An Investigation of the Reactions of Carbon Dioxide, Carbon Monoxide, Methane, Hydrogen, and Water over Iron, Iron Carbides, and Iron Oxides

Future long-duration manned space flights will require regenerative life-support systems. The Bosch process is one of several alternative regenerative life-support systems presently being evaluated by the National Aeronautics and Space Administration. 2H2 + CO2 = 2H20 + C Prototype Bosch units to reduce metabolic CO2 to carbon have been constructed and operated successfully with large recycle ratios. The water obtained per pass was, however, far less than that predicted from equilibrium calculations. An investigation was performed which determined this limitation to be due to oxide formation; the catalyst condition being controlled by PH2 /PH20 and/or PCO /PCO2 ratios. Carbide formation was shown to be slow, having little effect on efficient Bosch operation. Conclusions were drawn and the optimal recycle configuration and operating conditions were specified. In addition, a metallurgical investigation of morphological changes occurring during reaction was performed. Results indicate two distinct morphologies developed depending on temperature during the oxidation-reduction sequence. One is typical of a process controlled by solid state diffusion; the other by diffusion (gas)/interfacial reaction control. The effects of carbon fiber formation were shown along with the examination of individual carbon fibers.