Hydrogen storage fuel and method for producing same

Abstract

The technical problem to be addressed by the present invention is to provide a hydrogen storage fuel that has improved handling safety and is in a form suitable for storage and transportation. The hydrogen storage fuel is constituted in such a manner that ammonia (NH3) constituting a hydrogen storage medium is confined in the form of a solid cubic crystal in a borate glass matrix (B2O3-B(OH)3). The hydrogen storage medium is produced by: mixing diboron trioxide (B2O3) with an aqueous solution having ammonia (NH3) dissolved therein to prepare a mixed aqueous solution; and then freezing the mixed aqueous solution to produce a frozen solidified material. Subsequently, the frozen solidified material is freeze-dried, then water vapor (H2O) contained in the form of a gas and a boron compound (BHO) contained in the form of a gas in the frozen solidified material are discharged to concentrate ammonia (NH3) in the frozen solidified material, so that ammonia (NH3) is confined in the form of a solid cubic crystal in the borate glass matrix (B2O3-B(OH)3) under ambient temperature and ambient pressure.

Description

Hydrogen storage fuel and its manufacturing method

[0001] The present invention relates to a hydrogen storage fuel using ammonia, which is a hydrogen-containing compound, and a method for producing the hydrogen storage fuel.

[0002] Traditionally, reducing carbon dioxide emissions has been required to curb environmental destruction. To reduce carbon dioxide emissions, efforts are being made to supply renewable energy (natural energy) using solar and wind power. However, these natural energy sources have several limitations. Because electricity generated by solar and wind power depends on weather, it is difficult to ensure a stable supply that matches demand. Furthermore, there are geographical limitations to installing the necessary equipment. Therefore, it is necessary to develop energy storage technologies so that natural energy can be used when needed. One promising energy storage technology is the production of hydrogen through water electrolysis. Hydrogen can be converted into electricity using fuel cells and can also be directly burned as an alternative to fossil fuels. However, gaseous hydrogen has a low energy density due to its large volume, making it difficult to store and transport. Furthermore, liquid hydrogen must be stored at temperatures below 20 K, which poses a cost problem.

[0003] Therefore, as a hydrogen storage material that solves the problems of gaseous hydrogen, a material with a high density per volume and mass, which produces carbon dioxide (CO ) when burned, has been developed. ２ Ammonia, a hydrogen-containing compound that does not emit CO₂, has been attracting attention. Ammonia becomes liquid at 298 K and approximately 8 atmospheres, so it can be stored in a cylinder as a liquid at room temperature. It is expected that ammonia can be used directly as fuel for ammonia power generation and ammonia engines.

[0004] Ammonia can be synthesized on a large scale from atmospheric nitrogen and hydrogen using iron as a catalyst at high temperature and pressure by the Haber-Bosch process, which has led to the mass production of fertilizer to increase food production. In addition, a method has been developed to synthesize ammonia at low pressure by improving the Haber-Bosch process and using lithium (Li) compounds as catalysts. Furthermore, research is being conducted on the generation of ammonia on a small scale using ubiquitous natural energy. That is, nitrogen gas (N ２As a method for cleaving the strong N-N bond in (g)) to produce ammonia, methods using electric fields, discharges, and catalytic surface plasmon resonance are being investigated.

[0005] In the reverse reaction of the above, when an appropriate catalyst, such as zeolite (Zeolite) carrying nickel (Ni) or ruthenium (Ru), calcium hydrogen nitride (CaNH), or porous silica is used as a catalyst, ammonia can be converted into hydrogen gas (H ２ (g)) and nitrogen gas (N ２ (g)) can be converted back to hydrogen (H ２ ) can be collected.

[0006] Ammonia produced from hydrogen and atmospheric nitrogen using natural energy-based water electrolysis is called green ammonia. Green ammonia is expected to be an alternative energy source to fossil fuels and is attracting attention as a fuel for internal combustion engines and power generation systems.

[0007] In addition, a method for synthesizing ammonia that replaces the Haber-Bosch process has been proposed, as described in Patent Document 1.

[0008] An ammonia engine system that uses ammonia as fuel is disclosed in Patent Document 2.

[0009] International Publication No. 2014 / 115582 Pamphlet International Publication No. 2010 / 058807 Pamphlet

[0010] Incidentally, when liquid ammonia is discharged from a cylinder, it immediately vaporizes and becomes gaseous ammonia. Gaseous ammonia can easily be inhaled into the body, irritating the mucous membranes of the respiratory organs and potentially causing respiratory arrest due to shock. When inhaled into the body, it can increase the ammonia concentration in the body's blood, potentially causing loss of consciousness. Furthermore, if it gets into the eyes, it can cause eye damage.

[0011] As described above, gaseous ammonia is a substance that is extremely harmful to living organisms, and is difficult to store, manage, and transport, making it difficult to use as a widely applicable energy carrier.

[0012] In addition, when ammonia is cooled to 195.5 K or less under atmospheric pressure, it becomes a stable solid, its sublimation vapor pressure is reduced to 0.0609 bar, and it becomes odorless. Therefore, by being a stable solid at room temperature, ammonia can be safely stored and transported as a storage material for hydrogen, which is expected to be a new energy source.

[0013] Therefore, the technical object of the present invention is to provide a new hydrogen storage fuel that can solve the problems associated with ammonia, which constitutes a hydrogen storage medium and is a deleterious substance that is dangerous to living organisms, difficult to store, and difficult to transport.

[0014] Furthermore, a technical object of the present invention is to provide a hydrogen storage fuel that can be used safely and is in a form suitable for storage and transportation.

