JP5537232B2 - Method for reducing carbon monoxide concentration, hydrogen production apparatus, and fuel cell system - Google Patents

Description

  The present invention relates to a method for reducing a carbon monoxide concentration, a hydrogen production apparatus, and a fuel cell system.

  A fuel cell has a feature that high efficiency can be obtained because a free energy change caused by a combustion reaction of fuel can be directly taken out as electric energy. In addition to the fact that it does not emit harmful substances, it is being developed for various uses. In particular, solid polymer fuel cells are characterized by high power density, compactness, and operation at low temperatures.

  In general, as a fuel gas for a fuel cell, a gas containing hydrogen as a main component is used, and the raw materials thereof include natural gas, hydrocarbons such as LPG, naphtha and kerosene, alcohols such as methanol and ethanol, dimethyl ether and the like. Ether or the like is used. However, since elements other than hydrogen are also present in these raw materials, it is inevitable that carbon-derived impurities are mixed in the fuel gas supplied to the fuel cell.

  Among such impurities, carbon monoxide poisons platinum-based noble metals used as electrode catalysts for fuel cells. Therefore, if carbon monoxide is present in the fuel gas, sufficient power generation characteristics cannot be obtained. In particular, a fuel cell operated at a low temperature has a stronger carbon monoxide adsorption and is more susceptible to poisoning. Therefore, in a system using a polymer electrolyte fuel cell, it is indispensable that the concentration of carbon monoxide in the fuel gas is reduced.

  Examples of the method for reducing the carbon monoxide concentration include a method in which carbon monoxide in a reformed gas obtained by reforming a raw material is reacted with water vapor and converted into hydrogen and carbon dioxide, so-called water gas shift reaction. It is done. However, this method can reduce the carbon monoxide concentration only to about 0.5 to 1% by volume.

  As another method for reducing the carbon monoxide concentration, there is a method in which oxygen or an oxygen-containing gas (air or the like) is introduced into the reformed gas to convert the carbon monoxide into carbon dioxide. However, in this method, hydrogen present in a large amount in the reformed gas is also oxidized, so that hydrogen is lost and removal of carbon monoxide may be insufficient.

On the other hand, as shown in the following reaction formula (2), there is also a method of reducing the carbon monoxide concentration by methanating carbon monoxide with hydrogen and converting it to methane. In this method, if carbon dioxide is contained in the reformed gas, methanation of carbon dioxide, which is a side reaction, occurs, hydrogen may be lost, and the reaction may run away, resulting in a rapid increase in reaction temperature. Therefore, a method for selectively methanating only carbon monoxide is desired.
CO + 3H ₂ → CH ₄ + H ₂ O (2)

  For example, Patent Document 1 reports that the selectivity of methanation of carbon monoxide is improved by using a catalyst in which ruthenium is supported on a predetermined carrier.

JP 2007-196206 A

  However, conventional methods such as the method described in Patent Document 1 described above still have room for improvement with respect to the conversion rate of carbon monoxide and the concentration of hydrogen obtained.

  Accordingly, the present invention relates to a method for reducing the concentration of carbon monoxide in a raw material gas containing hydrogen and carbon monoxide, in which the conversion rate of carbon monoxide and the concentration of hydrogen obtained are improved, and a methanation reaction unit using this method An object of the present invention is to provide a hydrogen production apparatus and a fuel cell system.

The present invention is a method for reducing the concentration of carbon monoxide, comprising bringing a raw material gas containing hydrogen and carbon monoxide into contact with a catalyst, and reducing carbon monoxide in the raw material gas by methanation. Contains a support containing alumina and 0.3 to 3% by mass of ruthenium supported on the support, and the relative supporting depth X (Ru) of ruthenium in the radial direction in the catalyst cross section along the radial direction is as follows: A method for reducing the carbon monoxide concentration that satisfies the condition represented by the formula (1) is provided.
25 ≦ X (Ru) ≦ 50 (1)
[Wherein, X (Ru) represents the ratio (%) of the ruthenium loading depth to the radius of the catalyst cross section. ]

