Energy-saving preparation method of high-purity and high-crystallinity aluminum sol

Abstract

The application belongs to the technical field of inorganic functional material preparation, and discloses an energy-saving preparation method of high-purity and high-crystallinity aluminum sol. First, pseudo-boehmite powder prepared by an alcoholate method is mixed with deionized water, and hydrothermal crystallization treatment is performed to enrich the hydroxyl group on the surface of the pseudo-boehmite and improve the peptization performance of the pseudo-boehmite, so that high-crystallinity pseudo-boehmite slurry is obtained; then, an acid peptizing agent is added to the obtained slurry, and hydrothermal peptization treatment is performed, and the high-purity and high-crystallinity aluminum sol is obtained after cooling. The application adopts a two-step hydrothermal process of 'hydrothermal crystallization-hydrothermal peptization', and the drying step in the previous process is omitted, so that the energy consumption is greatly reduced. The particle size of the obtained aluminum sol is less than 100 nm, the Zeta potential is stably maintained at more than 30 mV, the colloidal stability is excellent, and no precipitation is generated after being placed for 6 months. The application has a wide process window, high controllability and high product purity, and is suitable for the fields of catalysis, ceramics, coating and lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional material preparation technology, and relates to an energy-saving preparation method for high-purity, high-crystallinity aluminum sol. Background Technology

[0002] Alumina sol (also known as alumina sol) is a stable colloidal system formed by positively charged hydrated alumina particles in an aqueous phase. It possesses characteristics such as high specific surface area, excellent adhesion, good thermal stability, and surface modifiability, and has wide applications in catalysis, ceramic manufacturing, textile fiber processing, coating, and new energy materials. (Note: The last part about boehmite appears to be unrelated and likely refers to another product or product.) ( ) is the main raw material for producing aluminum sol. The more surface-active hydroxyl groups there are, the more H is fixed. + With a high alkaline ratio, the alumina carrier prepared by this method exhibits a high sol-gel index, rapid gelation, and good wear resistance. Common methods for preparing boehmite include inorganic aluminum salt precipitation and aluminum alkoxide hydrolysis. Inorganic aluminum salt precipitation is prone to high levels of impurities such as sodium, limiting its application. Aluminum alkoxides have low boiling points and are easily purified (e.g., aluminum isopropoxide, aluminum sec-butoxide). Hydrolysis can produce high-purity boehmite, and the alcohols generated during hydrolysis are easily recovered. However, the alcohols generated from the hydrolysis of short-chain aluminum alkoxides are miscible with water. In the product system, boehmite exists in both the alcohol and aqueous solutions, and the surface hydroxyl groups compete with alkoxy groups, resulting in a low amount of surface hydroxyl groups and poor colloidal solubility. Long-chain aluminum alkoxides (which are difficult to purify) produce alcohols that are poorly soluble in water, leading to liquid stratification. In the product system, boehmite exists in the aqueous layer, and the amount of surface hydroxyl groups in the boehmite is high, resulting in good colloidal solubility. Crude boehmite, obtained from the hydrolysis of short-chain aluminum alkoxides, can also be enriched with hydroxyl groups through hydrothermal treatment, improving its crystallinity and colloidal solubility (Inorganic Salts Industry, 2022, 54, 54). CN114702053A discloses a steam-assisted method for enriching the surface of boehmite with hydroxyl groups. Crude boehmite is prepared by hydrolysis of aluminum alkoxides, and then contacted with steam in a high-pressure reactor at 100℃–160℃ for 1–6 h. This process enriches the surface of the boehmite with active hydroxyl groups, improving its colloidal solubility. This method solves the problem of high energy consumption in drying the product after hydrothermal treatment, but it is not easy to operate industrially and is currently not suitable for large-scale production. Furthermore, recent research progress indicates that aluminum sol made from highly crystalline boehmite after hydrothermal treatment exhibits enhanced performance in applications such as lithium batteries. To address the issues of low crystallinity and poor colloidal solubility of crude boehmite prepared by the alkoxide method, and the high energy consumption associated with preparing alumina sol from high-crystallinity boehmite prepared by hydrothermal treatment, this invention proposes a novel method for preparing alumina sol by hydrothermal crystallization of crude boehmite followed by hydrothermal preparation of the slurry with added acid. This method boasts low energy consumption, high purity and crystallinity of the product, small particle size, and excellent stability, making it of significant industrial application value. Summary of the Invention

