US1481373A - Process of producing alkali-metal cyanides - Google Patents

Description

tatented anmA 22, i240 V B. JACOBS, '0F WILMINGTON, EWE, vASSIGNOR T0 E. I. DU PONT DE NEMQU et wl WE.

ANY, 0F WILMNGTN, D 5 l rnocass or rnonncme an WE, A CORPORATION @F DELA-f .t i' I-METL CYNXDES.

Application `filed February 28,1%9, Serial No. 279,801. Renewed June 15, i923.

To aZZ 'whom it may concern.'

Be it known that I, CHARLES B. JACOBS, a citizen of the United States, residing at Wilmington, in the county of New Castle and State of Delaware, have invented new and usefullmprovements inv Processes .of Producing Alkali-Metal Cyanides, of which the folowing is a specification. This invention relates to a process of producing alkali-metal cyanides and pertains especially to a process in which free or elemental nitrogen in a pure state, or free or elemental nitrogen 1n nitrogen bearing gases, is caused to combine directly, in the presence of alkali-metal halides, with other compounds of the alkali-metas and wlth carbon to form alkali-metal cyanides.

The chief object of my invention is the formation of alkali-metal cyanides ai; lower temperatures, more economically, and in greater yields than have heretofore been obtainable by the reaction of gaseous nitrogen on compounds of the alkali-metals and carbon.

I am aware that it is not new to form alkali-metal cyanides by heating alkalimetal carbonates and carbon to a high temperature in nitrogen. This was observed as early as the year 1829 by Desfosses.

I am also aware that the addition of certain metals or 'their reducible compounds such as finely divided iron, manganese, chromium, nickel, etc., to alkali-metal compounds and carbon, cause the formation of alkali-metal cyanides to take place more abundantly and at lower temperature, when these mixtures are heated in nitrogen, than is the case when the alkali-metal compounds and carbon are heated alone in nitrogen.

Lewis `Thompson showed the use of finely divided iron for this purpose in 1839, and Victor Adler, in 1880, obtained patents in Germany claiming the use of finely divided iron and other metals which have the property of combining with and transmitting carbon, for the same purpose.

John E. Bucher, in 1912, led and'later x obtained patents for .the use of finely divided iron in the fixation of nitrogen as sodium cyanide.

I have shown in a previous application for a process for formin nitrogen compounds, filed in the U. S. atent Oflice. August 19, 1916, Serial No. 115,758, that alkalimetal cyanides may be formed in substantial vquantities by heating alkai-metal carbonate and carbon alone in nitrogen without the use of catalyzers to temperatures commercially available which do not cause undue deterioration of the retorts, providing the alkalimetal compound is brought into the most intimate physical contact with the carbon and the nitrogen. I have shown in said application -a means of establishing and maintaining these conditions which produce the necc sszliry contacts between vthe reacting materia s.

In a second application, Serial Number 137,808, tiled in the U. S. Patent Ofiice December 19, 1916, I have shown a method of preparing alkali-metal compounds and caron for treatment with nitrogen whereby the desired intim-ate contact of the reacting elements necessary to form alkali-metal cyanides, when alkali-metal compounds and carbon are heated alone in nitrogen, is established and maintained.

In a further study of the fixation of nitrogen as alkali-metal cyanides made with the object ofl reducing the temperature neces sary to form cyanides, when alkali-metal compounds, carbon and nitrogen are heated, or of materially increasing the yie` d of cyanides, I have made the discovery that the addition of alkali-metal halides to a finely ground mixture of sodium carbonate and coke, charcoal or like forms of carbon, caused the formation of sodium cyanide at temperatures below those at which cyanide is formed when carbon and alkali-metal .compounds other than the halides are heated alone in nitrogen.