[0015] Furthermore, other technical objects of the present invention will become more apparent from the following description with reference to the drawings.

[0016] The present invention is a novel solid hydrogen storage fuel that was completed as a result of intensive research by the present inventors in order to solve the above-mentioned technical problems, and is a hydrogen storage medium made of ammonia (NH ３ ) as a solid cubic crystal, and a borate glass matrix (B ２ O ３ -B(OH) ３ ) is trapped inside.

[0017] By the way, ammonia (NH ３ As shown in the phase diagram in Figure 1, the triple point temperature (T) is 195.5 K and the pressure (p) is 0.0609 bar. As shown in this phase diagram, ammonia (NH ３ ) is a solid cubic crystal (cubic-(NH)) at low temperatures below 195.5 K and under pressures above 0.0609 bar. ３ ) (cr)) can exist stably.

[0018] In addition, ammonia (NH ３) cannot exist in a solid form at room temperature and pressure, as shown in the pressure-temperature phase diagram of FIG.

[0019] Therefore, the present inventors have investigated the mechanism of the reaction of ammonia (NH ３ ) into a solid cubic crystal (cubic-(NH ３ We have been studying the medium to confine the material as a borate glass matrix (B ) (cr) ２ O ３ -B(OH) ３ ) was conceived. ２ O ３ -B(OH) ３ ) is diboron trioxide (B ２ O ３ It is produced by dehydrating an aqueous solution of diboron trioxide (B ２ O ３ When an aqueous solution of boron trioxide (B ２ O ３ ) component and orthoboric acid component (B(OH) ３ ) can be used as a base structure to prepare a glass matrix. ２ O ３ (gl)-B(OH) ３ It is written as (gl).

[0020] In this solution, ammonia (NH ３ ) is a cubic crystal (cubic-(NH ３ ) (cr)) and the borate glass matrix (B ２ O ３ -B(OH) ３ ) (gl)), it becomes possible for it to exist stably in a solid state at room temperature and pressure.

[0021] Solidified cubic ammonia (cubic-(NH ３ ) (cr)) is a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) to form a core-shell structure.３ ) (cr)) and a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ At the interface of the solid ammonia cubic crystal (cubic-(NH ３ )(cr))standard Gibbs energy of formation (Δ f G ° m ) and the Gibbs energy of this interface (Δ boundary G ° m ) is the sum of the gaseous ammonia (NH ３ (g)) Gibbs energy (Δ f G ° m ) and ammonia (NH ３ ) maintains a stable solid cubic crystal structure at room temperature and pressure.

[0022] Δ f G ° m (NH ３ (cr)) + Δ boundary G ° m <Δ f G ° m (NH ３ (g)), T / K>298.15...(1)

[0023] The borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) in which solid cubic ammonia (cubic-(NH ３ ) (cr)) is a hydrogen storage fuel that contains ammonia (NH ３ ) dissolved in an aqueous solution of diboron trioxide (B ２ O ３ ) can be mixed and freeze-dried to prepare a mixed aqueous solution.

[0024] Here, ammonia (NH ３ ) is an ammonium ion (NH ４＋ When this mixed aqueous solution is frozen and solidified using liquid nitrogen as a refrigerant, ammonia (NH ３ ) is the water component (H ２ O) freezes into a solid (ice) (H ２ 0(cr)) matrix, solid ammonium ions (NH ４ ＋ At low temperatures, when the mixed solution is frozen, the solid ammonium ions (NH ４ ＋ (cr)) is ammonia gas (NH ３ In order for the water component (H ２ O) is a solid ice (H ２ Hydroxide ions (OH) in O(cr) － However, when the mixed solution is frozen at low temperatures, the hydroxide ions (OH － (cr)) cannot move. As a result, solid ammonium ions (NH ４ ＋ (cr)) is concentrated without sublimation.

[0025] The frozen solidified mixture of the aqueous solution is then dried in a vacuum suctioned reduced pressure atmosphere. In this drying process, sublimated water vapor (H ２ O(g)) and diboron trioxide (B ２ O ３ The boron compound (BHO(g)) derived from the mixed aqueous solution is completely evacuated. The water vapor (H ２ When all the ammonium ions (NH O(g)) and boron compounds (BHO(g)) are exhausted, solid ammonium ions (NH ４ ＋ As shown in the schematic diagram of Figure 2, the borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) contains cubic ammonia (NH ３ (cr)).

[0026] In addition, the borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) is a solid product at room temperature and pressure.

[0027] Through the treatment process described above, ammonia (NH ３ ) as a solid cubic crystal in a borate glass matrix (B ２ O ３ -B(OH) ３ This product constitutes a hydrogen storage fuel that carries hydrogen in the form of ammonium.

[0028] By the way, ammonia (NH ３ ) dissolved in an aqueous solution of diboron trioxide (B ２ O ３ When the mixed aqueous solution containing ammonium pentaborate and ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) and ammonia borane (NH ３ BH ３ Therefore, the hydrogen storage fuel produced by freeze-drying this mixed aqueous solution contains ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) and ammonia borane (NH ３ BH ３ In this method, ammonia (NH ３ ) dissolved in an aqueous solution of diboron trioxide (B ２ O ３ The mixed aqueous solution containing boron (B) and nitrogen (N) is mixed with the ammonia (NH ３ The diboron trioxide (B ２ O ３ ) is preferably mixed.

[0029] The hydrogen storage fuel according to the present invention is hydrogen (H ２) as a storage medium for ammonia (NH ３ ) in a stable solid state at room temperature and atmospheric pressure, and a boric acid glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) allows for safe storage and also allows for safe and easy transportation.

