JP7517237B2 - Method and apparatus for producing tetrahydroborate - Google Patents

Description

This disclosure relates to a method and apparatus for producing tetrahydroborate.

Patent Document 1 discloses a method for producing sodium borohydride, an example of a tetrahydroborate salt. In this method, a mixture of sodium metaborate powder and aluminum particles is pulverized under a hydrogen atmosphere. This produces a mixed powder containing sodium borohydride powder and aluminum oxide powder.

International Publication No. 2015/190403

The sodium borohydride obtained by the mechanochemical method disclosed in Patent Document 1 is a powder, and depending on the size of the powder, there is a risk of it agglomerating with the aluminum oxide powder. For this reason, it is difficult to extract only the sodium borohydride powder from the mixed powder. The present disclosure provides a method and apparatus for producing tetrahydroborate that can appropriately separate the tetrahydroborate powder from a mixed powder containing tetrahydroborate powder and metal oxide powder.

One aspect of the present disclosure is a method for producing a tetrahydroborate, which comprises separating a tetrahydroborate powder from a mixed powder containing a tetrahydroborate powder and a metal oxide powder obtained by a mechanochemical process. The method includes the following steps (1) and (2):
(1) A step of dispersing the mixed powder in a non-polar liquid.
(2) Separating the non-polar liquid with the mixed powder dispersed therein into a tetrahydroborate powder, a non-polar liquid, and a metal oxide powder based on their specific gravities.

Tetrahydroborate and metal oxide do not dissolve in non-polar liquids. Therefore, in the dispersing step, the tetrahydroborate powder and metal oxide powder are dispersed in the non-polar liquid, for example, by stirring the non-polar liquid into which the mixed powder has been added. At this time, the non-polar liquid penetrates between the powder particles, eliminating the aggregation of the powder. Then, in the separating step, the dispersed tetrahydroborate powder and metal oxide powder are separated based on their specific gravities. Thus, according to this manufacturing method, the tetrahydroborate powder can be appropriately separated from the mixed powder containing the tetrahydroborate powder and the metal oxide powder.

In one embodiment, the specific gravity of the non-polar liquid may be intermediate between the specific gravity of the tetrahydroborate salt and the specific gravity of the metal oxide salt. In this case, in the separating step, the non-polar liquid containing the metal oxide powder and the tetrahydroborate salt powder is separated in the order of the metal oxide powder, the non-polar liquid, and the tetrahydroborate salt powder, for example, by gravity or centrifugal force. Thus, according to this manufacturing method, the tetrahydroborate salt powder can be more appropriately separated from the mixed powder containing the tetrahydroborate salt powder and the metal oxide powder.

In one embodiment, the dispersing step may include a step of pulverizing the mixed powder. In this case, in the dispersing step, the mixed powder produced by the mechanochemical method is pulverized. As a result, the non-polar liquid can more easily enter between the pulverized particles, which further suppresses particle aggregation and allows the particles to be more dispersed in the non-polar liquid. Therefore, according to this manufacturing method, the tetrahydroborate powder can be more appropriately separated from the mixed powder containing the tetrahydroborate powder and the metal oxide powder.

In one embodiment, the tetrahydroborate may include at least one of sodium borohydride, lithium borohydride, and potassium borohydride, and the metal oxide may include at least one of magnesium oxide and aluminum oxide. Sodium borohydride, lithium borohydride, and potassium borohydride have high hydrogen storage density per weight and are suitable for long-term storage at room temperature and pressure. Magnesium oxide and aluminum oxide are inexpensive and easily available. This production method can properly separate the tetrahydroborate from the metal oxide even when the tetrahydroborate and the metal oxide each contain the above-mentioned compounds, and can properly recover the tetrahydroborate, which is easy to use hydrogen for.

In one embodiment, the non-polar liquid may include at least one of a chain alkane, a cyclic alkane, a halogenated hydrocarbon, and an aromatic hydrocarbon. By dispersing the mixed powder using a non-polar liquid in which the tetrahydroborate salt and the metal oxide do not react and dissolve, loss of the tetrahydroborate salt in the separation step is reduced.

In one embodiment, the dispersing step may use a homogenizer or agitator mill to disperse the mixed powder in the non-polar liquid. This allows for better separation of the agglomerated mixed powder.

In one embodiment, the separation step may involve gravity separation using a centrifuge. In this case, the tetrahydroborate powder, the metal oxide powder, and the non-polar liquid can be separated more quickly than by sedimentation separation.

