CA1173627A - Extraction process - Google Patents

Abstract

ABSTRACT
EXTRACTION PROCESS
In the removal of H2S from a gas by contacting with an aqueous reactant solution containing an ion or a chelate of a polyvalent metal with formation of solid sulphur and reduced reactant and regeneration of the reactant with oxygen, the sulphur is recovered by extracting sulphur-containing aqueous solution with a liquid composition comprising one or more alkanols having 4 to 15 carbon atoms.

Description

- . -EXTRACTIO~ PROCESS

The inventiOn relates to a process for the removal of H2Sfrom a sour gaseous stream.
The presence of significant quantities of H2S and C02 in various "sour" inaustrial gaseous streams poses a persistent problem. A gaseous stream is named "sour" if it contains significant quantities of H2S and/or C02.
Although various procedures have been developed to remove and recover these contaminants, most such processes are deficient, for a variety of reasons.
In one cycl;c method currently attracting attention, the sour gaseous stream is contacted, preferably with a solvent which contains a regenerable reactant, to produce solid elemental sulphur which is recovered either prior or sub-sequent to regeneration. Suitable reactants include polyvalent ions of metals, such as iron, vanadium, copper, man~anese, and nickel, and include polyvalent metal chelates. Preferred re-actants 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 C02.
A problem associated with such processes is that the solid sulphur produced is of poor quality~ i.e., it is very finely divided and difficult to separate from the aqueous reactant ~5 solution. A process which provided for the efficient reaction of H2S and removal of the sulphur produced col~d have great economic lmportance.
It is an object of the inven-tion to provide an economic~l and efficient method for the reaction of H2S and for the re-moval of the sulphur produced.
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~l ~L 7 1, ~ 7 Accordingly, the invention provides 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 an aqueous reactant solution containing as reactant an effective amount of one o^r more polyvalent metal ions and/or one or more polyvalent metal chelate compounds to produce a sweet gaseous stream and an aqueous admixture containing sulphur and reduced reactant;
b) removing aqueous admixture from the contacting zone;
c) contacting said aqueous admixture in an extraction zone with a liquid composition comprising one or more alkanols having in the range of from 4 to 15 carbon atoms per molecule in an amount sufficient to remove at least the bulk of the sulphur from said aqueous admixture and, ~- form a separate liquid phase containing sulphur~and said composition, and forming a three phase mass comprising an upper liquid phase comprising solid sulphur and said composition, and a lower phase in contact with said upper phase~ said lower phase comprising aqueous admixture;
d) separating at least a portion of the upper phase, and recovering sulphur from the por-tion separated, e) separating aqueous admixture from the lower phase, and regenerating separated aqueous admixture in a regen~rati.on zone to produce an aqueous a & ixture containing a regener-ated reactant9 f) returning aqueous admixture from the regeneration zone to the contacting zone.

. ,. _ ~ =.: . .
--------- .. ..
-In the embodiment described above the reactant is regener-ate~ after ~ulphur has been extracted. According to another em~
bodiment of the invention the reactant is regenerated before sulphur extraction takes place. In the latter emboaiment the 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 an aqueous reactant solution containing as reac-tant an effective amount of one or more polyvalent metal ions and/or one or more polyvalent metal chelate compounds to produce a s-~eet gaseous stream and an aqueou~ ad-mixture containing sulphur and reduced reactant;
b) removing aqueous admixture from the contacting zone, and regenerating the aqueous admixture to produce a regener-ated aqueous admixture containing a regenerated reactant and sulphur;
c) contacting regenera-tea aqueous admixture in an extraction zone with aliquidcomposition comprising one or more alkanols having in the range of from 4 to 15 carbon atoms per molecule in an amount sufficient to remove at least the bulk of the sulphur from said regenerated aqueous admixture and form a separate liquid phase containing sulphur and said composition, and forming a three phase mass comprising an upper liquid phase comprising solid sulphur and said composition, and a lower phase in contact with said upper phase, said lower phase comprising regenerated aqueous admixture;
d) separating at least a portion of the upper phase, and recovering sulphur from the portion separated;
e) separating regenerated aqueous admixture from the lower phase, returnin~ regenerated aqueous admix-ture from the regeneration zone to the contacting zone.

