Process for the preparation of lithium aluminium hydride

Abstract

The present disclosure discloses a lithium aluminum hydride preparation method, comprising the following steps: S100: placing appropriate amounts of sodium aluminum hydride, lithium chloride and an initiator into an ether solution, and obtaining a mixed solution after fully stirring and reacting at normal temperature and pressure; S200: solid-liquid separating the mixed solution to obtain an ether solution containing lithium aluminum hydride and a precipitate; S300: distilling the ether solution containing lithium aluminum hydride at a certain temperature under reduced pressure to obtain dry lithium aluminum hydride crystals. The present disclosure uses low-cost sodium aluminum hydride and easily available lithium chloride as raw materials by adopting a single-element synthesis method, thereby reducing the production cost of existing lithium aluminum hydride.

Description

Technical Field

[0001] This disclosure belongs to the field of new energy materials and their preparation technology, specifically relating to a method for preparing lithium aluminum hydride. Background Technology

[0002] Lithium aluminum hydride (LiAlH4) is a complex aluminum hydride with a molecular formula of LiAlH4 and a molecular weight of 37.95. It is a very strong reducing agent in organic synthesis, especially for esters, carboxylic acids, and amides. Pure lithium aluminum hydride is relatively stable in dry air at 120°C, but it decomposes explosively upon contact with water. Lithium aluminum hydride is soluble in ether solvents such as diethyl ether and tetrahydrofuran, with a specific gravity of 0.917. Under vacuum and at 130°C, it decomposes into lithium hydride, aluminum, and hydrogen gas.

[0003] The existing process for preparing lithium aluminum hydride includes: ① slowly dissolving aluminum trichloride in diethyl ether to obtain an aluminum trichloride diethyl ether solution; ② preparing a suspension of lithium hydride, lithium aluminum hydride, and diethyl ether; ③ slowly adding the aluminum trichloride diethyl ether solution from ① to the suspension from ② and mixing and reacting; ④ after the reaction is completed, separating the solid and liquid phases to obtain an ether solution containing lithium aluminum hydride and a lithium chloride byproduct; ⑤ evaporating and drying the ether solution containing lithium aluminum hydride to obtain lithium aluminum hydride crystals.

[0004] The reaction equations involved in the above preparation process are as follows:

[0005] 4LiH + AlCl3 = LiAlH4 + 3LiCl

[0006] In the above preparation process, both the dissolution of aluminum chloride in diethyl ether and the reaction of aluminum chloride with lithium hydride release a large amount of heat, requiring strict control of the reaction rate and temperature; otherwise, an explosion is highly likely, posing a significant danger. Furthermore, this method uses lithium hydride obtained by high-temperature hydrogenation of metallic lithium, and as shown in the above formula, at least 4 moles of lithium hydride (LiH) are needed to produce 1 mole of lithium aluminum hydride (LiAlH4), resulting in high costs. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present disclosure aims to provide a method for preparing lithium aluminum hydride. This method uses inexpensive sodium aluminum hydride and readily available lithium chloride, obtained through elemental synthesis, as raw materials. This method can reduce the production cost of lithium aluminum hydride by at least 50%, and the resulting product has high purity and the solvent can be recycled, providing a technical route for large-scale industrial production.

[0008] To achieve the above objectives, this disclosure provides the following technical solutions:

[0009] A method for preparing lithium aluminum hydride includes the following steps:

[0010] S100: Place an appropriate amount of sodium aluminum hydride, lithium chloride and initiator in an ether solution, and stir the mixture thoroughly at room temperature and pressure to obtain a mixed solution;

[0011] S200: The mixed solution is separated into solid and liquid components to obtain an ether solution containing lithium aluminum hydride and a sodium chloride precipitate;

[0012] S300: The diethyl ether solution containing lithium aluminum hydride is distilled under reduced pressure at a certain temperature to obtain dry lithium aluminum hydride crystals.

[0013] Preferably, in step S100, the molar ratio of sodium aluminum hydride to lithium chloride is 1.0:1.0 to 1.1.

[0014] Preferably, in step S100, the molar ratio of sodium aluminum hydride to initiator is 1.0:0 to 0.1.

[0015] Preferably, in step S100, the purity of the sodium aluminum hydride is 95.00% to 99.50%.

