Production method for potassium borohydride

Abstract

The present invention provides a simple process for producing potassium borohydride. According to the present invention, a production method for potassium borohydride includes a reaction process for mixing solid starting materials that include an alkali metal compound, a fluoride, and at least one material selected from among aluminum and aluminum compounds and performing a heat treatment at a temperature above 560°C.

Description

Method for producing potassium borohydride

[0001] The present invention relates to a method for producing potassium borohydride.

[0002] Hydrogen fuel is gaining attention as an alternative energy source to fossil fuels, and potassium borohydride (PBH) is a promising hydrogen carrier for hydrogen storage, transportation, and generation. To popularize potassium borohydride as a hydrogen carrier in society, it is necessary to establish an optimal manufacturing method that takes into account mass production technology.

[0003] As a conventional method for producing potassium borohydride, for example, Patent Document 1 discloses a method for separating a powder of tetrahydroborate from a mixed powder containing a powder of tetrahydroborate obtained by a mechanochemical method and a powder of a metal oxide.

[0004] Furthermore, Patent Document 2 discloses a method for producing potassium borohydride by the steps of adding potassium metaborate to an excess of methanol and heating to reflux to obtain a solution containing potassium tetramethoxyborohydride, further distilling the solution to remove excess methanol and water to obtain a potassium tetramethoxyborohydride solid, and adding potassium tetramethoxyborohydride to a sodium hydride / white oil dispersion and stirring and heating.

[0005] Japanese Patent Publication No. 2022-164237 Chinese Patent Application Publication No. 110862070

[0006] The method of Patent Document 1 requires a step of dispersing a mixed powder containing a tetrahydroborate powder obtained by a mechanochemical method and a metal oxide powder in a non-polar liquid, which increases the number of manufacturing steps.

[0007] In the method of Patent Document 2, it is necessary to prepare a solution and a solid containing potassium tetramethoxyborate in advance, which makes the production process complicated.

[0008] An object of the present invention is to provide a method for producing potassium borohydride comprising simple steps.

[0009] The method for producing potassium borohydride according to the first aspect is characterized by comprising a reaction step of mixing solid raw materials containing an alkali metal compound, a fluoride, and at least one material selected from an aluminum compound and aluminum, and then performing a heat treatment at a temperature higher than 560°C.

[0010] In the first aspect, the method for producing potassium borohydride may further include, prior to the reaction step, a pretreatment step of mixing at least one material selected from the aluminum compound and aluminum with the fluoride.

[0011] In the first aspect, the pretreatment step may be carried out at a temperature of 100°C or higher and 330°C or lower.

[0012] In the first aspect, the reaction step may be carried out in a hydrogen atmosphere.

[0013] In a first embodiment, the alkali metal compound is potassium aluminum dioxide (KAiO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２ O) may be at least one selected from the group consisting of:

[0014] In the first aspect, the potassium borates are potassium metaborate (KBO). ２ ), potassium tetraborate (K ２ B ４ O ７ ) and potassium diborate (K ４ B ２ O ５ ) may be at least one selected from the above.

[0015] In the first aspect, the fluoride is sodium fluoride (NaF), sodium hexafluoroaluminate (Na ３ AlF ６ ), potassium hexafluoroaluminate (K ３ AlF ６ ), potassium fluoride (KF), potassium aluminum fluoride (KAIF ４ ), aluminum fluoride (AlF３ ) and lithium fluoride (LiF).

[0016] In a first embodiment, the aluminum compound is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO ２ ), alumina (Al ２ O ３ ) and aluminum fluoride.

[0017] In the first aspect, a molar ratio of aluminum contained in the solid raw material to boron contained in the solid raw material may be 4 / 3 or more.

[0018] In a first aspect, the solid raw material may further contain at least one of an alkali metal oxide and an alkaline earth metal oxide, and a molar ratio of the total of the alkali metal and alkaline earth metal contained in the solid raw material to the boron contained in the solid raw material may be 1.0 or more and 1.3 or less.

[0019] According to the first aspect, potassium borohydride can be produced through a simple process.

[0020] FIG. 1 shows a backscattered electron (BSE) image and element mapping image of a reaction product obtained by a scanning electron microscope (SEM) according to an example. FIG. 2A shows a backscattered electron image of region AR1 in FIG. 1 obtained by an energy dispersive X-ray spectrometer (EDS). FIG. 2B shows an EDS profile at position 001 shown in FIG. 2A. FIG. 2C shows an EDS profile at position 002 shown in FIG. 2A. FIG. 2D shows an EDS profile at position 003 shown in FIG. 2A. FIG. 2E shows an EDS profile at position 004 shown in FIG. 2A. FIG. 2F shows an EDS profile at position 005 shown in FIG. 2A. FIG. 3 shows a backscattered electron image and element mapping image of region AR1 in FIG. 1 obtained by EDS. FIG. 4 shows a backscattered electron image and element mapping image of region AR2 in FIG. 1 obtained by EDS. FIG. 5 is a process diagram showing a first manufacturing method of potassium borohydride. FIG. 6 is a process diagram showing a second manufacturing method of potassium borohydride. FIG. 7 is a process diagram showing a third manufacturing method of potassium borohydride. FIG. 8 is a process diagram showing a fourth manufacturing method of potassium borohydride. FIG. 9 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth manufacturing methods. FIG. 10 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. FIG. 11 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. FIG. 12 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. FIG. 13A is a front photograph of the appearance of a stirrer equipped with a plate-shaped (blade) stirrer using the sealed container shown in FIG. 10. FIG. 13B is a side photograph of the appearance of a stirrer equipped with a plate-shaped (blade) stirrer using the sealed container shown in FIG. 10. Fig. 14A is a photograph of a plate-shaped (blade) stirring bar taken out of the reaction product after stirring for a predetermined time using the sealed container shown in Fig. 10. Fig. 14B is a photograph of the reaction product taken out of the container after stirring for a predetermined time using the sealed container shown in Fig. 10.Fig. 15A is a photograph of the sealed vessel shown in Fig. 12 before the horizontal wide paddle (WP) stirrer is rotated to produce potassium borohydride. Fig. 15B is a photograph of the sealed vessel shown in Fig. 12 after the horizontal wide paddle (WP) stirrer is rotated to produce potassium borohydride. Fig. 16 is a reaction schematic diagram showing the potassium borohydride production reaction. Fig. 17 is a reaction schematic diagram showing the potassium borohydride production reaction. Fig. 18 is a reaction schematic diagram showing the potassium borohydride production reaction. Fig. 19 is a reaction schematic diagram showing the potassium borohydride production reaction. Fig. 20 is a reaction schematic diagram showing the potassium borohydride production reaction. Fig. 21 is a reaction schematic diagram showing the potassium borohydride production reaction.

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited thereto. The components of the embodiments described below can be combined as appropriate. In addition, some components may not be used. Furthermore, the components in the embodiments described below include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range.

[0022] The method for producing potassium borohydride according to this embodiment includes a reaction step and an extraction step. ４ It refers to a compound represented by the formula:

[0023] The reaction step is a step in which solid raw materials are mixed and heated.

[0024] The solid raw material contains at least one material selected from an alkali metal compound, a fluoride, an aluminum compound, and aluminum.

[0025] The alkali metal compounds contained in the solid raw materials include potassium aluminum dioxide (KAIO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２ At least one selected from the group consisting of hydroxybenzoates, ...

[0026] The potassium borates contained in the solid raw materials include potassium metaborate (KBO ２ ), potassium tetraborate (K ２ B ４ O ７ ) and potassium diborate (K ４ B ２ O ５ ) can be used, but is not limited to these.

