DE2101901A1 - Process for reducing the total sulfur content of Claus exhaust gases - Google Patents

Description

SHELL IWTERWATIONALE RESEARCH MAATSCHAPPIJ N.V.,.-Den Hague, Netherlands

"Process for reducing the total sulfur content of Claus exhaust "

Priority: September 21, 1970, Netherlands, No. 7 013 902.

The process for the production of elemental sulfur from hydrogen sulfide by partial oxidation of the same by means of oxygen or an oxygen-containing gas, for example air, and subsequent reaction of the sulfur dioxide formed from the hydrogen sulfide with the remaining part of the hydrogen sulfide in the presence of a

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Catalyst is known as the "Claus Process". This method, this is common both in refineries and for reprocessing of hydrogen sulfide obtained from natural gases is used, is carried out in a Claus plant, which has a combustion chamber and then one or more Xata - lysator beds as well as one or more condensers, which are arranged therebetween and in which the reaction products are cooled, and wherein the separated liquid sulfur is obtained. The different stages of the process can be represented by the following reaction equations. be asked:

2 H ₂ S + 3 O ₂ > 2 H ₂ O + 2 SO ₂ '· (1) "

'4 H ₂ S + 2 SO ₂ ^ = ^> 4 H ₂ O + S / ^ (2>,

while the overall reaction proceeds according to equation (3): 6 H ₂ S + 3 O ₂ 4— _> . 6 H ₂ O + 6 / _x S _x (3).

At temperatures below 500 ° C, the symbol χ in the above Equation the value of 8.

Since the yield of elemental sulfur obtained, based on the hydrogen sulfide used, is not completely is quantitative, a certain proportion of unconverted hydrogen sulfide and sulfur dioxide is obtained from the Claus process removed. These gases are usually burned in a furnace. - During this process all of the "hydrogen sulfide." converted into sulfur dioxide - and then discharged into the atmosphere through a high chimney. the The amount of sulfur obtained depends to a certain extent on.

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the total number of catalyst beds used in the Claus process. In principle, 98 ^c jo sulfur can be recovered using three beds.

In view of the increasingly stringent requirements for reducing air pollution, there is a need to consider Working of Claus exhaust gases according to the aforementioned type is less desirable. In addition, the well-known method is with a certain loss of sulfur yield associated.

The present invention now provides a method that does enables the total sulfur content of Claus exhaust gases or, more generally speaking, of exhaust gases from processes from Claus-? Type to decrease drastically. As a result of the invention Process, among other things, the recovery of sulfur is improved considerably.

The inventive method for reducing the total sulfur content of Claus exhaust gases is characterized in that the exhaust gases mentioned, the except hydrogen sulfide and Sulfur dioxide also contains carbon oxysulfide and / or carbon disulfide, along with a hydrogen and / or carbon monoxide containing gas at a temperature of more than 175 ° C over a catalyst based on one or more metals from group VI and / or group VIII of the periodic table of the elements on an inorganic oxide support are passed so that the exhaust gases treated in this way subsequently or simultaneously with a solid catalyst for conversion of carbon oxysulphide and / or carbon disulphide in hydrogen sulphide and that finally

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-A-

using gases with a adsorbent or absorbent for removing hydrogen sulphide from said gases contacted earth v /.

In the context of the present invention, the term “Claus exhaust gases” is to be understood as meaning those remaining gases, v / ie they are obtained after the last catalyst bed of a Claus plant. It is common. Claus's method using "using two." Carry out catalyst beds, but a third catalyst bed is often used. In addition to hydrogen sulfide and Skin sulfur dioxide at a ratio of approximately 2: 1 the exhaust gases of this type also include sulfur, oxygen, nitrogen and small proportions of inert gases, if the Claus plant is operated with air, as well as water in the form of water vapor, carbon dioxide and small amounts of carbon monoxide. Dependent on of the process management of the Claus process and / or the The presence of hydrocarbons in the feedstock for the Claus process, the exhaust gases from the Claus plant can also be carbon oxysulphide and / or carbon disulfide in addition to the aforementioned compounds. The amounts can range from 0.05 to 0.5 vol .- $ in the case of carbon oxysulfide and from 0.05 to 0.4 vol .- $ in the case of carbon disulfide.

The method according to the invention can also work very well Exhaust gases from a Claus process applied v / ground, v / elcher with a deficit of oxygen, based on the stoichiometric required amount, is operated.

