CA1045786A - Process for the treatment of gas streams containing hydrogen cyanide - Google Patents

Abstract

ABSTRACT

Ammonia, hydrogen cyanide and hydrogen sulfide contained in gas streams are separated from the gas streams by contact-ing the gas stream with an aqueous solution containing free oxygen for a time sufficient for the ammonia, hydrogen sul-fide and hydrogen cyanide to react with the oxygen present to form ammonium thiocyanate and water for further treatment or disposal.
The preferred disposal method involves combining the aqueous solution with products obtained by the combustion of a fuel in the presence of oxygen in proportions to totally vaporize the constituents of the waste aqueous solution and form a resultant gas stream at a temperature of 700°F or more.
The gas stream is then passed over a catalyst capable of hydrolyzing hydrogen cyanide to ammonia and/or nitrogen and hydrogenating any sulfur and sulfur dioxide present to hydrogen sulfide. The ammonia which is formed is then separated from the gas stream by conventional means, followed by separation, when present, of hydrogen sulfide.

Description

S~ 6 PROCESS FOR THE TREATMENT OF GAS STREAMS CONTAINING
_ HYDROGEN CYANIDE

Baclc~_ und of the Invention In -the treatment of fu~l gases such as coke oven gases and the like which contain ammonia, hydrogen cya-nide and hydrogen sulfide a common treating method is to contact the gas stream with an ammonium polysulfide wash. In this technique the ammonium polysulfide reacts with the hydrogen cyan~lde and ammonia to form ammonium thiocyanate, the reaction being represented by the fol-lowing equation: :

(NH4)2 S( l)+ HCN -~ NH3- ~ NH~SCN -~ (NH~)2 Sx (1) 1qD45786 1 In the pr~cticc of this method, finely divided sulfur is addc(l to thc solution i.n order ~o main~ain the sul~ur concentration rcquired to convert all or nearly all o the S hydro~cn cyanide to ~mmonlum thiocyanate.
Thc process is dc~icicnt in that it requircs the constant addition o~ sulfur to the solution rcpresenti.ng a raw matcrial expense. In addition to ~he difficulties .
presented in dissolving the sulur, problems exist with respect to disposal o the ammonium thiocyanate which is toxic in nature without causing pollution problems.
It has been proposed by others ~o incinerate the waste liquor to form a sulfurous vapor which is hydrogenated ~o form hydrogen sulide. The hydrogen sulide so ormed is :
15 .removed from the gas stream by conve~tiona1 processes such as the Stret~ord Process in which the hydrogen sulfide is converted to sulfur.
. If sulfur is added to the system in order to remove the hydrogen cyanide and the sulfur subsequen~ly conver~ed to hydrogen sul~ide which is; in turn~ reconverted into sul~ur, it introduces a sul~ur recycle stream to the p~ocess whicl~
~ncreases ~he load on the hydrogen sulfide removal processing steps.
For example, in the treatment o~ 45 million s~andard 2S cubic feet of coke oven gas typically containin~ about 15,125 lbs of sulfur as hydrogen sulide and 3,857 lbs. o~ hydrogen cyanide, it is required that at least 4,571 lbs. o sulur be present to react to the hydrogen cyanide ~o form ammonium thiocyanate.

~ 4 57 86 1 When the ammonl~ thiocyana~e is subsequently converted to hydrogcn sul~ide and ~nonia, it represents an increase in the hydrogen sulEide content o~ the gas s~ream by a factor o~
at leas~ 1.3. This rcpresents the ideal case which assumes 100% utilization o~ the sulfur in the solution prior to the subsequcn~ reduction o hydrogen sulide which is in turn convertcd to sul~ur which must in part be recyclcd. Morc ~ypically, the cxcess of sulfur is presen~ in the solution for efective reaction of hydrogen cyanide and the actor is usually about 1.5 times or more.
As a consequence, ~his necessitates the use of a correspondingly larger and more costly hydrogen sul~ide ~emoval plant and increases the ~perating cost o~ this plant in proportion to the lncreased a~lount o~ hydrogen sulide throughout.

