JP4670156B2 - Hydrogen generating method and hydrogen generating apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen generation method and a hydrogen generation apparatus, and more specifically, a hydrogen generation method for generating hydrogen by thermally decomposing a complex metal hydride in the presence of a lithium-containing composite oxide, and hydrogen generation therefor It relates to the device.
[0002]
[Prior art]
In modern society, hydrogen is an important chemical raw material that is used in large quantities in the synthetic chemical industry and petroleum refining. On the other hand, in order to solve future energy problems and environmental problems, hydrogen utilization technology as clean energy is considered to occupy an important position, and the development of fuel cells that store hydrogen and operate it as fuel is proceeding. It has been.
[0003]
Such fuel cells are gas-operated cells, in which the energy obtained from the reaction between hydrogen and oxygen is directly converted into electrical energy. Since such a fuel cell has a very high efficiency compared to a conventional combustion engine, a vehicle having a fuel cell is called a ZEV (Zero Emission Vehicle).
[0004]
On the other hand, as a method for storing hydrogen, a method of compressing and storing in a cylinder, a method of cooling to liquid hydrogen, a method of adsorbing on activated carbon, and a method of using a hydrogen storage alloy have been proposed. Among them, hydrogen storage alloys are considered to play a major role in moving media such as fuel cell vehicles, but there are many problems to be overcome.
[0005]
In recent years, therefore, a method of generating hydrogen by hydrolyzing a chemical hydride has attracted attention. Such methods include a method proposed by Powerball using sodium hydride (NaH) coated with resin, or a millennium using sodium borohydride (NaBH ₄ ) based on sodium hydroxide and a catalyst. A method proposed by Cell Corporation is known.
[0006]
Recently, research has also been conducted to generate hydrogen from chemical hydride by thermal decomposition instead of hydrolysis. For example, CM Jensen et al., Int. J. Hydrogen Energy 24 (1999) 461-465 proposes a method for thermally decomposing sodium aluminum hydride (NaAlH ₄ ) using titanium alkoxide as a catalyst. According to this document, NaAlH ₄ alone generates only 0.5 wt% hydrogen at 200 ° C., whereas the addition of the above catalyst results in 2 wt% hydrogen at 150 ° C. and 5 wt% hydrogen at 200 ° C. Is supposed to occur.
[0007]
[Problems to be solved by the invention]
However, when a fuel cell is mounted on an automobile to obtain its hydrogen source, the above-described method of hydrolyzing chemical hydride requires a large amount of water, which is difficult to put into practical use due to an increase in weight. There is a problem that there is. On the other hand, the method of pyrolysis of chemical hydride can be reduced in size and weight in the same manner as in the case of using a hydrogen storage alloy. However, the method described in the above document generates a small amount of hydrogen and a sufficient amount of hydrogen. There is a problem that heating at a high temperature of about 300 ° C. is necessary for the generation. There is also a problem that a sufficient amount of hydrogen cannot be generated in a short time.
[0008]
The present invention has been made in view of the above-mentioned problems of the prior art, and can reduce the heating temperature for hydrogen generation, and a sufficient amount of hydrogen can be generated in a short time even by such low temperature heating. An object of the present invention is to provide a method for generating hydrogen. Moreover, it aims at providing the hydrogen generator which can apply this hydrogen generating method.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors can reduce the heating temperature for hydrogen generation by combining a complex metal hydride and a specific composite oxide. It has been found that a sufficient amount of hydrogen can be generated in a short time even by low-temperature heating, and the present invention has been completed.
[0010]
That is, the hydrogen generation method of the present invention is characterized in that the 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 there.
[0011]
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 preferably carried out in the presence of 200 to 3000 ppm of water. Further, as the complex metal hydride, 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 used, and at least one complex metal hydride selected from the group consisting of lithium nickel oxide, lithium cobaltate, lithium manganate, lithium chromate is used as the lithium-containing composite oxide. It is preferable to use at least one lithium-containing composite metal oxide selected from the group consisting of lithium vanadate and lithium ferrate.
[0012]
The hydrogen generator of the present invention includes a container in which a complex metal hydride and a lithium-containing composite oxide are disposed, and heating the interior of the container to remove the complex metal hydride in the presence of the lithium-containing complex oxide. And heating means for generating hydrogen by pyrolysis.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be.
In the hydrogen generation method of the present invention, the complex metal hydride is heated in the presence of a lithium-containing composite oxide, whereby the complex metal hydride is thermally decomposed to generate hydrogen.
