METHODS OF WATER PRODUCTION

Aboard the Shuttle Orbiter water is generated using a hydrogen-oxygen fuel cell which produces both electricity and very pure water. Water can also be produced by reduction of CO2 by hydrogen over a suitable catalyst. The Sabatier and Bosch processes are two Carbon Dioxide Reduction Systems which have been studied extensively. The Sabatier method has been selected for ISSA. These three systems are presented below:

Production of Water by the Hydrogen Fuel Cell

Production of Water by the Sabatier Reaction

Current technology for the reduction of carbon dioxide to produce water aboard the International Space Station Alpha (ISSA) is embodied in the Sabatier Reactor.

For each mole of carbon dioxide reduced, this system produces two moles of water and one mole of methane. The methane is vented to space. For this reason, only half of the hydrogen consumed in this reaction can be recovered by electrolysis. The Sabatier reaction utilizes an alumina supported ruthenium catalyst and, in comparison to the Bosch reaction, has the advantage of greater thermodynamic favorability and higher reaction rates.

The primary disadvantage of the Sabatier process is that twice as much hydrogen is consumed as can be recovered by the electrolylsis of the produced water. This results in a substantial perturbation in the material balance for the production of oxygen from carbon dioxide. Using the Sabatier process either the hydrogen imbalance must be compensated for by resupply, or not all of the carbon dioxide can be processed.

REFERENCES

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Boyda, R.B., Lee, M.G., and Grigger, D.J., Sabatier Carbon Dioxide Reduction System for Space Station Freedom, SAE Technical Paper Series No. 921189, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Forsythe, R.K., Verostko, C.E., Cusick, R.J., and Blakely, R.L., A Study of Sabatier Reactor Operation, in Zero "G", SAE Technical Paper Series No. 840936, presented 14th Intersociety Conference on Environmental Systems, 1984.

Kashiwai, T., Matsumoto, H., Kamishima, N., Hatano, S., Nitta, K., and Ashida, A., Study of Oxygen Recovery Stystem using Reduction of Carbon Dioxide, SAE Technical Paper Series No. 951558, presented at 25th International Conference on Environmental Systems, San Diego, CA, July 10-13, 1995.

Lunde, P.J. Modeling, Simulation, and Operation of a Sabatier Reactor, Ind. Eng. Chem., Process Des. Dev., 13(3), 226-232, 1974.

Lunde, P.J. and Kester, F.L. Carbon Dioxide Methanation on a Ruthenium Catalyst, Ind. Eng. Chem., Process Des. Dev., 13(1):27-33, 1974.

Noyes, G.P., Carbon Dioxide Reduction Processes for Spacecraft ECLSS: A Comprehensive Review, SAE Technical Paper Series No., 881042, presented at 18th Intersociety Conference on Environmental Systems, San Francisco, CA, July 1988.

Noyes, G.P., and Cusick, R.J., An Advanced Carbon Reactor Subsystem for Carbon Dioxide Reduction, SAE Technical Paper Series No. 860995, presented 16th Intersociety Conference on Environmental Systems, San Diego, CA, July 14-16, 1986.

Otsuji, K., Hanabusa, O., Sawada, T., Satoh, S., and Minemoto, M., An Experimental Study of the Bosch and the Sabatier CO2 Reduction Processes, SAE Technical Paper Series No. 871517, presented 17th Intersociety Conference on Environmental Systems, Seattle, WA, July 1987.

Sabatier, P., and Senderens, J.B., Comptes Rendus Acad. Sci., 134, 689, 1902.

Samsonov, N.M., Kurmazenko, E.A., Gavrilov, L.I., Farafonov, N.S., Dokunin, I.V., Markin, S.V., Pavlova, T.N., Naumov, V.A., and Jakimenko, A.O., Results of Engineering Development of the Carbon Dioxide Reduction Assembly for a Space Station Integrated Life Support System, SAE Technical Paper Series No. 951557, presented at 25th International Conference on Environmental Systems, San Diego, CA, July 10-13, 1995.

