Adsorption System Based on Microlith® Technology and Its Progress in Fuel Cell, Spacecraft, and Chem-bio Warfare Defense Applications

The development of energy efficient, reduced-weight, regenerable adsorption systems for removal of environmental contaminants, such as CO2 in spacecraft cabin air, chemical/biological warfare agents (CWA), and toxic industrial chemicals (TICs) is an area of continuing interest to NASA and Department of Defense, respectively. Precision Combustion, Inc. (PCI) has designed and developed a sorption 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, can be coated with various zeolite/sorbent materials and can effectively adsorb a number of contaminants of interest. The Microlith elements also 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/sorbent coated on Microlith can reduce the system weight and volume compared to the conventional packed bed configurations. Another application of this Microlith-based sorption technology is for efficient hydrogen sulfide (H2S) removal from the reactor exhaust stream in a fuel reforming-fuel cell system. PCI developed zinc oxide (ZnO) coating process on the Microlith substrates with a high loading, and demonstrated that ZnO powder deposited on Microlith is capable to reach its nearly full capacity with high bed utilization. Our test showed that a fresh ZnO-coated Microlith system can achieve a H2S sorption capacity of up to ~33 wt.% (i.e., 0.33 gram of H2S uptake per gram of ZnO). This is a significant improvement from a typical H2S sorption capacity of 10-20 wt.% obtained using commercial ZnO pellets/extrudates. This paper describes the design, development, and optimization of the Microlith sorption technology for each of the above applications. We will also discuss the results obtained from various sorption tests, such as using CO2, water, and trace chemical contaminants for NASA cabin air cleaning/Environmental Control and Life Support System (ECLSS) application as well as using TICs for chem-bio warfare defense application. Additionally, the development of this technology for sulfur (e.g., H2S) removal in reforming/fuel cell application will be addressed.