The nature of the new process may bewhich I have carried out:

' Experiment #1.

illustrated by the following experiments A charge made up of finely divided in- Experiment #2d The same mixture of sodium carbonate, coke and sodium chloride, when heated in a retort for four hours at 800 to 850 C. (pyrometer reading) with nitrogen under a pressure of 15 lbs. per sq. in., showed on analysis 16.5% of sodium cyanide and no sodium cyanamide.

Experiment #3.

The same mixture when heated in the retort for six hours under the same conditions of temperature and nitrogen pressure showed on analysis 20.3% of sodium cyanide and no cyanamde.

I also made the discovery that the addition 'of alkali-metal halides together with the oxides of certain metals or with the metals particularly when they are present in a fine state of division to a mixture of sodium carbonate, coke, charcoal, and the like, caused a material increase in the formation of sodium cyanide in a shorter time, when the mixture was heated in contact with free nitrogen, whether pure or mixed with other gases, than when the alkali-metal halides alone or the metallic oxides or the metals alone were used. i

The process involving the conjoint use of alkali-metal halides with certain metallic oxides or metals, in the formation of cyanide from alkali-metal compounds, carbon and free or elemental nitrogen is fully described in my companion application for Letters Patent Serial No. 279802 tiled coincidently with this application in the United States Patent Ofiice. The present application is directed broadly to the use of alkalimetal halides in the synthesis of alkali-metal cyanides.

ln view of the very striking results obtained in these experiments at temperatures at which there is little or no eyanideformation when sodium carbonate and carbon are heated alone in nitrogen, the experiments were continued on a semi-commercial scale, and the proportion of sodium chloride was varied between Wide limits.

After many experiments with var ing proportions of sodium chloride, all of w ich gave cyanides at lower temperatures than they4 are usually formed, it was found that when the sodium chloride and the sodium carbonate were present in the charge in the proportion of the eutectic mixture (34.7 parts by weight of sodium chloride to 65.3 parts by weight of sodium carbonate) the highest yields of cyanide were obtained in a given time.

The charges which gave the best average results were made up of from 50 to 60% of the eutectic-mixture, to 40 to` 50% of coke, charcoal, or a mixture' of coke and charcoal, or coke with a small proportion of sawdust added to give porosity to the charge under the influenceof heat by driving out the volatile products of the sawdust. Good yields are still obtained, however, even if recieve the proportions of the reagents are changed considerably from those above mentioned. Thus with 40 parts of sodium carbonate and 40 parts of coke, there may be used from 10 to 25 parts of sodium chloride, although it has been found desirable to use about equa-l parts of sodium carbonate and coke, the ratio of the one to the other may vary without seriously decreasing the yield of cyanide. For instance, from 35 to 50 parts of sodium carbonate may be used with 40 parts of coke, and instead of Ll0A parts of coke from 35 to 50 parts may be used.

The average results of thirty-two experiments in whlch the charges were heated for six hours at temperatures between 850 and 900o C. (pyrometer readings) showed that 50% of the sodium carbonate present in the original charge had been -converted intOi sodium cyanide, with some high yields in which 55, 57, 59, 61 and 71% of the sodium carbonate had passed into cyanide.

Sodium fluoride, when substituted 'for the chloride, gave equally good and, under certain conditions, better results.

The exact function of the sodium chloride or fluoride in promoting the formation of alkali-metal cyanides at lower temperatures than they are usually formed is not well understood. Analyses of the finished products shows the same amount of sodium chloride and fluoride as was present in the original charges. There is no visible evidence of transformation or decomposition of the chloride or fluoride taking place during the reaction and no plausible chemical reaction can be written showing the participation of the halogen compound in bringing about the combination of sodium, carbon and nitrogen or their compounds to form sodium cyanide.

In the absence of any tangible evidence of chemical action, the View is held that the function of the halide compound in the reaction is a physical one, and has to do with the Whole complex melting point diagram of the system.

Besides acting as a iiux and dissolving away protecting coatings of already formed cyanides, liquefaction of the mass allows nitrogen to dissolve and increases the velocity of its action. These combined physical functions of the halide compound also bring about a more intimate physical contact between the reactive elements of the charge and oier an explanation of the lower temperature required for the cyanide formation.

