Magnesium hydride powder and preparation method thereof

Abstract

The invention provides magnesium hydride powder and a preparation method thereof. The preparation method comprises the following steps: filling a first magnesium particle group and a second magnesium particle group into a reactor, introducing hydrogen, and heating the reactor to a reaction temperature T1 of 305-310 DEG C through an external heating mechanism, so that the second magnesium particle group and at least part of hydrogen are subjected to a first hydrogenation reaction and heat is released; the first magnesium particle group is jointly heated by heat released by the reaction of the second magnesium particle group and hydrogen and an external heating mechanism, the first magnesium particle group and the remaining hydrogen are subjected to a second hydrogenation reaction, the reaction time for converting the first magnesium particle group into magnesium hydride powder is shortened, and the magnesium hydride powder with the preset purity is obtained. According to the preparation method provided by the invention, the problems of insufficient safety, slow hydrogenation kinetics and high energy consumption of a magnesium hydride preparation process in the prior art are effectively solved, and the hydrogenation efficiency is remarkably improved.

Description

Magnesium hydride powder and its preparation method Technical Field

[0001] This invention relates to the field of hydrogen energy storage material preparation technology, and more specifically, to a magnesium hydride powder and its preparation method. Background Technology

[0002] Energy is the fundamental driving force for human societal development. With population growth and economic expansion, the demand for energy continues to increase. Fossil fuels, due to their non-renewable nature, are gradually facing depletion pressures, while the large amounts of greenhouse gases such as carbon dioxide produced during their combustion also cause serious environmental problems. Against this backdrop, clean, efficient, and renewable hydrogen energy is considered one of the most promising secondary energy sources. Hydrogen has advantages such as high energy density, abundant sources, and clean combustion products, making it an important strategic choice for achieving energy transition and carbon neutrality goals.

[0003] Among hydrogen energy utilization methods, solid-state hydrogen storage materials have attracted widespread attention due to their high volumetric hydrogen storage density, good safety, and excellent reversible cycle performance. Magnesium hydride (MgH2), in particular, is considered one of the most promising hydrogen storage materials due to its high hydrogen storage capacity (theoretically approximately 7.6 wt%), abundant raw materials, and low cost. However, existing magnesium hydride preparation methods still face several challenges: on the one hand, excessively fine magnesium powder particles pose a significant risk of dust explosion in air, leading to safety hazards in large-scale preparation; on the other hand, excessively large particles result in sluggish hydrogenation kinetics, making the hydrogenation reaction time-consuming and energy-intensive, failing to meet the efficiency requirements for industrial preparation and application. Furthermore, traditional processes do not adequately utilize the heat of reaction, requiring continuous external heating to maintain the reaction, further increasing costs and energy consumption.

[0004] Therefore, how to improve the rate and energy utilization efficiency of hydrogenation reaction while ensuring safety, and prepare magnesium hydride powder with controllable particle size distribution and excellent hydrogen storage performance, has become a key problem that urgently needs to be solved in the field of solid-state hydrogen storage materials. Summary of the Invention

[0005] The main objective of this invention is to provide a magnesium hydride powder and its preparation method, in order to solve the problems of insufficient safety, slow hydrogenation kinetics, high energy consumption, and difficulty in controlling the particle size distribution and poor hydrogen storage performance of the magnesium hydride powder prepared in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for preparing magnesium hydride powder. This method includes: loading a first group of magnesium particles and a second group of magnesium particles into a reactor, introducing hydrogen gas, and heating the reactor to a reaction temperature T1 (305–310°C) using an external heating mechanism, so that the second group of magnesium particles undergoes a first hydrogenation reaction with at least a portion of the hydrogen gas, releasing heat; and using the heat released from the reaction between the second group of magnesium particles and hydrogen gas, along with the external heating mechanism, to heat the first group of magnesium particles, causing the first group of magnesium particles to undergo a second hydrogenation reaction with the remaining portion of the hydrogen gas. Furthermore, the reaction time for the first magnesium particle group to be converted into magnesium hydride powder is shortened, and magnesium hydride powder with a preset purity is obtained; wherein, the first magnesium particle group and the second magnesium particle group satisfy the following relationship: (1) Under the same reaction container and reaction conditions, equal amounts of the first magnesium particle group and the second magnesium particle group are reacted with hydrogen gas respectively, and the temperature difference between the first magnesium particle group and the second magnesium particle group at any same time is satisfied within the preset range in the curves of temperature change of their respective reaction systems over time; (2) The minimum particle size of the first magnesium particle group is greater than the maximum particle size of the second magnesium particle group.

[0007] Furthermore, the average particle size of the first magnesium particle group is 200–300 μm; the average particle size of the second magnesium particle group is 15–75 μm.

[0008] Furthermore, the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is (4-15):1; preferably (4-9):1.