~7~6~7 It has been found, surprisingly, that the compounds tlescribed exhibit the ability to extract the sulphur from the aqueous admixture. The upper phase, or a portion thereof, may then 'oe removed, preferably continuously, and the sul-phur recovered, e.g., by heating the solution and melting the sulphur to e~ect a separationO Concomitantly the lower phase, or a portion thereof, may then be separated, again preferably continuously, and the reactant therein regenerated by contacting the admixtur0 in a regeneration zone or zones wlth an oxygen-containing gas. Examples of oxygen-containing gases are air, air enriched with oxygen and pure oxygen. The oxygen oxides the reduced metal ions or the metal of the chelate or chelates to a higher valence state, and the regenerated mixture is returned to the contact zone. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of reactant present in the mixture. Preferably, tne oxygen-containing gas is supplied in an amount of from about 20 per cent to 200 per cent stoichiometric excess.
It has also been found that the stability of some reactants employed is temperature-dependent, i.e., if the temperature of the solutions is too high, some of the reactants tend to degrade or decompose. In particular, if tempera-tures above the melting point of sulphur are employed~ some systems, such as particular iron chelate systems, tend to decompose.
On the other hand, if a solvent is employed to extract the sulphur from the solution, problems may arise if the solvent exhibits signlficant solubility in the gaseous stream treated. Thus, a need has existed for a gas-treating system which would avoid the problems mentioned. This need is satisfied by sep-arating aqueous admixture separated in step b) or regenerated reactant-containing aqueous admixture into an aqueous solution containing reduced reactant or regen-erated reactant, respectively, and having reduced sulphur content and ~7~

an aqueous reactant slurry having increased sulphur content and contacting the said aqueous reactant slurry having increased sulphur content in step c) with the said composition.
Accordingly, the invention substantially reduces the possi-bility of reactant degradation by extracting the sulphur froma limited volume o~ admixture. Concomitantly, in the case of first separating sulphur and then reeenerating the redu~ed reactant, the lower phase, or a portion thereof, may then be separated, again preferably continuously, and the reactant therein regenerated by contacting the admixture in a regener-ation zone or zones with an oxygen-containing gas. The re-actant admixture may be regenerated separately, or, preferably, is regenerated in the same regeneration zone as the main stream of admixture. In the case of first regenerating the reduced reactant and then separating sulphur, the lower phase is prefer-ably returned to the contacting zone in step a).
A critical feature of this embodiment of the invention is the separation of the sulphur-containing admixture from the contacting zone or from the regeneration zone into two portions, a portion or stream having reduced sulphur content, and a portion or stream containing increased sulphur content, preferably a slurry. ~he ma~ner of separation is a matter of choice, and equipment such as a hydrocyclone or a centri~ugal separator may be employed. It is not necessary that absolutely all sulpllur be removed on a continuous basis in the process;
the process may suitably be operated with a very minor inventory or signi~icantly reduced content of sulphur in the system. In general, whether the sulphur is separated prior to or a~ter regeneration is a matter of choice, the important aspect being the contacting of the limited volume of the sulphur-containing admixture or "slurry" with the said composition.
Preferably, the "slurry" or concentrated stream will comprise

2 per cent to 30 per cent by volume (on a continuou3 basis) of the total stream from the contacting zone or regeneration zone.

