A method for preparing lithium aluminum hydride

Abstract

This invention belongs to the field of compound synthesis technology and provides a method for preparing lithium aluminum hydride. The method includes the following steps: mixing an organic solution of aluminum trichloride and an organic solution of lithium hydride to perform a displacement reaction, obtaining a mixture of lithium aluminum hydride; mixing the lithium aluminum hydride mixture with a hydrocarbon solvent and performing solid-liquid separation to obtain lithium aluminum hydride. Lithium aluminum hydride is insoluble in hydrocarbon solvents and precipitates out, further improving the yield of lithium aluminum hydride; simultaneously, unreacted aluminum trichloride dissolves in the hydrocarbon solvent, thereby increasing the main content of lithium aluminum hydride. The preparation process of this invention has high yield, stable product content, and is easy to implement and industrialize.

Description

Technical Field

[0001] This invention relates to the field of compound synthesis technology, and in particular to a method for preparing lithium aluminum hydride. Background Technology

[0002] Lithium aluminum hydride, also known as lithium aluminum hydride, is an inorganic compound with the chemical formula LiAlH4 and a density of 0.97 g / cm³. 3 Lithium aluminum hydride (LDH) has a melting point of 125°C and is a white or white-grayish crystalline powder. It is insoluble in hydrocarbons but soluble in ethers and tetrahydrofuran. Currently, LDH is widely used in organic and inorganic synthesis. It is also an additive for rocket propellants and high-energy fuels, possessing a very good market and development potential. However, LDH is a very strong reducing agent; water and protic solvents react violently with it to produce hydrogen gas, therefore these cannot be used as reaction solvents.

[0003] Currently, the processes used to prepare lithium aluminum hydride (LHA) fall into the following categories: 1) A solution of aluminum trichloride and diethyl ether is prepared, which is then reacted with a mixture of lithium hydride and diethyl ether. The diethyl ether is then evaporated to obtain solid lithium aluminum hydride (LHA); 2) Soluble lithium salts and aluminum salts are used as raw materials. A precipitant is added to an aqueous solution to co-precipitate lithium and aluminum ions. The precipitate is dried and decomposed at high temperature to obtain its oxide. This oxide is then hydrogenated to obtain a mixture of aluminum and lithium elements, which is then hydrogenated at room temperature and pressure to obtain LHA. However, the LHA obtained by these two processes generally has a main content of around 95%, which includes a certain amount of unreacted raw materials, making it difficult to obtain LHA with a main content of over 97%, and the main content of the product is unstable. Therefore, providing a process for preparing LHA with a stable and high main content of LHA is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for preparing lithium aluminum hydride.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing lithium aluminum hydride, comprising the following steps:

[0007] (1) A mixture of aluminum trichloride organic solution and lithium hydride organic solution was mixed to carry out a displacement reaction to obtain a mixture of aluminum hydride and lithium hydride.

[0008] (2) The mixture of lithium aluminum hydride is mixed with a hydrocarbon solvent and the solid and liquid are separated to obtain the lithium aluminum hydride.

[0009] Preferably, the organic solution of aluminum trichloride in step (1) is an ether solution, and the ether includes one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

[0010] Preferably, in step (1), the mass-to-volume ratio of aluminum trichloride to ether in the organic solution of aluminum trichloride is 60-180 g: 250-1500 mL.

[0011] Preferably, the organic solution of lithium hydride in step (1) is an ether solution, and the ether includes one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

[0012] Preferably, in step (1), the mass-to-volume ratio of lithium hydride to ether in the organic solution of lithium hydride is 14.27–43.80 g: 150–300 mL.

[0013] Preferably, the mass ratio of aluminum trichloride in the organic solution of aluminum trichloride to lithium hydride in the organic solution of lithium hydride in step (1) is 60-180: 14.27-43.80.

[0014] Preferably, the temperature of the reaction in step (1) is ≤40℃ and the time is 5 to 7 hours.

[0015] Preferably, the hydrocarbon solvent in step (2) is a polar hydrocarbon solvent, which is one or more of xylene, trimethylbenzene and dioxane.

