JPS6325814B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a catalyst carrier that has excellent thermal shock resistance and pressure resistance, and has a high specific surface area. In recent years, exhaust gas regulations from various industries have been tightened from the perspective of environmental conservation, and molded bodies made of transitional alumina such as activated alumina and alumina sol have a characteristic of having a higher specific surface area than other inorganic molded bodies. It is widely used as a catalyst carrier for denitration, deodorization, and internal combustion engines. However, molded bodies obtained from such transitional alumina have low thermal shock resistance and pressure resistance.For example, they are used in catalyst supports for automobiles, which require pressure resistance because the support itself is subjected to impact, or in cases where unburned hydrocarbons in exhaust gas If the carrier is subjected to large temperature changes such as rapid heat generation due to catalytic oxidation reaction of carbon monoxide or rapid cooling due to engine stop, cracks or damage will occur in the carrier, making it impossible to put it to practical use. On the other hand, molded bodies made from low thermal expansion materials such as cordierite, spodiumene, and mullite are used as catalysts or catalyst carriers in fields where thermal shock resistance and pressure resistance are required. The molded body generally has a low specific surface area of 1 m ² /g or less, so if a high specific surface area is required, the surface of the molded body may be coated with a substance having a high specific surface area such as activated alumina or alumina sol. , are used as catalyst carriers, but these catalyst carriers have a complicated manufacturing process, resulting in high costs, and the coating layer tends to peel off during use, resulting in a decrease in activity. In addition, in recent years, due to stricter exhaust gas regulations and demands for more compact equipment, honeycomb-shaped catalyst carriers for internal combustion engine exhaust gas have become mainstream, with approximately 400 holes per square inch. A honeycomb-shaped catalyst carrier with a very small pore diameter of 600 or more pores per catalyst is being developed. It is extremely difficult to uniformly coat a catalyst carrier with an extremely small pore size with an alumina layer, and the cost inevitably increases. In view of this situation, the present inventors have developed thermal shock resistance,
As a result of intensive research to find a catalyst carrier with excellent pressure resistance and high specific surface area,
Rehydratable alumina and general formula Li ₂ O・Al ₂ O ₃・XSiO ₂
(X represents an integer from 2 to 8) (hereinafter sometimes referred to as lithia alumina silicate) in a specific proportion. The inventors have discovered that a catalyst carrier that satisfies all of the above physical properties can be obtained by sintering the catalyst with a sintering method, and have completed the present invention. That is, the present invention uses 95 _to 10% by weight of _rehydratable alumina, general formula _{Li2O.Al2O3.XSiO2} (X is ₂ to 8
5 to 90% by weight of a compound represented by
A total of at least 50% by weight of rehydratable alumina and the compound represented by the above general formula is formed into an aggregate composition. An object of the present invention is to provide a method for producing a catalyst carrier, characterized in that the catalyst carrier is sintered. The method of the present invention will be explained in 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 ρ-alumina and amorphous alumina, and is industrially obtained from the Bayer process, for example. Alumina hydrates such as alumina trihydrate are heated to about 400 to 1200°C in hot gas to a fraction of the normal temperature.
About 0.5 to 15% can be obtained by contacting for ~10 seconds or by heating and holding alumina hydrate at about 250 to 900°C under reduced pressure for usually 1 minute to 4 hours.
