CA1176433A - Sulphur recovery process - Google Patents
Sulphur recovery processInfo
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- CA1176433A CA1176433A CA000402901A CA402901A CA1176433A CA 1176433 A CA1176433 A CA 1176433A CA 000402901 A CA000402901 A CA 000402901A CA 402901 A CA402901 A CA 402901A CA 1176433 A CA1176433 A CA 1176433A
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- reactant
- polyvalent metal
- solution
- acid
- sulphur
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- 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
In the removal of H2S and optionally CO2 from a gas by contacting with a reactant solution containing an ion or a chelate of a polyvalent metal with formation of solid sulphur and reduced reactant, the presence of an alkanol having 4 to 18 carbon atoms increases the crystal size of the sulphur;
the solution may contain an absorbent selective for CO2.
The presence of sodium thiocyanate, sodium dithionite, thio-diglycolic acid and/or 3,3-thiodipropionic acid addresses degradation of the chelates.
In the removal of H2S and optionally CO2 from a gas by contacting with a reactant solution containing an ion or a chelate of a polyvalent metal with formation of solid sulphur and reduced reactant, the presence of an alkanol having 4 to 18 carbon atoms increases the crystal size of the sulphur;
the solution may contain an absorbent selective for CO2.
The presence of sodium thiocyanate, sodium dithionite, thio-diglycolic acid and/or 3,3-thiodipropionic acid addresses degradation of the chelates.
Description
SULPHUR R~COVERY PXOCESS
~ he invention relates -to a process for the removal of H2S
from a sour gaseous stream.
~ he presence of significant quantities of H2S and C02 in various "sour" industrial gaseous streams poses a persistent problem. A gaseous stream is named l'sour" if it contains significant quantities of H2S a~d/or C02. Although various procedures have been developed to remove and recover these contaminants, most such processes are de~icient, for a variety of reasons.
In one cyclic method currently a-ttracting attention, the sour gaseous stream is contacted, prefer~bly with a solvent which contains a regenerable reactant, to produce solid elemental sulphur which is recovered either prior or subsequent to regeneration. Suitable reactants include polyvalent ions of metals such as iron, vanadium, copper, manganese, and nickel, and include polyvalent metal chelates. Preferred reactants are coordination complexes in which the polyvalent metals form chelates with specified organic acids.
In yet another process~ e.g., that disclosed in U.S. patent specification 4,091,073 C02 present in the gaseous stream is also removed by the use of a suitable absorbent selective for A problem associ~ted with such processes is that the solid sulphur produced i9 of poor qualit~, i.e., it is very finely divided and difficult to separate ~rom the reactant solution.
A process which provided for the efficient reaction of H2S
and removal of the sulphur produced could have great economic importance.
It is an object of the invention to provide an economical and efficient method for the reaction of H2S3nd for the removal of the sulphur produced.
Another object ;s to produce sulphur crystals which are of increased size.
A further object i.5 to address the problem of degradation or decomposition of the polyvalent metal chela-te.
Accordingly, the invention provides a process for the removal of ~2S from a sour gaseous stream, which process com-prises the following steps:-a) contacting the sour gaseous s-tream in a contacting zone at a temperature below the melting point of sulphur with a reactant solution containing an effective amo~mt of an oxidizing reactant comprising one or more polyvalent metal ions and!or one or more polyvalent metal chelate compounds and also an e~fective amount of a modifier comprising one or more alkanols having in the range of from ~ to 18 carbon atoms per molecule, b) separating a sweet gaseous stream from an admixture con-taining ~rystalline sulphur, a reduced reactant and the modifier, and c) isolating at least a portion of the said crystalline sulphur.
~e sulphur crystals p~esentin the admixture separated in step b), due to the presence of the modifier, are of improved quality, i.e., they have increased size. ~ence, the isolation of the crystalline sulphur in step c) is easier. The manner of isolating the sulphur is a matter of choice. For example, the crystals may be isolated by se-ttling, filtration, liquid flotation, or by suitable devices such as a hydrocyclone, etc.
The sulphur crys-tals have, for example, improved filterability.
The modifier is supplied in the reactant solu-tion in an effective or modifying amount, i.e., an amount sufficient to~ imp~ove the quality of the sulphur produced. This amount will clearly be :~'7~3~
a ~inor amount, i.e., less than about 6 per cent by weight, baaed on the weight o~ the total reactant solution, and normally will not be an amount ~ich exceeds suhstantially the solubility of the given modifier in the reactant solution. Xn general, those skilled in the art may-adjust the amount o~ modifier added to produce optimum results, good results being obtained~ in the case of aqueous mixtures, when the modi~ier is present in an amount of ~rom about 0.01 per cent by weight, based on the weight of the aqueous reactant solution, to an amount which is at or near the saturation level of the modifier in the reactant solution without ~orming a significant second layer or phase.
Accordingl~, the amount employed will normally range (depending on the alkanol~ from about 0.01 per cent to about 4 per cent by weight, based on the weight of the reactant solution, or slightly greater. The precise amount employed may be determined by experimentation~ it being generally observed that the higher the molecular weight of the alkanol employed, the lower the concentration required -to improve sulphur quality.
The reduced reactant may be given any suitable destination, but ~or economical reasons the reactant is preferably regener-ated. So, the reactant may be regenerated in a regeneration zone by contacting the reduced reactant with an oxygen-contain~
ing gas, producing a regenerated reac-tant-containing admixture.
At least a por-tion of the sulphur crystals may be isolated before regenerating the reactant, or at least a portion of the sulphur crystals may be isolated af~ter regeneration.
In other words, the reactant may be regenerated subsequent to step b) and prior to step c) or subsequent to step c).
~he regenerated reactant-containing admixture may be used in any suitable manner, preferably, the process according to the invention is operated as a cyclic procedure by returning this admixture, subsequent to the isolation of sulphur, to the contac-ting zone of step a). Modifier is still present in the returned admixture.
~he reduced polyvalent metal ions and/or reduced poly-valent metal chelate compounds are regenerated by contacting ~t76~
them with an oxygen-containing gas. Examples of' oxygen-containing gases. are air, air enrich~d with Qxy~en and pure o~ygen. The oxygen G~idize~ the reduced ~etal ions or the ~etal o~ the chelate or chelates to a higher valence state, and the regener-ated mixture îs suitably returned to the contact zone o~ step a),suitably after sulphur removal.
The reactant solution in step a) is suitably an agueous solution in those cases where H2S is the only contaminant to be removed f'rom a sour gaseous stream.
The process according to the present invention is very sui-table ~or the removal of H2S and C02 f'rom sour gaseous streams. So, in another embodiment of the invention, a sour gaseous stream containing H2S and C02 is contacted in step a) with a reactant solution also containing a li~uid absorbent selective f'or C02, the reactant solution and procedure in steps a), b) and c) being similar to that described hereinbef'ore. The absorbent is pre~erably selective for H2S as well. A purif'ied or "sweet" gaseous stream is produced which meets general in-dustrial and commercial H2S and C02 specifications. The C02 is absorbed and the H2S is immediately converted to sulphur by the poly~alent metal ion and/or polyvalent metal chelate.
In the process, the reactant is reduced, and the sulphur may be treated, as described hereinbef'ore. The sulphur crystals may be removed prior or subsequent to a regeneration of' the ad--mixture; the crystals produced are of` increased size. Prefer-ably, if' the ~olume of C02 absorbed is laree, the reactant-containing solution is treated, such as by heating or pressure reduction, to remove the bulk of' the C02 bef'ore regeneration o~ the reactant (either before or a~ter sulphur removal).
Alternatively, or if' small quantities of' C02 are absorbed, the C02 ~ay simply be stripped in the regeneration zone.
As indicated hereinbef'ore, the invention also provides in this embodiment ~or the regeneration of' the reactant and the absorbent. Specif'ically, the loaded absorbent admixture and the reduced polyvalent me-tal ions, poly~alent me-tal chelate, or mixtures thereof, are regenerated by contacting the mixture in a regeneration zone or zones with an oxygen-containing gas.
The o~ygen accQmplishes two functions, the strippi`ng of any C02 from the loaded absorbent ad~i~ture, and the oxidation of the reduced reactant to a higher oxidation state. ~he o~ygen (in whatever form supplied) is supplied in a stoichiometric equi-valent or excess with respect to the amount of reactant presen-t in the mixture. Preferably the oxygen is supplied in an amount in the range of from about 1.2 to about 3 times excess.