[0014]
The complex metal hydrides used herein, high content of hydrogen, LiAlH from the hydrogen by the lithium-containing composite oxide can be efficiently produced _{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 , Fe (BH ₄ ) ₂ are preferred, and among them, they are easily decomposed and have a theoretical capacity for hydrogen generation. more preferably LiAlH ₄ or NaAlH ₄ from higher, LiAlH ₄ according theoretical capacity of up to 10.8% by weight is particularly preferred. The complex metal hydride may be used as a single type, or may be used in combination of a plurality of types.
[0015]
The mechanism by which hydrogen is generated from the complex metal compound by thermal decomposition is, for example, considered to be based on the following reaction formula when the complex metal compound is LiAlH ₄ and thermally decomposed alone.
3LiAlH ₄ → Li ₃ AlH ₈ + 2Al + 3H ₂ (150 ~ 175 ° C)
Li ₃ AlH ₈ + 2Al → 3LiH + 3Al + 1.5H ₂ (180-220 ° C)
3LiH + 3Al → 3AlLi + 1.5H ₂ (387-425 ° C)
[0016]
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 even a low-temperature heating of about 150 ° C. is a short time Produces a sufficient amount of hydrogen. In the present invention, the reason why such a phenomenon occurs is not necessarily clear, but it is assumed that some kind of interaction occurs between the complex metal hydride and the lithium-containing composite oxide.
[0017]
The shape of the complex metal hydride can be appropriately selected from shapes such as powder and pellets, but is preferably powder because the contact area with the lithium-containing composite oxide can be increased.
[0018]
The lithium-containing composite oxide used in the present invention includes lithium oxide and at least one other metal oxide [for example, oxides of noble metal group elements (Pt, Pd, Rh, Ru, Au, etc.), base metals Element (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta, W, etc.), metalloid elements (B, Si, Ge, As, Sb, etc.) Compound metal oxide (double oxide) in the form of a compound, among which lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ , LiMn ₂ O ₄ ), Lithium chromate (LiCrO ₂ ), lithium vanadate (LiVO ₂ , LiV ₂ O ₄ ), and lithium ferrate (Li ₂ FeO ₄ , LiFeO ₂ ) are preferred.
[0019]
The lithium-containing composite metal oxide in the present invention includes composite metal oxides composed of lithium oxide and other two or more metal oxides. For example, a part of cobalt in lithium cobaltate is replaced with another element (for example, Ni, Mn, Al, Fe, B), and a part of nickel in lithium nickelate is replaced with another element (for example, Co, Mn, Al, Fe, B), lithium manganese manganate partially substituted with other elements (eg, Ni, Co, Al, Fe, B), lithium, cobalt and nickel In this case, a part of cobalt and / or nickel in the composite oxide is substituted with, for example, nickel.
[0020]
The shape of the lithium-containing composite metal oxide can be appropriately selected from powders, pellets, monoliths, plates, fibers, etc., but can increase the contact area with the complex metal hydride. It is preferable that it is a powder form.
[0021]
In the hydrogen generation method of the present invention, the amount of complex metal hydride and lithium-containing composite metal oxide used is not particularly limited. However, from the viewpoint of hydrogen generation efficiency, it is preferable to use 1 to 200 parts by weight of lithium-containing composite metal oxide, more preferably 1 to 100 parts by weight, based on 100 parts by weight of complex metal hydride. It is more preferable to use 50 parts by weight, and it is particularly preferable to use 5 to 15 parts by weight. Moreover, it is preferable that the heating temperature when heating a complex metal hydride in presence of lithium containing complex oxide is 100-170 degreeC, and it is more preferable that it is 145-155.
[0022]
In the present invention, the heating of the complex metal hydride coexisting with the lithium-containing composite oxide is preferably carried out in the presence of 200 to 3000 ppm (preferably 200 to 2000 ppm, more preferably 200 to 1000 ppm) of water. As a means for providing such moisture at the above concentration, a complex metal hydride and a lithium-containing composite oxide are arranged inside the container, and Na ₂ SO ₃ · 7H ₂ 0, AlCl ₃ · 6H ₂ O are placed in the vessel. , CaCl ₂・ 6H ₂ O, CoCl ₂・ 6H ₂ O, SnCl ₂・ 2H ₂ O, SrCl ₂・ 6H ₂ O, FeCl ₃・ 6H ₂ O, CuCl ₂・ 2H ₂ O, NiCl ₂・ 6H ₂ O, PdCl ₂・ 2H ₂ O, BaCl ₂・ 2H ₂ O, MgCl ₂・ 6H ₂ O, MnCl ₂・ 4H ₂ O, Al ₂ O ₃・ H ₂ O, NaBr ・ 2H ₂ O, Zn (NO ₃ ) ₂・6H ₂ O, Fe (NO ₃ ) ₃・ 9H ₂ O, Cu (NO ₃ ) ₂・ 3H ₂ O, Ni (NO ₃ ) ₂・ 6H ₂ O, Ba (OH) ₂・ 8H ₂ O, NaI ・ 2H Examples thereof include a method in which hydrates such as ₂ O, Na ₂ S · 9H ₂ O, FeSO ₄ · 7H ₂ O, NaH ₂ PO ₄ · 2H ₂ O and the like are further arranged. The hydrate preferably has a melting point of 150 ° C. or lower.