[0009] Furthermore, the testing process for the temperature change curve of the reaction system over time includes: setting the heating temperature of the reaction vessel to any temperature between 0 and 420°C, setting the hydrogen pressure to be the same during the reaction, allowing the first magnesium particle group and the second magnesium particle group to react with hydrogen respectively, and monitoring the temperature values ​​of the reaction system at different times to obtain the curve; preferably, the temperature difference is obtained by acquiring the corresponding temperature in the two curves at any same time within the reaction time range of 0 to 300 min, and calculating the difference between the two as the temperature difference.

[0010] Furthermore, during the first hydrogenation reaction, the initial pressure P0 of hydrogen in the reactor is 0.8–1.2 MPa; preferably 0.8–1 MPa.

[0011] Furthermore, during the second hydrogenation reaction, the hydrogen pressure P1 in the reactor is 2.5–3.0 MPa; preferably 2.6–3.0 MPa.

[0012] Furthermore, the reaction temperature T2 of the second hydrogenation reaction is 415–425 °C, and the time is 20–40 min.

[0013] Furthermore, in the preparation method, the initial pressure P0 is increased to pressure P1 at a pressurization rate of 0.3 to 0.4 MPa / min.

[0014] Furthermore, during the first hydrogenation reaction, a first stirring is performed at a rate of 180–320 rpm; and / or, during the second hydrogenation reaction, a second stirring is performed at a rate of 220–400 rpm.

[0015] To achieve the above objectives, another aspect of the present invention provides a magnesium hydride powder, which is prepared by the method for preparing the magnesium hydride powder described above in this application.

[0016] Furthermore, the D50 of the magnesium hydride powder is 100–102 μm, and the hydrogenation amount is 6.5–7.4%.

[0017] By applying the technical solution of this invention, this application utilizes a combination of a first group of magnesium particles with different particle sizes and a second group of magnesium particles, so that the smaller second group of magnesium particles undergoes a first hydrogenation reaction with at least a portion of the hydrogen gas, releasing heat during the reaction. This heat is then transferred to the larger first group of magnesium particles through the contact interface between the particles. The first group of magnesium particles uses this heat and an external heating mechanism to carry out a second hydrogenation reaction, thereby transforming the reaction process from an externally driven mode to a self-driven mode of reaction heat, thus shortening the reaction time and improving production efficiency.

[0018] In the above process, the smaller second group of magnesium particles has a larger specific surface area and more active sites. Compared with the larger first group of magnesium particles, it can adsorb and dissociate hydrogen molecules earlier, initiate the first hydrogenation reaction, and rapidly release the heat of reaction. This heat is conducted to the surface of the larger particles through the particle contact interface, prompting the larger first group of magnesium particles to quickly enter the hydrogenation process. This forms a synergistic hydrogenation process triggered by small particles and followed by larger particles. As a result, the above reaction gradually transitions from external heating to self-driven by the heat of reaction, significantly accelerating the reaction rate and shortening the overall reaction time.

[0019] Meanwhile, the presence of the first group of magnesium particles with larger particle size provides higher heat capacity and a stable heat exchange interface, which can absorb and balance local heat, prevent overheating and runaway, and thus ensure the stability of the reaction platform and batch-to-batch consistency.

[0020] Compared with the traditional method of using magnesium powder with a single particle size, the process of this application achieves efficient utilization of reaction heat while ensuring safety, reduces external energy consumption, and can achieve a higher degree of hydrogenation in a shorter time, thereby increasing the amount of hydrogenation of magnesium hydride powder and obtaining magnesium hydride powder of the preset purity in a shorter time, thus achieving an overall improvement in hydrogenation efficiency.

[0021] In summary, the preparation method provided in this application effectively solves the problems of insufficient safety, slow hydrogenation kinetics, and high energy consumption in the existing magnesium hydride preparation process, and significantly improves the hydrogenation efficiency. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0023] As described in the background art, existing methods for preparing magnesium hydride powder suffer from insufficient safety, slow hydrogenation kinetics, high energy consumption, and difficulty in controlling the particle size distribution and poor hydrogen storage performance of the resulting magnesium hydride powder. To address these technical problems, this application provides a method for preparing magnesium hydride powder, comprising: loading a first group of magnesium particles and a second group of magnesium particles into a reactor, introducing hydrogen gas, and heating the reactor to a reaction temperature T1 (305–310°C) using an external heating mechanism, so that the second group of magnesium particles undergoes a first hydrogenation reaction with at least a portion of the hydrogen gas, releasing heat; and using the heat released from the reaction of the second group of magnesium particles with hydrogen gas and the external heating mechanism to heat the first group of magnesium particles, causing the first group of magnesium particles to undergo a second hydrogenation reaction with the remaining portion of the hydrogen gas. The reaction time for the first magnesium particle group to be converted into magnesium hydride powder is shortened, and magnesium hydride powder with a preset purity is obtained; wherein, the first magnesium particle group and the second magnesium particle group satisfy the following relationship: (1) Under the same reaction container and reaction conditions, equal amounts of the first magnesium particle group and the second magnesium particle group are reacted with hydrogen gas respectively, and the temperature difference between the first magnesium particle group and the second magnesium particle group at any same time is satisfied within the preset range in the curve of temperature change of each reaction system over time; (2) the minimum particle size of the first magnesium particle group is greater than the maximum particle size of the second magnesium particle group.

