Kinetic modeling of benzene decomposition near 1000 K: The effects of toluene impurity

Kinetic data of Brooks et al. on the decomposition of C₆H₆ near 1000 K have been analyzed by computer modeling. The observed overall 3/2-order kinetics could be accounted for by a mechanism composed of 4 key reactions involving H atoms and C₆H₅ radicals using recently acquired rate constants. However, the appearance of CH₄ and the enhanced H₂ yields could only be explained by invoking the reactions of approximately 0.1% of toluene present in the system as reported by the authors. Overall, the decomposition reaction is dominated by the unimolecular dissociation of C₆H₆ followed by the short chain process, H+C₆H₆ = C₆H₅+H₂ and C₆H₅+C₆H₆ = C₁₂H₁₀+H, which result in the dehydrogenation of C₆H₆, producing C₁₂H₁₀+H₂. In order to account for the yield of H₂ quantitatively, the displacement reaction, C₆H₅CH₂+C₆H₆ = CH₂(C₆H₅)₂+H, was invoked and modeled to have the approximate rate constant, 8.4×10¹¹ exp(-11800/T) cm³ mol^-1 s^-1.