Lithium aluminum hydride preparation method and device
By heating and distillation of the lithium aluminum hydride ether solution and crystallization under reduced pressure, combined with crushing and screening, the hydrogen release rate of lithium aluminum hydride is adjusted, and the problem of excessive hydrolysis reaction and uncontrollable hydrogen release rate in the existing process is solved, and the adjustment and stability of the hydrogen release rate are achieved.
Patent Information
- Application Number
- CN202411817917.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-03-25
AI Technical Summary
In the existing preparation process for lithium aluminum hydride, the hydrolysis reaction is too severe, and there are safety risks. The water-interpretation hydrogen rate is uncontrollable, which cannot meet the demand for stable hydrogen production of hydrogen release devices.
The ether is recovered by heating and distillation of the aluminum hydride lithium ether solution to obtain a concentrated aluminum hydride lithium ether solution. The crystallization temperature and pressure are controlled during the crystallization process under reduced pressure, and the crystallization time of the aluminum hydride lithium crystal is adjusted to control its hydrogen release rate. At the same time, lithium aluminum hydride powder with a particle size within a specified range is obtained through crushing and sieving to ensure the stability of the hydrogen release rate.
The hydrogen release speed of lithium aluminum hydride is adjustable and relatively stable, which meets the demand for stable hydrogen production by the hydrogen release device, reduces safety risks, and improves the control of the preparation process.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of new energy material preparation, and specifically to a method and device for preparing lithium aluminum hydride. Background Art
[0002] Lithium aluminum hydride is a very promising hydrogen storage material with a molecular formula of LiAlH4, a molecular weight of 37.95, and a hydrogen storage density of up to 10.62%. Lithium aluminum hydride reacts violently with water to directly generate a large amount of heat and release a large amount of hydrogen. The hydrolysis hydrogen density is as high as 21.25%. The hydrolysis reaction equation is:
[0003] LiAlH4+4H2O=LiAl(OH)4+4H2
[0004] The main preparation process of lithium aluminum hydride is: ① slowly dissolve aluminum chloride in ether to obtain an ether solution of aluminum chloride; ② prepare lithium hydride, lithium aluminum hydride and ether into a suspension; ③ slowly add the ether solution of aluminum chloride in ① to the suspension in ② for mixed reaction; ④ after the reaction, separate the solid and liquid to obtain an ether solution of lithium aluminum hydride and a by-product of lithium chloride; ⑤ evaporate and dry the separated ether solution of lithium aluminum hydride to obtain lithium aluminum hydride crystals. The reaction equation is as follows:
[0005] 4LiH+AlCl3=LiAlH4+3LiCl
[0006] In addition, there is currently a preparation process for preparing lithium aluminum hydride using sodium aluminum hydride: ① directly mix sodium aluminum hydride and lithium chloride in an ether solution for reaction; ② after the reaction, solid-liquid separation is performed to obtain an ether solution of lithium aluminum hydride and a byproduct of sodium chloride; ③ the separated lithium aluminum hydride ether solution is evaporated and dried to obtain lithium aluminum hydride crystals. The reaction equation is as follows:
[0007] LiCl+NaAlH4=LiAlH4+NaCl
[0008] At present, the lithium aluminum hydride prepared by the above process is mainly used as a reducing agent in organic synthesis. When it is used directly as a hydrolysis hydrogenation material, there are safety hazards due to the excessively violent hydrolysis reaction, and its hydrolysis hydrogenation rate is uncontrollable, which cannot meet the hydrogen release device's demand for stable hydrogen production. Summary of the invention
[0009] In view of this, an embodiment of the present application provides a method and device for preparing lithium aluminum hydride. By improving the method for preparing lithium aluminum hydride, the hydrogen release rate of the prepared lithium aluminum hydride is adjustable and relatively stable.
