JP2002234701A - Method and apparatus for generating hydrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for generating hydrogen, by which the heating temperature for generating hydrogen can be lowered and a sufficient amount of hydrogen can be generated in a short time even at such a low temperature. SOLUTION: The method for generating hydrogen comprises heating a metal hydride complex in the presence of a compound oxide containing lithium and thermally decomposing the metal hydride complex to generate hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for generating hydrogen, and more particularly to a method for generating hydrogen by thermally decomposing a complex metal hydride in the presence of a lithium-containing composite oxide. The present invention relates to a generation method and a hydrogen generation device therefor.

[0002]

2. Description of the Related Art In modern society, hydrogen is an important chemical raw material that is used in large quantities in the synthetic chemical industry, petroleum refining, and the like. On the other hand, in order to solve future energy problems and environmental problems, hydrogen utilization technology as clean energy is considered to be important, and the development of fuel cells that store hydrogen and use it as fuel is underway. Have been.

[0003] Such fuel cells are gas operated cells, in which the energy obtained from the reaction of hydrogen and oxygen is directly converted to electrical energy. Since such a fuel cell has a much higher efficiency than a conventional combustion engine, a vehicle having a fuel cell is not compatible with a ZEV (Zero Emis
sion Vehicle).

On the other hand, as a method of storing hydrogen, a method of compressing and storing in a cylinder, a method of cooling into liquid hydrogen, a method of adsorbing on activated carbon, and a method of using a hydrogen storage alloy have been proposed. Although hydrogen storage alloys are considered to play a major role in mobile media such as fuel cell vehicles in the above method, there are many problems to be overcome.

In recent years, attention has been paid to a method for generating hydrogen by hydrolyzing chemical hydride. Examples of such a method include a method proposed by Powerball using sodium hydride (NaH) coated with a resin, and a millennium using sodium borohydride (NaBH ₄ ) as a base and adding sodium hydroxide and a catalyst. A method proposed by Cell Company is known.

In recent years, research has been conducted to generate hydrogen from chemical hydride by thermal decomposition instead of hydrolysis. For example, CM Jensen et al., Int.
Hydrogen Energy 24 (1999) 461-465 proposes a method for thermally decomposing sodium aluminum hydride (NaAlH ₄ ) using a titanium alkoxide as a catalyst. According to this document, NaAlH ₄ alone has 0.5% by weight at 200 ° C.
It is assumed that 2% by weight of hydrogen at 150 ° C. and 5% by weight of hydrogen at 200 ° C. are generated by adding the above catalyst.

[0007]

However, when a fuel cell is mounted on an automobile to obtain a hydrogen source, the above-described method of hydrolyzing chemical hydride requires a large amount of water, and thus requires a large amount of water. There is a problem that practical use is difficult due to the increase. On the other hand, the method of thermal decomposition of chemical hydride is considered to be possible to reduce the size and weight as in the case of using a hydrogen storage alloy, but the method of the above-mentioned literature generates a small amount of hydrogen and a sufficient amount of hydrogen. There is a problem that high-temperature heating of about 300 ° C. is necessary for generation. There is also a problem that a sufficient amount of hydrogen cannot be generated in a short time.

The present invention has been made in view of the above-mentioned problems of the prior art, and can reduce the heating temperature for generating hydrogen. An object of the present invention is to provide a hydrogen generation method capable of generating hydrogen. It is another object of the present invention to provide a hydrogen generator to which the hydrogen generation method can be applied.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, by combining a complex metal hydride with a specific composite oxide, heating for hydrogen generation has been achieved. The present inventors have found that the temperature can be lowered, and that a sufficient amount of hydrogen can be generated in a short time even by such low-temperature heating, and the present invention has been completed.

That is, the hydrogen generation method of the present invention is characterized in that a complex metal hydride is heated in the presence of a lithium-containing composite oxide to thermally decompose the complex metal hydride to generate hydrogen. Is what you do.

In the present invention, since the generation of hydrogen can be made more efficient, the heating of the complex metal hydride in the presence of the lithium-containing composite oxide is performed in the range of 200 to 3 times.
It is preferred to carry out in the presence of 000 ppm of water. Further, as the complex metal hydride, LiAlH ₄ , NaAl
_{H 4, LiBH 4, NaBH 4} , KAlH 4, KBH 4, Mg (BH 4) 2, Ca (B
As _{H 4) 2, Ba (BH} 4) 2, Sr (BH 4) 2 and Fe (BH ₄₎ using at least one complex metal hydride selected from the group consisting of _2, the lithium-containing composite oxide, nickel It is preferable to use at least one lithium-containing composite metal oxide selected from the group consisting of lithium oxide, lithium cobaltate, lithium manganate, lithium chromate, lithium vanadate and lithium ferrate.