[0024] In the above relationship (1), "equal amount" in "equal amount of first magnesium particle group and second magnesium particle group" means that the weight of the first magnesium particle group is the same as the weight of the second magnesium particle group, and the two magnesium particle groups react with hydrogen gas respectively.

[0025] This application utilizes a combination of a first group of magnesium particles with different particle sizes and a second group of magnesium particles. The smaller second group of magnesium particles undergoes a first hydrogenation reaction with at least a portion of the hydrogen gas, releasing heat during this reaction. This heat is then transferred to the larger first group of magnesium particles through the contact interface between the particles. The first group of magnesium particles uses this heat, along with an external heating mechanism, to carry out a second hydrogenation reaction. This transforms the reaction process from being driven by external heating to a self-driven reaction heat mode, thereby shortening the reaction time and improving production efficiency.

[0026] In the above process, the smaller second group of magnesium particles has a larger specific surface area and more active sites. Compared with the larger first group of magnesium particles, it can adsorb and dissociate hydrogen molecules earlier, initiate the first hydrogenation reaction, and rapidly release the heat of reaction. This heat is conducted to the surface of the larger particles through the particle contact interface, prompting the larger first group of magnesium particles to quickly enter the hydrogenation process. This forms a synergistic hydrogenation process triggered by small particles and followed by larger particles. As a result, the above reaction gradually transitions from external heating to self-driven by the heat of reaction, significantly accelerating the reaction rate and shortening the overall reaction time.

[0027] Meanwhile, the presence of the first group of magnesium particles with larger particle size provides higher heat capacity and a stable heat exchange interface, which can absorb and balance local heat, prevent overheating and runaway, and thus ensure the stability of the reaction platform and batch-to-batch consistency.

[0028] Compared with the traditional method of using magnesium powder with a single particle size, the process of this application achieves efficient utilization of reaction heat while ensuring safety, reduces external energy consumption, and can achieve a higher degree of hydrogenation in a shorter time, thereby increasing the amount of hydrogenation of magnesium hydride powder and obtaining magnesium hydride powder of the preset purity in a shorter time, thus achieving an overall improvement in hydrogenation efficiency.

[0029] In summary, the preparation method provided in this application effectively solves the problems of insufficient safety, slow hydrogenation kinetics, and high energy consumption in the existing magnesium hydride preparation process, and significantly improves the hydrogenation efficiency.

[0030] It should be noted that the amount of hydrogen added in this application refers to the weight percentage of hydrogen (H) in the magnesium hydride powder.

[0031] In a preferred embodiment, the reactor has a hollow shell structure, with an external heating mechanism disposed on its outer periphery. The external heating mechanism heats the reactor by heating heat transfer oil. This heating method is simple and easy to implement, and allows for precise control of the reactor temperature.

[0032] In this application, the pre-defined range for the relationship between the first and second magnesium particle groups as described in section (1) refers to a temperature difference of 10–35°C. This temperature difference is limited by the difference in particle size between the first and second magnesium particle groups, the number of the two particle groups, and their weight ratio.

[0033] In this application, the magnesium hydride powder with the preset purity refers to magnesium hydride powder with a purity of ≥90%, preferably 90%. Using the process described in this application, magnesium hydride powder with the preset purity can be obtained in a shorter time.

[0034] In a preferred embodiment, the average particle size of the first magnesium particle group is 200–300 μm, and the average particle size of the second magnesium particle group is 15–75 μm. Compared to other ranges, limiting the average particle sizes of the first and second magnesium particle groups to the above ranges is beneficial for better utilizing the reactivity of the second magnesium particle group, improving the efficiency of heat transfer from the first hydrogenation reaction to the first magnesium particle group, thereby shortening the reaction time and improving the hydrogenation efficiency.

[0035] In a preferred embodiment, the weight ratio of the first magnesium particle group to the second magnesium particle group is (4-15):1. The weight ratio of the first magnesium particle group to the second magnesium particle group includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the efficiency of the hydrogenation reaction, reducing energy consumption, and also to improving the safety of the reaction and the consistency of magnesium hydride powder obtained in each batch.

[0036] To further improve the efficiency of the hydrogenation reaction, shorten the reaction time, and reduce energy consumption, preferably, the weight ratio of the first magnesium particle group to the second magnesium particle group is (4-9):1.

