High specific surface area pseudo-boehmite powder and method for preparing the same

Abstract

This invention belongs to the field of boehmite powder preparation technology, and discloses a high specific surface area boehmite powder and its preparation method. The method includes: firstly, deeply cooling a macroscopic system containing aluminum salts to build a macroscopic cold energy reserve; then, at the instant of pulsed injection of an alkaline precipitant into the solution, utilizing the micro-area adiabatic space built by pausing external cooling, allowing the heat generated by the neutralization reaction to perform in-situ annealing of the newly formed crystal nuclei; finally, using the macroscopic cold energy reserve to quench and lock the annealed crystal nuclei. This invention, by synergistically coupling external cooling and reaction heat in space and time, transforms the traditional process of step-by-step low-temperature nucleation and high-temperature aging, where performance is at odds, into a physical process that is synergistically completed within a single cycle, thereby solving the problem of simultaneously achieving the two core performance indicators of high specific surface area and high thermal stability.

Description

Technical Field

[0001] This invention relates to a high specific surface area pseudoboehmite powder and its preparation method, belonging to the field of pseudoboehmite powder preparation technology. Background Technology

[0002] Currently, isothermal precipitation is a commonly used technique in the chemical synthesis of boehmite. Its principle involves maintaining the neutralization reaction of aluminum salts and alkali at a constant low temperature through an external cooling system, thereby inhibiting excessive grain growth and obtaining powder materials with a high specific surface area. However, as some applications demand higher structural stability of materials under high-temperature conditions, an inherent characteristic of this method in its process design makes it difficult to simultaneously meet the dual requirements of high specific surface area and high thermal stability. This is because the formation of boehmite involves two physical processes: rapid nucleation at low temperatures and a phase transformation requiring sufficient heat supply. The isothermal precipitation process relies on removing the heat released during the neutralization reaction. This separation of nucleation and crystallization steps in the process involves first maintaining a low-temperature environment within the reactor conducive to nucleation through external cooling, followed by a prolonged high-temperature aging process to provide energy for the phase transformation.

[0003] The inherent separation in this process leads to the following technical limitations: 1. The low-temperature conditions maintained to obtain a high specific surface area inhibit the transformation of newly formed particles into a stable crystalline phase, resulting in a lower initial crystallinity of the product and increasing the energy consumption and time load of subsequent aging steps; 2. The long-term high-temperature aging used to improve thermal stability leads to grain maturation and agglomeration, causing a decrease in specific surface area. Besides the aforementioned optimization approach through separation steps, some researchers in this field have attempted to prepare materials with specific morphologies by changing the reaction system and conditions. However, these methods have also failed to fundamentally overcome the aforementioned performance limitations. For example, Chinese invention patent CN118754176A discloses a template-free, mild method for preparing pseudo-boehmite microsphere powder. This method uses sodium aluminate as the aluminum source in a system composed of alcohol and ethyl acetate at 25°C. Up to 80 The essence of the technical concept of liquid-phase precipitation under mild conditions is to control the hydrolysis and precipitation rates at a relatively constant and mild temperature through chemical regulation (alcohol as a hydrolysis regulator and ethyl acetate as a precipitant) in order to obtain products with specific microstructures. However, this mild and almost isothermal reaction path avoids the technical challenge of high-temperature in-situ crystallization at the moment of formation of new crystal nuclei. Although this method can obtain a high initial specific surface area, the initial crystallinity and thermal stability of the product are inevitably limited due to the lack of a high-temperature treatment step. To improve its thermal stability, an independent long-term high-temperature aging step is still required. This inevitably returns to the old technical path of grain ripening and sharp reduction in specific surface area, and does not solve the core contradiction that it is difficult to achieve both high specific surface area and high thermal stability.

[0004] Therefore, how to utilize the heat generated during the reaction process to establish a preparation method that enables low-temperature nucleation and high-temperature phase transformation to be completed synergistically within a single process cycle has become the technical problem to be solved by this invention. Summary of the Invention

[0005] This invention provides a method for preparing high specific surface area pseudo-boehmite powder. Its main purpose is to solve the problem in the prior art that it is difficult to balance the specific surface area and thermal stability of the product and the process has high energy consumption due to the separation of low-temperature nucleation and high-temperature crystallization steps.

[0006] To achieve the above objectives, the present invention provides a method for preparing high specific surface area pseudo-boehmite powder, comprising the following steps performed cyclically:

[0007] Step a, Prerequisite Construction Step: Place a macroscopic system containing an aluminum salt solution in a reaction vessel, and use an external cooling system to set and maintain the overall temperature of the macroscopic system below 20°C. The depth of supercooling is used to build a macroscopic cold energy reserve for subsequent steps to quench the instantaneous high temperature of the micro-region;

[0008] Step b, constraint execution and structural optimization steps: Under the premise of macroscopic cold energy reserve, a quantitative amount of alkaline precipitant is injected into the high-speed stirred solution through a programmable metering pump within a pulse time of less than 5 seconds, and the external cooling system is paused within the pulse time to construct a transient adiabatic reaction space in the injected micro-region, thereby using the chemical energy generated by the neutralization reaction to complete the in-situ thermodynamic phase transition of the newly formed crystal nuclei; and after the phase transition is completed and before the micro-region is quenched in step c, the energy homogenization treatment of the crystal nuclei micro-region formed by the in-situ thermodynamic phase transition is performed through an ultrasonic transducer.