Another aspect of the present disclosure is a tetrahydroborate manufacturing apparatus that separates tetrahydroborate powder from a mixed powder containing tetrahydroborate powder and metal oxide powder obtained by a mechanochemical method. The manufacturing apparatus includes a dispersion section, a conveying section, and a separation section. The dispersion section disperses the mixed powder in a nonpolar liquid having a specific gravity intermediate between the specific gravity of the tetrahydroborate and the specific gravity of the metal oxide. The conveying section conveys the nonpolar liquid in which the mixed powder has been dispersed from the dispersion section. The separation section separates the nonpolar liquid in which the mixed powder has been dispersed into tetrahydroborate powder, the nonpolar liquid, and the metal oxide powder based on the specific gravity.

Tetrahydroborate and metal oxide do not dissolve in non-polar liquids. Therefore, in the dispersion section, for example, by stirring the non-polar liquid into which the mixed powder has been added, the tetrahydroborate powder and metal oxide powder are dispersed in the non-polar liquid. At this time, the non-polar liquid penetrates between the powder particles, eliminating the aggregation of the powder. Then, in the separation section, the dispersed tetrahydroborate powder and metal oxide powder are separated based on their specific gravities. In this way, with this manufacturing device, the tetrahydroborate powder can be appropriately separated from the mixed powder containing the tetrahydroborate powder and the metal oxide powder.

In one embodiment, the dispersion section may be a homogenizer or an agitator mill. As in the above-mentioned method for producing tetrahydroborate, the dispersion section can better disperse the mixed powder in the non-polar liquid, and can better separate the agglomerated mixed powder in the separation section.

In one embodiment, the separation section may be a centrifuge. As in the above-described method for producing tetrahydroborate, the tetrahydroborate powder, the metal oxide powder, and the non-polar liquid can be separated more quickly than by sedimentation separation.

According to the present disclosure, tetrahydroborate powder can be appropriately separated from a mixed powder containing tetrahydroborate powder and metal oxide powder.

FIG. 2 is a block diagram showing an example of a manufacturing apparatus according to an embodiment. 3 is a flowchart illustrating an example of a manufacturing method according to the embodiment. 1 is a graph showing the measurement results of diffracted X-ray intensity of a powder according to a comparative example. 1 is a graph showing the measurement results of diffracted X-ray intensity of a powder according to a comparative example. 1 is a graph showing the measurement results of diffracted X-ray intensity of powder according to an example. 1 is a graph showing the measurement results of diffracted X-ray intensity of powder according to an example.

Embodiments of the present disclosure will now be described with reference to the drawings. In the following description, identical or equivalent elements will be given the same reference numerals, and redundant descriptions will not be repeated.

Figure 1 is a block diagram showing an example of a manufacturing apparatus according to an embodiment. The manufacturing apparatus 1 shown in Figure 1 is an apparatus that separates a mixed powder containing a tetrahydroborate powder and a metal oxide powder obtained by a mechanochemical method (hereinafter, sometimes referred to as the "MC method").

A mixed powder containing tetrahydroborate powder and metal oxide powder (hereinafter, sometimes simply referred to as "mixed powder") is obtained by applying the MC method in the mechanochemical device 5. The tetrahydroborate salt contains at least one of sodium borohydride, lithium borohydride, and potassium borohydride. The metal oxide contains at least one of magnesium oxide and aluminum oxide. For example, sodium metaborate powder, aluminum particles, and hydrogen gas are supplied to the mechanochemical device 5, and the MC method is applied to obtain a mixed powder containing sodium borohydride powder and aluminum oxide powder. Cohesive forces are generated between the particles of the mixed powder. In particular, particles of different materials with a size of 100 μm or less contained in the mixed powder are prone to cohesion because the interparticle forces are dominant over the external forces applied to the particles by the MC method.

The manufacturing apparatus 1 includes an acquisition unit 10, a dispersion unit 20, a transport unit 30, a separation unit 40, a recovery unit 50, and a control unit 60. The acquisition unit 10 acquires mixed powder from the mechanochemical apparatus 5. The acquisition unit 10 has, for example, a hopper capable of storing the mixed powder, and piping connecting the mechanochemical apparatus 5 and the hopper. The mixed powder is sent from the mechanochemical apparatus 5 to the hopper via the piping.

