Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene

Abstract

Difluorochloromethane (CHClF2, R22) has been used as a refrigerant for air conditioners and a raw material for the manufacturing of fluorinated compounds such as tetrafluoroethylene (C2F4, TFE), and hexafluoropyropylene (C3F6, HFP). TFE has been produced by the pyrolysis of chlorofluoroparaffins especially, R22, in the temperature ranges of 750 - 950 degrees C. To improve the relatively poor yield of TFE, the catalytic pyrolysis of R22 over activated carbon supported Cu-based catalysts was investigated. The catalytic activities over the prepared catalysts were compared with those of a non-catalytic pyrolysis reaction. Alteration of reactivity as a function of reaction time was also observed. At 650 degrees C and 700 degrees C, the yield for TFE over 10wt% Cu/A.C catalyst was higher than that in the non-catalytic pyrolysis. Reduced Cu catalysts were more active than CuO catalysts and the selectivity of HFP increased with increasing the amount of Cu loading in Cu/A.C catalysts. It was found that the reduced Cu catalyst was undergoing surface modification during the pyrolysis of R22 due to the reaction of Cu/A. C catalyst with hydrogen fluoride produced during the catalytic pyrolysis. The fresh catalysts and catalysts after the reaction were characterized by XRD and EDS. The metal fluoride formed during the pyrolysis was either CaAlF5 or Ca2AlF7, or their mixture