JP2021038130A - Method for producing tetrahydroborate - Google Patents

Abstract

To provide a novel method for producing tetrahydroborate.SOLUTION: A method for producing tetrahydroborate comprises a heat treatment step in which a mixture of a borate and magnesium hydride is heated to 350°C or higher in a gas atmosphere containing hydrogen (H) as a constituent element.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for producing tetrahydroborate.

As a method for producing tetrahydroborate by hydrogenating the borate, a method of reacting sodium metaborate powder and magnesium powder for about 2 hours in a hydrogen atmosphere at about 550 ° C. and 2.3 MPa is known. .. (See, for example, Patent Document 1). Further, as another method, a method is known in which sodium metaborate powder and granular aluminum are reacted in a hydrogen atmosphere at about 300 ° C. and 1 MPa for about 1 hour while rolling and pulverizing the granular aluminum (for example, patent). Document 2).

Japanese Unexamined Patent Publication No. 2004-224648 International Publication No. 2015/190403

In the field of producing tetrahydroborate, various production methods are being studied from the viewpoint of industrial application.

It is an object of the present disclosure to provide a novel method for producing tetrahydroborate.

The method for producing tetrahydroborate according to one aspect of the present disclosure comprises a heat treatment step of heating a mixture of borate and magnesium hydride to 350 ° C. or higher in a gas atmosphere containing hydrogen (H) as a constituent element. is there.

In one embodiment, the heat treatment step may be carried out with the mixture flowing.

In one embodiment, the heat treatment step may be performed while exposing the mixture to plasma.

In one embodiment, the average particle size of borate may be 500 μm or less.

In one embodiment, the borate may be sodium metaborate.

In one embodiment, the production method may further include a step of reacting tetrahydroborate with water to obtain borate before the heat treatment step.

According to the present disclosure, it is possible to provide a novel method for producing tetrahydroborate. It can be said that the manufacturing method of the present disclosure is very suitable for industrial application because it can realize low cost and high productivity.

It is a schematic diagram which shows an example of the manufacturing apparatus of tetrahydroborate.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings as the case may be. However, the present disclosure is not limited to the following embodiments.

<Manufacturing method of tetrahydroborate>
The method for producing tetrahydroborate according to the present embodiment includes a heat treatment step of heating a mixture of borate and magnesium hydride to 350 ° C. or higher in a gas atmosphere containing hydrogen (H) as a constituent element.

(Heat treatment process)
In the heat treatment step, the above mixture is treated with hydrogen radicals (H radicals) generated from a gas containing hydrogen (H) as a constituent element. At this time, since magnesium hydride that can function as a reducing agent is used, the borate can also be treated with ^{hydride ions (H −) released from magnesium hydride.}

In the heat treatment step, the bond portion of the oxygen atom of the borate is cleaved to remove the oxygen atom, and the hydrogen radical is bonded to the electron pair to which the oxygen atom is bonded to hydrogenate the borate. .. For example, when sodium metaborate is used as the borate, the following reactions (1-1) and (1-2) are considered to occur in this step.
NaBO ₂ + 2MgH ₂ → NaBH ₄ + 2MgO (1-1)
NaBO ₂ + 8H ^* → NaBH ₄ + 2H ₂ O (1-2)

In this step, in producing tetrahydroborate by hydrogenating borate, it is not necessary to keep the reaction vessel at a high temperature and high pressure, and it is not necessary to continuously input a large amount of energy from the outside. Further, by using magnesium hydride, the processing time is significantly shortened as compared with the conventional process, so that the productivity can be improved. Therefore, the borate can be hydrogenated to produce tetrahydroborate at high speed and in large quantities.

