CARBON DIOXIDE CONTROL: SILVER OXIDE

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.

REFERENCES:

Colombo, G.V., and Mills, E.S., Regenerative Separation of Carbon Dioxide via Metallic Oxides, Chem. Eng. Prog. Symp. Ser., 62 (63), 89, 1966.

Colombo, G.V., Study of Regenerable CO2 Sorbents for Extravehicular Activity, AIAA Paper No. 73-1339, presented at AIAA Crew Equipment Systems Conference, Las Vegas, November 7-9, 1973.

Hart, J.M., Borghese, J.B., Chang, C.H., and Cusick, R.J., Portable Life Support System Regenerative Carbon Dioxide and Water Vapor Removal by Metal Oxide Absorbents Preprototype Hardware Development and Testing, SAE Technical Paper Series No. 921299, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Hart, J.M., Chang, C.H., Cusick, R.J., and Stonesifer, G.T., Comparison of Metal Oxide Absorbents for Regenerative Carbon Dioxide and Water Vapor Removal for Advanced Portable Life Support Systems, SAE Technical Paper Series No. 911343, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Nacheff, M.S., Chang, C.H., Colombo, G.V., and Cusick, R.J., Metal Oxide Regenerable Carbon Dioxide Removal System for an Advanced Portable Life Support System, SAE Technical Paper Series No. 891595, presented 19th Intersociety Conference on Environmental Systems, San Diego, July 24-26, 1989.

Ouellette, F.A., Winkler, H.E., and Smith, G.S., The Extended Duration Orbiter Regenerable CO2 Removal System, SAE Technical Paper Series No. 901292, presented at 20th International Conference on Environmental Systems, Williamsburg, VA, July 9- 12, 1990.

Copyright © 1996, James E. Atwater