The alkanols used in the present process have the general formula C H2 +1~I~ in which n is an integer in the range of from 4 to 18.
Preferably, the alkanol or alkanols in s-tep a) have in the range of from 4 to 12 carbon atoms per molecule. Particularly preferred alkanols are t-butanol, n-pentanol, n-octanol, n-decanol, n-undecanol, n-dodecanol, and mixtures thereof.
The particular type of gaseous stream treated is not critical, as will be evident to those skilled in the art.
Streams 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 procedures, e.g. gases produced by the gasi-fication of coal, petroleum, shale, tar sands, etc. Particularly preferred are coal gasifica-tion streams, natural gas streams and refinery feedstoeks composed of gaseous hydrocarbon streams, especially those feedstocks having a low ratio of H2S to C02, and other gaseous hydroearbon streams. The words "hydrocarbon stream(s)", as employed herein, are intended to include streams eontaining significant quantities of hydrocarbon (both paraf finie and aromatie), it being reeogni~ed that such streams may con~ain significant "impurities" not teehnically defined as a hydrocarbon. Streams containing principally a single hydro-carbon, e.g., ethane, are eminently suited to the process of the invention. Streams derived from the gasification and/or partial ~6~33 oxidation of gaseous or liquid hydrocarbon may be treated ac-cording to the invention. The H2S content of the type o~
gaseous streams contemplated will vary extensively, but, in general, will range ~rom 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 a~d C02 present are not generally a limiting factor in the process of the invention.
The temperatures employed in the contac-ting or absorption contact zone in step a) are not generally critical, except that the reaction is carried out at a temperature below the melting point of sulphur. In many commercial applications~ such as the removal of H2S (and, if desired, C02? from natural gas to meet pipeline specifications, contacting at ambient temperatures is desired, since the cost of refrigeration would exceed the benefits obtained due to increased absorption at the lower temperature. In general, temperatures in the range of from 10C to ôOC are suitable, and temperatures in the range of from 20 C to 45 C are preferred. Contact times may be in the range of from about 1 s to about 270 s or longer, with contact times in the range of from 2 s to 120 s being preferred.
Temperatures employed in the extraction zone will approximate those in the contacting of step a), except that they will always be below the ~elting point of sulphur.
Similarly, in the regeneration or in the stripping zone or zones, temperatures may be varied widely. Preferably, the regeneration zone should be maintained at substantially the same temperature as the absorption zone in step a). I~ heat is added to assist regeneration, cooling o~ the absorbent mixture is required be~ore return of the absorbent mixture to the absorption zone. In general~ temperatures in the range of from about 10 C to 80C, preferably 20C to 45C may be employed.
Pressure conditions in the absorption zone o~ step a) may vary widely, depending on the pressure o~ the gaseous ~3Lt7~3 stream to be treated. For example, pressures in the absorption zone 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 or desorption zone or zones, pressures may be varied considerably, and will preferably be in the range of from about 0.5 bar to about 3 or 4 bar. The pressure-temperature relationships involved are well understood by those skilled in the art, and need not be detailed herein. Other conditions of operation for this type of reaction pro-cess, e.g., pH, etc. are further described in United States patent specifica-tion 3,0G8,065, British patent specification 999,799 and United States patent specification 4,009,251. Preferably, if the iron chelate of nitrilotriacetic acid is used as a reactant, pH in the process of the invention will range from about 6 to about 7.5, and the molar ratio of the nitrilotriacetic acid to the iron is from about 1.2 to 1.4. The process is preferably carried out continuously.
~ s indicated, the H2S, when contacted, is quickly converted by the oxidizing polyvalent metal ions, polyvalent metal chelate, etc. to elemental sulphur. Since many polyvalent metal compour.dsand polyvalent metal chelates have limited solubility in many solvents or absorbents, the polyvalent metal compounds or chelates are preferably supplied in admixture with the liquid absorbent and water. The amount of polyvalent metal compound, polyvalent metal chelate, or mixtures thereof, supplied is an effective amount, i.e., an amount sufficient to convert all or substcmtially all of the H2S in the gaseous stream, and will gen-erally be on thc order of at least about 1 mol per mol or ll2S. Ratios in the range of from about 1 or 2 mol to about 15 mol of polyvalent metal compound or chelate per mol oE l12S may be used, with rat;os in the range of from about 2 mol per mol to about 5 mol of polyvalent metal compound or chelate per mol oE H2S
be:ing preferrecl. The manner of preparing the aqucous solution or admixture con-taining an absorbent is a matter oE choice. For ~6~L33 example, the compound or chelate may be added to the absorbent, and, if necess.ary, then ~ater added. The amount of water added will normally be just that amount necessary to achieve solution of the polyvalent meta]. compound or chelate, and can be determined by routine experimentation. Since the polyralent metal compound or chelate may have a significant solubility in the solvent, and si.nce water is produced by the reaction of the H2S and the ions or chelate, precise amounts of water to be added cannot be given. In the case of absorbents having a low solubility for the polyvalent metal ion or chelate, approximately 5 per cent to 10 per cent water by volume, based on the total volume of the absorbent mixture, will generally provide solvency.
Preferably, however, the polyvalent ions or chelate are added as an aqueous solution to the liquid absorbent. Where they are supplied as an aqueous solution, the amount of solution supplied may be about 20 per cent to about 80 per ce~t by volume of the total absorbent ad~ixture supplied to the absorption of step a).
A polyvalent metal chelate solution will generally be supplied as an aqueous solution having a concentration in the range o~
from about 0.1 molar to~out 2 or 3 molar~.ald a concentration of about 1.0 molar is preferred. If iron is used, the ligand to iron molar ratio may range from 1.1 to 1.6, preferably 1.2 to 1.4. In case the proces.s. according to the invention is carried out in the ahsence of an abs.orbent~ the polyvalent metal ion or polyvalent metal chelate solution will generally be supplied as an aqueous solution having a concentratïon of ~rom a'bout 0.1 molar to about 2 mol~.r, and a concentration of about 0.5 molar i.s preferred.
An~ pol~valent ~etal can he uaed, but iron, copper and manganese are pre.~erred, particularly iron. The polyvalent metal should 'be capable of o~idizin~ hydrogen s.ulphide, w.hile being reduced i'ts.el~ from a higher to a lower valence state., and should then be oxidizable by oxygen ~-om the lower valence state to the higher valence state in a typical redox reaction.
~i~6433 Other polyvalent metals which can be used include lead, mercury, palladium, platinum, tungsten, nickel, chromium, cobalt, vanadium, titanium, tantalum, zirconiuml molybdemlm, and tin. The metals are normally supplied as a salt, oxide, hydroxide, etc.
Preferred reactants are coordination complexes in which polyvalent metals form chelates with an acid having the general formula (X)3_n~N~(Y)n wherein n is an integer from 1 to 3; Y represents a carboxymethyl or 2-carboxyethyl group and X a 2-hydroxyethyl or 2-hydroxypropyl group or an alkyl group having from 1 to 4 carbon atoms; or - N - R N <
Y / Y wherein:
- from 2 to 4 of ~he groups Y represent carboxymethyl or 2-carboxyethyl groups;
- from O to 2 of the groups Y represent a 2-hydroxyethyl or 2-hydroxypropyl group;
- R represents an ethylene, a trimethylene, l-methyIethylene, 1,2-cyclo-hexylene or 1,2-benzylene group;
or with a mixture of such acids.
~;r ' ~76~33 The polyvalent metal chelates are readily formed in aqueous solution by reaction of an appropriate salt, oxide or hydroxide of the polyvalent metal and ~le chelating agent in the acid form or an alkali metal or a~monium salt thereof.
~xemplary chela~ing agents. include aminoacetic acids derived from ammonia or 2-hydroxyalkyl amines, such as glycine (amino-acetic acid), diglycine (i~inodiacetic acid~, ~TA (nitrilotri-acetic acid), a 2-hydroxyalkyl glycine; a dihydroxyalkyl-glycine, and hydroxyethyl- or hydroxypropyldiglycine, amino-acetic acids derived from ethylenediamine, diethylenetriamine,1,2-propylenediamine, and 1,3-propylenediamine, such as EDTA
(ethylenediaminetetraacetic ac~d), HEDTA (2-hydroxyethylethylene-diaminetriacetic acid), DETPA (diethylenetriaminepentaacetic acid), aminoacetic acid derivatives of cyclic 1,2-diamines, such as 1,2-diaminocyclohexane-~,N-tetraacetic acid, and 1,2-phenylenediamine~N,~-tetraacetic acid, and the amides of poly-aminoacetic acids disclosed in U.S. patent specification 3,580,950. The iron chelates of NTA and 2-hydroxyethylethylene-diaminetriacetic acid are preferred.
