KR100247521B1 - Catalyst for oxydizing hydrogen sulfide gas and recovery method of sulfur using the same - Google Patents

Abstract

A catalyst for selective oxidation of hydrogen sulfide gas as a catalyst for selective oxidation of hydrogen sulfide gas, comprising: amorphous mixed oxides of vanadium and phosphorus ((VO) ₂ P ₂ O ₇ ); And a non-acidic and non-basic carrier on which the amorphous mixed oxide is supported. Since the catalyst of the present invention maintains high catalytic activity even in the presence of water, by converting hydrogen sulfide, which is generated in a refinery or steel mill, into non-toxic elemental sulfur, it can be recovered, thereby greatly reducing the environmental pollution problem caused by hydrogen sulfide. It allows you.

Description

Catalyst for oxydizing hydrogen sulfide gas and recovery method of sulfur using the same}

The present invention relates to a catalyst capable of directly oxidizing hydrogen sulfide gas and a method for recovering elemental sulfur by treating a toxic hydrogen sulfide gas using the same, and more particularly, directly to selectively oxidize hydrogen sulfide gas even in the presence of water. And a method for recovering elemental sulfur that is a non-toxic solid phase by selectively oxidizing hydrogen sulfide on the catalyst.

Hydrogen sulfide is a colorless, odorous gas and acts as one of the substances that cause air pollution. Hydrogen sulfide can be generated in large quantities by biological action, but recently, as industrial facilities increase, a large amount of hydrogen sulfide is also generated from various industrial facilities, which causes more serious air pollution. Hydrogen sulfide is hardly removed once it is discharged into the atmosphere, and the damage can be reduced according to the structure and operation method of the discharge facility. Therefore, hydrogen sulfide discharged from industrial facilities can be efficiently removed before being released into the atmosphere. There is an urgent need for a method.

Industrial facilities that generate large amounts of hydrogen sulfide include crude oil, natural gas refining plants, and steel mills. Coal gasification facilities are also expected to emerge as new sources of emissions, especially in the process of removing hydrogen sulfide from these industrial facilities. Development is more urgent.

Until now, the method of removing hydrogen sulfide has mainly been the Claus reaction, in which hydrogen sulfide is thermally oxidized by a reaction system consisting of one high temperature furnace and two to three catalytic reactors. ) And catalytic reactions can be removed with non-toxic elemental sulfur.

First, in the thermal oxidation process, one-third of hydrogen sulfide (H ₂ S) is oxidized in a high temperature furnace at 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 produced 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 Klaus reaction on an alumina (Al ₂ O ₃ ) catalyst.

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However, the Klaus process has a limited sulfur recovery rate for the following reasons, making it difficult to increase the treatment efficiency of hydrogen sulfide to a desirable level.

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 is a high value exceeding 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, the moisture contained in the unreacted gas must be lowered to less than 4% through 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.

As another method, a method of converting hydrogen sulfide into elemental sulfur using a vanadium-based catalyst has been reported. For example, US Pat. No. 4,311,683, which discloses a pure V ₂ O ₅ catalyst in the form of a non-basic carrier, discloses 75-90% sulfur from a reaction gas having a hydrogen sulfide concentration of 500 ppm under a temperature condition of 100 psig and 232 ° C or less. It is described to obtain a recovery rate. In addition, U.S. Patent No. 4,576,814 discloses a 70-80% sulfur recovery rate using a two-component catalyst of V ₂ O ₅ -Bi ₂ O ₃ at a temperature of 246 ° C. or lower and in the presence of 3% by volume of water. U.S. Patent 5,512,258 discloses 2 vol% hydrogen sulfide when using A _{4 ± x} V _{2 ± y} O ₉ (A: Mg, Ca, Zn, 0 ≦ _x ≦ 0.2, 0 ≦ y ≦ 0.5) catalyst system, When the reaction gas containing 1% by volume of sulfur dioxide and oxygen (1% by volume) contains 30% by volume of water vapor, the conversion rate of hydrogen sulfide reaches 70-90% at the reaction temperature of 220 ° C. Is less than desirable.

