Hydrogen cyanide removal

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. 

Cmde HCl recovered from production of chlorofluorocarbons by hydrofluorination of chlorocarbons contains unique impurities which can be removed by processes described in References 53—62. CICN—CI2 mixtures generated by reaction of hydrogen cyanide and CI2 during the synthesis of (CICN) can be removed from the by-product HCl, by fractional distillation and recycling (see Cyanides) (59). 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

The waste gas remaining after removal of ammonia and recovery of hydrogen cyanide contains enough hydrogen and carbon monoxide that it is flammable and has enough heat value to make it a valuable fuel. It is usually used to displace other fuel ia boilers. 

After removal of the unreacted ammonia and recovery of hydrogen cyanide, the waste gas is essentially all hydrogen suitable for other chemical use. The advantages of the BMA process are the high ammonia and natural gas yields and the usehil hydrogen waste gas, but the high investment and maintenance for the converter is a decided disadvantage. 

A German process produces a high (99%) sodium cyanide assay by absorbing the gases from a BMA-type hydrogen cyanide reactor direcdy in sodium hydroxide solution (56). The resulting sodium cyanide solution is heated in a crystallizer to remove water, and form sodium cyanide crystals. 

Production of cyanohydrins is accompHshed through the base-cataly2ed combination of hydrogen cyanide and the carbonyl compound in a solvent, usually the cyanohydrin itself (17). The reaction is carried out at high dilution of the feeds, at 10—15°C, and pH 6.5—7.5. The product is continuously removed from the reaction 2one, cooled to push the equilibrium toward cyanohydrin formation, and then stabili2ed with mineral acid. Purification is usually effected by distillation. 

Direct hydrogen cyanide (HCN) gas in a fuel oil gasification plant to a combustion unit to prevent its release. 4. Consider using purge gases from the synthesis process to fire the reformer strip condensates to reduce ammonia and methanol. 5. Use carbon dioxide removal processes that do not release toxics to the environment. When monoethanolamine (MEA) or other processes, such as hot potassium carbonate, are used in carbon dioxide removal, proper operation and maintenance procedures should be followed to minimize releases to the environment. 

Normally, a layer of FeS scale, produced in the first reaction, protects the interior of the pipe or vessel. However, in the second reaction, cyanide removes the FeS protective scale exposing more free iron to react with H2S and releasing more hydrogen. Without protection, this cycle continues until blistering, cracking, and eventual total corrosion of equipment occurs. 

An approach to isobacteriochlorins1 ln-e makes use of Pd(II) or metal-free bilatrienes 1 as starting materials. Cyclization of the corresponding bilatriene derivatives is induced by base in the presence of palladium(II) or zinc(II) which exercise a template effect. Zinc can be readily removed from the cyclized macrotetracycles by acid whereas palladium forms very stable complexes which cannot be demetalated. Prior to the cyclization reaction, an enamine is formed by elimination of hydrogen cyanide from the 1-position. The nucleophilic enamine then attacks the electrophilic 19-position with loss of the leaving group present at the terminal pyrrole ring. 

The top product from column (F) is fed to a stripping column (G) from which hydrogen cyanide is removed overhead. 

The asymmetric synthesis achieved when the base is an optically active one is proof that the base is present in a transition state with the carbonyl and not just an agent for removal of protons from hydrogen cyanide. It has further been shown that asymmetric synthesis is still achieved even if the only optically active molecules present are quaternary ammonium compounds, i.e., positive ions without any protons to donate. This probably means that the important thing is to have some positive ion near the carbonyl oxygen, an actual covalent... 

DIAMOX A process for removing hydrogen sulfide and hydrogen cyanide from coke oven gas by absorption in aqueous ammonia. Developed by Mitsubishi Chemical Industries and Mitsubishi Kakoki Kaisha and operated in Japan. 

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