The role of formaldehyde in the oxidation of ethylene

Abstract
The oxidation of ethylene at temperatures in the region of 400 degrees C has been studied manometrically and analytically, and compared with the oxidation of formaldehyde under similar conditions. The observations of previous authors have been confirmed and extended with particular reference to the factors controlling the maximum rate of reaction. The oxidation of ethylene is closely dependent on the development of formaldehyde, which shows the behaviour to be expected of an agent for degenerate branching. There is a close parallelism between the variation of the activation energy of the oxidation of ethylene from 25 kcal at 350 degrees C to 53 kcal at 550 degrees C and of formaldehyde from 21 kcal at 350 degrees C to more than 40 kcal at 500 degrees C. Formaldehyde is produced in the oxidation of ethylene and attains a maximum concentration which is proportional to the ethylene pressure and independent of the oxygen pressure. The addition of formaldehyde to the reaction mixture reduces or removes the induction period without affecting the maximum rate of the reaction. Ethylene oxide plays a minor but significant part; it attains a stationary concentration in the reaction but is less effective than formaldehyde in reducing the induction period. A reaction scheme based on that proposed by Axford & Norrish (1948) for the oxidation of formaldehyde has been developed; it accounts satisfactorily for the observed facts.

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