Examples include those having a loss on ignition of % by weight. When looking at the physical properties of the rehydratable alumina used in the present invention, X-ray diffraction reveals that ρ-alumina and/or amorphous alumina is present in the rehydratable alumina in an amount of 20% by weight or more, preferably 30% by weight or more. It is fine as long as it is something. Rehydratable alumina is generally used having a particle size of about 50 μm or less, and is used in a mixing ratio of 10 to 95% by weight, preferably 30 to 90% by weight, with lithium alumina silicate. Regarding the mixing ratio of rehydratable alumina and lithia alumina silicate, if the content of rehydratable alumina is less than 10% by weight, no improvement in specific surface area will be observed, while if it exceeds 95% by weight, pressure resistance will increase. No improvement in strength or thermal shock resistance was observed. The main components of the crystal phase of the lithia alumina silicate used in the present invention are eucribtite (Li ₂ O・Al ₂ O ₃・2SiO ₂ ) and spodiumene (Li ₂ O・
Al ₂ O ₃・4SiO ₂ ), lithium orthoclaver (Li ₂ O・Al ₂ O ₃・6SiO ₂ ), petalite (Li ₂ O・
General formula Li ₂ O ・Al _{2 O 3 ・}Generally called low thermal expansion _lithium alumina silicate
It may be _a compound having a composition represented by used. If the content of lithia alumina silicate in the mixing ratio of rehydratable alumina and lithia alumina silicate is less than 5% by weight, the effect of reducing the coefficient of thermal expansion will be small and sufficient thermal shock resistance will not be obtained; If it exceeds % by weight, the specific surface area will be small and sufficient catalytic activity cannot be obtained. The particle size of lithia alumina silicate is such that it provides easy sinterability at low temperatures and does not significantly reduce the amount of macropores when formed into a molded product. Generally, the center particle size is 50~ 0.1μ, preferably 30 to 0.5μ is used. In carrying out the method of the present invention, rehydratable alumina and lithia alumina silicate are formed into an aggregate composition in the above composition range, which is then shaped, rehydrated,
Although it becomes a catalyst carrier through a sintering process, aggregates other than rehydratable alumina and lithia alumina silicate can be used within a range that does not impair the various physical properties aimed at by the present invention. These aggregates are not particularly limited as long as they are aggregates used in the field of catalyst supports, but generally α-alumina, silica, alumina hydrate, clay, talc, bentonite, and diatomaceous earth are used. , zeolite, cordierite, titania, zirconia, silica sol, alumina sol, mullite, chromia, activated carbon, etc., used at less than 50% by weight, preferably less than 30% by weight, more preferably less than 20% by weight in the aggregate composition. It will be done. Furthermore, if necessary, in order to increase the specific surface area and pore volume of the catalyst carrier, the addition of crystalline cellulose, synthetic resin, etc., addition of inorganic fibers to increase strength, and the step of supporting catalyst components after the carrier is formed are omitted. Catalytic components may be added for the purpose of enhancing catalytic performance or for the purpose of enhancing catalytic ability, and the range of the addition amount should be adjusted depending on the category of aggregate for inorganic substances and the intended use of the molded product for organic substances. Bye. 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 materials. When the rehydratable alumina in the aggregate composition is kneaded directly with water or water-containing substances, a rehydration reaction occurs during this process. For this reason, even if a rehydration treatment is performed after molding, desired strength cannot be imparted. The rehydration inhibitor may be any agent as long as it can inhibit the rehydration of the rehydratable alumina. Specifically, in the case of organic substances that are solid at room temperature, the solubility in water at room temperature is about 20% by weight or less. and preferably about 10% by weight or less. In addition, in the case of organic substances that are liquid at room temperature, the mutual solubility in water at room temperature is at most 50% or less, preferably
25% or less. More specifically, caproic acid, palmitic acid,
Fatty acids and their salts such as oleic acid, glycolic acid, caprylic acid, stearic acid, salicylic acid, trimethylacetic acid, lauric acid, cerotic acid, cinnamic acid, malonic acid, myristic acid, sebacic acid, benzoic acid, maleic anhydride, and wax; or these sulfonic acids, phosphoric acid substituted products, t-butyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol, cyclohexanol, menthol,
Alcohols such as cholesterin and naphthol, amines such as laurylamine, tetramethylenediamine, diethanolamine, and diphenylamine, n-
Alkanes such as heptadecane, n-octadecane, n-nonadecane, n-eicosane, naphthalene,
Aromatic compounds such as diphenyl and anthracene, starch, casein, cellulose and their derivatives, natural polymer compounds such as alginates, polyethylene, polyvinyl alcohol, polyvinyl chloride, polypropylene, sodium polyacrylate, polybutadiene, isoprene rubber, urethane Synthetic polymer compounds such as resins, paraffins such as liquid paraffin, soybean oil, white squeezed oil, light oil, kerosene, caprylic acid,
