CA1186490A - Process for the removal of h.sub.2s and co.sub.2 from gaseous streams - Google Patents
Process for the removal of h.sub.2s and co.sub.2 from gaseous streamsInfo
- Publication number
- CA1186490A CA1186490A CA000401798A CA401798A CA1186490A CA 1186490 A CA1186490 A CA 1186490A CA 000401798 A CA000401798 A CA 000401798A CA 401798 A CA401798 A CA 401798A CA 1186490 A CA1186490 A CA 1186490A
- Authority
- CA
- Canada
- Prior art keywords
- chelate
- iii
- absorbent
- removal
- sulphur
- 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
Links
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
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/52—Hydrogen sulfide
- B01D53/526—Mixtures of hydrogen sulfide and carbon dioxide
-
- 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
- B01D53/34—Chemical or biological purification of waste gases
-
- 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
- C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
- C01B17/05—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by wet processes
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10K—PURIFYING OR MODIFYING THE CHEMICAL COMPOSITION OF COMBUSTIBLE GASES CONTAINING CARBON MONOXIDE
- C10K1/00—Purifying combustible gases containing carbon monoxide
- C10K1/08—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors
- C10K1/10—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors with aqueous liquids
- C10K1/105—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors with aqueous liquids containing metal compounds other than alkali- or earth-alkali carbonates, -hydroxides, oxides, or salts of inorganic acids derived from sulfur
- C10K1/106—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors with aqueous liquids containing metal compounds other than alkali- or earth-alkali carbonates, -hydroxides, oxides, or salts of inorganic acids derived from sulfur containing Fe compounds
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/40—Capture or disposal of greenhouse gases of CO2
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2
Abstract
A B S T R A C T
FROM GASEOUS STREAMS
Process for the removal of H2S and CO2 from a gas by contacting with a solution of the Fe(III) chelate of nitrilo-triacetic acid in an absorbent comprising diethylene glycol monoethyl ether. The H2S is converted to sulphur and the CO2 is absorbed to produce a purified gas stream, and the Fe(III) chelate is converted to the Fe(II) chelate. The process may include sulphur removal and regeneration of the absorbent and the Fe(III) chelate.
FROM GASEOUS STREAMS
Process for the removal of H2S and CO2 from a gas by contacting with a solution of the Fe(III) chelate of nitrilo-triacetic acid in an absorbent comprising diethylene glycol monoethyl ether. The H2S is converted to sulphur and the CO2 is absorbed to produce a purified gas stream, and the Fe(III) chelate is converted to the Fe(II) chelate. The process may include sulphur removal and regeneration of the absorbent and the Fe(III) chelate.
Description
PROCESS FOR THE REMOVAL OF H2S .~ND C02 FROM GASEOUS STREAMS
The invention relates to a process f'or the removal of' H2S
and C02 f`rom a gaseous stream containing H2S and C02~
The presence of` significant quantities o~ HzS and C02 in various "sour" industrial gaseous streams poses a persistent problem. A gaseous stream is named "sour" i~ it contains signi~icant quantities o~ H2S and/or C02.
Although various procedures have been developed to remove and recover these contaminants, most such processes are un-attractive f'or a variety of` reasons. Accordingly, there remains a need f`or an e~ficient and low cost process to remove these undesired materials.
While some work has been done in the area of removal and conversion of H2S to sulphur by use of` iron complexes in waste gas streams, such processes generally are inapplicable directly to purificatio~ o~ hydrocarbon ~eedstock, coal gasification, or natural gas streams having hig~l ratios of` CO~ to H2S.F~ example, U.S. patent specif'ication 3~266,320 discloses the removal o~ H2S
from f`luids passing through or leaving industrial processes by adding to the polluted streams certain chelates o~ poly~
valent metals. The chelates are added in an amoun-t which is stoichiometrically substantially less than the amount of the pollutant, and the chelate- and pollutant-containing stream is contacted with oxygen. The preferred chelates are the iron, cobalt, and nickel chelates of' acetyl acetone, cyclop-entadiene, ethylenediaminetetraacetic acid, ~-hydroxyethylethylenediamine-triacetic acid, gluconic acid, tartaric acid and citric acid.
The chelate is said to catalyze the reaction.
As indicated, however, this procedure is unsuited to gaseous hydrocarbon f'eedstock, coal gasif`ication stream~ or natural gas 3~
treatment since no provision is made for C02 removal. More im-portantly, the use of oxygen with the materials contemplated would be intolerable. Finally, -the amounts of chelate employed in the paten-t specification are merely catalytic, and do not give the desired degree of H2S removal from gaseous streams.
Similarly, U.S. patent specification 3,622,273 discloses the removal of H2S from a gaseous stream by contacting the gaseous stream with a solution containing, by weight~ from 0.005 to 20 per cent of a ferric ion complex, from 25.0 to 99.945 per cent of water, and from 0.05 to 10.0 per cent of a buffering agent comprising an alkali metal carbonate and/or an alkali metal hydrogen carbonate. According to the patent speci fication, known complexing agents, such as nitrilotriacetic acid and ethylenediaminetetraacetic acid, present stability problems when employed in H2S removal. To overcome these problems, the patent specification specifies the addition of a buffer to the trçating solution, in the amount and type indicated pre-viously. The ferrous complex resulting from reaction of the ferric complex with the H2S may be regenerated separately and re-used indefinitely.
