CA1236682A - Process for the removal of hydrogen cyanide - Google Patents
Process for the removal of hydrogen cyanideInfo
- Publication number
- CA1236682A CA1236682A CA000467303A CA467303A CA1236682A CA 1236682 A CA1236682 A CA 1236682A CA 000467303 A CA000467303 A CA 000467303A CA 467303 A CA467303 A CA 467303A CA 1236682 A CA1236682 A CA 1236682A
- Authority
- CA
- Canada
- Prior art keywords
- solution
- ammonium
- polysulphide
- process according
- hydrogen cyanide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1418—Recovery of products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1425—Regeneration of liquid absorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1493—Selection of liquid materials for use as absorbents
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/02—Preparation of sulfur; Purification
- C01B17/06—Preparation of sulfur; Purification from non-gaseous sulfides or materials containing such sulfides, e.g. ores
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/16—Hydrogen sulfides
- C01B17/165—Preparation from sulfides, oxysulfides or polysulfides
Abstract
A B S T R A C T
PROCESS FOR THE REMOVAL OF HYDROGEN CYANIDE
Process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide, comprising the following steps:
(a) contacting said gaseous stream in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-ducing a solution containing ammonium polysulphide and ammonium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and ammonium thiocyanate from the contact zone;
(c) decomposing ammonium polysulphide and precipitating sulphur in the solution removed in step (b), thereby producing hydrogen sulphide, sulphur and a remaining ammonium thio-cyanate-containing solution;
(d) removing sulphur from said remaining solution and hydro-lyzing the ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulphide and carbon dioxide.
PROCESS FOR THE REMOVAL OF HYDROGEN CYANIDE
Process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide, comprising the following steps:
(a) contacting said gaseous stream in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-ducing a solution containing ammonium polysulphide and ammonium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and ammonium thiocyanate from the contact zone;
(c) decomposing ammonium polysulphide and precipitating sulphur in the solution removed in step (b), thereby producing hydrogen sulphide, sulphur and a remaining ammonium thio-cyanate-containing solution;
(d) removing sulphur from said remaining solution and hydro-lyzing the ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulphide and carbon dioxide.
Description
PROCESS FOR THE REMOVAL OF HYDROGEN CYANIDE
The invention relates to a process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide.
The presence of hydrogen cyan de (HEN) in various gaseous 5 streams complicates removal of additional impurities, e.g., removal of HIS or C32, and poses problems insofar as product quality and pollution control requirements are concerned. In particular, gas streams derived from the gasification of solid carbonaceous fuel, such as coal, generally have significant 10 minor quantities of HEN which must be dealt with before the gas is utilized.
Accordingly, a practical and efficient procedure for removing impurity HEN might hove great economic importance. The invention is such a process.
The invention, therefore, relates to a process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide, comprising the following steps:
(a) contacting said gaseous strewn in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-Dyson a solution containing ammonium po]ysulphide and am~onium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and amm~nium thiocyanate from the contact zone;
(at decomposing amm~nium polysulphide and precipitating Selfware in the solution removed in step (b), thereby producing , .
, .
I, 1~3~2 hydrogen sulfide, Selfware and a remaining ammonium trio-cyanate-containing solution;
Id) removing Selfware from said remaining solution and hydra-lying thy ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulfide and carbon dioxide.
The hydrolysis of the Anaheim thiocyanate is carried out under appropriate conditions of temperature and pressure, and clm~nia, carbon dioxide, and hydrogen sulfide are produced.
These gases may key recycled and/or recovered, if desired, by known techniques. The process is preferably operated continuously.