[0003] Through long-term experiments, the inventors of this application discovered that the pseudoboehmite generated by the hydrolysis of aluminum alkoxides has a low number of surface active hydroxyl groups and a low colloidal index. Hydrothermal treatment can enrich the surface of the pseudoboehmite with hydroxyl groups and improve its crystallinity and colloidal solubility, but drying the filter cake or slurry consumes a lot of energy. In view of this practical situation, this invention proposes an energy-saving preparation method for directly preparing aluminum sol by hydrothermal crystallization followed by hydrothermal colloidal treatment, obtaining high-purity, high-crystallinity aluminum sol. This invention provides the following technical solution:

[0004] An energy-saving preparation method for high-purity, high-crystallinity aluminum sol includes the following steps:

[0005] Step 1. Aluminum alkoxide is hydrolyzed and dried to prepare boehmite powder. The boehmite powder is mixed with deionized water and stirred evenly. Then it is transferred to a high-pressure reactor for hydrothermal crystallization treatment to obtain a highly crystalline boehmite slurry.

[0006] Step 2. Add a gelling agent to the high-crystallinity pseudo-boehmite slurry obtained in Step 1, stir evenly, and then transfer it to a high-pressure reactor for hydrothermal gelation treatment. After the reaction is completed, cool it, centrifuge to remove impurities, and obtain a high-purity, high-crystallinity aluminum sol.

[0007] In step 1, the aluminum alkoxide is one or a mixture of two or more of aluminum isopropoxide, aluminum sec-butoxide, and aluminum isooctoxide.

[0008] In step 1, the temperature of the hydrothermal crystallization treatment is 100~300 ℃, preferably 120~160 ℃; the time of the hydrothermal crystallization treatment is 2~24 h, preferably 3~6 h.

[0009] In step 1, the mass ratio of the pseudoboehmite powder to deionized water is 1:3 to 1:6.

[0010] In step 2, the temperature of the hydrothermal sol-gel treatment is 100~180℃, preferably 140~160℃; the time of the hydrothermal sol-gel treatment is 1~12 h, preferably 2~6 h.

[0011] In step 2, the adhesive solvent is one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, benzenesulfonic acid, and p-toluenesulfonic acid; the molar ratio of aluminum acid is 0.01~0.1, preferably 0.015~0.03.

[0012] The beneficial effects of this invention are as follows: This invention utilizes a two-step hydrothermal process of "hydrothermal crystallization-hydrothermal sol," eliminating the drying step in previous processes and significantly reducing energy consumption. The resulting aluminum sol has a particle size of less than 100 nm, a stable zeta potential above 30 mV, and excellent colloidal stability, showing no precipitation after 6 months of storage. This invention offers a wide process window, strong controllability, and high product purity, making it suitable for applications in catalysis, ceramics, coating, and lithium batteries. Attached Figure Description

[0013] Figure 1 The images show the XRD patterns of dried samples from specific embodiments and comparative examples.

[0014] Figure 2 This is a TEM image of the sample from Example 1.

[0015] Figure 3 The image shows a TEM image of sample 2 (Comparative Example 2).

[0016] Figure 4 The image shows a TEM image of sample 3 for comparison example.

[0017] Figure 5 The image shows a TEM image of sample 4, which is a comparative example.

[0018] Figure 6 This is a TEM image of the sample from Example 2.

[0019] Figure 7 This is a TEM image of the sample from Example 3. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings and technical solutions.