U.S. patent specification 4,091jO73 describes a process in which H2S and C02 are simultaneously removed from a variety of gas streams. The gas stream containing the sour gases is eontaeted with a solution of the Fe(IlI) ehelate of N-(2-hydro~y-ethyl)ethylenediaminetriacetic acid in a C02-selective solvent.
The H2S is converted to sulphur, the C02 is absorbed to produce a purified gas stream, and the Fe(III) chelate is eonverted to the Fe(II) ehelate. The process includes sulphur removal and simultaneous regeneration of the solvent and the Fe(III) chelate.
It is an object of the present invention to provide an economical and efficient method for the removal of H2S and C02 from a gaseous stream.
It is another object to produce high quality sulphur crystals ~hich settle readily.
Accordingly, the invention provides a process for the re-moval o~ H2S and C02 from a gaseous stream containing H2S and C02, which process comprises the following steps:-a) contacting the gaseous stream with a lean C02-selective absorbent mixture comprising diethylene glycol mono-etnyl ether and the Fe(III) chelate of nitrilotriacetic acid, and b) separating a sweet gaseous stream from an absorbent ad-mixture containing absorbed C0~, solid sulphur, and Fe(II) chelate o~ nitrilotriacetic acid.
A puri~ied or "sweet" gaseous stream is produced which meets general industrial and commercial H2S and C02 specifications.
The C02 is absorbed and the H2S is immediately conver-ted to sulphur by the Fe(III) chelate of nitrilotriacetic acid. In the process, the Fe(III) chelate is reduced to the Fe(II) chelate.
As indicated, a critical feature of the invention is the use of diethylene glycol monoethyl ether as the absorbent liquid.
This ether is also re~erred to as "carbitol" or ~'3,6-dioxaoctanol".
The solvent need not be pure, and, in general, will contain minor amounts of other materials. The use of this absorbent provides a system which can be virtually non-aqueous, has a high ~2S and C2 capacity, and has a low vapour pressure at typical operating temperatures. Additionally, the solutions exhibit good C02 selectivities.
The absorbent admixture separated in s-tep b) may be dis-carded, if desi~ed, but for economical reasons the Fe(III) chelate o~ nitrilotriacetic acid is suitably regenerated and the sulphur removed from the absorbent mixture. So, the Fe(II) chelate of nitrilotriacetic acid separated in step b) is prefer ably contacted with an oxygen-containing gas, producing a lean C02-selective absorbent mixture containing regenerated Fe(III) chelate of nitrilotriacetic acid.
The sulphur is suitably removed from absorbent admi~ture separated in step b) or from the lean C02-selective absorbent mixture containing the regenerated Fe(III) chelate. As the sulphur crystals settle readily, they can easily be removed.
S~phv.r removal from solution may be accomplished by means such as extraction, liquid flotation, filtration, or use of a hydro-cyclone, etc.
The lean C02-selective absorbent mixture containing regener-ated Fe(III) chelate of nitrilotriacetic acid may be used in any suitable manner; pre~erably, the process according to the invention is operated as a cyclic procedure by returning this lean mixture to step a) for use as lean absorbent mixture.
If significant quantities of C02 have been absorbed, the reactant-containing solution is preferably stripped, such as by heating or pressure reduction, to remove the bulk of the C02 before regeneration of the reactant (either prior or subsequent to sulphur removal). Alternatively, or if small quantities of C02 are absorbed, the C02 may simply be stripped during the regeneration. The regenerated absorbent mixture may then be returned to step a) for further use.
The particular type of gaseous stream trea-ted is not critical, as will be evident. ~treams particularly suited to removal of H2S and C02 by the process of the invention are, as indicated, naturally occurring gases, synthesis gases, process gases, and fuel gases produced by gasification pro cedures, e.g., gases produced by the gasification or liquefac-tion ofcocl .~nd gasification of petroleum, shale, tar sands, etc. Particularly preferred are coal gasifica-tion streams, natural gas streams and refinery feedstocks composed of gaseous hydrocarbon streams, and other gaseous hydrocarbon streams. The term "hydroCarbon stream(s)", as employed herein, is intended to include streams containing significant quantities of hydro-carbons (both paraffinic and aromatic), it being recognizedthat su-ch streamsmay contain significant "impurities" not technically defined as a hydrocarbon. Streams containing principally a single hydrocarbon, e.g., ethane, are eminently suited to the process of the invention. Streams derived from the gasification and/or partial oxidation of gaseous or liquid hydrocarbons may be treated by the process according to the invention. The H2S content of the type of streams contemplated will vary extensively, but, in general, will range from about 0.1 per cent to about 10 per cent by volume. C02 content may also vary, and may range from about 0.5 per cent to over 99 per cent by volume. Obviously, the contents of H2S and C02 present are not generally a limiting factor in the process of the in-vention.