The reactions for the process may be shown, as follows:
( 4)2 So ZNH4SCN + En + H S 3 Ix = 3 4 or 5) NH4SCN + 2H20- KIWI + H S 2NH
(N~I4)2SX 2NH3 -I HIS + Sol The particular gas streams treated according to the invention are not critical, as will be evident to those skilled in the art. Any gaseous stream containing ICON and from which it is desired to remove the HEN, and which itself does not react with the ammonium polysulphide or interfere substantially therewith may be treated according to the invention. Gaseous streams or effluents particularly suited to the invention include fuel gases produced by gasification procedures, e.g., fuel or effluent gases derived from or produced by the gasification of coal, petroleum, shale, tar sands, etc., wherein a significant quantity of HEN is present. In such gasification processes, the gaseous effluents are often quenched with water ` or gaseous liquids, and gaseous streams derived from stripping the liquid may contain HEN and may also be treated by the invention. me HEN content of such streams may vary, but the invention will preferably be employed with streams hazing an HEN
content of from 0.002 percent Jo 0.1 percent by volume. Higher .
., .
I
HEN contents even above 1 vowel are also possible. As indicated, the process of the invention is preferably continuous, i.e., make-up a~,monium sulfide or polysulphide is continuously supplied to the contact zone, and a portion or "bleed" of ammonium thiocyanate solution is continuously removed from the contact zone. The volumes of make-up and bleed will depend, inter alias on the concentration of HEN in the gaseous stream, and thus cannot be given with precision Those skilled in the art may suitably adjust solution fluky.
Suitable conditions, i.e., appropriate temperature and pressure, sufficient contact time, proper phi and appropriate concentrations of ammonium polysulphide and water ore employed to achieve the ICON conversion. Temperatures in the contact zone of from about 20 C to abut 80 C may be employed, with temperatures of from 25 C to 60 C being preferred. m e pi of the ammonium polysulphide solutions will range from about 8 to 10, preferably 8.5 to 9.5, and conceIItrations of ammonium polysulphide will preferably range from 0.01 to 1, preferably 0.1 to 0.5 moles per lithe. The most important variable controlling HEN removal and conversion is the amount of elemental Selfware available to maintain the polysulphide concentration. In general, the polysulphide solution will have at least a stoichiometric amount of the polysulphide Selfware with respect to the HEN, and preferably up to 3 or 4 times the stoichiometric amount. Elemental Selfware may be supplied in the contact zone to maintain this concentration. HIS and NH3 in the feed gas do not interfere with HEN removal or conversion, and NH3 may actually help rejuvenate the solution. The ammonium polysulphide solution may be supplied on a continuous basis to Jo the contact zone as make-up, or steps can be taken, in some cases, to generate the ammonium polysulphide to some extent in situ. Contact times may range f m m 1 to 8 units, preferably 3 to 5 minutes. m owe skilled in the art may select suitable contact or scrubbing devices to carry out the contacting or scrubbing.
As the HEN is removexl from the gaseous stream by reaction with the ammonium polysulphide solution, at least a portion of the solution, new containing ammonium thiocyanate, is removed.
In the portion of the solution ammDnium polysulphide is decomposed and Selfware precipitated. Preferably, the a~monium polysulphide is decomposed by lower m g the pi of the solution removed in step (b). Suitably, the solution removed is contacted or mixed with a sufficient amount of a suitable flurrying composition to lower the phi decompose ammonium polysulphide and precipitate Selfware, and produce HIS. The HIS released may be treated or recovered, as desired. Generally, leering of the pi to a range of 7.5 to 8 will be sufficient to precipitate the Selfware. Any suitable composition which will lower the pi the required amount may be employed. Suitably acids, such as H2S04, Hal, Eye and acetic acid solution, may be employed. Suitable acidic gases, which will be taken up or react in the solution, such as Hal or HIS, may be added to the solution. organic acids may be used, as well as other hydrogen ion supplying compositions. Moreover, the hydrogen ion-supplying material or composition need not be pure; even dilute solutions and those containing extraneous matter may be employed, so long as the extra cc~onents in the solution do not interfere with the ammonium polysulphide decomposition or react with the ammonium thiocyanate. As indicated, the hydrogen ion-supplying composition will be supplied in an amount sufficient to decompose the ammonium polysulphide and precipitate Selfware.
