Hydrothermal reaction system and method for preparing monodisperse nano boehmite

Abstract

The invention relates to a hydrothermal reaction system and method for preparing monodisperse nano boehmite, and belongs to the technical field of inorganic powder materials. The invention aims to overcome the problems of poor batch stability, easiness in scaling and amplification effect caused by non-uniform mixing in reaction equipment and coupling of nucleation and growth processes in the prior art for realizing monodispersity by relying on compounding of raw materials with specific particle sizes and accurate pH control. The system mainly comprises a stirring module and a partition temperature control system, and a high-shear dispersing head forms a high-speed shear homogenizing area and is used for instantaneous forced nucleation during slurry feeding; and the multi-layer blade stirrers positioned on the middle and lower layers and the static flow guide ring form a mild uniform circulation area for controllable growth of crystals. The method comprises the following steps: by utilizing the system and through sequential control, firstly starting the high-shear region to realize uniform nucleation, and then switching to the circulation region to complete crystal growth. The method is used for stably and efficiently preparing the monodisperse nano boehmite.

Description

Technical Field

[0001] This invention relates to the field of inorganic powder materials technology, specifically to a hydrothermal reaction system and method for preparing high-purity, monodisperse, and uniformly controllable nano-boehmite. Background Technology

[0002] Boehmite is an important industrial material widely used in fields such as lithium battery separator coating and high-end flame retardants. These high-end applications place extremely stringent requirements on the monodispersity, nanoscale particle size, and narrow particle size distribution of boehmite products.

[0003] Existing technology, patent CN113526534B, provides a method for preparing monodisperse nanoboehmite, relating to the field of inorganic powder materials technology. The monodisperse nanoboehmite has a particle size of 50–200 nm and a specific surface area of ​​10–50 m². 2 / g, is made from nano-sized aluminum hydroxide, submicron-sized aluminum hydroxide, and micron-sized aluminum hydroxide through hydrothermal reaction. The powder prepared by this patent has good monodispersity, and the particle size of the end product can be controlled by selecting the particle size of the raw materials, making production more convenient. Moreover, the obtained nano-sized boehmite not only has a uniform morphology, reaching the nanoscale, but also has a low specific surface area. This patent attempts to utilize the initial dissolution of nano-sized aluminum hydroxide in the system to form initial seed crystals, thereby guiding the directional growth of subsequent crystals to obtain a monodisperse product.

[0004] However, the realization of its monodispersity depends on the mixing of raw materials with specific particle size and specific ratio. This not only increases the cost of raw materials and the complexity of pretreatment, but also makes the performance of the final product very sensitive to the particle size fluctuation of the raw materials, and the batch stability faces challenges. This patent is essentially a strategy based on chemical thermodynamic control. It does not address or solve the fundamental problems of physical mass transfer and heat transfer inside the reaction equipment. In conventional stirred reactors, temperature gradients and concentration gradients are difficult to avoid, which leads to mutual interference between crystal nucleation and growth processes. This is the underlying reason for the wide particle size distribution and uneven morphology of the product. In addition, such conventional equipment generally suffers from the problem of easy scaling on the inner wall and stirring shaft.

[0005] Therefore, there is an urgent need in this field for a novel approach to preparing monodisperse nanoboehmite that addresses the above-mentioned problems by starting with the reaction process mechanism and through equipment-level innovation, and provides a more stable and scalable process that does not rely on special raw material formulations. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel hydrothermal reaction system and method based on reactor structure innovation and process timing control. This invention no longer relies on complex raw material formulations, but instead solves the control problems of nucleation and growth processes by creating an ideal physical reaction environment, thereby achieving the efficient and stable preparation of monodisperse nanoboehmite.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A hydrothermal reaction system for preparing monodisperse nanoboehmite includes a hydrothermal reactor body and a stirring module disposed inside the hydrothermal reactor body. The stirring module includes a high-speed shear homogenization unit located at the upper part of the hydrothermal reactor body and a mild circulating growth unit located in the lower middle part of the hydrothermal reactor body. It also includes a zoned temperature control system connected to the main body of the hydrothermal reactor. The zoned temperature control system can independently adjust the temperature of different areas in the upper, middle and lower parts of the main body of the hydrothermal reactor, and is also used to transport the precursor slurry to the precision feeding system in the high-speed shear homogenization unit.

[0008] Preferably, the high-speed shear homogenization unit is a high-shear dispersion head, and the mild circulating growth unit includes at least one layer of inclined paddle mixers.

[0009] Preferably, the mild circulating growth unit includes four layers of paddle agitators, and a static flow guide ring is provided between two adjacent layers of paddle agitators.