The dispersion unit 20 has a dispersion function of dispersing the mixed powder in a non-polar liquid. The non-polar liquid is a liquid that does not react with water and does not dissolve the tetrahydroborate and metal oxide that make up the mixed powder. The dispersion unit 20 is, for example, a homogenizer or an agitation mill. The agitation mill is, for example, a wet medium agitation mill. The dispersion unit 20 is, for example, connected to the acquisition unit 10 via piping. The dispersion unit 20 has, for example, a dispersion container and a pump that supplies the non-polar liquid into the dispersion container. The dispersion unit 20 stores the mixed powder sent from the hopper of the acquisition unit 10 via piping in the dispersion container.

The dispersion unit 20 disperses the mixed powder in a non-polar liquid having a specific gravity intermediate between the specific gravity of the tetrahydroborate and the specific gravity of the metal oxide. The dispersion unit 20 supplies the non-polar liquid to the mixed powder stored in the dispersion container, so that the non-polar liquid penetrates between the mixed powders and can suppress the aggregation of the mixed powders. Since the tetrahydroborate contained in the mixed powder does not react with the non-polar liquid, the dispersion unit 20 can disperse the mixed powder in the non-polar liquid without reducing the amount of tetrahydroborate. Even if clumps of tetrahydroborate powder and metal oxide powder remain, the non-polar liquid penetrates into the bond between the tetrahydroborate and the metal oxide, so that the tetrahydroborate and the metal oxide can be dispersed. The dispersion unit 20, for example, rotates the stirring arm for a predetermined time to allow the non-polar liquid to penetrate sufficiently between the mixed powders.

The non-polar liquid includes, for example, at least one of chain alkanes, cyclic alkanes, halogenated hydrocarbons, and aromatic hydrocarbons. Chain alkanes include, for example, pentane, hexane, heptane, octane, etc. Cyclic alkanes include, for example, cyclohexane, etc. Halogenated hydrocarbons include, for example, dibromomethane, tetrabromoethane, tetrachloromethane, chloroform, etc. Aromatic hydrocarbons include, for example, toluene, xylene, benzene, etc.

The non-polar liquid contains, for example, at least one of the above compounds, and is adjusted to have an intermediate specific gravity between the specific gravity of the tetrahydroborate and the specific gravity of the metal oxide. The specific gravity of the tetrahydroborate is about 0.6 g/cm ³ or more and about 1.2 g/cm ³ or less, and the specific gravity of the metal oxide is about 3.6 g/cm ³ or more and about 4.0 g/cm ³ or less. The intermediate specific gravity of the non-polar liquid refers to a specific gravity adjusted to be larger than the specific gravity of the tetrahydroborate and smaller than the specific gravity of the metal oxide. For example, the specific gravity of the non-polar liquid may be adjusted to be 1.3 g/cm ³ or more and 3.5 g/cm ³ or less, or may be adjusted to be 1.8 g/cm ³ or more and 2.8 g/cm ³ or less.

The dispersion unit 20 may have a function of pulverizing the mixed powder acquired from the acquisition unit 10. The pulverization of the mixed powder means to break up the mixed powder or to separate the mixed powder by making it finer. The dispersion unit 20, for example, stores balls, which are pulverization media, and the mixed powder in a dispersion container. In this case, the dispersion unit 20 rotates the stirring arm under wet conditions for a predetermined time in the dispersion container, moves the balls by bringing them into contact with the stirring arm, and pulverizes the mixed powder by colliding the balls with the mixed powder. By pulverizing the mixed powder, at least the average particle size of the mixed powder becomes smaller than the average particle size of the mixed powder when it was acquired from the mechanochemical device 5 by the acquisition unit 10. This makes it easier for the mixed powder to be dispersed in the non-polar liquid.

The conveying section 30 conveys the non-polar liquid in which the mixed powder is dispersed (hereinafter, may be simply referred to as "dispersion liquid") to the separation section 40. The conveying section 30 has, for example, a pipe that connects the dispersion container of the dispersion section 20 to the separation container of the separation section 40 described below, and a pump that sends the liquid in the pipe. The dispersion liquid in the dispersion section 20 is conveyed by the pump through the pipe to the separation section 40.

The separation unit 40 separates the dispersion liquid transported by the transport unit 30 into tetrahydroborate, nonpolar liquid, and metal oxide by gravity separation. Because the particle diameter of tetrahydroborate and the particle diameter of metal oxide are approximately the same value (e.g., values with no significant difference in order of magnitude), the separation unit 40 cannot use separation that utilizes particle diameter, such as a sieve. For this reason, the separation unit 40 separates the dispersion liquid by gravity.