As processes for the removal of H2S from sour gaseous streams generally represent significant costs to manufacturing operations, any improvements in such processes which increase their e~ficiency may have great economic importance. For example, where ligands or chelates o~ polyvalent metals are employed, degrada-tion or decomposition of the polyvalent metal chelates represents an important cost in the process, as ~ell as requirine measures for aecomposition product bleed or re-moval and addition o~ ~resh solution. Even in the case of pre-ferred chela-tes such as those o~ N-(2-hydrox~ethyl)ethylenedi-aminetriacetic acid and nitrilotriacetic acid, ligand decompo-sition, over a period of time, requires attention to prevent build-up of decompoaition products and consequent loas of e~ficiency.
7~33 According to a further aspect of the invention this problem is addressed when polyvalent metal Ghelate-containing solutions also contain a stabilizing amount of a first stabilizing composition comprising thiodiglycolic acid and/or 3,3-thiodiprop-ionic acid.
According to another aspect of the invention the problem of degradation or decomposition of polyvalent metal chelate-containing reactant solution is addressed when these solutions also contain a stabilizing amount of a second stabilizing composition comprising sodium thiocyanate and/or sodium dithionite.
Thiodyglycolic acid, 3,3-thiodipropionic acid, sodium thiocyanate and/or sodium dithi.onite may be used in reducing -the rate of degradation of the chelates employed. The first and second stabilizing compositions are supplied in a stabilizing amount, i.e., an amount sufficient to reduce or inhibit the rate of degradation.
The term "stabilizing amount" thus also includes those minor amounts of the stabilizers employed, which, while perhaps not exhibiting an especially discernible reduction of ligand rate of reduction, are effective, nonetheless, in conJunction with amounts of other non-interfering and non-reactive ligand stabilizing compositions, such as those described i.n Canadian patent application Serial No.
Ll15,525, filed November 15th, 1982, in reducing the llgand rate of degradation or decomposition. This amount may be determined by ex-perimentatl.on. In general, the amount employecl of the first stabilizing composi.tion will. range from about 0.005 to about 0.3 mol per litre of solution, with an amount of 0.03 to about 0.2 mol per litre being preferred. ln general, the amount employed of the second stabilizing composi.tion will range from about 0.01 to about -- ].1 --.~
6~
0.5 mol per litre of solution, with an amount of 0.05 to about 0.3 mol per litre being preferred. Those skilled in the art may adjust the amount of the first and of t~e second stabilizing compo~ition added to produce optimum results, a pr;mary consideration being simply the cost of the stabilizer added.
The absorbent~ employed in this invention are those ab-sorbents which have a high degree of selectiv;ty in absorbing C2 (and pre~erably ~2S as well) from the gaseous streams. Any of the known absorbents conventionally used which do not affect the activity of the polyvalent metal ions, polyvalent metal chelate, or mixtures thereof, and which exhibit sufficient solubility for the reactant or reactants may be employed. As indicated, the absorbent preferably has good absorbency for H2S
as well, in order to assist in the removal of any H2~ present in the gaseous mixtures. The particular absorbent chosen is a matter of choice, given these qualifications, and selection can be made by routine experimentation. For example, 3,6~dioxa octa~ol (also referred to as "Carbitol" or "diethylene glycol monoethyl ether"), propylene carbonate, 2,5,8,11,11~-pentaoxa-pentadecane (also referred to as 'itetraethylene glycol di-methyl ether7'), ~-methylpyrrolidone, tetrahydrothiophene 1,1-dioxide (also referred to as "Sulfolane"), meth~lisobutyl Xetone, 2,4-pentanedione, 2,5-hexanedione, 2-hydroxy-2-methyl-4-pentanone (also referred to as "diacetone alcohol"), hexyl acetate, cyclohexanone, 4-methyl-3-penten-2-one (also re~erred to as "mesityl oxide"), and 4-methyl-~-methoxy-pentanone-2 may be used. Suitable tem~erature and pressure relationships for different C02-selective absorbents are known, or can be calculated by those skilled in the art.
An absorption column might comprise two separate colum~s 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 material from the upper portion of the first column being fed ;nto the lower portion o~ the second column. Parallel operation of units~ i-s, o~ course, well ~76~L33 within -the scope of the invention.
As will be unders~ood the solutions or mixtures employed may contain other mat.eri`als or additives ~or given purposes.
For example, U.S. patent specification 3,~33,993 discloses the use of buffering agents, such as phosphate ana carbonate buf-fers. Similarly, U.S. patent spec;fication ~,009,251 describes various adaitives, such as sodium oxalate, soaium formate, sodium thiosulphate, and sodium acetate, which may be beneficial.
The inven-tion is further illustrated by means of the fol-lowing Examples.Co~arative Experiment A
X2S enters a contact vessel into which also enters an aqueous mixture containing 8.8 per cent by weight (based on the total weight of the mixture) of the Fe(III) chelate of nitrilo-triacetic acid. The pressure of the feed gas is about atmosphericand the temperature of the mixture is about 35C. A contact time of about 100 s is employed. In the mixture, the H2S is con-verted to elemental sulphur by the Fe(III) chelate, Fe(I~I) chelate in the process being converted to the Fe(II) chelate.
The sulphur produced is very fine and difficult to separate ~rom the solution.
A procedure similar to Comparative Experiment A is followed~
except that 0.05 per cent by weight (based on the total weight of the mixture) of n-decanol is added to the reactant solution.
The sulphur crystals are larger than those of Comparative Ex-periment A, the average particle size being approximately a~ order of magnitude larger in diameter.
EXAMP~E 2 -Sour gas, e.g., natural gas containing about 10 per cent H2S and 25 per cent by volume C02, enters an ab~orption vessel which contains an absorbent mixture composed of about 81 per cent sulfolane ~y weight (based on the total weight of the mixture), about 17 per cent by weight of an aqueous 0.5M solution of the Fe(III) chelate of 2-hydroxyethylethylenediaminetriacetic acid 6~33 and about ~.7%~ n-dodecanol. The pressure of the feed gas is about 3 bar, and the temperature of the absorbent mixture is about 35 C. A contact time of about ~80 s is emplo~ed in order to absorb virtually all C02 and react all the H2S. Purified or "sweet" gas is removed, the "s~eet" gas being of a purity suffi-cient to meet standard requirements. In the absorbent mix-ture~
the H2S is converted to elemental sulphur by the Fe(III) chelate, Fe(III) chelate in the process being converted to the Fe(II) chelate. The absorbent mi~ture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed con-tinuously and may be stripped to regenerate the chelate and recover C02.
EXAMPLES_3-~2 and Com~arative Experiments B-D
A series of runs were made at a temperature of 60 C in step a) and using a procedure similar to Comparative Experiment A to determine the effect of alkanols coming within the scope of the in~ention. The results are presented in Table I.
~'7~33 TABLE I
Examplef)- or Solution composition Alkanol S mea~
Comparative ~ ~Om éxcess vol. dia-Experiment g%w ~eHO~EDTA e) pH m(e~t)er _ _ .
