JP2006036579A - Method for producing hydrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing hydrogen capable of stably generating hydrogen without generating carbon monoxide or carbon dioxide as by-products, and without requiring much electric energy. <P>SOLUTION: This method for producing hydrogen comprises generating hydrogen by a chemical reaction of at least a metal selected from iron, indium, tin, magnesium and cerium or an oxide thereof with water, characterized in comprising a step of supplying an oxygen-containing gas into a reactor 10 housing the metal or oxide thereof in a form of a fixed bed and elevating the inside temperature of the reactor 10 by the oxidation reaction of the metal or oxide thereof, and a step of supplying water into the reactor 10 the temperature of which has been elevated to generate hydrogen by the oxidation reaction of the metal or oxide thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen production method suitable for supplying hydrogen to an apparatus requiring hydrogen, such as a fuel cell, a hydrogen burner, and an analytical instrument.

A fuel cell using hydrogen as a fuel is generally provided with a hydrogen generator for reforming methanol or the like into hydrogen by a partial oxidation method or a steam reforming method, and supplying this to the fuel cell. However, in such a method, carbon monoxide (CO) is by-produced with hydrogen, which poisons the fuel cell electrode. Therefore, it is necessary to remove CO to 10 ppm or less. However, if a CO removing means is installed, there is a problem that the reformer becomes large and expensive. In addition, the steam reforming method needs to be heated to a very high temperature of about 800 ° C. On the other hand, as a method that does not generate CO or CO ₂ , a UT-3 cycle using solar heat and a method disclosed in Japanese Patent Laid-Open No. 07-267601 have been proposed. However, since these methods use solar heat, there is a problem that a large-scale system is required and the cost is very high.

Japanese Patent Laid-Open No. 06-157003 proposes a method of generating hydrogen from iron scrap and steam using the oxidation heat of iron scrap and oxygen. The iron scrap to be used has a thickness of 0.5 to 5 mm, is an oxidation reaction only on the surface, is a slight amount of hydrogen generation, and is a reaction performed at a high temperature of 1000K or more.
JP 07-267601 A Japanese Patent Laid-Open No. 06-157003

  In view of the above problems, the present invention provides a hydrogen production method capable of stably generating hydrogen without producing carbon monoxide or carbon dioxide as a by-product and without requiring a large amount of electric energy. For the purpose.

  In order to achieve the above object, the present invention provides at least one metal of iron (Fe), indium (In), tin (Sn), magnesium (Mg), and cerium (Ce) or an oxide thereof and water. A hydrogen production method in which hydrogen is generated by a chemical reaction with an oxygen-containing gas supplied into a reaction vessel containing the metal or oxide thereof in a fixed bed type, and an oxidation reaction of the metal or oxide thereof And a step of increasing the temperature in the reaction vessel by supplying water into the reaction vessel having the increased temperature and generating hydrogen by an oxidation reaction of the metal or its oxide. To do.

In this way, first, by introducing an oxygen-containing gas such as air into the reaction vessel in which the metal or its oxide is stored in a fixed bed type, an exothermic reaction between the metal or its oxide and oxygen. (For example, in the case of pure iron, Fe + 3 / 4O ₂ → 1 / 2Fe ₂ O ₃ , ΔH = −412.1 kJ / mol, 298.15 K, 101.3 kPa). Then, after the temperature in the reaction vessel rises to a predetermined temperature due to the heat generated by this reaction, hydrogen is introduced into the reaction vessel this time, so that hydrogen is reacted by the reaction between the metal or its oxide and water. (For example, in the case of pure iron, Fe + 4 / 3H ₂ O → 1 / 3Fe ₃ O ₄ + 4 / 3H ₂ , ΔH = −50.4 kJ / mol, 298.15 K, 101.3 kPa). It should be noted that the low valent metal oxide that has become Fe ₃ O ₄ or the like by the reaction with water reacts with oxygen at a high temperature above a predetermined temperature and quickly reaches a high valent metal oxide such as Fe ₂ O _3. It can oxidize and allow an exothermic reaction to proceed (for example, in the case of iron oxide, Fe ₃ O ₄ + 1 / 4O ₂ → 3 / 2Fe ₂ O ₃ , ΔH = −118 kJ / mol, at a high temperature of 200 ° C. or higher, 298.15K, 101.3 kPa).