[0010] Preferably, the impeller agitator is an inclined blade turbine with an inclination angle of 30 to 60 degrees, and the static guide ring is fixed to the inner wall of the hydrothermal reactor body, with guide holes opened on its ring surface.

[0011] Preferably, the height-to-diameter ratio of the main body of the hydrothermal reactor is greater than 2.

[0012] A hydrothermal reaction method for preparing monodisperse nanoboehmite includes the following steps: S1. Prepare a precursor slurry by mixing aluminum source with deionized water, then start the partition temperature control system to heat the inside of the hydrothermal reaction system to the target reaction temperature, and replace the air in the reactor with inert gas. S2. Keep the high-speed shear homogenizing unit in high-speed operation, and pump all the precursor slurry prepared in the system preparation step into the working area of ​​the high-speed shear homogenizing unit through the precision feeding system, so as to complete the explosive homogenization in the upper region of the hydrothermal reactor body. S3. After all the precursor slurry has been pumped in, the high-speed shear homogenization unit is immediately stopped, and the mild circulation growth unit is then started, so that the crystal nuclei formed in the previous stage can grow crystals in the uniform flow field generated by the mild circulation growth unit to obtain boehmite slurry. S4. Finally, the boehmite slurry obtained from the time-sequence switching and controllable growth steps is subjected to solid-liquid separation and drying to obtain the monodisperse nano boehmite powder.

[0013] Preferably, in step S2, the rotational speed of the high-speed shear homogenizing unit is between 8000 rpm and 15000 rpm, and the feeding time of the precursor slurry is controlled between 10 seconds and 60 seconds.

[0014] Preferably, in step S3, the temperature of the region where the mild circulating growth unit is located is controlled by the partitioned temperature control system to be 0.5°C to 5°C lower than the temperature of the region where the high-speed shear homogenization unit is located.

[0015] Preferably, the aluminum source is industrial-grade boehmite, and the reaction temperature in the timing switching and controllable growth steps is 200°C to 280°C, and the reaction time is 2 hours to 8 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves instantaneous and explosive uniform nucleation through a high-speed shear homogenization zone, laying a solid foundation for the formation of monodisperse products. Combined with the stable growth environment provided by the mild and uniform circulation zone, it can effectively avoid secondary nucleation and ultimately obtain nano-boehmite with regular morphology.

[0017] This invention decouples the nucleation and growth steps through timing control, significantly shortening the core reaction time. The stable axial circulation formed by multiple layers of impellers and guide rings within the system effectively scours the inner wall of the reactor, eliminates flow dead zones, and improves the stability of continuous equipment operation and maintenance cycle.

[0018] This invention divides the stirring function into zones and supplements them with zoned temperature control and precision feeding, achieving independent and precise control of the two key stages of nucleation and growth in the hydrothermal crystallization process. This principle based on the coordinated design of flow field and thermal field ensures that the mixing and heat transfer efficiency of the system does not decrease significantly with the scale of production, greatly reducing the scale-up effect and providing a reliable guarantee for industrial production. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a system structure block diagram of the present invention.

[0020] In the diagram: 1. Main body of hydrothermal reactor; 2. Stirring module; 21. High-speed shear homogenization unit; 211. High-shear dispersion head; 22. Mild circulation growth unit; 221. Paddle agitator; 222. Static guide ring; 3. Zoned temperature control system. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0022] Example 1

[0023] like Figures 1-2 As shown in the prior art, as indicated by the authorized patent CN113526534B, achieving monodispersity of boehmite usually relies on complex raw material formulations. This invention provides a novel path to achieve this goal through equipment and process innovation. This embodiment provides a hydrothermal reaction system for preparing monodisperse nano boehmite, including a hydrothermal reactor body 1, a stirring module 2 disposed inside the hydrothermal reactor body 1, the stirring module 2 including a high-speed shear homogenization unit 21 located at the upper part of the hydrothermal reactor body 1 and a mild circulating growth unit 22 located in the middle and lower part of the hydrothermal reactor body 1, and also includes a partitioned temperature control system 3 connected to the hydrothermal reactor body 1. The partitioned temperature control system 3 can independently adjust the temperature of different regions in the upper, middle and lower parts of the hydrothermal reactor body 1, and is also used to transport the precursor slurry to the precision feeding system in the high-speed shear homogenization unit 21. The high-speed shear homogenization unit 21 is a high-shear dispersion head 211. The mild circulation growth unit 22 includes at least one layer of inclined paddle agitators 221. The mild circulation growth unit 22 includes four layers of paddle agitators 221, and a static guide ring 222 is provided between two adjacent layers of paddle agitators 221. The paddle agitator 221 is an inclined blade turbine, and the inclination angle of its blades is 30 degrees to 60 degrees. The static guide ring 222 is fixed to the inner wall of the hydrothermal reactor body 1, and a guide hole is opened on its ring surface. The height-to-diameter ratio of the hydrothermal reactor body 1 is greater than 2.

