CN1230158A - Process for 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

Method for recovering sulfur from SO2-containing gas stream

Sulfur-containing, especially _H2S -containing gases are released in many processes, such as petroleum refining, natural gas purification and synthesis gas production from coal or oil residues. This _H2S gas must be removed before the above gas is used. The most important reason for removing _H2S is to prevent the generation of _SO2 fume by the combustion of _H2S . As we all know, H ₂ S is also a very poisonous gas and has a bad smell.

The most common method of industrially removing _H2S from gases is absorption by liquid absorbents, which concentrates the _H2S and then converts the regenerated _H2S gas into harmless elemental sulfur.

In many cases it is also possible to omit the first step, ie the step of concentrating the H ₂ S and converting the H ₂ S directly to elemental sulfur.

One of the well-known and widely used methods for converting _H2S into elemental sulfur is the so-called Claus process. The Claus process works in different ways, depending on the _H2S content in the feed gas. In the most traditional scheme, a portion of the H ₂ S is combusted to produce SO ₂ , which is then further reacted with the remaining H ₂ S to form elemental sulfur.

A detailed description of the Claus process can be found in: R.N. Maddox "Gas and Liquid Sweetening"; Campbell Petroleum Series (1977) pp. 239-243 and in H.G. Paskall "Capabilities of the Modified Claus Process", publ. Western Research & Development. Calgary Alberta, Canada (1997).

The Claus method is based on the following reactions:

(1)

(2)

Reactions (1) and (2) form the overall reaction

(3)

A conventional Claus plant suitable for handling _H2S contents between 50 and 100% consists of a hot section (burner, combustion chamber, off-gas vessel and sulfur condenser) followed by a number of reactor sections (gas heating, packed catalyst reactor and sulfur condenser), usually consisting of two or three reactor sections. In the hot section, reactions (1) and (2) take place, and in the reactor section, only reaction (2), known as the Claus reaction, takes place. However, incomplete conversion of _H2S to elemental sulfur during the Claus reaction is mainly a result of incomplete progress of the Claus equilibrium reaction (2).

Therefore H ₂ S and SO ₂ maintain a certain content. From the standpoint of strict environmental requirements, the burning of such residual gases is never permitted. This so-called tail gas has to be desulfurized further. Tail gas treatment methods are known to those skilled in the art and have been published, for example, BGGoar, the tail gas purification method published at the 33rd Annual Conference on Gas Treatment, Norman, Oklahoma, March 7-9, 1983.

The well known and hitherto most effective method for tail gas desulfurization is the SCOT process described by Maddox in "Gas and Liquids Desulfurization" (1977). The sulfur recovery rate of SCOT method is 99.8-99.9%. Disadvantages of the SCOT method are high investment costs and high energy consumption.

Another method of increasing the efficiency of the Claus process is the SUPERCLAUS ^(R) process. In this method, the efficiency of the Claus method increases from 94-97% to over 99%.

The SUPERCLAUS® ^method is described in " ^SUPERCLAUS® , Solving the Limitations of Claus Devices", presented at the 38th Canadian Chemical Engineering Conference (October 25, 1988, Edmonton, Alberta, Canada).

The SUPERCLAUS ^(R) process is relatively inexpensive compared to other known tail gas treatment methods. In the SUPERCLAUS® ^process , reaction (2) is carried out with excess H ₂ S in the hot and Claus reactor stages, so that in the gas from the last Claus reactor stage, H ₂ S and SO The content of ₂ is about 1% (V) and 0.02% (V), respectively. In the downstream reactor section connected thereto, _H2S is selectively oxidized to elemental sulfur over specially selected oxidation catalysts according to the reaction described below.

(4)

These catalysts are disclosed in EPO242920 and EPO409353.

Thus, the tail gas from the SUPERCLAUS( ^R) reactor section still contains 0.02% (V) _H2S and about 0.2% (V) _SO2 and 0.2-0.5% (V) _O2 .

Another Claus process is described in U.S. Patent No. 4,280,990 to Jagodzinski et al. In this process, the Claus reaction (2) takes place in liquid sulfur at high pressure in the presence of a standard Claus catalyst, without condensation of water.