Therefore, as shown in the above reaction formula, carbon monoxide (CO) that poisons the electrode of the fuel cell is not by-produced, so there is no need to provide a CO removal means, and the device can be reduced in size and cost. Can do. The above reactions are all exothermic reactions and proceed spontaneously. Therefore, it is not necessary to heat to a high temperature of about 800 ° C. using a large amount of electric energy as in the steam reforming method, and the temperature is raised to a temperature range sufficient for generating hydrogen by starting from room temperature. . Furthermore, the metal or its oxide that has become unable to generate hydrogen after the completion of the reaction can generate hydrogen again by being reduced with a reducing agent such as hydrogen (for example, in the case of iron, Fe ₂ O ₃ + 3H ₂ → 2Fe + 3H ₂ O, Fe ₃ O ₄ + 4H ₂ → 3Fe + 4H ₂ O). Further, the metal or oxide thereof that undergoes an oxidation reaction with water and oxygen is housed in the same reaction vessel, and water and oxygen are circulated with the metal or oxide thereof fixed (so-called fixed bed flow type). Thus, heat generated by oxidation is stably stored in the reaction vessel, and hydrogen can be generated efficiently.

  As the iron, it is preferable to use at least one pure iron powder of cast iron powder, reduced iron powder, electrolytic iron powder, and atomized iron powder. By using such pure iron powder, the reactivity with oxygen and water can be improved, the temperature in the reaction vessel can be increased efficiently, and the hydrogen generation rate can also be improved.

  As the iron or iron oxide, a metal other than iron is preferably added and stored in the reaction vessel. Examples of metals other than iron include titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), aluminum (Al), gallium (Ga), and magnesium. (Mg), scandium (Sc), nickel (Ni), copper (Cu), or at least one metal of neodymium (Nd) is preferable. By adding these metals, when iron or iron oxide is repeatedly used in the oxidation-reduction reaction, particle growth due to sintering can be suppressed, and a decrease in hydrogen generation efficiency can be suppressed.

  As the metal other than iron, at least one of rhodium (Rh), iridium (Ir), platinum (Pt), ruthenium (Ru), and palladium (Pd) is also preferable. By adding these metals, hydrogen can be generated at a low temperature of 200 ° C. or lower without increasing the self-heating temperature of iron or iron oxide. That is, the amount of iron or iron oxide oxidized by oxygen can be decreased, the reaction of iron or iron oxide and water can be increased, and as a result, the amount of hydrogen generation can be increased.

  As described above, according to the present invention, there is provided a hydrogen production method capable of stably generating hydrogen without producing carbon monoxide or carbon dioxide as a by-product and without requiring a large amount of electric energy. Can do.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a hydrogen generation apparatus suitable for carrying out the hydrogen generation method according to the present invention. As shown in FIG. 1, the hydrogen generator has a reaction vessel 10 for generating hydrogen by chemically reacting water and metal therein, and an introduction for supplying water, air, and reducing gas into the reaction vessel 10. A pipe 21 and a discharge pipe 22 for discharging hydrogen generated in the reaction vessel 10 and unreacted water and air or nitrogen are provided. The reaction vessel 10 has a rectangular parallelepiped shape, and an introduction port 11 for communicating the inside of the reaction vessel 10 and the inside of the introduction tube 21 and the inside of the reaction vessel 10 and the inside of the discharge tube 21 are communicated on one surface 14 thereof. A discharge port 12 is arranged.

  In the reaction vessel 10, from the surface 14 on which the introduction port 11 and the discharge port 12 are arranged to be two layers of a layer having the introduction port 11 and a layer having the discharge port 12, the surface 15 is opposed to the opposite surface 15. And a straightening plate 30 extending linearly. The rectifying plate 30 is provided with a vent hole 31 at a position closer to the facing surface 15 than an intermediate point between the placement surface 14 such as the introduction port 11 and the facing surface 15 in order to communicate both layers.

  The layer including the introduction port 11 further vaporizes the introduced water by the filter 41, which stores the metal containing portion 17a that generates heat by reacting with air and that fixes the metal that generates hydrogen by reacting with water. For vaporization space 18 for the purpose. The vaporization space 18 is located between the inlet 11 and the metal storage part 17a. The filter 41 allows water to be introduced, air, and reducing gas to pass therethrough, but does not allow the contained metal to pass therethrough. On the other hand, the layer including the introduction port 11 constitutes a metal storage portion 17b that stores a metal that generates hydrogen by reacting with water in a fixed state. A filter 42 is provided between the metal storage portion 17 b and the discharge port 12 in order to prevent metal from scattering from within the reaction vessel 10. The filter 42 allows the generated hydrogen, unreacted water, air, and nitrogen to pass through, but does not allow the contained metal to pass through.