[0009] Step c, structure locking step: After the pulse time and energy homogenization process is completed, the external cooling system is restored, and the micro-region where the crystal nucleus that has completed phase transformation and energy homogenization is located is drawn into the macro cold energy reserve for forced heat exchange by stirring, thereby quenching the crystal nucleus and inhibiting its subsequent crystal growth.

[0010] Preferably, it further includes: real-time monitoring of the operating power consumption data stream of the programmable metering pump performing pulse injection; calculating the information entropy of the time series data formed by the operating power consumption data stream within a preset number of consecutive cycle periods; and when the value of the information entropy continues to rise and exceeds a preset entropy threshold, then feedforwardly increasing the total amount of alkaline precipitant injected or extending the pulse time in one or more subsequent cycles.

[0011] Preferably, the step of performing energy homogenization further includes: before applying the ultrasonic pulse for energy homogenization, transmitting a probe acoustic signal into the solution via an ultrasonic transducer and acquiring its echo signal to obtain a real-time acoustic impedance value characterizing the current acoustic properties of the solution; and determining the actual output power of the ultrasonic pulse according to the following rules: ,in, This refers to the actual output power of the ultrasonic pulse. As a reference output power; This is the real-time acoustic impedance value; This is the initial acoustic impedance value at the start of the preparation method; This is a preset compensation gain coefficient calibrated based on experimental data.

[0012] Preferably, the entire process of performing the cyclic steps further includes: continuously applying an alternating electric field with a frequency in the radio frequency band to the solution through one or more pairs of electrodes set on the reactor; wherein in step b, the injected alkaline precipitant forms a transient dielectric hot spot in the injected micro-region with a dielectric loss factor higher than that of the surrounding bulk solution, the transient dielectric hot spot selectively couples with the alternating electric field to absorb radio frequency energy and convert it into thermal energy, the thermal energy is superimposed with the chemical energy generated by the neutralization reaction, and together they are used to perform an in-situ thermodynamic phase transition on the newly formed crystal nuclei.

[0013] Preferably, the power consumption data stream is the instantaneous current or power data of the motor driving the programmable metering pump.

[0014] Preferably, the power density of the ultrasonic pulse applied in the energy homogenization step is set in the range of 10 W / cm² to 100 W / cm².

[0015] Preferably, in step a, the temperature range for the deep subcooling value is 5. Up to 15 .

[0016] Preferably, in step b, the pulse duration ranges from 0.5 seconds to 2 seconds.

[0017] Preferably, in step b, the alkaline precipitant is ammonia; in step a, the aluminum salt is aluminum sulfate; during the interval between two cycles, the external cooling system continues to run until the overall temperature of the macroscopic system recovers to the deep subcooling value, and then the next cycle begins.

[0018] A method for preparing high specific surface area pseudoboehmite powder: The high specific surface area pseudoboehmite powder is directly obtained, and the powder simultaneously possesses the following combination of structural and performance characteristics: its BET specific surface area, measured by nitrogen adsorption method, is [missing information]. to It is 800 in air atmosphere. After calcination at a certain temperature for 2 hours, the main crystalline phase determined by X-ray diffraction analysis was as follows: Furthermore, the primary particles of the powder have a near-monodispersive narrow particle size distribution.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This method establishes a novel preparation approach that no longer views the exothermic neutralization reaction and external cooling as opposing techniques. Instead, it couples the two in time and space. Specifically, through brief adiabatic pulse injection into the supercooled bulk solution, nucleation events and the occurrence of autogenous heat in a local micro-region are synchronized. Immediately afterwards, the micro-region is quenched using the macroscopic cooling of the bulk solution, so that the size of the newly formed crystal nuclei is immediately locked after obtaining the energy required for crystallization. The cyclic execution of this series of steps transforms the traditional process of low-temperature nucleation and high-temperature aging, which must be performed in steps and have mutually exclusive performance, into a coordinated physical process completed in a single cycle. This transforms the relationship between high specific surface area and high crystallinity from one of mutual constraints to a result jointly produced under the same mechanism.

[0021] 2. Based on the above preparation method, an ultrasonic pulse is applied during the brief interval between the completion of in-situ annealing and the occurrence of macroscopic quenching. This is not to utilize the conventional dispersing effect of the sound field, but rather to use it as a tool for the redistribution of energy in a micro-region. Within the instantaneously high-temperature micro-region formed by the pulse injection, there is a statistically uneven energy distribution. The cavitation and micro-disturbance caused by the sound field accelerate the heat exchange within this micro-region, making it more uniform. At the same time, it provides mechanical energy assistance for the lattice relaxation of the new crystal nuclei. In this way, by synergizing the chemical energy generated by the reaction itself with the externally applied mechanical energy at the moment of formation of the new crystal nuclei, the consistency of the microscopic quality of individual particles in the final product is guaranteed, avoiding the overall performance shortcomings caused by local annealing differences.