[0021] Example 1

[0022] Add 64.5 mL of deionized water to a polytetrafluoroethylene (PTFE) liner, place a magnetic stir bar, and set the rotation speed to 200 r / min. Add 15.5 g of pseudoboehmite powder (alumina content approximately 72%) obtained from the hydrolysis of aluminum isopropoxide to the liner, stir evenly, and then transfer to a 100 mL high-pressure reactor. Set the temperature to 160℃ and the time to 3 h. Add concentrated nitric acid to the hydrothermated slurry to adjust the acid-aluminum molar ratio to approximately 0.022, stir evenly, and then transfer to a 100 mL high-pressure reactor. Set the temperature to 140℃ and the time to 2 h, and the rotation speed to 200 r / min. After hydrothermal treatment, remove the colloid and centrifuge at 6000 r / min for 10 min. Collect the supernatant as aluminum sol (precipitate content less than 2%). The XRD pattern of the dried aluminum sol product is shown below. Figure 1 As shown, it is evident that the diffraction peaks of the sample in Example 1 are stronger than those of the raw material; in contrast, the XRD diffraction peaks of the raw material are very weak, which is a typical XRD pattern of boehmite, indicating that it is a poorly crystallized and incomplete boehmite. After hydrothermal treatment and sol-gel, the diffraction peaks of the product become significantly stronger, proving that it is a highly crystalline boehmite. TEM images are shown below. Figure 2 The product exhibits a typical lamellar structure with clear microcrystal edges, indicating high crystallinity and good dispersibility.

[0023] The obtained aluminum sol had an average particle size of 72 nm, a Zeta potential of 35.2 mV, a pH of 3.48, and good colloidal stability, with no precipitation after 6 months of storage. ICP analysis showed that the Na content in the dried aluminum sol powder was less than 10 ppm, the Fe content was less than 20 ppm, and the Si content was less than 30 ppm.

[0024] The process for preparing pseudoboehmite by hydrolysis of aluminum isopropoxide is as follows: 60 g of aluminum granules (processed from industrial aluminum ingots, purity 99.7%) were washed with ethanol and then dried in an 80℃ forced-air drying oven for 4 h. The dried aluminum granules were placed in a 1 L three-necked flask, and 400 g of isopropanol and 10 g of aluminum isopropoxide (catalyst) were added to the flask. The material in the three-necked flask was heated and refluxed for 4 h. Subsequently, vacuum distillation was performed, with the system pressure controlled below 0.005 MPa and the liquid temperature controlled between 180 and 200℃. The distillate was collected, and the distillate was aluminum isopropoxide. Take 408 g of freshly prepared liquid aluminum isopropoxide by vacuum distillation and add it to a 1 L three-necked flask. Under mechanical stirring (200 r / min) in an 80 °C water bath, add 125 g of deionized water to the three-necked flask containing aluminum isopropoxide. Use a peristaltic pump to add water at a rate of 4 mL / min. After the water is added, continue stirring for 4 h and then transfer the product to a vacuum drying oven. Dry it under vacuum at 60 °C for 6 h. The resulting boehmite is then pulverized and set aside for later use.

[0025] Comparative Example 1

[0026] Add 64.5 mL of deionized water to a polytetrafluoroethylene liner, place a magnetic stir bar, and set the rotation speed to 200 r / min. Add 15.5 g of pseudoboehmite powder (prepared in the same way as in Example 1) to the liner, stir evenly, and then add concentrated nitric acid at an acid-aluminum ratio of 0.022. Stir and gel at room temperature for 2 h, then remove and centrifuge at 6000 r / min for 10 min to obtain aluminum sol.

[0027] Testing revealed that the obtained aluminum sol contained a large amount of sediment, with a colloidal index of only 91.9%, indicating incomplete collation and failing to meet application requirements. Figure 1 It can be seen that the XRD diffraction peaks of the crude boehmite (raw material and Comparative Example 1) are very weak, and its crystallinity is very poor compared with other comparative examples and examples. The poor crystallinity results in its low colloidal index. In the XRD spectrum, Comparative Example 1 is the product after the raw material is acidified at room temperature and dried at high temperature. Because it has undergone high temperature hydration, the XRD diffraction peaks of the product of Comparative Example 1 are stronger than those of the raw material.

