The pyrolysis of ethane. A study of the dissociation reaction ˙2H5→ C2H4+˙H

Abstract

Measurements have been made of the rates at which methane and ethene are formed in the thermal decomposition of ethane at temperatures between 841 and 913 K and pressures over the range 0.9–930 Torr. The methane and ethene rates yield values for the rate coefficient of the dissociation reaction ^˙C₂H₅→ C₂H₄+^˙H. Experimental data have been compared with theoretical RRK and reduced fall-off curves. The limiting high-pressure rate constant at each of eight temperatures was obtained by extrapolation and from these the Arrhenius expression k_∞/s^–1= 10^{12.95 ± 0.20} exp (–38 000 ± 800/RT) was obtained where R= 1.987 cal K^–1 mol^–1. In experiments at 872.5 K and pressures >30 Torr the rates of formation of methane and butane yielded a value of 0.14 ± 0.02 for the ethyl radical disproportionation/combination ratio. At ethane pressures <30 Torr the ratio increased progressively as the pressure was reduced. From this observation it would appear that in the pyrolysis of ethane at low pressures, other reactions apart from the recombination of ethyl radicals are involved in chain termination.