Patented Oct. 1, 1935 2,015,668 UNITED STATES PATENT OFFICE 2,015,668 MANUFACTURE OF ALKAL META, CYANDES Harvey N. Gilbert, Niagara Falls, N. Y., assignor to The E. I. du Pont de Nemours & Company, -- Incorporated, Wilmington, Del, a corporation of Delaware No Drawing. Application February 16, 1933, Serial No. 657,109 11 Claims. (C. 23-79) This invention relates to the production of al The balanced equation for this reaction Will be kali metal cyanides, specifically sodium cyanide, as follows: from calcium cyanamide. Itihas previously been proposed to convert cal Na2--CaCN2-3C=2NaCN--CaC2 5 cium cyanamide to alkali metal cyanide by fusion As Will be seen from this reaction I preferably 5 With fluxes of various sorts, such as sodium chlo Supply three or more moles of carbon for each ride, Sodium cyanide and other Sodium con mole of cyanamide. The crude product pro pounds. A more recent proposal has been to con duced by this means then contains Sodium cya vert calcium cyanamide to Sodium cyanide by nide, calcium carbide formed in the reaction, cal 10 the reaction of elemental sodium with the cyan cium carbide that may have carried over from 10 amide according to the following equation: the crude cyanamide used, together with the other inert materials, such as calcium oxide, Na2--CaCN2--C=2NaCN--Ca Which may have been present in the raw material As a source of calcium cyanamide for this reac or which may have been formed by decomposition l6tion and the other reactions there has been used during the reaction. The crude product, usually 15 the commercial product known by that name or contains from about 10% to about 30% of cal by the name of 'line nitrogen'. This material cium carbide, depending upon the proportions of Contains various amounts of pure calcium cyan the various reactants used and upon the temper amide, usually about 60-66%. Hereafter when I ature at which the reaction is carried out. 20 speak of calcium cyanamide I refer to this crude I have found that this reaction may be carried 20 product containing various amounts of the pure Out at a temperature above red heat and that cyanamide and the residual material left during between 700, and 1000° C. it takes place very its preparation, such as calcium carbide, calcium readily; I prefer to heat the reactants to about oxide, free carbon etc. Further discussion of the 900° C. The boiling point of sodium is approx 26 invention will be illustrated by sodium as the imately 877. C. so that at the optimum reaction 25 alkali metal, but this is to be taken as representa temperatures the sodium is very easily dissemi tive since potassium or lithium can equally Well nated to all parts of the reaction mass as a vapor. be used. I have also found that the Sodium is very readily In the reaction shown by the above equation absorbed by the reaction mixture so that it is not 30: the calcium cyanamide by interaction. With the necessary that the sodium be intimately mixed 30 carbon and sodium gives theoretically tWO moles with the cyanamide and carbon before subjecting sodium cyanamide for each mole calcium cyan to reaction temperature when the reaction is car amide or each mole of calcium. In the process ried out at a temperature of 900° C. Thus I have heretofore proposed this calcium has been unu found that sodium may be placed in the bottom 35. tilized in that in the reaction itself or in the Sub of a vessel and covered with the reaction mixture 35 sequent operations such as dissolving in Water, of cyanamide and carbon, then, when Sufficiently it has been converted to calcium oxide or other heated, the Sodium vapor will permeate the mass unusable calcium compounds. Furthermore, the and react; or it is possible to generate the sodium elemental calcium in the product is a potential Vapors apart from the reaction vessel and lead Source of difficulty. it into the cyanamide-carbon mixture. For reac- 40 An object of this invention is to improve upon tions at lower temperatures, the sodium may be the use of calcium cyanamide according to the added in Solid or liquid form and the mixture above reaction by making use of the elemental stirred to uniformity at temperatures above the 45. calcium and converting it to a uSable product. melting point of sodium. A further object is to produce Sodium cyanide Crude calcium cyanamide or lime nitrogen, as 45 noted above, contains one mole of free carbon eficiently; and a further object is to produce for each mole of cyanamide. Thus, theoretically, acetylene from the reaction maSS. I Would add, according