Method for producing small-pore pseudo-boehmite by alcohol aluminum method

Abstract

The application discloses a method for producing small-pore pseudo-boehmite by an alcohol aluminum method and belongs to the field of inorganic porous catalytic material preparation. The method comprises the steps of aluminum source preparation, segmented low-temperature controlled-speed hydrolysis, composite seed induction gradient aging, solid-liquid separation and post-treatment. Through the synergistic effect of segmented hydrolysis, composite seed compounding, gradient aging and alcohol-water dual-phase regulation, key process parameters are controlled, and alcohol solvent is recycled and applied. The application solves the problems of the existing process, such as large pore size, discrete distribution and poor industrialization adaptability. The prepared pseudo-boehmite has a most probable pore size of 3-8 nm, a pore size distribution variation coefficient of no more than 15%, uniform pore size and high purity, can be adapted to different aluminum sources and production scales, can be mass-produced without adding new equipment, is suitable for high-end catalysis, new energy and other fields, and has significant technical progress and industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of inorganic porous catalytic material preparation technology, specifically relating to a method for producing small-pore pseudoboehmite using the aluminum alkoxide method. Background Technology

[0002] Boehmite, as the core precursor of γ-Al2O3 catalyst support, has its pore size, pore size distribution and specific surface area directly determining the core performance of downstream catalytic materials and new energy materials. Among them, boehmite with small pore size and narrow pore size distribution of 3-8nm is a key raw material in the fields of high-end catalysis and lithium battery separators, and there is an urgent market demand. Currently, the mainstream method in the industry is to prepare boehmite using a one-step high-temperature hydrolysis method with aluminum isopropoxide or aluminum sec-butoxide. This process is characterized by readily available raw materials and a simple process, but it has inherent defects that are difficult to overcome: During the one-step high-temperature hydrolysis process, local aluminum ions are prone to form highly supersaturated regions, leading to explosive generation of crystal nuclei with large size differences, which in turn causes grain agglomeration and makes it impossible to stably prepare products with small pore sizes of 3-8 nm. At the same time, existing processes mostly use seedless or single boehmite seed crystals, resulting in insufficient nucleation density. Combined with isothermal aging processes, this easily accelerates Ostwald ripening, leading to the dissolution of small grains and the growth of large grains, resulting in a discrete pore size distribution that cannot meet the requirements of high-end applications for narrow distribution. In addition, existing processes mostly use pure aqueous phase systems with high solid-liquid interface energy, which further aggravates the agglomeration of nanocrystals. Moreover, the alcohol solvent is only crudely removed and recovered as a byproduct, resulting in low recovery rate, which not only wastes raw materials and increases production costs, but also fails to achieve precise control of pore structure. The high-temperature drying process can also cause the collapse of boehmite pores, making it difficult to achieve both small pore size and high specific surface area.

[0003] More importantly, existing technologies lack publicly available solutions that synergistically couple segmented hydrolysis, composite seeding, gradient aging, alcohol-water two-phase control, and gentle drying. Each process unit is either an isolated improvement or a conventional optimization, failing to resolve the inherent industry contradictions of "hydrolysis rate versus grain uniformity, nucleation density versus ripening stability, and structural control versus industrial economics." This results in traditional aluminum alkoxide-based boehmite preparations consistently exhibiting problems such as large pore size, wide pore distribution, and insufficient specific surface area, making them unsuitable for high-end applications. Furthermore, the small-pore preparation technology developed in the laboratory stage cannot be transformed into industrial continuous production, further limiting industry development. Simultaneously, existing processes are incompatible with Yangzhou Zhongtianli New Materials Co., Ltd.'s self-produced aluminum alkoxide raw materials and existing production equipment, hindering the full utilization of the company's existing capacity for high-end product mass production. Therefore, an industrially feasible, structurally controllable, and equipment-compatible method for preparing small-pore boehmite is urgently needed. Summary of the Invention

[0004] In view of this, the present invention proposes a method for producing small-pore boehmite by the aluminum alkoxide method, aiming to overcome the inherent technical contradictions in the preparation of boehmite by the existing aluminum alkoxide method, solve the problems that traditional processes cannot stably prepare small-pore, narrow-pore-distribution boehmite, and have poor industrial adaptability and high production costs, and provide a preparation method with precise structure control, industrial mass production capability, and compatibility with existing equipment.

[0005] The technical solution of this invention is achieved as follows: This invention provides a method for producing small-pore pseudoboehmite using the aluminum alkoxide method, comprising the following steps:

[0006] (1) Aluminum source preparation: Dissolve aluminum isopropoxide or aluminum sec-butoxide in the corresponding alcohol solvent to prepare a 30-40 wt% aluminum alkoxide solution; (2) Segmented low-temperature controlled-rate hydrolysis: The aluminum alkoxide solution is subjected to two-stage hydrolysis. The first stage of hydrolysis is carried out at a low temperature of 10-25℃, in which deionized water is added dropwise to the aluminum alkoxide solution at a uniform rate, and the molar ratio of alcohol to water is controlled at 1:3-1:5, and the temperature of the reaction system is always ≤35℃. The second stage of hydrolysis is carried out by raising the temperature of the reaction system to 45-55℃ and stirring at low speed for 30-60 min to complete the hydrolysis reaction and obtain an amorphous aluminum hydroxide precursor slurry. (3) Composite seed-induced gradient aging: Add 0.3-1.2 wt% of composite seed to the precursor slurry, the composite seed being a composite system of nano-boehmite and high-purity pseudoboehmite; then adopt a two-stage gradient aging process, the first stage is 55-65℃ for 2-4h, the second stage is 75-85℃ for 1-2h, the pH of the reaction system is controlled at 8.0-9.5 throughout the process, and 25 wt% ammonia is used for adjustment; (4) Solid-liquid separation and post-treatment: The aged slurry is filtered, washed, dried and crushed to obtain the finished product of small-pore pseudo-boehmite.

[0007] In some embodiments, the mass ratio of nano-boehmite to high-purity boehmite in the composite seed crystal is 1:2-1:4; the particle size of the nano-boehmite is 20-50 nm, and the purity of the high-purity boehmite is ≥99.95%.

[0008] Nano-sized boehmite can provide a high density of heterogeneous nucleation sites, effectively reducing the nucleation activation energy and promoting the uniform generation of small-sized crystal nuclei, laying the foundation for the formation of small pores. High-purity boehmite can stabilize the boehmite crystal phase structure and inhibit the transformation of crystal nuclei into impurity phases such as gibbsite and boehmite. The two are compounded in a ratio of 1:2 to 1:4 to achieve synergistic nucleation and gradient growth, avoiding the defects of insufficient nucleation density or unstable crystal phase of a single seed. This ratio is not selected by conventional experiments, but is the optimal range determined by crystal nucleation thermodynamics calculations. Deviating from this ratio will lead to a significant increase in the coefficient of variation of pore size distribution, making it impossible to achieve the narrow distribution requirement. There is no public disclosure of such composite seed compounding and ratio in the existing technology.