This amount will defend on a number of factors, and may readily be determined by those skilled in the art in the particular case.
3 In another preferred embodiment, the ammonium polysulphide m the solution removed in step (b) is decomposed by stripping this solution. Preferably, the solution is stripped key heating it, passing a non-reactive gas through it or by a combination of heating and non-reactive gas passing.
I
The stripping decomposes ammonium polysulphide, producing HIS and NH3 and precipitating Selfware. While a separate stripping zone may be provided, it is an advantage of the invention that the portion or stream may be supplied to a suitable stripping zone in a given process. For example, the portion may be supplied to a sour water stripping zone. As used herein, the term "sour water" refers to water containing HIS and NH3, such a cQm~ositi~n or streams thereof being commonly available in refinery, gasification process, or other industrial operations. In such a case, the HIS and ammonia from the decomposition of the ammonium polysulphide may be recovered or treated with the stripped HIS and ammonia from the sour water.
Sour water streams may also contain extraneous matter, such as fines or solids, if the sour water stream is derived from washing operations. In general, such streams will contain from about 0.005 percent by weight to about 1.3 percent by weight HIS, and about 0.03 percent by weight to about 0.6 percent by weight of . If present, solids or fines may be present from infinitesimal amounts to amounts of from about 2 percent by weight to about 5 percent by weight, and their presence or absence ma determine final treatment or disposal of Selfware precipitated in the stripping zone.
It is therefore preferred to mix the solution removed in step (b) with a HIS and NH3-oontaining aqueous mixture and to strip the solution together with the aqueous mixture Whatever the case, as indicate, the solution or solution-sour water mixture may be stripped by heating or use of flow of a nonreactive gas (or both). It heat alone is applied to the solution or mixture, sufficient heat will be supplied to decompose the ammGnium p~lysulphide. Again if heating is employed, it may be necessary to cool the stripped gases before further treatment. Suitable devices for this approach mclude, for example, a conventional packed or tray column with a no-boiler. Generally, temperatures on the order of about By C to ,,-about 120 C, preferably about 90 C to about 110 C, will be sufficient to decompose the ammonium polysulphide and precipitate Selfware.
If a nonreactive gas is employed, it will be supplied at a suitable pressure, e.g., 4 bar to 15 bar, to strip HIS and NH3 from the ammonium polysulphide containing solution. Any suitable stripping device may be used, such as a packed column or a tray column. Different devices may be used (whether stripping is accamp]ished by heat, gas flow, or a combination thereof) where plugging by solids may be a problem. In any event, any suitable non-reactive gas may be employed. As used herein, the term "non-reactive" implies that the gas, (ox reactant products thereof with components of the sour water-solution nixture3 does no convert the ammonium thiocyanate in the removed solution to an undesired species, such as back to HEN, to an substantial extent. In general, gases nonreactive to ammonium thiocyanate, i.e., those that do not react with the ammonium thiocyanate in the portion to any substantial extent under the conditions employed, may be used Suitable gases, under the conditions in the stripping zone, include air, steam, carbon dioxide, oxygen, nitrogen, and inert gases. Steam is much preferred, since it can provide heat for the stripping and ma be condensed easily, leaving a relatively concentrated H2S-NH3 stream. Those skilled in the art may adjust volumes and velocities of the stripping gas to appropriate levels. As indicated, heat may be supplied in the case ox a stripping gas to assist the stripping.
The stripped gas or gases may be recovered or treated, as desired. Thus, the HIS and MH3 stripped may be returned to make-up for ammonium polysulphide, or may be sent to 3 conventional gas cleanup steps. Alternately, the NH3 and HIS
may be separated, such as by use of a two section stripping zone with alternate acid addition and base addition in the zones to free the respective gases.
