2 . The necessity for daily care of the sludge and the labor involved in it. The advantages of the process, however, seem to outweigh the disadvantages by a n adequate margin, and the process is, therefore, commended to the favorable consideration of engineers and chemists charged with the disposal of municipal sewage.
264 RIVERSIDE DRIVE ~ - E WY O R KCITY
MANUFACTURE AND USES OF CYANAMID' B y E J PRANKE
The problem of the fixation of atmospheric nitrogen is one which has engaged the attention of scientists for the greater part of a century. The rapid growth of the fertilizer industry that has attended the development of agricultural science, and the great increase in the number and extent of chemical industries, during the past fifty years, has emphasized the necessity for artificial methods of maintaining and increasing the world's stock of combined nitrogen. One of the influences that stimulated immediate action was the introduction in 1887 by MacArthur and Forest, and at about the same time independently by Siemens and Halske, of Berlin, of the Cyanide Process for leaching gold and silver from their ores. This produced a strong demand for cyanides, which had hitherto been used to the extent of only a few hundred tons a year, principally in the dye industry and to a smaller extent in electroplating. Attempts had been made early in the nineteenth century to bring about the direct synthesis of cyanogen from atmospheric nitrogen and carbon. Among other processes, that worked out in 1847 by Bunsen and Playfair, in which barium carbonate was heated in a n atmosphere of pure nitrogen, seemed promising, but did not prove to be commercially successful. The introduction of the electric furnace in 1894 by Moissan and by \Tillson, for the production of carbides on a large scale, gave new direction to the researches. Siemens & Halske, among others, adopted it for the working out of the problem of nitrogen fixation. I n 1895 they worked on the process of Prof. H. Mehner, which consisted in fusing a mixture of sodium carbonate and In carbon and conducting nitrogen through the hot mass. the same year they took up the process of Prof. Adolph Frank and Dr. Nicodem Caro, ~ h i c hconsisted in subjecting a mixture of barium carbide, sodium hydroxide, potassium hydroxide and carbon at a high temperature to the action of steam and nitrogen. Frank and Caro, with the cooperation of F. Rothe, soon learned that dry nitrogen is essential to successful absorption. In 1898 it was found that barium carbide alone, heated to a temperature of 7m to 800' Centigrade, in a n atmosphere of nitrogen, readily absorbs nitrogen and forms a product in which about 30 per cent. of the nitrogen is present as barium cyanide and about 70 per cent. as barium cyanamide. The reactions may be represented by the equations: BaC, N, = Ba(CN), N, = BaCN, C BaC, I t was further found that on fusion of this mass with soda the cyanamideisconverted to cyanide. This mass can then be leached with water, and the cyanide solution thus obtained can be converted to sodium ferrocyanide, which is easily separated in a pure form, and which can be sold as such or be converted into pure sodium cyanide by fusion with metallic sodium. The interruption in the production of gold in Africa, due to the Boer war, caused a decline in the price of cyanide, which stimulated the search for cheaper methods of production. I t was found that calcium carbide could not only be manufactured a t a lower cost, but it had the advantage of a lower molecular weight. With calcium carbide a temperature of from 1100to 1200' C. is required for absorption, but in this-case the nitrogen
+ +
hddresa before the Nashville Society, November 15, 1912
+
Cection of the Amerlcan Chemlcal
is fixed exclusively in the form of calcium cyanamide. On fusion with alkaline salts the cyanamide is readily converted to cyanide, and this can be extracted and purified in the usual manner. Agricultural experiments with the crude calcium cyanamide showed that this material is suitable for use as a nitrogenous fertilizer, and patents were issued in 1910 to Dr. Albert R. Frank, son of Prof. Adolph Frank, and to Herman Freudenberg, a co-worker of A. R. Frank, protecting the use of Cyanamid for this purpose. The basic patent protecting the process of manufacture of Cyanamid was issued to Prof. Dr. Adolph Frank and Dr. Nicodem Caro in 1908. The large demands of agriculture for cheap nitrogenous fertilizer materials have directed the efforts of the manufacturers towards the production of Cyanamid rather than of cyanides and other derivatives. At present the total output of sodium cyanide derived from Cyanamid is only about 2000 tons per annum, while the world's production of Cyanamid is estimated a t about 120,ooo tons per annum. MANUPACTURE
OF CYANAMID
