kinetically less stable CF3CFClCH3 under these conditions. Since for all the reaction steps involved in this complex reaction system the Gibbs free reaction enthalpy values are close to zero [1], the selectivity towards several reaction products is strongly dependent on the reaction parameters, e.g. temperature, pressure and molar ratio of the reactants. Based on the catalytic data obtained for fluorinated chromia as catalyst, a reaction path distinguishing direct chlorine against fluorine exchange versus hydrofluorination/dehydrochlorination is proposed.
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