RU2288888C1 - Catalyst for selective oxidation of hydrogen sulfide, method of preparation thereof, and a process of selectively oxidizing hydrogen sulfide to elemental sulfur - Google Patents

Abstract

FIELD: gas treatment processes and catalysts.

SUBSTANCE: invention relates to catalyst for selectively oxidizing hydrogen sulfide to sulfur in industrial gases containing 0.5-3.0 vol % hydrogen sulfide and can be used at enterprises of gas-processing, petrochemical, and other industrial fields, in particular to treat Claus process emission gases, low sulfur natural and associated gases, chemical and associated petroleum gases, and chemical plant outbursts. Catalyst for selective oxidation of hydrogen sulfide into elementary sulfur comprises iron oxide and modifying agent, said modifying agent containing oxygen-containing phosphorus compounds. Catalyst is formed in heat treatment of α-iron oxide and orthophosphoric acid and is composed of F₂O₃, 83-89%, and P₂O₅, 11-17%. Catalyst preparation method comprises mixing oxygen-containing iron compounds with modifying agent compounds, extrusion, drying, and heat treatment. α-Iron oxide used as oxygen-containing iron compound is characterized by specific surface below 10 m²/g, while 95% of α-iron oxide have particle size less than 40 μm. Orthophosphoric acid is added to α-iron oxide, resulting mixture is stirred, dried, and subjected to treatment at 300-700°C. Hydrogen sulfide is selectively oxidized to elemental sulfur via passage of gas mixture over above-defined catalyst at 200-300°C followed by separation of resultant sulfur, O₂/H₂S ratio in oxidation process ranging from 0.6 to 1.0 and volume flow rate of gas mixture varying between 900 and 6000 h^-1.

EFFECT: increased yield of elemental sulfur.

9 cl, 5 tbl, 9 ex

Description

The invention relates to a catalyst for the selective oxidation of hydrogen sulfide, a method for its production and a method for the selective oxidation of hydrogen sulfide to sulfur in industrial gases containing 0.5-3.0 vol.% Hydrogen sulfide, and can be used in gas processing, petrochemical and other industries, in particular for the purification of exhaust gases from the Klaus process, low-sulfur natural and associated petroleum gases, and emissions from chemical industries.

Currently, to extract sulfur from gases of various origin containing small concentrations of hydrogen sulfide, methods based on the oxidation of hydrogen sulfide to sulfur by the reaction are used:

in the gas phase in the presence of a solid catalyst ("Improved Claus sulphur recovery: Keeping abreast of the regulations", Sulfur, 1994, No. 231, p. 35-59). The practical implementation of this reaction with the achievement of a high sulfur yield is hindered by a number of reasons. The oxidation of hydrogen sulfide to sulfur can efficiently proceed in a limited temperature range (180-300 ° C): the upper temperature limit is due to the possibility of a homogeneous sulfur oxidation reaction in SO ₂ at a higher temperature, the lower one - catalyst deactivation due to sulfur condensation on the catalyst surface.

In addition, the selectivity of the oxidation of hydrogen sulfide to sulfur may decrease due to a number of adverse reactions. In particular, the selectivity can be reduced due to the oxidation of sulfur condensed on the surface of the catalyst:

or due to the reaction of oxidation of hydrogen sulfide to sulfur dioxide:

In the presence of water vapor in the exhaust gases, the use of catalysts active in the Klaus reaction, such as aluminum oxide and titanium dioxide, can lead to a decrease in the yield of sulfur due to the reversible Klaus reaction towards the formation of sulfur dioxide:

The problem of deep purification of exhaust gases by selective oxidation of hydrogen sulfide to sulfur reduces to the creation of a catalyst capable of selectively oxidizing hydrogen sulfide to elemental sulfur by reaction (1) and not contribute to the occurrence of side reactions (2) - (4).

A known catalyst used for the oxidation of hydrogen sulfide by oxygen to sulfur, containing, as active components, iron and vanadium oxides supported on alumina with S _beats. > 30 m ² / g and V _pore 0.4-0.8 cm ³ / g (US Patent No. 4197277, Cl. C 01 B 17/04, 1980). However, alumina with such a specific surface area still contains a certain amount of γ-Al ₂ O ₃ phase, which is active in the Klaus reaction and thus contributes to a decrease in the sulfur yield due to the Klaus reverse reaction (4).

