JP4783240B2 - Steam reforming catalyst, hydrogen production apparatus and fuel cell system - Google Patents

Description

  The present invention relates to a steam reforming catalyst, a hydrogen production apparatus using the steam reforming catalyst, and a fuel cell system having the hydrogen production apparatus.

The most important position in the hydrogen production process is a so-called hydrocarbon reforming technique for hydrocarbon compounds in which hydrocarbon compounds are reacted with steam to obtain hydrogen, carbon monoxide, carbon dioxide, methane, and the like. The steam reforming method is widely used because the equipment is cheaper than the partial oxidation method.
Conventional steam reforming catalysts are mainly nickel-based (see Patent Document 1). However, these catalysts are liable to cause carbon deposition and have the disadvantage that the activity decreases in a short time. For this reason, it is often operated at a relatively high pressure (2 MPa or more) and a high steam / carbon ratio (3.0 or more). However, in the case of a fuel cell system, the lower the reaction pressure, the better the handling of the device is preferable. A lower steam / carbon ratio is preferable from the viewpoint of efficiency.
In addition, kerosene is preferred as a raw material hydrocarbon for fuel cells because of its energy density, economy, and ease of handling. However, since the nickel-based catalyst tends to cause carbon deposition, the raw material hydrocarbon is limited to about naphtha from natural gas. It was.

On the other hand, ruthenium-based catalysts have attracted attention because they can perform a steam reforming reaction under a steam / carbon ratio condition lower than that of nickel-based catalysts because they have a carbon deposition suppressing effect. Examples of such ruthenium-based catalysts include those in which ruthenium is supported on an alumina support (see Non-Patent Document 1), and those in which a support in which cerium oxide is supported on an alkali metal oxide or an alkaline earth metal oxide is used. (See Patent Document 2), and those using a zirconia carrier (see Patent Document 3 and Patent Document 4).
However, the ruthenium-based catalyst easily aggregates at a high temperature and in a steam atmosphere, and its activity is greatly reduced. In addition, the agglomerated catalyst has a small number of surface metals, so that the influence of sulfur poisoning is increased and the catalyst life is greatly reduced, which is extremely problematic in practice.
JP-A-4-363140 JP-A-4-265156 JP-A-2-286787 JP-A-2-302304 Kasaoka et al., “The Journal of Fuel Association”, 1980, Volume 59, p. 25

  The present invention provides a long-life steam reforming catalyst in which active metal agglomeration is small under high temperature and steam atmosphere, and also provides a hydrogen production apparatus and a fuel cell system using the catalyst. .

  As a result of intensive studies on a method capable of suppressing the aggregation of active metals in the steam reforming reaction of hydrocarbons, the present inventors have found that this can be achieved by using a specific steam reforming catalyst, and completed the present invention. It is a thing.

That is, the present invention relates to steam reforming of hydrocarbon compounds obtained by supporting ruthenium and iridium and / or rhodium having a content of 0.1 to 5 times by weight of ruthenium on a carrier mainly composed of alumina. Relates to a catalyst.
The present invention also relates to the steam reforming catalyst as described above, wherein the support contains alumina and at least one inorganic oxide selected from rare earth element oxides and alkaline earth element oxides.
The present invention also provides the catalyst for steam reforming as described above, wherein the rare earth element oxide is an oxide of one or more rare earth elements selected from scandium, yttrium, lanthanum and cerium. About.
In the present invention, the alkaline earth element oxide is an oxide of one or more alkaline earth elements selected from magnesium, calcium and barium. Relates to a catalyst.
The present invention also relates to a hydrogen production apparatus characterized in that a reformed gas containing hydrogen as a main component is obtained from hydrocarbon compounds by a steam reforming reaction using the steam reforming catalyst described above.
The present invention also relates to a fuel cell system comprising the hydrogen production apparatus described above.

