CN102531015A - Method for preparing porous aluminum oxide superfine powder - Google Patents

Abstract

The invention provides a method for preparing porous aluminum oxide superfine powder by an improved hydrothermal method. In the present invention, aluminum inorganic salt is used as raw material, urea is used as co-precipitant, precursor is generated under hydrothermal conditions, and porous alumina ultrafine powder is prepared by calcining, which has high purity, narrow particle size distribution, and high porosity. are potentially suitable catalyst supports.

Description

A kind of preparation method of porous aluminum oxide superfine powder

technical field

The invention belongs to the field of fine chemicals, in particular to a method for preparing porous alumina superfine powder.

Background technique

Alumina ultrafine powder, due to its excellent characteristics such as high strength, high hardness, corrosion resistance, high temperature resistance, and large surface area, is used in many high-tech fields such as chemical catalysts, rare earth three-color phosphors, laser materials, functional ceramics, and artificial bones. has been widely used. In the field of chemical catalysts, porous alumina particles are often used as fluidized bed catalyst carriers for various chemical synthesis steps, such as hydrogenation, dehydrogenation, dehydration, etc. The particles are required to be nearly spherical and have sufficient porosity to hold the catalytic metal. . In the field of functional ceramics, it has high hardness, wear resistance and high mechanical strength, and can be used as integrated circuit substrates, friction plates and tool materials. High activity (so as not to affect the microstructure and mechanical properties of the sintered porcelain body). To give full play to the characteristics of alumina materials, the preparation of high-quality alumina particles is the key link, especially the ultrafine powder of high-purity alumina with narrow particle size distribution, low density, high porosity and submicron level.

The methods for preparing alumina powder include gas phase method, solid phase method and liquid phase method. The reaction conditions of the gas phase method are easy to control, the product is easy to be refined, and ultrafine powder with little or no agglomeration, small particle size and narrow distribution can be obtained, but the yield is low, the equipment operation is complicated, and the cost is high. The solid-phase method has complicated equipment, and the powder is not easy to collect, so it is not suitable for mass production. The most widely used is the liquid phase method, including aluminum salt thermal decomposition method, sol-gel method and precipitation method. The thermal decomposition of ammonium aluminum sulfate has the advantages of low raw material cost and simple process, but it produces toxic SO ₃ gas during the decomposition process, which has potential environmental pollution problems. The thermal decomposition method of ammonium aluminum carbonate has the advantages of low raw material cost and industrial production, but the synthesis of raw material ammonium aluminum carbonate requires strict conditions, requires a very slow feeding speed, and the local concentration is easily uneven, which affects production efficiency and product performance. The raw material of the sol-gel method is expensive metal alkoxide, the reaction is not easy to control, and it is not suitable for industrial production. The intermediate product of the precipitation method is often a colloidal aluminum hydroxide precipitate, which contains a large amount of water and hydroxyl groups. During the subsequent drying and calcination process, it is easy to produce hard agglomerates due to the capillary force between particles and the condensation of hydroxyl groups, which reduces the sintering activity.