Known iron oxide catalyst for the oxidation of hydrogen sulfide to sulfur in natural gases (AS USSR No. 871813, CL. 01 17/04, 1981), characterized by a low specific surface area (2 cm ² / g), a developed porous structure and the average pore radius is 2500 Å. Oxidation of hydrogen sulfide in the presence of this catalyst is recommended in the presence of excess (2-12 times) compared with the stoichiometrically necessary amount of oxygen, which increases the likelihood of formation of sulfur dioxide by reaction (2) and can lead to a decrease in selectivity with increasing temperature. Indeed, the degree of conversion of hydrogen sulfide to sulfur on this catalyst at 275 ° C is 89.5%, at 300 ° C - 62.3% (A.S. No. 967551, Cl. B 01 J 23/74, 1982). In addition, the specified catalyst is characterized by low mechanical strength and is intended for the purification of gas streams that do not contain water vapor.

A known catalyst (A.S. No. 967551, Cl. B 01 J 23/74, 1982) for producing sulfur by oxidation of hydrogen sulfide with oxygen in the air, containing 11.1-23.5 wt.% Iron oxide deposited on an aluminosilicate faience carrier composition , wt.%: alumina 22.4-24.0; magnesium oxide 0.59-0.62; calcium oxide 0.66-0.73, potassium oxide 0.3-0.4; sodium oxide 0.23-0.25, silicon oxide - the rest. One of the disadvantages of this catalyst is the complicated method of preparation, which includes preparing the carrier in the first stage by mixing a mixture of powders of kaolin, clay and quartz sand with water, followed by molding cuttings from the resulting paste, drying at 120 ° C for 14 hours and calcining in air for 30 hours at a temperature of 1200 ° C; and in the second stage, the carrier is impregnated with an iron (III) nitrate solution, followed by evaporation of the excess solution in a water bath with continuous stirring, drying at 120 ° C and calcination at 650 ° C for 4 hours. The described method of preparing the catalyst is very uneconomical because the need to prepare fine powders, calcine the carrier and catalyst at high temperatures for a long time, and the use of natural raw materials (clay, sand) and a complex impregnation procedure makes it difficult to obtain a catalyst reproducible properties by this method on an industrial scale.

A known catalyst for the oxidation of hydrogen sulfide in sulfur (A. S. No. 856974, Cl. With 01 17/04, 1981); containing oxides of iron and titanium, with the following content of components wt.%: iron oxide - 0.05-3.0, titanium dioxide - the rest. However, high activity on this catalyst can be achieved only when the process is carried out in two stages, with a separate supply of oxygen to each stage and the mandatory capture of the sulfur and water formed at each stage. In addition, the presence of titanium dioxide in the catalyst, which is known to have high catalytic activity in the Klaus reaction, will not allow to achieve a high sulfur yield during the purification of gas mixtures containing water vapor due to the reversible Klaus reaction (4).

Known solid porous oxide catalyst (US Patent No. 5603913, CL. 01 B 17/16, 1997) for the selective oxidation of hydrogen sulfide to sulfur, in which the atomic proportions of metals correspond to the formula Fe _A Mg _B Zn _C Cr _D , where A = 0, 5-10, B = 0.1-10, C = 0-1, D = 0-1, at B + C = 1, the specific surface area of the catalyst is 1-5 m ² / g, at least 90% of the pores have a diameter greater than 500 Å. Selective oxidation is carried out by passing a gas stream containing hydrogen sulfide and oxygen over the catalyst at a space velocity of 100-6000 h ^-1 and in the temperature range 180-300 ° C. The catalyst is prepared by precipitation of metal hydroxides from a solution containing salts of one or more metals, by adding to this solution an ammonia or alkali solution to pH 10-11, followed by filtering the finished precipitate, washing, molding, drying and calcining at a temperature of 600-1000 ° FROM. This method of preparation does not allow to obtain granules of catalyst having sufficient strength. Another disadvantage of this catalyst is the presence of a large amount of filtrate and wash water contaminated with metal cations, nitrate and chloride ions. In addition, one of the components of the catalyst - chromium - is toxic.