[0016] Preferably, the mass-to-volume ratio of aluminum trichloride in the organic solution of aluminum trichloride in step (1) to the hydrocarbon solvent in step (2) is 60-180 g: 300-900 mL.

[0017] The beneficial effects of this invention are:

[0018] This invention provides a method for preparing lithium aluminum hydride (LDH), comprising the following steps: mixing an organic solution of aluminum trichloride and an organic solution of lithium hydride to perform a displacement reaction, obtaining a mixture of LDH; mixing the LDH mixture with a hydrocarbon solvent and performing solid-liquid separation to obtain LDH. The reaction of this invention is relatively mild, and the temperature is easy to control, thus ensuring a stable reaction. LDH is insoluble in hydrocarbon solvents and precipitates out, further improving the yield of LDH. Simultaneously, unreacted aluminum trichloride dissolves in the hydrocarbon solvent, thereby increasing the main content of LDH. The preparation process of this invention has high yield, stable product content, and is easy to implement and industrialize. Detailed Implementation

[0019] This invention provides a method for preparing lithium aluminum hydride, comprising the following steps:

[0020] (1) A mixture of aluminum trichloride organic solution and lithium hydride organic solution was mixed to carry out a displacement reaction to obtain a mixture of aluminum hydride and lithium hydride.

[0021] (2) The mixture of lithium aluminum hydride is mixed with a hydrocarbon solvent and the solid and liquid are separated to obtain the lithium aluminum hydride.

[0022] In this invention, the organic solution of aluminum trichloride in step (1) is preferably an ether solution, and the ether preferably includes one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

[0023] In this invention, the mass-to-volume ratio of aluminum trichloride to ether in the organic solution of aluminum trichloride in step (1) is preferably 60-180g: 250-1500mL, more preferably 80-160g: 350-1000mL, and even more preferably 100-120g: 500-800mL.

[0024] In this invention, when the organic solution in the organic solution of aluminum trichloride in step (1) is an ether solution, the method for preparing the organic solution of aluminum trichloride includes the following steps:

[0025] Aluminum trichloride and ether are mixed to obtain an organic solution of aluminum trichloride (an ether solution of aluminum trichloride).

[0026] In this invention, the mixing temperature is preferably ≤40℃, more preferably ≤35℃, and even more preferably ≤30℃; the mixing pressure is preferably 95~105KPa, more preferably 97~103KPa, and even more preferably 100~101KPa; the mixing stirring speed is preferably 300~600r / min, more preferably 400~500r / min, and even more preferably 430~450r / min.

[0027] In this invention, the mixing is preferably achieved by adding ether dropwise to aluminum trichloride at a rate of 2–10 mL / min, more preferably 4–8 mL / min, and even more preferably 5–6 mL / min. After the dropwise addition is completed, stirring is continued at a speed of 300–600 r / min, more preferably 400–500 r / min, and even more preferably 430–450 r / min. The stirring time is preferably 4–5 h, more preferably 4.2–4.7 h, and even more preferably 4.4–4.5 h.

[0028] In this invention, the dissolution process of aluminum trichloride is an exothermic process. For some single ethers with low boiling points, dissolution and mixing need to be carried out under low-temperature cold bath conditions. Using a mixture of high-boiling-point ethers and low-boiling-point ethers to dissolve aluminum trichloride can further reduce the loss of ethers.

[0029] In this invention, the organic solution of lithium hydride in step (1) is preferably an ether solution, and the ether preferably includes one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

[0030] In this invention, the mass-to-volume ratio of lithium hydride to ether in the organic solution of lithium hydride in step (1) is preferably 14.27-43.80g:150-300mL, more preferably 20-35g:200-250mL, and even more preferably 25-30g:210-225mL.

[0031] In this invention, when the organic solution in the lithium hydride organic solution in step (1) is an ether solution, the method for preparing the lithium hydride organic solution includes the following steps:

[0032] Under an inert atmosphere, lithium hydride and ether are mixed to obtain an organic solution of lithium hydride (an ether solution of lithium hydride).