[0016] Preferably, in step S100, the initiator is a small amount of lithium aluminum hydride.

[0017] Preferably, in step S200, the solid-liquid separation of the mixed solution includes, but is not limited to, any of the following methods: static sedimentation, centrifugal filtration, and positive pressure filtration.

[0018] Preferably, in step S300, the diethyl ether solution containing lithium aluminum hydride is distilled under reduced pressure at a temperature of 30-90°C.

[0019] Preferably, in step S300, the diethyl ether solution containing lithium aluminum hydride is distilled under reduced pressure at a temperature of 70-90°C.

[0020] Preferably, in step S300, the diethyl ether solution containing lithium aluminum hydride is depressurized to -0.1 to -0.01 MPa.

[0021] Preferably, in step S300, the diethyl ether solution containing lithium aluminum hydride is depressurized to -0.04 to -0.02 MPa.

[0022] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0023] 1. This method has a mild reaction, with no significant temperature change throughout the reaction process, requiring no heat dissipation system, and the reaction is simple and safe;

[0024] 2. This method has a higher utilization rate of expensive lithium sources. Almost 1 mole of lithium chloride can generate 1 mole of lithium aluminum hydride, resulting in a lower overall cost. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for preparing lithium aluminum hydride according to an embodiment of the present disclosure;

[0026] Figure 2 It is by Figure 1 The diffraction pattern of lithium aluminum hydride crystals prepared by the method shown. Detailed Implementation

[0027] The following will refer to the appendix. Figures 1 to 2 Specific embodiments of this disclosure are described in detail. While specific embodiments of this disclosure are shown in the accompanying drawings, it should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0028] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out this disclosure; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of this disclosure. The scope of protection of this disclosure is determined by the appended claims.

[0029] To facilitate understanding of the embodiments of this disclosure, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of this disclosure.

[0030] In one embodiment, such as Figure 1 As shown, this disclosure provides a method for preparing lithium aluminum hydride, comprising the following steps:

[0031] 1. Weigh out 21.6g of sodium aluminum hydride (97% purity), 16.5g of lithium chloride, 0.74g of lithium aluminum hydride (a small amount of lithium aluminum hydride is used as an initiator to accelerate the reaction), and 480g of anhydrous diethyl ether in a molar ratio of 1:1:0.5 and place them into a reaction vessel. Stir at room temperature (25℃) and atmospheric pressure (one atmosphere) for 4 hours. After the reaction is complete, a mixed solution is obtained. During the stirring process, sodium aluminum hydride and lithium chloride undergo the following reaction:

[0032] NaAlH4 + LiCl = LiAlH4 + NaCl

[0033] 2. The mixed solution is subjected to solid-liquid separation by any one of the following methods: static precipitation, centrifugal filtration, and positive pressure filtration, to obtain an ether solution containing lithium aluminum hydride and a precipitate. The precipitate includes sodium chloride generated after the reaction, as well as unreacted lithium chloride and a small amount of impurities such as sodium aluminum hydride.

[0034] 3. The diethyl ether solution containing lithium aluminum hydride was subjected to a reduced pressure of -0.04 MPa at 70°C, and then distilled to obtain 12.93 g of dried sodium aluminum hydride crystals.

[0035] In another embodiment, this disclosure also provides a method for preparing lithium aluminum hydride, comprising the following steps:

[0036] 1. Weigh out 21.6g of sodium aluminum hydride (97% purity), 17.3g of lithium chloride, 0.74g of lithium aluminum hydride, and 480g of anhydrous diethyl ether in a molar ratio of 1:1.05:0.05 and place them into a reaction vessel. Stir at room temperature (25℃) and atmospheric pressure (one atmosphere) for 4 hours. After the reaction is complete, a mixed solution is obtained. During the stirring process, sodium aluminum hydride and lithium chloride undergo the following reaction:

[0037] NaAlH4 + LiCl = LiAlH4 + NaCl

[0038] S200: The mixed solution is subjected to solid-liquid separation by any one of the following methods: static precipitation, centrifugal filtration, and positive pressure filtration, to obtain an ether solution containing lithium aluminum hydride and a precipitate, wherein the precipitate includes sodium chloride generated after the reaction, as well as unreacted lithium chloride and a small amount of impurities such as sodium aluminum hydride.

