JP2007290888A - Method for producing hydrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply and efficiently producing and supplying hydrogen even at 0°C or lower temperature to facilitate use of a portable fuel cell under low temperature environment. <P>SOLUTION: This method for producing hydrogen comprises causing hydrogen producing reaction to take place by feeding antifreeze water having pH in the range of 4-10 and a freezing point of -5°C or lower to a hydrogen-generating material containing a metallic material of at least one kind selected from the group consisting of aluminum, magnesium and their alloys comprising particles of ≤100 μm particle diameter by ≥80 mass% and an exothermic material other than the metallic material generating heat by reaction with water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing hydrogen in which hydrogen is generated by a reaction between a metal material and water.

  In recent years, with the widespread use of cordless devices such as personal computers and mobile phones, secondary batteries as power sources are increasingly required to be smaller and have higher capacities. Currently, lithium ion secondary batteries have been put into practical use as secondary batteries that have high energy density and can be reduced in size and weight, and demand for portable power sources is increasing. However, depending on the type of cordless device used, this lithium secondary battery has not yet reached a level that guarantees sufficient continuous use time.

  Under such circumstances, a polymer electrolyte fuel cell has been studied as an example of a battery that can meet the above demand. Solid polymer fuel cells that use a solid polymer electrolyte as the electrolyte, oxygen in the air as the positive electrode active material, and fuel (hydrogen, methanol, etc.) as the negative electrode active material are expected to have higher energy density than lithium ion secondary batteries It is attracting attention as a battery system. The fuel cell can be used continuously as long as fuel and oxygen are supplied.

  There are several candidates for the fuel used in the fuel cell, but each has various problems, and a final decision has not yet been made. A direct methanol fuel cell that uses methanol as the fuel and reacts directly with the electrode is easy to miniaturize and is expected as a portable power source in the future, but has a problem of voltage drop due to methanol crossover, The expected energy density is not obtained.

  On the other hand, when hydrogen is used as a fuel, for example, a method of supplying hydrogen stored in a high-pressure tank or a hydrogen storage alloy tank has been put into practical use, but the volume and weight are increased, and the energy density is reduced. Therefore, it is not suitable as a portable power source. There is also a method in which a hydrocarbon-based fuel is used as the fuel and hydrogen is extracted by reforming it. However, since a reformer is required and problems such as heat supply and heat insulation to the reformer occur, it is still unsuitable as a portable power source.

Under such circumstances, a method has been proposed in which hydrogen is generated by a chemical reaction at a low temperature of 100 ° C. or lower and used as a fuel. In these methods, for example, a metal that generates hydrogen by reacting with water, such as aluminum, magnesium, silicon, and zinc, is used as a hydrogen source (see Patent Documents 1 to 5).
US Pat. No. 6,506,360 Japanese Patent No. 2566248 JP 2004-231466 A JP 2001-31401 A JP-T-2004-505879

  According to the method described in Patent Documents 1 to 3 in which aluminum is reacted with an alkali or an acid, hydrogen is easily generated chemically, but it is necessary to add an equivalent amount of alkali or acid suitable for aluminum. The risk to the human body in case of leakage is very high. In addition, there is a problem that the oxide or hydroxide as a reaction product forms a film on the surface of the metal, the inner metal cannot contact with water, and the oxidation reaction stops only on the surface of the metal. Since it is likely to occur, in the technique of Patent Document 3, the hydrogen generating material is configured with the aluminum ratio being 85 wt% or less.

  On the other hand, in the technique of Patent Document 4 which attempts to avoid the above problem by mechanically removing the surface film, there arises a problem that the apparatus becomes large, for example, mechanical equipment for removing the surface film is required. In Patent Document 5, alumina is added as a catalyst for making it difficult to form the hydroxide film, and hydrogen is generated at a relatively low temperature. However, the reaction proceeds when the water temperature is 10 ° C. or higher, and is not suitable for producing hydrogen in a lower temperature environment such as below freezing point.

  This invention is made | formed in view of the said situation, The objective is to provide the manufacturing method of hydrogen which can generate | occur | produce hydrogen easily in a low temperature environment.

