JP2005296755A - Steam reforming catalyst, steam reforming method, hydrogen production apparatus, and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam reforming catalyst for hydrocarbon compounds which catalyst advantageously performs purge with an oxygen-containing gas during, e.g., shutdown of a hydrogen production apparatus; a hydrogen production apparatus using the catalyst; and a fuel cell system. <P>SOLUTION: The steam reforming catalyst for hydrocarbon compounds comprises a carrier containing (a) alumina, (b) cerium oxide, and (c) barium oxide and/or magnesia as constituting components and rhodium carried by the carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steam reforming catalyst for hydrocarbon compounds. In particular, the present invention relates to a steam reforming catalyst of hydrocarbon compounds that can be advantageously purged with an oxygen-containing gas when the operation of the hydrogen production apparatus is stopped, and further, a steam reforming method using the catalyst, a hydrogen production apparatus, and The present invention relates to a fuel cell system.

In the operation of the fuel cell system, the system may be stopped for the purpose of responding to and checking electric power and heat demand. In this case, if the system is stopped while water and unreformed fuel are present in the system, it may cause catalyst deterioration, restartability deterioration, fuel leakage, and the like. Therefore, it is preferable to purge the interior of the system with an appropriate gas when the system is stopped. However, when a gas containing oxygen such as air is used as the purge gas, deterioration of the reforming catalyst due to oxygen cannot be ignored.
As a steam reforming catalyst, nickel, ruthenium, rhodium and the like are known to be effective (Patent Document 1), but as a catalyst system that achieves both a long-term operation life and resistance to purging with an oxygen-containing gas. No one with sufficient performance was known.
JP-A-4-281845

  An object of the present invention is to provide a steam reforming catalyst that achieves both a long-term operation life and resistance to purging with an oxygen-containing gas, and to provide a hydrogen production apparatus and a fuel cell system capable of stable long-term operation. And

As a result of earnest search for a steam reforming catalyst having high activity, capable of long-term operation, and excellent resistance to purge with an oxygen-containing gas, the present inventors have completed the present invention. is there.
That is, the present invention relates to a steam reforming catalyst of hydrocarbon compounds in which rhodium is supported on a carrier containing (a) alumina, (b) ceria, and (c) a barrier and / or magnesia as constituent components.
The present invention also relates to a steam reforming method, wherein a mixed gas containing carbon monoxide and hydrogen is produced from a raw material mixture containing hydrocarbon compounds and steam using the steam reforming catalyst.
In addition, the present invention has a reforming section for subjecting hydrocarbon compounds to a steam reforming reaction, and uses the steam reforming catalyst in the reforming section, and purges the reforming section with a gas containing oxygen when stopped. The present invention relates to a hydrogen production apparatus.
The present invention also relates to a hydrogen production apparatus comprising a step of treating a mixed gas containing carbon monoxide and hydrogen produced by the steam reforming method in a subsequent carbon monoxide removal step.
In addition, the present invention relates to the hydrogen production apparatus, wherein the carbon monoxide removal step includes a water gas reaction step and a subsequent carbon monoxide selective oxidation step.
The present invention also relates to a fuel cell system using hydrogen produced by the hydrogen production apparatus as a fuel.

Hereinafter, the present invention will be described in detail.
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.
The hydrocarbon compounds as the 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 saturated aliphatic hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, and eicosane. And unsaturated aliphatic hydrocarbons such as ethylene, propylene, butene, pentene and hexene, alicyclic hydrocarbons such as cyclopentane and cyclohexane, and aromatic hydrocarbons such as benzene, toluene, xylene and naphthalene. Moreover, these mixtures can also be used suitably, For example, the material which can be obtained cheaply industrially, such as natural gas, LPG, naphtha, gasoline, kerosene, and light oil, can be mentioned. 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.

