Preparation method of high-pore-volume theta-aluminum oxide

Abstract

The invention discloses a preparation method of high-pore-volume theta-aluminum oxide, which comprises the following steps: hydrolyzing aluminum alkoxide dispersed in an organic acid solvent to prepare an aluminum oxide precursor, and roasting at high temperature to prepare macroporous theta-aluminum oxide. The organic acid reacts with the aluminum alkoxide, the carboxylate partially substitutes alkoxy of the aluminum alkoxide, and the pH value of the reaction system is reduced, so that the hydrolysis rate of the aluminum alkoxide is reduced, and the structure and texture of the hydrolysate are more uniform and ordered. In addition, carboxylate radicals are adsorbed on the grain surface of the hydrolysate, the hydroxyl density of the surface is reduced, and product particles are not prone to being polymerized to form a compact structure through the hydrogen-bond interaction between hydroxyl groups. The pore volume of the aluminum oxide precursor obtained by hydrolysis and the stability of the pore volume are increased, and the pore volume of the derived theta-aluminum oxide is finally increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic materials, and particularly relates to a preparation method of high pore volume θ-aluminum oxide. Background Art

[0002] θ-aluminum oxide has characteristics such as good thermal stability, mechanical strength, developed pore structure, high specific surface area, strong adsorption performance, and certain surface activity, and is widely used as an adsorbent, ceramic material, and catalyst support. θ-aluminum oxide is usually obtained by high-temperature calcination of alumina precursors (such as boehmite, pseudoboehmite, bayerite, etc.). The thermal decomposition process of preparing θ-aluminum oxide from alumina precursors is a topological transformation, which means that the pore volume and specific surface area and other textural properties of the alumina precursors have a decisive influence on the textural properties of the derived θ-aluminum oxide.

[0003] Hydrolysis reaction using organoaluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide, and aluminum sec-butoxide is one of the common methods for preparing high-purity alumina precursors. However, the direct hydrolysis reaction rate of the aluminum alkoxide is very fast, the composition of the reaction system is uneven, and the reaction process is not unified, resulting in the disordered aggregation of hydrolysis products to form a relatively dense texture, with a small specific surface area and pore volume, and further resulting in a small specific surface area and pore volume of the derived θ-aluminum oxide.

[0004] In the currently disclosed methods for preparing high pore volume θ-aluminum oxide, the method of adding additives during the synthesis process of alumina precursors is mostly used to achieve the purpose of expanding the pore volume of alumina. For example, Patent CN103657739A discloses a method for preparing a mesoporous-macroporous composite structure alumina support. This method can flexibly and controllably synthesize an alumina support with a mesoporous-macroporous composite structure by mixing two pseudoboehmite dry gel powders. However, local overheating or uneven sintering may occur during the calcination process of different precursors, and the interaction between different precursors at high temperatures may lead to uncontrollable pore collapse. Patent CN119018919A discloses a method for preparing macroporous alumina. This method adds various additives such as potassium carbonate, triethoxysilane, and urea as pore expanders during the synthesis process of alumina precursors, effectively improving the porosity of macroporous alumina. However, adding these additives will introduce impurities that are difficult to remove, affecting the purity of the product alumina. Patent CN119114089A discloses a method for expanding the pores of alumina. This method uniformly mixes the pore expander with alumina and simultaneously drops deionized water, kneads it into a plastic body, and after calcination and grinding, porous alumina can be obtained. However, mechanical kneading is difficult to ensure the nano-level uniform dispersion of the pore expander in the alumina matrix and is difficult to precisely control the pore size distribution of the alumina after pore expansion.

[0005] Controlling the hydrolysis and polycondensation reaction process of aluminum alkoxide helps to synthesize alumina precursors with different degrees of structural density, which has a certain effect on regulating the pore volume of alumina. There are patents disclosing methods to control the hydrolysis and polycondensation reaction process by modifying the aluminum source and adding additives during the synthesis of alumina precursors. For example, Patent CN103342537B discloses a method to control the hydrolysis and polycondensation process of aluminum alkoxide by in-situ generating water. Although this method can effectively control the hydrolysis and polycondensation process, the raw materials acetone and aniline used are toxic, increasing the risk of operation. Patent CN106000245A discloses a method to effectively control the hydrolysis and polycondensation reaction process of aluminum alkoxide by adding an organic chelating agent. However, this method involves adding the hydrolysis solution containing the organic chelating agent multiple times, with high costs, complex process operations, long process time, and limited space for further regulation. Summary of the Invention