Precipitated Selfware is preferably removed from the remaining mixture or solution prior to hydrolysis. This may be accomplished by filtration or other appropriate technique. For example, since the temperature of the mixture or solution is ultimately to be raised to hydrolysis conditions, the temperature of the mixture may be raised to a point sufficient to melt the Selfware but not sufficient to cause hydrolysis of the ammonium thiocyanateO The molten Selfware may then be easily removed.
If the solution removed in step (b) is mixed with sour water, the volume ox solids in the sour water is high, arid the amount of Selfware is low, Selfware recovery may be uneconomic, and the recovered "sludge" may simply be sent to waste. Finally, the Selfware may simply be melted in the hydrolysis zone and recovered, recycled, or sent to waste.
Assuming prior Selfware removal, the ammonium thiocyanate-containing remaining mixture or solution is forwarded to a hydrolysis zone where it is subjected to conditions to hydrolyze the ammonium thiocyanate. Water may be added, if necessary. The NH3, HIS, and owe may be recovered or sent to conventional gas treatment steps. Temperatures in the hydrolysis zone are important, and will range from about 200 C to about 300 C. In general, pressures will range from about 20 to about 100 bar.
If Selfware recovery is made before the hydrolysis step, quite minor amounts of Selfware still may remain in the solution to be hydrolyzed. In that event, suitable provision May be made for recovery or removal to waste of this minor quantity The residual stream, after the ammonium thiocyanate hydrolysis, may be treated further, or may be used in other plant operations.
In order to demonstrate the removal of HEN from a gaseous stream, the follow my experiments were conducted.
Ply A stream of nitrogen containing 1 percent by volume HEN and 0.5 percent by volume HIS was passed at atmospheric pressure at a rate of 2 volleyers of gas per volume of solution per Nat into a flask containing a 0.3 M solution of ammonium sulfide having 1.56 M Selfware suspended therein. m e pi of the solution was 8.9, and the volume of gas treated was about 210 volumes of gas per volume of solution. Temperature of the system was maintained at about 80 C. Greater than 99.8 percent of the HEN
was roved and conversion to thiocyanate approached 100 percent.
In a similar manner, a series of runs was made, and the conditions and results ore, as set out below:
Solution: 0.30 M (NH4)2S
Gas Composition I HEN in No; HIS and NH3 content as indicated below Gas Flow Rate: 290-330 cumin Pressure: 1 bar Volume of EICN/Vol~ne of Solution 2.1 old Elemental Selfware in Initial NH in H S in HEN HEN
T Solution Solution Feed Feed Removed Converted (C) (M) pi (TV) (TV) (%) (%) __ __ 1.6 8.8 0 0.55 > 99.8 99 1.6 9 0 0.45 > 99.8 97 1.6 8.9 0 0.55 > 99.8 100 1.6 7 0 0.55 > g9.4 I
0.3 9 0 0.55 99.8 97 0.06 9 0 0.55 > go 76 0.5 9 1 0.55 > 99.8 100 0.5 7 1 0.55 > 99.4 96
The invention relates to a process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide.
The presence of hydrogen cyan de (HEN) in various gaseous 5 streams complicates removal of additional impurities, e.g., removal of HIS or C32, and poses problems insofar as product quality and pollution control requirements are concerned. In particular, gas streams derived from the gasification of solid carbonaceous fuel, such as coal, generally have significant 10 minor quantities of HEN which must be dealt with before the gas is utilized.
Accordingly, a practical and efficient procedure for removing impurity HEN might hove great economic importance. The invention is such a process.
The invention, therefore, relates to a process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide, comprising the following steps:
(a) contacting said gaseous strewn in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-Dyson a solution containing ammonium po]ysulphide and am~onium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and amm~nium thiocyanate from the contact zone;
(at decomposing amm~nium polysulphide and precipitating Selfware in the solution removed in step (b), thereby producing , .
, .
I, 1~3~2 hydrogen sulfide, Selfware and a remaining ammonium trio-cyanate-containing solution;
Id) removing Selfware from said remaining solution and hydra-lying thy ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulfide and carbon dioxide.