[0027] When potassium metaborate is used as the potassium borate, powdered potassium metaborate powder (potassium metaborate powder) is used. The maximum particle size of the potassium metaborate powder is preferably 100 μm or less. The potassium metaborate powder is obtained by grinding the powder to a certain degree and then passing it through a sieve with a mesh size of 100 μm. If the maximum particle size of the potassium metaborate powder exceeds 100 μm, the production efficiency of potassium borohydride may decrease. The maximum particle size of the potassium metaborate powder is more preferably less than 100 μm. That is, the potassium metaborate powder is preferably obtained by passing it through a sieve with a mesh size of less than 100 μm (for example, a sieve with a mesh size of 50 μm or less). In this case, the production efficiency of potassium borohydride can be further improved.

[0028] Since potassium metaborate powder contains moisture, the amount of potassium metaborate powder is preferably increased by the mass of moisture relative to the amount required for synthesizing potassium borohydride.

[0029] The aluminum contained in the solid raw material can be fragments such as powder material or scrap material. The aluminum fragments can be, for example, scrap material such as cutting chips or waste material. It is preferable that the aluminum fragments have as little content as possible of metals nobler than aluminum, which are impurities.

[0030] The amount of aluminum contained in the solid raw material is preferably 110% or more in molar ratio relative to the amount required for the synthesis of potassium borohydride. Although a portion of the excess aluminum is consumed by reaction with water, this also contributes to increasing the opportunity for contact with sodium metaborate when the amount of aluminum as raw material decreases as the reaction progresses, thereby improving the yield. The excess aluminum can be recovered and reused as metallic aluminum in the extraction step described below.

[0031] The average particle size of the aluminum powder contained in the solid raw material is preferably 1 μm or more, and the maximum particle size is preferably 10 mm or less. If the average particle size of the aluminum powder is less than 1 μm, it is prone to dust explosions and becomes difficult to handle, and the particles may easily adhere to each other and clump together. If the average particle size is greater than 10 mm, the specific surface area per mass becomes small, the reaction area decreases, and the initial reaction rate may be significantly reduced. The average particle size of the aluminum powder is more preferably 5 μm or more and 5 mm or less. In the present disclosure, the average particle size of the powder is the average particle size obtained as the particle size of the spherical equivalent diameter using a laser diffraction particle size distribution analyzer.

[0032] The aluminum compound contained in the solid raw material is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO ２ ), alumina (Al ２ O ３ ) and aluminum fluoride (AlF ３ At least one selected from the following can be used.

[0033] The fluorides contained in the solid raw materials include sodium fluoride (NaF), sodium hexafluoroaluminate (Na ３ AlF ６ ), potassium hexafluoroaluminate (K ３ AlF ６ ), potassium fluoride (KF), potassium aluminum fluoride (KAIF ４ ), aluminum fluoride (AlF ３At least one selected from the group consisting of sodium fluoride (NaF), sodium hexafluoroaluminate (Na ), and lithium fluoride (LiF) can be used. ３ AlF ６ ), potassium fluoride (KF), potassium aluminum fluoride (KAIF ４ ), potassium hexafluoroaluminate (K ３ AlF ６ ) and lithium fluoride (LiF) are preferred, and potassium fluoride (KF) and potassium aluminum fluoride (KAIF) are also preferred. ４ ) and potassium hexafluoroaluminate (K ３ AlF ６ ) is particularly preferred, and potassium fluoride (KF) is most preferred. Potassium fluoride generates potassium fluoride (KF) in the reaction system and can react with the oxide film of the aluminum particles. Therefore, by using potassium fluoride as the fluoride contained in the solid raw material, potassium borohydride (KBH ４ In addition, since potassium fluoride (KF) does not contain aluminum, the yield of aluminum fluoride (AlF ３ ) can be suppressed, so by using potassium fluoride (KF) as the fluoride contained in the solid raw material, it is possible to suppress the acidification of the reaction system caused by potassium borohydride (KBH ４ The yield of the compound (II) can be further improved.

[0034] The addition of fluoride promotes the production of potassium borohydride. Specifically, the fluoride reacts with the oxide film on the surface of the aluminum particles, improving the yield of the reaction product, potassium borohydride.

[0035] In the following description, the molar ratio of the total of the alkali metals and alkaline earth metals contained in the solid raw material to the boron (B) of the sodium borates contained in the solid raw material may be referred to as A / B (molar ratio). In this embodiment, the A / B (molar ratio) of the raw materials is preferably 1.0 or more and 1.3 or less. When A / B exceeds 1.3, the amount of alkali metal ions in the reaction system becomes excessive, resulting in a reduced yield. When A / B is less than 1.0, the amount of boron in the reaction system becomes excessive, resulting in a reduced yield.

[0036] In the reaction step, a product containing potassium borohydride is obtained by heat-treating the solid raw materials. In this disclosure, heat treatment refers to a process of heating. In the following description, heating temperature refers to the temperature during the heat treatment. The heating temperature can be the temperature measured by contacting a thermocouple with the outside of a sealed container into which the raw materials are placed.

[0037] The heating temperature in the reaction step is 560° C. or higher. If the heating temperature is lower than 560° C., the intermediate product potassium aluminum fluoride (KAIF ４ ) does not melt, and therefore potassium borohydride is not sufficiently produced. The heating temperature in the reaction step is preferably higher than 560°C, and more preferably 580°C or higher. This can improve the reaction rate and the production efficiency of potassium borohydride. The heating temperature in the reaction step is further preferably 620°C or higher. This can further improve the reaction rate without stirring in the reaction step and further improve the production efficiency of potassium borohydride.

[0038] The heating temperature in the reaction step is preferably less than 710°C. If the heating temperature is 710°C or higher, the produced potassium borohydride will thermally decompose, resulting in a reduced yield. The heating temperature in the reaction step is more preferably 660°C or lower. By setting the heating temperature to 660°C or lower, aluminum can exist in a solid state, so that the aluminum is maintained in a powder state rather than becoming droplets, increasing the specific surface area of ​​the aluminum and accelerating the reaction. This ensures a sufficient reaction rate and excellent production efficiency of potassium borohydride.

[0039] The reaction step is carried out in a hydrogen-containing gas atmosphere. When a hydrogen atmosphere is used, the maximum value of the hydrogen gas pressure (maximum hydrogen pressure) in the reaction step is preferably in the range of 0.5 MPa to 10 MPa, more preferably in the range of 0.5 MPa to 1 MPa. By setting the maximum hydrogen pressure in this range, the production efficiency of potassium borohydride is excellent, and an increase in equipment costs can be suppressed because a reaction vessel or equipment with excellent pressure resistance is not required.

[0040] The extraction step involves adding a mixture of solid raw materials to a polar solvent. This step allows potassium borohydride to be extracted from the reaction product. This results in potassium borohydride with fewer impurities.

[0041] In the extraction process, the mixture of solid raw materials is stirred with a polar solvent, which can improve the dissolution rate of potassium borohydride.

[0042] The polar solvent is, for example, water, and preferably pure water such as ion-exchanged water. This allows potassium borohydride (KBH ４ ) can be extracted from the reaction product.

[0043] The water used as the polar solvent is not limited to pure water, but may be a weakly acidic or alkaline aqueous solution. The pH of the water used as the polar solvent is preferably 5 or more and 11 or less.

[0044] When the polar solvent is water, the extraction step is preferably carried out at room temperature. ４ In the following description of the extraction step, unless otherwise specified, high temperature refers to a temperature of 80°C or higher and 100°C or lower, and room temperature refers to a temperature of 5°C or higher and 35°C or lower.

[0045] The polar solvent may be, for example, dimethyl sulfoxide. In this case, potassium borohydride (KBH ４When the polar solvent is dimethyl sulfoxide, the extraction step is preferably carried out at a temperature of 30°C or higher and 40°C or lower.