[0033] In this invention, the inert atmosphere is preferably argon or nitrogen; the mixing temperature is preferably 20-30°C, more preferably 22-28°C, and even more preferably 23-25°C; the pressure is preferably 95-105 kPa, more preferably 97-103 kPa, and even more preferably 100-101 kPa.

[0034] In this invention, the direct mixing of lithium hydride and ether can effectively slow down the reaction rate and prevent overheating and a sharp increase in temperature.

[0035] In this invention, the mass ratio of aluminum trichloride in the organic solution of aluminum trichloride to lithium hydride in the organic solution of lithium hydride in step (1) is preferably 60-180:14.27-43.80, more preferably 80-160:20-35, and even more preferably 100-120:25-30.

[0036] In this invention, the mixing in step (1) is preferably done by adding an organic solution of aluminum trichloride dropwise to an organic solution of lithium hydride, and then reacting after the addition is complete.

[0037] In this invention, if aluminum trichloride and lithium hydride are directly mixed, the reaction is too violent and the reaction temperature cannot be reasonably controlled. This invention uses ether as a solvent for the reaction, which is relatively mild, the reaction temperature is easy to control, and the reaction can proceed steadily.

[0038] In this invention, the stirring speed for mixing is preferably 400-600 r / min, more preferably 450-550 r / min, and even more preferably 500-530 r / min; the temperature is preferably ≤40℃, more preferably ≤35℃, and even more preferably ≤30℃; the dropping rate is preferably 6-10 mL / min, more preferably 7-9 mL / min, and even more preferably 7.5-8 mL / min.

[0039] In this invention, the chemical equation for the reaction in step (1) is:

[0040] AlCl3 + 4LiH = LiAlH4 + 3LiCl.

[0041] In this invention, the stirring speed of the reaction in step (1) is preferably 400-600 r / min, more preferably 450-550 r / min, and even more preferably 500-530 r / min; the temperature of the reaction is preferably ≤40℃, more preferably ≤35℃, and even more preferably ≤30℃; the time is preferably 5-7 h, more preferably 5.5-6.5 h, and even more preferably 6-6.2 h.

[0042] In this invention, after the reaction in step (1) is completed, the resulting system is post-processed to obtain a mixture of lithium aluminum hydride.

[0043] In this invention, the post-processing preferably includes the following steps:

[0044] (a) Under an inert atmosphere, the system obtained from the reaction is subjected to solid-liquid separation (filtration) to obtain solid lithium chloride and an organic solution (ether solution) of lithium aluminum hydride.

[0045] (b) Under an inert atmosphere, the organic solution (ether solution) of lithium aluminum hydride is concentrated by distillation to obtain a mixture of organic solution (ether solution) and lithium aluminum hydride. The organic solution (ether solution) can be recycled.

[0046] In this invention, the inert atmosphere in step (a) is preferably argon or nitrogen; the pore size of the filter membrane is preferably 3 to 5 μm, more preferably 3.5 to 4.5 μm, and even more preferably 3.7 to 4 μm.

[0047] In this invention, the inert atmosphere in step (b) is preferably argon or nitrogen; the pressure of the distillation is preferably 95-105 kPa, more preferably 97-103 kPa, and even more preferably 100-101 kPa; the target temperature for the distillation concentration is preferably 75-85°C, more preferably 77-83°C, and even more preferably 80-81°C.

[0048] In this invention, the hydrocarbon solvent in step (2) is preferably a polar hydrocarbon solvent, and the polar hydrocarbon solvent is preferably one or more of xylene, trimethylbenzene and dioxane.

[0049] In this invention, the mass-to-volume ratio of aluminum trichloride in the organic solution of aluminum trichloride in step (1) to the hydrocarbon solvent in step (2) is preferably 60-180g:300-900mL, more preferably 80-160g:500-800mL, and even more preferably 100-120g:600-700mL.