[0037] In a preferred embodiment, the process of testing the temperature-time curve of the reaction system includes: setting the heating temperature of the reaction vessel to any temperature between 0 and 420°C, setting the hydrogen pressure to be the same during the reaction, allowing the first and second magnesium particle groups to react with hydrogen respectively, and monitoring the temperature values ​​of the reaction system at different times to obtain the curve. Using the above testing method to obtain the temperature-time curve of the reaction system facilitates the selection of the first and second magnesium particle groups suitable for this application, forming a synergistic hydrogenation process triggered by small particles and followed by larger particles, thereby shortening the reaction time for the first magnesium particle group to convert into magnesium hydride powder.

[0038] To further shorten the reaction time for the first magnesium particle group to transform into magnesium hydride powder, preferably, the temperature difference is obtained by acquiring the corresponding temperatures on two curves at any equal time within the reaction time range of 0–300 min, and calculating the difference between the two curves. This temperature difference is 10–35 °C. This temperature difference is limited by the difference in particle size between the first and second magnesium particle groups, the quantity of the two particle groups, and their weight ratio.

[0039] In a preferred embodiment, during the first hydrogenation reaction, the initial pressure P0 of the hydrogen in the reactor is 0.8 to 1.2 MPa; preferably, the initial pressure P0 is 0.8 to 1 MPa.

[0040] In a preferred embodiment, during the second hydrogenation reaction, the hydrogen pressure P1 in the reactor is 2.5–3.0 MPa. The pressure P1 includes, but is not limited to, the above range. Limiting it within this range is beneficial for increasing the hydrogenation amount of the subsequently produced magnesium hydride powder, and also for improving the safety of the preparation process.

[0041] To further increase the amount of hydrogen added to the subsequently produced magnesium hydride powder and improve the safety of the preparation process, preferably, during the second hydrogenation reaction, the pressure P1 of hydrogen in the reactor is 2.6 to 3.0 MPa.

[0042] In a preferred embodiment, the reaction temperature T2 of the second hydrogenation reaction is 415–425°C, and the time is 20–40 min. The reaction temperature T2 and time of the second hydrogenation reaction include, but are not limited to, the above-mentioned ranges. Limiting them to the above-mentioned ranges is beneficial to increasing the hydrogenation amount of the subsequently obtained magnesium hydride powder, and also to improving the safety of the preparation process.

[0043] In a preferred embodiment, in the preparation method provided in this application, the initial pressure P0 is increased to pressure P1 at a pressurization rate of 0.3 to 0.4 MPa / min. Compared to other ranges, limiting the pressurization rate to the above range is beneficial to increasing the hydrogenation amount of the subsequently obtained magnesium hydride powder, and also to improving the safety of the preparation process.

[0044] In a preferred embodiment, the reactor is equipped with a stirring paddle; a first stirring is performed during the first hydrogenation reaction, and the stirring speed is 180–320 rpm. The stirring speed of the first stirring includes, but is not limited to, the above range. Limiting it to the above range is beneficial to ensure that the second magnesium particle group in the reactor comes into more sufficient contact with the introduced hydrogen gas, thereby improving the efficiency of the first hydrogenation reaction.

[0045] To further improve the efficiency of the first hydrogenation reaction, preferably, the first stirring rate is 200-250 rpm, or 280-320 rpm, or 180-220 rpm, or 220-260 rpm.

[0046] In a preferred embodiment, the reactor is a long-tube reactor.

[0047] In a preferred embodiment, a second stirring is performed during the second hydrogenation reaction, and the stirring rate is 220–400 rpm. The stirring rate includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the efficiency of the second hydrogenation reaction and to increasing the amount of hydrogen added to the obtained magnesium hydride powder.

[0048] In a preferred embodiment, the preparation method provided in this application further includes: ball milling the obtained product in an inert atmosphere, followed by sieving to obtain magnesium hydride powder with a particle size of 10–300 μm. This post-processing method facilitates the production of magnesium hydride powder with controllable particle size and higher appearance purity, thus meeting the dispersibility and film-forming properties requirements of magnesium hydride powder in different application scenarios. Simultaneously, processing in an inert atmosphere avoids contact between the product and air, which improves safety.

[0049] To improve the safety of the post-processing, in a preferred embodiment, the inert atmosphere includes, but is not limited to, one or more of nitrogen, argon, and helium.

[0050] In a preferred embodiment, milling media are added during the ball milling process, with a weight ratio of milling media to product of (19-21):1, a milling speed of 200-400 rpm, and a milling time of 2-6 hours. Compared to other ranges, limiting the weight ratio of milling media to product, the milling speed, and the milling time to the above range is beneficial for promoting collision and shearing between product particles, thereby achieving finer particle size and more uniform distribution of magnesium hydride powder, improving the activity and specific surface area of ​​magnesium hydride powder, and adapting to the dispersibility and film-forming properties of magnesium hydride powder in different application scenarios.