  The method for producing hydrogen of the present invention capable of achieving the above object is at least one metal material selected from the group consisting of aluminum, magnesium, and alloys thereof, and a heat generating material that generates heat by reacting with water. A method for producing hydrogen in which a hydrogen generating material containing a material other than the metal material is reacted with water to generate hydrogen, wherein the metal material has a particle diameter of 100 μm or less of 80% by mass or more. The material is contained in the ratio, and the water is non-freezing water having a pH in the range of 4 to 10 and a freezing point of −5 ° C. or lower.

  Since the hydrogen production method of the present invention enables simple and efficient production and supply of hydrogen even at 0 ° C. or lower, the use of fuel cells in a low temperature environment, particularly the use of portable fuel cells. Is possible.

  Hereinafter, the present invention will be described in detail. In the method for producing hydrogen of the present invention, at least one metal material selected from the group consisting of aluminum, magnesium, and alloys thereof, and a heat generating material that generates heat by reacting with water, and a material other than the metal material, When the hydrogen generating material containing is reacted with water, antifreeze water having a pH in the range of 4 to 10 and a freezing point of −5 ° C. or lower is used.

Since the above metal materials usually have a stable oxide film on the surface, even when they come into contact with water, the hydrogen generation reaction does not start immediately, but water gradually infiltrates from the surface to the inside, and the internal metal When aluminum or magnesium present in the state is in contact with water, the reaction represented by any of the following formulas (1) to (3) is considered to start.
2Al + 6H ₂ O → Al ₂ O ₃ .3H ₂ O + 3H ₂ (1)
2Al + 4H ₂ O → Al ₂ O ₃ .H ₂ O + 3H ₂ (2)
2Al + 3H ₂ O → Al ₂ O ₃ + 3H ₂ (3)

That is, even when water is supplied to the hydrogen generating material, the reaction does not occur until the hydrogen generation starts (usually several minutes to several tens of minutes), so the hydrogen generating material and the supplied water are at the ambient temperature. Depending on the temperature, the temperature will change. For example, when the reaction system is below freezing point, even if normal water (for example, tap water) is supplied, it freezes by the start of the reaction and water does not enter the metal material. This causes a problem that the hydrogen generation reaction cannot be started.

  On the other hand, once the hydrogen generation reaction starts, the reaction between the metal material and water is an exothermic reaction, so the temperature of the reaction system including water rises and the hydrogen generation reaction can be continued. Therefore, in order to generate hydrogen at a low temperature, it is necessary not to freeze the reaction water until the start of the hydrogen generation reaction. In the present invention, by setting the solidification temperature of a solution used for the reaction (a solution containing at least water) to −5 ° C. or lower, a hydrogen generation reaction at a low temperature is possible.

  As the antifreeze water, for example, a mixed solvent of water and an organic solvent such as ethylene glycol or ethanol, or an aqueous solution in which a water-soluble polymer such as polyoxyethylene or an inorganic salt such as sodium chloride is dissolved is used. However, the type of solute is not particularly limited. That is, in order to lower the freezing temperature of water, it is preferable to use freezing point depression in which the freezing point is lowered according to the concentration of the solute in the aqueous solution in which the solute is dissolved, but the kind of the solute is not particularly limited. Further, the concentration of the solute in the antifreeze water is not particularly limited as long as the freezing point is in the range of −5 ° C. or lower, but it is generally 5 wt% or more in order to lower the freezing point. On the other hand, in order to increase the reaction efficiency by setting the ratio of water to a certain value or more, the concentration of the solute is desirably 50 wt% or less. Moreover, it is preferable if the pH of the antifreeze water is in the range of 4 to 10 which is close to neutral, since the risk to the human body in the event of leakage is low.

  In the present invention, as the metal material, at least one selected from the group consisting of aluminum, magnesium, and alloys thereof is used, but the production method and shape thereof are not particularly limited, and mechanical powdering and atomization are used. A material having various shapes such as a scale shape, a substantially spherical shape, a spindle shape, a droplet shape, or a potato shape produced by a method or the like can be used.

