JP2013014452A - Method for producing hydrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing hydrogen with a small sized portable type of device at low energy consumption and low cost in a method of producing hydrogen using ethanol effectively.SOLUTION: The method of producing hydrogen is characterized by supplying air or nitrogen gas and ethanol gas to an atmospheric plasma generator to decompose ethanol molecules to generate hydrogen. In the atmospheric plasma generator, high frequency waves are applied between an inner electrode in a plasma reactor and an outer electrode in outside of the plasma reactor. Plasma discharge is induced between the inner wall of the plasma reactor and the inner electrode, and a gas to be treated is allowed to become contact with plasma, the gas to be treated is decomposed by a synergistic effect of plasma excitation and compulsive contact to plasma region, and activation by a catalyst in plasma and outside of plasma.

Description

  The present invention relates to a hydrogen production method for producing hydrogen gas that can be used for various fuels such as a fuel cell of an electric vehicle from ethanol as a biofuel.

  Conventionally, in the brewing industry, a large amount of bad alcoholic beverages that cannot be sold including ethanol is produced. On the other hand, in recent years, as a part of a bioenergy production method that contributes to solving environmental problems, a hydrogen source, in particular, a small portable type hydrogen production apparatus has been developed and put into practical use. In particular, it is attracting attention as an apparatus for producing fuel hydrogen for fuel cell vehicles from biofuel.

  In order to make effective use of the above-mentioned defective ethanol, research and development for producing hydrogen from ethanol molecules is being promoted as a new technology for producing electric power energy without giving an environmental load. Conventionally, decomposition of ethanol has been attempted by various catalytic reaction methods as hydrogen gas production methods.

Further, as this type of hydrogen gas production method, there are a method of decomposing methanol together with water, a method of decomposing metal hydride, MgH ₂ , CaH ₂ , NaH _{2 and the} like together with water molecules. However, it has not been put into practical use because it requires an expensive catalyst and the production cost of hydride is high. Furthermore, although a method for producing hydrogen by directly contacting and reacting magnesium metal and aluminum metal fine particles with water molecules has been attempted, it is difficult to control the hydrogen generation reaction, and it has not been put into practical use.

  Furthermore, as disclosed in Patent Documents 1 and 2, a method for producing a hydrogen generating material that decomposes water to generate hydrogen, which is obtained by rubbing and grinding aluminum or an aluminum alloy in water, and fine particles of 50 μm or less There is also a method in which the microparticles are subjected to an activation treatment by applying a temperature or ultrasonic impact to the microparticles, subjected to heat treatment at room temperature for several days, and then cooled to 5 ° C. and placed in a storage state. .

Japanese Patent No. 4169197 Japanese Patent No. 4169217

However, the above ethanol decomposition method using the conventional catalytic reaction method is often a high-temperature and high-pressure reaction, is inefficient, and has not yet been put into practical use. In particular, ethanol is an organic molecule having a simple structure, but it has been difficult to completely decompose it to produce three hydrogen molecules per molecule. Further, in the decomposition reaction using a catalyst, intermediate products such as HCOH and CH ₃ are generated together with hydrogen, and thus further additional reaction is necessary.

  In Patent Documents 1 and 2, a reaction vessel for storing a large amount of pure water and a large cutting device for rubbing and crushing aluminum or aluminum alloy in water are required. Thus, it has been difficult to realize a small portable type hydrogen gas production apparatus.

  Therefore, the present invention was created in view of the existing circumstances as described above, and the activation of metallic aluminum is not only the method of fine particle formation which is the principle of the patent literature, but also the porous formation of aluminum. In view of the fact that this method can also be achieved, in addition to using activated aluminum fine particles, the activation of the aluminum electrode is realized by the method of making the electrode porous. Accordingly, an object of the present invention is to provide a small and portable hydrogen production method that consumes less energy, is low in cost, and is environmentally friendly in the production of hydrogen gas using ethanol effectively.

  In order to solve the above-mentioned problems, in the present invention, a high frequency is applied between the internal electrode in the plasma reactor and the external electrode outside the plasma reactor, and plasma discharge is induced between the inner wall of the plasma reactor and the internal electrode. When the target gas is brought into contact with the plasma, the atmospheric pressure plasma is generated by the synergistic effect of plasma excitation, forced contact with the plasma region, and activation by the catalyst in and outside the plasma. Air or nitrogen gas and ethanol gas are supplied to the apparatus, and hydrogen is generated by decomposing ethanol molecules.

