Preparation method of high-purity aluminum sol, high-purity aluminum sol and application

Abstract

The invention belongs to the technical field of fine chemical engineering and new materials, and discloses high-purity aluminum sol as well as a preparation method and application thereof. Aiming at the problems of limited purity, high energy consumption and poor stability caused by multiple branches of a hydrolysis path in the prior art, aluminum isopropoxide and pseudo-boehmite are combined according to a specific ratio to form an aluminum source, and the molecular weight of the aluminum source is 1t; the method comprises the following steps: by using an organic amine catalyst with a molecular weight of 150 g / mol and pKa9-11, and combining pulse microwave energy input at the temperature of 50-70 DEG C, realizing directional regulation and control of a hydrolysis path by precisely regulating and controlling process parameters. The purity of the prepared alumina sol is greater than or equal to 99.999%, the impurity content is low, the particle size is uniform, the room-temperature storage stability is excellent, the process energy consumption is low, and the catalyst recovery rate is high. The aluminum sol can be widely applied to lithium battery ceramic diaphragm coatings, catalyst carriers and optical materials, can remarkably improve the performance of downstream products, and has outstanding creativity and industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals and new materials technology, specifically relating to a method for preparing high-purity aluminum sol, and also to the high-purity aluminum sol prepared by this method, as well as the application of the high-purity aluminum sol in lithium battery ceramic membrane coatings, catalyst supports and optical materials. Background Technology

[0002] High-purity aluminum sol, as a high-performance functional material, plays an irreplaceable role in many high-end fields such as lithium-ion battery ceramic separator coatings, LED phosphor carriers, catalyst carriers, and sapphire substrates. These applications place stringent requirements on the purity, particle size distribution, transparency, and long-term stability of aluminum sol, especially requiring extremely low levels of impurities such as Na, Fe, and Si. Currently, the mainstream methods for preparing aluminum sol in the industry mainly include aluminum alkoxide hydrolysis, boehmite acid hydrolysis, and aluminum hydroxide sol-gel method. In existing technologies, even by optimizing macroscopic parameters such as the acid / Al molar ratio and reaction temperature, or by using high-temperature hydrothermal processes, it is difficult to break through the upper limit of the purity of the prepared aluminum sol, and the purity varies greatly between batches; while the room-temperature acid hydrolysis method has the problem of even lower purity. The common defects of these methods stem from the multi-path competition mechanism in the aluminum source hydrolysis process: the main path is the ordered formation of Al-OH polymers, while the side paths form Al-OC residues or hybrids. Because the energy barrier of the side paths is lower, the side reactions occur preferentially, thus introducing trace impurities. Existing technologies can only be passively optimized through macroscopic parameters such as temperature, pH, and stirring time, and cannot actively intervene in the hydrolysis pathway branches at the molecular scale. This makes it difficult for the purity of aluminum sol to meet the requirements of high-end applications. At the same time, there are also problems such as high energy consumption, long process cycle, and insufficient product stability, which limit its further application in downstream high-end fields. Summary of the Invention

[0003] In view of this, the present invention proposes a method for preparing high-purity aluminum sol, which solves the problems of limited purity, insufficient stability and high energy consumption of aluminum sol in the prior art by precisely controlling the selection of raw materials, process parameters and reaction mechanism in the preparation process.

[0004] The technical solution of this invention is achieved as follows: This invention provides a method for preparing high-purity aluminum sol, comprising the following steps:

[0005] (1) Mix the aluminum source with deionized water and add acid to adjust the initial pH to 3-4; (2) Add an organic amine catalyst to carry out the hydrolysis reaction; (3) At a specific temperature, pulsed microwave energy input is applied to continuously perform hydrolysis reaction; (4) After hydrolysis, the pH is adjusted to a specific range, the catalyst is removed and the solution is concentrated to obtain high-purity aluminum sol.

[0006] In some embodiments, the aluminum source in step (1) is a mixture of aluminum isopropoxide and boehmite, wherein the aluminum isopropoxide has a purity of ≥99.9%, the boehmite has a particle size of <20μm, the mass ratio of the two is 70-90:10-30, and the mass ratio of water to aluminum source is 6:1-12:1.