[0051] In a preferred embodiment, the preparation method provided in this application further includes: subjecting the obtained product to magnetic separation and / or drying to obtain magnesium hydride powder. Magnetic separation can remove magnetic particles mixed in the product, thereby improving the purity of the magnesium hydride powder. Drying can reduce the content of moisture and volatile residues in the product, thereby helping to avoid the adverse effects of moisture on the performance of magnesium hydride powder during hydrogen storage.

[0052] The second aspect of this application also provides a magnesium hydride powder, which is prepared by the method described above. The preparation method provided by this application effectively solves the problems of insufficient safety, slow hydrogenation kinetics, and high energy consumption in existing magnesium hydride preparation processes, significantly improving hydrogenation efficiency. It should be noted that, due to the special nature of materials science and limitations of existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the prepared magnesium hydride powder. However, experiments show that the magnesium hydride powder obtained in this application has a more controllable particle size distribution and superior hydrogen storage performance.

[0053] In a preferred embodiment, the magnesium hydride powder has a D50 of 100–102 μm, a hydrogenation amount of 6.5–7.4%, and a BET specific surface area of ​​approximately 15 m². 2 / g, whiteness approximately 41. Due to the special nature of the materials field and the limitations of existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the magnesium hydride powder prepared above. However, experiments show that the magnesium hydride powder obtained in this application has a more controllable particle size distribution, higher specific surface area, better hydrogen storage performance, and a purer appearance.

[0054] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0055] It should be noted that the particle size and D50 of the magnesium hydride powder in this application were measured using a laser particle size analyzer; the BET specific surface area was measured using the nitrogen adsorption-desorption method.

[0056] Example 1

[0057] A method for preparing magnesium hydride powder includes:

[0058] (1) Weigh 5.95 kg of the first magnesium particle group with an average particle size of 250 μm and 1.05 kg of the second magnesium particle group with an average particle size of 50 μm; the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 5:1; wherein, the first magnesium particle group and the second magnesium particle group satisfy the following relationship: under the same reaction vessel (internal volume of 3.0 L) and reaction conditions (the heating temperature of the reaction vessel is set to 310 °C), 0.50 kg of the first magnesium particle group and 0.50 kg of the second magnesium particle group are reacted with hydrogen respectively, and the temperature change curve of each reaction system over time is measured. When the reaction reaches 20 min, the temperature difference between the first magnesium particle group and the second magnesium particle group is 15 °C.

[0059] (2) The first and second magnesium particle groups weighed in step (1) are loaded into a horizontal long tube reactor with a length of 1.3m. After the pressure is evacuated to 1kPa, argon gas is introduced to replace it once, and then the reactor is evacuated again. Hydrogen gas is introduced into the reactor to make the initial pressure P0 1.0MPa. Stirring is started at a speed of 250rpm. The heat transfer oil is heated by an external heating mechanism to heat the reactor to T1=310℃.

[0060] (3) Keep the temperature T1 constant and increase the pressure of hydrogen P1 to 2.8 MPa at a pressurization rate of 0.35 MPa / min to carry out the first hydrogenation reaction. After 30 min of reaction, the initial product system is obtained.

[0061] (4) When the temperature of the powder in the initial product system exceeds the external heating temperature, stop the external heating, keep stirring and adjust the hydrogen pressure to make the temperature 420℃ for the second hydrogenation reaction. The heat of reaction is dissipated through the reactor wall and the environment. After 300 minutes of reaction, the final product system is obtained.

[0062] (5) As the diffusion resistance of hydrogen in the magnesium powder particles increases, the heat release decreases and the temperature of the final product system begins to drop. When the temperature drops to 380°C, the hydrogen supply is stopped, and the system is cooled to room temperature under argon protection. After the hydrogen in the reactor is discharged and replaced with argon, the lid is opened and the powder is collected.

[0063] Example 2

[0064] A method for preparing magnesium hydride powder includes:

[0065] (1) Weigh 5.60 kg of the first magnesium particle group with an average particle size of 240 μm and 1.40 kg of the second magnesium particle group with an average particle size of 40 μm; the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 6:1; wherein, the first magnesium particle group and the second magnesium particle group satisfy the following relationship: under the same reaction vessel (internal volume of 3.0 L) and reaction conditions (the heating temperature of the reaction vessel is set to 308 °C), 0.50 kg of the first magnesium particle group and 0.50 kg of the second magnesium particle group are reacted with hydrogen respectively, and the temperature change curve of each reaction system over time is measured. When the reaction reaches 15 min, the temperature difference between the first magnesium particle group and the second magnesium particle group is 18 °C.

[0066] (2) The first and second magnesium particle groups weighed in step (1) are loaded into a horizontal long tube reactor with a length of 1.3m. After evacuating to a pressure of 1kPa, argon gas is introduced to replace the pressure once, and then the reactor is evacuated again. Hydrogen gas is introduced into the reactor to make the initial pressure P0 0.8MPa. Stirring is started at a stirring speed of 310rpm. The heat transfer oil is heated by an external heating mechanism to heat the reactor to T1=307℃.