[0024] The present invention also provides a hydrothermal reaction method for preparing monodisperse nanoboehmite, comprising the following steps: S1. Prepare the aluminum source and deionized water into a precursor slurry, then start the zoned temperature control system 3 to heat the inside of the hydrothermal reaction system to the target reaction temperature, and replace the air in the reactor with inert gas. S2. Keep the high-speed shear homogenization unit 21 in high-speed operation and pump all the precursor slurry prepared in the system preparation step into the working area of ​​the high-speed shear homogenization unit 21 through the precision feeding system, so as to complete the explosive homogenization in the upper area of ​​the hydrothermal reactor body 1. S3. After all the precursor slurry has been pumped in, the high-speed shear homogenization unit 21 is immediately stopped, and the mild circulation growth unit 22 is then started, so that the crystal nuclei formed in the previous stage can grow crystals in the uniform flow field generated by the mild circulation growth unit 22 to obtain boehmite slurry. S4. Finally, the boehmite slurry obtained from the time-series switching and controllable growth steps is subjected to solid-liquid separation and drying to obtain monodisperse nano boehmite powder.

[0025] In S2, the rotation speed of the high-speed shear homogenizing unit 21 is 8000 rpm to 15000 rpm, and the feeding time of the precursor slurry is controlled between 10 seconds and 60 seconds. In S3, the temperature of the area where the mild circulating growth unit 22 is located is controlled by the partition temperature control system 3, so that it is 0.5°C to 5°C lower than the temperature of the area where the high-speed shear homogenization unit 21 is located. The aluminum source is industrial-grade boehmite. The reaction temperature in the timing switching and controllable growth steps is 200℃ to 280℃, and the reaction time is 2 hours to 8 hours.

[0026] Example 2

[0027] The hydrothermal reaction system of this invention has a height-to-diameter ratio of 2.5 for the main body 1 of the hydrothermal reactor, and uses industrial-grade boehmite as the raw material. The specific implementation steps are as follows: Step 1: Mix industrial-grade boehmite with deionized water to prepare a slurry with a mass fraction of 20%. Step 2: Start the zoned temperature control system 3 to heat the upper, middle and lower temperature zones of the hydrothermal reactor body 1 to 240°C, and replace the air inside the reactor with nitrogen. Step 3: Start the upper high-shear dispersion head 211 and set the rotation speed to 12,000 rpm. At the same time, the precursor slurry is rapidly pumped into the area where the high-shear dispersion head 211 is located within 30 seconds through the precision feeding system (including a high-pressure metering pump); Step 4: After feeding is complete, immediately stop the high-shear dispersion head 211 and start the middle and lower layer inclined blade turbine stirrer at the same time, setting the speed to 200 rpm. Under these conditions, the crystal growth reaction continues for 4 hours. Step 5: After the reaction is complete, the slurry is quickly transferred to a cooling device, and then filtered, washed, and spray-dried to obtain the final boehmite powder.

[0028] The working process of the present invention will be described in detail below with reference to specific embodiments: In step 2, the system is preheated to the reaction temperature. The high-speed shear homogenization zone (upper layer) and the mild and uniform circulation zone (middle and lower layers) are physically ready, but the stirring module 2 has not yet been started and is waiting for specific process instructions. In step 3, when the precursor slurry is pumped in, the high-speed operation (12000 rpm) of the high-shear dispersion head 211 creates extremely high shear rates and energy densities in local areas. This leads to two key effects: first, large particle agglomerates in the slurry are broken up instantly, achieving ultimate mixing at the microscale; second, extremely high supersaturation and uniformity are established simultaneously, prompting a large number of crystal nuclei to be generated synchronously in a very short time (corresponding to a 30-second feed time) and in the same space. The core of this step is to use mechanical force to actively and forcibly create an ideal and short-lived nucleation environment, laying the foundation for obtaining a large number of initial crystal nuclei with uniform size. In step 4, the key operation is to immediately stop the high-shear head and start the intermediate agitator at the moment the feeding is completed. This timing switch clearly separates the intense nucleation stage from the gentle growth stage in time, achieving process decoupling and effectively preventing the generation of new, asynchronous crystal nuclei (i.e., secondary nucleation) due to uneven mixing or energy fluctuations during crystal growth. This is the core control logic to ensure the monodispersity of the final product. Once the nucleation stage is complete, the mild circulation zone composed of the multi-layered inclined blade turbine and the static guide ring 222 begins to operate. This structure does not pursue high shear, but rather aims to form a mild but powerful axial circulation flow throughout the entire reactor. This flow field ensures that all uniformly sized crystal nuclei generated in the previous stage can circulate within the hydrothermal reactor body 1, experiencing almost identical temperature and concentration fields, thereby obtaining equal growth opportunities and rates. The static guide ring 222 plays an important role in breaking up eddies and eliminating dead zones in this process, further ensuring the uniformity of the entire growth environment. At the same time, the scouring effect it generates also significantly reduces the risk of scaling.