[0010] The technical solutions provided by the embodiments of this application are as follows:
[0011] According to an embodiment of the first aspect of the present application, a method for preparing lithium aluminum hydride is provided, comprising:
[0012] The lithium aluminum hydride ether solution is heated and distilled to recover ether to obtain a concentrated lithium aluminum hydride ether solution;
[0013] The concentrated lithium aluminum hydride ether solution is crystallized under reduced pressure to obtain dry lithium aluminum hydride crystals; during the reduced pressure crystallization process, the crystallization time of the lithium aluminum hydride crystals is controlled within a specified time range by controlling the crystallization temperature and the crystallization pressure; the crystallization time of the lithium aluminum hydride crystals is positively correlated with the hydrogen release time of the lithium aluminum hydride crystals;
[0014] The dried lithium aluminum hydride crystals are crushed and sieved to obtain lithium aluminum hydride powder with a particle size within a specified range.
[0015] According to an embodiment of the second aspect of the present application, a lithium aluminum hydride preparation device is provided, comprising:
[0016] A concentration module is used to heat and distill the lithium aluminum hydride ether solution to recover ether, thereby obtaining a concentrated lithium aluminum hydride ether solution;
[0017] A crystallization module is used to reduce the pressure and crystallize the concentrated lithium aluminum hydride ether solution to obtain dry lithium aluminum hydride crystals; during the reduced pressure crystallization process, the crystallization time of the lithium aluminum hydride crystals is controlled within a specified time range by controlling the crystallization temperature and the crystallization pressure; the crystallization time of the lithium aluminum hydride crystals is positively correlated with the hydrogen release time of the lithium aluminum hydride crystals;
[0018] The crushing module is used to crush and screen the dried lithium aluminum hydride crystals to obtain lithium aluminum hydride powder with a particle size within a specified range.
[0019] As can be seen from the above scheme, the present application prepares lithium aluminum hydride in powder form by concentrating, crystallizing and crushing the lithium aluminum hydride ether solution. During the preparation process, by controlling the crystallization temperature and crystallization pressure, the reaction rate of the prepared lithium aluminum hydride in the aqueous solution can be controlled, thereby adjusting the speed of the hydrogen release rate; and by controlling the particle size of the lithium aluminum hydride powder obtained by crushing and screening within a specified range, the prepared lithium aluminum hydride releases a relatively stable hydrogen release rate during the hydrohydrogenation process, the performance is stable between different batches, and the pressure on the hydrogen supply system is small. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a flow chart of a method for preparing lithium aluminum hydride provided in an embodiment of the present application;
[0021] Figure 2 Schematic diagram of ether recovery during lithium aluminum hydride ether solution concentration provided in an embodiment of the present application;
[0022] Figure 3It is a schematic diagram of the hydrogen release rate of lithium aluminum hydride with different particle sizes provided in the examples of the present application. DETAILED DESCRIPTION
[0023] In order to make the purpose, technical scheme and advantages of the present application clearer, the specific embodiments of the present application are described in detail below in conjunction with the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the present application shown in the accompanying drawings and described according to the accompanying drawings are merely exemplary, and the present application is not limited to these embodiments.
[0024] It should also be noted here that in order to avoid obscuring the focus of the present application due to unnecessary details, the accompanying drawings mainly show structures and / or processing steps that are closely related to the scheme according to the present application, while omitting some other details that are not very relevant to the present application.
[0025] The technical solutions in the embodiments of the present application are described in detail below.
[0026] The present application embodiment provides a method for preparing lithium aluminum hydride, such as Figure 1 As shown, the method comprises the following steps:
[0027] Step 101, heating and distilling the lithium aluminum hydride ether solution to recover ether, to obtain a concentrated lithium aluminum hydride ether solution.
[0028] Step 101 may be referred to as the concentration stage of the preparation method. During the heating distillation in the concentration stage, in one embodiment, the heating temperature may be 50-90° C. and the pressure may be normal pressure. More specifically, in order to reduce energy consumption and improve efficiency, the heating temperature is preferably 70-90° C.
