JPWO2006093098A1 - Low temperature fuel cell system - Google Patents

Abstract

The present invention decomposes and removes harmful by-products such as formaldehyde produced during the anode reaction to the extent that they do not adversely affect the human body and the environment even if they are released into the atmosphere, and releases the exhaust gas directly into the atmosphere. The present invention relates to a low-temperature fuel cell system capable of The low-temperature fuel cell system of the present invention has a low-temperature fuel cell and means for decomposing and removing harmful by-products generated at the anode of the low-temperature fuel cell, and the means includes a reaction liquid derived from the anode and / or Or it is provided so that it may contact with the waste gas isolate | separated from the said reaction liquid.

Description

  The present invention relates to a fuel cell system operating at a low temperature.

    Among fuel cells, direct methanol type, solid polymer type, and phosphoric acid type fuel cells are also called low temperature type fuel cells because they are operated at a relatively low temperature of about 70 to 90 ° C. or about 200 ° C. Since these low-temperature fuel cells can operate at low temperatures, they have high startability, and can be used not only for portable devices but also for relatively small power sources for home use, business use, and automobile use.

  Since fuel cells take out electricity by the reverse reaction of water electrolysis, the only theoretical emission is water. However, not only hydrogen is used as a fuel, but also various side reactions occur, so that harmful compounds may be emitted.

  For example, although hydrogen is sometimes used as a fuel for a low-temperature fuel cell, alcohols such as methanol are used as a safer and more convenient one. In this case, alcohols are partially oxidized during power generation, and aldehydes and carboxylic acids are by-produced. For example, when methanol is used as a fuel, it is known that formaldehyde, formic acid, methyl formate and the like are by-produced mainly at the anode.

  Among these by-products, formaldehyde is a harmful chemical substance that causes sick house syndrome, and the generation of these harmful by-products during power generation must be suppressed as much as possible. However, the actual situation is that almost no efforts have been made to control these harmful by-products.

  As a few precedents, Japanese Patent Application Laid-Open No. 2003-123777 discloses a polymer electrolyte fuel cell in which a peroxide decomposition catalyst is added to a catalyst layer. The peroxide decomposition catalyst in this technique is one in which ruthenium or the like is supported on carbon black, zirconia, or the like, and the one used in the examples is only one in which a metal is supported on carbon black.

  However, an electrode catalyst for a polymer electrolyte fuel cell is generally one in which platinum or platinum-ruthenium is supported on carbon black. Therefore, the peroxide decomposition catalyst in the above publication cannot be distinguished at all from conventional electrode catalysts.

  As described above, there are very few techniques for suppressing by-products in a low-temperature fuel cell, and the effect is not sufficient. Therefore, in the conventional low-temperature fuel cell, harmful by-products such as formaldehyde are released to the outside, which may adversely affect the human body and the environment.

  Therefore, an object of the present invention is to decompose and remove harmful by-products such as formaldehyde by-produced during the anodic reaction at least to the extent that they do not adversely affect the human body and the environment even if released into the atmosphere, and the exhaust gas is left in the atmosphere as it is. It is an object of the present invention to provide a low-temperature fuel cell system that can be discharged into a battery.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies on a method that can effectively decompose and remove harmful by-products. As a result, it was found that if the reaction product discharged from the anode or the by-product contained in the exhaust gas separated from the reaction solution is decomposed and removed, the amount of harmful by-products released to the outside can be significantly suppressed. Completed the invention.

The low-temperature fuel cell system of the present invention is
A low-temperature fuel cell, and means for decomposing and removing harmful by-products generated at the anode of the low-temperature fuel cell,
The means is provided in contact with the anode-derived reaction liquid and / or the exhaust gas separated from the reaction liquid.