[0009] In some embodiments, in step (2), the deionized water droplet acceleration rate of the first stage of hydrolysis is controlled at 30-60 mL / (min·kg aluminum alkoxide), and the stirring speed is 200-250 r / min; the stirring speed of the second stage of hydrolysis is 150-180 r / min, and the heating rate is 2-3℃ / min.

[0010] The relative dropping rate per unit mass of aluminum alkoxide is suitable for different scales, including laboratory pilot-scale, pilot-scale, and large-scale industrial production, avoiding the limitations of absolute dropping rate caused by reactor volume and feed amount. The high stirring speed in the first stage of hydrolysis ensures rapid and uniform mixing of deionized water and aluminum alkoxide solution, avoiding aluminum ion supersaturation and agglomeration caused by local water excess. At the same time, the low temperature environment and suitable dropping rate work together to control the hydrolysis reaction rate within a reasonable range, avoiding explosive crystal nucleus formation. The reduced stirring speed and slow heating in the second stage of hydrolysis ensure complete hydrolysis of residual aluminum alkoxide while avoiding precursor particle breakage, laying a uniform precursor foundation for subsequent seed-induced crystallization. This combination of stirring speed and heating rate is a specific choice based on hydrolysis kinetics, balancing the completeness of hydrolysis and the uniformity of the precursor.

[0011] In some embodiments, in step (2), the alcohol-water molar ratio is limited to 1:3-1:5. This ratio is used to ensure complete hydrolysis while maintaining a suitable viscosity of the precursor slurry to avoid filtration difficulties.

[0012] The alcohol-water molar ratio is a key control parameter for the hydrolysis reaction. Based on the reaction mechanism of aluminum alkoxide hydrolysis, if the alcohol-water ratio is too low (<1:3), the amount of water is insufficient, which will lead to incomplete hydrolysis of aluminum alkoxide and residual unreacted aluminum alkoxide impurities, affecting product purity and pore structure. If the alcohol-water ratio is too high (>1:5), the excess water will cause the viscosity of the precursor slurry to increase sharply, which will not only increase the difficulty of stirring and filtration, but also aggravate grain agglomeration, resulting in larger pore size. This ratio range is the optimal range that balances complete hydrolysis, slurry flowability and pore structure control. It is a customized choice for specific technical problems and is not the conventional range of routine experiments.

[0013] In some implementations, in step (3), the heating rate of gradient aging is 1-2℃ / min; the low temperature heat preservation section is used to achieve uniform generation of crystal nuclei, and the medium temperature heat preservation section is used to suppress grain fusion and growth, and lock the small pore structure.

[0014] Gradient aging is the core method to overcome the problem of excessive grain growth caused by isothermal aging. Based on the Ostwald ripening mechanism, the low-temperature holding stage (55-65℃) can control the growth rate of crystal nuclei, ensuring uniform generation and consistent size of crystal nuclei, and avoiding excessive growth of local crystal nuclei. The medium-temperature holding stage (75-85℃) can moderately improve the purity of the crystal phase, and at the same time, the ripening process of dissolving small grains and growing large grains is blocked by temperature control, locking the small-pore structure. The slow heating rate can avoid crystal phase disorder and grain agglomeration caused by sudden temperature changes, ensuring that the crystallization process is stable and controllable. The existing isothermal aging technology cannot achieve this control effect, and there is no public information on gradient aging temperature and heating rate.

[0015] In some embodiments, in the hydrolysis reaction system of step (2), 15-25 vol% of the alcohol phase (based on the total volume of the hydrolysis reaction system) is actively retained as a crystal growth regulator; the alcohol phase is recovered by atmospheric distillation process with a distillation reflux ratio of 3:1-4:1 and an alcohol recovery rate of ≥95%; the recovered alcohol solvent is recycled to the aluminum source preparation process of step (1).

[0016] Unlike existing technologies that rapidly remove alcohol as a byproduct, this embodiment actively retains a certain proportion of the alcohol phase. Its core function is to form a monolayer solvation film on the surface of aluminum hydroxide grains, reducing the solid-liquid interfacial tension, inhibiting van der Waals aggregation between nanocrystals, and simultaneously preventing excessive dissolution of crystal faces by water molecules, maintaining crystal defects, and constructing a mesoporous structure with a high specific surface area. The atmospheric pressure distillation recovery process and the limitation of the reflux ratio can ensure the alcohol recovery rate while avoiding the accumulation of impurities during the recovery process, realizing a closed-loop solvent cycle, which reduces production costs and emissions of waste gas, wastewater, and solid waste. This dual design of "alcohol phase structure regulation + recycling" is not disclosed in existing technologies and is not common knowledge in conventional solvent recovery.

[0017] In some embodiments, in step (4), the drying process adopts flash drying at 180-220℃, the inlet temperature of flash drying is 180-220℃, the outlet temperature is 75-85℃, and the wind speed is 1.2-1.8m / s; the pulverizing process adopts airflow pulverization, the pulverizing pressure is 0.8-1.0MPa, and the finished particle size D50=5-8μm.

[0018] Traditional high-temperature drying can easily lead to the removal of hydroxyl groups from the surface of boehmite, causing pore shrinkage and collapse. In contrast, low-temperature flash drying at 180-220℃ can achieve rapid dehydration, shorten the high-temperature residence time of the material, and preserve the integrity of the precursor's pore structure to the greatest extent. At the same time, the appropriate combination of inlet and outlet temperatures and air velocity can prevent powder agglomeration. The pressure and particle size limitation of airflow pulverization can ensure the uniformity of the finished powder particle size and avoid pore damage during pulverization. It is also suitable for the molding requirements of downstream applications such as catalyst carriers and membrane coatings. This synergy between drying and pulverization processes is a specific design based on the preservation of pore structure and the adaptation to product applications, rather than a simple superposition of conventional low-temperature drying and pulverization.

[0019] In some embodiments, in step (3), the composite seed crystals are added after the second stage of hydrolysis and before the gradient aging begins, and are added in two parts: the first addition is 60% of the composite seed crystals, and the mixture is stirred for 10 minutes; the second addition is 40% of the composite seed crystals, and the mixture is stirred for 5 minutes to avoid seed crystal agglomeration.

[0020] The timing of adding composite seed crystals is crucial. After the second stage of hydrolysis, the precursor slurry is in a uniform amorphous state. Adding seed crystals at this time ensures that the seed crystals are in full contact with the precursor and exerts an inductive effect on heterogeneous nucleation. Adding seed crystals in two stages avoids local aggregation of seed crystals caused by adding them all at once, ensuring that the seed crystals are uniformly dispersed in the slurry and forming nucleation sites with uniform density. This ensures that the grain size is consistent during the subsequent crystallization process and avoids the dispersion of pore size. This addition method is designed based on seed crystal dispersion kinetics and can effectively solve the control failure problem caused by seed crystal agglomeration. There is no disclosure of such addition timing and method in the existing technology.

[0021] In some embodiments, the purity of aluminum isopropoxide or aluminum sec-butoxide in step (1) is ≥99.9%.

[0022] This implementation method, tailored to the actual production situation of the enterprise, uses high-purity aluminum alkoxide, which can meet the raw material requirements of this method without additional purification, thereby reducing production processes and costs.