In recent years, domestic and foreign scientific and technological workers have carried out extensive research in the field of preparing ultrafine alumina powder, especially the liquid phase method. The thermal decomposition method based on aluminum salt is as follows: Zhejiang Zhongming Science and Technology Co., Ltd. Chen Shuigao et al. spray the mixed solution of aluminum alcohol and organic solvent under a certain pressure into the combustion furnace for combustion by adding oxygen-enriched air atomization into the combustion furnace. The mixed gas containing alumina is cooled and collected by a high-voltage electrostatic precipitator to produce nano-scale high-purity alumina, which has uniform particle size and can be produced in one time, which can realize automatic continuous production (Chinese patent 02138014.7). Hong Huizhen of LG Chemical Co., Ltd. prepared α-alkanol with uniform particle shape and particle size distribution, and the content of alkali metals such as Na and K below 20ppm by esterification of aluminum alkoxide in glycol solution and thermal reaction of glycerol. -Alumina nanopowder (Chinese patent 03800065.2). The improved sol-gel method includes: Liu Xilai of China Petroleum & Chemical Co., Ltd. uses a weakly acidic peptizer, adds alumina monohydrate in stages, and at the same time adds alcohol compounds to increase the pore volume of the alumina carrier. After molding and drying , Roasted to prepare alumina carrier suitable for heavy and residual oil hydrogenation catalysts (Chinese patent 01114159.X). The preparation method of Yang Qinghe of China Petroleum & Chemical Co., Ltd. includes extruding boehmite, acid, water and extrusion aids, rapid drying, and roasting in a water vapor atmosphere at 600-800 ° C to obtain a concentrated pore distribution. , especially suitable for use as an alumina carrier for hydrodemetallization catalysts (Chinese patent 01134279.X). Based on the precipitation method, such as: Gao Lian, Shanghai Institute of Ceramics, Chinese Academy of Sciences, etc., use aluminum-containing inorganic salts as the main raw material, ammonium bicarbonate as the precipitating agent, and the precipitate is washed with deionized water, dried, and calcined to transform into α-Al2O3. Submicron and nanoscale alumina powders with a grain size of less than 400nm have less hard agglomeration and high firing activity, and are suitable for the preparation of high-grade alumina ceramic materials (Chinese patent 02111001.8). Zhang Liangmiao of Shanghai University, etc. used the ready-made and cheap raw materials of sodium aluminate and sodium bicarbonate solution to directly react with the alumina factory, and obtained a transparent sol for preparing nano-alumina materials through filtration, dispersion, washing, and acid addition. The main materials can be Recycling, low cost, suitable for mass production (Chinese patent 03129084.1). Li Wangxing of Aluminum Corporation of China, etc. used aluminum ammonium sulfate and ammonium bicarbonate as raw materials to react in a stirred reactor to form nano-structured spherical aluminum ammonium carbonate AACH, and obtained nano-structured spherical high-purity alumina after filtration, washing and roasting. It has the advantages of high product purity, low requirements on process conditions, environmental friendliness and pollution-free, and low cost (Chinese patent 200410100972.4). Yan Hengwei of Aluminum Corporation of China Co., Ltd. sprayed the aluminum salt solution into the ammonium bicarbonate solution in the stirring state after atomization by spraying, and added a surfactant to react, then precipitated, aged, filtered, washed, and carried out microwave treatment. Drying and calcining to obtain nano-alumina powder with less agglomeration and uniform particle size (Chinese patent 200710179656.4). Based on the weak force: Guo Fen of Beijing University of Chemical Technology and others used glucose or sucrose as raw materials, hydrothermally synthesized colloidal carbon spheres as a template, added them to the inorganic aluminum solution, separated, dried, and calcined, and finally obtained uniform size and controllable wall thickness 1. Nano-alumina hollow spheres with a porous structure on the surface. This method has simple process, safe operation and low cost (Chinese patent 200710119314.3). U.S. Norton Company Thomas etc. prepare nearly spherical particles composed of at least 98.5% alumina through the water slurry formed by ultrafine alumina, organic binder and aqueous phase containing dispersant, spray drying, heat treatment, and pulverization, which has enough porosity to maintain the conventional catalytic amount of catalytic metals, especially suitable for use as a carrier for fluidized bed catalysts at high temperatures (Chinese patent 90107723.2). These preparation methods are still insufficient compared with the application, especially the specific application requirements, such as high-quality alumina particles with narrow particle size distribution and high porosity used as catalyst supports.

The hydrothermal method has high reactivity, good dispersion and high crystallinity of the synthesized particles, and is an ideal method for preparing submicron/nanomaterials. The co-precipitation method is that the introduced precipitant releases the precipitated ions under certain reaction conditions to complete the co-precipitation process. It overcomes the shortcomings of the direct precipitation method such as uneven mixing of reactants, and can obtain powder materials with small particles and narrow particle size distribution. Therefore, it is of great practical value to develop a preparation method of porous alumina ultrafine powder based on co-precipitation hydrothermal reaction and low cost.

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Contents of the invention

The purpose of the present invention is to provide a method for preparing porous aluminum oxide superfine powder by improving the hydrothermal method. The present invention adopts following technical scheme:

1. A preparation method of porous alumina ultrafine powder, using aluminum inorganic salt as raw material, urea as co-precipitant, generating precursor under hydrothermal conditions, and calcining to prepare porous alumina ultrafine powder.

2. According to the preparation method described in item 1, it is characterized in that the aluminum inorganic salt is selected from commercially available analytically pure inorganic salts, such as aluminum nitrate hydrate Al(NO ₃ ) ₃ ×9H ₂ O, aluminum sulfate hydrate Al ₂ (SO ₄ ) ₃ × 18H ₂ O.

3. According to the preparation method described in Item 1, it is characterized in that the co-precipitant is commercially available analytically pure urea, and the molar ratio to aluminum ions is about 5:1-2:1, which decomposes to generate ammonia under heating conditions, Uniform precipitation of aluminum ions to generate precursors.

