JPS6225416B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for producing a carbon monoxide oxidation catalyst that has sufficient activity even at low temperatures and is inexpensive. BACKGROUND ART Conventionally, noble metals such as platinum and palladium have been generally used as catalysts for purifying unburned hydrocarbons, carbon monoxide, and nitrogen monoxide in gases discharged from various industries and various devices. However, catalysts made of precious metals are expensive, and their use in general-purpose appliances such as stoves, cooking ranges, and ventilation fans is currently restricted due to cost constraints. On the other hand, compounds of heavy metals such as manganese, iron, zinc, and copper are said to be effective as catalyst components, but they require a large amount of catalyst components compared to precious metal catalysts. It is difficult to obtain an effective catalyst using methods such as impregnation or coating on a honeycomb-shaped ceramic carrier used in the present invention. In addition, a method of kneading aggregate components and heavy metal compounds and forming the honeycomb-shaped ceramic carrier during production may be considered, but since the honeycomb carrier obtained by this method imparts strength to the compact through sintering, the honeycomb carrier after sintering is The specific surface area of a shaped ceramic carrier is at most 1 m ² /g or less, and its catalytic ability is extremely low. On the other hand, it is also possible to mix a heavy metal compound with activated alumina, etc., and make a spherical or rod-shaped activated alumina catalyst carrier by granulating the mixture, compression molding, etc.; Although it can exhibit catalytic performance in applications where the treated gas is forcibly brought into contact with the carrier, it is not suitable for applications such as catalysts for treating unburned gas in open atmospheres, for example for suspended oil stoves as shown in Figure 1. In,
Since the pressure drop of the catalyst layer is large, the contact area of unburned gas with the catalyst is small, and the oxidation rate of exhaust gas cannot be expected to be high. Furthermore, a method has been devised in which alumina cement is used instead of activated alumina as an oxidation catalyst for kerosene stoves (Japanese Patent Application Laid-Open No. 54-26984); The reaction causes strength deterioration, and cement itself has a low specific surface area, so it cannot be said to be an effective catalyst carrier. In view of this situation, the present inventors have improved the mechanical strength and
As a result of intensive research in order to obtain an oxidation catalyst and a catalyst carrier with an excellent oxidation rate of exhaust gas, the present invention was completed by discovering a method for manufacturing a carbon monoxide oxidation catalyst that satisfies all of the above conditions. That is, the present invention provides 10 to 90% by weight of a compound of at least one heavy metal selected from the group consisting of manganese, iron, zinc and copper, and 90% by weight of rehydratable alumina.
After treating an aggregate composition consisting of ~10% by weight and a total of at least 50% by weight of heavy metal compounds and rehydratable alumina with a rehydration inhibitor, or by rewatering the rehydratable alumina in advance. After treatment with a hydration inhibitor, the aggregate composition is mixed and kneaded with water and/or a water-containing substance to form a plastic composition, the plastic composition is extruded, and then rehydrated.
Monooxide monooxide formed into a hollow shape having at least one opening with a porosity of 20% or more and a specific surface area of 5 m ² /g or more, dried as necessary and fired at a temperature of 1000°C or less. The present invention provides a method for producing a catalyst for carbon oxidation. The present invention will be explained in more detail below. The rehydratable alumina used in the method of the present invention is transitional alumina other than α-alumina obtained by thermally decomposing alumina hydrate, such as ∫-alumina and amorphous alumina, and is industrially available from the Bayer process, for example. Alumina hydrates, such as alumina trihydrate, are brought into contact with hot gas at a temperature of about 400 to 1200°C, usually for a fraction of a second to 10 seconds, or alumina hydrates are brought into contact with a hot gas of about 250 to 900°C under reduced pressure. Approximately 0.5 ~ obtained by heating and holding for 1 minute ~ 4 hours
Examples include those having a loss on ignition of 15% by weight. In terms of physical properties, the rehydratable alumina used in the present invention is found to contain ∫-alumina and/or amorphous alumina in an amount of 20% by weight or more, preferably 30% by weight or more, as determined by X-ray diffraction. That's fine. Rehydratable alumina is generally used with a particle size of about 50μ or less, and the mixing ratio with heavy metal compounds of manganese, iron, zinc, and copper is 10 to 90% by weight, preferably 30 to 70% by weight. used in Regarding the mixing ratio of rehydratable alumina and heavy metal compounds, if the content of rehydratable alumina is less than 10% by weight, no improvement in mechanical strength is observed, while if it exceeds 90% by weight, heavy metal compounds cannot exhibit its oxidation catalytic ability. The heavy metal compound used in the present invention is a heavy metal compound selected from the group consisting of at least manganese, iron, zinc, and copper, and more specifically, iron oxide, iron hydroxide, iron carbonate, copper oxide. thing,
Examples include copper hydroxide, copper carbonate, zinc oxide, zinc hydroxide, zinc carbonate, manganese oxide, manganese carbonate, etc., and the mixing ratio with rehydratable alumina is 90%.