The temperatures employed in the contacting of step a) are not generally critical, except in the sense that the temper-atures employed must permit acceptable absorption of C02. In general, temperatures from 10C to 80C are suitable, and temperatures from 20 C to 45C are preferred. In many com-mercial applications, such as the removal of H2S and C02 from natural gas to meet pipeline specifications, contacting at ambient temperatures is preferred, since the cost of re-frigeration would exceed the benefits obtained due to in-creased absorption at the lower temperature. Contact times may be in the range from about 1 s to about 270 s or longer, with contact times in the range of from 2 s to 120 g being preferred.
Similarly, in the regeneration of the Fe(III) chela-te or strippin~,temperatures may be varied widely. Preferably, the regeneration should be carried out at substantially the same temperature as the absorption in step a). If heat is added to assist regeneration, cooling of the absorben-t mixture is re-quired before ret~rn of the absorbent mixture to step a). In general, temperatures in the range of from about 10C -to 80 C, preferably from 20C to 40 C, may be employed.
The pressure in step a) may vary widely, depending on the pressure of the gaseous stream to be treated~ For example, pressures in step a) may vary from 1 bar up to 152 or even 203 bar. Pressures in the range of from 1 bar to about 101 bar are preferred. In the regeneration of the Fe(III) chelate or desorption of CO2 pressures will range from about ] bar to about 3 or 4 bar. The pressure~temperature relationships involved are well understood by those skilled in the art, and need no-t be detailed herein. Other conditions of operation for this type of reaction process, e.g., pH, etc., are further described in United States patent specification 3,068,065 and United States pa-tent specification 4,009,251. Preferably, plI in the process of the invention will range from about 6 to about 7.5. The process is preferably conducted continuously, and the molar ratio of -the nitrilotriacetic acid to the iron is from about 1.2 to 1.4.
As indicated, the H2S, when contacted, is quickly con-verted by the Fe(III) chelate of nitrilotriacetic acid to elemental sulphur. Since the Fe(III) chelate (and the Fe(II) chelate) has limited solubility in many solvents or absorbents, it is a real advantage of the invention that the chelate has good solubility in the absorbent used in the process according to the invention, i.e., in diethylene glycol monoethyl ether (Carbitol). The chela-te is preferab`ly supplied in admixture with the liquid absorbent and water. The amount of chela-te supplied is that amount sufficient to convert all or substantially all of the H2S in the gaseous stream, and will generally be in the order of at least about 2 mol per mol of H2S. Ratios of from about 2 mol to about 15 mol of chelate per mol of ~2S may be used, with ratios of from about 2 mol per mol to about 5 mol of chelate per mol of H2S being pre-ferred. The manner of preparing the admixture is a matter of choice. Preferably, the chelate is added as an aqueous solution 6a to the llquid absorbent. Since -the chelate has significant solu-bility in the absorbent, and since water is produced by the reaction of the H2S and the chelate, precise amounts of water to be added cannot be given. In general, the amount of chelate solu-tion supplied may be about 20 per cent to about 80 per cen-t by volume of the total absorbent admixture supplied to the absorption zone. The Fe(III) chelate solution will generally be supplied as an aqueous solution having a concen-tration of from about 0.1 molar ~o about 1.5 molar. A composition of about 1 molar is preferred.
The loaded absorbent mixture is regenerated by contacting the mixture with an oxygen-containing gas. Examples of oxygen-containing gases are air9 air enriched with oxygen and pure oxygen.
T'ne oxygen accomplishes two ~unctions, the stripping of any residual C02 from the loaded absorbent mixture and the oxidation of the Fe(II) chelate of nitrilotriacetic acid to the Fe(III) chelate of nitrilotriacetic acid. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of Fe(II) chelate present in the mixture. Preferably, the oxygen gas is supplied in an amount in the range of Prom about 1.2 to 3 times excess.
The invention is further illustrated by means of the fol-lowing Example. This example is described with reference -to the accompanying drawing.
EXAMPLE
As shown, sour gas, e.g. natural gas containing about 0.5 per cent H2S, and 32 per cent by volume C02 in a line 1 enters an absorption column 2 (tray type) into which also en-ters an ab-sorbent mixture composed of 90 per cent diethylene glycol mono=
ethyl ether (by volume) and 10 per cent of an aqueous o.8 M
solution of the Fe(III) chelate of nitrilotriacetic acid. The pressure of the feed gas is about 84 bar and the temperature of the absorbent mixture is about 45 C. A con-tact time of about 45 s is employed in order to absorb virtually all C02 and react all the H2S. Purified or "sweet'gas leaves the absorption column 2 through a line 3. The "sweet" gas is of a purity sufficient to meet standard requirements. In the absorbent mixture, the H2S
is converted to elemental sulphur by the Fe(III) chelate, the Fe(III) chelate in the process being converted to the Fe(II) chelate. The absorbent mixture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed continuously and sent through a line 4 to a regenerator 5, which is a column.
