A high-purity macroporous pseudoboehmite and its preparation method

Abstract

This invention belongs to the field of catalyst supports, specifically relating to a high-purity macroporous pseudoboehmite and its preparation method. The preparation method uses organic aluminum alkoxide as raw material, which is hydrolyzed, followed by the addition of a pore-expanding agent for stirring and pore expansion. Then, it undergoes pressure aging, plate and frame filtration, countercurrent washing, and drying to finally obtain high-purity macroporous pseudoboehmite. This invention solves the technical problems of small pore volume and narrow pore size in existing aluminum alkoxide-based pseudoboehmite, as well as the complexity, high energy consumption, and difficulty in achieving both macroporous structure and high purity of existing pore-expanding technologies, by optimizing the hydrolysis, pore expansion, and aging process parameters. The pseudoboehmite prepared by this invention has a purity ≥99.9%, a pore volume of up to 0.81 mL / g, and an average pore size of up to 16.12 nm. Furthermore, the process is simple, has strong equipment compatibility, and low production cost, making it suitable for large-scale industrial production and applicable to high-end catalytic fields such as heavy oil hydrogenation and macromolecular catalysis.

Description

Technical Field

[0001] This invention belongs to the field of catalyst supports, specifically relating to a high-purity macroporous pseudoboehmite and its preparation method. Background Technology

[0002] The aluminum alkoxide method is the mainstream process for preparing high-purity boehmite, which has advantages such as regular crystal phase, high purity, and low impurity content, making it an important precursor for preparing high-end catalyst supports. However, boehmite prepared by the conventional aluminum alkoxide method generally suffers from small pore volume and narrow pore size, making it difficult to meet the requirements of large-pore structures in fields such as heavy oil hydrogenation and macromolecular catalysis. Therefore, there is an urgent need for efficient pore-expanding modification to improve the pore structure.

[0003] Existing pore-enlarging technologies mostly employ template control and process optimization to improve pore structure, but they still suffer from shortcomings such as uneven pore size distribution, easy collapse of pore channels after calcination, complex processes, and poor compatibility with existing production lines. These limitations make it difficult to reliably achieve a balance between large pore volume, large pore size, and high purity. Specifically:

[0004] CN121872422A discloses a method for producing large-pore pseudoboehmite using the aluminum alkoxide process. This method utilizes a biomimetic pore-expanding process combining cellulose nanocrystals and tartaric acid. First, a pretreated composite pore-expanding agent is added to the aluminum alkoxide solution, followed by a two-stage gradient hydrolysis, hydrothermal aging, and two-stage gradient calcination. The disadvantages include the need for ultrasonic pretreatment, the complexity of the two-stage calcination process, high energy consumption, high cost of cellulose nanocrystals, and stringent control over the pore-expanding agent ratio and process parameters. Furthermore, this technology involves an intermittent liquid-phase hydrolysis reaction.

[0005] CN120247066A discloses a method for preparing high-purity macroporous pseudoboehmite via steam hydrolysis. This method involves gas-phase hydrolysis using a mixture of organic solvent and water. First, the organic aluminum alkoxide reacts with the mixed steam in a tube furnace, followed by aging and filtration drying under a steam atmosphere. Disadvantages include small pore size (difficulty in achieving pores larger than 40 nm), aging time up to 64 hours, low production efficiency, high investment in tube furnace equipment, and difficulty in large-scale continuous production. This technology is a continuous gas-phase hydrolysis reaction.

[0006] CN121850030A discloses a method for preparing ultra-large porous pseudoboehmite. This method involves microwave stepwise hydrolysis of a composite aluminum alkoxide followed by pore expansion using a natural template. First, the composite aluminum alkoxide is subjected to gradient microwave hydrolysis to generate a uniform precursor, which is then subjected to hydrothermal pore expansion with konjac glucomannan and low-temperature plasma treatment. The disadvantages are that the composite aluminum alkoxide preparation process is cumbersome and time-consuming, the microwave and plasma equipment is expensive, the hydrothermal time is long (18–30 hours), energy consumption is high, and industrial scale-up is difficult. This technology is an intermittent microwave-assisted hydrothermal reaction.