It is used in a proportion of ~10% by weight, preferably 70-30% by weight. If the amount of the heavy metal compound added is less than 10% by weight, the oxidation catalytic ability will not be fully exhibited, while if it exceeds 90% by weight, the mechanical strength of the resulting catalyst will be low and the specific surface area will also decrease. Therefore, it is not preferred as a catalyst or catalyst carrier. The particle size of the heavy metal compound affects the activity of the catalyst and the mechanical strength of the molded product, but it is usually 0.05~
30μ and a specific surface area of 1 m ² /g or more is used. In practicing the present invention, the rehydratable alumina and the heavy metal compound form an aggregate composition in the above composition range,
It is then shaped and subjected to rehydration treatment and calcination treatment to become a catalyst or catalyst carrier, but aggregates other than rehydratable alumina and the above-mentioned heavy metal compounds may be used within a range that does not impair the various physical properties targeted by the present invention. I can do it. These aggregates are not particularly limited as long as they are aggregates used in the field of catalyst supports, but include α-alumina, silica, alumina hydrate, clay, talc, bentonite, diatomaceous earth, and zeolite. , cordierite, spodiumene, titania, zirconia, silica sol, alumina sol, mullite, chromia, activated carbon, etc., and are used in an amount of less than 50% by weight, preferably less than 30% by weight, more preferably less than 20% by weight in the aggregate composition. . Furthermore, if necessary, wood chips, cork grains, coal powder, activated carbon, charcoal, crystalline cellulose powder, methyl cellulose, carboxymethyl cellulose, starch, sucrose, gluconic acid, polyethylene can be used to increase the specific surface area and pore volume of the catalyst or catalyst carrier. Addition of flammable substances such as glycol, polyvinyl alcohol, polyacrylamide, polyethylene, polystyrene, etc., addition of inorganic fibers to increase strength, addition of catalyst components for the purpose of omitting the step of supporting the catalyst components after forming the carrier, etc. The addition amount range may be adjusted according to the category of aggregate for inorganic materials and the intended use of the molded product for organic materials. In the practice of this invention, the rehydratable alumina is
Partially or completely coated with an anti-rehydration agent prior to contact with water or water-containing substances. This is to prevent the rehydration alumina in the aggregate composition from causing a rehydration reaction in the extruder and becoming hardened and unmoldable. is sufficient as long as it can prevent water and rehydratable alumina from causing a rehydration reaction during extrusion molding, making it impossible to mold, specifically in the case of organic materials that are solid at room temperature. Examples include those having a solubility in water at room temperature of about 20% by weight or less, preferably about 10% by weight or less. Further, in the case of organic substances that are liquid at room temperature, examples thereof include those whose mutual solubility in water at room temperature is at most 50% or less, preferably 25% or less. More specifically, caproic acid, palmitic acid,
Oleic acid, glycolic acid, caprylic acid, stearic acid, salicylic acid, trimethylacetic acid, lauric acid, serotenic acid, cinnamic acid, malonic acid, myristic acid, sebacic acid, benzoic acid, maleic anhydride, caprylic acid, pelargonic acid, wax fatty acids and their salts, or their sulfonic acids, phosphoric acid substituted products, t-butyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol,
Alcohols such as cyclohexanol, menthol, cholesterin, naphthol, amines such as laurylamine, tetramethylenediamine, diethanolamine, diphenylamine, n-heptadecane, n-octadecane, n-nonadecane, n-
