CA2576948A1 - Process for treating hydrogen sulfide lean streams with partial combustion of feed stream - Google Patents

Abstract

This invention is directed to a process for the conversion of hydrogen sulfide into elemental sulfur by contacting the hydrogen sulfide feed gas with a sulfated solid oxide sorbent. Effluent from the first step is passed into a condenser to condense at least a portion of the elemental sulfur to a liquid sulfur product and a vapor phase product. The vapor phase product along with a source of oxygen is passed to a burner to generate a combustion product comprising sulfur oxides. The combustion product is passed to a second reactor to produce a solid phase product and a treated vapor phase product. Feed gas is introduced to the second reactor and the condensing and combustion steps are repeated to produce a sulfated solid oxide and a treated vapor stream comprising less than 50 ppm of sulfur oxides.

Description

PROCESS FOR TREATING HYDROGEN SULFIDE LEAN STREAMS WITH PARTIAL
COMBUSTION OF FEED STREAM

This application has been divided out of Canadian Patent Application Serial No.

2,317,749 filed internationally January 6, 1999 under PCT/US1999/00268, published as WO 99/34900:
This invention concems an improved process for cxsnversion of H2S to sulfur, using a sulfated MOST(Mobil Offgas Sulfur Treatment or Mobil Oil SOx TreatmeM) type catalyst or sorbent.
The sorbent is typically a magnesium=aluminate spinel, with oxidation promoters such as ceria and vanadia. The improvement consists of combusting part of the feed, converting some of the feed H2S
to SO2 prior to contacting the sulfated sorbent. Thus, much of the stoichiometric oxygen required for conversion of H2S to S Is supplied in the form of SO2 by this pre-combustion step, instead of all coming from the oxidized and sulfated solid sorbent. This can significantly decrease the amount of sorbent required, as well as the frequency of regenerations, thus reducing process cost. Optionaity.
one or more Claus reactors may be added to further increase sulfur recovery efficiency.
In a number of processes, such as the refining of crude oil, the purification of natural gas and the production of synthesis gas from, for example, fossil fuels, sulfur containing gas, in particular HZS.
containing gas, Is released. On account of its high toxicity and Its smell, the emission of H2S is not desirable. A number of processes directed to the removal of hydrogen sulfide from gases are known.
In some of these processes, hydrogen sultide is tirst concentrated by means of a liquid absorbent, whereafter the concentrated hydrogen sutfide gas Is converted Into elemental sulfur. In certain cases, it Is possible to omit the first step, I.e., concentrating the hydrogen sulfide, and to convert it dinecly to elemental sulfur. In other cases, partk:ularly in cases with reiativety low H2S
concentrations and higher COZ concentrations, frequently two or more concentration or separation steps are needed to produce sufficiently high hydrogen sulfide concentrations to allow economical conversion of hydrogen sulfide to_elementat sulfur.
One of the best known methods of converting hydrogen sulfide to elemental sulfur is the so-called Claus process. ln the Claus process, elemental sulfur Is produced by reacting 1-125 and SO2 in the presence of a catalyst. The. Claus system uses a combustion chamber which, at 950 to1350'C, converts 50 to 70% of sulfur contained in the feed gas into elemental sulfur.
Sulfur is condensed by cooling the reaction gas to a temperature below the dew point of sulfur, after which the nemaining gas is heated and further reacted over a catalyst. Normally, the -gas passes through at least two such Claus catalyst stages.
The diffefent stages of the Claus pmcess may be represented py the following equations:
ii2.S + 3/2 O2 4 SOi + H20 (n 2 H2S + SO2 -) 3 Sn + 2 H2O (11) The overall readion is:

3 H2S + 3 OZ 4 3 Sn + 3 H2O (III) Below 500 C, the symbol n has a value of approximately 8.
The final Claus exhaust gas stiN contains small amounts of H2S, SO2, CS2, COS, CO, and elemental sulfur in the fonn of a vapor or mist. The exhaust gas can be subjected to post-combustion to convert substantially all sulfur species to sulfur oxides, for example, $O2 and SO33, which are then emitted into the atmosphere.
Sutfur emitted as sulfur oxides.("SOx") Into the atmosphere with the exhaust gas may amount to 2 to 696 of the suffur contained in the feed gas In the fomt of H2S. In view of air pollution and the loss of sulfur Involved, further purification is desirable and is frequently mandated.
Claus aftertreatments have been developed. These are carried out after the last Claus stage or after the post-combustion. These aftertreatments Include, for example, dryand liquid phase processes for catalytic conversion of H2S and SOZ to elemental sulfur, catalytic hydrogenation and hydrolysis of sulfur compounds into HzS for further processing, and oxidation of all sulfur compounds into SOx for further processing by sorption in dry processes or In wet processes.
Commonly owned U.S. Patent No. 5,299,091 to Buchanan et ai., dlscioses the use of MOST
catalyst or sorbent following the Claus tail-gas desulfurization prooess.
Commonly owned U.S. Patent No. 5,514,351 is directed to desulfuriiing tail gas from sulfur reccvery units using sorbents.
t1 is desired to develop a process that is effective for conversion of hydrogen sulfide to elemental sulfur without the need for the use of the Claus process and any associated processes, such as a tail -gas treatment process and possibly an acid gas enrichment process, although they may be optionally added.
The process and system of the instant invention allow the direct conversion of hydrogen sulfide to sulfur, espedally from a gas having a higher concentration of carbon dioxide than hydrogen, su(fide, without the necessity of the Claus process or a tail gas treattrient process or an acid gas enrichment process. Such processes may optionally be employed however. The process of this invention generally comprises contacting a sulfated solid oxide with a gas comprising hydrogen.
sutfide at conditions effective to produce elemental sulfur;.the gas typically further compdslng no oxygen.
In one particular embodiment there is provided a process for the conversion of hydrogen sulfide to elemental sulfur, the process comprising:
(a) introducing a feed gas comprising hydfogen sulfide into a first reactor comprising a suifated sofid oxide sorbent, the sorbent further comptising a catalytic oxidation promoter, wherein the feed gas Is contacted with the sulfated solid oxide sorbent under conditions suffidenf to convad the hydrogen sulfide and sulfated solid oxide into a product mixture Comprising a first vapor phax prodctc;t and a solid phase product, the rate of. air addition being controlled by the temperature of the sorbent, the. first %iapor. phase pfoc-luct- comprising elemental sulfur vapor, water vapor and sulfur diexide, the solid phase prWuct oomprising desutfated solid oxide, the frst vapor phase pnoduct being passed from the firat reactor a" with unreacted hydrogen suifide as an effluent, and at least a portion of the so5d phase product dekg retained In the f'sst reactor 2a (b) passing.the -eftiuent from step (a)- into a condenser operated under conditions sufficient to condense at least a portion of the elemental sulfur to liquid sulfur, wherein a iiquid sulfur pt+oduct is obtained and a second vapor phase product Is formed, the second vapor phase product cornprising sulfur and hydrogen suifide, the second vapor phase pmduct being passed from the oondenser;
(c) passing the second vapor ohase product from step (b) along with a source of oxygen Into a bumer operated under conditions sufficient to convert substantially all of the sulfur and hyrlrogen sulfide In the second vapor phase product from step (b) to a combustion product comprising sulfur oxides;
(d) passing the comtwstion product from step (c) into a second reactor comprising a sdid oxide sorbent under conditieons suffident to combine the sutfur oxides from step (c) with the so6d oxide sorbent In the second reactor, thereby producing a solid phase product and a treated vapor phase product, the vapor phase product comprising less than 5 ppm of sulfur oxides, the solid phase product comprising a sulfated. solid oxide sorbent, the treated vapor phase product being passed from the second reactor and at teast a portion of the solid phase product being retained In the second reactor, (e) discontinuing the flow of feed gas into the first reactor, (f) discontinuing the fiow of combustion product Into the second reactor;