[0022] 3. This method further transforms the programmable metering pump that performs pulse injection or the transducer that applies acoustic field pulses from a simple instruction execution component into a process state sensing medium. During the reaction process, changes in the physical properties of the slurry system, such as viscosity, will be reflected in the fluctuations of the power consumption of the programmable metering pump or the changes in the acoustic impedance of the medium. This method monitors the operating data of these usually ignored execution components and uses it as an objective representation of the internal state evolution of the reaction system. Based on this, the parameters of subsequent pulse injection or acoustic field application are adjusted in a feedforward manner. This approach does not add new measurement hardware to the system, but rather transforms fixed programmed operations into an adaptive process that can respond to the internal dynamic evolution of the system by reusing the information of existing components. This ensures that the adaptive process maintains stable execution effects throughout the entire process and between different batches. Attached Figure Description

[0023] Figure 1 This is a block diagram of the closed-loop control system for the step-by-step coordinated reaction of the present invention;

[0024] Figure 2 This is a graph showing the relationship between pulse time, product specific surface area, and thermal stability in this invention.

[0025] Figure 3 This is a timing diagram of the closed-loop control for adaptive ultrasonic power adjustment in this invention. Detailed Implementation

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below. However, it should be understood that the following embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

[0027] The present invention discloses a method for preparing high specific surface area pseudo-boehmite powder. The process flow is designed as a series of steps circulated within a reaction vessel. The reaction vessel, as the implementation environment, is functionally defined to include a jacketed external cooling system capable of controlling the overall temperature of the system containing the aluminum salt solution within the vessel at 5°C. Up to 15 Within the specified range; simultaneously equipped with a programmable metering pump, whose flow control must ensure the injection of a preset volume of alkaline precipitant within a pulse time of 0.5 to 2 seconds; and a pump capable of providing no less than This method for preparing a high-power-density ultrasonic transducer transforms the two steps of low-temperature nucleation and high-temperature aging into a sequential process completed synergistically within a single cycle. The method's prerequisite construction step addresses the objective technical problem of establishing a low-temperature system with high heat capacity before the reaction begins, necessary to achieve the high supersaturation required for explosive nucleation and the high cooling rate required to subsequently inhibit crystal growth. Therefore, the initial state definition procedure of this method is set as follows: a solution system containing aluminum salt, wherein the aluminum salt being acted upon is aluminum sulfate, and its initial concentration is configured according to the target pore volume characteristics of the product; subsequently, an external cooling system is activated to set and maintain the overall temperature of the solution system below 20°C. The optimal temperature range for the deep supercooling value was determined to be 5. Up to 15 The basis for determining this range is: when the temperature is below 5... At this temperature, the solution viscosity increases, which is not conducive to the rapid mixing of reactants during subsequent pulse injections; and when the temperature is above 15°C... At that time, insufficient cold storage in the system would weaken the quenching effect of subsequent high-temperature micro-regions, making it difficult to effectively suppress the secondary growth of crystal nuclei. Therefore, this step constructs a low-temperature solution system for forced heat exchange in subsequent steps. The core of the method's constraint execution and structural optimization steps lies in utilizing the transient adiabatic reaction space constructed under low-temperature conditions to achieve in-situ treatment of newly formed crystal nuclei. Under the constraint of the low-temperature solution system, a fixed amount of alkaline precipitant (ammonia water) is injected into the high-speed stirred solution via a programmable metering pump within a pulse time of less than 5 seconds. An optimal pulse time range is 0.5 to 2 seconds. A key operation is... The external cooling system is paused during the pulse duration to create a transient adiabatic reaction space within the micro-region surrounding the injection point. Since the exothermic rate of the neutralization reaction is much greater than the heat conduction rate in the solution, this confines the chemical energy released by the reaction to the newly formed crystal nuclei, completing the in-situ thermodynamic phase transition of these amorphous hydrated alumina particles to an ordered pseudo-boehmite crystal phase. To address the statistical energy unevenness within the instantaneously high-temperature micro-region formed by the pulse injection, after the phase transition and before the micro-region is quenched in subsequent steps, the phase-transformed crystal nucleus micro-region undergoes energy homogenization treatment using an ultrasonic transducer. The power density of the ultrasonic pulse applied in this treatment step is set to... to Within a certain range, its function is to utilize the cavitation and micro-disturbances caused by the sound field to accelerate the heat exchange within the micro-region, making it tend to be uniform.