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The particular type of gaseous stream treated i~ not critical, as will be evident to those s~illed in the art.
Streams particularly sui`ted to removal o~ H2S by the process of the invention are, as indi`cated, naturally occurring gases, synthesis gases~ process gases, and fuel gases produced by gasification procedures, e.g., gases producedbythe gasi-~ication of coal, petroleum, shale, tar sands,etc. Particularly preferred are coal gasi~ication streams, natural gas streams and refinery ~eedstocks composed of gaseous hydrocarbon streams, especially those streams of this type having a low ratio of H2S to C02, and other gaseous h~rocarbon streams. The words "hydrocarbon stream(s)", as employed herein, are intended to include streams containing significant quantities of hydro-carbon (both paraffinic and aromatic), it being recognized that such streams may contain signi~icant "impurities" not technically defined as a hydrocarbon. Streams containing principally a single hydrocarbon, e.g.; ethane, are eminently suited to the process of the inven-tion. Streams derived from the gasification and/or partial oxidation of gaseous or liquid hy~rscarbon may be treated by the invention. The H2S
content of the.type o~ streams con-templated will ~ary ex tensively, but, in general, will range from abo~rt 0.1 per cent to about 10 per cent by ~olume. Obviously~ the contents of H2S present is not generally a limiting factor in the process of the invention.
Ihe temperatures employed in the contacting zone are not generally critical, except that the reaction is carried out a-t a temperature below the melting point of sulphur. In many com-mercial applications, such as the remo~al of ~2S from natural gas to meet pipeline specï~ications~ contacting at ~mbient temperatures is desired, since the cost o~ refrigeration would exceed the benefits obtained due to increased absorption at the lower temperature. In generPl, temperatures in the range sf ~rom 10C to 80C are suitable, and temperatures in the ~:~7~ 7 range of from 20C to 45C are preferred. Contact times may be in the range of from about 1 s to abou~t 270 s or longer, with contact times in the range of from 2 s to 120 s being preferred. Temperatures employed in the extract-ion zone will approximate those ;n the contacting zone, except that they will always be below the melting point of sulphur.
Similarly, in the regeneration or stripping zone or zones, temp-eratures may be varied widely. Preferably, the regeneration zone should be maintained at substan~ally the same temperature as the absorptin zone. If ~eat is added to assist regeneration, cooling of the absorbent mixture is required before return of the absorbent mixture to the absorption zone. In general, temperatures in the range of from about 10C to 80C, preferably 20C to 45C, may be employed.
Pressure condltions in the absorption zone may vary widely, depend-ing on the pressure of the gaseous 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 process, e.g., p}l, etc., are further described in United States patent specification 3,068,065 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 procedure is preferably conducted continuously.

~73~7 As indicated, -the H2S, when contacted, is quickly converted by the polyvalent metal ions, polyvalent metal chelate, etc., to elemental sulphur. The amount of polyvalent metal compound, polyvalent metal chelate) or mixtures there-of supplied is an effective amolmt, i.e., an amount sufficient to convert all or substantially all of the f-l2S in the gaseous stream, and will generally be on tha order of at least about 1 mol per mol of ~12S. Ratios in the range of from about 1 or 2 mol to about 15 mol of polyvalent metal compound or chelate per mol of H2S may be used, with ratios in the range of from about 2 mol per mol to about 5 mol of polyvalent metal compound or chelate per mol of H2S being preferred.
The manner of preparing the aqueous solution or admixture is a matter of choice.
The polyvalent metal ion or polyvalent metal chelate solution will generally be supplied as an aqueous solutlon having a concentration of from about 0.1 molar to about 2 molar and a concentration of about 0.6 to 0.8 molar is preferred.
Any polyvalent metal can be used, but iron, copper and manganese are preferred, particularly iron. The polyvalent metal should be capable of oxid-izing hydrogen sulphide, while being reduced itsel-f from a higher to a lower valence state, and should then be oxidizable by oxygen from the lower valence state to the higher valence state in a typical redox reaction. Other polyvalent metals which can be used include lead, mercury, palladium, plat:inum, tungsten, nickel, chromium, cobalt, vanadium, titanium, tantalum, zirconium, molybdenum, 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 formula (X)3-n~N ( )n 73~