[0046] FIG. 1 shows a backscattered electron (BSE) image and element mapping image of a reaction product of an example obtained by a scanning electron microscope (SEM: Energy Scanning Electron Microscope). The reaction product of FIG. 1 is the product of Test Example 5, which will be described later. The measurement sample of FIG. 1 was prepared by mixing and compacting the product of Test Example 5 with a dispersant (graphite powder), and then cutting it using a cross-section polisher (CP) process (ion milling). As a result, a cross section of the product appears on the surface of the measurement sample of FIG. 1. The image in the upper left of FIG. 1 (BSE image) is a backscattered electron image of the reaction product of the example. The other images in FIG. 1 (EDS (energy diversive X-ray spectrometer) images) are element mapping images obtained by EDS for potassium (K), oxygen (O), boron (B), fluorine (F), and aluminum (Al), respectively. The correspondence between the images and the elements is shown in the upper right corner of each image in FIG. 1. The distribution of each element shown in the EDS mapping image reveals the distribution of the composition. For example, the area where K and B are detected is considered to be the distribution of potassium borohydride (PBH), and the area where K, O, and Al are detected is considered to be the distribution of potassium iota alumina (K ０．６７ Al ６ O ９．３３ In the measurement range shown in Figure 1, the raw material potassium metaborate (KBO ２ On the other hand, within the measurement range shown in Figure 1, the presence of potassium borohydride (PBH) as the product, aluminum (Al) particles as the raw material, and potassium iota alumina (K) as the by-product were observed. ０．６７ Al ６ O ９．３３ ) are thought to account for the majority of the products shown in FIG.

[0047] FIG. 2A is a backscattered electron image of region AR1 in FIG. 1 obtained by EDS. FIG. 2B is a diagram showing an EDS profile at position 001 shown in FIG. 2A. FIG. 2C is a diagram showing an EDS profile at position 002 shown in FIG. 2A. FIG. 2D is a diagram showing an EDS profile at position 003 shown in FIG. 2A. FIG. 2E is a diagram showing an EDS profile at position 004 shown in FIG. 2A. FIG. 2F is a diagram showing an EDS profile at position 005 shown in FIG. 2A. FIG. 3 is a diagram showing a backscattered electron image and element mapping image of region AR1 in FIG. 1 obtained by EDS. The image in the upper left of FIG. 3 (BSE image) is a backscattered electron image of the reaction product according to the example. The other images (EDS images) in FIG. 3 are element mapping images obtained by EDS for potassium (K), oxygen (O), boron (B), fluorine (F), and aluminum (Al), respectively. The correspondence between the images and the elements is shown in the upper right corner of each image in FIG. 3.

[0048] As shown in FIG. 2B and FIG. 3, potassium metaborate (KBO) is present in the center of the particle on the left side of the region AR1 (the portion including the position 001). ２ ), the particles on the left side of the region AR1 are considered to be potassium metaborate (KBO) before the reaction. ２ ) particles and are presumed to be particles that have not been completely reacted. As shown in Figures 2C and 3, in the middle part of the particle on the left side of region AR1 (the part including position 002), potassium metaborate (KBO ２ ) is thought to be present. Also, as shown in Figure 3, ball-shaped ejecta occurred after the point analysis at position 002. This is thought to be because the impact of the beam irradiated during point analysis caused potassium hydride (KH) to gasify and eject, resulting in the formation of ball-shaped ejecta in the product. Therefore, in the middle part of the particle on the left side of area AR1, potassium metaborate (KBO ２ ) is presumed to be present in the region AR1. In addition, from the EDS profile in FIG. 2C and the mapping analysis results in FIG. 3, potassium oxide (KH) is present in the middle part (near position 002) of the particle on the left side of the region AR1. ２ O) and boron oxide (B ２ O ３) is thought to be present, but potassium oxide (K ２ As shown in Fig. 2D and Fig. 3, the outermost part of the particle on the left side of the region AR1 (the part including the position 003) is composed of potassium iota alumina (K ０．６７ Al ６ O ９．３３ ) are scattered throughout.

[0049] As shown in Figures 2E, 2F, and 3, the particles on the right side of region AR1 contain potassium metaborate (KBO). ２ ) and elemental aluminum (Al) are not present, so the particles on the right side of the region AR1 are considered to be potassium metaborate (KBO) ２ ) particles, and are presumed to be particles in which the reaction has been completed. As shown in Figures 2E and 3, potassium borohydride (PBH) is believed to be present in the outer part of the particle on the right side of region AR1 (the part including position 004). As shown in Figures 2F and 3, potassium iota alumina (K iota alumina) is believed to be present in the inner part of the particle on the right side of region AR1 (the part including position 005). ０．６７ Al ６ O ９．３３ ) is thought to be present. Here, a small amount of fluorine was detected inside the particle on the right side of the region AR1 (near the position 005). From this, it is believed that potassium iota alumina (K ０．６７ Al ６ O ９．３３ ) is thought to coexist with small amounts of fluoride.

[0050] Figure 4 shows backscattered electron images and elemental mapping images of region AR2 in Figure 1 obtained by EDS. The image in the upper left of Figure 4 (BSE image) is a backscattered electron image of the reaction product of the example. The other images (EDS images) in Figure 4 are elemental mapping images obtained by EDS for potassium (K), oxygen (O), boron (B), fluorine (F), and aluminum (Al), respectively. The correspondence between the images and the elements is shown in the upper right corner of each image in Figure 4. As shown in Figure 4, only aluminum (Al) is present in the center of the particles in region AR2, suggesting that the particles in region AR2 were aluminum particles before the reaction. The EDS mapping of oxygen (O) in Figure 4 reveals a ring-shaped area with a high oxygen concentration. This area is thought to correspond to the oxide film on the aluminum particle. Therefore, the surface of the aluminum particle before the reaction (original Al surface) is thought to have been the inner contour of the area with a high oxygen concentration. Since the particles in region AR2 are larger than the aluminum particles before the reaction, it is thought that the reaction has caused the product to grow outside the surface of the aluminum particles. From FIG. 4, it can be seen that the outside of the surface of the aluminum particles before the reaction is composed of potassium iota alumina (K ０．６７ Al ６ O ９．３３) is thought to be present. Therefore, it is thought that aluminum ions reacted with oxygen ions on the outside of the aluminum particles. From Figure 4, it is thought that potassium borohydride (PBH) was present in large amounts inside the surface of the aluminum particles before the reaction. Therefore, it is thought that potassium ions and boron ions migrated from the outside to the inside of the aluminum particles. As shown in Figure 4, ball-shaped ejecta were generated after point analysis of the area occupied by potassium borohydride (PBH). This is thought to be because potassium hydride (KH) was gasified by the influence of the beam irradiated during point analysis, resulting in the generation of ball-shaped ejecta. Therefore, it is presumed that potassium hydride (KH) is present in the area occupied by potassium borohydride (PBH). As shown in Figure 4, a ring-shaped area with a high fluorine concentration exists near the surface of the aluminum particles before the reaction, and it is thought that fluoride is present. Here, aluminum was also detected in part of the area where fluoride was present. Therefore, it is thought that potassium aluminum fluoride (KAIF) was present in part of the area near the surface of the aluminum particles. ４ ) crystals, etc. are thought to have been produced.

[0051] Hereinafter, first to fourth production methods, which are specific examples of the method for producing potassium borohydride according to the present embodiment, will be described in detail. In the following steps, unless otherwise specified, potassium fluoride is used as the fluoride, and potassium metaborate (KBO) separated as crystals is used as the potassium borates. ２ ) will be described. The first to fourth production methods described below are merely examples, and the present invention is not limited to these. For example, the method for producing potassium borohydride according to this embodiment may include only the third step (reaction step).