In this process, the hot section is operated at a pressure of 5-50 bar, after which the exit gas enters the reactor containing the catalyst at the same pressure. So the reaction between _H2S and _SO2 takes place at a pressure of 5-50 bar, by reaction sulfur condenses on the catalyst. Liquid sulfur circulates through the catalyst bed, dissipating the heat of reaction. The gas from the hot section contains about 7.9% (V) H ₂ S and 3.95% (V) SO ₂ , so H _{2 S:} SO ₂ =2:1. The temperature of the reactor in the first bed was set such that the outlet temperature was 275°C. In the second bed, the outlet temperature was set at 195°C. As can be seen from the examples of this process, this high percentage conversion of _H2S and _SO2 increases the pressure more favorably. To achieve Claus tail gas desulfurization, the same alternative method is also proposed. In this method, the Claus exhaust is pressurized to very high pressure.

Disadvantages of both the Claus process gas and Claus tail gas desulfurization methods are the high cost of _H2S gas (Claus feed gas) and air compressors and the high cost of tail gas compressors respectively; consumption, the risk of leakage of toxic H2S gas in these compressors of the desulfurization plant and other equipment, and the operational reliability of these compressors.

This is the reason why these methods have not found any industrial application so far. In the process described in US Patent No. 4,280,990, standard Claus catalysts are used. At the time the above patent was issued, activated alumina with a surface area of about 300 ^m2 /gr and an average pore diameter of about 50 A° was used as a Claus catalyst. Such catalysts are also described in US Patent No. 4,280,990.

In recent years, this approach has been developed, usually by setting a standard alumina catalyst in a Claus reactor. Therefore, it seems reasonable to think that other types of catalysts have not been studied, or that they are not available, or that they have not been developed. The working pressure depending on the _H2S and _SO2 concentrations was also not studied. Many of the experiments described in US Pat. No. 4,280,990 were performed at 2.5% (V) H ₂ S and 1.2% (V) SO ₂ .

US Patent No. 3447903 discloses another method, which is also applied in liquid sulfur based on the Claus method. According to this method, the reaction is catalyzed by the presence of small amounts of basic nitrogen compounds. From several examples, this compound is used in an amount of about 1-50 ppm. This method has never been applied industrially either.

It is an object of the present invention to provide an improved process for the recovery of sulfur from tail gas by which as much _SO2 and _H2S as possible are removed. More specifically, the purpose of the present invention is to provide a method by which the traditional sulfur recovery method is improved, and the sulfur recovery efficiency on an industrial scale is above 99.5%.

The present invention provides a method for the recovery of sulfur from a _SO2- containing gas stream by catalytic conversion of the _SO2 in the gas stream to elemental sulfur. Said process comprises the conversion of H in the presence of liquid sulfur and a catalyst system based on a heterogeneous catalyst catalyzing the Claus reaction, simultaneously in the presence of a basic nitrogen compound as a Claus reaction accelerator in the liquid sulfur ₂ S and SO ₂ .

Surprisingly, it has been found that, according to the process of the invention, a markedly increased efficiency of the conversion to elemental sulfur is achieved using a specific promoter of the heterogeneous catalyst. For example, liquid sulfur has long been used as a reaction medium. However, only the process according to the invention can be carried out at low pressure, ie at or slightly above atmospheric pressure.

This method can be done in many ways. The basic approach is that the catalyst is in direct contact with liquid sulfur supplied from an external source. Preferably this liquid sulfur already contains the amount of _H2S to be converted. Since the conversion efficiency is significantly increased, it is then possible to supply _H2S and _SO2 from the gas phase, but this results in lower efficiencies.

In the process of the present invention, in the presence of liquid sulfur containing a suitable catalyst, the reaction pressure is preferably 1-5 bar and the reaction temperature is preferably between 120-250 ° C, between H ₂ S and SO ₂ The reaction is carried out according to H ₂ S:SO ₂ =2:1, generating sulfur and water.

