Role of alkyl peroxy radicals in hydrocarbon oxidation between 300-750K
Alkylperoxy radicals are important intermediates formed during the oxidation of organic compounds in combustion and atmospheric environments. Because of their ubiquity, accurate kinetic, mechanistic and spectroscopic information are necessary in order to model combustion and atmospheric processes. A Molecular Modulation Kinetic Spectrometer (MMKS) and gas chromatographic analysis were used to confirm and extend available peroxy radical data. Bromine initiated photo-oxidation of isobutane, at 303K, provided a source of t-butylperoxy radicals. Subsequent radical reactions were inferred from the observed product distribution. Evidence of the importance of the t-butylperoxy radical reaction with hydrogen bromide, and of a terminating channel for the radical's self-reaction, were obtained. Bromine initiated photo-oxidation of hydrocarbons may provide a useful source of peroxy radicals difficult to generate by alternative methods. Azoethane and azomethane photo-oxidation provided sources of ethylperoxy and methylperoxy radicals respectively. MMKS experiments enabled kinetic and spectroscopic parameters to be extracted for the former radical and its self-reaction between 303-457K, and for the latter at 303K. In the case of the ethylperoxy radical, complementary end-product studies enabled mechanistic information to be extracted. End-product studies provided evidence of two decomposition channels for a β-alkylperoxyalkyl radical, generated in the hydrogen chloride catalysed decomposition of di-t-butyl peroxide at 393K. Thermochemically favourable O-heterocycle formation predominated over the alternative decomposition channel to olefin. A chemical kinetic model to describe the gas-phase oxidation of propane at `intermediate' temperatures was developed. The latter was used to investigate the enhancement of commercially valuable products by additive gas `addition'. Of the two additives tested, carbon monoxide and hydrogen peroxide, the former appeared more promising in modifying, favourably, the chemistry of the system.