JPS6120342B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for catalytic incineration of waste gas containing hydrogen sulfide, by contacting the waste gas with a stoichiometric excess of oxygen with respect to the hydrogen sulfide it contains in the presence of a catalyst. The invention also relates to catalyst compositions that can be used in accordance with such methods. In view of the increasingly stringent requirements regarding air pollution reduction, for the removal of hydrogen sulfide (H ₂ S) from process exhaust gases, and in addition:
Various operations have been developed to recover, if possible, the H ₂ S or reaction products of H ₂ S contained therein. For example, the well-known Claus process typically produces an effluent containing up to 2% or even more than 3% by weight of sulfur compounds, a substantial portion of which is _H2S . To remove this concentration of sulfur compounds, selective absorption by contacting the Claus exhaust gas with a suitable absorption solvent has been carried out after hydrogenation of the exhaust gas. In this operation, most of the desorbed H ₂ S after regeneration of the absorption solvent is returned to the Claus unit and nitrogen, CO ₂ and very small amounts of
The final exhaust gas or tail gas containing H ₂ S is incinerated. During incineration, _H2S is converted to sulfur dioxide ( _SO2 ) - a substance that is generally not subject to emission requirements as stringent as those applicable to _H2S . However, incineration is expensive due to the required heat input. Accordingly, research has been carried out on the catalytic conversion of H ₂ S in the exhaust or tail gas to SO ₂ , but there has been a problem with the concomitant formation of sulfur trioxide (SO ₃ ). To purify gases contaminated with hydrogen sulfide, metals such as nickel, iron, cobalt, manganese, zinc and copper, or their compounds, as main components, alone or from elements 4, 5 and 6 of the periodic table, are used. oxidizing the hydrogen sulfide in the presence of a catalyst containing a group metal or metalloid and in addition a small amount of an activating substance such as lead or bismuth or a compound thereof or an alkali metal compound or alkaline earth metal compound. A method is known in which: The amount of activator used is up to about 10% based on the weight of the total amount of metal present. The known catalysts mentioned above have the disadvantage that their activity decreases rapidly and it is necessary to raise the temperature by about 5° C. every 3 days. Additionally, about 10% of the hydrogen sulfide present is converted to _SO3 . SO ₃ is a very disadvantageous compound from the point of view of air pollution reduction. Therefore, an economical method for purifying H ₂ S-containing streams, especially exhaust gas streams of the type mentioned above, i.e.
Provides substantial conversion of _H2S values and concomitantly lower
There remains a need for a method of providing _SO3 emission values. The method should be economical in that the required heat input is as low as possible, as evidenced by the relatively low process temperature. Furthermore, the catalyst used should exhibit an activity that is constant over time. The present invention meets that need. The invention therefore provides a process for catalytic incineration of hydrogen sulfide-containing waste gases by contacting the hydrogen sulfide-containing waste gases with a stoichiometric excess of oxygen with respect to the contained hydrogen sulfide in the presence of a catalyst. The hydrogen sulfide-containing waste gas is mixed with bismuth in an amount of 0.6 to 10% by weight and copper in an amount of 0.5 to 5% by weight as catalytically active components, based on the total weight of the catalyst, at a temperature in the range of 150°C to 450°C. The above process involves contacting with oxygen in the presence of a catalyst comprising metals in the form of their oxides and/or their sulfides. Surprisingly, the use of a catalyst containing both bismuth (Bi) and copper (Cu) in particular proportions and amounts produces results that cannot be obtained by using comparable amounts of Cu or Bi alone. I discovered that. An unexpected aspect of the process of the present invention is the ability to utilize reaction temperatures, on a weight basis, that cannot be achieved with the use of Cu or Bi catalysts alone. Combustible materials present in the stream to be further treated, e.g.
H ₂ , CO, CH ₄ appear to be unaffected or substantially unaffected by the catalyst of the present invention. The SO ₂ produced is vented or recovered by methods known to those skilled in the art. Although the invention can obviously be applied to H ₂ S-containing streams with low to moderate H ₂ S concentrations, the present invention is also applicable to H ₂ S-containing exhaust gases from various processes and from which further It is ideally suited for the treatment of H ₂ S-containing exhaust gases where no or little recovery of H 2 S occurs. The invention, as indicated, is eminently suitable for the treatment of effluents from Claus plants.