In the catalyst, the intensity at the position where the intensity of the ruthenium concentration shows the maximum value with respect to the radial direction in the cross section of the catalyst along the radial direction is Y1, the position where 5% of the intensity of Y1 is P1, and the position of the outermost surface of the catalyst. When the position is P0 and the intermediate point between P0 and P1 is Pm, the maximum intensity Y2 of the ruthenium concentration in the region from Pm to P1 and the catalyst satisfying the condition that Y1 is expressed by the following formula (3) Is preferred. This further improves the conversion of carbon monoxide and the concentration of hydrogen obtained.
2 ≦ Y1 / Y2 ≦ 10 (3)

  The present invention also provides a hydrogen production apparatus having a methanation reaction unit for reducing carbon monoxide by methanation by the carbon monoxide concentration reducing method described above, and a fuel cell system including the hydrogen production apparatus.

  According to the present invention, a method for reducing the concentration of carbon monoxide in a raw material gas containing hydrogen and carbon monoxide, in which the conversion rate of carbon monoxide and the concentration of hydrogen obtained are improved, and the methanation reaction using this method A hydrogen production apparatus and a fuel cell system having a section can be provided.

It is a schematic cross section which shows one Embodiment of the catalyst in the method of this invention, and is sectional drawing when a catalyst is cut | disconnected by the plane along a radial direction. It is a schematic diagram which shows an example of a catalyst with suitable concentration distribution to the radial direction of the ruthenium of the catalyst in the method of this invention. It is a schematic cross section which shows an example of the reactor suitably used in the evaluation about the methanation reaction of carbon monoxide by a catalyst, and manufacture of high concentration hydrogen containing gas. It is a conceptual diagram which shows an example of the fuel cell system which concerns on embodiment of this invention. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst about the catalyst A1 by the line analysis using EPMA. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst by the line analysis using EPMA about catalyst A2. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst by the line analysis using EPMA about catalyst B1. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst about the catalyst A3 by the line analysis using EPMA. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst about the catalyst A4 by the line analysis using EPMA. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst about the catalyst A5 by the line analysis using EPMA. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst by the line analysis using EPMA about catalyst B2. It is a figure which shows the result of having measured the cross section when a catalyst is cut | disconnected by the plane along the radial direction of a catalyst about the catalyst A6 by the line analysis using EPMA.

  Hereinafter, although one embodiment of the present invention is described in detail, the present invention is not limited to this.

  In this embodiment, the method for reducing carbon monoxide is to bring hydrogen and carbon monoxide-containing source gas into contact with the catalyst, and reduce carbon monoxide in the source gas by methanation.

The catalyst contains a support containing alumina and 0.3 to 3% by mass of ruthenium supported on the support, and the relative support depth X (Ru) of ruthenium in the radial direction in the catalyst cross section along the radial direction. Satisfies the condition represented by the following formula (1).
25 ≦ X (Ru) ≦ 50 (1)
[Wherein, X (Ru) represents the ratio (%) of the ruthenium loading depth to the radius of the catalyst cross section. ]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the catalyst in the method of the present invention, and is a cross-sectional view when the catalyst is cut along a plane along the radial direction.
In the present specification, “ruthenium loading depth” indicates the distance from the outermost surface of the catalyst to a predetermined position where ruthenium is present in the radial direction of the catalyst. Here, the predetermined position where ruthenium is present refers to a position showing 1% of the intensity relative to the intensity at the position where the ruthenium concentration shows the maximum value by line analysis using EPMA.

  In the present specification, the “relative loading depth of ruthenium” refers to a value expressed as a percentage (%) of the ratio of the loading depth of ruthenium to the radius of the catalyst. That is, if the radius of the catalyst is R, the loading depth of ruthenium is C, and the relative loading depth of ruthenium is X (Ru), it means X (Ru) = C / R × 100 (%). When ruthenium is present from the outermost surface of the catalyst to the center position, X (Ru) = 100 (%).

  According to the method of the present embodiment, a catalyst in which the relative loading depth X (Ru) of ruthenium satisfies the above formula (1), more preferably 30 ≦ X (Ru) ≦ 48, more preferably 32 ≦ X (Ru) ≦. By using a catalyst satisfying 43, carbon monoxide is methanated with extremely high selectivity.

  FIG. 2 is a schematic diagram showing an example of a catalyst having a suitable concentration distribution of ruthenium in the radial direction of the catalyst in the method of the present invention, and shows the concentration distribution of ruthenium on a plane along the radial direction of the catalyst. .