Prior to entry to the regenerator 5, the sulphur in the ab-sorbent mixture may be removed in a sulphur separatïon zone (shown in dotted lïnes). Sulphur is removed from thïs zone via a line 13. However, s~phur recovery may also be accomplished at a later stage, as shown hereinafter. As sho~m, the bulk of the C02 absorbed is removed in a unit 6 by reduction of pressure.
The C02 liberated in the unit ~ is withdra~ via a line 12. Heat may be added to unit 6, if necessary. Any absorbent carried over with the vented C02 may be recovered by conventional equip-ment, such as a carbon absorp-tion bed (not shown), and recycled.
In the regenerator 5 the loaded absorbent mixture is con-tacted with excess air supplied via a line 7 to strip the re-maining C02 from the mixture and convert the Fe(II) chelate to the Fe(III) chelate. The temperature of the stripping column is about 45 C, and pressure in the column is maintained at about 2 bar. Spent air is removed from the regenerator 5 through a line 8, while regenerated absorbent mixture, which still con-tains elemental sulphur, is sent through a line 9 to a sulphur removal unit 10. In unit 10, which may be a settler, the sulphur is removed from the absorbent mixture and recovered via a line 14. The now ~lly regenerated absorbent mixture is returned via a line 11 to the absorption column 2.
An absorption col~lmn might comprise two separate columns in which the solution from the lower portion of the first column would be introduced into the upper portion of the second column, the gaseous materia] from the upper portion of the first column being fed into the lower portion of the second column.
Parallel operation o-f units is, of course, well within the scope of the invention.
The solutions or mixtures employed may contain other materials or additives for given purposes. For example, U.S.
patent specification 3,933,993 discloses the use of buffering agents, such as phosphate and carbonate buffers. Similarly, U.S. patent specification 4,009,251 describes various ~8~
additiYes, such as sodi1~m oxalate, sodium formate, sodium thiosulphate, and sodium acetate, which may be ~ene~icial.
The invention relates to a process f'or the removal of' H2S
and C02 f`rom a gaseous stream containing H2S and C02~
The presence of` significant quantities o~ HzS and C02 in various "sour" industrial gaseous streams poses a persistent problem. A gaseous stream is named "sour" i~ it contains signi~icant quantities o~ H2S and/or C02.
Although various procedures have been developed to remove and recover these contaminants, most such processes are un-attractive f'or a variety of` reasons. Accordingly, there remains a need f`or an e~ficient and low cost process to remove these undesired materials.
While some work has been done in the area of removal and conversion of H2S to sulphur by use of` iron complexes in waste gas streams, such processes generally are inapplicable directly to purificatio~ o~ hydrocarbon ~eedstock, coal gasification, or natural gas streams having hig~l ratios of` CO~ to H2S.F~ example, U.S. patent specif'ication 3~266,320 discloses the removal o~ H2S
from f`luids passing through or leaving industrial processes by adding to the polluted streams certain chelates o~ poly~
valent metals. The chelates are added in an amoun-t which is stoichiometrically substantially less than the amount of the pollutant, and the chelate- and pollutant-containing stream is contacted with oxygen. The preferred chelates are the iron, cobalt, and nickel chelates of' acetyl acetone, cyclop-entadiene, ethylenediaminetetraacetic acid, ~-hydroxyethylethylenediamine-triacetic acid, gluconic acid, tartaric acid and citric acid.
The chelate is said to catalyze the reaction.
As indicated, however, this procedure is unsuited to gaseous hydrocarbon f'eedstock, coal gasif`ication stream~ or natural gas 3~
treatment since no provision is made for C02 removal. More im-portantly, the use of oxygen with the materials contemplated would be intolerable. Finally, -the amounts of chelate employed in the paten-t specification are merely catalytic, and do not give the desired degree of H2S removal from gaseous streams.
Similarly, U.S. patent specification 3,622,273 discloses the removal of H2S from a gaseous stream by contacting the gaseous stream with a solution containing, by weight~ from 0.005 to 20 per cent of a ferric ion complex, from 25.0 to 99.945 per cent of water, and from 0.05 to 10.0 per cent of a buffering agent comprising an alkali metal carbonate and/or an alkali metal hydrogen carbonate. According to the patent speci fication, known complexing agents, such as nitrilotriacetic acid and ethylenediaminetetraacetic acid, present stability problems when employed in H2S removal. To overcome these problems, the patent specification specifies the addition of a buffer to the trçating solution, in the amount and type indicated pre-viously. The ferrous complex resulting from reaction of the ferric complex with the H2S may be regenerated separately and re-used indefinitely.
U.S. patent specification 4,091jO73 describes a process in which H2S and C02 are simultaneously removed from a variety of gas streams. The gas stream containing the sour gases is eontaeted with a solution of the Fe(IlI) ehelate of N-(2-hydro~y-ethyl)ethylenediaminetriacetic acid in a C02-selective solvent.
The H2S is converted to sulphur, the C02 is absorbed to produce a purified gas stream, and the Fe(III) chelate is eonverted to the Fe(II) ehelate. The process includes sulphur removal and simultaneous regeneration of the solvent and the Fe(III) chelate.