[0012] A hydrogen generator according to the present invention comprises a container in which a complex metal hydride and a lithium-containing composite oxide are arranged, and heating the inside of the container to convert the complex metal hydride into the lithium-containing composite oxide. And a heating means for thermally decomposing in the presence of to generate hydrogen.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the hydrogen generation method of the present invention, by heating a complex metal hydride in the presence of a lithium-containing composite oxide, the complex metal hydride is thermally decomposed to generate hydrogen.

As the complex metal hydride used here, LiAlH ₄ , NaAlH ₄ ,
_{LiBH 4, NaBH 4, KAlH 4} , KBH 4, Mg (BH 4) 2, Ca (BH 4) 2, Ba
(BH ₄ ) ₂ , Sr (BH ₄ ) ₂ , and Fe (BH ₄ ) ₂ are preferable, and among them, LiAlH ₄ is preferable because of easy thermal decomposition and high theoretical capacity of hydrogen generation.
And NaAlH ₄ are more preferable, and such a theoretical capacity is at most 10.
LiAlH ₄ which is 8% by weight is particularly preferred. The complex metal hydride may be used alone or in combination of two or more.

The mechanism by which hydrogen is generated from the complex metal compound by thermal decomposition is, for example, considered that the complex metal compound is LiAlH ₄ , and when this is thermally decomposed alone, the following reaction formula is used. 3LiAlH ₄ → Li ₃ AlH ₈ + 2Al + 3H ₂ (150-175 ℃) Li ₃ AlH ₈ + 2Al → 3LiH + 3Al + 1.5H ₂ (180-220 ℃) 3LiH + 3Al → 3AlLi + 1.5H ₂ (387〜 (425 ° C)

According to the method of the present invention, since LiAlH ₄ is heated in the state of coexisting with the lithium-containing composite oxide, the high-temperature heating shown in the above reaction formula is not necessary, and the low-temperature heating of about 150 ° C. Even in a short time, a sufficient amount of hydrogen is generated. In the present invention, the reason why such a phenomenon occurs is not necessarily clear, but is presumed to be due to some interaction between the complex metal hydride and the lithium-containing composite oxide.

The shape of the complex metal hydride can be appropriately selected from powders, pellets, and the like. However, since the contact area with the lithium-containing composite oxide can be increased, the complex metal hydride is preferably in the form of powder. preferable.

The lithium-containing composite oxide used in the present invention includes lithium oxide and at least one other metal oxide [for example, noble metal elements (Pt, Pd,
Oxides of Rh, Ru, Au etc., base metal elements (Y, La, Ce, Pr,
Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Mg, A
l, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr,
Oxide of Nb, Mo, In, Sn, Cs, Ba, Ta, W, etc.) and metalloid element (B, Si, Ge, As, Sb, etc.) (Multi-oxide), among which lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ , LiMnO ₂ )
Mn ₂ O ₄ ), lithium chromate (LiCrO ₂ ), lithium vanadate (LiVO ₂ , LiV ₂ O ₄ ), and lithium ferrate (Li ₂
FeO ₄ and LiFeO ₂ ) are preferred.

The lithium-containing composite metal oxide in the present invention also includes a composite metal oxide composed of a lithium oxide and two or more other metal oxides. For example, lithium cobalt oxide in which part of cobalt is replaced with another element (eg, Ni, Mn, Al, Fe, B),
A part of nickel in lithium nickelate is replaced by another element (for example, Co, Mn, Al, Fe, B), and a part of manganese in lithium manganate is another element (for example, Ni, Co, Al, Fe, B) and those in which part of cobalt and / or nickel in the composite oxide of lithium, cobalt, and nickel is replaced with, for example, nickel are also included.

The shape of the lithium-containing composite metal oxide can be appropriately selected from shapes such as powder, pellet, monolith, plate, and fiber, but increases the contact area with the complex metal hydride. It is preferable that the powder is in the form of a powder.