[0006] In view of the above problems, the present invention provides a new method for preparing θ-alumina with high pore volume. This method uses aluminum alkoxide as the raw material and organic acid as the solvent, prepares the alumina precursor through hydrolysis reaction, and finally obtains θ-alumina by high-temperature calcination of the alumina precursor. The prepared θ-alumina has high purity and high pore volume.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing θ-alumina with high pore volume, comprising the following steps: (1) Preparation of alumina precursor: Disperse aluminum alkoxide in an organic acid solvent, heat and stir to form a homogeneous mixture, add deionized water to it for hydrolysis reaction, and then obtain the alumina precursor after aging, filtration, and drying.

[0008] (2) Preparation of θ-alumina: High-temperature calcine the alumina precursor obtained in step (1) to obtain θ-alumina.

[0009] Further, the aluminum alkoxide in step (1) is one or a mixture of more of aluminum ethoxide, aluminum isopropoxide, and aluminum sec-butoxide.

[0010] Further, the molar ratio of the aluminum alkoxide, organic acid solvent, and deionized water in step (1) is 1:2:1 to 1:10:10, preferably 1:3:2 to 1:8:6.

[0011] Further, the organic acid solvent in step (1) is one or a mixture of more of formic anhydride, acetic anhydride, and propionic anhydride.

[0012] Further, the heating temperature in step (1) is 30 - 80 °C, and the heating time is 0.5 - 6 h.

[0013] Furthermore, the reaction temperature of the hydrolysis in step (1) is 30~100 °C, and the reaction time is 0.5~12 h. Preferably, the reaction temperature of the hydrolysis is 40~80 °C.

[0014] Furthermore, the aging temperature in step (1) is 80~160 °C, and the aging time is 6~48 h.

[0015] Furthermore, the drying temperature in step (1) is 80~130 °C, and the time is 6~24 h. Preferably, the drying temperature is 100~120 °C.

[0016] Furthermore, the calcination temperature in step (2) is 950~1150 °C, and the calcination time is 4~24 h.

[0017] The high pore volume θ-aluminum oxide obtained by the above preparation method has a pore volume of 0.55~0.75 cm 3 / g and an average pore diameter of 25~32 nm.

[0018] The beneficial effects of the present invention are as follows: In the present invention, an aluminum alkoxide is used as a raw material and an organic acid is used as a solution to prepare an alumina precursor, which is then calcined to prepare θ-aluminum oxide. The organic acid reacts with the aluminum alkoxide, and the carboxylate group partially replaces the alkoxy group of the aluminum alkoxide, while reducing the pH of the reaction system, thereby reducing the hydrolysis rate of the aluminum alkoxide. This makes the structure and texture of the hydrolysis product more uniform and ordered. In addition, the carboxylate group is adsorbed on the surface of the grains of the hydrolysis product, reducing the surface hydroxyl density and inhibiting the formation of a dense structure by the hydrogen bonding between the hydroxyl groups of the product particles. These effects increase the pore volume of the alumina precursor obtained by hydrolysis and the stability of the pore volume, and ultimately improve the pore volume of the derived θ-aluminum oxide. Description of the Drawings

[0019] Figure 1 XRD diagrams of Comparative Example 1 and Examples 1 to 4. Detailed Embodiments

[0020] In order to better illustrate the technical solutions of the present invention, the following will be further described in detail with reference to specific examples and the accompanying drawings. However, the protection scope of the present invention is not limited to the following description.

[0021] Example 1 (1) Preparation of alumina precursor: Weigh 40.56 g of anhydrous formic acid and add it to a three-necked flask containing 60.00 g of aluminum isopropoxide, and heat it to 30 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Dropwise add 26.47 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 0.5 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 80 °C for 6 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 6 h to obtain the alumina precursor.

[0022] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 950 °C for 8 h to obtain θ-alumina.

[0023] Example 2 (1) Preparation of alumina precursor: Weigh 54.08 g of anhydrous formic acid and add it to a three-necked flask containing 60.00 g of aluminum isopropoxide, and heat it to 50 °C. After stirring for 1 h, a uniformly dispersed mixture is formed. Dropwise add 26.47 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 1 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 100 °C for 10 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 10 h to obtain the alumina precursor.

[0024] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 10 h to obtain θ-alumina.