[0028] Comparative Example 2

[0029] The hydrothermal crystallization process was the same as in Example 1. After hydrothermal treatment, the slurry was dried in an oven at 80℃ for 12 h to obtain highly crystalline pseudoboehmite powder. 66.2 mL of deionized water was added to a beaker, a magnetic stir bar was placed inside, and the rotation speed was set to 200 r / min. 15 g of the dried powder was added to the beaker, stirred evenly, and then nitric acid was added to adjust the aluminum-aluminum molar ratio to approximately 0.022. The mixture was stirred at room temperature for 2 hours to gel, then centrifuged at 6000 r / min for 10 min to obtain aluminum sol (precipitate content less than 2%). The XRD pattern of the product is shown below. Figure 1 The strong diffraction peaks indicate its high crystallinity. Analysis showed that the obtained aluminum sol had an average particle size of 65 nm, a Zeta potential of 31.2 mV, and a pH of 3.58. TEM images are shown below. Figure 3 The microstructure of the product is basically the same as that in Example 1. This method proves that hydrothermal crystallization-drying of crude pseudoboehmite can prepare aluminum sol with high crystallinity, but the energy consumption is high after the drying process.

[0030] Comparative Example 3

[0031] The hydrothermal crystallization process was the same as in Example 1. Nitric acid was added to the hydrothermally crystallized slurry to adjust the aluminum-aluminum molar ratio to 0.022. The mixture was stirred at room temperature for 2 hours to achieve gelation. After centrifugation at 6000 r / min for 10 minutes, aluminum sol (precipitate content less than 2%) was obtained.

[0032] The obtained aluminum sol had an average particle size of 135 nm, a Zeta potential of 32.1 mV, and a pH of 3.32. TEM images are shown below. Figure 4 The microstructure is a typical lamellar structure, but the dispersibility is significantly weaker than that of Example 1. This indicates that without drying, directly dissolving the hydrothermally crystallized boehmite slurry at room temperature results in larger colloidal particles. This is because the surface of the boehmite particles in the slurry is encapsulated by water molecules, creating steric hindrance, making it difficult for H⁺ to attack active sites, resulting in insufficient dissolution and a aluminum sol particle size greater than 100 nm, limiting its application in many fields. In Example 1, hydrothermal dissolution promoted H⁺ attack on active sites, obtaining an aluminum sol with a colloidal particle size of less than 100 nm; in Comparative Example 2, the hydrothermally crystallized boehmite was dried, and although it was dispersed in water at room temperature, the water molecules failed to completely encapsulate the surface of the boehmite at low temperature and within a short time, resulting in insufficient H⁺ attack on active sites. + It is easier to attack active sites.

[0033] Comparative Example 4

[0034] Add 64.5 mL of deionized water to a polytetrafluoroethylene liner, place a magnetic stir bar, and set the rotation speed to 200 r / min. Add 15.5 g of pseudoboehmite powder (prepared in the same way as in Example 1) to the liner, stir evenly, and then add nitric acid to adjust the aluminum molar ratio to approximately 0.022. After stirring evenly, transfer the mixture to a 100 mL high-pressure reactor, set the temperature to 160℃, and the time to 3 h. After the reaction, centrifuge at 6000 r / min for 10 min to obtain aluminum sol (precipitate content less than 2%). Figure 1 In the XRD pattern, the diffraction peaks of the sample were significantly weaker than those of Example 1 and Comparative Example 2, indicating that the presence of acid inhibited the hydrothermal crystallization of boehmite.