[0007] Aluminum isopropoxide has a high purity base, which can reduce the introduction of initial impurities. Boehmite can help optimize the uniformity of the hydrolysis reaction through particle size control. When the two are mixed in a specific ratio, the purity baseline can be guaranteed by aluminum isopropoxide, while the dispersion of the reaction system can be adjusted by boehmite, avoiding the imbalance of reaction efficiency or purity caused by a single aluminum source. Limiting the mass ratio of water to aluminum source is to ensure that the hydrolysis reaction proceeds fully, while avoiding the problem of excessive water leading to increased energy consumption for subsequent concentration, or insufficient water causing incomplete local reaction and the formation of impurity aggregates.

[0008] In some embodiments, the acid in step (1) is nitric acid and / or acetic acid, H + The molar ratio with Al is 1:20-25.

[0009] Both nitric acid and acetic acid are mild acids that do not introduce additional metal impurities, and their acid strength is suitable for the hydrolysis requirements of the aluminum source; H is limited. + The specific molar ratio to Al is because excessive acid will exacerbate the side pathway reaction, leading to more impurities, while insufficient acid will fail to provide a suitable acidic environment for the hydrolysis reaction, affecting the orderly formation of Al-OH polymers in the main pathway. This ratio is precisely controlled to promote the main pathway reaction while suppressing the generation of side impurities.

[0010] In some embodiments, the amount of organic amine catalyst added in step (2) is 0.05-0.3 wt% of the mass of the reaction system, and the organic amine catalyst is selected from compounds with a molecular weight <150 g / mol and pKa 9-11.

[0011] Organic amines with a molecular weight <150 g / mol can diffuse rapidly in the reaction system, making full contact with side intermediates and avoiding untimely complexation due to slow diffusion. The pKa range of 9-11 precisely matches the Lewis acidity of side intermediates (such as intermediates containing Al-OR), enabling selective complexation of side intermediates rather than indiscriminately acting on main pathway intermediates. This effectively raises the energy barrier of the side pathway and inhibits the occurrence of side reactions from a thermodynamic perspective. The amount of catalyst added is limited because if the amount is too low, the side intermediates cannot be completely complexed, making it difficult to achieve the ideal pathway control effect. If the amount is too high, it may lead to sol aggregation, while increasing the difficulty and cost of subsequent catalyst recovery.

[0012] In some embodiments, the organic amine catalyst is triethylamine or dimethylamine.

[0013] Both triethylamine and dimethylamine meet the core requirements of molecular weight <150 g / mol and pKa 9-11. They are also readily available in industry and have good stability. Their Lewis basicity can precisely target side-branch intermediates, effectively raising the energy barrier of the side pathway, while not interacting strongly with the main pathway intermediates, ensuring the orderly formation of Al-OH bonds in the main pathway. Compared with other organic amine compounds, they are more suitable for the hydrolysis pathway regulation requirements of this invention.

[0014] In some embodiments, the temperature of the hydrolysis reaction in step (3) is 50-70°C, the power of the pulsed microwave is 400-800W, the pulse mode is on for 5-10 seconds and off for 10-15 seconds, and the total reaction time is 15-25 minutes.

[0015] A reaction temperature of 50-70℃ is considered mild, providing sufficient energy for the hydrolysis reaction while avoiding the exacerbation of side-path reactions caused by high temperatures. Pulsed microwaves are used instead of continuous microwaves because the pulsed mode allows for targeted energy injection. During the "on" phase, the main pathway molecular vibrations are activated, promoting the orderly formation of Al-OH polymers, while the "off" phase releases heat from the system, preventing the revival of side-path reactions due to excessive temperature. Compared to traditional continuous heating, this mode achieves precise targeted energy utilization. The microwave power and pulse time parameters are limited because too low a power cannot effectively activate the main pathway reaction, while too high a power may damage the stability of the reaction system. The specific pulse on / off time ratio and total reaction time are designed based on the main pathway reaction cycle, ensuring that the main pathway reaction is fully completed while suppressing side-path reactions to the greatest extent.

