Hydrogen cyanide process

Hydrogen Cyanide Process. This process, one of two used for the industrial production of malonates, is based on hydrogen cyanide [74-90-8] and chloroacetic acid [79-11-8]. The intermediate cyanoacetic acid [372-09-8] is esterified in the presence of a large excess of mineral acid and alcohol. 

Manufacture. The predominant manufacturing processes arc the hydrogen cyanide process and carbon monoxide process. 

Economic Aspects. Dimethyl and dieihyl malonaies are produced via the carbon monoxide process at Hiils (Germany i. Juzen (Japan), and Korean Fertilizers iS. Korea) they arc produced via ihe hydrogen cyanide process ai L.ouza (Switzerland) and Tateyama (Japan). Total capacity is estimated to be aboul 12,000 t/yr. Furthermore, producers are also reported in the People s Republic of China mid in Romania. 

Manufacture. Cyanoacciic acid and cyanoacetaies are industrially piodiicetl by the same route as the malonates using a modified hydrogen cyanide process, starting from a sodium chloroaeeiale solution v la a sodium cyanoacetale solution. 

Fig. 10.6. The hydrogen cyanide process. (Reprinted from Ind. Eng. Chem., 51, no. 10, 1235, 1959 Copyright 1959 by the American Chemical Society and reprinted by permission of the copyright owner.)...

The scope of the review is therefore essentially related to the two industrially used processes, the nitric acid synthesis and the Andrussow hydrogen cyanide process. Both these processes have been in large-scale use for several decades but basic understanding of the relevant physics, chemistry, and engineering is still incomplete. 

In 1937 I.G.-Farbenindustrie patented a method for the preparation of polyaminoacetonitriles, corresponding acids and their derivatives . The process, known as the hydrogen cyanide process, utilizes sodium cyanide in acid solution. The cyanomethylation takes place by treatment of the amine with formaldehyde and hydrogen cyanide. In the case of ethylenediamine reaction (2) takes place ethylenediaminetetraacetonitrile (1) is isolated to ensure that the resulting tetrasodium salt, after hydrolysis, is not contaminated by by-products. This synthesis can be performed as a continuous process and is also used to obtain other complexones. The use of hydrogen cyanide and of an acid medium gives rise to corrosion and safety problems. 

Compounds with active hydrogen add to the carbonyl group of acetone, often followed by the condensation of another molecule of the addend or loss of water. Hydrogen sulfide forms hexamethyl-l,3,5-trithiane probably through the transitory intermediate thioacetone which readily trimerizes. Hydrogen cyanide forms acetone cyanohydrin [75-86-5] (CH2)2C(OH)CN, which is further processed to methacrylates. Ammonia and hydrogen cyanide give (CH2)2C(NH2)CN [19355-69-2] ix.orn. 6<55i the widely used polymerization initiator, azobisisobutyronitrile [78-67-1] is made (4). 

Addition of Hydrogen Cyanide. At one time the predominant commercial route to acrylonitrile was the addition of hydrogen cyanide to acetylene. The reaction can be conducted in the Hquid (CuCl catalyst) or gas phase (basic catalyst at 400 to 600°C). This route has been completely replaced by the ammoxidation of propylene (SOHIO process) (see Acrylonitrile). 

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). 

In the final step the dinitrile is formed from the anti-Markovrukov addition of hydrogen cyanide [74-90-8] at atmospheric pressure and 30—150°C in the hquid phase with a Ni(0) catalyst. The principal by-product, 2-methylglutaronitrile/4j5 j5 4-ti2-, when hydrogenated using a process similar to that for the conversion of ADN to hexamethylenediamine, produces 2-meth5i-l,5-pentanediamine or 2-methylpentamethylenediamine [15520-10-2] (MPMD), which is also used in the manufacture of polyamides as a comonomer. 

Other Processes. Other methods iaclude reaction of lime, (CaO) with hydrogen cyanide (24) and reaction of limestone, (CaCO ), with ammonia (25). 

Some hydrogen cyanide is formed whenever hydrocarbons (qv) are burned in an environment that is deficient in air. Small concentrations are also found in the stratosphere and atmosphere. It is not clear whether most of this hydrogen cyanide comes from biological sources or from high temperature, low oxygen processes such as coke production, but no accumulation has been shown (3). 

In early times hydrogen cyanide was manufactured from beet sugar residues and recovered from coke oven gas. These methods were replaced by the Castner process in which coke and ammonia were combined with Hquid sodium to form sodium cyanide. If hydrogen cyanide was desired, the sodium cyanide was contacted with an acid, usually sulfuric acid, to Hberate hydrogen cyanide gas, which was condensed for use. This process has since been supplanted by large-scale plants, using catalytic synthesis from ammonia and hydrocarbons. 

Two synthesis processes account for most of the hydrogen cyanide produced. The dominant commercial process for direct production of hydrogen cyanide is based on classic technology (23—32) involving the reaction of ammonia, methane (natural gas), and air over a platinum catalyst it is called the Andmssow process. The second process involves the reaction of ammonia and methane and is called the BlausAure-Methan-Ammoniak (BMA) process (30,33—35) it was developed by Degussa in Germany. Hydrogen cyanide is also obtained as a by-product in the manufacture of acrylonitrile (qv) by the ammoxidation of propjiene (Sohio process). 

The Shawinigan process uses a unique reactor system (36,37). The heart of the process is the fluohmic furnace, a fluidized bed of carbon heated to 1350—1650°C by passing an electric current between carbon electrodes immersed in the bed. Feed gas is ammonia and a hydrocarbon, preferably propane. High yield and high concentration of hydrogen cyanide in the off gas are achieved. This process is presently practiced in Spain, AustraUa, and South Africa. 

In the BMA process, methane (natural gas) and ammonia are reacted without air being present (44). The reaction is carried out in tubes that are heated externally to supply the endothermic heat of reaction very similar to a reformer. Yield from ammonia and methane is above 90%. The off-gas from the converter contains more than 20 mol % hydrogen cyanide, about 70 mol % hydrogen, 3 mol % ammonia, 1 mol % methane, and about 1 mol % nitrogen from ammonia decomposition. 

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. 

The fluohmic process is a third process for manufacturing hydrogen cyanide, which is being appHed in Spain and AustraUa. This process involves the reaction of ammonia with a hydrocarbon, usually propane or butane, in a fluidized bed of coke particles. The endothermic heat of reaction is suppHed electrically through electrodes immersed in the fluid bed. Yields from propane and ammonia are reportedly above 85% and the waste gas is essentially hydrogen, but the costs for electricity are high. Thus this process is appHcable only when there is an inexpensive source of power. 

Recovery of hydrogen cyanide from coke-oven gases has been dormant in the early 1990s, but new methods involving environmental control of off-gas pollutants may be lea ding the way for a modest return to the recovery of cyanide from coke-oven gases (see Coal conversion process, carbonization). 

Almost all sodium cyanide is manufactured by the neutralization or wet processes in which hydrogen cyanide reacts with sodium hydroxide solution. 

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