[0025] Example 3 (1) Preparation of alumina precursor: Weigh 105.85 g of anhydrous acetic acid and add it to a three-necked flask containing 60.00 g of aluminum sec-butoxide, and heat it to 60 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Dropwise add 21.17 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 2 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 120 °C for 18 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 120 °C for 12 h to obtain the alumina precursor.

[0026] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1100 °C for 10 h to obtain θ-alumina.

[0027] Example 4 (1) Preparation of alumina precursor: Weigh 105.85 g of anhydrous acetic acid and add it to a three-necked flask containing 60.00 g of aluminum ethoxide, then heat to 60 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Dropwise add 15.88 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 8 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 140 °C for 12 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 110 °C for 16 h to obtain the alumina precursor.

[0028] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1150 °C for 6 h to obtain θ-alumina.

[0029] Example 5 (1) Preparation of alumina precursor: Weigh 130.57 g of anhydrous propionic acid and add it to a three-necked flask containing 60.00 g of aluminum isopropoxide, then heat to 80 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Dropwise add 26.47 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 3 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 160 °C for 16 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 12 h to obtain the alumina precursor.

[0030] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 4 h to obtain θ-alumina.

[0031] Example 6 (1) Preparation of alumina precursor: Weigh 40.56 g of anhydrous formic acid and 65.29 g of anhydrous propionic acid and add them to a three-necked flask containing 30.00 g of aluminum ethoxide and 30.00 g of aluminum isopropoxide, then heat to 60 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Dropwise add 21.17 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 3 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 160 °C for 12 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 12 h to obtain the alumina precursor.

[0032] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 12 h to obtain θ-alumina.

[0033] Example 7 (1) Preparation of alumina precursor: Weigh 40.56 g of anhydrous formic acid and 52.92 g of anhydrous propionic acid, add them into a three-necked flask containing 60.00 g of aluminum isopropoxide, and heat to 80 °C. After stirring for 1 h, a uniformly dispersed mixture is formed. Dropwise add 21.17 g of deionized water into the three-necked flask while maintaining a stable temperature during the process. After continuous reaction for 3 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 120 °C for 18 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 12 h to obtain the alumina precursor.

[0034] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 12 h to obtain θ-alumina.

[0035] Example 8 (1) Preparation of alumina precursor: Weigh 50.08 g of anhydrous acetic acid and 60.85 g of anhydrous propionic acid, add them into a three-necked flask containing 60.00 g of aluminum sec-butoxide, and heat to 80 °C. After stirring for 2 h, a uniformly dispersed mixture is formed. Dropwise add 23.09 g of deionized water into the three-necked flask while maintaining a stable temperature during the process. After continuous reaction for 10 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 160 °C for 24 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 120 °C for 12 h to obtain the alumina precursor.

[0036] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 4 h to obtain θ-alumina.

[0037] Example 9 (1) Preparation of alumina precursor: Weigh 13.52 g of anhydrous formic acid, 17.64 g of anhydrous acetic acid and 21.76 g of anhydrous propionic acid, add them into a three-necked flask containing 60.00 g of aluminum isopropoxide, and heat to 80 °C. After stirring for 2 h, a uniformly dispersed mixture is formed. Dropwise add 21.17 g of deionized water into the three-necked flask while maintaining a stable temperature during the process. After continuous reaction for 6 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 140 °C for 24 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 110 °C for 12 h to obtain the alumina precursor.

[0038] (2) Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1000 °C for 8 h to obtain θ-alumina.

[0039] Example 10 (1)Preparation of alumina precursor: Weigh 27.04 g of anhydrous formic acid, 35.28 g of anhydrous acetic acid and 43.52 g of anhydrous propionic acid and add them into a three-necked flask containing 60.00 g of aluminum ethoxide, and heat to 80 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Drop 31.76 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 3 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 160 °C for 48 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 110 °C for 24 h to obtain the alumina precursor.

[0040] (2)Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 1150 °C for 12 h to obtain θ-alumina.

[0041] Comparative Example 1 (using isopropanol as the solvent, compared with Example 1) (1)Preparation of alumina precursor: Weigh 52.96 g of isopropanol and add it into a three-necked flask containing 60.00 g of aluminum isopropoxide, and heat to 30 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Drop 26.47 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 0.5 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 80 °C for 6 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 100 °C for 6 h to obtain the alumina precursor.

[0042] (2)Preparation of θ-alumina: Calcinate the alumina precursor obtained in step (1) at 950 °C for 8 h to obtain θ-alumina.

