CA1071613A - Removal of hydrogen sulfide from gases - Google Patents
Removal of hydrogen sulfide from gasesInfo
- Publication number
- CA1071613A CA1071613A CA244,202A CA244202A CA1071613A CA 1071613 A CA1071613 A CA 1071613A CA 244202 A CA244202 A CA 244202A CA 1071613 A CA1071613 A CA 1071613A
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- solution
- iron
- chelating agent
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-
- 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
-
- 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
- B01D53/1456—Removing acid components
- B01D53/1468—Removing hydrogen sulfide
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
Abstract
Abstract of the Disclosure Hydrogen sulfide is removed from a gas stream in an oxidation-reduction system by contacting the gas stream with an aqueous alkaline chelated iron solution in which the iron is in the ferric state to absorb hydrogen sulfide and convert it to elemental sulfur which is recovered. The solution is regenerated by aeration. The chelated iron solu-tion contains two different types of chelating agents, on of which is selected to bind ferrous ions so as to prevent precipitation of ferrous sulfide, and the other of which is selected to bind ferric ions so as to prevent precipitation of ferric hydroxide. The absorption step of the process may be operated under either aerobic or anaerobic conditions.
Description
f~7~
RE:MOVAL O~ HYDROGEN Sl~LFIDE: FRO~l GAS~S
This invention relates to an improved process and to an improved reagent for the removal of hydrogen sulfide from gases and the recovery of sulfur. More particularly, the invention relates to improvements in the removal of hydrogen sulfide from gas streams in an oxidation-reduction system utilizing a reagent comprising an iron-chelate com-plex wherein the iron in its ferric state oxidizes the hydrogen sulfide to elemental sulfur and is concomitantly reduced to the errous state and wherein the reagent is regenerated by oxidation of the iron to the ferric state.
Numerous processes have been suggested for the removal of hydrogen sulfide rom gas streams, including (1) scrubbing with an alkaline or caustic solution, (2) inciner-- ation to form sulfur dioxide and scrubbing with an alkaline or caustic solution, (3) various dry oxidation processes using a solid catalyst or the like (e.g. the claus process), (4) various wet oxidation processes using a basic or alkaline solution containing a suspended or dissolved catalyst or oxidizing agent, and (5) selective absorption with an amine such as monoethanolamine or diethanolamine. However, the ___ foregoing types of processes are subject to various limita-tions which in many cases detract from their commercial feasibility. For example, in some instances the efficiency of removal of hydrogen sulfide is low or the reagent, solu-tion, or catalyst is expensive, unstable, or not easily regenerated. In other cases, disposal of ~aste products poses a serious problem. In still other cases, the operating or equipment costs are excessive or the process is diEicult to control.
.
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It has also been suggested to effect removal o~
hydrogen sulfide in an oxidation-reduction system by con-tacting the gas stream with a solution of a polyvalent metal cation (such as iron) complexed with a chelating agent (such as ethylene diamine tetra-acetic acid or a sodium salt thereof).
Iron in the ferric state oxidizes the hydrogen sulfide and is reduced to the ferrous state, the solution b~ng regener-ated by oxidation to convert the iron back to the fsrric state. For example, processes using a chelated iron reagent are disclosed in the following U~S. patents:
- Inventor Patent No. Date Hartley et al 3,068,065 Dec. ll, 1962 Pitts et al 3,097,925 July 16, 1963 Meuly et al 3,226,320 Dec. 28, 1965 Roberts et al 3,622,273 Nov. 23, 1971 Robarts et al 3,676,356 July 11, 1972 In addition, the above-listed Roberts et al patents refer to Czechoslovakian Patents Nos. 117,273, 117,274, and 117,277 as also disclosing the use of chelated iron solutions for this purpose.
A serious problem in the use of a chelated iron solution arises from the inherent instability of the sol-ution, particularly at higher pH levels. For example, if an aqueous solution of a complex of iron with ethylene diamine tetra-acetic acid (EDTA) or with nitrilotriacetic acid (NTA) is used, it is nec~ssary to exercise careful con-trol over the pH of the solution and the relative amounts - of iron and chelating agent. Although the solubility o~
hydrogen sulfide is greatest at the higher pH levels, at these conditions the complex readily decompose~ and iron in
RE:MOVAL O~ HYDROGEN Sl~LFIDE: FRO~l GAS~S
This invention relates to an improved process and to an improved reagent for the removal of hydrogen sulfide from gases and the recovery of sulfur. More particularly, the invention relates to improvements in the removal of hydrogen sulfide from gas streams in an oxidation-reduction system utilizing a reagent comprising an iron-chelate com-plex wherein the iron in its ferric state oxidizes the hydrogen sulfide to elemental sulfur and is concomitantly reduced to the errous state and wherein the reagent is regenerated by oxidation of the iron to the ferric state.
Numerous processes have been suggested for the removal of hydrogen sulfide rom gas streams, including (1) scrubbing with an alkaline or caustic solution, (2) inciner-- ation to form sulfur dioxide and scrubbing with an alkaline or caustic solution, (3) various dry oxidation processes using a solid catalyst or the like (e.g. the claus process), (4) various wet oxidation processes using a basic or alkaline solution containing a suspended or dissolved catalyst or oxidizing agent, and (5) selective absorption with an amine such as monoethanolamine or diethanolamine. However, the ___ foregoing types of processes are subject to various limita-tions which in many cases detract from their commercial feasibility. For example, in some instances the efficiency of removal of hydrogen sulfide is low or the reagent, solu-tion, or catalyst is expensive, unstable, or not easily regenerated. In other cases, disposal of ~aste products poses a serious problem. In still other cases, the operating or equipment costs are excessive or the process is diEicult to control.
.
~'7~
It has also been suggested to effect removal o~
hydrogen sulfide in an oxidation-reduction system by con-tacting the gas stream with a solution of a polyvalent metal cation (such as iron) complexed with a chelating agent (such as ethylene diamine tetra-acetic acid or a sodium salt thereof).
Iron in the ferric state oxidizes the hydrogen sulfide and is reduced to the ferrous state, the solution b~ng regener-ated by oxidation to convert the iron back to the fsrric state. For example, processes using a chelated iron reagent are disclosed in the following U~S. patents:
- Inventor Patent No. Date Hartley et al 3,068,065 Dec. ll, 1962 Pitts et al 3,097,925 July 16, 1963 Meuly et al 3,226,320 Dec. 28, 1965 Roberts et al 3,622,273 Nov. 23, 1971 Robarts et al 3,676,356 July 11, 1972 In addition, the above-listed Roberts et al patents refer to Czechoslovakian Patents Nos. 117,273, 117,274, and 117,277 as also disclosing the use of chelated iron solutions for this purpose.
A serious problem in the use of a chelated iron solution arises from the inherent instability of the sol-ution, particularly at higher pH levels. For example, if an aqueous solution of a complex of iron with ethylene diamine tetra-acetic acid (EDTA) or with nitrilotriacetic acid (NTA) is used, it is nec~ssary to exercise careful con-trol over the pH of the solution and the relative amounts - of iron and chelating agent. Although the solubility o~
hydrogen sulfide is greatest at the higher pH levels, at these conditions the complex readily decompose~ and iron in
- 2 -. - . :
t7 ~ 3 the ferric state is precipitated as ~erric hydro~i~e. I~
too little chelating agent is used relakive to the iron content, the iron in the ~errous state is loosely bound and tends to precipitate as ferrous sulfide at high pH levels. If the amount of chelating agent is too great relative to the iron content, the iron in the ferrous state is bound too strongly so that the solution is difficult to regenerate by oxidation.