wherein n is an integer from 1 to 3, Y represents a carboxymethyl or 2-csrboxy-ethyl group and X a 2-hydroxyethyl or 2-hydroxypropyl group o~ an alkyl group having from 1 to ~ carbon atoms; or N-~ R - N
Y / \ Y wherein:
- from 2 to ~ of the groups Y represent carboxymethyl or 2-carboxyethyl groups - from O to 2 of the groups Y represent a 2-hydroxyethyl or 2-hydroxypropyl group, and - R represents an ethylene, a trimethylene, l-methylethylene, 1,2-cyclohexylene or 1,2-benzylene group; or with a mixture of such acids.
The polyvalent metal chelates are readily formed in aqueous solution by reaction of an appropriate salt, oxide or hydroxide of the polyvalent metal and the chelating agent in the acid form or an alkali metal or ammonium salt thereof. Exemplary chelating agents include aminoacet.ic acids derived from ammonia or 2-hydroxyalkylamines, such as glycine ~aminoaceti.c acid), diglycine ~iminodiacetic acid), NTA (nitrilotriacetic acid), a 2-hydroxyalkyl glycine;
a dihydroxyalkylglycine, and hydroxyethyl- or hydroxypropyldiglycine;

, ... ...

~7~ 2~

~ o aminoacetic acids derived from ethylenediamine, diethylenetriamine, ~,2-propylenediaminej and ~,3-propylenediamine, such as EDTA
(ethylenediaminetetraacetic acid), ~EDTA (2-hydro~yethylethylene-diamlnetriacetic acid), DETP~ (diethylenetr;aminepentaacetic acid);
aminoacetic acid deriYatiYes of cyclic 1,2-diamines~ such as ~,2-diaminocyclohexane-~ tetraacetic acid, and 1,2-phenylene-diamine~ tetraacetic acid, and the amides of polyaminoacetic acids disclosed in U.S. paten-t specification No. 3~580,950. ~he iron chelates of NT~ and 2-hydroxyethylethylenediaminetriacetic acid are preferred.
~ he alkanols used in step c) ha~e the general formula CnX2n~10H, in which n is an integer from 4 through 15, preferably 10 through 1~. Mixtures thereof may be used in extracting or re-moving the st~phur from the aqueous admixture. As those skilled in the art will recogni7e, several of the alkanols or compositions are solids at ordinary temperatures, and heat, as necessary, will be provided to convert the solid to liquid for the extraction (and maintain the alkanol or composition as a liquid, if necessary). In general, alkanolsor compositions according to -the invention which have a melting point of 60C or below (preferably l~5C, or below) are preferred. Useful compounds are t-bu1;anol, n-penkanol, n-octanol, n-decanol, n-undecanol, n-dodecanol, and mixtures thereof. The com~
pound or compounds are supplied in an amount sufficient to remove at least the bulk of the st~phur from the admixture and form a separate phase comprising sl~phur and the compound or mixture of compounds. ~ecause the amou~t of the compotmd, or mixture o~ com-pounds, required is dependent on the amount of sulphur produced, which is, in turn, dependent on the content of H2S in -the gaseous stream to be treated9 precise amounts of the compounds cannot be given. ~hose skilled in the art may adjust the amot~t a as required.
In general, the amount ~ill range from about ~.0 per cent to about 200 per cent by Yolume, based on the a~ueous polyvalent metal ion or polyvalent metal chelate solution, with an amount of 5.0 per cent to about ~20 per cent by volume being preferred. ~he solid sulphur apparently is suspended preferentially in the compound, or ~i~ture of compot~ds, and ~ay be recovered easily. Ihe manner of ll recovering the sulphur is a matter of choice. For example, after separating the suspension (or a portion thereof), the sulphur may be recovered by set~ling, filtration, or by suitable devices such as a hydrocyclone. Preferably, however, the sulphur is melted, allowing separation by the simple expedient of allowing the sulphur to settle.
In order to describe the invention in greater detail, reference is made to the accompanying drawing. The values given herein relating to temper-atures, pressures~ compositions, etc. 9 should be considered merely exemplary and not as delimiting the invention. Figure l illustrates an embodiment of the invention wherein sulphur is extracted prior to regeneration. Figure 2 illus-trates an embodiment of the invention wherein an aqueous solution containing reduced reactant and having reduced sulphur content is separated rom an aqueous reactant slurry having increased sulphur content and the slurry is extracted prior to regeneration. Pigure 3 illustrates an embodiment whercin sulphur is extracted after regeneration.
As shown in Figure l of the drawing, a sour gaseous stream, e.g., natural gas containing about 0.5 per cent H2S, in a line l enters a contactor or column 2 (tray type) into which also enters an aqueous admixture comprising an aqueous 2.0 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 aqueous admixture is about ~15C. A contact time of about 120 s is employed in order to react all the H2S. Purified or "sweet" gaseous stream leaves column 2 through a line 3. The "sweet" gaseous stream is of a purity sufficient to meet standard requirements. In the admixture 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 aqueous admixture, containing the elemental sulphur, is removed .~