[0052] [First Manufacturing Method] FIG. 5 is a process diagram showing the first manufacturing method of potassium borohydride. As shown in FIG. 5, the first manufacturing method of potassium borohydride includes steps from step 1 (S-11) to step 4 (S-14). Step 1 (S-11) is a step of mixing aluminum powder, fluoride powder, and potassium borate and charging the mixture into a sealed container. Step 2 (S-12) is a step of heating the mixture to 400°C or higher and 610°C or lower after step 1 (S-11) and removing moisture with a vacuum pump. Here, the potassium borates and aluminum powder react while remaining in their solid phases. Step 3 (S-13) is a step of reacting the mixture at 560°C or higher and 660°C or lower in a sealed container filled with hydrogen gas after step 3 (S-13). The potassium borates and aluminum powder react while remaining in their solid phases. The fourth step (S-14) is a step of extracting potassium borohydride from the reaction product obtained in the third step (S-13). Here, the first step (S-11) is an example of a "pretreatment step", the third step (S-13) is an example of a "reaction step", and the fourth step (S-14) is an example of an "extraction step".

[0053] (a) First Step As a pretreatment step, after or before aluminum powder, potassium fluoride, and potassium borate powder are charged into a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the interior with a non-oxidizing gas atmosphere. These steps constitute the first step (S-11). That is, in the first step, all raw materials are mixed and charged into the sealed container. After the treated powder and potassium borate powder are mixed and charged into the sealed container, the timing for filling the sealed container with a non-oxidizing gas atmosphere may be either after or before the raw materials are charged into the sealed container.

[0054] In the first step, the temperature inside the sealed container when the raw materials are charged is not particularly limited, but is preferably less than 100°C from the viewpoint of workability.

[0055] The sealed container used in the first step is a container that has heat resistance and pressure resistance that can withstand high temperatures (e.g., 630°C) and high pressures (e.g., 10 MPa) and can ensure a sealed space for filling with gas. The sealed container is equipped with a stirring means. Details of the sealed container will be described later.

[0056] (b) Second Step The second step (S-12) shown in FIG. 5 is a step in which all raw materials are mixed and charged into a sealed container, and the inside of the sealed container is heated to 400°C or higher and 610°C or lower. The second step is a step in which residual moisture contained in the raw materials is degassed, and moisture that could not be degassed is reacted with aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. The second step is a step in which vaporized moisture (i.e., residual moisture contained in the raw materials in the sealed container) is reacted with aluminum, or a step in which moisture is removed from the reaction system by degassing using a vacuum pump.

[0057] (c) Third Step The third step (S-13) shown in FIG. 5 is a step of heating the inside of the sealed container to 560°C or higher and 660°C or lower, and introducing hydrogen gas. By achieving this temperature, the cyclical reaction described above can occur. In the third step, the stirring means in the sealed container was rotated to stir. In this way, a reaction product was obtained. Note that when the inside of the sealed container is heated to 620°C or higher in the third step, stirring is not required because the reaction proceeds without stirring.

[0058] In the third step, the sealed container used in the first and second steps may be used as is, or a different sealed container may be used. That is, the first to third steps may be carried out as steps in a single sealed container, or may be steps in different sealed containers.

[0059] (d) Fourth Step The fourth step (S-14) shown in FIG. 5 is a step of extracting potassium borohydride from the reaction product with a polar solvent. Here, the polar solvent is dimethyl sulfoxide. In the fourth step, the reaction product is stirred with dimethyl sulfoxide at 30°C or higher and 40°C or lower for 30 minutes or longer. This allows potassium borohydride (KBH ) to be extracted from the reaction product into the polar solvent. ４ ) is eluted. Then, potassium borohydride (KBH４ The extract containing the hydroxybenzoates is dried under reduced pressure.

[0060] By the above-mentioned first to fourth steps, potassium borohydride (KBH ４ ) can be generated.

[0061] Another manufacturing method will be described below, and a description of the same points as in the first manufacturing method will be omitted.

[0062] [Second Manufacturing Method] Figure 6 is a process diagram showing a second manufacturing method of potassium borohydride. As shown in Figure 6, the second manufacturing method of potassium borohydride includes steps from step 1 (S-21) to step 4 (S-24). Step 1 (S-21) is a step of mixing aluminum powder 52, potassium hydroxide powder 55, and fluoride powder 54, preheating the mixture at a temperature of 100°C to 330°C, and then mixing the mixture with potassium borate powder 51 and charging the mixture into a sealed container. Step 2 (S-22) is a step of heating the mixture to a temperature of 400°C to 610°C after step 1 (S-21) and removing moisture with a vacuum pump. Step 3 (S-23) is a step of introducing hydrogen gas after step 2 (S-22) and reacting the mixture at a temperature of 560°C to 660°C in a sealed container filled with hydrogen gas. The potassium borate powder 51 and the aluminum powder 52 react while remaining in a solid phase. The fourth step (S-24) is a step of extracting potassium borohydride from the reaction product obtained in the third step (S-23). ​​Here, the first step (S-21) is an example of a "pretreatment step," the third step (S-23) is an example of a "reaction step," and the fourth step (S-24) is an example of an "extraction step."

[0063] (a) First Step: In a pretreatment step, aluminum powder 52, fluoride powder 54, and potassium hydroxide powder 55 are mixed and rubbed together. After the treatment, the mixture is placed in a container, the lid is closed, and the atmosphere is kept at a humidity of 10% or less. The mixture is then placed in a furnace and heated in an atmosphere of 100°C to 330°C for 30 minutes or more. This causes some of the moisture contained in the raw materials to be released, and an aluminum oxide film is formed on the particle surfaces of the aluminum (Al) powder 52. These steps constitute the first step (S-21). That is, in the first step, aluminum and potassium hydroxide are premixed and heat-treated, and then all the raw materials are mixed and placed in a sealed container. In this first step, treatment in an atmosphere of 10% or less humidity prevents moisture from adhering to the aluminum, potassium hydroxide, and fluoride in the air, and also prevents oxidation of the aluminum.

[0064] (b) Second Step In the second step (S-22) shown in FIG. 6 , all of the mixed raw materials are loaded into a sealed container and the inside of the sealed container is heated to 400°C or higher and 610°C or lower. In the second step (S-22), the powder heat-treated in the first step (S-21) is cooled and then mixed with potassium borate powder. After or before the mixed powder is loaded into the sealed container, a non-oxidizing gas is introduced into the sealed container to fill the inside with a non-oxidizing gas atmosphere. Note that the timing for filling the sealed container with a non-oxidizing gas atmosphere after mixing the treated powder and potassium borate powder may be either after or before the raw materials are loaded into the sealed container. Thereafter, the inside of the sealed container is heated to 400°C or higher and 610°C or lower to degas the remaining moisture contained in the raw materials and react the moisture that could not be degassed with aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. That is, the second step (S-22) is a step of reacting aluminum with residual moisture contained in the raw materials in the sealed container, or a step of removing moisture from the reaction system by degassing using a vacuum pump.

[0065] (c) Third Step The third step (S-23) shown in FIG. 6 is a step of heating the inside of the sealed container to 560°C or higher and 660°C or lower, and introducing hydrogen gas. In the third step, the stirring means in the sealed container was rotated to stir. In this way, a reaction product was obtained. Note that when the inside of the sealed container is heated to 620°C or higher in the third step, stirring is not required because the reaction proceeds without stirring.

