CA2044067C - A catalyst for the oxidation of sulfur dioxide - Google Patents
A catalyst for the oxidation of sulfur dioxide Download PDFInfo
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- CA2044067C CA2044067C CA002044067A CA2044067A CA2044067C CA 2044067 C CA2044067 C CA 2044067C CA 002044067 A CA002044067 A CA 002044067A CA 2044067 A CA2044067 A CA 2044067A CA 2044067 C CA2044067 C CA 2044067C
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/78—Preparation by contact processes characterised by the catalyst used
- C01B17/79—Preparation by contact processes characterised by the catalyst used containing vanadium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/20—Vanadium, niobium or tantalum
- B01J23/22—Vanadium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8603—Removing sulfur compounds
- B01D53/8609—Sulfur oxides
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Abstract
A solid catalyst for the oxidation of sulfur dioxide in gas currents containing oxygen, which catalyst includes vanadium oxide and alkali metal oxides, alkali metal sulfates or mixtures thereof, as an active substance, silicon, aluminum, or mixtures thereof, in oxide form, for surface area enlargement, and titanium dioxide in anatase form, rutile form, or mixtures thereof, as a carrier material and a ceramic binder. The metals in these finely sintered components which impart discrete functions are present in certain atomic ratios. The fine sintering takes place according to a production method especially by means of differentiated conditions of drying, calcining and sintering. One use for the invention is the desulfurization of waste gases from combustion processes and industrial plants.
Description
Catalyst for The Oxidation Of Sulfur Dioxide This invention relates to a catalyst for the oxidation of sulfur dioxide contained in an oxygen-containing gas current. The catalyst includes the following components:
A) a catalytically active substance comprising:
Al) vanadium oxides and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof; and B) silicon, aluminum, or mixtures thereof, in the form of oxides, as a surface area enlarging component.
In addition t.o street traffic, waste gases from combustion processes and industrial plants also constitute a source of the existing environmental pollution. The waste gases contain air pollutants, such as nitrogen oxides, carbon monoxide, hydrocarbons and sulfur dioxide.
These pollutants are well known for their adverse impact on the environment.
If primary measures for the reduction of pollutant emissions have only a minor effect on the total emission of pollutants, then secondary measures, such as catalytic waste-gas cleaning methods, have to be employed.
Most of the combustion processes for fossil fuels takes place with fuel-air compositions which are leaner than stoichiometri~~. '.the catalytic waste-gas cleaning methods suitable for this purpose are the well known SCR
(selective catalytic reduction) method for denitration by means of ammonia and the use of oxidation catalysts containing noble metals for the oxidation of carbon monoxide, hydrocarbons and also sulfur dioxide. The sulfur dioxide can be further processed to sulfuric acid. A
combination of both methods is constituted by the method described in German Patent No. 36 O1 378, with which method waste gases can be freed of NOX and S02 with the creation of sulfuric acid.
For reasons of production technology, oxidation catalysts containing noble metals are not yet available in the necessary large geometric dimensions. It is still necessary to arrange individual, smaller monoliths over each other in order to obtain the necessary catalytic volume. Since dust settles out of dust-charged waste gases at the joints between adjacent monoliths, a great number of expensive dust blowers must be installed. In addition, the noble-metal component of these catalysts represents a considerable cost factor which can be tolerated in rather small waste-gas cl~saning systems, but which results in prohibitive investment costs in rather large systems, such as heating power stations or superpower stations. Finally, the catalytically active noble-metal component is especially sensitive t:o poisonous components present in flue gas which can deactivate the catalyst.
As already explained, the catalysts for use with dust-charged waste gases are maintained clean by means of soot or dust blowers which swirl the dust deposited on the approach side of t:he catalysts and at the joints of catalytic packets by means of hot vapor or hot air. The dust is thereby returned to the current of waste gas which entrains it through the catalytic conduits, thus removing it out of the reacaor. In order to reduce the number of cost intensive soot-blower devices in a catalytic reactor, it is necessary to have as few approach surfaces and joints as possible in reactors equipped with monolithic and/or honeycomb catalysts. A prerequisite for this is that the monolithic and/or honeycomb bodies should be produced with as great a piece length as possible. However, long monolithic and/or honeycomb bodies can not yet be produced in the case of coating catalysts containing noble metals.
Also, the use of saot or dust blowers functions only in the case of catalystsc in monolithic or honeycomb form.
Catalysts in bulk form can not be cleaned with the blowers, since the dust would only penetrate into deeper positions in the catalyst. The catalyst would fill with dust and the stoppage would remain. At the same time, there would be the danger of an uncontrolled turbulence of the bulk-material catalyst.
However, the noble-metal catalysts (e. g. platinum) used in the past t:o convert sulfur dioxide into sulfur trioxide, the anhydride of sulfuric acid, in the so-called contact method or especially base metal oxide catalysts (for example, vanadium pentoxide and alkali sulfate with silicon dioxide as carrier material) have been used exclusively in bulk form (as extruded blanks or rings).
For the reasons explained above, this technology was problematic for the treatment of waste gases containing sulfur oxide, especially if the waste gases were charged with dust. Dust deposits had to be removed by means of sieving out the catalyst.. The service life of such catalysts was therefore determined primarily by their mechanical strength.
It is one objective of this invention to produce a catalyst which is suitable for converting sulfur dioxide into sulfur trioxide. The sulfur dioxide may be contained in gas currents which include oxygen, or other components compounded with oxygen, or a gas containing oxygen. The catalyst may be used as a form body suitable as a bulk bed for the treatment of dust-free gas currents and as a monolithic or honeycomx> body for use in waste gas and flue gas cleaning systems sensitive to pressure loss and/or in dusty currents of air, waste gas or flue gas. The catalyst should be able to be readily brought into any form customary for bulb;-material catalysts, and they should be able to be manufacaured as a monolith or honeycomb body. A
catalyst formulation was developed to this end in accordance with the invention which is different from that of catalysts previously used for this purpose. The catalysts previous>ly used do not exhibit sufficient wear resistance as a bulk body or could not be processed in a sufficient manner into honeycomb bodies with sufficient strength.
