JP2006265480A - Hydrocarbon-containing gas desulfurization method and fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED To provide a hydrocarbon-containing gas desulfurization method that can be applied to a fuel cell system to obtain an excellent desulfurization effect, and a fuel cell system to which the desulfurization method is applied.
When a hydrocarbon-containing gas is supplied to a desulfurizer to remove a sulfur compound in the gas in a fuel cell system package, the gas is desulfurized on the upstream side filled with a desulfurizing agent containing zeolite. Desulfurization containing at least one selected from the group consisting of a metal element, a metal oxide and a metal component-supported oxide disposed at a temperature of 50 ° C. or higher after the desulfurization treatment in the vessel A A desulfurization method in which desulfurization treatment is performed in the desulfurizer B on the downstream side filled with the agent and a fuel cell system to which the desulfurization method is applied.
[Selection figure] None

Description

  TECHNICAL FIELD The present invention relates to a hydrocarbon-containing gas desulfurization method and a fuel cell system, and in particular, a raw material hydrocarbon for preventing poisoning by sulfur compounds of a catalyst in a reformer and a fuel cell unit mounted on the fuel cell system. The present invention relates to a method for desulfurizing contained gas and a fuel cell system to which the desulfurization method is applied.

  Patent Document 1 proposes a method for removing sulfur compounds in gaseous hydrocarbons. The publication discloses a method for removing a sulfur compound by combining a desulfurizing agent layer containing zeolite and a desulfurizing agent layer containing at least one selected from the group consisting of metal elements, metal oxides and metal component-supported oxides. It is disclosed. This combination of desulfurizing agent layers is effective to some extent as a desulfurization technique for hydrocarbon gas containing various sulfur compounds, but it has not always been fully satisfactory when considering incorporation into a fuel cell system.

  Even if a small amount of sulfur leaks from the desulfurizer to the subsequent stage, the reforming catalyst is damaged and a predetermined amount of hydrogen continuously supplied to the fuel cell cannot be obtained. For this reason, when the reforming catalyst is damaged, it is necessary to remove and replace the reformer, and replacement of the expensive reformer is extremely disadvantageous industrially. Therefore, it is important to prevent the sulfur compound from leaking out from the desulfurizer, even if it is a trace amount. Also, in the production of hydrogen used in fuel cells, the desulfurizer must be installed in the fuel cell system, particularly in general household and small business fuel cell systems where miniaturization is desired. Therefore, further downsizing of the desulfurizer has been required.

International Publication No. 04/058927

  An object of the present invention is to provide a desulfurizer filled with a desulfurizing agent containing zeolite, and a desulfurizer containing a desulfurizing agent containing at least one selected from the group consisting of metal elements, metal oxides and metal component-supported oxides. It is an object of the present invention to provide a hydrocarbon-containing gas desulfurization method capable of obtaining an excellent desulfurization effect by applying the above to a fuel cell system. Another object of the present invention is to prevent poisoning and damage of the reforming catalyst and the catalyst of the fuel cell, and to obtain a desired amount of hydrogen gas continuously, particularly when the fuel cell system is in operation. It is to provide a fuel cell system.

  In addition to a desulfurizer, auxiliary equipment such as a reformer, stack and pump are installed in the fuel cell system, so the heat released from these devices heats up the fuel cell system package during system operation. And a non-uniform temperature distribution is formed. The present inventors have paid attention to the actual situation in such a fuel cell system package, and have repeatedly studied on an improvement method for enhancing the desulfurization effect by the combined desulfurizer in relation to the arrangement and temperature conditions of these devices. . As a result, it was found that the method of incorporating each desulfurizer into the system in the operating state of the fuel cell system is extremely important, and that an excellent desulfurization effect can be obtained by the arrangement state and temperature control of each.

That is, the present invention
(1) In supplying a hydrocarbon-containing gas to a desulfurizer and removing sulfur compounds in the gas in the fuel cell system package, the upstream desulfurizer filled with a desulfurizing agent containing zeolite A desulfurization agent containing at least one selected from the group consisting of metal elements, metal oxides, and metal component-supported oxides, which is installed at a temperature of 40 ° C. or higher in a fuel cell system operating state after desulfurization treatment with A A desulfurization method, wherein the desulfurization treatment is performed in the desulfurizer B on the downstream side filled with
(2) The desulfurization method according to (1), wherein the desulfurizer A is installed at a temperature of 40 ° C. or lower when the fuel cell system is in operation.
(3) The desulfurization method according to (1) or (2) above, wherein the volume ratio of the desulfurizing agent charged in the desulfurizer A and the desulfurizer B is 0.1: 0.9 to 0.9: 0.1,

