JP2009001457A - Method and apparatus for hydrogen generation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for generating hydrogen which can be suitably applied even to fuel cell automobiles. <P>SOLUTION: The method for generating hydrogen comprises obtaining an arbitrary amount of hydrogen by thermally decomposing a metal hydride, then generating hydrogen by reacting a residual metal hydride remaining without being decomposed with water, and further generating hydrogen by reacting the metal by-produced by the thermal decomposition of the metal hydride with an aqueous alkali solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and apparatus for hydrogen generation, and more particularly to a method and apparatus capable of suitably generating hydrogen as a fuel for fuel cells using a metal hydride as a raw material.

  The problem of environmental destruction such as global warming due to the finite nature of fossil fuels or carbon dioxide emitted from fossil fuels is regarded as one of the most important issues to be solved for modern society. Under these circumstances, hydrogen is in the spotlight as an inexhaustible and ultimate clean energy source. In particular, fuel cells using hydrogen as an energy source have attracted attention as a technology in the 21st century. Is working on its development.

  However, in order to use hydrogen as an energy source in various industrial fields including fuel cells, many problems still remain in terms of hydrogen storage or storage technology. Various methods have been proposed for hydrogen storage and storage techniques. Typical methods include a method of storing as liquefied hydrogen in a cryogenic state, a method of storing in carbon nanotubes or fullerene, a method of storing in a hydrogen storage alloy, or a method of storing as hydride.

  Each of these methods has advantages and disadvantages in terms of safety, convenience, transportation efficiency, storage and storage efficiency, or energy balance between storage and storage and the fossil fuel required for the subsequent hydrogen release. For example, storage by liquefied hydrogen requires enormous cooling energy to liquefy hydrogen, and its use place and method are naturally limited from the viewpoint of the safety of the storage container. In the method using a hydrogen storage alloy, since these substances are made of heavy metals, their weight is heavy and the hydrogen storage efficiency is inferior per unit weight. In addition, the method using carbon nanotubes has not yet reached a level where the hydrogen storage capacity is satisfactory from the technical point of view, and the cost is high and the hydrogen storage capacity deteriorates over time due to repeated storage and release of hydrogen. There is a problem in the use of the period, which is limited in terms of practicality.

  The inventor has studied methods for producing hydrogen from metal hydrides. As a method of generating hydrogen from a metal hydride, hydrogen is generated by heating the hydride to thermally decompose (for example, see Patent Document 1) or by reacting the hydride with a liquid such as water or alcohol in a reaction vessel. (For example, refer to Patent Document 2 and Patent Document 3) and the like have been proposed.

  However, in the thermal decomposition method of metal hydride, when the thermal decomposition reaction proceeds and the remaining amount of metal hydride decreases, the reaction rate decreases, and a higher temperature is required for decomposition. The reason for this is not clear, but it is presumed that special activation energy is required to proceed the decomposition reaction due to the change in the crystal structure accompanying the progress of the reaction or the diffusibility of hydrogen in the crystal. Therefore, when hydrogen must be generated by thermal decomposition of a metal hydride under conditions that cannot be heated to a very high temperature, there is a problem that a part of the metal hydride remains without being decomposed. It is disadvantageous in the generation efficiency. For example, when applied to the production of hydrogen fuel for a fuel cell vehicle, the upper limit temperature that can be heated is usually about 120 ° C. due to the heat source restriction at the start or drive of the vehicle in the metal hydride pyrolysis method, and it does not decompose The hydride remains and the amount of hydrogen produced is reduced accordingly. Technically, it is possible to obtain higher temperatures, but this requires a large auxiliary loss, and the material of the hydride reactor needs to be heat resistant. Furthermore, since the hydrogen produced is also hot, it must be equipped with a cooling means. As a result, the overall size of the hydrogen generator is increased and the weight of the hydrogen generator is increased, so that the hydrogen generator does not become light and compact, and there are various problems in practical use.

  On the other hand, in the method of reacting a metal hydride with a liquid such as water, there is usually no unreacted hydride remaining. However, since this reaction proceeds rapidly and at a time, it is difficult to control the hydrogen generation rate as compared with the thermal decomposition method, and there is a difficulty in applying it as a hydrogen fuel generation device mounted on a fuel cell vehicle.

JP 2002-137901 A JP 2003-126777 A JP 2003-206101 A

  An object of the present invention is to provide an improved hydrogen generation method and apparatus that eliminates the disadvantages of the above-described metal hydride pyrolysis method, thereby efficiently generating hydrogen from the metal hydride. Is. Another object of the present invention is to provide a method and an apparatus for generating hydrogen that can be suitably applied to a fuel cell vehicle by controlling and generating hydrogen.