  In the steam reforming reaction of the present invention, the amount of steam introduced into the reaction system is a value 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). Preferably, it is in the range of 0.3 to 10, more preferably 0.5 to 5, and still more preferably 1 to 3. If this value is smaller than the above range, coke is liable to deposit on the catalyst and the hydrogen fraction cannot be increased. On the other hand, if it is larger, the reforming reaction proceeds but the steam generation facility and steam recovery facility May cause enlargement. 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 case of mainly obtaining carbon monoxide, carbon dioxide can be added to the raw material gas. The amount of carbon dioxide added in this case is defined as the ratio of the number of moles of carbon dioxide molecules to the number of moles of carbon atoms contained in the raw material (excluding carbon dioxide) (carbon dioxide / carbon ratio). It is 1-5, More preferably, it is the range of 0.1-3. However, it is not always necessary to add carbon dioxide for the purpose of producing hydrogen.

The steam reforming catalyst of the present invention is obtained by supporting rhodium on a carrier containing (a) alumina, (b) ceria, and (c) a barrier and / or magnesia as constituent components.
The rhodium loading method is not particularly limited, and a known method such as a normal impregnation method can be employed. Usually, as a rhodium salt or complex, it is dissolved in a solvent such as water, ethanol or acetone and impregnated into a carrier. As the metal salt or metal complex to be supported, chloride, nitrate, sulfate, acetate, acetoacetate, etc. are preferably used, and specific examples include compounds such as rhodium chloride, rhodium nitrate, and rhodium carbonyl. However, it is not limited to these.

  The rhodium content in the catalyst is usually 0.05 to 20% by mass, preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass as rhodium atoms. When the content is larger than this range, the aggregation of the active metal is increased, and the ratio of the metal appearing on the surface is extremely decreased, which is not preferable. In addition, when the amount is less than the above range, sufficient activity cannot be exhibited, so that a large amount of catalyst is required and the reactor needs to be enlarged more than necessary.

The support used in the catalyst of the present invention is composed of (a) alumina, (b) ceria, and (c) barrier and / or magnesia as constituent components. The composition ratio of ceria is 1 to 50% by mass, preferably 1.5 to 30% by mass, and more preferably 2 to 20% by mass with respect to alumina. The constituent ratio of the barrier and / or magnesia is also in the range of 1 to 50% by mass, preferably 1.5 to 30% by mass, and more preferably 2 to 20% by mass with respect to alumina. When these are less than the above-mentioned ratio, the effect of suppressing carbon deposition becomes insufficient, while when more than the above-mentioned ratio, the surface area becomes small and the activity is lowered, which is not preferable.
In addition, as long as the effect of the present invention is not impaired, the carrier may be used by appropriately mixing calcia, scandia, yttria, titania, zirconia, hafnia, tria, silica, silica alumina, zeolite, and the like as necessary. it can.

  By using the catalyst of the present invention described above, purging in the apparatus with a gas containing oxygen is possible when the hydrogen production apparatus is stopped. As the gas containing oxygen, air is usually used. However, a gas having a reduced oxygen concentration, such as combustion exhaust gas and air electrode off-gas of a fuel cell, can be used more preferably. The temperature of the reforming part at the time of purging is usually room temperature to 400 ° C, preferably 100 ° C to 300 ° C. If it is lower than this, water may condense and a sufficient purging effect may not be obtained. On the other hand, if it is higher than this, the catalyst may be deteriorated unexpectedly.

  There is no restriction | limiting in particular about the form of the reforming catalyst of this invention. For example, it is possible to use a catalyst formed by tableting and pulverized to an appropriate range, an extruded catalyst, an extruded catalyst added with an appropriate binder, a powdered catalyst, and the like. 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. Used catalysts can be used. 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.

  The reforming catalyst of the present invention thus obtained is activated by hydrogen reduction if necessary.

  As the form of the reactor used for the steam reforming reaction, a flow-type fixed bed reactor is preferably used, but a fluidized bed reactor can also be used. The shape of the reactor may be any known shape depending on the purpose of each process, such as a cylindrical shape or a flat plate shape.

