DE2101901C2 - Process for reducing the total sulfur content of exhaust gases containing sulfur dioxide - Google Patents

Description

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 the following Reaction of the sulfur dioxide formed from the hydrogen sulfide with the remaining part of the hydrogen sulfide in the presence of a catalyst Is as the "Claus Trial" known. This; Process that is often used both in refineries and for processing hydrogen sulfide obtained from natural gases, is carried out in a Claus plant that has a ver combustion chamber and then an or comprises a plurality of catalyst beds and one or more condensers arranged therebetween and in which the reaction products are cooled, and wherein the separated liquid sulfur

ίο is won. The different stages of the process can be represented by the following reaction equations:

2H ₂ S ₊ SO ₂ - 2HjO + 2SO ₂ (D.

4 HjS + 2 SO ₃ = 4 H ₃ + 6 / ^ (2),

while the overall reaction according to equation (3)

runs: 6 H ₂ S + 3 O ₂ · =>

At temperatures below 500 ° C, the symbol χ in the above equation has the value 8.

Since the yield of elemental sulfur obtained, based on the hydrogen sulfide used, nichl Is completely quantitative, there will be a certain proportion of unreacted hydrogen sulfide and sulfur dioxide removed from the Claus process. These gases are usually burned in a furnace - in this process all of the hydrogen sulfide is In Sulfur oxide transferred - and then via a tall chimney vented into the atmosphere. The amount of sulfur obtained depends in a certain amount The dimensions depend on the total number of catalyst beds used in the Claus process. In principle, 98% sulfur can be recovered if three

Beds are used.

In view of the increasingly stricter requirements regarding the reduction of air pollution, a processing of Claus exhaust gases according to the the aforementioned type less desirable. About it hln off is the well-known method with a certain Associated loss of sulfur yield.

Although there are still other methods of removing sulfur compounds from gases known which however, they are not suitable for explaining this beforehand tert technical problem of the detoxification of Claus- Dissolve exhaust gases. So describes the DE-PS 11 11614 and DE-PS 9 77 734 the hydrogenating conversion of organic sulfur compounds such as mercaptans or Disulfides, e.g. B. Present in coke gas or olefin gases

so can. However, Claus exhaust gases do not contain any organic sulfur compounds.

According to AT-PS 2 77 283, sulfur dioxide can be separated from hot exhaust gases by it at Temperatures from 300 to 600 ° C via a vanadium lumen Catalyst conducts and it thereby In elemental Schwe fel converts.

In addition to sulfur dioxide, Claus exhaust gases also contain other sulfur components, such as entrained ones Sulfur droplets, and therefore cannot after the in of AT-PS 2 77 283 specified Arbeltswelse detoxified will.

In addition, the required temperature range is at the known method is relatively high and therefore unfavorable in terms of energy technology.

The present invention now provides a method which makes it possible to measure the total sulfur content of exhaust gases containing sulfur dioxide from processes of the Claus type to decrease drastically. As a result of the

21 Ol 901

According to the method according to the invention, inter alia. the yield significantly improved in recovered sulfur.

The method according to the invention for reducing the total sulfur content of exhaust gases containing sulfur dioxide by converting them into hydrogen sulfide and separating the hydrogen sulfide from the exhaust gases, in which the exhaust gases are passed over a catalyst based on one or more metals from VI. and / or VIII. Group of the Periodic Table of the Elements on an inorganic oxidic support (catalyst I). Is characterized in that the Claus exhaust gases at 180 to 350 ° C together with a hydrogen and / or carbon monoxide-containing gas Upper are directed to catalyst I, and to simultaneously or subsequently at 200 to 350 ⁰ C with a Kohlenoxlsulfld and / or carbon disulfide in the Hydrogen sulfide converting catalyst (Catalyst H) can be contacted.