  The atmospheric pressure plasma generator is characterized in that the outer shape is a quartz glass tube, the electrode is formed by disposing an internal electrode at an inner center position of the quartz glass tube, and disposing an external electrode on the outer wall of the quartz glass tube. To do.

  The atmospheric pressure plasma generator is characterized in that the outer shape having the internal space is a flat plate type, and the electrodes are arranged above and below the inner space.

  Further, in the above atmospheric pressure plasma generator, the internal gas flow path is divided into two parts, each of which introduces air or nitrogen gas and ethanol gas, and decomposes ethanol molecules by plasma discharge decomposition and plasma emission of the introduced gas. It is characterized by.

  The atmospheric pressure plasma generation apparatus is characterized in that air by natural convection is introduced into the apparatus in order to excite nitrogen molecules by plasma discharge to emit ultraviolet rays.

  Furthermore, the ultraviolet rays obtained by exciting the nitrogen molecules are activated by irradiating the titanium dioxide catalyst through an ultraviolet transmitting material, and the ethanol molecules are decomposed by the photocatalytic effect of the activated titanium dioxide.

  In the above atmospheric pressure plasma generator, the internal electrode in contact with the ethanol molecule is formed of an active aluminum plate or an active aluminum netting material having high reactivity with water and carbon monoxide, and the electron emission of the electrode causes the generation of the ethanol molecule. It is characterized in that carbon and oxygen atoms generated from decomposed ethanol together with plasma decomposition are fixed and separated as an aluminum compound and graphite.

  In the present invention, ethanol molecules are excited and decomposed by plasma discharge. The basis of this technology is derived from the PACT (Plasma Assisted Catalytic Technology) method of Impact World Co., Ltd., but it is difficult to completely decompose ethanol only by this technology. In particular, it is necessary to devise electrode materials and reactor structures in order to produce hydrogen gas as purely as possible from ethanol and eliminate carbon dioxide emission. For example, the active aluminum material technology of Hydrodevice Co., Ltd. is applied to the electrode of the plasma reactor.

Therefore, in the hydrogen production method according to the present invention, a normal thermochemical reaction is not used, and a main method is a method of decomposing ethanol molecules by electrical plasma ions and electron impact. However, since plasma bombardment alone does not lead to complete decomposition of ethanol, a catalyst is placed in and outside the plasma to achieve complete decomposition. The cause of incomplete decomposition is the presence of carbon and oxygen atoms in ethanol. Usually, they lead to the production of CO ₂ molecules, but the present invention is aimed at reactor production and hydrogen production methods that do not release CO ₂ .

  According to the present invention, the hydrogen production from ethanol is realized by the combined use of the plasma discharge method and the catalytic reaction method, so that the energy consumption is small, whereby hydrogen gas can be produced inexpensively and in large quantities, It is possible to provide a small and portable hydrogen production method that is low cost and environmentally friendly. In particular, since the product contains almost no carbon dioxide, it can be expected to contribute greatly to environmental problems.

It is a block diagram which shows the outline of the hydrogen production apparatus by the separation gas type | mold plasma reactor which shows one form for implementing this invention. It is a block diagram which shows the outline of the hydrogen production apparatus by a mixed gas type plasma reactor. It is a system block diagram of the hydrogen production apparatus similarly by a mixed gas type plasma reactor.

Hereinafter, embodiments of the present invention will be described in detail.
The method of the present embodiment is based on the PACT method using an atmospheric pressure plasma generator that causes the decomposition of ethanol molecules to simultaneously cause plasma discharge decomposition and catalytic decomposition placed in the plasma. In addition, ethanol is completely decomposed by placing an external catalyst layer. Further, a TiO ₂ (titanium dioxide) photocatalyst is used as an internal catalyst.

Ultraviolet light is required for excitation of the TiO ₂ (titanium dioxide) photocatalyst. For this purpose, a method of ultraviolet radiation by plasma excitation of N ₂ (nitrogen) molecules is adopted. Therefore, nitrogen gas and ethanol gas are simultaneously supplied to the plasma reactor.

