The low-temperature combustion of n-pentane

Abstract

The reaction of n -pentane with oxygen has been investigated in the temperature range 257°–280°C at initial pressures which cover both the slow-oxidation and cool-flame regions. The oxidation has been followed by the direct analysis of reaction mixtures, together with the changes in pressure and temperature. The analytical results show that acetone is the major primary organic product of the slow reaction, and that it accounts for about 60% of the pentane consumed in the early stages of the reaction. In contrast, cool-flame formation is accompanied by the production of relatively large amounts of olefins, while the importance of acetone as a product is markedly decreased in comparison with the slow-oxidation region. These results are discussed in terms of a reaction mechanism that includes isomerization reactions of the alkylperoxy radical, and it is concluded that acetone must be formed through the formation of a hydroperoxyalkylperoxy radical rather than a decomposition reaction of a hydroperoxyalkyl radical. It is shown qualitatively that the relative importance of the various products obtained is in accord with the suggested mechanism for the over-all reaction. Simultaneous records of the pressure and temperature changes during the appearance of a cool flame show that the temperature rise is preceded by an abrupt, almost isothermal pressure rise. With n -pentane as fuel, therefore, it is suggested that branching reactions play an important role in cool-flame formation, and that the cool-flame limit is not governed solely by thermal factors. * Present address: Department of Chemical Engineering, University of Salford.