[0023] In some embodiments, the microporous pseudoboehmite prepared according to the method described in any of the above embodiments has a most probable pore size of 3-8 nm, a pore size distribution variation coefficient ≤15%, and a BET specific surface area ≥280 m². 2 / g, purity ≥99.95%, Na2O residue ≤50ppm.

[0024] The performance indicators of this product are the inevitable result of the coordinated control of various process units in this invention, and cannot be achieved by a single process improvement. The synergistic matching of small pore size, narrow distribution, high specific surface area, and high purity breaks the inherent contradiction of the traditional aluminum alkoxide method, which states that "small pore size and high specific surface area cannot be achieved simultaneously, and high purity and industrial economics cannot be achieved simultaneously." Its performance is superior to existing technology products, and it can directly replace imported high-end products. It is suitable for the core needs of high-end catalysis, new energy and other fields, further proving the creativity and practicality of the technical solution of this invention.

[0025] The present invention has the following advantages over the prior art: This invention abandons the approach of isolated improvement of process units or optimization of conventional parameters in existing technologies, and constructs a complete process system that synergistically couples segmented low-temperature controlled-rate hydrolysis, composite seed-induced gradient aging, alcohol-water dual-phase functionalization regulation, and mild flash drying. It achieves precise control of small-pore pseudo-boehmite throughout the entire crystal growth process, effectively overcoming the inherent defects of the traditional aluminum alkoxide method, such as hydrolysis grain agglomeration, uncontrollable pore size, discrete distribution, and insufficient specific surface area. At the same time, it solves the problems that laboratory technology cannot be transformed into industrial production and the poor compatibility between existing processes and enterprise equipment. Compared with existing processes involving one-step high-temperature hydrolysis, single seed crystal, and isothermal aging, this invention achieves synergistic optimization of small pore size, narrow pore size distribution, high specific surface area, and high purity through the synergistic effect of various process units. It requires no additional large-scale fixed asset investment, can be adapted to existing aluminum alkoxide production equipment, enables closed-loop solvent recycling, reduces production costs and waste emissions, and improves industrial economics. Furthermore, the process design of this invention is not a simple superposition of conventional process features; the process units are interdependent and inseparable, forming a complete crystal growth control chain. This produces synergistic effects that existing technologies could not predict, breaking through the technical bottleneck of traditional aluminum alkoxide methods that can only produce large-pore boehmite. It achieves import substitution for high-end boehmite, expands the application scenarios of boehmite, and has significant technological advancements and industrial application value. Detailed Implementation

[0026] 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.

[0027] Raw materials: Aluminum isopropoxide (99.9% purity), aluminum sec-butoxide (99.9% purity), isopropanol (99.8% purity), sec-butanol (99.8% purity), all produced by Yangzhou Zhongtianli; nano-diatomite (particle size 20-50nm, purity 99.9%, specific surface area ≥200m²). 2 / g); High-purity boehmite (purity ≥99.95%, specific surface area ≥300m²) 2 / g); deionized water (conductivity ≤10μS / cm).

[0028] 2. Equipment: Stainless steel reactor (500L for small-scale test, 5m for pilot-scale test) 3 Plate and frame filter (BMY1200), atmospheric distillation column (T800), flash dryer (SZG-100), air jet mill (QLM-80), BET surface area and pore size analyzer, XRD diffractometer, ICP-MS impurity detector, rotational viscometer.

[0029] Unified performance verification Performance verification must be performed within 24 hours after preparation to ensure the accuracy of the test results. The specific steps are as follows: 1. Detection of most probable pore size and coefficient of variation of pore size distribution: Using a BET surface area and pore size analyzer, 0.1g of finished product sample was weighed, degassed by vacuum drying at 110℃ for 2h, and then subjected to nitrogen adsorption-desorption test. The most probable pore size was calculated using the BJH model, and the coefficient of variation was calculated based on the pore size distribution curve (coefficient of variation = standard deviation of pore size / most probable pore size × 100%). Each sample was tested in parallel 3 times, and the average value was taken.

[0030] 2. BET specific surface area detection: The same BET test procedure as above is used. The specific surface area of ​​the sample is calculated by multi-point adsorption method. Each sample is tested in parallel 3 times and the average value is taken.

[0031] 3. Product purity and Na2O residue detection: Using an ICP-MS impurity detector, weigh 0.5g of finished product sample, digest it with a nitric acid-hydrofluoric acid mixed solution until completely transparent, and then make up to 50mL. Detect the total impurity content (purity = 1 - total impurity content × 100%) and Na2O residue in the sample. Each sample is tested in parallel 3 times, and the average value is taken.

[0032] 4. Alcohol recovery rate test: Collect the alcohol solvent recovered by distillation, weigh the recovered alcohol mass, and calculate the alcohol recovery rate (alcohol recovery rate = recovered alcohol mass / feed alcohol mass × 100%). Record the feed amount and recovery amount throughout the process for each example, verify twice in parallel, and take the average value.

[0033] 5. Crystal phase detection: Using an XRD diffractometer, the finished sample is ground into powder, pressed into tablets, and then subjected to XRD testing. The scanning range is 5°-80°. The crystal phase purity is determined by comparing the standard diffraction peak of boehmite with that of gibbsite, and the presence of boehmite and other impurity phases is detected.

[0034] 6. Slurry viscosity and filtration performance testing: After hydrolysis, the viscosity of the precursor slurry is tested using a rotational viscometer, and the filtration rate of the plate and frame filter (unit: L / h) is recorded to determine whether the filtration is smooth.

[0035] Example 1 Step 1: Aluminum source preparation. Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200 rpm, and the temperature was raised to 40℃. Stirring was continued for 30 minutes to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0036] Step 2: Segmented low-temperature controlled-rate hydrolysis. First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 20℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 200 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Increase the temperature of the reaction system to 50℃ at a heating rate of 2℃ / min. Adjust the stirring speed to 150 r / min and stir at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 20 vol% of the alcohol phase as a crystal growth regulator.

[0037] Step 3: Composite seed-induced gradient aging. Add 0.8 wt% (based on total slurry mass) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a mass ratio of 1:3. It is added in two stages: first, 60% of the composite seed is added and stirred for 10 min; second, 40% of the composite seed is added and stirred for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 8.8 and employ a two-stage gradient aging process: first, heat to 60℃ at a rate of 1.5℃ / min and hold for 3 h (low-temperature nucleation stage); then, heat to 80℃ at a rate of 1.5℃ / min and hold for 1.5 h (medium-temperature setting stage). Maintain a stirring speed of 100 r / min throughout the aging process.

[0038] Step 4: Solid-liquid separation and post-processing. The aged slurry is filtered through a plate and frame filter press to obtain a filter cake. The filter cake is washed with deionized water, using 50 kg of water per batch, until the conductivity of the filtrate reaches 40 μS / cm. The mother liquor (containing isopropanol) is sent to an atmospheric distillation column, with the distillation reflux ratio controlled at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol. The recovered isopropanol is reserved for subsequent aluminum source preparation processes. The washed filter cake is then sent to a flash dryer, with the inlet temperature set at 200℃, the outlet temperature at 80℃, the air velocity at 1.5 m / s, and the drying time at 30 min. The dried product is then sent to an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished particle size D50 = 6 μm, obtaining a small-pore pseudoboehmite product.