  In order to solve the above-described problems, the present invention provides a hydrogen generation method according to claim 1 that generates hydrogen from a metal hydride, and thermally decomposes the metal hydride to generate an arbitrary amount of hydrogen. A step of hydrolyzing an undecomposed hydride in the step to generate hydrogen, and a step of adding an alkaline aqueous solution to react with a metal by-produced by thermal decomposition of the hydride to generate hydrogen. It is characterized by comprising.

  The hydrogen generation method according to claim 2 is the method according to claim 1, wherein the metal hydride is at least one or a mixture of two or more selected from alane, CaH2 and Mg (AlH4) 2. It is characterized by.

  According to a third aspect of the present invention, there is provided the method for producing hydrogen according to the first or second aspect, wherein the aqueous alkaline solution is at least one aqueous solution selected from lithium hydroxide, sodium hydroxide and potassium hydroxide. Features.

  The hydrogen generator according to claim 4 is a container containing a metal hydride, a means for heating the hydride, a means for supplying water to the container, and an alkaline aqueous solution supplied to the container The hydride pyrolysis reaction, the hydrolysis reaction of the hydride remaining without being pyrolyzed, and the alkali aqueous solution reaction of the metal by-produced by the pyrolysis are carried out. Producing hydrogen.

  The hydrogen generation apparatus according to claim 5 is the apparatus according to claim 4, wherein the control means for controlling the flow rate and timing of each liquid supplied to the container is the water supply means and the alkaline aqueous solution supply means. It is characterized by being provided in.

  According to the present invention, there is no metal hydride remaining after the reaction, so the amount of hydrogen produced from the metal hydride per unit amount is greater than that produced by the pyrolysis reaction, and accordingly Hydrogen can be obtained efficiently. In addition, since a metal produced as a by-product by thermal decomposition of the hydride is also reacted with an alkaline aqueous solution and used to generate hydrogen, even more hydrogen can be obtained.

  Furthermore, according to the present invention, hydrogen generation is performed by a three-stage process, namely, a metal hydride thermal decomposition reaction, an undecomposed metal hydride hydrolysis reaction, and a by-product metal alkali reaction. Compared with the conventional metal hydride hydrolysis method, which is carried out in a one-step process, hydrogen can be obtained in a controlled state.

  Embodiments of the method and apparatus for hydrogen generation according to the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing an example of an apparatus for carrying out the method for producing hydrogen according to the present invention. In this figure, reference numeral 1 denotes a metal hydride container, in which a metal hydride 2 is filled. The container 1 is also provided with heating means 3 . As a heat source for the heating means 3 , for example, in the case of a fuel cell vehicle, the waste heat from the fuel cell is used during normal operation of the apparatus, but the waste heat from the fuel cell is not yet available as at the start. In some cases, heat obtained by electrical resistance heating or combustion of fossil fuels is used temporarily and supplementarily. For this reason, the heating means 3 includes a waste heat introduction pipe 4 and an auxiliary heating means 5, and fins 6 are arranged for improving the heating efficiency of the hydride. The fins 6 are connected to the waste heat introduction pipe 4 and the auxiliary heating means 5.

The heating means 3 only needs to be able to pyrolyze the hydride, so that the configuration need not be limited to the one described above. Moreover, a heating means may be arrange | positioned outside a container and a metal hydride may be heated from the outside.

  The container 1 is provided with water supply means 7 and alkaline aqueous solution supply means 8. As these liquid supply means 7 and 8, pipes are usually used. The amount and timing of water and alkaline aqueous solution supplied to the container 1 are controlled by control means provided in these means. Such a control means can be constituted by, for example, electromagnetic valves 9 and 10 provided in the liquid flow paths of the respective supply means 7 and 8 of water or alkaline aqueous solution and an electric circuit for operating these electromagnetic valves.

  An alkaline tank 11 for supplying an alkaline aqueous solution is connected to the alkaline aqueous solution supply means 8. The alkali tank 11 is provided with water supply means 13 having an electromagnetic valve 14, and an alkaline substance container 12 is accommodated therein. And water is introduce | transduced at the appropriate timing of operation | movement of this apparatus 1, and aqueous alkali solution is prepared. Of course, an alkaline aqueous solution may be placed in the tank from the beginning.

  As the water supplied to the water supply means 7, 13, for example, water generated by the operation of the fuel cell can be used.

  The metal hydride used in the present invention is a solid at room temperature, which reacts with water to release hydrogen, and a metal produced as a by-product after dehydrogenation reacts with an alkaline aqueous solution to release hydrogen. It is. Examples of such a hydride include alane (aluminum hydride AlH3), CaH2, and Mg (AlH4) 2. These hydrides are usually used alone, but may be used as a mixture of two or more.