[0029] As can be clearly seen from the combined description of Examples 1 and 2, the present invention is not a simple superposition of equipment or adjustment of process, but rather a combination of functional partitioning of equipment design and timing-switching process control, which realizes active, precise and independent control of the two key steps of nucleation and growth in hydrothermal crystallization.

[0030] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hydrothermal reaction system for preparing monodisperse nanoboehmite, characterized in that, It includes a hydrothermal reactor body (1) and a stirring module (2) disposed inside the hydrothermal reactor body (1). The stirring module (2) includes a high-speed shear homogenization unit (21) located on the upper part of the hydrothermal reactor body (1) and a mild circulation growth unit (22) located in the lower part of the hydrothermal reactor body (1). It also includes a zoned temperature control system (3) connected to the hydrothermal reactor body (1). The zoned temperature control system (3) can independently adjust the temperature of different areas in the upper, middle and lower parts of the hydrothermal reactor body (1), and is also used to transport the precursor slurry to the precision feeding system in the high-speed shear homogenization unit (21).

2. The hydrothermal reaction system for preparing monodisperse nanoboehmite according to claim 1, characterized in that, The high-speed shear homogenization unit (21) is a high-shear dispersion head (211), and the mild circulating growth unit (22) includes at least one layer of inclined paddle mixers (221).

3. The hydrothermal reaction system for preparing monodisperse nanoboehmite according to claim 2, characterized in that, The mild circulation growth unit (22) includes four layers of paddle mixers (221), and a static guide ring (222) is provided between two adjacent layers of paddle mixers (221).

4. The hydrothermal reaction system for preparing monodisperse nanoboehmite according to claim 3, characterized in that, The impeller agitator (221) is an inclined blade turbine with an inclination angle of 30 to 60 degrees. The static guide ring (222) is fixed to the inner wall of the hydrothermal reactor body (1) and has guide holes on its ring surface.

5. The hydrothermal reaction system for preparing monodisperse nanoboehmite according to claim 1, characterized in that, The height-to-diameter ratio of the main body (1) of the hydrothermal reactor is greater than 2.

6. A hydrothermal reaction method for preparing monodisperse nanoboehmite, employing the hydrothermal reaction system for preparing monodisperse nanoboehmite described in 1-5, characterized in that, Includes the following steps: S1. Prepare a precursor slurry by mixing aluminum source with deionized water, then start the partition temperature control system (3) to heat the inside of the hydrothermal reaction system to the target reaction temperature, and replace the air in the reactor with inert gas; S2. Keep the high-speed shear homogenizing unit (21) in a high-speed operating state, and pump all the precursor slurry prepared in the system preparation step into the working area of ​​the high-speed shear homogenizing unit (21) through the precision feeding system, so as to complete the explosive homogenization in the upper region of the hydrothermal reactor body (1). S3. After all the precursor slurry has been pumped in, the high-speed shear homogenization unit (21) is stopped immediately, and the mild circulation growth unit (22) is started. The crystal nuclei formed in the previous stage are allowed to grow crystals in the uniform flow field generated by the mild circulation growth unit (22) to obtain boehmite slurry. S4. Finally, the boehmite slurry obtained from the time-sequence switching and controllable growth steps is subjected to solid-liquid separation and drying to obtain the monodisperse nano boehmite powder.

7. The hydrothermal reaction method for preparing monodisperse nanoboehmite according to claim 6, characterized in that, In S2, the rotation speed of the high-speed shear homogenizing unit (21) is 8000 rpm to 15000 rpm, and the feeding time of the precursor slurry is controlled between 10 seconds and 60 seconds.

8. The hydrothermal reaction method for preparing monodisperse nanoboehmite according to claim 6, characterized in that, In S3, the temperature of the area where the mild circulating growth unit (22) is located is controlled by the partition temperature control system (3) so that it is 0.5°C to 5°C lower than the temperature of the area where the high-speed shear homogenization unit (21) is located.

9. The hydrothermal reaction method for preparing monodisperse nanoboehmite according to claim 6, characterized in that, The aluminum source is industrial-grade boehmite, and the reaction temperature in the timing switching and controllable growth steps is 200°C to 280°C, and the reaction time is 2 hours to 8 hours.

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