Alkanes such as eicosane, aromatic compounds such as naphthalene, diphenyl, and anthracene, starch, casein, cellulose, and their derivatives, natural polymer compounds such as alginates, polyethylene, polyvinyl alcohol, polyvinyl chloride, polypropylene, and sodium polyacrylate. , synthetic polymer compounds such as polybutadiene, isoprene rubber, and urethane resin, paraffins such as liquid paraffin, soybean oil, white squeezed oil, light oil, and kerosene, and aromatic hydrocarbons such as benzene, toluene, xylene, and kyumene. These anti-rehydration agents are added and mixed in such a proportion as to partially or completely cover the rehydrating alumina surface.The coating methods include adding and mixing directly to the powder, kneading and coating, or re-coating. If the anti-hydration agent is a solid substance that is difficult to coat directly on the powder, the anti-rehydration agent may be dissolved in an appropriate solvent such as alcohol or ether in advance and then coated. In the case of a powder, various methods can be used, such as directly immersing it in a rehydration inhibitor, or vaporizing the liquid and coating it on the powder surface. Of course, these may be used in combination. The amount of rehydration inhibitor added depends on the particle size distribution and composition of the aggregate, extrusion molding and subsequent rehydration processing conditions, but is usually 0.01% for rehydrating alumina.
It is used in a range of 30% by weight. If the amount added is less than 0.01% by weight, the effect of preventing rehydration will not be sufficient and the resin will harden due to heat during extrusion molding, making molding impossible. however,
When the rehydration inhibitor also serves as a binder, the amount added can be increased up to the upper limit of the amount added of the binder. The binder used in the extrusion molding of the catalyst and catalyst carrier of the present invention is not particularly limited as long as it is a known binder used in the production of alumina catalyst carriers, but examples include polyvinyl alcohol. , starch, cellulose, etc. The amount of binder added depends on the aggregate composition, particle size, extrusion molding conditions, and rehydration treatment conditions that make up the molded product, and cannot be determined unambiguously, but it is usually between 0 and 100% for the aggregate. It is carried out in a range of 30% by weight. If the amount of the binder added exceeds 30% by weight, it is not preferable because the molded product may become distorted or its strength may decrease when the rehydration inhibitor in the molded product disappears. If the rehydration inhibitor has a caking effect, it is of course possible to use it by adding only the amount lacking as a caking agent. In the practice of the present invention, the rehydration inhibitor may be premixed with at least a portion of the rehydratable alumina, and then mixed with aggregates and binders constituting the compact other than the rehydratable alumina in small amounts. Although it is more preferable to obtain a rehydration prevention effect using a rehydration inhibitor, it is also possible to add and mix the rehydration inhibitor to all aggregates. The aggregate constituting the molded body treated with the above-mentioned rehydration inhibitor is then extruded into a molded body having a desired shape, but the aggregate is preliminarily treated with water or a water-containing substance before being fed to the extruder. Alternatively, if the molding machine has a kneading function, it may be kneaded with aggregate and water or a water-containing substance in an extrusion molding machine to form a plastic composition and extrusion molding. The amount of water added during molding is generally in the range of about 20 to 70% by weight based on the aggregate constituting the molded body. In the present invention, water-containing substances include acids, alkalis,
It refers to an aqueous solution containing a catalyst component, a binder, and various other additives. The extrusion molding machine used in the present invention is not particularly limited in its mechanism as long as it is a known molding machine that can form a hollow shape, but for example,
U.S. Patent No. 3559252 if it has a honeycomb shape
Examples include die-shaped ones described in Japanese Patent Publication No. 51-1232, Japanese Patent Application Laid-Open No. 48-55960, and the like. In addition, for the purpose of improving the contact time with the processing gas passing through each core of the honeycomb-shaped formed body, a honeycomb-shaped formed body (e.g. Tokukai Akira