[0039] Example 2 Step 1: Aluminum source preparation. Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 233kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 30wt% aluminum isopropoxide solution. The solution was then cooled to 10℃ for later use.

[0040] Step 2: Segmented low-temperature controlled-rate hydrolysis. First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 10℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 30 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:3. Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 200 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Increase the temperature of the reaction system to 45℃ at a rate of 2℃ / min. Adjust the stirring speed to 150 r / min and stir slowly for 30 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 15 vol% of the alcohol phase as a crystal growth regulator.

[0041] Step 3: Composite seed-induced gradient aging. Add 0.3 wt% (based on total slurry mass) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (20 nm particle size) and high-purity pseudoboehmite in a 1:2 mass ratio, added in two stages: first, add 60% of the composite seed and stir for 10 min; second, add 40% of the composite seed and stir for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 8.0 and employ a two-stage gradient aging process: first, heat to 55℃ at a rate of 1℃ / min and hold for 2 h (low-temperature nucleation stage); then, heat to 75℃ at a rate of 1℃ / min and hold for 1 h (medium-temperature setting stage). Maintain a stirring speed of 100 r / min throughout the aging process.

[0042] Step 4: Solid-liquid separation and post-processing. The aged slurry is filtered by a plate and frame filter press to obtain a filter cake. The filter cake is washed with deionized water, using 50 kg of water per batch, until the conductivity of the filtrate reaches 45 μS / cm. The mother liquor (containing isopropanol) is sent to an atmospheric distillation column, with the distillation reflux ratio controlled at 3:1 and the distillation temperature at 82℃ to recover the isopropanol. The recovered isopropanol is reserved for subsequent aluminum source preparation processes. The washed filter cake is sent to a flash dryer, with the inlet temperature set at 180℃, the outlet temperature at 75℃, the air velocity at 1.2 m / s, and the drying time at 30 min. The dried product is sent to an air jet mill, with the milling pressure set at 0.8 MPa, and milled to a finished particle size D50 = 5 μm to obtain a small-pore pseudoboehmite product.

[0043] Example 3 Step 1: Aluminum source preparation. Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 150kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 40wt% aluminum isopropoxide solution. The solution was then cooled to 25℃ for later use.

[0044] Step 2: Segmented low-temperature controlled-rate hydrolysis. First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 25℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 60 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:5. Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 250 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Increase the temperature of the reaction system to 55℃ at a heating rate of 3℃ / min. Adjust the stirring speed to 180 r / min and stir at low speed for 60 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 25 vol% of the alcohol phase as a crystal growth regulator.

[0045] Step 3: Composite seed-induced gradient aging. Add 1.2 wt% (based on total slurry mass) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (50 nm particle size) and high-purity pseudoboehmite in a mass ratio of 1:4. The addition is done in two stages: first, add 60% of the composite seed and stir for 10 min; second, add 40% of the composite seed and stir for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 9.5 and employ a two-stage gradient aging process: first, heat to 65℃ at a rate of 2℃ / min and hold for 4 h (low-temperature nucleation stage); then, heat to 85℃ at a rate of 2℃ / min and hold for 2 h (medium-temperature setting stage). Maintain a stirring speed of 100 r / min throughout the aging process.

[0046] Step 4: Solid-liquid separation and post-processing. The aged slurry is filtered by a plate and frame filter press to obtain a filter cake. The filter cake is washed with deionized water, using 50 kg of water per batch, until the conductivity of the filtrate is 48 μS / cm. The mother liquor (containing isopropanol) is sent to an atmospheric distillation column, with the distillation reflux ratio controlled at 4:1 and the distillation temperature at 85℃ to recover the isopropanol. The recovered isopropanol is reserved for subsequent aluminum source preparation processes. The washed filter cake is sent to a flash dryer, with the inlet temperature set at 220℃, the outlet temperature at 85℃, the air velocity at 1.8 m / s, and the drying time at 30 min. The dried product is sent to an air jet mill, with the milling pressure set at 1.0 MPa, and milled until the finished particle size D50 = 8 μm to obtain a small-pore pseudoboehmite product.

[0047] Example 4 Step 1: Aluminum source preparation. Using aluminum sec-butoxide (99.9% purity) produced by Yangzhou Zhongtianli as the aluminum source, a 500L stainless steel reactor was used. 100kg of aluminum sec-butoxide and 200kg of sec-butanol were added. Stirring was started at 200 rpm, and the temperature was raised to 45℃. Stirring was continued for 30 minutes to prepare a 33.3wt% aluminum sec-butoxide solution. The solution was then cooled to 20℃ for later use.

[0048] Step 2: Segmented low-temperature controlled-rate hydrolysis. First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 20℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 200 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Increase the temperature of the reaction system to 50℃ at a heating rate of 2℃ / min. Adjust the stirring speed to 150 r / min and stir at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 20 vol% of the alcohol phase as a crystal growth regulator.

[0049] Step 3: Composite seed-induced gradient aging. Add 0.8 wt% (based on total slurry mass) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a mass ratio of 1:3. It is added in two stages: first, 60% of the composite seed is added and stirred for 10 min; second, 40% of the composite seed is added and stirred for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 8.8 and employ a two-stage gradient aging process: first, heat to 60℃ at a rate of 1.5℃ / min and hold for 3 h (low-temperature nucleation stage); then, heat to 80℃ at a rate of 1.5℃ / min and hold for 1.5 h (medium-temperature setting stage). Maintain a stirring speed of 100 r / min throughout the aging process.

[0050] Step 4: Solid-liquid separation and post-processing. The aged slurry is filtered by a plate and frame filter press to obtain a filter cake. The filter cake is washed with deionized water, using 50 kg of water per batch, until the conductivity of the filtrate is 42 μS / cm. The mother liquor (containing sec-butanol) is sent to an atmospheric distillation column, with the distillation reflux ratio controlled at 3.5:1 and the distillation temperature at 100℃ to recover sec-butanol. The recovered sec-butanol is reserved for subsequent aluminum source preparation processes. The washed filter cake is sent to a flash dryer, with the inlet temperature set at 200℃, the outlet temperature at 80℃, the air velocity at 1.5 m / s, and the drying time at 30 min. The dried product is sent to an air jet mill, with the milling pressure set at 0.9 MPa, and milled to a finished particle size D50 = 6 μm to obtain a small-pore pseudoboehmite product.

[0051] Example 5 Step 1: Aluminum source preparation. Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source, using a 5m... 3 Add 1000 kg of aluminum isopropoxide and 2000 kg of isopropanol to a stainless steel reactor. Start stirring at 200 r / min, heat to 40°C, and continue stirring for 30 min to prepare a 33.3 wt% aluminum isopropoxide solution. Cool to 20°C for later use.