In the case of the catalysts to date as described above, sulfur generated at high temperature undergoes a reverse reaction in the Klaus reaction in the presence of water, and thus sulfur selectivity is generated as a byproduct, thereby degrading sulfur selectivity. Therefore, the hydrogen sulfide is generally treated at a low temperature. At low temperatures, the catalyst itself is inactivated after long-term use, and sulfation is known to act as a cause of the catalyst deactivation.

Accordingly, an object of the present invention is to provide a catalyst for the selective oxidation of hydrogen sulfide, which can solve the above-mentioned problems and maintain sulfur selectivity at a desirable level even in the presence of excess water and can significantly reduce the deactivation phenomenon. will be.

Another object of the present invention is to provide a method for recovering elemental sulfur by selectively oxidizing hydrogen sulfide even when excess water is present using the catalyst.

In the present invention to achieve the above object, in the catalyst for the selective oxidation of hydrogen sulfide gas, vanadium and phosphorus amorphous mixed oxide ((VO) ₂ P ₂ O ₇ ); And a non-acidic and non-basic carrier on which the amorphous mixed oxide is carried. There is provided a catalyst for selective oxidation of hydrogen sulfide gas.

As the non-acidic / non-basic carrier, it is more preferable to use any one selected from the group consisting of silicon dioxide, silicon carbide, and alpha-alumina. In the case of a carrier catalyst, the weight of the carrier is preferably 60% by weight or less based on the total weight of the catalyst.

In order to achieve another object of the present invention, the present invention comprises the steps of introducing a mixed gas of the reaction gas containing hydrogen sulfide gas, oxygen and steam into a reactor equipped with a catalyst for the selective oxidation of hydrogen sulfide gas; And maintaining the reaction temperature in the reactor at 240 to 350 ° C., maintaining the volume ratio of oxygen / hydrogen sulfide to 0.5 to 1.0, and oxidizing under a condition of maintaining the space velocity at 3,000 to 500,000 / hr. A method for recovering elemental sulfur from hydrogen sulfide is provided.

In the above method, the reaction temperature is maintained at 250 to 325 ℃, the volume ratio of the oxygen / hydrogen sulfide is maintained at 0.5 to 0.6, and the space velocity is preferably maintained at 3,000 to 100,000 / hr.

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

The catalyst of the invention comprises a mixed oxide of vanadium and phosphorus, which is in the (VO) ₂ P ₂ O ₇ phase or in the amorphous mixed phase and optionally present in a supported form on the carrier. First, in the case of preparing a catalyst composed of (VO) ₂ P ₂ O ₇ phase, a mixed solution is prepared by dissolving V ₂ O ₅ and H ₃ PO ₄ in an aqueous oxalic acid solution, and then removing water by evaporation to dryness. Is made by heat treatment at about 500 ° C. under nitrogen atmosphere for several hours. In the case of an amorphous mixed oxide catalyst, V ₂ O ₅ and NH ₄ H ₂ PO ₄ are dissolved in an aqueous oxalic acid solution to prepare a mixed solution, and then a carrier is added thereto, evaporated to dryness to remove moisture, and then subjected to about 450 ° C. under an air atmosphere. It is made by heat treatment for several hours at. The VPO of the present invention exhibits catalytic activity alone but also in the form supported on a carrier. In the case of the form supported on the carrier, the weight of the carrier is preferably 60% by weight or less based on the total weight of the catalyst. This is due to the mechanism characteristic of the catalyst of the present invention in which it participates in the selective oxidation of hydrogen sulfide. That is, the catalyst is reduced by hydrogen sulfide during the reaction to lose lattice oxygen, and the catalyst which loses lattice oxygen is catalyzed by an oxidation-reduction mechanism in which activity is maintained by receiving lattice oxygen from gaseous oxygen again. The reaction proceeds. Therefore, the maintenance of the activity of the present reaction depends on the amount of lattice oxygen contained in the catalyst and whether or not the oxidation of the catalyst is caused by oxygen in the gas phase. Therefore, when the supported amount of mixed oxide is small, the amount of lattice oxygen included in the catalyst is small, and thus the activity decreases after a long time reaction at low space velocity and a relatively short time reaction at high space velocity.

