Method for preparing large-pore-volume high-peptization high-purity pseudo-boehmite

Abstract

The invention belongs to the technical field of inorganic material preparation, and provides a method for preparing large-pore-volume high-peptization high-purity pseudo-boehmite. Primary aluminum or refined high-purity aluminum is used as a raw material and reacts with alcohol to generate aluminum alkoxide, the aluminum alkoxide is mixed and reacted with water after being purified and refined, and the generated alcohol is separated and recycled after sufficient hydrolysis. And adding deionized water and a crystallization aid into the coarse pseudo-boehmite, carrying out hydrothermal stirring at 105-250 DEG C for 16-48 hours, and finally drying the slurry to obtain the large-pore-volume high-peptization high-purity pseudo-boehmite. The pseudo-boehmite disclosed by the invention is low in impurity content, the peptizing index is greater than 97%, and the pore volume is greater than 0.75 mL / g after the pseudo-boehmite is calcined at 550 DEG C for 3 hours. The large-pore-volume, high-peptization and high-purity pseudo-boehmite is prepared on the basis of aluminum alkoxide hydrolysis, microcrystal growth of the high-purity pseudo-boehmite is controlled in a water system, the problem that the pore volume of the pseudo-boehmite is seriously reduced after water is added is solved, and a proper raw material is provided for manufacturing a high-purity and large-pore-volume alumina carrier.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of inorganic functional materials, and relates to a method for preparing pseudo-boehmite with a large pore volume, high peptizability and high purity. Background Art

[0002] Pseudo-boehmite, also known as meta-boehmite, is a type of hydrated alumina with a special structure and an indefinite number of crystal waters. It appears as a white, non-toxic and odorless powder. It has a low crystallinity, small particle size, a very high specific surface area and pore volume, and good adsorption and peptizability. Pseudo-boehmite is an important precursor for the preparation of activated alumina and other materials, and thus has a wide range of applications in the fields of catalysis, adsorption, fine ceramics and new materials. In the field of catalysis, pseudo-boehmite is often used as the precursor of the alumina support, and plays a crucial role especially in the fields of petrochemical industry and automotive exhaust purification.

[0003] With the development of technology and the expansion of demand, the requirements for pseudo-boehmite are becoming more and more stringent, such as purity and pore structure. Taking the alumina supports for propane dehydrogenation and catalytic reforming in the petrochemical field as an example, a larger pore volume is beneficial to improving the diffusion efficiency of gas molecules in the catalyst, enhancing the conversion ability of the catalyst, reducing coking and avoiding the inactivation of the catalyst in a short time; higher purity reduces the influence of impurities on the catalytic active centers; good peptizability makes it easy to form high-strength alumina balls and prolongs the service life of the catalyst. Therefore, it is of great significance to develop pseudo-boehmite with a large pore volume, high peptizability and high purity.

[0004] Currently, the common synthetic methods of pseudo-boehmite in industry are carbonization method, double-aluminum precipitation method and alcoholate hydrolysis method. Among them, the pseudo-boehmite prepared by the carbonization method and double-aluminum precipitation method using inorganic aluminum salts as raw materials can achieve a large pore volume, but has a high impurity content and poor peptization property, which affects its application range. Hydrolysis of aluminum alkoxides (such as aluminum isopropoxide, aluminum sec-butoxide, etc.) as raw materials can synthesize pseudo-boehmite with a large pore volume and high purity, and has good peptization properties. For example, Chinese Patent CN 104192880A discloses a method for preparing high-purity pseudo-boehmite. Under stirring conditions, a hydrolysis solution containing a pore-forming agent is added to an aluminum isopropoxide-isopropanol solution according to a given ratio, and hydrolysis is carried out at 60-80 °C. After drying the hydrolysis product, high-purity pseudo-boehmite is obtained, and the pore volume can reach about 1.5 mL / g. Chinese Patent CN 110395756 A discloses a method for preparing pseudo-boehmite with a large pore volume, multi-channel and wide distribution, which includes the following operation steps: (1) reacting 2N-5N aluminum raw materials with alcohol to obtain aluminum alkoxide and keeping warm; (2) distilling and purifying, transferring the purified aluminum alkoxide to a hydrolysis reaction kettle, adding 1-8‰ of nano-boehmite seeds, adding an alcohol solution and keeping warm; (3) hydrolyzing, adding an auxiliary agent and keeping warm to obtain a pseudo-boehmite product with a large pore volume, multi-channel and wide distribution, and the pore volume is 1.0-1.3 mL / g. The master's thesis "Preparation of Catalytic Pseudo-Boehmite and Alumina by Hydrolysis of Aluminum Isopropoxide" (pages 17-25) by Liu Yuanli of Dalian University of Technology studied the hydrated alumina obtained by hydrolysis of aluminum alkoxide, and carried out a solvothermal reaction after mixing it with a water-organic solvent solution. The pore volume of the obtained pseudo-boehmite can reach more than 1.4 mL / g, and the peptization index is more than 95%. However, the pore structure of the macroporous pseudo-boehmite obtained by these aluminum alkoxide methods is unstable, and the pore volume decreases severely after adding water, which brings trouble to practical applications. Summary of the Invention

