SK2199A3 - Process for the recovery of sulfur from so2 containing gases - Google Patents

Abstract

The invention relates to a process for recovering sulfur from an SO2 containing gas stream through catalytic conversion thereof to elemental sulfur, comprising converting SO2 and H2S in the presence of liquid sulfur and a catalyst system based on a heterogeneous catalyst which catalyzes the Claus reaction, while as promoter for the Claus reaction a basic nitrogen compound is present in the liquid sulfur.

Description

Process for recovering sulfur from SO2 containing gases

Technical field

Many processes, such as oil refining, natural gas purification and the production of synthetic gas from coal or oil residues, release sulfur-containing gas, especially H2S. This H2S is removed prior to use of said gases. The most important reason for the removal of H2S is to prevent SO2 emissions from burning H2S. It is also known that H2S is a very toxic gas with an unpleasant odor.

BACKGROUND OF THE INVENTION

The most common industrial process is the removal of H 2 S by means of absorption liquids, by means of which H 2 S is concentrated and then the regenerated H 2 S is converted to elemental sulfur, which is harmless.

In several cases it is also possible to skip the first step, i. concentration of H2S and convert H2S directly into elemental sulfur.

One of the most well-known and widely used methods of converting H2S into elemental sulfur is the so-called " Claus way. The Claus process is carried out in different ways depending on the H2S content of the starting gas.

According to a general embodiment, part of the H 2 S is burned to SO 2, which then reacts with the remaining H 2 to form elemental sulfur.

Claus's method is described in detail in RN Maddox, Gas and Liquid Sweetening, Campbell Petroleum Serie (1977) pages 239 to 243, and in HG Paskall, Capabilities of the Modified Claus Process, published in Western Research & Development, Calgary, Alberta, Canada (1979). ).

Claus's method is based on the following reactions:

H ₂ S + 3 O ₂ -> 2 H 2 O + 2 SO 2, (1)

H ₂ S + 2 SO ₂ 4 H ₂ O + 6 S _n (2)

Reactions (1) and (2) give a summary reaction:

H ₂ S + O ₂ ^ 2 H ₂ O + 2 / n S _n (3)

Claus equipment suitable for treating gases containing 50 to 100% H ₂ O normally consists of a thermal stage (burner, combustion chamber, residual gas vessel and sulfur cooler) followed by several, normally two or three reactor stages (gas heating, reactor filled with catalyst and sulfur cooler). In the heat stage, reactions (1) and (2) take place, whereas in the reactor stage only reaction (2), known as the Claus reaction. However, the Claus method H ₂ S is not performed on elemental sulfur because the Claus equilibrium reaction (2) is not tightened to the end.

Therefore, some H ₂ S and SO ₂ remain. The combustion of this residual gas is no longer permitted in view of strict environmental requirements. This so-called. the residual gas must be further desulphurised. Methods for treating residual gas are known to those skilled in the art and are described, for example, in BG Goar, Tail Gas Clean-up Processes, reviewed at 33 ^rd Annual Gas Conditioning Conference, Norman, Oklahoma, March 7-9, 1983.

The best known and still the most effective method of desulfurization of residual gas is the SCOT method described in Maddox's "Gas and liquid sweetening (1977)". The SCOT process achieves 99.8 to 99.9% sulfur recovery. The disadvantages of the SCOT method are high investment costs and high energy consumption.

Another method that increases the efficiency of the Claus method is the SUPERCLAUS® method. In this way, the efficiency of the Claus method is increased from 94 to 97% to more than 99%.

SUPERCLAUS method is described in "SUPERCLAUS, the answer to Claus Plant limitations published on 38 ^'h

Canadian Chem. Eng. Conference, October 25, 1988, Edmonton, Alberta, Canada.

The SUPERCLAUS® process is cheaper than other known processes that deal with residual gas treatment. In the SUPERCLAUS® process, reaction (2) uses an excess of H2S in the heat stage and Claus reaction stages, so that in the gas leaving the last Claus reaction stage the H2S content is 1% by volume and the SO2 content is 0.02% by volume. In the upstream reactor stage associated with this last Claus reactor stage, H2S is selectively oxidized on a special selective elemental sulfur oxidation catalyst according to the following equation:

H ₂ S + O ₂ -> 2 H ₂ O + 2 n _n (4)

These catalysts are described in European patents 0 242 920 and 0 409 353.