to the above equation, two I accomplish these objects by having sufficient moles of carbon for each mole of pure calcium 50 carbon present during the reaction to provide cyanamide contained in the lime nitrogen and 50 sufficient carbon for each mole of calcium cyan the further carbon necessary would come from amide to be converted, and carrying out the reac the crude. I have found, however, that it is tion at such temperature, that some of the car preferable to have a slight excess of carbon and bon will combine with the elemental calcium to further that probably the carbon in the lime 55 produce calcium carbide in the reaction product. nitrogen is not as reactive as other more desirable 55 2 2,015,668 carbons so that I prefer to add the three moles of product, corresponding to the aforementioned carbon, as shown by the equation, in addition to yield, was 16% by weight. This calcium carbide the carbon already present. This, however, is not was determined by the amount of acetylene necessary and I do not wish to be restricted to evolved on immersing the product in water. this mode of operation but only to adding suf Eacample III ficient carbon to form calcium carbide in an ef ficient manner from the calcium released. A mixture the same as that used in the pre The carbon used in the reaction may be any ceding example was placed in the reactor and Suitable form of carbon free of deleterious nate maintained at about 900 C. for 17 minutes. A 10 rials which Would react with the other constitul yield of sodium cyanide equivalent to 86.8% of 0 ents to any appreciable extent to form products the theoretical based on the nitrogen in the crude Other than Sodium cyanide; thus I preferably use cyanamide or on the Sodium was obtained, and Wood charcoal although other forms are Suitable. there was a 75.8% yield of acetylene based on the The carbon is first finely ground and then mixed theoretical. The corresponding percentage of cal with the calcium cyanamide before subjecting to cium carbide present in the reaction product was 5 reaction. 24% by weight. The following examples will illustrate my in Eacample IV Vention. Eacample I A mixture as used in Example II was placed in 20 a reactor and maintained at 900 C. for 42 min- 20 46 grams of sodium were placed in the bottom utes. A yield of 92% sodium cyanide was ob of an iron reaction vessel, 1% inches in diam tained and 61.5% of theoretical of acetylene. The eter and 8 inches deep. Over this was placed corresponding percentage of calcium present in a mixture formed of 121 grams of calcium cyan the reaction product was 19.4% by weight. amide crude and 12 grams Wood charcoal. This While I show this reaction as taking place in 25 provided for approximately 2 moles of carbon per a Simple iron reactor it can also be run in any mole of CaCN2 actually present. The reaction other apparatus Suited for the materials and the vessel was placed in a molten lead bath which teinperature used. was at a temperature of 791 C. at the start but AS indicated in Example II, the crude mate ... which was raised over a period of 17 minutes to rial resulting from this reaction may be dissolved 30 a temperature of 923° C. There was no violence in water and treated with soda ash to precipi during the reaction. A small cover of asbestos tate the lime, filtered and thus give a solution of in the end of the reaction vessel was forced out Sodium cyanide from which the cyanide can be by gases evolved. The resulting product was recovered by any Suitable means. friable, gray in color and when added to Water I claim: 35 reacted very vigorously, evolving acetylene. The 1. Process of producing alkali metal cyanide yield of sodium cyanide was equivalent to about and calcium carbide which comprises reacting 73% of the theoretical based on the pure cyan above red heat calcium cyanamide and alkali amide in the crude. The yield calculated on the metal in the metallic state in the presence of basis of the sodium used was also about 73%. 40 more than one mole of total free carbon for 40 Eacample II each mole of pure calcium cyanamide. 2. Process of producing alkali metal cyanide 46 grams of Sodium were placed in the bottom and calcium carbide which comprises reacting of a reaction vessel as used in Example I and above 700° C. calcium cyanamide, alkali metal over this was placed a charge of 121 grams of in the metallic state and carbon, the free total 45 45 crude calcium cyanamide previously mixed with carbon present being sufficient to provide more 36 grams finely divided wood charcoal.