Preparation method of high-purity neutral flaky aluminum sol

Abstract

The invention discloses a preparation method of high-purity neutral flaky aluminum sol. The method adopts a specific composite organic acid as a dispersing agent, and comprises the following steps: (1) uniformly mixing and stirring pseudo-boehmite, the composite organic acid dispersing agent and a solvent, and heating and stirring under a heat preservation condition to obtain crude aluminum sol; (2) drying the crude aluminum sol in a spray drying manner to obtain dry gel; and (3) uniformly mixing the xerogel with a solvent, stirring under a heat preservation condition, and centrifugally removing impurities to obtain the aluminum sol. According to the preparation method, the malic acid and citric acid composite organic acid is adopted as the dispersing agent, and compared with a common inorganic acid dispersing agent in the prior art, the acid content of the aluminum sol is effectively reduced, so that the pH value of the product reaches a neutral range, and corrosion to equipment and pollution to the environment are reduced. The prepared aluminum sol is high in purity (greater than or equal to 99.5%), colloidal particles of the aluminum sol are of a regular sheet structure, the fluidity can be kept for more than 3 months at room temperature, and the problem of poor stability of the existing high-concentration aluminum sol is solved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional material preparation technology, specifically relating to a method for preparing high-purity neutral flake aluminum sol. Background Technology

[0002] Aluminum sol, as an important inorganic fine chemical, is widely used in catalyst supports, fine ceramic binders, and nano-coating materials due to its unique positive charge, good flowability, and strong binding properties. With the continuous expansion of industrial applications, the performance requirements for aluminum sol are increasing, especially the urgent need for high-purity aluminum sol with neutral pH and specific morphology.

[0003] In existing technologies, methods for preparing aluminum sol mainly include aluminum salt precipitation-acid hydrolysis, boehmite acid hydrolysis, and aluminum alkoxide hydrolysis-acid hydrolysis. However, these methods have many drawbacks: aluminum sol prepared by the aluminum acid hydrolysis method has a high acid content and strong corrosiveness, and produces a lot of acidic gases through thermal decomposition; aluminum sols obtained by the aluminum salt precipitation-acid hydrolysis method and the boehmite acid hydrolysis method have poor stability when the Al2O3 content is higher than 20wt%, making it difficult to maintain fluidity for a long time; aluminum sols prepared by existing methods are mostly acidic, and the preparation of neutral aluminum sols is difficult, and the purity is difficult to meet the requirements of high-end applications. For example, Chinese patent CN118771424A discloses a method for preparing low-acid, high-concentration stable aluminum sol, which uses boehmite and a single inorganic acid to treat and obtain aluminum sol. Its disadvantages are that the pH cannot reach the neutral range, the acid residue limits its application, and it lacks the ability to control the morphology of the colloidal particles, making it impossible to form a regular sheet-like structure. Chinese patent CN112744848A discloses a production process for aluminum sol, which includes: (1) making a first aluminum source and a first alkali source into a first contact to obtain a first reaction solution; (2) making the first reaction solution, a second aluminum source, and a second alkali source into a second contact to obtain a second reaction solution; (3) aging the second reaction solution to obtain a salt-containing aluminum sol; (4) performing ordinary electrodialysis on the salt-containing aluminum sol to obtain aluminum sol and recovered salt; (5) performing bipolar membrane electrodialysis on the recovered salt, etc. The disadvantage is that the reaction steps are complex, multiple reactants need to be introduced, and the preparation cost is high.

[0004] In addition, the dispersants commonly used in the prior art are mostly inorganic acids such as nitric acid and hydrochloric acid. There are no reports on technical solutions for preparing high-purity neutral flake aluminum sol using organic acids, especially complex organic acids, as dispersants.

[0005] Therefore, developing a method for preparing high-purity, neutral, stable aluminum sol with a specific flake morphology is of great significance for expanding the application fields of aluminum sol. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing high-purity, neutral, sheet-like aluminum sol. This method uses a specific composite organic acid as a dispersant and, through optimized preparation processes, obtains a high-purity, neutral, and highly stable sheet-like aluminum sol.

