JP2005255505A - Hydrogen supply method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply pure hydrogen containing no carbon monoxide at a low cost. <P>SOLUTION: The hydrogen supply method includes: a water decomposition process for decomposing water to produce hydrogen; a reducing process for reducing oxides with hydrogen from the water decomposition process to form a reduced body; and a hydrogen producing process for producing hydrogen by bringing the reduced body from the reducing process into contact with H<SB>2</SB>O. As the oxide, a metallic oxide such as iron oxide is suitably used. Hydrogen is easily obtained in a hydrogen demand site by transporting the easily handleable reduced body to the hydrogen demand site in place of directly transporting hydrogen produced by the water decomposition process to the hydrogen demand site. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrogen supply method capable of supplying hydrogen easily to a hydrogen demand point without using, for example, a high-pressure tank.

  Conventionally, partial oxidation and steam reforming methods using petroleum and natural gas as raw materials have been proposed as one of the methods for producing hydrogen. In these methods, a large amount of carbon dioxide gas is generated during hydrogen synthesis. .

  Therefore, as a method of not generating carbon dioxide gas, a method of Japanese Patent Application Laid-Open No. 07-267601 using solar heat has been proposed. However, this method requires a large system to use solar heat, and the cost increases accordingly.

As another method, a method of decomposing methane, which is a main component of natural gas, into carbon and hydrogen using a catalyst can be considered. For example, Japanese Patent No. 2767390 proposes thermal decomposition of hydrocarbons such as methane in the presence of a carbon substance having an outer surface of 1 m ² / g or more. However, this proposed method is disadvantageous because it needs to be heated to an extremely high temperature of about 1000 ° C. during pyrolysis. Japanese Patent No. 2838192 proposes a hydrocarbon decomposition catalyst such as methane in which a carbon compound is loaded with a nickel compound and at least one metal compound selected from alkali metals and alkaline earth metals. Has been. However, in this proposal, methane cannot be decomposed sufficiently due to thermodynamic restrictions, and since methane is mixed and supplied to a large amount of nitrogen gas, etc., the rate of decomposition of methane in the supply gas is low. Couldn't actually be used.

  In the case of a fuel cell using hydrogen and air as raw materials, a method of supplying hydrogen by steam reforming of methanol or gasoline is common, and many inventions have been proposed. However, in any of the proposed methods, carbon monoxide and carbon dioxide gas are generated at the same time. In particular, carbon monoxide requires a device for removing it to 10 ppm or less due to the problem of poisoning of the fuel cell electrode, and the cost is great. It is hanging on.

  On the other hand, as one of hydrogen supply methods, there is a method of supplying by a high pressure cylinder. However, the high-pressure cylinder has a large weight and a large capacity, and it is difficult to load a large amount of hydrogen in an automobile, and there are problems such as the risk of explosion.

  In addition, many proposals have been made to use hydrogen storage alloys in place of high-pressure cylinders as means for safely storing and transporting hydrogen. However, there is a problem that a high hydrogen pressure is required for hydrogen storage in the hydrogen storage alloy, or that the hydrogen storage alloy cannot be used in an atmosphere of air and water vapor when stored in such a hydrogen storage alloy.

  International Publication No. WO 01/96233 (Japanese Patent Application No. 2002-510383) decomposes hydrocarbons such as methane to generate hydrogen, and the metal oxide is reduced by this hydrogen to form a low-valence oxide or elemental metal. And a method for producing hydrogen by bringing this low-valent oxide or elemental metal into contact with water.

However, in this method, carbon is by-produced by a reaction such as CH ₄ → C + 2H ₂ in the first stage hydrogen generation step, and handling and treatment thereof are required.
JP 07-267601 A Japanese Patent No. 2767390 Japanese Patent No. 2838192 International Publication No. WO01 / 96233 (Japanese Patent Application No. 2002-510383)

  In view of the prior art as described above, the present invention can supply hydrogen at low cost without generation of carbon dioxide, carbon monoxide, and carbon, and at the same time does not include carbon monoxide as a hydrogen supply device such as a fuel cell. An object is to provide a method capable of supplying pure hydrogen.

The hydrogen supply method of the present invention (Claim 1) includes a water splitting step in which water is decomposed to generate hydrogen, a reduction step in which an oxide is reduced by hydrogen from the water splitting step to form a reductant, And a hydrogen generation step of generating hydrogen by bringing the reductant from the reduction step into contact with H ₂ O.

  The hydrogen supply method of the present invention (Claim 2) is characterized in that, in Claim 1, the oxide is a metal oxide, and the reductant is a low-valent metal oxide or metal. is there.

  According to the hydrogen supply method of the present invention (Claim 3), in Claim 2, the metal oxide includes at least one oxide of iron, indium, tin, magnesium, and cerium, Ti, Zr, V, Nb, It consists of at least one oxide of Cr, Mo, Al, Ga, Sc, Ni and Cu.

