2004 Volume 37 Issue 2 Pages 318-325
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 700–1000°C, 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)2C=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)2C=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 850–900°C 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.