[0016] In some embodiments, the stirring speed of the hydrolysis reaction in step (3) is 300 rpm.

[0017] A stirring speed of 300 rpm ensures uniform mixing of the reaction system, allowing the aluminum source, acid, catalyst, and microwave energy to come into full contact. This avoids problems such as incomplete reaction and impurity generation caused by excessively high local concentrations or uneven energy distribution. At the same time, it prevents turbulence in the system caused by excessively fast stirring speed, thus avoiding disruption of the orderly polymerization of intermediates and ensuring the stable progress of the main reaction pathway.

[0018] In some embodiments, in step (4), the pH is adjusted to 4.8-5.2, and the catalyst is removed by low-temperature vacuum distillation at a distillation temperature of <60°C and a catalyst recovery rate of >90%.

[0019] The pH was adjusted to 4.8-5.2 because this pH range matches the peak zeta potential of the aluminum sol, which can significantly improve the colloidal stability of the sol and prevent precipitation during storage. Low-temperature vacuum distillation was used to recover the catalyst because the temperature of <60℃ can avoid the agglomeration or deterioration of the aluminum sol caused by high temperature. At the same time, the vacuum environment can improve the distillation efficiency and achieve efficient recovery of the catalyst, which reduces production costs and waste emissions, meeting the requirements of green chemical industry. The design of catalyst recovery rate >90% further improves the economic and environmental benefits of the process.

[0020] In some embodiments, a high-purity aluminum sol is prepared by the preparation method described in any of the above embodiments, with a solid content of 35-45 wt% based on Al2O3, a purity of ≥99.999%, wherein the content of Na, Fe, and Si impurities is <3 ppm; the particle size is 5-8 nm, the particle size distribution variation is <5%; the zeta potential is >65 mV, the transparency is >98%, and no precipitation occurs after storage at room temperature for ≥18 months.

[0021] The performance indicators of this high-purity aluminum sol directly reflect the effects of the above-mentioned preparation method's pathway control. The synergistic effect of selectively complexing side intermediates and targeting the main pathway significantly suppresses impurity formation, thereby achieving high purity. Meanwhile, mild reaction conditions, precise pH adjustment, and stirring parameters ensure uniform sol particle size and stable zeta potential, ultimately giving the product excellent transparency and long-term storage stability. All indicators are interconnected and mutually supportive, jointly meeting the stringent requirements of high-end application scenarios.

[0022] In some embodiments, the high-purity aluminum sol is used for the coating of lithium battery ceramic separators, specifically by coating the aluminum sol with a polymer onto a substrate and drying it to form a nano-coating.

[0023] The high-purity aluminum sol of this invention has extremely low impurity content and uniform particle size. The nano-coating structure formed after being compounded with polymers is dense and uniform, which can reduce defects inside the coating and thus improve the ion conduction efficiency and cycle stability of lithium batteries. Compared with coatings prepared by traditional aluminum sol, its advantages in purity and uniformity are directly translated into improved battery performance.

[0024] In some embodiments, the high-purity aluminum sol is used as a catalyst support, specifically by loading the aluminum sol with precious metals for use in petrochemical catalysis.

[0025] High-purity aluminum sol, as a carrier, can prevent impurities from poisoning the active sites of precious metals. At the same time, the uniform particle size distribution can ensure that the active sites of precious metals are evenly dispersed, thereby improving the selectivity and efficiency of catalytic reactions. This solves the problem of poor catalytic performance caused by insufficient purity or uneven particle size of traditional catalyst carriers.

[0026] In some embodiments, the high-purity aluminum sol is used in optical materials, specifically as a carrier for LED phosphors.

[0027] This aluminum sol has high transparency and high purity. When used as a carrier for LED phosphors, it will not scatter or absorb light, thus ensuring the luminous efficiency of the phosphors. At the same time, its long-term stability can prevent carrier deterioration from affecting the lifespan of LED products. Compared with conventional aluminum sol carriers, it can better meet the high-end requirements of optical materials for light transmittance and stability.

