KR19980074498A - Catalyst for selective oxidation of hydrogen sulfide gas containing ammonia and water and method of removing hydrogen sulfide using the same - Google Patents

Abstract

The present invention provides a catalyst for the selective oxidation of hydrogen sulfide in which iron oxide is supported on a non-basic porous carrier, and by using the same, hydrogen sulfide can be directly oxidized with high efficiency to selectively remove hydrogen sulfide efficiently even under the presence of ammonia and water. It is about how. Since the catalyst of the present invention maintains high catalytic activity even in the presence of ammonia and water, hydrogen sulfide generated in a large amount in oil refineries or steel mills can be easily removed with non-toxic elemental sulfur or ammonium sulfate. Environmental pollution problems can also be solved.

Description

Catalyst for selective oxidation of hydrogen sulfide gas containing ammonia and water and method of removing hydrogen sulfide using the same

The present invention relates to a catalyst for directly oxidizing hydrogen sulfide gas and a method for removing toxic hydrogen sulfide gas using the same, and more particularly, a catalyst for directly and selectively oxidizing hydrogen sulfide gas even in the presence of ammonia and water. The present invention relates to a method for removing hydrogen sulfide by selectively oxidizing hydrogen sulfide on this catalyst and converting it into a non-toxic solid form of elemental sulfur or ammonium sulfate.

Hydrogen sulfide is a colorless, odorous gas and acts as one of the substances that cause air pollution. Hydrogen sulfide is generated in a large amount by biological action, but as industrial facilities increase, a large amount of hydrogen sulfide is also generated in various industrial facilities, resulting in more serious air pollution. Since such air pollution can reduce the degree of damage according to the structure and operation method of the discharge facility, a method for efficiently removing hydrogen sulfide emitted from an industrial facility is urgently required.

Industrial facilities that generate large amounts of hydrogen sulfide include crude oil, natural gas refining, and steelmaking, and the coal gasification process is expected to emerge as a new source. Especially, the method of removing hydrogen sulfide from these industrial facilities Development is urgent.

Until now, the method of removing hydrogen sulfide has mainly been the Claus reaction. According to this method, hydrogen sulfide is largely non-toxic through two steps, a thermal oxidation process and a catalytic reaction process. Can be removed with elemental sulfur.

First, in the thermal oxidation process, one-third of hydrogen sulfide (H ₂ S) is oxidized in a waste heat furnace of about 1100-1200 ° C. and converted to sulfur dioxide (SO ₂ ).

2H ₂ S + ₃ O ₂ → 2SO ₂ + 2H ₂ O. (1)

Subsequently, in the subsequent catalytic reaction process, unconverted hydrogen sulfide and sulfur dioxide generated in a high temperature furnace are controlled at a molar ratio of 2: 1, and converted to elemental sulfur by a condensation reaction known as a Klaus reaction on an alumina (Al ₂ O) catalyst.

2H ₂ S + SO ₂ 3 / nS _n + 2H ₂ O. (2)

However, the Klaus process has a limited sulfur recovery due to the following reasons, it does not completely process the hydrogen sulfide.

First, the Klaus reaction is thermodynamically reversible, so the equilibrium conversion is limited.

Second, since it is difficult to remove the water produced in the forward reaction, as a result, the reverse reaction of the Klaus reaction predominates, and the rate of removing hydrogen sulfide with elemental sulfur is lowered.

Third, it is difficult to accurately control the molar ratio of hydrogen sulfide and sulfur dioxide generated in a high temperature furnace to a stoichiometric ratio (H ₂ S / SO ₂ = 2: 1), thereby reducing the efficiency of the reaction.

Due to the problems described above, in the Klaus process, about 3-5% of the untreated gas is usually discharged. Incineration of these untreated gases produces more than about 1000 ppm of sulfur dioxide, which exceeds the recently tightened environmental law emission standards.