In the context of the present invention, the term “Claus-AIigase” is to be understood as meaning those remaining gases as they are after the last catalyst bed a Claus plant can be obtained. It is common for Claus processes to use two catalyst beds to be carried out, but a third catalyst bed is also often used. In addition to hydrogen sulfide and Sulfur dioxide with a ratio of approximately 2: 1, the exhaust gases of this type also contain sulfur, Oxygen, nitrogen and small amounts of inert gases, the Claus plant tails operated with air, as well Water in the form of steam, carbon dioxide and small amounts of calcium monoxide. Dependent on of the process management of the Claus process and / or the presence of hydrocarbons in the The exhaust gases from the Claus plant can also be used as feedstock for the Claus process and / or Contain carbon disulfide in addition to the aforementioned compounds. The amounts can range from 0.05 to 0.5 vol -96 In the case of carbon oxysulphide and of 0.05 to 0.4% by volume in the case of carbon disulfide.

The method according to the invention can also be applied very well to exhaust gases from a Claus process which is operated with a deficit of oxygen, based on the stoichlometrically required amount will.

After passing through the last catalyst bed and the The Claus exhaust gases normally have associated condenser for the production of elemental sulfur a temperature of 130 to 170 ° C. For the reduction stage above the catalytic converter I, the exhaust gases but have a higher temperature, so that these exhaust gases initially to a temperature of over 175 ° C, about the dew point of sulfur. Therefore, in the method according to the invention, the Claus exhaust gases are brought to a temperature in the region of 180 brought to 350 ° C, preferably to a temperature between 200 and 300 ° C.

The temperature increase in the process according to the invention to at least 180 ° C. is also of importance Considering the presence of small amounts of elemental sulfur, In the form of a mist In the exhaust gases. This unwanted sulfur mist disappears by an increase in temperature above the dew point of sulfur. It was also found that as a result of the Temperature increase to at least 180 ° C, because ·? Elemental sulfur is not present in the gas phase detrimental effect on the catalytic activity of the used reducing catalyst exercises.

After heating to a temperature in the range of 180 to 350 ° C in the process of the invention the Claus exhaust gases are passed over the catalyst I together with hydrogen or a hydrogen-containing gas to convert sulfur dioxide into hydrogen sulfide to reduce. At the same time, elemental sulfur is converted into hydrogen sulfide. The used Reduction catalysts I can be molybdenum, tungsten and / or chromium as a metal from group VI and / or preferably a metal from the Elsen group, for example cobalt, nickel and / or Elsen as the metal from the Group VIII included.

The Reduktionskaialysator I used can also be a Be a rhenium-containing catalyst, independently whether rhenium is combined with a Group VI and / or Group VIII metal. The rhenium can be used as a metallic element or in the form of an oxy des or sulfides are present.

Inorganic oxide carriers can be aluminum oxide, silicon oxide, magnesium oxide, boron oxide, Thorium oxide, zinc oxide or a mixture of two or more of these compounds can be used.

Suitable catalysts I for the process according to the invention are, for example, a Nl / Mo / Al ₂ O ₃ catalyst or a Co / Mo / Al ₂ O ₃ catalyst.

This catalyst I was preferably used in sulphured form in the process according to the invention. That Sulphidene can be prepared beforehand by means of a suitable suIfIdIerungsmittels, for example by means of a mixture of Hydrogen and hydrogen sulfide with 10 to 15 vol .-% hydrogen sulfide content. It is however, it is also possible to use the catalyst in to sulfidleren in situ by the Claus release itself.

Although atmospheric pressure is mainly used, in the method according to the invention if desired, slightly increased pressures can also be provided. During the reduction, the space becomes Schwlndlgkelt advantageous hard to 500 to 10,000 Nl to Claus- Deliveries / l of catalyst I and hour held.