It is an object of the present invention to provide an economical and efficient method for the removal of H2S and C02 from a gaseous stream.
It is another object to produce high quality sulphur crystals ~hich settle readily.
Accordingly, the invention provides a process for the re-moval o~ H2S and C02 from a gaseous stream containing H2S and C02, which process comprises the following steps:-a) contacting the gaseous stream with a lean C02-selective absorbent mixture comprising diethylene glycol mono-etnyl ether and the Fe(III) chelate of nitrilotriacetic acid, and b) separating a sweet gaseous stream from an absorbent ad-mixture containing absorbed C0~, solid sulphur, and Fe(II) chelate o~ nitrilotriacetic acid.
A puri~ied or "sweet" gaseous stream is produced which meets general industrial and commercial H2S and C02 specifications.
The C02 is absorbed and the H2S is immediately conver-ted to sulphur by the Fe(III) chelate of nitrilotriacetic acid. In the process, the Fe(III) chelate is reduced to the Fe(II) chelate.
As indicated, a critical feature of the invention is the use of diethylene glycol monoethyl ether as the absorbent liquid.
This ether is also re~erred to as "carbitol" or ~'3,6-dioxaoctanol".
The solvent need not be pure, and, in general, will contain minor amounts of other materials. The use of this absorbent provides a system which can be virtually non-aqueous, has a high ~2S and C2 capacity, and has a low vapour pressure at typical operating temperatures. Additionally, the solutions exhibit good C02 selectivities.
The absorbent admixture separated in s-tep b) may be dis-carded, if desi~ed, but for economical reasons the Fe(III) chelate o~ nitrilotriacetic acid is suitably regenerated and the sulphur removed from the absorbent mixture. So, the Fe(II) chelate of nitrilotriacetic acid separated in step b) is prefer ably contacted with an oxygen-containing gas, producing a lean C02-selective absorbent mixture containing regenerated Fe(III) chelate of nitrilotriacetic acid.
The sulphur is suitably removed from absorbent admi~ture separated in step b) or from the lean C02-selective absorbent mixture containing the regenerated Fe(III) chelate. As the sulphur crystals settle readily, they can easily be removed.
S~phv.r removal from solution may be accomplished by means such as extraction, liquid flotation, filtration, or use of a hydro-cyclone, etc.
The lean C02-selective absorbent mixture containing regener-ated Fe(III) chelate of nitrilotriacetic acid may be used in any suitable manner; pre~erably, the process according to the invention is operated as a cyclic procedure by returning this lean mixture to step a) for use as lean absorbent mixture.
If significant quantities of C02 have been absorbed, the reactant-containing solution is preferably stripped, such as by heating or pressure reduction, to remove the bulk of the C02 before regeneration of the reactant (either prior or subsequent to sulphur removal). Alternatively, or if small quantities of C02 are absorbed, the C02 may simply be stripped during the regeneration. The regenerated absorbent mixture may then be returned to step a) for further use.
The particular type of gaseous stream trea-ted is not critical, as will be evident. ~treams particularly suited to removal of H2S and C02 by the process of the invention are, as indicated, naturally occurring gases, synthesis gases, process gases, and fuel gases produced by gasification pro cedures, e.g., gases produced by the gasification or liquefac-tion ofcocl .~nd gasification of petroleum, shale, tar sands, etc. Particularly preferred are coal gasifica-tion streams, natural gas streams and refinery feedstocks composed of gaseous hydrocarbon streams, and other gaseous hydrocarbon streams. The term "hydroCarbon stream(s)", as employed herein, is intended to include streams containing significant quantities of hydro-carbons (both paraffinic and aromatic), it being recognizedthat su-ch streamsmay contain significant "impurities" not technically defined as a hydrocarbon. Streams containing principally a single hydrocarbon, e.g., ethane, are eminently suited to the process of the invention. Streams derived from the gasification and/or partial oxidation of gaseous or liquid hydrocarbons may be treated by the process according to the invention. The H2S content of the type of streams contemplated will vary extensively, but, in general, will range from about 0.1 per cent to about 10 per cent by volume. C02 content may also vary, and may range from about 0.5 per cent to over 99 per cent by volume. Obviously, the contents of H2S and C02 present are not generally a limiting factor in the process of the in-vention.
The temperatures employed in the contacting of step a) are not generally critical, except in the sense that the temper-atures employed must permit acceptable absorption of C02. In general, temperatures from 10C to 80C are suitable, and temperatures from 20 C to 45C are preferred. In many com-mercial applications, such as the removal of H2S and C02 from natural gas to meet pipeline specifications, contacting at ambient temperatures is preferred, since the cost of re-frigeration would exceed the benefits obtained due to in-creased absorption at the lower temperature. Contact times may be in the range from about 1 s to about 270 s or longer, with contact times in the range of from 2 s to 120 g being preferred.