[0029] In one embodiment, the heating and distillation is stopped when the concentration of the lithium aluminum hydride ether solution reaches 18% to 22% wt, so that the concentration of the concentrated lithium aluminum hydride ether solution is 18% to 22% wt. The selection of this concentration range has two main effects: first, if the concentration is further increased on this basis, the solution evaporates slowly under normal pressure, which will cause higher energy consumption; second, if the concentration is further increased on this basis, the complex precipitation of lithium aluminum hydride and ether begins to appear in the solution, which will affect the subsequent crystallization. More specifically, the heating and distillation can be stopped when the concentration of the lithium aluminum hydride ether solution reaches 20% wt.
[0030] In one embodiment, the lithium aluminum hydride ether solution in step 101 can be prepared in a variety of ways, such as reacting lithium hydride and aluminum chloride in an ether solution and filtering to obtain a supernatant, or reacting sodium aluminum hydride and lithium chloride in an ether solution and filtering to obtain a supernatant.
[0031] Step 102, crystallizing the concentrated lithium aluminum hydride ether solution under reduced pressure to obtain dry lithium aluminum hydride crystals.
[0032] Step 102 can be referred to as the crystallization stage of the preparation method. In the reduced pressure crystallization process, by controlling the crystallization temperature and the crystallization pressure, the crystallization time of the lithium aluminum hydride crystal can be controlled within a specified time range. Since the crystallization time of the lithium aluminum hydride crystal is positively correlated with the hydrogen release time of the lithium aluminum hydride crystal, by controlling the crystallization time of the lithium aluminum hydride crystal, the hydrogen release time of the lithium aluminum hydride crystal can be controlled to a certain extent, that is, the speed of the hydrogen release rate can be controlled.
[0033] In one embodiment, the crystallization time of lithium aluminum hydride crystals can be controlled to 300 to 1200 seconds by controlling the crystallization temperature and crystallization pressure, thereby controlling the hydrogen release time of lithium aluminum hydride crystals within a reasonable range. Specifically, the crystallization time of lithium aluminum hydride crystals can be controlled to 300 to 1200 seconds by controlling the crystallization temperature to 50-90°C and the crystallization pressure to -0.01 to -0.08Mpa (vacuum degree). Further, in order to reduce the difficulty of engineering implementation, the preferred crystallization temperature is 70-90°C and the crystallization pressure is -0.01 to -0.06Mpa (vacuum degree). It should be noted that the crystallization temperatures and pressures given above are examples, and those skilled in the art can select other crystallization temperatures and pressures according to actual needs to obtain the required crystallization time.
[0034] Step 103, crushing and screening the dried lithium aluminum hydride crystals to obtain lithium aluminum hydride powder with a particle size within a specified range.
[0035] Step 103 can be referred to as the crushing stage of the preparation method. In one embodiment, the specified range can be -50 mesh to +200 mesh, that is, the particle size of the lithium aluminum hydride powder after crushing and screening is -50 mesh to +200 mesh. By adopting this particle size range, on the one hand, it is possible to avoid the powder particles being too large, resulting in the inability to be evenly filled in the container, and then resulting in an unstable hydrogen release rate. On the other hand, if the powder particle size is to be further reduced, it may cause certain damage to the lithium aluminum hydride grains, resulting in enhanced sample activity and accelerated hydrogen release rate. Taking into account the crushing cost and safety factors, the preferred powder particle size is -50 mesh to +100 mesh.
[0036] It can be seen that the lithium aluminum hydride preparation method provided in the embodiment of the present application has the following advantages: during the preparation process, by controlling the crystallization temperature and the crystallization pressure, the reaction rate of the prepared lithium aluminum hydride in the aqueous solution can be controlled, thereby adjusting the speed of the hydrogen release rate; and, by controlling the particle size of the lithium aluminum hydride powder obtained by crushing and screening within a specified range, the hydrogen release rate of the prepared lithium aluminum hydride in the process of hydrogenation in water is relatively stable, the performance is stable between different batches, and the pressure on the hydrogen supply system is small.