(g) introducing the feed gas into the second reactor, wherein the feed gas Is contacted with the sulfated solid oxide generated in step (d) under conditions suffcient to convert the hydrogen sulfide and sulfated solid oxide into a product mixture comprising a third vapor phase product and a solid phase product, the thind vapor phase product comprising elemental sulfur vapor, water vapor, and sulfur dioxide, the solid phase product comprising desulfated solid oxide, the third vapor phase product being passed from the second reactor along with unreacted hydrogen sulfide as an effluent;
and at least a portion of the solid phase product being retained In the second reactor, (h) passing the effluent from step (g) into a condenser operated under conditions suft'ident to condense elemental sulfur to Iiquid suifur. wherein a liquid sulfur product is obtained and a fourth vapor phase product is fomned, the fourth vapor phase product comprising sulfur and hydrogen suifide, the fourth vapor phase product being passed from the condenser, (i) passing the fourth vapor phase product from step (h) along with a source of oxygen into a bumer operated under conditions sufficient to convert substantially all of the sulfur and hydrogen sulfide In the fourth vapor phase product to a combustion product comprising sulfur oxides;
and (i) passing the comtwstion product of step 01 into the flrst reactor under conditions sufficient to combine the sulfur oxides from step (e) with desulfated solid oxide In the first reactor, thereby pkoducing a sulfated soiid oxide and a treated vaporstream comprising less than 50 ppm of sdker oXdes.

2b A more spegfc embodiment. of this invenUon comprises introdudng a feed gas comprlsing hydrogen sulfide into a first reactor comprising a sulfated solid oxide, wherein the feed gas Is contacted with the sulfated solid oxide under conditions sufficient to oonvert the hydrogen sulfide and the sulfated solid oxide into a product mixture comprising a first vapor phase product and a solid phase product. This feed gas may be partially combusted in a pre-bumet.
Attemateiy, the feed gas may simuitaneousiy be contacted with air or another oxygen source and with the sulfated solid oxide.
Contact with H2S regenerates the sulfated solid oxide Hz.S. H2S is attractive because it Is availabie and can generate eiementai sulfur for recovery. But, as with some other regeneraticn gases, the reductive regeneration under H2S can be endothertnic. In some cases the endothenn may be so severe that it cools the bed off and shuts down the regeneration before It Is complete.
Probiems Involving endotherms arise more often If a low flow of highly concentrated H2S Is used, father than a dilute stream. Preheating the regeneration gas, as In the Instant invention, helps avoid .
endothennic probiems.