[0028] The structure-locking step of the method aims to quench the processed crystal nuclei using a low-temperature solution system to terminate their crystal growth. After the pulse time and energy homogenization treatment is completed, the external cooling system is restored, and stirring is used to entrain the micro-region containing the phase-transformed and energy-homogenized crystal nuclei into the surrounding low-temperature solution system for heat exchange, thereby quenching the crystal nuclei and inhibiting their subsequent ripening process. During the interval between cycles, the external cooling system continues to run until the overall temperature of the system returns to the aforementioned set deep supercooling value before starting the next cycle. To improve the process stability of this preparation method, a closed-loop adaptive adjustment mechanism can be introduced. This mechanism uses the motor operation data of the programmable metering pump to indirectly characterize the evolution of the internal state of the reaction system. This mechanism includes: real-time monitoring of the execution pulse. The system injects a power consumption data stream from the programmable metering pump, which is the instantaneous current or power data of the motor driving the programmable metering pump; calculates the information entropy of the time series data formed by the power consumption data stream within a preset number of consecutive cycles; sets a preset entropy threshold for this information entropy, the calibration procedure of which is as follows: run the method under stable process conditions, record the baseline value of the information entropy at this time, and then introduce a controllable disturbance and observe the critical point where the product particle size distribution deteriorates beyond the preset standard, and set the information entropy value corresponding to the critical point as the threshold; during production, when the calculated information entropy value continues to rise and exceeds the threshold, the control system feeds forward to increase the total amount of alkaline precipitant injected in one or more subsequent cycles or extends the pulse time to compensate for the impact caused by changes in the physical properties of the medium.

[0029] As another alternative implementation, the output power of the ultrasonic pulse in the energy homogenization step can be adaptively adjusted to cope with the dynamic changes in the acoustic impedance of the slurry during the reaction process. The adjustment procedure is as follows: before applying the ultrasonic pulse for energy homogenization, a probe acoustic signal is emitted into the solution through the same ultrasonic transducer and its echo signal is collected to obtain a real-time acoustic impedance value characterizing the current acoustic properties of the solution. The actual output power of the ultrasonic pulse is determined based on the following formula. : In the formula, This represents the actual output power of the ultrasonic pulse, measured in watts. This is a reference output power, measured in watts, whose value is determined experimentally and corresponds to the power value that achieves the expected energy equalization effect in the initial state. This is the real-time acoustic impedance value; The initial acoustic impedance value measured at the beginning of the preparation method; The calibration procedure for a preset compensation gain coefficient, determined through experimental data, is as follows: During the later stages of the reaction when the slurry viscosity is high, ultrasonic pulses with different gain coefficients are applied, and the uniformity of the particle size distribution of the final product is detected. The coefficient that restores the uniformity to its initial level is then determined. In addition, to address the insufficient heat release from the neutralization reaction due to the use of low-concentration reactants, an energy compensation implementation method can also be adopted; throughout the entire process of performing the cyclic steps, a step is also included in which an alternating electric field with a frequency in the radio frequency band is continuously applied to the solution through one or more pairs of electrodes set on the reactor; in this case, in step b, the injected alkaline precipitant forms a transient dielectric hot spot in the injected micro-region with a dielectric loss factor higher than that of the surrounding bulk solution. This hot spot selectively couples with the alternating electric field to absorb radio frequency energy and convert it into thermal energy. This portion of thermal energy is superimposed with the chemical energy released by the neutralization reaction and is used together to perform an in-situ thermodynamic phase transition on the newly formed crystal nuclei.

[0030] Example 1: This example illustrates the specific operation of the disclosed technical solution in a particular industrial application scenario. In a project developing an electrolyte separator precursor for solid-state lithium batteries, specific performance requirements were set for the pseudo-boehmite powder, namely, the powder must simultaneously possess at least the following specifications: The BET specific surface area supports high ionic conductivity; and at 800°C in an air atmosphere... After calcination for 2 hours, its main crystalline phase remains the same. To withstand the thermal shock during battery production and service; however, when using the isothermal precipitation process in this field, the low-temperature conditions set to obtain a high specific surface area result in insufficient crystallinity of the initial product. During the subsequent high-temperature aging process to improve thermal stability, this leads to grain ripening and agglomeration, causing a decrease in specific surface area and making it difficult to simultaneously meet the two performance indicators mentioned above. To address this technical problem, this project adopts the preparation method disclosed in this invention, which no longer seeks to remove the heat of neutralization reaction but utilizes it as an energy source. First, according to the prerequisite construction steps in the specific embodiment, a solution system containing aluminum sulfate is placed in a reaction vessel, and an external cooling system is activated to lower and maintain the overall temperature of the system at 10°C. This process constructs a low-temperature solution system for quenching subsequent micro-regions. Subsequently, the constraint execution and structural optimization steps are performed. Ammonia water is continuously pulsed into the high-speed stirred solution for 1 second using a programmable metering pump, while the operation of the external cooling system is paused during the injection. This creates a transient adiabatic reaction space around the injection point. The high concentration of reactants in this space triggers explosive nucleation, generating a large number of nanoscale amorphous hydrated alumina particles. Since the chemical energy released by the neutralization reaction cannot be conducted in time by the external cooling system and the surrounding low-temperature solution system, these newly generated particles undergo an in-situ thermodynamic phase transition in the same space, transforming them into highly crystalline pseudoboehmite nuclei.