[0050] In this invention, in step (2), the mixture of lithium aluminum hydride is mixed with a hydrocarbon solvent. Lithium aluminum hydride is insoluble in the hydrocarbon solvent and precipitates out in the form of a precipitate, which can further improve the yield of lithium aluminum hydride. At the same time, unreacted aluminum trichloride dissolves in the hydrocarbon solvent, which can increase the main content of lithium aluminum hydride.

[0051] In this invention, the hydrocarbon solvent is almost insoluble in water, achieving a water content of less than 50 ppm, which does not affect the main content of the product while improving the yield. Using the hydrocarbon solvent in this invention, the resulting lithium aluminum hydride has a higher main content, is more stable, and has a higher yield than traditional production processes.

[0052] In this invention, after mixing in step (2), the resulting precipitate is sequentially filtered, dried, pulverized, and ground under an inert atmosphere to obtain the aforementioned lithium aluminum hydride.

[0053] In this invention, the inert atmosphere is preferably argon or nitrogen; the pore size of the filter membrane is preferably 3-5 μm, more preferably 3.5-4.5 μm, and even more preferably 3.7-4 μm; within this pore size range, filtration will not occur; the vacuum degree of the drying is preferably -0.05 to -0.15 MPa, more preferably -0.07 to -0.13 MPa, and even more preferably -0.10 to -0.12 MPa; the drying temperature is preferably 65-80°C, more preferably 70-75°C, and even more preferably 72-73°C; the drying time is preferably 4-6 h, more preferably 4.5-5.5 h, and even more preferably 5-5.2 h; the ambient humidity of the drying environment is preferably ≤5%, more preferably ≤4%, and even more preferably ≤3%; the ambient humidity of the pulverizing environment is preferably ≤5%, more preferably ≤4%, and even more preferably ≤3%; the ambient humidity of the grinding environment is preferably ≤5%, more preferably ≤4%, and even more preferably ≤3%.

[0054] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1

[0056] Under conditions of 15℃, 100KPa, and 430r / min, 500mL of ether (300mL of ethylene glycol dimethyl ether and 200mL of diethyl ether) was added dropwise to 60g of aluminum trichloride at a rate of 6mL / min. After the addition was complete, the mixture was stirred at 430r / min for 4 hours to obtain an ether solution of aluminum trichloride. Under conditions of 25℃, 100KPa, and an argon atmosphere, 14.27g of lithium hydride was mixed with 150mL of n-butyl ether to obtain an ether solution of lithium hydride. Under the condition of 550 r / min, an aluminum trichloride ether solution was added dropwise to a lithium hydride ether solution at a dropping rate of 10 mL / min. After the addition was completed, the reaction was carried out at 30℃ and 550 r / min for 5 h. Under an argon atmosphere, the reaction system was filtered (membrane pore size 4 μm) to obtain lithium chloride solid and lithium aluminum hydride ether solution. Under a pressure of 100 kPa and an argon atmosphere, the lithium aluminum hydride ether solution was concentrated by distillation at a target temperature of 80℃ to obtain a mixture of ether solution and lithium aluminum hydride.

[0057] A mixture of lithium aluminum hydride was mixed with 300 mL of hydrocarbon solvent (100 mL of dioxane and 200 mL of xylene). The resulting precipitate was filtered (membrane pore size 4 μm) under an argon atmosphere and then dried for 6 h at a temperature of 80 °C, a humidity of 3%, a vacuum of -0.1 MPa, and an argon atmosphere. After drying, the precipitate was pulverized under a humidity of 3% and an argon atmosphere, and finally ground to obtain lithium aluminum hydride.

[0058] The lithium aluminum hydride obtained in this embodiment is a white powder. The mass of lithium aluminum hydride was weighed and found to be 16.25g. After calculation, the yield of lithium aluminum hydride in this embodiment was 95.15%, and the main content was 97.02%.

