JP3986586B2 - Hydrogen purification method for fuel cells - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying hydrogen for a low temperature fuel cell operating at a low temperature, and more particularly to a method for purifying hydrogen for a polymer electrolyte fuel cell (hereinafter referred to as “PEFC”). In particular, carbon monoxide contained in hydrogen produced by an organic compound reforming method exhibits a remarkable catalytic poisoning effect on platinum which is an electrode catalyst of a fuel cell operating at a low temperature. The present invention relates to a technique for effectively oxidizing a fuel cell even at a low temperature by oxidizing and removing carbon monoxide in the hydrogen using a highly active oxidation reaction catalyst.
[0002]
[Prior art]
Currently, in order to obtain hydrogen commercially in a wide area, a method of producing by reforming organic compounds, for example, hydrocarbons such as methane and propane, alcohols such as methanol, etc., particularly steam reforming is excellent. Are preferably used. However, hydrogen obtained by steam reforming under practical operating conditions contains about several percent of carbon monoxide. Carbon monoxide can be logically converted into hydrogen and carbon dioxide by a shift reaction with water vapor, so-called shift reaction, but there are limits to the reduction in terms of both equilibrium and catalytic activity. Even if it arranges, about 1% of carbon monoxide is a practical limit.
[0003]
On the other hand, when used as a fuel for a fuel cell, particularly when the PEFC is operated effectively, it is required to reduce the carbon monoxide concentration to several ppm or less. PEFC is an extremely effective fuel cell that can be operated from room temperature if hydrogen containing no carbon monoxide is used as a fuel. However, the catalytic poisoning effect of carbon monoxide becomes more prominent as the temperature becomes lower. When even a small amount contains carbon monoxide, the operation at a low temperature cannot be performed. Although a method for imparting carbon monoxide resistance using a platinum-ruthenium alloy as an electrode catalyst has been reported, the range in which sufficient carbon monoxide resistance is exhibited and the catalytic poisoning action of carbon monoxide is not exhibited is 100. Limited to high temperature above ℃.
[0004]
It has been suggested that by adding 6 to 13% of oxygen to the hydrogen gas supplied to the fuel cell, operation can be performed without causing a decrease in the voltage of the electric power generated from the fuel cell. However, when such a large amount of oxygen is added, there is a risk of gas explosion and non-electrochemical oxidation of hydrogen at the electrode becomes significant, resulting in a large loss of hydrogen, and a large temperature at the electrode surface. Distribution occurs, resulting in a significant drop in the generated voltage. If the concentration of carbon monoxide is 100 ppm or less, it has been reported that the amount of oxygen added to the hydrogen supplied to the electrode can be about 0.4%. However, the concentration of carbon monoxide is reduced to 100 ppm in advance. In this case, the coexistence of non-electrolytic oxidation at the electrode leads to an increase in the temperature distribution on the electrode surface, which reduces the fuel cell voltage. Bring.
[0005]
A method has been studied in which an oxygen-containing gas is added to hydrogen supplied to a fuel cell, and is brought into contact with an oxidation reaction catalyst in advance to oxidize and remove carbon monoxide in hydrogen. This method is excellent if there is no load on the fuel cell that performs complicated operations and there is an effective oxidation reaction catalyst. According to a report from Toyota Motor Corporation (2nd Fuel Cell Symposium Lecture Proceedings, page 235, 1995), the removal of oxidation with ruthenium catalyst at a reaction temperature of 100 ° C reduced the carbon monoxide concentration to 0 ppm. is there. However, this value is an analysis result by an analyzer having a carbon monoxide detection limit concentration of 20 ppm. In addition, it is reported that 150 ppm of carbon monoxide remains in the reaction result at 80 ° C., which is a lower temperature, indicating that the activity of the oxidation reaction catalyst at a low temperature is insufficient.
[0006]
When preparing a noble metal catalyst such as platinum or palladium, a halide or a halogen-containing compound is often used as a raw material. The most important thing is that the halogen-containing compound is soluble in water and easily supported, and most importantly, a finely dispersed supported catalyst can be easily obtained by using this raw material. The dispersion state of the noble metal is often related to the performance of the catalyst, and a catalyst in which the noble metal is dispersed is desired. Usually, when it is desired to remove halogen contained in the catalyst, the catalyst is subjected to high-temperature reduction treatment or oxidation treatment. When these catalysts are used for the oxidation reaction, they are used while containing a small amount of halogen, and are oxidized and removed in the reaction system as the oxidation reaction proceeds. As described above, there are few examples where the contained halogen causes a problem in the oxidation reaction.