The space velocity of the flow material introduced into the reactor (raw material + water vapor) is, GHSV is preferably 100~100,000h ^-1, more preferably 300~50,000h ^-1, more preferably 500～30,000H ^{- In} the range of ¹ , it is set in consideration of each purpose.
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 500-800 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 present invention also provides a hydrogen production apparatus comprising a step of treating a mixed gas containing carbon monoxide and hydrogen obtained by the steam reforming reaction in a subsequent carbon monoxide removal step.
The mixed gas containing carbon monoxide and hydrogen obtained by the steam reforming reaction 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 carbon monoxide needs to be removed as in a phosphoric acid fuel cell or a polymer electrolyte fuel cell, the carbon monoxide removing step is used in combination, so that it is suitably used as a raw material for hydrogen for the fuel cell. be able to.

  The removal of carbon monoxide can be performed by, for example, performing a shift process and a carbon monoxide selective oxidation process. The shift step is a step of converting carbon monoxide and water into hydrogen and carbon dioxide, and a catalyst containing a mixed oxide of iron-chromium, a mixed oxide of copper-zinc, platinum, ruthenium, iridium, etc. The carbon monoxide content is preferably reduced to 2% by volume or less, more preferably 1% by volume or less, and even more preferably 0.5% by volume or less. Usually, in the phosphoric acid fuel cell, the mixed gas in this state can be used as fuel.

  On the other hand, in the polymer electrolyte fuel cell, since it is necessary to further reduce the carbon monoxide concentration, the treatment is performed in a carbon monoxide selective oxidation step or the like. In this step, a catalyst containing iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver, gold, etc. is used, and preferably 0.5 mol relative to the remaining number of moles of carbon monoxide. The carbon monoxide concentration is reduced by selectively converting carbon monoxide to carbon dioxide by adding 10 to 10 times mol, more preferably 0.7 to 5 times mol, and further preferably 1 to 3 times mol. Let In this case, the carbon monoxide concentration can be reduced by reacting with the coexisting hydrogen simultaneously with the oxidation of carbon monoxide to generate methane.

The present invention also provides a fuel cell system using hydrogen produced by the hydrogen production apparatus as fuel.
Hereinafter, the fuel cell 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.

As a catalyst for the reformer 7, a steam reforming catalyst in which rhodium is supported on a carrier containing (a) alumina, (b) ceria, and (c) a barrier and / or magnesia as a constituent component is used. Filled. At this time, the steam / carbon ratio is preferably set to 1 to 20, more preferably 1.5 to 10, and further preferably 2 to 5. Also, the space velocity is above catalysts basis of distribution material (raw material + water vapor), at standard temperature and pressure terms, GHSV is preferably 100～100,000H ^-1, more preferably 300～50,000H ^-1, further Preferably, it is set in the range of 500 to 30,000 h- ¹ . The reformer reaction tube is heated by a burner 18 using fuel from the fuel tank and anode off-gas as fuel, preferably in the range of 200 to 1000 ° C., more preferably 300 to 900 ° C., and even more preferably in the range of 500 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.

The polymer electrolyte fuel cell 17 comprises an anode 12, a cathode 13, and a solid polymer electrolyte 14, and a fuel gas containing high-purity hydrogen obtained by the above method is provided on the anode side, and an air blower is provided on the cathode side. The air sent from 8 is introduced after appropriate humidification processing (a humidifier is not shown) if necessary.
At this time, a reaction in which hydrogen gas becomes protons and emits electrons proceeds at the anode, and a reaction in which oxygen gas obtains electrons and protons to become water proceeds at the cathode. 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, and platinum black and Pt catalyst supported on activated carbon are used for the cathode. Usually, both the anode and cathode catalysts are formed into a porous catalyst layer together with polytetrafluoroethylene, a low molecular weight polymer electrolyte membrane material, activated carbon, and the like as necessary.