  First, the cross-section when the catalyst was cut along the radial direction was measured for the intensity of the ruthenium concentration at a predetermined position by line analysis using EPMA, and the intensity at the position where the intensity showed the maximum value was expressed as Y1. And a position P1 indicating 5% intensity of Y1 is determined. Then, assuming that the position of the outermost surface of the catalyst is P0, an intermediate point Pm between P0 and P1 is determined. Next, in the region from Pm to P1, the intensity Y2 at which the intensity of the ruthenium concentration shows the maximum value is obtained.

In the method of this embodiment, the selectivity of methanation of carbon monoxide can be further improved by using a catalyst in which such Y1 and Y2 satisfy the condition represented by the following formula (3).
2 ≦ Y1 / Y2 ≦ 10 (3)
Further, Y1 / Y2 more preferably satisfies the condition of 2 ≦ Y1 / Y2 ≦ 7 from the viewpoint of further improving the selectivity of methanation of carbon monoxide, and satisfies the condition of 2 ≦ Y1 / Y2 ≦ 5. Is more preferable.

  The carrier is not particularly limited as long as it contains alumina as its component. For example, γ alumina or α alumina can be used. Γ-alumina is more preferable because of its large surface area and high affinity with ruthenium. A mixture of alumina and an inorganic oxide selected from silica, titania, zirconia, and the like can also be used. In the above catalyst, the shape, size and molding method of the carrier are not particularly limited. Further, at the time of molding, an appropriate binder may be added to improve moldability.

The carrier preferably has a spherical or cylindrical shape. The radius of the catalyst means the radius when the support is spherical, and the radius of the cross section cut parallel to the bottom surface when the support is cylindrical. The shape of a sphere or a cylinder includes not only a sphere and a cylinder strictly but also a part of which is deformed, but also includes what can be substantially regarded as a sphere or a cylinder. Further, in the case of a carrier having a shape other than a spherical shape or a cylindrical shape, the relative loading depth of the ruthenium can be controlled in accordance with the spherical shape or the cylindrical shape.
When the support is spherical, the average pore diameter of the support is not particularly limited, but is preferably less than 6 nm.

  Ruthenium is supported as an active metal on the carrier. However, when a metal other than ruthenium is added, a side reaction such as a reverse shift reaction proceeds. Therefore, the active metal is preferably only ruthenium.

  The amount of ruthenium supported on the carrier is 0.3 to 3% by mass, preferably 0.5 to 2% by mass, based on the carrier. If it is less than 0.3% by mass, the performance as a catalyst is not sufficient, and if it exceeds 3% by mass, the methanation reaction of carbon dioxide contained in the raw material gas proceeds at an accelerated rate, leading to a runaway reaction. There is a fear.

  The ruthenium loading method is also not particularly limited, and an impregnation method, an equilibrium adsorption method, and a competitive adsorption method using a metal solution obtained by dissolving a metal salt of a supported metal in a solvent are preferably employed. When using the competitive adsorption method, use competitive adsorbents such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, boric acid, formic acid, acetic acid, lactic acid, oxalic acid, citric acid, malic acid, etc. Can do. Among these, citric acid is preferable because the aqueous solution used for impregnation is easy to handle and the aqueous solution adsorbed on the catalyst surface is easily removed after ruthenium is supported.

  There is no particular limitation on the number of times of loading, and it is preferable to load all at the same time or in several times in the loading step. Further, it is more preferable that after ruthenium is supported by the competitive adsorption method in the first step, further ruthenium is supported by the impregnation method or the equilibrium adsorption method in the second step.

  The solvent used in the metal solution is not particularly limited as long as it can dissolve the metal salt, but water or ethanol is preferable.

The metal salt is not particularly limited as long as it is soluble in a solvent, but for Ru, RuCl ₃ .nH ₂ O, Ru (NO ₃ ) ₃ , K ₂ (RuCl ₅ (H ₂ O)), (NH ₄ ) ₂ RuCl ₆ , (Ru (NH ₃ ) ₆ ) Br ₃ , Ru (NH ₃ ) ₆ Cl ₃ , Na ₂ RuO ₄ , K ₂ RuO ₄ , Ru (CO) ₅ , [Ru (NH ₃ ) ₅ Cl] Cl ₃ , Ru ₃ (CO) ₁₂ and Ru (C ₅ H ₇ O ₂ ) ₂ are preferred. A plurality of metal salts may be mixed.