The invention relates to a catalyst for the oxidation of sulfur dioxide contained in an oxygen-containing gas current. The catalyst includes the following components:
A) a catalytica:Lly active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof; and B) silicon, aluminum, or mixtures thereof, in the form of oxides, as surface area enlarging components.
The catalyst is characterized in that it also contains C) titanium oxide in anatase form, rutile form or mixtures thereof as a carrier material and ceramic binder.
The catalyst is designed as a solid catalyst, optionally in monolithic or honeycomb form, in which a mixture of components A)-C) is present in a finely sintered form with atomic ratios between the metals of the components according to the following:
Al) :AZ) :B) :C)=(0.01-0.2) : (0.01-0.2) : (0.001-0.5) :1.
Preferably, the atomic ratios are as follows: (0.02-0.08):(0.02-0.08):(0.005-0.05):1.
The oxidation catalyst of the invention meets the following requirements in the designated area of use.
The catalyst is capable of converting more than 90~ of the sulfur dioxides in a waste gas to sulfur trioxide in a single method step. The catalyst can be manufactured in the form of monolithic or honeycomb bodies up to a length of 1000 mm, and it. fully meets the above requirements for maintaining a clean stage when loaded with dusty waste gas or flue gas. The temperature range in which the required conversion is achieved is very broad, and especially includes low temperatures. The kinetic behavior of the catalyst of this invention is considerably improved because the oxidation reaction proceeds in accordance with a time law of the first order, unlike was the case with most of the noble-metal-containing catalysts previously used. In the past, this has resulted in problems in the measuring of the necessary catalytic volume, especially in the case of high conversion requirements. The catalyst is a solid catalyst, that is, it contains catalytically active material through and through, which catalyst active material is exposed again and again by means of abrasion, for example, abra:>ion by means of the dust contained in the flue gases.
Another aspeca of this invention relates to a method for the production of the catalyst. The method is characterized in that components A) through C) are intensively proce~;sed to a homogeneous mass in finely divided form preferably with the addition of the additives customary for pre~;sing or extruding ceramic masses, namely, moistening agents, stabilizing medium, green-body binders, auxiliary deformation agents and, optionally, pore forming material. The mass is pressed or extruded to the desired green bodies, preferably to monolithic or honeycomb bodies, the green bodies a.re dried under a slow elevation of the temperature to at the most about 60°C. with controlled moisture of the ambient air, and are then calcined under gradual (step-by-step) elevation of the temperature in the ambient air to at least 500°C., and at the most 800°C. The calcined bodies are sintered at a temperature in this range for at least 12 hours, preferably 14-48 hours, and especially 18-36 hours.
Desalinated water, aqueous ammonia solution, monoethanol amine and alcohols can be used as moistening agents.
A) a catalytically active substance comprising:
Al) vanadium oxides and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof; and B) silicon, aluminum, or mixtures thereof, in the form of oxides, as a surface area enlarging component.
In addition t.o street traffic, waste gases from combustion processes and industrial plants also constitute a source of the existing environmental pollution. The waste gases contain air pollutants, such as nitrogen oxides, carbon monoxide, hydrocarbons and sulfur dioxide.
These pollutants are well known for their adverse impact on the environment.
If primary measures for the reduction of pollutant emissions have only a minor effect on the total emission of pollutants, then secondary measures, such as catalytic waste-gas cleaning methods, have to be employed.
Most of the combustion processes for fossil fuels takes place with fuel-air compositions which are leaner than stoichiometri~~. '.the catalytic waste-gas cleaning methods suitable for this purpose are the well known SCR
(selective catalytic reduction) method for denitration by means of ammonia and the use of oxidation catalysts containing noble metals for the oxidation of carbon monoxide, hydrocarbons and also sulfur dioxide. The sulfur dioxide can be further processed to sulfuric acid. A
combination of both methods is constituted by the method described in German Patent No. 36 O1 378, with which method waste gases can be freed of NOX and S02 with the creation of sulfuric acid.
For reasons of production technology, oxidation catalysts containing noble metals are not yet available in the necessary large geometric dimensions. It is still necessary to arrange individual, smaller monoliths over each other in order to obtain the necessary catalytic volume. Since dust settles out of dust-charged waste gases at the joints between adjacent monoliths, a great number of expensive dust blowers must be installed. In addition, the noble-metal component of these catalysts represents a considerable cost factor which can be tolerated in rather small waste-gas cl~saning systems, but which results in prohibitive investment costs in rather large systems, such as heating power stations or superpower stations. Finally, the catalytically active noble-metal component is especially sensitive t:o poisonous components present in flue gas which can deactivate the catalyst.
As already explained, the catalysts for use with dust-charged waste gases are maintained clean by means of soot or dust blowers which swirl the dust deposited on the approach side of t:he catalysts and at the joints of catalytic packets by means of hot vapor or hot air. The dust is thereby returned to the current of waste gas which entrains it through the catalytic conduits, thus removing it out of the reacaor. In order to reduce the number of cost intensive soot-blower devices in a catalytic reactor, it is necessary to have as few approach surfaces and joints as possible in reactors equipped with monolithic and/or honeycomb catalysts. A prerequisite for this is that the monolithic and/or honeycomb bodies should be produced with as great a piece length as possible. However, long monolithic and/or honeycomb bodies can not yet be produced in the case of coating catalysts containing noble metals.
Also, the use of saot or dust blowers functions only in the case of catalystsc in monolithic or honeycomb form.
Catalysts in bulk form can not be cleaned with the blowers, since the dust would only penetrate into deeper positions in the catalyst. The catalyst would fill with dust and the stoppage would remain. At the same time, there would be the danger of an uncontrolled turbulence of the bulk-material catalyst.