~L~l7~ 7 lla continuously and scnt through a line 4 to a depressurization and degassing unit 5j, and then to a sulphur extraction zone. The released gases are withdrawn from the unit 5 via a l,ine 16. Prior to entry into a unit 6, a stream o~ liquid n-decanol in a line 7 joins the line 4 in such a fashion that good mixing of the aqueous admixture and the decanol occurs. The decanol may, of course, be added in the unit 6~ either wholly or in part, and the volume ratio of aqueous ad-mixture to the decanol is approximately 1:1. Unit 6 is a separator in which separation takes place into an upper phase containing solid sulphur and decanol and a lo~er phase .c_ j~

62~

co~prising aqueous admixture.
In the unit 6, the decanol and aqueous ad:mixture are allowed to separate i`nto aM upper decanol layer or phase, and a lower aqueous admixture layer. ~urprisingly, even tho~gh:
sulphur norm~lly has a dsnsity greater than 1.0, the sulphur maybe said to "~loat" in the liquid decanol, and is easily separatea from the aqueous admixture. Large depths of a sulphur rich zone in ~lkanol can be built without sulphur sinking through the aqueous alkanol-phase interface. This considerably facilitates design of the process equipment. Decanol-sulphur mixture is removed from the separator 6 via a line 8 to a re-covery zone or tank 9, where the sulphur may be removed by warming the mixture to the melting point of sulphur. Option-ally, only a portion of the upper phase may be removed, a "clarified" portion being separable and recyclable, so that only a portion of the upper phase need be heated. In any event, upon melting, as shown, the sulphur sinks to the bottom of the tank 9, where it is easily removed via a line 15.
Deca~ol is removed via a line 7, preferably after cooling, for re-use. Make-up decanol is supplied to the line 7 via a line 17.
Concomi-tantly, the aqueous admixture is removed via a line 10 for regeneration of the Fe(II) chelate. The decanol is present in the aqueous admixture in an amount at or near the saturation level thereof. In a regeneration zone or column 11 the admixture is contac-ted with excess air in a line 12 to convert the Fe(II) chelate to the Fe(III) chelate. The temper-ature of the regeneration column 11 is about 45G, and pres-sure in the column is maintained at about 2 bar. Spent air i5 removed from the column 11 through a line 13, while regenerated aqueous admixture is returned via a line 14 to the contactor 2.
The arawing illustrates- the aspect of the invention wherein the extraction is carried out prior to regeneration. Removal of the sulphur after regeneration may be preferred in some in-stances, and may be accompl;shed by positioning of the .6~