[0035] The obtained aluminum sol had an average particle size of 179 nm, a Zeta potential of 15.1 mV, and a pH of 3.72. TEM images are shown below. Figure 5 The product still exhibits a typical lamellar structure, but with a large particle size and significant agglomeration. The resulting colloid shows obvious stratification after standing for one week, failing to meet application requirements. This method involves the high-temperature hydrothermal dissolution of crude boehmite with acid. The results demonstrate that hydrothermal crystallization of alkoxide-processed boehmite is a necessary condition for obtaining a highly crystalline and stable sol with a particle size below 100 nm.

[0036] Example 2

[0037] The process was essentially the same as in Example 1, except that the hydrothermal sol temperature was 160°C. The resulting aluminum sol had an average particle size of 65 nm, a Zeta potential of 34.5 mV, a pH of 3.35, and remained stable for more than 6 months. TEM images are shown below. Figure 6 It has a typical lamellar structure, good dispersibility, and relatively complete crystallization. Figure 1 The XRD pattern also confirmed that its crystallinity was significantly higher than that of the raw material.

[0038] Example 3

[0039] The process was essentially the same as in Example 1, except that the acid-to-aluminum ratio was 0.026. The resulting aluminum sol had an average particle size of 88 nm, a Zeta potential of 34.1 mV, a pH of 3.32, and remained stable for more than 6 months. TEM images are shown below. Figure 7 It has a typical lamellar structure, good dispersibility, and relatively complete crystallization. Figure 1 The XRD pattern also confirmed that its crystallinity was significantly higher than that of the raw material. With increased acidity, excessive H+... + It is easy to form "hydrogen bridges", which promotes the aggregation of colloidal particles. Therefore, the amount of acid needs to be strictly controlled according to the actual reaction conditions.

[0040] Example 4

[0041] The results were essentially the same as in Example 1, except that the pseudoboehmite was obtained by hydrolyzing aluminum sec-butoxide. The resulting aluminum sol had an average particle size of 63 nm, a Zeta potential of 37.5 mV, a pH of 3.62, and could be stably stored for more than 6 months.

[0042] The process for preparing pseudoboehmite by hydrolysis of sec-butanol is as follows: 100 g of commercially available aluminum sec-butoxide was added to a three-necked flask (500 mL). Under mechanical stirring (200 r / min) in a 90℃ water bath, 200 g of deionized water was added to the three-necked flask containing aluminum sec-butoxide. Water was added using a peristaltic pump at a rate of 4 mL / min. After the water addition was completed, stirring was continued for 4 h. The resulting slurry was then centrifuged at a speed of 6000 r / min. After centrifugation for 10 min, the supernatant was removed, and the precipitate was ultrasonically washed with water, followed by centrifugation for another 10 min (6000 r / min). The supernatant was then removed, and the precipitate was transferred to a forced-air drying oven and dried at 80℃ for 12 h. The resulting pseudoboehmite was then pulverized and set aside for later use.

[0043] Example 5

[0044] The results were essentially the same as in Example 1, except that the pseudoboehmite was obtained by hydrolyzing aluminum isooctanol. The resulting aluminum sol had an average particle size of 66 nm, a Zeta potential of 33.5 mV, a pH of 3.48, and could be stably stored for more than 6 months.

[0045] The process for preparing pseudoboehmite by hydrolysis of aluminum isooctanol is as follows: 10 g of high-purity aluminum block (purity 99.996%) was rinsed with ethanol and then dried in an oven at 80℃ for 4 h. The dried aluminum block was placed in a 500 mL three-necked flask, and 160 g of isooctanol and 1 g of aluminum isopropoxide (catalyst) were added to the flask. The material in the three-necked flask was heated and refluxed for 12 h. Then, the obtained product (crude aluminum isooctanol) was poured from the three-necked flask through a 100-mesh stainless steel sieve into a 500 mL three-necked flask. The aluminum isooctanol was continuously stirred at 200 r / min under a 95℃ water bath, while 150 g of deionized water was introduced using a peristaltic pump at a rate of 5 mL / min. After the water was added, stirring was continued for 4 h. The resulting mixture was centrifuged at 8000 r / min, and the supernatant was removed. The precipitate was transferred to a forced-air drying oven and dried at 80°C for 12 hours. The resulting pseudoboehmite was then pulverized and set aside for later use.