However, the noble-metal catalysts (e. g. platinum) used in the past t:o convert sulfur dioxide into sulfur trioxide, the anhydride of sulfuric acid, in the so-called contact method or especially base metal oxide catalysts (for example, vanadium pentoxide and alkali sulfate with silicon dioxide as carrier material) have been used exclusively in bulk form (as extruded blanks or rings).
For the reasons explained above, this technology was problematic for the treatment of waste gases containing sulfur oxide, especially if the waste gases were charged with dust. Dust deposits had to be removed by means of sieving out the catalyst.. The service life of such catalysts was therefore determined primarily by their mechanical strength.
It is one objective of this invention to produce a catalyst which is suitable for converting sulfur dioxide into sulfur trioxide. The sulfur dioxide may be contained in gas currents which include oxygen, or other components compounded with oxygen, or a gas containing oxygen. The catalyst may be used as a form body suitable as a bulk bed for the treatment of dust-free gas currents and as a monolithic or honeycomx> body for use in waste gas and flue gas cleaning systems sensitive to pressure loss and/or in dusty currents of air, waste gas or flue gas. The catalyst should be able to be readily brought into any form customary for bulb;-material catalysts, and they should be able to be manufacaured as a monolith or honeycomb body. A
catalyst formulation was developed to this end in accordance with the invention which is different from that of catalysts previously used for this purpose. The catalysts previous>ly used do not exhibit sufficient wear resistance as a bulk body or could not be processed in a sufficient manner into honeycomb bodies with sufficient strength.
The invention relates to a catalyst for the oxidation of sulfur dioxide contained in an oxygen-containing gas current. The catalyst includes the following components:
A) a catalytica:Lly active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof; and B) silicon, aluminum, or mixtures thereof, in the form of oxides, as surface area enlarging components.
The catalyst is characterized in that it also contains C) titanium oxide in anatase form, rutile form or mixtures thereof as a carrier material and ceramic binder.
The catalyst is designed as a solid catalyst, optionally in monolithic or honeycomb form, in which a mixture of components A)-C) is present in a finely sintered form with atomic ratios between the metals of the components according to the following:
Al) :AZ) :B) :C)=(0.01-0.2) : (0.01-0.2) : (0.001-0.5) :1.
Preferably, the atomic ratios are as follows: (0.02-0.08):(0.02-0.08):(0.005-0.05):1.
The oxidation catalyst of the invention meets the following requirements in the designated area of use.
The catalyst is capable of converting more than 90~ of the sulfur dioxides in a waste gas to sulfur trioxide in a single method step. The catalyst can be manufactured in the form of monolithic or honeycomb bodies up to a length of 1000 mm, and it. fully meets the above requirements for maintaining a clean stage when loaded with dusty waste gas or flue gas. The temperature range in which the required conversion is achieved is very broad, and especially includes low temperatures. The kinetic behavior of the catalyst of this invention is considerably improved because the oxidation reaction proceeds in accordance with a time law of the first order, unlike was the case with most of the noble-metal-containing catalysts previously used. In the past, this has resulted in problems in the measuring of the necessary catalytic volume, especially in the case of high conversion requirements. The catalyst is a solid catalyst, that is, it contains catalytically active material through and through, which catalyst active material is exposed again and again by means of abrasion, for example, abra:>ion by means of the dust contained in the flue gases.
Another aspeca of this invention relates to a method for the production of the catalyst. The method is characterized in that components A) through C) are intensively proce~;sed to a homogeneous mass in finely divided form preferably with the addition of the additives customary for pre~;sing or extruding ceramic masses, namely, moistening agents, stabilizing medium, green-body binders, auxiliary deformation agents and, optionally, pore forming material. The mass is pressed or extruded to the desired green bodies, preferably to monolithic or honeycomb bodies, the green bodies a.re dried under a slow elevation of the temperature to at the most about 60°C. with controlled moisture of the ambient air, and are then calcined under gradual (step-by-step) elevation of the temperature in the ambient air to at least 500°C., and at the most 800°C. The calcined bodies are sintered at a temperature in this range for at least 12 hours, preferably 14-48 hours, and especially 18-36 hours.
Desalinated water, aqueous ammonia solution, monoethanol amine and alcohols can be used as moistening agents.
Glass fibers of di:Efering sizes may be used as examples of the stabilizing media.
Cellulose denivat.ives such as carboxymethylcellulose or also non-substituted celluloses are suitable as binders.
The binder should impart sufficient stability to the paste to be produced after thE~ deformation in the state of the so-called green bodies.
In addition, polyethylene, polypropylene, polyvinyl alcohol, polyethylene oxide, polyacrylamide or polystyrene may also be used as binders.
In order to facilitate a pressing, or to improve the extrusion capability, auxiliary deformation and/or lubrication agents., such as bentonites, clays, organic acids, paraffin, waxes, silicone oils may also be added.
Finally, the porosity (pore volume, pore distribution) of the solid catalysts of the invention may also be adjusted in a purposeful manner by means of the addition of suitable pore forming materials. Such substances include, for example, fine carbons (activated carbons) or wood pulp, which burn out at the calcining temperatures to be used.
Advantageously, kneading units can be used for intensive mixing of the initial substances into a homogeneous kneaded mass. Kneaders with blades which are sigma-shaped or which move out in a shearing manner are preferred. Expensive method steps which are technically complicated and damaging to the environment: are avoided. Co-precipitation procedures and grinding procedures for preparing an intimate oxide mi~aure are eliminated. This results in a distinct reduction in the production cost, and at the same time eliminates the dependency on initial materials which are expensive to produce.
A particular advantage of the production method in accordance with this invention is the fact that commercially available oxides and chemically temperature-stable sulfates are exclusively used as initial materials.
Therefore, the use of hydroxide precursors or hydrated oxide precursors, which would necessitate additional processing measures, can be eliminated.
In contrast to frequently used denitration catalysts which contain titanium oxide and in which a catalytic action is attributed to this component, in the catalyst of this invention for the oxidation of sulfur dioxide, component C) of this compound exclusively assumes the function of a ceramic carrier and binder for the catalytically active substance A) and for its surface area enlarging additive B).
