US1317755A

US1317755A - Process of recovering hydrocyanic aged

Info

Publication number: US1317755A
Authority: US
Publication date: 1919-10-07
Anticipated expiration: 1936-10-07

Description

"G.H'.BUCHANAN.,

PROCESS 0F RECOVERING HYDROCYANIC ACID. APPLICATION FILED MAY?, 1919.

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GUY H. BUCHANAN, 0F BOSELLE, NEW J ERSEY, ASSIGNOR TO AMERICAN CYANMID COMPANY, 0F NEW YGRK, N. Y., A. CORPORATION 0F MAlNE.

PROCESS 0F BECOVERING HYDROCYNIC ACID. y

Specification of Letters Patent.

Patented oet. 7,' rare.

Application filed Hay 7, 1919. Serial No. 295,299.

To all whom t may concern.'

Be it known-that L GUY H. BUCHANAN, a y citizen of the United States, residing atRoselle, in the county of Union and State of N ew Jersey, have invented certain new and useful Improvements in Processes of Becovering Hydrocyanic Acid; and l do hereby declare the following to be a full, clear, and eXactdescription of the invention, suc-h as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of .recovering high grade hydrocyanic acid from a. crude form of cyanid, and has for its object to provide a method of obtaining such high grade product from low grade raw materials which will be more eitcient and less costlyv than -those heretofore proposed.

With these and other objects in view the invention vconsists in the novel steps and combinations of steps constituting the process. all as will be more fully hereinafter disclosed, and particularly pointed out in the claims.

ln order that the precise nature o this invention may be the more clearly understood it is said It is well known in the art that when the ordinary sodium orl potassium Cyanid of commerce, containing say Qtr-98% of the corresponding cyanid, is treated with a strong vmineral acid, hydroc-yanic acid is evolved and a conesponding sodium or potassium salt of the mineral acid used is left behind in the residue. F or instance, in the case of sodiumcyanid and sulfuric acid, the reaction takes place according-to the well known equation- The usual method heretofore employed of carrying out this operation was to place in a closed vessel ya quantity of sulfuric acid, of a strength varying from comparatively dilute acid up to 66 Baume. although the? majority of operators prefer the more dilute acid. It was then the practice to drop powdered or lump cyanid into the acid, the lump form being preferred, as yielding somewhat more hydrocyanic acid than the powdered form, especially when the cyanid is not substantially pure.

Later developments, however, in this art have shown it practical to dissolve the pure forms of cyanifl in lWater and ,to then add the solution to the sulfuric acid in a suitable generating vessel.

rlhis practice which has been quite highly developed since the outbreak of the European war, has shown eiiiciencies of hydrocyanic acid production upward of 75% but rarely have eiiciencies as high as 85% been obtained in long practice, and published reports of recent work in connection with poison gas have shown less than 80% for standard practice.

a crudeV or impure form of cyanid made from cyanamid and which may be considered to contain approximately 35% sodium cyanid, 40% calcium chlorid, 5% sodium chlorid, 15% of lime and 5% of miscellaneous impurities coming from the cyanamid and playingy no essential part in the operation. `When this said crude cyanid material is treated in the same manner as the pure cyanid, extremely poor results are obtained, the yield of hydrocyanic acid gas being usually less than 7 0% and in man v instances as low as 50%. The said crude cyanid can not .bedissolved completely in water because it contains-a considerable percentage o insoluble lime and other impurities, and further, if one attempts to prepare a solution the hydration of the lime causes the evolution of considerable heat, and 1t 1s well lmown that hot solutions of cyanid rapidly and spontaneously decompose.

Upon the treatment of this crude cyanid l with a mineral acid, such as sulfuric acid,

apptus as is used in the pure cyanid.

In the present lnventionl propose to use `The common practice heretofore recommended for the production of prussic acid involves the running of a solution of cyanid into the sulfuric acid. In such case, an excess of sulfuric acid ismaintained in the` generator throughout the major portion ofy the reaction and-this excess acid, for instance, could react upon the chlorids present in the crude cyanid forming hydrochloric acid, which would be evolved along wit-h the prussic acid, and not only contaminate the latter, but also give rise to serious corrosion difficulties in the apparatus used for recovering the prussic acid. It is therefore, necessary in handling the crude cyanid to prevent any such evolution of hydrochloric acid, and the present invention presents a way of successfully using crude cyanid such as described above, for the production of pure prussic acid.

