A test of thermal-ignition theory in autocatalytic reactions

Abstract

The Semenov-Frank-Kamenetskii treatment of thermal ignitions has been applied to a complex reaction scheme for the formation of hydrogen chloride in mixtures of hydrogen, chlorine, nitric oxide, and nitrosyl chloride. When conditions are chosen to lead to nonautocatalytic reactions, for example when nitric oxide is added but [NOCl] is low, the simple Frank-Kamenetskii treatment predicts pressure limits of ignition accurately. When nitrosyl chloride is added initially and the reaction is autocatalytic in nature, the basic equations for the rate of heat production and the rates of removal of reactants and additives, with values of the rate constants and other parameters measured in quite independent experiments, can be solved on a computer to derive the pressure limits of ignition accurately for a wide variety of conditions of temperature or additive concentration. The induction periods for the autocatalytic reaction are of the correct order of magnitude, although differences between two sets of experimental values cannot be accounted for. A complete correlation of the limits and of the slow reaction in different vessels requires changes in the values of the rate constants of the surface reactions of chlorine atoms and molecules, or changes in the reaction scheme. It is not possible without further experimental work to decide which are the best changes.