In US patent No. 5891415 (Cl. 01 B 17/16, 1999) for the process of selective oxidation of hydrogen sulfide into elemental sulfur, it is proposed to use a solid porous oxide catalyst in which the metal content corresponds to the formula Fe _A Zn _and , where A = 0.5- 10, B = 1-2, the specific surface is 2-5 m ² / g, more than 90% of the pores are larger than 500 Å. The catalyst is prepared by mixing iron and zinc oxides, ground in a ball mill by wet grinding so that the atomic ratio of Fe ₂ About ₃ : ZnO = 1: 1. The resulting paste is dried at room temperature for 24 hours, when humidity reaches 32-33%, the paste is molded into cuttings with a diameter of 4 mm, a length of 4-6 mm, dried at 140 ° C, then calcined for 3.5 hours at a temperature of 600 -1000 ° C. Selective oxidation is carried out by passing a gas stream containing hydrogen sulfide and oxygen over the catalyst at a space velocity of 100-6000 h ^-1 and in the temperature range 180-300 ° C. The main disadvantage of this catalyst is the need for strict adherence to the stoichiometric ratio of Fe and Zn and the calcination procedure in order to ensure complete binding of the individual Fe and Zn oxides to zinc ferrite, since the active component of this catalyst is zinc ferrite, and the presence of the free oxide phase is not bound in spinel, leads to rapid deactivation and a decrease in selectivity (Saleh Abdulhamid, Salim Ali, Kozharov A.I., Mirzai J.I. Partial oxidation of hydrogen sulfide to a ferrite catalyst x. Math. Azerbaijan technical colleges, 2000, N 5, 25-33).

The closest, in essence, is a catalyst that contains at least one catalytically active component in an amount of 1-10 wt.%, Selected from the group of oxides: iron, chromium, manganese, cobalt and / or nickel, as promoters contains phosphorus and / or alkali metal compounds in an amount of 0.05-1.0 wt.%, on a carrier - silicon dioxide, and is characterized by S _beats - 20-350 m ² / g and an average pore radius of 32-2980 Å (RF Patent No. 2070089, Cl. C 01 B 17/04, B 01 J 23/86, 1989). The catalyst according to the invention may additionally contain as a promoter from 0.05 to 1 wt.% Compounds of phosphorus or sodium. The catalyst is intended for the oxidation of hydrogen sulfide by oxygen in a fixed or fluidized bed at a temperature of 150-330 ° C and a molar ratio of O ₂ / H ₂ S equal to 0.5-1.5 in a gas mixture containing 1.5 vol.% H ₂ S, 30 vol.% Water vapor. The catalyst is prepared by impregnating the carrier in terms of moisture capacity with solutions containing complexes of iron ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, cellulose solution, and salt solutions of the promoting compounds. The disadvantages of the method of preparation of the catalyst are the use of complex expensive complexes of iron with organic ligands as a precursor of the active component, strict regulation of the stage of deposition of the catalytically active material on the carrier, the stages of drying and calcination of the catalyst necessary to obtain a catalyst with a uniform distribution of the active component. The disadvantage of the method of oxidizing hydrogen sulfide in the presence of this catalyst is the need to use an excess oxygen concentration compared to stoichiometrically necessary to prevent catalyst deactivation, since under these conditions the probability of sulfur oxidation increases, especially in the temperature range above 250 ° C.

The main disadvantage of this catalyst is that a high sulfur yield (above 80%) is achieved in a narrow temperature range (240-280 ° C). The catalyst described in this patent has insufficiently high activity at low temperatures, as a result, at a temperature of 240 ° C, the sulfur yield is not more than 60%. At temperatures above 270 ° C, the selectivity of the conversion of hydrogen sulfide to sulfur and the sulfur yield begin to decrease markedly due to the formation of SO ₂ , which leads to a decrease in the sulfur yield, which is only 62% at 300 ° C.

The basis of the present invention is the development of a catalyst and a method for the oxidation of hydrogen sulfide with oxygen in sulfur in the presence of 0-30 vol.% Water vapor, providing a higher sulfur yield at the oxidation stage in the temperature range 200-300 ° C compared with the prototype.