The Claus method is usually itself a "clean-up" method, in which:
partial oxidation of _H2S to _SO2 using an oxygen-containing gas (including pure oxygen) in the presence of a catalyst;
Elemental sulfur is then produced by reacting the resulting SO ₂ with the residual H ₂ S. The method includes:
It is often used in refineries and in the finishing of H ₂ S recovered from various gas streams, such as natural gas. Since the yield of elemental sulfur is not quantitative with respect to the introduced hydrogen sulfide, small amounts of unreacted H ₂ S, COS, CS ₂ and SO ₂ remain in the Claus exhaust gas. The amount of elemental sulfur recovered to some extent depends on the number of catalyst beds used in the Claus process. In principle, about 98% of the total sulfur obtained can be recovered if three catalyst beds are used. The present invention is eminently suited for the removal of _H2S from Claus plant effluents. Furthermore, as indicated, the Claus plant effluent or Claus flue gas may have been previously treated by Claus tail gas treatment methods. Such a method uses SO ₂ contained in the gas,
COS, CS ₂ and SO ₃ are reduced to H 2 S under suitable conditions in the presence _of a catalyst, absorbing the H ₂ S, then desorbing the H ₂ S and converting the desorbed H ₂ S into A step of recycling to the Claus plant may be included. When this treatment is carried out, the present invention provides for the oxidation of very little or reduced amounts of H ₂ S and its analogs remaining in the final exhaust gas by contacting said exhaust gas with oxygen under the conditions indicated. Provided by The catalyst used in the process of the invention will be a solid material containing copper and bismuth as catalytically active components. The particular form in which the catalytically active component is present in the catalyst, ie as a compound or as an element or compound bound in a support material, does not appear to be critical. If a carrier is used, the only obvious requirement regarding the source of the copper and bismuth is that the copper and bismuth be converted into solution, either as normal solutions (aqueous and organic solvents) or as solutions of copper or bismuth liquids or complexes. It is in the form. Certain salts and oxides and hydroxides of copper and bismuth may be changed during the preparation of the catalyst during heating in the reactor prior to use in the process of the invention;
Alternatively, it may be converted into another form under the described reaction conditions, but such material still functions as an effective catalyst in the defined process. For example, nitrates, nitrites, carbonates, hydroxides, citrates and acetates can be converted to the corresponding oxides and then sulfides under the reaction conditions defined herein. Salts such as phosphates, sulfates, chlorides and the like, which are stable or partially stable at the defined reaction temperatures, are equally effective under the described reaction conditions and are stable in the reactor. Such compounds that are converted to another stable form at are equally effective. However, copper nitrate and bismuth nitrate are preferred materials because they are inexpensive and readily soluble in water and can be easily deposited onto a carrier. The catalysts of the present invention are solid at room temperature or substantially solid under the reaction conditions (although some volatilization may occur). The presence of minimal amounts of Cu and Bi is essential to achieve a meaningful reduction in reaction temperature with concomitant COS conversion. Generally at least 0.5%Cu
and 0.6% Bi (all by weight) are required in the reaction zone, so that at least
A concentration of 0.8% Bi is preferred. The dramatic improvement over Cu and Bi alone is that the concentration of Cu is at least about 1.0
% and the concentration of Bi is at least about 2.0% (all by weight). When a support is used, for example, copper is usually present in an amount up to about 5% by weight, based on the total weight of the catalyst material. Preferably, the amount of Cu does not exceed about 3% by weight and Bi
The amount of preferably does not exceed 5% by weight. However, it is preferred that the amount of bismuth present in the catalyst is always such that the catalyst contains a high amount of bismuth and a low amount of copper. If solid compounds of Cu and Bi are used,
Alternatively, if high concentrations of Cu and Bi on the support are used, the catalytically active material is usually diluted with inert material so that the activity may be limited. Appropriate dilution to specific concentrations is within the art and need not be detailed here. As a method of introducing catalyst surfaces, excellent results were obtained by filling the reactor with catalyst particles of this definition. Catalyst particle size can vary widely, but typically the largest particles will at least pass through a Tyler standard screen with 2-inch openings, and the largest particles will pass through a Tyler screen with 1-inch openings. pass. Very small particle size carriers can be used, but the only real objection is that very small particles cause excessive pressure drops across the reactor. To avoid high pressure drops across the reactor, at least 50% by weight of catalyst should be retained on a 4 to 5 mesh Tyler standard screen. However, if a fluid bed reactor is used, the catalyst particles may be about 10 to 300
It may even be quite small, such as microns. Those skilled in the art can easily determine the appropriate particle size depending on the shape and size of the reactor and the applied gas rate. When a support is used, the catalytically active component is prepared in an aqueous solution or dispersion of the mentioned catalyst and the carrier particles and the solution or dispersion are deposited in or on the support. It can be deposited onto the carrier by methods known in the art, such as by mixing until mixed. The coated particles can then be dried in an oven at, for example, about 110°C.