In the hydrogen generation method of the present invention, the amounts of the complex metal hydride and the lithium-containing composite metal oxide are not particularly limited. However, from the viewpoint of hydrogen generation efficiency, the lithium-containing composite metal oxide is preferably used in an amount of 1 to 200 parts by weight, more preferably 1 to 100 parts by weight, and more preferably 3 to 100 parts by weight, based on 100 parts by weight of the complex metal hydride.
It is more preferably used in an amount of from 50 to 50 parts by weight, particularly preferably from 5 to 15 parts by weight. Further, the heating temperature when heating the complex metal hydride in the presence of the lithium-containing composite oxide is preferably 100 to 170 ° C,
More preferably, it is 145 to 155.

In the present invention, the lithium-containing composite oxidation
Heating of the complex metal hydride coexisting with the
0 ppm (preferably 200 to 2000 ppm, more preferably
(Preferably 200-1000 ppm) in the presence of water
It is preferable to carry out. Such moisture is provided at the above concentration.
Means include complex metal hydrides and lithium-containing composites.
The composite oxide is placed inside the container, and in the container, Na_TwoSO_Three・
7H_Two0, AlCl_Three・ 6H_TwoO, CaCl_Two・ 6H_TwoO, CoCl_Two・ 6H_TwoO, SnCl_Two
・ 2H_TwoO, SrCl_Two・ 6H_TwoO, FeCl_Three・ 6H_TwoO, CuCl_Two・ 2H_TwoO, NiC
l_Two・ 6H_TwoO, PdCl_Two・ 2H_TwoO, BaCl_Two・ 2H_TwoO, MgCl_Two・ 6H_TwoO, M
nCl_Two・ 4H_TwoO, Al _TwoO_Three・ H_TwoO, NaBr ・ 2H_TwoO, Zn (NO_Three)_Two・ 6H
_TwoO, Fe (NO_Three)_Three・ 9H_TwoO, Cu (NO_Three)_Two・ 3H_TwoO, Ni (NO_Three)_Two・ 6H
_TwoO, Ba (OH)_Two・ 8H_TwoO, NaI ・ 2H_TwoO, Na_TwoS ・ 9H_TwoO, FeSO_Four・ 7
H_TwoO, NaH_TwoPO_Four・ 2H_TwoA method to further arrange hydrates such as O
No. Hydrates having a melting point of 150 ° C or less
Is preferred.

Means for providing water at the above concentration include:
A method of directly supplying water as water vapor can also be adopted. In addition, steam may be supplied using a solution in which the above hydrate is dissolved in water. If the heating of the complex metal hydride coexisting with the lithium-containing composite oxide is carried out in the presence of moisture, the water is considered to react with the lithium-containing composite oxide, and therefore, It is assumed that hydrogen generation becomes more efficient and hydrogen generation becomes possible even at lower temperatures. When the water content is less than 200 ppm, the amount of contact between the lithium-containing composite oxide and water is reduced, and the efficiency tends to be insufficient. On the other hand, when it exceeds 3000 ppm, the hydrolysis of the complex metal hydride becomes more dominant than the reaction between the lithium-containing composite oxide and moisture, and the amount of the complex metal hydride subjected to the thermal decomposition reaction tends to decrease. .

In the present invention, the complex metal hydride and / or the lithium-containing composite oxide may be supported on a carrier, and the carrier may be heated in the loaded state to thermally decompose the complex metal compound to generate hydrogen. Good.

Such carriers include metal oxides such as titanium oxide (titania), nickel oxide, cerium oxide, zirconia, zeolite, alumina, silicon oxide, iron oxide, manganese oxide, cobalt oxide, zinc oxide, copper oxide, and the like. Carbonaceous materials such as activated carbon, graphite, activated char, coke, hard carbon (non-graphitizable carbon), and soft carbon (easy graphitizable carbon) are exemplified.

As a method for supporting the complex metal hydride and / or lithium-containing composite oxide on a carrier, there are an impregnation method, a precipitation method, a kneading method, an ion exchange method, a supercritical method using a supercritical fluid (International Publication No. WO 99/10167) and the like. The amount supported on the carrier is the carrier 10
The total amount of the complex metal hydride and the lithium-containing composite oxide is preferably 10 to 50 g per 0 g.

Next, a preferred embodiment of the hydrogen generator of the present invention will be described. FIG. 4 is a schematic view showing an example of a preferred embodiment of the hydrogen generator of the present invention. The hydrogen generator 1 is used to heat a reaction vessel 3 having a hydrogen discharge pipe 2 and the inside of the reaction vessel 3. The reaction vessel 3 is filled with a complex metal hydride 5 and a lithium-containing composite oxide 6.