The alkali-metal oxide or sulfate AZ used as a component of catal:ytically active substance A) assumes the function of a flux for active substance A1) in the catalytic composition of the invention at an operating temperature of 380°-500°C. A1) and A2) aid the sintering process between binder C) and surface area enlarging additive B) during the sintering of the additives for the catalyst.
It is also within t:he scope of this invention to use the catalyst of th.e invention for the oxidation of sulfur dioxide present in. a current of air or in a current of flue gas or waste gas containing oxygen.
The advantageous features of this invention will be more fully realized from the following detailed description, especially when considered in view of the attached figures, wherein:
FIG. 1 shows the sulfur dioxide to sulfur trioxide conversion rate as a function of temperature for Example 1;
FIG. 2 shows the sulfur dioxide conversion rate as a function of approach speed (AV) for Example 1;
FIG. 3 shows a comparison of the natural log of (1-S02 conversion) as a function of (AV)-1, for Examples 2-6 at 450°C.;
FIG. 4 shows a comparison of the natural log of (1-S02 conversion) as a function of (AV)-1, for Examples 3-6 at 425°C.~ and FIG. 5 shows the sulfur dioxide conversion rate as a function of temperature for Examples 7-10.
The catalyst and process in accordance with this invention will be illusl=rated in the following Examples.
The following substances are mixed in a kneading unit with sigma blades and subjected to a kneading process lasting 7 hours:
Titanium oxide (anatase) 4950 g Sili<:on dioxide 146 g Vanadium pentoxide 297 g Pota:>sium sulfate 297 g Water. 4542 g Clay 213 g Glass fibers 550 g Organic additives 164 g Ammonia 1150 g The kneaded mass i~~ subsequently extruded in a worm extruder to form bodies, heated with a temperature rise of 1°C. per hour to 50°C. and a relative moisture of approximately 100 to 80~, largely dried thereby and then heated further in stage~c of a maximum of 50°C. per 2 hours to 600°C. Then, the mixture is tempered by sintering for 24 hours at this temperature in air. The honeycomb bodies have 3 x 3 cells of a square cross section, a cell width of 5.5 mm and a wall thickness of 1.3 mm.
The activity test was carried out in a laboratory testing system under they following conditions:
V 1.13 m3/h i.N. moist AV*~ 16-52 m/h **~
LV 0.6 m/s i.N.
NO 100 ppm dry S02 600 ppm dry 02 5 % by vol. dry H20 7 % by vol. moist N2 Balance *' Surface load (volume stream/catalyst surface) **~ Flow rate FIG. 1 shows t:he temperature dependency of the catalytic activity of this catalyst at a surface charge of AV=52 m/h, which corresponds to a space velocity of approximately 20000 h-1. The conversion remains at a rather low level up to 3'15°C. but then rises sharply in a temperature window of about 50°C. wide and stabilizes after approximately 425°C'.. at 36-37$ conversion.
FIG. 2 shows the dependency of the S02 conversion on the surface charge of the catalyst at 450°C. The AV value (surface charge) was 16..4 m/h at first in the case of a catalytic honeycomb 350 mm long. By means of sawing off 30 mm at a time, the AV value was increased successively to 52 m/h. The AV range between 4 and 10 m/h, which is of interest for real operation, can not be accomplished in this laboratory testing system; however, conversion values around 80$ were found already at AV=15 m/h. Therefore, it can be expected that conversion values above 90$ can be reached and even distincaly exceeded in the range of 4-10 m/h.
The following substances are mixed in a kneading unit with blades which move out in a shearing manner and are kneaded for 12 hours to a paste (all data in kg):
Examp 1 e:
Component 2 3 4 5 6 Titanium oxide: 30.0 180.0 180.0 40.0 40.0 (anatase) Silicon dioxide 0.9 2.7 2.7 1.2 1.2 Ammonium 1.0 6.0 12.0 2.66 2.66 metavanadate Potassium 1.5 9.0 9.0 2.0 3.0 sulfate Water 16.5 100.0 100.0 20.5 20.0 Clay :L.S 9.0 9.0 2.0 2.0 Fibers :3.18 19.0 19.0 4.23 4.23 Organic :1.235 7.5 7.5 2.0 2.0 additives After kneading, the paste is placed into an extruder and pressed into honeycomb bodies. In Examples 2, 5 and 6, so-called quarter monoliths with 75 x 75 mm width and 500 mm length were extruded, and in Examples 3 and 4 solid monoliths with 150 x 150 mm width and 1000 mm length were produced. After drying and calcining, as in Example 1, tests were performed in a pilot plant system after a dry coal firing and also in an industrial-sized system, likewise after a dry coal firing. The composition of the flue gases in both of these systems corresponds within the framework of the customary range of variation to the composition indicated in Example 1, with the difference being that there was still approximately 12~ by volume C02 and a dust content of less than 50 mg/m3 present.
For the pilot system, flue gases are drawn off isokinetically after the dedusting and heated by means of electric heaters to the desired temperature. The catalysts are located in a heat-insulated reactor with a total of 12 gas-specimen removal and temperature measuring positions.
According to the DESONOXTM method of Degussa AG, the flue gases are denitrified at first according to the SCR method (selective catalytic reduction). Immediately afterward, the catalysts for the reduction of the nitrogen oxides with NH3 oxidation catalysts of the invention were installed.
The catalyst elements produced in accordance with the method of the invention in lengths of 1000 mm or 500 mm with side-edge lengths of 150 mm x 150 mm or 75 mm x 75 mm were sawed into elements with a length of 150 mm each for reasons of a detailed measurement of the conversion along the reaction stretch of the pilot system. A total of eight such elements were installed in series. The cell division was 4.2 mm.
FIGS. 3 and 4 show the evaluation of the measuring results on specimens from selected examples at 450° and 425°C., respectively. fhe application -In (1-r~) against 1/AV was selected in they sense of a reaction of the first order. The ordinate value of 2.3 corresponds to a conversion of 90~.
