(308f) Reaction of C2H4 Under Lower Temperature Fischer-Tropsch Conditions on a TiO2 Supported Cobalt Catalyst with Co-Feeding of H2 and Syngas

Reaction of C₂H₄ under
Lower Temperature Fischer-Tropsch Conditions on a TiO₂
Supported Cobalt Catalyst with Co-feeding of H₂ and Syngas

Xiaojun Lu*, Diane
Hildebrandt, Yusheng Zhang, and Xinying Liu

Material and
Process Synthesis; College of Science, Engineering, and Technology, University
of South Africa

Co-feeding of C₂H₄ to the
Fischer-Tropsch reaction system has been studied some
years back to investigate the effect of secondary reactions of the olefins in
the Fischer-Tropsch reaction. Some important
phenomena were observed and the conclusions were not consistent due to the
complexity of the Fischer-Tropsch reaction.
Researchers often found that it is very difficult to investigate certain
aspects independently in such complex reaction system. This work tries to investigate
one aspect at a time in the complex system. Three groups of experiments were
designed. The first group of experiments was designed to investigate the reaction
of C₂H₄ only on the supported Co catalyst. The purpose was
to investigate the possible secondary reactions of C₂H₄
without other reactants. The second experimental design was to add H₂
into the reaction system when keeping the feed of C₂H₄.
This was to investigate the reactions of C₂H₄ with the
presence of H₂. The C₂H₄ to H₂
ratio was adjusted in a wide range so that excessive amount of both of these
two reactants could be achieved. The third experimental design was to co-feed
synthesis gas (H₂/CO/N₂) when keeping the feed of C₂H₄.
The amount of syngas fed into the reaction system was controlled to ensure that
the main feed was still C₂H₄. This is different from the
feed ratio chose by other researcher in the past as the amounts of C₂H₄
co-fed by them was always far less than the syngas feed.

The results we have obtained in these
experiments are of big interests. C₂H₄ was found not to
react under the conditions applied when no other feed was introduced into the
reactor; while it reacts quickly when H₂ was co-fed.  The reaction temperature, when H₂
was co-fed, could be as low as 100^oC and only products of C₁
to C₅ were found. These results suggest that C₂H₄
can undertake several reaction pathways to form different products. Fischer-Tropsch synthesis reaction was found to occur, with the
presence of C₂H₄, when the operating temperature was at
140^oC, which is much lower than the temperature (higher than 180^oC
with Co as the catalyst) required for normal Fischer-Tropsch
synthesis. The reaction temperature required for reactions to happen changed to
around 190^oC when the feed of C₂H₄ was
stopped. The presence of C₂H₄ can promote the Fischer-Tropsch synthesis by lowering the reaction temperature.
This has not been reported in any existing literature. The products
distribution is quite different when both C₂H₄ and syngas
were fed and this leads to the understanding of the reaction mechanisms for the
Fischer-Tropsch Synthesis.

Keywords: Fischer-Tropsch Synthesis, C₂H₄ reaction, Reaction
Mechanism