extraction unit "af~er" the regeneration zone. Thus J regenerated liquid, still containing sulphur, may be passed via line 14 to units analogous or equivalent to units 6, 7, 8 and 9, sulphur recovered, and regenerated sulphur-free solu-tion returned via a line analogous to line 10 to contactor 2.
In Figure 2 a sour gaseous mixture, e~g., natural gas containing about 0.5 per cent H2S, in a line 1 enters a contactor or column 2 (tray type) into which also enters an aqueous admi~ture comprising an aqueous 2.0 M solu-tion of the Fe~III) chelate of nitrllotriacetic acid from a line 14. The pressure of the feed gas is about 84 bar and the temperature of the aqueous admixture is about 45C. A contact time of about 120 s is employed in order to react all the H2S. Purified or "sweet" gaseous stream leaves the column 2 through a line 3. The "sweet" gaseous stream is of a purity sufficien~ to meet standard requiremen~s. In the admixture, the H2S is converted to element-al sulphur by the Fe(III) chelate, the Fe(III~ chelate in the process being converted to the Fe(II) chelate. The aqueous admixture, containing the ele-mental sulphur, is removed continuously and sent through a line 4 to a depressurization and degassing unit 5, and then, further via the line 4, to a separation zone 20. The released gases are withdrawn from the unit 5 via a line 16. The separation zone 20 preferably comprises a unit~ such as a hydrocyclone, for separating the admixture into two portions, the major portion or stream having a reduced sulphur content (shown leaving ill a line 21), and a portion or stream having an increased sulphur co~ltent (shown leaving in a line 22). It is not necessary that all sulphur be removed from the portion separated in the line 21, and some sulphur retention ma~r be beneficial. Preferably, the amount of s~lphur removed in the hydrocyclone is sîmply balanced wi-t~ the rate of sulphur întake in the reactor 2, which is, of cours-e, de-pendent on the H2S content of the gaseous stream supplied viathe line 1. Those skilled in the art may appropriately adjust the rates of withdrawal of streams 21 and 22. Typically, stream 22 comprises 10 per cent by volume of the to-tal volume of admixture in line 4.
Accordingly, the fluid slurry in the line 22 proceeds to a separation zone 6. Prior to entry into the zone 6, a stream o~ n-dodecanol in a line 7 joins -the line 22 in such a fashion that good mixing of the aqueous admixture and the n-dodecanol occurs. The n-dodecanol may, of course, be added in the zone 6, either wholly or in part, and the volume ratio of aqueous ad-mixture to the n-dodecanol is approximately 1:1.
In the separation zone 6, the n-dodecanol and aqueous ad-mixture are allowed to separate into an upper n-dodecanol layer or phase, and a lower aqueous admixture layer. Surprisingly, even though sulphur normally has a density greater than 1.0, the sulphur may be said -to "float" in the n-decanol, and is easily separated ~rom the aqueous admixture. I.arge depths of a sulphur-rich zone in alkanol can be built with~ut sulphur si~ing through the aqueous-alkanol phase interface. r~his considerably facilitates design of the process equipment.
The n-dodecanol-su].phur mixture is removed from the separator 6 via a line 8 to a recovery zone or tank 9, where the sulphur may be removed by warming the mixture to the melting point of sulphur. Optionally, only a portion of the upper phase may be removed, a "clarified" portion being separable and recyclable, so that only a porti`on of the u~per phase need be heated.
