Lithium borohydride and preparation method thereof

Abstract

The invention discloses lithium borohydride and a preparation method thereof, and belongs to the technical field of hydrogen storage material preparation. The preparation method provided by the invention comprises the following steps: in a hydrogen atmosphere of 50bar, mixing lithium hydride, triethylamine borane and an organic solvent, and performing mechanical ball milling to obtain a mixture; and evaporating the solvent in the mixture, and carrying out heat treatment to obtain the lithium borohydride. Lithium borohydride is prepared through mechanical ball milling, the preparation process is high in safety coefficient, low in energy consumption, simple in process, mild in condition, adjustable in reaction process and easy to implement; the optimal yield is 80%, and the method is originally superior to other similar processes, has technical conditions for efficient mass production, and has a wide application prospect in hydrogen storage materials.

Description

Technical Field

[0001] The present application belongs to the technical field of hydrogen storage material preparation, and in particular relates to lithium borohydride and a preparation method thereof. Background Art

[0002] Lithium borohydride (LiBH4) has an extremely high theoretical hydrogen storage capacity (18.5wt%) and can be used as a hydrogen source and a high-capacity hydrogen storage material. It is also one of the most important reducing agents in organic chemistry. In industry, it can be used for bleaching wood pulp and electroless plating. It is a material with wide applications and good prospects.

[0003] Currently, the synthesis of lithium borohydride mainly relies on wet chemical methods or high-temperature and high-pressure reactions. These methods have many disadvantages, such as complex processes, harsh reaction conditions, and high energy consumption, resulting in high production costs for lithium borohydride, limiting its large-scale application. For example, lithium borohydride is commonly prepared industrially by ion exchange reactions using sodium borohydride and lithium chloride / bromide in ether or tetrahydrofuran solutions. The chemical reaction is: NaBH4 + LiCl → LiBH4 + NaCl↓. However, the lithium borohydride synthesized by this method has low purity, byproducts are difficult to remove, and may cause environmental pollution. In addition, although synthesizing lithium borohydride from lithium borohydride products through high-temperature and high-pressure reactions can improve product purity to a certain extent, it requires expensive equipment support, harsh reaction conditions, and poses safety risks.

[0004] Therefore, a lithium borohydride synthesis method with simple preparation process, mild reaction conditions, few by-products, low cost, high efficiency and easy operation is sought to further improve the comprehensive performance of lithium borohydride-based hydrogen storage materials and promote the application research of LiBH4 hydrogen storage materials. Summary of the Invention

[0005] The present application discloses lithium borohydride and a preparation method thereof, aiming to solve the technical problems of the existing lithium borohydride preparation process, such as complicated process, many by-products and high cost.

[0006] In order to achieve the above objectives, the technical solution of this application is:

[0007] A first aspect of the present application provides a method for preparing lithium borohydride, the preparation method comprising:

[0008] In a hydrogen atmosphere at 50 bar, lithium hydride, triethylamine borane and an organic solvent were mixed and then subjected to mechanical ball milling to obtain a mixture;

[0009] After the solvent in the mixture is evaporated, heat treatment is performed to obtain lithium borohydride.

[0010] In combination with the first aspect, preferably, the organic solvent is one of tetrahydrofuran, n-hexane, and diethyl ether.

[0011] In combination with the first aspect, preferably, the molar ratio of lithium hydride to triethylamine borane is 1:1.

[0012] In combination with the first aspect, preferably, during the mechanical ball milling, the ball-to-material ratio is 150-250:1.

[0013] In combination with the first aspect, preferably, when the mechanical ball milling is performed, the ball milling time is 12-48 hours, and the ball milling speed is 300-650 rpm.

[0014] In combination with the first aspect, preferably, when the mechanical ball milling is performed, the ball milling time is 24 hours and the ball milling speed is 500 rpm.

[0015] In combination with the first aspect, preferably, when performing mechanical ball milling, bidirectional ball milling is adopted, with forward and reverse rotations of 20 minutes each and a pause of 6 minutes.

[0016] In combination with the first aspect, preferably, the mixture is heated at 90-120° C. when the solvent in the mixture is evaporated.

[0017] In combination with the first aspect, preferably, the heat treatment is carried out at 90-120° C. for 24-36 hours.

[0018] The second aspect of the present application provides lithium borohydride prepared by the preparation method described in the first aspect.