  By performing steam reforming using the steam reforming catalyst of the present invention, active metal aggregation can be suppressed and catalyst life can be improved. As a result, a mixed gas containing hydrogen and carbon monoxide can be stably produced for a long period of time, and can be used as a fuel for a fuel cell or a raw material thereof.

Hereinafter, the present invention will be described in detail.
The steam reforming catalyst of the present invention is obtained by supporting ruthenium and iridium and / or rhodium having a content of 0.1 to 5 times the ruthenium content on a carrier mainly composed of alumina. .

As the main component of the catalyst carrier of the present invention, alumina is used, and in particular, α-alumina having high heat resistance and mechanical strength is preferably used.
The content of alumina in the catalyst carrier is preferably 71 to 98% by mass, more preferably 75 to 95% by mass, and most preferably 80 to 91% by mass.

The catalyst support of the present invention preferably contains a rare earth element oxide.
As the rare earth element, one or more rare earth elements selected from scandium, yttrium, lanthanum and cerium are preferably used, and lanthanum and cerium are more preferable.
The rare earth element content in the catalyst carrier is preferably 2 to 25 mass%, more preferably 5 to 20 mass%, in terms of the external ratio (alumina weight basis) with respect to alumina as the rare earth element oxide. More preferably, it is 10 to 15% by mass. When the content of the rare earth element oxide is more than 25% by mass, it is not preferable because aggregation increases and the ratio of the active metal appearing on the surface is extremely reduced. On the other hand, when the content is less than 2% by mass, carbon precipitation of the rare earth element The suppression effect is insufficient and is not preferable.

The catalyst support of the present invention preferably contains an alkaline earth element oxide.
As the alkaline earth element, it is preferable to use one or more alkaline earth elements selected from magnesium, calcium, and barium, and magnesium and barium are more preferable.
The content of the alkaline earth element in the catalyst carrier is preferably 0.1 to 15% by mass, more preferably, as an alkaline earth element oxide, in terms of the external ratio (based on alumina weight) with respect to alumina. Is 0.5 to 12% by mass, more preferably 1 to 10% by mass. When the content of the alkaline earth element oxide is more than 15% by mass, aggregation is increased and the ratio of the active metal appearing on the surface is extremely decreased. It is not preferable because the effect of suppressing the precipitation of carbon and the effect of improving the activity of earth elements are insufficient.

The catalyst carrier according to the present invention can be obtained by supporting rare earth elements and / or alkaline earth elements on alumina.
There is no particular limitation on the method for supporting the rare earth element and the alkaline earth element on the alumina support, and a known method such as a normal impregnation method or a pore fill method can be employed. Usually, it is dissolved in a solvent such as water, ethanol or acetone as a metal salt or complex and impregnated on an alumina carrier. As the metal salt or metal complex to be supported, chloride, nitrate, sulfate, acetate, acetoacetate and the like are preferably used.
There is no restriction | limiting in particular also about a carrying | support process, It can impregnate simultaneously or sequentially.
After the loading, water is removed by drying, but there is no particular limitation in this drying process, and a temperature of 100 to 150 ° C. under air or inert gas is preferably used. After the drying step, the carrier carrying the rare earth element and / or alkaline earth element is preferably fired at a temperature of 350 to 1000 ° C. When the temperature is lower than 350 ° C., immobilization of the supported element on the carrier is insufficient, which is not preferable. On the other hand, when the temperature is higher than 1000 ° C., the supported elements are aggregated, which is not preferable. The firing atmosphere is preferably in the air, and the gas flow rate is not particularly limited. The firing time is preferably 2 hours or more. When the time is shorter than 2 hours, immobilization of the supported element on the carrier is insufficient, which is not preferable. Thus, the catalyst carrier according to the present invention is obtained.