Samsonov, N.M. and et al, A Complex of Systems for Oxygen Recovery Aboard a Manned Space Station, SAE Technical Paper Series No. 932275, Society of Automotive Engineers, Warrendale, PA, 1993.

Secord, T.C. and Bonura, M.S., Operational Ninety-Day Manned Test of Regenerative Life Support Systems, SAE Technical Paper Series No. 901257, Society of Automotive Engineers, Warrendale, PA, 1990.

Son, C.H., and Barker, R.S., Comparative Test Data Assessment and Simplified Math Modelling for Sabatier CO2 Reduction Subsystem, SAE Technical Paper Series No. 921228, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Strumpf, H.J., Chin, C.Y., Lester, G.R., and Homeyer, S.T., Sabatier Carbon Dioxide Reduction System for Long-Duration Manned Space Application, SAE Technical Paper Series No. 911541, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Production of Water by the Bosch Reaction

The Bosch reaction produces only water and elemental carbon, allowing all of the hydrogen consumed to be recovered by electrolysis. This makes closure of the oxygen - carbon dioxide - water - oxygen loop possible.

The net reaction produces heat (2.3x10^3 J/g of carbon produced at 650C), and is the result of two successive reactions, one fast,

and a second rate controlling slow reaction.

The primary problems associated with the Bosch reactor are slow reaction rates and the generation of particulate carbon which fouls the catalyst surface and which plugs the catalyst bed. As shown below, the thermodynamics are also somewhat less favorable than those for the Sabatier Reaction.

Catalysts are critical to the Bosch process, due to the intrinsically slow kinetics. Iron, cobalt, and nickel catalyze the Bosch reaction. Minor additions of ruthenium significantly improve kinetics. The most commonly used catalyst is "steel wool" due to its relatively high exposed active surface. Significant surface reactions include the formation of carbide intermediates as well as oxide layers which poison catalytic activity. Typical reaction temperatures are in the range of 450 to 600C. Even at these relatively high temperatures single pass reduction efficiencies are typically below 10%, hence practical reactor designs require recycle operation. A more significant disadvantage is the inactivation of catalyst surfaces and the plugging of the reactor caused by a build-up of particulate carbon. While greater efficiencies in terms of material balances aboard spacecraft are possible using the Bosch reaction, much further development work will be required before the system is competitive with the Sabatier process from a practical standpoint.

Generalized Bosch Reactor Schematic.

REFERENCES

Arlow, M., and Traxler, G., CO2 Processing and O2 Reclamation System Selection Process for Future European Space Programmes, SAE Technical Paper Series No. 891548, Society of Automotive Engineers,Warrendale, PA, 1989.

Bunnel, C.T., Boyda, R.B., and Lee, M.G., Optimization of the Bosch CO2 Reduction Process, SAE Technical Paper Series No. 911451, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Minemoto, M., Etoh, T., Ida, H., Hatano, S., Kamishima, N., and Kita, Y., Study of Air Revitalization System for Space Station, SAE Technical Paper Series No. 891576, Society of Automotive Engineers,Warrendale, PA, 1989.

Noyes, G.P., Carbon Dioxide Reduction Processes for Spacecraft ECLSS: A Comprehensive Review, SAE Technical Paper Series No. 881042, Society of Automotive Engineers, Warrendale, PA, 1988.

Otsuji, K., Hanabusa, O., Sawada, T., Satoh, S., and Minemoto, M., An Experimental Study of the Bosch and the Sabatier CO2 Reduction Processes, SAE Technical Paper Series No. 871517, presented 17th Intersociety Conference on Environmental Systems, Seattle, WA, July 1987.

Sophonpanich, C., Manning, M.P., and Reid, R.C., "Utilization of Ruthenium and Ruthenium-Iron Alloys as Bosch Process Catalysts, SAE Technical Paper Series No. 820875, Society of Automotive Engineers,Warrendale, PA, 1982.

Wagner, R.C., et al., Maturity of the Bosch CO Reduction Technology for Space Station Application, SAE Technical Paper Series No. 880995, Society of Automotive Engineers,Warrendale, PA, 1988.

Copyright © 1996, James E. Atwater