[0028] The present invention has the following advantages over the prior art. This invention, through a systematic improvement of the aluminum sol preparation method, overcomes the limitations of existing technologies that rely solely on macroscopic parameter optimization, achieving targeted control of the hydrolysis pathway at the molecular scale. Compared to existing technologies, this invention effectively suppresses side-path reactions and significantly improves the purity of the aluminum sol through the synergistic effect of a specific aluminum source combination, a selective organic amine catalyst, and pulsed microwaves. This solves the core problems of limited purity limits and poor batch-to-batch consistency in existing technologies. The preparation process employs a mild reaction temperature and efficient pulsed microwave energy input, significantly reducing energy consumption and shortening the process cycle compared to traditional processes such as high-temperature hydrothermal methods, thus improving production efficiency. The catalyst can be efficiently recovered, reducing both production costs and environmental burden, aligning with the concept of green production. The high-purity aluminum sol prepared by this method outperforms existing products in terms of purity, particle size distribution, stability, and transparency. When applied to fields such as lithium battery ceramic separator coatings, catalyst supports, and optical materials, it can fully leverage its performance advantages, compensating for the shortcomings of existing materials in high-end applications, and demonstrating significant technological advancement and industrial application value. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0031] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0032] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0033] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain high-purity aluminum sol.

[0034] Example 2 Step 1: Weigh 90 parts of 99.95% pure aluminum isopropoxide and 10 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0035] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0036] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0037] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain high-purity aluminum sol.

[0038] Example 3 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0039] Step 2: Add 99% pure dimethylamine to the above system as a catalyst. The amount added is 0.3 wt% of the total mass of the reaction system. Stir until the catalyst is completely dissolved.

[0040] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0041] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain high-purity aluminum sol.

[0042] Example 4 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0043] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0044] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 700W, pulse mode "on for 7 seconds / off for 13 seconds", and continue the reaction for 22 minutes.

[0045] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain high-purity aluminum sol.

[0046] Example 5 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add acetic acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:25, and the initial pH of the system was adjusted to 3.5.

[0047] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0048] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0049] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain high-purity aluminum sol.

[0050] Comparative Example 1 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0051] Step 2: Without adding any organic amine catalyst, place the system directly into the reactor, set the temperature to 80℃ and the stirring speed to 300rpm, and heat the reaction continuously for 3 hours.

[0052] Step 3: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then the mixture is concentrated to obtain aluminum sol (without catalyst recovery step).

[0053] Comparative Example 2 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0054] Step 2: Add tributylamine (molecular weight 143 g / mol, pKa 8.9) as a catalyst to the above system. The amount added is 0.15 wt% of the total mass of the reaction system. Stir until the catalyst is completely dissolved.

[0055] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0056] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain aluminum sol.

[0057] Comparative Example 3 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0058] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0059] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55°C and the stirring speed to 300 rpm; start the continuous microwave at 600 W and continue the reaction for 20 minutes (total energy is the same as in Example 1).

[0060] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain aluminum sol.

[0061] Comparative Example 4 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0062] Step 2: Without adding organic amine catalysts, simply stir the system until homogeneous.

[0063] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0064] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then the mixture is concentrated to obtain aluminum sol (without catalyst recovery step).

[0065] Comparative Example 5 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0066] Step 2: Add 99% pure triethylamine to the above system as a catalyst. The amount added is 0.5 wt% of the total mass of the reaction system (exceeding the range of 0.05-0.3 wt% of this invention), and stir until the catalyst is completely dissolved.

[0067] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0068] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain aluminum sol.

[0069] In this comparative example, the amount of catalyst added exceeded the limits of this invention (0.5wt% > 0.3wt%). Excess organic amines not only selectively complex side branch intermediates, but also interact non-specifically with the Al-OH polymers generated in the main pathway, forming stable multi-component complexes. At the same time, excessive catalyst leads to an increase in the viscosity of the reaction system. These factors together hinder the separation and volatilization of the catalyst during the low-temperature vacuum distillation process, ultimately resulting in a catalyst recovery rate of only 60%, far lower than the recovery rate of over 90% in other embodiments of this invention.

