Pyrolysis of trifluoromethane to produce hexafluoropropylene

Abstract

Pyrolysis of a mixture of trifluoromethane (CHF3, R23) and tetrafluoroethylene (CF2=CF2, TFE) to produce hexafluoropropylene (CF3CF=CF2, HFP) was investigated by kinetic modeling and pyrolysis experiments. Product distributions from the pyrolysis of R23/TFE mixtures were estimated by a computer simulation using kinetic rate constants of individual reaction steps proposed in the literature and were compared with those obtained from pyrolysis experiments in a bench-scale tubular reactor, In addition, pyrolysis of the R23/TFE mixture in a mini-pilot-plant-scale reactor was investigated for the purpose of industrial application under the conditions of reaction temperatures of 700-1000 degreesC, contact times of 0.01-14 s, and R23/TFE molar ratios of 0.1-5. HFP was mainly produced, along with a small amount of byproducts such as perfluoroisobutylene [PFiB, (CF3)(2)C=CF2], CF3C=CCF3, C2F3H, CF3CHCF2, and CF3CF2CF= CF2. By mixing R23 and TFE in the feed or by recycling the unreacted R23 and TFE to the feed of fresh R23, the reaction temperature could be controlled by carefully utilizing the heat balance between the endothermic pyrolysis of R23 and the exothermic dimerization of TFE. It was found that the simultaneous pyrolysis of a mixture of R23 and TFE with an appropriate molar ratio gave a higher yield of HFP and a lower selectivity of PFiB, a very harmful byproduct, than the pyrolysis of R23 alone. In addition, the pyrolysis of the mixture of R23 and TFE produced less carbon powder and also required less energy to be externally supplied than the pyrolysis of R23.