The hydrolysis of the Anaheim thiocyanate is carried out under appropriate conditions of temperature and pressure, and clm~nia, carbon dioxide, and hydrogen sulfide are produced.
These gases may key recycled and/or recovered, if desired, by known techniques. The process is preferably operated continuously.
The reactions for the process may be shown, as follows:
( 4)2 So ZNH4SCN + En + H S 3 Ix = 3 4 or 5) NH4SCN + 2H20- KIWI + H S 2NH
(N~I4)2SX 2NH3 -I HIS + Sol The particular gas streams treated according to the invention are not critical, as will be evident to those skilled in the art. Any gaseous stream containing ICON and from which it is desired to remove the HEN, and which itself does not react with the ammonium polysulphide or interfere substantially therewith may be treated according to the invention. Gaseous streams or effluents particularly suited to the invention include fuel gases produced by gasification procedures, e.g., fuel or effluent gases derived from or produced by the gasification of coal, petroleum, shale, tar sands, etc., wherein a significant quantity of HEN is present. In such gasification processes, the gaseous effluents are often quenched with water ` or gaseous liquids, and gaseous streams derived from stripping the liquid may contain HEN and may also be treated by the invention. me HEN content of such streams may vary, but the invention will preferably be employed with streams hazing an HEN
content of from 0.002 percent Jo 0.1 percent by volume. Higher .
., .
I
HEN contents even above 1 vowel are also possible. As indicated, the process of the invention is preferably continuous, i.e., make-up a~,monium sulfide or polysulphide is continuously supplied to the contact zone, and a portion or "bleed" of ammonium thiocyanate solution is continuously removed from the contact zone. The volumes of make-up and bleed will depend, inter alias on the concentration of HEN in the gaseous stream, and thus cannot be given with precision Those skilled in the art may suitably adjust solution fluky.
Suitable conditions, i.e., appropriate temperature and pressure, sufficient contact time, proper phi and appropriate concentrations of ammonium polysulphide and water ore employed to achieve the ICON conversion. Temperatures in the contact zone of from about 20 C to abut 80 C may be employed, with temperatures of from 25 C to 60 C being preferred. m e pi of the ammonium polysulphide solutions will range from about 8 to 10, preferably 8.5 to 9.5, and conceIItrations of ammonium polysulphide will preferably range from 0.01 to 1, preferably 0.1 to 0.5 moles per lithe. The most important variable controlling HEN removal and conversion is the amount of elemental Selfware available to maintain the polysulphide concentration. In general, the polysulphide solution will have at least a stoichiometric amount of the polysulphide Selfware with respect to the HEN, and preferably up to 3 or 4 times the stoichiometric amount. Elemental Selfware may be supplied in the contact zone to maintain this concentration. HIS and NH3 in the feed gas do not interfere with HEN removal or conversion, and NH3 may actually help rejuvenate the solution. The ammonium polysulphide solution may be supplied on a continuous basis to Jo the contact zone as make-up, or steps can be taken, in some cases, to generate the ammonium polysulphide to some extent in situ. Contact times may range f m m 1 to 8 units, preferably 3 to 5 minutes. m owe skilled in the art may select suitable contact or scrubbing devices to carry out the contacting or scrubbing.
As the HEN is removexl from the gaseous stream by reaction with the ammonium polysulphide solution, at least a portion of the solution, new containing ammonium thiocyanate, is removed.
