SHORT COMMUNICATION Rate of and Additive Influences on the Oxidation of HCN

Abstract

The oxidation of HCN was studied in the temperature range of 1023–1098 K, using a Vycor stirred-flow reactor and dilute mixtures of HCN and oxygen in He. The rate was found to be 1.25-order in HCN and 0.5-order in oxygen. The activation energy and log frequency factor are 97.3 (kcal/mole) and 22.5 (using (1/mole)^0.25 sec⁻¹) respectively. The oxidation products for HCN/O2 mixtures were found to be CO², H²O, and N². The order indicates a complex mechanism is operating; however, the activation energy appears to be too large for a chain or surface mechanism.

In order to simulate the reaction environment that HCN would experience during heterocycle or coal combustion, additives were introduced to the reaction mixture. Benzene was added over a wide range of conditions, which did increase the rate of HCN consumption at low equivalence ratios, but at a ratio of about 0.85 the extent of consumption of all reactants decreased; HCN consumption dropped drastically and benzene consumption was reduced a small amount even at higher oxygen concentrations in the reactor. Clearly, a species is being produced which inhibits the reaction. No change in products was observed. Cyclohexane and toluene had about the same influence on the oxidation as did benzene. The addition of either acetylene or CO increased the consumption of HCN to nearly 100 percent, and also both of these promoted the formation of NO. The results produced by these additives cannot be explained on the basis of thermal effects since, at the concentrations used, the oxidation of many of these benzene mixtures was more exothermic than was the oxidation of the acetylene or CO mixtures. However, from these results it appears that CO and acetylene can produce a reaction pathway during oxidation that is not present when benzene or other hydrocarbons are oxidized. Several implications of these results concerning the mechanism of NO formation are discussed,