The following equation (1) expresses in toto the generally accepted reaction. by which sodium'cyanide is formed from sodium carbonate, carbon and nitrogen:

The chemistry of the reaction is more complicated than is indicated by the above maare equation. We know, for example, that in carrying out the above reaction in the ordinary manner by heating sodium Carbonate and carbon in nitrogen at from 950-1000 C., if the nitrogen supply is insuflicient, or cut off entirely, metallic sodium and also sodium carbide are formed as well as sodium cyanide.

ln the presence o a flux such as sodium chloride or sodium fluoride, or mixtures of the same, it is quite possible that the above reaction takes place through a succession of progressive steps and that the nitrogen is first combined in an intermediate compound formed at lower temperature, through which it passes tra-nsitorily into the cyanide.

The presence of sodium cyananiide found in the product of experiment #1, given above, favors this view. We know from Drechsels reaction (Jr. pr. Chem. 1880, 2, 21-77) that in the presence of carbon alkalimetal cyanamides take up carbon and pass into cyanides at temperatures below 800 C. F or this reason it was only in experiment #1, carried out at 730 C., that any trace of cyanamide was found in the product. lln experiments 2 and 3, conducted at temperatures above 800, only sodium cyanide was found in the product.

Cyanamides in general are known to form at lower temperatures than the corresponding cyanide, and the formation of sodium cyanide at lower temperature through the physical agency of sodium chloride or fluoride may possibly be explained by chemical reactions taking place in a manner similar to the following:

Combining all of these into one equation, we have the empirical equation:

(i) Na2co3+4c+x2=2naon+aoo given above.

rlhe sodium chloride and fluoride, by their fluxing action, allow the above reactions to come to equilibrium more speedily since they effect closer hysical contact of the reacting materials. hus, these reactions proceed to the right until true equilibrium is more nea-rly attained. In support of this View of the mechanism of sodium cyanide formation, the following facts, which are well established experimentally, may be cited:

1. Sodium oxide is always found in the finished product.

2. Sodium is reduced from sodium oxide at lower temperatures than from sodium carbonate-Gmelin-Kraut 2,' 1; 285.

3. Sodium carbide is formed when sodium is acted upon by carbon or carbon monoxide.

'4. Calcium carbide breaks down into a sub-carbide CaC' when heated with calcium luoride. The sub-carbide absorbs nitrogen readily and forms calcium cyanamide; see

Allmand, Applied Electro-Chemistry, l1:81; Arnold 1912; and Knox, Fixation of Atmospheric Nitrogen, 91, 92. By analogy, sodium carbide may follow the same course.

lt is of course possible that there-action .only proceeds as far as the formation of sodium carbide which, being an unsaturated compound, takes up nitrogen directly to form cyanide:

or it may follow the same course as calcium carbide shown by Allmand:

which, on further heating, with carbon, ac-

cording to Drechsel, passes into cyanide:4

rl'he nitrogen required for the production of cyanides by this process, as stated above, may be free or elemental nitrogen in a pure state, or it may be mixed with other gases, as, for example, with carbon monoxide, as in roducer gas.

n operating with producer gas as the source of nitrogen, certain precautions are necessary: Carbon dioxide destroys cyanide rapidly even at high temperatures and the producer gas used must contain the minimum quantity of C()2 in order to obtain practical results. The cyanide charge cannot be allowed to cool 0H' in producer gas, since the equilibrium for the equation gives almost pure CO above 900 C. while at 500 to 600 C. the product is almost all C02. By observing the proper precautions, the same results are obtained with producer gas as with free nitrogen.

'llhe nitrogen may be passed into or through the charge under ordinary atmospheric pressure but I prefer to use an absolute pressure of about 30 lbs. er sq. in. as it insures a higher concentration of the nitrogen in the charge and more intimate contact. The function of the pressure is purely physical.