In order to solve the above problems, an additional process for treating untreated sulfide (tail-gas) discharged from the Klaus process is required. Currently, various methods have been developed and used in the field as tail gas treatment (TGT) of the Klaus process. However, these processes generally use adsorption or absorption methods, which makes it difficult to continuously operate the equipment in that wastes are generated after treatment or periodic regeneration processes are required. As the post-treatment process, the following processes have been used.

First, a process of removing hydrogen sulfide by hydrogenation of an untreated gas and then selectively oxidizing the produced hydrogen sulfide on a catalyst and recovering elemental sulfur as the most efficient process among post-treatment processes.

2H ₂ S + O ₂ → 2 / nS _n + 2H ₂ O. (3)

Representative methods using this method are MODOP (MODOP: Mobil Direct Oxidation Process: EP-0 078 690-A2) and Super Claus (US 5,286,697) process.

The Modoop process converts hydrogen sulfide with oxygen in a stoichiometric ratio directly to elemental sulfur on a titanium dioxide (TiO ₂ ) -based catalyst.The conversion rate to elemental sulfur is more than 99.6% when used in a three-step process including the Klaus process. Very high. However, it is limited by moisture in that about 30% by volume of moisture contained in unreacted gas must be lowered to less than 5% by dehydration before entering the catalytic reactor.

On the other hand, the superclaus process is similar to the Mododo process, but recovers elemental sulfur directly by reacting hydrogen sulfide and excess oxygen on an iron oxide (Fe ₂ O ₃ ) catalyst without dehydration. This is very high, over 99%. However, since the superclaus process does not involve dehydration, in order to prevent poisoning of the catalyst by water and to limit the Klaus reaction, it is usually necessary to react excess oxygen at an order of 10 or more times the equivalent ratio, thus the total gas to be treated. Since the amount of is increased and oxygen must be reacted at a high equivalent ratio as described above, there is a disadvantage in that it is difficult to process a high concentration hydrogen sulfide gas of 2 vol% or more.

On the other hand, in the smelting process used in the smelting process of steel mills, coke is used as a fuel, and hydrogen sulfide generated in this process is concentrated using aqueous ammonia. The concentrated hydrogen sulfide is separated from ammonia through a degassing process and treated by the Klaus process. However, since hydrogen sulfide is not completely separated, less than about 2% of hydrogen sulfide remains in the ordination, and incineration also exceeds the emission standard under environmental law. In addition, the conventional catalysts are usually most of those that work in the absence of ammonia and water is not suitable for removing the hydrogen sulfide discharged through the process through the oxidation. Therefore, there is an urgent need to develop a method that can be removed by selectively oxidizing hydrogen sulfide even in the presence of ammonia and water and converting it into non-toxic elemental sulfur or sulfur compounds.

Accordingly, an object of the present invention is to oxidize hydrogen sulfide because it is highly resistant to water and ammonia, which is not considered at all in the post-treatment process of the conventional Klaus process, and has high activity even under low concentrations of oxygen. It is to provide a catalyst that can increase the conversion to elemental sulfur.

Another object of the present invention is to provide a method for selectively oxidizing hydrogen sulfide even in the presence of water and ammonia to remove it with non-toxic elemental sulfur or sulfur compounds.

In order to achieve the above object, in the present invention, a catalyst for the selective oxidation of hydrogen sulfide gas containing ammonia and water is provided with a catalyst characterized in that 1 to 40% by weight of iron oxide is supported on a non-basic porous carrier.

The non-basic porous carrier is not particularly limited as long as it is non-basic, particularly neutral and porous, but it is preferable to use silicon dioxide or alpha-alumina.

In order to achieve another object of the present invention, in the present invention, a reaction gas containing hydrogen sulfide gas is reacted with oxygen under a catalyst in the presence of ammonia and water to convert hydrogen sulfide contained in the reaction gas into elemental sulfur or non-toxic sulfur compound. In the method for removing hydrogen sulfide, there is provided a method wherein the catalyst is iron oxide supported on a non-basic porous carrier.