(4) The desulfurization method of (1), (2) or (3) above, wherein the zeolite has a beta (BEA) and / or faujasite (FAU) structure,
(5) The desulfurizing agent in the desulfurizer A is at least one metal selected from the group consisting of Ag, Cu, Ni, Zn, Mn, Fe, Co, alkali metal, alkaline earth metal, and rare earth metal together with zeolite. The desulfurization method of (1) to (4) above containing the components, and (6) the desulfurization agent in the desulfurizer B is Ag, Cu, Ni, Zn, Mn, Fe, Co, Al, Si, alkali metal, alkali The desulfurization method according to any one of (1) to (5) above, which includes at least one metal component selected from the group consisting of earth metals and rare earth metals, and (6) desulfurization by the method according to any one of claims 1 to 6 A fuel cell system using a hydrogen-containing gas obtained by reforming a treated hydrocarbon-containing gas;
Is to provide.

  According to the method of the present invention, the desulfurization treatment of the sulfur-containing hydrocarbon gas requires a much smaller amount of the desulfurization agent than the conventional desulfurization agent, and therefore the desulfurizer can be downsized. In addition, since sulfur compounds in hydrocarbons can be efficiently removed, it is extremely industrially advantageous. In addition, since there is substantially no risk of the sulfur compound leaking from the desulfurizer, poisoning of the reformer and the catalyst of the fuel cell can be highly prevented, and an excellent fuel cell system can be constructed. .

  In the desulfurization method of the present invention, the desulfurizer A filled with a desulfurizing agent containing zeolite is installed in a relatively low temperature region in the fuel cell system, preferably in a region under a temperature condition of 40 ° C. or less. The hydrocarbon gas containing various sulfur compounds is first supplied to the desulfurizer. The desulfurized gas is then selected from the group consisting of metal elements, metal oxides and metal component-supported oxides disposed in a relatively high temperature region within the system, i.e., a temperature region above 40 ° C. The desulfurizer B filled with the desulfurizing agent containing at least one kind is supplied. In the method of the present invention, it is important to selectively arrange both desulfurizers containing such different desulfurizing agents under different temperature and environmental condition atmospheres. As described above, the desulfurizer installed on the upstream side varies depending on the type and amount of the sulfur compound contained in the gas, but it is usually at a relatively low temperature of about room temperature, preferably 40 ° C. or less, more preferably The desulfurizer on the downstream side is disposed at a temperature of 40 ° C. or higher, preferably at a temperature of 50 to 80 ° C., to perform the desulfurization treatment. As the installation site of the upstream desulfurizer, for example, the vicinity of the exhaust fan for exhaust in the fuel cell system, the vicinity of the installation location of the instruments, etc., and the installation site of the downstream desulfurizer, for example, For example, near the reformer.

  As the desulfurizing agent filled in the first desulfurizer A of the present invention, one containing zeolite, preferably one containing a metal component together with zeolite is used. The zeolite used preferably has a beta (BEA) and / or faujasite (FAU) structure. Such zeolites include, for example, β-type, X-type and Y-type zeolites. These can be used alone or in combination of two or more.

  The metal components used in the first desulfurizer A together with zeolite were selected from the group consisting of Ag, Cu, Ni, Zn, Mn, Fe, Co, alkali metals, alkaline earth metals, and rare earth metals. At least one metal component is included. Examples of the alkali metal include potassium and sodium, and examples of the alkaline earth metal include calcium and magnesium. Moreover, as a rare earth metal, lanthanum, cerium, etc. can be mentioned typically. A desulfurization agent containing zeolite and metal components can be effectively prepared by a method in which a metal component is supported on zeolite. Specifically, an aqueous solution containing a metal water-soluble compound to be supported and zeolite are mixed well, washed with water, dried, and fired. Especially as a metal component, Ag and Cu are preferable, and content of the metal component in a desulfurization agent is 1-40 mass% normally, Preferably, it is 5-30 mass%.

  On the other hand, the desulfurization agent charged in the desulfurizer B on the downstream side is selected from the group consisting of metal elements, metal oxides, and metal component-supported oxides. The specific metal components are preferably selected from the group consisting of Ag, Cu, Ni, Zn, Mn, Fe, Co, Al, Si, alkali metals, alkaline earth metals and rare earth metals. Examples of the alkali metal include potassium and sodium, and examples of the alkaline earth metal include calcium and magnesium. Moreover, as a rare earth metal, lanthanum, cerium, etc. are mentioned preferably. These metal components are preferably supported on a porous inorganic oxide support, and in particular, those in which at least one of Ag, Cu, and Ni is supported are preferable. Each metal component can be advantageously employed by ordinary supporting means such as a coprecipitation method or an impregnation method.