[0052] Step 2: Segmented low-temperature controlled-rate hydrolysis. First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 20℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide) (equivalent to an absolute dropping rate of 45 L / min), controlling the alcohol-water molar ratio at 1:4. Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 200 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Increase the temperature of the reaction system to 50℃ at a heating rate of 2℃ / min. Adjust the stirring speed to 150 r / min and stir slowly for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 20 vol% of the alcohol phase as a crystal growth regulator.

[0053] Step 3: Composite seed-induced gradient aging. Add 0.8 wt% (based on total slurry mass) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a mass ratio of 1:3. It is added in two stages: first, 60% of the composite seed is added and stirred for 10 min; second, 40% of the composite seed is added and stirred for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 8.8 and employ a two-stage gradient aging process: first, heat to 60℃ at a rate of 1.5℃ / min and hold for 3 h (low-temperature nucleation stage); then, heat to 80℃ at a rate of 1.5℃ / min and hold for 1.5 h (medium-temperature setting stage). Maintain a stirring speed of 100 r / min throughout the aging process.

[0054] Step 4: Solid-liquid separation and post-processing. The aged slurry is filtered by a plate and frame filter press to obtain a filter cake. The filter cake is washed with deionized water, using 500 kg of water per batch, until the conductivity of the filtrate reaches 40 μS / cm. The mother liquor (containing isopropanol) is sent to an atmospheric distillation column, with a distillation reflux ratio of 3.5:1 and a distillation temperature of 83℃ to recover isopropanol. The recovered isopropanol is reserved for subsequent aluminum source preparation processes. The washed filter cake is sent to a flash dryer, with the inlet temperature set at 200℃, the outlet temperature at 80℃, the air velocity at 1.5 m / s, and the drying time at 30 min. The dried product is sent to an air jet mill, with a grinding pressure set at 0.9 MPa, and ground to a finished particle size D50 = 6 μm to obtain a small-pore pseudoboehmite product.

[0055] Example 6 Step 1: Aluminum source preparation. Commercially available aluminum isopropoxide (99.5% purity) was selected as the aluminum source. 100 kg of the aluminum isopropoxide was added to a 500L stainless steel reactor, followed by 200 kg of isopropanol. Stirring was started at 200 r / min, and the temperature was raised to 40℃. Stirring was continued for 30 min to prepare a 33.3 wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0056] Step 2: Segmented low-temperature controlled-rate hydrolysis. Completely consistent with Example 1: First stage hydrolysis at 20℃, deionized water droplet acceleration rate of 45mL / (min·kg aluminum isopropoxide mass), alcohol-water molar ratio of 1:4, system temperature ≤35℃, stirring speed of 200r / min; Second stage hydrolysis with temperature increased to 50℃ at 2℃ / min, stirring speed of 150r / min, aging for 45min, retaining 20vol% alcohol phase (based on total system volume).

[0057] Step 3: Composite seed-induced gradient aging. Completely consistent with Example 1: Add 0.8wt% (total mass of slurry) of composite seed (30nm nano-boehmite: high-purity pseudoboehmite = 1:3, added in two batches), adjust the pH to 8.8 (using 25wt% ammonia water, drop rate ≤ 5mL / min), gradient aging 60℃ / 3h → 80℃ / 1.5h, heating rate 1.5℃ / min.

[0058] Step 4: Solid-liquid separation and post-treatment. Completely consistent with Example 1: filtration and washing until the conductivity of the filtrate is 43 μS / cm, isopropanol distillation recovery (reflux ratio 3.5:1, temperature 83℃), flash drying (200℃ / 80℃, air velocity 1.5m / s), and air jet milling (0.9MPa, D50=6μm).

[0059] Comparative Example 1 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0060] Step 2: Hydrolysis reaction. The segmented low-temperature rate-controlled hydrolysis is cancelled and replaced with conventional one-step high-temperature hydrolysis: the temperature control jacket of the reactor is turned on, the reaction system is heated to 65°C, deionized water is added at once, the alcohol-water molar ratio is controlled at 1:4, the stirring speed is maintained at 200 r / min, and stirring is carried out for 45 min to complete the hydrolysis reaction and obtain aluminum hydroxide slurry. During the reaction, 20 vol% of the alcohol phase is actively retained as a crystal face growth regulator (the other hydrolysis-related parameters are the same as in Example 1).

[0061] Step 3: Composite seed-induced gradient aging. Completely consistent with Example 1: 0.8 wt% (based on total slurry mass) of composite seed was added to the precursor slurry. This composite seed was a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a 1:3 mass ratio, added in two stages: first, 60% of the composite seed was added and stirred for 10 min; second, 40% of the composite seed was added and stirred for 5 min to ensure uniform seed dispersion. After addition, the pH of the reaction system was adjusted to 8.8, and a two-stage gradient aging process was adopted: first, the temperature was increased to 60℃ at a rate of 1.5℃ / min and held for 3 h (low-temperature nucleation stage); then, the temperature was increased to 80℃ at a rate of 1.5℃ / min and held for 1.5 h (medium-temperature setting stage). During the aging process, the stirring speed was maintained at 100 r / min.

[0062] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0063] Comparative Example 2 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0064] Step 2: Segmented low-temperature controlled-rate hydrolysis. Completely consistent with Example 1: First stage hydrolysis: The temperature control jacket of the reactor is turned on, maintaining the reaction system temperature at 20℃. Deionized water is added dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. The reaction temperature is monitored in real time during the addition to ensure the system temperature remains ≤35℃. Simultaneously, the stirring speed is maintained at 200 r / min. After the addition is complete, the second stage hydrolysis begins. Second stage hydrolysis: The reaction system is heated to 50℃ at a heating rate of 2℃ / min. The stirring speed is adjusted to 150 r / min, and the mixture is stirred at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, 20 vol% of the alcohol phase is actively retained as a crystal growth regulator.

[0065] Step 3: Seed-induced aging. The composite seed crystal was removed and replaced with a conventional single seed crystal: 0.8 wt% (based on the total mass of the slurry) of high-purity pseudoboehmite seed crystal (without nano-boehmite) was added to the precursor slurry in one go, and stirred for 15 min. After addition, the pH of the reaction system was adjusted to 8.8, and a two-stage gradient aging process (consistent with Example 1) was adopted: first, the temperature was increased to 60℃ at a heating rate of 1.5℃ / min and held for 3 h; then, the temperature was increased to 80℃ at a heating rate of 1.5℃ / min and held for 1.5 h, maintaining a stirring speed of 100 r / min throughout the aging process.

[0066] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0067] Comparative Example 3 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0068] Step 2: Segmented low-temperature controlled-rate hydrolysis. Completely consistent with Example 1: First stage hydrolysis: The temperature control jacket of the reactor is turned on, maintaining the reaction system temperature at 20℃. Deionized water is added dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. The reaction temperature is monitored in real time during the addition to ensure the system temperature remains ≤35℃. Simultaneously, the stirring speed is maintained at 200 r / min. After the addition is complete, the second stage hydrolysis begins. Second stage hydrolysis: The reaction system is heated to 50℃ at a heating rate of 2℃ / min. The stirring speed is adjusted to 150 r / min, and the mixture is stirred at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, 20 vol% of the alcohol phase is actively retained as a crystal growth regulator.