[0019] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0020] The preparation method provided in the present application successfully prepares lithium borohydride by mechanical ball milling. On the one hand, under a hydrogen atmosphere, lithium hydride and triethylamine borane are directly reacted in a liquid phase by means of the mechanical energy of the mechanical ball mill, followed by evaporation of the solvent and heat treatment to obtain lithium borohydride. The process is simple, has a high safety factor, low energy consumption, mild conditions, a controllable reaction process, and is easy to implement. On the other hand, the preparation method provided in the present application has an optimal yield of 80%, which is superior to other similar processes and has the technical conditions for efficient mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0022] Figure 1 XRD patterns of A1, A2, A3, B1 and B2-lithium borohydride provided in the examples of this application;

[0023] Figure 2 FTIR images of A1, A2, A3, B1 and B2-lithium borohydride provided in the examples of this application;

[0024] Figure 3 Non-isothermal hydrogen release curves of A1, A2, A3, B1 and B2-lithium borohydride provided in the examples of the present application;

[0025] Figure 4 XRD patterns of A1, A4, A5 and A6-lithium borohydride provided in the examples of this application;

[0026] Figure 5 FTIR spectra of A1, A4, A5 and A6-lithium borohydride provided in the examples of the present application;

[0027] Figure 6 Non-isothermal hydrogen release curves of A1, A4, A5 and A6-lithium borohydride provided in the examples of the present application;

[0028] Figure 7 XRD spectra of A1, A7, A8 and A9-lithium borohydride provided in the examples of the present application;

[0029] Figure 8 FTIR spectra of A1, A7, A8 and A9-lithium borohydride provided in the examples of the present application;

[0030] Figure 9 Non-isothermal hydrogen release curves of A1, A7, A8 and A9-lithium borohydride provided in the examples of the present application;

[0031] Figure 10 This is an SEM image of lithium borohydride of A5-lithium borohydride provided in the examples of this application. DETAILED DESCRIPTION

[0032] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0034] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0036] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0037] It should be noted that all raw materials and reagents in the examples of the present application were purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0038] In a first aspect, an embodiment of the present application provides a method for preparing lithium borohydride, the preparation method comprising:

[0039] In a hydrogen atmosphere at 50 bar, lithium hydride, triethylamine borane and an organic solvent were mixed and then subjected to mechanical ball milling to obtain a mixture;

[0040] After the solvent in the mixture is evaporated, heat treatment is performed to obtain lithium borohydride.

[0041] Among them, on the one hand, under a hydrogen atmosphere, with the help of the mechanical energy of mechanical ball milling, lithium hydride and triethylamine borane are directly reacted in a liquid phase, the solvent is evaporated and heat treated to obtain lithium borohydride. The process is simple, has a high safety factor, low energy consumption, mild conditions, and a controllable reaction process, which is easy to implement; on the other hand, the preparation method provided in this application has an optimal yield of 80%, which is better than other similar processes and has the technical conditions for efficient mass production.

[0042] In the examples of the present application, the organic solvent is preferably one of tetrahydrofuran, n-hexane, and diethyl ether. The selection of these solvents can ensure that they do not undergo redox reactions with the product, thereby avoiding the generation of by-products and improving product purity and yield.

[0043] In the embodiment of the present application, the molar ratio of lithium hydride to triethylamine borane is preferably 1: 1. By controlling the reaction ratio, the kinetic properties of the prepared lithium borohydride can be effectively improved, and a higher hydrogen storage capacity can be ensured.

[0044] In the embodiments of the present application, when mechanical ball milling is performed, the ball-to-material ratio is preferably 150-250:1. The ball milling time is preferably 12-48h, more preferably 24h, and the ball milling speed is preferably 300-650rpm, more preferably 500rpm. Bidirectional ball milling is adopted, with forward and reverse rotations of 20min each and a pause of 6min. Among them, by controlling these process parameters, it can be ensured that there are enough grinding balls to fully contact and collide with the material, so that the material can be ground more evenly in all directions, thereby improving the grinding efficiency and the uniformity of mixing. The equations in the reaction process are as follows:

[0045] LiH+C6H 15 N-BH3+H2→LiBH4

[0046] In the embodiment of the present application, the mixture is heated at 90-120° C. to evaporate the solvent. The mixture is heat-treated in an open environment to evaporate a large amount of the solvent into a solid state, and then heat-treated in a closed environment at 90-120° C. for 24-36 hours to completely remove the solvent.