  Further, as the porous inorganic oxide carrier, for example, silica, alumina, silica-alumina, titania, zirconia, zeolite, magnesia, diatomaceous earth, white clay, clay and zinc oxide are preferably used practically. Of these, an alumina carrier and a silica-alumina carrier are particularly preferred.

In the desulfurizing agent filled in the desulfurizer B, for example, a method of supporting metal silver using alumina as a carrier is carried out by impregnating and supporting an aqueous solution of a water-soluble silver compound on alumina and drying it at a temperature of about 80 to 150 ° C And then calcined at a temperature of about 200 to 400 ° C. for easy preparation. In the desulfurization agent filled in the desulfurizer B, the supported total metal content (as oxide) is usually 5 to 90% by mass from the viewpoint of desulfurization performance and mechanical strength of the desulfurization agent, and the carrier. Is preferably in the range of 95 to 10% by mass, and the total metal content (as oxide) is 40 to 90% by mass, and further 70 to 90% by mass when supported by the coprecipitation method. When it is carried, the content is preferably 5 to 40% by mass.

  In the combination of the desulfurizer A and the desulfurizer B in the method of the present invention, the volume ratio range of 0.1: 0.9 to 0.9: 0.1 is preferably employed as the desulfurizing agent to be filled in each. Such a capacity ratio range is extremely practical for the removal of various sulfur compounds contained in the hydrocarbon gas, and is suitable as a desulfurization agent for producing hydrogen gas for fuel cells. A particularly preferable volume ratio range is 0.2: 0.8 to 0.8: 0.2.

  In the method of the present invention, the raw hydrocarbon gas is desulfurized by maintaining the desulfurizer A installed in the fuel cell system in an operating state under relatively low temperature conditions, preferably at a temperature of 40 ° C. or lower. It is extremely important that the treated gas is then desulfurized in a desulfurizer B installed in a temperature environment of 40 ° C. or higher in the system. Usually, as raw material hydrocarbon gas, for example, natural gas, city gas, LPG and dimethyl ether contain hydrogen sulfide, mercaptans, sulfides, disulfides, thiophenes and carbonyl sulfide. By controlling the desulfurization temperatures of the desulfurizer A and the desulfurizer B according to the method of the invention, that is, the desulfurizer A and the desulfurizer B to be filled, a high desulfurization effect can be obtained.

  In the fuel cell system of the present invention, the hydrogen-containing gas obtained by reforming the hydrocarbon-containing gas thus desulfurized is used. As the reforming treatment of the hydrocarbon-containing gas subjected to the desulfurization treatment, a conventionally known method, for example, contacting the desulfurization-treated hydrocarbon-containing gas with a partial oxidation reforming catalyst, an autothermal reforming catalyst or a steam reforming catalyst. Thus, hydrogen is produced by partial oxidation reforming, autothermal reforming or steam reforming, respectively. In this reforming treatment, the concentration of the sulfur compound in the desulfurized hydrocarbon-containing gas is preferably 0.05 ppm by volume or less, particularly preferably 0.02 ppm by volume or less from the viewpoint of the life of each reforming catalyst.

The partial oxidation reforming is a method for producing hydrogen by a partial oxidation reaction of hydrocarbon, and in the presence of a partial oxidation reforming catalyst, the reaction pressure is usually from normal pressure to 5 MPa, the reaction temperature is from 400 to 1,100 ° C., The reforming reaction is performed under the conditions of GHSV 1,000-100,000 h ⁻¹ and oxygen (O ₂ ) / carbon molar ratio 0.2-0.8.
Autothermal reforming is a method in which partial oxidation reforming and steam reforming are combined, and in the presence of a self-reforming catalyst, reaction pressure is usually from normal pressure to 5 MPa, reaction temperature from 400 to 1,100 ° C., oxygen (O ₂ ) The reforming reaction is carried out under the conditions of a carbon molar ratio of 0.1 to 1, steam / carbon molar ratio of 0.1 to 10 and GHSV of 1,000 to 100,000 h- ¹ .
Further, steam reforming is a method of producing hydrogen by bringing steam into contact with a hydrocarbon, usually in the presence of a steam reforming catalyst, at a reaction pressure of normal pressure to 5 MPa, a reaction temperature of 200 to 900 ° C., steam / The reforming reaction is carried out under conditions of a carbon molar ratio of 1.5 to 10 and a GHSV of 1,000 to 100,000 h- ¹ .