[0007] According to one aspect of the present invention, an object of the present invention is to provide a method for preparing high-purity neutral flake aluminum sol, comprising the following steps:

[0008] (1) Preparation of crude aluminum sol: Boehmite is mixed with composite organic acid dispersant and solvent and stirred evenly. The mixture is heated and stirred at 60~180℃ for 3~10h to obtain crude aluminum sol.

[0009] (2) Preparation of dry gel: The crude aluminum sol obtained in step (1) is dried by spray drying to obtain dry gel;

[0010] (3) Preparation of refined aluminum sol: The dry gel obtained in step (2) is mixed evenly with the solvent and stirred for 2-8 hours under the condition of keeping warm at 40-120℃. After centrifugation to remove impurities, aluminum sol is obtained.

[0011] Preferably, the composite organic acid dispersant in step (1) is a mixture of malic acid and citric acid, with a molar ratio of 1:0.1 to 1:1.5, more preferably 1:0.3 to 1:0.8.

[0012] Preferably, the molar ratio of pseudoboehmite to composite organic acid dispersant in step (1) is 1:0.01 ~ 1:1.0, more preferably 1:0.05 ~ 1:0.5.

[0013] Preferably, the mass ratio of boehmite to solvent in step (1) is 1:2 to 1:20, more preferably 1:4 to 1:7.

[0014] Preferably, the solvent in step (1) is a mixture of deionized water and ethanol, with a mass ratio of 1:1 to 10:1, and more preferably 2:1 to 5:1.

[0015] Preferably, the solvent in step (1) further includes 1% to 3% of glycerol by total mass, more preferably 1% to 1.5%.

[0016] Preferably, the feed inlet temperature of the spray drying method in step (2) is 220~450℃, more preferably 300~380℃.

[0017] Preferably, the outlet temperature of the spray drying method in step (2) is 70~120℃, more preferably 95~110℃.

[0018] Preferably, the conditions for centrifugation to remove impurities in step (3) are: centrifugation speed of 5000~6000 r / min and centrifugation time of 15~20 min.

[0019] According to one aspect of the present invention, an object of the present invention is to provide a high-purity neutral flake aluminum sol, wherein the Al2O3 content is 25wt%~32wt%, the pH is 6.0~7.0, the average particle size is 35~60nm, the sol retains its fluidity at room temperature for more than 3 months, preferably 3 to 9 months, and the purity is ≥99.5%, with Al element mainly in the form of Al2O3. 13 It exists in the form of a monomer with an aluminum content of ≤5%, and the granules have a regular sheet-like structure with an aspect ratio of 1:1 to 5:1, more preferably 1:1 to 3:1, and even more preferably 1:1 to 2.5:1.

[0020] Beneficial effects

[0021] This invention uses a composite organic acid of malic acid and citric acid as a dispersant. Compared with the inorganic acid dispersants commonly used in existing technologies, this effectively reduces the acid content of the aluminum sol, bringing the product's pH to a neutral range and reducing equipment corrosion and environmental pollution. The prepared aluminum sol has high purity (≥99.5%), with Al element mainly in the form of Al. 13 It exists in a low-monomer aluminum content form with excellent bonding properties, effectively preserving the pore volume of the catalyst when used as a catalyst support. The aluminum sol particles have a regular, plate-like structure with unique morphological characteristics, showing potential application value in fields such as nano-coatings. The product has a high concentration, good stability, and can maintain its fluidity for more than 3 months at room temperature, solving the problem of poor stability in existing high-concentration aluminum sols. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 Transmission electron microscope image showing the high-purity neutral flake aluminum sol prepared according to Example 1.

[0024] Figure 2 This is a particle size distribution diagram showing the high-purity neutral flake aluminum sol prepared according to Example 1. Detailed Implementation

[0025] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0026] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0027] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0028] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0029] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover a range from 39.50 to 40.49.

[0030] This application employs a malic acid-citric acid composite organic acid dispersant, wherein malic acid is a dibasic weak acid and citric acid is a tribasic weak acid, and their pKa ranges highly match the target pH (6.0~7.0). The synergistic effect of these two substances provides a mild H+ dispersant. + This allows for the gradual protonation of interlayer hydroxyl groups in boehmite, avoiding particle aggregation caused by the "instantaneous strong protonation" of inorganic acids. The tricarboxylic acid structure can interact with Al... 3+ The formation of a stable six-membered ring chelate, with the dicarboxyl group of malic acid assisting in bridging and dispersion, together form a dual "chelation-dispersion" effect, making the aluminum sol particles (average particle size 35~60nm) more stable.