Examples include carboxylic acids such as pelargonic acid, 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 ether before coating, or the anti-rehydration agent may be coated with a liquid substance. In this case, various methods can be used, such as directly immersing the powder in the rehydration inhibitor or vaporizing the liquid to coat the powder surface. The amount of rehydration inhibitor added depends on the aggregate particle size distribution, composition, rehydration treatment conditions, etc., but is usually used in the range of 0.01 to 30% by weight based on rehydration alumina. . If the amount added is less than 0.01% by weight, the rehydration prevention effect will not be sufficient and the desired bonding strength will not be achieved by rehydration treatment after molding into the desired molded article. The molding method in the method of the present invention can be carried out by any method generally used for manufacturing catalyst carriers, such as dish granulation method, extrusion molding method, pressing method, casting method, etc. Naturally, the form of the molded product is not limited. Further, operations up to forming a molded body, such as mixing of aggregates, kneading method, added binder, molding aid, etc., may be carried out by known methods for each molding method. The molded body after molding is subjected to a rehydration treatment. Such treatment may be carried out by a method already known for the production of activated alumina carriers, and the treatment is carried out in water at room temperature to 100°C, or in water vapor or water vapor-containing gas at room temperature to 150°C for 1 minute to 1 week. . It is also possible to rehydrate by leaving it in a closed container at room temperature and pressure for a long time. The thus rehydrated molded body is then subjected to air drying, hot air drying, high frequency drying, and then removal of adhering moisture by a known method, followed by sintering at a temperature of 1000 to 1300°C. If the sintering temperature is less than 1000°C, sufficient compressive strength and thermal shock resistance cannot be imparted, while if it exceeds 1300°C, the specific surface area will drop significantly, which is not appropriate. The sintering time varies depending on the sintering temperature, the composition of the molded body, and the physical properties of the final molded body, but it is usually 30
Baked in a range of minutes to 24 hours. The compact obtained in this way has a specific surface area of 5 to 120 m ² /g, a compressive strength of 100 Kg/cm ² or more, a thermal shock resistance temperature of 500°C or more, and the alumina components after sintering are mainly γ- and θ- It has the physical properties of alumina. The reason why the molded product obtained in the present invention is able to improve the compressive strength and specific surface area more than the arithmetic average of the mixing ratio of rehydratable alumina and lithium alumina silicate is not clear, but it is likely that rehydration is possible. The surface of the fine alumina particles activated by the hydration reaction is dragged by the shrinkage caused by the sintering of the lithium alumina silicate particles, increasing their contact surface area and starting sintering at a previously unimaginable low temperature. The chemical reaction with the particles promotes sintering, and the strength increases significantly due to the interparticle bonds formed, and the thermal shock resistance also increases depending on the decrease in the apparent coefficient of thermal expansion and the increase in strength. It is considered that Furthermore, it is also assumed that the alpha-ization of the rehydratable alumina particles is suppressed by the presence of lithium alumina silicate, and that the specific surface area decreases little despite the progress of sintering. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. In the present invention, thermal shock resistance, compressive strength, and specific surface area were measured by the following methods. Thermal shock resistance: A sample was taken out of a furnace maintained at a high temperature and placed on a brick at room temperature, and the highest temperature at which no cracks occurred was defined as the thermal shock resistance temperature. Compressive strength: using an Instron strength tester 2
The average value of about 10 samples obtained at a strain rate of mm/min was defined as the compressive strength. Specific surface area: Based on BET method. Example 1 70 parts by weight of activated alumina powder containing 30 parts by weight of ρ-alumina with an average particle size of 6 μ obtained by calcining a kibsite-type alumina hydrate was mixed with ρ-alumina during kneading raw material aggregate and in an extrusion molding machine. 2.8 parts by weight of wax was added to prevent the rehydration reaction from occurring (hereinafter referred to as a rehydration inhibitor), and the average particle size was
A mixture of 30 parts by weight of 5μ petalite powder, 5 parts by weight of methyl cellulose as extrusion aids, and 35 parts by weight of water was kneaded for 30 minutes using a screw kneader, and then fed into a screw type extruder, with a wall thickness of 0.25 mm on one side. Approximately 95mm with 1mm square core unit
A honeycomb-shaped catalyst carrier of ψ×10 mm was molded. Next, this carrier was rehydrated in warm water at 90°C for 24 hours, and then heated at 100°C/hour to 900°C.