The results found thereby show that SOZ conversions to S03 above 90~ can be achieved without problems, such that the fixing at a minimum temperature of 450°C. necessary in the case of a noble-metal catalyst is no longer necessary, and that the kinetics of the S02 oxidation belong approximately to a time law of the first order.
The test specimens used in the industrial-size system were removed after a running time of more than 1000 operating hours and installed into the described pilot system for determination of activity. No reductions of activity were able to be determined.
The following substances were mixed in a kneading unit with blades which move out and subjected to a kneading process for 5 hours (all data in g):
Example Component 7 8 9 10 Titanium oxide 667 ~~ *~
(Pyrogenic) Silicon dioxide 70 (pyrogenic) Ammonium 37.1 metavanadate Potassium sulfate 20.2 40.4 0 32.3 Caesium sulfate 20.2 0 40.4 8.1 Water 260 Clay 25.3 ~~ ~~ n Glass fibers 72.4 Typical organic 15.7 additives, in-cluding carboxy-methyl cellulose Ammonia 30 ~~ ~~ n *) = always same amounts in Example 7 After the kneading, the paste obtained is processed to extruded blanks. '.Che drying and calcining again took place according to Example 1, but with a final temperature of the drying of 60°C. here and with a final moisture of 70g relative moisture. The temperature during calcining was increased here to only 500°C., and the matter was then sintered for 48 hours at: this temperature.
FIG. 5 shows the temperature-dependent activity behavior of the catalysts prepared in this manner under the testing conditions cited in Example 1, at a surface charge (AV) of 23 m/h.
The following substances were mixed in a kneading unit with blades which move out in a shearing manner and subjected to a kneading process for 5 hours (all data in g) Example Component 11 12 13 14 15 Titanium oxide 700 700 770 470 700 (80% by weight anatase + 20%
by weight rutile) Silicon dioxide 70 70 2 300 (precipitated silica) Aluminium oxide 7p (7-A1203) Vanadium 7.5 130 42 42 42 pentoxide Potassium sulfate160.0 10 42 42 42 Water 300 250 220 300 300 Clay 30 25 25 25 25 Glass fibers 73 73 73 73 73 Organic additives,17 17 17 17 17 including carboxy-methyl cellulose Ammonia 50 50 50 50 50 The production of Examples 11-14 took place in a similar manner to Example 1. The produced catalysts met the basic values for the' concentration ranges of the components A1, A2, B arid C produced in accordance with this invention. It turned out that all production measures of the method in accordance with this invention, such as the kneading process, extrusion, drying, calcining, and sintering, can be readily carried out within this framework. Mechanically stable form bodies with an appropriate catalytic acaivity are obtained in every instance.
Example 11 showed that a catalyst composed in this manner exhibits an especially high activity even at low temperatures.
Example 15 showed that the co-use of A1203 also results in increased activity.
Cellulose denivat.ives such as carboxymethylcellulose or also non-substituted celluloses are suitable as binders.
The binder should impart sufficient stability to the paste to be produced after thE~ deformation in the state of the so-called green bodies.
In addition, polyethylene, polypropylene, polyvinyl alcohol, polyethylene oxide, polyacrylamide or polystyrene may also be used as binders.
In order to facilitate a pressing, or to improve the extrusion capability, auxiliary deformation and/or lubrication agents., such as bentonites, clays, organic acids, paraffin, waxes, silicone oils may also be added.
Finally, the porosity (pore volume, pore distribution) of the solid catalysts of the invention may also be adjusted in a purposeful manner by means of the addition of suitable pore forming materials. Such substances include, for example, fine carbons (activated carbons) or wood pulp, which burn out at the calcining temperatures to be used.
Advantageously, kneading units can be used for intensive mixing of the initial substances into a homogeneous kneaded mass. Kneaders with blades which are sigma-shaped or which move out in a shearing manner are preferred. Expensive method steps which are technically complicated and damaging to the environment: are avoided. Co-precipitation procedures and grinding procedures for preparing an intimate oxide mi~aure are eliminated. This results in a distinct reduction in the production cost, and at the same time eliminates the dependency on initial materials which are expensive to produce.
A particular advantage of the production method in accordance with this invention is the fact that commercially available oxides and chemically temperature-stable sulfates are exclusively used as initial materials.
Therefore, the use of hydroxide precursors or hydrated oxide precursors, which would necessitate additional processing measures, can be eliminated.
In contrast to frequently used denitration catalysts which contain titanium oxide and in which a catalytic action is attributed to this component, in the catalyst of this invention for the oxidation of sulfur dioxide, component C) of this compound exclusively assumes the function of a ceramic carrier and binder for the catalytically active substance A) and for its surface area enlarging additive B).
The alkali-metal oxide or sulfate AZ used as a component of catal:ytically active substance A) assumes the function of a flux for active substance A1) in the catalytic composition of the invention at an operating temperature of 380°-500°C. A1) and A2) aid the sintering process between binder C) and surface area enlarging additive B) during the sintering of the additives for the catalyst.
It is also within t:he scope of this invention to use the catalyst of th.e invention for the oxidation of sulfur dioxide present in. a current of air or in a current of flue gas or waste gas containing oxygen.
The advantageous features of this invention will be more fully realized from the following detailed description, especially when considered in view of the attached figures, wherein:
FIG. 1 shows the sulfur dioxide to sulfur trioxide conversion rate as a function of temperature for Example 1;
FIG. 2 shows the sulfur dioxide conversion rate as a function of approach speed (AV) for Example 1;
FIG. 3 shows a comparison of the natural log of (1-S02 conversion) as a function of (AV)-1, for Examples 2-6 at 450°C.;
FIG. 4 shows a comparison of the natural log of (1-S02 conversion) as a function of (AV)-1, for Examples 3-6 at 425°C.~ and FIG. 5 shows the sulfur dioxide conversion rate as a function of temperature for Examples 7-10.
The catalyst and process in accordance with this invention will be illusl=rated in the following Examples.