According to such a hydrogen generator 1, when the inside of the reaction vessel 3 is heated to a predetermined temperature (preferably 100 to 170 ° C.) by the heating device 4, the complex metal hydride 5
Is thermally decomposed in the presence of the lithium-containing composite oxide 6 to generate hydrogen in a high yield. And this hydrogen generator 1
Is discharged from the hydrogen discharge pipe 2 and supplied to, for example, a reaction cell (not shown) for a fuel cell. Therefore, by controlling the internal temperature and the like of the reaction vessel 3 according to the amount of energy to be taken out as electric power, the amount of hydrogen supplied to the reaction cell for the fuel cell can be adjusted, and the required electric output can be obtained. it can.

Although the preferred embodiment of the hydrogen generator of the present invention has been described above, the device of the present invention is not limited to the above embodiment. For example, the heating device 4 to be used is not particularly limited, and may be an electric heater, an electromagnetic heater, or a heating unit of a type using external heat. The reaction vessel 3 may further include a complex metal hydride supply unit for supplying (supplementing) the complex metal hydride 5 and a water supply unit for supplying (supplementing) moisture.

[0030]

EXAMPLES The present invention will now be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 100 mg of lithium aluminum hydride (LiAlH ₄ ) and lithium cobalt oxide (LiCoO ₂ )
100 mg were thoroughly mixed while powdering in a mortar. 200 mg of the obtained mixture was filled in a sample cell tube (manufactured by Suzuki Shokan Co., Ltd., Model SC-4, capacity: about 5 cm ³ ), and a PCT (pressure, composition, temperature) measuring device (Suzuki Shokan Co., Ltd., P69-01, PCT-4SDWIN)
The mixture was heated from room temperature to 200 ° C. over 40 minutes (heating rate: 4.5 ° C./min), and the relationship between the heating temperature and the amount of generated hydrogen was measured. FIG. 1 shows the measurement results.

Comparative Example 1 Lithium cobaltate (LiCo
O ₂₎ without using, lithium aluminum hydride (LiAlH ₄₎
Alone, and 100 mg of the obtained powder was used in Example 1.
Was filled in the same sample cell tube as above, and the temperature was raised from room temperature to 200 ° C. in the same manner as in Example 1, and the relationship between the heating temperature and the amount of generated hydrogen was measured. FIG. 2 shows the measurement results.

As is apparent from a comparison between FIG. 1 and FIG. 2, in Comparative Example 1, hydrogen was gradually generated from 180 ° C., whereas in Example 1, a large amount of hydrogen was rapidly generated from around 150 ° C. Was observed. Further, it was found that the amount of hydrogen generated up to 200 ° C. was much higher in Example 1 than in Comparative Example 1.

Example 2 100 mg of lithium aluminum hydride (LiAlH ₄ ) and lithium cobalt oxide (LiCoO ₂ )
100 mg were thoroughly mixed while powdering in a mortar. 200 mg of the obtained mixture was filled in the same sample cell tube as in Example 1. 150 ° C
Was set in a temperature-controlled oil bath, the gas generated through a silicone rubber hose connected to the sample cell tube was replaced with water, and the amount of hydrogen generated up to 30 minutes after the start of heating was measured. FIG. 3 shows the measurement results.
In addition, 2000 ppm of moisture (saturated steam) was present in the silicone rubber hose.

Example 3 Example 2 was repeated except that 100 mg of lithium aluminum hydride (LiAlH ₄ ) was replaced by 100 mg of sodium aluminum hydride (NaAlH ₄ ).
The amount of generated hydrogen was measured in the same manner as described above. Figure 3 shows the measurement results.
Shown in The amount of water (saturated steam) in the silicone rubber hose was the same as in Example 2.

Example 4 100 mg of lithium aluminum hydride (LiAlH ₄ ), 100 mg of sodium aluminum hydride (NaAlH ₄ ), and lithium cobalt oxide (LiCoO ₂ )
100 mg were thoroughly mixed while powdering in a mortar. 300 mg of the obtained mixture was filled in the same sample cell tube as in Example 2, and the amount of generated hydrogen was measured in the same manner as in Example 2. FIG. 3 shows the measurement results. The amount of water (saturated steam) in the silicone rubber hose was the same as in Example 2.