According to the present invention the difficulties encountered in the prior art systems are avoided by means of a novel and improved chelated iron solution and a process for using the same for removlng hydrogen sulfide from gas streams.
The novel and improved solution contains two different types of chelating agents, one of which is capable of binding iron in the ferrous sta~e to prevent formation of ferrous sulfide, and the other of which is capable of binding iron in the ferric state to prevent formation of ferric hydroxide.
The invention in its broad aspect comprehends a composition for use in removing hydrogen sulfide from a gas, which composition comprises an aqueous solution of chelated iron containing at least two iron chelating agents. One of the iron chelating agents is an amine type chelating agent which is capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide, and at least one of the chelating agents is a polyhydroxy type chelating agent which is capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide.
The invention further comprehends a continuous oxidation-reduction process for the removal of hydrogen sulfide from a gas stream by contacting the gas stream with an aqueous '', ~ -
t7 ~ 3 the ferric state is precipitated as ~erric hydro~i~e. I~
too little chelating agent is used relakive to the iron content, the iron in the ~errous state is loosely bound and tends to precipitate as ferrous sulfide at high pH levels. If the amount of chelating agent is too great relative to the iron content, the iron in the ferrous state is bound too strongly so that the solution is difficult to regenerate by oxidation.
According to the present invention the difficulties encountered in the prior art systems are avoided by means of a novel and improved chelated iron solution and a process for using the same for removlng hydrogen sulfide from gas streams.
The novel and improved solution contains two different types of chelating agents, one of which is capable of binding iron in the ferrous sta~e to prevent formation of ferrous sulfide, and the other of which is capable of binding iron in the ferric state to prevent formation of ferric hydroxide.
The invention in its broad aspect comprehends a composition for use in removing hydrogen sulfide from a gas, which composition comprises an aqueous solution of chelated iron containing at least two iron chelating agents. One of the iron chelating agents is an amine type chelating agent which is capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide, and at least one of the chelating agents is a polyhydroxy type chelating agent which is capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide.
The invention further comprehends a continuous oxidation-reduction process for the removal of hydrogen sulfide from a gas stream by contacting the gas stream with an aqueous '', ~ -
- 3 -~3 ; ' . ., `, .
:
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chelating iron solutlon containing iron in the ferric state for oxidizing hydrogen sulfide to elemental sulfur, thereby being reduced to the ferrous state. The elemental sulfur is separated from the solution, and chelated iron solution is regenerated by oxidation by contacting the solution with an oxygen-containincJ gas to convert iron in ferrous state to the ferric state. The aqueous chelated iron solution contains at least two iron chelating agenks, at least one of the iron chelating agents being an amine type chelating agent capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide. At least one oE the chelating agents is a polyhydroxy type chelating agent capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide, thereby to improve the stability of the solution.
In the accompanying drawings:
Fig. 1 is a schematic process flow diagram showing one method of practicing the invention wherein oxidation of hydrogen sulfide and regeneration of the solution are carried out concurrently in the same reaction zone; and Fig. 2 is a schematic process flow diagram showing an alternate method of practicing the invention wherein regeneration of the solution is effected in a separate reaction zone.
The present ;nvention utilizes a unique reagent for removal of hydrogen sulfide which comprises an aqueous alkaline solut~on of iron ancl two difEerent types of chelating agents selected for different purposes, as described in .
~ 4 -.
~ 7~3 11 greater de~ail below. The hydrogen sulfide-con-taining gas stream is contacted or scrubbed wi~h the chelated iron solution in which the iron is in the ferric state to effect oxidation of the hydrogen sulfide to elemental sulfur with concomitant reduction of the iron from ~he higher valence or ferric state to the lower valence or ferrous state~ The solution is regenerated, in the same reaction zone or in a separate reaction zone, by aeration or the like to oxidize the iron to the ferric state.
The chemistry of the oxidation-reduc~ion system is represented by the following equations:
(1) H2S (g) ~ ~ZS (aq-) (2) H2S (aq.) + OE ~-~ HS- + H20 _ -2 o
:
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chelating iron solutlon containing iron in the ferric state for oxidizing hydrogen sulfide to elemental sulfur, thereby being reduced to the ferrous state. The elemental sulfur is separated from the solution, and chelated iron solution is regenerated by oxidation by contacting the solution with an oxygen-containincJ gas to convert iron in ferrous state to the ferric state. The aqueous chelated iron solution contains at least two iron chelating agenks, at least one of the iron chelating agents being an amine type chelating agent capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide. At least one oE the chelating agents is a polyhydroxy type chelating agent capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide, thereby to improve the stability of the solution.
In the accompanying drawings:
Fig. 1 is a schematic process flow diagram showing one method of practicing the invention wherein oxidation of hydrogen sulfide and regeneration of the solution are carried out concurrently in the same reaction zone; and Fig. 2 is a schematic process flow diagram showing an alternate method of practicing the invention wherein regeneration of the solution is effected in a separate reaction zone.
The present ;nvention utilizes a unique reagent for removal of hydrogen sulfide which comprises an aqueous alkaline solut~on of iron ancl two difEerent types of chelating agents selected for different purposes, as described in .
~ 4 -.
~ 7~3 11 greater de~ail below. The hydrogen sulfide-con-taining gas stream is contacted or scrubbed wi~h the chelated iron solution in which the iron is in the ferric state to effect oxidation of the hydrogen sulfide to elemental sulfur with concomitant reduction of the iron from ~he higher valence or ferric state to the lower valence or ferrous state~ The solution is regenerated, in the same reaction zone or in a separate reaction zone, by aeration or the like to oxidize the iron to the ferric state.
The chemistry of the oxidation-reduc~ion system is represented by the following equations:
(1) H2S (g) ~ ~ZS (aq-) (2) H2S (aq.) + OE ~-~ HS- + H20 _ -2 o
(4) 2Fe+3 -~ S~2--~2Fe~2 + S
(5) 2Fe~2 + 1/2 2 + FI20 ~ 2Fe~3 ~ 2 OE
However, since the iron in the system is present in two dif-ferent valencè states there are also competing side reactions which can occur, resulting in loss o iron and rendering the solution ineffective for removal of hydrogen sulfide.`
(A) Fe~2 ~ S~2-~FeS~
(B) Fe~3 ~ 3(OH) ~Fe(OEI) Although the process can be operated over a wide range of pH, it is prefexred to maintain the pH of the sol-ution at from about 7 to about 13, with the optimum range being from about 8 to about 10.5. At the preferred and optimum ranges of pH hydrogen sulfide is absorbed effectively by the alkaline solution, but.the side reactions (A) and (B) would predominate in an ionic iron solution so that all - 30 ferrou~ and ferric ions would soon precipitate out.
,.
In accordance with the present invention, the iron is complexed with two ~ifferent types of chelating agents to prevent loss of iron from the solution at the aforementioned pH levels. The Type A chelating agent is selected to prevent side reaction (A) by forming a complex with ferrous ions in solution:
Fe 2 ~ ChelA ~-~(Fe ChelA)+2 This complex binds ferrous ions sufficiently strongl~ to maintain the concentration such that the solubility product constan~ for ferrous sulfide is not exceeded. Therefore, ferrous ions in solution will be preferentially bound as chelates of Type A, and no ferrous sulfide will precipitate.