The first vapor phase product comprises elemental sulfur vapor, water vapor and sulfur dioxide, and the solid phase product comprises desulfated solid oxide. The first vapor phase product is passed from the first reactor along with unreacted hydrogen sulfide as an effluent, and at least a portion of the solid phase product is retained in the first reactor. The first vapor phase effluent is passed into a condenser operated under conditions sufficient to condense at least a portion of the elemental sulfur to liquid sulfur. thus producing a liquid sulfur product and forming a second vapor phase product. The second vapor phase product comprises sulfur and hydrogen sulfide. The second vapor phase product Is directed from the condenser along with a source of oxygen, such as air, into a bumer. The bumer is operated under conditions suffident to convert substantially all of the sulfur and hydrogen sulfide contained in the second vapor phase product to a combustion product comprising sulfur oxides and frequentiy containing excess oxygen. The coinbustion product is passed into a second reactor comprising a solid oxide. Thesecond reactor is operated under conditions sufficient to combine the sulfur oxides with the solid oxide, thereby producing a solid phase product and a treated vapor phase product. The treated vapor phase product typically comprises less than 50 ppm of sulfur oxides, and the solid phase product cwmprises a sulfated solid oxide. The treated vapor phase product Is passed from the second reactor and at least a portion of the solid phase product Is retained in the second reactor.
Figure 1 Illustrates the pmcess described above, without recycle to feed. For every 4 moles of HzS entering with the feed, roughly one. mole of 'SO3' In the fonn of sulfated sorbent, must be supplied in order to supply enough oxygen to react with the incoming H2S.
Three moles of the incoming HzS react with the sulfated sorbent to form elemental sulfur, according to the reaction shown in Figure 1. Ide.ally. the sulfur is captured by the condenser and removed from the process.
After the sulfate capacity of the sorbent has been exhausted, one more mole of H2S breaks through the fornnerly sutfated bed at the front of the process and is converted to SOZ
and S03 in the bumer.
This SOx is captured on the sorbent bed at the end of the process, in a sulfate form that may be described as MgOSO 3. At the end of a cyde, the bed positions are switched via valve changes.
It may be inefficient to supply all of the requin;d oxygen via sulfated sorbent, since that results in high amounts and/or rapid tumover of the sorbent. Sorbent cost is a major component of the overall process cost, and sorbent aging is directly related to cycling frequency. In this invention a porlion of the feed is combusted, converting some H2S to SO2. This SOz can react with HZS over the sulfated sorbent bed to fotm elemental sulfur plus water. Thus, not all of the oxygen is supplied by the sorbent. . .
Figure 2 shows an illustrative example. If 13% of the feed is combusted. the sorptiorVdesorption demand on the sorbent drops to 80% of the original demand, if half of the oxygen supplied in the form of SO2 via the precombustor is utilized to convert H2S to S plus H2). Thus, the sorbent amount and vessel sizes necessary might be decreased by 20%. Ideally, if a third of the feed was combusted, essentially all the sulfur could be extracted via the n:adion of 2 H2S with 1 S02 to form 3S and 21-120. However, that would leave no H2S left to regenerate the sorbent. This reacfion is difficult to ddve to completion in any event. Combustion of 10 to 30% of the feed is preferred. Figure 2 illustrates the addition of supplementary fuel. Heat exchangers may be optionally used to remove heat, if desired.
Further advantages of the precombustion scheme described here are that the effluent from the combustion can be supplied at a high temperature of approximately 1093 to (approximately 2000= to 2500 F). When mixed with the main flow of modestiy preheated feed, a temperature of around 648 C (1200 F), as required for effective regeneration of the sorbent bed, can be obtained. Furthermore, the total gas flow through the "suifated' bed is Increased, which can help supply heat for the endothetmic desorption pnmss. The effective concentrdtion of the-reduang H2S
(H2S remaining after reaction with SO2) is decreased which should also help in combating endotherms in the sorbent bed.
Because the reaction of H2S and S02 is typically equilibrium limited, and this equilibrium is particuiariy unfavorable at the preferred MOST temperatures of 593 to 648 C
(1100 to 1200 F), it is likely that some unconverted H2S and SOz wiii break through the initiai "suifated" sorbent bed. These sulfur species will be converted to SOx in the main bumer, and sorbed on the final MOST sorbent bed, increasing the load on the sorbent.
The sulfur recovery of the process may -be greatly enhanced by adding one or more low-temperature catatytic r eactors, such as a standard Claus reactor or a tower temperature MOST
sorbent bed, after the initiai sulfur condenser. as-shown In Figure 3. The cataiyst should be resisfant to activity loss via sulfation, since the gas mixture contacting it may be SOz-rich during part of the cycle. This may rule out conventionai alumina Claus catalyst. Titania-based catalyst may be prefemed. With each reactor or sorbent bed Is assodated a reheater and sulfur condenser. The reheat may be via heat exchanger by mbdng in hot gases, from eisewhere in the process or from a tocai bumer.
Figure 3 shows an iliustrative example, wkh part#ai feed combustion and a low-temperature catalytic reactor downstream of the initiai suthu condenser. If one-quarter of the feed Is combusted, the sorption/desorplion demand on the sorbent drops to 25% of the original demand, If all the oxygen supplied in the form of S02 via the precombustor is utilized to convert HZS to sulfur plus H20. Thus, the sorbent amount used and vessel sizes empioyed might be decreased by 75%.
Thus, a large decrease In the sorbent cost and/or decrease in frequency of regenerations may be obtained, at the price of Installing more equipment. The added equipment, however, is conventional and operated essentialiy at steady state.
Figures 4-6 aN employ direct air addition to the sulfated solid sorbent bed which is being regenerated, instead of using a pre-bumer as in Figures 1-3. This a simplified approach. A sorbent comprising a cataiytic oxidation promoter should promote H2S oxidation at temperatures over 538 C
(1000 F). Oxidation may also occur at temperatures below 538 C (1000 F). The sorbent bed, if containing such a promoter, will already be in the range of 538 to 704'C
