Spherical alumina carrier and method for producing the same

Abstract

The application aims to provide a spherical alumina carrier and a preparation method thereof, and belongs to the technical field of material synthesis. 2 The alumina carrier prepared by the application has a surface covered with hexagonal plate-shaped alumina particles, the hexagonal plate-shaped alumina particles grow in a directional manner on the surface of the alumina carrier and in the micrometer spherical pores, the size of the hexagonal plate-shaped alumina particles is 0.5-1 micrometers, the plate-shaped particles are interwoven to form 100-600 nm channels, the specific surface area of the spherical alumina carrier is 160-290 m 2 / g, and the pore volume is 0.8-1.0 mL / g. The alumina carrier prepared by the application has an open surface channel, a body phase containing through macroporous channels, a uniform carrier morphology, high mechanical strength, and is easy to be filled into a reactor bed, and is suitable for preparing a catalyst for a heterogeneous catalytic reaction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material synthesis, and particularly relates to a spherical alumina carrier and a preparation method thereof. BACKGROUND

[0002] As a traditional catalyst carrier material, alumina has the characteristics of mature technology, adjustable pore structure, low use cost and easy processing into a shape, and is widely used in the preparation of various catalysts. According to the requirements of different reactions on pore structure and surface acidity, various alumina production processes and products are formed, such as titanium-containing, zirconium-containing and other composite alumina products for improving the action of alumina and active metals, fluorine-containing, chlorine-containing and other alumina products for improving the surface acidity of alumina carrier, and high stack ratio, low stack ratio, high specific surface area, high purity and other alumina products. The pore structure of alumina is derived from the stacking gap between particles or granules, but the pore diameter of alumina synthesized by conventional methods is generally less than 15 nm, which cannot meet the needs of heavy residue oil hydroprocessing, therefore, researchers have carried out a large amount of research on the synthesis method of large-pore structure alumina.

[0003] CN109722280A discloses a carrier for hydroprocessing, a catalyst and a preparation method and application thereof. The carrier in the method is an alumina-based carrier, which comprises a main body alumina and rod-shaped alumina, and at least part of the rod-shaped alumina is distributed on the outer surface of the main body alumina and in micron-level pores with a pore diameter of 3-10 μm. The preparation method of the carrier is as follows: first, a carrier intermediate is prepared, then the carrier intermediate is immersed in an ammonium bicarbonate solution, then it is sealed and heat treated, and after heat treatment, the material is dried and calcined to prepare a hydroprocessing catalyst carrier. The method adjusts the pore structure of the carrier by directional growth of rod-shaped alumina in the carrier, but the firmness of the rod-shaped particles on the surface of the alumina prepared by the method needs to be further improved.

[0004] CN107913691A discloses an alumina carrier containing large pores and a preparation method thereof. The preparation method of the alumina carrier is as follows: first, pseudo-boehmite powder and sesbania powder are added to a kneader and mixed uniformly, then a butadiene-styrene rubber emulsion with a particle size of 10-500 nm is prepared, and an organic acid or an inorganic acid is added thereto; then the acid solution containing the butadiene-styrene rubber emulsion is added to the pseudo-boehmite powder and the sesbania powder and kneaded uniformly, and after extrusion, molding, drying and calcination, an alumina carrier containing large pores is obtained. The alumina carrier prepared by the method has a large number of 60-400 nm pores, which affects the mechanical strength of the carrier.

[0005] CN104646005A discloses a poor quality heavy oil hydrodemetallization catalyst and a preparation method thereof. The catalyst uses alumina as a carrier and group VIII and group 6B elements, particularly Ni-Mo, as active components. The preparation method of the catalyst is to treat the carrier particles after molding and calcination with an acid solution with continuously increasing concentration. The opening of the surface pores of the alumina carrier prepared by this method needs to be improved. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a spherical alumina carrier and a preparation method thereof. The alumina carrier has open surface pores, contains through macropores in the bulk phase, has uniform morphology, high mechanical strength, and is easy to pack into a reactor bed, and is suitable for preparing catalysts for heterogeneous catalytic reactions.