4. According to the preparation method described in item 1, it is characterized in that the temperature of the hydrothermal reaction is controlled within 120-180 degrees Celsius, and the reaction time is controlled within 1-20 hours.

5. According to the preparation method described in item 1, it is characterized in that the temperature of calcination is controlled within 600-1000 degrees Celsius, and the reaction time is controlled within 1-20 hours.

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Compared with the prior art, the present invention has the following advantages: water phase reaction, low cost, and the prepared porous alumina superfine powder has high purity, narrow particle size distribution and high porosity, and is a potentially suitable catalyst carrier.

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Description of drawings

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Fig. 1 Transmission electron microscope TEM picture of porous alumina ultrafine powder; Fig. 2 Powder X-ray diffraction pattern of porous alumina ultrafine powder.

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Detailed ways

Example 1: Dissolve 0.2 g urea in 6.0 ml deionized water, then add 8.0 ml Al(NO ₃ ) ₃ ×9H ₂ O aqueous solution (0.2 M), stir evenly, and transfer the solution into a 40 ml stainless steel pressure-resistant reactor. After reacting at 150°C for 20 hours, the resulting white precipitate was centrifuged, washed three times with deionized water and absolute ethanol, dried in vacuum, and calcined at 800°C for 15 hours to obtain a white powder. Figure 1 is its transmission electron microscope image, which shows that it is porous ultrafine particles; Figure 2 is its powder X-ray diffraction image, which shows that it is high-purity g-alumina.

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Example 2: Dissolve 0.2 g urea in 6.0 ml deionized water, then add 8.0 ml Al ₂ (SO ₄ ) ₃ ×18H ₂ O aqueous solution (0.2 M), stir evenly, and transfer the solution into a 40 ml stainless steel pressure-resistant reaction kettle After reacting at 150°C for 20 hours, the obtained white precipitate was separated by centrifugation, washed three times with deionized water and absolute ethanol, dried in vacuum, and calcined at 800°C for 15 hours to obtain a white powder. Through transmission electron microscopy and powder X-ray diffraction analysis, it is similar to porous alumina ultrafine powder.

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Example 3: Dissolve 0.3 g urea in 6.0 ml deionized water, then add 8.0 ml Al ₂ (SO ₄ ) ₃ ×18H ₂ O aqueous solution (0.2 M), stir evenly, and transfer the solution into a 40 ml stainless steel pressure-resistant reaction kettle , after reacting at 150°C for 10 hours, the resulting white precipitate was centrifuged, washed three times with deionized water and absolute ethanol, dried in vacuum, and calcined at 800°C for 10 hours to obtain a white powder. Through transmission electron microscopy and powder X-ray diffraction analysis, it is similar to porous alumina ultrafine powder.

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Example 4: Dissolve 0.4 g of urea in 6.0 ml of deionized water, then add 8.0 ml of Al(NO ₃ ) ₃ ×9H ₂ O aqueous solution (0.2 M), stir evenly, and transfer the solution into a 40 ml stainless steel pressure-resistant reactor. After reacting at 150°C for 10 hours, the resulting white precipitate was centrifuged, washed three times with deionized water and absolute ethanol, dried in vacuum, and calcined at 800°C for 10 hours to obtain a white powder. Through transmission electron microscopy and powder X-ray diffraction analysis, it is similar to porous alumina ultrafine powder.

Claims (5)

1. the preparation method of a porous alumina superfine powder is a raw material with the al inorganic salt, is coprecipitator with urea, under hydrothermal condition, generates presoma, makes the porous alumina superfine powder through calcining.

2. preparation method according to claim 1 is characterized in that, al inorganic salt is selected commercially available analytical pure inorganic salt for use, like nitric hydrate aluminium Al (NO ₃) ₃* 9H ₂O, hydrazine aluminum sulfate Al ₂(SO ₄) ₃* 18H ₂O.

3. preparation method according to claim 1 is characterized in that, coprecipitator is commercially available analytical pure urea, is about 5:1-2:1 with aluminum ions mol ratio, and it decomposes generation ammonia under heating condition, and the precipitation from homogeneous solution aluminum ion generates presoma.

4. preparation method according to claim 1 is characterized in that, the temperature of hydro-thermal reaction is controlled in 120-180 degree centigrade, and the reaction times was controlled in 1-20 hour.

5. preparation method according to claim 1 is characterized in that, the incinerating temperature is controlled in 600-1000 degree centigrade, and the reaction times was controlled in 1-20 hour.

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