In the process of the invention, suitable catalysts have a large macroporous structure. These catalysts consist of activated alumina with a small amount of microporous structure and a large amount of meso- and macroporous structure. The pores of the medium pore structure, macroporous structure and super macroporous structure of these activated alumina account for more than 65% of the total pore volume. It is also possible to use catalysts having these properties as support materials which are impregnated with active substances such as metal oxides. These catalysts are often referred to as "promoted catalysts".

In general, these catalysts can be considered useful in catalyzing Claus reactions. In addition to the activated alumina already discussed, other known catalysts for this reaction are also suitable. Examples include titanium dioxide and supported metal oxides.

We have found that the reaction between _H2S and _SO2 to form sulfur and water is also promoted when water vapor is added to the gas to be treated at a pressure below 5 bar, or when water vapor is present in the gas to be treated, Likewise, the efficiency can be significantly increased by proper choice of residence time.

At pressures below 5 bar, _SO2 reacts with _H2S in the same way to form sulfur and water when sulfur exists in the form of polysulfides. It has been found that when the gas to be treated contains oxygen, this oxygen hardly reacts with _H2S or the sulfur present to form _SO2 .

The main advantage of the process of the present invention is the reaction at low pressure, whereby all the disadvantages of the process described in US Pat. No. 4,280,990 are eliminated.

In the process of the present invention, the SO2-containing _gas can also be treated by adding _H2S gas to the _SO2 -containing gas, or predissolving _H2S in liquid sulfur.

In the process of the present invention, when _H2S is pre-dissolved in liquid sulfur, this results in a higher conversion of _SO2 and offers the advantage that the control of the required conversion of _H2S to _SO2 can be considerably simplified, Since the _H2S dissolves first, the unused _H2S residue is deposited on the sulfur, so the sulfur can be loaded by the _H2S again.

Surprisingly, it has been found that, in the process of the present invention, the conversion efficiency of _H2S and _SO2 into sulfur and water is significantly increased when small amounts of basic nitrogen compounds are present in the sulfur, even at operating The point at which virtually complete equilibrium is reached at temperature.

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

The use of tertiary alkanolamines is preferred because they do not form sulfamate, have a high boiling point, and because of the convenience of these amines.

The present invention will now be more clearly understood with reference to the accompanying drawings. In FIG. 1 , the gas containing H ₂ S and SO ₂ is sent through pipe 1 to reactor 2 which is equipped with catalyst 3 .

Liquid sulfur is supplied via line 4 and passes the catalyst with the incoming gas. Liquid sulfur is produced from the reaction between _H2S and _SO2 on the catalytic bed. After the reaction of _H2S and _SO2 , the exhaust gas is discharged through pipe 5.

Liquid sulfur is passed from the reactor to cooler 7 via pipe 6, where the heat of reaction is dispersed. Sulfur is recycled to reactor 2 via line 4 by means of pump 8 . Generated sulfur is discharged through pipe 9 .

In Fig. 2, H ₂ S gas containing more than 90% (V) of H ₂ S is transported through pipe 1 to a Claus unit 10 consisting of a hot section and two subsequent catalytic reaction sections.

The air required for the Claus reaction is supplied via pipe 11. Sulfur formed in the hot and reactor sections is discharged via pipe 12 . The tail gas still containing H ₂ S and SO ₂ from the second catalytic reactor section is sent to the reactor 2 containing the catalyst 3 via the pipe 13 . On the catalyst bed, liquid sulfur is fed via pipe 4 . After the _H2S and _SO2 have reacted on the catalyst bed to form sulfur, the tail gas leaves the reactor via pipe 5. Liquid sulfur leaves the reactor via line 6 and cooler 7 for recycling to reactor 2. Generated sulfur is discharged through pipe 9 . Alternatively, a basic nitrogen compound can be added via line 14.

In Fig. 3, a preferred variant of the process according to the invention is depicted, in which the _H2S -containing gas is fed via pipe 1 to a Claus unit 10 consisting of a hot section followed by two catalytic sections.

The air required for the Claus reaction is supplied via pipe 11. Sulfur formed in the hot and reactor sections is discharged via pipe 12 . The tail gas still containing H ₂ S and SO ₂ from the second catalytic reactor stage is sent to SUPERCLAUS unit 15 via pipe 13 .