The content of the ammonia is 5 to 30% by volume based on the reaction gas, the water content is preferably 1 to 80% by volume relative to the reaction gas. In addition, the content of hydrogen sulfide in the reaction gas is preferably 1 to 20% by volume.

The selective oxidation of hydrogen sulfide by the catalyst is preferably carried out under conditions of 200 to 340 ° C., preferably 240 to 300 ° C., and a molar ratio of oxygen / hydrogen sulfide 0.5 to 6, especially 0.5 to 4.

Hereinafter, the present invention will be described in more detail.

The hydrogen sulfide selective oxidation catalyst of the present invention is characterized by converting toxic hydrogen sulfide into non-toxic substances by selectively oxidizing hydrogen sulfide to elemental sulfur or ammonium sulfate even in the presence of ammonia and water.

The catalyst used in the present invention is used in a form in which iron oxide is supported on a carrier, especially a non-basic carrier, because if the carrier is basic, the reverse reaction of the Klaus can be activated to reduce the sulfur recovery rate. If the conditions are satisfied, there is no particular limitation as a carrier, but preferably silicon dioxide (SiO ₂ ) or alpha alumina (α-Al ₂ O ₃ ) or the like may be used.

The method for supporting the iron oxide on the carrier is not particularly limited, but it is preferable to use the following method.

First, the iron salt is dissolved in a solvent and supported on a carrier, followed by drying to evaporate the solvent. Subsequently, the mixed salt of oxygen and an inert gas is calcined to convert the supported salt into the corresponding oxide. The choice of solvent depends on the type of salt used, and drying is preferably carried out for 2-10 hours under oxygen and an inert gas atmosphere in the temperature range of 80-130 ° C., with the temperature rise being controlled in stages. .

The catalyst prepared as described above preferably has an iron oxide content of 1 to 40% by weight based on the total weight of the catalyst. When the content of these oxides is less than 1% by weight, the catalytic effect of these compounds is insignificant, and 40% by weight. This is because the conversion rate of hydrogen sulfide is not maintained at a high level.

The catalyst prepared by the above process is charged to the reactor and reacted with a mixed gas of ammonia, water and hydrogen sulfide in the range of 200 to 340 ° C., preferably 240 to 300 ° C., hydrogen sulfide is oxidized to form elemental sulfur and ammonium sulfate. It is removed by recovery in the form of a mixture. When the reaction temperature is less than 200 ℃ the elemental sulfur produced is physically deposited on the surface of the catalyst to lower the activity of the catalyst, when the temperature exceeds 340 ℃ hydrogen sulfide conversion rate is reduced to less than 80%.

In addition, the reaction conditions are preferably in a range in which the molar ratio of oxygen / hydrogen sulfide is 0.5 to 6, in particular 0.5 to 4, and in this range, a high hydrogen sulfide conversion rate can be obtained regardless of the reaction temperature.

The catalyst of the present invention exhibits high activity even in the presence of ammonia and water, including 5 to 30% by volume of ammonia, in particular 5 to 20% by volume, 1 to 80% by volume of water, and particularly 10 to 60% by volume of the reaction gas. It is preferable that it is done. This is because, when water is present in excess of this range, water acts as a toxic factor, greatly degrading the properties of the catalyst, and when ammonia is present in excess of 30% by volume, it is difficult to use commercially. to be.

In addition, the catalyst of the present invention exhibits high activity even when hydrogen sulfide is present in high concentrations, and when the hydrogen sulfide content in the reaction gas is up to 20% by volume, in particular, 1 to 20% by volume is suitable for maintaining the desired activity. . This is because a conventional treatment method is effectively used for the treatment of hydrogen sulfide present in a high concentration beyond this range, and the present invention aims to treat hydrogen sulfide present at a relatively low concentration.

Hereinafter, the features of the present invention will be described in more detail with reference to Examples, but the present invention is not necessarily limited to the following Examples.

In the examples, the conversion rate of hydrogen sulfide and the selectivity of elemental sulfur and ammonium sulfate were calculated as follows.