BackRround of the Invention Disposal o~ such aqueous solutions from such operations without causing water poLlution ~hen becomes di~icult and expensive because ~he usual methods for converting toxic cyanide and/or thiocyanate ~ons to innocuous sub~tances are re~at~vely ine~ective, Because of the difficulties in disposing of spent waste solu~ions containing ~yanide and/or thiocyana~e compounds~ the treatment o~ ~as streams to remove hydrogen cyanide, while essential to hydrogen sulfide removal, has not been widely practiced. Rather, it has been the more general practice to leave hydrogen sul~ide in the coke oven gas. Wh~n this gas is consumed as a fuel the resulting flue gases con~ain more sul~ur dioxlde than is con~istcnt with the goals o~ most air pollution control a~cncics.

~ 57~
For example, it is quite u~ual to burn c~ke o~en gas with a hydrogen sulfide content of 5,000 to 10,000 ppm by volume even though khe United States Environmental Protection Agency has recommended that such gas be treated to reduce hydrogen sulfide content less than 180 ppm by volume.
Statement of the Invention :
In accordance with the present invention there is provided a process for the elimination of cyanide constituents contained in aqueous waste cyanide containing liquors comprising an ammonium poylsulfide solution containing ammonium thiocyanate and sulphur resulting from the treatment of fuel gases containing at least hydrogen cyanide and hydrogen sulfide which comprises: -a) admi~ing the aqueous waste cyanide containing liquor with products of combustion of an organic fuel with oxygen in an amount essentially equal to that required to achieve combustion of the oryanic fuel to form a resultant gas stream in which the ammonium thiocyanate is decomposed to hydrogen sulfide and hydrogen cyanide in the presence of the products oE combustion of the resultant gas stream comprising water, hydrogen cyanide and hydrogen sulfide and being at a temperature of at least 700F;
b) contacting the resultant gas stream with a supported ~;
catalyst in the preæence of a source o~ hydrogen, which catalyst selected from the metals oE Group VA, Group VI~, the Eourth period o~ Group VIII and the Rare Earth Series of the Periodic ~able, for a time sufficient to at least hydrolyze the hydrogen cyanide to form a residual gas stream containing hydrogen sulfide and a nitrogen compound selected from the group consisting oE ammonia, nitrogen and mixtures thereof and to hydrogenate the sulphur to hydrogen sulEide;
c) treating the residual gas streamto remove the ammonia present and hydrogen sulfide therefrom.

_ ~ _ .

~45~7~36 Also in accordance with the invention thexe is provided a process for the elimination of cyanide constituents cont~ined in aqueous waste cyanide containing liquors com-prising an ammonium polysulfide solution containing ammonium thiocyanate and sulfur, which process comprises:
(a) admixing the aqueous waste cyanide containing liquor with the products of combustion of an organic fuel with oxygen to form a resultant gaseous stream in which the ammonium thiocyanate is decomposed to hydrogen sulfide and hydrogen cyanide in the presence of the products of combustion, the resultant gas stream comprising at least water and hydrogen cyanide, and being at a temperature of at least 700F;
(b) contacting the resultant gas stream with a supported catalyst in the presence o~ a source oE hydrogen which catalyst contains at least one metal selected from the metals of Group VA, Group VIA, the fourth period of Group VIII
and the Rare Earth Series of the Periodic Table, for a time sufficient to hydrolyze the hydrogen cyanide to form a residual gas stream containing a nitrogen compound selected from the group consisting of ammonia, nitrogen and mixtures thereof and to hydrogenate the sulphur to hydrogen sulphide;
~ c) treating the residual gas stream for removal o~ ammonia.
The present invention therefore provides an improved method for the treatment of gas streams containing hydrogen cyan~de, hydrogen sul~ide, ammonia and mixtures to removes these constituents. There is also provided an improved method for converting waste water solutions containing cyanide consti-tuents to convert these constituents to ammonia and/or nitrogen.
Gas streams cont~ining hydrogen cyanide, hydrogen a -.