B 8 10 4.5 none ) 1.9 3 8 10 4.5 Dodecanol6.9 (500 ppm) 4 8 10 4.5 Decanol17.1 (500 ppm) C 8 10 4.5 no~e ) 5.2 8 10 4.5 Decanol13.7 (500 ppm) 6 8 10 4.5 Decanol23.8 (570w) 7 8 10 4.5 Neodol 9112.3 (500 ppm) ) 8 8 10 4.5 Neodol 9120.3 (5%w) D 4 20 8 none 4.4 9 4 20 8 Decanol (30 ppm)4.8 4 20 8 Decanol8.8 (300 ppm) 11 4 20 8 Neodol 914.9 (30 pp~) 12 4 20 8 ~eodoi 918.9 _ _ _ _ (300 ppm) _ a) Determined by Coulter Counter. This method of analysi6 iB described in "Partic~e Size Measurement" by T. Allen, third edition, Powder Technology Series, edited by Chapman and Hall (1981~.
b)anld) Two different batches o~ the same solutïon recipe.
c) "Neodol 91" is a trade mark ~or a mixture of primary n-alkanols ha~ïng 9 to 11 carbon atoms per molecule.
e) 2-hydro~yethylethylenediaminetriacetic acid.
f) In Arabic numerals. g) In capital le-tters ~76~3~
~XAMPLE 13 Sour gas, e.g., nat~ral gas containing about 8 . o per cent H2~ and ]5 per cent b~ Yolu~e C02, enters an a~s;orption ~essel which contains- an ab~orbent ~i~ture composed of 8~ per cent carbitol (3,6-dioxaoctanol or dïethylene glycol monoethyl ether) by weight (based on the total weigh of the ~ixture), 17 per cent of an aqueous o.8M solution of the Fe(III) chelate of nitrilotriacetic acid and 2.0%w dodecanol.
The pressure o~ the feed gas ;s about 6.2 bar and the temper-ature of the absorbent mixture is about 35 C. A con-tact time of about 180 s is employed in order to absorb virtuall~ all C2 and react all the H2S. Purified or "sweet" gas is re-moved, the "~weet" gas bein~ of a purity sufficient to meet standard requirements. In the absorbent mixture, the H2S is con~erted to elemental sulphur by the Fe(III) chelate, Fe(III) chelate in the process being conYerted to the Fe(II) chelate. The absorbent mixture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed con-tinuously and may be stripped to regenerate the chelate and recover C02.
Comparative Experimen-t E
An aqueous solution (150 ml) of the Fe chelate of nitrilotriacetic acid as placed in a vessel, and a stream of pure H2S was sparged into the solution with rapid stirring.
Temperature of the solutior was 35C, and the solution con-tained 0.27 mol per litre iron as Fe . Nitrilotriacetic acid ligand was present in 40 per cen-t mol excess, basis the iron. Sixty microlitres of 1~decanol (300 parts p~r million by weight) were also added to the solution. The pH of the solution was 7, and pressure was atmospheric. Addi-tion o~ the H2~ (360 ml) was con-tinued un-til approximately 70 per cent of the Fe was converted to the Fe state, which took abou-t
~ he invention relates -to a process for the removal of H2S
from a sour gaseous stream.
~ he presence of significant quantities of H2S and C02 in various "sour" industrial gaseous streams poses a persistent problem. A gaseous stream is named l'sour" if it contains significant quantities of H2S a~d/or C02. Although various procedures have been developed to remove and recover these contaminants, most such processes are de~icient, for a variety of reasons.
In one cyclic method currently a-ttracting attention, the sour gaseous stream is contacted, prefer~bly with a solvent which contains a regenerable reactant, to produce solid elemental sulphur which is recovered either prior or subsequent to regeneration. Suitable reactants include polyvalent ions of metals such as iron, vanadium, copper, manganese, and nickel, and include polyvalent metal chelates. Preferred reactants are coordination complexes in which the polyvalent metals form chelates with specified organic acids.
In yet another process~ e.g., that disclosed in U.S. patent specification 4,091,073 C02 present in the gaseous stream is also removed by the use of a suitable absorbent selective for A problem associ~ted with such processes is that the solid sulphur produced i9 of poor qualit~, i.e., it is very finely divided and difficult to separate ~rom the reactant solution.
A process which provided for the efficient reaction of H2S
and removal of the sulphur produced could have great economic importance.
It is an object of the invention to provide an economical and efficient method for the reaction of H2S3nd for the removal of the sulphur produced.
Another object ;s to produce sulphur crystals which are of increased size.
A further object i.5 to address the problem of degradation or decomposition of the polyvalent metal chela-te.
Accordingly, the invention provides a process for the removal of ~2S from a sour gaseous stream, which process com-prises the following steps:-a) contacting the sour gaseous s-tream in a contacting zone at a temperature below the melting point of sulphur with a reactant solution containing an effective amo~mt of an oxidizing reactant comprising one or more polyvalent metal ions and!or one or more polyvalent metal chelate compounds and also an e~fective amount of a modifier comprising one or more alkanols having in the range of from ~ to 18 carbon atoms per molecule, b) separating a sweet gaseous stream from an admixture con-taining ~rystalline sulphur, a reduced reactant and the modifier, and c) isolating at least a portion of the said crystalline sulphur.
~e sulphur crystals p~esentin the admixture separated in step b), due to the presence of the modifier, are of improved quality, i.e., they have increased size. ~ence, the isolation of the crystalline sulphur in step c) is easier. The manner of isolating the sulphur is a matter of choice. For example, the crystals may be isolated by se-ttling, filtration, liquid flotation, or by suitable devices such as a hydrocyclone, etc.
The sulphur crys-tals have, for example, improved filterability.
The modifier is supplied in the reactant solu-tion in an effective or modifying amount, i.e., an amount sufficient to~ imp~ove the quality of the sulphur produced. This amount will clearly be :~'7~3~
a ~inor amount, i.e., less than about 6 per cent by weight, baaed on the weight o~ the total reactant solution, and normally will not be an amount ~ich exceeds suhstantially the solubility of the given modifier in the reactant solution. Xn general, those skilled in the art may-adjust the amount o~ modifier added to produce optimum results, good results being obtained~ in the case of aqueous mixtures, when the modi~ier is present in an amount of ~rom about 0.01 per cent by weight, based on the weight of the aqueous reactant solution, to an amount which is at or near the saturation level of the modifier in the reactant solution without ~orming a significant second layer or phase.
Accordingl~, the amount employed will normally range (depending on the alkanol~ from about 0.01 per cent to about 4 per cent by weight, based on the weight of the reactant solution, or slightly greater. The precise amount employed may be determined by experimentation~ it being generally observed that the higher the molecular weight of the alkanol employed, the lower the concentration required -to improve sulphur quality.
The reduced reactant may be given any suitable destination, but ~or economical reasons the reactant is preferably regener-ated. So, the reactant may be regenerated in a regeneration zone by contacting the reduced reactant with an oxygen-contain~
ing gas, producing a regenerated reac-tant-containing admixture.
At least a por-tion of the sulphur crystals may be isolated before regenerating the reactant, or at least a portion of the sulphur crystals may be isolated af~ter regeneration.
In other words, the reactant may be regenerated subsequent to step b) and prior to step c) or subsequent to step c).
~he regenerated reactant-containing admixture may be used in any suitable manner, preferably, the process according to the invention is operated as a cyclic procedure by returning this admixture, subsequent to the isolation of sulphur, to the contac-ting zone of step a). Modifier is still present in the returned admixture.
~he reduced polyvalent metal ions and/or reduced poly-valent metal chelate compounds are regenerated by contacting ~t76~
them with an oxygen-containing gas. Examples of' oxygen-containing gases. are air, air enrich~d with Qxy~en and pure o~ygen. The oxygen G~idize~ the reduced ~etal ions or the ~etal o~ the chelate or chelates to a higher valence state, and the regener-ated mixture îs suitably returned to the contact zone o~ step a),suitably after sulphur removal.
The reactant solution in step a) is suitably an agueous solution in those cases where H2S is the only contaminant to be removed f'rom a sour gaseous stream.
The process according to the present invention is very sui-table ~or the removal of H2S and C02 f'rom sour gaseous streams. So, in another embodiment of the invention, a sour gaseous stream containing H2S and C02 is contacted in step a) with a reactant solution also containing a li~uid absorbent selective f'or C02, the reactant solution and procedure in steps a), b) and c) being similar to that described hereinbef'ore. The absorbent is pre~erably selective for H2S as well. A purif'ied or "sweet" gaseous stream is produced which meets general in-dustrial and commercial H2S and C02 specifications. The C02 is absorbed and the H2S is immediately converted to sulphur by the poly~alent metal ion and/or polyvalent metal chelate.
In the process, the reactant is reduced, and the sulphur may be treated, as described hereinbef'ore. The sulphur crystals may be removed prior or subsequent to a regeneration of' the ad--mixture; the crystals produced are of` increased size. Prefer-ably, if' the ~olume of C02 absorbed is laree, the reactant-containing solution is treated, such as by heating or pressure reduction, to remove the bulk of' the C02 bef'ore regeneration o~ the reactant (either before or a~ter sulphur removal).