Various other catalyst preparation methods known to those skilled in the art may be used. Very useful carriers (and diluents) are fused alumina (Alundum), silica, silicone carbide (Carborundum), pumice, diatomaceous earth, asbestos, zeolites and the like. Particularly preferred are fused alumina or other alumina supports and silica. The carrier can be of any shape, including irregular shapes. Another way to introduce the required surface is to use small diameter tubes as reactors, the tube walls of which are catalytic or coated with a catalytic material. If the tube wall is the only source of catalyst, the tube wall will generally have a diameter of less than 3/4 inch.
It has an inside diameter of no more than an inch, preferably a diameter of no more than about 1/2 inch. Other methods can be used to introduce the catalyst surface. For example, fluidized bed technology may be used. The concentration of _H2S in the stream being treated can vary widely. Thus, it will be recognized by those skilled in the art that the concentration can range from trace amounts to quite significant amounts, and that _H2S concentration is generally not a limiting factor of the present invention. For example, the concentration of _H2S in the gas being treated can be from 0.005% to 5.0% or even 10.0% (on a molar basis). The concentrations of COS and CS ₂ present in the Claus effluent are typically small, such as in the range of about 0.01% to about 0.5% (on a molar basis). The reaction conditions used can vary considerably. Although the temperature at which the reaction is carried out is not critical, it is an advantage of the present invention that relatively low or moderate temperatures can be used. 150℃ or so
A temperature of 450°C is quite satisfactory, but a temperature of 250°C or
A temperature of 420°C is preferred. Similarly, the working pressure is not critical and a wide range of pressures may be used. For example, the total pressure in the systems of the present invention is typically atmospheric or above atmospheric, although in some embodiments a partial vacuum may be used. Preferably, the pressure is in the range of relatively high pressures, such as atmospheric to 5 atmospheres or even higher to 10 atmospheres. Water vapor may be present in the system and is preferred in some cases. The flow rates of the _H2S -containing gas and oxygen are primarily a matter of choice. However, as recognized by those skilled in the art, relatively low space velocities improve conversion levels. Generally, about
Gas flow rates of 1000 GHSV to about 50,000 GHSV may be used, with rates of 2000 GHSV to about 25,000 GHSV being preferred. Good results, but 2000 or more
Obtained using a space velocity of 10000GHSV. Accordingly, the contact time can vary widely and range from about 0.07 seconds to about 4.0 seconds, and from about 0.14 seconds to about 2.0 seconds.
A contact time of seconds is preferred. The amount of oxygen supplied to the reaction zone is important in that a stoichiometric excess, preferably a large excess, of oxygen is desired to react all of the _H2S and COS and _CS2 present. . Generally, at least twice and usually up to five times the stoichiometric amount of oxygen required for the reaction may be provided. Preferably, an excess of about 20 to about 280% of the stoichiometric amount of oxygen is provided, based on all total combustibles. 100 times the stoichiometric amount or even higher 200
Even twice as high amounts of oxygen can be supplied if desired. The oxygen may be supplied as relatively pure oxygen, as air, or as a mixture of air and oxygen, and may also be supplied with other components containing significant amounts of oxygen and other components that do not significantly interfere with the reaction in question. It can also be supplied from a gas stream. EXAMPLES The following experiments were conducted to demonstrate the invention. In each experiment, synthesis tail gas containing _H2S and other sulfur compounds is passed through a reactor containing the catalyst. Oxygen is introduced as air from a separate line. The temperature is measured by suitable means and the conversion results obtained by analysis of the effluent stream from the reactor. Using this general procedure, catalysts containing Bi and Cu were deposited on alumina (Kaiser A-201 spherical gamma-alumina 4x6 mesh) in amounts of 3% and 1% by weight, respectively, based on the total weight of the catalyst. Samples were collected using a Copper and bismuth were deposited as basic solutions of nitrates.
