The work reported in this thesis is concerned with the study, by a gravimetric method, of the reaction of carbon dioxide with a high-purity carbon derived from the polymer cellulose triacetate. Particular attention has been paid to the influence on reaction kinetics of hydrogen, both residual in the carbon and as a gaseous impurity. The factors which affect the rate of reaction of carbons with oxidising gases are discussed and an account of the accepted theory of kinetics and mechanisms of the carbon-carbon dioxide reaction is given, together with some features of the reaction not accounted for by this theory. Heat treatment of cellulose triacetate carbons in the range 1273K-1773K was found to produce a maximum in the rate of reaction with carbon dioxide. The observed maximum has been accounted for in terms of two competing processes, elimination of hydrogen resulting in enhanced reactivity and the annealing of active sites resulting in a decrease in reactivity. A number of additional experiments have been performed in an attempt to separate the effects of different factors on the kinetics; these include a study of the effects of isothermal annealing of carbons and chemical pre-treatments with hydrogen and chlorine. A compensation effect, i.e. a linear relationship between all measured values of activation energy E and log A, the pre-exponential factor in the Arrhenius equation has been observed. A review of the literature relevant to the compensation effect is given and some examples of its application, particularly to gas-carbon reactions, are discussed. A theoretical treatment relating particularly to the carbon-carbon dioxide reaction has been developed and used as a basis for interpretation of the experimental results.
|Date of Award||1975|