Method for preparing magnesium borohydride by solution method

Abstract

The invention discloses a method for preparing magnesium borohydride by a solution method, and relates to the technical field of hydrogen storage materials. The method comprises the following steps: dissolving MgCl2 in tetrahydrofuran to form a magnesium source solution, dissolving NaBH4 in isopropylamine to form a boron-hydrogen source solution, mixing the two solutions, and stirring to react; carrying out centrifugation and microfiltration membrane suction filtration separation on the reacted mixture to remove solid impurities so as to obtain a clarified filtrate; and carrying out vacuum desolventizing treatment on the filtrate to finally obtain solid magnesium borohydride. The method is simple in process flow, can be completed under mild conditions, and has the advantages of low raw material cost and high operation safety; the prepared magnesium borohydride product has excellent performance of lower initial hydrogen desorption temperature, and the temperature is only 115.8 DEG C. The method is especially suitable for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of hydrogen storage materials, in particular to a method for preparing magnesium borohydride by solution method. BACKGROUND

[0002] The massive consumption of non-renewable fossil fuels such as coal, oil and natural gas is leading to an increasingly severe energy crisis and causing environmental problems such as global warming and air pollution. Hydrogen energy, as a renewable and clean energy, is considered an ideal choice to replace fossil energy due to its abundant resources, high heat value and zero carbon emissions. At present, the core challenge of building a "production-storage-transportation-use" full-chain hydrogen energy system lies in breaking through the bottleneck of hydrogen storage technology, including improving hydrogen storage density, enhancing safety and controlling cost, which are the key factors to promote the large-scale and industrial development of hydrogen energy. Among the existing hydrogen storage technologies, solid-state hydrogen storage is considered to be a promising way due to its high safety, high volumetric hydrogen storage density and potential low cost.

[0003] Magnesium borohydride is one of the research focuses of high-performance hydrogen storage materials, with high mass hydrogen storage density (theoretical value up to 14.9wt.%), moderate hydrogen release kinetics and good safety, and has great application potential in future hydrogen energy economy. At present, the synthesis technology of magnesium borohydride is mainly ion exchange method, and the core reaction is the double decomposition reaction between alkali metal borohydride and magnesium halide. The main process routes include solid-phase ball milling-condensation reflux method and liquid-phase ball milling method. The operation steps of the solid-phase ball milling-condensation reflux method are as follows: first, the alkali metal borohydride and magnesium halide are placed in the ball mill pot according to the stoichiometric ratio for ball milling; then the powder after ball milling is transferred to a three-necked flask equipped with a condensation device, ethyl ether solvent is added and the reaction is continuously stirred under reflux condition; finally, the reaction mixture is filtered and the obtained filtrate is treated to remove the solvent to obtain white solid magnesium borohydride product. The general chemical reaction equation of this method is as follows:

[0004] 2MBH4+MgX2→Mg(BH4)2+2MX (M = Li, Na; X = Cl, Br)

[0005] The chemical reaction of liquid-phase ball milling method is the same as above, but the difference in process is that the reactants (alkali metal borohydride and magnesium halide) and solvent ethyl ether are placed in the ball mill pot at one time for ball milling reaction; after the reaction is completed, the solid-liquid mixture in the pot is directly filtered and the subsequent desolvation treatment is carried out to obtain the final product.

[0006] In summary, the above-mentioned synthesis path based on ion exchange reaction has the following problems: 1. Due to the harsh conditions such as high temperature, high pressure or high-energy ball milling of the existing method, and the desolvation treatment temperature usually needs to be higher than 200℃, therefore, there are generally problems of high energy consumption and high cost; 2. Due to the reaction system usually involving flammable, explosive or toxic reagents, and under high-energy ball milling conditions, the operation safety risk is high, and the reaction period is too long, which is not suitable for large-scale industrial production; 3. The product prepared has more impurities and higher thermodynamic stability, so the product hydrogen release temperature is high, which needs high temperature of 260-580℃ to release hydrogen.

[0007] Therefore, it is of great significance to develop a new method for preparing magnesium borohydride under mild conditions and suitable for large-scale production. SUMMARY

[0008] The present application aims to provide a method for preparing magnesium borohydride by solution method to overcome the defects of high energy consumption, high preparation cost and high product hydrogen release temperature in the prior art.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a method for preparing magnesium borohydride by solution method, comprising the following steps:

[0010] Step one, prepare MgCl2 / tetrahydrofuran solution and NaBH4 / isopropylamine solution respectively, the preparation of MgCl2 / tetrahydrofuran solution is to add MgCl2 into tetrahydrofuran in an inert atmosphere glove box, and stir until completely dissolved at constant temperature; the preparation of NaBH4 / isopropylamine solution is to add NaBH4 into isopropylamine in an inert atmosphere glove box, and stir until completely dissolved;

[0011] Step two, mix the above two solutions in the glove box, stir and react to obtain a mixed solution;

[0012] Step three, centrifuge the mixed solution for several times, collect the supernatant; combine the supernatant and extract to obtain a clear filtrate;

[0013] Step four, in the glove box, perform vacuum desolvation treatment on the filtrate under temperature control conditions to precipitate solid magnesium borohydride product.