Next, the 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), and the like. Membrane Electrode Assembly: 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 15 is electrically connected to the anode and the cathode.
The anode off-gas is combusted in the burner 18 and used to warm the reforming tube, and then discharged. The cathode off gas is discharged from the exhaust port 16.

  According to the present invention, there is provided a steam reforming catalyst, which has been difficult in the past and has no decrease in activity even by purging with an oxygen-containing gas when the operation is stopped, and has excellent durability in normal operation. A fuel cell system using the above is provided.

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

[Catalyst preparation example]
(1) γ-alumina having a surface area of 165 g / cm ² is used as the catalyst carrier (1).
(2) To 1-gamma alumina having a surface area of 165 g / cm ² , add 1M cerium nitrate aqueous solution so that the amount of supported CeO ₂ becomes 12% by mass and 1M barium nitrate aqueous solution so that the amount of supported BaO becomes 5% by mass. It was impregnated and dried, dried at 120 ° C. for 12 hours, and then air calcined at 800 ° C. for 3 hours to obtain a catalyst carrier (2).
(3) Add 1M cerium nitrate aqueous solution so that the amount of supported CeO ₂ is 12% by mass and 1M magnesium nitrate aqueous solution so that the amount of supported MgO is 5% by mass to γ-alumina having a surface area of 165 g / cm ^2. It was impregnated and dried, dried at 120 ° C. for 12 hours, and then air calcined at 800 ° C. for 3 hours to obtain a catalyst carrier (3).

(A) The carrier (1) is impregnated with 0.1M ruthenium chloride aqueous solution so that the supported amount of ruthenium metal is 2% by mass, dried and dried at 120 ° C. for 12 hours, and then at 700 ° C. Hydrogen reduction is performed for 3 hours to obtain a catalyst (A).
(B) The carrier (2) is impregnated with 0.1M ruthenium chloride aqueous solution so that the supported amount of ruthenium metal is 2% by mass, dried and dried at 120 ° C. for 12 hours, and then at 700 ° C. Hydrogen reduction is performed for 3 hours to obtain a catalyst (B).
(C) The carrier (1) was impregnated with a 0.1M rhodium chloride aqueous solution so that the loading amount was 2% by mass as rhodium metal, dried and dried at 120 ° C. for 12 hours, and then at 700 ° C. Hydrogen reduction is performed for 3 hours to obtain a catalyst (C).
(D) The carrier (2) is impregnated with a 0.1M rhodium chloride aqueous solution so that the loading amount is 2% by mass as rhodium metal, dried and dried at 120 ° C. for 12 hours, and then at 700 ° C. Hydrogen reduction is performed for 3 hours to obtain a catalyst (D).
(E) The carrier (3) was impregnated with 0.1M rhodium chloride aqueous solution so that the supported amount as rhodium metal was 2% by mass, dried and dried at 120 ° C. for 12 hours, and then at 700 ° C. Hydrogen reduction is performed for 3 hours to obtain a catalyst (E).

[Comparative Example 1]
The catalyst (A) is tablet-molded, pulverized, and sized in the range of 250 to 500 μm, charged in a fixed bed flow reactor, desulfurized kerosene (0.05 mass ppm or less as sulfur atoms) and steam A steam reforming reaction was performed using a mixed gas as a raw material.
Assuming DSS (Daily Start-up & Shut-down) operation, the experiment was conducted as follows. One cycle consists of start-up, steady state, and stop. At start-up, the temperature of the catalyst is raised from 30 ° C to 150 ° C in an air atmosphere for 20 minutes, steam is introduced, the air is stopped, and then the catalyst is raised to 500 ° C in 30 minutes. The temperature is raised, kerosene is introduced, and then the temperature is raised to 700 ° C. in 15 minutes. The reaction is carried out in a steady state at 700 ° C. for 80 minutes, during which the conversion rate is measured. At the time of stop, kerosene is stopped, the temperature is lowered to 300 ° C. in 20 minutes, air is introduced, the steam is stopped, and then the temperature is lowered to 30 ° C. in 20 minutes. The above was made into DSS1 cycle, and this was repeated. The reaction conditions were a steam / carbon ratio of 3.0, a catalyst amount of 6 cm ³ , and a desulfurized kerosene flow rate of 0.244 g / min.