The (Fe ChelA)~2 complex is readily oxidized by atmospheric oxygen to Fe+3 ~ ChelA, as shown in Equation (5). The Type B chelating agent is selected to prevent side reaction ~B) by forming a complex with ferric ions in the solution-- Fe~3 + chelB ~-~(Fe~ChelB)+3 This complex binds ferric ions sufficiently strongly to maintain the concentration such that the solubility pxoduct constant for ferric hydroxide is not exceeded. Therefore, ferric ions in solution will be bound as Type B chelates~
and no ferric hydroxide will precipitate. The (Fe Chel~)~3 complex readily reac~s with sulfide ions to produce elemental sulfur, as shown in Equation (4).
From Equations (4) and (5) it can be seen that the rate of oxidation of ferrous iron must be twice the rate of hydrogen sulfide absorption. A sufficiently aerated solution can absorb only a small amount of oxygen~ Oxygen absorption appears to be a critical step in regenerating the solution, and the rate of aeration may limit the capacity of the process ' ~
!
.. . .
or the stability of the solu-tion. Therefore i-t is impor-tant that the scrubbing solution be aerated as completely and efficiently as possible. As indicated in Equations (1) through (5), two equivalents of hydroxide are removed by the hydrogen sulfi~e, and two equivalents of hydroxide are produced. This makes pH adjustments minimal.
Ag the Type A chelating agent, the invention uses (either singly or as a mixture) the polyamino polycarboxylic acids, the polyamino hydroxyethyl polycarboxylic acids, or tha polyphosphonomethylamines, the latter being phosphorus analogs of the polyamino polycarboxylic acids. Usually the aforementioned types of chelating agents will be used in the form of theix alkali metal salts, particularly the sodium salts. The polyamino polyacetic acids and the polyamino hydroxyethyl polyacetic acids, or their sodium salts, are particularly desirable.
As the Type B chelating agent, the invention uses the sugars, the reduced sugars, or the sugar acids. Examples of suitable sugars are the disaccharides, such as sucrose, lactose, and maltose, and the monosaccharides, such as glu-cose and fructose. Examples of suitable sugar acids are gluconic acid and glucoheptanoic acid, which may be used in the form of their alkali metal salts particularly,sodium salts. The reduced sugars, however, are preferred for the Type B chelating agent since there is no possibility o~
hydrolysis or oxidation at a potential aldehyde group.
Examples of suitable reduced sugars are sorbitol and mannitol.
As described in more detail in the specific examples below, excellent results have been obtained using a mixture of the sodium salte of ethylene diamine tetra-acetic acid .
1, ~7~3 and N-hydroxyethyl ethylene diamine triacetic acid as the Type A chelating agent and using sorbitol as the Type B
chelating agent. Aqueous solutions of the aforementioned Type A chelating agents are available commercially from the Dow chemical co. under the trademarks "Versene lO0" (Na~EDTA) and ~Versenol 120~ (~a3HEDT~). The use of this mixture of Type A chelating agents is particularly advantageous since it insures the desired iron complexing effect not only in the optimum pE range of from about 8 to about 10.5 but also at pH levels above and below this range.
The chelated iron solution of the present invention is prepared by dissolving a suitable iron salt in water and adding the required amounts of the Type A and Type B chelating agents. To this solution the alkaline material is then added to provide a concentrate which can be diluted with water as required to obtain the operating solution having the desired pH and iron content. The iron content of the solution may vary over a wide range, dependent upon the gas being treated and other factors. Solutions having an iron content of from about 200 ppm to about 5000 ppm are preferred. In preparing the concentrate it is desirable always to add the chelating agents before the alkaline ayent so as to avoid precipitation of iron. However, the presence of the two types of chelating agents improves the stability of the solution so that no gxeat care is required in making up the solution to prevent precipitation of iron 'hydroxide.
For economy, the amounts of the respective chelating agents need be no greater than required to complex the amount of iron present in either valence state, and in general lesser amounts can be used. In particular, it is desirable, for .
ease of regeneration, that the molar ra-tio of ~ype A
chelating agent ~ iron be not greater than 2:1 and pre-ferably from about 1:1 to about 1.5:1. The iron s~lt is preferably a ferric salt such as ferric chloride, ferric sulfate, or ferric n.itrate. However, it is also possible to use a ~errous salt.such as ferrous sulfate, but in this case the solution must be aerated prior to use in order to insure oxidation of the chelated iron to the ferric state.
The alkaline material is preferably sodium carbonate or sodium hydroxide or mixtures thereo~, although other com-patible alkaline compounds may be used.
The process flow for the oxidation-reduction system using the chelated iron solu~ion of the present in-, .. ..
vention will depend upon the hydrogen sulfide content of the gas stream being treated and the nature of the other com-ponents of the gas stream. Fig. l illustrates a process flow in which the oxidation of hydrogen.sulfide and the regeneration of th~ chelated iron solution are carried out concurrently in the same reaction zone, this arrang~m~nt ~ 20 being referred to as aerobic absorption processing or aerobic : operation. The process flow of Fig. 1 is particularly adapted for use in treating a waste gas stream containing a relatively low concentration of hydrogen sulfide (e.g. 50-100 ppm or less) and which is free of hydrocarbons or other . materials which shuuld not b~ mixed with air.or oxygen~
Referring to Fig. 1, the reaction system compris~s an absorption tower or scrubber 10 containing a central con-tact zone illustrated schematically at 11. This zone may comprise any suitable liquid-vapor contac~ing means such as the conventional packed beds, plates or trays. The inlet gas containing hydrogen sulfide is in-troduced into the tower 10 through a blower 12 and a conduit 13 below the contact zone 11 for passage upwardly therethrough. A flow control damper 15 is provided in the conduit 13. Typically, the inlet gas has a low hydrogen sulfide content on the order of 50 ppm and is free of hydrocarbons, e.g. the off-gas from a xanthate plant producing rayo~ or cellophane, or from a sewage plant.
The chelated iron solution of the present invention is supplied by a line 14 to sprays or distribution nozzles 16 located in an enlarged upper section 17 of the tower 10 and passes downwardly through the contact zone 11 in counter-current relation to the upwardly flowing gas stream. The treated gas exits from the tower 10 through a demister zone 18 in the section 17 and an outlet 19 having a flow control damper 21. Make-up water may be added to the system, as required, through a line 22 communicating with sprays 23 located above the demister zone 18. Make-up chelated iron solution may be added, as ~required, through a line 24 com-municating with the tower 10 below the contact zone 11.
In the arrangement illustrated in Fig. 1 the bottom portion of ~e absorption tower 10 is used as a reservoir ~or the chelated iron solution which fills the bottom of the tower to a level, indicated at 26, below the point of introduction of gas through the conduit 13. The chelated iron solution is continuously recirculated from the bottom of the tower 10 to the nozzles 16 through a line 27, a pump 28, and a line 29 connected to the line 14. A
portion of the chelated iron solution may be bled from ~he system through a line 31, as may be required.
~, . .
~ -- 10 --.