  Although it is necessary to remove the solvent after the metal is supported on the carrier, any method of natural drying in air, heat drying, or deaeration drying under reduced pressure can be employed. In addition, although it is also preferably performed after drying, it is preferably performed at a temperature of 300 to 800 ° C. for 1 to 5 hours in a hydrogen atmosphere. In the prepared catalyst, chloride ions derived from a carrier or a supported metal salt may remain, but the chloride ion concentration needs to be 100 mass ppm or less. Preferably it is 80 mass ppm or less, Most preferably, it is 50 mass ppm or less. When the chloride ion concentration is higher than 100 ppm by mass, aggregation of the supported metal is promoted and CO selective oxidation activity is lowered. When the catalyst prepared by the above method is put to practical use, hydrogen reduction is usually performed as a pretreatment. The conditions are 100 to 800 ° C., preferably 150 to 250 ° C., for 1 to 5 hours, preferably 1 to 3 hours.

  The relative loading depth of ruthenium can be adjusted, for example, by changing the concentration of the competitive adsorbent, changing the temperature at the time of loading, or reducing the pressure. The Y1 / Y2 can be adjusted by, for example, setting the number of times of loading to 2 times or more, changing the temperature at the time of loading, reducing pressure, or the like.

  As the raw material gas containing carbon monoxide and hydrogen, hydrocarbons usually used as starting raw materials (raw fuels) for fuel cells or oxygen-containing hydrocarbons such as alcohols and ethers are used by various methods. A gas mainly containing hydrogen obtained by performing the reforming reaction is used. The raw fuel includes natural gas, LPG, naphtha, kerosene, gasoline or various equivalents thereof, hydrocarbons such as methane, ethane, propane and butane, various alcohols such as methanol and ethanol, and ethers such as dimethyl ether. Etc. are used.

  The method for reforming the raw fuel is not particularly limited, and various methods such as a steam reforming method, a partial oxidation reforming method, and autothermal reforming can be used. Any of these methods can be employed in the present embodiment.

If the raw fuel containing sulfur is supplied to the reforming process as it is, the reforming catalyst will be poisoned, the activity of the reforming catalyst will not be expressed, and the life will be shortened. Prior to this, it is preferable to desulfurize the raw fuel. The conditions for the desulfurization reaction vary depending on the state of the raw fuel and the sulfur content, and thus cannot be generally stated, but the reaction temperature is usually preferably from room temperature to 450 ° C, particularly preferably from room temperature to 300 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. Preferably in the range of 0.01～15H ^-1 when SV raw materials is a liquid, more preferably in the range of 0.05～5H ^-1, range 0.1～3H ^-1 are particularly preferred. When using a gas precursor is preferably in the range of 100～10,000H ^-1, more preferably in the range of 200～5,000H ^-1, range 300～2,000H ^-1 are particularly preferred.

Further, although the reforming reaction conditions are not necessarily limited, usually, the reaction temperature is preferably 200 to 1000 ° C, particularly preferably 400 to 850 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. SV is preferably 0.01 to 40 h ⁻¹ , particularly preferably 0.1 to 10 h ⁻¹ . The gas (reformed gas) obtained by the reforming reaction contains hydrogen as a main component, but other components include carbon monoxide, carbon dioxide, water vapor, and the like.

  In the present embodiment, it is possible to directly use the above reformed gas as a raw material gas, but it is also possible to use a gas in which the carbon monoxide concentration is reduced to some extent by pretreating such a reformed gas in advance. Examples of such pretreatment include a method of reacting carbon monoxide in the reformed gas with water vapor to convert it into hydrogen and carbon dioxide in order to reduce the concentration of carbon monoxide in the reformed gas, so-called water gas shift reaction. . Examples of the pretreatment other than the water gas shift reaction include a method of adsorptive separation of carbon monoxide or a method of membrane separation.