The separation unit 40 is, for example, a centrifuge, and has a separation container and a drive mechanism that applies a rotational force (centrifugal force) to the liquid in the separation container. The separation unit 40 stores the dispersion liquid sent by the transport unit 30 in the separation container. The dispersion liquid in the separation container is centrifuged by the centrifugal force applied by the drive mechanism, and is separated according to its specific gravity. At this time, since the specific gravity of the non-polar liquid supplied to the dispersion unit 20 is intermediate between the specific gravity of the tetrahydroborate and the specific gravity of the metal oxide, the dispersion liquid separates into three layers in the separation container. For example, layers of tetrahydroborate, non-polar liquid, and metal oxide are formed in that order from the center of rotation.

The recovery section 50 recovers the tetrahydroborate powder separated in the separation container by the separation section 40. The recovery section 50 has a mechanism for pumping out the tetrahydroborate powder in the separation container or for pushing out the tetrahydroborate powder from the separation container.

The control unit 60 is connected to each component of the manufacturing apparatus 1. The control unit 60 is configured as a PLC (Programmable Logic Controller) as an example. The control unit 60 may be configured as a normal computer system including a CPU (Central Processing Unit), a main storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory), an input device such as a touch panel or a keyboard, an output device such as a display, and an auxiliary storage device such as a hard disk. The control unit 60 is provided with, for example, an operation panel that can be operated by an operator. The control unit 60 controls the movement of each component of the manufacturing apparatus 1, such as the acquisition of the mixed powder in the acquisition unit 10, the grinding and dispersion of the mixed powder in the dispersion unit 20, the transportation of the dispersion liquid in the transport unit 30, the separation of the dispersion liquid in the separation unit 40, and the recovery of the tetrahydroborate in the recovery unit 50.

Next, a method for producing tetrahydroborate will be described. FIG. 2 is a flow chart showing an example of a production method according to an embodiment. The production method shown in FIG. 2 is started by the control unit 60 based on an instruction from an operator, for example, when a mixed powder containing tetrahydroborate powder and metal oxide powder is obtained in the mechanochemical device 5.

First, the acquisition unit 10 in the manufacturing apparatus 1 acquires the mixed powder from the mechanochemical apparatus 5 as an acquisition process (S11). The acquisition unit 10 acquires the mixed powder from the mechanochemical apparatus 5 via piping and stores it in a hopper. The dispersion unit 20 acquires the mixed powder from the hopper of the acquisition unit 10 into a dispersion container as an acquisition process (S11). When the dispersion unit 20 acquires a predetermined amount of mixed powder, the control unit 60 ends the acquisition process (S11) and moves on to the next process.

Then, the dispersion unit 20 disperses the mixed powder in the non-polar liquid as a dispersion process (S13: an example of a dispersion step). The dispersion unit 20 supplies the non-polar liquid to the mixed powder stored in the dispersion container. The dispersion unit 20 rotates the stirring arm for a predetermined time to allow the non-polar liquid to penetrate between the mixed powder. This disperses the tetrahydroborate and the metal oxide in the non-polar liquid. Note that a crushing process (an example of a crushing step) may be performed during the dispersion process. In this case, the dispersion unit 20 crushes the mixed powder by bringing a ball into contact with the stirring arm rotating in the dispersion container set under wet conditions for a predetermined time, thereby moving the ball and colliding with the mixed powder. When a predetermined time has elapsed since the stirring arm started to rotate, the control unit 60 ends the dispersion process (S13) and moves to the next process.

Then, the transport unit 30 transports the dispersion liquid to the separation unit 40 as a transport process (S15). The transport unit 30 transports the dispersion liquid stored in the dispersion container to the separation container of the separation unit 40 through a pipe. When the transport unit 30 has transported a predetermined amount of dispersion liquid into the separation container, the control unit 60 ends the transport process (S15) and moves on to the next process.

Then, the separation unit 40 separates the dispersion liquid into tetrahydroborate, nonpolar liquid, and metal oxide by gravity separation as a separation process (S17: an example of a separation step). The separation unit 40 centrifuges the separated liquid to separate the metal oxide powder, nonpolar liquid, and tetrahydroborate powder into three layers according to their specific gravities. When the separation unit 40 performs centrifugation for a predetermined time and stops rotation, the control unit 60 ends the separation process (S17) and moves on to the next process.

Then, the recovery unit 50 recovers the tetrahydroborate from the dispersion liquid separated into three layers in the separation container as a recovery process (S19). The recovery unit 50 obtains the separation container from the separation unit 40, and recovers the tetrahydroborate powder by pumping it out of the separation container or by pushing the tetrahydroborate powder out of the separation container. When a predetermined amount of tetrahydroborate has been recovered in the recovery process (S19), the control unit 60 ends the recovery process (S19) and ends the method for producing tetrahydroborate.