In the portion of the solution ammDnium polysulphide is decomposed and Selfware precipitated. Preferably, the a~monium polysulphide is decomposed by lower m g the pi of the solution removed in step (b). Suitably, the solution removed is contacted or mixed with a sufficient amount of a suitable flurrying composition to lower the phi decompose ammonium polysulphide and precipitate Selfware, and produce HIS. The HIS released may be treated or recovered, as desired. Generally, leering of the pi to a range of 7.5 to 8 will be sufficient to precipitate the Selfware. Any suitable composition which will lower the pi the required amount may be employed. Suitably acids, such as H2S04, Hal, Eye and acetic acid solution, may be employed. Suitable acidic gases, which will be taken up or react in the solution, such as Hal or HIS, may be added to the solution. organic acids may be used, as well as other hydrogen ion supplying compositions. Moreover, the hydrogen ion-supplying material or composition need not be pure; even dilute solutions and those containing extraneous matter may be employed, so long as the extra cc~onents in the solution do not interfere with the ammonium polysulphide decomposition or react with the ammonium thiocyanate. As indicated, the hydrogen ion-supplying composition will be supplied in an amount sufficient to decompose the ammonium polysulphide and precipitate Selfware.
This amount will defend on a number of factors, and may readily be determined by those skilled in the art in the particular case.
3 In another preferred embodiment, the ammonium polysulphide m the solution removed in step (b) is decomposed by stripping this solution. Preferably, the solution is stripped key heating it, passing a non-reactive gas through it or by a combination of heating and non-reactive gas passing.
I
The stripping decomposes ammonium polysulphide, producing HIS and NH3 and precipitating Selfware. While a separate stripping zone may be provided, it is an advantage of the invention that the portion or stream may be supplied to a suitable stripping zone in a given process. For example, the portion may be supplied to a sour water stripping zone. As used herein, the term "sour water" refers to water containing HIS and NH3, such a cQm~ositi~n or streams thereof being commonly available in refinery, gasification process, or other industrial operations. In such a case, the HIS and ammonia from the decomposition of the ammonium polysulphide may be recovered or treated with the stripped HIS and ammonia from the sour water.
Sour water streams may also contain extraneous matter, such as fines or solids, if the sour water stream is derived from washing operations. In general, such streams will contain from about 0.005 percent by weight to about 1.3 percent by weight HIS, and about 0.03 percent by weight to about 0.6 percent by weight of . If present, solids or fines may be present from infinitesimal amounts to amounts of from about 2 percent by weight to about 5 percent by weight, and their presence or absence ma determine final treatment or disposal of Selfware precipitated in the stripping zone.
It is therefore preferred to mix the solution removed in step (b) with a HIS and NH3-oontaining aqueous mixture and to strip the solution together with the aqueous mixture Whatever the case, as indicate, the solution or solution-sour water mixture may be stripped by heating or use of flow of a nonreactive gas (or both). It heat alone is applied to the solution or mixture, sufficient heat will be supplied to decompose the ammGnium p~lysulphide. Again if heating is employed, it may be necessary to cool the stripped gases before further treatment. Suitable devices for this approach mclude, for example, a conventional packed or tray column with a no-boiler. Generally, temperatures on the order of about By C to ,,-about 120 C, preferably about 90 C to about 110 C, will be sufficient to decompose the ammonium polysulphide and precipitate Selfware.
If a nonreactive gas is employed, it will be supplied at a suitable pressure, e.g., 4 bar to 15 bar, to strip HIS and NH3 from the ammonium polysulphide containing solution. Any suitable stripping device may be used, such as a packed column or a tray column. Different devices may be used (whether stripping is accamp]ished by heat, gas flow, or a combination thereof) where plugging by solids may be a problem. In any event, any suitable non-reactive gas may be employed. As used herein, the term "non-reactive" implies that the gas, (ox reactant products thereof with components of the sour water-solution nixture3 does no convert the ammonium thiocyanate in the removed solution to an undesired species, such as back to HEN, to an substantial extent. In general, gases nonreactive to ammonium thiocyanate, i.e., those that do not react with the ammonium thiocyanate in the portion to any substantial extent under the conditions employed, may be used Suitable gases, under the conditions in the stripping zone, include air, steam, carbon dioxide, oxygen, nitrogen, and inert gases. Steam is much preferred, since it can provide heat for the stripping and ma be condensed easily, leaving a relatively concentrated H2S-NH3 stream. Those skilled in the art may adjust volumes and velocities of the stripping gas to appropriate levels. As indicated, heat may be supplied in the case ox a stripping gas to assist the stripping.
