| dc.description.abstract | The oxidation of ethane like that of other aliphatic hydrocarbons,
apart from methane, can proceed by two distinct mechanisms. One
operates above and the other below ca. 4OO°C. Analytical work on ethane
oxidation has shown that in the later stages of the high temperature
oxidation ethylene is the major product whereas in the low temperature
region oxygenated compounds are the major products. Through the
development of gas chromatography it is now possible to analyse the
products in the early stages of reaction. The aim of the present work
was to apply this technique to the analysis of the products in the
initial stages of ethane oxidation and to determine the relative
importance of ethylene and of oxygenated compounds in the early stages.
At the same time analysis of the products formed throughout the course
of the whole reaction would provide valuable analytical data for the
elucidation of the oxidation mechanism.
The oxidations were carried out in a static system between
318-386°C using mixtures of different composition. The relative yields
of the initial products did not change appreciably when the ethanesoxygen
ratio was altered by a factor of six. However the initial yields
changed with temperature, and at the higher temperature ethylene was the
main initial product whereas at the lower temperatures formaldehyde
predominated. A value is given for the difference in activation energy
between the reactions producing ethylene and formaldehyde. The kinetics
of the oxidation at 362°C were investigated and the variation of the
acceleration constant with oxygen, ethane, "inert" gas, and ethylene
oxide pressure was determined.
Ethylene oxidations were carried out at 318 and 362°C with mixtures
of different composition and the products from "both the early and
later stages of reaction were examined. The oxidation of acetaldehyde
at 362°C was also investigated and a mechanism for the oxidation has
been put forward.
In the latter part of this thesis the experimental results were
discussed. It appears that the degradation of the ethane molecule
is a stepwise process involving the intermediate formation of ethylene
and formaldehyde. It was concluded that the ethylene was formed by
oxygen abstracting hydrogen directly from ethyl radicals, and that the
formaldehyde was formed by isomerisation and decomposition of ethyl
peroxy radicals. In the later stages of reaction the ethylene and
formaldehyde are themselves oxidised, ethylene mainly to formaldehyde,
and formaldehyde to the final oxidation products carbon monoxide,
carbon dioxide, and water. A mechanism involving the intermediate
formation of a cyclic peroxide has been proposed for the oxidation of
ethylene to formaldehyde. As no experiments were carried out on the
oxidation of formaldehyde the scheme proposed by Lewis and von Elbe
for formaldehyde oxidation has been adopted. A reaction scheme,
which can explain the formation of the products of ethane oxidation
and which embodies the basic schemes of ethylene and formaldehyde
oxidations, has been put forward for the oxidation of ethane. | en |