[0031] The completion of this in-situ thermodynamic phase transition provides thermodynamically stable nuclei for the subsequent structure-locking step. Immediately afterwards, the external cooling system is restored, and with vigorous stirring, this high-temperature micro-region containing numerous phase-transformed nuclei is rapidly dispersed into the surrounding area at a temperature of 10°C. In a low-temperature solution system, the system absorbs heat within the micro-regions, quenching these crystal nuclei. This quenching process not only achieves high crystallinity but also terminates the subsequent crystal growth process, thus locking the size at the nanometer level. The aforementioned prerequisite construction steps, constraint execution and structure optimization steps, and structure locking steps are repeated as a complete cycle until the final pH value of the system reaches the preset value. The pseudoboehmite powder prepared by this method, after testing, has a BET specific surface area of ​​[missing value]. X-ray diffraction analysis showed that it was at 800 The main crystalline phase after calcination for 2 hours is This powder possesses both structural and performance characteristics that are considered mutually restrictive in the isothermal precipitation process.

[0032] Example 2: To verify the technical effectiveness of the preparation method disclosed in this invention in simultaneously improving the specific surface area and thermal stability of pseudoboehmite powder, as well as the applicability of key process parameters, this comparative experiment was designed and executed. The experimental platform was a 5L standard reactor equipped with a jacketed external cooling system and a high-speed stirring device. The temperature control accuracy of the cooling system was ±0.5°C. The raw materials used in the experiment were a 1.5 mol / L aluminum sulfate solution and a 25% ammonia solution. The product properties were determined by nitrogen adsorption method, measuring its BET specific surface area, and analyzed by X-ray diffraction in a muffle furnace at 800°C. The main crystalline phase, calcined in air for 2 hours, was used to evaluate its thermal stability. This experiment included one sample group and five control groups. The core process conditions for each sample group are shown in Table 1. The sample group of this invention fully adopted the preparation method described in the specific embodiments, and the initial temperature of the reaction system was set to 10 °C. The pulse injection time was 1 second, and external cooling was paused during the pulse injection; control group A used a conventional isothermal precipitation process, i.e., at 20... The sedimentation was carried out at a constant temperature, and the resulting slurry was then cooled to 95°C. The mixture was aged for 12 hours; control group B was prepared at 10... Precipitation was carried out at low temperature, but without any subsequent heat treatment; control group C used the same pulse injection and pause cooling steps as the sample group of this invention, but the initial temperature of the reaction system was set to 25°C. Control groups D and E were used to verify the applicability of the deep supercooling temperature range, and they were respectively in 2 and 25 Perform the same cyclic steps as the present invention sample at the initial temperature.

[0033] Table 1: Core process conditions and performance test results for each group

[0034]

[0035] Analysis of the experimental data in Table 1 shows that the product obtained by the sample group using the method of the present invention... While having a specific surface area, it also possesses a specific surface area of ​​800 The transition to stability Phase thermal stability; although the product of control group A has acceptable thermal stability, its specific surface area is only [missing information]. The results for control group B showed that although simple low-temperature precipitation could achieve a high specific surface area, the product's thermal stability was unsatisfactory due to the lack of effective thermodynamic phase change treatment. Control groups C and E showed similar results, with their specific surface areas both decreasing to [missing data]. This indicates that in the absence of a low-temperature solution system to provide a quenching medium, newly formed crystal nuclei will grow and agglomerate due to the inability to be cooled in time; the results of control group D show that when the initial temperature is below 5... During the experiment, an increase in slurry viscosity was observed, which adversely affected mass and heat transfer control. Experimental data indicated that combining the low-temperature solution system formed in the preliminary construction step, the pulse injection and transient adiabatic reaction space in the constrained execution step, and the quenching treatment in the structure locking step, and within 5... Up to 15 Performing the process within the deep supercooling range is a necessary condition for preparing pseudoboehmite powders that have both high specific surface area and high thermal stability.

[0036] Example 3: This example combines Figures 1 to 3 This paper describes a high specific surface area pseudoboehmite powder and its preparation method, such as... Figure 1As shown, this method begins with the input of raw materials, namely the supply of aluminum salt solution and alkaline precipitant. Its core process is designed as a cyclical operation, comprising three key steps: Step A, preliminary setup, where a macroscopic cold storage is constructed within the reactor through external cooling, preferably within a temperature range of 5°C. Up to 15 Step B, Pulse Reaction and Structure Optimization, involves in-situ thermodynamic phase transition of newly formed crystal nuclei within a transient adiabatic micro-region constructed by pausing external cooling, through pulsed injection of an alkaline precipitant. Step C, Structure Locking, involves quenching the phase-transformed crystal nuclei by restoring external cooling to inhibit their subsequent growth. The execution of this cycle is controlled in real time by a process adaptive control module. This module monitors the power consumption data stream of the programmable metering pump (i.e., the metering pump in the figure) and calculates the information entropy, adjusting the injection parameters in a feedforward manner. Simultaneously, an energy homogenization module can be coupled in step B. This module homogenizes the energy of the micro-region by applying ultrasonic pulses to ensure the consistency of crystal nuclei quality. Its output power can be adaptively adjusted based on the real-time monitored acoustic impedance value through a dynamic acoustic impedance compensation mechanism until the entire reaction system reaches the preset reaction endpoint, obtaining a high specific surface area pseudo-boehmite powder product.