Similarly, in the regeneration of the Fe(III) chela-te or strippin~,temperatures may be varied widely. Preferably, the regeneration should be carried out at substantially the same temperature as the absorption in step a). If heat is added to assist regeneration, cooling of the absorben-t mixture is re-quired before ret~rn of the absorbent mixture to step a). In general, temperatures in the range of from about 10C -to 80 C, preferably from 20C to 40 C, may be employed.
The pressure in step a) may vary widely, depending on the pressure of the gaseous stream to be treated~ For example, pressures in step a) may vary from 1 bar up to 152 or even 203 bar. Pressures in the range of from 1 bar to about 101 bar are preferred. In the regeneration of the Fe(III) chelate or desorption of CO2 pressures will range from about ] bar to about 3 or 4 bar. The pressure~temperature relationships involved are well understood by those skilled in the art, and need no-t be detailed herein. Other conditions of operation for this type of reaction process, e.g., pH, etc., are further described in United States patent specification 3,068,065 and United States pa-tent specification 4,009,251. Preferably, plI in the process of the invention will range from about 6 to about 7.5. The process is preferably conducted continuously, and the molar ratio of -the nitrilotriacetic acid to the iron is from about 1.2 to 1.4.
As indicated, the H2S, when contacted, is quickly con-verted by the Fe(III) chelate of nitrilotriacetic acid to elemental sulphur. Since the Fe(III) chelate (and the Fe(II) chelate) has limited solubility in many solvents or absorbents, it is a real advantage of the invention that the chelate has good solubility in the absorbent used in the process according to the invention, i.e., in diethylene glycol monoethyl ether (Carbitol). The chela-te is preferab`ly supplied in admixture with the liquid absorbent and water. The amount of chela-te supplied is that amount sufficient to convert all or substantially all of the H2S in the gaseous stream, and will generally be in the order of at least about 2 mol per mol of H2S. Ratios of from about 2 mol to about 15 mol of chelate per mol of ~2S may be used, with ratios of from about 2 mol per mol to about 5 mol of chelate per mol of H2S being pre-ferred. The manner of preparing the admixture is a matter of choice. Preferably, the chelate is added as an aqueous solution 6a to the llquid absorbent. Since -the chelate has significant solu-bility in the absorbent, and since water is produced by the reaction of the H2S and the chelate, precise amounts of water to be added cannot be given. In general, the amount of chelate solu-tion supplied may be about 20 per cent to about 80 per cen-t by volume of the total absorbent admixture supplied to the absorption zone. The Fe(III) chelate solution will generally be supplied as an aqueous solution having a concen-tration of from about 0.1 molar ~o about 1.5 molar. A composition of about 1 molar is preferred.
The loaded absorbent mixture is regenerated by contacting the mixture with an oxygen-containing gas. Examples of oxygen-containing gases are air9 air enriched with oxygen and pure oxygen.
T'ne oxygen accomplishes two ~unctions, the stripping of any residual C02 from the loaded absorbent mixture and the oxidation of the Fe(II) chelate of nitrilotriacetic acid to the Fe(III) chelate of nitrilotriacetic acid. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of Fe(II) chelate present in the mixture. Preferably, the oxygen gas is supplied in an amount in the range of Prom about 1.2 to 3 times excess.
The invention is further illustrated by means of the fol-lowing Example. This example is described with reference -to the accompanying drawing.
EXAMPLE
As shown, sour gas, e.g. natural gas containing about 0.5 per cent H2S, and 32 per cent by volume C02 in a line 1 enters an absorption column 2 (tray type) into which also en-ters an ab-sorbent mixture composed of 90 per cent diethylene glycol mono=
ethyl ether (by volume) and 10 per cent of an aqueous o.8 M
solution of the Fe(III) chelate of nitrilotriacetic acid. The pressure of the feed gas is about 84 bar and the temperature of the absorbent mixture is about 45 C. A con-tact time of about 45 s is employed in order to absorb virtually all C02 and react all the H2S. Purified or "sweet'gas leaves the absorption column 2 through a line 3. The "sweet" gas is of a purity sufficient to meet standard requirements. In the absorbent mixture, the H2S
is converted to elemental sulphur by the Fe(III) chelate, the Fe(III) chelate in the process being converted to the Fe(II) chelate. The absorbent mixture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed continuously and sent through a line 4 to a regenerator 5, which is a column.
Prior to entry to the regenerator 5, the sulphur in the ab-sorbent mixture may be removed in a sulphur separatïon zone (shown in dotted lïnes). Sulphur is removed from thïs zone via a line 13. However, s~phur recovery may also be accomplished at a later stage, as shown hereinafter. As sho~m, the bulk of the C02 absorbed is removed in a unit 6 by reduction of pressure.
The C02 liberated in the unit ~ is withdra~ via a line 12. Heat may be added to unit 6, if necessary. Any absorbent carried over with the vented C02 may be recovered by conventional equip-ment, such as a carbon absorp-tion bed (not shown), and recycled.