[0037] To facilitate understanding of the lithium aluminum hydride preparation method provided in the present application, it is described below in conjunction with specific examples.
[0038] Examples 1-3
[0039] Examples 1-3 correspond to the concentration stage of the lithium aluminum hydride preparation method provided in the present application, specifically, the concentration process of the lithium aluminum hydride ether solution at 50-90°C.
[0040] The lithium aluminum hydride ether solution concentration step used in Example 1-3 is as follows: under nitrogen protection, 1000g lithium aluminum hydride ether solution (concentration 5.6%wt) is added to a distillation apparatus, and ether is evaporated and recovered at three temperatures of 50°C, 70°C, and 90°C, respectively, and after the solution becomes viscous, a concentrated lithium aluminum hydride ether solution (hereinafter referred to as a concentrated solution) and recovered ether are obtained. The concentration of the solution is calculated based on the amount of recovered ether.
[0041] The curve of ether recovery during the entire concentration process is as follows Figure 2 As shown. The concentration process can be divided into three stages: the first stage is the system heating stage, at this time the ether solution and the system gradually heat up, the evaporated ether solution condenses and refluxes in the kettle, and no condensate is precipitated; the second stage is the solvent constant rate evaporation stage, the evaporation rate is basically constant, and about 500g of ether can be recovered in this stage; the third stage is the solvent deceleration evaporation stage, the amount of ether recovered per unit time gradually decreases to zero, and the amount of ether recovered in this stage is 200-250g. Figure 2 It can be clearly seen that the higher the concentration temperature, the shorter the total concentration time. From the perspective of energy consumption and efficiency, the concentration effect is best when the temperature is 70-90℃.
[0042] At the three temperatures of 50°C, 70°C and 90°C, the concentration of the concentrated solution obtained is shown in Table 1, and the concentration is in the range of 18%-22%wt. If the concentration is to be further increased on this basis, the following effects will be caused: First, under normal pressure, the solution evaporates slowly and the energy consumption is high; second, at this time, the complex precipitation of lithium aluminum hydride and ether begins to appear in the solution, which will affect the subsequent crystallization. Therefore, the concentration of the concentrated solution is 18%-22%wt. Combined with the solution state and system energy consumption, the concentration is preferably 20%wt.
[0043] Table 1
[0044]
[0045] Embodiment 4-12
[0046] Examples 4-12 correspond to the crystallization stage of the lithium aluminum hydride preparation method provided in the present application, and specifically provide a comparison of the crystallization time and hydrogen release time of lithium aluminum hydride ether concentrate under different temperature and pressure conditions.
[0047] The crystallization step of lithium aluminum hydride ether concentrate used in Example 4-12 is as follows: under nitrogen protection, 100g of concentrated lithium aluminum hydride ether solution (concentration 20%wt) is added to a drying crystallization device, and dried and crystallized at a temperature of 50 to 90°C and a pressure of -0.01 to -0.007Mpa (vacuum degree) to obtain lithium aluminum hydride crystals. In order to facilitate the inspection of the hydrogen release time of the lithium aluminum hydride crystals, the lithium aluminum hydride crystals can be further crushed and sieved to obtain lithium aluminum hydride powder, and the particle size is controlled at -50 to +200 mesh.
[0048] The hydrolysis and hydrogenation steps used in Example 4-12 are as follows: Under an argon atmosphere, 0.5 g of lithium aluminum hydride powder is weighed and pressed into a tablet with a diameter of 16 mm using a tablet press. Specifically, the pressure is 4t, and the pressure is maintained for 10 seconds to obtain a disc-shaped lithium aluminum hydride. The tablet is used for hydrolysis and hydrogenation.
