JP5726513B2 - Fuel cell desulfurization system, fuel cell hydrogen production system, fuel cell system, and hydrocarbon fuel desulfurization method - Google Patents

Description

  The present invention relates to a fuel cell desulfurization system, a fuel cell hydrogen production system, a fuel cell system, and a hydrocarbon fuel desulfurization method.

  In general, a gas mainly composed of hydrogen is used as a fuel gas for a fuel cell, and a hydrocarbon-based fuel such as natural gas, LPG, naphtha, or kerosene is used as a raw material. These hydrocarbon fuels containing carbon and hydrogen are treated at high temperature on a catalyst together with steam, partially oxidized with an oxygen-containing gas, or subjected to a self-heat recovery type reforming reaction in a system where steam and oxygen-containing gas coexist. Hydrogen obtained by the above is used as fuel hydrogen for fuel cells.

  The catalyst used for the fuel reforming until the production of fuel hydrogen for the fuel cell, the subsequent carbon monoxide removal, and the cathode electrode is used in a reduced state such as noble metal or copper. There are many. In such a state, sulfur acts as a catalyst poison, and there is a problem that the catalytic activity of the hydrogen production process or the battery itself is lowered, and the efficiency is lowered.

  As a method for removing sulfur from fuel for a fuel cell, for example, a method using metal-supported zeolite is known.

Japanese Patent Laid-Open No. 10-237473

  By the way, the hydrocarbon fuel used as the raw material for fuel hydrogen of the fuel cell may contain various impurities in addition to sulfur. For example, city gas may contain water that is a temporary poison for the desulfurization agent. When the amount of water in the gas becomes high, the performance of the desulfurizing agent is temporarily lowered, and sulfur is not sufficiently removed. Impurities mixed in hydrocarbon fuels vary in type and concentration, making it difficult to deal with poisons of desulfurization agents.

  The present invention relates to a highly durable fuel cell desulfurization system and hydrogen production system capable of maintaining a desired desulfurization performance for a long period of time even when a hydrocarbon fuel containing a desulfurization agent poison is supplied. It is another object of the present invention to provide a fuel cell system and a hydrocarbon fuel desulfurization method.

  In order to solve the above problems, the present invention is a desulfurization system for a fuel cell, comprising a desulfurization section for removing sulfur compounds from a circulating hydrocarbon fuel containing sulfur compounds, and the desulfurization sections are different. Consists of a plurality of zeolites carrying active metals at a concentration, and the plurality of zeolites are arranged in order from the highest to the lowest active metal concentration from the upstream side to the downstream side in the flow direction of the hydrocarbon fuel. A desulfurization system for a fuel cell having a desulfurizing agent is provided.

  According to the fuel cell desulfurization system of the present invention, by including the desulfurization section having the above-described configuration, even if a hydrocarbon fuel containing a desulfurization agent poison is supplied, it is included in the hydrocarbon fuel. Sulfur compounds can be sufficiently removed over a long period of time.

  For this reason, the present inventors can adsorb the poisonous substance by the zeolite in which the active metal disposed upstream is supported at a high concentration, and the activity of the zeolite catalyst disposed thereafter is sufficiently maintained. It is thought that it is possible to suppress the sulfur from slipping to the subsequent stage.

  In the fuel cell desulfurization system of the present invention, from the viewpoint of desulfurization performance, the zeolite is preferably X-type zeolite or Y-type zeolite, and the active metal is preferably Ag or Cu.

  The hydrocarbon fuel may contain a hydrocarbon compound having 4 or less carbon atoms.

  The fuel cell desulfurization system of the present invention may further include a fuel supply unit that supplies a hydrocarbon fuel containing 0.001 to 2% by volume of moisture at 25 ° C. and containing a sulfur compound to the desulfurization unit.

  In addition, the moisture content as used in this specification is the value which converted the dew point temperature measured with the dew point meter into the moisture content in 25 degreeC.

  The present invention also provides a fuel cell hydrogen production system comprising: the fuel cell desulfurization system of the present invention; and a hydrogen generation unit that generates hydrogen from a hydrocarbon-based fuel that has passed through the desulfurization unit of the fuel cell desulfurization system. To do.

  According to the hydrogen production system of the present invention, by providing the fuel cell desulfurization system of the present invention, even if a hydrocarbon-based fuel containing a desulfurization agent poison is supplied, a sulfur compound is generated in the hydrogen generating part. Can be suppressed over a long period of time, whereby the production efficiency of hydrogen can be sufficiently maintained over a long period of time.

  The present invention also provides a fuel cell system comprising the fuel cell hydrogen production system of the present invention.

  According to the fuel cell system of the present invention, even when a hydrocarbon-based fuel containing a desulfurization agent poison is supplied, the fuel cell can be stably supplied with the fuel hydrogen by providing the hydrogen production system of the present invention. The power generation efficiency can be sufficiently maintained over a long period of time.

  The present invention also provides a hydrocarbon-based fuel desulfurization method in which a hydrocarbon-based fuel containing a sulfur compound is circulated in descending order of the active metal concentration of a plurality of zeolites carrying active metals at different concentrations.