  Further, in order to efficiently generate a reaction with the water in the antifreeze water even at a low temperature and to start a hydrogen generation reaction in a short time, the metal material should have a small particle size, and particles having a particle size of 100 μm or less. Is preferably contained in a proportion of 80% by mass or more. The average particle size is preferably 70 μm or less, and particularly when the average particle size is 30 μm or less, the reaction efficiency can be further improved.

  On the other hand, as the particle size of the metal material is smaller, the hydrogen generation rate is increased. However, if the particle size is smaller than 0.1 μm, the stability in the air is lowered and the handling becomes difficult. The particle size of the metal material is preferably 0.1 μm or more because the filling density of the hydrogen generating material is reduced as the particle size is reduced.

  The particle size of the metal material can be measured by, for example, a laser diffraction / scattering method. Specifically, it is a particle size distribution measurement method using a scattering intensity distribution detected by irradiating a measurement target substance dispersed in a liquid phase such as water with a laser beam. “Microtrack HRA” manufactured by Nikkiso Co., Ltd. can be used. More simply, a metal material having a target particle size can be obtained by classifying particles with a sieve. For example, by classifying a metal material with a sieve having an opening of 50 μm, a powder having a particle size of 50 μm or less can be obtained. Obtainable. In addition, the average particle diameter in this invention means the value of 50% diameter in the volume-based integrated fraction.

  When an aluminum alloy or a magnesium alloy is used as the metal material, the composition thereof is not particularly limited, but it is desirable that the content of aluminum or magnesium related to hydrogen generation is large, and the content is 80% by mass or more. It is good and it is more preferable that it is 85 mass% or more.

Examples of additive elements (alloy elements) in aluminum alloys include silicon, iron, copper, manganese, magnesium, zinc, nickel, titanium, lead, tin, and chromium, and contain two or more of these alloy elements. It doesn't matter. In addition, examples of the additive element (alloy element) in the magnesium alloy include aluminum, zinc, zirconium, silicon, iron, copper, manganese, nickel, and rare earth elements, and contains two or more of these alloy elements. It doesn't matter.

  In the present invention, in order to shorten the time from the contact between the metal material and water to the start of hydrogen generation, a heat generating material that generates heat by reacting with water and a material other than the metal material is used as described above. A hydrogen generating material is formed by coexisting with a metal material. Examples of the exothermic materials include substances that form hydroxides by reaction with water, compounds that generate heat by hydration, such as alkali metal oxides (such as lithium oxide), alkaline earth metal oxides ( Calcium oxide, magnesium oxide, etc.), alkaline earth metal chlorides (calcium chloride, magnesium chloride, etc.), alkaline earth metal sulfate compounds (calcium sulfate, etc.), etc., easily react with water and come into contact with water In such a case, a substance that immediately generates heat may be used. Due to the presence of such materials, when antifreeze water is supplied to the hydrogen generating material, the temperature of the metal material and water temporarily rises, and the penetration of water into the metal material particles described above is promoted. Thus, the time until the start of hydrogen generation can be shortened, and hydrogen generation at a lower temperature can be handled.

  The ratio of the heat generating material is preferably 1% by mass or more, more preferably 3% by mass or more, based on the total amount with the metal material, in order to sufficiently exhibit the temperature rising effect. On the other hand, if the heat is generated more than necessary, the hydrogen generation reaction may not be controlled, so depending on the type of heat generating material, it is preferably 20% by mass or less, more preferably less than 15% by mass. It is particularly desirable that the content be 10% by mass or less.

  The hydrogen generating material used in the present invention further includes hydrophilic oxides (alumina, silica, magnesia, zirconia, zeolite, zinc oxide, etc.), carbon, water-absorbing polymers (celluloses such as carboxymethyl cellulose, polyvinylpyrrolidone, etc. , Polyvinyl alcohol, polyacrylic acid, and the like) may be added. The above-mentioned reaction accelerator improves the contact between the metal material and water, prevents the reaction product produced by the reaction of the metal material with water and the unreacted metal material from condensing. It is thought that there is an effect such that water easily penetrates.