~LB457~
sulfide and ammonia, such as coke oven gas, are treated for removal of these constituents by an aqueous absorption solution containing ~ree oxygen in which the hydrogen cyanide reacts with oxygen, hydrogen sulfide and ammonia to form ammonium ~.
5 thiocyanate and water by the reaction: -NH3 ~ H2S ~ HCN ~ 1/22 ~ NH4SCN ~ H20 (2) ~ .
and yield a gas stream essentially free of hydrogen cyanide :
and substantially reduced in hydrogen sulfide and ammonia. ~: -The ammonia and hydrogen sulfide required for the reaction are normally present in the gas stream, or where necessary provided, in part, by the aqueous solution.
The solution which retains the ammonium thiocyanate, :
when it becomes spent, is disposed of or preferably treated for conversion of the ammonium thi.ocyanate to hydrogen sulfide 4b -t -` ~4S7~6 and ammonia and/or nitrogen. The amount of hydrogen sulfide to be removed from the gas stream as sul-Eur is the same as the hydrogen sulfide content of -th~
treated gas stream rather than a system containing 1.3 to 1.5 times the amount of hydrogen sulfide present in the gas stream.
In particular, -the gas stream, such as a coke oven gas stream, is normally brought int~ contact with an aqueous absorption solution in which the total dissolved solid content is approximately 170 to 230 grams per liter.
Of this, the thiocyanate ion will be presen-t in an amoun-t Erom about 95 to abou-t 140 grams per liter, thiosulEate ion in an amount up to about 20 grams per liter, sulfate lon in an amount ~Ip to 0.5 graMs per ~i-ter, ammonia in an amount from 20 to 55 grams per liter, Eree sul~ur in an amount up to about 55 grams per liter, and dissolved Eree oxygen in an amount up to solution sat-uration at the temperature employed.
Because the reaction is favored by operating at elevated temperatures, the temperature o~ the solution employed in treating the gas stream pre~`erab:Ly ranges ~rom about 60 to about 150F.
~ s a portion o~ the solut:lon becomes spent, it is preEerably treated for conversion of ammonium thiocyan-ate to hydrogen sul:~ide and ammonia and~or nitrogen.
'I'reatment o~ the waste water stream is accomplished by admixing the waste wa-ter stream with the products of combustion of an organic fuel with oxygen typically as air in proportion to fl~rm a resultant gaseous mixture at a -temperature oE about 700 F or more. This results in the ~0~786 vaporization of water, hydrogen cyanide and, if present .
decomposi.tion of substances such as ammonium thiocyanate, to hydrogen cyanide, ammonia and hydrogen sulfide. If any sulfur or sulfur compounds are present in the was-te solution, they too are vaporized.
The resultant gas stream is then passed through a catalytic conversion zone containing a catalyst compri-sing at least one metal of Groups VA, VIA, the fourth period of Group VIII and the Rare Earth Series of the . .
Periodic Table normally in the sulfide state, supported on alumina, silica or alumina-silica for a time suffi-cient to hydrolyze the hydrogen cyanide to ammonia and/
or nitrogen and simultaneously hydrogenate in the pres-enc.e of a source of hydrogen or a hydrogen donor, any sulfur and sulfur dioxide present to hydrogen sul:~ide, The gas stream is then cooled to a temperature con~onent for the removal of ammonia and, where present, hydrogen sulfide by known techniques.
The D.ra~
The attached drawing illustrates one scheme for treating gas streams containing ammonia, hydrogen cya-nide and hydrogen sulfide and :E`or treat:Lng spent solu-tions to eliminate hydrogen cyanide to permit sa:E`e remov~:L o:E hydrogen ~ L:E`Lcle ancl ammon:la and for cl:lspo~
of the wast~ l~quoriso formed.
Des_ iption One aspect of the process o:~ the present inven-tion comprises contacting a gas stream, such as coke oven fuel gas which con-tains hydrogen cyanide, ammonia and hydrogen sulfide as impurities with an aqueous solution containing free oxygen - 6 _ . .