In the present embodiment, in order to reduce carbon monoxide in the reformed gas and increase hydrogen, it is preferable to use the reformed gas as a raw material gas that is further subjected to a water gas shift reaction. The concentration can be reduced more effectively. The reaction conditions for the water gas shift reaction are not necessarily limited depending on the composition of the reformed gas and the like, but the reaction temperature is usually preferably 120 to 500 ° C, and particularly preferably 150 to 450 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. Space velocity (SV) is preferably 100~50,000h ^-1, especially 300～10,000H ^-1 are preferred.

  The carbon monoxide concentration in the raw material gas is usually 0.1 to 2% by volume. On the other hand, the hydrogen concentration in the source gas is usually 40 to 85% by volume. The source gas may contain, for example, nitrogen, carbon dioxide, etc. as components other than carbon monoxide and hydrogen.

When the methanation reaction of carbon monoxide is carried out by bringing a raw material gas containing hydrogen and carbon monoxide into contact with the catalyst, the reaction pressure is from normal pressure to 1 MPa in consideration of the economics and safety of the fuel cell system. Is preferable, and normal pressure to 0.2 MPa is particularly preferable. The reaction temperature is not particularly limited as long as it lowers the carbon monoxide concentration. However, the reaction rate is low at low temperatures and the selectivity is low at high temperatures. -300 degreeC is more preferable, and 200-240 degreeC is especially preferable. If GHSV is too high, the methanation reaction of carbon monoxide does not proceed easily. On the other hand, if it is too low, the apparatus becomes too large. Therefore, the range of 1,000 to 50,000 h ⁻¹ is preferable, particularly 3,000 to 3,000. A range of 30,000 h ⁻¹ is preferred.

FIG. 3 is a schematic cross-sectional view showing an example of a reaction apparatus suitably used as a methanation reactor for performing a methanation reaction of carbon monoxide. The reaction apparatus shown in FIG. 3 is a fixed bed flow type reaction apparatus, and FIG. 3 shows a cross-sectional view of the reaction apparatus cut along a plane along the gas flow direction.
In the reaction apparatus shown in FIG. 3, the inside of the reaction vessel 21 is filled with a catalyst, and a gas inlet 23 is provided on the upstream side of the catalyst layer 22 and a gas outlet 24 is provided on the downstream side. Yes. A heater 25 for heating the catalyst layer 22 is disposed at a position corresponding to the catalyst layer 22 on the outer periphery of the reaction vessel 21.
A source gas containing hydrogen and carbon monoxide is introduced from the gas inlet 23 of the reaction vessel 21.

  Further, the fuel cell system according to the present embodiment includes a hydrogen production apparatus and a fuel cell stack, and includes, for example, the configuration of FIG. FIG. 4 is a schematic view showing an example of the fuel cell system of the present embodiment.

  In FIG. 4, the fuel in the fuel tank 3 flows into the desulfurizer 5 through the fuel pump 4. The desulfurizer 5 can be filled with, for example, a copper-zinc-based or nickel-zinc-based sorbent. At this time, if necessary, a hydrogen-containing gas from at least one of the downstream of the reformer 7, the downstream of the shift reactor 9, the downstream of the methanation reactor 10, and the anode off-gas can be added. The fuel desulfurized in the desulfurizer 5 is mixed with water from the water tank 1 through the water pump 2, introduced into the vaporizer 6, vaporized, and sent to the reformer 7.

  As the catalyst filled in the reformer 7, a nickel-based, ruthenium-based, or rhodium-based catalyst can be used. The reaction tube of the reformer 7 is heated by a burner 17 using fuel from the fuel tank 3 and anode off gas as fuel, and is preferably adjusted to a range of 350 to 700 ° C.

  The reformed gas containing hydrogen and carbon monoxide produced in this manner is passed through the shift reactor 9 and the methanation reactor 10 in order, so that the carbon monoxide does not affect the characteristics of the fuel cell. The concentration is reduced. As an example of the catalyst used in the shift reactor, the shift reactor 9 includes an iron-chromium catalyst and / or a copper-zinc catalyst. The methanation reactor 10 uses the catalyst of this embodiment.

