Pyrolysis of a mixture of trifluoromethane and tetrafluoroethylene 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 the computer simulation and the pyrolysis. Experiments were carried out at the temperature ranges of 700-1000degreesC, molar ratios of R23/TFE=0.1-5.0 and contact times of 0.01-14.00 s. Product distributions for the pyrolysis of R23/TFE were estimated by the computer simulation and were confirmed by pyrolysis experiment. HFP and TFE were mainly produced with a small amount of by-products such as perfluoroisobutylene ((CF3)(2) C=CF2, PFiB), CF3CCCF3, C2F3H, CF3CHCF2 and CF3CF2CFCF2. It was proposed as a reaction mechanism that HFP might be produced from R23 through the following consecutive reaction: CHF3-->CF2=CF2-->C4F8-->CF3CF=CF2-->(CF3)(2)C=CF2, and that perfluoroisobutylene, the most harmful by-product, might be predominately formed by a reaction mechanism involving HFP and carbene [:CF2]. It was found that optimum conditions of the pyrolysis of R23/TFE mixtures experimentally determined were the molar ratio of R23/TFE=1-4, the reaction temperature of 850-900degreesC and the residence time of 0.5-2 seconds. The reaction temperature could be controlled by carefully utilizing the heat balance between an endothermic pyrolysis of R23 and an exothermic dimerization of TFE.