Although, as indicated above, the conditions under which the new process can be carried out may be widely varied, one preterred embodiment of my process is exemplified in the following description taken in connection with the accompanying drawing which shows a view in vertical section through the center of an apparatus which I have found to be suitable for carrying out' a valve 4 for introducing the nitrogen,theY

pipe 3 ending in a distributor 5 near the bottom of the retort. A charging hol'e in the head 2 for introducing the charge is closed with a plug 6 and an outlet 7 1s also provided in the head 2 for the escape of the gases given oil' in the reaction, together with the excess of nitrogen or producer gas used in the operation. The pipe 7 ends in a cross carrying the valves 8, 9 and 10 as shown. The pipe having valve 8 leads to a manometer (not shown). The valve 9 is for taking gas samples during the operation. The retort is also fitted witha pyrometer pocket 11 and a therinocouple 12 for indicating the temperature of the charge during the o eration. The retort proper is set inside o au outside iron casing 13, covered with a fireclay composition 14 to protect it from oxidation by the gases of the combustion chamber 15. The combustion chamber 15, in which the retort 1 and casing 13 are placed, is similar to the ordinary steel-soaking it furnace in which steel ngots are heate before being rolled.

Tn carrying out the operation of manufacturing sodium cyanide the retort l is first closed tight and the charge, which, for example, consists of of the eutectic mixture and 40% of coke, equivalent to approximately 39% of sodium carbonate, 21% of sodium chloride, and 40% of coke, isrintroduced through` the charging hole until the retort is' filled about two-thirds full. The retort is then placed inside the rotective iron casing within the furnace, an the'connections made to the manometer and to the source of nitrogen' supply, as indicated in the retort through the valve 4. The valve 8 is now o ened to the manometer and the outlet or b ceder valve 10 adjusted, so that the desired absolute pressure Aof about 2 atmospheres is obtained inside the retort. Tn view of the high temperature it is not practicable vto exceed a pressure of about 20 pounds per sq. in. above atmospheric pressure (i. e., 35 pounds absolute pressure). The beneficial e'ect of pressure is noticemanera connections b roken to the nitrogen supplyl and the retort' sealed by closing the valves 8, 9, 10 and 4f. The retort is then lifted from the furnace by a suitable hoistand another` retort already charged set in theV furnace and the operation repeated.

The hot retort is transferred to a cooling room and when it has cooled to room temperature, its contents are dumped by removing the flanged head 2; the flanged head is then again fastened to the retort and the latter recharged, for the second opera'tion,

through the opening made by removing the plug 6.

.The product from the retort containing sodium cyanide is placed in air-tight cans until it can be extracted for the production of high grade sodium cyanide or hydrolyzed for the production of ammonia by the means usually employed for these purposes. To the resulting residue in either case is added the necessary make-up of sodium carbonate and carbon and after drying and thoroughly mixing the remade charge is again furnaced for the production of more cyanide. This operation may be repeated until such time as the impurities from the coke have built up to such an extent that they interfere with the proper operation of the process, when the soluble sodium salts, consistin of sodium carbonate, sodium hydrate rom the oxide present) and sodium chloride, or fluor- 1de, as the case may be, are dissolved from the insoluble carbon residue, evaporated, drled, and made up with a new lot of carbon. Byl selecting a form of carbon low 1n ash the furnacing operation may be repeated many times before an entire removal of carbon becomes necessary.

It will be understood that l may depart widely from the charges and proportions o the mixtures given above; that I may vary the proportion of chlorides or uorides to the other alkali-metal compounds, and that in placeof alkali-metal carbonate l may use other compounds of the alkalimetals, such as sulphates, hydroxides, and the like; or that I ma use varying proportions of a mixture o various alkali-metal halides in the mixtures with other alkalimetal compounds and make many changes in the methods of manipulation or of the aplll() menare paratus without departing from the spirit and scope of the invention.

