A comparative study of non-oxidative pyrolysis and oxidative cracking of cyclohexane to light alkenes

Naphthene is generally considered difficult to convert in traditional pyrolysis, but the ring rupture becomes fairly easy with the presence of oxygen in the gas phase oxidative cracking of the model compound, cyclohexane. About 86.8% conversion of cyclohexane, 43.7% yield of light alkenes, 6.6% yield of benzene and 14.3% yield of CO could be obtained at 750 °C, at which temperature the pyrolysis of cyclohexane was negligible, while at 850 °C, the total yield of alkenes, benzene and CO was as high as 80% (50%, 12% and 18%, respectively) with 98% conversion of cyclohexane. The gas phase oxidative cracking process could be run in an autothermal way (cyclohexane/O2 mole ratio of 0.69–0.8 in theory), which would minimize energy consumption and capital costs of the whole process. CO prevailed in the produced COx and the yield of CO2 was always below 1%, which means about 90% of CO2 emission by fuel burning in pyrolysis would be saved. The gas phase oxidative cracking process appears to be an environmentally benign and efficient route for light alkene production with naphthene rich feedstocks.