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After passing through the last catalyst bed and the associated condenser for recovery of elemental sulfur, the Claus exhaust gases normally have a temperature of 130 to 17O ⁰ C up. For the reduction stage over the catalysts based on metals of groups VI and / or VIII, the exhaust gases must, however, have a higher temperature, so that these exhaust gases must first be heated to a temperature of over 175 ° C. The Claus exhaust gases are preferably brought to a temperature in a range from 180 to 350 ^° C., in particular to a temperature between 200 and 300 ° C. "

The Temperature is ^one J0igerung to over 175 C also important in view of the presence of small amounts of elemental sulfur in the form of a mist in the exhaust gases. This undesirable sulfur mist disappears when the temperature rises above the sulfur dew point. It was also found that as E _r result of the temperature increase to over 175 C> preferably to about 180 ⁰ C, the presence of elemental sulfur in the gas phase does not exert an adverse effect on the catalytic activity of reaching for use the reduction catalyst.

After heating to a temperature of over 175 ° C, the Claus exhaust gases are passed over the catalyst together with hydrogen or a hydrogen-containing gas . ' Metals from Group VI and / or Group VIII passed to reduce sulfur dioxide to hydrogen sulfide. At the same time, elemental sulfur is converted into hydrogen sulfide. The reduction catalysts used can-.

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Be catalysts, the molybdenum, tungsten and / or chromium as a metal from group VI and / or preferably a Metal from the iron group, for example cobalt, nickel and / or iron as ^ metal from group VIII. The reduction catalyst used can also be a rhenium-containing catalyst, u.zw. independently of , whether rhenium is combined with a metal from Group VI and / or Group VIII. The rhenium can be used as a metallic element or in the form of an oxide or sulfide.

Aluminum oxide, silicon oxide, magnesium oxide, boron oxide, thorium oxide, zirconium oxide or a mixture of two or more other compounds can be used as inorganic oxide carriers. Suitable heduction catalysts for use in the process according to the invention are, for example, a Ni / Mo / Al ₀ 0_ catalyst or a Co / Mo / Al ₀ 0 catalyst.

The Group VI and / or Group VIII metal catalyst is preferably used in sulfided form. The sulphiding can beforehand using a suitable suIfidierungsmittel, for example by means of a mixture of hydrogen and hydrogen sulphide with 10 to 15% by volume of hydrogen sulphide content, be effected. However, it is also possible to use the catalyst in situ through the Claus exhaust gases to sulfide yourself.

-Containing gas treatment of the exhaust gases with a hydrogen and / or carbon monoxide is preferably carried out at a temperature in a range of 180 to 35O ⁰ C, preferably at a temperature between 200 and 300 ⁰ C.

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Although atmospheric pressure is mainly used, if desired, slightly increased pressures can also be provided. 'During the reduction, the Rauinge speed is advantageous to 500 to 10,000 Nl of Claus exhaust gases / 1 catalyst and Hour held.

As containing hydrogen and / or carbon monoxide Gas can advantageously be used a gas that contains both compounds, for example town gas, water gas, Synthesis gas, etc. It is also possible to use pure hydrogen or pure carbon monoxide. Suitable hydrogen-rich Gases or gas mixtures represent the exhaust gases of a catalytic reforming plant, that produced in a hydrogen plant Gas or - from a treatment system for "saturated raw-

(Oil)
gases from petroleum / obtained gas.

The hydrogen-containing gas preferably contains at least 20% by volume of hydrogen or an equivalent amount of hydrogen and / or carbon monoxide. The hydrogen or the hydrogen-containing gas is used in such an amount that the ratio of hydrogen to sulfur dioxide 3 J 1 bis 15 ί 1. This ratio is preferably at 5.5 ί 1 to 8 ί 1. ·

. The ranges mentioned remain the same if mixtures of reducing gases are used which contain hydrogen as well as carbon monoxide, or if only carbon monoxide is used, because the carbon monoxide is the hydrogen is equivalent. If elemental sulfur is also present in the Claus exhaust gases, the "required hydrogen and / or Amount of carbon monoxide also on elemental sulfur as a percentage of sulfur dioxide can be calculated.