[0031] In addition, in step (1) of the preparation method of the present invention, the solvent may further include a small amount of glycerol. Glycerol has moderate viscosity, and adding a small amount can appropriately increase the viscosity of the mixed solvent. This mild viscosity increase can slow down the settling rate of the boehmite particles during the dispersion process, prolong the interaction time between the composite organic acid dispersant and the hydroxyl groups on the particle surface, avoid particle agglomeration caused by excessively high local concentrations, and lay the foundation for the subsequent formation of uniform sheet-like particles. The polyhydroxy structure in the glycerol molecule can form a hydrogen bond network with malic acid and citric acid, indirectly regulating the H in the system. + The release rate. Compared to a single water-ethanol solvent, the addition of glycerol results in a milder and more uniform protonation of the complex organic acids, preventing the destruction of interlayer hydroxyl groups in boehmite by "instantaneous strong protonation," ensuring the integrity of the colloidal structure, and simultaneously promoting the release rate of Al. 13 Cluster formation and stability.

[0032] In the preparation method according to the present invention, step (2) employs spray drying, with an inlet temperature of 220~450℃, more preferably 300~380℃; preferably, the outlet temperature of the spray drying in step (2) is 70~120℃, more preferably 95~110℃. Since this application uses a malic acid-citric acid composite organic acid dispersant, its thermal decomposition temperature is approximately 150~200℃. An inlet temperature of 300~380℃ ensures rapid drying of droplets in the high-temperature zone (short residence time, usually <10s), avoiding excessive decomposition of the dispersant. At the same time, high temperature promotes rapid film formation on the droplet surface, reducing the loss of effective components. The outlet temperature of 95~110℃ ensures that the final water content of the dry gel is controlled below 5%, and avoids excessively high temperature leading to excessive hardness of the dry gel particles, affecting subsequent redispersibility with the solvent.

[0033] In the high-purity neutral flake aluminum sol prepared by the method according to the present invention, Al element is mainly in the form of Al. 13 It exists in the form of a single aluminum content ≤5%, the so-called "Al" 13 "Form" refers to the aluminum element in aluminum sol as a thiol aluminum oxide cluster cation (commonly referred to in the industry as "Al"). 13 The "cluster" form is a key active species in aluminum sol with specific chemical structures and excellent properties.

[0034] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0035] Example 1

[0036] 100g of boehmite (Al2O3 content 75%) was mixed with 18g of composite organic acid dispersant (12g of malic acid and 6g of citric acid, molar ratio 1:0.35) and 500g of solvent (350g of deionized water and 150g of ethanol, mass ratio 7:3). The mixture was stirred at 300r / min and heated and stirred at 120℃ for 6h to obtain crude aluminum sol.

[0037] The crude aluminum sol was spray-dried at an inlet temperature of 350°C and an outlet temperature of 100°C to obtain a dry gel.

[0038] Take 90g of dry gel and mix it with 225g of solvent (157.5g of deionized water and 67.5g of ethanol, with a mass ratio of about 7:3). Stir at 80℃ for 4h and centrifuge at 5500r / min for 18min to remove impurities to obtain aluminum sol product.

[0039] Testing revealed that the aluminum sol contained 28 wt% Al₂O₃, had a pH of 6.5, an average particle size of 45 nm, and a purity of 99.7%. It maintained good fluidity even after being left at room temperature for three months. The Al element was primarily Al₂O₃. 13 The proportion of the form is 85%, the monomer aluminum content is 3%, the granules have a plate-like structure, and the aspect ratio is about 1.2:1.

[0040] Example 2

[0041] 100g of pseudoboehmite (Al2O3 content 75%) was mixed with 16g of composite organic acid dispersant (11g of malic acid and 5g of citric acid, molar ratio 1:0.32) and 400g of solvent (267g of deionized water and 133g of ethanol, mass ratio approximately 2:1). The mixture was stirred at a speed of 300r / min and heated and stirred at 100℃ for 8h to obtain crude aluminum sol.