- ~@;i~ 3 For regeneration of the chelated iron solukion, atmospheric air is drawn -through a screened inlet 32 by blower 33 and is supplied through a line 34 to nozzles 36 disposed in the lower portion of the tower 10 so that the air is bubbled through the volume of solution in the bottom of the tower, thereby thoroughly aerating the solution to oxidize the ferrous .iron to ~erric iron. The effluent air passes upwardly through the tower 10 along with the feed gas and exits with the treated gas through the outlet 19.
In the contact zone 11 the hydrogen sulfide in the inlet gas is oxidized to elémental sulfur by the chelated iron solution, as heretofore described, and the sulfur solids are present as a slurry in the treating solution in the bot-tom of the tower. A portion o~f`th~s slurry, usually in the ~orm of a froth, is continuously withdrawn from the tower 10 through a line 37 to a slurry tank 38. The sulfur slurry is withdrawn from the bottom of the slurry tank through a line 39 by a pump 41 and is supplied through a line 42 to a fi:l-tration step, in this case a continuous drum filter ~3. A
portion of the sùlfur slurry is recirculated to the tank 38 through a line 44.
. Wet sulfur product is recovered from the drum fil-ter 43 through a line 46 and may be washed (not shown), to the extent that the water balance of the system permits, in ordèr to recover absorbed chelated iron. If desired, the wet sulfur product may be dried in an autoclave (not shown) to obtain a dr~ high purity sulfur product. The filtrate is withdrawn from the drum filter 43 through a line 47 to a receiver 48. Vapor or gas is removed from the top of the 3Q receiver 48 through a line 49 by a vacuum pump 51 and is ..
introduced by a line 52 to the absorption tower 10 belo~7 the contact zone 11. Liquid filtrate is withdrawn from the bottom of the receiver 48 through a line 53 by a pump 54 and is recirculated through line 14 to the absorption tower lO. A portion of the iltrate may be bled from the system through a line 56, as desired.
Fig. 2 illustrates a process flow, in accordance with the invention, which is particularly adapted for the treatment of gas streams containing hydrocarbons and xela-tively high concentrations of hydrogen sulide, e.g. a sour natural gas containing 1-5% hydrogen sulfide. In this system the removal of hydrogen sul~id~ and the regeneration of the chelated iron solution are carried out in separate reaction zones, this arrangement being rearred to as anaerobic ab-sorption processing or anaerobic operation.
Referring to Fig. 2~ a venturi scrubber 60 is utilized for primary contact in order to accommodate the -high hydrogen-sulfide concentration in the feed gas. ~he gas is introduced to the scrubber through a line 61, and a portion of the chelated iron solution is introduced to the scrubber 60 through a line 62. The lower portion of the scrubber 60 co~nunicates with the lower portion of an ab-sorption tower 63 by means of an enlarged conduit 64. The gas flows rom the scrubber 60 and passes upwardly through a contact zone 66 in countercurrent relation with a down~
wardly flowing portion o~ the chelated iron solution sup-plied from line 62 and a line 67 to nozzles or sprays 68 disposed above the contact zone 66. The treated gas exits from the top o the tower 63 throuyh a line 69 a~ter passiny through a demister zone 70.
- 12 ~
~' , "
Chelated iron solu-tion accumulates in the boffDm portions of the scrubber 60 and the tower 63, as indicated by the liquid level 71. A portion of the solution may be bled from the ~ottom of ~e scrubber 60 through a line 72, as desired. The solution accumulating in the bottom of the tower 63 is withdrawn through a line 73 by a pump 74 an~ is discharged through lines 76 and 77 into an oxidizer or re-generation vessel 78. If necessary, a heat exchanger or coolèr 79 may be interpo~e~ in the line 76. In the vessel 78 the chelated iron solution is oxidiæed or regenerated by introduction of atmospheric air drawn through a screened inlet 81 by a blower 82 and supplied by a line 83 to nozzles 84 located in the ~wer portion of the vessel 78 below the liguid level indicated at 86. The air bu~s through and aerates the solution, as previously described, and exits from the vessel 78 through a conduit 87. ~he regeneratad solution is continuously withdrawn from the bottom of the vessel 78 through a line 88 by a pump 89 and is recirculated thraugh lines 62 and 67 to the scrubber:60 and the tower 63.
The sulfur slurry i5 continuously withdrawn from the ves~el 78 through a conduit 91 to a drum filter 92, as previously described in connection with Fig. 1. Wet sulfur product is removed at a line 93, and filtrate is passed to a receiver 94 through a line 96. Vapor or gas is wi.~hdrawn from ~e receiver 94 through a line 97 by a vacuum pump 98 and is vented through a line 99 into the air exit conduit 87 of the vessel 78. Filtrate is withdrawn from the bottom of the receiver 94 through a line 101 and is recirculated . by a pump 102 through line 77 to the regeneration vessel 78, a portion of the filtrate being bled from the system through ., ; - 13 -:, :
- , a line 103, if desired.
In either the Fig. 1 or the Fig. 2 process flow arrangements the operating temperature and pressure are not critical and may vary over a wide range. Practically speakiny, however, the process will normally be operated at ambient or room temperature and at atmospheric pressure or slightly above.
The following examples will serve to illustrate the invention but are not to be construed as limiting the invention:
- Example 1 A chelated iron concentrate was prepared using a concentrated aqueous solution of Na4EDTA (~RSEN~ M 100) and a concentrated aqueous solution of Na3HEDTA (VERSENO~, 120 ) as the Type A chelating agents and using sorbitol as the Type B chelating agent. The composition of the concentrate was as follows on a weight per cent basis:
; Water 55.9%
FeCl3 (39 wt. % aqueous solution) 13.4 VERSENE M Powder (Na4EDTA) 6.3 VERSENOL 120 (41 wt. % aqueous solution Na3HEDTA) 6.3 Sorbitol (70 wt~ % aqueous solution) 6O3 ~aOH (50 wt. % aqueous solution) 3.6 Na2C3 8.2 100.0%
The concentrate was diluted with sufficie~t water to provide an operating solution having an iron content of 200 ppm. This solution was used succes~fully for about two weeks in a continuous aerobic operation using a pilot plant ~ .
~ . . . .
scale countercurrent absorption column. The p~l of -the solution was maintained within t~e range of from about 8.5 to about 9.5. The gas treated was an off-gas from a xanthate process having a hydrogen sulfide content which varied be-tween about 25 ppm and about 70 ppm. The outlet gas had a hydrogen sulfide content of 5 ppm or less, and the efficiency of hydrogen sulfide removal ranged from about 80% to about 95% dependent upon the hydrogen sulfide content of the feed gas.
Example 2 A laboratory scrubber of the frit-ted glass disk type was employed to treat an inlet air stream containing 1 to 2% hydrogen sulfide with a chelated iron solution. The solution concentrate was prepared by mixing 10 ml. of 39 wt. % aqueous ferric chloride with 64 g. of SEQLENE ES-40 and 10 g. of Na4EDTA, and then adding 20 g. of 50 wt. %
aqueous sodium hydroxide. This concentrate was then diluted with sufficient water to provide 500 g. of solution. SEQLENE
ES-40 is a 40 wt. % aqueous solution of the sodium salt of glucoheptanoic acid as available commercially from Pfanstiehl Labs., Inc.
