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The Trace Contaminant Control System (TCCS) removes most hazardous contaminants from the space station atmosphere using a carbon bed, but some must be destroyed in a high temperature catalytic oxidizer. While the oxidizer is protected from catalyst poisons by the carbon bed, if contaminant loads are greater than anticipated, the catalyst may be exposed to a variety of poisons. Thus, we studied the effect of halocarbons, sulfides and nitrogen compounds on the catalytic activity and the products produced. We found that even if poisoning occurs, the catalyst will recover, and will not produce toxic partial oxidation products.

The objective of this SBIR Phase I project was to identify catalysts that are active for ammonia conversion and are also selective for nitrogen and water. Our approach to the problem was centered on the development of a bifunctional catalyst, which could separate adsorbed oxygen and nitrogen atoms, thereby reducing NOx formation. The results of our project demonstrated that our approach was successful. We prepared a group of catalysts and tested them for ammonia oxidation activity. We identified a catalyst formulation that was active for ammonia oxidation at low temperatures in the presence of water and produced very little NOx. We used kinetic data to generate a rate model that predicts 100% ammonia conversion in the full-scale system at a temperature 50°C lower than the current design.

Incineration is a promising method for converting biomass and human waste into CO2 and H2O during extended planetary exploration. However, incineration produces small amounts of NOX and SO2 in the effluent, which must be removed. TDA Research has developed a safe and effective process to remove NOX and SO2 from waste incinerator product gas streams. In our process, NO is catalytically oxidized to NO2, using a low temperature oxidation catalyst developed at TDA. Wet scrubbers then remove the NO2, with most of the NO2 converted into an aqueous solution that can be used as a plant nutrient. A packed bed containing a basic sorbent, also developed at TDA, removes SO2 from the effluent. As part of an SBIR Phase II project, TDA designed and constructed a pilot scale effluent cleaning system, which will be used with the incinerator at NASA Ames Research Center.

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.

As manned spacecraft travel farther from Earth, the cost of delivering the payloads to space increases dramatically. For example the cost of delivering a payload to low Earth orbit currently is about $10,000/lb. On the other hand the cost of delivering a payload to Mars may be up to 40 times greater and therefore missions to deep space place a strong emphasis on reducing launch weight and eliminating resupply requirements. The Vapor Phase Catalytic Ammonia Removal (VPCAR) system, which is being developed to purify water, is an example of this focus. In addition to having a lower launch weight than the Water Recycle System (WRS) currently used on the International Space Station, it also has no resupply requirements. A key step in the VPCAR system is the catalytic oxidation of ammonia and volatile hydrocarbons to benign compounds such as carbon dioxide, water, and nitrogen. Currently platinum-based commercial oxidation catalysts are being used for these reactions.

Paradoxically, trace contaminant control systems that suffer unexpected upsets and malfunctions can release hazardous gaseous contaminants into a spacecraft cabin atmosphere causing potentially serious toxicological problems. Trace contaminant control systems designed for spaceflight typically employ a combination of adsorption beds and catalytic oxidation reactors to remove organic and inorganic trace contaminants from the cabin atmosphere. Interestingly, the same design features and attributes which make these systems so effective for purifying a spacecraft’s atmosphere can also make them susceptible to system upsets. Cabin conditions can be contributing causes of phenomena such as adsorbent “rollover” and catalyst poisoning can alter a system’s performance and in some instances release contamination into the cabin. Evidence of these phenomena has been observed both in flight and during ground-based tests.

The possibility and consequences of a fire on board a spacecraft and the subsequent effects of the resultant toxic gases and smoke on the crew, equipment and mission is an ever-present hazard for the National Aeronautics and Space Administration (NASA). The necessity to remove these contaminants in the presence of high levels of humidity and carbon dioxide has prompted the development of a new prototype atmospheric filter (smoke eater) that can scrub acid gases, basic gases, and carbon monoxide from a spacecraft atmosphere in a post-fire event to a concentration below one half the Spacecraft Maximum Allowable Concentration (SMAC) levels. TDA Research, Inc. (TDA) is developing an advanced smoke eater to remove combustion byproducts. The material makeup of the smoke eater will also be applicable to spacecraft evacuation masks and the shipboard atmospheric revitalization system.