  In the present invention, the partial oxidation reforming catalyst, the autothermal reforming catalyst, and the steam reforming catalyst can be appropriately selected from conventionally known catalysts, and in particular, ruthenium-based and nickel-based catalysts. System catalysts are preferred. Moreover, as a support | carrier of these catalysts, the support | carrier containing at least 1 type chosen from manganese oxide, a cerium oxide, and a zirconia can be mentioned preferably. The support may be a support made of only these metal oxides, or may be a support made by adding the above metal oxide to another refractory porous inorganic oxide such as alumina.

Next, the fuel cell system of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic flow diagram showing an example of a fuel cell system of the present invention. In FIG. 1, the desulfurizer A and the desulfurizer B are collectively referred to as a desulfurizer 23.
According to FIG. 1, the fuel in the fuel tank 21 is supplied to the desulfurizer 23 via the supply line 22. The fuel desulfurized in the desulfurizer 23 is mixed with water from the water tank via the water pump 24 and then introduced into the vaporizer 1 to vaporize the water and sent to the reformer 31.
The reformer 31 is filled with the above-described reforming catalyst, and any one of the above-described reforming reactions is performed from the fuel mixture (mixed gas containing water vapor and hydrocarbon fuel) fed into the reformer 31. Produces hydrogen.

  The hydrogen produced in this way is sent to the fuel cell after the CO concentration is reduced to a level that does not affect the characteristics of the fuel cell through the CO converter 32 and the CO selective oxidation furnace 33. The fuel cell 34 is a polymer electrolyte fuel cell including a polymer electrolyte 34C between a negative electrode 34A and a positive electrode 34B. The hydrogen-rich gas obtained by the above method is applied to the negative electrode side, and the air sent from the air blower 35 is applied to the positive electrode side after appropriate humidification treatment as necessary (a humidifier is not shown). )be introduced.

At this time, a reaction in which hydrogen gas becomes protons and emits electrons proceeds on the negative electrode side, and a reaction in which oxygen gas obtains electrons and protons to become water proceeds on the positive electrode side, and a direct current flows between both electrodes 34A and 34B. Will occur. Platinum black, activated carbon-supported Pt catalyst or Pt-Ru alloy catalyst is used for the negative electrode, and platinum black, Pt catalyst supported on activated carbon is used for the positive electrode.
The surplus hydrogen can be used as fuel by connecting the burner 31A of the reformer 31 to the negative electrode 34A side. Further, in the separator 36 connected to the positive electrode 34B side, water and exhaust gas generated by the combination of oxygen and hydrogen in the air supplied to the positive electrode 34B side are separated, and the water is used for generation of water vapor. be able to.
In the fuel cell 34, since heat is generated with power generation, an exhaust heat recovery device 37 can be attached to recover the heat for effective use. The exhaust heat recovery device 37 includes a heat exchanger 37A that takes away the heat generated during the reaction, a heat exchanger B that exchanges heat taken by the heat exchanger 37A with water, a cooler 37C, and these heat exchanges. The hot water obtained in the heat exchanger 37B can be effectively used in other equipment and the like, and the pumps 37D for circulating the refrigerant to the coolers 37A and 37B and the cooler 37C.

  Next, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.

[Preparation of desulfurization agent]
Desulfurizing agent A: β-zeolite [HSZ-930NHA manufactured by Tosoh Corporation] 2 kg of calcined product at a temperature of 500 ° C., an aqueous solution obtained by dissolving 350 g of silver nitrate “Wako Pure Chemical Industries, Special Grade” in 10 liters (L) of water And the ion exchange was performed by stirring for 4 hours. Thereafter, the solid material is washed with water, filtered, dried at 120 ° C. for 12 hours at 120 ° C., and calcined at 400 ° C. for 3 hours to obtain a desulfurization agent A containing 6% by mass of Ag. It was.

On the other hand, nickel sulfate hexahydrate “Wako Pure Chemical Industries, Special Grade” 73.02 kg and copper sulfate pentahydrate “Wako Pure Chemical Industries, Special Grade” 15.13 kg were added to 800 L of water heated to 80 ° C. Dissolved and mixed with 1.60 kg of pseudoboehmite [Catalyst Industries, “C-AP”, 67% by mass as Al ₂ O ₃ ], then added 30 L of 0.5 mol / liter sulfuric acid aqueous solution. To pH 2 (adjustment solution A). Further, 60.0 kg of sodium carbonate was dissolved in 800 L of water heated to 80 ° C., and 18.02 kg of water glass [manufactured by Nippon Chemical Industry Co., Ltd., “J-1”, Si concentration 29 mass%] was added (preparation). Liquid B). The preparation liquid A and the adjustment liquid B were mixed while being kept at 80 ° C. and stirred for 1 hour. Thereafter, the precipitated cake is washed with 6000 L of water, filtered, dried at 120 ° C. for 12 hours in a blow dryer, and further calcined at 350 ° C. for 3 hours to contain Ni 50 mass% and Cu 13 mass%. Desulfurizing agent B was obtained. The desulfurizing agent A and the desulfurizing agent B thus obtained were each molded to 0.5 to 1 mm and filled into the desulfurizers A and B for practical use.