[0007] Based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0008] To address the problems of small pore volume and narrow pore diameter in existing boehmite technologies, this invention provides a method for preparing high-purity macroporous boehmite, comprising the following steps: (1) After mixing organic aluminum alkoxide with water, hydrolyze the mixture at 60-100℃ for 1-6 hours to obtain a hydrolysis system; wherein: The weight ratio of the organic aluminum alkoxide to water is 1:3-6; the organic aluminum alkoxide is aluminum n-butoxide, aluminum isopropoxide, or aluminum sec-butoxide. (2) Add a pore-expanding agent to the hydrolysis system and stir to obtain a pore-expanding system; (3) The pore-expanding system is heated and aged to obtain an aged system; (4) The aging system is filtered and separated to obtain solid filter material; (5) Wash the solid filter material to obtain clean material; (6) After drying the clean material, the high-purity macroporous pseudoboehmite is obtained.

[0009] Preferably, in step (2), a pore-expanding agent is added to the hydrolysis system and stirred for 0.5-1.5 hours to obtain a pore-expanding system; And / or, the amount of the pore-expanding agent added is 2-8% of the dry weight of alumina; wherein the dry weight of alumina is calculated based on the amount of aluminum butoxide fed during hydrolysis being completely reacted into alumina.

[0010] And / or, the pore-expanding agent is polyethylene glycol; the polyethylene glycol is one or a combination of two or more of PEG-400, PEG-600, and PEG-2000.

[0011] Preferably, in step (3), the pore-expanding system is heated to 80-150°C and aged for 4-12 hours to obtain an aged system.

[0012] Preferably, in step (4), the aging system is filtered by a plate and frame filter press to separate solids and liquids, thereby obtaining solid filter material.

[0013] Preferably, in step (5), the solid filter material is subjected to pressure filtration and countercurrent washing with purified water 1-4 times to obtain clean material.

[0014] Preferably, in step (6), the clean material is dried at 90-150°C for 6-12 hours to obtain the high-purity macroporous pseudoboehmite.

[0015] Based on the same technical concept, another aspect of the present invention is to provide a high-purity macroporous pseudoboehmite obtained by the preparation method described above.

[0016] This invention addresses the shortcomings of existing technologies by achieving a balance between macroporous structure and high purity through process optimization and the synergistic effect of low-cost pore-expanding agents. Specific beneficial effects are as follows: 1. Significantly improved pore structure performance: This invention uses a pore-expanding agent and processes such as pressure holding and aging to effectively control the pore growth of pseudoboehmite. The product pore volume can reach 0.81 mL / g, and the average pore diameter can reach 16.12 nm. Compared with the unexpanded product, the pore volume is increased by 58.8% and the average pore diameter is increased by 73.9%, which can meet the application requirements of large pore structure in fields such as heavy oil hydrogenation and macromolecular catalysis.

[0017] 2. High product purity: It retains the high purity advantage of the aluminum alkoxide method for preparing pseudoboehmite, without the need to introduce complex impurity components. The final product purity is ≥99.9%, with extremely low impurity content, which meets the purity requirements of high-end catalyst supports.

[0018] 3. Simple process and strong compatibility: It does not require complex processes such as ultrasonic pretreatment, multi-stage gradient calcination, microwave hydrolysis or low-temperature plasma. Production can be completed using only conventional reaction kettles, plate and frame filter presses and drying equipment. It is highly compatible with existing aluminum alkoxide production lines and has low equipment modification costs.

