Catalytic pyrolysis of chlorodifluoromethane over metal fluoride catalysts to produce tetrafluoroethylene

Abstract

The catalytic pyrolysis of chlorodifluoromethane (CHCIF2, R22) over aluminum fluoride, calcium fluoride and their physical mixtures were investigated. The conversion of R22 and the selectivity of tetrafluoroethylene (TFE) over prepared catalysts were compared with those over a non-catalytic pyrolysis. The conversion of R22 in the catalytic pyrolysis was significantly higher than that in the non-catalytic case under the tested conditions. In the catalytic pyrolysis of R22, the selectivity for trifluoromethane (CHF3, R23) decreased with time-on-stream (TOS), whereas the selectivity for tetrafluoroethylene (C2F4, TFE) increased. The Cu-promoted catalysts were more selective toward TFE than Cu-unpromoted catalysts. It was found that the enhanced TFE yield over Cu-promoted metal fluoride catalysts may be explained by the increased heat transfer effect. The physical mixture catalysts showed the highest selectivity and yield for TFE. This result may be interpreted as due to the surface modifications, Such as the formation of bimetallic fluoride and the variation of fluorine content on the surface of catalyst, caused by the attack of HF produced during the pyrolysis of R22. (c) 2005 Elsevier B.V. All rights reserved.