Alternatively, or if' small quantities of' C02 are absorbed, the C02 ~ay simply be stripped in the regeneration zone.
As indicated hereinbef'ore, the invention also provides in this embodiment ~or the regeneration of' the reactant and the absorbent. Specif'ically, the loaded absorbent admixture and the reduced polyvalent me-tal ions, poly~alent me-tal chelate, or mixtures thereof, are regenerated by contacting the mixture in a regeneration zone or zones with an oxygen-containing gas.
The o~ygen accQmplishes two functions, the strippi`ng of any C02 from the loaded absorbent ad~i~ture, and the oxidation of the reduced reactant to a higher oxidation state. ~he o~ygen (in whatever form supplied) is supplied in a stoichiometric equi-valent or excess with respect to the amount of reactant presen-t in the mixture. Preferably the oxygen is supplied in an amount in the range of from about 1.2 to about 3 times excess.
The alkanols used in the present process have the general formula C H2 +1~I~ in which n is an integer in the range of from 4 to 18.
Preferably, the alkanol or alkanols in s-tep a) have in the range of from 4 to 12 carbon atoms per molecule. Particularly preferred alkanols are t-butanol, n-pentanol, n-octanol, n-decanol, n-undecanol, n-dodecanol, and mixtures thereof.
The particular type of gaseous stream treated is not critical, as will be evident to those skilled in the art.
Streams 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 procedures, e.g. gases produced by the gasi-fication of coal, petroleum, shale, tar sands, etc. Particularly preferred are coal gasifica-tion streams, natural gas streams and refinery feedstoeks composed of gaseous hydrocarbon streams, especially those feedstocks having a low ratio of H2S to C02, and other gaseous hydroearbon streams. The words "hydrocarbon stream(s)", as employed herein, are intended to include streams eontaining significant quantities of hydrocarbon (both paraf finie and aromatie), it being reeogni~ed that such streams may con~ain significant "impurities" not teehnically defined as a hydrocarbon. Streams containing principally a single hydro-carbon, e.g., ethane, are eminently suited to the process of the invention. Streams derived from the gasification and/or partial ~6~33 oxidation of gaseous or liquid hydrocarbon may be treated ac-cording to the invention. The H2S content of the type o~
gaseous streams contemplated will vary extensively, but, in general, will range ~rom 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 a~d C02 present are not generally a limiting factor in the process of the invention.
The temperatures employed in the contac-ting or absorption contact zone in step a) are not generally critical, except that the reaction is carried out at a temperature below the melting point of sulphur. In many commercial applications~ such as the removal of H2S (and, if desired, C02? from natural gas to meet pipeline specifications, contacting at ambient temperatures is desired, since the cost of refrigeration would exceed the benefits obtained due to increased absorption at the lower temperature. In general, temperatures in the range of from 10C to ôOC are suitable, and temperatures in the range of from 20 C to 45 C are preferred. Contact times may be in the range of from about 1 s to about 270 s or longer, with contact times in the range of from 2 s to 120 s being preferred.
Temperatures employed in the extraction zone will approximate those in the contacting of step a), except that they will always be below the ~elting point of sulphur.
Similarly, in the regeneration or in the stripping zone or zones, temperatures may be varied widely. Preferably, the regeneration zone should be maintained at substantially the same temperature as the absorption zone in step a). I~ heat is added to assist regeneration, cooling o~ the absorbent mixture is required be~ore return of the absorbent mixture to the absorption zone. In general~ temperatures in the range of from about 10 C to 80C, preferably 20C to 45C may be employed.
Pressure conditions in the absorption zone o~ step a) may vary widely, depending on the pressure o~ the gaseous ~3Lt7~3 stream to be treated. For example, pressures in the absorption zone 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 or desorption zone or zones, pressures may be varied considerably, and will preferably be in the range of from about 0.5 bar to about 3 or 4 bar. The pressure-temperature relationships involved are well understood by those skilled in the art, and need not be detailed herein. Other conditions of operation for this type of reaction pro-cess, e.g., pH, etc. are further described in United States patent specifica-tion 3,0G8,065, British patent specification 999,799 and United States patent specification 4,009,251. Preferably, if the iron chelate of nitrilotriacetic acid is used as a reactant, pH in the process of the invention will range from about 6 to about 7.5, and the molar ratio of the nitrilotriacetic acid to the iron is from about 1.2 to 1.4. The process is preferably carried out continuously.
~ s indicated, the H2S, when contacted, is quickly converted by the oxidizing polyvalent metal ions, polyvalent metal chelate, etc. to elemental sulphur. Since many polyvalent metal compour.dsand polyvalent metal chelates have limited solubility in many solvents or absorbents, the polyvalent metal compounds or chelates are preferably supplied in admixture with the liquid absorbent and water. The amount of polyvalent metal compound, polyvalent metal chelate, or mixtures thereof, supplied is an effective amount, i.e., an amount sufficient to convert all or substcmtially all of the H2S in the gaseous stream, and will gen-erally be on thc order of at least about 1 mol per mol or ll2S. Ratios in the range of from about 1 or 2 mol to about 15 mol of polyvalent metal compound or chelate per mol oE l12S may be used, with rat;os in the range of from about 2 mol per mol to about 5 mol of polyvalent metal compound or chelate per mol oE H2S
be:ing preferrecl. The manner of preparing the aqucous solution or admixture con-taining an absorbent is a matter oE choice. For ~6~L33 example, the compound or chelate may be added to the absorbent, and, if necess.ary, then ~ater added. The amount of water added will normally be just that amount necessary to achieve solution of the polyvalent meta]. compound or chelate, and can be determined by routine experimentation. Since the polyralent metal compound or chelate may have a significant solubility in the solvent, and si.nce water is produced by the reaction of the H2S and the ions or chelate, precise amounts of water to be added cannot be given. In the case of absorbents having a low solubility for the polyvalent metal ion or chelate, approximately 5 per cent to 10 per cent water by volume, based on the total volume of the absorbent mixture, will generally provide solvency.
Preferably, however, the polyvalent ions or chelate are added as an aqueous solution to the liquid absorbent. Where they are supplied as an aqueous solution, the amount of solution supplied may be about 20 per cent to about 80 per ce~t by volume of the total absorbent ad~ixture supplied to the absorption of step a).
A polyvalent metal chelate solution will generally be supplied as an aqueous solution having a concentration in the range o~
from about 0.1 molar to~out 2 or 3 molar~.ald a concentration of about 1.0 molar is preferred. If iron is used, the ligand to iron molar ratio may range from 1.1 to 1.6, preferably 1.2 to 1.4. In case the proces.s. according to the invention is carried out in the ahsence of an abs.orbent~ the polyvalent metal ion or polyvalent metal chelate solution will generally be supplied as an aqueous solution having a concentratïon of ~rom a'bout 0.1 molar to about 2 mol~.r, and a concentration of about 0.5 molar i.s preferred.
An~ pol~valent ~etal can he uaed, but iron, copper and manganese are pre.~erred, particularly iron. The polyvalent metal should 'be capable of o~idizin~ hydrogen s.ulphide, w.hile being reduced i'ts.el~ from a higher to a lower valence state., and should then be oxidizable by oxygen ~-om the lower valence state to the higher valence state in a typical redox reaction.
~i~6433 Other polyvalent metals which can be used include lead, mercury, palladium, platinum, tungsten, nickel, chromium, cobalt, vanadium, titanium, tantalum, zirconiuml molybdemlm, and tin. The metals are normally supplied as a salt, oxide, hydroxide, etc.
Preferred reactants are coordination complexes in which polyvalent metals form chelates with an acid having the general formula (X)3_n~N~(Y)n wherein n is an integer from 1 to 3; Y represents a carboxymethyl or 2-carboxyethyl group and X a 2-hydroxyethyl or 2-hydroxypropyl group or an alkyl group having from 1 to 4 carbon atoms; or - N - R N <
Y / Y wherein:
- from 2 to 4 of ~he groups Y represent carboxymethyl or 2-carboxyethyl groups;
- from O to 2 of the groups Y represent a 2-hydroxyethyl or 2-hydroxypropyl group;
- R represents an ethylene, a trimethylene, l-methyIethylene, 1,2-cyclo-hexylene or 1,2-benzylene group;
or with a mixture of such acids.