[0019] 4. High production efficiency and low energy consumption: The aging time is controlled at 4-12 hours, which is significantly shorter than the longest aging time of 64 hours in the existing technology, and the production cycle is significantly reduced; at the same time, there is no need for high-temperature calcination and special energy equipment, and the production energy consumption is greatly reduced.

[0020] 5. Low production cost: The polyethylene glycol pore expander used is widely available and inexpensive, and the amount added is only 2-8% of the dry weight of alumina, which further reduces the overall production cost of the product. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] Example 1 This invention provides a method for preparing high-purity macroporous pseudoboehmite, the method comprising the following steps: (1) Pretreatment of the reactor: The stainless steel reactor is cleaned with deionized water three times, and the residual water is drained. Then it is preheated to 80°C for use.

[0023] (2) Hydrolysis reaction: Add 1 kg of aluminum n-butoxide to the preheated reactor, then slowly add 4.5 kg of deionized water, turn on the stirring device, control the stirring rate to 150 r / min, and carry out the hydrolysis reaction for 3.5 h at a constant temperature of 80℃ to obtain a homogeneous hydrolysis system.

[0024] (3) Pore expansion treatment: After the hydrolysis reaction is completed, keep the stirring rate constant and add PEG-600 to the reactor (the amount added is 5% of the dry mass of alumina, and the dry mass of alumina is calculated based on the complete reaction of aluminum butoxide to alumina). Continue stirring for 1 hour to fully mix the pore expansion agent with the hydrolysis system to obtain the pore expansion system.

[0025] (4) Constant temperature aging: After stirring, close the vent valve of the reactor, raise the temperature inside the reactor to 120°C, and keep it at a constant temperature for 8 hours to obtain the aged system.

[0026] (5) Solid-liquid separation: After aging, the material in the reactor is cooled to room temperature and separated by plate and frame filter press. The filter pressure is controlled at 0.3 MPa to obtain solid filter material.

[0027] (6) Countercurrent washing: Transfer the solid filter material to the washing tank and use filter press water for countercurrent washing. The amount of water used for each wash is twice the mass of the solid filter material. Wash for a total of 3 times. During the washing process, the stirring rate is controlled at 100r / min. After each wash, filter press dewatering is performed to obtain clean material.

[0028] (7) Drying and pulverizing: Spread the clean material evenly on a tray with a thickness of 2cm, put it into a hot air circulating drying oven, dry it at 120℃ for 9h, take it out after drying, pulverize it with a pulverizer and pass it through a 200-mesh sieve to obtain high-purity macroporous pseudoboehmite with a purity ≥99.9%.

[0029] Example 2 This invention provides a method for preparing high-purity macroporous pseudoboehmite, the method comprising the following steps: (1) Pretreatment of the reactor: The stainless steel reactor is cleaned with deionized water three times, and after draining the residual water, it is preheated to 60°C for use.

[0030] (2) Hydrolysis reaction: Add 1 kg of aluminum isopropoxide to the preheated reactor, then slowly add 3 kg of deionized water, turn on the stirring device, control the stirring rate to 120 r / min, and carry out the hydrolysis reaction for 6 h at a constant temperature of 60℃ to obtain a uniform hydrolysis system.

[0031] (3) Pore expansion treatment: After the hydrolysis reaction is completed, keep the stirring rate unchanged, add PEG-2000 (2% of the dry mass of alumina) to the reactor, and continue stirring for 0.5h to fully mix the pore expansion agent with the hydrolysis system to obtain the pore expansion system.

[0032] (4) Constant temperature aging: After stirring, close the vent valve of the reactor, raise the temperature inside the reactor to 80°C, and keep it at a constant temperature for 12 hours to obtain the aged system.

[0033] (5) Solid-liquid separation: After aging, the material in the reactor is cooled to room temperature and separated by plate and frame filter press. The filter pressure is controlled at 0.25 MPa to obtain solid filter material.