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Under the expression 'tester catalyst for conversion from carbon oxysulfide and / or carbon disulfide to hydrogen sulfide " It is understood to mean "any solid material that catalyzes at least one of the following reactions can:

COS + H ₂ O (steam) H ₂ S + CO ₂ (1) COS . + E ₀ HpS + CO (2)

CS ₀ + H ₀ O (steam) H ₅ S + COS (5) ₂ + 2H ₂ O (steam). - ■ ■ ^ 2H ₅ S + CO ₂ (4-)

This catalyst is preferably selected from a group consisting of aluminum oxide, bauxite, activated clays, aluminum phosphate, Thorium oxide and magnesium chloride includes. Purely practical Oxide-based catalysts are preferred for purposes; Particularly preferred are catalysts made from aluminum oxide exist or contain it. The aluminum oxide can optionally be mixed with a highly concentrated aqueous alkali metal phosphate solution be impregnated, for example with a solution with a content of 30 or more wt .-% Tripotassium phosphate and / or dipotassium orthophosphate.

As a solid catalyst for the conversion of carbon oxysulfide and / or carbon disulfide according to one or more of the above reactions, aluminum oxide is preferred because this material has a very high conversion activity. This conversion activity increases with the specific surface area of the catalyst and therefore aluminum

oxide with a specific surface area of more than 50 m / g preferably used.

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The exhaust gases, which together with a hydrogen and / or Gas containing carbon monoxide over a group VI and / or group VIII metal-based catalyst have been passed, are subsequently or simultaneously brought into contact with said solid catalyst. The space velocity is advantageously from 500 to 30,000 Nl gas / l solid catalyst and hour set.

Simultaneous contact of the Claus exhaust gases with the two, catalysts is possible by using a mixture of Group VI and / or Group VTII metal catalysts " lysators with the solid catalyst in a fixed acceptor bed possible. On the other hand, the two catalysts can also in a single reaction vessel in the form of two or more separate catalyst beds are arranged, the height of each catalyst bed depending on the for the .Both catalysts desired space velocity of the gas is varied.

The exhaust gases with a hydrogen and / or carbon monoxide containing gas are preferably treated at a temperature of 200 to 35O ° C with the said solid Catalyst brought into contact. The method according to the present invention offers the great advantage that a Intermediate cooling or intermediate heating of the exhaust gases is not required. The Claus exhaust gases and the treated ones Exhaust gases can pass over the Group VI and / or Group VIII metal catalyst at substantially the same temperature

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passed and with the solid catalyst for the conversion of Carbon oxysulphide and / or carbon disulfide in contact to be brought.

• Under the expression "essentially the same temperature". should be understood that. " apart from temperature variations as they typically occur during normal operation, the average temperatures of the two catalysts by more than 30 different ⁰ Cvoneinander.

After being brought into contact with the solid catalyst, the treated exhaust gases are then treated with an adsorbent or absorbent to separate hydrogen sulphide brought in contact. For this purpose, common means can be used that chemically or hydrogen sulfide physically bind. These gowns can be divided into solid and liquid funds. A very suitable solid adsorbent is activated carbon, either as such or impregnated with solutions of chemical compounds that in turn are using Hydrogen sulfide can react. Other suitable solid adsorbents are the oxides of certain metals, for example iron oxide and zinc oxide. However, liquid absorbents are used more frequently. Well known absorbents of this kind are aqueous solutions of alkanolamines, amines, ammonia, alkali metal carbonates, and the smaller ones May contain amounts of other compounds such as arsenic trioxide, selenic acid and / or telluric acid, potassium phosphate, sulfalan etc. It is also possible to use solutions with oxidizing properties so that elemental sulfur is formed.

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These latter solutions generally consist of an absorbent for hydrogen sulfide, in which an oxidizing agent or catalyst is dissolved or else is suspended. Suitable oxidizing agents and / or catalysts are polythionates, iron oxide, thioaromatics, iron cyanide complexes, Permanganates or bichromates.

If activated charcoal is used as adsorbent, the adsorption is preferably conducted at a temperature of 20 bi 15O ⁰ C and a Eaumgeschwindigkeit 750-2000 Nl gas / l activated charcoal and hour performed.

The adsorbents or absorbents M used are preferably regenerable, so that they can be regenerated after loading, while the released gas containing hydrogen sulfide can be circulated and returned to the Claus plant, for example. The exhaust gases freed from sulfur compounds by the process according to the invention, which now consist predominantly of nitrogen and carbon dioxide and contain smaller proportions of hydrogen and traces of hydrogen sulfide, can be discharged into the atmosphere. If necessary, these exhaust gases can first be burned in the usual way before they are fed to the chimney.

