The cool flame combustion of hydrocarbons I—Cyclohexane

Abstract

The combustion of cyclohexaneoxygen mixtures between 230° and 350°C has been studied using a static system and different reaction vessel surfaces. The oxidation was followed by measuring pressure and temperature changes and by analysis. The cool flame limits were determined both for a 1:1 mixture (temperature/total pressure limits) and at constant temperature (total pressure/composition limits). Cool flames were most easily obtained with an uncoated vessel. Packing this vessel or coating the unpacked vessel with potassium chloride or lead oxide inhibited cool flame formation. Outside the cool flame limits there was a zone of slow combustion, except with a potassium chloride coated vessel. At around 250°C the main organic products in the initial stages of the combustion were cyclohexylhydroperoxide, lower aldehydes and acetone, whereas at above 300°C, or after the passage of a cool flame, they were olefins (particularly cyclohexene). By preforming C 6 H 11 OOH in the uncoated vessel it was shown that its concentration governed the length of the induction period before a cool flame. Possible elementary processes occurring in the system, in particular reactions of cyclohexylperoxy radicals and the general mechanism of cool flame formation and quenching are discussed.