50-127886), drying of honeycomb shaped body,
A honeycomb-shaped molded body is formed by bending the thin mold in at least one direction in the extrusion direction in order to prevent cracking, distortion, etc. due to expansion and contraction of the honeycomb-shaped molded body during firing (for example, Japanese Patent Application Laid-Open No. 51-565) ), and an extrusion molding machine in which a thin wall constituting the outer periphery of a honeycomb-shaped molded body is attached with a color ring, or a thick outer periphery is formed by a die structure to improve impact strength. The outer shape and core shape of the hollow molded body may be any geometric shape such as square, rectangle, triangle, hexagon, or circle, and the thickness of the cells forming the core and the length of the hollow molded body may be The core cross-sectional area and the total cross-sectional area of the core forming surface (outer shape) of the hollow molded body may be arbitrarily determined depending on the application. Although the term extrusion molding is used in the present invention, if the above-mentioned method of preventing rehydratable alumina from hardening in the equipment during kneading and extrusion is used, molded products can also be produced by injection molding, transfer molding, etc. Since it can be manufactured, this molding method is also within the scope of the extrusion molding method described herein. The molded product extruded in this way is then heated in water vapor at room temperature to 150°C, particularly preferably 80 to 100°C, for a sufficient time to rehydrate in order to increase the impact strength and mechanical strength of the molded product itself. in a water vapor-containing gas or at a temperature above room temperature, particularly preferably at 80°C.
It is rehydrated by keeping it in water above ℃. When using a rehydration inhibitor that is insoluble in water at the above temperature, for example, when polyvinyl chloride is used, it is immersed in a solvent such as alcohol, ether, or ester to destroy or dissolve the coating layer. As a result, the molded body is rehydrated with water contained in the molded body. Rehydration generally occurs for 1 minute to 1 week. The longer the rehydration time and the higher the temperature, the more solidification of the molded product progresses and a product with greater mechanical strength can be obtained, so the higher the rehydration temperature, the shorter the rehydration time. It is also possible to leave it in a closed container at room temperature and pressure for rehydration over a long period of time. The molded body rehydrated in this way is then subjected to a known method such as natural drying, hot air drying, or vacuum drying to remove adhering moisture, and then heat-treated at a temperature of 1000°C or less to remove the moisture in the molded body. Removes moisture and activates. In carrying out the present invention, a drying step after the rehydration treatment is not essential. In other words, by making the temperature gradient during firing gentle, temperatures ranging from room temperature to 300°C can be achieved.
This can be done by firing for 24 hours and then firing at 300°C to 1000°C for 6 to 12 hours. If combustible substances are mixed in the molded product during firing, heat treatment is performed at a temperature of approximately 250°C or higher,
Dissipate combustible substances. When activating and removing combustible substances at the same time, for example, place a compact containing a combustible substance on a bed and blow hot air or combustion gas at a predetermined temperature containing enough oxygen to burn the combustible substance. This can be done by passing. The molded product obtained by the above method has a specific surface area of approximately 5 m ² /
g or more, and a compressive strength of 20 kg/cm ² or more, and is extremely superior in specific surface area compared to conventional catalysts or catalyst supports containing heavy metal compounds hardened with alumina cement. The mechanical strength imparted is 1200 to 2000℃ compared to the conventional method.