[0043] Comparative Example 2 (using anhydrous butyric acid as the solvent, compared with Example 4) (1)Preparation of alumina precursor: Weigh 155.30 g of anhydrous butyric acid and add it into a three-necked flask containing 60.00 g of aluminum ethoxide, and heat to 60 °C. After stirring for 0.5 h, a uniformly dispersed mixture is formed. Drop 15.88 g of deionized water into the three-necked flask while keeping the temperature stable. After continuous reaction for 8 h, stop stirring, transfer the mixture in the flask to a high-pressure hydrothermal autoclave, and age it hermetically at 140 °C for 12 h. After the aging is completed, pour out the mixture in the hydrothermal autoclave and perform suction filtration. Subsequently, dry the obtained solid at 110 °C for 16 h to obtain the alumina precursor.

[0044] (2) Preparation of θ-aluminum oxide: The aluminum oxide precursor obtained in step (1) was calcined at a temperature of 1150 °C for 6 h to obtain θ-aluminum oxide.

[0045] Table 1 Textural parameters of the obtained θ-aluminum oxide The nitrogen adsorption and desorption tests were carried out on the examples and comparative examples using an ASAP 2460 full-automatic sorptometer produced by Micrometrics Company of the United States, and the textural parameters of the obtained θ-aluminum oxide were listed in Table 1. It can be seen from Table 1 that the pore volume of the θ-aluminum oxide prepared by calcining the aluminum oxide precursor synthesized with one or more of formic anhydride, acetic anhydride, and propionic anhydride as the solvent is all above 0.55 cm 3 / g, and the maximum pore volume of the examples is as high as 0.75 cm 3 / g, which is significantly better than that of the θ-aluminum oxide synthesized under the conditions of Comparative Example 1 and Comparative Example 2.

[0046] Figure 1 XRD patterns of Comparative Example 1 and Examples 1 to 4. It can be found that characteristic diffraction peaks of θ-aluminum oxide appear at 31.45 o 、32.74 o 、36.85 o 、38.76 o 、44.83 o and 67.36 o respectively, corresponding to the diffraction of the (-401), (002), (111), (401), (-112) and (710) crystal planes of the θ-aluminum oxide crystal structure, which is consistent with the diffraction peaks of the JCDPS standard card (PDF NO.023-1009), indicating that they are all pure-phase θ-aluminum oxide.

[0047] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of high pore volume θ-aluminum oxide, characterized in that: It includes the following steps: (1) Prepare an alumina precursor: Disperse an aluminum alkoxide in an organic acid solvent, heat and stir to form a homogeneous mixture, then add deionized water thereto for hydrolysis reaction, and then obtain the alumina precursor after aging, filtration and drying; (2) Prepare θ-alumina: Calcinate the alumina precursor obtained in step (1) at a high temperature to obtain θ-alumina.

2. The preparation method according to claim 1, characterized in that: The aluminum alkoxide described in step (1) is a mixture of one or more of aluminum ethoxide, aluminum isopropoxide, and aluminum sec-butoxide.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the aluminum alkoxide, the organic acid solvent, and the deionized water described in step (1) is 1:2:1 to 1:10:

10.

4. The preparation method according to claim 1, characterized in that: The organic acid solvent described in step (1) is a mixture of one or more of anhydrous formic acid, anhydrous acetic acid, and anhydrous propionic acid.

5. The preparation method according to claim 1, characterized in that: The heating temperature in step (1) is 30 to 80 °C, and the heating time is 0.5 to 6 h.

6. The preparation method according to claim 1, characterized in that: The hydrolysis reaction temperature in step (1) is 30 to 100 °C, and the hydrolysis reaction time is 0.5 to 12 h.

7. The preparation method according to claim 1, characterized in that: The aging temperature in step (1) is 80 to 160 °C, and the aging time is 6 to 48 h.

8. The preparation method according to claim 1, wherein: The drying temperature in step (1) is 80 to 130 °C, and the drying time is 6 to 24 h.

9. The preparation method according to claim 1, wherein: The calcination temperature in step (2) is 950 to 1150 °C, and the calcination time is 4 to 24 h.

10. A high pore volume θ-aluminum oxide obtained by the preparation method according to any one of claims 1 to 9, characterized in that: The pore volume of the high pore volume θ-alumina is 0.55~0.75 cm 3 / g, and the average pore diameter is 25~32 nm.

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