Comparative Example 2 100 mg of lithium aluminum hydride (LiAlH ₄ ) was pulverized in a mortar, and 100 mg of titanium alkoxide (Ti (OBu) ₄ , titanium tetrabutoxide) was added and mixed. The resulting mixture 2
00 mg was filled in the same sample cell tube as in Example 2,
Further, the amount of generated hydrogen was measured in the same manner as in Example 2. FIG. 3 shows the measurement results. The amount of water (saturated steam) in the silicone rubber hose was the same as in Example 2.

Comparative Example 3 Comparative Example 2 was repeated except that 100 mg of sodium aluminum hydride (NaAlH ₄ ) was used instead of 100 mg of lithium aluminum hydride (LiAlH ₄ ).
The amount of generated hydrogen was measured in the same manner as described above. Figure 3 shows the measurement results.
Shown in The amount of water (water vapor) in the silicone rubber hose was the same as in Example 2.

Comparative Example 4 100 mg of lithium aluminum hydride (LiAlH ₄ ) and 100 mg of sodium aluminum hydride (NaAlH ₄ ) were sufficiently mixed in a mortar while pulverized in a mortar, and titanium alkoxide (Ti (OBu) ) ₄ , 100 mg of titanium tetrabutoxide) were added and mixed.
300 mg of the obtained mixture was filled in the same sample cell tube as in Example 2, and the amount of generated hydrogen was measured in the same manner as in Example 2. FIG. 3 shows the measurement results. The amount of water (saturated steam) in the silicone rubber hose was the same as in Example 2.

In FIG. 3, Example 2 and Comparative Example 2,
As is clear from comparison between Example 3 and Comparative Example 3, Example 4 and Comparative Example 4, heating the complex metal hydride in the presence of the lithium-containing composite oxide is more effective in heating in the presence of the titanium alkoxide. It was found that more hydrogen was generated in a shorter time than it did.

[0041]

As described above, according to the hydrogen generation method of the present invention, the heating temperature for hydrogen generation can be lowered, and even with such low temperature heating, a sufficient amount of hydrogen can be generated in a short time. Becomes possible. Therefore, the hydrogen generation method and the hydrogen generation device of the present invention are very useful in making complex metal hydrides usable as a hydrogen supply source for fuel cells.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a heating temperature and an amount of generated hydrogen in Example 1.

FIG. 2 is a diagram showing a relationship between a heating temperature and an amount of generated hydrogen in Comparative Example 1.

FIG. 3 is a graph showing the change over time in the amount of hydrogen generated in Examples 2 to 4 and Comparative Examples 2 to 4.

FIG. 4 is a schematic view showing a preferred embodiment of the hydrogen generator of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydrogen generator, 2 ... Hydrogen discharge pipe, 3 ... Reaction vessel, 4
... heating device, 5 ... complex metal hydride, 6 ... lithium-containing composite oxide, 7 ... hydrogen.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshitsugu Kojima 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. No. 1 Inside Toyota Motor Corporation (72) Inventor Harumichi Nakanishi No. 1 Toyota Town, Toyota City, Aichi Prefecture F-term inside Toyota Motor Corporation (Reference) 5H027 AA02 BA14

Claims (4)

[Claims] 1. A method for generating hydrogen, comprising heating a complex metal hydride in the presence of a lithium-containing composite oxide to thermally decompose the complex metal hydride to generate hydrogen. 2. The hydrogen generating method according to claim 1, wherein the heating is performed in the presence of 200 to 3000 ppm of water. 3. The complex metal hydride is LiAlH ₄ , NaAl
_{H 4, LiBH 4, NaBH 4} , KAlH 4, KBH 4, Mg (BH 4) 2, Ca (B
_{H 4) 2, Ba (BH} 4) is _2, Sr (BH _{4) 2} and Fe (at least one complex metal hydride BH ₄₎ selected from the group consisting of _2, the lithium-containing composite oxide, nickel Lithium oxide,
The hydrogen generation according to claim 1 or 2, wherein the hydrogen generation is at least one lithium-containing composite metal oxide selected from the group consisting of lithium cobaltate, lithium manganate, lithium chromate, lithium vanadate and lithium ferrate. Method. 4. A container in which a complex metal hydride and a lithium-containing composite oxide are disposed, and the inside of the container is heated to thermally decompose the complex metal hydride in the presence of the lithium-containing composite oxide. A heating means for generating hydrogen at least.