In the presence of a catalyst prepared by the above-described process, when the gas containing hydrogen sulfide and oxygen gas are reacted at 250 to 350 ° C., hydrogen sulfide is smoothly oxidized and recovered in the form of elemental sulfur. In this case, when the reaction temperature is lowered below 250 ° C., the catalyst is deactivated, and when it exceeds 350 ° C., the recovery of sulfur falls. At this time, the reaction conditions of the oxygen / hydrogen sulfide ratio is in the range of 0.5 to 1.0, the space velocity of the inlet gas is preferably in the range of 3,000 to 1,000,000 / h, more preferably the reaction temperature is 250 to 325 ℃, oxygen / hydrogen sulfide ratio Is in the range of 0.5 to 1.0, and the space velocity of the inlet gas is preferably in the range of 3,000 to 500,000 / h. On the other hand, it is more preferable if the space velocity is in the range of 3,000 to 100,000 / h and the other reaction conditions are the same as above.

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.

<Example 1>

6.0 g of V ₂ O ₅ and 6.5 g of H ₃ PO ₄ were dissolved in 400 ml of 10 wt% oxalic acid aqueous solution, and a mixed solution was prepared by evaporation to dryness to remove VOHPO ₄ .0.5H ₂ O. This was treated under nitrogen atmosphere at 500 ° C. for 4 hours to prepare a VPO catalyst including (VO) ₂ P ₂ O ₇ phase. The catalyst was charged to the reactor, and then supplied with a mixed gas containing 5% by volume of hydrogen sulfide, 2.5% by volume of oxygen, and the remaining amount of helium.

After the space velocity was fixed at 12,000 / h and the reaction temperature was changed to 220 to 370 ° C., the oxidation reaction of hydrogen sulfide was performed, and the conversion rate, sulfur selectivity, and sulfur recovery rate of hydrogen sulfide were measured.

Conversion Rate of Hydrogen Sulfide and Selectivity of Sulfur Dioxide According to Reaction Temperature Temperature (℃) H ₂ S conversion rate (%) SO ₂ selectivity (%) Sulfur recovery rate (%) 220250275300325350370 97959390878378 99.5999896949187 96.594.191.186.481.875.567.9

As can be seen from Table 1, the sulfur recovery yield was found to be more than 80% in the reaction temperature range of 220-325 ℃. However, at 220 ° C., the sulfur recovery rate is rapidly decreased when the catalyst is used for a long time due to the deactivation of the catalyst. Therefore, according to the catalyst of the present invention, it can be used stably for a long time without deactivation of the catalyst at a high temperature in comparison with the conventional catalyst that was used mainly at a temperature of 245 ℃ or less despite the catalyst deactivation phenomenon.

<Example 2>

The hydrogen sulfide conversion rate, sulfur dioxide selectivity and sulfur are shown in Table 2 below, except that 5-30% by volume of water vapor is added to the mixed gas, and hydrogen sulfide oxidation is carried out under the same conditions as in Example 1. Expressed as recovery.