  According to the hydrocarbon-based fuel desulfurization method of the present invention, even if the hydrocarbon-based fuel contains a desulfurization agent poisonous substance, sulfur compounds in the hydrocarbon-based fuel can be sufficiently removed over a long period of time. it can.

  In the hydrocarbon fuel desulfurization method of the present invention, from the viewpoint of desulfurization performance, the zeolite is preferably X-type zeolite or Y-type zeolite, and the active metal is preferably Ag or Cu.

  The hydrocarbon fuel may contain a hydrocarbon compound having 4 or less carbon atoms.

  The hydrocarbon fuel can contain 0.001-2% by volume of water at 25 ° C. According to the hydrocarbon-based fuel desulfurization method of the present invention, desulfurization can be stably performed over a long period of time even when a hydrocarbon-based fuel containing water in the above proportion is desulfurized.

  According to the present invention, a highly durable fuel cell desulfurization system capable of maintaining a desired desulfurization performance for a longer period of time even when a hydrocarbon-based fuel containing a desulfurization agent poison is supplied, hydrogen A manufacturing system, a fuel cell system, and a hydrocarbon-based fuel desulfurization method can be provided.

It is a conceptual diagram which shows an example of the fuel cell system which concerns on embodiment of this invention. It is a mimetic diagram showing an example of a desulfurization system concerning an embodiment of the present invention.

  FIG. 1 is a conceptual diagram showing an example of a fuel cell system according to an embodiment of the present invention. The fuel cell system 1 includes a fuel supply unit 2, a desulfurization unit 3, a hydrogen generation unit 4, a cell stack 5, an off-gas combustion unit 6, a water supply unit 7, a water vaporization unit 8, and an oxidant supply unit. 9, a power conditioner 10, and a control unit 11. Each part is connected by piping (not shown) in the flow shown in FIG. In the present embodiment, the fuel supply unit 2 and the desulfurization unit 3 constitute a fuel cell desulfurization system 20.

  The fuel supply unit 2 supplies hydrocarbon fuel to the desulfurization unit 3. Here, as the hydrocarbon-based fuel, a compound containing carbon and hydrogen (may contain other elements such as oxygen) in the molecule or a mixture thereof is used. Examples of hydrocarbon fuels include hydrocarbons, alcohols, ethers, and biofuels. These hydrocarbon fuels are derived from conventional fossil fuels such as petroleum and coal, and synthesized from syngas. A fuel-derived one or a biomass-derived one can be used as appropriate. Specific examples of hydrocarbons include methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, and light oil. Examples of alcohols include methanol and ethanol. Examples of ethers include dimethyl ether. Biofuels include biogas, bioethanol, biodiesel, and biojet. In the present embodiment, a gas containing methane as a main component (for example, city gas, town gas, natural gas, biogas, etc.) or LPG supplied through a pipeline is suitable. Can be used for

  When using a hydrocarbon-based fuel supplied from a pipeline, temporary poisons such as moisture may be mixed due to damage to the pipeline. According to the desulfurization section 3 according to the present invention, even when such a hydrocarbon fuel is supplied, the desulfurization performance is maintained over a longer period than the desulfurization section not having the configuration according to the present invention. It becomes possible to do.

  In the present embodiment, the hydrocarbon fuel preferably contains a hydrocarbon compound having 4 or less carbon atoms. Specific examples of the hydrocarbon compound having 4 or less carbon atoms include saturated aliphatic hydrocarbons such as methane, ethane, propane, and butane, and unsaturated aliphatic hydrocarbons such as ethylene, propylene, and butene. The hydrocarbon-based fuel is preferably a gas containing a hydrocarbon compound having 4 or less carbon atoms, that is, a gas containing one or more of methane, ethane, ethylene, propane, propylene, butane and butene. Moreover, as gas containing a C4 or less hydrocarbon compound, the gas containing 80 volume% or more of methane is preferable, and the gas containing 85 volume% or more of methane is more preferable.

The hydrocarbon fuel generally contains a sulfur compound. Examples of the sulfur compound include sulfur compounds originally mixed in hydrocarbons and the like, and compounds contained in odorants for detecting gas leaks. Examples of sulfur compounds originally mixed in hydrocarbons include hydrogen sulfide (H ₂ S), carbonyl sulfide (COS), carbon disulfide (CS ₂ ), and the like. As the odorant, alkyl sulfide, mercaptan alone or a mixture thereof is used. For example, diethyl sulfide (DES), dimethyl sulfide (DMS), ethyl methyl sulfide (EMS), tetrahydrothiophene (THT), tert-butyl mercaptan ( TBM), isopropyl mercaptan, dimethyl disulfide (DMDS), diethyl disulfide (DEDS) and the like are used. The sulfur compound is contained in an amount of about 0.1 to 10 mass ppm in terms of sulfur atom based on the total amount of hydrocarbon fuel.

