| ABSTRACT |
For the purpose of reducing the amount of carbon dioxide discharged from
power plants, we developed a carbon dioxide decomposition technology which
used activated iron oxides. Activated iron oxides are formed by deoxidizing
iron oxides over hydrogen. They have a spinel structure and are strong
reducing agents. When carbon dioxide gas is ventilated and allowed to react
with them, oxygen atoms in molecules of carbon dioxide become incorporated
into the oxygen deficient parts of the iron oxides. The carbon atoms in
the carbon dioxide molecules are fixed to the surface of the iron oxides.
The fixed carbon atoms are highly reactive and converted into methane by
hydrogen. These reactions proceed in the range of 300 to 400. We carried
out studies on the iron oxides concerning properties, configuration and
temperature to elucidate their optimum working conditions. The gas containing
20% carbon dioxide (nitrogen balanced) by volume was completely decomposed
by the iron oxides at 350 in a laboratory test. The concentration of
the gas was equal to that of the exhaust gas of LNG power plants. Next,
we developed a technology to utilize the carbon atoms that fixed on the
iron oxides. We also optimized methanation using the iron oxides as well
as carbon dioxide decomposition. The fixed carbon atoms were converted
almost completely into methane by hydrogenation at 350. A system to effectively
utilize carbon was also investigated. It was concluded that repeatedly
alternating between carbon dioxide decomposition reaction and the methanation
reaction while circulating a gas mixture of unreacted hydrogen and produced
methane could generate methane at high concentrations of 80% and greater
from the carbon dioxide of the exhaust gas.
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