[0069] Step 3: Composite seed-induced aging. The two-stage gradient aging was cancelled and replaced with conventional isothermal aging using existing technology: 0.8 wt% (based on the total mass of the slurry) of composite seed (consistent with Example 1, nano-boehmite: high-purity pseudoboehmite = 1:3) was added to the precursor slurry in two batches and stirred evenly. After the addition was completed, the pH of the reaction system was adjusted to 8.8, and the temperature was increased to 80°C at a rate of 1.5°C / min. The mixture was kept at this temperature for 4.5 h (consistent with the total gradient aging time in Example 1). During the aging process, the stirring speed was maintained at 100 r / min.

[0070] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0071] Comparative Example 4 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0072] Step 2: Segmented low-temperature controlled-rate hydrolysis. The alcohol-water two-phase retention is eliminated, replaced by conventional pure aqueous phase hydrolysis: First stage hydrolysis: The temperature control jacket of the reactor is turned on to maintain the reaction system temperature at 20℃. Deionized water is added dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. The reaction temperature is monitored in real time during the addition to ensure that the system temperature remains ≤35℃. Simultaneously, the stirring speed is maintained at 200 r / min. After the addition is complete, the second stage hydrolysis begins. Second stage hydrolysis: The reaction system is heated to 50℃ at a heating rate of 2℃ / min. The stirring speed is adjusted to 150 r / min, and the mixture is stirred at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. After hydrolysis, the alcohol phase in the system is rapidly removed; no alcohol phase is retained, and no alcohol recovery is performed.

[0073] Step 3: Composite seed-induced gradient aging. Completely consistent with Example 1: 0.8 wt% (based on total slurry mass) of composite seed was added to the precursor slurry. This composite seed was a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a 1:3 mass ratio, added in two stages: first, 60% of the composite seed was added and stirred for 10 min; second, 40% of the composite seed was added and stirred for 5 min to ensure uniform seed dispersion. After addition, the pH of the reaction system was adjusted to 8.8, and a two-stage gradient aging process was adopted: first, the temperature was increased to 60℃ at a rate of 1.5℃ / min and held for 3 h (low-temperature nucleation stage); then, the temperature was increased to 80℃ at a rate of 1.5℃ / min and held for 1.5 h (medium-temperature setting stage). During the aging process, the stirring speed was maintained at 100 r / min.

[0074] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1 (alcohol-free recovery): The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the washed filter cake is then fed into a flash dryer, with the inlet temperature set at 200℃, the outlet temperature at 80℃, the air velocity at 1.5 m / s, and the drying time at 30 min; the dried product is then fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0075] Comparative Example 5 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0076] Step 2: Segmented low-temperature controlled-rate hydrolysis. Completely consistent with Example 1: First stage hydrolysis: The temperature control jacket of the reactor is turned on, maintaining the reaction system temperature at 20℃. Deionized water is added dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:4. The reaction temperature is monitored in real time during the addition to ensure the system temperature remains ≤35℃. Simultaneously, the stirring speed is maintained at 200 r / min. After the addition is complete, the second stage hydrolysis begins. Second stage hydrolysis: The reaction system is heated to 50℃ at a heating rate of 2℃ / min. The stirring speed is adjusted to 150 r / min, and the mixture is stirred at low speed for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, 20 vol% of the alcohol phase is actively retained as a crystal growth regulator.

[0077] Step 3: Seed-induced aging. Using existing technology combined with the following approach: the composite seed crystal was removed and replaced with a single high-purity boehmite seed crystal (consistent with Comparative Example 2). Gradient aging was also removed and replaced with isothermal aging (consistent with Comparative Example 3). Specifically, 0.8 wt% of high-purity boehmite seed crystal was added to the precursor slurry in a single addition and stirred for 15 min. The pH was adjusted to 8.8, and the temperature was raised to 80℃ for isothermal aging for 4.5 h, maintaining a stirring speed of 100 r / min throughout the aging process.

[0078] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0079] Comparative Example 6 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0080] Step 2: Hydrolysis reaction. A conventional one-step high-temperature hydrolysis method (consistent with Comparative Example 1) was used: the temperature control jacket of the reactor was opened, the reaction system was heated to 65°C, deionized water was added in one go, the alcohol-to-water molar ratio was controlled at 1:4, the stirring speed was maintained at 200 r / min, and stirring was carried out for 45 min to complete the hydrolysis reaction, obtaining aluminum hydroxide slurry. During the reaction, 20 vol% of the alcohol phase was actively retained as a crystal growth regulator.

[0081] Step 3: Seed-induced aging. An existing technology was used in conjunction with the following method: the composite seed crystal was retained (same as in Example 1), but gradient aging was cancelled and replaced with isothermal aging (same as Comparative Example 3). Specifically, 0.8 wt% of the composite seed crystal (nano-boehmite: high-purity pseudoboehmite = 1:3) was added to the precursor slurry in two batches, stirred evenly, the pH was adjusted to 8.8, and the temperature was raised to 80℃ for isothermal aging for 4.5 h, maintaining a stirring speed of 100 r / min during the aging process.

[0082] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0083] Comparative Example 7 Step 1: Aluminum source preparation. Completely consistent with Example 1: Aluminum isopropoxide (99.9% purity) produced by Yangzhou Zhongtianli was selected as the aluminum source. A 500L stainless steel reactor was used. 100kg of aluminum isopropoxide was added, followed by 200kg of isopropanol. Stirring was started at 200r / min, and the temperature was raised to 40℃. Stirring was continued for 30min to prepare a 33.3wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0084] Step 2: Segmented low-temperature controlled-rate hydrolysis. Deviation from the parameter range only: First stage hydrolysis: Open the temperature control jacket of the reactor to maintain the reaction system temperature at 20℃. Add deionized water dropwise to the aluminum alkoxide solution at a rate of 45 mL / (min·kg aluminum alkoxide), controlling the alcohol-water molar ratio at 1:2 (deviation from the 1:3-1:5 range of claim 1). Monitor the reaction temperature in real time during the dropwise addition to ensure the system temperature remains ≤35℃. Maintain a stirring speed of 200 r / min. After the dropwise addition is complete, proceed to the second stage hydrolysis. Second stage hydrolysis: Heat the reaction system to 50℃ at a heating rate of 2℃ / min, adjust the stirring speed to 150 r / min, and stir slowly for 45 min to complete the hydrolysis reaction, obtaining an amorphous aluminum hydroxide precursor slurry. During the reaction, actively retain 20 vol% of the alcohol phase as a crystal growth regulator.

[0085] Step 3: Composite seed-induced gradient aging. Deviating only from the parameter range: Add 0.8 wt% (based on the total mass of the slurry) of composite seed to the precursor slurry. This composite seed is a mixture of nano-boehmite (30 nm particle size) and high-purity pseudoboehmite in a mass ratio of 1:1 (deviating from the 1:2-1:4 range of claim 2). The addition is done in two stages: first, add 60% of the composite seed and stir for 10 min; second, add 40% of the composite seed and stir for 5 min to ensure uniform seed dispersion. After addition, adjust the pH of the reaction system to 8.8 and employ a two-stage gradient aging process (consistent with Example 1): first, heat to 60°C at a rate of 1.5°C / min and hold for 3 h; then, heat to 80°C at a rate of 1.5°C / min and hold for 1.5 h. Maintain a stirring speed of 100 r / min throughout the aging process.

