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 XPath I : XPath II: -XPath III : XPath 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.