[0005] Based on the above technical problems, the macroporous pseudo-boehmite prepared by the aluminum alkoxide method in the prior art mainly relies on organic solvents to form pores. After drying, a large number of alkoxy groups remain on the surface, which plays an anti-agglomeration role. Macropores are easily formed by the stacking between particles. However, after mixing with water, the alkoxy groups on the surface are replaced by hydroxyl groups, and the structure collapses under the action of hydrogen bonds and surface tension during the drying process, resulting in a decrease in pore volume. The present invention proposes to control the microcrystal growth of high-purity pseudo-boehmite in an aqueous system based on the hydrolysis of aluminum alkoxides, and prepare macroporous high-peptization high-purity pseudo-boehmite, avoiding the problem of severe decrease in the pore volume of pseudo-boehmite after adding water.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing macroporous high-peptization high-purity pseudo-boehmite, the steps are as follows:

[0008] Step 1. Mix metallic aluminum, alcohol, and a catalyst, and reflux for 2 to 24 hours to obtain crude aluminum alkoxide. After purification, the crude aluminum alkoxide is obtained as liquid aluminum alkoxide.

[0009] Step 2. Stir and mix the liquid aluminum alkoxide obtained in Step 1 with water at 75 to 95 °C for hydrolysis. After mixing, continue stirring for 2 to 12 hours, and then separate and recover the alcohol produced by hydrolysis.

[0010] Step 3. Mix the pseudo-boehmite or pseudo-boehmite wet material obtained in Step 2 with an aqueous crystallization solution and stir to prepare a pseudo-boehmite slurry. Then, carry out hydrothermal stirring at 105 to 250 °C for 16 to 48 hours to obtain a pseudo-boehmite slurry.

[0011] Step 4. Dry the pseudo-boehmite slurry obtained in Step 3, and the resulting product is macroporous high peptization high-purity pseudo-boehmite. The content of Na2O in the macroporous high peptization high-purity pseudo-boehmite is less than 0.002 wt.%, the content of Fe2O3 is less than 0.015 wt.%, the content of SiO2 is less than 0.015 wt.%, the peptization index is greater than 97%, and the pore volume of the alumina obtained by calcining at 550 °C for 3 hours is greater than 0.75 mL / g.

[0012] The metallic aluminum described in Step 1 is primary aluminum or aluminum ingots, aluminum blocks, aluminum grains, aluminum beans, aluminum sheets, etc. processed from high-purity aluminum refined from primary aluminum.

[0013] The alcohol described in Step 1 is one of isopropyl alcohol, sec-butyl alcohol, and isooctyl alcohol.

[0014] The catalyst described in Step 1 is an aluminum alkoxide self-catalyst or anhydrous aluminum trichloride.

[0015] The purification method of the crude aluminum alkoxide described in Step 1 is vacuum distillation or filtration.

[0016] The molar ratio of the aluminum alkoxide to water described in Step 2 is 1:3 to 1:100.

[0017] The crystallization solution described in Step 3 is a mixture of water and a crystallization aid. The crystallization aid is one of ammonium carbonate, ammonium bicarbonate, ammonium citrate, ammonia, choline, diethanolamine, and triethanolamine; the mass ratio of the crystallization aid to water is less than 1:50.

[0018] Further, in the pseudo-boehmite slurry prepared in Step 3, the mass content of alumina is 5 to 15%.

[0019] Advantages of the present invention: The method of the present invention controls the pore formation by the method of microcrystal growth and accumulation of high-purity pseudo-boehmite by the aluminum alkoxide method in an aqueous system. Compared with the method of adding a pore-forming agent or solvent for pore formation in the conventional aluminum alkoxide method, the pore structure of the obtained macroporous high-purity pseudo-boehmite has good stability in an aqueous system; at the same time, the use of organic solvents and reagents is reduced, and the operation is safer. Description of the Drawings

[0020] Figure 1 It is the XRD pattern of the product of Specific Example 1.

[0021] Figure 2 It is the TEM image of the product of Specific Example 1. Detailed Description of the Invention

[0022] The following describes in detail the specific implementation manners of the present invention in combination with the technical solutions.