  Hydrocarbon fuels may contain substances that poison active metals of desulfurization agents such as moisture and carbon monoxide. When the hydrocarbon fuel contains water, it can contain 0.001 to 2% by volume of water at 25 ° C.

  In the present embodiment, since the desulfurization system according to the present invention including the desulfurization section 3 is constructed, long-term desulfurization performance can be achieved even when using hydrocarbon fuels containing poisonous substances and sulfur compounds as described above. Can be maintained over time.

  The desulfurization section 3 is composed of a plurality of zeolites supporting active metals at different concentrations, and the plurality of zeolites are from those having a high active metal concentration to a downstream from the upstream side to the downstream side in the flow direction of the hydrocarbon fuel. The desulfurizing agent is arranged in the order as follows. FIG. 2 is a schematic diagram illustrating an example of a desulfurization system according to the present embodiment. The desulfurization unit 3a has a desulfurization agent that is formed by laminating three catalyst layers 101, 102, and 103 including zeolite supporting an active metal. In FIG. 2, the arrow A indicates the upstream side in the hydrocarbon fuel flow direction, and the arrow B indicates the downstream side. The catalyst layer 101 contains zeolite having active metal supported at the highest concentration, and the active metal concentration decreases in the order of the catalyst layers 102 and 103.

  The desulfurization unit 3 can be prepared by preparing a plurality of zeolites having different concentrations of the supported active metal and filling them in a predetermined container in order from the lowest or highest active metal concentration. In addition, the layer containing the zeolite having the highest concentration of the active metal is disposed on the upstream side in the flow direction of the hydrocarbon fuel.

  The number of catalyst layers is not particularly limited, but 3 to 7 layers are preferable from the viewpoints of desulfurization taxability improvement and cost.

The _zeolite, X-type zeolite of SiO 2 / _Al 2 _{O 3} molar ratio 2.7 to _3, Y-type zeolite of SiO 2 / _Al 2 _{O 3} molar ratio 4.5 to _5, SiO 2 / _Al 2 _{O 3} molar Examples thereof include mordenite zeolite having a ratio of 20 to 22. Among these, X-type zeolite and Y-type zeolite are preferable in terms of desulfurization performance.

  Examples of the active metal include Ag, Cu, and Zn. Among these, Ag and Cu are preferable in terms of desulfurization performance.

  The range of the amount of copper supported is preferably 3 to 20% by mass, more preferably 5 to 15% by mass on the basis of zeolite from the viewpoint of improving the desulfurization performance.

  As a method for supporting copper, an ion exchange method is preferably used. As the zeolite used for ion exchange, various types such as sodium type, ammonium type and proton type can be used, and the sodium type is most preferably used. On the other hand, copper is usually prepared as a cation dissolved in water. Specific examples thereof include aqueous solutions of copper sulfate, copper nitrate, copper chloride, and copper acetate, and aqueous solutions of copper complex ions such as copper ammine complex ions. The density | concentration of the aqueous solution containing a copper ion is 0.1-10 mass% normally as a copper density | concentration, Preferably it is the range of 0.5-5 mass%.

  The ion exchange method is not particularly limited, but usually the above-mentioned zeolite is added to the above-mentioned solution containing the cationic copper, and it is usually 0 to 90 ° C., preferably 20 to 70 ° C. for 1 hour to The ion exchange treatment is performed for several hours, preferably with stirring. Next, the solid matter is separated by means such as filtration and washed with water, and then dried at a temperature of 50 to 200 ° C., preferably 80 to 150 ° C. This ion exchange treatment can be repeated. Next, if necessary, it may be fired at 200 to 600 ° C., preferably 300 to 500 ° C. for about several hours. By such a method, the target copper ion exchange zeolite can be obtained.

  Zeolite supporting copper produced by the above method is made by extrusion molding, tableting molding, rolling granulation, spraying using alumina, silica, clay mineral, etc., or a precursor thereof such as boehmite as an appropriate binder. It can be molded and used in a conventional manner such as drying and firing as necessary. In addition, it is also preferable to preliminarily mold the zeolite and then apply the ion exchange method.

  The range of the supported amount of silver is preferably 10 to 30% by mass, more preferably 15 to 25% by mass on the basis of zeolite from the viewpoint of improving the desulfurization performance.

  An ion exchange method is preferably used as a method for supporting silver. As the zeolite used for ion exchange, various types such as sodium type, ammonium type and proton type can be used, and the sodium type is most preferably used. On the other hand, silver is usually prepared as a cation dissolved in water. Specific examples thereof include an aqueous solution of silver nitrate and silver perchlorate, an aqueous solution of silver ammine complex ion, and the like, and an aqueous silver nitrate solution is most preferably used. The density | concentration of the aqueous solution containing silver ion is 0.5-10 mass% normally as a density | concentration of silver, Preferably it is the range of 1-5 mass%.