[0059] Example 2

[0060] Under conditions of 15℃, 101 kPa, and 440 r / min, 1000 mL of ether (600 mL of ethylene glycol dimethyl ether and 400 mL of tetrahydrofuran) was added dropwise to 120 g of aluminum trichloride at a rate of 6 mL / min. After the addition was complete, the mixture was stirred at 450 r / min for 5 h to obtain an ether solution of aluminum trichloride. Under conditions of 25℃, 101 kPa, and a nitrogen atmosphere, 28.54 g of lithium hydride was mixed with 300 mL of diethyl ether to obtain an ether solution of lithium hydride. At 5℃ and 550 r / min, an ether solution of aluminum trichloride was added dropwise to an ether solution of lithium hydride at a dropping rate of 8 mL / min. After the addition was completed, the reaction was carried out at 31℃ and 550 r / min for 7 h. Under a nitrogen atmosphere, the reaction system was filtered (membrane pore size 3 μm) to obtain solid lithium chloride and an ether solution of lithium aluminum hydride. Under a pressure of 101 kPa and a nitrogen atmosphere, the ether solution of lithium aluminum hydride was concentrated by distillation at a target temperature of 80℃ to obtain a mixture of ether solution and lithium aluminum hydride.

[0061] A mixture of lithium aluminum hydride was mixed with a hydrocarbon solvent (600 mL dioxane). The resulting precipitate was filtered (membrane pore size 3 μm) under a nitrogen atmosphere and then dried for 6 h at a temperature of 80 °C, a humidity of 4%, a vacuum of -0.12 MPa, and a nitrogen atmosphere. After drying, the precipitate was pulverized under a humidity of 4% and a nitrogen atmosphere, and finally ground to obtain lithium aluminum hydride.

[0062] The lithium aluminum hydride obtained in this embodiment is a white powder. The mass of lithium aluminum hydride was weighed and found to be 32.91 g. After calculation, the yield of lithium aluminum hydride in this embodiment was 96.34% and the main content was 97.15%.

[0063] Example 3

[0064] Under conditions of 10℃, 100KPa, and 450r / min, 1500mL of diethyl ether was added dropwise to 180g of aluminum trichloride at a rate of 5.5mL / min. After the addition was complete, the mixture was stirred at 450r / min for 5 hours to obtain an ether solution of aluminum trichloride. Under conditions of 27℃, 100KPa, and argon atmosphere, 43.80g of lithium hydride was mixed with 300mL of tetrahydrofuran to obtain an ether solution of lithium hydride. Under conditions of 26℃ and 600r / min... Under the condition of 10 mL / min, an aluminum trichloride ether solution was added dropwise to a lithium hydride ether solution. After the addition was completed, the reaction was carried out at 30 °C and 600 r / min for 7 h. Under an argon atmosphere, the reaction system was filtered (membrane pore size 5 μm) to obtain lithium chloride solid and lithium aluminum hydride ether solution. Under an argon atmosphere and a pressure of 100 kPa, the lithium aluminum hydride ether solution was concentrated by distillation at a target temperature of 80 °C to obtain a mixture of ether solution and lithium aluminum hydride.

[0065] A mixture of lithium aluminum hydride was mixed with 900 mL of hydrocarbon solvent (400 mL xylene and 500 mL dioxane). The resulting precipitate was filtered (membrane pore size 5 μm) under an argon atmosphere and then dried for 6 h at 80 °C, 2% humidity, -0.13 MPa vacuum, and an argon atmosphere. After drying, the precipitate was pulverized under an argon atmosphere at 2% humidity and then ground to obtain lithium aluminum hydride.

[0066] The lithium aluminum hydride obtained in this embodiment is a white powder. The mass of lithium aluminum hydride was weighed and found to be 49.52 g. After calculation, the yield of lithium aluminum hydride in this embodiment was 96.64% and the main content was 97.21%.