[0049] Table 2 shows the hydrogen release performance of lithium aluminum hydride under different crystallization conditions. As shown in Table 2, by controlling the crystallization temperature and pressure, the hydrogen release time of lithium aluminum hydride can be controlled within the range of 300 to 1200 seconds, thereby achieving control of the hydrogen release rate of lithium aluminum hydride. The longer the crystallization time, the longer the hydrogen release time of the obtained lithium aluminum hydride. This is because a longer crystallization time can ensure that the lithium aluminum hydride grains are fully grown, the grains are more complete and larger in size. The surface energy of the grains is reduced, the activity is reduced, and the hydrogen release time is delayed. Although the hydrogen release effect equivalent to high temperature and low vacuum can be achieved by increasing the vacuum degree at low temperature, it is easier to achieve in engineering to increase the temperature than to increase the vacuum degree, and a relatively low vacuum degree is more conducive to ether recovery. Therefore, it is preferred to crystallize at a temperature of 70-90°C and a pressure of -0.01 to -0.06Mpa.
[0050] Table 2
[0051]
[0052] Examples 13-16
[0053] Examples 13-16 correspond to the crushing stage of the lithium aluminum hydride preparation method provided in the present application.
[0054] Take the lithium aluminum hydride crystals obtained under the crystallization conditions of 70℃ and -0.045Mpa, crush them and pass them through 50 mesh, 100 mesh, and 200 mesh sieves in turn. Get 4 samples with different particle size specifications of +50 mesh, -50 mesh to +100 mesh, -100 mesh to +200 mesh, and -200 mesh. Take 32g of lithium aluminum hydride of four specifications respectively, and put them into a cylindrical metal shell with a diameter of 36mm, a height of 70mm, and one end sealed. Then use a press to compact, the molding pressure is 1.2t, and the pressure is maintained for 30s. Use the above material column for hydrolysis and hydrogenation.
[0055] Figure 3 The comparison of hydrogen release rates of lithium aluminum hydride with different particle sizes is shown as an example. Figure 3 As shown in the figure, the hydrogen release rate of samples above 50 mesh fluctuates and is very unstable. This is because the powder particle size is large and cannot be evenly and densely packed in the shell. The overall hydrogen release rate of samples below 200 mesh is relatively stable, but the hydrogen release rate is faster in the initial stage. This is because the powder is broken too small, which causes certain damage to the lithium aluminum hydride grains, resulting in enhanced sample activity and faster hydrogen release rate. The overall hydrogen release rate of the two groups of samples with 50-100 mesh and 100-200 mesh is stable, and hydrogen can be supplied stably. The hydrogen release rates of the four groups of samples are basically the same in the middle of hydrogen release, and the powder particle size has little effect on the hydrogen release rate. This is mainly because the hydrogen release rate of lithium aluminum hydride is determined by the grain size. The grains of lithium aluminum hydride powder used in this experiment are mainly concentrated in the range of 50-100um, and the powder particles larger than 200 mesh (75um) are actually formed by the agglomeration of fine lithium aluminum hydride grains. Therefore, although the powder particle size is different, the grain size of the powder is actually basically the same, and the hydrogen release rate is basically the same. From the results, in order to ensure the stability of the hydrogen release rate of the material, the particle size of the powder should be controlled within the range of -50 mesh to +200 mesh. However, considering the crushing cost and safety factors, the preferred particle size range is -50 mesh to +100 mesh.
[0056] It should be noted that the above embodiments are examples of the method for preparing lithium aluminum hydride provided in the present application. Based on the content provided in the present application, those skilled in the art can easily think of other implementation methods, such as other distillation methods, other crushing methods, etc. If they can achieve the same or similar effects, they should be deemed to be within the scope of protection of the present application.
[0057] Based on the same concept as the lithium aluminum hydride preparation method provided in the embodiment of the present application, the embodiment of the present application also provides a lithium aluminum hydride preparation device, which specifically includes: a concentration module, a crystallization module and a crushing module.