  In conventional fuel cells, little consideration has been given to suppressing harmful by-products such as formaldehyde. On the other hand, according to the low-temperature fuel cell system of the present invention, the release of harmful by-products that adversely affect the human body and the environment can be significantly suppressed. Therefore, the low-temperature fuel cell system of the present invention is very useful industrially as it can be used for power generation systems for home use and business use, and power sources for portable devices and automobiles.

It is a schematic diagram of a low temperature fuel cell system having a fuel circulation line for circulating a reaction liquid derived from an anode and reusing it as fuel.

The low-temperature fuel cell system of the present invention is
A low-temperature fuel cell, and means for decomposing and removing harmful by-products generated at the anode of the low-temperature fuel cell,
The means is provided in contact with the anode-derived reaction liquid and / or the exhaust gas separated from the reaction liquid.

  The “low temperature fuel cell” of the present invention is not a solid oxide fuel cell that operates at a high temperature of, for example, about 800 to 1000 ° C., but a direct methanol type that operates at a relatively low temperature of about 70 to 90 ° C. or about 200 ° C. And solid polymer type and phosphoric acid type fuel cells.

  The “hazardous by-product” of the present invention is a compound produced by the anode reaction from the fuel itself supplied to the low-temperature fuel cell or from the substance supplied accompanying the fuel, and has a negative effect on the human body and the environment. It means what can be done. More specifically, for example, when methanol is used as the fuel, the following reaction occurs at the cathode and anode of the low temperature fuel cell.

Anode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O

  However, at the anode, formaldehyde, formic acid, methyl formate, and the like in which methanol is partially oxidized are generated. In particular, formaldehyde is a harmful compound that causes sick house syndrome. In the present invention, these harmful by-products such as formaldehyde are treated.

  Since the harmful by-products are mainly produced at the anode, in the present invention, means for decomposing and removing harmful by-products produced at the anode of the low-temperature fuel cell are used as the reaction liquid derived from the anode and / or the reaction liquid. Provided in contact with the exhaust gas separated from

  The “means for decomposing and removing harmful by-products generated at the anode” in the present invention is not particularly limited as long as it can effectively decompose harmful by-products generated at the anode, and for example, a catalyst using a metal catalyst. Examples include catalytic cracking.

  What is necessary is just to select suitably the kind of catalyst as a decomposition removal means of this invention according to the kind of by-product to produce | generate. For example, a solid catalyst containing one or more elements selected from the group consisting of Pt, Pd, Ru, Ir, Au, and Ag can be given. Such solid catalysts are generally well known, and any of these known solid catalysts can be used in the present invention. For example, carbon-containing carriers such as activated carbon, metal oxides such as silica, alumina, titania, zirconia, multi-metal oxides such as silica-alumina, titania-silica, titania-zirconia, or titanium-silicon composite oxide Examples thereof include a solid catalyst in which a composite oxide such as a titanium-based composite oxide such as a titanium-zirconium composite oxide is used as a carrier and a noble metal is supported thereon. Among these, a solid catalyst in which the noble metal is supported on a carbon-containing carrier such as activated carbon is preferably used. For example, when a solid catalyst containing activated carbon is used under wet conditions, oxygen in the liquid is selectively adsorbed, so that the decomposition reaction of harmful substances proceeds efficiently. These solid catalysts can be easily prepared according to generally known methods.

  The activated carbon used as the carrier preferably has a pore volume with a radius of 4 nm or more and less than 10 nm of 0.05 mL / g or more, more preferably 0.2 mL / g or more. If activated carbon having a pore structure in the above range is used as a carrier, harmful by-products can be removed more efficiently. Here, the pore volume of the activated carbon was measured by a nitrogen adsorption method performed under conditions of 77K, 10.5 Torr or less (about 1400 Pa or less) using an automatic gas adsorption device such as Omni soap 360CX manufactured by Beckman Coulter, for example. It can be determined by calculating a pore distribution curve from the adsorption isotherm by the BJH method.