As described above, the manufacturing apparatus 1 and manufacturing method can appropriately separate the tetrahydroborate powder from the mixed powder containing the tetrahydroborate powder and the metal oxide powder. Tetrahydroborate and metal oxide do not dissolve in non-polar liquids. Therefore, in the dispersion process (S13), the dispersion unit 20 stirs the non-polar liquid into which the mixed powder has been added, for example, to disperse the tetrahydroborate powder and the metal oxide powder in the non-polar liquid. At this time, the non-polar liquid enters between the powder particles, and thus the agglomeration of the powder is also eliminated. Then, in the separation process (S17), the separation unit 40 separates the dispersed tetrahydroborate powder and the metal oxide powder based on their specific gravities.

In addition, since the specific gravity of the non-polar liquid is intermediate between the specific gravity of the tetrahydroborate salt and the specific gravity of the metal oxide salt, the powder is separated by gravity or centrifugal force in the following order: metal oxide powder, non-polar liquid, tetrahydroborate powder.

The dispersion process (S13) also includes a pulverization process by the dispersion unit 20. In this case, in the dispersion process (S13), the mixed powder produced by the mechanochemical device 5 is pulverized. As a result, the non-polar liquid can more easily enter between the pulverized particles, further suppressing particle aggregation and allowing the particles to be more dispersed in the non-polar liquid. Therefore, according to this manufacturing device 1 and manufacturing method, the tetrahydroborate powder can be more appropriately separated from the mixed powder containing the tetrahydroborate powder and the metal oxide powder.

The tetrahydroborate salt contains at least one of sodium borohydride, lithium borohydride, and potassium borohydride, and the metal oxide contains at least one of magnesium oxide and aluminum oxide. Sodium borohydride, lithium borohydride, and potassium borohydride have high hydrogen storage density per weight and are suitable for long-term storage at room temperature and pressure. Magnesium oxide and aluminum oxide are inexpensive and easy to obtain. This manufacturing apparatus 1 and manufacturing method can properly separate the tetrahydroborate salt from the metal oxide, even when the tetrahydroborate salt and the metal oxide each contain the above-mentioned compounds, and can properly recover the tetrahydroborate salt, which is easy to use hydrogen for.

The non-polar liquid contains at least one of chain alkanes, cyclic alkanes, halogenated hydrocarbons, and aromatic hydrocarbons. In the dispersion process (S13) of the dispersion unit 20, the mixed powder is dispersed using a non-polar liquid in which tetrahydroborate and metal oxide do not react and do not dissolve, thereby reducing the loss of tetrahydroborate in the separation step.

In the dispersion process (S13), the dispersion unit 20 is a homogenizer or agitation mill, which disperses the mixed powder in a non-polar liquid. This allows the agglomerated mixed powder to be more appropriately separated.

In the separation process (S17), the separation section 40 is a centrifuge, and performs specific gravity separation by centrifugation. In this case, the tetrahydroborate powder, the metal oxide powder, and the non-polar liquid can be separated more quickly than by sedimentation separation.

The above-described embodiment shows an example of the manufacturing apparatus 1 and manufacturing method according to the present disclosure. The manufacturing apparatus 1 and manufacturing method according to the present disclosure are not limited to the manufacturing apparatus 1 and manufacturing method according to the embodiment. For example, the manufacturing apparatus 1 may be configured to include only the dispersion section 20, the conveying section 30, and the separation section 40. For example, the manufacturing method may be configured to include only the dispersion process (S13) and the separation process (S17).

The manufacturing apparatus 1 may execute the manufacturing method using a part or all of the configuration of the mechanochemical apparatus 5. The dispersion section 20 may not execute a pulverization process. The non-polar liquid supplied in the dispersion section 20 may be a liquid having a specific gravity intermediate between that of the tetrahydroborate and that of the metal oxide, as well as a liquid having a specific gravity smaller than that of the tetrahydroborate or a liquid having a specific gravity larger than that of the metal oxide. The separation section 40 may not be a centrifuge. The separation section 40 may separate, for example, into three layers of metal oxide powder, non-polar liquid, and tetrahydroborate powder by gravity without applying centrifugal force. In this case, the separation section 40 may be a sedimentation separator.