[0066] (d) Fourth Step The fourth step (S-24) shown in FIG. 6 is a step of extracting potassium borohydride from the reaction product with a polar solvent. Here, the polar solvent is dimethyl sulfoxide. In the fourth step, the reaction product is stirred with dimethyl sulfoxide at 30°C or higher and 40°C or lower for 30 minutes or longer. This allows potassium borohydride (KBH ) to be extracted from the reaction product into the polar solvent. ４ ) is eluted. Then, potassium borohydride (KBH ４ The extract containing the hydroxybenzoates is dried under reduced pressure.

[0067] [Third Manufacturing Method] Figure 7 is a process diagram showing a third manufacturing method of potassium borohydride. As shown in Figure 7, the third manufacturing method of potassium borohydride includes steps from a first step (S-31) to a fourth step (S-34). The first step (S-31) is a step of mixing aluminum powder 52 and potassium hydroxide powder 55 and preheating them at a temperature of 100°C to 330°C. The second step (S-32) is a step of mixing the mixture with fluoride powder 54 and potassium borate powder 51 after the first step (S-31) and charging the mixture into a sealed container. The third step (S-33) is a step of heating the mixture after the second step (S-32) at a temperature of 400°C to 610°C and removing moisture with a vacuum pump, and then introducing hydrogen gas and reacting it at a temperature of 560°C to 660°C in a sealed container filled with hydrogen gas. The potassium borate powder 51 and the aluminum powder 52 react while remaining in a solid phase. The fourth step (S-34) is a step of extracting potassium borohydride from the reaction product obtained in the third step (S-33). Here, the first step (S-31) is an example of a "pretreatment step," the third step (S-33) is an example of a "reaction step," and the fourth step (S-34) is an example of an "extraction step."

[0068] (a) First Step: In a pretreatment step, aluminum powder 52 and potassium hydroxide powder 55 are mixed and rubbed together. After the treatment, the mixture is placed in a container, the lid is closed, and the atmosphere is kept at a humidity of 10% or less. The mixture is then placed in a furnace and heated at a temperature of 100°C to 330°C for 30 minutes or more. This causes some of the moisture contained in the potassium hydroxide to be released into the aluminum (Al), forming an aluminum oxide coating on the particle surfaces of the aluminum (Al) powder 52. The heat-treated powder is then cooled and mixed with potassium borate powder and fluoride powder. After or before the mixed powder is charged into a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the interior with a non-oxidizing gas atmosphere. The above steps constitute the first step (S-31). That is, in the first step, aluminum and potassium hydroxide are premixed and heat-treated, and then all raw materials are mixed and charged into the sealed container. In this first step, by treating in an atmosphere with a humidity of 10% or less, it is possible to prevent moisture in the air from adhering to the aluminum, potassium hydroxide, and fluoride, and to prevent oxidation of the aluminum. After mixing the treated powder with potassium borate powder, the sealed container may be filled with a non-oxidizing gas atmosphere either before or after the raw materials are charged into the sealed container.

[0069] (b) Second Step The second step (S-32) shown in FIG. 7 is a step of charging all of the mixed raw materials into a sealed container and heating the inside of the sealed container to 400°C or higher and 610°C or lower. The second step is a step of degassing residual moisture contained in the raw materials. The second step is a step of reacting residual moisture contained in the raw materials in the sealed container with aluminum, or a step of degassing with a vacuum pump to remove moisture from the reaction system.

[0070] (c) Third Step In the third step (S-33) shown in FIG. 7, the inside of the sealed container was heated to 560°C or higher and 660°C or lower, and hydrogen gas was introduced. In the third step, the stirring means in the sealed container was rotated to stir. In this way, a reaction product was obtained. Note that when the inside of the sealed container is heated to 620°C or higher in the third step, stirring is not required because the reaction proceeds without stirring.

[0071] (d) Fourth Step The fourth step (S-34) shown in FIG. 7 is a step of extracting potassium borohydride from the reaction product with a polar solvent. Here, the polar solvent is dimethyl sulfoxide. In the fourth step, the reaction product is stirred with dimethyl sulfoxide at 30°C or higher and 40°C or lower for 30 minutes or longer. This allows potassium borohydride (KBH ) to be extracted from the reaction product into the polar solvent. ４ ) is eluted. Then, potassium borohydride (KBH ４ The extract containing the hydroxybenzoates is dried under reduced pressure.

[0072] [Fourth Manufacturing Method] Figure 8 is a process diagram showing the fourth manufacturing method of potassium borohydride. As shown in Figure 8, the fourth manufacturing method of potassium borohydride includes steps from step 1 (S-41) to step 4 (S-44). Step 1 (S-41) is a step of mixing aluminum powder 52, potassium hydroxide powder 55, fluoride powder 54, and potassium borate powder 51, placing the mixture in a sealed container, filling it with a non-oxidizing gas, and then sealing it. Step 2 (S-42) is a step of heating the sealed container after step 1 (S-41) to a temperature of 400°C to 610°C to react moisture generated from the raw materials with fluoride, generating gaseous hydrogen fluoride, which then reacts with aluminum to produce aluminum fluoride on the aluminum surface. Step 3 (S-43) is a step of carrying out a reaction at a temperature of 560°C to 660°C in a sealed container filled with hydrogen gas after step 2 (S-42). The potassium borates and aluminum powder react in a solid phase. The fourth step (S-44) is a step of extracting potassium borohydride from the reaction product obtained in the third step (S-43). Here, the first step (S-41) is an example of a "pretreatment step," the third step (S-43) is an example of a "reaction step," and the fourth step (S-44) is an example of an "extraction step."

[0073] (a) First Step As a pretreatment step, aluminum powder 52, potassium hydroxide powder 55, and fluoride powder 54 are mixed and rubbed together in an atmosphere with a humidity of 10% or less, and then potassium borate powder 51 is added. These are then charged into a sealed container. After or before charging, a non-oxidizing gas is introduced into the sealed container to fill the interior with a non-oxidizing gas atmosphere. This completes the first step (S-41). The timing for introducing the non-oxidizing gas may be after or before charging the raw materials into the sealed container. Note that the method for mixing the raw materials is not limited to this; all of the raw materials, i.e., aluminum powder 52, potassium hydroxide powder 55, fluoride powder 54, and potassium borate powder 51, may be mixed and rubbed together at the same time.

[0074] 8 is a step of heating the inside of the sealed container to 400° C. or more and 610° C. or less after sealing the sealed container. The second step is a step of removing residual moisture contained in the raw material by reacting it with aluminum (Al).

[0075] (c) Third Step The third step (S-43) shown in FIG. 8 is a step of heating the inside of the sealed container to 560°C or higher and 660°C or lower, and introducing hydrogen gas. In the third step, the stirring means in the sealed container was rotated to stir. In this way, a reaction product was obtained. Note that when the inside of the sealed container is heated to 620°C or higher in the third step, stirring is not required because the reaction proceeds without stirring.

[0076] (d) Fourth Step The fourth step (S-44) shown in FIG. 8 is a step of extracting potassium borohydride from the reaction product with a polar solvent. Here, the polar solvent is dimethyl sulfoxide. In the fourth step, the reaction product is stirred with dimethyl sulfoxide at 30°C or higher and 40°C or lower for 30 minutes or longer. This allows potassium borohydride (KBH ) to be extracted from the reaction product into the polar solvent. ４ ) is eluted. Then, potassium borohydride (KBH ４ The extract containing the hydroxybenzoates is dried under reduced pressure.

[0077] (Sealed Container) Here, an example of a sealed container that can be used in the first to fourth manufacturing methods will be described.

[0078] 9 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth manufacturing methods. As shown in FIG. 9, the sealed container 10A has a cylindrical container body 12 with a round bottom and a removable disk-shaped lid 14 that seals the container body 12. A temperature-controllable heater 16 is disposed on the outside of the lower part of the container body 12, and the contents of the container body 12 are heated by the heater 16. In addition, an O-ring 18 is disposed on the upper end surface of the container body 12, which is in close contact with the lid 14 to ensure airtightness of the interior. When the lid 14 is closed, the lid 14 is in close contact with the O-ring 18 against the container body 12.