(1000 to 1300 F) foiiowing sulfate adsorption, so it wili be preheated. Figure 4 illustrates one mode of controi, using a thennocoupie near the entrance to the sorbent bed in order to regulate air flow to achieve desired bed tempenature for regeneration, which for a sorbent comprising an oxidation promoter should be in the range of 482' to 760 C (900' to 14000F), preferably 583 to 704 C (1100 to 1300 F). Figures 4 and 5 illustrate the same situations as Figures 2 and 3, with the substitution of direct air addition to the sorbent bed instead of the use of a prebumer to partially combust the feed.
Generally, the amount of air added is suffidentiy low that enough H2S remains in the 5 stream to accomplish sorbent regeneration. At this point, it Is desirable to oxidize less than one-third of the H2S at this point, with 10 to 30% preferred.
The embodiment of Figure 6 differs from that of Figure 5 only in that it illustrates a post-bumer after the nsgenerating bed. In an H2S-rich stream. it may not be possible to add as much oxygen as desirable without driving the temperature so high in the bed that it might damage the sorbent. The remainder of the air could be added In the post-bumer, where higher temperatures may be allowed and where heat-removal means can be Incorporated to moderaWthe temperature in the bumer. In a Claus plant setting, this is the prefeRed means of regenerating MOST sorbent.
Treating sour gases in Exploration and Production applications has been identified as a promising application for MOST technology. A recent Engineering study, 'Economic applications for MOST Applications', by K.O. Kong, estimated a modest (10%) cost advantage for MOST
('Claustess' production of S, using 1-12S to regenerate sorbent) versus conventional technology (in which an add gas enricher, followed by Claus treatment, then selective amine absorption are employed) for an E and P situation In which the add gas contains much COz.
Conventional Claus fumaces have difficuky pnocessing such streams.
Figure 1 is a block flow representation of a process for producing elemental sulfur directly from a hydrogen suifide source typically having a relatively low hydrogen sulfide concentration and a higher concentration of carbon dioxide. In the embodiment of Figure 1, approximateiy one mole S03 must be deposited on the sorbent to react with 3 moles of incoming H2S In feed.
Figure 2 Illustrates a departure from Figure 1, wherein a portion of the c;ombustion product (oorrtaining SOI and S03, SOx) Is recyded to the feed gas to the sulfated solid sorbent. Thirteen percent (13%) of the feed stream is combusted, assuming reaction I goes halfway to completion.
0.53 S02 + 1.07 1-128 - 1.6S + 1.07 H20 (rxn 1) 0.8 S03 + 2.4 H2S +-- 32S + 2.4 H20 (rxn 2) Figure 3 illustrates the block flow process of Figure 2 with the added feature of a low temperature catalyst bed downstream of the sulfur condenser. Twenty-frve percent (25%) of the feed stream is combusted, assuming reacUon 1 goes to completion over the combined catalyst beds.
SOz + 2H2S 4-- 3S + 2 H2O (rxn 1) 0.25 S03 + 0.75 1-12S =-- S+ 0.75 HZO (r)n 2) Figure 4 illustrates the block flow process of Figure 2, with the change of partially combusting the feed gas directly in the sulfated solid sorbent bed rather than using a pre-bumer. Thirteen percent (13%) of the feed stream is combusted. assuming reaction I goes halfway to completion.
0.53 SO2 + 1.07 H2S ~-- 1.6S + 1.07 H20 (rxn 1) 0.8 803 + 2.4 HzS +- 3.2S + 2.4 H20 (rxn 2) Figure 5 illustrates the block flow process of Figure 3. with the change of partially combusting the feed gas directly in the sulfated solid sorbent bed rather than using a pre-bumer. Twenty-tive percent (25%) of the feed stream Is combusted, assuming reaction I goes to completion over the combined catalyst beds.
SOz + 2H2S - 3S + 2 H20 (rxn 1) 0.25 S03 + 0.75 H2S - S+ 0.75 HZO (rxn 2) Figure 6 illustrates the block flow process of Figure 5, with the change of the addition of the post-bumer downstream of the sulfated solid sorbent bed in order to oxidize breakthrough H2S
streams. Twenty-five (25%) of the feed stream is combusted, assuming reaction I goes to completion over the combined catalyst beds.
S02 + 2H2S ~-- 3S + 2 H20 (rxn 1) 0.25 S03 + 0.75 H2S ~-- S + 0.75 H20 (rxn 2) This invention relates to a process for the direct conversion of hydrogen sulfide to elemental sulfur. This solid oxide based process is useful to replace or use In conjunction with a Claus plant, a Claus tail gas unit and an acid gas enricher. A typical hydrogen sulfide conversion process includes the use of a hydrogen suifide gathering system, such as a solvent (e.g., amine) absorber/stripper system, followed by a Claus plant, which Is in tum followed by a Claus tail gas unit. In some cases, such as where carbon dioxide, and possibly other sulfur spedes, are present, and the hydrogen sutfide is available in low concentrations, the initial hydrogen suifide gathering system Is frequently foliowed by a second hydrogen sulfide gathering system or an acid gas enricher, such as a FiexsorbTu amine absorber/stripper system. As mentioned above, the process of the instant Invention converts hydrogen sulfide directly to elemental sulfur by contacting the hydrogen sulfide with a sulfated catalyst. An advantage of this invention is that the Claus plant, the Claus tail gas unit, and the acid gas enricher processes are not required to convert the hydrogen sutfide to eiemental sulfur aithough they may be present. This invention Is most useful to treat lean gas streams typically containing less than 50% H2S, specifically less than 25% H2S, more specifically less than 20% H2S
on a volume, molar or weight basis.
The catalytic functioning of dry solid oxides for applications involving the reduction of sulfur oxides to elemental sulfur and/or H2S, or the concentration of sulfur oxides for subsequent reaction in a downstream processing unit may be broadly typified by the reaction scheme illustrated below.
Solid Oxide + S02 + 1/2 02 -+ Solid Oxide0SO3 (114) Soitd Oxk1eeSO3 + Reduoing Gas -+ Removed Sulfur (V) Species + "Reduced Solid Oxide"
"Reduced Solid Oxide" + 02 -+ Solid Oxide (VI) Reaction IV indicates the oxidative reaction of SOz, which is thought to occur via the oxidation of sulfur oxide mixtures (i.e., SO2 and S03) and the combination of the 6% with the solid oxide on the catalyst. In the open literature, this has been called "Cataiyst Sulfation," and after the combination with the solid oxide, the sulfur oxide-containing material Is commonly called a "Sulfated Cataiyst." As used herein, "suifation" Is intended to refer both to chemlsorption, such as would include sorption of SO3, and physisorption, such as might be depicted MeS03, where M is the sorbent.