  The hydrogen supply method of the present invention (Claim 4) is the reductant obtained in any one of Claims 1 to 3, wherein the water splitting step and the hydrogen generation step are performed at different locations, and obtained in the reduction step. It has the process of moving to the location where the said hydrogen generation process is performed.

In the hydrogen supply method of the present invention, an oxide such as a metal oxide is reduced by hydrogen generated by decomposing water to form a reductant such as an elemental metal or a low-valent oxide state, This reductant is brought into contact with H ₂ O (water, water vapor, water vapor-containing gas, etc.) to generate hydrogen. Unlike hydrogen gas, this reductant is easy to handle such as transportation and can be stored and moved at room temperature.

  According to the present invention, hydrogen generated in the water splitting process is not directly transferred to the demand point, but a reductant that is easy to handle can be transferred to the demand point, and hydrogen can be easily obtained at the hydrogen demand point.

In the water splitting process, hydrogen is generated by water splitting, so that no carbon, carbon monoxide, or carbon dioxide gas is generated. Furthermore, since hydrogen is generated by bringing the reductant and H ₂ O into contact with each other at the demand location, high-purity hydrogen that is not mixed with carbon monoxide or the like can be generated.

  According to the present invention, small-scale devices and movable devices that require hydrogen, such as fuel cells, fuel cell vehicles, or local equipment, factories, households, welding hydrogen burners, etc. are required. High purity hydrogen can be safely supplied to the apparatus at low cost.

The present invention relates to a water splitting step for generating hydrogen, a reduction step for generating a reductant using hydrogen from the water splitting step, and a hydrogen that takes out hydrogen by reacting the reductant with H ₂ O. Generating step.

Hereinafter, each step will be described in detail.
A: Water splitting step In this water splitting step, hydrogen is generated by a water splitting reaction of 2H ₂ O → 2H ₂ + O ₂ . This decomposition is preferably electrolysis by a solid polymer electrolyte water electrolysis type, an alkaline membrane water electrolysis type, or the like, but may be water decomposition utilizing a catalyst, a photocatalyst, plasma, radiation, or a microorganism.

B: Reduction step In this reduction step, the oxide is reduced using hydrogen generated in the water splitting step to generate a reductant.

A metal oxide is suitable as this oxide. As the metal oxide, at least one of iron oxide (Fe ₃ O ₄ , Fe ₂ O ₃ , FeO), indium oxide, tin oxide, magnesium oxide, and cerium oxide is preferable. A metal oxide (MO _X ) may be supported on a carrier such as alumina, zinc oxide, magnesia, activated carbon, titania, zeolite, and the like.

  This reduction reaction is preferably carried out in a reactor equipped with a heater or configured to provide heat from an external heat source to the reaction zone. Specifically, the metal oxide is stored in a portable cassette equipped with a heater, and hydrogen from the water splitting process is introduced into the cassette while heating the inside of the cassette with the heater, and a reduction reaction is performed. It is preferred to do so. The water produced by the reduction reaction is usually taken out from the cassette as water vapor.

  This cassette may be integrated with the water splitting apparatus that performs the above-described step A.

  When the oxidation / reduction of metal oxide (especially iron oxide) is repeated, the metal aggregates or sinters and the activity gradually decreases. In order to prevent this decrease in activity, at least one oxide of Ti, Zr, V, Nb, Cr, Mo, Al, Ga, Sc, Ni, and Cu is converted into the metal oxide (oxide for reduction / reduction). May be added. When the metal oxide is other than magnesium oxide (for example, iron oxide, indium oxide, tin oxide), magnesium oxide may be added. In order to perform this addition, the metal oxide (for example, nitrate) for oxidation / reduction oxide is co-precipitated from a solution containing the metal salt of the metal oxide to be added, and then calcined. It is preferable to use a mixture of The amount of the metal oxide to be added is preferably about 0.5 to 30 mol%, particularly about 0.5 to 15 mol% with respect to the metal oxide for oxidation / reduction.

C: Hydrogen generation step In this hydrogen generation step, hydrogen is generated by bringing the reductant obtained in the reduction step into contact with H ₂ O (gas containing liquid water, water vapor, and water vapor). Preferably, a metal low-valent oxide or elemental metal is brought into contact with water vapor, and hydrogen is generated, for example, according to a reaction of MO _X-1 + H ₂ O → MO _X + H ₂ (X ≧ 1).

  This reaction is carried out at less than 600 ° C, preferably 250-450 ° C. As a result, the reduction reaction in which the generated hydrogen reduces the metal oxide in situ is prevented. That is, when the temperature is higher than 600 ° C., the reaction proceeds to the left and hydrogen is not generated. Therefore, in the hydrogen generation step, the reaction temperature is set to less than 600 ° C.