[0014] Further, in the above-mentioned step one: the amount of MgCl2 is 0.557g, and the amount of tetrahydrofuran is 100mL; the amount of NaBH4 is 0.55g, and the amount of isopropylamine is 100mL.

[0015] Further, in the preparation of MgCl2 / tetrahydrofuran solution, stir at 500rpm for 1h at 25-35℃; stir NaBH4 / isopropylamine solution at 500rpm for 1h.

[0016] Further, the reaction condition in step two is stirring at 500 rpm for 12 h.

[0017] Further, the centrifugal treatment in step three is carried out at a speed of 9000 rpm for 10 min, repeated for 3 times, and the suction filtration is carried out using a 0.22 μm microporous filter membrane.

[0018] Further, the desolvation treatment in step four is carried out at a temperature of 30 ℃, a vacuum pump air suction rate of 2 L / s, and a treatment time of 3 h.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] 1. The prior art uses MgCl2 and NaBH4 as raw materials to carry out ion exchange through high-energy ball milling, because the reaction conditions of the two are harsh. The present application finds a good solvent for MgCl2 and NaBH4, and the solvent can also separate Mg(BH4)2 and NaCl. Therefore, the present application proposes a solution method using MgCl2 and NaBH4 as raw materials, which can be carried out under mild stirring conditions at room temperature. The process flow is simple, the raw material cost is low, the reaction is completed in one step, and the operation is safe and low-risk.

[0021] 2. The present application discards the harsh conditions such as high temperature, high pressure or high-energy ball milling required by the prior art, significantly reduces the energy consumption of the production process, and reduces the preparation cost. At the same time, the reaction period is short, the desolvation temperature is reduced, and it is particularly suitable for large-scale industrial production.

[0022] 3. The magnesium borohydride product prepared by the method of the present application has a low initial hydrogen release temperature of only 115.8 ℃, and excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 XRD pattern of the magnesium borohydride material prepared in Example 1;

[0024] Figure 2 XRD pattern of the magnesium borohydride material prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0025] Figure 3 SEM pattern of the magnesium borohydride material prepared in Example 1;

[0026] Figure 4 FTIR pattern of the magnesium borohydride material prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0027] Figure 5 TPD curve of the magnesium borohydride material prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0028] Figure 6MS chart of the magnesium borohydride material prepared for Example 1. DETAILED DESCRIPTION

[0029] In order to illustrate the objects, technical solutions and advantages of the present application more clearly, the present application will be further described in detail below with reference to examples.

[0030] Example 1, a method for preparing magnesium borohydride by a solution method, comprising the following steps:

[0031] Step 1, preparation of raw material solution:

[0032] Preparation of MgCl2 / tetrahydrofuran solution: in an inert atmosphere glove box, 0.557 g of anhydrous MgCl2 was added to 100 mL of tetrahydrofuran solution, and stirred at 30°C and 500 rpm for 1 h until completely dissolved, to obtain MgCl2 / tetrahydrofuran solution;

[0033] Preparation of NaBH4 / isopropylamine solution: 0.55 g of NaBH4 was added to 100 mL of isopropylamine solution, and stirred at room temperature for 1 h until completely dissolved, to obtain NaBH4 / isopropylamine solution.

[0034] Step 2, mixing reaction: in the glove box, the MgCl2 / tetrahydrofuran solution obtained in step 1 was mixed with the NaBH4 / isopropylamine solution, a magnetic stirrer was put in, and stirred at a speed of 500 rpm for 12 h to obtain a mixed solution.

[0035] Step 3, separation and purification: the mixed reaction solution obtained in step 2 was centrifuged at a speed of 9000 rpm for 10 min, and the supernatant was collected; the above centrifugation operation was repeated twice, for a total of 3 times; all the supernatants were combined, and microfiltration was performed using a microporous filter membrane with a pore size of 0.22 μm, to obtain a clear and transparent filtrate.

[0036] Step 4, solvent removal and product collection: in the glove box, the filtrate obtained in step 3 was placed at 30°C, and vacuum desolvation treatment was performed using a vacuum pump with a pumping rate of 2 L / s for 3 h, until the solid product was completely precipitated, to obtain white solid magnesium borohydride.