The atmospheric pressure plasma generator has a structure and characteristics different from those of the conventional low pressure plasma apparatus.
That is, (1) It is necessary to create an ionosphere by applying a high voltage of about 10 kV in order to cause discharge in a gas at atmospheric pressure. (2) Since a ceramic partition is placed between the electrodes and no electronic current flows between the electrodes and only the induced current is used, the power used is small. (3) Since the nature of atmospheric pressure plasma changes in the discharge space (position), the plasma generation is made as uniform as possible to increase the efficiency of the hydrogen generation reaction. For this purpose, it is important to extract carbon atoms and oxygen atoms as separate compounds instead of carbon dioxide (CO ₂ ).

Therefore, in the present embodiment, carbon atoms and oxygen atoms are separated as an aluminum compound by using metallic aluminum as an electrode material. Furthermore, a TiO ₂ catalyst (network) having a large surface area is installed as an adsorbent, and carbon atoms and the like are removed by accumulating graphite formed thereon. Furthermore, an appropriate catalyst layer is disposed outside the plasma reactor.

The decomposition reaction of ethanol is a thermal reaction using a catalyst, depending on the reaction conditions.
C ₂ H ₅ OH → HCOH + CH ₄
C ₂ H ₅ OH + H ₂ O → 4H ₂ + CO ₂ + C (graphite)
The production of carbon dioxide gas is normal. In ethanol molecular decomposition using a plasma reactor, the following reaction progress is realized using an aluminum discharge electrode. That is, since bio-generated ethanol always contains water,
(TiO ₂ catalyst)
2C ₂ H ₅ OH + H ₂ O + 2Al → 7H ₂ + 4C (graphite) + Al ₂ O ₃
(Plasma discharge)
Devise the reactor so that the main reaction is For this plasma decomposition reaction,
C ₂ H ₅ OH → 2H ₂ + 2C + H ₂ O
2Al + 3H ₂ O → 3H ₂ + Al ₂ O ₃
Plasma vapor phase reactions, and surface reactions on the electrodes.

In the method of this embodiment, aluminum used as the internal electrode material has an important role in generating a reaction product. That is, the aluminum electrode to be used has a very strong reactivity with water, and in particular, an active aluminum material having a strong ability to produce aluminum oxide (Al ₂ O ₃ ) is used. The active aluminum material used as an electrode is a special aluminum material that is made porous by surface treatment, has a large surface area, and contains aluminum hydride (AlH ₃ ) inside.

  There are two methods for producing hydrogen from ethanol using a plasma reactor. One is a mixed method in which ethanol is supplied together with nitrogen gas to the plasma reactor as described above. This method is easy to implement and the structure of the plasma reactor is simple. However, there is a problem that nitrogen gas is mixed in the produced hydrogen, and a somewhat large apparatus is required for the post-treatment.

  On the other hand, a method in which nitrogen gas and ethanol gas are separated and introduced into the plasma reactor can be considered, but the plasma apparatus is complicated and cannot be easily implemented. The method of the present invention employs a method of simultaneously realizing the generation of double plasma of nitrogen gas (air) plasma and ethanol plasma.

  As described above, the gas separation type method of supplying nitrogen gas and ethanol gas separately to the plasma reactor and the mixed type method of supplying nitrogen gas and ethanol gas mixed have advantages and disadvantages, respectively. . That is, in the gas separation type method, the plasma reactor is different from the normal structure, and the reactor is not easily manufactured. However, high purity hydrogen gas can be produced using only ethanol as a raw material. On the other hand, the mixed type method has a simple plasma reactor structure and is easy to manufacture. Nitrogen molecules in the produced hydrogen are separated by a high-purity hydrogen production apparatus using a Pd (palladium) membrane, but separation is not easy when the amount of nitrogen gas is large.

  In this embodiment, two types of methods are tried. Below, the concrete structure by these two methods is demonstrated.

FIG. 1 shows the structure of a cylindrical separated gas plasma reactor.
That is, this separated gas type plasma reactor has a silicone plug 2a in which an inner electrode 2 (porous aluminum electrode) serving as an aluminum discharge electrode is sealed at both ends of the quartz glass tube 1 in the center of the cylindrical quartz glass tube 1. 2b. The internal electrode 2 is formed of an active aluminum plate or an active aluminum net member having high reactivity with water and carbon monoxide. The quartz glass tube 1 is filled with a photocatalyst 3 made of glass wool and titanium dioxide (TiO ₂ ) so as to surround the inner electrode 2.

  One silicone plug 2a is provided with an introduction tube 4a for supplying ethanol gas so as to face the quartz glass tube 1. Further, a discharge pipe 4b for discharging hydrogen gas passes through the other silicone plug 2b and faces the quartz glass pipe 1. The introduction pipe 4a and the discharge pipe 4b are arranged on opposite sides with the central photocatalyst 3 interposed therebetween.