[Confirmation of the effectiveness of the production method based on the amount of hydrogen generated]
A verification example will be described in which the amount of hydrogen generated when reacting with water is compared between a powder obtained by the manufacturing method according to the embodiment and a mixed powder containing a tetrahydroborate powder and a metal oxide powder obtained by a mechanochemical method. Tetrahydroborate can capture hydrogen as a hydrogen carrier and release hydrogen. A hydrogen carrier is a substance that can transport and store hydrogen. The greater the proportion of tetrahydroborate contained in the target powder, the greater the amount of hydrogen (amount of hydrogen generated) generated by the reaction of the target powder with water. Therefore, by comparing the amount of hydrogen generated, it can be verified which of the powder obtained by the manufacturing method according to the embodiment and the mixed powder containing a tetrahydroborate powder and a metal oxide powder obtained by a mechanochemical method contains more tetrahydroborate.

Example 1
A powder was obtained by the manufacturing method according to the embodiment. As a mixed powder containing a tetrahydroborate powder and a metal oxide powder obtained by a mechanochemical method, 10 g of a mixed powder of sodium borohydride and magnesium oxide was prepared. Hexane and dibromomethane were mixed and adjusted to have a specific gravity intermediate between the specific gravity of sodium borohydride and the specific gravity of magnesium oxide to obtain a non-polar liquid. A bead mill was used as the dispersion section 20, and 10 g of the mixed powder of sodium borohydride and magnesium oxide was mixed and ground while being dispersed in the non-polar liquid (dispersion treatment (S13)). Next, a centrifuge was used as the separation section 40, and the liquid containing the sodium borohydride powder was separated based on the specific gravity (separation treatment (S17)). Approximately 1/3 of the solid content in the separated liquid was taken out from the top and dried to obtain a powder.

Example 2
In Example 2, a non-polar liquid whose specific gravity was not adjusted relative to the mixed powder was used. The non-polar liquid was hexane. The other conditions were the same as in Example 1.

(Comparative Example 1)
In Comparative Example 1, a non-polar liquid whose specific gravity was not adjusted relative to the mixed powder was used. The non-polar liquid was hexane. In addition, the separation process (S17) was not performed. The other conditions were the same as those in Example 1.

(Comparative Example 2)
In Comparative Example 2, a non-polar liquid whose specific gravity was not adjusted with respect to the mixed powder was used. The non-polar liquid was hexane. In addition, the dispersion treatment (S13) was not performed. The other conditions were the same as those in Example 1.

(Comparative Example 3)
The powder according to Comparative Example 3 is a mixed powder containing a tetrahydroborate powder obtained by a mechanochemical method and a metal oxide powder, that is, in Comparative Example 3, the dispersion treatment (S13) and the separation treatment (S17) were not performed.

(Evaluation results)
In Examples 1 and 2 and Comparative Examples 1 to 3, 2 g of powder was reacted with water to generate hydrogen, and the amount of hydrogen was measured. The results are shown in Table 1. Table 1 shows the results of the amount of hydrogen generated in Examples 1 and 2 and Comparative Examples 1 to 3. The adjustment conditions in Table 1 refer to the outline of the treatment carried out for the above-mentioned Examples 1 and 2 and Comparative Examples 1 to 3. The amount of hydrogen generated in Table 1 is the amount of hydrogen (L) obtained by reacting 2 g of powder in Examples 1 and 2 and Comparative Examples 1 to 3 with water. When sodium borohydride reacts with water, hydrogen is released and sodium borohydride remains. The purity in Table 1 is the ratio (%) of each measured amount of hydrogen generated (L) to the theoretical value (L) of the amount of hydrogen generated when 2 g of sodium borohydride powder reacts completely with water. In the evaluations in Table 1, samples with a purity of 70% or more are marked with "○" as they generate sufficient hydrogen, samples with a purity of 54% or more are marked with "△" as they generate most of the hydrogen, and samples with a purity of less than 54% are marked with "×" as they do not generate sufficient hydrogen. Note that if the purity of tetrahydroborate is 54% or more, the energy density of the tetrahydroborate is higher than the energy density of other hydrogen carriers.

As shown in Table 1, comparing Example 2 and Comparative Example 1, the amount of hydrogen generated was twice as much when separation treatment (S17) was performed. This suggests that Example 2 has a greater amount of sodium borohydride per given amount of powder than Comparative Example 1. In other words, it was confirmed that separation treatment (S17) is an appropriate method for separating tetrahydroborate from the mixed powder.

In addition, comparing Example 2 and Comparative Example 2, the amount of hydrogen generated was twice as much when dispersion treatment (S13) was performed. This suggests that Example 2 has a greater amount of sodium borohydride per given amount of powder than Comparative Example 2. In other words, it was confirmed that dispersion treatment (S13) is an appropriate method for separating tetrahydroborate from the mixed powder.