The residual gas from the SUPERCLAUS® reactor stage then contains 0.02% by volume H2S, 0.2% by volume SO2 and 0.2 to 0.5% by volume O2.

Another Claus method is described in U.S. Pat. No. 4,280,990 to Jagodzinsky et al. wherein the Claus reaction (2) is carried out in liquid sulfur in the presence of a standard Claus catalyst at elevated pressure without condensation of water.

In this process the thermal stage is operated at a pressure of 5.10 ⁵ to 5.10 ⁶ Pa (5-50 bar), in which the exit gas at the same pressure injected into the reactor, which is filled with a catalyst. The reaction between H2S and SO2 therefore occurs at a pressure of between 5.10 ⁵ and 5.10 ⁶ Pa (5-50 bar), due to which the sulfur condenses on the catalyst. The liquid sulfur circulates on the surface of the catalyst to dissipate the heat of reaction. The gas from the heat stage contains 7.9% by volume of H2S and 3.95% by volume of SO2, so the H2S: SO2 ratio is 2: 1. The reaction temperature in the first layer, which is set as the exit temperature, is 275 ° C.

The outlet temperature in the second layer is set at 195 ° C. An example of the above method shows that the conversion of this high percentage of H 2 S and SO 2 is better performed at elevated pressure. Alternatively, the same method is proposed for desulfurization of Claus residual gas. In this case, the Claus residual gas is supplied at a relatively high pressure.

The disadvantages of this desulfurization process for both the Claus process gas and the Claus residual gas are the high cost of H2S (Claus feed) and air compressors, the high cost of the residual gas compressor, the high energy consumption of these compressors, the risk of toxic H2S leakage from these compressors and other parts of the equipment and the operational reliability of these compressors.

This is why this method has not yet appeared in a commercial application. In the process described in US Patent 4,280,990, a standard Claus catalyst is used. At the time of the above patents, activated alumina with a surface area of 300 m ² / g, with an average pore size of 5 nm (50 Angstroms), was used as Claus catalyst. Such catalysts are also described in U.S. Patent 4,280,990.

In the years when this process was developed, standard aluminum catalyst was commonly installed in Claus reactors. It is therefore possible that no further research has been done with other types of catalysts, or that these catalysts have not been available or have not yet been developed. However, no research has been conducted to investigate the dependence of the required working pressure on the H2S and SO2 concentration. Most of the experiments described in U.S. Pat. No. 4,280,990 is performed with 2.5% by volume H2S and 1.2% by volume SO2.

U. U.S. Patent 3,447,903 discloses another method which is also based on the application of the Claus method in liquid sulfur.

According to this method, the reaction is catalyzed by the presence of a small amount of a basic nitrogenous compound. The examples show that 1 to 50 ppm of this material is used. This process has not yet been commercially utilized.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved process for recovering sulfur from residual gases by which H2S and SO2 are removed as much as possible. In particular, it is an object of the invention to provide a method by which conventional sulfur recovery methods are improved in such a way that on an industrial scale more than 99.5% of the regeneration efficiency is achieved.

The invention provides a method of recovering sulfur from a stream of SO2 containing gases by catalytic conversion to elemental sulfur, characterized in that SO2 and H2S are converted in the presence of liquid sulfur and a catalyst system based on a heterogeneous catalyst to catalyze Claus reaction. compound as a Claus reaction promoter.

It has been found that by the method of the invention utilizing a specific promoter of a heterogeneous catalyst, the conversion efficiency to elemental sulfur is improved. The use of liquid sulfur as a reaction medium has been known for a long time. However, the method according to the invention provides the possibility to carry out this method at low pressures, i. at atmospheric or slightly elevated pressure.

The process can be carried out in several ways. It is essential that the catalyst be in direct contact with the liquid sulfur that is supplied from external sources. Advantageously, the liquid sulfur already contains a certain amount of H2S to be converted, since the conversion efficiency is thereby clearly increased. Thus, it is possible to supply both H 2 S and SO 2 from the gas phase, but this procedure provides lower efficiency.

The process of the invention, the reaction between H2 S and SO2 in a ratio of H2 S: SO2 = 2: 1 producing sulfur and water is carried out in the presence of liquid sulfur with a suitable catalyst at a pressure preferably between 1.10 ⁵ and 5.10 ⁵ Pa (1 and 5 bar) and a temperature of preferably between 120 and 250 ° C.