[0037] like Figure 2 As shown in the figure, the horizontal axis represents the pulse time in seconds, and the left vertical axis represents the BET surface area in seconds. The right-hand vertical axis is Content, expressed as a percentage (%). In the graph, the solid line connecting solid dots represents the trend of BET specific surface area change, and the dashed line connecting solid dots represents... The trend of content change can be clearly seen from the graph. As the pulse time increases from 0.5 seconds, the BET specific surface area and... The content of all samples showed a trend of first increasing and then decreasing, and reached a peak simultaneously when the pulse time was 1 second. Among them, the BET specific surface area exceeded 420. ,and The content also reached a high level of 92%. For example... Figure 3As shown, this process is a sequential process involving five interactive objects: a controller, an ultrasonic transducer, a reaction solution, a power calculation unit, and a parameter storage. Its specific execution logic is as follows: Before each energy homogenization process, the controller first reads the initial acoustic impedance value and the reference power value from the parameter storage, and instructs the ultrasonic transducer to emit a probe acoustic wave signal (i.e., the probe wave in the figure) into the reaction solution. After receiving the echo signal, the ultrasonic transducer calculates the real-time acoustic impedance value characterizing the current acoustic properties of the reaction solution and transmits this real-time acoustic impedance value to the power calculation unit. Subsequently, the power calculation unit calculates the impedance change ratio by comparing the real-time acoustic impedance value with the initial acoustic impedance value, and applies a preset compensation gain coefficient to finally determine the actual output power required for this ultrasonic pulse. This set operating power is sent to the ultrasonic transducer, which applies a precise power ultrasonic pulse to the reaction solution for energy homogenization. After processing, the controller receives feedback indicating completion, thus completing a closed-loop adaptive power adjustment and energy homogenization operation.

[0038] Example 4: In the industrial production of boehmite, the concentration differences or ambient temperature fluctuations between batches of raw materials pose an engineering challenge to maintaining the consistency of the final product's quality across batches. This example provides a closed-loop control mechanism for adaptive pulse parameter adjustment using the operating power consumption data stream of a programmable metering pump, and outlines the determination procedure for its core algorithm and key parameters. To quantify the volatility of the programmable metering pump's operating power consumption data stream, information entropy is introduced as an indicator to measure its uncertainty. Its calculation procedure is set as follows: First, during continuous execution... In the next pulse injection step, instantaneous power data of the motor driving the metering pump is collected at a fixed sampling frequency to form a time series dataset; secondly, the range of all power values ​​in the dataset is divided into equal parts. The data series is divided into several quantization intervals, and the number of data points falling within each interval is counted, with their corresponding probabilities calculated. Finally, the information entropy of the time series data is calculated according to the following formula. : In the formula, Information entropy, measured in bits; This represents the total number of quantized intervals; For the data point to fall on the 1st The probability of each interval.

[0039] The preset entropy threshold used as the basis for logical judgment is determined through a standardized offline calibration experimental procedure: the initial state of this procedure is defined as follows: using a standard batch of raw materials that has been confirmed to meet the central specifications, the preparation method of this invention is executed on an experimental platform with controlled environmental parameters; the first step is to use the standard batch of raw materials to complete one preparation process, and record the average value of the information entropy sequence calculated during the stable phase of this process, which is defined as the baseline information entropy. The second step involves preparing multiple sets of perturbed batches of raw materials, each with a known, gradient-like deviation from the standard batch in the concentration of key components, such as ±0.5%, ±1.0%, and ±1.5%. The third step involves repeating the entire preparation process using these perturbed batches of raw materials, recording the standard deviation of the primary particle size distribution of the final product for each set of experiments, and simultaneously recording the average information entropy of the corresponding process. The fourth step is to determine the critical point where the standard deviation of the particle size distribution exceeds the upper limit of the product specification. The value serves as the basis for determining the preset entropy threshold; in a specific instance of this calibration process, the baseline information entropy... The average information entropy was measured using 2.5 bits in a batch with a concentration deviation of +1.0%. The standard deviation of the particle size distribution of the product exceeded the upper limit of the specification for the first time, so the preset entropy threshold was set to 3.0 bits. By executing the above calibration procedure, the preset entropy threshold was determined, so that the preparation method can automatically compensate for changes in the internal state of the system caused by factors such as fluctuations in raw material batches in subsequent continuous production, based on the comparison result between the real-time calculated information entropy and the threshold.

[0040] Example 5: To maintain a constant effective intensity of the ultrasonic pulses applied during the energy homogenization step throughout the entire preparation process, in order to cope with the dynamic changes in acoustic impedance caused by the increase in solid content in the slurry system, the reference output power in the adaptive adjustment mechanism of the specific implementation method needs to be adjusted. With preset compensation gain coefficient Perform offline calibration; the first step of this calibration procedure is to determine The process involves the following steps: in the initial stage of the preparation method, i.e., when the acoustic impedance of the slurry is at its initial value... Multiple parallel experiments were conducted, with all process parameters remaining consistent across groups except for the applied ultrasonic pulse power density. After preparation, particle size analysis was performed on the final products obtained from each group of experiments. The power density used in the experiment with the smallest standard deviation of the primary particle size distribution was set as the baseline output power. .