  In the solid catalyst containing the noble metal, which is the decomposition and removal means of the present invention, the content of the noble metal is usually 0.05% by mass or more and less than 50% by mass, preferably 0.05% by mass or more and less than 10% by mass. is there. If the content is less than 0.05% by mass, sufficient performance may not be obtained. On the other hand, if the content is 50% by mass or more, the effect may be saturated and the catalyst performance may not be improved.

  There is no restriction | limiting in particular about the shape of a solid catalyst, It can select suitably so that the liquid which should be processed on the surface of a solid catalyst can contact uniformly. For example, a solid catalyst in which a noble metal element is supported on a honeycomb-shaped carrier is preferably used. Furthermore, the conditions for decomposing harmful by-products may be appropriately adjusted depending on the type of harmful by-products, and can be set to room temperature and normal pressure, for example, but may be heated. However, when heating, the temperature of the fuel should be determined with caution because the fuel itself may be decomposed.

  What is necessary is just to determine the installation method of the decomposition removal means of this invention by the decomposition removal means to be used. For example, when a solid catalyst is used as the decomposition and removal means, the reaction solution derived from the anode is discharged from the low-temperature fuel cell through a packed bed filled with the solid catalyst formed into a spherical shape, ring shape, cylindrical shape, honeycomb shape, or the like. It may be provided in the line for Moreover, you may provide in the line for discharging | emitting the waste gas isolate | separated from the reaction liquid derived from an anode other than the said line or the said line.

  The low-temperature fuel cell system of the present invention preferably further has a fuel circulation line for circulating the anode-derived reaction liquid and reusing it as fuel. This is because the fuel can be efficiently recycled by recycling the fuel, and when harmful by-products are generated at the anode, emission of harmful by-products to the outside can be further reduced. Such a low-temperature fuel cell system will be described with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of the low-temperature fuel cell system of the present invention, where 1 is a fuel cell, 2 is a water separator, 3 is a fuel tank, and 4 is a fuel circulation tank.

  The low-temperature fuel cell system has a fuel circulation line for circulating at least the reaction liquid derived from the anode and reusing it as fuel together with the low-temperature fuel cell. That is, in the fuel cell, fuel is supplied to the anode, but unreacted fuel and the like are discharged after the anode reaction. In this embodiment, this is recovered, and unnecessary compounds are separated, mixed with fuel and the like, and supplied to the anode again. Thereby, it is possible to efficiently generate power and to reduce harmful by-products released to the outside.

  That is, in this embodiment, harmful by-products generated by the anode reaction are decomposed and the concentration thereof is reduced, so that volatilization of harmful by-products is not significantly suppressed and the environment is not contaminated. Since it is recycled, the amount of harmful by-products emitted to the outside can be reduced. Hereinafter, the fuel circulation line of the present invention will be described in detail with reference to FIG.

  FIG. 1 illustrates the case where methanol is used as the fuel. That is, when methanol and water are supplied from the fuel supply line 14 to the anode, carbon dioxide is discharged together with unreacted methanol and water. The carbon dioxide is recovered together with methanol and water by the anode reaction liquid recovery line 15 and is carried to the fuel circulation tank 4.

  The “fuel circulation tank” is for separating carbon dioxide from the collected anode reaction liquid, mixing it with fuel and the like, and then supplying it again to the anode of the fuel cell. More specifically, the exhaust gas discharge line 16 for discharging carbon dioxide; a concentration meter that measures the concentration of fuel in the recovered anode reaction solution; the recovered anode reaction solution, fuel, water, and the like based on the concentration A mixer that mixes the components at an appropriate ratio is provided. The fuel circulation tank 4 constitutes a fuel circulation line together with the anode reaction liquid recovery line 15 and the fuel supply line 14.