In the regenerator 5 the loaded absorbent mixture is con-tacted with excess air supplied via a line 7 to strip the re-maining C02 from the mixture and convert the Fe(II) chelate to the Fe(III) chelate. The temperature of the stripping column is about 45 C, and pressure in the column is maintained at about 2 bar. Spent air is removed from the regenerator 5 through a line 8, while regenerated absorbent mixture, which still con-tains elemental sulphur, is sent through a line 9 to a sulphur removal unit 10. In unit 10, which may be a settler, the sulphur is removed from the absorbent mixture and recovered via a line 14. The now ~lly regenerated absorbent mixture is returned via a line 11 to the absorption column 2.
An absorption col~lmn might comprise two separate columns in which the solution from the lower portion of the first column would be introduced into the upper portion of the second column, the gaseous materia] from the upper portion of the first column being fed into the lower portion of the second column.
Parallel operation o-f units is, of course, well within the scope of the invention.
The solutions or mixtures employed may contain other materials or additives for given purposes. For example, U.S.
patent specification 3,933,993 discloses the use of buffering agents, such as phosphate and carbonate buffers. Similarly, U.S. patent specification 4,009,251 describes various ~8~
additiYes, such as sodi1~m oxalate, sodium formate, sodium thiosulphate, and sodium acetate, which may be ~ene~icial.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the removal of H2S and CO2 from a gaseous stream containing H2S and CO2, which process comprises the following steps:-a) contacting the gaseous stream with a lean CO2-selec-tive absorbent mixture comprising diethylene glycol monoethyl ether and the Fe(III) chelate of nitrilotriacetic acid, and b) separating a sweet gaseous stream from an absorbent admixture containing absorbed CO2, solid sulphur, and Fe(II) chelate of nitrilotriacetic acid.
2. A process as claimed in claim 1, in which the Fe(II) chelate of nitrilotriacetic acid separated in step b) is sub-jected to a regeneration by contacting it with an oxygen-containing gas, producing a lean CO2-selective absorbent mixture containing regenerated Fe(III) chelate of nitrilotriacetic acid.
3. A process as claimed in claim 2, in which sulphur is removed from absorbent admixture separated in step b) or from the lean CO2-selective absorbent mixture containing regenerated Fe(III) chelate, respectively.
4. A process as claimed in claim 3, in which lean CO2-selective absorbent mixture containing regenerated Fe(III) chelate is returned to step a) for use as the lean absorbent mixture.
5. A process as claimed in claim 2, in which prior to regeneration of the FE(III) chelate and before or after the removal of sulphur, CO2 is stripped from absorbent mixture con-taining absorbed CO2 and Fe(II) chelate of nitrilotriacetic acid.
6. A process as claimed in claim 2, in which heat is supplied to assist in the said regeneration.
7. A process as claimed in claim 1, in which the gaseous stream containing H2S and CO2 is a hydrocarbon stream or a stream derived from the gasification of coal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US267,181 | 1981-05-26 | ||
| US06/267,181 US4368178A (en) | 1981-05-26 | 1981-05-26 | Process for the removal of H2 S and CO2 from gaseous streams |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1186490A true CA1186490A (en) | 1985-05-07 |
Family
ID=23017659
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000401798A Expired CA1186490A (en) | 1981-05-26 | 1982-04-28 | Process for the removal of h.sub.2s and co.sub.2 from gaseous streams |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4368178A (en) |
| EP (1) | EP0066306B1 (en) |
| JP (1) | JPS57197022A (en) |
| KR (1) | KR830009796A (en) |
| AU (1) | AU549726B2 (en) |
| BR (1) | BR8203006A (en) |
| CA (1) | CA1186490A (en) |
| DE (1) | DE3263862D1 (en) |
| IN (1) | IN156108B (en) |
| ZA (1) | ZA823574B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5667760A (en) * | 1995-08-15 | 1997-09-16 | Sweeney; Charles T. | Methods for sweetening hydrocarbons |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IN168471B (en) * | 1985-08-23 | 1991-04-13 | Shell Int Research | |
| US4871520A (en) * | 1985-08-23 | 1989-10-03 | Shell Oil Company | Process and composition for H2 S removal |
| US5149460A (en) * | 1985-08-23 | 1992-09-22 | Shell Oil Company | Composition for H2 S removal |
| US4859436A (en) * | 1985-08-23 | 1989-08-22 | Shell Oil Company | H2 S removal process and composition |
| US4816238A (en) * | 1986-05-01 | 1989-03-28 | The Dow Chemical Company | Method and composition for the removal of hydrogen sulfide from gaseous streams |