[0047] It should be noted that the preparation process of the present application does not require the addition of catalysts and carrier materials, significantly reducing the types and quantities of raw materials required. This optimization not only simplifies the preparation process but, more importantly, effectively reduces impurity generation, thereby significantly improving the purity and quality of the final product.

[0048] In a second aspect, the present invention also provides lithium borohydride prepared by the preparation method described in the first aspect. The lithium borohydride prepared by the above preparation method has excellent structural stability, improved yield, and has broad application prospects in hydrogen storage materials.

[0049] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0050] Example 1

[0051] This embodiment provides a method for preparing Al-lithium borohydride, which specifically includes:

[0052] S101: In a glove box filled with Ar, weigh 0.05 mol LiH (0.4 g) and 0.05 mol C6H 18BN (5.8 g) was added into a 220 mL stainless steel ball mill, followed by 50 mL of C6H 14 Add to the above reactants. Stainless steel ball milling beads with diameters of 3, 6, and 12 mm were added to the ball mill, and the mass ratio of the added ball milling beads was 100:60:40. The final amount of ball milling beads added was 200 g, and then the ball mill was sealed and transferred out of the glove box. 50 bar H2 was filled into the ball mill to make up for the lack of H2 source in the synthesis of lithium borohydride. The ball milling process was a bidirectional mode, rotating forward for 20 minutes, pausing for 6 minutes, and then reversing for 20 minutes, for a total of 36 times to obtain a lithium borohydride mixture containing n-hexane.

[0053] S102: The ball mill is then transferred to a glove box, and the mixture in the ball mill is transferred to a conical flask. The mixture is then heated and vacuumed on a heating table to remove the solvent. When the solvent is completely evaporated and solids appear, heating and vacuuming are stopped. The mixture is transferred to a quartz crucible, and the quartz crucible containing the sample is transferred to a muffle furnace and heat-treated at 90-120°C for 12-36 hours. After the heat treatment is completed, Al-lithium borohydride is obtained.

[0054] The equation for the reaction process is as follows:

[0055] LiH+C6H 15 N-BH3+H2→LiBH4

[0056] After the reaction is completed, the theoretical yield is 0.05 mol LiBH4 (0.05 mol * 21.78 = 1.1 g), and after the actual reaction is completed, 0.88 g LiBH4 is obtained. The final yield of LiBH4 is:

[0057] Yield (LiBH4) = actual production / theoretical production*100% = 0.88 / 1.1*100% = 80%.

[0058] Example 2

[0059] The component ratio, preparation operation and process parameters of A2-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the organic solvent selected in this example is different, that is, diethyl ether, to prepare A2-lithium borohydride.

[0060] Example 3

[0061] The component ratio, preparation operation and process parameters of A3-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the organic solvent selected in this example is different, that is, tetrahydrofuran, to prepare A3-lithium borohydride.

[0062] Example 4

[0063] The component ratio, preparation operation and process parameters of A4-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 24 hours and the ball milling speed is 300 rpm to prepare A4-lithium borohydride.

[0064] Example 5

[0065] The component ratio, preparation operation and process parameters of A5-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 24 hours and the ball milling speed is 500 rpm to prepare A5-lithium borohydride.

[0066] Example 6

[0067] The component ratio, preparation operation and process parameters of A6-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 24 hours and the ball milling speed is 650 rpm to prepare A6-lithium borohydride.

[0068] Example 7

[0069] The component ratio, preparation operation and process parameters of A7-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 12 hours and the ball milling speed is 500 rpm to prepare A7-lithium borohydride.

[0070] Example 8

[0071] The component ratio, preparation operation and process parameters of A8-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 36 hours and the ball milling speed is 500 rpm to prepare A8-lithium borohydride.

[0072] Example 9

[0073] The component ratio, preparation operation and process parameters of A9-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the ball milling time in this example is 48 hours and the ball milling speed is 500 rpm to prepare A9-lithium borohydride.

[0074] At the same time, in order to verify the comprehensive performance of the lithium borohydride prepared in the above examples, the present application provides the following comparative examples for detailed description.

[0075] Comparative Example 1

[0076] The component ratio, preparation operation and process parameters of B1-lithium borohydride prepared in this example are basically the same as those in Example 1, except that the organic solvent selected in this example is different, that is, acetone is used to prepare B1-lithium borohydride.

