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In closed environments such as space stations, it is necessary to eliminate CO2 produced by the metabolisms of crew members, for their life support, and to regenerate the air by supplying O2 to make up for the deficiency. If humans are to be in space only a short time, it is in general advantageous to adsorb CO2 with lithium hydroxide, and to supply O2 from tanks. But when the stay in space is long, it is essential to establish a highly reliable and energy-efficient system to recover CO2 in high concentrations and regenerate O2 from this recovered CO2 Fig. 1 shows the system presently conceived, which is roughly divided into the following processes: A process that removes and concentrates CO2 from the air; a CO2 reduction process that separates carbon from CO2 and obtains water; and a water electrolysis process that decomposes water electrically and recovers O2.

One of the important feature in the Environment Control and Life Support System required to support long duration mission at the Space Station is an oxygen supply for the human metabolism. The recovery of oxygen from the concentrated carbon dioxide through chemical methods will give significant advantage to the Space Station by reducing the supply requirement of the consumables, such as oxygen bottles. Oxygen recovery plants using the Bosch reaction and the Sabatier reaction are experimentally developed and tested. The Bosch reaction has been considered to produce carbon and water directly from carbon dioxide by the hydrogenization process. But it seems to proceed through two steps with carbon monoxide as the intermediate product. Also the total production rate is relatively low and the carbon deposited is less solid. The Sabatier reaction requires two steps to achieve carbon and water, with methane as the intermediate product.