Reaction V involves the reduction or regeneration of the so-called sulfated catalyst. The sutfur oxides are reteased primariiy as a mixture of SOz, elemental sulfur, 1-12S, and other sulfur containing compounds. The reaction also leads to a solid oxide which reacts with oxygen and thus is termed a "Reduced Solid Oxide." A partial list of gases generally considered as reductants suitable to induce the release of the sulfur compounds are hydrogen containing streams (e.g., steam reformer or naphtha reformer hydrogen, catalytic hydrogenation unit purge streams, etc.), and hydrocarbons such as propane.
Reaction VI represents the oxidative calcination of the "Reduced Solid Oxide."
It may be the reaction of air or other suitable oxidizing media with the reduced solid oxide, and yields a calcined solid oxide which may undergo more cycles of reactions IV through VI above. If desired, reaction VI
may be combined with reaction IV to eliminate one processing step.
Dry sulfur oxide removal processes have typically experienced iimited sulfur oxide loading capability. A process recently disdosed in commonly assigned U.S. Patent No.
5,229,091 to Buchanan et al., Increases the loading capability of the solid oxide significantly, up to 60 wt.% S03 on solid oxide.
A generalized representation of some of the readions believed, without intending to be bound thereby, to be involved in the process of the instant Invention is given below.
Soiid Oxide*SO3 + 3H2S 4 "Reduced Solid Oxide" + 4/x SX + 31i20 Solid OxidefaS03 + 1=12S 4 "Reduced Solid Oxide" +% + SOz + H20 The hydrogen sulfide acid gas contacts the sulfated solid oxide and produces a 75%
seiectivity to eiemental sulfur. The products of this set of reactions are primarily elemental sulfur, water vapor, and sulfur dioxide, however, side reactions leading to other products are aiso possible.
Any diluent compounds in the acid gas other than hydrogen sulfide, such as hydrocarbons, nitrogen, carbon dioxide and carbon monoxide, among others, typically pass through the sulfated catalyst bed unreacted, react with one or more of the other compounds present, possibly to produce additional sulfur, or aid in the production of sulfur compounds from the solid oxide. The heat capacity of these diluent compounds also acts as a source of heat for the endothertnic reactions described above.
A process for the direct conversion of hydrogen sulfide to elemental sulfur is illustrated In Figure 1. A feed gas comprising hydrogen sulfide is directed through line 210 over at least one solid oxide bed 220, where the gas passes over a sulfated solid oxide operated at conditions effective to altow removal of suifur compounds from the sulfated solid oxide. According to the method of this invention, the feed gas typically contains no measurable oxygen at the point that it passes over the sulfated solid oxide. As described above, the hydrogen sulfide reacts with the sulfated solid oxide to produce elemental sulfur in a vapor phase, among other components. The stream comprising the elemental sulfur is then directed from the solid oxide bed 220 through line 225 to a sulfur condenser 230. l.iquid sulfur is condensed In the sulfur condenser 230, and is withdrawn through line 235 and a vapor product Is withdrawn through line 240. The vapor product passing through line 240 is directed to a bumer 245 where oxidizable components are combusted with air introduced through line 250 and, optionaily, combustible fuel, such as natural gas, introduced through line 255. The gaseous combustion products comprising sulfur oxides are directed from the bumer 245 through line 260 to a bed of generally unsulfated solid oxide 265, operated at conditions such that sulfur oxides are chemisorbed onto the solid oxide. Treated gas comprising a small amount, e.g., typically less than 50 ppm sulfur oxides, is discharged from the bed of partially or completely unsulfated solid oxide 265 through line 270.
Typical conditions for the contact of the sulfated solid oxide with the hydrogen sulfide containing feed gas indude a temperature of 482' to 760=C (900' to 1400=F), spedfically 593' to 704'C (1100' to 1300'F), and a pressure of typically 0.10 to 10 atmospheres,.
specificaiiy 0.5 to 5 atmospheres. Lower contact temperatures tend to produce higher percentages of elemental sulfur in the product gases. The gas stream is typically passed over the solid oxide at a gas hourly space velocity (GHSV) of 10 to 20,000 hr', spedfically 20 to 10,000 hr', more specifically 50 to 1,000 hr'.
The feed gas stream may also contain carbon dioxide, carbon monoxide, sulfur dioxide, and water vapor, among other components that are typically present in acid gas streams.
The feed gas may be heated to the desired temperature directly or indirectly as desired, for example, the feed gas may be heated In a fired heater orin a=heat exchanger.
Altematively, at least part of the feed gas may be partially combusted or combusted substoidtiometricaliy using a soune of oxygen, such as air, and if needed, fuel, such as natural gas or fuel gas, to heat the feed gas to the desired temperature. Also, the feed gas may be heated to the desired temperature by combusting fuel with a source of oxygen and then combining the hot combustion products with the hydrogen suifide containing feed gas. The feed gas may also be heated using a combination of the above descr9bed methods. The total amount of feed gas needed is that which provides at least 75 to 1000%
of the stoichiometric reducing gas requirement and 75 to 1000% of the thermal gas requirements at the desired temperature. The thermal requirement of the hydrogen suifide containing feed gas is that volume required to achieve and maintain the temperature desired for contacting the feed gas with the solid oxide. it should be noted that the reaction of hydrogen sulfide with the sulfated solid oxide according to the method of this invention is typically endothermic. Exothermic reactions involving hydrogen sulfide to produce elemental sulfur, e.g., partial oxidation, are possible, but are not induded as part of this invention.
The feed gas flow should be discontinued from the bed when the desired amount of sulfur compounds have been removed from the bed, for example after removal of 25%, specificaliy 33%, more specifically 50%, still more specifically 75%, and most specifically all or almost all of the sulfur compounds from the bed. A possible indicator of this point would be the temperature of the bed or of the exit gas. Typically the bed will cool off during the desulfation of the solid oxide. Useful temperature indicators may include the temperature of the bed or of the exit gas; a temperature differential between the temperature of the bed or the exit gas at the time of Introduction of feed gas to the bed and at some later time; a rate of change in the temperature of the bed or the exit gas; or some combination of these indicators.
The sutfur condenser is typically operated at a temperature of 121' to 177"C