[0023] Example 1

[0024] Take 60 g of aluminum pellets (processed from industrial aluminum ingots, with a purity of 99.7%) and rinse them with deionized water, then dry them in an oven at 80 °C for 4 h; put the dried aluminum pellets into a 1-L three-necked flask, add 400 g of isopropanol and 10 g of aluminum isopropoxide to the three-necked flask. Heat and reflux the materials in the three-necked flask for 4 h; then carry out vacuum distillation, control the pressure in the system below 0.005 MPa, control the temperature of the liquid at 180 - 220 °C, and collect the distillate. Take 408 g of freshly prepared aluminum isopropoxide obtained by vacuum distillation and add it to a 1-L three-necked flask. Under an 80 °C water bath and with mechanical stirring (150 r / min), add 125 g of deionized water to the three-necked flask containing aluminum isopropoxide using a peristaltic pump, and the water addition rate is 4 mL / min; after the water addition is completed, continue stirring for 4 h and then transfer the product to a vacuum drying oven and dry it under vacuum at 60 °C for 6 h. Take 100 g of the dried sample (with an alumina content of 74%) and put it into a 1-L hydrothermal autoclave, add 600 g of deionized water and 3 g of concentrated ammonia water (mass concentration 25%), and carry out hydrothermal stirring at 130 °C for 24 h, with a stirring rate of 500 r / min. The slurry obtained after hydrothermal treatment is dried in a spray dryer, with an inlet air temperature of 240 °C and an outlet air temperature of 100 °C. Figure 1 It is the XRD diffraction pattern of the obtained product, indicating that the product is pseudoboehmite with a relatively high crystallinity; Figure 2 It is the TEM image of the obtained product. The product is in the form of thin flakes and accumulates to form a pore structure. The Na2O content of the obtained product is 0.0004 wt.%, the Fe2O3 content is 0.0032 wt.%, the SiO2 content is 0.0056 wt.%, and the peptization index is 98.4%. The pore volume of the alumina obtained by calcination at 550 °C for 3 h is 0.78 mL / g.

[0025] Comparative Example 1

[0026] The conditions and parameters are the same as those in Example 1, but 3 g of concentrated ammonia water is not added to the hydrothermal crystallization agent. The pore volume of the alumina obtained by vacuum drying the sample after hydrolysis and calcining at 550 °C for 3 h is 1.29 mL / g. The pore volume of the alumina obtained by calcining the final product at 550 °C for 3 h is 0.49 mL / g. This shows that ammonia plays a role in controlling the growth and stacking structure of boehmite microcrystals, so the obtained boehmite has a larger pore volume.

[0027] Comparative Example 2

[0028] The conditions and parameters are the same as those in Example 1, but the hydrothermal crystallization agent consists of 540 g of deionized water and 60 g of concentrated ammonia water. The peptization index of the final product is 99.4%, and the pore volume of the alumina obtained by calcining at 550 °C for 3 h is 0.45 mL / g. This shows that it is not the low-boiling-point characteristic of ammonia that makes it a pore-forming agent. Only ammonia with an appropriate concentration can control the growth and stacking of boehmite microcrystals.

[0029] Comparative Example 3

[0030] The conditions and parameters are the same as those in Example 1, but the hydrothermal time is 12 h. The peptization index of the final product is 98.7%. The pore volume of the alumina obtained by calcining at 550 °C for 3 h is 0.58 mL / g. This also shows that it is not the low-boiling-point characteristic of ammonia that makes it a pore-forming agent. Appropriate microcrystal growth time is required to form large pores.

[0031] Example 2

[0032] Take 90 g of high-purity aluminum sheets (cut from high-purity aluminum with a purity of 99.99%) and rinse them with deionized water, then dry them in an oven at 80 °C for 4 h; put the dried aluminum sheets into a 1-L three-necked flask, add 360 g of isopropanol and 0.5 g of anhydrous aluminum trichloride to the three-necked flask. Heat and reflux the materials in the three-necked flask for 18 h; then pour the obtained product (crude aluminum isopropoxide) from the three-necked flask through a 100-mesh sieve into a 1-L three-necked flask. The remaining hydrolysis, hydrothermal and drying conditions and parameters are the same as those in Example 1. The Na2O content of the obtained product is 0.0005 wt.%, the Fe2O3 content is 0.0012 wt.%, the SiO2 content is 0.002 wt.%, and the peptization index is 98.6%. The pore volume of the alumina obtained by calcining at 550 °C for 3 h is 0.77 mL / g.