The stripped gas or gases may be recovered or treated, as desired. Thus, the HIS and MH3 stripped may be returned to make-up for ammonium polysulphide, or may be sent to 3 conventional gas cleanup steps. Alternately, the NH3 and HIS
may be separated, such as by use of a two section stripping zone with alternate acid addition and base addition in the zones to free the respective gases.
Precipitated Selfware is preferably removed from the remaining mixture or solution prior to hydrolysis. This may be accomplished by filtration or other appropriate technique. For example, since the temperature of the mixture or solution is ultimately to be raised to hydrolysis conditions, the temperature of the mixture may be raised to a point sufficient to melt the Selfware but not sufficient to cause hydrolysis of the ammonium thiocyanateO The molten Selfware may then be easily removed.
If the solution removed in step (b) is mixed with sour water, the volume ox solids in the sour water is high, arid the amount of Selfware is low, Selfware recovery may be uneconomic, and the recovered "sludge" may simply be sent to waste. Finally, the Selfware may simply be melted in the hydrolysis zone and recovered, recycled, or sent to waste.
Assuming prior Selfware removal, the ammonium thiocyanate-containing remaining mixture or solution is forwarded to a hydrolysis zone where it is subjected to conditions to hydrolyze the ammonium thiocyanate. Water may be added, if necessary. The NH3, HIS, and owe may be recovered or sent to conventional gas treatment steps. Temperatures in the hydrolysis zone are important, and will range from about 200 C to about 300 C. In general, pressures will range from about 20 to about 100 bar.
If Selfware recovery is made before the hydrolysis step, quite minor amounts of Selfware still may remain in the solution to be hydrolyzed. In that event, suitable provision May be made for recovery or removal to waste of this minor quantity The residual stream, after the ammonium thiocyanate hydrolysis, may be treated further, or may be used in other plant operations.
In order to demonstrate the removal of HEN from a gaseous stream, the follow my experiments were conducted.
Ply A stream of nitrogen containing 1 percent by volume HEN and 0.5 percent by volume HIS was passed at atmospheric pressure at a rate of 2 volleyers of gas per volume of solution per Nat into a flask containing a 0.3 M solution of ammonium sulfide having 1.56 M Selfware suspended therein. m e pi of the solution was 8.9, and the volume of gas treated was about 210 volumes of gas per volume of solution. Temperature of the system was maintained at about 80 C. Greater than 99.8 percent of the HEN
was roved and conversion to thiocyanate approached 100 percent.
In a similar manner, a series of runs was made, and the conditions and results ore, as set out below:
Solution: 0.30 M (NH4)2S
Gas Composition I HEN in No; HIS and NH3 content as indicated below Gas Flow Rate: 290-330 cumin Pressure: 1 bar Volume of EICN/Vol~ne of Solution 2.1 old Elemental Selfware in Initial NH in H S in HEN HEN
T Solution Solution Feed Feed Removed Converted (C) (M) pi (TV) (TV) (%) (%) __ __ 1.6 8.8 0 0.55 > 99.8 99 1.6 9 0 0.45 > 99.8 97 1.6 8.9 0 0.55 > 99.8 100 1.6 7 0 0.55 > g9.4 I
0.3 9 0 0.55 99.8 97 0.06 9 0 0.55 > go 76 0.5 9 1 0.55 > 99.8 100 0.5 7 1 0.55 > 99.4 96
Claims (11)
1. Process for the removal of hydrogen cyanide from a gaseous stream containing hydrogen cyanide, comprising the following steps:
(a) contacting said gaseous stream in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-ducing a solution containing ammonium polysulphide and ammonium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and ammonium thiocyanate from the contact zone;
(c) decomposing ammonium polysulphide and precipitating sulphur in the solution removed in step (b), thereby producing hydrogen sulphide, sulphur and a remaining ammonium thio-cyanate-containing solution;
(d) removing sulphur from said remaining solution and hydro-lyzing the ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulphide and carbon dioxide.