  In addition, the aqueous alkaline solution used in the present invention may be any one that generates hydrogen by reacting with a metal by-produced by dehydrogenation of a metal hydride. Examples of such an alkaline aqueous solution include an aqueous solution of an alkali hydroxide such as lithium hydroxide, sodium hydroxide, or potassium hydroxide. Usually, these aqueous solutions are used alone, but of course, they may be used in combination.

  Next, the process of hydrogen generation according to the present invention will be described by taking, as an example, the case where alan is used as a metal hydride and an aqueous sodium hydroxide solution is used as an alkaline aqueous solution.

  When Alane is heated by a heating means, it is thermally decomposed and hydrogen is released by the reaction of the following formula 1. In order for this reaction to proceed smoothly, a temperature of 100 to 140 ° C. is required. In the case of a fuel cell vehicle, the waste heat from the fuel cell is usually 80 to 120 ° C., so this thermal decomposition reaction is performed relatively slowly. By adjusting the temperature in the container, the amount of hydrogen to be generated and the generation rate can be adjusted. However, when the amount of remaining alane decreases as the reaction proceeds, the decomposition rate becomes extremely slow at the above heating temperature, and some alane remains undecomposed unless heated to a high temperature. When the heating temperature is 120 ° C. or lower, usually about 20% of allan remains without being decomposed.

AlH3 → Al + 3 / 2H2 …………… Formula 1
Assuming that 20% of alane is left without thermal decomposition, the amount of hydrogen produced from 1 mol of alane by this reaction is
It is calculated as 1 mol × (1 mol−0.2 mol) × 3/2 mol = 1.2 mol.

  Next, when water is supplied to the container, the remaining alane (corresponding to 0.2 mol) undergoes a hydrolysis reaction, and hydrogen is released by the following formula 2.

AlH3 + 3H2O → Al (OH) 3 + 3H2 …………… Formula 2
The hydrogen produced by this reaction is
Calculated as 0.2 mole x 3 mole = 0.6 mole.

  Finally, an aqueous sodium hydroxide solution is supplied to the container. Metallic aluminum (corresponding to 0.8 mol) by-produced by thermal decomposition of alane represented by the above formula 1 reacts with an aqueous sodium hydroxide solution, and hydrogen is released by the following formula 3.

Al + NaOH + H2O → NaAlO2 + 3 / 2H2 …………… Formula 3
The hydrogen produced by this reaction is
0.8 mol (Al) x 3/2 mol (H2) = 1.2 mol.

  In the conventional metal hydride hydrolysis method, when Alane reacts with water, 3 mol of hydrogen is generated from 1 mol of Alane at a time according to the above formula 2. On the other hand, according to the present invention, as described above, 1.2 mol by the thermal decomposition reaction of the metal hydride of formula 1 (in the case of a thermal decomposition rate of 80%), then 0.6 mol by the hydrolysis reaction of formula 2, and The final reaction with the alkaline aqueous solution of Formula 3 can be extracted in 1.2 stages with hydrogen in 3 stages. Therefore, according to the present invention, since the amount of hydrogen to be generated can be controlled by controlling the timing of performing the reactions in each of these stages, the size and weight of the tank for storing the generated hydrogen gas can be reduced. For this reason, the hydrogen generation method and apparatus of the present invention can be applied particularly conveniently in a place where the installation space of the apparatus is narrow and the weight is limited, such as a fuel cell vehicle.

It is explanatory drawing which shows an example of the apparatus for implementing the method of the hydrogen production | generation which concerns on this invention.

Explanation of symbols

1 Metal hydride container 2 Metal hydride
3 Heating means 7 Water supply means 8 Alkaline aqueous solution supply means 9, 10 Solenoid valve

Claims (5)

  A method of generating hydrogen from a metal hydride, the step of thermally decomposing the hydride to generate an arbitrary amount of hydrogen, and the step of hydrolyzing the undecomposed hydride in the step to generate hydrogen. And a step of generating hydrogen by adding an aqueous alkali solution and reacting with a metal produced as a by-product by thermal decomposition of the hydride.   The method for generating hydrogen according to claim 1, wherein the metal hydride is at least one kind or a mixture of two or more kinds selected from alane, CaH2 and Mg (AlH4) 2.   The method for producing hydrogen according to claim 1 or 2, wherein the alkaline aqueous solution is at least one aqueous solution selected from lithium hydroxide, sodium hydroxide and potassium hydroxide.   A container containing a metal hydride; means for heating the hydride; means for supplying water to the container; and means for supplying an alkaline aqueous solution to the container. Hydrogen produced by carrying out a thermal decomposition reaction of a hydride, a hydrolysis reaction of a hydride remaining without being thermally decomposed, and an alkali aqueous solution reaction of a metal produced as a by-product of the thermal decomposition to generate hydrogen Generator.   5. The hydrogen generator according to claim 4, wherein a control means for controlling the flow rate and timing of each liquid supplied to the container is provided in the water supply means and the alkaline aqueous solution supply means.

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