Quantitative interpretation to the chain mechanism of free radical reactions in cyclohexane pyrolysis

Pyrolysis of cyclohexane was conducted with a plug flow tube reactor in the temperature range of 873-973 K. Based on the experimental data, the mechanism and kinetic model of cyclohexane pyrolysis reaction were proposed. The kinetic analysis shows that overall conversion of cyclohexane is a first order reaction, of which the rate constant increased from 0.0086 to 0.0225 to 0.0623 s⁻¹ with the increase of temperature from 873 to 923 to 973 K, and the apparent activation energy was determined to be 155.0±1.0 kJ-mol⁻¹. The mechanism suggests that the cyclohexane is consumed by four processes: the homolysis of C-C bond (Path I), the homolysis of C-H bond (Path II) in reaction chain initiation, the H-abstraction of various radicals from the feed molecules in reaction chain propagation (Path III), and the process associated with coke formation (Path IV). The reaction path probability (RPP) ratio of X_{Path I} : X_{Path II}: -X_{Path III} : X_{Path IV} was 0.5420 : 0.0045 : 0.3897 : 0.0638 at 873 K, and 0.4336 : 0.0061 : 0.4885 : 0.0718 at 973 K, respectively.