[0079] The lid 14 has an opening in its center, a cylindrical portion erected near the opening, and a motor 20 disposed above the cylindrical portion. The motor 20 powers the stirring means of the sealed container 10A. The stirring means includes the motor 20, a stirring rod 22 connected to the rotation shaft of the motor 20, and a plurality of pin-shaped stirring bars 22A arranged in a direction perpendicular to the axis of the stirring rod 22. When the lid 14 is attached to the container body 12, the tip of the stirring rod 22 reaches a lower region inside the container body 12. In other words, when the motor 20 is driven, the pin-shaped stirring bars 22A rotate together with the stirring rod 22, stirring the contents of the container body 12.

[0080] The lid 14 is further provided with a first pipe 24 and a second pipe 30 that communicate with the inside of the container body 12. The first pipe 24 is connected to a hydrogen gas supply source (not shown) via a hydrogen gas supply valve 26 and to a vacuum pump (not shown) via an exhaust valve 28. That is, when the hydrogen gas supply valve 26 is opened, hydrogen gas is supplied into the container body 12, and when the exhaust valve 28 is opened, the inside of the container body 12 is degassed. The second pipe 30 is also connected to a pressure gauge 32, which allows the pressure inside the container body 12 to be measured.

[0081] Fig. 10 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The sealed container 10B of Fig. 10 differs from the sealed container 10A of Fig. 9 in the stirring means. In the sealed container 10B of Fig. 10, a stirring rod 22 that rotates inside the container body 12 is provided at the lower end with multiple plate-shaped scrapers 35, forming a multi-blade scraper (MB). That is, the stirring means of Fig. 10 includes the stirring rod 22 and multiple plate-shaped scrapers 35.

[0082] Figure 13A is a front view of a stirrer equipped with a plate-shaped (blade) stirrer when using the sealed container shown in Figure 10. Figure 13B is a side view of a stirrer equipped with a plate-shaped (blade) stirrer when using the sealed container shown in Figure 10. Figure 14A is a photograph of a plate-shaped (blade) stirrer removed from the sealed container shown in Figure 10 after stirring for a predetermined period of time. Figure 14B is a photograph of the reaction product removed from the sealed container shown in Figure 10 after stirring for a predetermined period of time. As shown in Figure 14A, the reaction product in the form of balls resting on the blade and an adhesion layer adhering to the container wall can be seen.

[0083] Fig. 11 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The sealed container 10C of Fig. 11 differs from the sealed container 10A of Fig. 9 in the stirring means. In the sealed container 10C of Fig. 11, a ribbon-shaped scraper 36 is provided at the lower end of the stirring rod 22 that rotates inside the container body 12. That is, the stirring means of Fig. 11 includes the stirring rod 22 and a plurality of plate-shaped scrapers 36.

[0084] FIG. 12 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The sealed container 10D of FIG. 12 differs from the sealed container 10A of FIG. 9 in that the container body 12 is horizontally placed and the stirring rod 22 rotating inside the container body 12b is provided with a wide paddle stirrer 37 via a support. That is, the stirring means of FIG. 12 includes the stirring rod 22 and the wide paddle stirrer 37. When the wide paddle stirrer 37 of the sealed container 10D of FIG. 12 is used for stirring, the raw material is scooped up by the paddle surface as the wide paddle stirrer 37 rotates. While the raw material is being scooped up by the paddle surface or while the scooped raw material falls, raw material particles collide with each other, resulting in a good reaction.

[0085] Fig. 15A is a photograph before potassium borohydride was produced by rotating the horizontal wide paddle (WP) stirrer of the sealed vessel shown in Fig. 12. Fig. 15B is a photograph after potassium borohydride was produced by rotating the horizontal wide paddle (WP) stirrer of the sealed vessel shown in Fig. 12.

[0086] Although an example of a sealed container that can be used in the first to fourth manufacturing methods has been described above, the sealed container that can be used in this embodiment is not limited to the sealed containers 10A to 10D described above. For example, a ball mill that can be heated and introduced with hydrogen gas may also be used as the sealed container. Furthermore, if stirring is not performed, the sealed container does not need to have a stirring means.

[0087] (Potassium borohydride production reaction) The potassium borohydride production reaction according to the present invention will be described in detail below.

[0088] In the reaction step, a production reaction occurs due to heat treatment of the solid raw material, and potassium borohydride is produced. Figures 16 to 21 are reaction schematic diagrams that illustrate the potassium borohydride production reaction. The potassium borohydride production process will be described in detail with reference to the reaction schematic diagrams (Figures 16 to 21). Note that the action described below is not limited to potassium fluoride. For example, potassium aluminum fluoride (KAIF ４Fluorides containing potassium, such as potassium fluoride (KF), are double salts containing potassium fluoride (KF), and therefore can supply potassium fluoride to the reaction system. Therefore, fluorides other than potassium fluoride can also have the same effect as potassium fluoride.

[0089] As shown in Fig. 16, in the early stage of the reaction, potassium fluoride (KF) 103 comes into contact with aluminum (Al) particles 101 due to stirring, and potassium fluoride (KF) adheres to the aluminum (Al) particles 101. This adhesion causes the aluminum oxide film 101b on the surface 101a of the aluminum (Al) particle to react with potassium fluoride (KF) 103 through the reactions of the following formulas (1) and (2), to form potassium aluminum fluoride (KAIF) ４ ) 105 and potassium oxide (K ２ O)113 is generated in the reaction process. ４ ), the generated potassium aluminum fluoride (KAIF ４ The reaction mixture 105 becomes liquid and adheres to the surface 101a of the aluminum (Al) particles. The reactions of the following formulas (1) and (2) proceed even in an atmosphere without hydrogen: KF + Al ２ O ３ →K ２ O+AlF ３ ... (1) K ２ O+AlF ３ → KAlF ４ ... (2)

[0090] As shown in FIG. 17, potassium aluminum fluoride (KAIF) formed on the surface of the aluminum (Al) particle 101 ４ ) 105 is converted to potassium oxide (K ２ O)113 to form needle-shaped iota alumina (K ０．６７ Al ６ O ９．３３ ) 101c and potassium hexafluoroaluminate (K ３ AlF ６ ) is generated. ４ +28K ２ O→3K ０．６７ Al ６ O９．３３ +K ３ AlF ６ ... (3) Potassium hexafluoroaluminate (K ３ AlF ６ ) is liquid potassium aluminum fluoride (KAIF ４ ) 105, it can come into contact with the aluminum (Al) particles 101. As a result, potassium hexafluoroaluminate (K ３ AlF ６ ) reacts with aluminum (Al) to form potassium aluminum fluoride (KAIF ４ ) 105 and elemental potassium (K). Elemental potassium reacts with hydrogen to form potassium hydride (KH) according to the following formula (5): ３ AlF ６ +Al → 3KAlF ４ +3K...(4) 2K+H ２ →2KH...(5)

[0091] As shown in Figure 18, potassium hydride (KH) produced by the reaction of formula (5) is a gas and can move between particles. This allows the gaseous potassium hydride (KH) to be converted into potassium metaborate (KBO). ２ ) particle 102 and potassium metaborate (KBO ２ ) and potassium borohydride (KBH ４ ) 111 and potassium oxide (K ２ O) 113. Potassium borohydride (KBH ４ ) 111 and potassium oxide (K ２ O)113 is potassium metaborate (KBO ２ ) is generated so as to permeate the surface of the particles 102. ２ →KBH ４ +2K ２ O...(6)