[0034] (6) Countercurrent washing: Transfer the solid filter material to the washing tank and use filter press water for countercurrent washing. The amount of water used for each wash is twice the mass of the solid filter material. Wash twice in total. During the washing process, the stirring rate is controlled at 80 r / min. After each wash, filter press dewatering is performed to obtain clean material.

[0035] (7) Drying and pulverizing: Spread the clean material evenly on a tray with a thickness of 2cm, put it into a hot air circulating drying oven, dry it at 90℃ for 12h, take it out after drying, pulverize it with a pulverizer and pass it through a 200-mesh sieve to obtain high-purity macroporous pseudoboehmite with a purity ≥99.9%.

[0036] Example 3 This invention provides a method for preparing high-purity macroporous pseudoboehmite, the method comprising the following steps: (1) Pretreatment of the reactor: The 50L stainless steel reactor was cleaned with deionized water three times, and the residual water was drained. Then it was preheated to 100℃ for use.

[0037] (2) Hydrolysis reaction: Add 1 kg of aluminum sec-butoxide to the preheated reactor, then slowly add 6 kg of deionized water, turn on the stirring device, control the stirring rate to 180 r / min, and carry out the hydrolysis reaction for 1 h at a constant temperature of 100℃ to obtain a homogeneous hydrolysis system.

[0038] (3) Pore expansion treatment: After the hydrolysis reaction is completed, keep the stirring rate constant and add PEG-400 (8% of the dry mass of alumina) to the reactor. Continue stirring for 1.5h to fully mix the pore expansion agent with the hydrolysis system to obtain the pore expansion system.

[0039] (4) Constant temperature aging: After stirring, close the vent valve of the reactor, raise the temperature inside the reactor to 150°C, and keep it at a constant temperature for 4 hours to obtain the aged system.

[0040] (5) Solid-liquid separation: After aging, the material in the reactor is cooled to room temperature and separated by plate and frame filter press. The filter pressure is controlled at 0.35 MPa to obtain solid filter material.

[0041] (6) Countercurrent washing: Transfer the solid filter material to the washing tank and use filter press water for countercurrent washing. The amount of water used for each wash is twice the mass of the solid filter material. Wash for a total of 4 times. During the washing process, the stirring rate is controlled at 120 r / min. After each wash, filter press dewatering is performed to obtain clean material.

[0042] (7) Drying and pulverizing: Spread the clean material evenly on a tray with a thickness of 2cm, put it into a hot air circulating drying oven, dry it at 150℃ for 6 hours, take it out after drying, pulverize it with a pulverizer and pass it through a 200-mesh sieve to obtain high-purity macroporous pseudoboehmite with a purity of ≥99.9%.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not add polyethylene glycol pore expander, and the preparation method includes the following briefly described steps: (1) Add 1 kg of aluminum n-butoxide to the reactor, then add 4.5 kg of deionized water, and hydrolyze at 80 °C for 3.5 h to obtain the hydrolysis system; (2) Stir for 1 hour after hydrolysis is complete; (3) After stirring, the temperature in the reactor is raised to 120°C and aged for 8 hours to obtain the aged system; (4) After aging, the material is filtered by a plate and frame filter press to separate solids and liquids, and obtain solid filter material. (5) The solid filter material is subjected to pressure filtration and countercurrent washing with purified water three times to obtain clean material; (6) The cleaned material is dried at 120°C for 9 hours to obtain pseudoboehmite.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that the aging temperature is lower and the aging time is extended accordingly. The preparation method includes the following steps: (1) Add 1 kg of aluminum n-butoxide to the reactor, then add 4.5 kg of deionized water, and hydrolyze at 80 °C for 3.5 h to obtain the hydrolysis system; (2) After hydrolysis, PEG-600 (5% of the dry mass of alumina) was added to the reactor and stirred for 1 hour to obtain the pore-expanding system; (3) After stirring, the temperature in the reactor is raised to 60°C and aged for 15 hours to obtain the aged system; (4) After aging, the material is filtered by a plate and frame filter press to separate solids and liquids, and obtain solid filter material. (5) The solid filter material is subjected to pressure filtration and countercurrent washing with purified water three times to obtain clean material; (6) The cleaned material is dried at 120°C for 9 hours to obtain pseudoboehmite.