[0007] The present application adopts the following technical solutions:

[0008] A spherical alumina carrier, wherein the outer surface of the alumina carrier is covered with hexagonal flake-shaped alumina particles, the hexagonal flake-shaped alumina particles grow directionally on the surface of the alumina carrier and in the micrometer spherical pores, the size of the hexagonal flake-shaped alumina particles is 0.5-1 μm, the flake-shaped particles interweave to form 100-600 nm pores, and the specific surface area of the spherical alumina carrier is 160-290 m 2 / g, and the pore volume is 0.8-1.0 mL / g.

[0009] Further, the coverage of the hexagonal flake-shaped alumina particles on the outer surface of the alumina carrier is 90%-100%, and the coverage refers to the percentage of the surface area occupied by the hexagonal flake-shaped alumina particles on the outer surface of the alumina carrier to the outer surface area of the alumina carrier.

[0010] Further, the filling degree of the hexagonal flake-shaped alumina particles in the micrometer spherical pores in the bulk phase is 50%-90%, and the filling degree refers to the percentage of the volume of the hexagonal flake-shaped alumina particles filled in the micrometer spherical pores in the bulk phase to the volume of the micrometer spherical pores.

[0011] A preparation method of a spherical alumina carrier is as follows:

[0012] Firstly, carbon particles and aluminum sol are uniformly mixed, and drop ball molding is performed, and the molded product is dried and calcined to obtain an alumina carrier containing spherical pores;

[0013] Secondly, the alumina carrier is placed in an organic ammonium solution for one-time and two-time hydrothermal treatment, and the treated material is dried and calcined to obtain a final alumina carrier.

[0014] Further, the particle size of the carbon particles in the first step is preferably 1-5 μm, and more preferably spherical carbon particles with a particle size of 1-5 μm; the mass ratio of the carbon particles to the aluminum sol is 0.1%-0.5%.

[0015] Further, the preparation method of the aluminum sol in the first step is known in the art, which generally comprises uniformly mixing pseudo-boehmite with a certain volume of distilled water, and then adding a certain amount of acid solution to acidify under stirring to obtain the aluminum sol. The pseudo-boehmite preferably has a pore diameter greater than 12.5 nm, and more preferably is prepared by an aluminum sulfate-sodium metaaluminate method. The acid solution is one or a mixture of several of nitric acid, acetic acid, formic acid and oxalic acid, and is preferably nitric acid solution. The solid content of the aluminum sol is 15%-35%.

[0016] Further, the drop ball forming technique in the first step is known in the art, which is generally completed in an oil-ammonia column device. The oil phase of the oil-ammonia column device is one or a mixture of several of ethyl ether, toluene, machine oil, petroleum ether and mineral oil, and the water phase is an ammonia water solution. The height of the oil phase is 10-30 cm, and the height of the water phase is 5-35 cm.

[0017] Further, the drying temperature in the first step is 120-180 ℃, and the drying time is 1-8 hours; the calcination temperature is 450-600 ℃, and the calcination time is 4-8 hours, and the calcination is performed in an oxygen atmosphere.

[0018] Further, the organic ammonium solution in the second step comprises one of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide, and is preferably tetraethylammonium hydroxide.

[0019] Further, the first hydrothermal treatment in the second step is a sealed hydrothermal treatment in the organic ammonium solution, and the sealed container is preferably an autoclave. The mass concentration of the organic ammonium solution is 0.8%-2.0%, and the solution amount is enough to completely immerse the solid material. The first hydrothermal treatment temperature is 80-120 ℃, and the treatment time is 1-4 hours.

