Disposal of Activated Carbon from Chemical Agent Disposal Facilities (2009) / Chapter Skim
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4 Interactions of Chemical Agents with Activated Carbon
4 Interactions of Chemical Agents with Activated Carbon
Pages 33-44
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From page 33... ...
In contrast to physical adsorption, chapter explains some adsorption fundamentals and chemical adsorption involves the formation of chemithe known reactions of agents on activated carbon. cal bonds between adsorbate molecules and functional These are prerequisites for understanding the chemi- groups on the adsorbent surfaces, interactions that cal fates and levels of agent loadings on carbon.
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From page 34... ...
. length of an adsorption wave front, which is the adsor- These functional groups cause the activated carbate fluid-phase concentration profile, passing through bon surfaces to exhibit some polarity, which plays a a bed of carbon in a fixed-bed adsorber is characterized specific role in attracting chemical agents containing as the active mass transfer zone (Figure 4-1)
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From page 35... ...
In 2007, several carbon samples from the Anniston Chemical Agent Disposal Facility (ANCDF) were analyzed for residual nerve agents GB and VX at government and contractor surety laborato TABLE 4-1 Agent Loadings on Cocoanut Activated Carbon Relative Humidity Maximum Loading Agent (%)
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From page 36... ...
labof the hydrolysis product is attributed to the low oratory indicated the presence of volatile VX impurivolatility of VX in the ambient air stream. (The vapor ties, hydrolysis by-products, and degradation products TABLE 4-2 Analytical Results of HVAC and PFS Carbon Samples Collected from ANCDF in January 2007 HVAC Bank 1 HVAC Bank 2 PFS Carbon New Carbon Headspace vapor analysis GB < 1.5 × 10–5 mg/m3 Same as Bank 1 Not analyzed Not analyzed VX < 5.1 × 10–7 mg/m3 Thermal desorption followed GB < 1.0 × 10–4 mg/m3 Same as Bank 1 Not analyzed Not analyzed by GC/MS/FPDa VX < 1.0 × 10–4 mg/m3 Solid-phase NMR, MAS 31P or GB < 1,500 ppm No phosphorus compound Relatively large Relatively small MAS 1H VX < 1,500 ppm was detected at a detection water peaks water peaks IMPA = 13 wt percentb limit of 1,500 ppm EMPA = Nondetectb Solvent extraction followed by GBc Not analyzed Not analyzed Not analyzed GC/MS VX < 20 ppb Remaining filter capacityd 12 percent 100 percent Not analyzed 100 percent (control)
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From page 37... ...
Therefore, it can be concluded that very little of the GB Reactions low-volatility VX was transported by the heating, ventilation, and air conditioning system and adsorbed on Figure 4-3 shows 31P MAS NMR spectra from a the carbon during the processing of the VX munitions recent study. A reaction-time profile is revealed for at Anniston Chemical Agent Disposal Facility. 10 weight percent GB on wet coconut shell carbon containing 13 weight percent water at room temFinding 4-4. Chemical agent has not been observed perature.
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From page 38... ...
Army Edgewood bitmap Chemical and Biological Center, and David Friday, Houston Advanced Research Center, "Adsorbent analysis of Anniston Chemical Agent Disposal Facility MDB Bank 1 and Bank 2 filter samples," Presentation to the committee, July 23, 2008. IMPA, isopropyl methylphosphonic acid.
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From page 39... ...
SOURCE: Leonard Buettner, John Mahle, George Wagner, Tara Sewell, and Nicole Fletcher, all of the U.S. Army Edgewood bitmap Chemical and Biological Center, and David Friday, Houston Advanced Research Center, "Adsorbent analysis of Anniston Chemical Agent Disposal Facility MDB Bank 1 and Bank 2 filter samples," Presentation to the committee, July 23, 2008.
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From page 40... ...
Recommendation 4-2. The Chemical Materials Note that 50°C would not be a practical temperature for HVAC Agency should determine the length of time required air at a chemical agent disposal facility.
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From page 41... ...
It is believed that if sufficient HCl reactions continue to completion or trace amounts of is present during solvent extraction and subsequent agent remain on the carbon samples. To determine GC/MS analysis, some of the major sulfonium ions ppb levels of detection of residual agents on carbon, such as CH-TG may decompose and react with chloride other analytical approaches, such as extraction of ion to form HD.
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From page 42... ...
tion isotherm would be needed to correlate loadings with gas-phase concentrations at agent loadings near 20 ppb. Third, a pure-component adsorption isotherm METHODS FOR DETERMINING CHEMICAL would not even apply to the real system, which would AGENT LOADING ON ACTIVATED CARBON contain coadsorbed amounts of other components, such The shipping of agent-exposed carbon to off-site as water and degradation products.
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From page 43... ...
Indirect methods for GB obtained by Southwest Research Institute from involving the removal of the adsorbates from the carbon new unused carbon samples loaded with isopropyl and analyzing them separately could be investigated: methylphosphonic acid and hydrofluoric acid is the best These include chromatography, solid-liquid extraction, indication of the extent of re-formation for the current or thermal/vacuum desorption (LeVan and Carta, 2007)
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From page 44... ...
2008. Ad sorbent Analysis of Anniston Chemical Agent Disposal Facility MDB ing, and a strongly adsorbed solvent (the "displacer")
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