In addition, when comparing Comparative Examples 1, 2, and 3, the amount of hydrogen generated did not change. This result suggests that the amount of sodium borohydride per given amount of powder obtained in the recovery process (S19) does not change when only one of the dispersion process (S13) or separation process (S17) is performed on the mixed powder. In other words, it was suggested that a method including only one of the dispersion process (S13) or separation process (S17) is not appropriate as a method for separating sodium borohydride from the mixed powder. Thus, as a result of comparing Example 2 with Comparative Examples 1 to 3, it was confirmed that tetrahydroborate can be appropriately separated from the mixed powder by performing both the dispersion process (S13) and the separation process (S17).

The amount and purity of hydrogen generated in Example 1 was higher than those in Example 2 and Comparative Examples 1 to 3. Comparing Example 1 and Example 2, the amount of hydrogen generated was greater when a non-polar liquid adjusted to have a specific gravity intermediate between that of sodium borohydride and that of magnesium oxide was used. This result suggests that Example 1 contains a greater amount of sodium borohydride per given amount of powder than Example 2. In other words, it was confirmed that using a non-polar liquid adjusted to have a specific gravity intermediate between that of tetrahydroborate and that of metal oxide is a more appropriate method for separating tetrahydroborate from the mixed powder.

[Composition analysis results]
The diffracted X-ray intensity at each diffraction angle was measured by XRD (X-ray diffraction) for the powders according to Examples 1 and 2 and Comparative Examples 1 and 3. Fig. 3 is a graph showing the measurement results of the diffracted X-ray intensity of the powder according to Comparative Example 3. Fig. 4 is a graph showing the measurement results of the diffracted X-ray intensity of the powder according to Comparative Example 1. Fig. 5 is a graph showing the measurement results of the diffracted X-ray intensity of the powder according to Example 2. Fig. 6 is a graph showing the measurement results of the diffracted X-ray intensity of the powder according to Example 1.

The horizontal axis of each graph shown in Figures 3 to 6 is the diffraction angle (degrees) indicating the angle of the scanning axis, and the vertical axis of each graph is the intensity (CPS) indicating the number of diffracted X-rays captured by the detector per second. Hereinafter, the diffracted X-ray intensity may be simply referred to as intensity. Note that in Figures 3 to 6, the scale is changed in each figure to improve the visibility of the peak intensity on the vertical axis. Also, _NaBH4 in Figures 3 to 6 indicates the peak of sodium borohydride, and MgO indicates the peak of magnesium oxide.

First, the measurement results of Comparative Example 3, which is the mixed powder before the manufacturing method is performed, will be described. As shown in Figure 3, peaks of sodium borohydride and magnesium oxide were confirmed in the measurement results of Comparative Example 3. In this way, it was confirmed that the mixed powder before the manufacturing method is performed contains sodium borohydride and magnesium oxide. Furthermore, the intensity of the sodium borohydride peak was smaller than the intensity of the magnesium oxide peak.

Next, the measurement results of the mixed powders produced by each manufacturing method will be described. As shown in FIG. 4, the measurement results of Comparative Example 1 (dispersion + liquid with unadjusted specific gravity) also confirmed peaks of sodium borohydride and magnesium oxide. Thus, it was confirmed that the mixed powder of Comparative Example 1 contains sodium borohydride and magnesium oxide. The intensity of the sodium borohydride peak was smaller than the intensity of the magnesium oxide peak. Compared to Comparative Example 3, the ratio of the sodium borohydride peak intensity to the magnesium oxide peak intensity was approximately the same. This confirmed that even when the manufacturing method of Comparative Example 1 was carried out, there was no significant change in the composition and structure of the mixed powder compared to before the manufacturing method was carried out.

As shown in FIG. 5, the measurement results for Example 2 (dispersion + separation + non-adjusted specific gravity liquid) also confirmed the presence of sodium borohydride peaks and magnesium oxide peaks. Thus, it was confirmed that the mixed powder of Example 2 contains sodium borohydride and magnesium oxide. The intensity of the sodium borohydride peak was greater than the intensity of the magnesium oxide peak. Compared to Comparative Example 3, the ratio of the sodium borohydride peak intensity to the magnesium oxide peak intensity was greater. Therefore, it was confirmed that by performing the manufacturing method of Example 2, the purity of sodium borohydride was increased compared to the mixed powder before performing the manufacturing method.

