JPH051056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a thermally stable catalyst carrier composition. Specifically, the present invention improves the heat resistance of conventional activated alumina and stabilized alumina so that they can continue to have a high surface area even when exposed to high temperatures exceeding 1000°C for long periods of time, particularly at 1200°C for 200 hours. The present invention relates to a method for producing a stabilized alumina composition, that is, an alumina-silica composite oxide, which has a specific surface area of at least 20 m ² /g even after the calcination treatment. [Prior art] Activated alumina is a substance with a high surface area and excellent heat resistance. Taking advantage of its properties, it can be used in various catalysts such as automobile exhaust gas purification catalysts, industrial exhaust gas treatment catalysts, and catalytic combustion catalysts. It is used as a carrier, etc. However, activated alumina has the disadvantage that when exposed to high temperatures of around 1000℃ or higher, its crystal structure changes and it eventually becomes α-alumina, resulting in a decrease in specific surface area.To prevent this, the above-mentioned In such fields of application, silica, alkaline earth elements, rare earth elements, and the like are usually added as stabilizers to activated alumina in the form of oxides, hydroxides, or various compounds. In this case, the activated alumina and the above-mentioned stabilizer essentially coexist as a mixture;
At temperatures below 1000℃ or 1100-1400
Although the stabilizing effect can be seen when exposed to high temperatures for a very short period of several hours, even at high temperatures of
When exposed to high temperatures exceeding 1000℃ for a long period of time, for several tens of hours or more, oxides of α-alumina and stabilizers, and even low-surface-area composite oxides of alumina and stabilizers with spinel or perovskite structures, are destroyed. It is known that the specific surface area decreases rapidly. For example, silicon dioxide (SiO ₂ ) is added to activated alumina.
5 to 10% by weight of silica sol is added and immersed,
The product calcined at 1000° C. after drying has a specific surface area of about 90 m ² /g and is stabilized, but it is a mixture of activated alumina and amorphous silica. Further, when this was fired at 1200° C. for 5 hours, although some α-alumina formation was observed, the specific surface area was 28 m ² /g, and it was still quite stable. However, when exposed for an additional 100 hours at 1200°C, it eventually changed to an α-alumina and cristobalite structure.
It becomes SiO ₂ and the specific surface area decreases to 3 to 5 m ² /g. On the other hand, the heat resistance temperature required of the above-mentioned catalysts is increasing year by year, and heat resistance of 1000° C. or higher is becoming required. Particularly in large-capacity boilers and gas turbines, where the application of catalytic combustion methods has been considered in recent years, the catalyst temperature is 1000 to 1200℃, and depending on the conditions, 1300 to 1300℃.
As these catalysts reach temperatures as high as 1500°C, if stabilized alumina manufactured by conventional methods is used as a support for these catalysts, the catalysts undergo a large thermal history and their specific surface area rapidly decreases over time. This has the disadvantage that the catalyst activity decreases as a result. Furthermore, there is a risk that cracks may occur in the catalyst layer and the catalytic active sites may peel off. [Objective of the Invention] The object of the present invention is to overcome the above-mentioned problems in heat resistance of activated alumina or alumina stabilized by conventional methods, and to maintain α-alumina even when exposed to high temperatures exceeding 1000°C for a long time. It is an object of the present invention to provide a method for producing a carrier composition for a catalyst that has little change in crystal structure, has heat resistance that allows it to maintain a high surface area, and as a result has little deterioration in catalytic performance. [Structure of the Invention] In order to achieve the above object, the present invention includes a mixed aqueous solution of alumina hydrate and colloidal silica,
Production of a thermally stable catalyst carrier composition made of a composite oxide of alumina and silica by adding a basic compound to thicken and gel the mixed aqueous solution, drying and calcining the resulting gel. even after firing at 1200℃ for 200 hours.