[0023]
As a means for providing moisture at the above concentration, a method of directly supplying water as water vapor can be employed. Further, water vapor may be supplied using a solution in which the above hydrate is dissolved in water. When the complex metal hydride coexisting with the lithium-containing composite oxide is heated in the presence of moisture, the moisture is considered to react with the lithium-containing composite oxide. It is assumed that hydrogen generation is more efficient and hydrogen generation is 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 the water decreases, and thus the degree of efficiency tends to be insufficient. On the other hand, when it exceeds 3000 ppm, the hydrolysis of the complex metal hydride is more dominant than the reaction between the lithium-containing composite oxide and moisture, and the amount of the complex metal hydride used for the thermal decomposition reaction tends to decrease. .
[0024]
In the present invention, hydrogen may be generated by supporting a complex metal hydride and / or a lithium-containing composite oxide on a support, and heating both in the supported state to thermally decompose the complex metal compound.
[0025]
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, activated carbon, graphite. And carbonaceous materials such as activated char, coke, hard carbon (non-graphitizable carbon), and soft carbon (graphitizable carbon).
[0026]
Examples of a method for supporting a complex metal hydride and / or a lithium-containing composite oxide on a support include an impregnation method, a precipitation method, a kneading method, an ion exchange method, and a supercritical method using a supercritical fluid (International Publication No. WO99 / 10167). No. gazette). The supported amount on the carrier is preferably 10 to 50 g in total of the complex metal hydride and the lithium-containing composite oxide with respect to 100 g of the carrier.
[0027]
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 for heating 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.
[0028]
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 present in the presence of the lithium-containing composite oxide 6. Under high temperature to produce hydrogen in high yield. And the hydrogen 7 obtained with this hydrogen generator 1 is discharged | emitted from the hydrogen discharge pipe 2, and is supplied to the reaction cell (not shown) for fuel cells, for example. Therefore, the amount of hydrogen supplied to the reaction cell for the fuel cell can be adjusted by controlling the internal temperature of the reaction vessel 3 according to the amount of energy to be taken out as electric power, and the required electrical output can be obtained. it can.
[0029]
The preferred embodiment of the hydrogen generator of the present invention has been described above, but the apparatus 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 means of a type using external heat. The reaction vessel 3 may further include a complex metal hydride supply unit for supplying (replenishing) the complex metal hydride 5 and a water supply unit for supplying (supplementing) moisture.
[0030]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.
[0031]
Example 1
100 mg of lithium aluminum hydride (LiAlH ₄ ) and 100 mg of lithium cobaltate (LiCoO ₂ ) were mixed thoroughly while being powdered 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 PCT (pressure / composition / temperature) measuring device (manufactured by Suzuki Shokan Co., Ltd., P69-01 Using PCT-4SDWIN), the mixture was heated from room temperature to 200 ° C. over 40 minutes (temperature increase rate: 4.5 ° C./min), and the relationship between the heating temperature and the amount of hydrogen generated was measured. The measurement results are shown in FIG.
[0032]
(Comparative Example 1)
Without using lithium cobalt oxide (LiCoO ₂ ), only lithium aluminum hydride (LiAlH ₄ ) was pulverized, and 100 mg of the obtained powder was filled in the same sample cell tube as in Example 1, and Example 1 In the same manner as above, the temperature was raised from room temperature to 200 ° C., and the relationship between the heating temperature and the amount of hydrogen generation was measured. The measurement results are shown in FIG.
[0033]
As is clear by comparing 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 generation was observed from around 150 ° C. . It was also found that the amount of hydrogen generated up to 200 ° C. was overwhelmingly higher in Example 1 than in Comparative Example 1.
