High Capacity RCA Sorbents for Increased Cycle Times

NASA is interested in improving the method to control CO2 and water in the Exploration Extravehicular Mobility Unit (xEMU) to meet the ambitious objectives of the Artemis program, which includes human presence on the surface of the Moon and Mars. The technology that is planned to be used is the RCA which utilizes two beds that are alternately used to remove CO2 and H2O and then are regenerated by exposure to space vacuum. The RCA utilizes an amine-based sorbent (SA9T), and although it has good reversible CO2 uptakes, higher capacities are desired to maintain lower CO2 levels and to reduce power consumption and O2 losses. In addition, this sorbent emits low levels of ammonia which must be removed from the suit using a separate technology. In the SBIR Phase I project, Reaction Systems successfully developed new sorbents that outperformed SA9T and reduced ammonia emissions. Tests carried out on selected sorbents and SA9T over a wide range of CO2 partial pressures indicated that a new sorbent had cycle times that were over a factor of two greater than for SA9T at the higher CO2 pressures, which results in a 44% reduction in number of half cycles in the Standard EVA. Ammonia emissions are also over an order of magnitude lower for the new sorbent compared to SA9T. In the Phase II project, Reaction Systems will continue developing the new sorbent to a TRL that will allow it to be incorporated into new space suits for advanced missions. Tasks include optimizing the composition and preparation, performing lifetime measurements, evaluating the effect that contaminants could have and finally testing at full scale. The full scale tests will be carried out in a custom CO2 control module similar in design to the RCA but will have more accessibility to the sorbent beds. In addition, the module will be installed in Reaction Systems full scale ventilation loop that can simulate pressures, flow rates, and humidity levels encountered in the suit during an EVA. NASA is interested in improving methods to control CO2 and water in the xEMU to meet the Artemis program objectives, which includes human presence on the Moon and Mars. The RCA will be used in these missions, which uses two beds that alternately remove CO2 and H2O and then are regenerated by space vacuum. Although the current SA9T sorbent has good reversible CO2 uptakes, higher capacities are desired. The sorbent also emits ammonia which must be removed using a separate technology.   In the SBIR Ph I project, Reaction Systems developed new sorbents that outperformed SA9T and reduced ammonia emissions. Tests carried out on selected sorbents and SA9T over a wide range of CO2 partial pressures indicated that a new sorbent had cycle times over a factor of two greater than SA9T at the higher CO2 pressures, resulting in a 44% reduction in number of half cycles in the Standard EVA. Ammonia emissions are also over an order of magnitude lower. In the Phase II project, Reaction Systems will continue developing the new sorbent to a TRL that will allow it to be incorporated into new space suits. Optimize the sorbent composition and preparation to determine if its performance can be improved over the already very promising results obtained in Phase I. Select the candidate sorbents prepared using optimized methods that have improved performance over the results obtained to date. Demonstrate the new sorbent will meet the lifetime requirement. Show that hazardous levels of compounds such as ammonia are not emitted by the sorbent. Demonstrate that the sorbent is not affected by the presence of potential contaminants that could be present in the suit including CO, furan, formaldehyde and methyl mercaptan. Show that larger quantities of sorbent can be prepared so it can be tested at full scale under realistic operating conditions in Reaction Systems’ ventilation loop. Verify performance of the optimized sorbent at full scale in a custom fabricated CO2 module that is installed in Reaction Systems’ full scale ventilation loop over multiple simulated EVA missions and show that it will maintain acceptable CO2 partial pressures in the system over a wide range of metabolic rates.

In addition to its use in the space suit, this technology could be used for CO2 control in a space craft cabin.  The current technology, the CDRA, uses pressure and temperature swing adsorption cycle to remove CO2 and the thermal cycling causes the molecular sieve sorbent to break down into dust particles, which clog filters or end up in the cabin air.  A sorbent that does not require a temperature increase for regeneration could reduce power consumption and eliminate dust. The technology could also be used for control of CO2 emissions from power plants. The concentration of CO2 in the atmosphere has increased from 280 ppm to over 400 ppm over the last 50 years primarily due to CO2 emissions from fossil fuel combustion. An effective method could be used to remove CO2 from the effluent and compress it into a concentrated liquid for sequestration, storage, or use.

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