The problem is achieved using a catalyst for the selective oxidation of hydrogen sulfide in elemental sulfur, including iron oxide and a modifying additive. As a modifying additive, the catalyst contains oxygen-containing phosphorus compounds, while the catalyst is formed during the heat treatment of α-iron oxide and phosphoric acid and has the following composition, wt.% In terms of oxide: Fe ₂ O ₃ 83-89; P ₂ O ₅ 11-17.

The total pore volume of the catalyst is in the range of 0.08-0.25 cm ³ / g.

The catalyst preferably contains pores with a radius of 40-500 Å of less than 20% of the total pore volume, and the specific surface area is less than 10 m ² / g of catalyst.

The catalyst may further comprise a promoter in the form of at least one of a metal oxide selected from the group: chromium, zinc, manganese, cobalt, cerium, zirconium in an amount of from 0.01 to 2 wt.%.

The catalyst can be made in the form of a handle, ring, block honeycomb structure.

The objective is achieved by a method for producing a catalyst for the selective oxidation of hydrogen sulfide into elemental sulfur, including the mixing of oxygen-containing iron compounds and compounds of modifying additives, extrusion, drying and heat treatment. As an oxygen-containing iron compound, α-iron oxide is used, which has a specific surface area of less than 10 m ² / g and 95% of α-iron oxide has a particle size of less than 40 μm, a compound of modifying additive, orthophosphoric acid, is added to α-iron oxide, mixed dried and heat treated at a temperature of 300-700 ° C.

When mixing iron and phosphoric acid compounds, plasticizing additives are additionally added, if necessary, in an amount of up to 5 wt.%.

The problem is also achieved using the method of selective oxidation of hydrogen sulfide to elemental sulfur by passing the gas mixture over the catalyst at a temperature of 200-300 ° C, followed by separation of the formed sulfur. The oxidation is carried out in the presence of a catalyst, while the ratio of O ₂ / N ₂ S varies between 0.6-1.0 and the volumetric transmission rate of the gas mixture is 900-6000 h ^-1 .

The concentration of water vapor in the reaction mixture may be 0-30 vol.%.

A distinctive feature of the proposed method for the oxidation of hydrogen sulfide to elemental sulfur is the use of a catalyst containing α-iron oxide and oxygen-containing phosphorus compounds, as well as the oxidation of hydrogen sulfide at a ratio of O ₂ / H ₂ S not exceeding 1.0. Carrying out the hydrogen sulfide oxidation reaction under conditions when the O ₂ / H ₂ S ratio is close to the stoichiometrically necessary for the selective oxidation of hydrogen sulfide to sulfur, reduces the likelihood of a sulfur oxidation reaction with oxygen to form sulfur dioxide, especially in the temperature range above 250 ° C.

The specified set of distinctive features gives the object properties that allow you to achieve your goal - the use of the proposed catalyst and the method of oxidation of hydrogen sulfide into elemental sulfur provides a higher yield of sulfur in the temperature range 200-300 ° C in comparison with the prototype.

The catalyst is prepared as follows.

Α-iron oxide is loaded into the mixer, 95% of which have a particle size of less than 40 microns. With continuous stirring, phosphoric acid diluted with water is added. If necessary, modifying additives are added to the catalyst. The mass is mixed, molded, dried, heat treated, and a catalyst of a given composition is obtained.

Table 1 presents the conditions for the preparation of the catalyst. Tables 2-5 show the catalytic properties.

The essence of the invention is illustrated by the following examples:

Example 1

To prepare the catalyst mass, 300 g of α-iron oxide, 95% of which have a particle size of less than 40 μm, are loaded into the mixer, and 40 ml of phosphoric acid, 50 ml of water and 10 ml of glycerol are added with continuous stirring. After stirring for 30-60 minutes, the mass is molded, dried at a temperature of 100-120 ° C for 4 hours and calcined at a temperature of 400 ° C for 5 hours. The catalyst has the shape of a handle.