[Comparative Example 2]
The reaction was performed in the same manner as in Comparative Example 1 except that the catalyst (B) was used instead of the catalyst (A).

[Comparative Example 3]
The reaction was performed in the same manner as in Comparative Example 1 except that the catalyst (C) was used instead of the catalyst (A).

[Example 1]
The reaction was performed in the same manner as in Comparative Example 1 except that the catalyst (D) was used instead of the catalyst (A).

[Example 2]
The reaction was performed in the same manner as in Comparative Example 1 except that the catalyst (E) was used instead of the catalyst (A).

FIG. 2 shows the results of the change over time in the DSS operation using the catalysts A, B, C, D and E, organized by the conversion rate and the number of DSS cycles.
As is apparent from FIG. 2, when the catalysts (D) and (E) are used, since the time during which the conversion rate can be maintained at about 100% after purging with air has been drastically increased, the deterioration of the catalyst has been reduced. It can be seen that it has been relaxed.

[Example 3]
The catalyst (D) is tablet-molded, pulverized, and sized in the range of 250 to 500 μm, charged into a fixed bed flow reactor, desulfurized kerosene (0.05 mass ppm or less as sulfur atoms) and steam A steam reforming reaction was continuously performed at 700 ° C. using the mixed gas as a raw material. FIG. 3 shows changes with time in catalyst deterioration during continuous operation. As can be seen from FIG. 3, the catalyst of the present invention is a catalyst having excellent durability.

[Example 4]
In the fuel cell system having the configuration shown in FIG. 1, the test was performed using the catalyst (D) as the catalyst of the reformer 7 and kerosene as the fuel. At this time, the steam / carbon ratio of the raw material introduced into the reformer 7 was set to 3.0. As a result of analyzing the gas at the anode inlet, it contained 72% by volume of hydrogen (excluding water vapor).
During the test period, the reformer operated normally and no decrease in the activity of the catalyst was observed. The fuel cell also operated normally and the electric load 15 was operated smoothly.

It is the schematic which shows an example of the fuel cell system of this invention. It is a figure which shows the relationship between the kerosene conversion and the DDS cycle number in the DDS operation using the catalyst AE. FIG. 3 is a diagram showing a relationship between kerosene conversion rate and elapsed time in a steam reforming reaction using a catalyst D.

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 Selective oxidation reactor 12 Anode 13 Cathode 14 Solid polymer electrolyte 15 Electric load 16 Exhaust port 17 Polymer electrolyte fuel cell 18 Heating burner

Claims (6)

  A steam reforming catalyst of a hydrocarbon compound obtained by supporting rhodium on a carrier containing (a) alumina, (b) ceria, and (c) a barrier and / or magnesia as constituent components.   A steam reforming method comprising producing a mixed gas containing carbon monoxide and hydrogen from a raw material mixture containing hydrocarbon compounds and steam using the steam reforming catalyst according to claim 1.   A reforming section for performing a steam reforming reaction of hydrocarbon compounds, and using the steam reforming catalyst according to claim 1 in the reforming section, and purging the reforming section with a gas containing oxygen at the time of stoppage. The hydrogen production apparatus characterized by the above-mentioned.   A hydrogen production apparatus comprising a step of treating a mixed gas containing carbon monoxide and hydrogen produced by the steam reforming method according to claim 2 in a subsequent carbon monoxide removal step.   5. The hydrogen production apparatus according to claim 4, wherein the carbon monoxide removal step comprises a water gas reaction step and a subsequent carbon monoxide selective oxidation step. 6. A fuel cell system using hydrogen produced by the hydrogen production apparatus according to claim 3 as fuel.

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