[0030] Solid ammonia (NH ３ ) can be used as a hydrogen storage fuel and as a hydrogen energy carrier that can be widely and generally used, and is useful as a fuel for ammonia engine systems, ammonia power generation systems, and other ammonia-fueled equipment.

[0031] Ammonia (NH ３ ) pressure-temperature phase diagram. ３ ) is a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) solid cubic ammonia (NH ３ FIG. 1 is a schematic diagram showing a core-shell structure in which ammonia (NH ３ ) in an aqueous solution of diboron trioxide (B ２ O ３ 1 is a photograph showing the appearance of a hydrogen storage fuel that has been solidified by freeze-drying a mixed aqueous solution containing a mixture of ammonia cubic crystals (NH ３ 1 is a graph showing the relationship between the diffraction angle (θ) of the peaks of the (111), (210) and (211) planes of (cr) and the lattice constant. 2 is a graph showing the temperature-weight change of the hydrogen storage fuel according to the present embodiment.

[0032] Hereinafter, a hydrogen storage fuel and a method for producing the same according to the present embodiment will be described with reference to the drawings.

[0033] The hydrogen storage fuel according to this embodiment is ammonia (NH ３ ) is a solid cubic crystal at room temperature and pressure, and is contained in a borate glass matrix (B ２ O ３ -B(OH) ３ (gl)) and is composed of the

[0034] Incidentally, ammonia (NH ３ ) is assumed to have a triple point temperature (T) of 195.5 K and a pressure (p) of 0.0609 bar, as shown in the pressure-temperature phase diagram of FIG. 1. ４ ) is converted to ammonia (NH ３ ) is a solid cubic crystal (cubic-(NH)) at low temperatures below 195.5 K and under pressures above 0.0609 bar. ３ ) (cr)) can exist stably. Therefore, ammonia (NH ３ As shown in the phase diagram in Figure 1, ZnO cannot exist as a solid cubic crystal at room temperature and pressure.

[0035] In this embodiment, ammonia (NH ３ ) into a solid cubic crystal (cubic-(NH ３ ) (cr)) as a borate glass matrix (B ２ O ３ -B(OH) ３ (gl)) is a hydrogen storage fuel that can exist stably in a solid state at room temperature and pressure.

[0036] The hydrogen storage fuel according to this embodiment is produced using a production apparatus shown in Fig. 3. As shown in Fig. 3, this production apparatus adds diboron trioxide (B ２ O ３The system comprises a reaction vessel 1 into which an aqueous solution containing the (cr) powder is poured, a copper vacuum chamber 2 in which the reaction vessel 1 is housed, and a main cooling chamber 3 filled with liquid nitrogen. The vacuum chamber 2 is placed inside the main cooling chamber 3, which is filled with liquid nitrogen with a boiling point of 77.5 K, and is cooled together with the reaction vessel 1 by the liquid nitrogen filled in the main cooling chamber 3.

[0037] The vacuum chamber 2 housing the reaction vessel 1 is connected to the outside of the main cooling chamber 3 via an exhaust valve 4. The exhaust valve 4 is attached to hermetically seal the main cooling chamber 3. This exhaust valve 4 opens and closes the vacuum chamber 2 by operating an on-off valve provided inside.

[0038] A vacuum pump 5 is connected to the vacuum chamber 2. A gas trap mechanism 6 is provided between the vacuum pump 5 and the vacuum chamber 2. This gas trap mechanism 6 is installed in an auxiliary cooling chamber 7 and is cooled by liquid nitrogen filled in the auxiliary cooling chamber 7. The vacuum chamber 2 and the gas trap mechanism 6 are connected via a connecting pipe 8. One end of this connecting pipe 8 is connected to the vacuum chamber 2 via an exhaust valve 4, and the other end passes through the auxiliary cooling chamber 7 and is inserted into the gas trap mechanism 6, thereby connecting the main cooling chamber 3 and the gas trap mechanism 6.

[0039] The vacuum pump 5 is connected to the gas trap mechanism 6 via a vacuum pump connecting pipe 9. One end of the vacuum pump connecting pipe 9 is connected to the vacuum pump 5, and the other end passes through the auxiliary cooling tank 7 and is inserted into the gas trap mechanism 6, connecting the vacuum pump 5 and the exhaust gas trap mechanism 6.

[0040] Therefore, the inside of the vacuum chamber 2 is suctioned and depressurized by the vacuum pump 5 via the gas trap mechanism 6. The gas sucked from the vacuum chamber 2 by driving the vacuum pump 5 is discharged to the outside of the vacuum chamber 2 via the exhaust valve 4, introduced into the gas trap mechanism 6 via the connecting pipe 8, and cooled by the liquid nitrogen filled in the auxiliary cooling tank 7.

[0041] A rubber cap 10 is provided on the top of the reaction vessel 1 placed in the vacuum chamber 2. A minute through-hole 11 is formed in this cap 10. When the inside of the vacuum chamber 2 is evacuated, the reaction vessel 1 is evacuated through the through-hole 11 in a state cooled by the liquid nitrogen filled in the main cooling tank 3.

[0042] The process of producing the hydrogen storage fuel according to this embodiment using the production apparatus having the above-described configuration will be described.

[0043] First, the starting material, ammonia (NH ３ ) aqueous solution and diboron trioxide (B ２ O ３ (cr)) powder was prepared and added to the ammonia water. ２ O ３ (cr) Prepare a mixed aqueous solution by mixing the powders.