[0092] As shown in FIG. 19, potassium aluminum fluoride (KAIF) produced by the reaction of formula (4) ４ ) also becomes vapor above its melting point, and can move between particles. This allows gaseous potassium aluminum fluoride (KAIF ４) is potassium metaborate (KBO ２ ) particle 102 and potassium metaborate (KBO ２ ) potassium oxide (K) on the surface of the particle 102 ２ O)113 reacts with iota alumina (K ０．６７ Al ６ O ９．３３ ) 101c and potassium hexafluoroaluminate (K ３ AlF ６ ) is generated. At this time, potassium metaborate (KBO ２ The droplet-like product 115 is formed on the surface of the particle 102. The droplet-like product 115 is formed by the liquid potassium aluminum fluoride (KAIF ４ ) 105, potassium hexafluoroaluminate (K ３ AlF ６ ) is dissolved in the solution. Here, potassium hexafluoroaluminate (K ３ AlF ６ ) concentration increases, the liquid potassium aluminum fluoride (KAIF ４ ) is difficult to evaporate, so the gas potassium aluminum fluoride (KAIF ４ ) is more easily absorbed. ４ +28K ２ O→3K ０．６７ Al ６ O ９．３３ +K ３ AlF ６ ... (7)

[0093] As shown in FIG. 20, the above reaction produces potassium hexafluoroaluminate (K ３ AlF ６ As a result, the concentration of potassium aluminum fluoride (KAIF) on the surface 101a of the aluminum (Al) particle decreases. ４ ) 105 becomes easy to evaporate, and potassium metaborate (KBO) is evaporated from the surface 101a of the aluminum (Al) particle. ２ ) particles 102, potassium aluminum fluoride (KAIF ４) gases move more easily. On the other hand, liquid potassium aluminum fluoride (KAIF ４ ) 105 and potassium hexafluoroaluminate (K ３ AlF ６ The droplet-like product 115 containing the aluminum (Al) moves as a liquid to the surface 101 a of the aluminum (Al) particle, whereby the reactions of formulas (4) and (5) occur again.

[0094] Furthermore, potassium borohydride (KBH ４ ) also has a large vapor pressure at temperatures above 620°C, allowing it to move through space, and becomes potassium borohydride (KBH ４ ) is a mixture of potassium hydride (KH) and potassium oxide (K ２ O) to the surface of the aluminum.

[0095] As shown in FIG. 21, the above mechanism results in a cyclic reaction, and potassium borohydride (KBH ４ ) 111 is generated.

[0096] (Test Examples) Hereinafter, the present embodiment will be described in more detail with reference to test examples that illustrate the effects of the present embodiment, but the present embodiment is not limited to these.

[0097] Table 1 shows the raw materials, production conditions, and results of Test Examples 1 to 16. In the tests, reaction products according to Test Examples 1 to 16 were synthesized using the raw materials and production conditions shown in Table 1. In Test Examples 1 to 16, reaction products were produced using the first and third steps of the first production method described above, except for the conditions specifically described below. That is, in Test Examples 1 to 16, the second and fourth steps were not performed. In Table 1 and the following description, K / B refers to the A / B (molar ratio) when the alkali metal and alkaline earth metal contained in the raw materials is potassium (K) only. Furthermore, the maximum hydrogen pressure refers to the maximum value of the hydrogen partial pressure in the sealed container during the reaction step. Furthermore, the stirring speed refers to the peripheral speed of the stirring means described above. Furthermore, in Table 1 and the following examples, "pure water" refers to ion-exchanged water, and the pH of the ion-exchanged water is 5.5 or more and 7.5 or less.

[0098]

[0099] In Test Example 1, the product was subjected to semi-quantitative analysis by the X-ray diffraction (XRD) Rietveld method to determine the content of potassium borohydride (KBH ４ The rate was calculated.

[0100] In Test Examples 2 to 16, the content of potassium borohydride (KBH ４ The iodine titration rate was determined by iodine titration. Details of the iodine titration method are as follows: Iodine titration method: (1) 50 mg of sample (reaction product) was weighed to the nearest 0.1 mg and placed in a weighing bottle. (2) The sample collected in (1) above was transferred to a 200 ml Erlenmeyer flask with a stopper. 40 ml of a 20 g / L NaOH solution was added to this Erlenmeyer flask with a stopper, and the flask was heated in a water bath to completely decompose the unreacted aluminum powder. (3) After cooling the decomposition product from (2) above to room temperature, 20.0 ml of iodine solution (concentration 0.05 mol / L) was added using a volumetric pipette, the flask was stopped, and the flask was left in the dark for 15 minutes. (4) 3 ml of hydrochloric acid was added to the left-behind product from (3) above, and the mixture was shaken well, followed by titration with sodium thiosulfate (concentration 0.1 mol / L). (5) The titration was completed when the purple color of iodine turned colorless. (6) A blank test was performed without adding any sample, and the potassium borohydride content was calculated. The formula used to calculate the content is shown below. ４ Formula for calculating the rate (KBH ４ Rate (mass %) = {(A - B) x 0.1 x f x 53.94 / 8} / C x 100 The variables and constants in the above formula are as follows: A: Titration value (ml) of blank test sodium thiosulfate solution (concentration 0.1 mol / L) B: Titration value (ml) of sample solution sodium thiosulfate solution (concentration 0.1 mol / L) f: Factor of sodium thiosulfate solution (concentration 0.1 mol / L) C: Sample amount (mg) 53.94: Molecular weight of potassium borohydride (g / mol) 8: Normality of potassium borohydride solution (concentration 1 mol / L)

[0101] In Test Example 1, the reaction rate was calculated based on the amount of hydrogen consumed in the reaction step, that is, the difference between the maximum hydrogen pressure and the minimum hydrogen pressure under the reaction conditions.

[0102] Test Example 1 Test Example 1 is a comparative example. In the first step (pretreatment step), potassium metaborate (KBO) was used as a raw material, as shown in Table 1. ２ 7.24 g of potassium fluoride (KF) powder, 1.00 g of potassium fluoride (KF), and 3.817 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means. After charging, hydrogen gas was introduced into the sealed container as a non-oxidizing gas. Here, the K / B ratio of Test Example 1 was 1.19. In the third step (reaction step), the sealed container was heated to 522°C, hydrogen gas was introduced, and the mixture was stirred at a stirring speed of 30 rpm using the stirring means in the sealed container. The maximum partial pressure of the hydrogen gas in the reaction step was 0.78 MPa. Through the above steps, a reaction product according to Test Example 1 was obtained.

[0103] Test Example 2 is a comparative example. As shown in Table 1, in Test Example 2, a reaction product according to Test Example 2 was obtained in the same manner as Test Example 1, except that the heating temperature and maximum hydrogen pressure were as shown in Table 1.

[0104] Test Example 3 Test Example 3 is an example. As shown in Table 1, in Test Example 3, a reaction product according to Test Example 3 was obtained in the same manner as Test Example 2, except that the heating temperature was set as shown in Table 1.

[0105] Test Example 4 Test Example 4 is an example. As shown in Table 1, in Test Example 4, a reaction product according to Test Example 4 was obtained in the same manner as Test Example 2, except that the heating temperature was as shown in Table 1.

[0106] Test Example 5 is an example. As shown in Table 1, in Test Example 5, a reaction product according to Test Example 5 was obtained in the same manner as Test Example 2, except that the heating temperature was as shown in Table 1 and stirring was not performed.

[0107] Test Example 6 is an example. As shown in Table 1, in Test Example 6, a reaction product according to Test Example 6 was obtained in the same manner as Test Example 2, except that the heating temperature in the reaction step was as shown in Table 1 and stirring was not performed.