H ₂ S conversion rate (%) =

SO ₂ selectivity (%) =

Selectivity of elemental sulfur and ammonium sulfate (%)

=

Example 1

The solution obtained by dissolving iron citrate in distilled water was impregnated in pre-dried silicon dioxide, and then water was evaporated using a rotary vacuum evaporator. Subsequently, the resultant was dried at 120 ° C. for 12 hours and then calcined at 500 ° C. for 5 hours with a mixed gas of oxygen and nitrogen, so that iron oxide (Fe ₂ O ₃ ) was added to silicon dioxide (SiO ₂ ) in a range of 0.5 wt% to 40 wt% See Table 1) to carry the supported catalyst. In addition, a catalyst composed only of iron oxide without being supported on a carrier was also prepared.

The obtained catalyst was charged to a reactor and then fed with a mixed gas containing 5% by volume of hydrogen sulfide, 2.5% by volume of oxygen, 10% by volume of ammonia, 60% by volume of water, and the remaining amount of helium.

After the reaction was carried out at a fixed space velocity of 60,000 ^{hr −1} and a reaction temperature of 260 ° C., conversion of hydrogen sulfide and selectivity to sulfur dioxide were measured and shown in Table 1 below.

TABLE 1

Conversion Rate of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to the Amount of Iron Oxide Supported

In the above experimental conditions, even if the supported amount of iron oxide is 1.0% by weight, the catalyst of the present invention exhibits activity at a desirable level, but exhibits catalytic activity at a more preferred level when supported at a ratio of 5% to 20% by weight. Seems to be. In addition, when iron oxide was used on its own without being supported on a carrier, the conversion rate of hydrogen sulfide was found to be less than 70%.

Example 2

As an experiment to investigate the effect of the reaction temperature on the activity of the iron oxide catalyst, the reaction temperature was 240 ℃, 260 ℃, 280 ℃, 300 ℃, 320 ℃ using a catalyst having a support ratio of iron oxide to the carrier 10% by weight The reaction was carried out under the same conditions as in Example 1 except that the experiment was carried out while changing to 360 ° C., and the conversion rate of hydrogen sulfide and the selectivity to sulfur dioxide were measured and shown in Table 2.

TABLE 2

Conversion Rate of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to Reaction Temperature

Under the above conditions, the conversion rate of hydrogen sulfide is maintained close to 90% until the reaction temperature is 300 ℃, the conversion rate of hydrogen sulfide is maintained at 80% or more even at 340 ℃ and no sulfur dioxide is produced, but since then the conversion rate of hydrogen sulfide It dropped significantly and the production amount of sulfur dioxide increased. These results may be varied by changing the reaction conditions, but in general, the range of suitable reaction temperatures seems to be up to 300 ° C.

Example 3

The catalyst was prepared in the same manner as in Example 1 except that the molar ratio of oxygen / hydrogen sulfide was changed from 0.5 to 4.0 by changing the concentration of oxygen from 2.5 to 20% by volume and the reaction temperature was changed to 260-340 ° C. The reaction was carried out under the same conditions as in Example 1, and the conversion rate of hydrogen sulfide and the selectivity of sulfur dioxide were measured, and the results are shown in Table 3.

TABLE 3

Conversion Rate of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to Oxygen Concentration

As the volume of oxygen increases, the conversion rate of hydrogen sulfide increases, but the production of sulfur dioxide also increases. In particular, sulfur dioxide was not produced at a reaction temperature of 260 ° C. Therefore, the catalyst of the present invention can efficiently remove hydrogen sulfide even at an excessive oxygen concentration.

Example 4

Hydrogen sulfide was carried out in the same manner as in Example 1, except that the concentration of ammonia was changed from 5% to 30% by volume using a catalyst prepared in the same manner as in Example 1, and the experiment was carried out at 260 ° C. The conversion rate and the selectivity of sulfur dioxide were measured and the results are shown in Table 4.