  Since this reaction is an endothermic reaction, it is necessary to give reaction heat in the hydrogen generation step, and therefore the reaction temperature is set to about 100 ° C. In the above reduction step, when a metal oxide is contained in the cassette and the reduction reaction is performed, in this hydrogen generation step, water or water vapor is supplied into the cassette while heating the entire cassette or inside the cassette. To remove hydrogen from the cassette.

  Since the extracted hydrogen is of a high purity that does not contain carbon monoxide or the like, when this hydrogen is supplied to a fuel cell or the like, it is not necessary to take measures against poisoning of the electrode by carbon monoxide.

  When hydrogen generated in this hydrogen generation step is supplied to the fuel cell to perform a power generation operation, heat is generated along with this operation. This heat may be given as reaction heat in the hydrogen generation step. In this way, effective use of heat can be achieved, and in the hydrogen generation process, the reaction can be continued by the heat from the fuel cell only by applying heat with a heater or the like only at the start of the process. It becomes possible.

  In the hydrogen generation step, when the reductant is oxidized, the reductant is returned to the reduction step. When the reductant is accommodated in the cassette, the cassette may be returned to the reduction process.

[Example 1]
A water splitting process, a reduction process, and a hydrogen generation process were performed by the system shown in FIG. The system of FIG. 1 includes a solid polymer type water electrolysis hydrogen generator 10 and a cassette 20 containing iron oxide. The inside of the polymer electrolyte water electrolysis hydrogen generator 10 is partitioned into a cathode chamber and an anode chamber by an ion exchange membrane 11, and a catalyst electrode 12 and a titanium / platinum electrode 13 are disposed in each chamber. By supplying pure water into the apparatus 10 and applying a voltage to the electrode 13 from the power source 14, hydrogen is generated at the anode and oxygen is generated at the cathode. Hydrogen from the anode is introduced into the cassette 20 through the pipe 16, the three-way valve 17, and the pipe 18 to reduce the metal oxide 21. The cassette 20 is installed in the heating furnace 25.

  Water vapor generated by the reduction is introduced into the cold trap 30 through the pipe 22. The inside of the cold trap 30 can be sucked by a vacuum pump through a pipe 31, a three-way valve 32 and a pipe 33. The inside of the cassette 20 can also be sucked by a vacuum pump through the pipe 18, the three-way valve 17 and the pipe 19. A sampling pipe 34 is connected to the three-way valve 32, and the collected gas is analyzed by a gas chromatograph.

  In the cassette 20, 0.1 g of ferric trioxide (Wako Pure Chemical Industries, Ltd.) was added as a metal oxide, and the heating furnace 25 was set so that the cassette temperature was 400 ° C. Hydrogen generated by the solid polymer water electrolysis hydrogen generator 10 was introduced into the cassette 20 to reduce the metal oxide. Water vapor generated during the reduction was aggregated in the cold trap 30 at the dry ice temperature (−78 ° C.).

  The reactor (cassette) was heated to 400 ° C., and a predetermined amount of hydrogen and argon were introduced from the solid polymer type water electrolysis hydrogen generator 10 to first reduce the metal oxide. Regeneration of hydrogen from the reduced metal oxide was performed by introducing water vapor together with argon into the reactor heated to 400 ° C. after the reduction. FIG. 2 shows the state of decomposition of water vapor at 400 ° C. by reduction with hydrogen and reduced iron oxide. At a time point (a minute) in FIG. 2, 1000 μmol of hydrogen was introduced to reduce ferric trioxide, and then oxidation and reduction were repeated.

  As shown in FIG. 2, the amount of hydrogen generated by the introduction of water vapor from the time point b at the end of the first reduction to the time point c at the end of hydrogen generation was about 700 μmol, which was slightly reduced from the amount of hydrogen introduced at the time point a. Almost the same amount of hydrogen could be generated up to the second to fourth times.

It is a systematic diagram which shows an Example. It is a graph which shows the result of an Example.

Explanation of symbols

10 Polymer Electrolyte Hydrogen Electrogen Generator 20 Cassette 30 Cold Trap

Claims (4)

A water splitting process for splitting water to generate hydrogen;
A reduction step of reducing the oxide with hydrogen from the water splitting step to form a reductant;
A hydrogen generation step in which hydrogen is generated by contacting a reductant from the reduction step with H ₂ O;
A hydrogen supply method comprising:   2. The hydrogen supply method according to claim 1, wherein the oxide is a metal oxide, and the reductant is a low-valent metal oxide or a metal.   3. The metal oxide according to claim 2, wherein the metal oxide includes at least one oxide of iron, indium, tin, magnesium, and cerium, and Ti, Zr, V, Nb, Cr, Mo, Al, Ga, Sc, Ni, and Cu. A hydrogen supply method comprising: at least one oxide selected from the group consisting of:   The process of any one of claims 1 to 3, wherein the water splitting step and the hydrogen generation step are performed at different locations, and the reduced product obtained in the reduction step is transferred to the location where the hydrogen generation step is performed. A hydrogen supply method comprising:

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