A gas can advantageously be used as the gas containing water and / or carbon monoxide which contains both compounds, e.g. town gas, Water gas, synthesis gas and the like. Pure hydrogen or pure carbon monoxide can also be used. Suitable hydrogen-rich gases or gas mixtures are the exhaust gases of a catalytic reforming plant, the Gas produced in or from a hydrogen plant a treatment plant represents rare saturated raw gases obtained from petroleum (petroleum).

The hydrogen-containing gas preferably contains at least 20% by volume of hydrogen or an equivalent Amount of hydrogen and / or carbon monoxide. Of the Hydrogen or the hydrogen-containing gas is in a used in such an amount that the ratio of hydrogen to sulfur oxide is 3: 1 to 15: 1. This The ratio is preferably from 3.5: 1 to 8: 1. The mentioned areas stay the same, though Mixtures of reducing gases are used, which contain both hydrogen and carbon monoxide, or if only carbon monoxide is used, because carbon monoxide is equivalent to hydrogen. When elemental sulfur is in the Claus exhaust is also available, the required hydrogen and / or calculate the amount of carbon monoxide on elemental sulfur as a percentage of sulfur oxide! will.

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The catalyst Ii used in the process according to the invention, the at least one of the following reactions can catalyze

COSh H ₂ O (steam) ^ H ₁ S + CO, u) ν H ₁ O (steam) ί = ώ 2 HjO (DampO ^ HjSh co (3) COS + H ₂ ί = ± H ₂ S + COS (4 y CS, + 1 H ₂ S + CO ₇ CS _{2 +}

is preferably made of alumina, bauxite, activated clays, Alumintumphosphat, thorium oxide and / o ^r magnesium chloride. For practical purposes, oxide-based catalysts are preferred, especially those made of or containing aluminum oxide. If desired, the aluminum oxide can be impregnated with a highly concentrated aqueous alkali metal phosphate solution, for example with a solution containing 30 or more percent by weight of tricallum phosphate and / or dicallum orthophosphate.

Aluminum oxide is preferred because of its very high conversion activity, which is related to the specific Surface area of the catalyst II increases. Aluminum oxide with a specific surface area of more than 50 mVg is therefore preferred: used.

The exhaust gases treated in the catalytic converter I are then or simultaneously with the catalytic converter II In Brought in touch. The space velocity is advantageously from 500 to 30,000 standard l gas / l catalyst II and hour set.

Simultaneous contact of the Claus exhaust gases with the two catalysts I and II Is by using a mixture of the two catalysts possible in a fixed acceptor bed. On the other hand, the two catalysts can also be used in a single one Reaction vessels are arranged in the form of two or more separate catalyst beds, wherein the height of each catalyst bed as a function of the space velocity desired for the two catalysts of the gas is varied.

The method according to the present invention offers the great advantage that intermediate cooling or reheating of the exhaust gases is not required will. The Claus exhaust gases and the resulting treated exhaust gases can be at substantially the same temperature passed over the catalyst I and brought into contact with the catalyst II.

The expression "essentially the same temperature" is intended to mean that, apart from Temperature fluctuations as they are common catfish during occur during normal operation, the average temperatures of the two catalysts are no longer than 30 ° C differ from each other.

After coming into contact with the catalytic converter II, the treated exhaust gases are then with brought into contact with an adsorbent or absorbent for the separation of hydrogen sulfide. to the usual means can be used for this purpose, which bind the hydrogen sulfide chemically or physically. These funds can be in solid and liquid Funds are divided. A very suitable solid adsorbent is activated carbon, either as such or impregnated with solutions of chemical compounds which in turn react with hydrogen sulfide can. Other suitable solid adsorbents are the oxides of certain metals, for example Elsenic oxide and zinc oxide. However, liquid absorbents are more commonly used. Well known Absorbents of this type are aqueous solutions from Alkanolamines ^ amines «, Ληΐίϊΐοηίύίι. AiWii ßiiten that also contain lesser amounts of other compounds like Ar ^ .nirfpxyd, S-isic acid and / or parturic acid contain! Ucru; - .; · ,, i <alfin: .- M; jsnti »i ader sulfolane.