Calcium cyanamide is formed in accordance with the equation CaC, N, = CaCN, C. The raw materials, therefore, are calcium carbide and nitrogen, Calcium carbide is formed in accordance with the equation CaO 3C = CaC, CO. The raw materials for this reaction, therefore, are lime and coke. For the production of carbide, lime, from I inch to 2% inches inch, are mixed, in the proportions in size, and coke, about demanded by the equation, to produce a carbide about 80 per cent. pure. The mixture is shoveled continuously into a 3-phase electric furnace. The furnace consists of a supporting base and four retaining brick walls mhich are filled with the lime and coke mixture, into which is submerged three carbon electrodes carrying the current. The resistance of the materials t o the passage of the current raises them to a temperature a t which the lime melts freely and combines with the coke to form liquid carbide. At intervals, as the carbide accumulates, it is tapped off through a suitable tapping hole a t the side of the furnace into iron cars. After cooling, the carbide is crushed and ground to a fine powder, and is then packed in perforated cylindrical steel cans in the axis of which is a cylindrical paper core. The can with the carbide is set in a brick walled oven, slightly larger than the can, and is covered with an iron lid. A carbon pencil is run through the paper core in the axis of the can. Upon passage of the electric current, the carbide is heated, nitrogen is admitted to the can, and the absorption takes place very readily, raising the temperature to about I I O O O to I Z O O O C., a t which point it is maintained until the absorption is complete. N, = CaCN,. C is exothermic, and The reaction CaC, the heat given out is almost sufficient to maintain the mass a t the combining temperature. Upon completion of the reaction the cans are removed and the product is allowed to cool. I t is a bluish black solid, containing small glistening crystals of pure calcium cyanamide.
+
+
+
+
+
+
PREPARATION
The nitrogen required for the manufacture of Cyanamid Is separated from the air by either the liquid air process or the copper oxide process. The latter is in use a t present by the American Cyanamid Company. The copper oxide process is based upon the ease with which heated copper combines with oxygen. The very finely divided copper suspended in a mass of asbestos or other inert material is contained in. boiler shells provided with means for supplying heat externally. Air is pumped through the retort, which is a t about gooo C., and is completely deprived of its oxygen. The nitrogen is then freed from carban dioxid by passage through a caustic soda tower. The moisture
I 60
T H E JOUR-YAL OF I S D i Y ; S T R I 2 4 L A N D ESGIArEERI.\-G
is removed by refrigeration, followed by passage of the gas through layers of lime, and finally through calcium chloride. The nitrogen must be pure and dry, since otherwise there is a destruction in the nitrifying ovens of the carbon pencil and of calcium carbide in accordance with the following reactions
c+o=co
+ + + + +
+
C H,O = CO H, CO CaC, = CaO + 3C aCaC, = aCaO gC CO, H,O CaC, = CaO C,H, 30 CaC, = CaO zC0 The oxidized copper in the nitrogen separation retorts is reduced in place by reducing gases, such as natural gas.
+ + +
PREPARATION FOR VSE AS A FERTILIZER MATERIAL
The crude Cyanamid obtained from the nitrifying ovens, after cooling, is crushed to a fine powder, and is passed into rotating, slightly imlined, steel cylinders, in which i t is treated with sufficient water to eliminate the carbide and to slake the calcium oxide. A further slight addition of water is made before the material is run through briquetting machines. The resulting bricks harden rapidly and are stored until they can be crushed just prior to shipment. Crushing is done in a series of rolls with intermediate screens, the final product having a coarseness of about I j- to go-mesh screens. It is packed in ordinary fertilizer bags and distributed in carload lots to manufacturers of mixed fertilizers. The material so prepared contains nitrogen equivalent to about 19 per cent. ammonia. I t analyses approximately as follows Calcium Cyanamide 4jYG Iron and Alumina zYG Calcium Carbonate 4y0 Silica 2% Calcium Hydroxide 27YG Combined water 4Y0 Calcium Sulphide I yo Free moisture 1% Free Carbon 14% USES OF CYANAMID
A t present, Cyanamid is used in this country principally for agricultural purposes. It is known to have a fertilizing value equal or superior to that of other common products used for the same purpose. Some of the earlier experiments with this material indicated a n uncertain action on very acid moor soils, but the same thing is true of other fertilizers requiring nitrification prior to absorption by the plant, and is the fault of the soil and not of the fertilizer. Such soils must be restored to normal condition before fertilizers can be expected to have their full effect. In other cases, experimenters applied quantities far in excess of those used in practical agriculture, and obtained a lower efficiency of utilization than with the normal applications As a general conclusion from the hundreds of recorded experiments and from the testimony of practical agriculturists, i t may be said that when Cyanamid is used in the same way as other fertilizers are used in ordinary practice, its efficiency of utilization is about the same as that of the high-grade fertilizer materials, and superior to that of the low-grade fertilizer mat erials . The particular advantage of Cyanamid as alfertilizer material lies in the advantageous effects that follow its admixture with other constituents of complete fertilizers. It greatly. improves the mechanical condition of such mixtures, and by its alkaline properties prevents the escape of valuable nitrogen oxides and of bag-rotting hydrochloric acid, set free by the action of free acids in acid phosphate upon nitrates and chlorides in the mixtures. Statements have been made that there is a loss of ammonia from Cyanamid during long-continued storage. I t has been found, indeed, that the nitrogen percentage in stored material does decrease, especially in very damp climates, but it has been determined by very careful experiments both on a small scale a n d on a large scale in fertilizer factories, that such decrease in
.