[0070] Comparative Example 6 Step 1: Weigh 100 parts of 99.95% pure aluminum isopropoxide (single aluminum source, no boehmite), add deionized water, and control the mass ratio of water to aluminum source to be 8:1; add 0.2 mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0071] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0072] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300 rpm; start the pulse microwave, set the parameters to power 600W, pulse mode "on for 8 seconds / off for 12 seconds", and continue the reaction for 20 minutes.

[0073] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain aluminum sol.

[0074] Comparative Example 7 Step 1: Weigh 80 parts of 99.95% pure aluminum isopropoxide and 20 parts of 10μm boehmite, mix them thoroughly, and then add deionized water, controlling the mass ratio of water to aluminum source to be 8:1; add 0.2mol / L nitric acid to the mixture to adjust the pH. + The molar ratio of Al to Al was 1:22, and the initial pH of the system was adjusted to 3.5.

[0075] Step 2: Add 99% pure triethylamine to the above system as a catalyst, the amount added is 0.15 wt% of the total mass of the reaction system, and stir until the catalyst is completely dissolved.

[0076] Step 3: Place the system in a microwave reactor, set the reaction temperature to 55℃ and the stirring speed to 300rpm; start the pulse microwave, set the parameters to power 600W and pulse mode "on for 15 seconds / off for 5 seconds" (exceeding the 5-10 second on range of this invention), and continue the reaction for 20 minutes.

[0077] Step 4: After the reaction is complete, ammonia water is slowly added to the system to adjust the pH to 5.0 at a rate of 0.05 pH / min; then low-temperature vacuum distillation is performed, with the distillation temperature controlled at 55℃, to recover the catalyst; finally, the system is concentrated to a solid content of 40 wt% based on Al2O3 to obtain aluminum sol.

[0078] Performance verification 1. Purity and impurity content testing: Inductively coupled plasma mass spectrometry (ICP-MS) was used to detect the aluminum sol prepared in each example and comparative example, and the contents of three impurities, Na, Fe and Si, were determined. Combined with the theoretical content of Al2O3 in the aluminum sol, the total purity of the aluminum sol was calculated.

[0079] 2. Particle size and particle size distribution test: Dynamic light scattering (DLS) was used to test the particle size of each sample at 25℃ and 90° scattering angle. Each sample was tested 3 times and the average value was taken as the particle size data. The percentage of particle size distribution variation was obtained by calculating the coefficient of variation of particle size distribution.

[0080] 3. Zeta potential test: The zeta potential of each sample was tested using a zeta potential meter at 25°C. Each sample was tested 5 times, and the average value was taken as the final zeta potential data.

[0081] 4. Storage stability test: Seal each sample and place it in a room temperature (25±2℃) environment. Observe the samples regularly to see if precipitation or stratification occurs, and record the longest time that the sample remains in a uniform and stable state.

[0082] 5. Side path suppression rate test: Infrared spectroscopy (IR) was used to analyze the spectra of each sample, and the Al-OH characteristic peak (3400 cm⁻¹) was compared. -1 (near) and the characteristic peak of Al-OC of the side product (1050 cm⁻¹) -1 The peak intensity ratio (near) was used as a benchmark to calculate the side path inhibition rate of each sample, based on the side path response level of Comparative Example 1 (side path inhibition rate of 0%).

[0083] 6. Catalyst recovery rate test: Collect the catalyst recovered by distillation during the post-processing of each sample, weigh and record the recovered mass, and calculate the catalyst recovery rate by comparing it with the initial added catalyst mass.

[0084] Performance verification results

[0085] Note: "-" in the table indicates that there is no corresponding test item (comparative examples 1 and 4 did not add catalyst, so there is no catalyst recovery rate data); the impurity content is the measured value of Na, Fe and Si elements, all of which meet "<3ppm" (example) or exceed this range (comparative examples); storage stability is judged by "no precipitation and no stratification".