~45786 1 for a timc sufficicnt for the ammonia, hydrogen sulide and hydro~en cyanide to react with the oxygen present by the ~eneral reaction:
NH3 ~ H2S ~ HCN ~ 1/202 ~ NH4 SCN ~ H20 ~2) to fo~m ammonium thiocyanate and water and a gas stream esscn~ially free o~ hydrogen cyanide and substantially reduced in ammonia and hydro~en sulfide.
A portion o~ the liquor as it contains the products of reac~ion is then discardcd or furthcr treated, pre~erably by vaporization by admixture with the products of com~ustion in a vaporiza-ion zone to totally ~asify the spent liquor and convert the ~mmonium thiocyanate to ammonia, hydrogen sulfide and hydrogen cyanide and then pass~d to a catalytic conversion zone where the hydrogen cyanide is converted to ammon~a an~/or nitro~en.
If excess oxygen is present, sulfur dioxide may be ~ormed which when passed through the catalytic conversion zone where sulfur, i~ present, ~s hydrogenated to hydrogen sulide, and where sulfur dioxide is also hydrog~nated to hydrogen sulfide.
The resul~ant gas stream which contains ammon~ a~d hydrogen sulfide ~s then processed by convcn~ional means for extraction of ammonia and hydrogen sulide prior ~o ventlng the gas strcam to th~ atmosphere.
Becausc oxygen is used to convert the extracted hydrogen sulfide, ammonia and hydrogen cyanide to ammonium thiocyana~e as opposed to an ammonium polysul~ide solution, equipment requircm~nts for removal of hydro~cn sulfide are only those 3 necessary to copc with the original sul~ur prescnt as .

.. : ' : ' ;. ' . ' ' ' ' , ~ 786 1 hydro~en sulfide as opposed to additional hydrogen sul~ide generated when an ammonium polysulide wash is used to remove hydrogen sulfide, hydrogen cyanide and ammonia ~rom the gas s~ream.
With reference no~ to the Drawing, the aqueous oxygen containing solution from oxidizing tank 10 is passed to wash tower 12 by line 14 in countercurrent ~low with the fuel gas containin~ hydrogen cyanide, ammonia and hydrogen sulfide entering wash_b~7cr 12 by line 16~
The temperature of the wash solution entering wash tower 12 is controlled and either cooled or heated dependin~
upon thc temperaturc desired us~n~ hea~ cxch~n~cr 18.
~n gcncr~l, thc comp~sition o~ the solution enter~ng wash to~cr 12 l-as a ~otal dissolvcd solids conten~ o~ ~rom lS 170 to 230 grams per liter o which thiocyanate ion is present in an ~mount of irom about 95 to about 140 grams per liter thiosulate ion in an ~mount o~ ~rom 0 to about 20 grams per litcr, sulfite ion in an amount o~ from O to about 0.5 grams per liter, these being associated with 20 about 20 to about 5S grams per litcr o the dissolved ammonia. There may also be present up to about 55 grams per liter free sulfur, the balance of the solution is essentially wa~er and oxygen in an amount up to solut-ion Z5 fiaturation a~ the temperature and pressure employed.
Oxygen is supplied to the solution in oxidation tank 10 by air blo~er 20 which bubbles air through the solution.
Exhaust gases leaving tank l0 are passed through coolcr 22 ~nd Icnoclc out pot 24 before bein~ vented to the atmospll~re.
3 TIlc solution condcnscd in condcnser 22 returns to oxidi~in~
tank 10 by line 26.

,11.

1~4~7~6 1 I~ desired, air can also be pumped direc~ly into the w~sh tower 12 ~or the required xeactions by line 28.
In wash to-~er 12 the gas stream while 10wing in countcrcurrcnt flow with the liquid in wash tower 12 is subjected to the following reactions:

2~H3 ~ 2H2S ~ 202 ~ (NH4)~S203 2 (NH4)2S23 ~ 2HCN ~ 2NH4scN ~ H20 ~ 2 (4) In reaction (3),the ammonia and hydrogen sulide combine with the oxygcn which is present to ~orm ammonium thiosulfate and water. The ammonlum thiosulate then reacts by rcaction (4) with hydrogen cyanide to ~orm ammonium thiocyanate, wa~er and rcleasing some o~ the oxy~en back to the wash solution.
The reactions may be carr~ed out at any desired temperature or pressure. However, i~ is expedient to carry out ~he reactions at moderatcly elevatcd temperatures, with solution tempera~ures ~rom about 60 to about 150F ~;
being conveniently employed.
The solution wi~hdra~ ~rom the base o wash tower 12 is spllt. A por~ion ~s retu~ned to oxidiæcr tanlc 10 by line 30, and the balance discarded with the general proviso that a liquid level control valve 32 is made avail~ble to draw o~ a por~ion o~ the passage to an incinera~or or other disposal means, in order to main~ain a constant level in the basc o~ the wash tower 12;
~ncineration may be made by any convenient means.
For instance, if the total sulur contcnt is su~;cicntly 30 low, the discarded portion of the wash liquor may be . . .