  Further, on the outer wall of the quartz glass tube 1, a cylindrical external electrode 5 as a stainless steel electrode having a rough surface is disposed with a predetermined gap G with respect to the outer wall, and the external electrode 5 and the internal electrode 2 are arranged. Is connected via a 10 kV AC power supply. The external electrode 5 itself is grounded. The gap G is filled with glass wool and air, so that nitrogen molecules are plasma-excited by a high frequency voltage applied between the electrodes 2 and 5 to generate ultraviolet rays.

In the separated gas plasma reactor having the above-described configuration, two-phase plasma of nitrogen gas and ethanol gas is separated by a quartz glass tube 1 that transmits ultraviolet rays. That is, two plasmas of air introduced by natural convection and ethanol gas introduced from the introduction tube 4a are simultaneously generated in one apparatus, and ultraviolet rays from excited nitrogen molecules pass through the quartz glass tube 1. The photocatalyst 3 containing TiO ₂ inside is irradiated. Then, carbon atoms and oxygen atoms generated from the decomposed ethanol are fixed and separated as an aluminum compound and graphite together with plasma decomposition of ethanol molecules by electron emission of the internal electrode 2, and only hydrogen gas is recovered through the discharge pipe 4b.

FIG. 2 shows the structure of a flat plate type mixed gas plasma reactor.
That is, a gas supply port 11a is provided at one end of the upper surface of the flat stainless steel frame 11 having an inner space, and a gas discharge port 11b is provided at the other end of the upper surface. A plasma reactor 12 is disposed in the center of the inner space of the stainless steel frame 11, and gas retention layers 13a and 13b as catalyst layers are disposed on both sides thereof. The plasma reactor 12 is filled with a photocatalyst 16 (titanium dioxide) made of TiO ₂ between ceramic substrates 14a and 14b arranged on the upper and lower sides thereof. One ceramic substrate 14a (upper side) is connected to a stainless steel electrode 15a which is a negative electrode. The other ceramic substrate 14b (lower side) is connected to an aluminum electrode 15b which is a plus electrode.

The mixed gas plasma reactor having the above configuration supplies ethanol gas into the plasma reactor 12 through the gas supply port 11a using nitrogen gas as a carrier gas. In this case, since the gas retention layers 13a and 13b, which are additional catalyst layers, can be installed before and after the plasma reactor 12, it is possible to generate plasma with uniform space. Under the photocatalyst 16 made of activated TiO ₂ that is plasma-discharged by applying a high voltage to the stainless steel electrode 15a and the aluminum electrode 15b, the ethanol molecules are plasma-decomposed and impurity gas generated from the decomposed ethanol is removed from the aluminum electrode. 15b and gas retention layers (catalyst layers) 13a and 13b are decomposed, and only hydrogen gas is discharged from the gas discharge port 11b and collected.

  In both types of plasma reactors, the internal electrode 2 and the aluminum electrode 15b are composed of an active aluminum electrode having a rough surface, which improves discharge characteristics and removes carbon and oxygen generated from cracked ethanol as compounds. Further, the external electrode 5 is made of stainless steel, and similarly has a rough structure so that plasma discharge is easy (low voltage).

  As shown in FIG. 1, a separation gas type plasma reactor was prototyped and its characteristics were evaluated. An AC high voltage of about 10 kV was applied at 10 kHz, and a stable condition was imposed to achieve both external air plasma and internal ethanol plasma. Nitrogen molecules were excited by generating air discharge plasma on the outside, ultraviolet rays were emitted, and the titanium photocatalyst was irradiated through quartz glass. In order to stabilize both plasmas, it is necessary to appropriately adjust the type and density of the material placed in the plasma reactor. First, the internal plasma discharge stability conditions were determined, and then the internal material (glass fiber, etc.) and applied voltage were changed so that the external plasma was stabilized while finely adjusting the conditions. As a result of the test, 70 to 80% of the introduced ethanol molecules were decomposed, but undecomposed ethanol was observed. Generation of hydrogen gas was confirmed by gas combustion method and fuel cell operation. HCOH was contained in the product gas as an impurity gas. In addition, an odor reminiscent of ozone generation was observed from the air plasma side, but it was easily removed by putting charcoal adsorbent into the air-cooled exhaust system.