~;r ' ~76~33 The polyvalent metal chelates are readily formed in aqueous solution by reaction of an appropriate salt, oxide or hydroxide of the polyvalent metal and ~le chelating agent in the acid form or an alkali metal or a~monium salt thereof.
~xemplary chela~ing agents. include aminoacetic acids derived from ammonia or 2-hydroxyalkyl amines, such as glycine (amino-acetic acid), diglycine (i~inodiacetic acid~, ~TA (nitrilotri-acetic acid), a 2-hydroxyalkyl glycine; a dihydroxyalkyl-glycine, and hydroxyethyl- or hydroxypropyldiglycine, amino-acetic acids derived from ethylenediamine, diethylenetriamine,1,2-propylenediamine, and 1,3-propylenediamine, such as EDTA
(ethylenediaminetetraacetic ac~d), HEDTA (2-hydroxyethylethylene-diaminetriacetic acid), DETPA (diethylenetriaminepentaacetic acid), aminoacetic acid derivatives of cyclic 1,2-diamines, such as 1,2-diaminocyclohexane-~,N-tetraacetic acid, and 1,2-phenylenediamine~N,~-tetraacetic acid, and the amides of poly-aminoacetic acids disclosed in U.S. patent specification 3,580,950. The iron chelates of NTA and 2-hydroxyethylethylene-diaminetriacetic acid are preferred.
As processes for the removal of H2S from sour gaseous streams generally represent significant costs to manufacturing operations, any improvements in such processes which increase their e~ficiency may have great economic importance. For example, where ligands or chelates o~ polyvalent metals are employed, degrada-tion or decomposition of the polyvalent metal chelates represents an important cost in the process, as ~ell as requirine measures for aecomposition product bleed or re-moval and addition o~ ~resh solution. Even in the case of pre-ferred chela-tes such as those o~ N-(2-hydrox~ethyl)ethylenedi-aminetriacetic acid and nitrilotriacetic acid, ligand decompo-sition, over a period of time, requires attention to prevent build-up of decompoaition products and consequent loas of e~ficiency.
7~33 According to a further aspect of the invention this problem is addressed when polyvalent metal Ghelate-containing solutions also contain a stabilizing amount of a first stabilizing composition comprising thiodiglycolic acid and/or 3,3-thiodiprop-ionic acid.
According to another aspect of the invention the problem of degradation or decomposition of polyvalent metal chelate-containing reactant solution is addressed when these solutions also contain a stabilizing amount of a second stabilizing composition comprising sodium thiocyanate and/or sodium dithionite.
Thiodyglycolic acid, 3,3-thiodipropionic acid, sodium thiocyanate and/or sodium dithi.onite may be used in reducing -the rate of degradation of the chelates employed. The first and second stabilizing compositions are supplied in a stabilizing amount, i.e., an amount sufficient to reduce or inhibit the rate of degradation.
The term "stabilizing amount" thus also includes those minor amounts of the stabilizers employed, which, while perhaps not exhibiting an especially discernible reduction of ligand rate of reduction, are effective, nonetheless, in conJunction with amounts of other non-interfering and non-reactive ligand stabilizing compositions, such as those described i.n Canadian patent application Serial No.
Ll15,525, filed November 15th, 1982, in reducing the llgand rate of degradation or decomposition. This amount may be determined by ex-perimentatl.on. In general, the amount employecl of the first stabilizing composi.tion will. range from about 0.005 to about 0.3 mol per litre of solution, with an amount of 0.03 to about 0.2 mol per litre being preferred. ln general, the amount employed of the second stabilizing composi.tion will range from about 0.01 to about -- ].1 --.~
6~
0.5 mol per litre of solution, with an amount of 0.05 to about 0.3 mol per litre being preferred. Those skilled in the art may adjust the amount of the first and of t~e second stabilizing compo~ition added to produce optimum results, a pr;mary consideration being simply the cost of the stabilizer added.
The absorbent~ employed in this invention are those ab-sorbents which have a high degree of selectiv;ty in absorbing C2 (and pre~erably ~2S as well) from the gaseous streams. Any of the known absorbents conventionally used which do not affect the activity of the polyvalent metal ions, polyvalent metal chelate, or mixtures thereof, and which exhibit sufficient solubility for the reactant or reactants may be employed. As indicated, the absorbent preferably has good absorbency for H2S
as well, in order to assist in the removal of any H2~ present in the gaseous mixtures. The particular absorbent chosen is a matter of choice, given these qualifications, and selection can be made by routine experimentation. For example, 3,6~dioxa octa~ol (also referred to as "Carbitol" or "diethylene glycol monoethyl ether"), propylene carbonate, 2,5,8,11,11~-pentaoxa-pentadecane (also referred to as 'itetraethylene glycol di-methyl ether7'), ~-methylpyrrolidone, tetrahydrothiophene 1,1-dioxide (also referred to as "Sulfolane"), meth~lisobutyl Xetone, 2,4-pentanedione, 2,5-hexanedione, 2-hydroxy-2-methyl-4-pentanone (also referred to as "diacetone alcohol"), hexyl acetate, cyclohexanone, 4-methyl-3-penten-2-one (also re~erred to as "mesityl oxide"), and 4-methyl-~-methoxy-pentanone-2 may be used. Suitable tem~erature and pressure relationships for different C02-selective absorbents are known, or can be calculated by those skilled in the art.
An absorption column might comprise two separate colum~s 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 material from the upper portion of the first column being fed ;nto the lower portion o~ the second column. Parallel operation of units~ i-s, o~ course, well ~76~L33 within -the scope of the invention.
As will be unders~ood the solutions or mixtures employed may contain other mat.eri`als or additives ~or given purposes.
For example, U.S. patent specification 3,~33,993 discloses the use of buffering agents, such as phosphate ana carbonate buf-fers. Similarly, U.S. patent spec;fication ~,009,251 describes various adaitives, such as sodium oxalate, soaium formate, sodium thiosulphate, and sodium acetate, which may be beneficial.
The inven-tion is further illustrated by means of the fol-lowing Examples.Co~arative Experiment A
X2S enters a contact vessel into which also enters an aqueous mixture containing 8.8 per cent by weight (based on the total weight of the mixture) of the Fe(III) chelate of nitrilo-triacetic acid. The pressure of the feed gas is about atmosphericand the temperature of the mixture is about 35C. A contact time of about 100 s is employed. In the mixture, the H2S is con-verted to elemental sulphur by the Fe(III) chelate, Fe(I~I) chelate in the process being converted to the Fe(II) chelate.
The sulphur produced is very fine and difficult to separate ~rom the solution.
A procedure similar to Comparative Experiment A is followed~
except that 0.05 per cent by weight (based on the total weight of the mixture) of n-decanol is added to the reactant solution.
The sulphur crystals are larger than those of Comparative Ex-periment A, the average particle size being approximately a~ order of magnitude larger in diameter.
EXAMP~E 2 -Sour gas, e.g., natural gas containing about 10 per cent H2S and 25 per cent by volume C02, enters an ab~orption vessel which contains an absorbent mixture composed of about 81 per cent sulfolane ~y weight (based on the total weight of the mixture), about 17 per cent by weight of an aqueous 0.5M solution of the Fe(III) chelate of 2-hydroxyethylethylenediaminetriacetic acid 6~33 and about ~.7%~ n-dodecanol. The pressure of the feed gas is about 3 bar, and the temperature of the absorbent mixture is about 35 C. A contact time of about ~80 s is emplo~ed in order to absorb virtually all C02 and react all the H2S. Purified or "sweet" gas is removed, the "s~eet" gas being of a purity suffi-cient to meet standard requirements. In the absorbent mix-ture~
the H2S is converted to elemental sulphur by the Fe(III) chelate, Fe(III) chelate in the process being converted to the Fe(II) chelate. The absorbent mi~ture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed con-tinuously and may be stripped to regenerate the chelate and recover C02.
EXAMPLES_3-~2 and Com~arative Experiments B-D
A series of runs were made at a temperature of 60 C in step a) and using a procedure similar to Comparative Experiment A to determine the effect of alkanols coming within the scope of the in~ention. The results are presented in Table I.
~'7~33 TABLE I
Examplef)- or Solution composition Alkanol S mea~
Comparative ~ ~Om éxcess vol. dia-Experiment g%w ~eHO~EDTA e) pH m(e~t)er _ _ .