The following substances are mixed in a kneading unit with sigma blades and subjected to a kneading process lasting 7 hours:
Titanium oxide (anatase) 4950 g Sili<:on dioxide 146 g Vanadium pentoxide 297 g Pota:>sium sulfate 297 g Water. 4542 g Clay 213 g Glass fibers 550 g Organic additives 164 g Ammonia 1150 g The kneaded mass i~~ subsequently extruded in a worm extruder to form bodies, heated with a temperature rise of 1°C. per hour to 50°C. and a relative moisture of approximately 100 to 80~, largely dried thereby and then heated further in stage~c of a maximum of 50°C. per 2 hours to 600°C. Then, the mixture is tempered by sintering for 24 hours at this temperature in air. The honeycomb bodies have 3 x 3 cells of a square cross section, a cell width of 5.5 mm and a wall thickness of 1.3 mm.
The activity test was carried out in a laboratory testing system under they following conditions:
V 1.13 m3/h i.N. moist AV*~ 16-52 m/h **~
LV 0.6 m/s i.N.
NO 100 ppm dry S02 600 ppm dry 02 5 % by vol. dry H20 7 % by vol. moist N2 Balance *' Surface load (volume stream/catalyst surface) **~ Flow rate FIG. 1 shows t:he temperature dependency of the catalytic activity of this catalyst at a surface charge of AV=52 m/h, which corresponds to a space velocity of approximately 20000 h-1. The conversion remains at a rather low level up to 3'15°C. but then rises sharply in a temperature window of about 50°C. wide and stabilizes after approximately 425°C'.. at 36-37$ conversion.
FIG. 2 shows the dependency of the S02 conversion on the surface charge of the catalyst at 450°C. The AV value (surface charge) was 16..4 m/h at first in the case of a catalytic honeycomb 350 mm long. By means of sawing off 30 mm at a time, the AV value was increased successively to 52 m/h. The AV range between 4 and 10 m/h, which is of interest for real operation, can not be accomplished in this laboratory testing system; however, conversion values around 80$ were found already at AV=15 m/h. Therefore, it can be expected that conversion values above 90$ can be reached and even distincaly exceeded in the range of 4-10 m/h.
The following substances are mixed in a kneading unit with blades which move out in a shearing manner and are kneaded for 12 hours to a paste (all data in kg):
Examp 1 e:
Component 2 3 4 5 6 Titanium oxide: 30.0 180.0 180.0 40.0 40.0 (anatase) Silicon dioxide 0.9 2.7 2.7 1.2 1.2 Ammonium 1.0 6.0 12.0 2.66 2.66 metavanadate Potassium 1.5 9.0 9.0 2.0 3.0 sulfate Water 16.5 100.0 100.0 20.5 20.0 Clay :L.S 9.0 9.0 2.0 2.0 Fibers :3.18 19.0 19.0 4.23 4.23 Organic :1.235 7.5 7.5 2.0 2.0 additives After kneading, the paste is placed into an extruder and pressed into honeycomb bodies. In Examples 2, 5 and 6, so-called quarter monoliths with 75 x 75 mm width and 500 mm length were extruded, and in Examples 3 and 4 solid monoliths with 150 x 150 mm width and 1000 mm length were produced. After drying and calcining, as in Example 1, tests were performed in a pilot plant system after a dry coal firing and also in an industrial-sized system, likewise after a dry coal firing. The composition of the flue gases in both of these systems corresponds within the framework of the customary range of variation to the composition indicated in Example 1, with the difference being that there was still approximately 12~ by volume C02 and a dust content of less than 50 mg/m3 present.
For the pilot system, flue gases are drawn off isokinetically after the dedusting and heated by means of electric heaters to the desired temperature. The catalysts are located in a heat-insulated reactor with a total of 12 gas-specimen removal and temperature measuring positions.
According to the DESONOXTM method of Degussa AG, the flue gases are denitrified at first according to the SCR method (selective catalytic reduction). Immediately afterward, the catalysts for the reduction of the nitrogen oxides with NH3 oxidation catalysts of the invention were installed.
The catalyst elements produced in accordance with the method of the invention in lengths of 1000 mm or 500 mm with side-edge lengths of 150 mm x 150 mm or 75 mm x 75 mm were sawed into elements with a length of 150 mm each for reasons of a detailed measurement of the conversion along the reaction stretch of the pilot system. A total of eight such elements were installed in series. The cell division was 4.2 mm.
FIGS. 3 and 4 show the evaluation of the measuring results on specimens from selected examples at 450° and 425°C., respectively. fhe application -In (1-r~) against 1/AV was selected in they sense of a reaction of the first order. The ordinate value of 2.3 corresponds to a conversion of 90~.
The results found thereby show that SOZ conversions to S03 above 90~ can be achieved without problems, such that the fixing at a minimum temperature of 450°C. necessary in the case of a noble-metal catalyst is no longer necessary, and that the kinetics of the S02 oxidation belong approximately to a time law of the first order.
The test specimens used in the industrial-size system were removed after a running time of more than 1000 operating hours and installed into the described pilot system for determination of activity. No reductions of activity were able to be determined.
The following substances were mixed in a kneading unit with blades which move out and subjected to a kneading process for 5 hours (all data in g):
Example Component 7 8 9 10 Titanium oxide 667 ~~ *~
(Pyrogenic) Silicon dioxide 70 (pyrogenic) Ammonium 37.1 metavanadate Potassium sulfate 20.2 40.4 0 32.3 Caesium sulfate 20.2 0 40.4 8.1 Water 260 Clay 25.3 ~~ ~~ n Glass fibers 72.4 Typical organic 15.7 additives, in-cluding carboxy-methyl cellulose Ammonia 30 ~~ ~~ n *) = always same amounts in Example 7 After the kneading, the paste obtained is processed to extruded blanks. '.Che drying and calcining again took place according to Example 1, but with a final temperature of the drying of 60°C. here and with a final moisture of 70g relative moisture. The temperature during calcining was increased here to only 500°C., and the matter was then sintered for 48 hours at: this temperature.
