Cyanamide calcium

Also known as nitrolim and lime nitrogen. The fresh product contains approximately 55 per cent, of calcium cyanamide, 20 p>er cent, of lime, 12 per cent, of graphite and small amounts of other impurities. It should be protected from moisture when stored in order to prevent slow polymerisation to dicyano-diamide. 

It is prepared commercially by treating cyanamide (from calcium cyanamide) with ammonium sulphide ... 

The synthesis of these disubstituied thioureas takes place in three steps. First the alkyl bromide is prepared by the action of hydrobromic acid on the corresponding alcohol (518). Then the dialkylcyanamide is obtained by treatment at 25°C with calcium cyanamide. The yields are of the order of 30 to 60%. Thioureas are obtained in a third step from the cyanamide by reaction at 40 C with HjS in the presence of pyridine. Yields ranged from 57 to 90% (518),... 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

Some commonly used primary nutrient fertilizers are incidentally also rich sources of calcium. Ordinary superphosphate contains monocalcium phosphate and gypsum in amounts equivalent to all of the calcium originally present in the phosphate rock. Triple superphosphate contains soluble monocalcium phosphate equivalent to essentially all the P2 5 product. Other fertilizers rich in calcium are calcium nitrate [10124-37-5] calcium ammonium nitrate [39368-85-9] and calcium cyanamide [156-62-7]. The popular ammonium phosphate-based fertilizers are essentially devoid of calcium, but, in view of the natural calcium content of soils, this does not appear to be a problem. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Dormex. Dormex [156-62-7] (Alzodep, hydrogen cyanamide) (26) should not be confused with the same term used for calcium cyanamide. Its other names include carbamide, cyanogenamide, and amidocyanogen. The compound is easily prepared by the continuous carbonation of calcium cyanamide in water (see Cyanamides). 

At about the same time that the Birkeland-Eyde process was developed, the Frank-Caro cyanamide process was commercialized (14). In this process limestone is heated to produce lime, which then reacts with carbon in a highly energy-demanding reaction to give calcium carbide. Reaction with N2 gives calcium cyanamide [150-62-7] which hydrolyzes to ammonia and calcium carbonate (see Cyanamides). 

Plants can also be pests that need to be controlled, particulady noxious weeds infesting food crops. Prior to 1900, inorganic compounds such as sulfuric acid, copper nitrate, sodium nitrate, ammonium sulfate, and potassium salts were used to selectively control mustards and other broadleaved weeds in cereal grains. By the early 1900s, Kainite and calcium cyanamid were also used in monocotyledenous crops, as well as iron sulfate, copper sulfate, and sodium arsenate. Prom 1915 to 1925, acid arsenical sprays, carbon bisulfate, sodium chlorate, and others were introduced for weed control use. Total or nonselective herbicides kill all vegetation, whereas selective compounds control weeds without adversely affecting the growth of the crop (see Herbicides). 

Preparation. Hexagonal boron nitride can be prepared by heating boric oxide with ammonia, or by heating boric oxide, boric acid, or its salts with ammonium chloride, alkaU cyanides, or calcium cyanamide at atmospheric pressure. Elemental nitrogen does not react with boric oxide even in the presence of carbon, though it does react with elemental boron at high temperatures. Boron nitride obtained from the reaction of boron trichloride or boron trifluoride with ammonia is easily purified. 

Calcium carbide is also used to produce calcium cyanamide [156-62-7] CaCN2, (see Cyanamudes). 

Calcium cyanamide (lime nitrogen) has been used as a fertiliser (6). It hydrolyses ia moist soil to produce ammonia ... 

Calcium cyanamide can be converted to calcium cyanide [592-01-8], used ia cyanidation of metallic ores and production of sodium cyanide and ferrocyanides (11) (see Cyanides). Calcium cyanamide has also been used to make cyanamide which ia turn is the starting material for important iadustrial organic syntheses. 

In the United States calcium carbide-based acetylene is mainly used in the oxyacetylene welding market although some continues to be used for production of such chemicals as vinyl ethers and acetylenic alcohols. Calcium carbide is used extensively as a desulfurizing reagent in steel and ductile iron production allowing steel mills to use high sulfur coke without the penalty of excessive sulfur in the resultant steel (see Sulfurremoval and recovery). Calcium cyanamide production continues in Canada and Europe (see Cyanamides). 

Reaction With Nitrogen. Calcium cyanamide is produced from calcium carbide... 

The largest use for calcium carbide is in the production of acetylene for oxyacetylene welding and cutting. Companies producing compressed acetylene gas are located neat user plants to minimize freight costs on the gas cylinders. Some acetylene from carbide continues to compete with acetylene from petrochemical sources on a small scale. In Canada and other countries the production of calcium cyanamide from calcium carbide continues. More recentiy calcium carbide has found increased use as a desulfurizing reagent of blast-furnace metal for the production of steel and low sulfur nodular cast iron. 

In North America, calcium cyanamide is no longer used as fertiliser, but it has limited use in special agricultural appHcations for defoHants, fungicides, herbicides, and as a weed killer. The primary industrial use is as a chemical intermediate for the manufacture of calcium cyanide, hydrogen cyanamide solution, and dicyandiamide. Calcium cyanamide is also used to add nitrogen to steel. 

For the manufacture of calcium cyanamide, cmde calcium carbide (ca 3.36 x 1.68 mm or 6 x 12 mesh) can be used, whereas for cyanamide and dicyandiamide, a 74 p.m (200 mesh) anhydrous carbide is used. 

For agricultural uses, a fully hydrated calcium cyanamide powder containing 2% oil is used for dusting appHcations for general fertilizer use, the hydrated material is granulated with water in rotary dmms and dried giving a 2.38 x 0.32 mm (8 x 48 mesh) product. 

In the final fourth step cyanamide is manufactured from calcium cyanamide by continuous carbonation ia an aqueous medium (Fig. 1) (22). 

The calcium cyanamide feed is weU mixed with the recycled slurry and filtrate ia a feed vessel. The calcium cyanamide is added at a rate to maintain a pH of 6.0—6.5 ia the cooling tank. The carbonation step can be conducted ia a turbiae absorber with a residence time of 1—2 min. After the carbonation step, the slurry is held at 30—40°C to complete the formation of calcium carbonate, after which the slurry is cooled and filtered. AH equipment for the process is preferably of stainless steel. The resulting solution is used directiy for conversion to dicyandiamide. 

Of the four steps described above, only the first two consume large amounts of energy, especially the calcium carbide step. With increasing energy costs, attention should be focused on alternatives for making calcium cyanamide. 

Reaction of lime and urea forms calcium cyanate [6860-10-2] (26) which is then converted to calcium cyanurate [32665-90-0], the latter gives calcium cyanamide at a higher temperature ... 

The product obtained is white calcium cyanamide whereas the product obtained from limestone and coal contains carbonaceous (graphite) impurities. None of these processes has been commercially exploited. 

Economic Aspects. A peakia calcium cyanamide production was probably reached ia 1962 when the world production for fertilizer use was of the order of 1,000,000 metric tons of calcium cyanamide per year, and for iadustrial use approximately 300,000 t (excluding the then USSR). In 1990, the total production of cyanamide products was about half that of 1962. The largest producers are ia Japan, Germany, and Canada. 

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