| US4781901A (en) * | 1986-05-01 | 1988-11-01 | The Dow Chemical Company | Method and composition for the removal of hydrogen sulfide and carbon dioxide from gaseous streams |
| US5004588A (en) * | 1988-01-15 | 1991-04-02 | Chevron Research & Technology Company | Process for removal of hydrogen sulfide from gaseous stream |
| US5430664A (en) * | 1992-07-14 | 1995-07-04 | Technitrol, Inc. | Document counting and batching apparatus with counterfeit detection |
| US5736117A (en) * | 1995-09-29 | 1998-04-07 | Marathon Oil Company | Sulfur debonding agent enhancing sulfur recovery from a hydrogen sulfide conversion process |
| US5885538A (en) * | 1997-07-02 | 1999-03-23 | Quaker Chemical Corporation | Method and composition for the regeneration of an aminal compound |
| AU7492900A (en) * | 1999-09-15 | 2001-04-17 | Eickmeyer And Associates | Method and composition for removing co2 and h2s from gas mixtures |
| US7771195B2 (en) * | 2001-10-29 | 2010-08-10 | Align Technology, Inc. | Polar attachment devices and method for a dental appliance |
| US6929423B2 (en) * | 2003-01-16 | 2005-08-16 | Paul A. Kittle | Gas recovery from landfills using aqueous foam |
| JP4862314B2 (en) * | 2005-08-05 | 2012-01-25 | 栗田工業株式会社 | Method and apparatus for desulfurization of gas containing hydrogen sulfide |
| US8414853B2 (en) * | 2008-03-21 | 2013-04-09 | Alstom Technology Ltd | System and method for enhanced removal of CO2 from a mixed gas stream via use of a catalyst |
| CN101502741B (en) | 2009-02-16 | 2011-01-05 | 北京博源恒升高科技有限公司 | Method for removing SOx from gas using polyethylene glycol |
| CN103432890B (en) | 2013-09-10 | 2015-12-09 | 北京博源恒升高科技有限公司 | Modified poly (ethylene glycol) removes the method for SOx in gas |
| CN103495340B (en) | 2013-10-15 | 2015-11-18 | 北京博源恒升高科技有限公司 | The method of SOx in compound alcamines solution removal gas |
| CN103623689B (en) | 2013-12-12 | 2016-06-29 | 北京博源恒升高科技有限公司 | The method of SOx in polyhydric alcohol composite solution elimination gas |
| CN103611391B (en) | 2013-12-12 | 2016-01-20 | 北京博源恒升高科技有限公司 | Glycols composite solution removes the method for SOx in gas |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2881047A (en) * | 1956-05-29 | 1959-04-07 | Laurence S Reid | Method of simultaneously removing hydrogen sulfide from gaseous mixtures and producing sulfur therefrom |
| US3068065A (en) * | 1956-08-24 | 1962-12-11 | Humphreys & Glasgow Ltd | Method of removing hydrogen sulphide from gases |
| US3266320A (en) * | 1963-06-13 | 1966-08-16 | Garrett Corp | Vector balanced pressure ratio transducer |
| FR1492797A (en) * | 1965-09-18 | 1967-08-25 | Inst Francais Du Petrole | Process for purifying sulphide gas and producing sulfur |
| GB1279637A (en) * | 1968-10-31 | 1972-06-28 | Lummus Co | Solvent and process for acid gas scrubbing |
| US3622273A (en) * | 1970-02-06 | 1971-11-23 | Nalco Chemical Co | Method for the removal of hydrogen sulfide from gaseous streams |
| US4009251A (en) * | 1973-08-27 | 1977-02-22 | Rhodia, Inc. | Process for the removal of hydrogen sulfide from gaseous streams by catalytic oxidation of hydrogen sulfide to sulfur while inhibiting the formation of sulfur oxides |
| US3933993A (en) * | 1974-06-28 | 1976-01-20 | General Electric Company | Use of concentrated chelated iron reagent for reducing pollutant content of a fluid |
| US4091073A (en) * | 1975-08-29 | 1978-05-23 | Shell Oil Company | Process for the removal of H2 S and CO2 from gaseous streams |
-
1981
- 1981-05-26 US US06/267,181 patent/US4368178A/en not_active Expired - Lifetime
-
1982
- 1982-04-22 DE DE8282200482T patent/DE3263862D1/en not_active Expired
- 1982-04-22 EP EP82200482A patent/EP0066306B1/en not_active Expired
- 1982-04-28 CA CA000401798A patent/CA1186490A/en not_active Expired
- 1982-05-03 IN IN494/CAL/82A patent/IN156108B/en unknown
- 1982-05-22 KR KR1019820002265A patent/KR830009796A/en unknown
- 1982-05-24 BR BR8203006A patent/BR8203006A/en not_active IP Right Cessation
- 1982-05-24 ZA ZA823574A patent/ZA823574B/en unknown
- 1982-05-24 JP JP57086708A patent/JPS57197022A/en active Granted
- 1982-05-24 AU AU84092/82A patent/AU549726B2/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5667760A (en) * | 1995-08-15 | 1997-09-16 | Sweeney; Charles T. | Methods for sweetening hydrocarbons |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0066306B1 (en) | 1985-05-29 |
| JPS57197022A (en) | 1982-12-03 |
| JPH0144370B2 (en) | 1989-09-27 |
| EP0066306A1 (en) | 1982-12-08 |
| AU549726B2 (en) | 1986-02-06 |
| IN156108B (en) | 1985-05-18 |
| AU8409282A (en) | 1982-12-02 |
| ZA823574B (en) | 1983-03-30 |
| DE3263862D1 (en) | 1985-07-04 |
| US4368178A (en) | 1983-01-11 |
| BR8203006A (en) | 1983-05-10 |
| KR830009796A (en) | 1983-12-23 |
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