Solutions with oxydiciend; -i properties can also be used can be used so that elemental sulfur is formed.

See these last-mentioned solutions; in general from an absorbent for hydrogen sulfide, in which an oxidizing agent or catalyst is dissolved or also suspended. Suitable oxidizing agents and / or catalysts are polythionates, iron oxide, thloaromatics, iron cyanide grains, permanganates or dichromates.

When activated carbon is used as the adsorbent, the adsorption is preferable to a Temperature of 20 to 150 ° C and a space velocity of 750 to 2000 Nl gas / l activated carbon and Hour carried out.

The adsorbents or absorbents used are preferably regenerable so that they can after Loads can be regenerated, while the released, Gas containing hydrogen sulphide circulated and returned to the Claus plant, for example can be.

The exhaust gases freed from sulfur compounds by the method according to the invention are now predominantly consist of nitrogen and carbon dioxide and smaller proportions of hydrogen and traces of hydrogen sulfide may be discharged into the atmosphere. Desired failures can be caused by these exhaust gases are burned in the usual catfish before they are fed to the chimney.

The invention is further illustrated in the following examples explained:

example 1

A synthetic Claus exhaust gas was reduced over a sulfided Co / Mo / AljOj catalyst (3.2 parts by weight Co / 13.4 parts by weight Mo / 100 parts by weight Al ₂ Oj), a mixture of Hydrogen and carbon monoxide was used. The synthetic Claus exhaust gas, the sulfur dioxide content of which varied and which contained approximately 0.1 % by volume of carbon oxysulphide, was passed over the catalyst together with the reducing gas, maintaining a space velocity of 1700 standard l gas / l catalyst per hour. The composition of the entire gas mixture was as follows:

The catalyst was in the form of particles with a 0.3 to 0.6 mm (30 to 5C mesh) size used.

The sulphidation of the catalyst was carried out at a maximum temperature of 375 ° C. and a pressure of 10 kg / cm ² using a H ^ HjS gas mixture which contained .2.5% by volume of hydrogen sulphide. The temperature was gradually increased from room temperature to 375 ° C. during a 4 hour bead. After the sulfiding of the catalyst "Ό ° C was cooled, said Schwefelwasswi; ioff containing gas mixture without interruption -ygeführi was, followed ^ HU urde ₁ H" sserstoffgas escort over the catalyst una

SO ₂ different H ₂ 0.5 to 0.6 vol .- * CO 0.3 to 0.4 vol -96 H ₂ S 1.2 vol -96 COS 0.1 vol -96 N ₂ rest

21 Ol 901

the reduction of Claus exhaust gases began. The experiment was carried out at different reduction temperatures performed. The results are in the following Table reproduced:

Tabel:

SOj content Reaction Conversion, ' In the gas temperature mixture, ° C H ₂ CO H Vol .- * (Mission- Γη (aerial) *. SOj content after I ₂ + CO reduction Vol.- *

222
250
250
280

34 65 45

27 100 50

63 100 80

89 100 94

Example 2

0.001
0.001
0.0.1
0.001

Gas together before the reduction after the reduction setting, SO ₂ 0.18 <0.002 S, 0.018 H ₂ 1.5 0.8 HP 29 30th H ₂ S 1.3 1.7 COS 0.05 0.05 N ₂ rest rest

The Ges. Aumwandlung. based on the amount of ^v .>, tssersloff. is 45%.