Examples of the gas containing hydrogen (H) as a constituent element include hydrogen gas, ammonia (NH ₃ ) gas, hydrocarbon gas and the like. By using ammonia gas, the heating temperature of the mixture required for the heat treatment step can be kept low. This is because ammonia is relatively easy to dissociate, and hydrogen radicals are easily generated in the vicinity of the mixture due to the dissociation of ammonia even at a low mixture temperature. In addition, by using a gas containing an element that is more easily oxidized than hydrogen, such as hydrocarbons (CH ₄ , C ₂ H ₂ , C ₆ H _{6, etc.), the oxygen atom bond of the borate is cleaved.} The effect of removing oxygen atoms can be enhanced. This is expected to improve the production speed of tetrahydroborate. Aiming at the same effect, the gas atmosphere containing hydrogen (H) as a constituent element may contain a gas containing an element that is more easily oxidized than hydrogen, such as carbon monoxide. By using such a gas in combination with a gas containing hydrogen (H) as a constituent element, the effect of cutting the bond portion of the oxygen atom of the borate to remove the oxygen atom can be further enhanced.

When the heat treatment step is carried out while generating plasma in the system as described later, the gas atmosphere containing hydrogen (H) as a constituent element contains hydrogen such as argon gas, helium gas, neon gas and the like. A gas that produces a penning effect in combination may be included. As a result, the plasma concentration can be kept high, and plasma can be stably and widely generated, so that the production rate of tetrahydroborate is expected to be improved.

From the viewpoint of facilitating the generation of hydrogen radicals (H radicals) generated from a gas containing hydrogen (H) as a constituent element, the pressure in the system in the heat treatment step is preferably about 10 to 150 Pa in absolute pressure. When plasma is generated, the plasma density can be increased by reducing the pressure of the raw material gas to this extent.

From the viewpoint of facilitating the generation of hydrogen radicals (H radicals) generated from a gas containing hydrogen (H) as a constituent element, the heat treatment temperature in the heat treatment step is 350 ° C. or higher, but may be 400 ° C. or higher. The upper limit of the heat treatment temperature is not particularly limited, but may be, for example, 600 ° C. The reaction between water produced by the reaction of oxygen dissociated from borate and hydrogen and tetrahydroborate is suppressed by the heat of heat treatment. The time for heat-treating the mixture depends on the amount of the mixture and the like, but can be, for example, 1 hour or less, and may be 0.5 hours or less.

Since a heat treatment step generally used for a semiconductor process or the like can be used, both the equipment cost and the operation cost can be suppressed at low cost. It can be said that the manufacturing method according to the present embodiment including the heat treatment step is suitable for industrial application.

The heat treatment step may be carried out while exposing the mixture to plasma, i.e. generating plasma in the system. The plasma used for the plasma treatment is generated from a raw material gas containing the above-mentioned gas containing hydrogen (H) as a constituent element.

The plasma may be either microwave plasma (plasma excited by microwaves) or RF plasma (plasma excited by RF (Radio Frequency)). These plasmas may be pulse-excited or DC-excited.

By using microwaves, high-density and wide-range non-equilibrium plasma is generated, so that the rate of producing tetrahydroborate can be increased. In addition, the water generated by the reaction of oxygen atoms dissociated from the borate with plasma can be effectively heated and evaporated or ionized by microwaves, so that the produced tetrahydroborate reacts with water. It is possible to suppress the return to borate. As a result, the rate of producing tetrahydroborate can be increased.

As the microwave, for example, a microwave having a frequency band of industrially usable and having a frequency of 1 GHz or higher capable of generating a dense non-equilibrium plasma can be used, and a microwave having a frequency of 2.45 GHz is preferable. Can be used.

In the case of microwave plasma, for example, the microwave power for generating a plasma atmosphere can be 300 W or more.

On the other hand, since RF plasma is a plasma widely used in the industrial world, both equipment cost and operating cost can be suppressed at low cost. Since RF plasma generates a wide range of non-equilibrium plasma, the rate of producing tetrahydroborate can be increased. The excitation frequency used to generate RF plasma is generally 13.56 MHz in Japan from the viewpoint of legal regulations.