  The polymer electrolyte fuel cell 16 includes an anode 11, a cathode 12, and a solid polymer electrolyte 13. A raw material gas having a reduced carbon monoxide concentration obtained by the above method is provided on the anode 11 side. In this case, the air sent from the air blower 8 is introduced after appropriate humidification treatment if necessary. At this time, a reaction in which hydrogen gas becomes protons and emits electrons proceeds at the anode 11, and a reaction in which oxygen gas obtains electrons and protons to become water proceeds at the cathode 12. In order to promote these reactions, platinum black and Pt catalyst or Pt-Ru alloy catalyst supported on activated carbon are used for the anode 11, and platinum black and Pt catalyst supported on activated carbon are used for the cathode 12, respectively. In general, both the anode 11 and cathode 12 catalysts are formed into a porous catalyst layer together with polytetrafluoroethylene, a low molecular weight polymer electrolyte membrane material, activated carbon or the like as necessary.

  Next, the above-mentioned porous catalyst layer is laminated on both sides of a polymer electrolyte membrane known by a trade name such as Nafion (DuPont), Gore (Gore), Flemion (Asahi Glass), Aciplex (Asahi Kasei), etc. Then, a MEA (Membrane Electrode Assembly) is formed. Further, the fuel cell is assembled by sandwiching the MEA with a separator having a gas supply function, a current collecting function, particularly an important drainage function in the cathode, and the like made of a metal material, graphite, carbon composite and the like. The electric load 14 is electrically connected to the anode 11 and the cathode 12. The anode off gas is consumed in the burner 17. The cathode off gas is discharged from the exhaust port 15.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.

[Catalyst preparation]
(Catalysts A1, A2, A3, A4)
A commercially available particulate γ-alumina carrier is loaded with 0.5% by mass of ruthenium chloride in the form of a metal Ru using a citric acid aqueous solution as a competitive adsorbent, and after removing moisture by drying, it is reduced. A Ru / Al ₂ O ₃ catalyst (A1) was prepared.
Here, catalysts having different Ru loading depth and concentration distribution by changing the concentration of the citric acid aqueous solution, which is a competitive adsorbent, were designated as catalyst A1, catalyst A2, catalyst A3, and catalyst A4, respectively.
(Catalyst B1)
A catalyst prepared in the same manner as the catalyst A1 except that the amount of metal Ru was 2% by mass was designated as catalyst B1.
(Catalyst A5, A6)
In a first step, a commercially available particulate γ-alumina support was supported with ruthenium chloride having a metal Ru content of 0.25% by mass using a citric acid aqueous solution of a competitive adsorbent, and moisture was removed by drying. Subsequently, in the second step, Ru / Al ₂ O ₃ catalyst (A5) is prepared by supporting ruthenium chloride of 0.25 wt% in terms of metal Ru by impregnation method, removing moisture by drying, and then reducing. did.
Here, catalysts having different Ru loading depth and concentration distribution by changing the concentration of the citric acid aqueous solution as the competitive adsorbent were designated as catalyst A5 and catalyst A6, respectively.
(Catalyst B2)
A catalyst prepared in the same manner as the catalyst A5 except that the amount of metal Ru was 2% by mass was defined as catalyst B2.

(Examples 1-6, Comparative Examples 1 and 2)
[Methanation reaction]
The above-mentioned catalyst was charged in the reaction apparatus shown in FIG. 3 and hydrogen reduction was performed at 200 ° C. for 1 hour as a pretreatment.

Next, a raw material gas containing hydrogen (H ₂ ), carbon monoxide (CO), and carbon dioxide (CO ₂ ) was supplied to the catalyst layer, and a methanation reaction of carbon monoxide in the raw material gas was performed. The reaction conditions were such that GHSV was 8,000 h ⁻¹ and the reaction temperature (catalyst layer inlet temperature) was 200 to 240 ° C. Further, the raw material gas composition, as standard _conditions, H 2: 55.5% by volume, CO: 5,000 volume ppm, _CO 2: 24 _volume%, H 2 O: was 20 volume%.

  In the carbon monoxide methanation reaction, the gas composition at the downstream end of the catalyst layer was measured when a predetermined time had elapsed from the start of the reaction. TCD gas chromatography was used for gas analysis. The results are shown in Tables 1 and 2.