FIG. 5 shows the temperature-dependent activity behavior of the catalysts prepared in this manner under the testing conditions cited in Example 1, at a surface charge (AV) of 23 m/h.
The following substances were mixed in a kneading unit with blades which move out in a shearing manner and subjected to a kneading process for 5 hours (all data in g) Example Component 11 12 13 14 15 Titanium oxide 700 700 770 470 700 (80% by weight anatase + 20%
by weight rutile) Silicon dioxide 70 70 2 300 (precipitated silica) Aluminium oxide 7p (7-A1203) Vanadium 7.5 130 42 42 42 pentoxide Potassium sulfate160.0 10 42 42 42 Water 300 250 220 300 300 Clay 30 25 25 25 25 Glass fibers 73 73 73 73 73 Organic additives,17 17 17 17 17 including carboxy-methyl cellulose Ammonia 50 50 50 50 50 The production of Examples 11-14 took place in a similar manner to Example 1. The produced catalysts met the basic values for the' concentration ranges of the components A1, A2, B arid C produced in accordance with this invention. It turned out that all production measures of the method in accordance with this invention, such as the kneading process, extrusion, drying, calcining, and sintering, can be readily carried out within this framework. Mechanically stable form bodies with an appropriate catalytic acaivity are obtained in every instance.
Example 11 showed that a catalyst composed in this manner exhibits an especially high activity even at low temperatures.
Example 15 showed that the co-use of A1203 also results in increased activity.
Claims (16)
1. A catalyst for the oxidation of sulfur dioxide contained in an oxygen-containing gas current, said catalyst comprising:
A) a catalytically active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof;
B) silicon, aluminum or mixtures thereof, in the form of oxides, as a surface area enlarging component; and C) titanium oxide in anatase form, rutile form or mixtures thereof, as a carrier material and a ceramic binder;
wherein said catalyst is a solid catalyst having catalytic active material through and through; and wherein a mixture of the components A) through C) is present in a finely sintered form with atomic ratios between the metals of tree components according to A1):A2):B):C) in the range of (0.01-0.2):(0.01-0.2):(0.001-0.5):1.
A) a catalytically active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof;
B) silicon, aluminum or mixtures thereof, in the form of oxides, as a surface area enlarging component; and C) titanium oxide in anatase form, rutile form or mixtures thereof, as a carrier material and a ceramic binder;
wherein said catalyst is a solid catalyst having catalytic active material through and through; and wherein a mixture of the components A) through C) is present in a finely sintered form with atomic ratios between the metals of tree components according to A1):A2):B):C) in the range of (0.01-0.2):(0.01-0.2):(0.001-0.5):1.
2. The catalyst according to claim 1, wherein the catalyst is in a monolithic or honeycomb form.
3. The catalyst according to claim 1 or 2, wherein the ratio of A1):A2):B):C) is in the range of (0.02-0.08):(0.02-0.08):(0.005-0.05):1.
4. The catalyst according to claim 1, 2 or 3, wherein the catalyst further includes at least one additive member selected from the group consisting of a moistening agent, a stabilizing medium, a green-body binder, an auxiliary deformation agent, or a pore forming material.
5. The catalyst according to claim 1, 2 or 3, wherein the catalyst further includes glass fibers.
6. The catalyst according to any one of claims 1 to 5, wherein the catalyst further includes a binder selected from the group consisting of cellulose derivatives, polyethylene, polypropylene, polyvinyl alcohol, polyethylene oxide, polyacrylamide, and polystyrene.
7. The catalyst according to any one of claims 1 to 5, wherein the catalyst further includes a cellulose derivative.
8. A method for the production of a catalyst for the oxidation of sulfur dioxide contained in an oxygen-containing gas current, said catalyst comprising:
A) a catalytically active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof;
B) silicon, aluminum or mixtures thereof, in the form of oxides, as a surface area enlarging components and C) titanium oxide in anatase form, rutile form or mixtures thereof, as a carrier material and a ceramic binder;
wherein said catalyst is a solid catalyst having catalytic active material through and through; and wherein a mixture of the components A) through C) is present in a finely sintered form with atomic ratios between the metals of the components according to A1):A2):B):C) in the range of (0.01-0.2):(0.01-0.2):(0.001-0.5):1;
said method comprising:
intensively processing components A) through C) to a homogeneous mass in finely divided form;
pressing or extruding the mass to a desired green body;
drying the green body under a slow elevation of the temperature to at the most 60°C. with controlled moisture of the ambient air;
calcining under gradual elevation of the temperature in the ambient air to the range of 500°C.-800°C.; and sintering at a temperature in this range for at least 12 hours.
A) a catalytically active substance comprising:
A1) vanadium oxide; and A2) alkali metal oxide, alkali metal sulfate or mixtures thereof;
B) silicon, aluminum or mixtures thereof, in the form of oxides, as a surface area enlarging components and C) titanium oxide in anatase form, rutile form or mixtures thereof, as a carrier material and a ceramic binder;
wherein said catalyst is a solid catalyst having catalytic active material through and through; and wherein a mixture of the components A) through C) is present in a finely sintered form with atomic ratios between the metals of the components according to A1):A2):B):C) in the range of (0.01-0.2):(0.01-0.2):(0.001-0.5):1;
said method comprising:
intensively processing components A) through C) to a homogeneous mass in finely divided form;
pressing or extruding the mass to a desired green body;
drying the green body under a slow elevation of the temperature to at the most 60°C. with controlled moisture of the ambient air;
calcining under gradual elevation of the temperature in the ambient air to the range of 500°C.-800°C.; and sintering at a temperature in this range for at least 12 hours.
9. The method according to claim 8, further including adding an additive to enhance pressing or extruding, said additive being at least one member selected from the group consisting of moistening agents, stabilizing medium, green-body binders, auxiliary deformation agents, and pore forming materials; wherein said additive is added prior to pressing or extruding.
10. The method according to claim 9, wherein the additive is a stabilizing medium which includes glass fibers.
11. The method according to claim 8, 9 or 10, wherein the temperature during t:he drying is elevated at the rate of about 1°C. per hour.