[0042] The crude aluminum sol was spray-dried at an inlet temperature of 320°C and an outlet temperature of 95°C to obtain a dry gel.

[0043] Take 90g of dry gel and mix it with 200g of solvent (133g of deionized water and 67g of ethanol, mass ratio 2:1). Stir at 60℃ for 6 hours and centrifuge at 5000r / min for 20 minutes to remove impurities to obtain aluminum sol product.

[0044] Testing revealed that the aluminum sol contained 25 wt% Al₂O₃, had a pH of 6.2, an average particle size of 38 nm, and a purity of 99.5%. It maintained good fluidity even after being left at room temperature for three months. The Al element was primarily Al₂O₃. 13 The proportion of the form is 82%, the monomer aluminum content is 4%, the granules have a plate-like structure, and the aspect ratio is 1.4:1.

[0045] Example 3

[0046] 100g of boehmite (75% Al2O3 content) was mixed with 23.2g of composite organic acid dispersant (13.2g of malic acid and 10g of citric acid, molar ratio 1:0.53) and 600g of solvent (429g of deionized water and 171g of ethanol, mass ratio approximately 5:2). The mixture was stirred at 300r / min and heated and stirred at 150℃ for 4h to obtain crude aluminum sol.

[0047] The crude aluminum sol was spray-dried at an inlet temperature of 370°C and an outlet temperature of 105°C to obtain a dry gel.

[0048] Take 90g of dry gel and mix it with 250g of solvent (179g of deionized water and 71g of ethanol, mass ratio 5:2). Stir at 100℃ for 3h and centrifuge at 6000r / min for 15min to remove impurities to obtain aluminum sol product.

[0049] Testing revealed that the aluminum sol contained 31 wt% Al₂O₃, had a pH of 6.8, an average particle size of 52 nm, and a purity of 99.6%. It maintained good fluidity even after being left at room temperature for three months. The Al element was primarily Al₂O₃.13 The proportion of the form is 88%, the monomer aluminum content is 2%, the granules have a plate-like structure, and the aspect ratio is 1.6:1.

[0050] Example 4

[0051] The aluminum sol product was prepared in the same manner as in Example 1, except that 507.5g of solvent (350g of deionized water, 150g of ethanol, and 7.5g of glycerol (approximately 1.47% of the total solvent weight), with a deionized water to ethanol mass ratio of 7:3).

[0052] Testing revealed that the aluminum sol contained 32 wt% Al₂O₃, had a pH of 6.5, an average particle size of 47 nm, and a purity of 99.7%. It maintained good fluidity even after being left at room temperature for three months. The Al element was primarily Al₂O₃. 13 The proportion of the form is 85%, the monomer aluminum content is 3.1%, the granules have a plate-like structure, and the aspect ratio is about 1.05:1.

[0053] Comparative Example 1

[0054] 100g of boehmite (Al2O3 content 75%) was mixed with 4.5g of nitric acid and 500g of deionized water, stirred at 300r / min, and heated and stirred at 120℃ for 6h to obtain crude aluminum sol.

[0055] The crude aluminum sol was spray-dried at an inlet temperature of 350°C and an outlet temperature of 100°C to obtain a dry gel.

[0056] Mix 90g of dry gel with 225g of deionized water, stir at 80℃ for 4h, and centrifuge at 5500r / min for 18min to remove impurities to obtain aluminum sol product.

[0057] Testing revealed that the aluminum sol contained 26 wt% Al₂O₃, had a pH of 3.2, an average particle size of 85 nm, and a purity of 98.2%. After being left at room temperature for 20 days, its fluidity significantly decreased, and the Al element was primarily Al₂O₃. 13 The proportion of the form is 60%, the monomer aluminum content is 15%, and the granules have an irregular block structure.

[0058] Comparative Example 2

[0059] 100g of boehmite (Al2O3 content 75%) was mixed with 4.5g of hydrochloric acid and 500g of deionized water, stirred at 300r / min, and heated and stirred at 120℃ for 6h to obtain crude aluminum sol.

[0060] The crude aluminum sol was spray-dried at an inlet temperature of 350°C and an outlet temperature of 100°C to obtain a dry gel.