  The method of ion exchange is not particularly limited, but usually the above-mentioned zeolite is added to the above solution containing cationic silver, and it is usually 0 to 90 ° C., preferably 20 to 70 ° C. for 1 hour to The ion exchange treatment is performed for several hours, preferably with stirring. Next, the solid matter is separated by means such as filtration and washed with water, and then dried at a temperature of 50 to 200 ° C., preferably 80 to 150 ° C. This ion exchange treatment can be repeated. Next, if necessary, it may be fired at 200 to 600 ° C., preferably 250 to 400 ° C. for about several hours. By such a method, the target silver ion exchange zeolite can be obtained.

  Zeolite carrying silver produced by the above method is alumina, silica, clay mineral, etc., using these precursors such as boehmite as an appropriate binder, extrusion molding, tableting molding, rolling granulation, It can be molded and used by a normal method such as spray drying and firing as necessary. In addition, it is also preferable to pre-mold zeolite and apply the above ion exchange method thereafter.

  Usually, the desulfurization condition is preferably that the hydrocarbon fuel is vaporized. The desulfurization temperature is preferably 100 ° C. or less, for example, in the range of −50 ° C. to 100 ° C., more preferably in the range of −20 ° C. to 80 ° C., further preferably in the range of 0 to 60 ° C., and still more preferably in the range of 10 to 50 ° C. Selected by range.

When using a hydrocarbon-based fuel that is a gas at normal temperature and normal pressure, such as city gas, GHSV is selected between 10 and 20000 h ⁻¹ , preferably between 10 and 7000 h ⁻¹ . When GHSV is lower than 10 h ⁻¹ , the desulfurization performance is sufficient, but since the desulfurizing agent is used more than necessary, the desulfurizer becomes excessively unfavorable. On the other hand, if GHSV is larger than 20000 h ⁻¹ , sufficient desulfurization performance cannot be obtained. In addition, liquid fuel can also be used as a hydrocarbon fuel, and in that case, a range of 0.01 to 100 h ⁻¹ can be selected as LHSV.

  The pressure conditions are usually selected in the range of normal pressure to 1 MPa (gauge pressure, the same shall apply hereinafter), preferably normal pressure to 0.5 MPa, and more preferably normal pressure to 0.2 MPa. Most preferred.

  The hydrocarbon-based fuel from which the sulfur content has been removed by the desulfurization unit 3 is supplied to the hydrogen generation unit 4. The hydrogen generator 4 and the desulfurization system 20 constitute a hydrogen production system 30. The hydrogen generator 4 includes a reformer that reforms the hydrocarbon-based fuel after desulfurization using a reforming catalyst, and generates a hydrogen-rich gas. The reforming method in the hydrogen generating unit 4 is not particularly limited, and for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be employed. The reforming temperature is usually 200 to 800 ° C, preferably 300 to 700 ° C. The hydrogen generator 4 may have a configuration for adjusting the properties in addition to the reformer reformed by the reforming catalyst depending on the properties of the hydrogen rich gas required by the cell stack 5. For example, when the type of the cell stack 5 is a polymer electrolyte fuel cell (PEFC) or a phosphoric acid fuel cell (PAFC), the hydrogen generation unit 4 is configured to remove carbon monoxide in the hydrogen-rich gas. (For example, a shift reaction part and a selective oxidation reaction part). The hydrogen generation unit 4 supplies a hydrogen rich gas to the anode 12 of the cell stack 5.

  Examples of the reforming catalyst include those having a catalyst carrier containing cerium oxide or a rare earth element oxide mainly composed of cerium oxide, and an active metal supported on the carrier.

  As the active metal, Ru or Rh is preferably used. As the loading amount of Ru or Rh, the atomic ratio of cerium to Ru or Rh (Ce / Ru or Ce / Rh) is 1 to 250, preferably 2 to 100, more preferably 3 to 50. When the atomic ratio is out of the above range, sufficient catalytic activity may not be obtained, which is not preferable. The amount of Ru or Rh supported is 0.1 to 3.0% by mass, preferably 0.5 to 3.0% by weight, based on the catalyst weight (total weight of catalyst support and active metal), with Ru or Rh as the metal equivalent. 2.5% by mass.

  The method for supporting Ru or Rh on the catalyst carrier is not particularly limited, and can be easily performed by applying a known method. For example, an impregnation method, a deposition method, a coprecipitation method, a kneading method, an ion exchange method, a pore filling method and the like can be mentioned, and the impregnation method is particularly desirable. The starting material for Ru or Rh used in the production of the catalyst varies depending on the above-mentioned supporting method and can be appropriately selected. Usually, a Ru or Rh chloride or a Ru or Rh nitrate is used. For example, when the impregnation method is applied, a method of preparing a solution of Ru or Rh salt (usually an aqueous solution), impregnating the carrier, drying, and firing as necessary can be exemplified. Firing is usually performed in air or a nitrogen atmosphere, and the temperature is not particularly limited as long as it is equal to or higher than the decomposition temperature of the salt, but is usually 200 to 800 ° C, preferably 300 to 800 ° C, more preferably 500. About ~ 800 ° C is desirable. In the present invention, it is usually possible to prepare a catalyst by supporting Ru or Rh on a catalyst carrier and then performing a reduction treatment at 400 to 1000 ° C., preferably 500 to 700 ° C. in a reducing atmosphere (usually a hydrogen atmosphere). Preferably employed. The above reforming catalyst may be in a form in which other noble metals (platinum, iridium, palladium, etc.) are further supported.