B 8 10 4.5 none ) 1.9 3 8 10 4.5 Dodecanol6.9 (500 ppm) 4 8 10 4.5 Decanol17.1 (500 ppm) C 8 10 4.5 no~e ) 5.2 8 10 4.5 Decanol13.7 (500 ppm) 6 8 10 4.5 Decanol23.8 (570w) 7 8 10 4.5 Neodol 9112.3 (500 ppm) ) 8 8 10 4.5 Neodol 9120.3 (5%w) D 4 20 8 none 4.4 9 4 20 8 Decanol (30 ppm)4.8 4 20 8 Decanol8.8 (300 ppm) 11 4 20 8 Neodol 914.9 (30 pp~) 12 4 20 8 ~eodoi 918.9 _ _ _ _ (300 ppm) _ a) Determined by Coulter Counter. This method of analysi6 iB described in "Partic~e Size Measurement" by T. Allen, third edition, Powder Technology Series, edited by Chapman and Hall (1981~.
b)anld) Two different batches o~ the same solutïon recipe.
c) "Neodol 91" is a trade mark ~or a mixture of primary n-alkanols ha~ïng 9 to 11 carbon atoms per molecule.
e) 2-hydro~yethylethylenediaminetriacetic acid.
f) In Arabic numerals. g) In capital le-tters ~76~3~
~XAMPLE 13 Sour gas, e.g., nat~ral gas containing about 8 . o per cent H2~ and ]5 per cent b~ Yolu~e C02, enters an a~s;orption ~essel which contains- an ab~orbent ~i~ture composed of 8~ per cent carbitol (3,6-dioxaoctanol or dïethylene glycol monoethyl ether) by weight (based on the total weigh of the ~ixture), 17 per cent of an aqueous o.8M solution of the Fe(III) chelate of nitrilotriacetic acid and 2.0%w dodecanol.
The pressure o~ the feed gas ;s about 6.2 bar and the temper-ature of the absorbent mixture is about 35 C. A con-tact time of about 180 s is employed in order to absorb virtuall~ all C2 and react all the H2S. Purified or "sweet" gas is re-moved, the "~weet" gas bein~ of a purity sufficient to meet standard requirements. In the absorbent mixture, the H2S is con~erted to elemental sulphur by the Fe(III) chelate, Fe(III) chelate in the process being conYerted to the Fe(II) chelate. The absorbent mixture, containing the elemental sulphur, absorbed C02 and the Fe(II) chelate, is removed con-tinuously and may be stripped to regenerate the chelate and recover C02.
Comparative Experimen-t E
An aqueous solution (150 ml) of the Fe chelate of nitrilotriacetic acid as placed in a vessel, and a stream of pure H2S was sparged into the solution with rapid stirring.
Temperature of the solutior was 35C, and the solution con-tained 0.27 mol per litre iron as Fe . Nitrilotriacetic acid ligand was present in 40 per cen-t mol excess, basis the iron. Sixty microlitres of 1~decanol (300 parts p~r million by weight) were also added to the solution. The pH of the solution was 7, and pressure was atmospheric. Addi-tion o~ the H2~ (360 ml) was con-tinued un-til approximately 70 per cent of the Fe was converted to the Fe state, which took abou-t
2 to 3 min. The flow of the H2S and the stirrin~ action were then discontinued, oxygen in excess was sparged into the solution, and stirring re~umed ~or 15 min., thus. regenerating the Fe , and completi~g one cycle. The procedure was re-peated for 5 cycles~ the time of regeneration varying up to 30 min, at which time the solutîon was removed from the vegsel and filtered. The s~lphNr produced was washed, dried, and weighed.
A small amount (3 ml) of solution was removed for analysis of nitrilotriacetic acid. The remainder of the solution was then returned to the vessel, and a small amo~mt of H2S04 was added to bring the pH back to 7. The general procedure was ~ollowed for 5 cycles, and the filtration, acid addition (if necessary), analysis, etc. was repeate ~ A total o~ 15 cycles was run, and 30 microlitres of 1-decanol were added after the 6th and 12th cycles. The di~ference in weight between initial Neight of nitrilotriacetic acid ligand and that remaining after 15 cycles was calculated, and is a measure of loss of ligand per unit weight of sulphur produced. The result is shown in Table II.
A procedure similar to that of Comparative Experiment E
was followed, except that the solution also contained 0.05M
thiodiglycolic acid. The result is shown in Table II.
A procedure similar to that of Comparative Experiment E
was followed, except that the solution contained 0.05M
A small amount (3 ml) of solution was removed for analysis of nitrilotriacetic acid. The remainder of the solution was then returned to the vessel, and a small amo~mt of H2S04 was added to bring the pH back to 7. The general procedure was ~ollowed for 5 cycles, and the filtration, acid addition (if necessary), analysis, etc. was repeate ~ A total o~ 15 cycles was run, and 30 microlitres of 1-decanol were added after the 6th and 12th cycles. The di~ference in weight between initial Neight of nitrilotriacetic acid ligand and that remaining after 15 cycles was calculated, and is a measure of loss of ligand per unit weight of sulphur produced. The result is shown in Table II.
A procedure similar to that of Comparative Experiment E
was followed, except that the solution also contained 0.05M
thiodiglycolic acid. The result is shown in Table II.
A procedure similar to that of Comparative Experiment E
was followed, except that the solution contained 0.05M
3,3-thiodipropionic acid. The result is shown in Table II.
~ABLE II
First stabilizing Grams of ligand lost composition per ~ram of sulphur ____produced Comparatlve Experiment E none 0.14 Example 14 thiodiglycolic acid 0.09 Example 15 3,3-thiod;propionic 0. 11 acid 6~33 Comparative Experiment F
An aqueous &olution (150 ml) of the Fe chelate of nitrilotriacetic acid was placed ln a vessel, and a stream of pure ~2S was sparged into the solution with rapid stirring.
Temperature of the solution was 35 C, and the solution con-tained 0.27 mol per litre iron as ~e . ~itrilotriacetic acid ligand was present in ~0 per cent mol excess, basis the iron. Sixty microlitres of 1-decanol (300 parts by million by weight) were also added -to the solution. ~he pH of the solution was 7, and pressure was atmospheric. Addition of the H2S ~360 ml) was continued until approximately 70 per cent of the Fe was converted to the Fe state, which took about 2 to 3 min. The flow of the X2S and the stirring action were then discontinued, oxygen in excess was sparged into the solution, and stirring resumed for 15 min3 thus regenerating the Fe , and completing one cycle. The procedure was re-peated for 5 cycles, the time of regeneration varying up to 30 min, at which time the solution was removed from the vessel and filtered. The sulphur produced was washed, dried, and weighed. A small amount (3 ~L) of solution was removed for analysis of nitrilotriacetic acid. The remainder of the solution was then returned to the vessel, and a small amount of H2S04 was added to bring the pH back to 7. The general procedure was followed for 5 cycles1 and the filtration, acid addition (if necessary), analysis, etc. was repeated. A total of' 15 cycles was run, and 30 microlitres of 1-decanol were added after the 6th and 12th cycles. The dif~erence in weight between initia:L weight of nitrilotriacetic acid ligand and that remaining af'ter 15 cycles was caLc~Lated, and is a measure of loss of lieand per ~nit weight of' sulphur produced. I'he result is shown in Table III.
EXAMP~E 16 A procedure simîlar to that of Compara-tive Experiment F
was ~'ollowed, except that the solution a'Lso contai'ned O.lM
sodium thiocyanate. The result is shown in Table III.
~1~6433 ~9 EXAMPLE 17.
A procedure similar.to that of.Comparative Experiment F
~as followed, except.that.the.s:olution contained O.lM sodium dithionite. The res,ult i.s. s~own i~ Table III.
-TABLE'I:II
Second stabilizing Grama of ligand lost compositionper gram of sulphur produced Comparative Experiment E none 0.14 Example 16 sodium thiocyanate o.o6 Example 17 sodium dithionite o.o6 ,. ~
, ~ :
.
:~ :
:: :
~:
:::
:;:
~ABLE II
First stabilizing Grams of ligand lost composition per ~ram of sulphur ____produced Comparatlve Experiment E none 0.14 Example 14 thiodiglycolic acid 0.09 Example 15 3,3-thiod;propionic 0. 11 acid 6~33 Comparative Experiment F
An aqueous &olution (150 ml) of the Fe chelate of nitrilotriacetic acid was placed ln a vessel, and a stream of pure ~2S was sparged into the solution with rapid stirring.