  By-product decomposition and removal means when the fuel is circulated and reused is installed in the fuel circulation line. For example, the anode reaction liquid recovery line 15, the inside of the fuel circulation tank 4, the exhaust gas discharge line 16, or the fuel supply line 14 of FIG. Preferably, in order to perform an efficient process, it is provided in the fuel circulation line before the collected anode reaction liquid is mixed with fuel or the like. That is, it is preferably provided in the anode reaction liquid recovery line 15, the inside of the fuel circulation tank 4, the exhaust gas discharge line 16, or two or more thereof. Thereby, the density | concentration of harmful substances, such as formaldehyde in the carbon dioxide gas discharge | released in the air | atmosphere from the exhaust gas discharge line 16, can be reduced effectively. Further, if a decomposition and removal means is directly provided in the exhaust gas discharge line 16, harmful by-products contained in the gas released to the outside can be directly decomposed.

  When harmful by-products are brought into contact with the solid catalyst together with oxygen, harmful substances can be decomposed and removed more effectively. Therefore, for example, when disposing and removing means is provided in the anode reaction liquid recovery line 15, an inlet for introducing an oxygen-containing gas such as oxygen gas or air is provided in front of the location where the solid catalyst is installed, and the oxygen-containing gas is collected in the recovered anode reaction liquid. Is preferably supplied. In the case where the fuel circulation tank 4 is provided, an inlet for introducing the oxygen-containing gas may be provided at a location where the oxygen and the solid catalyst effectively contact each other.

  On the other hand, on the cathode side, mainly supplied oxygen and protons react to generate water. In addition, when air is supplied as unreacted oxygen or an oxygen-containing gas in addition thereto, nitrogen is also discharged from the cathode side. In addition, a part of the fuel supplied to the anode side permeates the electrolyte membrane and is oxidized on the cathode side, thereby generating a trace amount of carbon dioxide.

  These exhaust components from the cathode are conveyed to the water separation device 2 through the cathode side line 11 where they are separated into gaseous components such as carbon dioxide and water. The obtained water is transported through the line 12, mixed with the fuel supplied from the fuel tank 3, and transported to the fuel circulation tank 4 through the line 13.

  The line 12 may be provided with a moisture storage tank so as to hold excess cathode-generated water and supply it when water is insufficient. The amount of water supplied from the line 12 to the line 13 can be adjusted based on the methanol concentration in the fuel measured by a methanol concentration meter installed in the fuel circulation tank 4.

  The water separation device 2 is a device that separates a gas component such as carbon dioxide from a discharge component from the cathode and discharges it to the outside, and a normal gas-liquid separation device can be used. The fuel tank 3 is a device that holds fuel or a mixture of fuel and water and supplies fuel or the like to the fuel circulation tank 4 through the line 13 as necessary, and a normal fuel tank can be used.

  The fuel or the like supplied from the fuel tank 3 is mixed with water produced at the cathode, further mixed with the anode reaction solution collected inside the fuel circulation tank 4, and supplied again to the anode. As a result, power can be generated efficiently.

  According to the low-temperature fuel cell system of the present invention, it is possible to remarkably suppress the amount of harmful by-products released from a conventional fuel cell to the outside that may adversely affect the human body and the environment. Therefore, the present invention brings the fuel cell, which is expected to be used as a power source for business use and home use, to a practical use.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Catalyst preparation example 1
8-32 mesh crushed activated carbon (GLC Chemical Co., Ltd., GLC) was impregnated into a predetermined amount of a dinitrodiammine platinum nitrate acidic solution. Subsequently, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours in a 5% hydrogen-containing nitrogen stream. The obtained catalyst is referred to as catalyst A. The platinum content of the catalyst A was 3% by mass.

Catalyst preparation example 2
Catalyst B was prepared in the same manner as in Catalyst Preparation Example 1, except that a nitric acid acidic solution of dinitrodiammine palladium was used instead of an acidic nitric acid solution of dinitrodiammine platinum. The obtained catalyst B had a palladium content of 5% by mass.