Example 1
Desulfurization in which a stainless steel desulfurizer A having a diameter of 4.0 cm is filled with 300 g of the desulfurizing agent A, installed in a 1 kW PEFC fuel cell system at an average temperature of 30 ° C., and 150 g of desulfurizing agent B is filled. The vessel B was installed at a location where the average temperature during operation was 50 ° C. on the downstream side to desulfurize commercially available LP gas. A sampling boat for measuring the sulfur concentration of the desulfurized gas was provided at the outlet of the desulfurizer B in order to grasp the performance of the desulfurizing agent. A reformer and a fuel cell are disposed downstream thereof.
A power generation test was conducted by supplying commercially available LP gas having an average sulfur concentration of 5.7 ppm by mass to the fuel cell system. When the total power generation amount reached 5600 kWh, the sulfur concentration at the outlet of the desulfurizer B reached 0.05 mass ppm.

(Comparative Example 1)
The same operation as in Example 1 was performed except that the desulfurizer A was installed at an average temperature of 30 ° C and the desulfurizer B was installed at an average temperature of 35 ° C. When the total power generation amount reached 4500 kWh, the sulfur concentration at the outlet of the desulfurizer B reached 0.05 mass ppm. Compared to Example 1, the desulfurization function of the desulfurization agent was significantly lower. Therefore, it is understood that the desulfurizer B on the downstream side is effective at a relatively high temperature of 40 ° C. or higher.

(Comparative Example 2)
The same operation as in Example 1 was performed except that the desulfurizer A was installed at a position in the fuel cell system where the average temperature was 50 ° C. and the desulfurizer B was 30 ° C. When the total power generation amount reached 4100 kWh, the sulfur concentration at the outlet of the desulfurizer B reached 0.05 mass ppm. As can be seen in comparison with Comparative Example 1, it can be seen that the desulfurizer A has a low desulfurization ability at a high temperature.

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

Explanation of symbols

1: Vaporizer 2: Fuel cell system 20: Hydrogen production system 21: Fuel tank 23: Desulfurizer 31: Reformer 32: CO converter 33: CO selective oxidation furnace 34 :: Fuel cell 34
34A: Negative electrode 34A
34B: Positive electrode 34B
34C: Polymer electrolyte 36: Gas water decomposer 37: Waste heat recovery device 37A: Heat exchanger 37B: Heat exchanger 37C: Cooler

Claims (7)

  When a hydrocarbon-containing gas is supplied to the desulfurizer and the sulfur compound in the gas is removed in the fuel cell system package, the gas is desulfurized in the upstream desulfurizer A filled with a desulfurizing agent containing zeolite. After the treatment, a desulfurization agent containing at least one selected from the group consisting of metal elements, metal oxides and metal component-supported oxides, which are installed at a temperature of 40 ° C. or higher in the fuel cell system operating state, is filled. A desulfurization method characterized in that the desulfurization treatment is performed in the desulfurizer B on the downstream side.   2. The desulfurization method according to claim 1, wherein the desulfurizer A is installed in a portion having a temperature of 40 ° C. or lower when the fuel cell system is operating.   The desulfurization method according to claim 1 or 2, wherein the volume ratio of the desulfurizing agent charged in the desulfurizer A and the desulfurizer B is 0.1: 0.9 to 0.9: 0.1.   The desulfurization method according to any one of claims 1 to 3, wherein the zeolite has a beta (BEA) and / or faujasite (FAU) structure.   The desulfurizing agent in the desulfurizer A contains at least one metal component selected from the group consisting of Ag, Cu, Ni, Zn, Mn, Fe, Co, alkali metal, alkaline earth metal and rare earth metal together with zeolite. The desulfurization method according to any one of claims 1 to 4.   The desulfurizing agent in the desulfurizer B includes at least one metal component selected from the group consisting of Ag, Cu, Ni, Zn, Mn, Fe, Co, Al, Si, alkali metal, alkaline earth metal, and rare earth metal. The desulfurization method according to any one of claims 1 to 5. A fuel cell system using a hydrogen-containing gas obtained by reforming a hydrocarbon-containing gas desulfurized by the method according to claim 1.

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