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Abstract

The gas phase oxidation of n-butane has been studied at sub-atmospheric pressures in the temperature range 280 - 420°C. The effect of the variation of initial temperature and initial pressure on the mechanism of oxidation has been assessed from observations of the kinetic changes and the variation of the nature and distribution of products.

Section 1 examines the most recent theories on the mechanism of oxidation of hydrocarbons and particular attention is focussed on the primary chain-propagation reactions. The effect of molecular structure on the mechanism of oxidation is considered in detail and it is shown that high molecular weight hydrocarbons oxidise by different routes from low molecular weight hydrocarbons. The morphological phenomenon of cool flames is considered in the light of the foregoing variation in mechanism of oxidation.

Section 2 describes the experimental techniques used in the present study. A standard static vacuum system was employed in which pressure changes were monitored by means of a strain-gauge pressure transducer and temperature changes by micro-thermocouples. Reaction products were identified and estimated by gas chromatography.

The kinetic and analytical results are presented in Section 3. Changes in physical parameters are related to the initial temperature and pressure. It is shown that at temperatures below ca. 330°C cool flames propagate from the walls of the reactor, whereas above this temperature they propagate from the centre of the reactor. Details of the variation of the concentration of reaction products with time are given and the percentage yields of these products, during the early stages of reaction, are related to the initial reaction conditions.

The results are discussed in Section 4 in which it is concluded that the major chain-propagation sequence involves α- and β-hydroperoxybutyl radicals at low initial temperatures. Further oxidation of β-hydroperoxybutyl radicals gives rise to acetaldehyde and acetone in relatively large yields, whereas the β-scission decomposition of α-hydroperoxybutyl radicals, which occurs predominantly at the reactor walls, is responsible for the formation of but-1-ene and but-2-ene. At higher initial temperatures, however, the chain-propagation cycle involves principally α-hydroperoxybutyl radicals which undergo homogeneous β-scission decomposition reactions to form the major products but-1-ene and but-2-ene. Furthermore, at high initial temperatures the further oxidation of β-hydroperoxybutyl radicals is of minor importance.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > Q Science (General) Q Science > QD Chemistry T Technology > TP Chemical technology
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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