[0108] Test Example 7 is an example. As shown in Table 1, in Test Example 7, a reaction product according to Test Example 7 was obtained in the same manner as Test Example 2, except that the heating temperature in the reaction step was as shown in Table 1 and stirring was not performed.

[0109] Test Example 8 is an example. As shown in Table 1, in Test Example 8, the reaction product of Test Example 7 was obtained in the same manner as Test Example 2, except that the heating temperature in the reaction step was as shown in Table 1.

[0110] Test Example 9 is an example. As shown in Table 1, in Test Example 9, a reaction product according to Test Example 9 was obtained in the same manner as Test Example 5, except that the maximum hydrogen pressure in Test Example 9 was set to that shown in Table 1.

[0111] Test Example 10 is a comparative example. As shown in Table 1, in Test Example 10, a reaction product according to Test Example 10 was obtained in the same manner as Test Example 5, except that no fluoride was added and the reaction step was carried out by stirring at a stirring speed of 30 rpm using a stirring means in a sealed container. In Test Example 10, K / B was 1.00.

[0112] Test Example 11 Test Example 11 is an example. As shown in Table 1, in Test Example 11, a reaction product according to Test Example 11 was obtained in the same manner as in Test Example 5.

[0113] Test Example 12 is an example. As shown in Table 1, in Test Example 12, 0.611 g of KAlF was used as the fluoride instead of potassium fluoride (KF) powder. ４ A reaction product according to Test Example 12 was obtained in the same manner as in Test Example 5, except that powder was used. In Test Example 12, K / B was 1.05.

[0114] Test Example 13 Test Example 13 is an example. As shown in Table 1, in Test Example 13, 0.481 g of aluminum fluoride (AlF) was used instead of potassium fluoride (KF) powder as the fluoride. ３ A reaction product according to Test Example 13 was obtained in the same manner as in Test Example 5, except that the powder was used. In Test Example 13, K / B was 1.00.

[0115] Test Example 14 Test Example 14 is an example. As shown in Table 1, in Test Example 14, potassium metaborate (KBO) was used as the alkali metal compound. ２ ) powder 4.43 g and potassium tetraborate (K ２ B ４ O ７ A reaction product according to Test Example 14 was obtained in the same manner as in Test Example 5, except that 2.01 g of the powder was used. In Test Example 14, K / B was 1.00.

[0116] Test Example 15 Test Example 15 is an example. As shown in Table 1, in Test Example 15, potassium metaborate (KBO) was used as the alkali metal compound. ２ ) powder 3.04 g and potassium tetraborate (K ２ B ４ O ７ A reaction product according to Test Example 15 was obtained in the same manner as in Test Example 5, except that 2.98 g of the powder was used. In Test Example 15, K / B was 0.91.

[0117] Test Example 16 is an example. As shown in Table 1, in Test Example 16, a reaction product according to Test Example 16 was obtained in the same manner as Test Example 5, except that the amount of potassium fluoride (KF) powder was 1.50 g. In Test Example 16, K / B was 1.29.

[0118] As shown in Table 1, potassium borohydride was not produced in Test Example 10, where no fluoride was added, whereas potassium borohydride was produced in Test Examples 1 to 9 and 11 to 16, where fluoride was added. This shows that potassium borohydride can be produced by adding fluoride.

[0119] As shown in Table 1, in Test Examples 3 to 9 and Test Examples 11 to 16 in which the heating temperature was higher than 560°C, the KBH ４ This shows that potassium borohydride can be efficiently obtained by setting the heating temperature to 580°C or higher.

[0120] As shown in Table 1, in Test Examples 3 to 9 and Test Examples 11 to 16 in which the heating temperature was 580°C or higher, the KBH ４ This shows that potassium borohydride can be efficiently obtained by setting the heating temperature to 580°C or higher.

[0121] As shown in Table 1, in Test Examples 5 to 7, Test Example 9, and Test Examples 11 to 16, in which the heating temperature was 620°C or higher, the KBH ４ This shows that by increasing the heating temperature to 620°C or higher, potassium borohydride can be obtained more efficiently without stirring.

[0122] As shown in Table 1, in Test Examples 14 and 16 in which K / B was 1.00 or more, the KBH was higher than that in Test Example 15 in which K / B was less than 1.00. ４ This shows that potassium borohydride can be efficiently obtained by setting K / B to 1.00 or more.

[0123] 10A to 10D Sealed container 12, 12b Container body 14 Lid 16 Heater 18 O-ring 20 Motor 22 Stirring rod 22A Stirring bar 24 First pipe 26 Hydrogen gas supply valve 28 Exhaust valve 30 Second pipe 32 Pressure gauge 35 Scraper 36 Ribbon-shaped scraper 37 Wide paddle stirrer 51 Potassium borate powder 52 Aluminum powder 54 Fluoride powder 55 Potassium hydroxide powder 101 Aluminum (Al) particle 101a Surface of aluminum (Al) particle 101b Aluminum oxide coating 101c Iota alumina (K ０．６７ Al ６ O ９．３３ ) 102 Potassium metaborate (KBO ２ ) particles 103 potassium fluoride (KF) 105 potassium aluminum fluoride (KAIF ４ ) 111 Potassium borohydride (KBH ４ ) 113 Potassium oxide (K ２ O) 115 product

Claims

1. A method for producing potassium borohydride, comprising a reaction step of mixing solid raw materials containing an alkali metal compound, a fluoride, and at least one material selected from the group consisting of an aluminum compound and aluminum, and then heat treating the mixture at a temperature higher than 560°C.

2. The method for producing potassium borohydride according to claim 1, further comprising a pretreatment step of mixing at least one material selected from the aluminum compound and aluminum with the fluoride prior to the reaction step.

3. The method for producing potassium borohydride according to claim 2, wherein the pretreatment step is carried out at a temperature of 100°C or higher and 330°C or lower.

4. A method for producing potassium borohydride according to any one of claims 1 to 3, characterized in that the reaction step is carried out in a hydrogen atmosphere.

5. The alkali metal compound is potassium aluminum dioxide (KAIO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２ 4. The method for producing potassium borohydride according to claim 1, wherein the compound is at least one selected from the group consisting of ammonium nitrate, ...

6. The potassium borates are potassium metaborate (KBO ２ ), potassium tetraborate (K ２ B ４ O ７ ) and potassium diborate (K ４ B ２ O ５ 6. The method for producing potassium borohydride according to claim 5, wherein the potassium borohydride is at least one selected from the group consisting of:

7. The fluoride is sodium fluoride (NaF), sodium hexafluoroaluminate (Na ３ AlF ６ ), potassium fluoride (KF), potassium aluminum fluoride (KAIF ４ ), potassium hexafluoroaluminate (K ３ AlF ６ ), aluminum fluoride (AlF ３ 4. The method for producing potassium borohydride according to claim 1, wherein the potassium borohydride is at least one selected from the group consisting of potassium fluoride (LiF) and lithium fluoride (LiF).

8. The aluminum compound is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO ２ ), alumina (Al ２ O ３ ) and aluminum fluoride (AlF ３ 4. The method for producing potassium borohydride according to claim 1, wherein the potassium borohydride is at least one selected from the group consisting of:

9. A method for producing potassium borohydride according to any one of claims 1 to 3, characterized in that the molar ratio of aluminum contained in the solid raw material to boron contained in the solid raw material is 4 / 3 or more.

10. A method for producing potassium borohydride according to any one of claims 1 to 3, characterized in that the solid raw material further contains at least one of an alkali metal oxide and an alkaline earth metal oxide, and the molar ratio of the total of the alkali metals and alkaline earth metals contained in the solid raw material to the boron contained in the solid raw material is 1.0 or more and 1.3 or less.

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