[0058] The concentration module is used to heat and distill the lithium aluminum hydride ether solution to recover ether, thereby obtaining a concentrated lithium aluminum hydride ether solution;
[0059] A crystallization module is used to reduce the pressure and crystallize the concentrated lithium aluminum hydride ether solution to obtain dry lithium aluminum hydride crystals; during the reduced pressure crystallization process, the crystallization time of the lithium aluminum hydride crystals is controlled within a specified time range by controlling the crystallization temperature and the crystallization pressure; the crystallization time of the lithium aluminum hydride crystals is positively correlated with the hydrogen release time of the lithium aluminum hydride crystals;
[0060] The crushing module is used to crush and screen the dried lithium aluminum hydride crystals to obtain lithium aluminum hydride powder.
[0061] The implementation process of the functions and effects of each module in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, which will not be repeated here.
[0062] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.
[0063] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technical solution that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.
Claims
1. A method for preparing lithium aluminum hydride, characterized in that: include: The lithium aluminum hydride ether solution is heated and distilled to recover ether to obtain a concentrated lithium aluminum hydride ether solution; crystallizing the concentrated lithium aluminum hydride ether solution under reduced pressure to obtain dry lithium aluminum hydride crystals; In the process of reduced pressure crystallization, the crystallization time of lithium aluminum hydride crystals is controlled within a specified time range by controlling the crystallization temperature and the crystallization pressure; the crystallization time of lithium aluminum hydride crystals is positively correlated with the hydrogen release time of lithium aluminum hydride crystals; The dried lithium aluminum hydride crystals are crushed and sieved to obtain lithium aluminum hydride powder with a particle size within a specified range.
2. The method according to claim 1, characterized in that When the concentration of the lithium aluminum hydride ether solution reaches 18% to 22% wt, heating and distillation are stopped to obtain a concentrated lithium aluminum hydride ether solution.
3. The method according to claim 1, characterized in that The temperature of the heating distillation process is 50-90° C. and the pressure is normal pressure.
4. The method according to claim 3, characterized in that The temperature of the heating distillation process is 70-90°C.
5. The method according to claim 1, characterized in that The step of controlling the crystallization time of lithium aluminum hydride crystals within a specified time range comprises: The crystallization time of lithium aluminum hydride crystals is controlled within 300 to 1200 seconds.
6. The method according to claim 5, characterized in that The controlling of crystallization temperature and crystallization pressure comprises: The crystallization temperature is controlled to be 50-90°C and the crystallization pressure is -0.01~-0.08Mpa.
7. The method according to claim 6, characterized in that The controlling of crystallization temperature and crystallization pressure comprises: The crystallization temperature is controlled to be 70-90°C and the crystallization pressure is -0.01~-0.06Mpa.
8. The method according to claim 1, characterized in that The particle size of the lithium aluminum hydride powder after crushing and screening is -50 mesh to +200 mesh.
9. The method according to claim 8, characterized in that The particle size of the lithium aluminum hydride powder after crushing and screening is -50 mesh to +100 mesh.
10. A lithium aluminum hydride preparation device, characterized in that: include: A concentration module is used to heat and distill the lithium aluminum hydride ether solution to recover ether, thereby obtaining a concentrated lithium aluminum hydride ether solution; A crystallization module, used for reducing the pressure and crystallizing the concentrated lithium aluminum hydride ether solution to obtain dry lithium aluminum hydride crystals; In the process of reduced pressure crystallization, the crystallization time of lithium aluminum hydride crystals is controlled within a specified time range by controlling the crystallization temperature and the crystallization pressure; the crystallization time of lithium aluminum hydride crystals is positively correlated with the hydrogen release time of lithium aluminum hydride crystals; The crushing module is used to crush and screen the dried lithium aluminum hydride crystals to obtain lithium aluminum hydride powder with a particle size within a specified range.