  The metal stored in the metal storage unit 17 is any one of iron (Fe), indium (In), tin (Sn), magnesium (Mg), and cerium (Ce). It has high hydrogen generation efficiency and excellent durability against repeated redox. Among these, Fe is particularly preferable. When using Fe, pure iron powder, such as cast iron powder, reduced iron powder, electrolytic iron powder, and atomized iron powder, is more preferable. These metals are not limited to pure metals, and may be, for example, low-valent metal oxides such as FeO. The pure metal or low-valent metal oxide is a powder of 1 nm to 100 μm, preferably 1 nm to 10 μm, and can be used as a hydrogen generating medium even if it is in a powder form as it is, but has a pellet shape, a cylindrical shape, a honeycomb structure, a nonwoven fabric shape, etc. It is preferable to select a shape suitable for the reaction and store it in the metal storage unit 17. The pure metal or metal oxide can be supported on any one of alumina, zinc oxide, magnesia, silica, and titania (the metal oxide described in International Publication No. 01/096233 pamphlet, It can be used as a metal oxide according to the present invention).

  In the case of using Fe or a low-valent metal oxide of Fe, it is preferable to add a metal other than Fe in order to increase the generation efficiency of hydrogen. As the metal to be added, titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), aluminum (Al), gallium (Ga), magnesium (Mg) , Scandium (Sc), nickel (Ni), copper (Cu), neodymium (Nd), at least one metal selected from the first group, or rhodium (Rh), iridium (Ir), platinum (Pt It is preferable to add at least one metal selected from the second group consisting of ruthenium (Ru) and palladium (Pd). Among these, Mo and Al are more preferable as the first group, and Rh and Ir are more preferable as the second group. Further, at least two kinds of metals selected at least one from each of the first group and the second group can be added. As for the compounding ratio of the metal to add, 0.1-30 mol% is preferable and 0.5-15 mol% is more preferable when all the metals are 100 mol%. When the blending ratio is less than 0.1 mol%, the effect of improving the hydrogen generation efficiency is not recognized. On the other hand, if it exceeds 30 mol%, the efficiency of the Fe redox reaction is lowered, which is not preferable. The preparation method of Fe and the metal to be added is performed by a physical mixing method, an impregnation method, a coprecipitation method, or the like, and the coprecipitation method is particularly preferable.

  The reaction vessel 10 is made of a metal such as stainless steel or aluminum, a ceramic such as alumina or zirconia, or a heat-resistant plastic such as phenol resin or polyphenylene sulfide, and has a structure that can withstand heat and internal / external pressure. . Although a rectangular parallelepiped shape is shown in FIG. 1, it may be another hexahedron, a columnar shape or a truncated cone shape. When reaction container 10 becomes high temperature, it is preferable to cover reaction container 10 with a heat insulating material. As the heat insulating material, glass fiber, silica fiber, silica powder molded body and the like can be used. The vaporization space 18 can be filled with ceramic balls, glass wool, silica wool or the like in order to efficiently vaporize and disperse the introduced water.

According to the above configuration, first, air is introduced into the reaction vessel 10 from the introduction port 11. The introduced air diffuses through the vaporization space 18 to the entire metal storage portion 17a, and further diffuses through the vent hole 31 to the entire adjacent metal storage portion 17b. The metal in the metal storage part 17 is oxidized by oxygen in the air, and the metal itself is self-heated. As a result, the temperature rises by itself to a temperature range sufficient to generate hydrogen at startup from room temperature (for example, in the case of pure iron, Fe + 3 / 4O ₂ → 1 / 2Fe ₂ O ₃ , ΔH = −412.1 kJ / Mol, 298.15K, 101.3 kPa).

  At this time, it is preferable to introduce air (oxygen) so that the temperature of the metal in the reaction vessel 10 is in the range of 50 to 600 ° C. If the temperature of the metal is less than 50 ° C., the amount of water (liquid) introduced is small, and the metal oxidation reaction (hydrogen generation reaction) by water vapor (gas) does not proceed actively. On the other hand, in order to heat to a temperature exceeding 600 ° C., it is necessary to carry out a large amount of metal oxidation reaction (exothermic reaction) with oxygen, and since there is almost no amount of metal that can react with water vapor, the amount of hydrogen generation decreases. It is not preferable. The metal temperature is more preferably in the range of 100 to 400 ° C. Air in which all or part of oxygen contained by reacting with the metal is consumed is discharged from the discharge pipe 22.