The temperature was raised at a rate of 30°C/hour up to 1100°C, and then
It was sintered at 1100°C for 2 hours. Table 1 shows the physical properties of the honeycomb catalyst carrier thus obtained. For comparison, the same as Example 1 was used except that the mixing ratio of the activated alumina powder and petalite powder was changed to 98 parts by weight of activated alumina powder, 2 parts by weight of petalite powder, 5 parts by weight of activated alumina powder, and 95 parts by weight of petalite powder. A honeycomb-shaped catalyst carrier was produced in the same manner. Table 1 shows the physical properties of the carrier thus obtained.

[Table] Example 2 3.6 parts by weight of wax as a rehydration inhibitor was added to 90 parts by weight of the same activated alumina powder as in Example 1 to produce β-spodium powder with a center particle size (50% particle size) of 8μ.
A mixture of 10 parts by weight, 6 parts by weight of methyl cellulose and 40 parts by weight of water as extrusion aids was kneaded for 30 minutes using a screw kneader, and then a honeycomb-shaped catalyst carrier was formed in the same manner as in Example 1. This carrier was then rehydrated under the same conditions as in Example 1, and then heated at 900 °C under the same heating conditions as in Example 1.
The temperature was raised to 1050°C at a rate of 30°C/hour, and sintered at the same temperature for 2 hours. The honeycomb-shaped catalyst carrier thus obtained had a bulk density of 1.50 g/cm ³ , a specific surface area of 100 m ² /g, a compressive strength of 200 Kg/cm ² and a thermal shock resistance temperature of 600°C. Example 3 50mmψ/40mmψ×30mm using the same method as Example 1
A tubular catalyst carrier was molded. This carrier was then rehydrated under the same conditions as in Example 1, and then heated at 900 °C under the same temperature conditions as in Example 1.
The temperature was raised to 1150°C at a rate of 30°C/hour, and sintered at the same temperature for 2 hours. The tubular catalyst carrier thus obtained had a bulk density of 1.60 g/cm ³ , a specific surface area of 60 m ² /g, and a pressure resistance.
520Kg/cm ² (in the axial direction of the tube), 50Kg/cm ² (in the direction perpendicular to the tube axis), and a thermal shock resistance temperature of 1100°C. Comparative Example 1 70 parts by weight of calcined alumina powder consisting mainly of γ-alumina with an average particle size of 8 μ obtained by calcining boehmite type alumina hydrate at 600°C was added with an average particle size of 5 μ.
After kneading a mixture of 30 parts by weight of petalite powder, 4 parts by weight of methylcellulose as an extrusion aid, and 25 parts by weight of water using a screw unit for 30 minutes,
The catalyst carrier was fed into a screw type extruder to form the same honeycomb-shaped catalyst carrier as in Example 1. This carrier was then sintered under the same conditions as in Example 1. The honeycomb-shaped catalyst carrier obtained in this way has a bulk density of 1.4 g/cm ³ , a specific surface area of 30 m ² /g, and a pressure resistance.
It had a weight of 80Kg/cm ² and a thermal shock resistance temperature of 280°C. Comparative Example 2 A honeycomb-shaped catalyst carrier formed under the same conditions as in Example 1 was sintered under the same conditions as in Example 1 without performing rehydration treatment. The honeycomb-shaped catalyst carrier thus obtained had a bulk density of 1.43 g/cm ³ , a specific surface area of 35 m ² /g, and a pressure resistance.