[0020] Further, the second hydrothermal treatment in the second step is a sealed hydrothermal treatment in the organic ammonium solution, and the sealed container is preferably an autoclave. The type of the organic ammonium solution can be the same as or different from that in the first hydrothermal treatment, and is preferably the same. The mass concentration of the organic ammonium solution is 3.5%-12.5%, and the solution amount is enough to completely immerse the solid material. The second hydrothermal treatment temperature is 140-180 ℃, and the treatment time is 4-10 hours.

[0021] Further, the drying temperature in the second step is 100-160 ℃, and the drying time is 2-10 hours; the calcination temperature is 450-650 ℃, and the calcination time is 4-10 hours.

[0022] The beneficial effects of the present application are as follows:

[0023] 1.The present application adds carbon particles to an aluminum sol, and after calcination of the carrier, the carbon particles are removed by oxidation, forming micrometer spherical pores in the carrier bulk phase. When the alumina carrier containing micrometer spherical pores is immersed in an organic ammonium solution twice and subjected to a sealed hydrothermal treatment, the alumina grains undergo rehydration and secondary growth under the action of the organic ammonium solution, sealing, and hydrothermal treatment, and grow directionally into hexagonal plate-like pseudoboehmite on the surface of the alumina carrier and in the micrometer spherical pores, and the pseudoboehmite is converted into hexagonal plate-like alumina after calcination. The hexagonal plate-like alumina is interwoven to form 100-600μm channels on the surface of the carrier and in the micrometer spherical pores. The macroporous channels on the surface of the carrier facilitate the diffusion of macromolecular reactants into the interior of the carrier, and the macroporous channels in the micrometer spherical pores provide a reaction site for macromolecular reactants.

[0024] 2.The twice hydrothermal treatment makes the size of the hexagonal plate-like alumina particles more uniform, and the surface coverage and micrometer spherical pore filling degree are higher. The micrometer spherical pores are highly filled with hexagonal plate-like alumina particles, and the plate-like particles support each other, providing macroporous channels while making the carrier have high strength.

[0025] 3.During the preparation of the carrier, the content of 100-600μm channels in the carrier can be adjusted by adjusting the amount of carbon particles added, so that alumina carriers with different channel structures can be flexibly prepared according to the needs of different reactions. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a scanning electron microscope cross-sectional view of the micrometer spherical pore-containing alumina carrier prepared in Example 1.

[0027] Figure 2 is a scanning electron microscope view of the outer surface of the alumina carrier A1 prepared in Example 1.

[0028] Figure 3 is a scanning electron microscope cross-sectional view of the alumina carrier A1 prepared in Example 1. DETAILED DESCRIPTION

[0029] The technical solutions and technical effects of the present application will be further illustrated below in conjunction with examples, but are not limited to the following examples.

[0030] The microstructure of the sample is characterized by a scanning electron microscope, and the specific operation is as follows: acceleration voltage 8KV, acceleration current 10µA, working distance 8mm.

[0031] Preparation of carbon particles:

[0032] The preparation method of the carbon particles used in the method of the present application is described in the reference: Preparation of Starch-based Porous Carbon Materials and Their Methylene Blue Adsorption Performance [J]. Journal of Dalian University of Technology, 2020, 39(6):434-438. The prepared carbon particles have a spherical particle morphology, and the particle size is 1-5μm.

[0033] Example 1

[0034] (1) Take 150 grams of pseudo-boehmite (sulfate aluminum-sodium aluminate method preparation, can be 13 nm in pore size), add 400 grams of distilled water, stir until uniform, and add 23 ml of concentrated nitric acid to acidify into a sol; take 200 grams of the above aluminum sol, add 0.7 grams of carbon particles prepared in the above method, then stir the mixture until uniform; drop the mixed sol into an oil ammonia column device to form a ball, age the formed material for 3 hours, then dry at 140°C for 6 hours, and calcine under oxygen atmosphere at 500°C for 6 hours to obtain a micrometer spherical pore alumina carrier, the cross-sectional scanning electron microscope image of the carrier is shown in Figure 1 .