12. The method according to any one of claims 8 to 11, wherein the temperature during calcining is elevated at the rate of no more than 50°C. per two hours.
13. The method according to any one of claims 8 to 12, wherein the catalyst is formed into a monolithic or honeycomb body.
14. The method according to any one of claims 8 to 13, wherein the sintering takes place for 14 to 48 hours.
15. The method according to any one of claims 8 to 13. wherein the sintering takes place for 18 to 36 hours.
16. Use of the catalyst according to any one of claims 1 to 7 for the oxidation of sulphur dioxide present in an air stream or an oxygen-containing waste gas or smoke stream.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4018324A DE4018324C1 (en) | 1990-06-08 | 1990-06-08 | |
| DEP4018324.6 | 1990-06-08 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2044067A1 CA2044067A1 (en) | 1991-12-09 |
| CA2044067C true CA2044067C (en) | 2000-11-28 |
Family
ID=6408003
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002044067A Expired - Fee Related CA2044067C (en) | 1990-06-08 | 1991-06-07 | A catalyst for the oxidation of sulfur dioxide |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0460388B1 (en) |
| JP (1) | JPH04227056A (en) |
| KR (1) | KR100199525B1 (en) |
| CN (1) | CN1031926C (en) |
| CA (1) | CA2044067C (en) |
| DE (2) | DE4018324C1 (en) |
| RU (1) | RU2047350C1 (en) |
| ZA (1) | ZA912800B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997004867A1 (en) * | 1995-07-31 | 1997-02-13 | Jury Grigorievich Egiazarov | Catalyst for use in obtaining sulphur by the claus process and a process for manufacturing the same |
| US7381676B1 (en) | 2007-01-16 | 2008-06-03 | Exxonmobil Chemical Patents Inc. | Catalyst composition and its use thereof in aromatics alkylation |
| WO2009118873A1 (en) | 2008-03-27 | 2009-10-01 | イビデン株式会社 | Honeycomb structure |
| WO2009118871A1 (en) | 2008-03-27 | 2009-10-01 | イビデン株式会社 | Honeycomb structure |
| CN102530888B (en) * | 2012-01-31 | 2013-11-27 | 刘立文 | Method for preparing sulfuric acid by using sulfur dioxide |
| CN102716756A (en) * | 2012-06-16 | 2012-10-10 | 江苏龙源催化剂有限公司 | Preparation method and application of honeycomb type sulfur dioxide catalyst |
| JP2014062015A (en) * | 2012-09-21 | 2014-04-10 | Sumitomo Metal Mining Co Ltd | Method for sieving solid catalyst |
| DE102014005153B4 (en) * | 2014-04-08 | 2023-12-14 | Andreas Döring | Exhaust gas aftertreatment system and method for exhaust gas aftertreatment |
| WO2019170406A1 (en) * | 2018-03-07 | 2019-09-12 | Basf Se | Shaped catalyst body in the form of tetralobes of uniform wall thickness |
| CN113800479A (en) * | 2021-10-29 | 2021-12-17 | 山东京博众诚清洁能源有限公司 | Process for preparing electronic-grade sulfuric acid by cyclic absorption method |
| CN114433069A (en) * | 2022-01-26 | 2022-05-06 | 浙江科卓环保科技有限公司 | Production process of high-ash flue gas honeycomb denitration catalyst |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1086218B (en) * | 1956-08-13 | 1960-08-04 | Ici Ltd | Process for the production of catalysts for the oxidation of sulfur dioxide to sulfur trioxide |
| US3969274A (en) * | 1974-03-14 | 1976-07-13 | National Distillers And Chemical Corporation | Fixed bed catalyst |
| IT1197899B (en) * | 1986-10-20 | 1988-12-21 | Alusuisse Italia Spa | OXIDATION CATALYST AND PROCEDURE FOR ITS PREPARATION |
| JP2580239B2 (en) * | 1988-04-01 | 1997-02-12 | 三菱重工業株式会社 | Method for producing gas parallel flow type sulfurous acid gas oxidation catalyst |
| DE68919505T2 (en) * | 1988-04-08 | 1995-06-22 | Mitsubishi Heavy Ind Ltd | Catalyst filter, method for producing a catalyst filter and method for treating combustion gases with a catalyst filter. |
| SE464688B (en) * | 1989-02-27 | 1991-06-03 | Eka Nobel Ab | CATALYST FOR REDUCING NITROGEN OXIDES AND USING THEREOF |
-
1990
- 1990-06-08 DE DE4018324A patent/DE4018324C1/de not_active Expired - Lifetime
-
1991
- 1991-04-15 ZA ZA912800A patent/ZA912800B/en unknown
- 1991-04-22 EP EP91106428A patent/EP0460388B1/en not_active Expired - Lifetime
- 1991-04-22 DE DE59102409T patent/DE59102409D1/en not_active Expired - Fee Related
- 1991-05-08 CN CN91103089A patent/CN1031926C/en not_active Expired - Fee Related
- 1991-06-05 RU SU914895448A patent/RU2047350C1/en active
- 1991-06-07 JP JP3136048A patent/JPH04227056A/en active Pending
- 1991-06-07 CA CA002044067A patent/CA2044067C/en not_active Expired - Fee Related
- 1991-06-07 KR KR1019910009368A patent/KR100199525B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0460388B1 (en) | 1994-08-03 |
| CA2044067A1 (en) | 1991-12-09 |
| EP0460388A1 (en) | 1991-12-11 |
| DE59102409D1 (en) | 1994-09-08 |
| CN1057212A (en) | 1991-12-25 |
| RU2047350C1 (en) | 1995-11-10 |
| KR920000375A (en) | 1992-01-29 |
| ZA912800B (en) | 1992-01-29 |
| JPH04227056A (en) | 1992-08-17 |
| CN1031926C (en) | 1996-06-05 |
| KR100199525B1 (en) | 1999-06-15 |
| DE4018324C1 (en) | 1992-02-06 |
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