Pressure-Swing Adsorption of Trace Contaminants Using Carbon Sorbent Monoliths

The current trace-contaminant (TC) control technology involves a packed bed of acid-impregnated granular charcoal, which is difficult to regenerate, and this sorbent is at present considered a consumable. The preferred implementation of TC control is pressure-swing adsorption (PSA) using a regenerable sorbent, where TCs are adsorbed on the sorbent in adsorption steps, which are followed by sorbent regeneration by exposure to space vacuum (desorption steps). The adsorption-desorption steps are repeated cyclically in parallel beds, which ensures continuous TC removal. A similar approach has been used in carbon-dioxide control, with a cycle time of a few minutes, and it is desirable to adopt the same time scale in TC control. In addition, the use of sorbent monoliths is advantageous due to the low pressure drop and low fan-power requirement. In this paper, results are presented on the development of vacuum-regenerable TC sorbents for use in the Exploration Portable Life Support System (xPLSS). The sorbents were derived from 3D-printed polymer monoliths (e.g., honeycomb structures), which were then carbonized and oxidized in order to develop porosity, and also to enhance the TC-sorption capacity. Results are presented on the following aspects of carbon-sorbent development: (1) monolith fabrication; and (2) sorbent-performance in terms of TC-sorption and vacuum-regeneration. The use of predominantly microporous carbon monoliths is associated with the following benefits: (a) high trace contaminant sorption capacity; (b) low pressure drop; (c) rapid vacuum (pressure-swing) desorption due to thin monolith walls and low pressure drop; (d) high mechanical strength [2,3] and resistance to attrition; (e) good thermal management (high thermal conductivity and low adsorption/desorption thermal effects associated with physisorption); (f) good resistance to dusty environments; (g) non-toxic, non-flammable sorbents made of high-purity carbon; and (h) the flexibility to 3D-print/fabricate sorbent monoliths with optimized channel geometries that ensure uniform flow distribution throughout the sorbent.