The plasma may be equilibrium plasma. As a result, the plasma density and the ion temperature can be increased, so that the effect of cleaving the oxygen atom bond portion of the borate and dissociating the oxygen atom is enhanced. As a result, the rate of producing tetrahydroborate can be increased. In addition, since water generated by the bond between oxygen atoms dissociated from borate and plasma can be effectively evaporated or ionized by high energy, the produced tetrahydroborate reacts with water to borate. You can prevent it from returning to. As a result, the rate of producing tetrahydroborate can be increased.

The heat treatment step can be carried out while flowing the above mixture. This allows the mixture to be evenly treated with plasma.

When the heat treatment step is carried out while generating plasma in the system, the heat treatment step can be carried out while further supplying thermions. ^{Since hydride ions (H −} ) generated by the reaction between plasma and thermions promote hydrogenation of magnesium-based raw materials, the rate of producing magnesium hydride can be increased.

The mass ratio of magnesium hydride to the mass of the borate in the mixture of borate and magnesium hydride is preferably 1/5 to 5/1, more preferably 1/2 to 2/1. .. When the mass ratio is 1/5 or more, borate can be easily reduced or hydrogenated, while when it is 5/1 or less, the amount of magnesium hydride used can be suppressed and the cost can be easily reduced.

The mixture may further contain a hygroscopic agent. That is, borate may be subjected to heat treatment together with a hygroscopic agent. Examples of the hygroscopic agent include quicklime, silica gel, bentonite, magnesium chloride, calcium chloride and the like. Thereby, the heat treatment efficiency can be further improved.

(Preheating process)
The production method according to the present embodiment may further include a preheating step of heating the mixture before the heat treatment step. By this step, the water contained in the borate hydrate as water of crystallization can be removed in advance. Therefore, unnecessary water does not exist in the heat treatment step, the heat treatment efficiency can be improved, and the speed of producing tetrahydroborate can be increased.

The preheating step can be carried out under the conditions of, for example, 40 to 360 ° C. for 0.1 to 6 hours, depending on the type and amount of borate contained in the mixture.

(Borate preparation process)
The production method according to the present embodiment further includes a step of reacting tetrahydroborate with water to obtain borate before the heat treatment step (and before the preheating step if a preheating step is provided). Good. Tetrahydroborate is used as a hydrogen carrier, and hydrogen is extracted and used by adding water to tetrahydroborate at the hydrogen demand field, and then the boron salt, which is the residue generated in the chemical reaction, is returned to the hydrogen supply field. By hydrogenating again, tetrahydroborate can be regenerated. Since hydrogen can be transported and stored by repeatedly causing dehydrogenation and rehydrogenation, hydrogen can be transported and stored at low cost. For example, when sodium tetrahydroborate is used as the tetrahydroborate, the following reaction (2) is considered to occur in this step.
NaBH ₄ + 2H ₂ O → NaBO ₂ + 4H ₂ (2)

(Separation process)
In the object to be treated after the heat treatment step, tetrahydroborate, magnesium oxide, and in some cases unreacted magnesium hydride are mixed. Therefore, the production method according to the present embodiment may further include a separation step of separating the target tetrahydroborate from the object to be treated. Examples of the separation method (classification method) include a gravity classification method, an inertial classification method, and a centrifugal classification method.

<Borate and tetrahydroborate>
(Borate)
Examples of the borate include borates such as metaborate, tetraborate, and pentaborate. Examples of the metaborate include NaBO ₂ , KBO ₂ , LiBO ₂ , Ca (BO ₂ ) ₂ , Mg (BO ₂ ) _{2, and the} like. Examples of the _{tetraborate include Na 2} B ₄ O ₇ , Na ₂ O ・_{2 BO 3} , K ₂ O ・ B ₂ O ₃ , Li ₂ B ₄ O ₇ , Mg ₃ B ₄ O _{9 and the} like. Examples of the pentaborate include NaB ₅ O ₈ , Na ₂ O, 5B ₂ O ₃ , KB ₅ O ₈ , K ₂ O, 5B ₂ O ₉ , LiB ₅ O _{8, and the} like. Further, a natural borates Minerals _{Na 2 B 4 O 7 · 10H} 2 O, Na 2 B 4 O 7 · 4H 2 O, Ca 2 B 6 O 11 · 5H 2 O, CaNaB 5 O 9 · 6H 2 O , Mg ₇ Cl ₂ B ₁₇ O _{30 and the} like can also be used. Sodium metaborate may be used as the borate from the viewpoints of availability, acquisition cost, chemical stability, ease of hydrogen desorption, hydrogen storage density, and the like.