[0077] Comparative Example 2

[0078] The component ratio, preparation operation and process parameters of B2-lithium borohydride prepared in this comparative example are basically the same as those in Example 1, except that no organic solvent is added in this comparative example to prepare B2-lithium borohydride.

[0079] The comparison of the addition of organic solvents and ball milling conditions in the above embodiments and comparative examples is shown in Table 1:

[0080] Table 1 Addition of organic solvents and ball milling conditions for Examples 1-9 and Comparative Examples 1-2

[0081]

[0082] In order to verify the structural characteristics of the lithium borohydride prepared in the examples of this application, the lithium borohydride prepared in the examples was subjected to structural tests, and the test results are as follows: Figure 1-2 As shown. Among them, Figure 1 is the XRD pattern of lithium borohydride; Figure 2 This is the FTIR spectrum of lithium borohydride.

[0083] according to Figure 1 As is known, the XRD patterns of the lithium borohydride prepared in the examples of this application, synthesized in n-hexane, ether, and tetrahydrofuran solvents, show perfect correspondence with the diffraction peaks of commercially available LiBH4 crystals, with no impurity peaks present. However, impurity peaks were observed in the XRD patterns of lithium borohydride synthesized without the addition of solvents, and the diffraction peak intensities were weak, indicating that the synthesized lithium borohydride without the addition of solvents was impure and had poor crystallinity. Furthermore, no diffraction peaks were observed for lithium borohydride in acetone solvent, indicating that acetone is not conducive to the synthesis of lithium borohydride.

[0084] according to Figure 2 As far as we know, in n-hexane, ether, tetrahydrofuran solvents and no solvent added, the peaks at 1124, 2238, 2291 and 2221 cm -1 The infrared absorption peaks of the BH bond in LiBH4 were detected at 40°C, which were attributed to the bending vibration and stretching vibration of the BH bond in LiBH4. However, no infrared vibration peaks of LiBH4 were found in acetone solvent, which is consistent with the above XRD analysis.

[0085] The lithium borohydride prepared in Examples 1-3 and Comparative Examples 1-2 was subjected to a non-isothermal hydrogen release performance test. The specific test process is as follows:

[0086] Step 1: In a glove box, weigh approximately 60 mg of sample and place it into a reactor. The reactor is then sealed, taken out, and connected to a Sieverts hydrogen storage tester.

[0087] Step 2: Evacuate the chamber and set up a non-isothermal hydrogen release test program, generally heating from room temperature to 600°C at 2°C / min.

[0088] Step 3: After the vacuum is completed, wait for 10 minutes, click the instrument to start the test and record the test data. After the test is completed, save the test data and close the test program.

[0089] according to Figure 3 Figure 2 shows a comparison of the non-isothermal hydrogen release curves of lithium borohydride prepared in Examples 1-3 and Comparative Examples 1-2. As can be seen from the figure, the non-isothermal hydrogen release curves of lithium borohydride prepared in n-hexane, diethyl ether, and tetrahydrofuran solvents are essentially identical to those of commercial LiBH4, and the hydrogen release capacity is 1 wt% higher than that of commercial lithium borohydride under the same test conditions. The hydrogen release capacity of lithium borohydride prepared without solvent addition is far lower than that of commercial LiBH4. Furthermore, lithium borohydride synthesized in acetone solvent releases virtually no hydrogen, indicating that virtually no lithium borohydride is generated.

[0090] Among the various solvents mentioned above, n-hexane was preferred. The hydrogen desorption properties of lithium borohydride synthesized at different ball milling speeds and times were discussed. The structural characterization and non-isothermal hydrogen desorption properties of lithium borohydride synthesized in n-hexane at different ball milling speeds (300, 400, 500, and 650 rpm) for 24 hours were also investigated.

[0091] according to Figure 4 As can be seen, the XRD spectra of lithium borohydride prepared at different ball milling speeds for 24 hours in n-hexane solvent are shown. The XRD spectra show that the characteristic diffraction peaks of lithium borohydride prepared at different ball milling speeds are consistent with those of commercial LiBH4, and no impurity phase is found, indicating the successful synthesis of lithium borohydride.

[0092] according to Figure 5 As we know, the FTIR spectra of lithium borohydride prepared in n-hexane solvent with ball milling time of 24h and different ball milling speeds are shown. The characteristic peak of the bending vibration of BH bond in lithium borohydride (1124cm -1 ) and the stretching vibration characteristic peaks of BH bonds (2224, 2283 and 2291 cm -1 ).