[0067] (3) Keep the temperature T1 constant and increase the pressure of hydrogen P1 to 2.7 MPa at a pressurization rate of 0.32 MPa / min to carry out the first hydrogenation reaction. After 25 min of reaction, the initial product system is obtained.

[0068] (4) When the temperature of the powder in the initial product system exceeds the external heating temperature, stop the external heating, keep stirring and adjust the hydrogen pressure to make the temperature 418℃ for the second hydrogenation reaction. By maintaining the temperature difference between the powder and the outer jacket at 10-20℃, local overheating is avoided. The heat of reaction is dissipated through heat exchange between the reactor wall and the environment. The final product system is obtained after 270 min of reaction.

[0069] (5) As the diffusion resistance of hydrogen in the magnesium powder particles increases, the heat release decreases and the temperature of the final product system begins to drop. When the temperature drops to 380°C, the hydrogen supply is stopped, and the system is cooled to room temperature under the protection of an inert gas. After the hydrogen in the reactor is discharged and replaced with argon, the lid is opened and the powder is collected.

[0070] Example 3

[0071] A method for preparing magnesium hydride powder includes:

[0072] (1) Weigh 25.5 kg of the first magnesium particle group with an average particle size of 260 μm and 4.5 kg of the second magnesium particle group with an average particle size of 45 μm; the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 5.8:1; wherein the first magnesium particle group and the second magnesium particle group satisfy the following relationship: under the same reaction vessel (internal volume of 6.0 L) and reaction conditions (the heating temperature of the reaction vessel is set to 309 °C), 1.00 kg of the first magnesium particle group and 1.00 kg of the second magnesium particle group are reacted with hydrogen gas respectively, and the temperature change curve of each reaction system over time is measured. When the reaction reaches 18 min, the temperature difference between the first magnesium particle group and the second magnesium particle group is 16 °C.

[0073] (2) The first and second magnesium particle groups weighed in step (1) are loaded into a horizontal long tube reactor with a length of 3.0m. After evacuating to a pressure of 0.8kPa, argon gas is introduced to replace the pressure twice, and then the reactor is evacuated again. Hydrogen gas is introduced into the reactor to make the initial pressure P0 1.1MPa. Stirring is started at a speed of 200rpm. The heat transfer oil is heated by an external heating mechanism to heat the reactor to T1=310℃.

[0074] (3) Keep the temperature T1 constant and increase the pressure of hydrogen P1 to 2.9 MPa at a pressurization rate of 0.38 MPa / min to carry out the first hydrogenation reaction. After 35 min of reaction, the initial product system is obtained.

[0075] (4) When the temperature of the powder in the initial product system exceeds the external heating temperature, stop the external heating, keep stirring and adjust the hydrogen pressure to make the temperature 420℃ for the second hydrogenation reaction. The heat of reaction is dissipated through heat exchange with the environment through the reactor wall. Keep stirring throughout the process to ensure the dynamic balance between heat release and heat dissipation. After 260 min of reaction, the final product system is obtained.

[0076] (5) As the diffusion resistance of hydrogen in the magnesium powder particles increases, the heat release decreases and the temperature of the final product system begins to drop. When the temperature drops to 380°C, the hydrogen supply is stopped, and the system is cooled to room temperature under the protection of an inert gas. After the hydrogen in the reactor is discharged and replaced with argon, the lid is opened and the powder is collected.

[0077] Example 4

[0078] The difference from Example 1 is that this preparation method further includes:

[0079] Step (6): The product obtained in step (5) is ball-milled in an inert atmosphere with a ball-to-material ratio of 20:1, a rotation speed of 300 rpm, and a time of 4 h. Then, the product is sieved under argon protection.

[0080] Step (7) The product obtained in step (6) is dried at a temperature of 45°C for 6 hours to obtain magnesium hydride powder.

[0081] Example 5

[0082] A method for preparing magnesium hydride powder includes:

[0083] (1) Weigh 6.30 kg of the first magnesium particle group with an average particle size of 270 μm and 0.70 kg of the second magnesium particle group with an average particle size of 30 μm; the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 9:1; wherein, the first magnesium particle group and the second magnesium particle group satisfy the following relationship: under the same reaction vessel (internal volume of 3.5 L) and reaction conditions (the heating temperature of the reaction vessel is set to 315 °C), 0.50 kg of the first magnesium particle group and 0.50 kg of the second magnesium particle group are reacted with hydrogen gas respectively, and the temperature change curve of each reaction system over time is measured. When the reaction reaches 12 min, the temperature difference between the first magnesium particle group and the second magnesium particle group is 22 °C.