The catalytic properties of the sample are determined using catalyst granules in the form of cuttings with a diameter of 5 mm and a length of 5-6 mm in a flow-type reactor at a space velocity of 4000 h ^-1 , the concentration of hydrogen sulfide (volume fractions,%) - 1.2; the concentration of water vapor (volume fractions,%) - 30, the ratio of O ₂ / H ₂ S equal to 0.8. The temperature is increased stepwise, with an interval of 20 ° C, from 200 to 300 ° C, then reduced in the reverse order. The catalytic properties are characterized by the degree of conversion of hydrogen sulfide, selectivity and sulfur output, the values of which are calculated by determining the input and output concentrations of the reactants using a chromatograph.

The results of comparing the catalytic properties of this catalyst and the prototype (example 10 from the description of the patent of the Russian Federation No. 2070089) are presented in table.2.

Example 2

Similar to example 1, only for the preparation of the catalyst add 50 ml of phosphoric acid and the calcination of the catalyst is carried out at 700 ° C.

Catalytic properties are determined by the method described in example 1.

Example 3

Similar to example 1, only the calcination of the catalyst is carried out at a temperature of 300 ° C. The catalyst is in the form of a ring.

The determination of catalytic properties is carried out using a catalyst fraction with a particle size of 0.4-0.6 mm in a flow-type reactor at a space velocity of 12000 h ^-1 , the concentration of hydrogen sulfide (volume fractions,%) - 1.2; the concentration of water vapor (volume fractions,%) - 30, the ratio of O ₂ / H ₂ S equal to 0.8. The temperature is increased stepwise, with an interval of 20 ° C, from 200 to 300 ° C, then reduced in the same order. The catalytic properties are characterized by the degree of conversion of hydrogen sulfide, selectivity and sulfur output, the values of which are calculated by determining the input and output concentrations of the reactants using a chromatograph.

The results of comparing the catalytic properties of this catalyst and the prototype (example 4 from the description of the patent of the Russian Federation No. 2070089) are presented in table.3.

Example 4

Similar to example 1, only with stirring 30 ml of phosphoric acid are added, polyethylene oxide is used as a plasticizer and the catalyst is formed into a honeycomb block.

The catalytic properties were determined according to the method described in example 3, characterized in that the ratio of O ₂ / H ₂ S is 1.

Example 5

Similar to example 1, only in α-iron oxide add a promoter - cerium oxide in an amount of 0.01 wt.% And do not use a plasticizer.

Catalytic properties were determined by the method described in example 3, characterized in that the ratio of O ₂ / H ₂ S is 0.6.

Example 6

Similar to example 1, only promoters are introduced into α-iron oxide — zirconium oxide in an amount of 1.5 wt.% And cerium oxide in an amount of 0.5 wt.% And do not use a plasticizer.

The catalytic properties were determined by the method described in example 1. It differs in that the volumetric flow rate is 900 h ^-1 . The results are presented in table 4.

Example 7

Similar to example 1, only zinc oxide in the amount of 0.5 wt.% And manganese oxide in the amount of 1.5 wt.% Are introduced into the iron oxide as promoters. The catalytic properties were determined according to the procedure described in example 1. It differs in that the water vapor content in the reaction mixture is 20 vol.%. The results are presented in table 5.

Example 8

Similar to example 1, only chromium oxide and cobalt oxide are introduced into the iron oxide as promoters in an amount of 1.0 wt.% Each. The catalytic properties were determined according to the procedure described in example 1. It differs in that the water vapor content in the reaction mixture is 10 vol.%. The results are presented in table 5.

Example 9

Similar to example 1, only for the preparation of the catalyst do not use a plasticizer. The catalytic properties were determined according to the procedure described in example 1. It differs in that the reaction mixture does not contain water vapor. The results are presented in table 5.

A comparison of the results of studying the dependence of sulfur yield on the temperature of the known and proposed catalysts presented in Tables 2 and 3 shows that the proposed catalyst for the selective oxidation of hydrogen sulfide to sulfur provides a technical result: a higher sulfur yield in the entire temperature range studied. Using the proposed catalyst due to the higher activity per unit volume will allow the use of smaller load to obtain a high yield of sulfur and increase the capacity of existing reactors. The data presented in table 4 indicate that a change in the volumetric velocity of the gas stream from 4000 h ^-1 to 900 h ^-1 practically does not affect the sulfur output. This will ensure high efficiency of purification of industrial exhaust gases from hydrogen sulfide during gas processing with a variable gas flow rate, for example, exhaust gases from the Klaus process in oil refineries. The data presented in table 5 show that the proposed method for the oxidation of hydrogen sulfide allows a high sulfur yield to be achieved regardless of the concentration of water vapor in the processed gas and therefore is suitable for the desulfurization of hydrogen sulfide-containing gases of various origins, for example, Claus process exhaust gases, fuel gases, coke oven gases, exhaust gases of various chemical enterprises, etc.