[0044] In this embodiment, solid cubic ammonia (cubic-(NH ３ ) (cr)) in a borate glass matrix (B ２ O ３ -B(OH) ３ In order to confine the carbon nanotubes in the core-shell structure shown in Figure 2, it is desirable to form sufficient B-N bonds. Therefore, the mixed aqueous solution is prepared by adding ammonia (NH ３ ) aqueous solution (ammonia water) and diboron trioxide (B ２ O ３ (cr)) is adjusted so that the amount of boron and nitrogen is 4.6 × 10 －３ Adjust to make it molar.

[0045] In this embodiment, the mixed aqueous solution contains ammonia (NH ３ Ammonia water containing 29 wt% of boron trioxide (B) with a purity of 99.9% was used. ２ O ３ (Cr) powder was used. Then, ammonia water and diboron trioxide (B ２ O ３The boron (B) and nitrogen (N) powders are mixed in a mixed aqueous solution so that the ratio of boron (B) to nitrogen (N) in the mixed aqueous solution is 1:1. In this embodiment, the mixed aqueous solution is a solution of 0.3 mL of ammonia water and 0.5 mL of diboron trioxide (B ２ O ３ (cr)) powder 160 mg was mixed.

[0046] In addition, ammonia water and diboron trioxide (B ２ O ３ The boron (B) and nitrogen (N) powders may be mixed in an appropriate ratio so long as the ratio of boron (B) to nitrogen (N) in the mixed aqueous solution is approximately 1:1. For example, ammonia water can be mixed with ammonia (NH ３ ) at a ratio of 20 to 30 wt%, and ２ O ３ The purity of the (cr) powder used is in the range of 95 to 99.9%.

[0047] The mixed aqueous solution used in this embodiment contains diboron trioxide (B ２ O ３ (cr)) powder is charged into a reaction vessel 1, and ammonia water is poured into the reaction vessel 1 to prepare the powder.

[0048] The upper opening of the reaction vessel 1 filled with the mixed aqueous solution prepared by injecting the ammonia water is covered with a cap 10 .

[0049] The reaction vessel 1 filled with the mixed aqueous solution is placed in the vacuum chamber 2 of the manufacturing apparatus described above. The vacuum chamber 2 containing the reaction vessel 1 is placed in a main cooling chamber 3 filled with liquid nitrogen having a boiling point of 77.5K.

[0050] Next, the main cooling tank 3 is filled with liquid nitrogen, and the vacuum tank 2 installed in the main cooling tank 3 and the reaction vessel 1 housed in the vacuum tank 2 are cooled. At this time, the mixed aqueous solution in the reaction vessel 1 contains at least ammonia (NH ３ The mixed aqueous solution is then cooled to a temperature of 195.5K or lower, at which point the solution solidifies, and frozen into a solidified mass. The frozen state of the mixed aqueous solution in the reaction vessel 1 is then maintained for 1 to 2 hours.

[0051] Thereafter, the exhaust valve 4 provided on the vacuum chamber 2 is opened, and the vacuum pump 5 is driven to evacuate the inside of the vacuum chamber 2 and reduce the pressure. This evacuation is carried out for an appropriate time in the range of 2 to 5 hours. When the vacuum chamber 2 is evacuated, the inside of the reaction vessel 1 is also evacuated and reduced in pressure through the through-hole 11 provided in the cap 10. By evacuating the reaction vessel 1, the mixed aqueous solution frozen and solidified in the reaction vessel 1 is freeze-dried.

[0052] When the frozen solidified material in the reaction vessel 1 is freeze-dried, the frozen solidified material sublimes and generates sublimation water vapor (H ２ O(g)) is exhausted to the outside of the reaction vessel 1 through the through-hole 11, and is then suctioned into the vacuum chamber 2, and is then exhausted to the outside of the vacuum chamber 2 through the exhaust valve 4. Then, sublimated water vapor (H ２ O(g)) is discharged, thereby concentrating the ammonia component contained in the frozen solid.

[0053] In this embodiment, when the frozen solidified material in the reaction vessel 1 is freeze-dried, gaseous hydrogen nitride (NH(g)) and boron compounds (BHO(g)) are inevitably generated. These hydrogen nitride (NH(g)), boron compounds (BHO(g)) and sublimated water vapor (H ２ The hydrogen nitride (NH(g)), boron compound (BHO(g)), and sublimated water vapor (H O(g)) introduced into the gas trap mechanism 6 are sucked in by the vacuum pump 5, exhausted to the outside of the vacuum chamber 2 through the exhaust valve 4, and then discharged to the outside of the vacuum chamber 2 through the connecting pipe 8, and introduced into the gas trap mechanism 6. ２ O(g)) is cooled and frozen by liquid nitrogen filled in the auxiliary cooling tank 7 in which the gas trap mechanism 6 is installed, and is recovered as ammonia borate water.

[0054] That is, by cooling the gas trap mechanism 6 with liquid nitrogen, hydrogen nitride (NH(g)), boron compound (BHO(g)), and sublimed water vapor (H ２ O(g)) is coagulated to form an ammoniacal borate solution, which is then removed from the processing system where the mixed aqueous solution is freeze-dried.

[0055] After the freeze-drying process of the mixed aqueous solution filled in the reaction vessel 1 is carried out for an appropriate period of 2 to 5 hours, the vacuum chamber 2 with the reaction vessel 1 stored therein is removed from the main cooling chamber 3 and collected. The vacuum chamber 2 is subjected to a sudden change in temperature when it is removed from the main cooling chamber 3. The sudden change in temperature of the vacuum chamber 2 may cause condensation inside, which may cause the frozen solid inside the reaction vessel 1 to absorb moisture.