The borate can be in powder form from the viewpoint of further improving the heat treatment efficiency. At that time, the average particle size of borate can be 500 μm or less, and may be 100 μm or less. The lower limit is not particularly limited, but can be 0.1 μm.

(Tetrahydroborate)
Examples of the tetrahydroborate include hydrides corresponding to the borates exemplified above. For example, when metaborate is used as the borate _{, NaBH 4 , KBH 4} , LiBH ₄ , Ca (BH ₄ ) ₂ , Mg (BH ₄ ) _{2, and the} like can be mentioned.

<Tetrahydroborate production equipment>
FIG. 1 is a schematic view showing an example of an apparatus for producing tetrahydroborate. The apparatus 100 shown in FIG. 1 includes a reaction vessel 10 designed so that the atmosphere and pressure can be adjusted, and a sample holder 11 provided in the reaction vessel 10 on which a mixture (mixture of a cylinder and magnesium hydride) S can be placed. An infrared heating device 12 provided outside the reaction vessel 10 for heating the sample holder 11, a glass conduction rod 13 for conducting infrared rays from the infrared heating device 12 to the sample holder 11, and a mixture S in the sample holder 11 are allowed to flow. A vibration generator 14 for this purpose, a vacuum pump 16 attached to the reaction vessel 10 via a pipe 15 and capable of exhausting the atmosphere in the reaction vessel 10, and a filament 17 for generating thermoelectrons in the reaction vessel 10 are provided. It includes a borate treatment mechanism and a raw material gas supply mechanism including an ammonia gas cylinder 30, a hydrogen gas cylinder 31, and a hydrogen mixed gas cylinder 32.

Further, in order to generate plasma as needed, the apparatus 100 includes a microwave oscillator 20, an isolator 21, a power monitor 22, a tuner 23, and a microwave generation mechanism and a microwave generation mechanism including a rectangular coaxial waveguide converter 24. The flexible coaxial waveguide 40 for conducting the microwave oscillated from the above to the borate treatment mechanism is provided between the flexible coaxial waveguide 40 and the reaction vessel 10, and the microwave can propagate while shielding the atmosphere. A quartz plate (dielectric) 41 and a pipe 42 for supplying the raw material gas supplied from the raw material gas supply mechanism to the borate treatment mechanism are provided.

When plasma is generated, the introduced raw material gas is reduced to a predetermined pressure in the reaction vessel 10, and the electrons accelerated by the electric field due to the microwave and the raw material gas molecules collide with each other to generate plasma P. appear. As a result, the mixture of borate and magnesium hydride is heat-treated and plasma-treated to obtain tetrahydroborate.

Hereinafter, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited to these Examples.

(Experimental Example 1)
Tetrahydroborate was produced using the apparatus shown in FIG. NaBO ₂ · _{4H 2} O as the borate (meth sodium borate tetrahydrate: Kishida Chemical Co., Ltd., content of 98 wt%) was prepared. This was pulverized with a ball mill and heated at 360 ° C. for 2 hours to remove water of crystallization _{to obtain powdered NaBO 2} (anhydrous sodium metaborate). The average particle size of powdered NaBO _{2 was 100 μm.} The average particle size was measured with a digital microscope.