The invention is explained in more detail in the following examples: "

Example 1: A synthetic Claus exhaust gas was over a sulfided Co / Mo / A ^ O, catalyst (3.2 parts by weight Co / 13.4 parts by weight Ko / 100 parts by weight Al ₀ O ₂ ) using a mixture of hydrogen and carbon monoxide

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became. The synthetic Claus exhaust gas, its sulfur dioxide content varied and about 0.1 vol% carbon oxysulfide was passed over the catalyst together with the reducing gas, with a space velocity of 1700 Nl gas / l catalyst and hour was observed. the The composition of the entire gas mixture was as follows:

SO «different

H ₂ 0.5 to 0.6% by volume

CO. 0.3 to 0.4% by volume

H ₂ S 1.2% by volume

COS 0.1 Vol .- #

N ₂ 'remainder

The catalyst was used in the form of particles 0.3 to 0.6 mm (30 to 50 mesh) in size.

The sulfiding of the catalyst was carried out at a maximum temperature of 375 ° C. and a pressure of 10 kg / cm using an H ₂ / H S gas mixture which contained 12.5% by volume of hydrogen sulfide. The temperature was gradually increased from room temperature to 375 ° C over a 4 hour period. After sulfiding, the catalyst was ^{cooled to 100 °} C., the gas mixture containing hydrogen sulfide being fed in without interruption; then only hydrogen gas was passed over the catalyst and finally the reduction of the Claus exhaust gases was started. The experiment was carried out at different reduction temperatures. The results are given in the following table:

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Tabel

S0 ₂ content in Reaction Conversion, % CO H ₂ + CO SO content Gas mixture,
Vol .-% (insert
material) temperature
⁰ C H ₂ 65 45 after reduction 0.17 222 34 100 50 <0.001 • 0.17 250 27 100 80 <0.001 0.36 250 63 100 94 <0.03 0.36 280. 89 <0.001

Example 2: A synthetic Claus exhaust gas, that, besides sulfur dioxide and hydrogen sulphide, also contains a small proportion of carbon oxysulphide and gaseous elementary elements Containing sulfur was measured at 220 C using the same sulfided Co / Mo / AlpO -, - catalyst as it was used for the experiments was used in Example 1, reduced with hydrogen. -'The exhaust gas was together with hydrogen over the said Catalyst with a Eaumge s speed it of 1400 Nl gas / • 1 catalyst and hour out. The composition of the entire gas mixture before and after the reduction is shown in the following table:

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Gas composition, before the reduction r
I.
after the reduction so ₂ 0.18. φ
<0.002. ^S 8 0.018. ^Η 2 1.5 0.8 • H ₂ O • 29. • 30 H ₂ S., 1.3. 1.7 COS 0.05 0.05 ^Ν 2 rest rest

The total conversion, "based on the" ^ close consumed Hydrogen, is 45%.

Example 1 3: A Claus exhaust gas that contains about 0.1% by volume Carbon oxysulphide in addition, to 0.17% by volume of sulfur dioxide and Containing 1.2% by volume of hydrogen sulfide, was combined with a hydrogen-containing gas via a sulfided Co / LIo / A ^ O ^ catalyst as used in Example 1 at a temperature of 222 ° C and with a space velocity of 1700 Nl gas / l catalyst per hour. The composition of the gas after the reduction was as follows:

COS
CO ₂
H ₂

1.3 vol # 1.3 vol #

1.5%

1.0% by volume 36% by volume remainder

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The gas having the above composition was then fed with two different space velocities at a temperature of 22J ⁰ C over a bed of activated alumina (particle size 0.3 "to 0.6 mm) to hydrolyze the carbonyl sulfide. At a space velocity of 20,000 The conversion of the carbon oxysulphide was 80%, while at a space velocity of 10,000 Nl gas / l catalyst and hour a conversion of 95 % was achieved.

Example 4: After the hydrolysis of the carbon oxy-

sulfides, the gas, which now mainly contained hydrogen sulfide as a sulfur compound, was brought into contact with activated carbon, which has a particle size of 3 eub> a specific surface of 1200 m / g, a density of 0.42 and a pore volume of 0 , 60 ial / g. The temperature was 13O ⁰ C • and the space velocity was set at 910 Nl gas / l of catalyst per hour. 98% of the hydrogen sulfide was adsorbed.