TABLE 4

Conversion of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to Ammonia Concentration

As the concentration of ammonia increased, the conversion rate of hydrogen sulfide increased and no sulfur dioxide was produced. Thus, the catalyst of the present invention enables high sulfur recovery even under conditions in which excess ammonia is present.

Example 5

Using a catalyst prepared in the same manner as in Example 1, except that the hydrogen sulfide concentration was changed from 1% to 20%, the oxygen concentration was fixed at 1/2 of the hydrogen sulfide concentration, and the reaction temperature was fixed at 260 ° C. The reaction was carried out under the same conditions as in Example 2 to measure the conversion of hydrogen sulfide and the selectivity of sulfur dioxide, and the results are shown in Table 5.

TABLE 5

Conversion of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to Concentration of H ₂ S

Table 5 shows that when the concentration of hydrogen sulfide is as low as 1%, the conversion rate of hydrogen sulfide reaches 100%, and even if the concentration of hydrogen sulfide is high, the removal efficiency of hydrogen sulfide is maintained high. Therefore, the catalyst of the present invention is more effective when hydrogen sulfide is present in low concentration, but can be used even when hydrogen sulfide is present in high concentration.

Comparative Example 1

For comparison, under the same conditions as in Example 1 except that the reaction was carried out at 260 ° C. using a conventional catalyst showing high activity for the selective oxidation of hydrogen sulfide in the absence of ammonia and water instead of the iron oxide catalyst. The reaction was carried out. As the conventional catalysts as described above, TiO ₂ / SiO ₂ and SnO ₂ / SiO ₂ were used, all of which were used in a form supported on the carrier at a ratio of 10% by weight. In each reaction, the conversion rate of hydrogen sulfide and selectivity to sulfur dioxide were measured, and the results are shown in Table 6.

TABLE 6

Conversion rate of hydrogen sulfide and selectivity of sulfur dioxide according to the conventional catalyst

Comparing Table 6 and Table 1, it can be seen that the iron oxide catalyst of the present invention has a much higher hydrogen sulfide conversion rate than the conventional catalyst at the same reaction temperature. That is, the iron oxide catalyst of the present invention is very effective for selectively treating hydrogen sulfide even in the presence of ammonia and water.

As described above, according to the present invention, by using a catalyst in which iron oxide is supported on a non-basic porous carrier for selective oxidation of hydrogen sulfide, hydrogen sulfide can be directly and selectively oxidized with high efficiency even under the presence of ammonia and water. Therefore, the hydrogen sulfide generated in a large amount in the refinery or steel mill can be easily removed with non-toxic elemental sulfur or ammonium sulfate, and thus the environmental pollution caused by hydrogen sulfide can be solved.

Claims (8)

A catalyst for the selective oxidation of hydrogen sulfide gas containing ammonia and water, characterized in that iron oxide is supported by 1 to 40% by weight on a non-basic porous carrier. The catalyst for selective oxidation of hydrogen sulfide according to claim 1, wherein the carrier is selected from silicon dioxide and alpha-alumina. In a method for removing hydrogen sulfide by reacting a reaction gas containing hydrogen sulfide gas with oxygen under a catalyst in the presence of ammonia and water to convert hydrogen sulfide contained in the reaction gas into elemental sulfur or non-toxic sulfur compounds, the catalyst is iron oxide Method for removing hydrogen sulfide, characterized in that 1 to 40% by weight on the non-basic porous carrier. 4. The method of claim 3 wherein the carrier is silicon dioxide or alpha-alumina. The method of claim 3, wherein the content of the hydrogen sulfide in the reaction gas is 1 to 20% by volume. 4. The method of claim 3, wherein the water content is 1 to 80% by volume with respect to the reaction gas. The method of claim 3, wherein the reaction is carried out at 240 to 300 ℃ hydrogen sulfide removal method, The hydrogen sulfide removal method according to claim 3, wherein the reaction is carried out under the condition that the molar ratio of hydrogen sulfide in oxygen / reaction gas is 0.5 to 4.