Next, ruthenium and iridium and / or rhodium are supported on the obtained carrier.
The content of ruthenium in the catalyst of the present invention is preferably from 0.3 to 5 mass%, more preferably from 1 to 4 mass% as a ruthenium atom in terms of an external ratio (based on the weight of the carrier) with respect to the carrier. %, More preferably 2-3 mass%. When the content of ruthenium is more than 5% by mass, the active metal agglomeration increases and the proportion of the metal that appears on the surface is extremely reduced. On the other hand, when the content is less than 0.3% by mass, sufficient activity is obtained. Since it cannot be shown, a large amount of supported catalyst is required, and problems such as the need to enlarge the reactor more than necessary arise.

As an active metal other than ruthenium, iridium and / or rhodium, preferably iridium is supported.
The iridium and / or rhodium content in the catalyst of the present invention needs to be 0.1 to 5 times by weight, preferably 0.3 to 3 times by weight, more preferably 0. .5 to 2 times by weight. When the content of iridium and / or rhodium is more than 5 times the content of ruthenium, the ratio of ruthenium that appears on the surface is extremely unfavorable. On the other hand, when the content of iridium and / or rhodium is less than 0.1 times by weight, iridium and In addition, the effect of rhodium on the ruthenium aggregation is insufficient, which is not preferable.

  There are no particular limitations on the active metal loading method, and a known method such as a normal impregnation method or a pore fill method can be employed. Usually, it is dissolved in a solvent such as water, ethanol or acetone as an active metal salt or complex, and impregnated in a carrier. As the metal salt or metal complex to be supported, chloride, nitrate, sulfate, acetate, acetoacetate, etc. are preferably used. Specifically, ruthenium chloride, ruthenium acetylacetonate, rhodium chloride, rhodium nitrate, chloride Examples of the compound include iridium, but are not limited thereto.

There is no restriction | limiting in particular also about a carrying | support process, It can impregnate simultaneously or sequentially. The number of times of loading is not particularly limited, and the impregnation can be performed once or several times.
After the loading, water is removed by drying, but there is no particular limitation in this drying process, and a temperature of 100 to 150 ° C. under air or inert gas is preferably used.
The supported catalyst thus obtained is activated by performing reduction treatment or metal immobilization treatment as necessary. The treatment method is not particularly limited, and gas phase reduction or liquid phase reduction under a hydrogen flow is preferably used.

There is no restriction | limiting in particular about the form of the catalyst for steam reforming of this invention. For example, a catalyst formed by tableting and pulverized to an appropriate range, a catalyst formed by adding an appropriate binder and extruded, a powdered catalyst, and the like can be used. Alternatively, a metal is supported on a carrier formed by tableting and pulverized to an appropriate range, an extruded carrier, a powder or a carrier formed into an appropriate shape such as a sphere, ring, tablet, cylinder, or flake. A spherical catalyst is preferable from the viewpoint of mechanical strength.
Further, a catalyst obtained by forming the catalyst itself into a monolith shape, a honeycomb shape, or the like, or a monolith using a suitable material, a honeycomb coated with a catalyst, or the like can be used.

  As a form of the reactor used for the steam reforming reaction, a flow type fixed bed reactor is preferably used. There is no restriction | limiting in particular about the shape of a reactor, It can take any well-known shape according to the objective of each process, such as cylindrical shape and flat plate shape. A fluidized bed reactor can also be used.

  The steam reforming reaction in the present invention refers to a reaction in which hydrocarbon compounds are reacted with steam in the presence of a catalyst to convert to a reforming gas containing carbon monoxide and hydrogen. When reacting with steam, it also includes the case of accompanying an oxygen-containing gas (autothermal reforming reaction).

  The hydrocarbon compounds used as a raw material are organic compounds having 1 to 40 carbon atoms, preferably 1 to 30 carbon atoms. Specific examples include saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, aromatic hydrocarbons, etc. In addition, saturated aliphatic hydrocarbons and unsaturated aliphatic hydrocarbons are linear or cyclic. Can be used regardless. Aromatic hydrocarbons can be used regardless of whether they are monocyclic or polycyclic. Such hydrocarbon compounds can contain substituents. As the substituent, either a chain or a ring can be used, and examples thereof include an alkyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an aralkyl group. These hydrocarbon compounds may be substituted with a substituent containing a hetero atom such as a hydroxy group, an alkoxy group, a hydroxycarbonyl group, an alkoxycarbonyl group, or a formyl group.