Over a period of 24 hours of continuous operation there was substantially complete removal of hydrogen sulfide, and the sulfur was readily recovered from the used solution by filtration. The operation was continued successfully for more than 200 hours with the addition of small amounts of fresh chelated iron solution from time to time as required.
Example 3 The procedure of Example 2 was followed using a chelated iron solution prepared from a concentrate of 2.5 ml~
~' .
:
of 39 wt. % aqueous ferric chlori~e, 3.1 g. of ~ucro~e, 4 g.
of Na4EDTA, and 5 g. of sodium carbonate, the concentrate being diluted with water to provide 175 g. of solution.
Substantially complete removal of hydrogen sulfide was ob-tained over a continuous operation of 12 days.
Example 4 Following the same procedure as in Example 2, substantially complete removal of hydrogen sulfide was ob-tained using another chelated iron solution. The concentrate was prepared by mixing 2.5 ml. of 39 wt. % aqueous ferric - chloride with 16 g. of SEQLENE ~I ES-40, 5.2 g. of DEQUEST 2000 4 g. of 50 wt. % aqueous sodium hydroxide, and 2 g. of sodium carbonate. This concentrate was diluted with water to pro-vide 175 g. of operating solution.
DEQUEST M 2006 is an aqueous solution of the sodium salt of tris (phosphonomethyl) amine as available commer-cially from Monsanto Co. DE~U~ST 2054, which may also be used, is an aqueous solution of the sodium salt of N,N,~',N' tetrakis (phosphonomethyl) hexamethyl~ne diamine as available commercially from Monsanto Co.
Example 5 The procedure of Example 2 was followed in effectively removing hydrogen sulfide with a chelated iron solution prepared from a concentrate comprising 14 ml. of 39 wt. % aqueous ferric chloride, 33.6 g. of Na4EDTA, 13 g.
of 70 wt. % aqueous sorbitol, and 14 g. of sodium carbonate~
The concentrate was diluted with water to obtain 3785 ml. or 1 gallon of operating solution. It was noted that when - ` hydrogen sulfide without air was introduced, a small amount of ferrous sulfide was formed, but when air was reintroduced ~. ..
,~r~
along with ~he hydrogen sulfide, the ferrous sulfide was oxidized and disappeared, .
' .
: - 17 -
However, since the iron in the system is present in two dif-ferent valencè states there are also competing side reactions which can occur, resulting in loss o iron and rendering the solution ineffective for removal of hydrogen sulfide.`
(A) Fe~2 ~ S~2-~FeS~
(B) Fe~3 ~ 3(OH) ~Fe(OEI) Although the process can be operated over a wide range of pH, it is prefexred to maintain the pH of the sol-ution at from about 7 to about 13, with the optimum range being from about 8 to about 10.5. At the preferred and optimum ranges of pH hydrogen sulfide is absorbed effectively by the alkaline solution, but.the side reactions (A) and (B) would predominate in an ionic iron solution so that all - 30 ferrou~ and ferric ions would soon precipitate out.
,.
In accordance with the present invention, the iron is complexed with two ~ifferent types of chelating agents to prevent loss of iron from the solution at the aforementioned pH levels. The Type A chelating agent is selected to prevent side reaction (A) by forming a complex with ferrous ions in solution:
Fe 2 ~ ChelA ~-~(Fe ChelA)+2 This complex binds ferrous ions sufficiently strongl~ to maintain the concentration such that the solubility product constan~ for ferrous sulfide is not exceeded. Therefore, ferrous ions in solution will be preferentially bound as chelates of Type A, and no ferrous sulfide will precipitate.
The (Fe ChelA)~2 complex is readily oxidized by atmospheric oxygen to Fe+3 ~ ChelA, as shown in Equation (5). The Type B chelating agent is selected to prevent side reaction ~B) by forming a complex with ferric ions in the solution-- Fe~3 + chelB ~-~(Fe~ChelB)+3 This complex binds ferric ions sufficiently strongly to maintain the concentration such that the solubility pxoduct constant for ferric hydroxide is not exceeded. Therefore, ferric ions in solution will be bound as Type B chelates~
and no ferric hydroxide will precipitate. The (Fe Chel~)~3 complex readily reac~s with sulfide ions to produce elemental sulfur, as shown in Equation (4).
From Equations (4) and (5) it can be seen that the rate of oxidation of ferrous iron must be twice the rate of hydrogen sulfide absorption. A sufficiently aerated solution can absorb only a small amount of oxygen~ Oxygen absorption appears to be a critical step in regenerating the solution, and the rate of aeration may limit the capacity of the process ' ~
!
.. . .
or the stability of the solu-tion. Therefore i-t is impor-tant that the scrubbing solution be aerated as completely and efficiently as possible. As indicated in Equations (1) through (5), two equivalents of hydroxide are removed by the hydrogen sulfi~e, and two equivalents of hydroxide are produced. This makes pH adjustments minimal.
Ag the Type A chelating agent, the invention uses (either singly or as a mixture) the polyamino polycarboxylic acids, the polyamino hydroxyethyl polycarboxylic acids, or tha polyphosphonomethylamines, the latter being phosphorus analogs of the polyamino polycarboxylic acids. Usually the aforementioned types of chelating agents will be used in the form of theix alkali metal salts, particularly the sodium salts. The polyamino polyacetic acids and the polyamino hydroxyethyl polyacetic acids, or their sodium salts, are particularly desirable.
As the Type B chelating agent, the invention uses the sugars, the reduced sugars, or the sugar acids. Examples of suitable sugars are the disaccharides, such as sucrose, lactose, and maltose, and the monosaccharides, such as glu-cose and fructose. Examples of suitable sugar acids are gluconic acid and glucoheptanoic acid, which may be used in the form of their alkali metal salts particularly,sodium salts. The reduced sugars, however, are preferred for the Type B chelating agent since there is no possibility o~
hydrolysis or oxidation at a potential aldehyde group.
Examples of suitable reduced sugars are sorbitol and mannitol.
As described in more detail in the specific examples below, excellent results have been obtained using a mixture of the sodium salte of ethylene diamine tetra-acetic acid .
1, ~7~3 and N-hydroxyethyl ethylene diamine triacetic acid as the Type A chelating agent and using sorbitol as the Type B
chelating agent. Aqueous solutions of the aforementioned Type A chelating agents are available commercially from the Dow chemical co. under the trademarks "Versene lO0" (Na~EDTA) and ~Versenol 120~ (~a3HEDT~). The use of this mixture of Type A chelating agents is particularly advantageous since it insures the desired iron complexing effect not only in the optimum pE range of from about 8 to about 10.5 but also at pH levels above and below this range.
The chelated iron solution of the present invention is prepared by dissolving a suitable iron salt in water and adding the required amounts of the Type A and Type B chelating agents. To this solution the alkaline material is then added to provide a concentrate which can be diluted with water as required to obtain the operating solution having the desired pH and iron content. The iron content of the solution may vary over a wide range, dependent upon the gas being treated and other factors. Solutions having an iron content of from about 200 ppm to about 5000 ppm are preferred. In preparing the concentrate it is desirable always to add the chelating agents before the alkaline ayent so as to avoid precipitation of iron. However, the presence of the two types of chelating agents improves the stability of the solution so that no gxeat care is required in making up the solution to prevent precipitation of iron 'hydroxide.