It had a weight of 100Kg/cm ² and a thermal shock resistance temperature of 300°C. Comparative Example 3 A honeycomb-shaped catalyst carrier that had been molded and rehydrated under the same conditions as Example 1 was heated under the same conditions as Example 1 and fired at 950 g for 2 hours. The honeycomb-shaped catalyst carrier thus obtained had a bulk density of 1.36 g/cm ³ , a specific surface area of 110 m ² /g, a compressive strength of 50 Kg/cm ² and a thermal shock resistance temperature of 220°C. Comparative Example 4 The honeycomb catalyst of Comparative Example 3 was sintered at 1350°C for 2 hours. The honeycomb-shaped catalyst carrier thus obtained had a bulk density of 1.8 g/cm ³ , a specific surface area of 1 m ² /g or less, and a compressive strength of 300 Kg/cm ² . Example 4 70 parts by weight of the same activated alumina powder and 30 parts by weight of petalite powder as in Example 1 were mixed, 30 parts by weight of water was added, and a spherical catalyst carrier with a diameter of 4 to 6 mm was formed using a dish granulator. Next, this carrier was preliminarily rehydrated at room temperature (20°C) for 24 hours, and then rehydrated in warm water at 90°C for 24 hours. Firing is 100℃/hour up to 900℃, 1100℃
℃ at a heating rate of 50℃/hour and then further to 1100℃
It was sintered for 2 hours. The spherical catalyst carrier thus obtained has a bulk density of
1.55g/cm ³ , specific surface area 75m ² /g, pressure resistance 75Kg
(5 mmψ particle size product). Comparative Example 5 35 parts by weight of water was added to 100 parts by weight of the same activated alumina powder as in Example 1, and a spherical catalyst carrier was formed in the same manner and under the same conditions as in Example 4, followed by rehydration treatment and sintering. The spherical catalyst carrier thus obtained has a bulk density of
1.35g/cm ³ , specific surface area 25m ² /g, pressure resistance 15Kg
(5 mmψ particle size product). Example 5 2.4 parts by weight of wax as a rehydration inhibitor was added to 60 parts by weight of the same activated alumina powder as in Example 1, and 10 parts by weight of β-spodumene powder with an average particle size of 3 μm and 30 parts by weight of α1-alumina with an average particle size of 6 μm were added. parts, and 3.6 parts by weight of methyl cellulose as extrusion aids, and 30 parts by weight of water.
The mixture to which parts by weight were added was kneaded for 30 minutes using a screw kneader, and then a honeycomb-shaped catalyst carrier was formed in the same manner as in Example 1. This carrier was then rehydrated under the same conditions as in Example 1, followed by sintering at 1050°C for 2 hours. The honeycomb-shaped catalyst carrier obtained in this way has a bulk density of 1.75 g/cm ³ , a specific surface area of 80 m ² /g, and a pressure resistance.
It had a weight of 270Kg/cm ² and a thermal shock resistance temperature of 600°C. Example 6 2.8 parts by weight of wax as a rehydration inhibitor was added to 70 parts by weight of the same activated alumina powder as in Example 1, 30 parts by weight of β-eucryptite powder with a center particle size of 3μ, and 5 parts by weight of methyl cellulose as an extrusion aid. After adding 35 parts by weight of water and kneading the mixture for 30 minutes using a screw kneader, a honeycomb-shaped catalyst carrier was formed in the same manner as in Example 1. This carrier was then rehydrated under the same conditions as in Example 1, and then heated at 900 °C under the same temperature conditions as in Example 1.
The temperature was raised to 1100°C at a rate of 30°C/hour, and sintered at the same temperature for 2 hours. The honeycomb-shaped catalyst carrier obtained in this way has a bulk density of 1.50 g/cm ³ , a specific surface area of 70 m ² /g, and a pressure resistance.
It had a weight of 200Kg/cm ² and a thermal shock resistance temperature of 800°C.

Claims (1)

[Claims] 1. Rehydratable alumina 95-10% by weight, general formula
Li ₂ O・Al ₂ O ₃・XSiO ₂ (X represents an integer from 2 to 8)
Molding an aggregate composition consisting of 5 to 90% by weight of the compound represented by the above formula and at least 50% by weight in total of rehydratable alumina and the compound represented by the above general formula, and rewatering the molded material. After processing this, 1000 ~
A method for producing a catalyst carrier characterized by sintering at a temperature of 1300°C.