Next, 1.0 g of _{powdered NaBO 2 is weighed, and 0.8 g of MgH 2} (magnesium hydride: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number 137-17391) powder is added thereto to prepare a mortar and pestle. Used to stir and mix. The obtained mixture (Sample S) was placed on the sample holder 11, and the sample holder 11 was placed in the reaction vessel 10. As the reaction vessel 10, a vessel having a volume of 2.5 L was used. The inside of the reaction vessel 10 ^{was evacuated to 10 -4} Pa, and ammonia gas was supplied into the reaction vessel 10 after adjusting the flow rate to 50 sccm. Then, the exhaust speed was adjusted so that the pressure in the reaction vessel 10 was maintained at 110 Pa. The power of the infrared heating device 12 was turned on, and the sample S was heated to 400 ° C. via the glass conduction rod 13 and the sample holder 11.

During the heat treatment, the sample holder 11 was vibrated by the vibration generator 14 to cause the sample S to flow. The heat treatment time was 30 minutes.

After the elapse of the predetermined processing time, the power of the vibration generator 14 and the infrared heating device 12 was turned off, and the supply of ammonia gas was stopped. Then, the inside of the reaction vessel 10 was released to the atmosphere, and the heat-treated sample was taken out.

(Experimental Example 2)
Tetrahydroborate was produced in the same manner as in Experimental Example 1 except that the heat treatment of Sample S was carried out while generating plasma in the reaction vessel 10. Specifically, the power of the microwave oscillator 20 was turned on, and a microwave having a frequency of 2.45 GHz was incident on the reaction vessel 10. At that time, the tuner 23 was adjusted so that the microwave reflected power was minimized. The microwave incident power was 350 W and the microwave reflected power was 70 W. Ammonia plasma excited by microwaves was generated in the reaction vessel 10, and the sample S placed on the sample holder 11 was subjected to plasma treatment together with heat treatment.

After the elapse of the predetermined processing time, the power of the microwave oscillator 20, the vibration generator 14, and the infrared heating device 12 was turned off, and the supply of ammonia gas was stopped. Then, the inside of the reaction vessel 10 was released to the atmosphere, and the heat-treated sample was taken out.

(Evaluation)
The infrared absorption spectrum of the sample was measured using a Fourier transform infrared spectrophotometer FT / IR-6300 (manufactured by Nippon Spectroscopy Co., Ltd., product name). As a result of the measurement, in all the experimental examples, the peak of BO bond derived from anhydrous sodium metaborate decreased, and the peak of B—H bond derived from sodium tetrahydroborate increased. From this, it was confirmed that sodium tetrahydroborate can be obtained by heat-treating anhydrous sodium metaborate together with magnesium hydride.

10 ... Reaction vessel, 11 ... Sample holder, 12 ... Infrared heating device, 13 ... Glass conduction rod, 14 ... Vibration generator, 15 ... Piping, 16 ... Vacuum pump, 17 ... Filament, 20 ... Microwave oscillator, 21 ... Isolator , 22 ... Power monitor, 23 ... Tuner, 24 ... Rectangular coaxial waveguide converter, 30 ... Ammonia gas bomb, 31 ... Hydrogen gas bomb, 32 ... Hydrogen mixed gas bomb, 40 ... Flexible coaxial waveguide, 41 ... Quartz plate (dielectric) ), 42 ... Piping, 100 ... Tetrahydroborate production equipment, P ... Plasma, S ... Mixture.

Claims (6)

A method for producing tetrahydroborate, which comprises a heat treatment step of heating a mixture of borate and magnesium hydride to 350 ° C. or higher in a gas atmosphere containing hydrogen (H) as a constituent element. The production method according to claim 1, wherein the heat treatment step is carried out while flowing the mixture. The production method according to claim 1 or 2, wherein the heat treatment step is carried out while exposing the mixture to plasma. The production method according to any one of claims 1 to 3, wherein the average particle size of the borate is 500 μm or less. The production method according to any one of claims 1 to 4, wherein the borate is sodium metaborate. The production method according to any one of claims 1 to 5, further comprising a borate preparation step of reacting tetrahydroborate with water to obtain borate before the heat treatment step.

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