Development of a Pilot Scale Reactor for the Selective Oxidation of Ammonia to Nitrogen and Water

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. Unfortunately, these catalysts convert ammonia (NH₃) to NO and NO₂ (collectively referred to as NO_X), which are more hazardous than ammonia.

In this SBIR Phase II project, TDA Research (TDA) and Hamilton Sundstrand Space Systems International (HSSSI) are optimizing the design of the oxidation reactor. We have identified catalyst formulations that convert ammonia to nitrogen and water with high selectivity under representative reaction concentrations. We also carried out kinetic analyses of the most active catalysts so that we can express the reaction rate as a function of reactant pressure and temperature. We then used these rate expressions to design and construct a pilot scale oxidation reactor that operates at the reduced pressures expected in the VPCAR system. The results of the pilot scale testing will be used to finalize the design of the oxidation reactor on the full-scale unit.