In the process according to the invention, suitable catalysts have a structure with large macropores. These catalysts include those activated alumina having small microporous structures and a large volume of mesa and macropores. These activated alumina have mesa, macro, and ultrastructure that occupy more than 65% of the total pore volume. It is also possible to use a catalyst having these properties as a carrier which is impregnated with an active material, for example a metal oxide. These catalysts are often referred to as activated catalysts.

In general, catalysts that catalyze the Claus reaction are useful. In addition to the activated alumina already discussed, other catalysts suitable for this reaction, such as titanium dioxide or supported metal oxides, are known.

It has been found that when water vapor is added to the gas to be treated at pressures lower than 5.10 ⁵ Pa (5 bar), or when the gas already present, only promotes the reaction between H2S and SO2 to sulfur and water. In addition, the efficiency can be greatly enhanced by a suitable choice of residence time.

It was also established that at pressures lower than 5.10 ⁵ Pa (5 bar) polysulfides react the sulfur present in the same way as SO2 H2S to form sulfur and water. It has been found that if the gas contains oxygen, this oxygen hardly reacts with H2S or sulfur present to form SO2 if it does not react at all.

The main advantage of the process of the invention is the reaction at low pressure, a result which eliminates all the disadvantages of the process of U.S. Pat. U.S. Patent No. 5,201,516; 4,280,990.

It is also possible by the process of the invention to treat SO2 containing gases by adding H2S gas to these gases or by preferentially dissolving H2S in liquid sulfur.

According to the process of the invention, it was found that when H ₂ S was preferably dissolved in liquid sulfur, the process provided higher conversion to SO ₂ and provided the advantage of comparatively great simplification of the control of the desired H2S for SO2 conversion, since dissolved, unused H2S remains in sulfur then H2S may be saturated again.

Surprisingly, it has been found that by the presence of a small amount of basic nitrogen compound in sulfur, the process of the invention greatly increases the efficiency of converting H2S and SO2 into sulfur and water even to a point where a virtually complete equilibrium is reached at a given temperature.

Suitable basic nitrogen compounds are amines (such as alkylamines), alkanolamines (such as MEA, DGA, DEA, DIPA, MDEA, TEA), ammonia, ammonium salts, aromatic nitrogen compounds (such as quinoline, morpholine).

Preferably, tertiary alkanolamines are used because they do not form amidosulfates, have a high boiling point and are relatively inexpensive.

The invention will be further explained with reference to the drawing. In Figure 1, the gases containing H 2 S and SO 2 are fed via line 1 to the reactor 2 in which the catalyst 3 is located.

Liquid sulfur is fed via line 4 and fed to the catalyst together with the feed gas. Liquid sulfur is formed on the catalyst by reaction between H2S and SO2. The off-gas after reaction between H2S and SO2 is removed via line 5.

Liquid sulfur is discharged via line 6 from the reactor to a cooler 7 where reaction heat is consumed. By means of a pump, the sulfur is recirculated to the reactor 2 via line 4. The resulting sulfur is removed via line 9.

In Figure 2, gas containing more than 90% by volume of H 2 S is supplied via line X to Claus apparatus 10, consisting of a thermal stage followed by two catalytic reactor stages.

The air required for the Claus reaction is supplied via line 11. The sulfur generated in the heat stage and reactor stages is removed via line 12. The residual gas from the second catalytic stage, which still contains H2S and SO2, is added via line 13 to the reactor 2 where the catalyst is located.

3. Liquid sulfur is supplied to the catalyst surface via a line

4. After the reaction of H2S and SO2 on the surface of the catalyst to form sulfur, the residual gas leaves the reactor via line 5. Liquid sulfur leaves the reactor via line 6 and is recirculated to the reactor 2 via condenser 7. The resulting sulfur is discharged via line 9. pipeline 14.

Figure 3 shows a preferred embodiment of the process according to the invention, wherein the H 2 S-containing gases are fed via line 1 to Claus apparatus 10 consisting of a thermal and subsequently two catalytic reactor stages.

The air required for the Claus reaction is supplied via line 11. The sulfur produced in the heat stage and reactor stages is removed via line 12. The residual gas from the second catalytic reactor stage, which still contains H2S and SO2, is supplied via line 13 to SUPERCLAUS 15.

Through line 16 the air for selective oxidation is supplied, with liquid sulfur being discharged through line 17. The residual gas is fed via line 13 to the reactor 2 in which the catalyst 3 is located. Liquid sulfur is supplied to the catalyst surface via line 4.