  The catalyst support for the reforming catalyst is preferably a support containing cerium oxide or a rare earth element oxide containing cerium oxide as a main component in an amount of 5 to 40% by mass and aluminum oxide in an amount of 60 to 95% by mass.

Although it does not specifically limit as a cerium oxide, The 2nd cerium oxide (commonly called ceria) is preferable. The method for preparing cerium oxide is not particularly limited, and for example, cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O, Ce (NO ₃ ) _4, etc.), cerium chloride (CeCl ₃ .nH ₂ O) ), Cerium hydroxide (Ce (OH) ₃ , Ce (OH) ₄ .H ₂ O, etc.), cerium carbonate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O, Ce ₂ (CO ₃ ) ₃ · 5H ₂ O Etc.), cerium oxalate, cerium (IV) ammonium oxalate, cerium chloride and the like as starting materials, and can be prepared by a known method, for example, firing in air.

  The rare earth element oxide mainly composed of cerium oxide can be prepared from a salt of a mixed rare earth element mainly composed of cerium. In the rare earth element oxide mainly composed of cerium oxide, the content of cerium oxide is usually 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. Examples of rare earth elements other than cerium oxide include scandium, yttrium, lanthanum, protheodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and other elements. Is mentioned. Of these, oxides of each element of yttrium, lanthanum, and neodymium are preferable, and oxides of lanthanum are particularly preferable. Of course, the crystal form is not particularly limited, and any crystal form may be used.

  Examples of the aluminum oxide include alumina and double oxides of aluminum and other elements such as silicon, copper, iron, and titanium. Typical examples of the double oxide include silica alumina. . Of these, alumina is particularly desirable, and the alumina is not particularly limited, and any crystal form such as α, β, γ, η, θ, κ, and χ can be used, and the γ type is particularly preferable. Alumina hydrates such as boehmite, bayerite, and gibbsite can also be used. Silica alumina is not particularly limited, and any crystal form can be used. Aluminum oxide can be used without any problem even if it contains a small amount of impurities.

  The composition ratio of cerium oxide and rare earth element oxide mainly composed of cerium oxide in the catalyst carrier of the reforming catalyst is preferably 5 to 40% by mass, and more preferably 10 to 35% by mass. When the rare earth element oxide containing cerium oxide and cerium oxide as a main component is less than 5% by mass, the carbon precipitation suppressing effect, the activity promoting effect, and the heat resistance improving effect in the presence of oxygen are insufficient, which is not preferable. On the other hand, when the amount is more than 40% by mass, the surface area of the support is decreased, and sufficient catalytic activity may not be obtained.

  60-95 mass% is preferable and, as for the composition ratio of the aluminum oxide in the catalyst support | carrier of a reforming catalyst, 65-90 mass% is more preferable. When the composition ratio of the aluminum oxide is less than 60% by mass, the surface area of the support is decreased, so that sufficient catalytic activity may not be obtained. This is not preferable because the effect and the effect of improving heat resistance in the presence of oxygen are insufficient.

  The method for producing the catalyst carrier of the reforming catalyst is not particularly limited, and can be easily produced by a known method. For example, it can be produced by impregnating aluminum oxide with an aqueous solution of cerium or a rare earth element salt containing cerium as a main component, followed by drying and baking. The salt used at this time is preferably a water-soluble salt. Specific examples of the salt include nitrates, chlorides, sulfates, acetates, and the like. Nitrate or organic acid salt is preferable. Firing is usually performed in air or an oxygen atmosphere, and the temperature is not particularly limited as long as it is equal to or higher than the decomposition temperature of the salt. As another method for preparing the carrier, it can also be prepared by a coprecipitation method, a gel kneading method, or a sol-gel method.

  Although the catalyst carrier can be obtained in this way, it is preferable to calcinate the catalyst carrier in the atmosphere of air or oxygen before supporting Ru or Rh. As a calcination temperature at this time, it is 500-1400 degreeC normally, Preferably it is 700-1200 degreeC. Further, for the purpose of increasing the mechanical strength of the catalyst carrier, a small amount of a binder such as silica or cement can be added to the catalyst carrier. The shape of the catalyst carrier of the reforming catalyst is not particularly limited, and can be appropriately selected depending on the form in which the catalyst is used. For example, an arbitrary shape such as a pellet shape, a granule shape, a honeycomb shape, or a sponge shape is adopted.

  The shape of the reforming catalyst is not particularly limited, and can be appropriately selected depending on the form in which the catalyst is used. For example, an arbitrary shape such as a pellet shape, a granule shape, a honeycomb shape, or a sponge shape is adopted.