  Specific examples of hydrocarbon compounds that can be used in the present invention include methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, Saturated aliphatic hydrocarbons such as eicosan, unsaturated aliphatic hydrocarbons such as ethylene, propylene, butene, pentene and hexene, cyclic hydrocarbons such as cyclopentane and cyclohexane, and aromatic hydrocarbons such as benzene, toluene, xylene and naphthalene. Can be mentioned. Moreover, these mixtures can also be used conveniently. Examples thereof include materials that can be obtained industrially at low cost, such as natural gas, LPG, naphtha, gasoline, kerosene, and light oil. Specific examples of the hydrocarbon compound having a substituent containing a hetero atom include methanol, ethanol, propanol, butanol, dimethyl ether, phenol, anisole, acetaldehyde, acetic acid and the like.

  Moreover, the raw material which contains hydrogen, water, a carbon dioxide, carbon monoxide etc. in the said raw material can also be used. For example, when hydrodesulfurization is carried out as a pretreatment of the raw material, the hydrogen residue used in the reaction can be used as it is without separation.

  If the concentration of sulfur contained in the hydrocarbon compound used as a raw material is too high, the reforming catalyst of the present invention may be deactivated. Therefore, the concentration is preferably 50 mass ppb as the mass of sulfur atoms. Hereinafter, it is more preferably 20 mass ppb or less, and still more preferably 10 mass ppb or less. For this reason, if necessary, it is preferable to desulfurize the raw material in advance.

There is no restriction | limiting in particular in the sulfur concentration in the raw material used for a desulfurization process, If it can convert into the said sulfur concentration in a desulfurization process, it can be used.
Although there is no particular limitation on the desulfurization method, a method in which hydrodesulfurization is performed in the presence of an appropriate catalyst and hydrogen and the generated hydrogen sulfide is absorbed by zinc oxide or the like can be given as an example. Examples of the catalyst that can be used in this case include catalysts containing nickel-molybdenum, cobalt-molybdenum, and the like as components. On the other hand, a method of sorbing a sulfur component in the presence of an appropriate sorbent and, if necessary, coexisting with hydrogen can also be employed. Examples of sorbents that can be used in this case include sorbents mainly composed of copper-zinc as shown in Japanese Patent No. 2654515, Japanese Patent No. 2688749, and so on. Examples thereof include an adhesive.
There is no restriction | limiting in particular also in the implementation method of a desulfurization process, You may implement by the desulfurization process installed immediately before the steam reforming reactor, and you may use the hydrocarbon which processed in the independent desulfurization process.

  In the steam reforming reaction using the catalyst of the present invention, the amount of steam introduced into the reaction system is defined as the ratio of the number of moles of water molecules to the number of moles of carbon atoms contained in the raw material hydrocarbon compounds (steam / carbon ratio). The value is preferably 0.3 to 10, more preferably 0.5 to 5, and still more preferably 2 to 3. If this value is less than 0.3, coke is likely to be deposited on the catalyst and the hydrogen fraction cannot be increased. On the other hand, if it is more than 10, the reforming reaction proceeds but the steam generating equipment, steam There is a risk of enlarging the recovery equipment. There are no particular restrictions on the method of addition, but it may be introduced into the reaction zone at the same time as the raw material hydrocarbon compounds, or it may be introduced in portions from separate positions or several times in the reactor zone. Also good.