[0084] (2) The first and second magnesium particle groups weighed in step (1) are loaded into a horizontal long tube reactor with a length of 1.3m. After evacuating to a pressure of 1kPa, argon gas is introduced to replace the pressure once, and then the reactor is evacuated again. Hydrogen gas is introduced into the reactor to make the initial pressure P0 1.0MPa. Stirring is started at a stirring speed of 240rpm. The heat transfer oil is heated by an external heating mechanism to heat the reactor to T1=315℃.

[0085] (3) Keep the temperature T1 constant and increase the pressure of hydrogen P1 to 2.95 MPa at a pressurization rate of 0.40 MPa / min to carry out the second hydrogenation reaction. After 28 min of reaction, the initial product system is obtained.

[0086] (4) When the temperature of the powder in the initial product system exceeds the external heating temperature, stop the external heating and set the target temperature platform of the reactor to 420℃; use the "temperature-pressure" follow-up strategy to finely adjust the hydrogen pressure so that the powder temperature deviates from the platform by ±5℃ and returns to the stable range. After reacting for 240 minutes, the final product system is obtained.

[0087] (5) When the temperature of the final product system naturally cools to 380°C, stop the hydrogen gas supply, cool to room temperature under argon protection, remove the hydrogen gas from the reactor and replace it with argon gas, then open the lid to take out the powder and collect the magnesium hydride powder.

[0088] Example 6

[0089] The difference from Example 1 is that the average particle size of the first magnesium particle group is changed to 200 μm and the average particle size of the second magnesium particle group is changed to 50 μm, so that the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 4:1. The remaining steps are the same as in Example 1.

[0090] Example 7

[0091] The difference from Example 1 is that the average particle size of the first magnesium particle group is changed to 300 μm and the average particle size of the second magnesium particle group is changed to 20 μm, so that the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is 15:1. The remaining steps are the same as in Example 1.

[0092] Comparative Example 1

[0093] The difference from Example 1 is that in step (1), an equal amount of the first magnesium particle group is used instead of the second magnesium particle group, that is, magnesium powder of different particle sizes is not weighed. The remaining steps are the same as in Example 1.

[0094] The magnesium hydride powders prepared in all the above-mentioned embodiments and comparative examples of this application were tested for particle size, D50, BET specific surface area, hydrogenation amount and whiteness.

[0095] The above embodiments of the present invention achieve the following technical effects:

[0096] Specifically, the process involves: loading a first and second group of magnesium particles into a 1.3m long horizontal tubular reactor, evacuating it, replacing it with argon, and then evacuating again. Hydrogen is introduced to create an initial pressure P0, stirring is initiated, and the powder temperature is stabilized at T1 by external heat transfer oil heating. Subsequently, T1 is maintained while the hydrogen pressure is increased to P1 to initiate the hydrogenation reaction. When the powder temperature exceeds the external heating temperature due to the exothermic reaction, external heating is stopped, and the bed temperature is stabilized at around 420℃ by fine-tuning the hydrogen pressure to maintain a stable hydrogenation process driven by the heat of reaction. After the temperature naturally drops to a certain level, hydrogen supply is stopped, and the mixture is cooled under inert gas protection, hydrogen is released, and the powder is replaced with argon before the lid is opened and the powder is collected. This process is repeated under the same reactor conditions and temperature / pressure settings. Under the given path, when the preset purity of 90% is used as the criterion, the reaction time required to obtain magnesium hydride powder that meets the preset purity is about 6 hours, based on the following particle size combination: the first magnesium particle group has an average particle size of about 250 μm, the second magnesium particle group accounts for 10% and has an average particle size of about 50 μm. However, after particle size adjustment, the reaction time required to obtain magnesium hydride powder that meets the preset purity is shortened to about 5 hours. The resulting magnesium hydride powder has a particle size distribution of 10–300 μm and a D50 of 100–102 μm, a specific surface area of ​​about 15 m² / g, a whiteness of about 41, and a hydrogenation amount of not less than 7 wt%.

[0097] This application utilizes a combination of a first group of magnesium particles with different particle sizes and a second group of magnesium particles. The smaller second group of magnesium particles undergoes a first hydrogenation reaction with at least a portion of the hydrogen gas, releasing heat during this reaction. This heat is then transferred to the larger first group of magnesium particles through the contact interface between the particles. The first group of magnesium particles uses this heat, along with an external heating mechanism, to carry out a second hydrogenation reaction. This transforms the reaction process from being driven by external heating to a self-driven reaction heat mode, thereby shortening the reaction time and improving production efficiency.

[0098] In the above process, the smaller second group of magnesium particles has a larger specific surface area and more active sites. Compared with the larger first group of magnesium particles, it can adsorb and dissociate hydrogen molecules earlier, initiate the first hydrogenation reaction, and rapidly release the heat of reaction. This heat is conducted to the surface of the larger particles through the particle contact interface, prompting the larger first group of magnesium particles to quickly enter the hydrogenation process. This forms a synergistic hydrogenation process triggered by small particles and followed by larger particles. As a result, the above reaction gradually transitions from external heating to self-driven by the heat of reaction, significantly accelerating the reaction rate and shortening the overall reaction time.