[0045] Comparative Example 3 The difference between this comparative example and Example 1 is that the aging temperature is higher and the aging time is appropriately reduced. The preparation method includes the following simplified steps: (1) Add 1 kg of aluminum n-butoxide to the reactor, then add 4.5 kg of deionized water, and hydrolyze at 80 °C for 3.5 h to obtain the hydrolysis system; (2) After hydrolysis, PEG-600 (5% of the dry mass of alumina) was added to the reactor and stirred for 1 hour to obtain the pore-expanding system; (3) After stirring, the temperature in the reactor is raised to 180°C and aged for 2 hours to obtain the aged system; (4) After aging, the material is filtered by a plate and frame filter press to separate solids and liquids, and obtain solid filter material. (5) The solid filter material is subjected to pressure filtration and countercurrent washing with purified water three times to obtain clean material; (6) The cleaned material is dried at 120°C for 9 hours to obtain pseudoboehmite.

[0046] Detection example The products obtained in Example 1 and Comparative Examples 1-3 were tested using the following methods: (i) The method for detecting pore volume and specific surface area is as follows: Weigh 0.15-0.2g of the sample that has been calcined at 600℃ for 2h into a sample tube of known weight m1, place it in the degassing station of the specific surface area and porosity analyzer, degas it at 300℃ for 2h, cool it to room temperature, and weigh the total weight m2 of the sample tube and the sample. Calculate the sample mass m = m2 - m1. Place the sample tube into the instrument analysis station, pour liquid nitrogen into the Dewar flask, check that the pressure of high-purity nitrogen and high-purity helium is normal, input the sample mass m, and start the analysis using the BET method. Record the specific surface area and pore volume results.

[0047] (ii) The average aperture is calculated using the following formula: Average pore size (nm) = 4 × (pore volume (mL / g) / specific surface area (m²) 2 / g))×1000.

[0048] The test results are shown in Table 1.

[0049] Table 1

[0050] Analysis and Conclusion: Through long-term research, the inventors discovered that macropore volume depends on the development of large pore size and interconnected channels, while ultra-high specific surface area is formed by the stacking of a large number of micropores. The two structures are structurally mutually exclusive. Only by maintaining a moderate specific surface area can an optimal match be achieved with macropore volume, while simultaneously considering performance such as mass transfer efficiency in catalytic reactions. Based on this principle, the data in Table 1 are analyzed in detail below.

[0051] 1. Directional regulation of pore structure mutual repulsion by pore-expanding agents Compared with Comparative Example 1, under the same hydrolysis and aging process parameters, Example 1 with the addition of 5% PEG-600 pore expander showed an increase in pore volume from 0.61 mL / g to 0.81 mL / g (an increase of 32.8%), an increase in average pore size from 11.09 nm to 16.12 nm (an increase of 45.4%), and an increase in specific surface area from 220 m² / g. 2 / g decreased to 201m 2 / g (decreased by 8.6%).

[0052] Polyethylene glycol, as a space-occupying pore-expanding agent, inhibits the formation of micropores smaller than 10 nm to some extent by inserting into the intergranular gaps of the pseudo-boehmite precursor. More importantly, it guides the directional growth of grains to form large-diameter pores and interconnected channels. Therefore, this inevitably leads to a decrease in the proportion of micropores and a slight decrease in the total specific surface area. However, in this invention, the decrease in specific surface area is controllable, ultimately reaching 201 nm. 2 The / g ratio remains within a moderate and efficient range. It solves the mass transfer bottleneck of macromolecular reactants through large pores, while retaining sufficient active site loading capacity, thus avoiding the problem of insufficient catalytic activity caused by excessive sacrifice of specific surface area in pursuit of large pores.