Results of Oxidation Reaction of Hydrogen Sulfide with Water Content Moisture content (%) division Temperature (℃) 250 275 300 325 5 % Conversion 96 94 90 88 Selectivity (%) 96 93 91 88 Yellow recovery rate (%) 92.2 87.4 81.9 77.4 10 % Conversion 94 92 89 84 Selectivity (%) 96 92 89 85 Yellow recovery rate (%) 90.2 84.6 79.2 71.4 20 % Conversion 92 90 86 80 Selectivity (%) 95 90 85 81 Yellow recovery rate (%) 87.4 81.0 73.1 64.8 30 % Conversion 90 85 81 75 Selectivity (%) 95 90 87 79 Yellow recovery rate (%) 85.5 76.5 70.5 59.3

From Table 2, the mixed oxide catalyst of vanadium and phosphorus has a relatively high yield of sulfur even in the presence of excess water vapor. The higher the content of water vapor, the lower the yield of sulfur is, but by adjusting the reaction temperature, even when the content of water vapor is 30%, more than 80% of sulfur recovery can be obtained.

<Example 3>

Dissolving 6.0 g of V ₂ O ₅ and 8.4 g of NH ₄ H ₂ PO _{4 in} 700 ml of 10 wt% aqueous solution of oxalic acid to prepare a mixed solution, followed by addition of 17 g of silicon dioxide as a carrier, followed by evaporation to dryness to remove moisture. It was. Subsequently, after drying at 130 ° C. for about 6 hours, firing was performed while flowing air at 450 ° C. for about 6 hours. The catalyst thus obtained was confirmed to be XRD (X-ray diffraction), and was amorphous. In addition, by comparing the weight of the carrier before and after supporting, it was confirmed that about 40% by weight of amorphous VPO as a catalyst phase was supported (VPO (40% by weight) / SiO ₂ ). The specific surface area of silicon dioxide used as the carrier was 300 m ² / g and the average pore diameter was 150 mm 3 (manufactured by Davisil, Aldrich). The prepared catalyst was charged in a reactor and then subjected to oxidation of hydrogen sulfide under the same conditions as in Example 1, and the results are shown in Table 3.

Oxidation of Hydrogen Sulfide by VPO (40 wt%) / SiO ₂ Catalyst According to Reaction Temperature Temperature (℃) H ₂ S conversion rate (%) SO ₂ selectivity (%) Sulfur recovery rate (%) 250275300325 97969390 99989895 96.094.191.185.5

As can be seen from Table 3, the catalyst on which V-P-O is loaded at about 40% by weight also enables the achievement of the sulfur recovery equivalent to that of the uncarried mixed oxide catalyst.

<Example 4>

In order to determine the activity of the catalyst according to the ratio of oxygen / hydrogen sulfide and the presence of water, in Example 1, the reaction temperature was 250 ° C., the space velocity was 96,000 / h, and water was not added to the mixed gas. Hydrogen sulfide was oxidized under the same conditions as in Example 1 except that 30 vol% of the added oxygen was used as a reactor to change the oxygen / hydrogen sulfide ratio as described in Table 4 below. Table 4 shows.

Oxidation reaction of hydrogen sulfide according to oxygen / hydrogen sulfide ratio and presence of water Oxygen / Sulfide Consumption If no water is added When 30% by volume of water is added % Conversion Selectivity (%) Yellow recovery rate (%) % Conversion Selectivity (%) Yellow recovery rate (%) 0.40.50.60.81.0 9095989999 9999887670 89.194.186.275.269.3 7390959798 9993836342 72.383.778.961.141.2

When oxygen is present at a ratio of less than 1/2, which is the oxygen / hydrogen sulfide equivalent ratio according to the reaction in the oxidation reaction for converting hydrogen sulfide to elemental sulfur, the selectivity is high but the conversion rate is low, and exceeds 1/2, regardless of the presence of water. In the presence of oxygen, the conversion is high but the selectivity is greatly reduced. Therefore, an optimum sulfur recovery yield can be obtained when oxygen is present in an equivalent ratio, that is, when oxygen / hydrogen sulfide ratio = 0.5.

<Example 5>

In order to determine the catalytic activity according to the concentration of hydrogen sulfide present in the reaction gas, the reaction temperature was set to 270 ° C in Example 1, and hydrogen sulfide under the same conditions as in Example 1 except that the concentration of hydrogen sulfide in the reaction gas was changed. To perform the oxidation reaction of the results are shown in Table 5.