In any event, upon melting, as shown, the sulphur sinks to the bottom of tank 9 from whence ;t is easily removed via a line 15. The n-dodecanol is removed via the line 7, and is 2~7 re-used. Make-up dodecanol is supplied to the line 7 Yia ~ line 17. Excess heat in the solvent may be removed, pre~erably in unit 6 or 12, as desired. The lower aqueous layer in unit 6 is removed via a line 23; the decanol is present in the aqueous layer in an amount at or near the saturation level thereof.
Concomitantly, a~ noted, the aqueous admixture i5 removed from the separation zone 20 via the line 21 for regeneration of the Fe(II) chelate. As sho~n, the lower aqueous la~er in the line 23 joins the line 21 prior to entry into a regenera-tion zone 11, although separate entry into the zone 11 is entirely feasible. In regeneration zone or column 11 the admixture is contacted with excess air in line 12 to convert the ~e(II) chelate to the Ee(III) chelate. The temperature of the regener-ation column is about 45G, and pressure in the column is maintained at about 2 bar. Spent air is removed ~rom the col-lmn 11 through a line 13, while regenerated aqueous admixture is returned via the line 14 to the contactor 2. Make-up aqueous reactant solution ~ay be supplied via a line 18.
As indicated, Figure 2 illustrates the aspect of the in-vention wherein the extraction is carried out prior to regener-ation. Removal of the sulphur afte~ regeneration may be pre-ferred in some instances, and may be accomplished by positioning of the extraction unit "after" the regeneration zone; this embodiment is illustrated in Figure 3. RefereIlce numerals in Figures 1, 2 and 3 which are the same refer to analogous or equivalent units.
Accordingly, in Figure 3, the sulphur-containing liquid is passed, after degassing in the degassing unit 59 via the line 4 to regenerator 11 where it is regener~ted, as previously described. The regenerated sulphur-containing admixture is removed via the line 30, and passed to the centri~ugal separator 2Q where it is separa-ted into a regenerated reactant solution having reduced sulphur content and a sulphur-containing slurry.
The regenerated reactant solution is returned via the line 14 ~7,~27 to the contactor 2, while the slurry is removed, via the line 22 to the separation zone 6. In the sepa-ration zone 6, the slurry is contacted with n-decanolg as described hereinbefore, e.g.
via line 7, and regenerated reactant solution is returned, via the lines 22 and 14, to the contactor 2. Sulphur-contai~ing decanol i5 removed v;a line 8, and may be treated to recover sulphur and decanol, ;n unit 9, as described in relation to Figure 2.
While the invention has been illustrated with particular apparatus, those skilled in the art will appreciate that except where specified, other equivalent or analogous units may be employed. The term "zones", as employed in the specification and claims, includes, where suitable, the use of segmented equipment operated in series, or the division of one unit into multiple units because of size constraints, etc. For ex~mple, a contacting column 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 material ~rom the upper portion of the first column being fed into the lower portion of the second column. Pa~allel operation of units is, of course, well within the ~cope of the nvention .
Again, as will be understood by those skilled in the art, the solution~ or mixtures employed may contain other materials or additives for given purposes. For example, U.S. patent speci-fication 3,933,993 discloses the use o~ buffering agents, such as phosphate and carbo~ate buffers. Similarly, U.S. patent specification ~,009,251 describes various additives, such as sodium oxalate, sodium formate~ sodium thiosulphate and ~odium acetate, which may be beneficial.