  In the hydrogen production method of the present invention, antifreeze water having a pH in the range of 4 to 10 and a freezing point of −5 ° C. or lower is supplied into the reaction vessel in which the hydrogen generating material is disposed. Hydrogen can be taken out by reacting the water contained in the metal with the metal material contained in the hydrogen generating material. At this time, the amount of generated hydrogen can be controlled by controlling the supply amount of the antifreeze water.

  The material and shape of the reaction vessel are not particularly limited as long as the reaction vessel can accommodate a hydrogen generating material, but the material does not easily penetrate the antifreeze water and hydrogen and does not break even when heated to about 100 ° C. Is preferred. For example, resins such as polyethylene and polypropylene, heat resistant glass and metals such as aluminum and iron can be preferably used. Also, the means for supplying antifreeze water is not particularly limited. When supplying the antifreeze water from the outside of the reaction vessel, for example, a supply port for antifreeze water is provided in the reaction vessel and a pump or the like is connected. The antifreeze water can be supplied into the container.

  Here, the reaction container in which the hydrogen generating material is accommodated may be a cartridge that can be attached to and detached from the electronic device main body and the fuel cell main body. In this case, a storage unit for storing the antifreeze water may be provided inside the reaction vessel so that it is convenient for carrying, and the antifreeze water can be supplied from the storage unit to the hydrogen generating material. Accordingly, it is only necessary to omit the supply port of the non-freezing water and the pump and to provide at least a hydrogen discharge port in the reaction vessel, so that hydrogen can be easily produced. For this reason, compared with the case where antifreeze water is supplied from the outside of the container, the apparatus can be easily simplified and miniaturized, and the configuration can be more preferable as a portable fuel source.

  In addition, the storage part of the antifreeze water provided in the reaction vessel can be configured by enclosing the antifreeze water in a bag made of a resin film such as a polyethylene film, and opens a hole in the bag. If the antifreeze water in the storage unit is brought into contact with the hydrogen generating material by a simple means such as, hydrogen can be generated and function as a hydrogen production apparatus.

Hydrogen generated using the method for producing hydrogen of the present invention does not contain CO and CO ₂ which are problematic when reforming hydrocarbon fuels to produce hydrogen, and water is involved in the reaction. Therefore, since hydrogen gas contains moderate moisture, it can be suitably used as a fuel for a polymer electrolyte fuel cell that operates at 100 ° C. or lower.

  Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited only to the following examples.

Example 1
The average particle diameter produced by the gas atomization method: 3 μm aluminum powder (ratio of particles having a particle diameter of 100 μm or less: 100 mass%) and calcium oxide powder are mixed in a mortar, and these are contained in the ratio shown in Table 1. A hydrogen generating material was prepared. 1 g of this hydrogen generating material was put in a sample bottle, 4 g of 25 mass% ethanol aqueous solution (pH: 7, freezing point: −15 ° C.) was added as antifreeze water and left for 48 hours, and hydrogen generated during that time was collected. The test was performed at −5 ° C., and the volume of collected hydrogen was measured to determine the amount of hydrogen generated. The results are shown in Table 1.

(Example 2)
Average particle size: In the same manner as in Example 1 except that aluminum powder having an average particle size of 30 μm (ratio of particles having a particle size of 100 μm or less: 100% by mass) was used as the metal material instead of the aluminum powder having an average particle size of 3 μm. Thus, a hydrogen generating material was prepared and the amount of hydrogen generated was determined.

(Example 3)
A hydrogen generating material was prepared in the same manner as in Example 2 except that calcium chloride powder was used as the heat generating material instead of the calcium oxide powder, and the amount of hydrogen generated was determined.

(Comparative Example 1)
The test was performed in the same manner as in Example 1 except that ion-exchanged water (freezing point: 0 ° C.) was used instead of the 25 mass% ethanol aqueous solution, but the ion-exchanged water was not Due to freezing, no hydrogen evolution reaction occurred.