CHEJlISTRI’
Feb., I 9 1 3
the nitrogen percentage is due not to any actual loss of nitrogen, but to the increase in the weight of the material, due to its absorption of carbon dioxide and of moisture from the atmosphere. Part of the moisture absorbed is fixed chemically into forms from which it is not recovered on heating in a drying oven, hence it is necessary, when testing the storing qualities of this fertilizer, to weigh the material before and after the period of exposure and to determine the nitrogen percentage each time. SOIL ACTIOS O F CYANAMID
I t has been definitely established by the researches of Ulpiani and Kappen, among others, that cyanamid applied to the soil is completely converted in the course of a few days into urea, by the catalytic action of the colloids and other constituents of the soil, in accordance with the following reactions: CaCN, zH,O = Ca(OH), H,CN, H,CN, H,O = CO(NH,), The urea is further converted by bacterial action and possibly by chemical processes into ammonia, which further reacts with zeolites, humates, and other soil constituents, to form double ammonium salts, that are retained as a part of the soil, until further bacterial action or the solvent effect of plant roots makes them available to vegetation. Cyanamid is said to be completely utilized by the crop in from 60 to 80 days.
+
+
+
OTHER USES
When Cyanamid is subjected to the action of superheated steam under pressure of several atmospheres, it is converted almost quantitatively into ammonia and calcium hydroxide. It thus serves as a convenient and cheap source of pure ammonia. By the Ostwald process, which uses thoria and ceria as catalytic agents, ammonia can be commercially converted into nitric acid. By fusion of Cyanamid Tyith alkaline salts in the presence of carbon, cyanides are easily produced and can be separated and purified as desired. When Cyanamid is extracted with water between 7oo and 1 0 o O C., nearly all of the nitrogen is converted into dicyandiamide (H,CN,),. This compound is used in the dye industry and also in the explosives industry in place of ammonium oxalate to reduce the temperature of the explosive gases. Other derivatives, such as urea, guanidin and its salts, and various dicyandiamidin salts are now being manufactured in Germany. One or both of the hydrogen atoms in the amide group in cyanamide, CN.NH,, can be replaced by metals, alkyl or aryl groups, alcohol groups, aldehyde groups, and others, thus leading to a n immense number of organic derivatives. The possibilities in this field have been investigated but little. Various compounds of Cyanamid, and its derivatives, with alkaline salts and carbonaceous materials, are made and sold in Germany under the names of Ferrodur, Intensit, Hessolin, and others. These compounds, known as “hardening” or “cementing” powders, are used in place of cyanides, ferrocyanides, waste leather and similar materials, for case-hardening of steels. These products containing Cyanamid are not only cheap but they are efficient for the purposes for which they are intended. FUTURE OF CYANAMID INDUSTRY
The Cyanamid industry is undoubtedly only in its infancy. At present there are four factories in Germany, four in Italy, two in France, and one each in Austria, Norway, Sweden, Switzerland, Japan, and America. The American Cyanamid Company built its first plant at Niagara Falls, Ontario, in 1909, beginning commercial manufacturing January Ist, 1910. Additions to the plant, which will be completed in March, 1913, will give a capacity of 25,000 tons per annum, and by the end of the year the full productive capacity of the company, including the extensions now under way, should bejo,ooo tonsperannum. NASHVILLE. TENN.