`~457~6 1 simply burncd provided the S02 conSent of the ~lue gas stream is within acccptable standards for emissions.
The solution which is returned to oxidiæer tank 10 is provided with make-up oxygen and watcr for return to wash to~er 12 by line 14.
The balancc of the solution wi~hdral~ from wash tower 12 which is regarded as spent solution and is preferably passed by line 34 to combustion-vapori~ation zone 36 where it is admixed with the products of combustion o a fuel with oxygen, normally provided as air, in proportions such that there is ~orsned a resultant vaporized gas stream having a temperature o ~rom about 70~F ~o about 2000F ox more in which the matcrials dissolv~d or cntrained in the aqucous solution are ~aporizcd and where the ammoniusn thiocyanate is decomposed ~o hydrogen cyanide, ~nonia and hydro~en sul~ide.
If excess oxygen is present in the combustion products, sulfur dioxide snay also be ormed. Xf the aqueous spent solution contains tars, complete gasiication o~ ~he ~ars 20 requires a higher rcsultant gas temperaturel namely a temperaturc of abou~ 1000F or mor~.
With particular reerence to th~ ~rawing~ the aqueous waste liquor is ed into a combustion-vaporization zone 36 where it is admiY~cd w~h ~he produc~s o combustion ol ~ ~ucl ~itl~
2S oxy~n, norml~lly providcd as ail, ~n proportions SllCh tha~
~herc is ormcd ~ resuLt~n~ vapori7cd gas stre3m l~avin~ ~
tempcraturc o~ abou~ 700F to a~ou~ 2000DF or morc in which prcera~1y rom abou~ 1000F to a~ou~ 2000F the mat~rials dissolvcd or cn~r~inc~ in tllc ~queous solu~ion are v~porized . -10-~ D4S~86 or decomposed to form a gas stream including water, hydrogen cyanide and ammonia and, if present, hydrogen sulfide as well as vaporized free sulfur.
In addition, where compounds containing the thiocyanate radical are present they are decomposed to hydrogen cyanide and hydrogen sulfide.
Total vaporization of the waste water stream may be achieved by simply spraying the waste water stream into a combus-tion chamber where a hydrocarbon fuel such as a fuel gas, or oil, preferably, a fuel capable of burning with little or no soot formation, is consumed in the presence of oxygen, typically provided as air.
In combusting the fuel, the fuel to air ratio is preferably adjusted such that the products of combustion contain little or no residual oxygen to minimize the formation of sulfur dioxide.
More preferably, the fuel is burned in a deficiency of oxygen to produce hydrogen and carbon monoxide, the latter being subsequently converted to hydrogen by a water-gas shift reaction in a subsequent catalysis zone.
An alternative convenient method of totally gasi~ying the aqueous waste cyanide containing liquors is to combine the products o~ combustion and the waste solution in a ~luid-ized bed (not shown) containing an inert material such as sand which serves as a heat sink to provide the heat required to totally gasify the waste liquor.
After the gasification step, the resultant vapors are passed to catalysis zone where the hydrogen cyanide is hydrolyzed to ammonia and/or nitrogen, depending on the tempera ture employed. Any sulfur and sulfur dioxide present are simultaneously hydrogenated to hydrogen sulfide in the presence of internally formed or e~ternally generated hydrogen.
This is accomplished by passing the gasified stream from the vaporization-combustion zone 36, optionally through a precipitation zone 38, where any solids entrained in the gas stream, such as from a fluidized bed may settle out, then to a catalytic reactor 40 containing one or more metals selected from Group VA, Group VIA, the fourth period of Group VIII and the Rare Earth Series of the Periodic Table, normally in the sulfide form, as defined by Mendeleef and published in the Periodic Chart of the Atoms by W. N. Welch Manufacturing Company, deposited on a support such as alumina, silica or alumina-silica.
In the preferred embodiment, the catalyst contains one or more sulfides of the metals iron, nic~el, cobalt, molybdenum, vanadium, thorium, uranium and the like deposited or co-precipitated on the support.
The most preferred catalyst is a supported sulfide of cobalt and molybdenum which is capable of completely hydrolyzing hydrogen cyanide to ammonia and/or nitrogen as well as hydrogenating sulfur and sulfur dioxide to hydro~en sulfide at temperature of about 700F up to about 2000F