Having thus 'described my invention, what i claim is:

l. The process of making an alkali-metal cyanide, which comprises heatin'g in contact with nitrogen a mixture containing an alkali-metal halide, a compound of an alkali-metal other than a halide, and carbon to a temperature suicient to edect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkalimetal cyanide.

2. The process of making sodium cyanide which comprises heating in conta/ct with nitrogen a mixture containing a sodium halide, sodium carbonate, and carbon, to a temperature sucient to eect a reaction between the carbon, nitrogen, and the sodium carbonate to form sodium cyanide.

3. The process of making sodium cyanide, which comprises heating in contact with nitrogen a mixture containinoe sodium Huoride, sodium'carbonate, and car on, to a 'temperature sudicient to edect a reaction between the nitrogen, carbon and the sodium carbonate` to form sodium c anide.

4. The process of maklng an alkali-metal cyanide, which comprises heating in contact with 'a nitrogen-bearing gas a mixture containing an alkali-metal halide, a compound of an 'alkali-metal other than a halide, and carbon, to a temperature suicient to etect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkali-metal cyanide.

5. The process omaking sodium cyanide which comprises heating in contact with a nitrogen-bearing gas a mixture containing a sodium halide, sodium carbonate, and carbonto a temperature sucient to effect a reaction between the carbon, nitrogen, and

th?1 sodium carbonate to form sodium cyan1 e.

6. The process of making sodium cyanide, which comprises heatinlg 1n contact with a nitrogen-bearing gas a mixture containing sodium iuoride, sodium. carbonate, and carbon, to a temperature suiicient to edect a reaction between the nitrogen, carbon, and the sodium carbonate to form sodium cyanide.

7. rThe process of making en alkali-metal cyanide, which comprises making'a mixture of an alkali-metal halide, a compound of an alkali-metal other than a halide, and carbon, heating the mixture in a closed retort to a temperature of from 800 to 970 C., and subjectmg the heated mixture to the action of nitro en, substantially as described.

.8. he process of making sodium cyanide, which comprises making a mixture of a sodium halide, sodium carbonate and carbon, heating the mixture in a closed retort to a` temperature of from 800 to 970 C., and subjecting the heated mixture to the action of nitrogen, substantially as described.

9. rihe process of making sodium cyanide, which consists in making a mixture ofsodium fluoride, sodium carbonate and carbon, heating the mixture in a closed retort to a temperature of from 800 to 970 C., and subjecting the heated mixture to the action ot nitrogen, substantially as described.

10. The'process of making an alkali-metal cyanide, which comprises making a mixture of an alkali-metal halide, a compound of an' alkali-metal other thana halide, and carbon, heating the mixture in a closed retort to a. temperature of from 800 to 97 0 C., and subjecting the heated mixture to the action of a nitrogen-bearing gas, substantially as de scribed.

11. rihe process of making sodium cyanide, which comprises making a mixture of a sodium halide, sodium carbonate and carbon, heating the mixture in a closed retort to a temperature of from 800 to 970 C., and subjecting the heated mixture to the action of a nitrogen-bearing gas, substantially as described.

12. The process of' making sodium cyanide, `which consists in making a mixture of sodium iiuoride, sodium carbonate and carbon, heating the mixture in a closed retort to a temperature of from 800 to 970 C., and subjecting the heated mixture to the action of a nitrogen-bearing gas, substantially as described.

13. The process. of making an alkali-metal cyanide, which comprises heating in contact with nitrogen underan absolute pressure of about two atmospheres a mixture containing an alkali-metal halide, a compound of an alkali-metal other than a halide, and carbon, to a temperature suiicient to effect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkali-metal cyanide.

14. The process of making sodium cyanide which comprises heating in contact with nitrogen under an absolute pressure of about two atmospheres a mixture containing a sodium halide, sodium carbonate, and carbon,

to a temperature suicient to effect a reaction between the carbon, nitrogen, and the sodi-y um carbonate to form sodium cyanide.

