Sorbents for Removal of Cyanide Species from Gas Streams
DOD-Air Force Phase I Contract No. FA8651-04-C-0268
This SBIR Phase I addressed the identification of new sorbent materials for the removal of cyanides and other high vapor pressure chemical agents from air. Phase I consisted of the preparation, screening, and initial optimization of materials drawn from selected compositional/structural categories. Key Phase I results were as follows: 1) A number of materials, drawn from three structural/compositional categories, were evaluated for uptake of HCN from dry air. A number of candidates displayed promising breakthrough times, C*t values, and capacities. The best materials gave complete removal (to <1 ppm) of HCN at ambient temperature, with no products of oxidation, decomposition, etc. being observed. 2) Regenerability was demonstrated with several candidates. Regeneration produced predominantly HCN, with low levels of nitrogen oxides in some instances. 3) Modifications of lead candidates arising from coarse screening were synthesized and evaluated under the same conditions, resulting in the identification of variants possessing performance superior to that of a C2A1 mask carbon. 4) Preferred candidates were subjected to cold (0 °C) and humidity (100%). Lower temperature resulted in enhanced uptake of HCN, while humidity resulted in suppression of HCN adsorption. 5) Improved tolerance to humidity was obtained by employing a pretreatment procedure. 6) Preferred candidates were incorporated into pellets and tested. One candidate displayed the same performance as in powdered form while the other gave considerably lower performance. 7) Best performance obtained under ambient conditions at a residence time of 0.3s was breakthrough time >7.5 hours, C*t > 400,000 mg•min/m3, and sorbent capacity > 14 wt%.
The technology, being developed, would enable replacement of existing cyanide filters with more compact adsorbers which can be easily regenerated on-site. The technology would find use in the military sector for protection of personnel from certain agents and would also find use in homeland defense applications for protection of personnel at civilian installations and for protection of American homes.
Other applications would include protection of emergency first-responders and of workers from cyanide emanating from certain sources. Additional applications in gas purification and environmental control can be expected: Materials identified during Phase I possess capacity for HCN and, possibly, for H2S and organosulfides. Thus, use in desulfurization of gas streams can be envisioned. Additionally, use in liquid fuels desulfurization is a potential application.