Sept ., 1922
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMIXTRY
expense of shipping inert or valueless material thus avoided. While the manufacture of fertilizers has for many years shown a steady healthy growth, it is now rising from the plane of a big business conducted largely along “rule of thumb”
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lines t o that of a true chemical industry founded upon sound scientific principles, which make for higher efficiency, greater economy, and better service to both the individual and the nation.
Developments in Nitrogen Fixation’ By J. M. Braham FIXEDNITROGEN RESEARCH LABORATORY, WASHINGTON, D . C.
HE PROBLEM of cheaply obtaining nitrogen in forms suitably combined for use in agriculture, the industries, and in punitions is probably the most important one confronting the chemical industry at the present time. The dependence of the food supply of the world on combined nitrogen is well known; nitrogen compounds occupy an important place in the industries; and the very great importance of combined nitrogen from a military standpoint requires no explanation. The use of the practically inexhaustible supply of free nitrogen in the atmosphere to supplement the inadequate natural sources of combined nitrogen is a development of the last twenty years. This relatively new industry of nitrogen fixation is undergoing rapid developments in many countries. I n the present paper an attempt has been made to indicate the general lines of development, the progress and the present status of nitrogen fixation. In such a short article, however, only the most important developments can be considered.
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FIXATION PROCESSES Although a large number of processes for the fixation of nitrogen have been suggested and more or less thoroughly tried out, there are at the present time only three in successful commercial operation. These, in the order of their development, are the Arc, Cyanamide, and Direct Synthetic Ammonia (Haber). None of the other processes thus far suggested appear to give promise of commercial development in the very near future. THEARCPRocEss-The arc process is the oldest and in many respects the simplest, consisting essentially in passing air through a specially constructed electric furnace in which the union of nitrogen and oxygen is effected, and then absorbing the oxides of nitrogen in water. Important experiments in the early development of this process were performed by Bradley and Lovejoy at their plant a t ”iagara Falls in 1902-1904. The process was being developed a t the same time in Norway by Birkeland and Eyde, and in 1903 they succeeded in starting the first successful industrial plant. No improvements of a fundamental nature have been made in this process since the early period of its operation. The changes that have been made from time to time have been largely limited to furnace design and operation, and the various present forms of the process differ only in these two respects. The principal handicap of the process is the very large power requirement-about 67,000 k. w. h. per ton of nitrogen fixed. Its profitable operation is, therefore, limited to regions in which very cheap electric power, off-peak as well as continuous, is available. Another rather serious handicap is the low concentration of nitric oxide in the furnace gases, which results in high absorption and concentration costs. Notwithstanding these difficulties, there are at present about 1 For a complete discussion of the nitrogen problem, with particular reference to the United States, attention is called to a recently published 350-page report entitled “Report on the Fixation and Utilization of Nitrogen,” prepared by the Nitrate Division, Ordnance Office, War Department, assisted by the Fixed Nitrogen Research Laboratory, Department of Agriculture, on which the present brief summary is largely based.
twelve arc-process plants located in Norway, Switzerland, Austria, Germany, France, Italy, Canada, and the United States. Their combined maximum production capacity is, however, quite small, being approximately 36,000 metric tons per annum, which is only about 6 per cent of the world’s total nitrogen fixation capacity. Norway, with her abundance of cheap water power, produces about 85 per cent of the total output of this process. The arc process plant of the American Nitrogen Products Company of Seattle is the only one in the United States. Its capacity is about 300 tons of fixed nitrogen per annum. Although somewhat less than 2.5 per cent of the total energy input of the arc process is absorbed in nitric oxide formation, the possibility of drastic reductions in the power requirements by modifications, such as in furnace design, seems quite doubtful. It appears that the process in any of its present forms is essentially a thermal one, the main function of the electric discharge being to produce the very high temperatures that favor nitric oxide formation: From this viewpoint the thermal efficiency is probably much above 50 per cent, and hence the possibility of a large reduction in the power required seems doubtful. The possibility of finding conditions under which the actual energy input more nearly approaches the heat of nitric oxide formation is of course not precluded. Research on the nature of chemical reactions in other types of electric discharge, such as in the corona, may lead to the development of a much more efficient process. Such a process, however, would be of a very different nature from the present arc process. In view of the exceedingly high-power requirements, the high cost of absorption and concentration of the product, and the fact that the process does not appear to offer possibilities of decided improvements, it seems improbable that the arc process in its present forms will continue to be an important factor in nitrogen fixation. THECYANAMIDE PRocEss-That nitrogen combines with calcium carbide, when heated to 1000° to l l O O o C., to form calcium cyanamide, was discovered by Frank and Car0 in Germany in the course of an investigation on the production of cyanides, Impetus was given to the development of this fixation process by the discovery that the crude product could either be used directly as a fertilizer or converted to ammonia simply by autoclaving. The first commercial plant was operated in 1906, and following this the new industry grew rapidly. By 1913 there were about 15 plants with an estimated capacity of 300,000 metric tons of crude calcium cyanamide-or lime-nitrogen as it is frequently called-operating in nine countries. It underwent an enormous expansion during the war since it and the arc process were the only ones in operation outside of Germany. A t the end of the war there were 35 cyanamide plants located in Germany, Austria, France, Scandinavia, Italy, Switzerland, Japan, Canada, and the United States. Their estimated total maximum production capacity a t that time was 1,625,000 metric tons, corresponding to about 325,000 metric tons of nitrogen. Actual production to capacity was not reached, however, since a number of plants were just being completed when the war ended. It is understood that a number of these plants have since been dismantled. There is only one cyanamide plant in the United States. It is located a t Muscle Shoals, Ala., and has a capacity of 40,000 tons of fixed nitrogen per annum. The cyanamide process a t the present time is in a comparatively high state of development, and therefore a decided reduction in the cost of fixed nitrogen by this process seems doubtful. I n this connection it may be pointed out that since the cost of the raw materials, limestone, coke, and coal, are practically fixed, the possible economies in the process must come principally in the lowering of the energy requirements for carbide production
