Destructive sorbents

NANOSCALE OXIDES AS DESTRUCTIVE SORBENTS FOR HALOGENATED HYDROCARBONS... 

Keywords nanocrystalline oxides aerogels destructive sorbents halocarbons MgO TiCh titanium oxydifluoride carbon coating... 

In the current publication we shall discuss the specific features of the reactions of nanoscale MgO and Ti02 with chlorofluorocarbons and the effect of carbon on the performance of the destructive sorbents. 

Nanocrystalline oxides have exceptionally high reactivity with respect to halocarbons. First of all, the temperature of their reaction with halocarbons is much lower than observed for bulk analogs. It is thus possible to carry out destructive adsorption reactions at fairly low temperatures. This is especially important for the development of effective destructive sorbents for neutralization of toxic compounds at mild temperatures. We have also demonstrated that nanocrystalline oxides can be used as precursors for the synthesis of novel halogenated nanocrystalline materials. 

Of special interest are composite materials consisting of carbon-coated nanocrystalline oxides. Such permeable carbon coating not only provides high stability of the destructive sorbents under atmospheric conditions, but in some cases shown in this publication considerably increases their reactivity. Elucidation of the mechanism of this interesting phenomenon will require further research. 

Stengl, V. Bakardjieva, S. Marikova, M. Subrt, J. Oplustil, F. Olsanska, M. Aerogel nanoscale aluminum oxides as a destructive sorbent for mustard gas. Ceramics-Silikaty 2003, 47 (4), 175-180. 

The sin >lcst flue gas desulfurisation technology is furnace injection, where a dry sorbent is injected into the upper part of the furnace to react with the SO2 in the flue gas. The finely grained sorbent is distributed quickly and evenly over the entire cross section in the upper part of the furnace in a location where the teiiq>erature is in the range of 750-12 50 C. Commercially available and cheap limestone (CaC03) or hydrated lime (Ca(OH)j) is used as sorbent. The sorbent reacts with SO2 and O2 to form CaS04. Below 750 C the reaction rate is too low. At temperatures over 1250 C the surface of the sorbent will be sintered, and the structure of the pores will be destructed, reducing the active surface area, The major part of S02-rcmoval takes place within 1 to 2 seconds. 

The effect of SO2 gas has been also examined in relation with the behavior of ceria as sorbent/catalyst for the removal/destruction of this pollutant [187]. An O K edge XANES study complemented XPS data (see above) showing that contact with SO2 produces sulfates which thermally decompose in the 390-670 K range, and that the presence of anion vacancies favors the formation of SO3 instead of SO4. The promotion of ceria with copper was shown to enhance the SO2 removal activity in all cases (reduced/oxidized state). 

Both at the analytical and preparative stages of TLC, effective visualization or detection is crucial to obtain pure compounds, and poor detection may result in low recovery of product from the sorbent. Detection is either nondestructive, following which the compounds may be recovered from the sorbent (e.g., ultraviolet [UV] detection), or destructive, by which the compounds are contaminated by the detection reagent and are unrecoverable from the sorbent... 

No universal method exists for the disposal of carcinogenic compounds such as MBOCA (HSDB 1991). Rroduct residues and sorbent media containing MBOCA have been packaged in epoxy-lined drums and disposed of at ERA-approved sites (OHM/TADS 1985). Destruction via chemical reaction is another method that has been used to dispose of small amounts of MBOCA (HSDB 1991). This method, in which MBOCA is oxidized with potassium permanganate, is generally used for laboratory wastes containing small amounts of MBOCA. 

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