[0099] Meanwhile, the presence of the first group of magnesium particles with larger particle size provides higher heat capacity and a stable heat exchange interface, which can absorb and balance local heat, prevent overheating and runaway, and thus ensure the stability of the reaction platform and batch-to-batch consistency.

[0100] Compared with the traditional method of using magnesium powder with a single particle size, the process of this application achieves efficient utilization of reaction heat while ensuring safety, reduces external energy consumption, and can achieve a higher degree of hydrogenation in a shorter time, thereby increasing the amount of hydrogenation of magnesium hydride powder and obtaining magnesium hydride powder of the preset purity in a shorter time, thus achieving an overall improvement in hydrogenation efficiency.

[0101] In summary, the preparation method provided in this application effectively solves the problems of insufficient safety, slow hydrogenation kinetics, and high energy consumption in the existing magnesium hydride preparation process, and significantly improves the hydrogenation efficiency.

[0102] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing magnesium hydride powder, characterized in that, The preparation method includes: loading a first magnesium particle group and a second magnesium particle group into a reactor, introducing hydrogen gas, and heating the reactor to a reaction temperature T1 by an external heating mechanism, wherein the reaction temperature T1 is 305-310°C, so that the second magnesium particle group reacts with at least a portion of the hydrogen gas in a first hydrogenation reaction and releases heat; heating the first magnesium particle group by the heat released from the reaction of the second magnesium particle group with hydrogen gas and the external heating mechanism, wherein the first magnesium particle group reacts with the remaining portion of the hydrogen gas in a second hydrogenation reaction, and the reaction time for the first magnesium particle group to be converted into the magnesium hydride powder is shortened, and the magnesium hydride powder with a preset purity is obtained; wherein the first magnesium particle group and the second magnesium particle group satisfy the following relationship: (1) under the same reaction vessel and reaction conditions, equal amounts of the first magnesium particle group and the second magnesium particle group react with hydrogen gas respectively, and the temperature difference between the first magnesium particle group and the second magnesium particle group at any same time in the curves of temperature change of their respective reaction systems is measured, which satisfies a preset range; (2) the minimum particle size of the first magnesium particle group is greater than the maximum particle size of the second magnesium particle group.

2. The method for preparing magnesium hydride powder according to claim 1, characterized in that, The average particle size of the first magnesium particle group is 200-300 μm; the average particle size of the second magnesium particle group is 15-75 μm; and / or, the ratio of the average particle size of the first magnesium particle group to the average particle size of the second magnesium particle group is (4-15):

1.

3. The method for preparing magnesium hydride powder according to claim 1, characterized in that, The testing process for the temperature change curve of the reaction system over time includes: setting the heating temperature of the reaction vessel to any temperature between 0 and 420°C, setting the pressure of the hydrogen gas to be the same during the reaction, allowing the first magnesium particle group and the second magnesium particle group to react with hydrogen gas respectively, and monitoring the temperature values ​​of the reaction system at different times to obtain the curve; the temperature difference is obtained by acquiring the corresponding temperature in the two curves at any same time within the reaction time range of 0 to 300 min, and calculating the difference between the two, which is the temperature difference.

4. The method for preparing magnesium hydride powder according to any one of claims 1 to 3, characterized in that, During the first hydrogenation reaction, the initial pressure P0 of hydrogen in the reactor is 0.8 to 1.2 MPa.

5. The method for preparing magnesium hydride powder according to claim 4, characterized in that, During the second hydrogenation reaction, the pressure P1 of hydrogen in the reactor is 2.5 to 3.0 MPa.

6. The method for preparing magnesium hydride powder according to claim 4, characterized in that, The reaction temperature T2 of the second hydrogenation reaction is 415-425℃, and the time is 20-40 min.

7. The method for preparing magnesium hydride powder according to claim 5, characterized in that, In the preparation method, the initial pressure P0 is increased to the pressure P1 at a pressurization rate of 0.3 to 0.4 MPa / min.

8. The method for preparing magnesium hydride powder according to claim 1, characterized in that, During the first hydrogenation reaction, a first stirring is performed at a speed of 180–320 rpm; and / or, during the second hydrogenation reaction, a second stirring is performed at a speed of 220–400 rpm.

9. A magnesium hydride powder, characterized in that, The magnesium hydride powder is prepared by the method for preparing magnesium hydride powder according to any one of claims 1 to 8.

10. The magnesium hydride powder according to claim 9, characterized in that, The magnesium hydride powder has a D50 of 100–102 μm and a hydrogenation amount of 6.5–7.4%.