Next, when the inside of the reaction vessel 10 is in the above temperature range where hydrogen can be generated, water is introduced into the reaction vessel 10 from the introduction tube 21 this time. The introduced water quickly vaporizes in the vaporization space 18 and becomes water vapor. The water vapor diffuses from the vaporization space portion 18 to the metal housing portion 17 a and diffuses to the metal housing portion 17 b through the vent hole 31. The metal in the metal storage portion 17 is oxidized by water vapor to generate hydrogen (for example, in the case of pure iron, Fe + 4 / 3H ₂ O → 1 / 3Fe ₃ O ₄ + 4 / 3H ₂ , ΔH = −50.4 kJ / mol) 298.15 K, 101.3 kPa). The generated hydrogen and unreacted water vapor are discharged from the discharge port 12. This gas containing hydrogen is introduced into a system that requires hydrogen, such as a fuel cell.

Then, when the metal in the metal storage unit 17 is completely oxidized and the reaction is completed, a reducing gas such as hydrogen is introduced into the reaction vessel 10 from the introduction pipe 21 and oxidized in the metal storage unit 17. Reduction of the metal is performed (for example, in the case of iron, Fe ₂ O ₃ + 3H ₂ → 2Fe + 3H ₂ O, Fe ₃ O ₄ + 4H ₂ → 3Fe + 4H ₂ O). By reducing the oxidized metal, the metal can be subjected to the aforementioned oxidation reaction again and can be used repeatedly. The heating temperature at this time is preferably 200 to 600 ° C. from the viewpoint of reduction efficiency.

  The gas used as the reducing agent may be hydrogen filled in a high-pressure cylinder, but a hydrocarbon such as a liquid hydrogen cylinder or methane (methane gas, natural gas or hydrocarbon raw material such as petroleum) is used as a catalyst. Hydrogen generated by cracked hydrogen, hydrogen generated by a steam reforming method using hydrocarbons and steam, hydrogen generated by methanol reforming, hydrogen generated by electrolysis of water, or the like can also be used. In either case, it is preferable to remove moisture and supply dry hydrogen before supplying it into the reaction vessel.

  As described above, according to the present embodiment, it is possible to start from room temperature and react to a temperature range sufficient to generate hydrogen by simply introducing oxygen from the introduction pipe 21 without using a large amount of electric energy. The temperature inside the container 10 can be raised. Further, since carbon (C) is not included in the reaction in the reaction vessel 10, carbon monoxide (CO) that poisons the electrode of the fuel cell is not discharged from the discharge pipe 22 together with hydrogen. Furthermore, the metal or its oxide in the metal storage part 17 which has become unable to generate hydrogen after the reaction is completed can be repeatedly generated with hydrogen by reducing with a reducing gas such as hydrogen. Further, a metal that is oxidized by oxygen and a metal that is oxidized by water are stored in the same metal storage unit 17, and the metal is fixed (so-called fixed bed flow type) to supply water and oxygen. Thus, heat generated by oxidation is stably stored in the reaction vessel 10, and hydrogen can be generated efficiently.

In the above description, only water is introduced after air is introduced and initially heated. However, air can be introduced together with water after the initial heating. As a result, in the reaction vessel 10, heat can be generated by the reaction of oxygen and metal in the air simultaneously with the generation of hydrogen by the reaction of water vapor and metal. The low valent metal oxide became Fe ₃ O ₄ or the like in reaction with water more than a predetermined temperature (for example, in the case of iron oxide, 200 ° C. or higher) Fe ₂ O reacts with high temperature if oxygen _It can rapidly oxidize to a high valent metal oxide such as ₃ to cause an exothermic reaction (for example, in the case of iron oxide, Fe ₃ O ₄ + 1 / 4O ₂ → 3/2 Fe ₂ O ₃ , ΔH = − 118 kJ / mol, 298.15 K, 101.3 kPa).

  When air is introduced together with water, the temperature in the metal housing portion 17 is further increased as compared with the case where only water is introduced, so that temperature control can be achieved by introducing air. Conditions such as the structure of the reaction vessel, the amount of water and air introduced, and the amount of metal to be filled can be set so that all oxygen in the air is consumed by oxidation of the metal and oxygen is not discharged from the discharge port 12. preferable. In addition, when carbon dioxide in the air may be reduced to carbon monoxide and discharged together with hydrogen, the introduced air may be absorbed by carbon dioxide absorbents such as caustic soda and lime water through the air. preferable. Even if carbon dioxide is not removed in advance, the concentration of carbon monoxide can be suppressed to 10 ppm or less which does not significantly poison the electrode of the fuel cell by setting the introduction amounts of water and air. Pure oxygen may be introduced instead of air as the oxygen-containing gas.

  Further, the water to be introduced by exchanging heat of the oxidation reaction heat in the reaction vessel 17 or hydrogen discharged at a high temperature from the discharge pipe 22 and water introduced from the introduction pipe 21 by a heat exchanger (not shown) or the like. Can be preheated. Thereby, the thermal efficiency of a hydrogen production apparatus can be improved.