[0041] In determining The second step in this calibration procedure is to determine The process involves first performing a complete preparation process without power compensation, and then, near the reaction endpoint, when the slurry's acoustic impedance reaches its maximum value. At this point, a product sample was collected and its particle size distribution standard deviation was analyzed; subsequently, the preparation process was repeated until the slurry acoustic impedance approached... At that time, the adaptive adjustment mechanism as described in the specific implementation is activated, and a set of gradient-changing parameters is used respectively. Multiple sets of experiments were conducted; after preparation, particle size analysis was performed on each set of products, and the product whose particle size distribution standard deviation could be restored to the same level as the product in the initial stage of the reaction was selected. The value is determined as the preset compensation gain coefficient; after the parameters set by this procedure are applied to the control system, this preparation method can effectively compensate for changing operating conditions in subsequent production.

[0042] Example 6: This example provides a calibration procedure for key process parameters of an alternative implementation method for energy compensation by applying an alternating electric field under weak exothermic conditions. In some production scenarios, due to the use of low-concentration aluminum sulfate solution and ammonia, the chemical energy generated by the reaction in the pulse injection step is insufficient to completely transform the newly formed crystal nuclei into highly crystalline pseudoboehmite, thus affecting the thermal stability of the final product. To address this condition, a radio frequency energy compensation mechanism is activated, and its operating parameters are pre-calibrated. The first step of this calibration procedure is to determine the frequency of the alternating electric field, which is selected in the range of 10MHz to 100MHz. Within this frequency range, the alkaline precipitant... Polar molecular systems such as ammonia exhibit high dielectric loss factors, while the dielectric loss factor of the hydrated aluminum ion electrolyte system, which is the main body of the solution, is relatively low, thus allowing for selective heating. The second step of this procedure is to determine the output power of the alternating electric field. The process is as follows: First, using the target low-concentration raw material, the preparation method of this invention is fully executed once without applying an alternating electric field to obtain a reference sample. Second, while keeping the frequency and all other process parameters constant, multiple parallel experiments are conducted by applying a set of gradient-varying output powers to obtain a set of samples corresponding to different compensation powers. Finally, the reference sample and the set of samples are heated together at 800°C. The samples were calcined in air for 2 hours, and the main crystalline phase composition of each sample was analyzed by X-ray diffraction.

[0043] In a specific example of this calibration procedure, the main crystalline phase of the calcined product of the reference sample is: This indicates that its thermal stability does not meet the requirements; after applying a gradient change in output power, it was found that at an output power of 300W, the main crystalline phase of the calcined product of the corresponding sample stably transformed for the first time. The main crystal phase remains unchanged at higher power. In order to control energy consumption while meeting performance requirements, 300W was determined as the working power setting value under this specific low-concentration raw material system. After the parameters set by this procedure are applied to the control system, the preparation method can stably obtain pseudoboehmite powder that meets the thermal stability requirements under the condition of using low-cost raw materials.

[0044] To further verify the core technical concept of synergistically completing low-temperature nucleation and in-situ high-temperature phase transformation within a single cycle in the method of this invention from the reverse perspective, and to demonstrate its decisive role in technical effect compared to existing technologies, the following comparative example 1 is set up.

[0045] Comparative Example 1: The experimental platform, raw material specifications, and product performance characterization methods used in this comparative example were consistent with those described in Example 2. Specifically, the experimental platform was a 5L standard reactor equipped with a jacketed external cooling system and a high-speed stirring device; the raw materials used were a 1.5mol / L aluminum sulfate solution and a 25% ammonia solution; the product performance was determined by nitrogen adsorption method to measure its BET specific surface area, and by X-ray diffraction analysis of its performance in a muffle furnace at 800°C. The main crystalline phase, calcined in air for 2 hours, was used to evaluate its thermal stability. This comparative example employs a conventional technique combining isothermal precipitation with subsequent high-temperature aging, well-known in the art. The essential difference between this and the method of this invention is that it does not use the pulse injection-pause cooling-quenching locking technique claimed in this invention, which synergistically completes low-temperature nucleation and high-temperature phase transformation within a single cycle. The specific preparation process is as follows: the stirring device and external cooling system of the reactor are turned on, and the temperature of the 1.5 mol / L aluminum sulfate solution inside the reactor is precisely controlled and maintained at 20°C. Under constant temperature conditions, ammonia solution with a mass fraction of 25% was continuously added to the solution via a programmable metering pump until the pH value of the system reached 7.5, thus obtaining a pseudo-boehmite slurry. After the precipitation step was completed, the external cooling system was turned off, and heating was started to raise the temperature of the slurry in the reactor at 5°C. The rate increased to 95 / min The slurry was subjected to a high-temperature aging process at this temperature for 12 hours. During this process, the viscosity of the slurry was observed to gradually change with the extension of aging time. After aging, the resulting product was subjected to the same washing, filtering, and drying processes as in Example 1 to obtain the final powder sample, which was then subjected to performance testing.