In the steam reforming reaction using the catalyst of the present invention, the space velocity of the flow material introduced into the reactor, GHSV is preferably 10～10,000H ^-1, more preferably 50～5,000H ^-1, further Preferably it is the range of 100-3,000h- ¹ . LHSV is preferably in the range of 0.05 to 5.0 h ⁻¹ , more preferably 0.1 to 2.0 h ⁻¹ , and still more preferably 0.2 to 1.0 h ⁻¹ .
Although reaction temperature is not specifically limited, Preferably it is 200-1000 degreeC, More preferably, it is 300-900 degreeC, More preferably, it is the range of 400-800 degreeC.
The reaction pressure is not particularly limited and is preferably carried out in the range of atmospheric pressure to 20 MPa, more preferably atmospheric pressure to 5 MPa, and further preferably atmospheric pressure to 1 MPa. It is also possible to implement.

  The mixed gas containing carbon monoxide and hydrogen obtained by the steam reforming reaction using the catalyst of the present invention can be used as it is as a fuel for a fuel cell in the case of a solid oxide fuel cell. In addition, when removal of carbon monoxide is required, such as phosphoric acid fuel cells and polymer electrolyte fuel cells, it should be used suitably as a raw material for fuel cell hydrogen by using a carbon monoxide removal step in combination. Can do.

  The present invention also provides a hydrogen production apparatus characterized in that a reformed gas containing hydrogen as a main component is obtained from a hydrocarbon (fuel) such as natural gas, LPG, naphtha, or kerosene by a steam reforming reaction using the catalyst. I will provide a. Furthermore, the present invention provides a fuel cell system having the hydrogen production apparatus.

Hereinafter, the battery system of the present invention will be described. FIG. 1 is a schematic view showing an example of a fuel cell system of the present invention.
In FIG. 1, the fuel in the fuel tank 3 flows into the desulfurizer 5 through the fuel pump 4. The desulfurizer can be filled with, for example, a copper-zinc-based or nickel-zinc-based sorbent. At this time, if necessary, the hydrogen-containing gas from the carbon monoxide selective oxidation reactor 11 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.

  The catalyst of the present invention is used as the catalyst of the reformer 7 and is filled in the reformer. The reformer reaction tube is heated by a burner 18 using fuel from the fuel tank and anode off-gas as fuel, and is preferably in the range of 200 to 1000 ° C., more preferably 300 to 900 ° C., and further preferably 400 to 800 ° C. Adjusted.

  The reformed gas containing hydrogen and carbon monoxide produced in this way passes through the high temperature shift reactor 9, the low temperature shift reactor 10, and the carbon monoxide selective oxidation reactor 11 in sequence, so that the carbon monoxide concentration is reduced. It is reduced to the extent that it does not affect the characteristics of the fuel cell. Examples of catalysts used in these reactors include an iron-chromium-based catalyst for the high-temperature shift reactor 9, a copper-zinc-based catalyst for the low-temperature shift reactor 10, and a ruthenium-based catalyst for the carbon monoxide selective oxidation reactor 11. A catalyst etc. can be mentioned.

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

[Example 1]
(1) α-alumina (BET surface area 5 m ² / g, pore volume 0.4 ml / g) is used as catalyst carrier A.
(2) Supporting cerium (III) nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 98% or more) and magnesium nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 99% or more) on catalyst carrier A An impregnated amount of 13% by mass of cerium oxide and an amount of 5% by mass of supported magnesium oxide is impregnated and dried at 150 ° C. for 8 hours or more, and then air calcined at 800 ° C. for 8 hours. This is referred to as catalyst carrier B.
(3) Ruthenium (III) chloride n hydrate (Wako Pure Chemical Industries, Ltd .: purity 99.9% or higher) and iridium chloride (III) (Wako Pure Chemical Industries, Ltd .: purity 97% or higher) are added to the catalyst carrier B. , Each impregnated and supported at an external ratio of 3% by mass of metal, dried at 120 ° C. for 12 hours or more, and then hydrogen reduced at 500 ° C. for 1 hour. This is referred to as catalyst A.