In carrying out the presentprocess, I proceed in the following manner, reference being had to the accompanying drawing forming a part of this speciiication in which the figure is a diagrammatic sectional view of` one form of apparatus suitable'therefom- Into a suitable generating vessel 1 made of acid resisting material, I introduce a predetermined quantity of water, for example, three or four times the weight of the crude cyanid I vintend to use, and to this said water I add the said crude cyanid in the form of dry thin flakes such as it occurs on the open market. Or I may charge the dry flakes into vthe generator and then add to it the requisite quantity of water as indicated above, it not affecting the process as to which method of operation is used. I immediately close up the generator ,l and as rapidly as possible run' in the equivalent amount of sulfuric or other mineral acid necessary for decomposing the sodium cyanid in the crude cyanid added. yThe lime present being a strongly alkaline compound,

with a greater aiinity for acid than the sodium cyanid, naturally my acid addition must also be ample to take care of the free lime present, but in'no case do I add suffe cient acid to more than take care of the alkalinity ofthe solution, and the sodium cyanid present, althougho ay small excess of sulfuric acid is not harmful if this said excess is notl too great. It is not necessary to add sulicient acid to decompose the chlorids completely or ity,`my acid addition amounts to approxisodium cyanid.v

The acid is run in quite rapidly through in fact in any considerable part. For example, the common practice in carrying out the prior process above mentioned is to add one part 66 B. sulfuric acid to one part 9698% sodium cyanid; whereas in the case of crude cyanid, on account of its alkalinmately l times as much as is used in the case of pure cyamd for the samelcontent of a supply pipe/2,z consuming less' than ten minutes for a charge of as much as 500 pounds of crude 'cyanid at an operation. The solution in the generator heats up and a considerable quantity of prussic acid is evolved and passes out through a pipe 3 to the recovery apparatus, not shown. The rest' of the prussic acid generated dissolves in the bulk of `the solution used and I indit a simple mat-ter to drive this out by the direct introduction of a very small quantity of steam which is forced from a pipe 4 through' the solution in the generator. IBy operating in this way, I have repeatedly obtained 93% recovery of hydrocyanic acid in fairly concentrated form and havel at times obtained as much as These recoveries are considerably above those obtained in the older process operating on pure cyanid. Y

To avoid the contamination AofI the hydrocyanic acid by hydrochloric acid I make the acid addition at the bottom of the generator and underneath the surface of the emulsion of crude cyanid and Water present. In this way I always have present an excess of unreacted cyani'd which would be decomposed by any hydrochloric'acid set free in the bottom of the apparatus and consequently I obtain hydrocyanic acid practically free' from 'hydrochloric acid. In many experiments I `have found no hydrochloric acid or at most traces in undeterminate quantities in my recovered hydrocyanic acid. To insure absolute freedom from even traces of hydrochloric acid, I may insert in the pipe line 3 conveying the hydrocyanic Y acid to the recovery plant lumps of lime stone 5 which absorb the hydrdchloric acid and do not react upon hydrocyanic acid. This apparatus is simple and easy to main-l tain and the oonsumptionof lime stone for long time operation .is practicably negligible. I am aware that it has been proposed to steam jacket generators for making hydrocya-nic acid but I have found it a very decided'improvement to directly introduce livesteam in the generator and I thereby ascribe my extremely high recoveries ih' part to this introduction of l1ve steam directly into thek generator.

The hydrocyanic acid produced byl the present method of generation is of essen- ,may vary the details of the above procedure wlthout departing from the spirit of the invention` and therefore, I do 110i" wish t0 b@ limited to the above disclosure except as `may be required by the claims.

What I claim is l 1. The process of producing hydrocyanic acid from raw material containing a substantial percentage of impurities, which consists in mixing said raw material with water; subjecting' said mixture to the action 'of a mineral zicid introduced beneath the surface of said mixture, whereby hydrocyanic acid gas is evolved; subjecting said mixture to the direct action of steam, whereby any gas which may be dissolved in said mixture is driven oi'; passing the evolved gas through a scrubber; and suitably recovering said hydrocyauic acid gas, substantially as described.