For economy, the amounts of the respective chelating agents need be no greater than required to complex the amount of iron present in either valence state, and in general lesser amounts can be used. In particular, it is desirable, for .
ease of regeneration, that the molar ra-tio of ~ype A
chelating agent ~ iron be not greater than 2:1 and pre-ferably from about 1:1 to about 1.5:1. The iron s~lt is preferably a ferric salt such as ferric chloride, ferric sulfate, or ferric n.itrate. However, it is also possible to use a ~errous salt.such as ferrous sulfate, but in this case the solution must be aerated prior to use in order to insure oxidation of the chelated iron to the ferric state.
The alkaline material is preferably sodium carbonate or sodium hydroxide or mixtures thereo~, although other com-patible alkaline compounds may be used.
The process flow for the oxidation-reduction system using the chelated iron solu~ion of the present in-, .. ..
vention will depend upon the hydrogen sulfide content of the gas stream being treated and the nature of the other com-ponents of the gas stream. Fig. l illustrates a process flow in which the oxidation of hydrogen.sulfide and the regeneration of th~ chelated iron solution are carried out concurrently in the same reaction zone, this arrang~m~nt ~ 20 being referred to as aerobic absorption processing or aerobic : operation. The process flow of Fig. 1 is particularly adapted for use in treating a waste gas stream containing a relatively low concentration of hydrogen sulfide (e.g. 50-100 ppm or less) and which is free of hydrocarbons or other . materials which shuuld not b~ mixed with air.or oxygen~
Referring to Fig. 1, the reaction system compris~s an absorption tower or scrubber 10 containing a central con-tact zone illustrated schematically at 11. This zone may comprise any suitable liquid-vapor contac~ing means such as the conventional packed beds, plates or trays. The inlet gas containing hydrogen sulfide is in-troduced into the tower 10 through a blower 12 and a conduit 13 below the contact zone 11 for passage upwardly therethrough. A flow control damper 15 is provided in the conduit 13. Typically, the inlet gas has a low hydrogen sulfide content on the order of 50 ppm and is free of hydrocarbons, e.g. the off-gas from a xanthate plant producing rayo~ or cellophane, or from a sewage plant.
The chelated iron solution of the present invention is supplied by a line 14 to sprays or distribution nozzles 16 located in an enlarged upper section 17 of the tower 10 and passes downwardly through the contact zone 11 in counter-current relation to the upwardly flowing gas stream. The treated gas exits from the tower 10 through a demister zone 18 in the section 17 and an outlet 19 having a flow control damper 21. Make-up water may be added to the system, as required, through a line 22 communicating with sprays 23 located above the demister zone 18. Make-up chelated iron solution may be added, as ~required, through a line 24 com-municating with the tower 10 below the contact zone 11.
In the arrangement illustrated in Fig. 1 the bottom portion of ~e absorption tower 10 is used as a reservoir ~or the chelated iron solution which fills the bottom of the tower to a level, indicated at 26, below the point of introduction of gas through the conduit 13. The chelated iron solution is continuously recirculated from the bottom of the tower 10 to the nozzles 16 through a line 27, a pump 28, and a line 29 connected to the line 14. A
portion of the chelated iron solution may be bled from ~he system through a line 31, as may be required.
~, . .
~ -- 10 --.
- ~@;i~ 3 For regeneration of the chelated iron solukion, atmospheric air is drawn -through a screened inlet 32 by blower 33 and is supplied through a line 34 to nozzles 36 disposed in the lower portion of the tower 10 so that the air is bubbled through the volume of solution in the bottom of the tower, thereby thoroughly aerating the solution to oxidize the ferrous .iron to ~erric iron. The effluent air passes upwardly through the tower 10 along with the feed gas and exits with the treated gas through the outlet 19.
In the contact zone 11 the hydrogen sulfide in the inlet gas is oxidized to elémental sulfur by the chelated iron solution, as heretofore described, and the sulfur solids are present as a slurry in the treating solution in the bot-tom of the tower. A portion o~f`th~s slurry, usually in the ~orm of a froth, is continuously withdrawn from the tower 10 through a line 37 to a slurry tank 38. The sulfur slurry is withdrawn from the bottom of the slurry tank through a line 39 by a pump 41 and is supplied through a line 42 to a fi:l-tration step, in this case a continuous drum filter ~3. A
portion of the sùlfur slurry is recirculated to the tank 38 through a line 44.
. Wet sulfur product is recovered from the drum fil-ter 43 through a line 46 and may be washed (not shown), to the extent that the water balance of the system permits, in ordèr to recover absorbed chelated iron. If desired, the wet sulfur product may be dried in an autoclave (not shown) to obtain a dr~ high purity sulfur product. The filtrate is withdrawn from the drum filter 43 through a line 47 to a receiver 48. Vapor or gas is removed from the top of the 3Q receiver 48 through a line 49 by a vacuum pump 51 and is ..
introduced by a line 52 to the absorption tower 10 belo~7 the contact zone 11. Liquid filtrate is withdrawn from the bottom of the receiver 48 through a line 53 by a pump 54 and is recirculated through line 14 to the absorption tower lO. A portion of the iltrate may be bled from the system through a line 56, as desired.
Fig. 2 illustrates a process flow, in accordance with the invention, which is particularly adapted for the treatment of gas streams containing hydrocarbons and xela-tively high concentrations of hydrogen sulide, e.g. a sour natural gas containing 1-5% hydrogen sulfide. In this system the removal of hydrogen sul~id~ and the regeneration of the chelated iron solution are carried out in separate reaction zones, this arrangement being rearred to as anaerobic ab-sorption processing or anaerobic operation.
Referring to Fig. 2~ a venturi scrubber 60 is utilized for primary contact in order to accommodate the -high hydrogen-sulfide concentration in the feed gas. ~he gas is introduced to the scrubber through a line 61, and a portion of the chelated iron solution is introduced to the scrubber 60 through a line 62. The lower portion of the scrubber 60 co~nunicates with the lower portion of an ab-sorption tower 63 by means of an enlarged conduit 64. The gas flows rom the scrubber 60 and passes upwardly through a contact zone 66 in countercurrent relation with a down~
wardly flowing portion o~ the chelated iron solution sup-plied from line 62 and a line 67 to nozzles or sprays 68 disposed above the contact zone 66. The treated gas exits from the top o the tower 63 throuyh a line 69 a~ter passiny through a demister zone 70.
- 12 ~
~' , "
Chelated iron solu-tion accumulates in the boffDm portions of the scrubber 60 and the tower 63, as indicated by the liquid level 71. A portion of the solution may be bled from the ~ottom of ~e scrubber 60 through a line 72, as desired. The solution accumulating in the bottom of the tower 63 is withdrawn through a line 73 by a pump 74 an~ is discharged through lines 76 and 77 into an oxidizer or re-generation vessel 78. If necessary, a heat exchanger or coolèr 79 may be interpo~e~ in the line 76. In the vessel 78 the chelated iron solution is oxidiæed or regenerated by introduction of atmospheric air drawn through a screened inlet 81 by a blower 82 and supplied by a line 83 to nozzles 84 located in the ~wer portion of the vessel 78 below the liguid level indicated at 86. The air bu~s through and aerates the solution, as previously described, and exits from the vessel 78 through a conduit 87. ~he regeneratad solution is continuously withdrawn from the bottom of the vessel 78 through a line 88 by a pump 89 and is recirculated thraugh lines 62 and 67 to the scrubber:60 and the tower 63.