Table 2. Catalytic properties Example No. The reaction temperature, ° C The degree of conversion of H ₂ S,% The selectivity of the conversion of H ₂ S in sulfur,% The yield of sulfur,% one 200 55 98 54 220 67 98 66 240 85 97 82 260 91 97 88 280 94 96 90 300 98 89 87 2 200 74 98 73 220 87 96 84 240 89 95 85 260 98 93 91 280 one hundred 88 88 300 one hundred 76 76 200 fifteen 96 fourteen example 10 of 220 34 96 33 descriptions 240 57 95 54 RF patent 260 83 93 77 No. 2070089 280 98 90 88 300 one hundred 56 56

Table 5. Catalytic properties Example No. The concentration of water vapor,% vol. The reaction temperature, ° C The degree of conversion of H ₂ S,% The selectivity of the conversion of H ₂ S in sulfur,% The yield of sulfur,% 7 twenty 200 55 one hundred 55 220 67 99 66 240 86 98 84 260 95 97 92 280 96 97 92 300 99 92 91 8 10 200 56 one hundred 56 220 68 one hundred 68 240 87 98 85 260 93 97 90 280 97 94 91 300 one hundred 92 92 9 0 200 64 one hundred 64 220 74 one hundred 74 240 89 96 85 260 97 94 91 280 one hundred 92 92 300 one hundred 91 91

Claims (9)

1. The catalyst for the selective oxidation of hydrogen sulfide to elemental sulfur, including iron oxide and a modifying additive - a phosphorus compound, characterized in that it contains oxygen-containing phosphorus compounds as a modifying additive, while the catalyst is formed during the heat treatment of α-iron oxide and phosphoric acid and has the following composition, wt.% in terms of oxide: Fe ₂ O ₃ 83-89 P ₂ O ₅ 11-17. 2. The catalyst according to claim 1, characterized in that the total pore volume is in the range of 0.08-0.25 cm ³ / g 3. The catalyst according to claim 1, characterized in that it contains pores with a radius of 40-500 Å less than 20% of the total pore volume and the specific surface area is less than 10 m ² / g of catalyst. 4. The catalyst according to claim 1, characterized in that it further comprises a promoter in the form of at least one of a metal oxide selected from the group: chromium, zinc, manganese, cobalt, cerium, zirconium in an amount of from 0.01 to 2 wt.%. 5. The catalyst according to claim 1, characterized in that it is made in the form of a handle, ring, block honeycomb structure. 6. A method of producing a catalyst for the selective oxidation of hydrogen sulfide into elemental sulfur, comprising mixing oxygen-containing iron compounds and compounds of modifying additives, extrusion, drying and heat treatment, characterized in that α-iron oxide, which has a specific surface area of less than 10, is used as the oxygen-containing iron compound m ² / g and 95% α-iron oxide has a particle size of less than 40 microns, a compound of modifying additive - phosphoric acid is added to α-iron oxide, mixed, dried and carried out heat treatment at a temperature of 300-700 ° C. 7. The method according to claim 6, characterized in that when mixing the compounds of iron and phosphoric acid, plasticizing additives are additionally added in an amount of up to 5 wt.%. 8. The method of selective oxidation of hydrogen sulfide to elemental sulfur by passing the gas mixture over the catalyst at a temperature of 200-300 ° C followed by separation of the sulfur formed, characterized in that the oxidation is carried out in the presence of a catalyst according to any one of claims 1 to 5, the ratio of O ₂ / H ₂ S varies between 0.6-1.0 and the volumetric transmission rate of the gas mixture is 900-6000 h ^-1 . 9. The method according to claim 8, characterized in that the concentration of water vapor in the reaction mixture is 0-30 vol.%.