[0046] Example 6

[0047] Other conditions and parameters were the same as in Example 1, except that the pseudoboehmite used was commercially available high-purity pseudoboehmite (commonly known as SB powder, produced by the alkoxide method, with a Na content of less than 20 ppm) produced by Sasol GmbH, Germany; the resulting aluminum sol had an average particle size of 63 nm, a Zeta potential of 36.4 mV, and a pH of 3.37. Before hydrothermal treatment, the SB powder had a gel solubility index of over 99%, and the resulting sol had an average particle size of 55 nm when gelled at an acid-aluminum ratio of 0.03.

[0048] Example 7

[0049] Other conditions and parameters were the same as in Example 1, except that the boehmite used was commercially available domestic high-purity boehmite (produced by alkoxide method, Na content less than 20 ppm); the average particle size of the resulting aluminum sol was 67 nm, the Zeta potential was 35.7 mV, and the pH value was 3.57. Before hydrothermal treatment, the colloidal index of the high-purity boehmite was less than 90%. Based on an acid-aluminum ratio of 0.03, the average particle size of the resulting sol was 83 nm.

[0050] Comparative Example 5

[0051] Other conditions and parameters were the same as in Example 1, except that the boehmite used was commercially available domestic common boehmite (produced by carbonization method, Na content greater than 1000 ppm); the resulting product was a white slurry containing a large amount of precipitate. Before hydrothermal treatment, the colloidal index of commercially available common boehmite was over 99%, and the average particle size of the sol obtained was 45 nm according to an acid-aluminum ratio of 0.03; however, after hydrothermal treatment, the colloidal solubility of the product decreased significantly, indicating that impurities such as Na affected the hydrothermal crystallization of boehmite, resulting in poorer colloidal solubility of the product.

Claims

1. An energy-saving preparation method for high-purity, high-crystallinity aluminum sol, characterized in that, Includes the following steps: Step 1. Aluminum alkoxide is hydrolyzed and dried to prepare boehmite powder. The boehmite powder is mixed with deionized water and stirred evenly. Then it is transferred to a high-pressure reactor for hydrothermal crystallization treatment to obtain a highly crystalline boehmite slurry. Step 2. Add a gelling agent to the high-crystallinity pseudo-boehmite slurry obtained in Step 1, stir evenly, and then transfer it to a high-pressure reactor for hydrothermal gelation treatment. After the reaction is completed, cool it, centrifuge to remove impurities, and obtain a high-purity, high-crystallinity aluminum sol.

2. The energy-saving preparation method of high-purity, high-crystallinity aluminum sol according to claim 1, characterized in that, In step 1, the aluminum alkoxide is one or a mixture of two or more of aluminum isopropoxide, aluminum sec-butoxide, and aluminum isooctoxide.

3. The energy-saving preparation method of high-purity, high-crystallinity aluminum sol according to claim 1, characterized in that, In step 1, the temperature of the hydrothermal crystallization treatment is 100~300 ℃, and the time of the hydrothermal crystallization treatment is 2~24 h.

4. The energy-saving preparation method of high-purity, high-crystallinity aluminum sol according to claim 1, characterized in that, In step 1, the mass ratio of the pseudoboehmite powder to deionized water is 1:3 to 1:

6.

5. The energy-saving preparation method of high-purity, high-crystallinity aluminum sol according to claim 1, characterized in that, In step 2, the temperature of the hydrothermal sol-gel treatment is 100~180℃, and the time of the hydrothermal sol-gel treatment is 1~12 h, preferably 2~6 h.

6. The energy-saving preparation method of high-purity, high-crystallinity aluminum sol according to claim 1, characterized in that, In step 2, the adhesive solvent is one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, benzenesulfonic acid, and p-toluenesulfonic acid; the molar ratio of aluminum acid is 0.01~0.1.

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