[0056] Therefore, in this embodiment, the vacuum chamber 2 is removed from the main cooling chamber 3 with the exhaust valve 4 closed and its interior evacuated. The vacuum chamber 2 is then maintained in an evacuated state for a period of time sufficient for the interior of the reaction vessel 1 housed therein to reach room temperature. In this embodiment, the vacuum chamber 2 is maintained in an evacuated state for at least 2-3 hours, thereby preventing sudden temperature changes and suppressing the occurrence of condensation. By suppressing condensation within the vacuum chamber 2, the frozen solidified material within the reaction vessel 1 is prevented from becoming wet, and the freeze-dried state can be maintained.

[0057] Then, when the temperature inside the vacuum chamber 2 has sufficiently reached room temperature, the reaction vessel 1 is removed from the vacuum chamber 2. The product of the mixed aqueous solution freeze-dried in the reaction vessel 1 is collected as a powdery solid.

[0058] The starting material for the solidified body produced in this embodiment is ammonia water, and diboron trioxide (B ２ O ３ When the mixed aqueous solution containing ammonia (cr) is freeze-dried, the ammonia water turns into solid ammonia cubic crystals (cubic-(NH ３ ) (cr)) is produced, and diboron trioxide (B ２ O ３ (cr)) to B ２ O ３ component and orthoboric acid component (B(OH) ３ ) borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) is generated.

[0059] The mixed aqueous solution was freeze-dried to produce solid cubic ammonia (cubic-(NH３ ) (cr)) and a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ In the solidified body consisting of the boron nitride (BN) and boric acid glass matrix (B), the N atoms and B atoms are strongly bonded to each other to form boron nitride (BN). ２ O ３ (gl)-B(OH) ３ (gl)) forms a strong B—N bond at the glass interface.

[0060] As mentioned above, cubic ammonia (cubic-(NH ３ )(cr))standard Gibbs energy of formation (Δ f G ° m ) and a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) Gibbs energy (Δ boundary G ° m ) is the sum of the gaseous ammonia (NH ３ (g)) standard Gibbs energy of formation (Δ f G ° m ) has a deeper negative value than the cubic ammonia (cubic-(NH ３ )(cr)) is a stable solid with a cubic crystal structure at room temperature and pressure.

[0061] Therefore, the ammonia (NH ３ ) dissolved in an aqueous solution of diboron trioxide (B ２ O ３ The solidified material produced by freeze-drying the mixed aqueous solution containing ammonia (NH ３ ) is solidified as a cubic crystal at room temperature and pressure, and a borate glass matrix (B ２ O ３ -B(OH) ３ (gl)). This solidified body constitutes a hydrogen storage fuel with solid ammonia as the water storage medium. This hydrogen storage fuel is used as fuel for ammonia engine systems, ammonia power generation systems, and other ammonia-fueled equipment.

[0062] Next, an example of a hydrogen storage fuel according to the present invention will be described. The example shown below is ammonia (NH ３ ) in a solid state, and the present invention is not limited to this example.

[0063] In this example, ammonia (NH ３ ) and diboron trioxide (B) with a purity of 99.9%. ２ O ３ (cr)) powder was prepared and dissolved in ammonia water. ２ O ３ The mixed aqueous solution was prepared by mixing diboron trioxide (B(cr)) powder with the reaction vessel 1 used in the manufacturing apparatus shown in FIG. ２ O ３ (cr)) powder and then ammonia water is injected.

[0064] Here, ammonia water and diboron trioxide (B ２ O ３ The boron (B) and nitrogen (N) powders were mixed so that the ratio of boron (B) to nitrogen (N) in the mixed aqueous solution was 1:1. That is, in the mixed aqueous solution of this example, the amounts of boron (B) and nitrogen (N) were both 4.6 × 10 －３ Diboron trioxide (B) was added to 0.3 mL of ammonia water to obtain 1 mole. ２ O ３ (cr)) powder 160 mg was mixed.

[0065] Then, the reaction vessel 1 filled with the mixed aqueous solution has a cap 10 placed on the upper opening, and is housed and placed in the vacuum chamber 2 of the manufacturing equipment. The vacuum chamber 2 in which the reaction vessel 1 is placed is placed in the main cooling chamber 3 filled with liquid nitrogen. At this time, the exhaust valve 4 of the vacuum chamber 2 is closed and the vacuum chamber 2 is placed in a sealed state. Next, the main cooling chamber 3 is filled with liquid nitrogen having a boiling point of 77.5 K, and the vacuum chamber 2 and the reaction vessel 1 placed in this vacuum chamber 2 are cooled. At this time, the mixed aqueous solution in the reaction vessel 1 contains at least ammonia (NH ３The mixed aqueous solution was then cooled to 195.5 K or below, at which point the solution solidifies, and frozen into a solidified body. The frozen state of the mixed aqueous solution in the reaction vessel 1 was then maintained for one hour.

[0066] Thereafter, the exhaust valve 4 provided on the vacuum chamber 2 was opened, and the vacuum pump 5 was driven to evacuate and reduce the pressure inside the vacuum chamber 2 for two hours. When the vacuum chamber 2 was evacuated, the inside of the reaction vessel 1 was also evacuated and reduced in pressure through the through-hole 11 provided in the cap 10. By evacuating the reaction vessel 1, the frozen solidified mixture of the aqueous solution frozen and solidified inside the reaction vessel 1 is freeze-dried.

[0067] When the frozen solidified material in the reaction vessel 1 is freeze-dried, the frozen solidified material sublimes and generates sublimation water vapor (H ２ O(g)) is exhausted to the outside of the reaction vessel 1 through the through-hole 11, and is then suctioned into the vacuum chamber 2, and is then exhausted to the outside of the vacuum chamber 2 through the exhaust valve 4. Then, sublimated water vapor (H ２ O(g)) is discharged, thereby concentrating the ammonia component contained in the frozen solid.