Next, as shown in FIG. 2, a mixed gas type plasma reactor having a simple plasma reactor structure was manufactured and tested. In the test machine, nitrogen gas and ethanol gas were mixed and sent into the reactor, and the reactivity and reaction products were observed. A system diagram of the apparatus used is shown in FIG. In this case, pure nitrogen gas (pressure 0, 1 atm, flow rate of about 50 ml / min) supplied from a gas cylinder was used. Ethanol was supplied as a (N ₂ + C ₂ H ₅ OH) mixed gas from the ethanol container to the plasma reactor by bubbling nitrogen gas. The plasma reactor is connected to a high-frequency and high-voltage power source that can be adjusted by a voltage regulator connected to a 100 V input power source. Assuming that incompletely decomposed impurities are mixed in the generated hydrogen and nitrogen mixed gas, this gas was passed through an impurity gas adsorption layer container containing charcoal adsorbent to remove the impurity gas. Thereafter, only (H ₂ + N ₂ ) gas was recovered and supplied to the fuel cell. Production of hydrogen was confirmed by power generation of the fuel cell, and it was found that about 50% of hydrogen was present in nitrogen gas. Several percent of CO ₂ and HCOH were observed as impurities. Since the current flowing during the reaction is about 10 mA, the power used is about 100 W.

  It is expected that low-quality liquor produced in the brewing industry will be used effectively and converted to hydrogen energy to become a new energy industry. Since it is possible to produce hydrogen by decomposing organic molecules other than ethanol by the method of the present invention, it is considered that there are future applications and developments. In the method of the present invention, since the method for producing hydrogen is small and light, it can be used as a hydrogen source for fuel cell vehicles, as well as a fuel (energy) source for various moving means such as airplanes, ships, and electric motorcycles. Can also be used.

G Gap 1 Quartz glass tube 2 Internal electrode 2a, 2b Silicone plug 3, 16 Photocatalyst (titanium dioxide)
4a introduction pipe 4b discharge pipe 5 external electrode 11 stainless steel frame 11a gas supply port 11b gas discharge port 12 plasma reactor 13a, 13b gas retention layer (catalyst layer)
14a, 14b Ceramic substrate 15a Stainless steel electrode 15b Aluminum electrode

Claims (7)

  A high frequency is applied between the internal electrode in the plasma reactor and the external electrode outside the plasma reactor, and a plasma discharge is induced between the plasma reactor inner wall and the internal electrode to bring the gas to be treated into contact with the plasma. Air or nitrogen gas and ethanol gas are supplied to an atmospheric pressure plasma generator that decomposes the target gas by synergistic effects of plasma excitation, forced contact with the plasma region, and activation by a catalyst in and outside the plasma. A method for producing hydrogen, comprising decomposing ethanol molecules to produce hydrogen.   The atmospheric pressure plasma generator is characterized in that the outer shape is a quartz glass tube, the electrode is formed by arranging an internal electrode at the inner center position of the quartz glass tube, and arranging an external electrode on the outer wall of the quartz glass tube. The method for producing hydrogen according to claim 1.   2. The hydrogen production method according to claim 1, wherein the atmospheric pressure plasma generator has a flat outer shape having an internal space, and the electrodes are arranged above and below the inner space.   The atmospheric pressure plasma generator is characterized in that an internal gas flow path is divided into two parts, each of which introduces air or nitrogen gas and ethanol gas, and decomposes ethanol molecules by plasma discharge decomposition and plasma emission of the introduced gas. The method for producing hydrogen according to any one of claims 1 to 3.   5. The hydrogen according to claim 1, wherein the atmospheric pressure plasma generator introduces air by natural convection into the apparatus in order to excite nitrogen molecules by plasma discharge to emit ultraviolet rays. Production method.   6. The ultraviolet rays obtained by exciting the nitrogen molecules are activated by irradiating the titanium dioxide catalyst through an ultraviolet transmitting material, and the ethanol molecules are decomposed by the photocatalytic effect of the activated titanium dioxide. Hydrogen production method.   In the atmospheric pressure plasma generator, the internal electrode in contact with ethanol molecules is formed from a network of active aluminum that is highly reactive with water, carbon monoxide, and oxygen atoms. 7. The method for producing hydrogen according to claim 1, wherein carbon and oxygen atoms produced from cracked ethanol are fixed and separated as an aluminum compound and graphite.

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