  Further, in the hydrogen generation unit 4, it is preferable that water vapor is supplied from the water vaporization unit 8 to the hydrogen generation unit 4 because water vapor is required to reform the hydrocarbon-based fuel. The water vapor is preferably generated by heating the water supplied from the water supply unit 7 in the water vaporization unit 8 and vaporizing it. Heating of the water in the water vaporization unit 8 may use heat generated in the fuel cell system 1 such as recovering heat of the hydrogen generation unit 4, heat of the off-gas combustion unit 6, or exhaust gas. Moreover, you may heat water using other heat sources, such as a heater and a burner separately. In FIG. 1, only heat supplied from the off-gas combustion unit 6 to the hydrogen generation unit 4 is described as an example, but the present invention is not limited to this.

  Hydrogen rich gas is supplied from the hydrogen production system 30 to the fuel cell system 1 through a pipe connecting the hydrogen production system 30 and the cell stack 5. Electric power is generated in the cell stack 5 using this hydrogen-rich gas and an oxidizing agent. The type of the cell stack 5 in the fuel cell system 1 is not particularly limited, and examples thereof include a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), and phosphoric acid. A fuel cell fuel cell (PAFC), a molten carbonate fuel cell (MCFC), and other types can be employed. It should be noted that the components shown in FIG. 1 may be omitted as appropriate according to the type of cell stack 5, the reforming method, and the like.

  The oxidant is supplied from the oxidant supply unit 9 through a pipe connecting the oxidant supply unit 9 and the fuel cell system 1. As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removal method), or oxygen-enriched air is used.

  The cell stack 5 generates power using the hydrogen rich gas from the hydrogen generation unit 4 and the oxidant from the oxidant supply unit 9. The cell stack 5 includes an anode 12 to which a hydrogen-rich gas is supplied, a cathode 13 to which an oxidant is supplied, and an electrolyte 14 disposed between the anode 12 and the cathode 13. The cell stack 5 supplies power to the outside via the power conditioner 10. The cell stack 5 supplies the hydrogen rich gas and the oxidant, which have not been used for power generation, to the off gas combustion unit 6 as off gas. Note that a combustion section (for example, a combustor that heats the reformer) provided in the hydrogen generation section 4 may be shared with the off-gas combustion section 6.

  The off gas combustion unit 6 burns off gas supplied from the cell stack 5. The heat generated by the off-gas combustion unit 6 is supplied to the hydrogen generation unit 4 and used for generation of a hydrogen rich gas in the hydrogen generation unit 4. The fuel supply unit 2, the water supply unit 7, and the oxidant supply unit 9 are configured by, for example, a pump and are driven based on a control signal from the control unit 11.

  The power conditioner 10 adjusts the power from the cell stack 5 according to the external power usage state. For example, the power conditioner 10 performs a process of converting a voltage and a process of converting DC power into AC power.

  The control unit 11 performs control processing for the entire fuel cell system 1. The control unit 11 includes, for example, a device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output interface. The control unit 11 is electrically connected to the fuel supply unit 2, the water supply unit 7, the oxidant supply unit 9, the power conditioner 10, and other sensors and auxiliary equipment not shown. The control unit 11 acquires various signals generated in the fuel cell system 1 and outputs a control signal to each device in the fuel cell system 1.

  Next, the hydrocarbon fuel desulfurization method and hydrogen production method of the present invention will be described.

  In the hydrocarbon-based fuel desulfurization method of the present invention, a hydrocarbon-based fuel containing a sulfur compound is circulated in descending order of the active metal concentration of a plurality of zeolites carrying active metals at different concentrations.

  Examples of the hydrocarbon fuel containing a sulfur compound include the hydrocarbon fuels described above.

  Specific means for circulating hydrocarbon-based fuels in descending order of the active metal concentration of a plurality of zeolites carrying active metals at different concentrations includes the fuel supply unit 2 and the desulfurization unit 3 described above. . That is, the hydrocarbon fuel is supplied to the desulfurization unit 3 by the fuel supply unit 2, and the hydrocarbon fuel supplied from the fuel supply unit is brought into contact with the desulfurization agent in the desulfurization unit 3.

  Usually, the desulfurization condition is preferably that the hydrocarbon fuel is vaporized. The desulfurization temperature is preferably 100 ° C. or less, for example, in the range of −50 ° C. to 100 ° C., more preferably in the range of −20 ° C. to 80 ° C., further preferably in the range of 0 to 60 ° C., and still more preferably in the range of 10 to 50. It is selected in the range of ° C.

When using a hydrocarbon-based fuel that is a gas at normal temperature and normal pressure, such as city gas, GHSV is selected between 10 and 20000 h ⁻¹ , preferably between 10 and 7000 h ⁻¹ . When GHSV is lower than 10 h ⁻¹ , the desulfurization performance is sufficient, but since the desulfurizing agent is used more than necessary, the desulfurizer becomes excessively unfavorable. On the other hand, if GHSV is larger than 20000 h ⁻¹ , sufficient desulfurization performance cannot be obtained. In addition, liquid fuel can also be used as a hydrocarbon fuel, and in that case, a range of 0.01 to 100 h ⁻¹ can be selected as LHSV.

