Browsing by Author "Espinosa, Nicolas J."
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Item Pressure-Swing Adsorption of Trace Contaminants Using Carbon Sorbent Monoliths(50th International Conference on Environmental Systems, 7/12/2021) W�jtowicz, Marek A.; Cosgrove, Joseph E.; Serio, Michael A.; Carlson, Andrew E.; Hostetler, John M.; Espinosa, Nicolas J.; Chullen, CindaThe 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.Item The Effect of Carbonization Conditions on the Performance of Ammonia Sorbents Derived from Polyether Ether Ketone (PEEK)(2020 International Conference on Environmental Systems, 2020-07-31) Wójtowicz, Marek A.; Cosgrove, Joseph E.; Serio, Michael A.; Carlson, Andrew E.; Espinosa, Nicolas J.; Hostetler, John M.; Chullen, CindaThe current trace-contaminant (TC) control technology involves a packed bed of acid-impregnated granular charcoal, which is difficult to regenerate. The use of predominantly microporous monolithic carbon produced by carbonization of polyether ether ketone (PEEK) was previously proposed. In this paper, the effect of carbonization conditions on sorbent performance is reported. Although the target application will involve carbon monoliths (e.g., honeycomb structures), granular sorbents were used in this study so that their performance could be compared with the currently used reference carbon (available only in the granular form). The PEEK polymer was carbonized at temperatures 700–1,050 °C, which was followed by carbon activation to a burn-off of 20%. Activation was carried out in a flow of air at 325 °C. The carbon pore structure was characterized using nitrogen adsorption isotherm data. The PEEK-derived sorbents were tested for ammonia sorption in a laboratory packed-bed system. Sorbent regeneration was evaluated by exposing ammonia-saturated sorbents to high vacuum at room temperature for 6 hours, and subsequently re-testing their ammonia-sorption performance. All the PEEK-derived carbons were found to be highly microporous, and their surface area increased with the increasing carbonization temperature. In contrast, the initial equilibrium ammonia sorption capacity was found to decrease as the carbonization temperature increased. All sorbents showed a significant loss of sorption capacity after the first sorption-regeneration cycle, but no performance loss was observed in subsequent cycles. It was found that the presence of oxygen complexes on the carbon surface greatly enhanced ammonia sorption on carbon. In addition, PEEK-derived sorbents were shown to exhibit favorable sorption-regeneration characteristics, as compared with the acid-treated activated carbon.