[0068] In this embodiment, when the frozen solid in the reaction vessel 1 is freeze-dried, gaseous hydrogen nitride (NH(g)) and boron compounds (BHO(g)) are inevitably generated. These hydrogen nitride (NH(g)), boron compounds (BHO(g)) and sublimated water vapor (H ２ The hydrogen nitride (NH(g)) and boron compound (BHO(g)) introduced into the gas trap mechanism 6 are mixed with the sublimated water vapor (H ２ O(g)) is cooled and frozen by liquid nitrogen filled in the auxiliary cooling tank 7 in which the gas trap mechanism 6 is installed, and is recovered as ammonia borate water. The recovered ammonia borate water is taken out of the processing system in which the mixed aqueous solution is freeze-dried.

[0069] After the freeze-drying process of the mixed aqueous solution filled in the reaction vessel 1 described above is carried out for two hours, the vacuum chamber 2 with the reaction vessel 1 housed therein is removed to the outside of the main cooling chamber 3 and recovered. At this time, the vacuum chamber 2 is removed from the main cooling chamber 3 with the exhaust valve 4 closed and the inside of the vacuum chamber 2 evacuated to a vacuum. The vacuum chamber 2 is maintained in an evacuated state for a time period until the inside of the reaction vessel 1 housed therein reaches room temperature sufficiently. In this example, the vacuum chamber 2 is maintained in an evacuated state for at least two hours, and when the inside of the vacuum chamber 2 reaches room temperature sufficiently, the reaction vessel 1 housed in the vacuum chamber 2 is removed. The product of the mixed aqueous solution freeze-dried in the reaction vessel 1 is recovered as a white powdery solid, as shown in the photograph in FIG. 4. Commercially available ammonia water contains vaporized ammonia (NH ３ Although the solid ammonia (NH4) produced in this example has a strong pungent odor, ３ The product, which was mainly composed of (cr), was odorless.

[0070] The product produced as a white powder solid was ground into a fine powder and identified by X-ray diffraction (XRD). The X-ray diffraction (XRD) pattern of this product at 297 K was shown in Figure 5 (a), and the main product was solid ammonia (NH ３ That is, the X-ray diffraction (XRD) pattern of the product, which shows a main peak at a diffraction angle (2θ) of 30.00 deg, corresponds to that of solid ammonia (NH ), which is shown by Olovson and Templeton using a low-temperature in situ XRD method at 77 K, the boiling point of liquid nitrogen. ３ (cr)) matched the shape.

[0071] At atmospheric pressure (1 atm), ammonia (NH ３ It was confirmed that solid ammonia (NH3), the main product produced in this example, exists as a stable solid even at room temperature. ３ The lattice constant of (cr) was investigated.

[0072] First, solid ammonia (NH３ (cr)) has a cubic ammonia crystal structure, and this ammonia cubic (NH ３ The lattice constant (a) was calculated from the peak diffraction angles (θ) of the (111), (210) and (211) planes of the crystal (cr) according to the following formula (2): ２ θ=λ ２ / 4a ２ ・(h ２ +k ２ +l ２ ) ... (2)

[0073] Here, the wavelength of Kα rays emitted from pure copper (Cu) used in the X-ray diffraction (XRD) method is 0.154056 nm. h, k, and l are plane indices. ３ The lattice constant was calculated by extrapolating the results obtained from the diffraction angles (θ) of the peaks of the (111), (210) and (211) planes of (cr) up to 90 degrees. That is, as shown in FIG. 6, the lattice constant obtained from each plane was multiplied by 1 / 2 (cos ２ The lattice constant was determined by plotting the angle of the crystal grains against the angle (θ / sinθ+cos2θ / θ) and extrapolating it up to 90 degrees by the least squares method.

[0074] The main product produced in this example was solid cubic solid ammonia (NH ３ The lattice constants of solid cubic ammonia (NH ３ The lattice constants of the Cr-based alloys were compared with those of the Cr-based alloys.

[0075] The solid cubic solid ammonia (NH ３ The lattice constant of (cr) was 0.5165 nm, which agreed well with the lattice constants of 0.5138 nm and 0.5073 nm determined by in situ XRD at 171 K and 77 K reported by Olovoson and Templeton.

[0076] The lattice constant in this example is 0.0027 nm larger than the lattice constant at 171 K shown by Olovoson and Templeton. This is believed to be due to the difference in thermal expansion.

[0077] Therefore, the solid cubic ammonia (NH ３ The volume expansion coefficient (α) calculated from the difference between the lattice constant of (cr) and the lattice constant at 171 K given by Olovoson and Templeton is 1.26 × 10 －４ On the other hand, the volume expansion coefficient calculated from the difference between the lattice constants at 171 K and 77 K, as shown by Olovoson and Templeton, was 3.32 × 10 －４ It was.

[0078] From the viewpoint of the volume expansion coefficient, the solid ammonia cubic crystal (NH ３ (cr)) and 171K, and the thermal expansion coefficient (α) of solid ammonia (NH ３ As mentioned above, a good correspondence was found between the thermal expansion coefficient (α) of cubic solid ammonia (NH ３ As revealed by the verification from the viewpoint of the lattice constant and thermal expansion coefficient of cubic ammonia (NH3), the product produced by this example is a solid ammonia cubic crystal (NH4) that is solidified under normal pressure and temperature. ３ (cr)) as the main product.