The catalyst was then dried and calcined at 481°C for 1 to 2 hours before use. The operating conditions are shown in more detail in Table 1. Significant H ₂ S removal was obtained and the results for two different space velocities are shown in the table.

[Table] (Reference reactor outlet)

[Table] Based on total flammable materials including hydrogen

Table Example Using a procedure similar to the example, catalysts containing 3% by weight only bismuth on alumina (based on the weight of active material and support) and 1% by weight only copper on alumina (based on the weight of active material and support) were prepared. (based on the weight of material and support) were prepared and tested. The results are shown in the table and compared with the results for the catalyst according to the invention.

TABLE The data in the table clearly demonstrate the superiority of the Cu-Bi catalyst in terms of reduced SO ₃ concentration in the product gas. The combined catalyst according to the invention also shows very high conversions of carbonyl sulfide and carbon disulfide. Under the described reaction conditions, carbonyl sulfide conversion is better than 50%, and carbon disulfide conversion is better than 90%.
better than

Claims (1)

[Scope of Claims] 1. A method for catalytic incineration of hydrogen sulfide-containing waste gas by contacting the hydrogen sulfide-containing waste gas with a stoichiometric excess of oxygen with respect to the contained hydrogen sulfide in the presence of a catalyst, comprising: Waste gas containing hydrogen sulfide,
At temperatures ranging from 150°C to 450°C, bismuth in an amount of 0.6 to 10% by weight and copper in an amount of 0.5 to 5% by weight, based on the total weight of the catalyst, are added as catalyst active components to the metals, their oxides and A method as described above, comprising contacting with oxygen or an oxygen-containing gas in the presence of a catalyst comprising/or in the form of their sulfides. 2. The method of claim 1, wherein the catalyst comprises 0.8 to 5% by weight bismuth and 0.5 to 3% by weight copper. 3. Claims 1 or 2, wherein the catalyst contains a high amount of bismuth and a low amount of copper.
The method described in section. 4. A method according to any one of claims 1 to 3, wherein the oxygen is supplied in an amount up to five times the stoichiometric amount of oxygen required. 5 The oxygen is between 20 and 20% of the stoichiometric amount of oxygen.
4. A method according to claim 4, which is over-fed by 280%. 6. The method according to any one of claims 1 to 5, wherein the hydrogen sulfide-containing waste gas is Claus exhaust gas. 7. The method according to any one of claims 1 to 5, wherein the hydrogen sulfide-containing waste gas is an exhaust gas from a Clauster gas treatment method. 8 The hydrogen sulfide-containing waste gas is 0.005 to 5.0%
8. A method according to any one of claims 1 to 7, comprising molar _H2S . 9. The method according to any one of claims 1 to 8, wherein the temperature is 250°C to 420°C. 10 Including copper and bismuth as support materials and catalytically active components, with copper in an amount of 0.5 to 5% by weight and bismuth in an amount of 0.6 to 10% by weight, based on the total weight of the catalyst composition, and these metals , catalyst compositions present in the form of their oxides and/or their sulfides. 11. The catalyst composition of claim 10, wherein the support material is selected from the group comprising fused alumina, silica and alumina. 12 0.5 to 3.0% copper and 0.8 to 3.0% by weight
Catalyst composition according to claim 10 or 11, comprising 5.0% by weight of bismuth and wherein the support material is alumina, preferably gamma alumina. 13. Catalyst composition according to any one of claims 10 to 12, in which bismuth is present in a high amount and copper is present in a low amount.