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Claims (20)

- 16 claims 1. A method for reducing the total sulfur content of Claus exhaust gases, characterized in that the exhaust gases mentioned, which apart from hydrogen sulfide and cchv / efeldioxyd also contain carbon oxysulfide and / or carbon disulfide, together with a gas containing hydrogen and / or carbon monoxide at a temperature of more than 175 ° C via a catalyst based on one or more metals from group VI and / or group VIII of the periodic system of the elements on an inorganic oxide carrier v / earth that the exhaust gases treated in this way then or "simultaneously with a solid catalyst for converting carbon oxysulphide and / or carbon disulphide into hydrogen sulphide and that I finally contact the gases with an adsorbent or absorbent for separating hydrogen sulphide from said gases. 2. The method according to claim 1, characterized in that the Claus exhaust gases at a temperature of 180 to 350 'C, preferably from 200 to 300 ° C., passed over the catalyst containing at least one metal from group VI and / or group VIII v / earth. 3. The method according to claim 1 or 2, characterized by gekenrizeichnet, that those containing a hydrogen and / or carbon nonoxide Gas treated exhaust gases at a temperature of? 0G "to 350 C with the solid catalyst for the conversion of carbon oxysulphide and / or carbon disulfide in hydrogen sulfide in Brought into contact. 209815/0875 4. The method according to claim 1 bio 3, characterized in that the treatment over the catalyst containing at least one group VI and / or group VIII metal or /. over the solid catalyst for converting COS and / or CS ₂ to hydrogen sulfide "takes place at essentially the same temperature. 5. The method according to claim 1 to 4, characterized in that that the gas containing hydrogen and / or carbon monoxide Contains at least 20 Vol .- ^ hydrogen. 6. The method according to claim 1 to 5, characterized in that the hydrogen-containing gas used is hydrogen ". 7. The method according to claim 1 to 6, characterized gekennzeiqhnet, that the gas containing hydrogen and / or carbon monoxide in an amount corresponding to a ratio of hydrogen to sulfur dioxide from 3: 1 to 15: 1 is used, 8. The method according to claim 1 to 7, characterized in that » that the catalyst contains molybdenum, tungsten and / or chromium and / or a metal from the iron group, in particular cobalt. 9. The method according to claim 1 to 8, characterized in ™ that aluminum oxide is used as an inorganic oxide carrier, 10. The method according to claim 1 to 9, characterized in that the at least one metal from group VI and / or group VIII containing catalyst in sulfided form is verv / ends. 11. The method according to claim 10, characterized in that · said catalyst sulphides in situ by means of the Claus exhaust gases will. 209815/0876 12. Method according to claims 1 to 11, characterized in that the Claus exhaust gases are passed over the catalyst at an Eaungeach speed of 500 to 10,000 Nl gas / l catalyst and hour. 13. The method according to claim 1 to 12, characterized in that that the solid catalyst for converting carbon oxysulphide or carbon disulphide into hydrogen sulphide from aluminum oxide, Bauxite, activated clays, aluminum phosphate, thorium oxide and / or magnesium chloride. 14. The method according to claim 13, characterized in that that aluminum oxide is used as a solid catalyst, which is mixed with a highly concentrated aqueous alkali metal phosphate solution is impregnated. 15. The method according to claim 1 to 14, characterized in that that the at least one metal of group VI and / or group VIII-containing catalyst and said further solid Catalyst come in a single reactor in the form of zv / ei or more separate catalyst beds for use. 16. The method according to claim 1 to 14 »characterized in that the treated exhaust gases over said solid catalyst with a room speed of 500 to 30,000 Π1 Gas / 1 catalyst and hour are passed. 17. The method according to claim 1 to 16, characterized in that that a solid adsorbent, preferably activated carbon, is used. 18. The method according to claim 17, characterized in that the gases with activated carbon at a space velocity of 750 to 2 GOO Nl gas / 1 activated carbon and hour at a temperature i Contact used:
209815/0875 door from 20 to 150 ⁰ C are brought into contact. 19. The method according to claim 1 to 16, characterized in that a liquid absorbent, preferably one
aqueous solution of an amine or alkanolamines is used. 20. The method according to claim 19, characterized in that
that the liquid absorbent also contains an oxidizing agent or catalyst, 209815/0875