(250 to 350'F) and a pressure of 0.1 to 10 atmospheres to condense the elemental sulfur without condensing water.
Products from the sulfur condenser include elemental sulfur and a vapor stream. The vapor stream comprises at least one of elemental sulfur, sulfur dioxide, hydrogen suliide and water vapor, among other components.
The temperature in the bumer mentioned above is typically held within the range of 538' to 1371 C (1000 to 2500 F), and, preferably, the bumer is operated to maintain an atmosphere effective to convert substantially all of the sulfur compounds In the gas stream to sulfur oxides (SN.
Typically, the bumer converts at least 85%, specifically at least 90%, more specifically at least 9596.
most specifically at least 99% of the sulfur compounds in the vapor stream to sulfur oxides. This conversion level Is referred to herein as substantially all of the sulfur compounds. The bumer Is typically operated at a pressure of 0.1 to 10 atmospheres and contains an excess oxygen concentration of 0.1 to 10 mo1.96, specifically 2 to 4 moi.96 excess oxygen, and more specifically sufficient oxygen to satisfy the requirements of equations (IV) and (VI) as described above (e.g., at least one-half mole of oxygen per mole of S02 present). The bumer may also comprise one or more catalysts effective for oxidization of sulfur compoundsto sulfur oxides.
Supplemental fuel may be added to the bumer to maintain the desired reaction temperature. This supplemental fuel may be any commonly available combustible fuel, e.g., natural gas, refinery or petrochemical fuel gas, solid, gaseous or liquid hydrocarbons.
Other feed streams which contain at least one sulfur compound may also be introduced into the bumer, such as gas streams that have low HzS concentrations, contain substantial amounts of hydrocarbons, or contain other sulfur compounds. These other feed streams are fnequently low volume streams that are. produced as byproducts of other treating or gas handling pmcesses, examples of these streams include SO2 containing streams and mercaptan containing streams among others. Typically, according to the method of this invention, the total amount of sulfur contained In these other feed streams is less than twice the total amount of sulfur In the feed gas, specifically less than the amount of sulfur in the feed gas, more specifically less than half the amount in the feed gas, most specifically less than one-quarter the total amount of sulfur in the feed gas.
The solid oxide, mentioned above, which Is at ieast partially unsulfated and which contacts the sulfur oxides produced in the bumer, Is typically operated at a temperature of 20411 to 9829C
(4000 to 1800'F), specifically 482' to 760'C (900' to 1400'F), more specificaily 538' to 7040C (1000' to 1300'F), a pressure of 0.1 to 10 atmospheres, spedfically 0.5 to 5 atmospheres, with an inlet oxidizing agent or oxygen (O2) concentration of at least one-half mole per mole of S02 in the vapor stream, and at a flow rate sufficient to provide a gas houriy space velocity (GHSV) of 500 to 20,000 hr ', spedfically 3,000 to 5,000 hr'. The solid oxide Is operated under conditions effective to remove substantially all of the sulfur oxides from the vapor stream. The term "substantially atl" is used herein to Fefer to removal of at least 85%, spedfically at least 90%, more specifically at least 95%, most specifically at least 99%, of the suifur oxides in the vapor stream. According to the method of this invention, it is possible to produce a treated gas containing less than 50 ppm SOx, specifically less than 10 ppm SO, more specifically less than 5 ppm SO1, most specifically less than 1 ppm SOx. An additional benefd of operating within these parameters is that.any carbon monoxide in the vapor 5 stream Is typically converted to carbon dioxide which can be released Into the atmosphere.
When sutfur oxide breakthrough is detected or some other switch criteria has been met, the flow of the sulfur oxide containing vapor stream across the solid oxide is stopped, and the feed gas stream comprising hydrogen sutfide is directed over the solid oxide to release at least a portion of the sulfur compounds from the solid oxide. Suitable means may be used to detect sulfur oxide 10 breakthrough, such as a SiemenUltramat'm 22Pinfrared analyzer or comparable equipment, or suitable means may be used to determine the desired switchpoint, such as a timer or a total flow integrator,:which means may also comprehend the sulfur,oxide concentration of the vapor stream.
Also, similar to the system described above for determining when to stop feed gas flow, temperature of the solid oxide bed or the gas leaving the solid oxide bed may be used as the switch criteria. Here, the sulfation reaction is typically exothermic, so the bed 4emperature may increase as the reaction continues.
This Invention can be used to advantage with the catalyst being disposed In any conventional solid catalyst system, in ebullating catalyst bed systems, in systems which fnvolve continuously conveying or circulating catalyst from one bed of solid oxide to anothar.
fixed bed systems and the like. Typical of the circulating catalyst bed systems are the conventional moving bed and fluidized bed reactor-regenerator systems. Both of these circulating bed systems are conventionally used in hyrfixar:bon conversion, e.g., hydrocarbon cracking.
The form and the partide size of the solid oxide are not critical to the present invention and may vary depending, for example, on the type of solid catalyst system employed. Non-limiting examples of the.shapes of the solid oxide for use in the present invention include balls, pebbles, spheres, exhudates, channeled monoiiths, honeycomb monoliths, microspheres, pellets or structural shapes, such as lobes, pills, cakes; powders, granules, and the like, formed using conventional methods, such as extrusion or spray drying. Where, for example, the final particles are designed for use as a fixed bed, the partides may preferably be formed Into particles having a minimum dimension of at least 0.0254 cm (0.01 inch) and a maximum dimension of up to 1.27 or 2.54 cm (one-half to one inch) or more. Spherical partides having a diameter of 0.0762 to 0.635 cm (0.03 to 0.25 Jndt), preferably 0.0762 to 0.381 cm (0.03 to 0.15 ind-), are often useful, especially In fixed bed or moving bed operations. With regard to fluidized systems, It Is preferred that the major amount by weight of the partides have a diameter in the range of 10 microns to 250 microns, more preferably 20 microns to 150 microns.
The solid oxide useful in this invention typically has a surface area (by the conventional B.E.T. method) In the range of 5 m'/gm. to 600 m2/gm., specifically 15 m2/gm.
to 400 m2/gm., and more specifically 20 m2/gm. to 300 mZ/gm.