[0039] 2. The diethyl ether solution containing lithium aluminum hydride was subjected to a reduced pressure of -0.04 MPa at 70°C, and then distilled to obtain 13.57 g of dried sodium aluminum hydride crystals.

[0040] In another embodiment, this disclosure also provides a method for preparing lithium aluminum hydride, comprising the following steps:

[0041] 1. 21.6 g of sodium aluminum hydride (97% purity), 17.3 g of lithium chloride, 0.74 g of lithium aluminum hydride, and 480 g of anhydrous diethyl ether were added to a reaction vessel in a molar ratio of 1:1.1:0.05. The mixture was stirred for 4 hours at room temperature (25°C) and atmospheric pressure (one atmosphere) until the reaction was complete, resulting in a mixed solution. During the stirring process, the sodium aluminum hydride and lithium chloride underwent the following reaction:

[0042] NaAlH4 + LiCl = LiAlH4 + NaCl

[0043] 2. The mixed solution is subjected to solid-liquid separation by any one of the following methods: static precipitation, centrifugal filtration, and positive pressure filtration, to obtain an ether solution containing lithium aluminum hydride and a precipitate. The precipitate includes sodium chloride generated after the reaction, as well as unreacted lithium chloride and a small amount of impurities such as sodium aluminum hydride.

[0044] 3. The diethyl ether solution containing lithium aluminum hydride was subjected to a reduced pressure of -0.04 MPa at 70°C, and then distilled to obtain 13.64 g of dried sodium aluminum hydride crystals.

[0045] The above three examples are lithium aluminum hydride prepared when the molar ratio of sodium aluminum hydride to lithium chloride is 1:1 to 1:1.1. When the molar ratio of sodium aluminum hydride to lithium chloride is 1:1, the yield is 82.79%; at 1:1.05, the yield is 87.13%; and at 1:1.1, the yield is 87.61% (yield here = actual amount of lithium aluminum hydride obtained / theoretical amount of lithium aluminum hydride generated. Taking the first example, the reaction used 21.6g of sodium aluminum hydride with a purity of 97%, which is equivalent to 0.3880mol. According to the reaction equation, 0.3880mol of lithium aluminum hydride can be generated, which is equivalent to 14.7246g by mass; the actual amount of lithium aluminum hydride obtained is 12.93g, minus the 0.74g of lithium aluminum hydride initiator, which is 12.19g. 12.19 / 14.7246≈82.79%. The yields in subsequent examples are all calculated using this method and will not be repeated).

[0046] Based on the three examples above, it can be seen that the yield of lithium aluminum hydride gradually increases with the increase of lithium chloride addition. The yield approaches its limit at a molar ratio of 1:1.05, and further increasing the amount of lithium chloride yields little benefit. This is because both sodium aluminum hydride and lithium chloride are insoluble in diethyl ether, and the reaction is similar to a solid-solid reaction in an unreacted medium, making complete reaction impossible. Even if adding excess lithium chloride can promote the forward reaction, boundary effects still exist. Considering lithium utilization, the optimal molar ratio of sodium aluminum hydride to lithium chloride is 1:1.05.

[0047] In another embodiment, this disclosure also provides a method for preparing sodium aluminum hydride. Unlike the previous embodiments, in this embodiment, the molar ratio of sodium aluminum hydride, lithium chloride and lithium aluminum hydride is 1:1.05:0, and the masses are 21.6g, 17.3g and 0g respectively. The other reaction conditions are the same, and finally 7.08g of dried sodium aluminum hydride crystals are obtained.

[0048] In another embodiment, this disclosure also provides a method for preparing sodium aluminum hydride. Unlike the previous embodiments, in this embodiment, the molar ratio of sodium aluminum hydride, lithium chloride, and lithium aluminum hydride is 1:1.05:0.1, and the masses are 21.6g, 17.3g, and 1.48g respectively. The other reaction conditions are the same, and finally 14.35g of dried sodium aluminum hydride crystals are obtained.