[0086] Step 4: Solid-liquid separation and post-processing. Completely consistent with Example 1: The aged slurry is fed into a plate and frame filter press for filtration to obtain a filter cake; the filter cake is washed with deionized water, using 50 kg of water per batch, until the filtrate conductivity reaches 40 μS / cm; the filtered mother liquor (containing isopropanol) is fed into an atmospheric distillation column, controlling the distillation reflux ratio at 3.5:1 and the distillation temperature at 83℃ to recover isopropanol, which is then kept for later use; the washed filter cake is fed into a flash dryer, with the flash dryer inlet temperature set at 200℃, outlet temperature at 80℃, air velocity at 1.5 m / s, and drying time at 30 min; the dried product is fed into an air jet mill, with the milling pressure set at 0.9 MPa, and milled until the finished product particle size D50 = 6 μm, obtaining the pseudoboehmite product.

[0087] Comparative Example 8 Step 1: Aluminum source preparation. Commercially available aluminum isopropoxide (99.0% purity) was selected as the aluminum source. 100 kg of the aluminum isopropoxide was added to a 500L stainless steel reactor, followed by 200 kg of isopropanol. Stirring was started at 200 r / min, and the temperature was raised to 40℃. Stirring was continued for 30 min to prepare a 33.3 wt% aluminum isopropoxide solution. The solution was then cooled to 20℃ for later use.

[0088] Step 2: Segmented low-temperature controlled-rate hydrolysis. Completely consistent with Example 1: First stage hydrolysis at 20℃, deionized water droplet acceleration rate of 45mL / (min·kg aluminum isopropoxide mass), alcohol-water molar ratio of 1:4, system temperature ≤35℃, stirring speed of 200r / min; Second stage hydrolysis with temperature increased to 50℃ at 2℃ / min, stirring speed of 150r / min, aging for 45min, retaining 20vol% alcohol phase (based on total system volume).

[0089] Step 3: Composite seed-induced gradient aging. Completely consistent with Example 1: Add 0.8wt% (total mass of slurry) of composite seed (30nm nano-boehmite: high-purity pseudoboehmite = 1:3, added in two batches), adjust the pH to 8.8 (using 25wt% ammonia water, drop rate ≤ 5mL / min), gradient aging 60℃ / 3h → 80℃ / 1.5h, heating rate 1.5℃ / min.

[0090] Step 4: Solid-liquid separation and post-treatment. Completely consistent with Example 1: filtration and washing until the conductivity of the filtrate is 45 μS / cm, isopropanol distillation recovery (reflux ratio 3.5:1, temperature 83℃), flash drying (200℃ / 80℃, air velocity 1.5m / s), and air jet milling (0.9MPa, D50=6μm).

[0091] Performance verification results Example Performance Verification Results Table

[0092]

[0093] Comparative Performance Verification Results Table

[0094]

[0095] Example 1, serving as a standard baseline example, fully covers all the core technical features of claims 1-10 of this invention. Through the synergistic effect of segmented low-temperature rate-controlled hydrolysis, gradient aging induced by composite seeds, alcohol-water two-phase regulation, and solvent recycling, a sample with a most probable pore size of 5.2 nm, a pore size distribution variation coefficient of 12.0%, and a BET specific surface area of ​​315 m² was successfully prepared. 2The product, with a purity of 99.97% and a Na2O residue of only 32 ppm, exhibits a 96.2% alcohol recovery rate. Its pure crystal phase and smooth filtration performance fully demonstrate that the core synergistic system of this invention can stably achieve the technical effects of small pores, narrow pore size distribution, high purity, and high recovery rate, providing a fair comparison benchmark for all subsequent comparative examples. Examples 2-3 serve as parameter boundary examples, respectively covering the upper and lower limits of parameters such as the alcohol-water molar ratio and composite seed ratio defined in the claims. Verification results show that even under parameter boundary conditions, a qualified product with a most probable pore size of 3.2-7.8 nm and a coefficient of variation ≤14.5% can still be stably prepared, and all performance indicators meet the requirements of the claims. This proves that the parameter range defined in this invention is not a conventional experimental screening, but rather an effective threshold for the stable preparation of small-pore boehmite; deviation from this range leads to a sharp deterioration in performance. Example 4 replaced the aluminum source with aluminum sec-butoxide, and Example 5 expanded the production scale to the industrial pilot level. The performance indicators of both were basically the same as those of Example 1, further proving that the technical solution of the present invention does not rely on a single aluminum source, can be adapted to the existing self-produced raw materials of enterprises, and can be successfully scaled up to industrial production. It solves the industry pain point that the existing laboratory micro-hole preparation technology cannot be transformed into industrial mass production, and strengthens the industrial application value of the present invention. The data of Example 6 meets all the indicators of claim 10, proving that commercially available conventional high-purity aluminum source (99.5%) can be stably adapted to this method.

[0096] Comparative Examples 1-7, through changes to a single variable, specifically verified the irreplaceability of the core features of this invention and the limitations of combining them with existing technologies. Comparative Example 1 lacks the segmented hydrolysis feature and employs conventional one-step high-temperature hydrolysis, even while retaining all other core features, the most probable pore size of the product still increases to 14.8 nm, the coefficient of variation rises to 28.5%, and the specific surface area decreases to 220 m². 2 / g, the alcohol recovery rate dropped significantly to 78.5%, fully demonstrating that segmented hydrolysis is the core of controlling grain agglomeration and achieving micropore control, and cannot be replaced by conventional one-step hydrolysis, refuting the argument that "segmented hydrolysis is not innovative." Comparative Example 2 removed the composite seed and replaced it with the conventional single pseudo-boehmite seed of the existing technology, resulting in an increase in product pore size to 9.2nm, a coefficient of variation of 22.3%, and the appearance of a small amount of boehmite impurity phase in the crystal phase, proving that the composite seed system can achieve the dual effects of synergistic nucleation and crystal phase stability, which a single seed cannot achieve, refuting the argument that "composite seed is not innovative." Comparative Example 3 changed gradient aging to conventional isothermal aging, and the product pore size increased to 11.5nm, with a coefficient of variation of 20.1%, indicating that gradient aging can effectively block Ostwald ripening and lock in the small pore structure, an effect that conventional isothermal aging cannot achieve, further confirming the inventiveness of gradient aging. Comparative Example 4 eliminated the alcohol-water two-phase control, adopted a pure aqueous system, and did not perform alcohol recovery, resulting in a product pore size of 8.5 nm, a coefficient of variation of 18.2%, an alcohol recovery rate of less than 80%, and an aggravated powder agglomeration. This proves that the retention of alcohol-water two-phase control can not only inhibit grain agglomeration, but also improve solvent recovery and utilization rate. This is different from the common knowledge of conventional solvent crude removal and refutes the doubt that "alcohol-water two-phase control is not innovative".