[0035] (2) Take an appropriate amount of the alumina carrier prepared in step (1) and add it to a high-pressure kettle polytetrafluoroethylene lining, add a tetraethylammonium hydroxide solution with a concentration of 1.2 wt% to completely immerse the alumina carrier, seal the high-pressure kettle, and then perform a first hydrothermal treatment, the first hydrothermal treatment temperature is 100°C, and the treatment time is 2 hours. After the treatment, the material is separated by liquid-solid separation, a tetraethylammonium hydroxide solution with a concentration of 9.5 wt% is added again, the high-pressure kettle is sealed, and then a second hydrothermal treatment is performed, the second hydrothermal treatment temperature is 155°C, and the treatment time is 7 hours. After the treatment, the material is dried at 140°C for 5 hours and calcined at 600°C for 6 hours to obtain the alumina carrier A1 of the present application, the properties of the carrier are shown in Table 1, the outer surface scanning electron microscope image is shown in Figure 2 , and the cross-sectional scanning electron microscope image is shown in Figure 3 .

[0036] Example 2

[0037] The same as Example 1, except that the amount of carbon particles added in step (1) is 0.5 grams. In step (2), the tetraethylammonium hydroxide is replaced with tetrapropylammonium hydroxide, the solution concentration is 1.5 wt%, the hydrothermal treatment temperature is 90°C, and the treatment time is 2.5 hours. In the second hydrothermal treatment, the tetraethylammonium hydroxide is replaced with tetrapropylammonium hydroxide, the solution concentration is 7.5 wt%, the hydrothermal treatment temperature is 165°C, and the treatment time is 5.5 hours, to obtain the alumina carrier A2 of the present application, the properties of the carrier are shown in Table 1.

[0038] Example 3

[0039] The same as Example 1, except that the amount of carbon particles added in step (1) is 0.9 grams. In step (2), the tetraethylammonium hydroxide solution concentration is 0.9 wt%, the hydrothermal treatment temperature is 80°C, and the treatment time is 3.5 hours. In the second hydrothermal treatment, the tetraethylammonium hydroxide solution concentration is 11.5 wt%, the hydrothermal treatment temperature is 175°C, and the treatment time is 4 hours, to obtain the alumina carrier A3 of the present application, the properties of the carrier are shown in Table 1.

[0040] Example 4

[0041] The same as example 1, except that the amount of carbon particles added in step (1) is 0.3 g. In the first hydrothermal treatment of step (2), the concentration of the tetraethylammonium hydroxide solution is 1.8 wt%, the hydrothermal treatment temperature is 110°C, and the treatment time is 1.5 hours. In the second hydrothermal treatment, the concentration of the tetraethylammonium hydroxide solution is 4.5 wt%, the hydrothermal treatment temperature is 145°C, and the treatment time is 9 hours. An alumina support A4 according to the present application is prepared, and the properties of the support are shown in Table 1.

[0042] Comparative Example 1

[0043] The same as example 1, except that the tetraethylammonium hydroxide in step (2) is replaced by ammonia water of the same concentration. A comparative alumina support A5 is prepared, and the properties of the support are shown in Table 1.

[0044] Comparative Example 2

[0045] The same as example 1, except that the tetraethylammonium hydroxide in step (2) is replaced by sodium hydroxide of the same concentration. A comparative alumina support A6 is prepared, and the properties of the support are shown in Table 1.

[0046] Comparative Example 3

[0047] The same as example 1, except that the hydrothermal treatment is not performed in a sealed autoclave, but is performed under atmospheric pressure in a condenser reflux device. A comparative alumina support A7 is prepared, and the properties of the support are shown in Table 1.

[0048] Table 1 Properties of alumina supports

[0049]

[0050] From Table 1, Figure 2 and Figure 3 it can be seen that the surface of the alumina support prepared by the method of the present application is covered and filled with hexagonal plate-like alumina particles, and the surface coverage and pore filling degree are high. The hexagonal plate-like alumina particles interweave on the surface of the support and in the pores to form a large number of 100-600 μm macropore channels.