Not only can it achieve strength comparable to ceramic bonding through high-temperature firing, but since it can only be activated by firing at temperatures below 1000°C, there is extremely little reduction in the specific surface area of heavy metal compounds, and the firing temperature is low. The combustion equipment materials, equipment maintenance costs, and fuel consumption are extremely low, and its industrial value is extremely high. The carbon monoxide oxidation catalyst of the present invention is used in a hollow form having a porosity of 20% or more, a specific surface area of 5 m ² /g or more, and at least one opening. If the porosity is less than 20%, even if it is used as a catalyst for oxidizing the gas emitted when igniting and/or extinguishing a kerosene stove, the pressure drop will be high and the gas will either not be able to pass through, or it will flow elsewhere and there will be insufficient exhaust gas. oxidation cannot be achieved. On the other hand, when the specific surface area is less than 5 m ² /g, the dispersibility of the heavy metal catalyst is poor, which is disadvantageous in terms of initial activity and thermal deterioration. As a method for improving the physical properties of the carbon monoxide oxidation catalyst thus obtained, an auxiliary catalyst component other than the heavy metal compound consisting of manganese, iron, zinc, and copper is added and mixed into the catalyst and the aggregate constituting the catalyst carrier. Alternatively, impregnation is also possible. Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples. Example 1 1 part by weight of stearic acid was added as a rehydration inhibitor to 50 parts by weight of activated alumina powder containing 30 parts by weight of ∫-alumina with an average particle diameter of about 6 μ obtained by burning gibbsite-type alumina hydrate. After kneading for 30 minutes in a crusher and coating, a mixture of 50 parts by weight of manganese dioxide with an average particle size of 1μ, further adding 4.8 parts by weight of methyl cellulose and 35 parts by weight of water as extrusion aids was kneaded for 30 minutes using a screw kneader. The catalyst was fed into a screw type extruder to form a 100 mm x 100 mm honeycomb-shaped catalyst body having a square core unit with a wall thickness of 1 mm and a side of 4 mm. (Porosity: 64%) Next, this carrier was rehydrated in hot water at 90°C for 24 hours, and then heated to 700°C at a heating rate of 100°C/Hr.
It was further baked at 700°C for 1 hour. The catalyst body obtained in this way has a specific surface area of 95 m ² /
The alumina constituting ^the catalyst body was mainly composed of γ-alumina. Next, using this catalyst, the space velocity
The CO conversion rate at 400℃ and 600℃ of air gas containing 200ppm carbon monoxide at 20000hr ^-1 was measured. The results are shown in Table 1.

[Table] Example 2 45 parts by weight of activated alumina powder treated with stearic acid as in Example 1 was added with an average particle size of 0.3μ.
A mixture of 5 parts by weight of Fe ₂ O ₃ , 50 parts by weight of 1μ manganese dioxide, and 5 parts by weight of methylcellulose and 37 parts by weight of water as extrusion aids was kneaded for 30 minutes using a screw kneader and then fed to a screw type extruder. A pipe-shaped catalyst body (porosity: 25%) with an outer diameter of 10 mm, an inner diameter of 5 mm, and a length of 10 mm was molded. This carrier was then rehydrated under the same conditions as in Example 1, heated to 600°C at a rate of 100°C/Hr, and fired at 600°C for 1 hour. The catalyst body thus obtained has a specific surface area of 88
The main component of the alumina constituting the catalyst body in terms of m ² /g was γ-alumina. Compressive strength and space velocity after heating this catalyst at 400℃, 600℃, and 800℃ for 3 hours
300℃ of air gas containing CO200ppm at 5000hr ^-1
CO conversion at ~700°C was measured. The results are shown in FIGS. 2 and 3. Comparative example 1 Alumina cement 50 containing 10% by weight of Fe ₂ O ₃
A mixture of 50 parts by weight of manganese dioxide having an average particle diameter of 1 μm and 10 parts by weight of water was press-molded at a pressure of 500 kg/cm ² to form a pipe-shaped catalyst carrier having the same shape and dimensions as in Example 2. Next, this molded body
100 per hour after curing for 48 hours at 20℃ and 90% humidity
The temperature was raised to 600°C at a temperature increase rate of 10°C, and the mixture was further baked at 600°C for 1 hour. (Specific surface area: 2 m ² /g) The catalyst body thus obtained was treated in the same manner as in Example 2, and the compressive strength and CO conversion rate were measured. The results are shown in FIGS. 2 and 3. Comparative Example 2 The CO conversion rate was measured under the same conditions as Example 1 using a catalyst body (porosity 16%) in which 3/4 of the pores of the honeycomb-shaped catalyst body obtained in Example 1 were closed. did. The results are shown in Table 2.

[Table] Comparative Example 3 Same as Example 1 except that 5 parts by weight of manganese dioxide, 5 parts by weight of methyl cellulose, and 40 parts by weight of water were added to 95 parts by weight of activated alumina powder treated with 1.9 parts by weight of stearic acid as in Example 1. A honeycomb-shaped catalyst body was obtained by this method. (Specific surface area 150m ² /g, compressive strength
(90 Kg/cm ² ) Using this catalyst, the CO conversion rate was measured under the same conditions as in Example 1. The results are shown in Table 3.