[Example 2]
In Example 1, iridium (III) chloride was changed to rhodium (III) chloride trihydrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 95% or more) as catalyst B.
[Example 3]
In Example 1, the catalyst C was prepared by changing the magnesium nitrate hexahydrate to barium nitrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 99% or more).
[Example 4]
In Example 1, cerium (III) nitrate hexahydrate was converted to lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 98% or more) as catalyst D.

[Comparative Example 1]
In Example 1, the catalyst E was not supported with iridium (III) chloride, and only supported with ruthenium (III) chloride nhydrate in the same manner as in Example 1.
[Comparative Example 2]
In Example 1, the catalyst F was prepared by supporting only iridium (III) chloride in the same manner as in Example 1 without supporting ruthenium (III) chloride hydrate.
[Comparative Example 3]
The catalyst G having the iridium content of 0.05 mass% in Example 1 is designated as catalyst G.

<Steam reforming reaction>
The catalyst was evaluated by a steam reforming reaction. The reaction used a fixed bed microreactor. The catalyst loading is 6 cm ³ . Desulfurized kerosene (density 0.793 g / cm ³ , sulfur content 0.05 mass ppm) was used as a hydrocarbon raw material. The reaction conditions are as follows. Reaction temperature 550 ° C., reaction pressure 0.1 MPa, steam / carbon ratio 3.0 mol / mol, LHSV 3.0 h ⁻¹ .
In addition, the catalyst was subjected to high-temperature hydrothermal treatment in order to evaluate the aggregation resistance of the active metal. The conditions are as follows. Reaction temperature 800 ° C., reaction time 4 hours, reaction pressure 0.1 MPa, water flow rate 15 cc / h.
The reaction gas was quantitatively analyzed using a gas chromatograph. Table 1 shows the conversion rates of the raw materials obtained from the composition of the product gas before and after the high-temperature hydrothermal treatment (reaction time 1 hour). Here, the conversion rate in Table 1 is the ratio of the raw material converted to CO, CH ₄ , CO ₂ and is calculated based on carbon.

  As is apparent from Table 1, after the high-temperature hydrothermal treatment, the catalysts A to D show a higher kerosene conversion rate than the catalysts E to G. Further, when comparing catalyst A and catalyst B, iridium has a higher effect of addition than rhodium.

It is the schematic which shows an example of the fuel cell system of this invention.

Explanation of symbols

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 High temperature shift reactor 10 Low temperature shift reactor 11 Carbon monoxide selective oxidation reactor 12 Anode 13 Cathode 14 Solid height Molecular electrolyte 15 Electric load 16 Exhaust port 17 Polymer electrolyte fuel cell 18 Heating burner

Claims (6)

An external ratio (based on the weight of the support) of 0.3 to 5% by mass of ruthenium and iridium and / or rhodium that is 0.5 to 2 times the ruthenium content, α-alumina as a main component , scandium And one or more rare earth element oxides selected from yttrium, lanthanum and cerium and one or more alkaline earth element oxides selected from magnesium, calcium and barium. A catalyst for steam reforming of hydrocarbon compounds. The steam reforming catalyst according to claim 1, wherein the content of α-alumina in the catalyst carrier is 71 to 98% by mass. 3. The steam reforming according to claim 1, wherein the content of the rare earth element oxide in the catalyst support is 2 to 25% by mass with respect to α-alumina in terms of external ratio (α-alumina weight basis). Catalyst. The content of the alkaline earth element oxide in the catalyst carrier is 0.1 to 15% by mass in terms of an external ratio (α alumina weight basis) with respect to α alumina. A steam reforming catalyst according to claim 1.   A hydrogen production apparatus, wherein a reformed gas containing hydrogen as a main component is obtained from a hydrocarbon compound by a steam reforming reaction using the steam reforming catalyst according to any one of claims 1 to 4. A fuel cell system comprising the hydrogen production apparatus according to claim 5.

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