[0034]
(Example 2)
100 mg of lithium aluminum hydride (LiAlH ₄ ) and 100 mg of lithium cobaltate (LiCoO ₂ ) were mixed thoroughly while being powdered in a mortar. The same sample cell tube as in Example 1 was filled with 200 mg of the obtained mixture. This sample cell tube is set in an oil bath whose temperature is controlled at 150 ° C., and the gas generated through the silicone rubber hose connected to the sample cell tube is replaced with water, and the amount of hydrogen generated for 30 minutes after the start of heating is reduced. It was measured. The measurement results are shown in FIG. In the silicon rubber hose, 2000 ppm of water (saturated water vapor) was present.
[0035]
(Example 3)
The amount of hydrogen generation was measured in the same manner as in Example 2 except that 100 mg of sodium aluminum hydride (NaAlH ₄ ) was used instead of 100 mg of lithium aluminum hydride (LiAlH ₄ ). The measurement results are shown in FIG. The amount of water (saturated water vapor) in the silicone rubber hose was the same as in Example 2.
[0036]
Example 4
100 mg of lithium aluminum hydride (LiAlH ₄ ), 100 mg of sodium aluminum hydride (NaAlH ₄ ), and 100 mg of lithium cobaltate (LiCoO ₂ ) were mixed thoroughly while being powdered in a mortar. 300 mg of the obtained mixture was filled in the same sample cell tube as in Example 2, and the hydrogen generation amount was measured in the same manner as in Example 2. The measurement results are shown in FIG. The amount of water (saturated water vapor) in the silicone rubber hose was the same as in Example 2.
[0037]
(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 thereto and mixed. 200 mg of the obtained mixture was filled in the same sample cell tube as in Example 2, and the amount of hydrogen generated was measured in the same manner as in Example 2. The measurement results are shown in FIG. The amount of water (saturated water vapor) in the silicone rubber hose was the same as in Example 2.
[0038]
(Comparative Example 3)
The amount of hydrogen generation was measured in the same manner as in Comparative Example 2 except that 100 mg of sodium aluminum hydride (NaAlH ₄ ) was used instead of 100 mg of lithium aluminum hydride (LiAlH ₄ ). The measurement results are shown in FIG. The amount of water (water vapor) in the silicone rubber hose was the same as in Example 2.
[0039]
(Comparative Example 4)
Lithium aluminum hydride (LiAlH ₄ ) 100 mg and sodium aluminum hydride (NaAlH ₄ ) 100 mg were mixed well while being powdered in a mortar, and then titanium alkoxide (Ti (OBu) ₄ , titanium tetrabutoxide) 100 mg. Was 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 hydrogen generation was measured in the same manner as in Example 2. The measurement results are shown in FIG. The amount of water (saturated water vapor) in the silicone rubber hose was the same as in Example 2.
[0040]
As is apparent from comparison of Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4 in FIG. 3, the complex metal hydride was formed in the presence of the lithium-containing composite oxide. It was found that more hydrogen was generated in the heating in a shorter time than in the presence of titanium alkoxide.
[0041]
【The invention's effect】
As described above, according to the hydrogen generation method of the present invention, the heating temperature for hydrogen generation can be lowered, and a sufficient amount of hydrogen can be generated in a short time even by such low temperature heating. Therefore, the hydrogen generation method and the hydrogen generation apparatus according to the present invention are very useful for making the complex metal hydride available as a hydrogen supply source of a fuel cell.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between heating temperature and hydrogen generation amount in Example 1. FIG.
2 is a graph showing the relationship between the heating temperature and the amount of hydrogen generated in Comparative Example 1. FIG.
FIG. 3 is a graph showing changes 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 container, 4 ... Heating device, 5 ... Complex metal hydride, 6 ... Lithium containing complex oxide, 7 ... Hydrogen.

Claims (4)

By heating at least one complex metal hydride selected from the group consisting of LiAlH ₄ and NaAlH _{4 in} the presence of a lithium-containing composite oxide, the complex metal hydride is thermally decomposed to generate hydrogen. The hydrogen generation method.   The method for generating hydrogen according to claim 1, wherein the heating is performed in the presence of 200 to 3000 ppm of water. Before SL lithium-containing composite oxide, lithium nickel acid, lithium cobaltate, lithium manganate, lithium chromic acid, is at least one lithium-containing composite metal oxide selected from the group consisting of lithium vanadate and ferrate lithium The hydrogen generation method according to claim 1 or 2. A container in which at least one complex metal hydride selected from the group consisting of LiAlH ₄ and NaAlH ₄ and a lithium-containing composite oxide are disposed; and heating the inside of the container to contain the complex metal hydride in the lithium And a heating means for generating hydrogen by pyrolysis in the presence of the composite oxide.

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