[0061] Mix 90g of dry gel with 225g of deionized water, stir at 80℃ for 4h, and centrifuge at 5500r / min for 18min to remove impurities to obtain aluminum sol product.

[0062] Testing revealed that the aluminum sol contained 25 wt% Al₂O₃, had a pH of 2.8, an average particle size of 92 nm, and a purity of 97.8%. It exhibited gelation after being left at room temperature for 15 days. The Al element was primarily Al₂O₃. 13 The proportion of the form is 55%, the monomer aluminum content is 18%, and the granules have an irregular particle structure.

[0063] Comparative Example 3

[0064] 100g of boehmite (Al2O3 content 75%) was mixed with 22.5g of a single organic acid (malic acid) and 500g of solvent (350g of deionized water and 150g of ethanol, mass ratio 7:3). The mixture was stirred at 300r / min and heated and stirred at 120℃ for 6h to obtain crude aluminum sol.

[0065] The crude aluminum sol was spray-dried at an inlet temperature of 350°C and an outlet temperature of 100°C to obtain a dry gel.

[0066] Take 90g of dry gel and mix it with 225g of solvent (350g of deionized water and 150g of ethanol, mass ratio 7:3). Stir at 80℃ for 4h and centrifuge at 5500r / min for 18min to remove impurities to obtain aluminum sol product.

[0067] Testing revealed that the aluminum sol contained 24 wt% Al₂O₃, had a pH of 5.7, an average particle size of 78 nm, and a purity of 98.5%. After being left at room temperature for one month, its fluidity decreased, and the Al element was mainly composed of Al₂O₃. 13 The proportion of the form is 70%, the monomer aluminum content is 10%, and the granules have a mixed structure of sheet and block.

[0068] 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 neutral flake aluminum sol, comprising the following steps: (1) Preparation of crude aluminum sol: Boehmite is mixed with composite organic acid dispersant and solvent and stirred evenly. The mixture is heated and stirred at 60~180℃ for 3~10h to obtain crude aluminum sol. (2) Preparation of dry gel: The crude aluminum sol obtained in step (1) is dried by spray drying to obtain dry gel; (3) Preparation of refined aluminum sol: The dry gel obtained in step (2) is mixed evenly with the solvent and stirred for 2-8 hours under the condition of keeping warm at 40-120℃. After centrifugation to remove impurities, aluminum sol is obtained.

2. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, The composite organic acid dispersant mentioned in step (1) is a mixture of malic acid and citric acid, with a molar ratio of 1:0.1 to 1:1.5, more preferably 1:0.3 to 1:0.

8.

3. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, In step (1), the molar ratio of pseudoboehmite to composite organic acid dispersant is 1:0.01 ~ 1:1.0, more preferably 1:0.05 ~ 1:0.

5.

4. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, In step (1), the mass ratio of boehmite to solvent is 1:2 to 1:20, more preferably 1:4 to 1:

7.

5. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, The solvent in step (1) is a mixture of deionized water and ethanol, with a mass ratio of 1:1 to 10:1, more preferably 2:1 to 5:

1. More preferably, the solvent also includes 1% to 3% of glycerol by total mass, more preferably 1% to 1.5%.

6. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, The feed inlet temperature for the spray drying method described in step (2) is 220~450℃, more preferably 300~380℃.

7. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, The outlet temperature of the spray drying method described in step (2) is 70~120℃, more preferably 95~110℃.

8. The method for preparing high-purity neutral flake aluminum sol according to claim 1, characterized in that, The conditions for centrifugation to remove impurities in step (3) are: centrifugation speed 5000~6000 r / min, centrifugation time 15~20 min.

9. A high-purity neutral flake aluminum sol prepared by the preparation method according to any one of claims 1 to 8, wherein, The Al₂O₃ content is 25wt%~32wt%, the pH is 6.0~7.0, the average particle size is 35~60nm, it can maintain fluidity at room temperature for more than 3 months, preferably 3 to 9 months, and the purity is ≥99.5%. The Al element is mainly Al₂O₃. 13 It exists in the form of a monomer with an aluminum content of ≤5%, and the granules have a regular sheet-like structure with an aspect ratio of 1:1 to 5:1, more preferably 1:1 to 3:1, and even more preferably 1:1 to 2.5:1.

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