The pyrolysis of ethane in the presence of nitric oxide

The kinetics of the ethane pyrolysis have been studied at temperatures from 550 to 596°C and with 0 to 62% of added nitric oxide. The rates of production of various products were studied by gas chromatography; ethylene, hydrogen, methane, nitrogen, water, nitrous oxide and acetonitrile were found as primary products, with hydrogen cyanide, carbon monoxide, acetaldehyde, n ‐butane, 1‐butene, cis ‐ and trans ‐2‐butene and 1,3‐butadiene as secondary products. For all the primary products the orders with respect to C 2 H 6 and NO were determined, as were the activation energies at two different percentages of NO (15.7 and 45.5%). Nitric oxide was found to be rapidly consumed with a finite initial rate, and the rate of production of H 2 O was close to that of C 2 H 4 at higher nitric oxide pressures. A mechanism is proposed which gives good agreement with all of the observed results. Its main features are: ( 1 ) Initiation takes place mainly by the unimolecular dissociation of ethane; there is no evidence for or against the process NO + C 2 H 6 → HNO + C 2 H 5 ; ( 2 ) NO scavenges ethyl radicals to form acetaldoxime which decomposes, and in this way the breakdown of C 2 H 5 is hastened; ( 3 ) termination takes place mainly by the unimolecular decomposition of acetaldoxime to give inactive products. Some of the relevant rate parameters are evaluated. Reactions are proposed to account for the formation of the secondary products observed.