[Line analysis using EPMA]
Regarding the catalysts A1 to A4 and the catalyst B1 which are catalysts with controlled Ru loading depth, the cross section when the catalyst was cut along a plane along the radial direction of the catalyst was measured by line analysis using EPMA. FIG. 5 shows the results of catalyst A1, FIG. 6 shows the results of catalyst A2, FIG. 7 shows the results of catalyst B1, FIG. 8 shows the results of catalyst A3, and FIG. 9 shows the results of catalyst A4. The horizontal axis in these figures indicates the relative position (%) in the radial direction of the catalyst. Here, the “relative position in the radial direction” refers to a value expressed as a percentage (%) of the ratio of the distance from the outermost surface position of the catalyst to a predetermined position along the radial direction of the catalyst with respect to the radius. The outermost surface position is 0 (%) and the center position is 100 (%). The vertical axis represents the intensity of ruthenium concentration at a predetermined relative position.

  For catalyst A5, catalyst A6, and catalyst B2, which are catalysts in which the concentration distribution of Ru in the radial direction is controlled, the cross section when the catalyst is cut along a plane along the radial direction of the catalyst is measured by line analysis using EPMA did. FIG. 10 shows the result of the catalyst A5, FIG. 11 shows the result of the catalyst B2, and FIG. 12 shows the result of the catalyst A6.

  Based on the results of the line analysis using the EPMA, X (Ru) and Y1 / Y2 of the catalysts A1 to A6 and the catalysts B1 to B2 were calculated. The results are shown in Tables 1 and 2.

As is clear from Tables 1 and 2, in each of Examples 1 to 6, the conversion rate of carbon monoxide when the methanation reaction was performed was 95% or more, and the H ₂ concentration (wet basis) was 54% or more by volume. On the other hand, in Comparative Example 1, the CO conversion rate is insufficient, and in Comparative Example 2, the H ₂ concentration is low.

  DESCRIPTION OF SYMBOLS 1 ... Water tank, 2 ... Water pump, 3 ... Fuel tank, 4 ... Fuel pump, 5 ... Desulfurizer, 6 ... Vaporizer, 7 ... Reformer, 8 ... Air blower, 9 ... Shift reactor, 10 ... Meta Nation reactor, 11 ... anode, 12 ... cathode, 13 ... solid polymer electrolyte, 14 ... electric load, 15 ... exhaust port, 16 ... solid polymer fuel cell, 17 ... heating burner, 21 ... reaction vessel, 22 ... catalyst layer, 23 ... gas inlet, 24 ... gas outlet, 25 ... heater.

Claims (4)

A method for reducing the concentration of carbon monoxide, comprising bringing a source gas containing hydrogen and carbon monoxide into contact with a catalyst to reduce carbon monoxide in the source gas by methanation,
The catalyst contains a support containing alumina and 0.3 to 3% by mass of ruthenium supported on the support, and the relative support depth X (Ru) of ruthenium in the radial direction in the cross section of the catalyst along the radial direction. There meets the condition represented by the following formula (1),
A method for reducing a carbon monoxide concentration, wherein the carrier has a spherical or cylindrical shape .
25 ≦ X (Ru) ≦ 50 (1)
Wherein, X (Ru), the ratio of ruthenium supported depth to the radius of the catalyst section of (%) shows the A ruthenium supported depth, with respect to the radial direction of the catalyst, the ruthenium from the outermost surface of the catalyst The predetermined position where ruthenium exists is 1% of the intensity relative to the intensity at the position where the ruthenium concentration shows the maximum value by line analysis using EPMA. The position which shows the intensity | strength of . ] The catalyst has Y1 at the position where the intensity of the ruthenium concentration shows the maximum value with respect to the radial direction in the cross section of the catalyst along the radial direction, P1 at the position showing 5% of the intensity of Y1, and the outermost surface of the catalyst. When the position is P0 and the intermediate point between P0 and P1 is Pm, the maximum intensity Y2 of the ruthenium concentration in the region from Pm to P1 and the catalyst satisfying the condition represented by the following formula (3), Y1. The method for reducing the carbon monoxide concentration according to claim 1.
2 ≦ Y1 / Y2 ≦ 10 (3)   The hydrogen production apparatus which has a methanation reaction part which reduces carbon monoxide by methanation by the carbon monoxide concentration reduction method of Claim 1 or 2.   A fuel cell system comprising the hydrogen production apparatus according to claim 3.