The development of energy efficient, reduced-weight, regenerable adsorption systems for removal of environmental contaminants, such as CO₂ in cabin air and chemical warfare agents (CWA) in battlefields is an area of continuing interest to NASA and the Department of Defense. Precision Combustion, Inc. (PCI) has designed and developed an adsorption technology using a bed consisting of metal meshes coated with a zeolite or molecular sieve sorbent. The metal mesh elements, trademarked and patented as Microlith^® by PCI,¹ can effectively adsorb a number of contaminants of interest and have the potential for direct electrical heating. The ability to directly, resistively heat the Microlith^® substrate offers the potential for relatively rapid periodic regenerations instead of the longer thermal cycles typical of packed bed adsorbers. As a result, a regenerable adsorber using zeolite/adsorbent coated on Microlith^® can reduce the system weight and volume compared to conventional packed bed configurations.

Another application of this Microlith^®-based adsorption technology is for efficient hydrogen sulfide (H₂S) removal from the reactor exhaust stream in fuel reforming-fuel cell systems. PCI developed zinc oxide (ZnO) coating process on the Microlith^® with a high loading, and demonstrated that ZnO powder deposited on Microlith^® is capable to reach its full capacity with high bed utilization. Our experiment showed that a fresh ZnO-coated Microlith^® system can achieve up to ~33 wt.% H₂S sorption capacity (i.e., 0.33 gm of H₂S uptake per gram of ZnO washcoat). This is a significant improvement from a typical H₂S sorption capacity of 10-20 wt.% obtained using commercial ZnO extrudates.

Here, the design, development, and optimization of the Microlith^® adsorption technology will be presented. We will discuss the results obtained from various sorption tests, such as using CO₂, water, and trace organic contaminants for NASA cabin air cleaning/ECLSS application as well as using freon and cyanide for chem-bio warfare defense application. Additionally, the development of this technology for sulfur (e.g., H₂S) removal in fuel cell application will be addressed.

References

¹ U.S. Patent #5,051,241, September 24, 1991.