Claims (19)

C L A I M S

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 an aqueous reactant solution containing as reactant an effective amount of one or more polyvalent metal ions and/or one or more polyvalent metal chelate compounds to produce a sweet gaseous stream and an aqueous ad-mixture containing sulphur and reduced reactant, b) removing aqueous admixture from the contacting zone;
c) contacting said aqueous admixture in an extraction zone with a liquid composition comprising one or more alkanols having in the range of from 4 to 15 carbon atoms per molecule in an amount sufficient to remove at least the bulk of the sulphur from said aqueous admixture and form a separate liquid phase containing sulphur and said composition, and forming a three phase mass comprising an upper liquid phase comprising solid sulphur and said composition, and a lower phase in contact with said upper phase, said lower phase comprising aqueous admixture;
d) separating at least a portion of the upper phase, and recovering sulphur from the portion separated, e) separating aqueous admixture from the lower phase, and regenerating separated aqueous admixture in a regener-ation zone to produce an aqueous admixture containing a regenerated reactant, f) returning auqous admixture from the regeneration zone to the contacting zone.

2. A process as claimed in claim 1, wherein at least a portion of the upper phase separated in step (d) is, after sulphur removal, returned to the extraction zone.

3. 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 an aqueous reactant solution containing as reactant an effective amount of one or more polyvalent metal ions and/or one or more polyvalent metal chelate compounds to produce a sweet gaseous stream and an aqueous ad-mixture containing sulphur and reduced reactant, b) removing aqueous admixture from the contacting zone, and regenerating the aqueous admixture to produce a regener-ated aqueous admixture containing a regenerated reactant and sulphur;
c) contacting regenerated aqueous admixture in an extraction zone with a liquid composition comprising one or more alkanols having in the range of from 4 to 15 carbon atoms per molecule in an amount sufficient to remove at least the bulk of the sulphur from said regenerated aqueous admixture and form a separate liquid phase containing sulphur and said composition, and forming a three phase mass comprising an upper liquid phase comprising solid sulphur and said composition, and a lower phase in contact with said upper phase, said lower phase comprising regenerated aqueous admixture;
d) separating at least a portion of the upper phase, and recovering sulphur from the portion separated, e) separating regenerated aqueous admixture from the lower phase, returning regenerated aqueous admixture from the regeneration zone to the contacting zone.

4. A process as claimed in claim 3, in which at least a portion of the upper phase separated in step (d) is, after sulphur removal 3 returned to the extraction zone.

5. A process as claimed in claim 1 or 3, in which the said composition is used in step c) in an amount in the range of from 1.0 to 200% by volume, calculated on the aqueous poly-valent metal ion and/or polyvalent metal chelate solution.

6. A process as claimed in claim 1 or 3, in which the said composition is used in step c) in an amount in the range of from 5.0 to 120% by volume, calculated on the aqueous poly-valent metal ion and/or polyvalent metal chelate solution.

7. A process as claimed in claim 1 or 3, in which the sulphur is recovered by melting from the portion separated in step d).

8. A process as claimed in claim 1 or 2, in which aqueous admixture separated in step b) is separated into an aqueous solution containing reduced reactant and having reduced sulphur content and an aqueous reactant slurry having increased sulphur content and the said aqueous reactant slurry having increased sulphur content is contacted in step c) with the said composition.

9. A process as claimed in claim 3 or 4, in which regenerated reactant-containing aqueous admixture is separated into an aqueous solution containing regenerated reactant and having reduced sulphur content and an aqueous reactant slurry having increased sulphur content and the said aqueous reactant slurry having increased sulphur content is contacted in step c) with the said composition.

10. A process as claimed in claim 1 or 3, in which the said aqueous reactant slurry having increased sulphur content comprises in the range of from 2% to 30% by volume of the total of the aqueous admixture separated in step b) or of the regenerated reactant-containing aqueous admixture separated in step b).

11. A process as claimed in claim 1 or 3, in which one or more alkanols having in the range of from 10 to 14 carbon atoms per molecule are applied in the said liquid composition.

12. A process as claimed in claim 1 or 3, in which the liquid composition has a melting point of not more than 60°C.

13. A process as claimed in claim 1 or 3, 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-hydroxypropyl group, and - R represents an ethylene, a trimethylene, 1-methylethylene, 1,2-cyclohexyleneor 1,2-benzylene group;
or with a mixture of such acids.

14. A process as claimed in claim 1 or 3, in which the reactant is a coordination complex of a polyvalent metal with an aminoacetic acid derived from ethylenediamine.

15. A process as claimed in claim 1 or 3, in which the reactant is a coordination complex of a polyvalent metal with an amino-acetic acid derived from ammonia.

16. A process as claimed in claim 1 or 3, in which the polyvalent metal is iron.

17. A process as claimed in claim 1 or 3, in which the reactant is a coordination complex of iron with 2-hydroxyethylethylene-diaminetriacetic acid.

18. A process as claimed in claim 1 or 3, in which the reactant is a coordination complex of iron with nitrilotriacetic acid.

19. A process as claimed in claim 1 or 2, in which the sour gaseous stream is a hydrocarbon stream or a stream derived Prom the gasification of coal.