[Table] Comparative Example 4 Same method as in Example 1 using 5 parts by weight of activated alumina powder treated with 0.1 parts by weight of stearic acid as in Example 1, 95 parts by weight of manganese dioxide, 3 parts by weight of methyl cellulose, and 35 parts by weight of water. A honeycomb-shaped catalyst body (specific surface area: 10 m ² /g) was obtained. This catalyst body had a compressive strength of 10 kg/cm ² and was extremely brittle. Example 3 50 parts by weight of activated alumina powder treated with stearic acid as in Example 1 and 74 parts by weight of basic copper carbonate,
In addition, polyethylene oxide 5 is used as an extrusion aid.
parts by weight and 35 parts by weight of water were kneaded using a screw kneader for 30 minutes, and then fed to a screw extruder to form a honeycomb-shaped catalyst body having the same shape as in Example 1. Next, this catalyst body was rehydrated in steam at 100℃ for 72 hours, and then heated at 100℃/
Raise the temperature to 500℃ at a heating rate of Hr, and further increase the temperature to 1 at 500℃
Baked for an hour. (Specific surface area 120m ² /g, compressive strength 80
Kg/cm ² ) Using the obtained catalyst body, the conversion rate of CO was measured under the same conditions as in Example 1. The results are shown in Table 4.

[Table] Example 4 Average particle size of manganese dioxide in Example 1
A honeycomb-shaped catalyst body was obtained in the same manner except that zinc oxide with a thickness of 0.1 μm was used. The catalyst body thus obtained has a specific surface area of 100
m ² /g and compressive strength of 70 Kg/cm ² , and the main component of the alumina constituting the catalyst body was γ-alumina. Next, using this catalyst, the space velocity
The CO conversion rate of air gas containing 200 ppm of carbon monoxide at 300℃ and 500℃ was measured at 20000hr ^-1 . The results are shown in Table 5.

[Table] Example 5 Example 1 except that in Example 1, activated alumina powder and manganese dioxide were mixed in advance, 1.5 parts by weight of stearic acid was added as a rehydration inhibitor, and the mixture was kneaded for 30 minutes using a crusher for coating. A honeycomb-shaped catalyst body was obtained in the same manner as above. The catalyst body thus obtained has a specific surface area of 95
m ² /g and compressive strength of 85 Kg/cm ² , the alumina constituting the catalyst body was mainly composed of γ-alumina. Next, using this catalyst, the space velocity
The CO conversion rate at 400℃ and 600℃ of air gas containing 200ppm carbon monoxide at 20000hr ^-1 was measured. The results are shown in Table 6.

【table】 [Brief explanation of the drawing]

Figure 1 shows a front view of a kerosene stove equipped with an exhaust gas oxidation catalyst, and in the figure, 1...
Top plate, 2...Oil stove body, 3...Combustion part and chimney, 4...Reflector, 5...Knob for operating the combustion wick, 6...Catalyst tank suspension fittings, 7...Catalyst tank made of wire mesh , 8...represents a catalyst body. FIG. 2 compares the thermal deterioration of the catalyst of the present invention and a conventional catalyst using alumina cement, and FIG. 3 compares the CO conversion rates.

Claims (1)

[Claims] 1 Compound of at least one heavy metal selected from the group consisting of manganese, iron, zinc and copper 10-90
After treating an aggregate composition comprising 90 to 10% by weight of rehydratable alumina and a total of at least 50% by weight of heavy metal compounds and rehydratable alumina with a rehydration inhibitor, or After pre-treating the rehydratable alumina with a rehydration inhibitor, the aggregate composition is mixed and kneaded with water and/or a water-containing substance to form a plastic composition, and the plastic composition is extruded. , then rehydrated, dried if necessary, and fired at a temperature of 1000°C or less to produce a material with a porosity of 20
% or more, and a catalyst for carbon monoxide oxidation integrally molded into a hollow shape having at least one opening with a specific surface area of 5 m ² /g or more.