Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

INTRODUCTION28 1Gas andalrI------**--*. I,Inner coneWaterFig. 1. Separated flame burner.IOuter conereaction the rate of reaction of intermediate can be reduced drastically by physicalmeans-reduction of the pressure or temperature, or both-or by chemicalquenching (addition of an inhibitor), it may prove possible to extract quantitiesof intermediate sufficient for characterization. Smithells and Ingle’ suggested in1892 that if the inner and outer cones of a Bunsen flame were separated out, thenit would be possible to determine the intermediate substances formed in the innercone by analysis of the gases in the outer cone. The separated flame technique hasbeen perfected by Gaydon2. 3, who produced “struck-back‘’ hydrocarbon flames ina burner consisting of two concentric water-cooled steel tubes (Fig. 1). The rapidchilling quenches the interconal gases, and Gaydon was able to show by chemicalanalysis of the collected products that they contain large amounts of both formaldehydeand peroxidic substances, together with some acid.Direct “on-line” analytical techniques may also be used. Typical of these studiesis that made by Bradley et aL4 of stabilised cool flames in the oxidation of acetaldehydeand propionaldehyde. A fine quartz probe was attached to an A.E.I. MS 10mass spectrometer, and could be moved through the cool flame. In this waycomposition profiles were obtained for reactant aldehyde and oxygen and also forcarbon dioxide, carbon monoxide, formaldehyde, methane and methanol.‘Reactionchamber