The sulfur slurry i5 continuously withdrawn from the ves~el 78 through a conduit 91 to a drum filter 92, as previously described in connection with Fig. 1. Wet sulfur product is removed at a line 93, and filtrate is passed to a receiver 94 through a line 96. Vapor or gas is wi.~hdrawn from ~e receiver 94 through a line 97 by a vacuum pump 98 and is vented through a line 99 into the air exit conduit 87 of the vessel 78. Filtrate is withdrawn from the bottom of the receiver 94 through a line 101 and is recirculated . by a pump 102 through line 77 to the regeneration vessel 78, a portion of the filtrate being bled from the system through ., ; - 13 -:, :
- , a line 103, if desired.
In either the Fig. 1 or the Fig. 2 process flow arrangements the operating temperature and pressure are not critical and may vary over a wide range. Practically speakiny, however, the process will normally be operated at ambient or room temperature and at atmospheric pressure or slightly above.
The following examples will serve to illustrate the invention but are not to be construed as limiting the invention:
- Example 1 A chelated iron concentrate was prepared using a concentrated aqueous solution of Na4EDTA (~RSEN~ M 100) and a concentrated aqueous solution of Na3HEDTA (VERSENO~, 120 ) as the Type A chelating agents and using sorbitol as the Type B chelating agent. The composition of the concentrate was as follows on a weight per cent basis:
; Water 55.9%
FeCl3 (39 wt. % aqueous solution) 13.4 VERSENE M Powder (Na4EDTA) 6.3 VERSENOL 120 (41 wt. % aqueous solution Na3HEDTA) 6.3 Sorbitol (70 wt~ % aqueous solution) 6O3 ~aOH (50 wt. % aqueous solution) 3.6 Na2C3 8.2 100.0%
The concentrate was diluted with sufficie~t water to provide an operating solution having an iron content of 200 ppm. This solution was used succes~fully for about two weeks in a continuous aerobic operation using a pilot plant ~ .
~ . . . .
scale countercurrent absorption column. The p~l of -the solution was maintained within t~e range of from about 8.5 to about 9.5. The gas treated was an off-gas from a xanthate process having a hydrogen sulfide content which varied be-tween about 25 ppm and about 70 ppm. The outlet gas had a hydrogen sulfide content of 5 ppm or less, and the efficiency of hydrogen sulfide removal ranged from about 80% to about 95% dependent upon the hydrogen sulfide content of the feed gas.
Example 2 A laboratory scrubber of the frit-ted glass disk type was employed to treat an inlet air stream containing 1 to 2% hydrogen sulfide with a chelated iron solution. The solution concentrate was prepared by mixing 10 ml. of 39 wt. % aqueous ferric chloride with 64 g. of SEQLENE ES-40 and 10 g. of Na4EDTA, and then adding 20 g. of 50 wt. %
aqueous sodium hydroxide. This concentrate was then diluted with sufficient water to provide 500 g. of solution. SEQLENE
ES-40 is a 40 wt. % aqueous solution of the sodium salt of glucoheptanoic acid as available commercially from Pfanstiehl Labs., Inc.
Over a period of 24 hours of continuous operation there was substantially complete removal of hydrogen sulfide, and the sulfur was readily recovered from the used solution by filtration. The operation was continued successfully for more than 200 hours with the addition of small amounts of fresh chelated iron solution from time to time as required.
Example 3 The procedure of Example 2 was followed using a chelated iron solution prepared from a concentrate of 2.5 ml~
~' .
:
of 39 wt. % aqueous ferric chlori~e, 3.1 g. of ~ucro~e, 4 g.
of Na4EDTA, and 5 g. of sodium carbonate, the concentrate being diluted with water to provide 175 g. of solution.
Substantially complete removal of hydrogen sulfide was ob-tained over a continuous operation of 12 days.
Example 4 Following the same procedure as in Example 2, substantially complete removal of hydrogen sulfide was ob-tained using another chelated iron solution. The concentrate was prepared by mixing 2.5 ml. of 39 wt. % aqueous ferric - chloride with 16 g. of SEQLENE ~I ES-40, 5.2 g. of DEQUEST 2000 4 g. of 50 wt. % aqueous sodium hydroxide, and 2 g. of sodium carbonate. This concentrate was diluted with water to pro-vide 175 g. of operating solution.
DEQUEST M 2006 is an aqueous solution of the sodium salt of tris (phosphonomethyl) amine as available commer-cially from Monsanto Co. DE~U~ST 2054, which may also be used, is an aqueous solution of the sodium salt of N,N,~',N' tetrakis (phosphonomethyl) hexamethyl~ne diamine as available commercially from Monsanto Co.
Example 5 The procedure of Example 2 was followed in effectively removing hydrogen sulfide with a chelated iron solution prepared from a concentrate comprising 14 ml. of 39 wt. % aqueous ferric chloride, 33.6 g. of Na4EDTA, 13 g.
of 70 wt. % aqueous sorbitol, and 14 g. of sodium carbonate~
The concentrate was diluted with water to obtain 3785 ml. or 1 gallon of operating solution. It was noted that when - ` hydrogen sulfide without air was introduced, a small amount of ferrous sulfide was formed, but when air was reintroduced ~. ..
,~r~
along with ~he hydrogen sulfide, the ferrous sulfide was oxidized and disappeared, .
' .
: - 17 -
Claims (31)
1. A composition for use in removing hydrogen sulfide from a gas, which composition comprises an aqueous solution of chelated iron containing at least two iron chelating agents, at least one of said iron chelating agents being an amine type chelating agent (A) capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide, and at least one of said chelating agents being a polyhydroxy type chelating agent (B) capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide.
2. A composition according to Claim 1, which has a pH in the range of from 7 to 13.
3. A composition according to Claim 1 or 2, wherein the chelating agent (A) is selected from polyamino poly-carboxylic acids and their alkali metal salts, polyamino hydroxyethyl polycarboxylic acids and their alkali metal salts, polyphosphonomethyl amines and their alkali metal salts, and mixtures of the foregoing, and the celating agent (B) is selected from sugars, reduced sugars and sugar acids and their alkali metal salts.
4. A composition according to Claim 1 or 2, wherein the chelating agent (A) is selected from polyamino polyacetic acids and their alkali metal salts, polyamino hydroxyethyl polyacetic acids and their alkali metal salts and mixtures of the foregoing, and the chelating agent (B) is a reduced sugar selected from sorbitol and mannitol.
5. A composition according to Claim 1 or 2, wherein the chelating agent (A) comprises a mixture of the sodium salts of ethylene diamine tetraacetic acid and N-hydroxyethyl ethylene diamine triacetic acid, and the chelating agent (B) comprises sorbitol.
6. A continuous oxidation-reduction process for the removal of hydrogen sulfide from a gas stream by con-tacting the gas stream with an aqueous chelated iron solution containing iron in the ferric state for oxidizing hydrogen sulfide to elemental sulfur, thereby being reduced to the ferrous state, separating elemental sulfur from the solution, and regenerating the solution by oxidation by contacting the solution with an oxygen-containing gas to convert iron in ferrous state to the ferric state, wherein the aqueous chelated iron solution contains at least two iron chelating agents, at least one of said iron chelating agents being an amine type chelating agent (A) capable of binding iron in the ferrous state to prevent precipitation of ferrous sulfide, and at least one of said chelating agents being a polyhydroxy type chelating agent (B) capable of binding iron in the ferric state to prevent precipitation of ferric hydroxide, thereby to improve the stability of the solution.