[0037] Comparative Example 1, which is different from Example 1 in that the amount of NaBH4 in step 1 is 0.5 g. The remaining steps and parameters are exactly the same as those of Example 1.

[0038] Comparative Example 2, which is different from Example 1 in that the amount of NaBH4 in step 1 is 0.6 g. The remaining steps and parameters are exactly the same as those of Example 1.

[0039] In order to prove the composition of the magnesium borohydride prepared by the method of the present application, XRD test was performed. The test results are shown in Table 1. Figure 1As shown, the prepared magnesium borohydride is consistent with the β-Mg(BH4)2standard card, indicating that the magnesium borohydride is successfully synthesized by the method.

[0040] Figure 2 The XRD of the magnesium borohydride prepared in Example 1, Comparative Example 1 and Comparative Example 2 is compared, and it can be seen from the figure that when the NaBH4charge in Comparative Example 1 is 0.5 g, the crystallinity of the magnesium borohydride is poor;

[0041] When the NaBH4charge in Comparative Example 2 is 0.6 g, there is unreacted NaBH4in the product;

[0042] When the NaBH4charge in Example 1 is 0.55 g, the magnesium borohydride has good crystallinity and no other impurities. See also Figure 3 , the SEM image of the magnesium borohydride prepared in Example 1 shows that the sample presents an irregular agglomerate structure, the surface is rough, and is densely covered with a large number of fine particles.

[0043] Figure 4 The FTIR of the magnesium borohydride prepared in Example 1, Comparative Example 1 and Comparative Example 2 is shown in the figure, and it can be seen that it contains B-H bond, indicating that the magnesium borohydride is successfully prepared.

[0044] Figure 5 The TPD of the magnesium borohydride prepared in Example 1, Comparative Example 1 and Comparative Example 2 is shown in the figure, and it can be seen that hydrogen release can start at low temperature, at 500℃, the hydrogen release amount of Example 1 is about 4.6wt.%, the hydrogen release amount of Comparative Example 1 is about 3.5wt.%, and the hydrogen release amount of Comparative Example 2 is about 4.8wt.%.

[0045] Figure 6 The MS image of the magnesium borohydride prepared in Example 1 is shown in the figure, and it can be seen that Example 1 has four hydrogen release peaks, which are 115.8℃, 227.5℃, 356.0℃ and 385.0℃, respectively.

[0046] Although the present application has been described in detail with reference to the accompanying drawings and examples, it is not a limitation on the scope of protection of the present application, and those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A method for preparing magnesium borohydride using a solution method, characterized in that: Includes the following steps: Step 1: Prepare MgCl2 / tetrahydrofuran solution and NaBH4 / isopropylamine solution separately. The MgCl2 / tetrahydrofuran solution is prepared by adding MgCl2 to tetrahydrofuran in an inert atmosphere glove box and stirring at a constant temperature until completely dissolved. The NaBH4 / isopropylamine solution is prepared by adding NaBH4 to isopropylamine in an inert atmosphere glove box and stirring until completely dissolved. Step 2: Mix the two solutions in a glove box and stir to react, obtaining a mixed solution; Step 3: Centrifuge the mixture several times and collect the supernatant; combine the supernatants and filter to obtain a clear filtrate; Step 4: In a glove box, the filtrate is subjected to vacuum desolventizing treatment under temperature control to precipitate solid magnesium borohydride product.

2. The method for preparing magnesium borohydride by solution method according to claim 1, characterized in that: In step one: the amount of MgCl2 used is 0.557g, the amount of tetrahydrofuran is 100mL; the amount of NaBH4 used is 0.55g, and the amount of isopropylamine is 100mL.

3. The method for preparing magnesium borohydride by solution method according to claim 2, characterized in that: In the preparation of the MgCl2 / tetrahydrofuran solution, the mixture was stirred at 500 rpm for 1 hour at 25-35℃; the NaBH4 / isopropylamine solution was stirred at 500 rpm for 1 hour.

4. The method for preparing magnesium borohydride by solution method according to claim 3, characterized in that: The reaction conditions in step two are: stirring at 500 rpm for 12 hours.

5. The method for preparing magnesium borohydride by solution method according to claim 4, characterized in that: In the centrifugation process of step three: the centrifugation speed is 9000 rpm, the centrifugation time is 10 min, and it is repeated 3 times; a 0.22 μm microporous filter membrane is used for vacuum filtration.

6. The method for preparing magnesium borohydride by solution method according to claim 5, characterized in that: The solvent removal conditions in step four are: temperature 30℃, vacuum pump pumping rate 2L / s, and treatment time 3h.

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