  A test for generating hydrogen was performed using the apparatus shown in FIG. The apparatus shown in FIG. 2 is an atmospheric pressure fixed bed flow type reaction apparatus, in which a reaction gas generated in a cylindrical stainless steel reaction vessel 50 is introduced into a water trap apparatus 51 to agglomerate water in the reaction gas. Then, a part of this gas was sampled and measured with a gas chromatograph 52. The flow rate of the reaction gas was measured with a flow meter 53. At the same time, the temperature of the central sample in the reaction vessel 50 was measured. The reaction vessel 50 was covered with a heat insulating material made of silica fiber and kept warm.

Iron stored in the reaction vessel 50 was prepared by an impregnation method and 3.6 mol% of Al was added (BET specific surface area 52.1 m ² / g, average particle size 0.11 μm). The sample was formed into a pellet, and 778 g was placed in the reaction vessel 50, hydrogen for reduction was introduced, and a reduction reaction was performed at 500 ° C. for 6 hours in an electric furnace (not shown). A sample after the reduction was taken out and weighed in nitrogen as an inert gas, and it was 582 g. The sample was again packed in the reaction vessel 50 and the test was started.

  First, air from which carbon dioxide was removed with caustic soda was introduced into a reaction vessel 50 at a normal temperature at a flow rate of 1.2 L / min, and an oxidation reaction between reduced iron and oxygen in the air was performed. Then, 40 minutes after the introduction of air, room temperature water was introduced into the reaction vessel 50 together with air at a flow rate of 1.0 mL / min. The experiment was terminated 270 minutes after the introduction of air. The results of the measured hydrogen generation rate and the sample temperature in the reaction vessel are shown in FIG.

  As shown in FIG. 3, hydrogen was generated immediately at the moment when water was added, and the hydrogen generation rate of about 1 L / min was stably maintained for about 120 minutes. Thereafter, the hydrogen generation rate decreased, and hydrogen was not generated about 200 minutes after the introduction of water. During this time, the total amount of hydrogen generated was 151 L. During the reaction, in addition to hydrogen, nitrogen in the air was contained at about 0.9 L / min, but oxygen, carbon dioxide, and carbon monoxide were not detected by gas chromatography. As described above, it was confirmed that the conditions under which oxygen is not discharged together with hydrogen can be set depending on the amounts of water and air introduced.

  As a comparative example, an experiment was performed in the same procedure as in the above example except that no air was introduced. The result is shown in FIG. As shown in FIG. 4, since air was not introduced, the temperature of the sample in the reaction vessel 50 did not rise and remained at room temperature, and even when water was introduced, generation of hydrogen could not be confirmed. .

It is sectional drawing which shows simply an example of the apparatus suitable for implementation of the hydrogen manufacturing method which concerns on this invention. It is a schematic diagram which shows the outline of the reaction apparatus used by the hydrogen generation test. It is a graph which shows the sample temperature at the time of introduce | transducing oxygen and water, and a hydrogen generation rate. It is a graph which shows the sample temperature at the time of introduce | transducing only water and a hydrogen generation rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reaction container 11 Inlet port 12 Outlet port 17 Metal storage part 18 Vaporization space part 21 Introducing pipe 22 Outlet pipe 30 Current plate 31 Vent hole 41, 42 Filter 50 Reaction container 51 Water trap apparatus 52 Gas chromatograph 53 Flowmeter

Claims (5)

  A hydrogen production method in which hydrogen is generated by a chemical reaction between at least one of iron, indium, tin, magnesium, and cerium or an oxide thereof and water, and the metal or the oxide is stored in a fixed bed type. A step of supplying an oxygen-containing gas to the inside of the reaction vessel and increasing the temperature in the reaction vessel by an oxidation reaction of the metal or its oxide; and supplying water into the reaction vessel having the increased temperature; Or a process for generating hydrogen by an oxidation reaction of the oxide.   The hydrogen production method according to claim 1, wherein the iron is at least one pure iron powder of cast iron powder, reduced iron powder, electrolytic iron powder, and atomized iron powder.   The hydrogen production method according to claim 1, wherein a metal other than iron is added to the iron or iron oxide and is stored in the reaction vessel.   The method for producing hydrogen according to claim 3, wherein the metal other than iron is at least one of titanium, zirconium, vanadium, niobium, chromium, molybdenum, aluminum, gallium, magnesium, scandium, nickel, copper, and neodymium. .   The method for producing hydrogen according to claim 3, wherein the metal other than iron is at least one of rhodium, iridium, platinum, ruthenium, and palladium.

Images