~V4~
or more at a space velocity of 1000 volumes of gasified stream per hour (measured a-t sta~dard conditions) per unit volume o:f catalys-t at atmospheric pressure and where the gas:i:fied stream con-tains sufficient hydrogen and/or carbon monoxide which generates hydrogen by a water~gas shift reaction to form hydrogen for the : , hydrogenation reaction.
Other c,atalysts such as a supported uranium-thor-ium iron or nickel may be used e~fectively ~t higher temperatures such as 1000 F or more or where the spnce velocity is reduced.
As indicated, hydrogen is required in the gas stream where sulfur compounds are present in a concen-tration at least equal to that required to hydrogena-te the sulfur and sulfur dioxide to hydrogen sul:~ide in hydrogenation/hydrolysis reactor 40. ~, ~ Iydrogen may be supplied ahead of the hydrogenation/
hydrolysis reactor 40 by any convenient method incl~di~ ,:
admixture of a hydrogen containing gas with the gasified vapors.
A convenient alternative, is to operate the combus-tion zone with a de:~iciency of air to produce hydrogen and carbon monox:Lde, the latter being convehted ko hy-clrog~n b~y a waker-~a~ sh:L:~k reaatrl.an cakalyz.ed by the hydrogenation/hydrolysis catalyst employed in reactor 40.
Following completion of the hydrolysis and hydroge~nation reactions, the vapor stream is cooled and treated ~or removal of ammonia and hydrogen sulfide by known methods.

~04~5786 The gas stream, for instance, may be cooled by pas-sage through waste heat boller 42 to a -temperature con-sonent f'or removal of ammonia and, if presen-t, hydrogen sulfide.
When hydrogen sulfide is present, a most expedient way of removing the ammonia is to con-tact the gas stream with either sulfuric or phosphoric acid to form ammonium sulfate or ammonium phosphate which settle from the liq-uor as crystals and may be recoverd therefrom by any conventional means as products of commerce. In the alt-ternative, ammonia can be extracted as such.
With respect to the removal of` hydrogen sulfide, any number of extraction methods are feasible with abs-orption methods being preferred.
~ or instance, the cooled process gas may be passed -through alkaline absorption solutions which are cont:in-uously regenerated by oxidat:Lon to produce sulfur using catalysts such as sodium vanadate, sodium anthraquinone disulfonate, solium arsenate, sodium ferrocyanide, iron oxide, iodine and like catalysts.
A convenient alternative is to use regenerative absorption so'lut:Lorls such as am:Lnes, sulfonates, potas-sium carbonate and the like. These solut:Lons belng typ:Lca.~.ly r@g~ncratcd by steam str:LppLng to p;rocluce hydrogen sulfide.
The preilerred extractions system is that Icnown as the "Strct~ord Pro~ess" which employed a solution con-ta:ining sodium carbonate, sodium vanada-te, and sodium anthraquinone-disulfonic acid as the absorben-t used in the absorber.