1.5. The process of making sodium cyanide,'which comprises heating in contact with nitrogen under an absolute pressure of about two atmos heres a mixture containing sodilum uori e, sodiumcarbonate, and carbon,

to a temperature suicient to edect a reaction between the nitrogen, carbon and the sodium carbonate to form sodium cyanide.

16. The rocess of making an alkali-metal cyanide which comprises passing nitrogen gas under 'an absolute pressure of from about 23 to 35 pounds per square inch in contact with a mixture containing an alkalimetal halide, a compound of an alkalimetal other than a halide, and carbon, while maintaining said mixture at a temperature suiiicient to etect a reaction between the carbon, nitrogen and second alkali-metal compound to form an alkali-metal cyanide,

17. rlhe process of making sodium cyanide which comprises passing nitrogen gas under an absolute pressure of from about 23 to 35 pounds per square inch in contact with a mixture containing a sodium halide, sodium carbonate and carbon, while maintaining said mixture at a temperature sufficient to eect a reaction between the carbon, nitrogen and alkali-metal compound to form sodium cyanide.

18. The process of makingv sodium cyanide which comprises passing nitrogen gas under an absolute pressure of from 23 to 35 pounds per square inch in contact with a mixture containing sodium fluoride, sodi um carbonate and carbon, while maintaim ing said mixture at a temperature suiiicient to effect a reaction between the carbon, nitrogen and sodium carbonate to form sodium cyanide.

19. The process of making an alkali-metal cyanide, which comprises heating in a retort in contactwith nitrogen a mixture containing an alkali-metal halide, a compound of an alkali-metal other than a halide and carbon, to a temperature suilicient to eiect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkali-metal cyanide, and maintaining the nitrogen at a pressure a little below the minimum pressure capable of causing injurious distortion of the retort at the temperature at whichit is maintained during the reaction.

20. rThe process of makin an alkali-metal cyanide which comprises heating in -contact with .n nitrogen a mixture containing from 10 to 25 parts of an alkali-metal halide, from 35 to 50 parts of a compound of an alkali-metal .other than a halide, and from 35 to 50 parts of carbon, to a temperature sufiicient to effect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkali-meta1 cyanide.

' l Lemma 21. The process of making sodium cyanide which comprises heating in -contact with nitrogen a mixture containin from 10 to 25 parts of a sodium halide, rom 35 to 5() parts of sodium carbonate, and from 35 to 5() parts of carbon to a temperature sufiicient to eHect a reaction between the carbon, nitrogen and the sodium carbonate to form sodium cyanide.

22. The process of making sodium cyanide, which comprises heating in contact with nitrogen a mixture containing from 10 to 25 parts of sodium fluoride, from 35 to 5() parts of sodium carbonate, and from 35 to parts of carbon, to a temperature sufficient to effect a reaction between the carbon. nitrogen and the sodium carbonate to form sodium cyanide.

23. The process of making an alkali-metal cyanide which comprises heating in contact with nitrogen a mixture containing about 20 parts of lari alkali-metal halide, about 40 parts of a compound of an alkali-metal other than a halide, and about 40 parts of carbon, to a temperature sufficient to effect a reaction between the carbon, nitrogen and the second alkali-metal compound to form an alkali-metal cyanide.

24. The process of making sodium cyanide which comprises heating in contact with nitrogen a mixture containing about 20 parts of sodium halide, about 40 parts of sodium carbonate, and about 40 parts of carbon, to a temperature suilicient to effect a reaction between the carbon, nitrogen and the sodium carbonate to form sodium cyanide.

25. The process of making sodium cyanide which comprises heating in contact with nitrogen a mixture containing about 20 parts of sodium fluoride, about 40 parts of sodium carbonate, and about 40 parts of carbon to a temperature suiiicient to effect a reaction between the carbon, nitrogen and the sodium carbonate to form sodium cyav nide.

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