The formation of hydrogen in ethylene pyrolysis at 900 K

Ethylene at concentrations of 2.7 × 10−3 to 1.0 × 10−2 mol L−1 has been pyrolyzed at 900 K in a flow system. The products ethane and hydrogen have been analyzed by gas chromatography. The results are consistent with a mechanism in which these products are initially formed as follows: equation image Reaction [1] occurs only 1 to 2% as often as the addition reaction, equation image The latter reaction is close to equilibrium. Taking the rate constant, k4, and the equilibrium constant, K2, from the literature and making small adjustments for minor processes, k1 is found to be (9 ± 3) × 107 L mol−1 s−1. Here the uncertainty is intended to encompass errors in the present work and in the literature parameters. A secondary source of hydrogen was also observed. Its dependence on ethylene concentration was consistent with formation from an intermediate with six carbon atoms, such as cyclohexene.