(Comparative Example 2)
Hydrogen generation in the same manner as in Example 1 except that aluminum powder having an average particle diameter of 150 μm (ratio of particles having a particle diameter of 100 μm or less: 26 mass%) was used instead of the aluminum powder having an average particle diameter of 3 μm. The material was prepared and the amount of hydrogen generation was determined.

  The measurement results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1.

Example 4
Average particle diameter: In the same manner as in Example 1, except that magnesium powder having a particle diameter of 45 μm or less (the ratio of particles having a particle diameter of 100 μm or less: 100 mass%) selected by a sieve was used instead of the aluminum powder of 3 μm. Thus, a hydrogen generating material was prepared and the amount of hydrogen generated was determined.

(Comparative Example 3)
Hydrogen generation in the same manner as in Example 1 except that magnesium powder having an average particle size of 150 μm (ratio of particles having a particle size of 100 μm or less: 22% by mass) was used instead of the aluminum powder having an average particle size of 3 μm. The material was prepared and the amount of hydrogen generation was determined.

  The measurement results of Example 4 and Comparative Example 3 are shown in Table 2.

  As is clear from Tables 1 and 2, the hydrogen generating material is composed of a metal material containing particles of 100 μm or less in a proportion of 80% by mass or more, and the water supplied to the hydrogen generating material has a pH in the range of 4 to 10 In Examples 1 to 4 in which the antifreezing water had a freezing point of -5 ° C or lower, the reaction proceeded even at a low temperature of -5 ° C, and a sufficient amount of hydrogen could be generated. In particular, when the ratio of the metal material is 85% by mass or more, the reaction efficiency is increased, and favorable results are obtained.

  On the other hand, in Comparative Example 1 in which normal water was supplied, water could not be solidified to generate hydrogen, and among the particles constituting the metal material, the proportion of particles of 100 μm or less was less than 80% by mass. In Examples 2 and 3, the reaction did not proceed sufficiently, and the hydrogen generation amount was significantly reduced as compared with the above Examples.

(Example 5)
A hydrogen generating material 6 (however, the ratio of metal material: 95% by mass) similar to that in Example 1 is accommodated in a reaction container 1 including a container 2 and a lid 3 shown in FIG. By continuously supplying the antifreeze water 7 used in Example 1 into the container from the supply port 4 at a rate of 0.07 ml / min, the hydrogen generating material 6 and water are reacted to generate hydrogen. This was taken out through the hydrogen outlet 5. The extracted hydrogen is supplied to a polymer electrolyte fuel cell comprising a positive electrode that reduces oxygen, a negative electrode that oxidizes hydrogen, and a solid electrolyte disposed between the positive electrode and the negative electrode. The amount was measured. The test was conducted at -5 ° C. As a result, the output gradually increased, a stable output of 170 mW / cm ² was obtained, and it was confirmed that it sufficiently functions as a fuel source for driving the fuel cell.

It is a schematic diagram which shows the hydrogen production apparatus used for experiment of Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Storage container 3 Lid 4 Water supply port 5 Hydrogen discharge port 6 Hydrogen generating material 7 Antifreeze water 8 Pump

Claims (5)

A hydrogen generating material containing at least one metal material selected from the group consisting of aluminum, magnesium, and alloys thereof, and a heat generating material that generates heat by reacting with water and is a material other than the metal material, A method for producing hydrogen by generating hydrogen by reacting with
The metal material contains particles having a particle size of 100 μm or less in a proportion of 80% by mass or more,
As the water, non-freezing water having a pH in the range of 4 to 10 and a freezing point of −5 ° C. or lower is used.   2. The method for producing hydrogen according to claim 1, wherein a ratio of the metal material in the total amount of the metal material and the heat generating material is more than 85 mass% and not more than 99 mass%.   The method for producing hydrogen according to claim 1 or 2, wherein the heat generating material is at least one compound selected from the group consisting of calcium oxide, magnesium oxide, calcium chloride, magnesium chloride, and calcium sulfate.   The method for producing hydrogen according to claim 1, wherein the heat generating material is calcium oxide. The method for producing hydrogen according to claim 1, wherein an average particle diameter of the metal material is 30 μm or less.

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