Non-limiting examples of suitable solid oxides for use in the present invention include the porous solids, alumina, silica, silica-alumina, natural and synthetic zeolites, adivated carbon, spinels, days and combinations thereof. Gamma (K) alumina, chi-eta-rho (X, R, P) alumina, delta (a) alumina, and theta (0) alumina are particularly useful as solid oxides and supports In the present invention because of their high surface areas. While alpha (a) alumina and beta (p) alumina can be used as solid oxides, they are not as effective as gamma, chi-eta-rho, delta and theta alumina. One or more oxides of other metals can also be used as solid oxides, either alone or In combination with alumina or as spinels, such as, for example, bismuth, manganese, yttrium, antimony, tin, Group IA
metals, Group IIA metals, rare earth metals, and combinations thereof.
Magnesium aluminates are particularly useful as solid oxides. These may be magnesium or aluminum rich with magnesium aluminate spinels prefemad. Lanthanum and cerium are preferred rare earth metals. Naturally occurring rare earths, such as In the form of baestenite, are also useful solid oxides. Elemental copper or copper compound solid oxides can also be used. The copper oxide can be cuprous oxide (Cu20) and/or cupric oxide (CuO). Other copper compounds can be used, such as copper pl) sulfate, copper (il) acetate, copper (11) foffnate, copper (II) nitrate and/orcopper (11) chloride. The solid oxide can also be a blend/mixture of high density and low density rnaterials, such as of the above-identified metal oxides.
Aiso;'a metal or metal oxide may be depoaited on the solid oxide or may be used alone. The metal or metal oxide part of the solid oxide can be supported; carried and held on a refractory support or carrier material which also provides part of the solid oxide. The support controls the attrition and surface area characteristics of the solid oxide. The support preferably has a surface area greater than 10 mZ/g and most preferably from 20 m2/g to 500 m2/g for best results. Su'itable supports Include, but are not limited to, silica, alumina, silica-alumina, zirconia, titania, thoria, kaolin or other days, diatomaceous earth, boria, and/or mullite: The support can comprise the same material as the-metal or metal oxide part of the solid oxide.
The solid oxide may be combined with a matrix or binder, induding the supports mentioned above, preferably alumina. The solid oxide may also be used without a matrix or binder. The support matetial may also be present in the bed containing the solid oxide in particles separate from the particles of solid oxide. Also. optionally present in the bed containing the solid oxide may be partides of an inert material, wherein the term "inert" Is used herein to represent materials that are tess effedive than the solid oxide when used in the sulfation/desulfation cydes described herein.
The solid oxide can be impregnated or otherwise coated with at least one oxidizing cataiyst or promoter that promotes the removal of nitrogen oxides, the oxidation of S02 to S03 In the presence of oxygen, and the removal of the sulfur compounds from the solid oxide. It is believed that SO3 Is more readily combined with the solid oxide than SO2. One useful catalyst is ceria (cerium oxide). Another useful catalyst Is platinum. Yet another useful catatyst is vanadium. Other catalytic metals, both free and In a combined form, preferably as an oxide forrn, can be used, either alone or in combination with each other or in combination with ceria and/or alumina, such as rare earth metals, metals fmm Group VIII of the Periodic Table, chromium, vanadium.
rhenium, tungsten, silver, and combinations thereof. The promoter can comprise the same material as the solid oxide.
An even distribution of the promoter is preferred for best results and to minimize solid oxide erosion.
Useful Group IA metals include lithium, sodium, potassium, rubidium, and cesium. Useful Group IIA metals indude magnesium, calcium, strontium, and barium. Useful Group VIII metals are the Group VIII noble metals (the platinum family of metals) induding ruthenium, rhodium, palladium, osmium, iridium, and platinum. Also useful are Group IB metals, Group IIB
metals, and Group VIA
metals. The rare earth metals are also useful and are refened to as the lanthanides. Suitable rare earth metals include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. More preferably, the promoter may be selected from the rare earth metals, the platinum group metals and mixtures thereof. Particularly good results are achieved when the promoter is cerium and/or platinum, with cerium giving outstanding results.
A second promoter, if present, may be selected from the metal or the metal oxide form of iron, nickel, titanium, chromium, manganese, cobalt, germanium, tin, bismuth, molybdenum, antimony, vanadium and mixtuces thereof. More preferably, the second promoter;is selected from iron, nickel, cobalt, manganese, tin, vanadium and mixtures thereof.
Additional metals may be also incorporated Into the solid oxide. For example, the solid oxide may include small or trace amounts of additional metals or metal oxides, such as lanthanum, iron, sodium,: calcium, popper, and titanium.
The specific amounts, of the promoters included in the solid oxide, if present at all, may vary widely. Preferably, the first promoter Is present in an amount between 0.001 to=20% by weight, cakxtlated as elemental metal, of the solid oxide, and the seeond promoter Is present in an amount between 0.001 to 10% by weight, calculated as elemental metal, of the solid oxide. Preferably, the solid oxide Includes 0.1 to 20%, more preferably 0.2 to 20%, and still more preferably 0.5 to 1596, by weight of rare earth metal, calculated as elemental metal. Of course, if a platinum group metal is employed in the solid oxide, very much reduced concentrations (e.g., in the parts per thousand to parts per million (ppm) range) are employed. If vanadium is included as the second promoter, it is preferably present in an amount of 0.01 to 7%, more preferably 0.1 to 5%, and still more preferably 0.5 to 2% by weight of vanadium, calculated as elemental metal.
The promoters may be associated with the solid oxide using any suitable technique or combination of techniques; including, for example, impmgnation, coprecipitation, ion-exchange and the like, well known in the art. Also, the promoters may be added during synthesis of the solid oxide.
Thus, the promoters may be an integral part of the solid oxide or may be in a phase separate from the solid oxide (e.g., deposited on the solid oxide) or both. These metal components may be associated with the solid oxide together or In any sequenee or by the same or different association techniques. Cost considerations favor the preferred procedure in which the metal components are associated together with the solid oxide. Impregnation may be carried out by contacting the solid oxide with a solution, preferably an aqueous solution, of the metal salts.
It may not be necessary to wash the solid oxide after certain soluble metal salts (such as nitrate, sulfate or acetate) are added. After impregnation with the metal satts, the solid oxide can be dried and calcined to decompose the satts, forming an oxide in the case of a nitrate, sulfate or acetate.
The above-mentioned solid oxides are generally discussed in U.S. Patent No.
4,692,318 to Tolpin et ai.
In one general aspect, the present invention may Involve use of a solid oxide which is repn3sented by the following empirical formula MgmAlyO=
where the atomic ratio of x to y ranges from 0.1 to 10, and where z is at least as required to accommodate the valances of the Mg and Al components of the solid oxide. This solid oxide may have the spinel structure and may contain at least one of the promoters described above.
Metal-containing spineis according to the above empirical formula tiiat are useful in the present invention include the alkaline earth metal spinels, in particular magnesium (first metal) and aluminum (second metai)-oontaining spinel. Other alkaline earth metal ions;
such as calcium, strontium, barium and mixtures thereof, may replace all or a part of the magnesium ions. Similarly, other metal Ions, such as iron, chromium, vanadium, manganese, gallium, boron, cobaft, Group 18 metals, Group IV metals, Group VA metals, the platinum group metals, the rare earth metals, Te, Nb, Ta. Sc, Zn, Y, Mo, W. Ti, Re, U, Th and mixtures thereof, may replace all or a part of the aluminum ions, preferabiy only a part of the aluminum tons.
-The metat:containing spinels useful in the pnssent'inventioh inay be derived from conventionai and well known-sources. For example, these spineis may be naturaNy occunring or may be synthesized using techniques well known In the art. Thus, a detailed description of such techniques Is not induded herein. A particulariy useful process forpn3paring the solid oxide Is presented In U.S. Patant No. 4,728,635.
The Group IA, IIA. IB metals, Group 1IB metals, Group IV metals.-Group VA
metals, Group VIA. and Group Vlil metals refemed to herein are those listed In the Periodic Table of the Elements In the llandbook of Chemistro and Phvsics (61st Edition).
Free magnesia and/or alumina (i.e., apart from the alkaline earth metal containing spinel) also may be induded in the present solid oxide, e.g., using conventional techniques. For example, in one embodiment, the solid oxide preferably includes 0.1 to 30% by weight of free magnesia (calculated as MgO).
As mentioned above, potential solid oxides are magnesia rich, magnesium aluminate spinels.
One example of such a spinel is a commercial magnesia rich, magnesium aiuminate spinel cxtntaining 0 to 100 wL% excess magnesia, 5 to 15 wt.% cerium, and 1 to 5 wt.96 vanadium. These solid oxides are substantially descxibed in U.S. Patent Nos. 4,790,982 to Yoo et al.; 4,472,267 to Yoo et ai.; and 4,469,589 to Yoo et al. In general, the magnesium aluminate spinels useful in the present invention may be prepared by methods which are conventional and well known in the art.
Figure 2 illustrates precombustion of the feed. Figure 1 is modified so that a portion of the feed gas of line 210 is diverted to a pre-bumer 205 through line 200, when: it is combusted with air (line 202) and additionai fuel (such as natural gas) is added pine 204) prior to retuming to line 210 through line 207.
Figure 3 Illustrates the block flow process of Figure 2 with the added feature of a low temperature catalyst bed downstream of the sulfur condenser 230. Vapor product is withdrawn through Gne 240, is reheated in vessel 241 and passes through low temperature catalyst bed 242 for further combustion. Sulfur Is condensed out In vessel 244 and removed through line 243. Vapor then passes to tx,mer 245 riu+ough hne 246. The low temperature catalyst bed may be a standard Claus reactor or a iower temperature MOST sorbent bed.
Figure 4 employs direct air addiiion to the sulfated solid sorbent bed which is being regenerated. Air enters the sorbent bed through line 205. The flow rate of the air is regulated by a thermocouple within the sorbent bed. Fuel gas may be added dirediy to the sorbent bed through line 213. A portion of the fuel may bypass the sorbent bed through line 212 and enter line 225, for comtwstion downstream. The rest of the process is the same as that iiiustrated In Figure 1.
Figure 5 Illustrates the situation of Figure 3, with direct air addition to the sorbent bed (as shown In Figure 4) rather=than the use of a prebumer .
Figure 6 illustrates a post-bumer following the solid sorbent bed being regenerated. Fuel gas partialiy combusted In the solid sorbent bed (as depicted In Figures 4 and 5) enters a post burner 234 through iine 225: Additional-airis added through line 231 arld-additidnal"fuefis added througb Ns 232. Vapor exits the post-burrt6r 234 through line 233 and sulfur fs oondertsect out in vessel 230.
20. Condensed sulfur is. removed- throuph Nne 235. Vapot is withdraMn through iine 240, isrehealed in vessef 241 amd passed to low temperature catalyst bed 242 thnough iine 238 for hrruw vombusion.
Vapor eails bed 242 through line 236 and sulfur is condensed out In vesset 244. The condensed sulfur Is removed thnwgh line 243 and the vapor passes through Nne 246 to bumer 245,whene oxidizable components are combusted with air entering through line 250.
Additional tuel (such as natural gas) may be added through line 255. Gaseous combustion products comprising sWfur oxides are directed through line 260 to generally unsulfated solid oxide bed 265, operated at conditions such that sulfur oxides are chemisorbed onto the solid oxide.
Treated gas is dischatged from the bed 265 through line 270.

