The control of trace contaminants on the International Space Station (ISS) is carried out by a combination of activated carbon absorption and catalytic oxidation. The carbon bed absorbs most hydrocarbons, chloro and chlorofluorocarbons (CHCs and CFCs) while the catalytic oxidizer removes compounds such as methane, ethylene, ethane, and carbon monoxide that cannot be absorbed by the charcoal bed. Unfortunately, the Space Station catalyst of 0.5% palladium on alumina does not effectively oxidize CHCs and CFCs, and in fact is powerfully poisoned by them (Wright et al. 1996). Thus, even though the charcoal bed has little affinity for CFCs and CHCs, it must be sized to completely remove these compounds in order to protect the crew and prevent poisoning of the catalytic oxidizer.
TDA Research Inc. (TDA), under contract to NASA-JSC, has designed, built, and tested an all-catalytic trace contaminant control system (TCCS) to be used in Phase III of the Early Human Testing Program. The TCCS does not have a charcoal bed; it consists of a blower, a high flow moderate temperature catalyst bed, a low flow high temperature catalyst bed, a high efficiency regenerative heat exchanger, and an acid gas removal bed. The system has only one moving part (the blower), effectively controls hydrocarbons including methane, CFCs and CHCs, and effectively oxidizes ammonia (NH3) to N2 and water without generating NOx. The catalysts are not poisoned by CFCs or CHCs, and oxidation products are acid gases rather than chlorine or fluorine gas.