[0053] 2. The key influence of aging temperature on pore structure equilibrium Aging temperature, by regulating grain growth rate and pore development process, determines the balance between macroporous structure and specific surface area. Comparative Example 1 and Comparative Example 2: When the aging temperature was reduced from 120°C to 60°C, even with an extended aging time of 15 hours, the product pore volume still decreased to 0.45 mL / g, the average pore size decreased to 7.47 nm, while the specific surface area increased to 241 m². 2 / g. This is the result of ultra-high specific surface area achieved by building up micropores: the aging temperature is too low to provide enough energy for grain growth and pore reconstruction, the space occupation effect of the pore expander is difficult to exert, and only a large number of micropores of uniform size can be formed in the system, resulting in an artificially high specific surface area. However, the pores are narrow and the mass transfer resistance is extremely high, which cannot meet the requirements of macromolecular catalytic reactions such as heavy oil hydrogenation.

[0054] Comparative Example 1 and Comparative Example 3: When the aging temperature increased from 120°C to 180°C, the average pore size was slightly higher than that of Example 1 (16.48 nm), the pore volume decreased to 0.75 mL / g, and the specific surface area decreased significantly to 182 m². 2 / g. This is because excessively high aging temperatures can lead to excessive agglomeration and growth of grains, resulting in the disappearance of a large number of micropores and the collapse and merging of some mesopore structures, causing excessive loss of specific surface area; at the same time, excessively large grain size will reduce the thermal stability of the material, making it prone to sintering during subsequent calcination and catalytic reactions, further leading to the destruction of the pore structure.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing high-purity macroporous pseudoboehmite, characterized in that, The preparation method includes the following steps: (1) After mixing organic aluminum alkoxide with water, hydrolyze the mixture at 60-100℃ for 1-6 hours to obtain a hydrolysis system; wherein: The weight ratio of the organic aluminum alkoxide to water is 1:3-6; the organic aluminum alkoxide is aluminum n-butoxide, aluminum isopropoxide, or aluminum sec-butoxide. (2) Add a pore-expanding agent to the hydrolysis system and stir to obtain a pore-expanding system; (3) The pore-expanding system is heated and aged to obtain an aged system; (4) The aging system is filtered and separated to obtain solid filter material; (5) Wash the solid filter material to obtain clean material; (6) After drying the clean material, the high-purity macroporous pseudoboehmite is obtained.

2. The method for preparing high-purity macroporous pseudoboehmite according to claim 1, characterized in that, In step (2), a pore-expanding agent is added to the hydrolysis system and stirred for 0.5-1.5 hours to obtain a pore-expanding system; And / or, the amount of the pore-expanding agent added is 2-8% of the dry weight of alumina; And / or, the pore-expanding agent is polyethylene glycol; the polyethylene glycol is one or a combination of two or more of PEG-400, PEG-600, and PEG-2000.

3. The method for preparing high-purity macroporous pseudoboehmite according to claim 1, characterized in that, In step (3), the pore-expanding system is heated to 80-150℃ and aged for 4-12 hours to obtain the aged system.

4. The method for preparing high-purity macroporous pseudoboehmite according to claim 1, characterized in that, In step (4), the aging system is filtered by a plate and frame filter press to separate solids and liquids, and solid filter material is obtained.

5. The method for preparing high-purity macroporous pseudoboehmite according to claim 1, characterized in that, In step (5), the solid filter material is subjected to pressure filtration and countercurrent washing with purified water 1-4 times to obtain clean material.

6. The method for preparing high-purity macroporous pseudoboehmite according to claim 1, characterized in that, In step (6), the clean material is dried at 90-150℃ for 6-12 hours to obtain the high-purity macroporous pseudoboehmite.

7. High-purity macroporous boehmite obtained by the preparation method according to any one of claims 1-6.

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