[0079] In the product produced in this example, the X-ray diffraction (XRD) pattern at 297 K shows that the main product is solid cubic ammonia (NH ３ In addition to the peaks of ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) (cr)), and ammonium borane (NH ３ BH ３ These peaks correspond to the diboron trioxide (B ２ O ３ (cr)) is an unavoidable impurity phase.

[0080] Next, the main product of this example, solid cubic ammonia (NH３ (cr)) to gaseous ammonia (NH ３ The process by which solid ammonia (NH ３ The X-ray diffraction (XRD) pattern of the product containing cubic ammonia (NH3) was obtained when the product was kept in an atmosphere of 363K for 4 hours (14.4ks) as shown in Figure 5(b). ３ (cr)) is converted into gaseous hydrogen (H ２ (g)) is eliminated.

[0081] NH ３ (cube) = 3 / 2H ２ (g) + N (radical) ... (3) Here, N (radical) is atomic nitrogen, which is unstable, so it is used as a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) reacts immediately with the B, O, and H components to form ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ (cr)).

[0082] As a result, as shown in FIG. 5(b), the remaining ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) peak was observed. That is, when the product of this example was produced, and when the ammonia cubic crystal (NH ３ (cubic)) to hydrogen (H ２ (g)) Ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) peak was detected.

[0083] As a result, the solid ammonia cubic crystals (NH ３(cr)) at low temperatures, i.e., with little energy consumption, to produce gaseous hydrogen (H ２ (g)) can be converted into

[0084] The solid cubic ammonia (NH ３ The X-ray diffraction (XRD) pattern of the product containing ammonium pentaborate tetrahydrate (NH (cr)) when it was kept under an atmosphere of 793 K for 4 hours (14.4 ks) is shown in Figure 5 (c). At this time, the product of this example was kept under an atmosphere of 363 K for 4 hours, and the remaining ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ It was confirmed that the peaks of (cr) and (cr) disappeared. This is the result of the progress of thermal decomposition shown in the following formula (4).

[0085] NH ４ B ５ O ８ 4H ２ O)(cr) = NH ３ (g) + 4H ２ O(g) + 2B ２ O ３ (gl)+BHO(g)+1 / 2O ２ ...(4)

[0086] As a result, as shown in FIG. 5(c), the remaining glass matrix B ２ O ３ (gl)-B(OH) ３ Only a broad X-ray diffraction (XRD) pattern of (gl) was observed. ３ (g)) is thermally decomposed to produce gaseous hydrogen (H ２ (g)) and nitrogen (N ２ (g)) and hydrogen (H ２ (g)) can be recovered.

[0087] As a result, the product produced by this example is a solid ammonia cubic crystal (NH ３ (cr)) and borate glass matrix B ２ O ３ (gl)-B(OH) ３As described above, this solidified body is produced by the strong bonding of N atoms and B atoms to generate boron nitride (BN), and the borate glass matrix (B ２ O ３ (gl)-B(OH) ３ At the glass interface of (gl), a strong B-N bond is formed. As a result, ammonia cubic (cubic-(NH ３ )(cr))standard Gibbs energy of formation (Δ f G ° m ) and a borate glass matrix (B ２ O ３ (gl)-B(OH) ３ (gl)) interface Gibbs energy (Δ boundary G ° m ) is the sum of the gaseous ammonia (NH ３ (g)) standard Gibbs energy of formation (Δ f G ° m ) and has a deeper negative value than cubic ammonia (cubic-(NH ３ )(cr)) maintains a cubic crystal form as a stable solid at room temperature and pressure.

[0088] Therefore, the ammonia (NH ３ ) dissolved in an aqueous solution of diboron trioxide (B ２ O ３ The solidified material produced by freeze-drying the mixed aqueous solution containing ammonia (NH ３ ) is formed as a solid cubic crystal in a borate glass matrix (B ２ O ３ -B(OH) ３ ) and a structure in which the ammonia is trapped in a solid cubic crystal (NH ３ The hydrogen storage fuel is composed of Cr(II) as a hydrogen carrier.

[0089] Next, the ammonia cubic crystal (NH ３ (cr)) and ammonia (NH ３ ) and ammonium pentaborate tetrahydrate ((NH ４ B ５ O８ (H ２ O) ４ The thermal decomposition process of Cr(Cr) was investigated.

[0090] The solid cubic ammonia (NH ３ As shown in the temperature-weight change diagram in Figure 7, the hydrogen storage fuel containing ammonia (cr) did not show any weight loss below 325K. This is because ammonia becomes solid cubic ammonia (NH ３ (cr)) as ammonia storage medium and borate glass matrix (B ２ O ３ -B(OH) ３ ) and remains confined inside.

[0091] As shown in FIG. 7, the weight of the hydrogen storage fuel of this example decreased slowly when heated from 325 K to 363 K, and rapidly when heated from 363 K to 750 K. This is because the ammonia cubic particles (NH ３ The hydrogen of (cr) is released, and ammonium pentaborate tetrahydrate ((NH ４ B ５ O ８ (H ２ O) ４ This is believed to be due to the thermal decomposition of hydrogen (Cr). Hydrogen has the smallest atomic weight, and as a result, the weight loss from 325K to 363K is gradual.

[0092] Here, the ammonia water shown in this example contains diboron trioxide (B ２ O ３ (cr)) powder is mixed with an aqueous solution, which is then frozen and evacuated to a vacuum. ３ (cr)) is a borate glass matrix (B ２ O ３ -B(OH) ３The chemical composition of the product trapped in the pores (gl) was measured, and the composition ratio was as follows: N 6.1 mol%, H 47.8 mol%, B 11.9 mol%, O 34.2 mol%.

[0093] In this measurement, N and H were measured by the combustion thermal conductivity method, B was measured by the ICP method, and O was estimated as the remainder of N, H, and B.