This liquid sulfur comes from the column 18 in which the sulfur is in contact with the H2S-containing gas which is fed via line 1 from the Claus apparatus. In column 18, a portion of the H2S from the gas is mixed into liquid sulfur. Then, the surface of the catalyst treated H 2 S dissolved in the liquid sulfur with _SO2 to form sulfur, the tail gas leaves the reactor via line

5. Liquid sulfur leaves the reactor 2 via line 6 and is recirculated via line 19 via line 19 to column 18. The resulting sulfur is discharged via line 9.

In the column, sulfur is again added to H2S and fed via line 20 to reactor 2, pump 21, cooler 22 and line

4. If necessary, basic nitrogenous substances are fed into the liquid sulfur via line 14.

The invention is further illustrated by the following examples.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The Claus reaction is carried out in the apparatus described in Figure 2, ie in the Claus apparatus with two catalytic steps. Claus gas containing 90% by volume of H2S, corresponding to 36 kmol / h, 3.5% by volume of CO ₂ , 2% by volume of hydrocarbons, 4.5% by volume of H2O and 19.5 kmol / h of oxygen in the heat stage is supplied to the heat stage. air. The H2S content of the residual gas after the second catalytic stage is 0.58% by volume, the SO2 content of the same gas being 0.29% by volume and the water content of the same gas being 33.2% by volume. The sulfur recovery efficiency of the Claus apparatus is 94%.

The residual gas at 120 kmol / h, at a temperature of 150 ° C and a pressure of 1.13.10 ⁵ Pa (1.13 bar) is fed to the catalyst bed as outlined in Figure 2. Catalyst 3 is an activated meso and macroporous alumina. structure.

Liquid sulfur is circulated on the catalyst bed at a rate of 50 m ³ / h at a temperature of 150 ° C. The temperature of the circulating sulfur is maintained by constant dissipation of the reaction heat generated in the condenser. So that the sulfur level in the reactor does not rise very quickly, from time to time the sulfur is drained from the system. The H2S content of the gas leaving the catalyst surface is 0.188% by volume, while the SO2 content of the same gas is 0.088% by volume. Thus, in the reactor, the conversion of H2S to sulfur is 68% and the conversion of SO2 is 70%.

The overall sulfur recovery efficiency of the Claus plant, which is controlled by these reactor stages in which the reaction between H2S and SO2 in liquid sulfur is then greater than 97.7%.

Example 2

In the same apparatus as described in Figure 2, an aromatic amine (quinoline) is added to the circulating sulfur via line 14. The amount of quinoline addition is such that its concentration in the sulfur stream in the reactor is 500 ppm by weight.

The Claus gas in the heat stage is the same as in Example 1, but at the same time 19.85 kmol / h of oxygen is added in the form of air to give as much SO2 as H2S in the residual gas after the second catalytic stage. The content of both SO2 and H2S in the residual gas is then 0.46% by volume and the water content in the same gas is 33% by volume. The H2S content of the residual gas leaving the catalyst surface is 0.046% by volume, while the SO2 content of the same gas is 0.018% by volume. Thus, in the reactor, the conversion of H2S to sulfur is 90% and the conversion of SO2 is 96%.

The overall sulfur recovery efficiency of the Claus plant, which is controlled by these reactor stages, in which the reaction between H2S and SO2 in liquid sulfur takes place, is then greater than 99.0%.

Example 3

In the apparatus as described in Figure 3, the SUPERCLAUS reactor stage is placed downstream of the second catalytic stage of the Claus apparatus to allow selective oxidation of H2S to sulfur in the gas from the second catalytic stage. The residual gas from the SUPERCLAUS stage is fed to the catalyst bed as outlined in Figure 3. Before the Claus gas is introduced into the thermal stage, it is first in countercurrent contact with the sulfur stream in the mixing vessel. The Claus feed gas flowing into this contact vessel is the same as in Example 1. 0.193 kmol / h H2S is dissolved in the contact vessel in sulfur. This removes H2S from the Claus feed gas, which is introduced into the heat stage. To the heat stage, 18.87 kmol / h of oxygen is introduced in the form of air. An additional 1.40 kmol / h of oxygen as air is fed to the SUPERCLAUS stage. The H2S content of the residual gas after the SUPERCLAUS step is 0.032% by volume, the SO2 content of the same gas being 0.189% by volume and the O2 content of the same gas being 0.5% by volume. The residual gas from the SUPERCLAUS stage at 122 kmol / h, at a temperature of 130 ° C and a pressure of 1.13.10 ⁵ Pa (1.13 bar) is absolutely fed to the catalyst layer as outlined in Figure 3. Liquid sulfur is passed through the layer, coming from the contact vessel. Tertiary alkanolamine (TEA) is added to liquid sulfur.