Claims (4)

1. A process for the conversion of hydrogen sulfide to elemental sulfur, the process comprising:
(a) introducing a feed gas comprising hydrogen sulfide into a first reactor comprising a sulfated solid oxide sorbent, the sorbent further comprising a catalytic oxidation promoter, wherein the feed gas is contacted with the sulfated solid oxide sorbent under conditions sufficient to convert the hydrogen sulfide and sulfated solid oxide into a product mixture comprising a first vapor phase product and a solid phase product, the rate of air addition being controlled by the temperature of the sorbent, the first vapor phase product comprising elemental sulfur vapor, water vapor and sulfur dioxide, the solid phase product comprising desulfated solid oxide, the first vapor phase product being passed from the first reactor along with unreacted hydrogen sulfide as an effluent, and at least a portion of the solid phase product being retained In the first reactor;
(b) passing the effluent from step (a) into a condenser operated under conditions sufficient to condense at least a portion of the elemental sulfur to liquid sulfur, wherein a liquid sulfur product is obtained and a second vapor phase product Is formed, the second vapor phase product comprising sulfur and hydrogen sulfide, the second vapor phase product being passed from the condenser, (c) passing the second vapor phase product from step (b) along with a source of oxygen into a burner operated under conditions sufficient to convert substantially all of the sulfur and hydrogen sulfide in the second vapor phase product from step (b) to a combustion product comprising sulfur oxides;
(d) passing the combustion product from step (c) into a second reactor comprising a solid oxide sorbent under conditions sufficient to combine the sulfur oxides from step (c) with the solid oxide sorbent In the second reactor, thereby producing a solid phase product and a treated vapor phase product, the vapor phase product comprising less than 5 ppm of sulfur oxides, the solid phase product comprising a sulfated solid oxide sorbent, the treated vapor phase product being passed from the second reactor and at least a portion of the solid phase product being retained in the second reactor;
(e) discontinuing the flow of feed gas into the fust reactor, (f) discontinuing the flow of combustion product into the second reactor, (g) introducing the feed gas into the second reactor, wherein the feed gas is contacted with the sulfated solid oxide generated in step (d) under conditions sufficient to convert the hydrogen sulfide and sulfated solid oxide into a product mixture comprising a third vapor phase product and a solid phase product, the third vapor phase product comprising elemental sulfur vapor, water vapor, and sulfur dioxide, the solid phase product comprising desulfated solid oxide, the third vapor phase product being passed from the second reactor along with unreacted hydrogen sulfide as an effluent;
and at least a portion of the solid phase product being retained in the second reactor;
(h) passing the effluent from step (g) into a condenser operated under conditions sufficient to condense elemental sulfur to liquid sulfur, wherein a liquid sulfur product is obtained and a fourth vapor phase product is formed, the fourth vapor phase product comprising sulfur and hydrogen sulfide, the fourth vapor phase product being passed from the condenser;
(i) passing the fourth vapor phase product from step (h) along with a source of oxygen into a burner operated under conditions sufficient to convert substantially all of the sulfur and hydrogen sulfide in the fourth vapor phase product to a combustion product comprising sulfur oxides;
and (j) passing the combustion product of step (i) into the first reactor under conditions sufficient to combine the sulfur oxides from step (e) with desulfated solid oxide in the first reactor, thereby producing a sulfated solid oxide and a treated vapor stream comprising less than 50 ppm of sulfur oxides.

2. The process of claim 1, wherein the effluent from step (a) passes into a post-burner for further combustion prior to entering the condenser of step (b).

3. The process of claim 1, in which the second vapor phase product of step (b) is passed to a catalytic reactor which is operated at a relatively lower temperature than the reactor of step (a) for additional sulfur removal prior to entering the burner of step (c).

4. The process of claim 3, wherein the catalytic reactor which is operated at relatively lower temperature is selected from the group consisting of a Claus reactor and a sulfated solid oxide sorbent bed.