As shown in FIG. 6, the measurement results of Example 1 (dispersion + separation + specific gravity adjustment liquid) also confirmed the presence of sodium borohydride peaks and magnesium oxide peaks. Thus, it was confirmed that the mixed powder of Example 1 contains sodium borohydride and magnesium oxide. The intensity of the sodium borohydride peak was greater than the intensity of the magnesium oxide peak. Compared to Comparative Example 3, the ratio of the sodium borohydride peak intensity to the magnesium oxide peak intensity was greater. Furthermore, compared to Example 2, the ratio of the sodium borohydride peak intensity to the magnesium oxide peak intensity was greater. Therefore, it was confirmed that the purity of sodium borohydride was increased by performing the manufacturing method of Example 1 compared to the mixed powder before performing the manufacturing method and the mixed powder of Example 2.

As described above, the ratio of the peak intensity of sodium borohydride to the peak intensity of magnesium oxide was highest in the order of Example 1, followed by Example 2 and Comparative Example 1 (Comparative Example 3). In other words, the graphs in Figures 3 to 6 also suggest that, similar to the results in Table 1, the amount of sodium borohydride per given amount of powder was greatest in the order of Example 1, Example 2 and Comparative Example 1 (Comparative Example 3), and that the purity of the sodium borohydride was high.

Therefore, the graphs of Figures 3 and 4, as well as the results of Table 1, confirm that a method including only the dispersion treatment (S13) is not suitable for separating sodium borohydride from the mixed powder. The graphs of Figures 4 and 5, as well as the results of Table 1, confirm that a method of performing both the dispersion treatment (S13) and the separation treatment (S17) is suitable for separating tetrahydroborate from the mixed powder. The graphs of Figures 5 and 6, as well as the results of Table 1, confirm that the use of a non-polar liquid adjusted to have a specific gravity intermediate between the specific gravity of tetrahydroborate and the specific gravity of the metal oxide is a more suitable method for separating tetrahydroborate from the mixed powder.

1... manufacturing device, 10... acquisition section, 20... dispersion section, 30... transport section, 40... separation section, 50... recovery section, 60... control section.

Claims (10)

1. A method for producing a tetrahydroborate, comprising separating a powder of the tetrahydroborate from a mixed powder containing a powder of the tetrahydroborate and a powder of a metal oxide obtained by a mechanochemical method, the method comprising the steps of:
Dispersing the mixed powder in a non-polar liquid;
separating the non-polar liquid having the mixed powder dispersed therein into the tetrahydroborate powder, the non-polar liquid, and the metal oxide powder based on specific gravity;
A method for producing a tetrahydroborate salt, comprising: The method for producing tetrahydroborate according to claim 1, wherein the specific gravity of the non-polar liquid is intermediate between the specific gravity of the tetrahydroborate and the specific gravity of the metal oxide. The method for producing tetrahydroborate according to claim 1 or 2, wherein the dispersing step includes a step of pulverizing the mixed powder. The method for producing tetrahydroborate according to any one of claims 1 to 3, wherein the tetrahydroborate includes at least one of sodium borohydride, lithium borohydride, and potassium borohydride, and the metal oxide includes at least one of magnesium oxide and aluminum oxide. The method for producing tetrahydroborate according to any one of claims 1 to 4, wherein the non-polar liquid contains at least one of a chain alkane, a cyclic alkane, a halogenated hydrocarbon, and an aromatic hydrocarbon. The method for producing tetrahydroborate according to any one of claims 1 to 5, wherein in the dispersing step, the mixed powder is dispersed in the non-polar liquid using a homogenizer or a stirring mill. The method for producing tetrahydroborate according to any one of claims 1 to 6, wherein the separation step is performed by gravity separation using a centrifuge. An apparatus for producing tetrahydroborate, which separates a powder of tetrahydroborate from a mixed powder containing a powder of tetrahydroborate and a powder of a metal oxide obtained by a mechanochemical method, comprising:
A dispersion unit that disperses the mixed powder in a non-polar liquid;
a conveying section that conveys the non-polar liquid in which the mixed powder has been dispersed from the dispersing section;
a separation section that separates the non-polar liquid in which the mixed powder is dispersed into the tetrahydroborate powder, the non-polar liquid, and the metal oxide powder based on specific gravity;
An apparatus for producing a tetrahydroborate comprising: The apparatus for producing tetrahydroborate according to claim 8, wherein the dispersion section is a homogenizer or an agitation mill. The apparatus for producing tetrahydroborate according to claim 8 or 9, wherein the separation section is a centrifuge.

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