[0093] according to Figure 6 As is known, the non-isothermal hydrogen release curves of lithium borohydride prepared at different ball milling speeds for 24 hours in n-hexane solvent and heated to 600°C at a heating rate of 2°C / min are shown. As can be seen from the figure, at 600°C, the lithium borohydride prepared at a ball milling speed of 500 rpm releases more hydrogen than those prepared at other speeds, releasing approximately 13 wt% H2.

[0094] The lithium borohydride synthesized in n-hexane at a ball milling speed of 500 rpm and different ball milling times of 12, 36, and 48 h were further investigated for structural characterization and non-isothermal hydrogen release performance testing, as shown in Examples 1, 7, 8, and 9.

[0095] according to Figure 7 As known, the XRD spectra of lithium borohydride prepared in n-hexane solvent at a ball milling speed of 500 rpm and different ball milling times show that no other diffraction peaks are detected in the prepared lithium borohydride.

[0096] according to Figure 8 As we know, the FTIR spectra of lithium borohydride prepared in n-hexane solvent at a ball milling speed of 500 rpm and different ball milling times are shown. The infrared characteristic peaks of BH bonds in lithium borohydride (2383, 2291, 2221 and 1127 cm -1 ).

[0097] according to Figure 9 As is known, the non-isothermal hydrogen release curves of lithium borohydride prepared at different milling times in n-hexane at a ball mill speed of 500 rpm and heated to 600°C at a heating rate of 2°C / min are shown. As can be seen from the figure, the amount of hydrogen released after milling for 12 hours at 600°C is lower than that at other milling times, with approximately 11.8 wt% H2 released. The amounts of hydrogen released after milling for 24, 36, and 48 hours are essentially the same, and 12.9 wt% H2 can be released when heated to 600°C.

[0098] Based on the verification of the above examples, n-hexane was selected as the solvent for synthesizing lithium borohydride, and the optimal ball milling process parameters were a ball milling time of 24 h and a ball milling speed of 500 rpm.

[0099] according to Figure 10 As known, the SEM image of lithium borohydride synthesized in n-hexane solvent at a ball milling speed of 500 rpm and a ball milling time of 24 hours. From the figure, it can be seen that the synthesized lithium borohydride is in a large block shape with many small blocks stacked on its surface.

[0100] Therefore, the preparation method provided in the present application achieves the successful preparation of lithium borohydride by mechanical ball milling. On the one hand, under a hydrogen atmosphere, with the help of the mechanical energy of mechanical ball milling, lithium hydride and triethylamine borane are directly reacted in a liquid phase, and then the solvent is evaporated to obtain lithium borohydride. This method has a high safety factor, low energy consumption, mild conditions, a controllable reaction process, and is easy to implement. On the other hand, the preparation method provided in the present application has an optimal yield of 80%, which is far superior to other similar processes, has the technical conditions for efficient mass production, and has broad application prospects.

[0101] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0102] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing lithium borohydride, characterized in that: The preparation method comprises: In a hydrogen atmosphere at 50 bar, lithium hydride, triethylamine borane and an organic solvent were mixed and then subjected to mechanical ball milling to obtain a mixture; After the solvent in the mixture is evaporated, heat treatment is performed to obtain lithium borohydride.

2. The preparation method according to claim 1, characterized in that The organic solvent is one of tetrahydrofuran, n-hexane and ether.

3. The preparation method according to claim 1, characterized in that The molar ratio of the lithium hydride to triethylamine borane is 1:

1.

4. The preparation method according to claim 1, characterized in that During the mechanical ball milling, the ball-to-material ratio is 150-250:

1.

5. The preparation method according to claim 1, characterized in that When the mechanical ball milling is performed, the ball milling time is 12-48 hours and the ball milling speed is 300-650 rpm.

6. The preparation method according to claim 5, characterized in that During the mechanical ball milling, the ball milling time is 24 h and the ball milling speed is 500 rpm.

7. The preparation method according to claim 5, characterized in that The mechanical ball milling was performed by bidirectional ball milling, with forward and reverse rotations of 20 minutes each and a pause of 6 minutes.

8. The preparation method according to claim 1, characterized in that The mixture is heated at 90-120° C. to evaporate the solvent.

9. The preparation method according to claim 1, characterized in that During the heat treatment, the temperature is kept at 90-120° C. for 24-36 hours.

10. Lithium borohydride prepared by the preparation method according to any one of claims 1 to 9.

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