  The pressure conditions are usually selected in the range of normal pressure to 1 MPa (gauge pressure, the same shall apply hereinafter), preferably normal pressure to 0.5 MPa, and more preferably normal pressure to 0.2 MPa. Most preferred.

<Preparation of zeolite catalyst>
(Catalyst 1)
A silver nitrate aqueous solution was prepared by adding 600 ml of distilled water to 19 g of silver nitrate. Next, the mixture was mixed with 50 g of commercially available NaY-type zeolite powder having a SiO ₂ / Al ₂ O ₃ (molar ratio) = 4.5 with stirring to perform ion exchange. Then, it was washed with distilled water so as not to leave nitrate radicals. After washing, it was dried overnight at 180 ° C. in air. 5 g of an alumina binder was mixed with 30 g of the powdery silver exchanged zeolite after drying, and extrusion molding was performed at 1 mmφ to obtain catalyst 1. The amount of silver supported in Catalyst 1 was 15% by mass based on the carrier.

(Catalyst 2)
The catalyst 2 was obtained in the same manner as the catalyst 1 except that the silver nitrate used was changed to 12.7 g and the supported amount of silver was 10% by mass based on the carrier.

(Catalyst 3)
The catalyst 3 was obtained in the same manner as the catalyst 1 except that the silver nitrate used was changed to 6.3 g and the supported amount of silver was 5 mass% based on the carrier.

(Catalyst 4)
To 40 g of copper sulfate pentahydrate, 600 ml of distilled water was added to prepare an aqueous copper sulfate solution. Next, the mixture was mixed with 50 g of commercially available NaY-type zeolite powder having a SiO ₂ / Al ₂ O ₃ (molar ratio) = 4.5 with stirring to perform ion exchange. Then, it washed with distilled water so that a sulfate radical might not remain. After washing, it was dried overnight at 180 ° C. in an air stream. 5 g of an alumina binder was mixed with 30 g of the powdered copper-exchanged zeolite after drying, and extrusion molding was performed at 1 mmφ to obtain catalyst 4. The supported amount of copper in the catalyst 4 was 15% by mass based on the carrier.

(Catalyst 5)
The catalyst 5 was obtained in the same manner as the catalyst 4 except that the copper sulfate pentahydrate used was changed to 26.8 g and the supported amount of copper was changed to 10% by mass based on the carrier.

(Catalyst 6)
The catalyst 6 was obtained in the same manner as the catalyst 4 except that the copper sulfate pentahydrate used was changed to 13.2 g and the supported amount of copper was changed to 5% by mass based on the carrier.

(Catalyst 7)
A silver nitrate aqueous solution was prepared by adding 600 ml of distilled water to 19 g of silver nitrate. Next, the mixture was mixed with 50 g of commercially available NaX-type zeolite powder with SiO ₂ / Al ₂ O ₃ (molar ratio) = 2.7 with stirring, and ion exchange was performed. Then, it was washed with distilled water so as not to leave nitrate radicals. After washing, it was dried overnight at 180 ° C. in air. 5 g of an alumina binder was mixed with 30 g of the powdered silver exchanged zeolite after drying, and extrusion molding was performed at 1 mmφ to obtain a catalyst 7. The supported amount of silver in the catalyst 7 was 15% by mass based on the carrier.

(Catalyst 8)
The catalyst 8 was obtained in the same manner as the catalyst 7 except that the silver nitrate used was changed to 12.7 g and the supported amount of silver was 10% by mass based on the carrier.

(Catalyst 9)
The catalyst 9 was obtained in the same manner as the catalyst 7 except that the silver nitrate used was changed to 6.3 g and the supported amount of silver was 5% by mass based on the carrier.

<Production of desulfurization system and desulfurization of hydrocarbon fuel>
Example 1
In a fixed bed flow type reaction tube, catalyst 1, catalyst 2 and catalyst 3 were filled in this order with 8 ml, 8 ml and 8 ml, respectively, to prepare a catalyst layer in which the above three kinds of zeolite were laminated. The relative value of the active metal concentration is catalyst 1 / catalyst 2 / catalyst 3 = 1 / 0.67 / 0.33.

From the catalyst 1 layer side of the reaction tube filled with the catalyst layer, fuel 1 (city gas) having the composition shown in Table 1 is circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. It was.

  The sulfur concentration in the gas at the inlet and outlet of the reaction tube at this time was measured by SCD (Sulfur Chemiluminescence Detector) gas chromatography, and the sulfur atom equivalent concentration of the sulfur compound in the outlet gas based on the total amount of hydrocarbon fuel was 0. The time when 0.05 ppm by volume or more was recorded as the sulfur breakthrough time. The results are shown in Table 2.

(Example 2)
Desulfurization was performed in the same manner as in Example 1 except that fuel 2 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure instead of fuel 1. Went. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Example 3)
Desulfurization was performed in the same manner as in Example 1 except that fuel 3 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure instead of fuel 1. Went. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

Example 4
A fixed bed flow type reaction tube was filled with catalyst 4, catalyst 5 and catalyst 6 in this order at 8 ml, 8 ml and 8 ml, respectively, to prepare a catalyst layer in which the above three types of zeolite were laminated. The relative value of the active metal concentration is catalyst 4 / catalyst 5 / catalyst 6 = 1 / 0.67 / 0.33.