Air for selective oxidation is supplied via line 16 . And liquid sulfur is discharged through pipe 17 . The tail gas is delivered to the reactor 2 containing the catalyst 3 through the pipe 13 . On the catalyst bed, liquid sulfur is fed via pipe 4 .

Liquid sulfur from column 18, which has been contacted with the _H2S -containing gas, is conveyed via line 1 to the Claus unit. In column 18, the liquid sulfur is combined with the _H2S from the gas. After _H2S is dissolved in liquid sulfur, it reacts with _SO2 on the catalyst bed to generate sulfur, and the tail gas leaves the reactor through pipe 5. Liquid sulfur leaves reactor 2 via line 6 and is recycled to column 18 via line 19 by means of pump 8 . Generated sulfur is discharged through pipe 9 . In the column, the sulfur absorbs the H ₂ S again and is sent again to the reactor 2 via pipe 20 , pump 21 , cooler 22 and pipe 4 . Basic nitrogen compounds can be fed to the liquid sulfur via line 14, if desired.

The invention is further illustrated by the following examples.

Example 1

Using the apparatus described in Figure 2, the Claus reaction was carried out in a Claus apparatus with two catalytic stages. Supply 90.0% (V) H ₂ S (36.OKmol/h), 3.5% (V) CO ₂ , 2.0% (V) hydrocarbons, 4.5% (V) H ₂ O and 19.5Kmol/h to the hot section _O2 acts as the Claus gas of air oxygen. The volume percentage of H ₂ S in the tail gas after the second catalytic stage is 0.58% (V), while the content of SO ₂ therein is 0.29% (V) and the content of water therein is 33.2% (V). The sulfur recovery of the Claus unit is 94%.

The tail gas at a temperature of 150° C. and a pressure of 1.13 bar is sent to the catalyst bed shown in FIG. 2 at a rate of 120 Kmol/h. Catalyst 3 is activated alumina with medium pore structure and large pore structure. On the catalyst bed, liquid sulfur circulates at 150°C in an amount of 50m ³ /h. The temperature of the circulating sulfur is kept constant by dispersing the reaction heat released by the process in the cooler. In order not to let the sulfur content in the reactor rise too high, some sulfur is purged from the system at any time. The percentage of _H2S in the gas after the catalyst bed is 0.188% (V), and the percentage of _SO2 in it is 0.088% (V), so the conversion rate of H2S into sulfur in the reactor is 68% , The conversion rate of SO ₂ into sulfur was 70%.

Thus, the overall sulfur recovery for the reaction between _H2S and _SO2 in liquid sulfur in the Claus unit following this reactor section is above 97.7%.

Example 2

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

The Claus gas fed to the hot section is the same as in Example 1, however, the oxygen supplied as air oxygen is now 19.85Kmol/h so that after the second catalytic section, the _SO2 in the tail gas is like _H2S many. The volume percentages of H ₂ S and SO ₂ in the tail gas are both 0.46%, and the water content is 33.0% (V). After the catalyst bed, the volume percent of _H2S in the tail gas was 0.046% and that of _SO2 was 0.018%. The conversion of _H2S to sulfur in the reactor was 90% and the conversion of _SO2 was 96%.

Thus, in the Claus unit following this reactor section, the total sulfur recovery from the reaction between _H2S and _SO2 in liquid sulfur is above 99.0%.

Example 3

In the plant depicted in Figure 3, a SUPERCLAUS reactor section is placed after the second catalytic section of the Claus unit for the selective oxidation of _H2S in the gas from the second catalytic section to sulfur. The tail gas from the SUPERCLAUS section is sent to the catalyst bed shown in Figure 3. The Claus gas is first contacted countercurrently with a sulfur stream in a contact vessel before passing through the hot section. The Claus feed gas flowing into the contact vessel was the same as in Example 1. In the contact vessel, H ₂ S dissolves in sulfur at a rate of 0.193 Kmol/h and is therefore withdrawn from the Claus feed gas passing through the hot section. Oxygen was supplied to the hot section as air oxygen at a rate of 18.87 Kmol/h. In addition, oxygen as air oxygen was supplied to SUPERCLAUS at a rate of 1.40 Kmol/h. The H ₂ S content in the tail gas after the SUPERCLAUS section is 0.032% (V), while the SO ₂ content is 0.189% (V) and the oxygen content is 0.50% (V). The off-gas from the SUPERCLAUS section is delivered to the catalyst bed shown in FIG. 3 in an amount of 122 Kmol/h at a temperature of 130° C. and a pressure of 1.13 bar (absolute). Liquid sulfur from the contacting vessel is passed over the catalyst bed and tertiary alkanolamine (TEA) is added to the liquid sulfur.