[0033] Example 3

[0034] Take 30 g of aluminum sheets (cut from high-purity aluminum with a purity of 99.99%), rinse them with deionized water, and then dry them in an oven at 80 °C for 4 h. Put the dried aluminum sheets into a 1-L three-necked flask, add 480 g of isooctanol and 0.5 g of anhydrous aluminum trichloride to the three-necked flask. Heat the materials in the three-necked flask and reflux for 12 h. Then pour the obtained product (crude aluminum isooctylate) from the three-necked flask through a 100-mesh sieve into a 2-L three-necked flask. Under a 90 °C water bath and mechanical stirring (120 r / min), introduce 600 mL of deionized water into the three-necked flask, use a peristaltic pump for feeding, and the feeding rate is 15 mL / min. After the feeding is completed, continue stirring for 6 h, then centrifuge the slurry at a centrifugation rate of 6000 r / min, remove the upper clear liquid, and add deionized water and 1.5 g of concentrated ammonia water to the lower material to prepare a slurry with a slurry mass of 600 g. The remaining hydrothermal and drying conditions are the same as those in Example 1. The Na2O content of the obtained product is 0.0005 wt.%, the Fe2O3 content is 0.0012 wt.%, the SiO2 content is 0.0026 wt.%, and the peptization index is 98.2%. The pore volume of the alumina obtained by calcination at 550 °C for 3 h is 0.82 mL / g.

[0035] Example 4

[0036] The conditions and parameters are the same as those in Example 3, but the temperature of the stirring hydrothermal treatment is 220 °C. The Na2O content of the obtained product is 0.0003 wt.%, the Fe2O3 content is 0.0016 wt.%, the SiO2 content is 0.0027 wt.%, and the peptization index is 97.2%. The pore volume of the alumina obtained by calcination at 550 °C for 3 h is 0.76 mL / g.

[0037] Example 5

[0038] The conditions and parameters are the same as those in Example 3, but add deionized water and 3 g of concentrated ammonia water to the lower material to prepare a 1200-g slurry, and carry out stirring hydrothermal treatment in a 2-L hydrothermal autoclave. The Na2O content of the obtained product is 0.0004 wt.%, the Fe2O3 content is 0.0014 wt.%, the SiO2 content is 0.0023 wt.%, and the peptization index is 98.6%. The pore volume of the alumina obtained by calcination at 550 °C for 3 h is 0.98 mL / g.

Claims

1. A method for preparing high-purity pseudo-boehmite with large pore volume and high peptization, characterized in that: Here are the steps: Step 1. Mix metal aluminum, alcohol and catalyst and reflux for 2 to 24 hours to obtain crude aluminum alkoxide, and purify the crude aluminum alkoxide to obtain liquid aluminum alkoxide; Step 2. The liquid aluminum alkoxide obtained in step 1 is stirred and mixed with water at 75 to 95° C. for hydrolysis, and the stirring is continued for 2 to 12 hours after mixing, and then the alcohol produced by the hydrolysis is separated and recovered; Step 3. The pseudo-boehmite or pseudo-boehmite wet material obtained in step 2 is mixed and stirred with an aqueous crystallization liquid to prepare a pseudo-boehmite slurry, and then stirred and hydrothermaled at 105 to 250° C. for 16 to 48 hours to obtain a pseudo-boehmite slurry; Step 4. Dry the pseudo-boehmite slurry obtained in step 3, and the obtained product is macroporous, highly peptized, and highly pure pseudo-boehmite.

2. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The metallic aluminum described in step 1 is raw aluminum or high-purity aluminum refined from raw aluminum and processed into aluminum ingots, aluminum blocks, aluminum grains, aluminum beans, and aluminum sheets.

3. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The alcohol in step 1 is one of isopropanol, sec-butyl alcohol and isooctyl alcohol.

4. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The catalyst in step 1 is an aluminum alkoxide self-catalyst or anhydrous aluminum chloride.

5. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The crude aluminum alkoxide described in step 1 is purified by vacuum distillation or filtration.

6. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The molar ratio of the aluminum alkoxide to water in step 2 is 1:3 to 1:

100.

7. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: The crystallization liquid described in step 3 is a mixture of water and a crystallization aid, and the crystallization aid is one of ammonium carbonate, ammonium bicarbonate, ammonium citrate, ammonia, choline, diethanolamine, and triethanolamine; the mass ratio of the crystallization aid to water is less than 1:

50.

8. The method for preparing high-purity pseudo-boehmite with large pore volume and high peptization according to claim 1, characterized in that: In the pseudo-boehmite slurry prepared in step 3, the mass content of aluminum oxide is 5-15%.

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