[0086] The comparison results between the examples and comparative examples show that the present invention successfully prepared a high-purity aluminum sol with a purity ≥99.999%, uniform particle size, and excellent stability through a specific ratio combination of aluminum isopropoxide and boehmite, an organic amine catalyst with a molecular weight <150 g / mol and pKa 9-11, pulsed microwave energy input, and precise process parameter control. The side path inhibition rate exceeded 85%, no precipitation occurred after 18 months of storage at room temperature, and the catalyst recovery rate exceeded 90%. In contrast, Comparative Example 1, which is closest to the prior art, lacked path control methods, resulting in a purity of only 99.99% and significantly insufficient stability. Comparative Examples 2-4 demonstrate that organic amines, continuous microwaves, or single-path control methods not limited by the present invention cannot overcome the 5N purity bottleneck. Comparative Examples 5-7 show that catalyst dosage, pulse parameters, or single aluminum sources exceeding the limits of the present invention lead to performance degradation or a decrease in overall effect. The above results fully verify that the preparation method of the present invention is not a simple combination of existing technologies or optimization of conventional parameters. The synergistic effect of its core innovative features is the key to achieving excellent effects such as high purity, low energy consumption, and high stability, and it has significant creative and industrial application value.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity aluminum sol, characterized in that, Includes the following steps: (1) Mix aluminum source with deionized water and add acid to adjust the initial pH to 3-4; the aluminum source is a mixture of aluminum isopropoxide and boehmite, the purity of aluminum isopropoxide is ≥99.9%, the particle size of boehmite is <20μm, the mass ratio of the two is 70-90:10-30, and the mass ratio of water to aluminum source is 6:1-12:1; (2) Add an organic amine catalyst, wherein the amount of organic amine catalyst added is 0.05-0.3 wt% of the mass of the reaction system, and the organic amine catalyst is selected from compounds with a molecular weight <150 g / mol and pKa 9-11; (3) At 50-70°C, a pulsed microwave energy input is applied to carry out the hydrolysis reaction. The power of the pulsed microwave is 400-800W, the pulse mode is on for 5-10 seconds and off for 10-15 seconds, and the total reaction time is 15-25 minutes. (4) After hydrolysis, adjust the pH to 4.8-5.2, remove the catalyst and concentrate to obtain high-purity aluminum sol.

2. The preparation method according to claim 1, characterized in that, The acid mentioned in step (1) is nitric acid and / or acetic acid, H + The molar ratio with Al is 1:20-25.

3. The preparation method according to claim 1, characterized in that, The organic amine catalyst mentioned in step (2) is triethylamine or dimethylamine.

4. The preparation method according to claim 1, characterized in that, In step (3), the stirring speed of the hydrolysis reaction is 300 rpm; in step (4), the catalyst is removed by low-temperature vacuum distillation, the distillation temperature is <60℃, and the catalyst recovery rate is >90%.

5. The preparation method according to claim 1, characterized in that, In step (3), the power of the pulsed microwave is 500-700W, the pulse mode is 6-8 seconds on and 11-13 seconds off, and the total reaction time is 18-22 minutes.

6. A high-purity aluminum sol, characterized in that, Prepared by any one of the preparation methods described in claims 1-5, the solid content of Al2O3 is 35-45wt%, the purity is ≥99.999%, and the impurity content of Na, Fe and Si is <3ppm; the particle size is 5-8nm, the particle size distribution variation is <5%; the zeta potential is >65mV, the transparency is >98%, and no precipitation occurs after storage at room temperature for ≥18 months.

7. An application of the high-purity aluminum sol as described in claim 6, characterized in that, The aluminum sol is used for the coating of the ceramic separator of lithium battery. Specifically, the aluminum sol and polymer are coated on the substrate and dried to form a nano-coating. The mass ratio of the aluminum sol to the polymer is 1:1.5, and the battery ion conductivity corresponding to the coating is ≥13.2mS / cm.

8. An application of the high-purity aluminum sol as described in claim 6, characterized in that, The aluminum sol is used as a catalyst support, specifically by loading noble metals onto the aluminum sol for petrochemical catalysis, with a catalytic selectivity >96%.

9. An application of the high-purity aluminum sol according to claim 6, characterized in that, The aluminum sol is used in optical materials, specifically as a carrier for LED phosphors, with a transmittance >99%.

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