II. SYNTHETIC PaocEssEs.—The world's re quirements for nitrogen compounds in the last few years, 1914 to 1918, were so great that the destructive distillation processes were insuffi dent to meet the demand. As a result, several processes for the fixation of atmospheric nitro gen developed in the last two decades have been successfully applied on a commercial scale. This has been particularly the case in Germany which could not have lasted for more than a year at war without the cyanamid and Haber processes.
1. The Haber
this process, nitrogen and hydrogen are directly combined to form ammonia. The mixed gases are passed at high pressures, 200 atmospheres or more, and at temperatures of 500 to 700 degrees C over a catalyst, such as osmium, uranium or palladium, when combination occurs resulting in the forma tion of ammonia to the extent of 3 to 12 per cent of the mixed gases. The ammonia formed is then separated by cooling and the remaining gases, together with fresh nitrogen and hydro gen, pumped over the catalizer again. Heating of the gases is effected electrically, the power consumption for the whole process being one fourth to one-sixth of that required by the cyanamid process. Since the power consump tion is so low the production of synthetic am monia by the Haber process need not be con fined to districts having large amounts of cheap power. It is particularly important in a process depending upon the action of catalysts (which are very sensitive to impurities), that gases of the highest degree of purity be used. Nitrogen of satisfactory quality is obtained by the frac tional distillation of liquid air. For the manufac ture of hydrogen the electrolytic process pro duces a gas of higher purity than that obtained by any other commercial process, and is there fore, of great value in this connection (see sec tion on hydrogen and oxygen). In the United States the Haber process has not been a com mercial success owing to failure to overcome the engineering difficulties of working with gases of high pressures. In Germany the Haber process, as already mentioned, has been de veloped much further than in the United States. Consult Haber and Le Rossignol, 'Zeitschrift fiir Elektrochemie' (1913, 19, 53, 72, abstracted in Journal, Society of Chemical Industry, 1913) ; 'Bericht' (1907, 40, 2144) ;
2. Cyanamid Process.—Ammonia is pro duced indirectly in this process by the following reactions: (a) Ca0 + 3C= CaC. CO.
(b) CaC. C (c) CaCN, 3%P-- CaCO. (a) Quicklime is mixed with coke and allowed to react at the highest temperature of the electric furnace. The molten calcium car bide thus formed is run off, cooled and ground in ball mills filled with nitrogen gas.
(b) The powdered calcium carbide is next charged into small electric resistance furnaces and a current of pure nitrogen gas passed through. The start of the reaction requires some electrical energy, after which the tempera ture is maintained by the.heat of reaction. Cal cium cyanamid is formed.
(c) The calcium cyanamid or nitro gen)) is finely powdered and treated in stirred autoclaves with high pressure steam and a dilute solution of caustic soda. The ammonia begins to evolve in large quantities at four to five atmospheres. This process requires a large amount of cheap electrical energy and high initial outlay of capital for equipment 3. Serpek When bauxite (the mineral hydrated alumina) is heated with coal in an atmosphere of nitrogen at 1,700° to 1,800° C. in an electric furnace, the following reaction takes place: A.20. ± 3C Ne=2AIN 3CO.
Absorption of nitrogen begins at 1,100° C., is rapid at 1,500° C. and extremely rapid at 1,800° C. The reaction is endothermic (213,220 calories being absorbed, according to Richards). The aluminum nitride formed is treated with caustic soda, forming ammonia and sodium aluminate: AiN + 3NaOH c=NH,.± Na.A.08.
According to German Patent 243,839 (Badische Company), the formation of nitride from alumina and coal is facilitated by the addition of certain catalysts, 5 to 10 per cent of the oxides of Si, Ti, Zr, V, Be, Mo, Ur, Ce, Cr, which are capable of forming stable nitrides. Consult Serpek, British Patent 13,086 (1910) ; Richards, J. W., Transactions American Elec tro Chemical Society (1913, 23, 35) ; Tucker, S. A., Journal Society Chemical Industry (1913, 32, 1143) ; Fraenkel, 'Zeitschrift fiir Elektro chetnie) (1913, 19, 362).
Preparation of Anhydrous Ammonia.— Aqua ammonia obained by either a destructive distillation or synthetic process is distilled and the ammonia vapors dried by passing over quicklime. The dry gas is then generally com pressed and liquefied in steel cylinders, a pres sure of 6.5 atmospheres being required at plus 10° C. The purified ammonia formed in the process may also be dried and liquefied directly.
The principal use of anhydrous ammonia is for refrigeration, as in the manu facture of artificial ice. When liquefied am monia is allowed to expand in a suitable machine the fall in temperature is sufficient to freeze water. Consult Lunge, Tar and Vincent, C., 'Ammonia and Its Marten, G. and Barbour, William, 'Industrial Nitrogen Compounds' ; 'Synthesis of Ammonia and Oxidation to Nitric Acid) (in Metallurgy and Chemistry, 17, 345) ' • Boyce, J.
C., 'Bibliography of Production' of Synthetic Nitric Acid and Synthetic Ammonia) (in Metal lurgy and Chemistry, 17, 328); 'Nitrogen Fixa tion Patents) (in Metallurgy and Chemistry,17 606) ; Hosmer 'Literature of the Nitrogen In dustry, 1912-1916> (in Journal Industrial Engi neering and Chemistry, 9, 424).
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