Silver oxide reacts with carbon dioxide in the presence of water to yield silver carbonate.
The chemisorption reaction can be reversed at elevated temperature.
These two reactions form the basis for the thermally regenerable CO2 removal system which is currently in the final stages of development for use in the Portable Life Support Subsystem (PLSS) housed in the Extravehicular Mobility Unit (EMU) worn by astronauts during EVA. In this application, expended sorbent will be removed from the PLSS and regenerated in the cabin of the Shuttle Orbiter or within the International Space Station Alpha.
Several metal oxides show potential for use as reversible CO2 chemisorbents. Table I presents the densities, CO2 capacities, and specific regeneration energies for various alkali metal, alkaline earth, and transition metal oxides.
Inspection of the above indicates that in addition to silver oxide, magnesium oxide and zinc oxide are also viable candidates for use as CO2 sorbents in life support systems. To date, however, neither of these oxides has been shown to load to theoretical capacity following thermal regeneration. A composite chemisorbent composed of a mixture of silver oxide and zinc oxide has shown promise.
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