Thereafter, the sulfur is returned to the contact vessel. The amount of the recycle stream is set so that sufficient _H2S relative to _SO2 is delivered to the catalyst bed so that there is a minimum of 1:1 _H2S : _SO2 .

The concentration of H ₂ S in the exhaust gas after the catalyst bed is 0.015% (V), and the content of SO ₂ is 0.011% (V). Thus, the conversion rate of H ₂ S to sulfur in the reactor is 92%, and the conversion rate of SO ₂ is 94%.

Thus, in a Claus plant following this reactor section after the SUPERCLAUS reactor section, the total sulfur recovery from the reaction between _H2S and _SO2 in liquid sulfur is above 99.5%.

Claims (14)

1. one kind is passed through SO ₂Be catalytically converted into elementary sulfur from containing SO ₂Air-flow in reclaim the method for sulphur, described method is included in liquid sulfur and there is catalyzed conversion SO down in catalyst system ₂And H ₂S, described catalyst system are the heterogeneous catalyst systems of catalysis claus reaction, have the promotor basic nitrogen compound of claus reaction simultaneously in described liquid sulfur.

2. by the process of claim 1 wherein that promotor is selected from amine, alkyl amine, alkanolamine, ammonia, ammonium salt and fragrant nitrogen compound.

3. by the method for claim 2, wherein promotor is selected from Monoethanolamine MEA BASF, diethanolamine, DGA, DIPA, MDEA and trolamine.

4. by the method for claim 2 or 3, wherein use tertiary amine.

5. by the method for claim 1-4, the porous alumina that wherein uses porous alumina or be loaded with metal oxide on porous alumina is made the active heterogeneous catalyst of Crouse.

6. by the method for claim 5, wherein the surface-area of aluminum oxide is at least 150m ²/ g.

7. by the method for claim 6, wherein the aperture is that the pore volume in 5nm or littler hole is less than 35% (V) in the pore volume of measuring with nitrogen.

8. by the method for claim 1-7, this method is to carry out under the pressure of 1-5 crust.

9. by the method for claim 1-8, this method is to carry out under 120-250 ℃ temperature.

10. press the method for claim 1-9, wherein H ₂S is dissolved in the liquid sulfur, after this with SO ₂Contact.

11. by the method for claim 10, wherein H ₂The gas that S content is at least 0.5% (V) contacts with liquid sulfur, thus section H ₂S is dissolved in liquid sulfur, after this, and containing H ₂The gas delivery of S is to Cross unit, a part of thus H ₂S is heated and changes into SO ₂, after this, in one or several conversion zone, in the catalysis Cross unit, generate sulphur, after separate sulfur, the gaseous mixture that obtains is containing dissolved H ₂The existence of the liquid sulfur of S directly transforms down, or if desired, is optionally transforming behind the oxidation step.

12. by the method for claim 1-10, wherein H ₂The tail gas that S content is at least the Cross unit catalytic section of 0.25% (V) contacts with liquid sulfur, thus at least a portion H ₂S is dissolved in liquid sulfur, after this, in the presence of the heterogeneous catalyst system of catalysis claus reaction and in liquid sulfur in the presence of the basic nitrogen compound as claus reaction promotor, the above-mentioned H that contains ₂The liquid sulfur of S with contain SO ₂The gas contact.

13. by the method for claim 1-12, wherein in the weight of liquid sulfur, the amount of promotor is 1-1000ppm, is preferably 1-50ppm.

14. by the method for claim 1-13, wherein reaction is in bed of catalyst particles or is loaded with thereon and carries out on other material of catalyzer and wherein these particles or carrier substance soaked into liquid sulfur.

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