[0046] Table 2: Core process conditions and performance test results of Comparative Example 1

[0047]

[0048] Experimental results show that, although the conventional low-temperature precipitation-high-temperature aging separation process can ensure that the final product has qualified thermal stability (the main crystalline phase is stable after calcination) through long-term high-temperature aging treatment, the conventional low-temperature precipitation-high-temperature aging separation process can ensure that the final product has qualified thermal stability. However, this aging process inevitably leads to grain maturation and agglomeration, a physical process that directly results in a significant decrease in the specific surface area of ​​the product, with its BET specific surface area being only [missing information]. The results are far lower than those obtained by the method of this invention. This result objectively confirms that, in the absence of the core technical concept of in-situ annealing of newly formed crystal nuclei using self-generated heat of reaction and immediate quenching and locking as claimed in this invention, the two key performance indicators of high specific surface area and high thermal stability are indeed mutually restrictive under the conventional technical framework, and it is difficult to achieve both simultaneously.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high specific surface area pseudo-boehmite powder, characterized in that, This includes repeatedly executing the following steps: Step a, Prerequisite Construction Step: Place a macroscopic system containing an aluminum salt solution in a reaction vessel, and use an external cooling system to set and maintain the overall temperature of the macroscopic system below 20°C. The depth of supercooling is used to build a macroscopic cold energy reserve for subsequent steps to quench the instantaneous high temperature of the micro-region; Step b, constraint execution and structural optimization steps: Under the premise of macroscopic cold energy reserve, a quantitative amount of alkaline precipitant is injected into the high-speed stirred solution through a programmable metering pump within a pulse time of less than 5 seconds, and the external cooling system is paused within the pulse time to construct a transient adiabatic reaction space in the injected micro-region, thereby using the chemical energy generated by the neutralization reaction to complete the in-situ thermodynamic phase transition of the newly formed crystal nuclei; and after the phase transition is completed and before the micro-region is quenched in step c, the energy homogenization treatment of the crystal nuclei micro-region formed by the in-situ thermodynamic phase transition is performed through an ultrasonic transducer. Step c, structure locking step: After the pulse time and energy homogenization process is completed, the external cooling system is restored, and the micro-region where the crystal nucleus that has completed phase transformation and energy homogenization is located is drawn into the macro cold energy reserve for forced heat exchange, thereby quenching the crystal nucleus.

2. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, Also includes: Real-time monitoring of the operating power consumption data stream of the programmable metering pump that performs pulse injection; Calculate the information entropy of the time-series data formed by the running power consumption data stream within a preset number of consecutive cycles; And when the information entropy value continues to rise and exceeds a preset entropy threshold, the total amount of alkaline precipitant injected in one or more subsequent cycles is increased or the pulse time is extended.

3. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, The energy homogenization process further includes: before applying the ultrasonic pulse for energy homogenization, transmitting a probe acoustic signal into the solution via an ultrasonic transducer and acquiring its echo signal to obtain a real-time acoustic impedance value characterizing the current acoustic properties of the solution; and determining the actual output power of the ultrasonic pulse according to the following rules: ,in, This refers to the actual output power of the ultrasonic pulse. As a reference output power; This is the real-time acoustic impedance value; This is the initial acoustic impedance value at the start of the preparation method; This is a preset compensation gain coefficient calibrated based on experimental data.

4. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, Throughout the cyclic process, the process also includes: continuously applying an alternating electric field with a frequency in the radio frequency band to the solution through one or more pairs of electrodes placed on the reactor; wherein in step b, the injected alkaline precipitant forms a transient dielectric hot spot in the injected micro-region with a dielectric loss factor higher than that of the surrounding bulk solution. This transient dielectric hot spot selectively couples with the alternating electric field to absorb radio frequency energy and convert it into thermal energy. This thermal energy is superimposed with the chemical energy generated by the neutralization reaction and is used together to perform an in-situ thermodynamic phase transition on the newly formed crystal nuclei.

5. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 2, characterized in that, The operating power consumption data stream is the instantaneous current or power data of the motor driving the programmable metering pump.

6. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, The power density of the ultrasonic pulses applied in the energy homogenization process is set to be in the range of 10 W / cm² to 100 W / cm².

7. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, In step a, the temperature range for the deep subcooling value is 5. Up to 15 .

8. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, In step b, the pulse duration ranges from 0.5 seconds to 2 seconds.

9. The method for preparing a high specific surface area pseudo-boehmite powder according to claim 1, characterized in that, In step b, the alkaline precipitant is ammonia; in step a, the aluminum salt is aluminum sulfate; during the interval between two cycles, the external cooling system continues to run until the overall temperature of the macroscopic system returns to the deep subcooling value, and then the next cycle begins.

10. A high specific surface area pseudoboehmite powder directly obtained by the preparation method of high specific surface area pseudoboehmite powder according to claim 1, characterized in that, The powder possesses the following combination of structural and performance characteristics: its BET specific surface area, measured by nitrogen adsorption, is [missing information]. to ; It is at 800 in air atmosphere After calcination at a certain temperature for 2 hours, the main crystalline phase determined by X-ray diffraction analysis was as follows: Furthermore, the primary particles of the powder have a near-monodispersive narrow particle size distribution.

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