CARBON DIOXIDE CONTROL: SOLID PHASE AMINES

Primary and secondary alkanolamines react with dissolved CO2 in a two step sequence, forming first a zwitterion (1), which then transfers a proton to an un-ionized amine, forming the corresponding carbamate (2). The reaction of tertiary amines with CO2 proceeds by the formation of a protonated amine and a bicarbonate anion (3).

The chemical structures of three common alkanolamine CO2 sorbents, monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA) are given below:

The Solid Phase Amine CO2 sorbents work by analogous reactions between airborne CO2, water vapor, and the amine bearing functional groups of the polymer. Early work in this area investigated the used of anion exchange resins bearing amine functional groups. Currently more specialized polymers are used. The thermally regenerable CO2 removal system for the Shuttle Extended Duration Orbiter (EDO) uses Amberlite XAD-7 polystyrene-co-divinylbenzene beads coated with polyethyleneimine. Under heat and/or vacuum, the chemisorption reactions are reversed and the polymeric sorbent is regenerated.

REFERENCES:

Boehm, A.M., and Ouellette, F.A., Chamber Testing of CO2 Removal Systems Using Solid Amines, SAE Technical Paper Series No. 951488, presented at 25th International Conference on Environmental Systems, San Diego, CA, July 10-13, 1995.

Graf, J.C., and Spexarth, G.R., The Impact of Trace Contaminants on the Shuttle Orbiter Regenerative CO2 Removal System, SAE Technical Paper Series No. 951540, presented at 25th International Conference on Environmental Systems, San Diego, CA, July 10-13, 1995.

Graf, J.C., Dall-Bauman, L.A., and Jeng, F.F., Characterization of an Improved Solid Amine for a Regenerative CO2 Removal System, SAE Technical Paper Series No. 932292, presented at 23rd International Conference on Environmental Sysems, Colorado Springs, July 1993.

Jeng, F.F., Williamson, R.G., Ouellette, F.A., Edeen, M.A., and Lin, C.H., Adsorbent Testing and Mathematical Modeling of a Solid Amine Regenerative CO2 & H2O Removal System, SAE Technical Paper Series No. 911364, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991.

Johnson, S.R., and Garrard, G.G., Regenerative Trace Contaminant Control: New Test Method for Effects on Solid Amine, SAE Technical Paper Series No. 921349, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Nalette, T.A., Blaser, R.W., Coleman, W., et al., Development of an Advanced Solid Amine Humidity and CO2 Control System for Potential Space Station Extravehicular Activity Application, SAE Technical Paper Series No. 881062, presented at 18th Intersociety Conference on Environmental Systems, July 1988.

Otsubo, K, Tanemura, T., Nitta, K., Oguchi, M., Nakabayasi, N., Kimura, S., and Kuroda, H., Evaluation of Solid Amine CO2 Adsorbing Characteristics, SAE Technical Paper Series No. 921334, presented 22nd International Conference on Environmental Systems, Seattle, WA, July 13-16, 1992.

Copyright © 1996, James E. Atwater