2. rlhe process of producing hydmcyanic acid from ycrude cyanids derived from cyanamid and which contain a substantial percentage ofinsoluble impurities, which consists in mixing said crude cyanids with water to form an emulsion; introducing sulfuric acid beneath the surface of said emuling o hydrocyanic acid gas; passing steam gas through a `scrubber; and suitably recovering said hydrocyanic acid gas, substantially as described.

3. rlhe process of producing hydrocyainc` acid from crude cyanids which contain a substantial percentage of impurities in the form of chlorids which consists in mixing said crude cyanids with water; subjecting said mixture to the action of sulfuric acid introduced beneath the surface thereof, whereby 'hydrocyanic acid. gas is evolved and any hydrochloric acid produced is caused to react with lthe cyanids present; passing steam through said mixture to drive ofi'l any of the evolved gas which may be dissolved therein; and collecting and treating said evolved gas to remove any hydrochloric acid passing over therewith, substanv tially as described.

4. The process of increasing the yield of substantially pure hydrocyanic acid obtainable from low grade cyanids derived from cyanamid and which contain alkaline imthrough the said mixture to drive off any ofthe said gas which may be Vdissolved therein; suitably treating the said gas to remove any impurities` therefrom; and suitably recovering the said treated gas,- substantially as described.

5. The process of producing substantially pure hydrocyanic acid from low grade cyanids which contain a substantial percentage of impurities in the form of chlorids and lime which consists in mixing said low grade cyanids with water; treating said mixture with a suiicient quantity of sulfuric acid to neutralize the limey present and to decompose the cyanids to evolve hydrocyanic acid gas; introducing steam be- -low the surface of said mixture to drive olf acid from low grade cyanids which contain a substantial percentage ofimpurities in the form of chlorids and lime which consists in mixing said low grade cyanids with water to form an emulsion; treatingsaid emulsion with a sufficient quantity of sulfuric acid to neutralizel the same and to reactwith the cyanids Ypresent to evolve hydrocyanic acid gas, the said sulfuric acid being introduced below the surface of said emulsion whereby any hydrochloric acid produced is caused to react with said cyanids; introducing steam below the surface of said emulsion to drive od any of the hydrocyanic acid gas-which may be dissolved therein; passing said gas through a lime stone scrubber to remove any hydrochloric acid contained therein; and suitably recovering said gas, substantially as described.

7. The process of producing hydrocyanic acid from low grade cyanids which contain a substantial percentage of impurities in the form of chlorids and lime` which consists in mixing said low ter to form an emulslon; treating said emulsiony with a suicient quantity of 'sulfuric acid .to neutralize the same and to react with the cyanids present to evolve hydrocyanic acid gas, the vsaid sulfuric acid being introduced below the surface of `said emulsion whereby any hydrochloric acid produced is caused to react with said cyanids; lntroducing steam below the surface of said purities which consists in mixing said low' grade cyanids with water; adding to said mixture a suiicient quantity of a mineral acid to substantially neutralize the same and to decompose the cyanid present, drivemulsion to drive 0H any ofthe hydrocyanic acid gas which may be dissolved there.- in; passing said gas through a rectifying column; and suitably recovering said gas, substantially as described.

ade cyanids with waf 8. The process of produclng llydrocyanicl acid from low grade cyanidsv which contain a substantial percentage of impurities in the form of chlorids and lime which consists in mixing said low grade cyanids with Water t0 form an emulsion; treat-ing said emulsion with a sufficient quantity of sulfuric acid to neutralize the saine and to react with the cyanids present to evolve hydrocyanic acid gas, the said sulfuric acid beingintroduced below the surface of said emulsion whereby any hg; drochloric acid produced is caused to react `with said cyanids; introducing steam below the surface of said emulsion to drive ol' any of the hydrocyanic acid gas which may be dissolvedv therein; passing said gas through a combined limestone scrubber and rectifying column; and suitably recovering 15 said gas, substantially as described.

In .testimony whereof I aiix my signature, in presence of two Witnesses.

GUY H. BUCHANAN. Witnesses:

E. M. FITZGERALD, E. H. BOHN.