(a) contacting said gaseous stream in a contact zone with a solution containing ammonium polysulphide to convert hydrogen cyanide into ammonium thiocyanate, thereby pro-ducing a solution containing ammonium polysulphide and ammonium thiocyanate, and a gas stream having reduced hydrogen cyanide content;
(b) removing at least a portion of the solution containing ammonium polysulphide and ammonium thiocyanate from the contact zone;
(c) decomposing ammonium polysulphide and precipitating sulphur in the solution removed in step (b), thereby producing hydrogen sulphide, sulphur and a remaining ammonium thio-cyanate-containing solution;
(d) removing sulphur from said remaining solution and hydro-lyzing the ammonium thiocyanate in said remaining solution, producing ammonia, hydrogen sulphide and carbon dioxide.
2. Process according to claim 1, in which ammonium poly-sulphide is decomposed by lowering the pH of the solution removed in step (b).
3. Process according to claim 2, in which the pH is lowered to a value ranging from 7.5 to 8.
4. Process according to claim 2 or 3, in which the pH is lowered by addition of a H2SO4-, HCl-, HNO3- or CH3COO-solution or H2S- or HCl-gas to the solution removed in step (b).
5. Process according to claim 1, in which ammonium poly-sulphide is decomposed by stripping the solution removed in step (b).
6. Process according to claim 5, in which the solution is stripped by heating it, by passing a non-reactive gas through it or by a combination of heating and non-reactive gas passing.
7. Process according to claim 6, in which the solution is heated to a temperature of 80-120°C.
8. Process according to claim 6 or 7, in which the non-reactive gas is selected from air, steam, carbon dioxide, nitrogen and the inert gases.
9. Process according to claim 5, in which the solution removed in step (b) is mixed with a H2S- and NH3-containing aqueous mixture, and the solution is stripped together with the aqueous mixture.
10. Process according to claim 1, in which the amount of ammonium polysulphide solution supplied in step (a) contains at least a stoichiometric amount of polysulphide with respect to the hydrogen cyanide.
11. Process according to claim 1, in which the gaseous stream comprises a stream derived from the gasification of solid carbonaceous fuel.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US556,256 | 1983-11-29 | ||
| US556,257 | 1983-11-29 | ||
| US06/556,256 US4505881A (en) | 1983-11-29 | 1983-11-29 | Ammonium polysulfide removal of HCN from gaseous streams, with subsequent production of NH3, H2 S, and CO2 |
| US06/556,257 US4508693A (en) | 1983-11-29 | 1983-11-29 | Solution removal of HCN from gaseous streams, with pH adjustment of reacted solution and hydrolysis of thiocyanate formed |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1236682A true CA1236682A (en) | 1988-05-17 |
Family
ID=27071104
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000467303A Expired CA1236682A (en) | 1983-11-29 | 1984-11-08 | Process for the removal of hydrogen cyanide |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1236682A (en) |
| GB (1) | GB2150550A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5053380A (en) * | 1989-12-21 | 1991-10-01 | Union Carbide Chemicals And Plastics Technology Corporation | Cu-al catalyst for hydrogenation |
| US5008235A (en) * | 1989-12-21 | 1991-04-16 | Union Carbide Chemicals And Plastics Technology Corporation | Catalysts of Cu-Al-third metal for hydrogenation |
| US5142067A (en) * | 1989-12-21 | 1992-08-25 | Union Carbide Chemicals & Plastics Technology Corporation | Hydrogenation with Cu-Al-X catalysts |
-
1984
- 1984-11-08 CA CA000467303A patent/CA1236682A/en not_active Expired
- 1984-11-27 GB GB08429931A patent/GB2150550A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2150550A (en) | 1985-07-03 |
| GB8429931D0 (en) | 1985-01-03 |
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