Temperature of the solution was 35 C, and the solution con-tained 0.27 mol per litre iron as ~e . ~itrilotriacetic acid ligand was present in ~0 per cent mol excess, basis the iron. Sixty microlitres of 1-decanol (300 parts by million by weight) were also added -to the solution. ~he pH of the solution was 7, and pressure was atmospheric. Addition of the H2S ~360 ml) was continued until approximately 70 per cent of the Fe was converted to the Fe state, which took about 2 to 3 min. The flow of the X2S and the stirring action were then discontinued, oxygen in excess was sparged into the solution, and stirring resumed for 15 min3 thus regenerating the Fe , and completing one cycle. The procedure was re-peated for 5 cycles, the time of regeneration varying up to 30 min, at which time the solution was removed from the vessel and filtered. The sulphur produced was washed, dried, and weighed. A small amount (3 ~L) of solution was removed for analysis of nitrilotriacetic acid. The remainder of the solution was then returned to the vessel, and a small amount of H2S04 was added to bring the pH back to 7. The general procedure was followed for 5 cycles1 and the filtration, acid addition (if necessary), analysis, etc. was repeated. A total of' 15 cycles was run, and 30 microlitres of 1-decanol were added after the 6th and 12th cycles. The dif~erence in weight between initia:L weight of nitrilotriacetic acid ligand and that remaining af'ter 15 cycles was caLc~Lated, and is a measure of loss of lieand per ~nit weight of' sulphur produced. I'he result is shown in Table III.
EXAMP~E 16 A procedure simîlar to that of Compara-tive Experiment F
was ~'ollowed, except that the solution a'Lso contai'ned O.lM
sodium thiocyanate. The result is shown in Table III.
~1~6433 ~9 EXAMPLE 17.
A procedure similar.to that of.Comparative Experiment F
~as followed, except.that.the.s:olution contained O.lM sodium dithionite. The res,ult i.s. s~own i~ Table III.
-TABLE'I:II
Second stabilizing Grama of ligand lost compositionper gram of sulphur produced Comparative Experiment E none 0.14 Example 16 sodium thiocyanate o.o6 Example 17 sodium dithionite o.o6 ,. ~
, ~ :
.
:~ :
:: :
~:
:::
:;:
Claims (22)
1. A process for the removal of H2S from a sour gaseous stream, which process comprises. the following steps:-a) contacting the sour gaseous stream in a contacting zone at a temperature below the melting point of sulphur with a reactant solution containing an effective amount of an oxidizing reactant comprising one or more polyvalent metal ions and/or one or more polyvalent metal chelate compounds and also an effective amount of a modifier comprising one or more alkanols having in the range of from 4 to 18 carbon atoms per molecule, b) separating a sweet gaseous stream from an admixture containing crystalline sulphur, a reduced reactant and the modifier, and c) isolating at least a portion of the said crystalline sulphur.
2. A process as claimed in claim 1, in which the alkanol or alkanols is (are) applied in step a) in an amount in the range of from 0.01 to 4% by weight, calculated on the reactant solution.
3. A process as claimed in claim 1, in which the reduced reactant present in the admixture separated in step b) or left behind subsequent to step c), is contacted in a regener-ation zone with an oxygen-containing gas, producing a regener-ated reactant-containing admixture.
4. A process as claimed in claim 3, in which regenerated reactant-containing admixture is returned to the contacting zone in step a).
5. A process as claimed in claim 1, in which an aqueous solution is applied as the reactant solution in step a).
6. A process as claimed in claim 5, in which the modifier is applied in an amount at or near the saturation level thereof in the aqueous reactant solution.
7. A process as claimed in claim 1, in which the sour gaseous stream also contains CO2 and a liquid absorbent selective for CO2 is applied in the reactant solution in step a), the admixture separated in step b) also containing absorbed CO2.
8. A process as claimed in claim 7, in which a liquid absorbent selective for CO2 and H2S is applied in the reactant solution in step a), the admixture separated in step b) also containing absorbed CO2.
9. A process as claimed in claim 7 or 8, in which prior or subsequent to sulphur isolation in step e), CO2 is stripped from the admixture separated in step b) and containing reduced reactant and the modifier.
10. A process as claimed in any one of claims 1, 5 or 7, in which one or more alkanols having in the range of from 4 to 12 carbon atoms per molecule are applied in the modifier in step a).
11. A process as claimed in any one of claims 1, 5 or 7, in which t-butanol, n-pentanol, n-octanol, n-decanol, n-undecanol and/or n-dodecanol are applied in the modifier in step a).
12. A process as claimed in any one of claims 1, 5 or 7, in which the reactant solution contains one or more polyvalent metal chelate compounds and a stabilizing amount of a first stabilizing composition comprising thiodiglycolic acid and/or 3,3-thiodipropionic acid.
13. A process as claimed in any one of claims 1, 5 or 7, in which the reactant solution contains one or more polyvalent metal chelate compounds and a first stabilizing composition comprising thiodiglycolic acid and/or 3,3-thiodipropionic acid in an amount in the range of from 0.005 to 0.3 mol per litre of solution.
14. A process as claimed in any one of claims 1, 5 or 7, in which the reactant solution contains one or more polyvalent metal chelate compounds and a stabilizing amount of a second stabilizing composition comprising sodium thiocyanate and/or sodium dithionite.
15. A process as claimed in any one of claims 1, 5 or 7, in which the reactant solution contains one or more polyvalent metal chelate compounds and a second stabilizing composition comprising sodium thiocyanate and/or sodium dithionite in an amount in the range of from 0.01 to 0.5 mol per litre of solution.
16. A process as claimed in claim 1, in which the reactant is a coordination complex of a polyvalent metal with an acid having the general formula:-(X)3-n-N-(Y)n wherein n is an integer in the range of from 1 to 3, Y represents a carboxy-methyl or 2-carboxyethyl group and X a 2-hydroxyethyl or 2-hydroxypropyl group or an alkyl group having in the range of from 1 to 4 carbon atoms; or wherein:
- from 2 to 4 of the groups Y represent carboxymethyl or 2-carboxyethyl groups - from 0 to 2 of the groups Y represent a 2-hydroxyethyl or 2-hydroxy-propyl group and - R represents an ethylene, a trimethylene, 1-methyl-ethylene, 1,2-cyclohexylene or 1,2-benzylene group, or with a mixture of such acids.
- from 2 to 4 of the groups Y represent carboxymethyl or 2-carboxyethyl groups - from 0 to 2 of the groups Y represent a 2-hydroxyethyl or 2-hydroxy-propyl group and - R represents an ethylene, a trimethylene, 1-methyl-ethylene, 1,2-cyclohexylene or 1,2-benzylene group, or with a mixture of such acids.
17. A process as claimed in claim 16, in which the reactant is a coordination complex of a polyvalent metal with an aminoacetic acid derived from ethylenediamine.
18. A process as claimed in claim 16, in which the reactant is a coordination complex of a polyvalent metal with an aminoacetic acid derived from ammonia.
19. A process as claimed in any one of claims 16 to 18, in which the polyvalent metal is iron.
20. A process as claimed in any one of claims 1, 5 or 7, in which the reactant is a coordination complex of iron with 2-hydroxyethylethylenediaminetriacetic acid.
21. A process as claimed in any one of claims 1, 5 or 7, in which the reactant is a coordination complex of iron with nitrilotriacetic acid.
22. A process as claimed in any one of claims 1, 5 or 7, in which the sour gaseous stream is a hydrocarbon stream or a stream derived from the gasification of coal.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US26720181A | 1981-05-26 | 1981-05-26 | |
| US06/324,359 US4382918A (en) | 1981-11-24 | 1981-11-24 | Method of removing hydrogen sulfide from gases utilizing a stabilized iron chelate solution |
| US06/324,357 US4388293A (en) | 1981-11-24 | 1981-11-24 | H2 S Removal |
| US324,359 | 1981-11-24 | ||
| US324,357 | 1981-11-24 | ||
| US267,201 | 1994-07-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176433A true CA1176433A (en) | 1984-10-23 |
Family
ID=27401950
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000402901A Expired CA1176433A (en) | 1981-05-26 | 1982-05-13 | Sulphur recovery process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1176433A (en) |
-
1982
- 1982-05-13 CA CA000402901A patent/CA1176433A/en not_active Expired
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