Example 3

A Claus exhaust gas containing about 0.1% by volume of carbon oxysulphide in addition to 0.17% by volume sulfur oxide and 12% by volume Containing hydrogen sulfide, was sulfidated together with a hydrogen-containing gas Co / Mo / AljOj catalyst as used in Example 1 was, at a temperature of 222 ° C and with a space velocity of 1700 Nl gas / l catalyst and hour is taught. The composition clc> · Gas after reduction was as follows:

the niiiicr Schwefeldloxyd and hydrogen sulfide also contained a small proportion of carbonyl sulfide and gaseous elemental sulfur, was extruded at 220 ° C using the same sulfiding Co / Mo / AI, O _r catalyst as was used for the experiments in Example 1, reduced with hydrogen . The exhaust gas was passed over the said catalyst together with hydrogen at a space velocity of 1400 standard l gas / l catalyst per hour. The composition of the entire gas mixture before and after the reduction is shown in the following table:

IUS

(ÖS

CO ₂

H, '
H, O

1.3 Vo \ .-%
1.3% by volume
1.5 VoI- ¹ V,
1.0 VoI- ¹ V,
36 vol .- '*,
rest

The gas with the above composition was then flowed at two different space velocities A bed of activated aluminum oxide (particle size 0.3 to 0.6 mm) to add the carbon oxysulphide hydrolyze. At a bar speed of 20,000 standard l of gas / l of catalyst and hour, this was Conversion of carbon oxysulphide * 80%, while at A conversion of 95% is achieved at a space velocity of 10,000 Nl gas / l catalyst and hour became.

Example 4

After hydrolysis of the carbon oxysulfide, the gas, which now mainly contained hydrogen sulfide as a sulfur compound, was brought into contact with activated carbon, which had a particle size of 3 mm, a specific surface area of 1200 mVg, an electrical density of 0.42 and a pore volume of 0.60 ml / g. The temperature was 130 ⁰ C and the Raumgi schwlndlgki: gas / l of catalyst per hour was lt set to 910 Nl. 98% of the hydrogen sulfide was adsorbed.

Claims (10)

21 Ol 901 claims: 1. Process for reducing the total sulfur content of exhaust gases containing sulfur dioxide by converting it into hydrogen sulfide and separating the hydrogen sulfide from the exhaust gases, in which the exhaust gases together with a reducing gas via a catalyst based on an or several metals from the VI. and / or VIII. Group of the Periodic Table de. Elements on one inorganic oxidic support (catalyst I) are passed, characterized in that Claus exhaust gases at 180 to 350 ° C together with a hydrogen and / or carbon monoxide containing Gas are passed over the catalyst I and that they are simultaneously or subsequently at 200 to 350.degree be brought into contact with a carbon sulfide and / or carbon disulfide in the hydrogen sulfide converting catalyst (catalyst II). 2. The method according to claim 1, characterized in that the gas containing hydrogen and / or carbon monoxide is at least 20 vol.-3> Contains hydrogen. 3. The method according to claim 1 or 2, characterized in that the hydrogen and / or carbon monoxide-containing gas is used in an amount corresponding to a ratio of hydrogen to sulfur dioxide of 3: 1 to 15: 1. 4. The method according to claim 1 to 3, characterized in that the catalyst I molybdenum, Tungsten and / or chromium and / or a metal from the Elsen group. In particular, contains cobalt. 5. The method me claim 1 to 4, characterized characterized in that the catalyst I is used in sulphurized form. 6. The method according to claim 1 to 5, characterized in that the Claus exhaust gases with a Space velocity of 500 to 10,000 standard l gas / l catalyst and hour passed over catalyst I. will. 7. The method according to claim 1 to 6, characterized in that the catalyst II consists of aluminum oxide, bauxite, activated clays, aluminum phosphate, Thorium oxide and / or magnesium chloride. 8. The method according to claim 7, characterized in that aluminum oxide is used with a highly concentrated aqueous alkali metal phosphate solution is impregnated. 9. The method according to claim I to 8, characterized in that the catalysts I and II In a single reactor in the form of two or more separate catalyst beds can be used. 10. The method according to claim 1 to 9, characterized characterized in that the treated exhaust gases over the catalyst II with a space velocity of 500 to V) OOO Nl gas / 1 catalyst and hour are passed.