It is disclosed that the catalyst carrier composition has unprecedented heat resistance, having a specific surface area of 20 m ² /g or more. The present invention will be explained in detail below. The feature of the present invention is that a basic compound is added to a mixed aqueous solution of alumina hydrate and colloidal silica to thicken and gel the alumina hydrate and colloidal silica, and the gelled product is dried and then fired. There is a particular thing. Normally, methods for producing composite oxides include precipitation methods, impregnation methods, mixing methods, coprecipitation methods, etc., and most of the solid industrial catalysts currently in use are composites of each composition using these methods. It is used. However, in the precipitation method, due to the difference in the solubility product of each composition, in the impregnation method, due to the movement of each composition when the slurry obtained by impregnation or immersion is dried and fired, and in the mixing method, due to the solid phase reaction. It is difficult to mix each composition uniformly, and because the particle size of each composition is uneven, it is difficult to uniformly disperse the stabilizer into alumina, and free alumina and stabilizer exist. I can't avoid that. When exposed to high temperatures for a long time, these eventually become oxides or aluminates of α-alumina and the stabilizer, causing a decrease in the specific surface area. In addition, in the co-precipitation method, the difference in the solubility product of the hydroxides of alkaline earth elements and rare earth elements as carriers and aluminum is small, and precipitation occurs almost simultaneously, but metal ions in a soluble state due to the difference in solubility products Precipitation due to adsorption and inclusion does not occur completely and co-precipitation is difficult to occur, so the operation is highly influenced by conditions such as precipitating agent, temperature, and pH, and strict operation is required. When preparing a large amount for industrial use, preparation with a high concentration solution is unlikely to result in coprecipitation and only produces a homogeneous precipitate, so it must be prepared multiple times with a low concentration solution. It is difficult to control the particle size of the product, and operations such as filtration and washing are complicated, making it impractical. On the other hand, the catalyst carrier composition of the present invention is made into a thickened gel by adding a basic compound to a homogeneous mixed aqueous solution of alumina hydrate and colloidal silica, and at that time, silica is uniformly dispersed in aluminum. Therefore, by dry-aging this material, it will have a high surface area even after long-term high-temperature firing. The reason for this is not well understood, but when a basic compound is added to the stable region of alumina hydrate and colloidal silica, a PH change occurs, and the electric double layer that causes repulsion between particles does not function sufficiently. Under these conditions, the particles come together, forming bonds with silica as the crosslinking source, forming a composite with highly dispersed silica as the core and aluminum surrounding it, preventing alumina from becoming pregelatinized. It is expected that this will result in a thermally stable catalyst support composition. Ammonia and ammonia carbonate are suitable basic compounds for thickening and gelling a homogeneous mixed aqueous solution of alumina hydrate and colloidal silica, and these compounds are usually used in the form of an aqueous solution. Furthermore, it is also possible to use aliphatic amines such as trimethylamine. In addition, when adding a basic compound, the basic compound is gradually added while thoroughly stirring the homogeneous mixed aqueous solution to bring the pH to between 7 and 10, preferably PH.
The homogeneous aqueous solution can be made to thicken and become a kelp by adjusting the viscosity between 8 and 9. At this time, if the pH is less than 7, sufficient gelation will not occur, and if the pH is greater than 10, the gelled colloidal silica will dissolve, which is not preferable. When thickening and gelling a mixed aqueous solution of alumina hydrate and colloidal silica using a basic compound, the temperature range is 10 to 150°C, more preferably 20 to 150°C.
It is appropriate to maintain the temperature in the 80℃ range. If the temperature during thickening gelation exceeds 150°C, the gel produced during gelation will dry at the same time, and the drying rate is too fast, causing the silica in the alumina gel to move to the surface layer and cause the silica to dry. Undesirable uneven distribution occurs. Furthermore, at temperatures below 10°C, it is difficult to form a gel in which colloidal silica is uniformly dispersed, and therefore it is necessary to stir and mix for a long time, which is not practical. Further, during or after gelation, it is appropriate to sufficiently knead and stir the mixture while maintaining the temperature in the range of 10 to 150°C for at least 20 minutes, preferably 30 minutes or more. As a result, it is possible to uniformly disperse the silica in a form in which the aluminum is almost completely surrounded by the silica as the core. In drying the solid material after gelation, aging is not necessary and may be carried out immediately after sufficient stirring and kneading. When drying, rapid high-temperature drying is undesirable because the silica moves to the surface layer of the solid material, so the temperature is gradually raised in a dryer with a narrow temperature distribution such as a hot air circulation dryer, and eventually the temperature reaches 150~150℃. It is preferable to dry at 200°C for 10 hours or more. Calcination may be carried out after the dry solid is roughly pulverized to about 500 microns or, if necessary, after pulverized to about 20 to 30 microns. The dried powder is then calcined in the presence of air at a temperature range of 500 to 1100°C, preferably 600 to 1000°C for at least 3 hours to obtain a finished catalyst carrier composition. The heat-resistant catalyst carrier composition obtained as described above contains alumina in a range of 80-99.5% by weight, preferably 88-99.2% by weight, and silica in a range of 0.5-20% by weight, preferably 0.8-99.5% by weight. Preference is given to those having a composition in the range of 12% by weight. Furthermore, oxides of alkaline earth elements, rare earth elements, etc. may be contained in an amount of up to 10% by weight in the finished catalyst carrier composition. Examples include oxides of magnesium, strontium, yttrium, lanthanum, cerium, neodymium, titanium, zircon, chromium, tin, and the like. These elements can be introduced as a catalyst composition by using them together in the form of water-soluble salts when a mixed aqueous solution of alumina hydrate and colloidal silica is thickened and gelled using a basic compound. I can do it. As the alumina raw material, an amorphous alumina hydrate having a boehmite structure or a precipitated boehmite structure that is partially soluble in inorganic or organic acids is suitable, and alumina hydrates such as gibbsite or diaspore are not preferred. When silica is less than 0.5% by weight, silica has almost no effect as a stabilizer, and
When the amount exceeds 20% by weight, the effect as a stabilizer is recognized, but when fired for a long time, mullite, which is a composite oxide with alumina, begins to be produced, and its effect decreases. As colloidal silica, any type of hydrogen ion concentration such as acidic, neutral, or basic can be used, but acidic silica is particularly preferable, and the particle size may be 50 millimicrons or less, especially 10 to 10 mm. 20
Millimicron ones are preferred. If sodium present as a silica sol stabilizer is contained in an amount of 0.1% or more as sodium oxide, the effect of silica as an alumina stabilizer will be weakened, so sodium oxide is preferably 0.05% or less. Next, the present invention will be specifically explained using examples. However, the composition, manufacturing method, etc. are not limited to these. Example 1 662 g of boehmite (manufactured by Condeia, trade name: Dispural) with a specific surface area of 150 m ² /g
was added to 1,830 ml of water containing 19.6 ml of 60% nitric acid, and stirred for 1 hour using a homomixer to partially dissolve the mixture to obtain an alumina sol. Next, this sol was transferred to a kneader heated to 80°C, and 126 g of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name: Snowtex) was added while stirring, and 2N ammonia water was further produced. was gradually added dropwise until the pH of the solution reached 8. After adding the ammonia water, continue kneading and stirring with the kneader for 20 minutes, then put the gelled solid into a hot air circulation dryer.