[0049] In the two embodiments described above, the molar ratios of sodium aluminum hydride and lithium aluminum hydride were 1:0 and 1:0.1, respectively. Compared to the previous embodiment where the molar ratio of sodium aluminum hydride and lithium aluminum hydride was 1:0.05, the yield of lithium aluminum hydride was 48.08% when the molar ratio was 1:0.05, 87.13% when the molar ratio was 1:0.1, and 87.40% when the molar ratio was 1:0.1. It can be seen that the yield of lithium aluminum hydride gradually increases with the increase of the small amount of lithium aluminum hydride added as an initiator. At a ratio of 1:0.05, the yield is close to its limit, and further increasing the amount of lithium chloride yields little benefit. This is because lithium aluminum hydride acts as an initiator in this reaction; without lithium aluminum hydride, the reaction starts slowly, and the sodium aluminum hydride reaction is less than 50%. After adding a certain amount of lithium aluminum hydride, the reaction proceeds rapidly. From a cost perspective, the optimal ratio of lithium aluminum hydride to aluminum hydride is 1:0.05.

[0050] In another embodiment, this disclosure also provides a method for preparing lithium aluminum hydride. Unlike the previous embodiments, in this embodiment, sodium aluminum hydride with a purity of 95% is used. 22.0g of sodium aluminum hydride, 17.3g of lithium chloride, and 0.74g of lithium aluminum hydride are weighed in a molar ratio of 1:1.05:0.05. The remaining reaction conditions are the same, and finally 11.94g of dried sodium aluminum hydride crystals are obtained.

[0051] In another embodiment, this disclosure also provides a method for preparing lithium aluminum hydride. Unlike the previous embodiment, in this embodiment, sodium aluminum hydride with a purity of 99.5% is used. 21.1g of sodium aluminum hydride, 17.3g of lithium chloride, and 0.74g of lithium aluminum hydride are weighed in a molar ratio of 1:1.05:0.05. The remaining reaction conditions are the same, and finally 15.12g of dried sodium aluminum hydride crystals are obtained.

[0052] Compared to the aforementioned example, which also used sodium aluminum hydride, lithium chloride, and lithium aluminum hydride in a molar ratio of 1:1.05:0.05 and had sodium aluminum hydride purity of 97%, the yield of lithium aluminum hydride was 76.25% when the purity of sodium aluminum hydride was 95%, 87.13% when the purity was 97%, and 97.46% when the purity was 99.5%. It can be seen that the yield of lithium aluminum hydride increases rapidly with the increase of sodium aluminum hydride purity. Industrially synthesized sodium aluminum hydride contains impurities such as aluminum powder and sodium aluminum hexahydride. Even at low temperatures, the aluminum powder can catalyze the decomposition of lithium aluminum hydride. Therefore, sodium aluminum hydride with a purity below 97% will result in a lower yield of lithium aluminum hydride due to the catalytic effect of the aluminum powder. To improve the yield of lithium aluminum hydride, it is necessary to purify the sodium aluminum hydride to remove impurities such as aluminum powder. From the perspective of cost and process complexity, using sodium aluminum hydride with a purity of over 95% can meet the actual production needs.

[0053] Furthermore, this disclosure also includes modified experiments on the second embodiment described above, adjusting the reaction temperature and pressure in steps 3 and 4 to 30°C and -0.1 MPa, 50°C and -0.07 MPa, and 90°C and -0.02 MPa, respectively. It should be noted that below 90°C, obtaining solid crystals of lithium aluminum hydride requires depressurization; otherwise, lithium aluminum hydride cannot be efficiently crystallized from diethyl ether. This is because lithium aluminum hydride and diethyl ether form a complex, requiring greater energy to separate the lithium aluminum hydride from the diethyl ether. Heating alone would require a temperature of at least 110°C, but higher crystallization temperatures would lead to the decomposition of lithium aluminum hydride, resulting in a decrease in purity. Therefore, depressurization is necessary to obtain pure lithium aluminum hydride.

[0054] Table 1 shows the relationship between temperature and pressure on the crystallization of lithium aluminum hydride diethyl ether solution.