[0094] Next, the amount of ammonia cubic crystals (NH ３ (cr)), ammonium pentaborate (NH ４ B ５ O ８ (H ２ O) ４ ) (cr)), and borate glass matrix (GM) (0.17B ２ O ３ , 0.83B(OH) ３ The mole percent and weight percent concentrations of each phase of NH (gl) are shown in Table 1 below. ３ (cr) is 37 mol% or 11 mass%, NH ４ B ５ O ８ (H ２ O) ４ is 5 mol% or 24 mass%, GM (0.17B ２ O ３ , 0.83B(OH) ３ (gl)) was 58 mol % or 65 mass %.

[0095] Then, ammonia cubic (NH ３ The molar and weight percent concentrations of N and H in (cr) were 25 mol% and 82.2 mass% for N, and 75 mol% and 17.8 mass% for H.

[0096] The mixed aqueous solution was then transferred to a borate glass matrix (B ２ O ３ -B(OH) ３(gl)) with 11 mass% of ammonia cubic crystals (NH ３ The weight percent concentrations of N and H in (cr) were 9 mass% for N and 2 mass% for H.

[0097] That is, 2 mass% of hydrogen in the sample was converted into ammonia cubic (NH ３ (cr)) and the borate glass matrix (B ２ O ３ -B(OH) ３ (gl)) and is released as gaseous hydrogen. In the temperature-weight change diagram shown in Figure 7, the temperature at which 2 mass% of hydrogen is lost is found to be 358 K. Therefore, it was found that the analysis based on this composition analysis is in good agreement with the results of the temperature-weight change diagram shown in Figure 7.

[0098] Conventionally, gaseous ammonia (NH ３ (g)) is heated to a high temperature of 673K ​​and nitrogen gas (N ２ (g)) and hydrogen gas (H ２ (g)) and hydrogen gas (H ２ A method for recovering hydrogen (H (g)) using a palladium (Pd) separation membrane has been proposed. The hydrogen storage fuel of this embodiment is hydrogen (H ２ ) into solid cubic ammonia (NH ３ (cr)) and at low temperatures of 325K to 358K, ２ ) in a borate glass matrix (B ２ O ３ -B(OH) ３ (gl)) is passed through the gaseous hydrogen (H ２ (g)) can be separated. ２ This significantly reduces the energy required to store and reseparate the uranium.

[0099] Therefore, the hydrogen storage fuel of this embodiment is ammonia (NH ３ ) into solid cubic ammonia (NH ３ (cr)), and by heating it at a temperature slightly higher than room temperature, it can be converted into gaseous hydrogen (H２ (g)) can be extracted. Furthermore, by heating at a higher temperature, ammonia (NH ３ (g)) can be extracted, which can be decomposed using an ammonia decomposition catalyst to produce hydrogen.

[0100] The hydrogen storage fuel according to this embodiment can be transported and stored as a solid product under normal temperature and pressure conditions.

[0101] The hydrogen storage fuel according to the present invention is used as fuel for an ammonia engine system, an ammonia power generation system, and other ammonia fuel devices.

[0102] REFERENCE SIGNS LIST 1 Reaction vessel 2 Vacuum chamber 3 Main cooling chamber 4 Exhaust valve 5 Vacuum pump 6 Gas trap mechanism 7 Auxiliary cooling chamber

Claims

1. A solid hydrogen storage fuel, such as ammonia (NH ３ ) is a solid cubic crystal at room pressure and temperature, and is formed in a borate glass matrix (B ２ O ３ -B(OH) ３ A hydrogen storage fuel characterized in that the hydrogen is confined in a hydrogen storage tank.

2. As an inevitable impurity, ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) and ammonia borane (NH ３ BH ３ 2. The hydrogen storage fuel according to claim 1, wherein the hydrogen storage fuel is mixed with 3. Ammonia (NH ３ ) was dissolved in an aqueous solution of diboron trioxide (B ２ O ３ ) to prepare a mixed aqueous solution, and then the mixed aqueous solution is frozen to prepare a frozen solid. Thereafter, the frozen solid is freeze-dried to remove water vapor (H ２ O) and boron compounds (BHO) contained as gas are discharged, and ammonia (NH ３ ) is concentrated, ３ ) in a borate glass matrix (B ２ O ３ -B(OH) ３ The hydrogen storage fuel is trapped as a solid cubic crystal in a hydrogen storage tank at room temperature and pressure.

4. The mixed aqueous solution is prepared by adding ammonia (NH) to boron (B) and nitrogen (N) in a ratio of 1:

1. ３ ) was dissolved in an aqueous solution of diboron trioxide (B ２ O ３ 4. The method for producing hydrogen storage fuel according to claim 3, wherein the hydrogen storage fuel is mixed with the above-mentioned.

5. The ammonia (NH ３ ) is an inevitable impurity, ammonium pentaborate tetrahydrate (NH ４ B ５ O ８ (H ２ O) ４ ) and ammonia borane (NH ３ BH ３ ) together with the borate glass matrix (B ２ O ３ -B(OH) ３ 4. The method for producing hydrogen storage fuel according to claim 3, wherein the hydrogen storage fuel is solidified by confining the hydrogen storage fuel in a hydrogen storage tank.

6. A method for producing a hydrogen storage fuel according to any one of claims 3 to 5, characterized in that the mixed aqueous solution is cooled with liquid nitrogen to be frozen and solidified.

7. A method for producing hydrogen storage fuel according to any one of claims 3 to 5, characterized in that the frozen solid is subjected to a decompression treatment and freeze-dried while being cooled with liquid nitrogen.

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