Claims

1. A spherical alumina carrier, characterized in that: The outer surface of the alumina carrier is covered with hexagonal flake-shaped alumina particles, which are directionally grown on the surface of the alumina carrier and in the micron-sized spherical pores. The size of the hexagonal flake-shaped alumina particles is 0.5-1 μm, and the flake-shaped particles interweave to form channels of 100-600 nm. The specific surface area of ​​the spherical alumina carrier is 160-290 m². 2 / g, pore volume is 0.8-1.0mL / g; The coverage of the hexagonal alumina particles on the outer surface of the alumina carrier is 90%-100%, where coverage refers to the percentage of the surface area occupied by the hexagonal alumina particles on the outer surface of the alumina carrier. The filling degree of the hexagonal alumina particles in the bulk micron-sized spherical pores is 50%-90%, where the filling degree refers to the percentage of the volume filled by the hexagonal alumina particles in the bulk micron-sized spherical pores relative to the volume of the micron-sized spherical pores. The method for preparing the spherical alumina support includes the following steps: The first step involves uniformly mixing carbon particles with aluminum sol, forming drop balls, and then drying and calcining the formed material to obtain an alumina carrier with spherical pores. The calcination temperature is 450-600℃, and the calcination time is 4-8 hours. The calcination is carried out in an oxygen atmosphere. The second step involves placing the alumina carrier in an organic ammonium solution for one and two hydrothermal treatments. After treatment, the material is dried and calcined to obtain the final alumina carrier. The organic ammonium solution includes one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

2. The spherical alumina carrier according to claim 1, characterized in that: The carbon particles mentioned in the first step have a particle size of 1-5 μm and are spherical carbon particles; the mass ratio of carbon particles to aluminum sol is 0.1%-0.5%.

3. The spherical alumina carrier according to claim 1, characterized in that: The preparation method of the aluminum sol in the first step is as follows: Boehmite is mixed evenly with distilled water, and then acidified by adding an acid solution under stirring. The boehmite has a pore size greater than 12.5 nm. The acid solution includes one or more of nitric acid, acetic acid, formic acid, and oxalic acid solutions. The solid content of the aluminum sol is 15%-35%.

4. The spherical alumina carrier according to claim 1, characterized in that: The droplet forming described in the first step is completed in an oil-ammonia column apparatus. The oil phase of the oil-ammonia column apparatus includes one or more of diethyl ether, toluene, machine oil, and petroleum ether, and the aqueous phase is an ammonia solution. The height of the oil phase is 10-30 cm, and the height of the aqueous phase is 5-35 cm.

5. A spherical alumina carrier according to claim 1, characterized in that: The drying temperature in the first step is 120-180℃, and the drying time is 1-8 hours.

6. The spherical alumina carrier according to claim 1, characterized in that: The primary hydrothermal treatment is a sealed hydrothermal treatment carried out in an organic ammonium solution with a mass concentration of 0.8%-2.0%. The amount of solution used is sufficient to completely submerge the solid material. The primary hydrothermal treatment temperature is 80-120℃, and the treatment time is 1-4 hours.

7. A spherical alumina carrier according to claim 1, characterized in that: The secondary hydrothermal treatment in the second step is a sealed hydrothermal treatment in an organic ammonium solution, the type of which may be the same as or different from that in the primary hydrothermal treatment; the mass concentration of the organic ammonium solution in the secondary hydrothermal treatment is 3.5%-12.5%, the solution volume is sufficient to completely immerse the solid material, the secondary hydrothermal treatment temperature is 140-180℃, and the treatment time is 4-10 hours; the drying temperature in the second step is 100-160℃, and the drying time is 2-10 hours; the calcination temperature is 450-650℃, and the calcination time is 4-10 hours.

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