[0097] Comparative Examples 5 and 6 specifically verify the limitations of existing technology combinations. Comparative Example 5 uses the existing technology combination of "segmented hydrolysis + single seed crystal + isothermal aging", while Comparative Example 6 uses the existing technology combination of "one-step hydrolysis + composite seed crystal + isothermal aging". The pore size of the products of both exceeds 10nm, the coefficient of variation is ≥24.0%, and the specific surface area is significantly reduced. Neither can meet the small pore and narrow distribution requirements specified in this invention. This clearly proves that the simple combination of conventional processes in the existing technology cannot achieve the technical effect of the "segmented hydrolysis + composite seed crystal + gradient aging" synergistic system of this invention. The synergistic effect of this invention is not a simple superposition of the features of the existing technology, but rather produces unexpected technical progress, refuting the question that "existing technology combinations can replace this invention". Comparative Example 7 deviated only from the range of alcohol-water molar ratio and composite seed ratio parameters defined in this invention, resulting in incomplete hydrolysis, excessive slurry viscosity, and difficulty in filtration. The product pore size increased to 15.5 nm, with a coefficient of variation of 29.8%, and all performance indicators deteriorated significantly. This further proves that the parameter range defined in this invention is a customized range designed specifically for this purpose, rather than a routine test screening in the field, refuting the question of "parameters lacking inventiveness". Comparative Example 8 (99.0% purity) had a pore size and coefficient of variation slightly exceeding the limit of claim 10 (coefficient of variation 16.8% > 15%), proving that "purity ≥ 99.5%" is the key range for achieving a narrow distribution of small pores.

[0098] In summary, the comparative verification results of the foregoing embodiments and comparative examples clearly demonstrate that the present invention, through the synergistic coupling of segmented low-temperature rate-controlled hydrolysis, gradient aging induced by composite crystals, alcohol-water two-phase regulation, and solvent recycling, successfully overcomes the inherent defects of existing aluminum alkoxide methods in the preparation of pseudoboehmite, such as large pore size, discrete distribution, poor industrial adaptability, and low solvent utilization. The core features of the technical solution of the present invention are interdependent and indispensable; the parameter range is reasonable and has a clear effect threshold. Existing technologies and conventional combinations thereof cannot achieve the same technical effect, demonstrating significant non-obviousness. Furthermore, the technical solution of the present invention is adaptable to different aluminum sources and different production scales, requiring no additional large-scale production equipment. It can achieve mass production of high-end small-pore pseudoboehmite based on the company's existing production capacity. The product performance is stable and meets the application requirements of high-end fields, demonstrating significant technological advancement and industrial application value, and providing sufficient and effective exemplification support for the claims.

[0099] 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 producing small-pore pseudoboehmite using the aluminum alkoxide process, characterized in that, Includes the following steps: (1) Aluminum source preparation: Dissolve aluminum isopropoxide or aluminum sec-butoxide in the corresponding alcohol solvent to prepare a 30-40 wt% aluminum alkoxide solution; (2) Segmented low-temperature controlled-rate hydrolysis: The aluminum alkoxide solution is subjected to two-stage hydrolysis. The first stage of hydrolysis is carried out at a low temperature of 10-25℃, in which deionized water is added dropwise to the aluminum alkoxide solution at a uniform rate, and the molar ratio of alcohol to water is controlled at 1:3-1:5, and the temperature of the reaction system is always ≤35℃. The second stage of hydrolysis is carried out by raising the temperature of the reaction system to 45-55℃, stirring and maturing for 30-60 min to complete the hydrolysis reaction and obtain an amorphous aluminum hydroxide precursor slurry. (3) Composite seed-induced gradient aging: 0.3-1.2 wt% of composite seed based on the total mass of the precursor slurry is added to the precursor slurry. The composite seed is a compound system of nano-boehmite and high-purity pseudoboehmite. Then, a two-stage gradient aging process is adopted. The first stage is 55-65℃ for 2-4 hours and the second stage is 75-85℃ for 1-2 hours. The pH value of the reaction system is controlled at 8.0-9.5 throughout the process. (4) Solid-liquid separation and post-treatment: The aged slurry is filtered, washed, dried and crushed to obtain the finished product of small-pore pseudo-boehmite.

2. The method according to claim 1, characterized in that, In the composite seed crystal, the mass ratio of nano-boehmite to high-purity boehmite is 1:2-1:4; the particle size of the nano-boehmite is 20-50 nm, and the purity of the high-purity boehmite is ≥99.95%.

3. The method according to claim 1, characterized in that, In step (2), the deionized water droplet acceleration rate of the first stage of hydrolysis is controlled at 30-60 mL / (min·kg mass of aluminum isopropoxide or aluminum sec-butoxide), and the stirring speed is 200-250 r / min; the stirring speed of the second stage of hydrolysis is 150-180 r / min, and the heating rate is 2-3℃ / min.

4. The method according to claim 1, characterized in that, In step (2), the alcohol-water molar ratio is limited to 1:3-1:

5. This ratio is used to ensure complete hydrolysis reaction while maintaining a suitable viscosity of the precursor slurry to avoid filtration difficulties.

5. The method according to claim 1, characterized in that, In step (3), the heating rate of gradient aging is 1-2℃ / min; the low temperature heat preservation section is used to achieve uniform generation of crystal nuclei, and the medium temperature heat preservation section is used to suppress grain fusion and growth, and lock the small pore structure.

6. The method according to claim 1, characterized in that, In the hydrolysis reaction system of step (2), 15-25 vol% of the alcohol phase is actively retained as a crystal growth regulator; the alcohol phase is recovered by atmospheric distillation process with a distillation reflux ratio of 3:1-4:1 and an alcohol recovery rate of ≥95%; the recovered alcohol solvent is recycled to the aluminum source preparation process of step (1).

7. The method according to claim 1, characterized in that, In step (4), the drying process adopts flash drying at 180-220℃, the inlet temperature of flash drying is 180-220℃, the outlet temperature is 75-85℃, and the wind speed is 1.2-1.8m / s; the pulverization process adopts airflow pulverization, the pulverization pressure is 0.8-1.0MPa, and the finished particle size D50=5-8μm.

8. The method according to claim 1, characterized in that, In step (3), the composite seed crystals are added after the second stage of hydrolysis and before the gradient aging begins, and are added in two parts: the first addition is 60% of the composite seed crystals, and the mixture is stirred for 10 minutes; the second addition is 40% of the composite seed crystals, and the mixture is stirred for 5 minutes to avoid seed crystal agglomeration.

9. The method according to claim 1, characterized in that, The purity of aluminum isopropoxide or aluminum sec-butoxide in step (1) is ≥99.9%.

10. The small-pore pseudoboehmite prepared according to any one of claims 1-9, characterized in that, The most probable pore size of the microporous pseudoboehmite is 3-8 nm, the coefficient of variation of pore size distribution is ≤15%, and the BET specific surface area is ≥280 m². 2 / g, purity ≥99.95%, Na2O residue ≤50ppm.

Images