Catalyst preparation example 3
Catalyst C was prepared in the same manner as in Catalyst Preparation Example 1 except that an aqueous ruthenium nitrate solution was used instead of the acidic solution of dinitrodiammineplatinum nitrate. The obtained catalyst C had a ruthenium content of 5% by mass.

Catalyst preparation example 4
Titanium dioxide powder (manufactured by Rhône-Poulenc, DT51) was compression molded with a tableting machine and then crushed, divided into 8-32 meshes, and sized. The 8-32 mesh titanium dioxide was impregnated into a predetermined amount of an acidic solution of dinitrodiammineplatinum nitrate. Subsequently, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours in a 5% hydrogen-containing nitrogen stream. The obtained catalyst is referred to as catalyst D. The platinum content of the catalyst D was 3% by mass.

Catalyst preparation example 5
Catalyst E was prepared in the same manner as in Catalyst Preparation Example 4, except that an acidic solution of dinitrodiammine palladium nitrate was used instead of the acidic solution of nitric acid platinum nitrate. The palladium content of the obtained catalyst E was 5% by mass.

Catalyst preparation example 6
Zirconium dioxide powder (EPL, manufactured by Daiichi Rare Element Co., Ltd.) was compression molded with a tableting machine and then pulverized, divided into 8-32 meshes, and sized. The 8-32 mesh zirconium dioxide was impregnated into a predetermined amount of a dinitrodiammineplatinic acid nitrate solution. Subsequently, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours in a 5% hydrogen-containing nitrogen stream. The obtained catalyst is referred to as catalyst F. The platinum content of the catalyst F was 3% by mass.

Catalyst preparation example 7
Carbon black powder (manufactured by Mitsubishi Chemical Corporation, Ketjen Black) was impregnated into an acidic solution of dinitrodiammine palladium in a predetermined amount. Subsequently, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours in a 5% hydrogen-containing nitrogen stream. The obtained catalyst is referred to as catalyst G. The platinum content of the catalyst G was 60% by mass.

Catalyst preparation example 8
Carbon black powder (manufactured by Mitsubishi Chemical Corporation, Ketjen Black) was impregnated into a predetermined amount of a dinitrodiammine platinum and ruthenium nitrate acidic solution. Subsequently, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours in a 5% hydrogen-containing nitrogen stream. The obtained catalyst is referred to as catalyst H. The platinum and ruthenium contents of the catalyst H were 40% by mass and 20% by mass, respectively.

Example 1
The catalyst G obtained in Catalyst Preparation Example 7 was added to a mixed solution of a perfluoromethanesulfonic acid resin solution (manufactured by Aldrich, 5 mass% Nafion solution) and an organic solvent, and the mixture was stirred to obtain a paste-like electrode composition Prepared. This paste electrode composition was applied to conductive carbon paper to prepare a cathode electrode. The amount of the catalyst G applied to the cathode electrode was 2 mg / cm ² in terms of platinum weight. Further, an anode electrode was produced in the same manner using the catalyst H obtained in Catalyst Preparation Example 8. These electrodes and a solid polymer electrolyte membrane (Nafion 117, manufactured by DuPont) were overlapped so that the catalyst-coated surface was in contact with the solid polymer electrolyte membrane, and then the temperature was 130 ° C. and the pressure was 100 kg / cm ² for 5 minutes. The membrane electrode assembly was produced by hot pressing. The electrode area of this membrane electrode assembly was 25 cm ² . This membrane electrode assembly was incorporated into an experimental fuel cell unit cell to obtain a fuel cell.

A 4 mol / L aqueous methanol solution was supplied to the anode side of the obtained fuel cell at 5 mL / min, oxygen was supplied to the cathode side at 250 mL / min, and the cell temperature was 90 ° C. to generate power at 400 mA / cm ² . At this time, a catalyst packed bed filled with 300 mL of the catalyst A obtained in Catalyst Preparation Example 1 was installed on the anode outlet side line (corresponding to the anode reaction liquid recovery line in FIG. 1). In addition, air was supplied from the inlet side of the catalyst packed bed at a rate of 35 mL / min so that the anode reaction liquid passed through the catalyst packed bed in a sufficiently mixed state with air.