7. A process according to Claim 6, wherein the solution has a pH in the range of from 7 to 13.
8. A process according to Claim 6, wherein the chelating agent (A) is selected from polyamino poly-carboxylic acids and their alkali metal salts, polyamino hydroxyethyl polycarboxylic acids and their alkali metal salts, polyphosphonomethyl amines and their alkali metal salts, and mixtures of the foregoing, and the chelating agent (B) is selected from sugars, reduced sugars and sugar acids and their alkali metal salts.
9. A process according to Claim 6, wherein the chelating agent (A) is selected from polyamino poly-acetic acids and their alkali metal salts, polyamino hydroxyethyl polyacetic acids and their alkali metal salts and mixtures of the foregoing, and the chelating agent (B) is a reduced sugar selected from sorbitol and mannitol.
10. A process according to Claim 6, wherein the chelating agent (A) comprises a mixture of the sodium salts of ethylene diamine tetraacetic acid and N-hydroxyethyl ethylene diamine triacetic acid, and the chelating agent (B) comprises sorbitol.
11. A process according to Claim 7, wherein the chelating agent (A) is selected from polyamino poly-carboxylic acids and their alkali metal salts, polyamino hydroxyethyl polycarboxylic acids and their alkali metal salts, polyphosphonomethyl amines and their alkali metal salts, and mixtures of the foregoing, and the chelating agent (B) is selected from sugars, reduced sugars and sugar acids and their alkali metal salts.
12. A process according to Claim 7, wherein the chelating agent (A) is selected from polyamino poly-acetic acids and their alkali metal salts, polyamino hydroxyethyl polyacetic acids and their alkali metal salts and mixtures of the foregoing, and the chelating agent (B) is a reduced sugar selected from sorbitol and mannitol.
13. A process according to Claim 7 wherein the chelating agent (A) comprises a mixture of the sodium salts of ethylene diamine tetraacetic acid and N-hydroxyethyl ethylene diamine triacetic acid, and the chelating agent (B) comprises sorbitol.
14. A process according to Claim 6, 7 or 8, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5.
15. A process according to Claim 9, 10 or 11, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10 .5.
16. A process according to Claim 12 or 13, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5.
17. A process according to Claim 6, 7 or 8, wherein the solution has a pH in the range of from 8 to 10.5 and a molar ratio of the chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1.
18. A process according to Claim 9, 10 or 11, wherein the solution has a pH in the range of from 8 to 10.5 and a molar ratio of the chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1.
19. A process according to Claim 12 or 13, wherein the solution has a pH in the range of from 8 to 10.5 and a molar ratio of the chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1.
20. A process according to Claim 6, 7 or 8, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
21. A process according to Claim 9, 10 or 11, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
22. A process according to Claim 12 or 13, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
23. A process according to Claim 6, 7 or 8, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected in anaerobic operat-ion in separate reaction zones.
24. A process according to Claim 9, 10 or 11, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected in anaerobic operation in separate reaction zones.
25. A process according to Claim 12 or 13, wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected in anaerobic operation in separate reaction zones.
26. A process according to Claim 6, 7 or 8, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
27. A process according to Claim 9, 10 or 11, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
28. A process according to Claim 12 or 13, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected concurrently in aerobic operation in the same reaction zone.
29. A process according to Claim 6, 7 or 8, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream With the solution and the regeneration of the solution are effected in anaerobic operation in separate reaction zones.
30. A process according to Claim 9, 10 or 11, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelat-ing agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected in anaerobic operation in separate reaction zones.
31. A process according to Claim 12 or 13, wherein the solution contains sufficient alkaline material selected from sodium hydroxide, sodium carbonate, and mixtures thereof to provide a solution pH in the range of from 8 to 10.5, and the solution has a molar ratio of chelating agent (A) to iron in the solution in the range of from 1:1 to 1.5:1, and wherein the contacting of the gas stream with the solution and the regeneration of the solution are effected in anaerobic operation in separate reaction zones.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55127975A | 1975-02-20 | 1975-02-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1071613A true CA1071613A (en) | 1980-02-12 |
Family
ID=24200600
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA244,202A Expired CA1071613A (en) | 1975-02-20 | 1976-01-26 | Removal of hydrogen sulfide from gases |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS6010773B2 (en) |
| CA (1) | CA1071613A (en) |
| DE (1) | DE2606277C2 (en) |
| GB (1) | GB1538925A (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2740039A1 (en) * | 1977-09-06 | 1979-03-15 | Heinz Hoelter | Two=stage gas scrubber - with acid and alkaline treatment branch over common fluid sump |
| JPS5484876A (en) * | 1977-12-19 | 1979-07-06 | Nippon Steel Corp | Apparatus for withdrawing desulfurizing liquid in oxidation-reduction desulfurization method |
| EP0011517A3 (en) * | 1978-10-06 | 1980-07-23 | Rhone-Poulenc Industries | Process and apparatus for removing hydrogen sulfide from gas streams |
| FR2437863A1 (en) * | 1978-10-06 | 1980-04-30 | Rhone Poulenc Ind | Continuous removal of hydrogen sulphide from a gas - comprising treatment with aq. polyvalent metal chelate, oxidn., sepn. and sulphur removal with chlorinated hydrocarbon |
| FR2463637A1 (en) * | 1979-08-17 | 1981-02-27 | Rhone Poulenc Ind | Hydrogen sulphide elimination from gases - by treatment with aq. soln. of polyvalent metal chelate and oxidn. (DK 5.5.80) |
| CN102397744B (en) * | 2011-04-28 | 2013-10-16 | 中国石油天然气股份有限公司 | Compound sulfur dispersant of complex iron desulfurization solution |
| CN109663484A (en) * | 2017-10-17 | 2019-04-23 | 中国石油化工股份有限公司 | High performance vulcanization hydrogen inhales disappear liquid and purposes |
| CN110551543A (en) * | 2019-09-12 | 2019-12-10 | 欧润吉生态环保(浙江)有限公司 | Device for deep desulfurization of biogas |
| CN115738599B (en) * | 2022-11-23 | 2024-06-04 | 攀钢集团攀枝花钢铁研究院有限公司 | At the same time absorb NOxPreparation method of complexing denitration liquid of CO |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3097925A (en) * | 1958-04-17 | 1963-07-16 | Atlantic Refining Co | Method of recovering sulphur |
| DE1253858B (en) * | 1962-10-05 | 1967-11-09 | Koppers Gmbh Heinrich | Process for removing organic sulfur compounds, which have little or no water solubility, from gases |
-
1976
- 1976-01-26 CA CA244,202A patent/CA1071613A/en not_active Expired
- 1976-01-30 GB GB385976A patent/GB1538925A/en not_active Expired
- 1976-02-13 JP JP51014100A patent/JPS6010773B2/en not_active Expired
- 1976-02-17 DE DE19762606277 patent/DE2606277C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6010773B2 (en) | 1985-03-20 |
| JPS51107273A (en) | 1976-09-22 |
| GB1538925A (en) | 1979-01-24 |
| DE2606277C2 (en) | 1985-05-23 |
| DE2606277A1 (en) | 1976-09-09 |
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