~gl5786 The absorbed hydrogen sul~ide is oxidized to sulphur in the absorber and an associated time tank and the absorption solution regenerated by oxida-tion typically us:ing air as -the oxidizer.
The sul~ur~is recovered from -the solution by con-ventional menas such as ~lotation, ~iltration, centri-fuging, melting, decanting under pressure and the like.
In carrying out the process of this invention, it is also -feasible to convert the hydrogen cyanide in catalysis zone l~ directly to inert nitrogen by maintain-ing a reducing atmosphere in the catalysis zone and raising the temperature at which hydrolysis is carried out. This can eliminate in whole or in part the ne~d ~or extracting ammonia with the expense o~ operating a-t higher conversion temperatures.
While applicable to the speci~ic solution ~or the treatment o~ gas streams descr:ibed herein, the waste liquor disposal technique can be applied to any aqueous cyanide containing liquor.
As used herein, there~ore, the term "aqueous waste cyanide containing liquors" means an aqueous solution conta:Lning compounds assac.Lated w:Lth the cyanLde rac1lcaL
(-C - N) as such or as the thiocyanate radical (-S - C -N) whlch re~uLks 1'rom the rcmoval o~ hydrogen cyan:ld~ ~`rom gas streams. This hydrogen cyanide may be removed alone or typically with other compounds such as ~ree sul~ur hydroger1 ~ul~:Lde (~12S), ammon:La (N~13), cresols, phenols tars and the like.

~D4S7~

1 The aqueous waste cyanide containing liquors to be treated in accordance with the practice o the.inven~ion are, for example, those formed from the treatment of a fuel gas, such as a coke oven gas, by any aqueous wash including the S above which removes hydrogen cyanide.

1 , ' , ' ..

2 ~ .

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Claims (8)

1. A process for the elimination of cyanide constituents contained in aqueous waste cyanide containing liquors compris-ing an ammonium polysulfide solution containing ammonium thiocyanate and sulfur resulting from the treatment of fuel gases containing at least hydrogen cyanide and hydrogen sulfide which comprises:
(a) admixing the aqueous waste cyanide containing liquor with products of combustion of an organic fuel with oxygen in an amount essentially equal to that required to achieve combustion of the organic fuel to form a resultant gas stream in which the ammonium thiocyanate is decomposed to hydrogen sulfide and hydrogen cyanide in the presence of the products of combustion, the resultant gas stream comprising water, hydrogen cyanide and hydrogen sulfide and being at a temperature of at least 700°F;
(b) contacting the resultant gas stream with a supported catalyst in the presence of a source of hydrogen, which catalyst contains at least one metal selected from the metals of Group VA, Group VIA, the fourth period of Group VIII
and the Rare Earth Series of the Periodic Table, for a time sufficient to at least hydrolyze the hydrogen cyanide to form a residual gas stream containing hydrogen sulfide and a nitrogen compound selected from the group consisting of ammonia, nitrogen and mixtures thereof and to hydrogenate the sulfur to hydrogen sulfide;
(c) treating the residual gas stream to remove the ammonia present and hydrogen sulfide therefrom.

2. A process as claimed in claim 1 in which hydrolysis is carried out at a temperature of from about 700 to about 2000°F.

3. A process as claimed in claim 1 in which hydrolysis and hydrogenation are carried out at a temperature from about 1000 to about 2000°F.

4. A process as claimed in claim 1 in which the supported catalyst contains cobalt and molybdenum.

5. A process for the elimination of cyanide constituents contained in aqueous water cyanide containing liquors comprising an ammonium polysulfide solution containing ammonium thiocyanate and sulfur, which process comprises:
(a) admixing the aqueous waste cyanide containing liquor with the products of combustion of an organic fuel with oxygen to form a resultant gaseous stream in which the ammonium thiocyanate is decomposed to hydrogen sulfide and hydrogen cyanide in the presence of the products of combustion, the resultant gas stream comprising at least water and hydrogen cyanide, and being at a temperature of at least 700°F;
(b) contacting the resultant gas stream with a supported catalyst in the presence of a source of hydrogen, which catalyst contains at least one metal selected from the metals of group VA, Group VIA, the fourth period of Group VIII
and the Rare Earth Series of the Periodic Table, for a time sufficient to hydrolyze the hydrogen cyanide to form a residual gas stream containing a nitrogen compound selected from the group consisting of ammonia, nitrogen and mixtures thereof and to hydrogenate the sulfur to hydrogen sulfide;
(c) treating the residual gas stream for removal of ammonia.

6. A process as claimed in claim 5 in which the residual gas stream is treated for the separation therefrom of the hydrogen sulfide present and formed.

7. A process as claimed in claim 5 in which hydrolsis is carried out at a temperature of from about 700 to about 2000°F.

8. A process as claimed in claim 5 in which the supported catalyst contains cobalt and molybdenum.