It was dried at 150°C for 12 hours. The dry solids are then ground in an atomizer for 10
After turning it into a powder of ~20 microns, it was calcined at 800℃ for 5 hours to produce 4.8% by weight of silica and 4.8% by weight of alumina.
A composite oxide containing 95.2% by weight was obtained. Example 2 Alumina sol having a crystalline form with a precipitated boehmite structure and a specific surface area of 245 m ² /g (manufactured by Nissan Chemical Industries, Ltd.)
2500g and colloidal silica (manufactured by Catalysts Chemical Industry Co., Ltd.)
154.8g was put into a kneader heated to 60℃, and while stirring, the pH of the kneaded product was adjusted by adding 1N ammonium carbonate aqueous solution.
It was gradually added dropwise so that the amount of water was 9. After raising the temperature to 80°C and kneading and stirring for 20 minutes, the mixture was placed in a dryer kept at 120°C and dried for 15 hours. Next, after coarsely pulverizing the dry solid, it was heated at 800℃ for 5 minutes.
After calcining for a period of time, a composite oxide containing 8.5% by weight of silica and 91.5% by weight of alumina was obtained. Comparative Example 1 Colloidal silica (manufactured by Nissan Chemical Industries ^, Ltd., trade name:
A mixed solution of 126g (Snowtex) and 470g of water was immersed in the mixture and evaporated to dryness while thoroughly mixing and stirring. Then, pulverization in the same manner as in Example 1,
After firing, a composite oxide containing 4.8% by weight of silica and 95.2% by weight of alumina was obtained. Example 3 The composite oxides obtained in Examples 1 and 2 and Comparative Example 1 were fired at 1200°C for 20 hours, 50 hours, 100 hours, 200 hours, and 300 hours in an air atmosphere, respectively, and the surface area was Measurement was performed using a BET type specific surface meter using nitrogen gas as the adsorbed gas. Table 1 shows the surface area measurement results. From Table 1, the composite oxides obtained in Examples 1 and 2 have a specific surface area of 20 m ² /g or more even after calcination at 1200°C for 200 hours, and are thermally stable catalyst carrier compositions. I understand that. On the other hand, the composite oxide produced by the immersion method in Comparative Example 1 was 20
It was stabilized up to the time of firing, but after 50 hours of firing the surface area changed significantly over time and the stabilizing effect disappeared. 【table】

Claims (1)

[Claims] 1. A basic compound is added to a mixed aqueous solution of alumina hydrate and colloidal silica to thicken the mixed aqueous solution into a gel, and the resulting gel is dried and fired. A method for producing a heat-resistant catalyst carrier composition. 2. The heat-resistant catalyst carrier composition is 80% as alumina.
~99.5wt% range and 0.5~20 as silica
A method according to claim 1, characterized in that it has a composition in the range of % by weight. 3. Add the basic compound to the mixed aqueous solution.
The method according to claim 1 or 2, characterized in that the pH is adjusted between 7 and 10. 4. The method according to claim 1, 2 or 3, wherein the basic compound is ammonia, ammonium carbonate or aliphatic amines. 5 Claims 1, 2, 3, or 4, characterized in that the alumina hydrate is amorphous, has a boehmite structure, or a solidified boehmite structure, and is partially soluble in acids. the method of. 6 Claim 1, characterized in that the thickening and gelling of the mixed aqueous solution of alumina hydrate and colloidal silica is carried out at a temperature range of 10 to 150°C;
2. The method described in 2, 3, 4 or 5.