  The formaldehyde concentration at the inlet side and outlet side of the catalyst packed bed was measured by 2,4-dinitrophenylhydrazine-high performance liquid chromatograph method. Specifically, a glass collecting tube containing a 0.5% by mass boric acid aqueous solution was immersed in an ice water bath, and the anode reaction solution to be measured was introduced into the glass collecting tube for 10 minutes. Next, pure water was added to the collected liquid to make a predetermined amount to obtain a measurement sample. 0.1 g of this sample is weighed into a test tube, 0.9 g of a perchloric acid aqueous solution of 2,4-dinitrophenylhydrazine is added and mixed, and formaldehyde contained in the sample is reacted with 2,4-dinitrophenylhydrazine. 2,4-dinitrophenylhydrazone was produced. Thereafter, 1 g of acetonitrile was added, and 2,4-dinitrophenylhydrazone in the obtained solution was analyzed by high performance liquid chromatography to quantify formaldehyde.

The conditions for high performance liquid chromatography are as follows:
Equipment used: Hitachi HPLC-UV
Column: Shiseido CAPCELLPAK C18AQ (5 μm, 4.6 mmφ, 25 cm)
Column temperature: 40 ° C
Eluent: Water / acetonitrile = 50/50 (mass conversion)
Flow rate: 0.5 mL / min UV detection wavelength: 355 nm
The measurement results are shown in Table 1.

Examples 2-6
Electricity was generated in the same manner as in Example 1 except that the catalysts B to F were used in place of the catalyst A, and the formaldehyde concentration in the anode reaction solution was measured. The results are shown in Table 1.

  As can be seen from the above results, the formaldehyde concentration in the anode reaction solution that was originally 20 mg / L could be reduced to less than 1.5 mg / L. If the concentration in the anode reaction solution can be reduced to this level, the amount of formaldehyde that volatilizes and is discharged together with carbon dioxide is considered to be a problem-free amount. Furthermore, if the anode reaction solution after the catalyst treatment is circulated and used, it is considered that the amount of formaldehyde discharged to the outside can be further suppressed. As described above, it has been demonstrated by the examples that the system of the present invention can efficiently generate power without releasing harmful by-products to the environment.

Claims (7)

A low-temperature fuel cell, and means for decomposing and removing harmful by-products generated at the anode of the low-temperature fuel cell,
A low-temperature fuel cell system, wherein the means is provided so as to come into contact with an anode-derived reaction liquid and / or exhaust gas separated from the reaction liquid.   The low-temperature fuel cell system according to claim 1, further comprising a fuel circulation line for circulating the anode-derived reaction liquid and reusing it as fuel.   The low-temperature fuel cell system according to claim 1 or 2, wherein methanol is used as a fuel.   The low-temperature fuel cell system according to claim 3, which is for decomposing and removing formaldehyde, formic acid and methyl formate as harmful by-products.   The means for decomposing and removing harmful by-products is a solid catalyst containing one or more elements selected from the group consisting of Pt, Pd, Ru, Ir, Au and Ag, and carbon. A low-temperature fuel cell system according to any one of the above. The fuel circulation line has an anode reaction liquid recovery line, a fuel circulation tank, and a fuel supply line;
3. The low-temperature fuel cell system according to claim 2, wherein means for decomposing and removing harmful by-products is provided inside the anode reaction liquid recovery line and / or the fuel circulation tank. The fuel circulation line has an anode reaction liquid recovery line, a fuel circulation tank, and a fuel supply line;
The fuel circulation tank has an exhaust gas discharge line for discharging exhaust gas separated from the recovered anode reaction liquid,
The low-temperature fuel cell system according to claim 2 or 6, wherein the exhaust gas emission line has means for decomposing and removing harmful by-products.