The sulfur is then returned to the contact vessel. The magnitude of the circulating stream is adjusted such that enough H2S relative to SO2 is applied to the catalyst surface such that the H2S: SO2 ratio is at least 1: 1.

The concentration of H2S in the off-gas from the catalyst bed is 0.015% by volume, while the SO2 content in the same gas is 0.011% by volume. Thus, in the reactor, the conversion of H2S to sulfur is 92% and the conversion of SO2 is 94%.

The total sulfur recovery efficiency of the SUPERCLAUS reactor stage controlled by this reactor stage in which the reaction between H2S and SO2 in liquid sulfur is then greater than 99.5%.

Industrial usability

The invention provides a method for recovering sulfur from a stream of SO2 containing gases by catalytic conversion to elemental sulfur, characterized in that the SO2 and H2S are converted in the presence of liquid sulfur and the catalyst system is based on a heterogeneous catalyst catalysing Claus reaction. a basic nitrogenous compound as a Claus promoter.

Claims (14)

Patent claims 1, the H2S-containing gas stream is fed to a Claus apparatus by means of which part of the H2S is thermally converted to SO2 ** and where, in one or more stages, sulfur is produced in the Claus catalytic apparatus and the gas mixture thereby obtained is converted directly after sulfur separation; necessary after a selective oxidation step in the presence of liquid sulfur containing dissolved H 2 S. A process for obtaining sulfur from a stream of SO2 containing gases by catalytic conversion to elemental sulfur, characterized in that SO2 and H2S are converted in the presence of liquid sulfur and a catalyst system based on a heterogeneous catalyst and a promoter, wherein the heterogeneous catalyst catalyzes Claus reaction the Claus reaction promoter is a basic nitrogen compound in liquid sulfur. The process of claim 1, wherein the promoter is selected from the group consisting of amines, alkanolamines, ammonia, ammonium salts, and aromatic nitrogen compounds. The method of claim 2, wherein the promoter is selected from the group consisting of monoethanolamine, diethanolamine, DGA, DIPA, MDEA, and triethanolamine. Process according to claim 2 or 3, characterized in that a tertiary amine is used. Process according to Claims 1 to 4, characterized in that a porous alumina or a porous alumina equipped with a metal oxide is used as Claus active heterogeneous catalyst. Method according to claim 5, characterized in that the alumina has a surface area of at least 150 m ² / g. The method of claim 6, wherein the pore volume existing in the pores with a diameter of 5 nm or less, as determined by nitrogen, is less than 35% by volume. The process according to claims 1 to 7, characterized in that it is carried out at a pressure of ^{10 5} to 5 ^{10 5} Pa. The method according to claims 1 to 8, characterized in that it is carried out at a temperature of 120 to 250 ° C. Η Process according to claims 1 to 9, characterized in that H ₂ S is dissolved in liquid sulfur, which is then in contact with SO 2. The method of claim 10, wherein the H2S-containing gas is at least 0.5% by volume with liquid sulfur to dissolve a portion of the H2S in the sulfur and then The process according to claims 1 to 10, characterized in that the residual gas of the catalytic stage of the Claus apparatus having an H 2 S content of at least 0.25% by volume is contacted with liquid sulfur, whereby part of the H 2 S is dissolved in liquid sulfur. H2S-containing liquid sulfur is contacted with SO2-containing gases in the presence of a catalyst system based on a heterogeneous catalyst, catalysing the Claus reaction, wherein a basic nitrogenous compound is present as the promoter of the Claus reaction in the liquid sulfur. Process according to claims 1 to 12, characterized in that the amount of promoter based on the weight of liquid sulfur is between 1 and 1000, preferably between 1 and 50 ppm. y The process according to claims 1 to 14, characterized in that the reaction is carried out on a solid surface of the catalytic particles or other bodies on which the catalyst is supplied and characterized in that the particles or bodies are irrigated with liquid sulfur.