From the catalyst 4 layer side of the reaction tube filled with the catalyst layer, fuel 2 (city gas) having the composition shown in Table 1 is circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. It was. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Example 5)
In a fixed bed flow type reaction tube, catalyst 7, catalyst 8 and catalyst 9 were filled in this order at 8 ml, 8 ml and 8 ml, respectively, to prepare a catalyst layer in which the above three kinds of zeolite were laminated. The relative value of the active metal concentration is catalyst 7 / catalyst 8 / catalyst 9 = 1 / 0.67 / 0.33.

From the catalyst 7 layer side of the reaction tube filled with the catalyst layer, fuel 2 (city gas) having the composition shown in Table 1 is circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. It was. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Comparative Example 1)
A fixed bed flow type reaction tube was filled with the catalyst 2 at a filling amount of 24 ml to prepare a catalyst layer. Fuel 1 (city gas) having the composition shown in Table 1 was circulated through this reaction tube under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Comparative Example 2)
Desulfurization in the same manner as in Comparative Example 1 except that fuel 2 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure instead of fuel 1. Went. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Comparative Example 3)
Desulfurization in the same manner as in Comparative Example 1 except that fuel 3 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure instead of fuel 1. Went. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Comparative Example 4)
A fixed bed flow-type reaction tube was filled with the catalyst 5 at a filling amount of 24 ml to prepare a catalyst layer. In this reaction tube, fuel 2 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

(Comparative Example 5)
A fixed bed flow type reaction tube was filled with the catalyst 8 at a filling amount of 24 ml to prepare a catalyst layer. In this reaction tube, fuel 2 (city gas) having the composition shown in Table 1 was circulated under the conditions of GHSV: 6000 h ⁻¹ , temperature of 30 ° C., and atmospheric pressure. Then, the sulfur breakthrough time was measured in the same manner as in Example 1.

  As shown in Table 2, a plurality of zeolites having different active metal concentrations are arranged in order from the highest to the lowest active metal concentration from the upstream side to the downstream side in the distribution direction of the city gas that is a hydrocarbon fuel. Thus, it was confirmed that by providing a concentration gradient of the active metal, the sulfur breakthrough time can be made longer than when there is no concentration gradient.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel supply part, 3 ... Desulfurization part, 4 ... Hydrogen generation part, 5 ... Cell stack, 20 ... Desulfurization system, 30 ... Hydrogen production system.

Claims (10)

A desulfurization system for a fuel cell,
A desulfurization section for removing the sulfur compound from the circulating hydrocarbon fuel containing the sulfur compound;
The desulfurization part is composed of a plurality of zeolites carrying active metals at different concentrations, and the plurality of zeolites have a high to low active metal concentration from the upstream side to the downstream side in the flow direction of the hydrocarbon fuel. have a desulfurizing agent are arranged in the order in which the,
A desulfurization system for a fuel cell , wherein the active metal is any one of Cu and Ag . 2. The plurality of zeolites according to claim 1, wherein the zeolite is an X-type zeolite on which Ag is supported, an Y-type zeolite on which Ag is supported, an X-type zeolite on which Cu is supported, or a Y-type zeolite on which Cu is supported. Desulfurization system for fuel cells.   The desulfurization system for a fuel cell according to claim 1 or 2, wherein the hydrocarbon fuel includes a hydrocarbon compound having 4 or less carbon atoms.   4. The fuel supply unit according to claim 1, further comprising a fuel supply unit that supplies 0.001 to 2% by volume of water at 25 ° C. and supplies a hydrocarbon-based fuel containing a sulfur compound to the desulfurization unit. Fuel cell desulfurization system.   A fuel comprising: the fuel cell desulfurization system according to any one of claims 1 to 4; and a hydrogen generation unit that generates hydrogen from the hydrocarbon-based fuel that has passed through the desulfurization unit of the fuel cell desulfurization system. Battery hydrogen production system.   A fuel cell system comprising the hydrogen production system for a fuel cell according to claim 5. A step of causing a hydrocarbon-based fuel containing a sulfur compound to circulate in order from the active metal concentration of a plurality of zeolites supporting active metal at different concentrations , wherein the active metal is one of Cu and Ag; A desulfurization method for hydrocarbon fuel, which is characterized in that it exists . The plurality of zeolites are X-type zeolite on which Ag is supported, Y-type zeolite on which Ag is supported, X-type zeolite on which Cu is supported, or Y-type zeolite on which Cu is supported. A method for desulfurizing hydrocarbon fuels.   The method for desulfurizing a hydrocarbon fuel according to claim 7 or 8, wherein the hydrocarbon fuel includes a hydrocarbon compound having 4 or less carbon atoms.   The hydrocarbon-based fuel desulfurization method according to any one of claims 7 to 9, wherein the hydrocarbon-based fuel contains 0.001 to 2% by volume of water at 25 ° C.

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