[0055] Table 1

[0056] 0Mpa Almost no precipitation Almost no precipitation Almost no precipitation Almost no precipitation -0.01Mpa Almost no precipitation Almost no precipitation Almost no precipitation Slow precipitation -0.02Mpa Almost no precipitation Almost no precipitation Almost no precipitation rapid precipitation -0.03Mpa Almost no precipitation Almost no precipitation Slow precipitation rapid precipitation -0.04Mpa Almost no precipitation Almost no precipitation rapid precipitation rapid precipitation -0.05Mpa Almost no precipitation Slow precipitation rapid precipitation rapid precipitation -0.06Mpa Almost no precipitation rapid precipitation rapid precipitation rapid precipitation -0.07Mpa Almost no precipitation rapid precipitation rapid precipitation rapid precipitation -0.08Mpa Almost no precipitation rapid precipitation rapid precipitation rapid precipitation -0.09Mpa Slow precipitation rapid precipitation rapid precipitation rapid precipitation -0.1Mpa rapid precipitation rapid precipitation rapid precipitation rapid precipitation

[0057] As shown in Table 1, the lower the temperature, the higher the required vacuum level. Considering factors such as energy consumption, efficiency, and the ease of ether recovery, the optimal crystallization conditions are a temperature of 70℃~90℃ and a pressure of -0.04Mpa~-0.02Mpa.

[0058] Table 2 shows the yield and purity data of lithium aluminum hydride obtained in all the above examples.

[0059] Table 2

[0060]

[0061] As shown in Table 2, the purity of lithium aluminum hydride prepared by the method described in this paper is all above 98%, and changes in different parameters only affect the yield of the final product. This is because the raw materials sodium aluminum hydride, lithium chloride, and the byproduct sodium chloride used in this process are all insoluble in diethyl ether. The diethyl ether solution obtained from the reaction contains only lithium aluminum hydride, and only lithium aluminum hydride crystals can be obtained after vacuum distillation and drying. Therefore, the obtained lithium aluminum hydride has high purity.

[0062] Figure 2 The XRD pattern of lithium aluminum hydride prepared by the process shown in this method is shown. It can be seen that the positions of the diffraction peaks in the figure are basically one-to-one with the characteristic peaks on the standard card PDF 73-0461 (LiAlH4), especially the main peaks at 20°, 23°, 27° and 30° are completely consistent. Therefore, it is indicated that the sample contains only the lithium aluminum hydride phase and no other impurities.

[0063] While the invention has been described above with reference to exemplary embodiments, the scope of protection of the invention is not limited to the embodiments described above. It will be apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the scope and spirit of the invention. The scope of the invention is defined only by the appended claims and their equivalents.

Claims

1. A method for preparing lithium aluminum hydride, comprising the following steps: S100: Place an appropriate amount of sodium aluminum hydride, lithium chloride, and initiator in an ether solution, and stir thoroughly for 4 hours at room temperature (25°C) and atmospheric pressure (1 atm) to obtain a mixed solution; wherein, the molar ratio of sodium aluminum hydride to lithium chloride is 1.0:1.0-1.1, the molar ratio of sodium aluminum hydride to initiator is 1.0:0.05-0.1, and the initiator is lithium aluminum hydride; S200: The mixed solution is separated into solid and liquid components to obtain an ether solution containing lithium aluminum hydride and a precipitate; S300: The ether solution containing lithium aluminum hydride is distilled under reduced pressure at a certain temperature to obtain dry lithium aluminum hydride crystals; wherein, the ether solution containing lithium aluminum hydride is distilled under reduced pressure at a temperature of 30-90°C, and the pressure of the ether solution containing lithium aluminum hydride is reduced to -0.1 to -0.01 MPa.

2. The method for preparing lithium aluminum hydride according to claim 1, wherein, In step S100, the purity of the sodium aluminum hydride is 95.00% to 99.50%.

3. The method for preparing lithium aluminum hydride according to claim 1, wherein, In step S200, the solid-liquid separation of the mixed solution includes any of the following methods: static precipitation, centrifugal filtration, and positive pressure filtration.

4. The method for preparing lithium aluminum hydride according to claim 1, wherein, In step S300, the diethyl ether solution containing lithium aluminum hydride is distilled under reduced pressure at a temperature of 70-90°C.

5. The method for preparing lithium aluminum hydride according to claim 1, wherein, In step S300, the diethyl ether solution containing lithium aluminum hydride is depressurized to -0.04 to -0.02 MPa.

Images