Oxidation of Hydrogen Sulfide with Different Hydrogen Sulfide Concentrations in Reaction Gas Hydrogen sulfide concentration (vol%) H ₂ S conversion rate (%) SO ₂ selectivity (%) Sulfur recovery rate (%) 5102040 93949697 98989796 91.192.193.193.1

As can be seen from Table 5, using the V-P-O catalyst it is possible to obtain a high sulfur recovery rate irrespective of the hydrogen sulfide concentration in the reaction gas.

<Example 6>

In order to determine the reaction efficiency according to the space velocity, the reaction was carried out in the same manner as in Example 1 except that the reaction temperature was set to 270 ° C. and the results are shown in Table 6 below.

Oxidation of Hydrogen Sulfide According to Space Velocity Space velocity (/ h) H ₂ S conversion rate (%) SO ₂ selectivity (%) Sulfur recovery rate (%) 1,0003,00010,000100,0001,000,000 93.994.094.394.592.0 98.598.098.298.398.5 92.592.192.692.990.6

As can be seen from Table 6, the sulfur recovery was almost high regardless of the space velocity, and the catalyst activity was good enough to be used even at a high space velocity of about 1,000,000 / h. However, as can be seen from the above table, in the case of 1,000,000 / h or more, it can be seen that the yield of sulfur is slightly reduced. From the above Table 6, which is data on an example of the oxidation reaction of hydrogen sulfide according to the above space velocity, it is preferable to maintain the reaction conditions in the range of 3,000 to 1,000,000 / h (hydrogen sulfide conversion of 92% or more, sulfur recovery yield). More than 90%), although not shown in Table 6 above, 500,000 / h, which is the median of the space velocity of 100,000 / h and 1,000,000 / h, is expected to be 91%. It is obvious that more preferable results can be obtained by maintaining the space velocity range with the upper limit as 3,000 to 500,000 / h. In addition, as shown in Table 6, it can be seen that the most desirable effect (recovery rate of 92% or more) is maintained when the space velocity is maintained in the range of 3,000 to 100,000 / h.

As described above, according to the present invention, since hydrogen sulfide can be achieved by directly oxidizing hydrogen sulfide to a high efficiency selectively even under the presence of water, hydrogen sulfide generated in a large amount in a refinery or an iron and steel plant is non-toxic. By converting and recovering elemental sulfur, it is possible to greatly reduce the environmental pollution problem caused by hydrogen sulfide.

Claims (5)

A catalyst for the selective oxidation of hydrogen sulfide gas, comprising: amorphous mixed oxides of vanadium and phosphorus ((VO) ₂ P ₂ O ₇ ); And a non-acidic and non-basic carrier on which the amorphous mixed oxide is supported. The method of claim 1, The carrier is a catalyst for the selective oxidation of hydrogen sulfide gas, characterized in that selected from the group consisting of silicon dioxide, silicon carbide and alpha-alumina. The method of claim 1, The carrier is a catalyst for the selective oxidation of hydrogen sulfide gas, characterized in that contained in 60% by weight or less based on the total weight of the catalyst. Introducing a mixed gas of a reaction gas containing hydrogen sulfide gas, oxygen, and water vapor into a reactor equipped with a catalyst for the selective oxidation of the hydrogen sulfide gas of any one of claims 1 and 2; And Maintaining a reaction temperature in the reactor at 240 to 350 ° C., maintaining a volume ratio of oxygen / hydrogen sulfide at 0.5 to 1.0, and oxidizing under a condition of maintaining a space velocity at 3,000 to 500,000 / hr. A method for recovering elemental sulfur from hydrogen sulfide. The method of claim 4, wherein The reaction temperature is maintained at 250 to 325 ℃, the volume ratio of the oxygen / hydrogen sulfide is maintained at 0.5 to 0.6, the method for recovering elemental sulfur from hydrogen sulfide, characterized in that the space velocity is maintained at 3,000 to 100,000 / hr.