[0067] Comparative Example 1

[0068] Under conditions of 10℃, 100KPa, and 450r / min, 1500mL of diethyl ether was added dropwise to 180g of aluminum trichloride at a rate of 5.5mL / min. After the addition was complete, the mixture was stirred at 450r / min for 5 hours to obtain an ether solution of aluminum trichloride. Under conditions of 27℃, 100KPa, and argon atmosphere, 43.80g of lithium hydride was mixed with 300mL of tetrahydrofuran to obtain an ether solution of lithium hydride. Under conditions of 26℃ and 600r / min... Under the condition of 10 mL / min, an aluminum trichloride ether solution was added dropwise to a lithium hydride ether solution. After the addition was completed, the reaction was carried out at 30 °C and 600 r / min for 7 h. Under an argon atmosphere, the reaction system was filtered (membrane pore size 5 μm) to obtain lithium chloride solid and lithium aluminum hydride ether solution. Under an argon atmosphere and a pressure of 100 kPa, the lithium aluminum hydride ether solution was concentrated by distillation at a target temperature of 80 °C to obtain a mixture of ether solution and lithium aluminum hydride.

[0069] The mixture of lithium aluminum hydride was dried for 6 hours at 80°C, 2% humidity, -0.12 MPa vacuum, and argon atmosphere. After drying, it was pulverized under 2% humidity and argon atmosphere, and finally ground to obtain lithium aluminum hydride.

[0070] The lithium aluminum hydride obtained in this comparative example is a grayish-white powder. The mass of lithium aluminum hydride was 45.24 g. After calculation, the yield of lithium aluminum hydride in this example was 88.27%, and the main content was 95.18%.

[0071] In other words, the main content and yield of lithium aluminum hydride obtained without further processing with hydrocarbons are not as high as those obtained after processing with hydrocarbon reagents, and the product color is not white enough.

[0072] As can be seen from the above embodiments, the present invention provides a method for preparing lithium aluminum hydride, comprising the following steps: mixing an organic solution of aluminum trichloride and an organic solution of lithium hydride to carry out a displacement reaction to obtain a mixture of lithium aluminum hydride; mixing the lithium aluminum hydride mixture with a hydrocarbon solvent and performing solid-liquid separation to obtain lithium aluminum hydride. Lithium aluminum hydride is insoluble in hydrocarbon solvents and precipitates out in the form of a precipitate, which can further improve the yield of lithium aluminum hydride; at the same time, unreacted aluminum trichloride dissolves in the hydrocarbon solvent, thereby increasing the main content of lithium aluminum hydride; the preparation process of the present invention has high yield, stable product content, easy process flow, and is easy to industrialize.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing lithium aluminum hydride, characterized in that, Includes the following steps: (1) A mixture of organic solution of aluminum trichloride and organic solution of lithium hydride was mixed to carry out a displacement reaction to obtain a mixture of lithium aluminum hydride; (2) The mixture of lithium aluminum hydride and hydrocarbon solvent is mixed and separated into solid and liquid components to obtain the lithium aluminum hydride.

2. The preparation method according to claim 1, characterized in that, In step (1), the organic solution of aluminum trichloride is an ether solution, and the ether contains one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass-to-volume ratio of aluminum trichloride to ether in the organic solution of aluminum trichloride is 60-180 g: 250-1500 mL.

4. The preparation method according to claim 3, characterized in that, In step (1), the organic solution of lithium hydride is an ether solution, and the ether includes one or more of ethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran and n-butyl ether.

5. The preparation method according to claim 4, characterized in that, In step (1), the mass-to-volume ratio of lithium hydride to ether in the organic solution of lithium hydride is 14.27–43.80 g: 150–300 mL.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of aluminum trichloride in the organic solution to lithium hydride in the organic solution is 60-180: 14.27-43.

80.

7. The preparation method according to claim 6, characterized in that, The reaction in step (1) is carried out at a temperature of ≤40℃ for 5 to 7 hours.

8. The preparation method according to claim 7, characterized in that, The hydrocarbon solvent in step (2) is a polar hydrocarbon solvent, which is one or more of xylene, trimethylbenzene and dioxane.

9. The preparation method according to claim 8, characterized in that, In step (1), the mass-to-volume ratio of aluminum trichloride in the organic solution to the hydrocarbon solvent in step (2) is 60-180 g: 300-900 mL.