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Title: The kinetics and mechanism of oxidation and halogenation reactions in the gas phase
Author: Knox, John Henderson
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1963
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Abstract:
THE WORK described in this thesis has been carried out over the last ten years at the Chemistry Department of the University of Edinburgh. The work is in the field of gas phase reaction kinetics. Two main aspects of the subject have been studied - gas phase halogenation and gas phase oxidation. These are connected experimentally by the extensive use of gas chromatography as the analytical tool. The author's early studies in both fields were amongst the first in which gas chromatography was applied to reaction kinetics. The work on competitive halogenation reactions (that is the halogenation of mixtures) has resulted in the accurate determination for the first time of forty rate constants and Arrhenius parameters of reactions of the general type: X + RH = XH + R (X = F, CI, Br) and an attempt has been made to give a theoretical interpretation of the A factors of these reactions using a simple model. The results should be of particular value as a check on any more sophisticated theoretical calculations which may be made in the future. They may also form the basis of a valuable method for the accurate determination of bond strengths in hydrocarbons. The work on oxidation developed from a study of the cool flame oxidation of propane carried out for a Ph.D. degree. By the use of gas chromatography for the analysis of the products from the earliest stages of the oxidation of propane between 318 and 475°C and of ethane between 320 and 386°C it has been established that at least 80$ of the alkane initially removed appears in the products as an olefin with the same number of carbon atoms. The most probable reactions are (with propane for example). X may be H0₂ but there are thermochemical arguments against this view and the nature of X is still a matter for speculation. Below 400°C the minor products are apparently formed by decomposition of the RO₂ radical but above 400°c pyrolysis reactions of the alkyl radicals become important. By oxidising mixtures of alkanes it has been established that the radical, or radical mixture, X has a reactivity between that of Cl and CH₃O and is therefore unlikely to be HO₂ which is expected to be much more selective than CH₃0 or Cl. Kinetic studies of the oxidation of propane and ethane at about 320°C have shown that surface reactions are kinetically important during the induction period and that the autocatalysis of the oxidations is assisted by the formation of olefins which probably yield branching intermediates more readily than the parent alkanes. The overall mechanism of alkane and olefin oxidation, taking account of the above observations, is discussed in the most recent papers of the series on the oxidation of ethane and ethylene. The thesis concludes with a brief section on the author's work on various aspects of gas chromatography.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.743477  DOI: Not available
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