Hydrogen cyanide adsorption

Graph 14 Relation between hydrogen cyanide adsorption on clothing and temperature in a delousing chamber with circulating air system (schematic).123... 

The cement mortar samples, in contrast to the lime mortar samples, exhibit a higher cyanide concentration by a factor of two. The higher iron content of the cement mortar samples may be the reason for this, since the cyanide content increases proportionally to the iron content (see the last column of Table 19). In addition, hydrogen cyanide adsorption was certainly favored by the higher inner surface area of the cement mortar as compared to lime mortar. 

Graph 14 Relation between hydrogen cyanide adsorption on... 

Anstice, P.J.C., and Alder, J.F., The effect of sulphur dioxide exposure under controlled environmental conditions on the challenge performance of copper- and chromate-impregnated active carbon against hydrogen cyanide, Adsorpt. Sci. Technol., 15(7), 531-540 (1997). 

Adsorption of cyanide anions can be affected by adsorption of cations. In the solutions containing nonspecifically adsorbed anions, the nature of alkali metal cations was found to influence the measured value of the electrode capacitance at potentials more negative than —0.6 V (versus standard hydrogen electrode (SHE)). At < —l.OV adsorption of CN ions was enhanced in the presence of Li+ and Na+ cations, and inhibited in the presence of Cs+ ions [81]. A combined SERS and density-functional theory has been applied to study cyanide adsorption at Au electrode [82]. The authors have arrived at the conclusion that the polarity of Au—CN bonds falls between that of Au—Cl and Au—Br surface bonds. The binding strength for three different gold surfaces decreased in the order ... 

If hydrogen cyanide (HCN), the reactive compound in Zyklon B, were only bound to the walls by adsorption (adhesion),313 there would not be any detectable residues today anymore, due to the volatility of hydrogen cyanide (boiling point 25.7°C) all the hydrogen cyanide involved would long since have evaporated. 

A The adsorption of hydrogen cyanide on solid surfaces decreases with rising temperature, according to Langmuire (see Graph 3).352... 

Closer inspection reveals that this somewhat superficial and largely self-evident evaluation is by no means exhaustive, and concrete experimental studies on adsorptive reactors expose both additional pitfalls and benefits that are often specific for a particular reaction system and decisive for the success or otherwise of adsorptive reactor concepts. Before illustrating this point with the help of four examples with which the author is personally acquainted - the Claus reaction, the direct hydrogen cyanide synthesis from ammonia and carbon monoxide and, to a lesser extent, the water-gas shift reaction and the Deacon process - it is worthwhile briefly reviewing other reaction systems for which the potential of adsorptive reactors has been examined (Tab. 7.2). 

The second reaction used to illustrate various features of adsorptive reactors is the direct synthesis of hydrogen cyanide from ammonia and carbon monoxide ... 

Fig. 7.11. Catalytic activities and deactivation in the adsorptive direct synthesis of hydrogen cyanide due to unfavorable redox conditions.

Tretyakov and Filimonov (219) describe a coordinative interaction between benzonitrile and aprotic sites on magnesium oxide, and Zecchina et al. (256) came to the same conclusion for the adsorption of propionitrile, benzonitrile, and acrylonitrile on a chromia-silica catalyst. Chapman and Hair (257) observed an additional chemical transformation of benzonitrile on alumina-containing surfaces, which they describe as an oxidation. Knozinger and Krietenbrink (255) have shown that acetonitrile is hydrolyzed on alumina by basic OH- ions, even at temperatures below 100°C. This reaction may be described as shown in Scheme 2. The surface acetamide (V) is subsequently transformed into a surface acetate at higher temperatures. Additional reactions on alumina are a dissociative adsorption and polymerizations (255) analogous to those observed for hydrogen cyanide by Low and Ramamurthy (258), and a dissociative adsorption. Thus, acetonitrile must certainly be refused as a probe molecule and specific poison. 

SAFETY PROFILE A highly corrosive irritant to the eyes, skin, and mucous membranes. Mildly toxic by inhalation, Explosive reaction with alcohols + hydrogen cyanide, potassium permanganate, sodium (with aqueous HCl), tetraselenium tetranitride. Ignition on contact with aluminum-titanium alloys (with HCl vapor), fluorine, hexa-lithium disilicide, metal acetylides or carbides (e.g., cesium acetylide, rubidium ace-tylide). Violent reaction with 1,1-difluoro-ethylene. Vigorous reaction with aluminum, chlorine + dinitroanilines (evolves gas). Potentially dangerous reaction with sulfuric acid releases HCl gas. Adsorption of the acid onto silicon dioxide is exothermic. See also HYDROGEN CHLORIDE (AEROSOL) and HYDROCHLORIC ACID. 

This chapter provides a comprehensive summary of surface science involved in the application of activated carbon for air cleaning from inorganic gases such as hydrogen sulfide, sulfur dioxide, nitric dioxide, hydrogen cyanide, and from VOCs. The emphasis is placed on the role of activated carbons surfaces, either unmodified or modified in the processes of adsorption and catalytic oxidation-reduction of these pollutants. 

Alder, J.F., Fielden, P.R., and Smith, S.J. (1988). The adsorption of hydrogen cyanide by impregnated activated carbon cloth. Part I studies on cobalt and nickel acetatates as impregnants for hydrogen cyanide removal. Carbon, 25, 701-11. 

Safavi, A., Maleki, N. and Shahbaazi, H.R. (2004) Indirect determination of cyanide ion and hydrogen cyanide by adsorptive stripping voltammetry at a mercury electrode. Anal Chim Acta, 503 (2), 213-221. 

Hydrogen cyanide, acrylonitrile, and acetonitrile adsorption on NaX and HY have been observed (20). Stronger interactions occur on the zeolite than on silica since the frequency shifts are greater. The nitriles interact with the cations in NaX and with the hydroxyl groups and dehydroxylated sites on HY zeolite. Acetonitrile, acetonitrile-d3, and benzonitrile have been adsorbed on various cation and HY zeolites (4). For acetonitrile, the C=N bond frequency is higher than that of the liquid phase and varies with cation, indicating that the adsorption of molecules is associated with the cation. A linear correlation is found between the cation electrostatic field and the CN bond frequency. 

Glass and metal containers are not recommended for collection of HCN samples this is due to adsorption of the compound onto the walls of such containers. Good results are achieved when HCN is adsorbed onto porous materials, from which it can be desorbed with a solvent or by using thermal methods. For HCN detection in biological samples (e.g., in blood), a HS analysis method may be applied. Hydrogen cyanide detectability with a thermionic nitrogen detector may reach 1 pg in a sample. 

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