[0007]
On the other hand, in the case of a ruthenium catalyst, there are few examples of industrialization, there are only synthesis of cyclohexene by partial hydrogenation of benzene, synthesis of ammonia, etc., and there is no practical example of oxidation reaction.
[0008]
On the other hand, the relationship between the ruthenium catalyst and the halogen contained in the catalyst has been studied. According to a report by Ohira et al. (The Chemical Society of Japan 50th Spring Annual, 1X26, 1X27 (1985)), using a catalyst prepared with ruthenium chloride as a raw material and silica and alumina as a support, hydrogen reduction temperature and residual Studies have been made on chlorine and the amount of hydrogen or carbon monoxide adsorbed on the catalyst. According to the results, it has been reported that chlorine remains in the catalyst even when the hydrogen reduction temperature of the catalyst is raised, and that the adsorption amount of hydrogen and carbon monoxide increases when the residual amount of chlorine decreases. . However, there is no description of how residual chlorine affects the oxidation removal reaction of carbon monoxide in hydrogen.
[0009]
[Problems to be solved by the invention]
Since carbon monoxide contained in hydrogen lowers the output voltage of the fuel cell, thorough reduction of carbon monoxide is required for highly efficient operation of PEFC. In the operation at low temperature, which is a major feature of PEFC, reduction is particularly required. For this reason, high activity and high selectivity at low temperature of the oxidation reaction catalyst of carbon monoxide are required. In particular, activity at 100 ° C. or lower, further 80 ° C. or lower is required. When considering various operating conditions, activity at room temperature is also an important issue.
[0010]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors of the present invention added a gas containing oxygen to a hydrogen gas containing carbon monoxide produced by a steam reforming reaction of an organic compound and mixed gas. When the mixed gas is brought into contact with an oxidation reaction catalyst for carbon monoxide, carbon monoxide can be effectively removed by using a catalyst mainly composed of ruthenium metal containing substantially no halogen as the catalyst. As a result, the present invention has been completed.
[0011]
That is, the present invention adds a gas containing oxygen to hydrogen gas containing carbon monoxide produced by a steam reforming reaction of an organic compound to form a mixed gas, and the mixed gas is used as an oxidation reaction catalyst for carbon monoxide. This is a method for purifying hydrogen for a fuel cell using a catalyst mainly composed of a ruthenium metal containing substantially no halogen as the catalyst. The catalyst used in the present invention has a halogen content of 500 ppm or less, preferably 200 ppm or less, more preferably 100 ppm or less. Further, it is extremely effective to pretreat the catalyst in a gas containing hydrogen as a main component and use it in the reaction without contacting with the air after that.
[0012]
By using the purification method of the present invention, it is possible to selectively oxidize and remove carbon monoxide in hydrogen gas containing carbon monoxide produced by a reforming reaction of an organic compound from room temperature. This enables high-efficiency operation of PEFC, particularly at low temperatures, which is a feature of PEFC.
[0013]
Various compounds are known as ruthenium compounds. However, when used for the preparation of the catalyst of the present invention, ruthenium halide is mentioned as an easily available and inexpensive compound. Ruthenium chloride is particularly preferable. Moreover, the complex containing the halogen prepared from these halides is also used.
[0014]
The catalyst used in the present invention is preferably used as a supported catalyst supported on a carrier. Any carrier can be used as long as it is usually used as a carrier. For example, alumina, silica alumina, silica gel, molecular sieve 3A, ZSM-5, zeolite X, zeolite Y, zeolite represented by zeolite beta, and representative by MCM-41. Examples of effective materials include mesoporous zeolite, zirconia, titania, rare earth oxides, calcium oxide, magnesium oxide, basic oxides represented by zinc oxide, and activated carbon. . Any shape can be used, but it is also effective to be used as a granular shape such as a spherical shape or a columnar shape, or as a molded product typified by a honeycomb or the like.
[0015]
The method of supporting these carriers can be prepared by various methods. For example, a precipitation method such as a coprecipitation method, a sol-gel method, an ion exchange method, an impregnation method and the like are effective.
By the above method, the prepared catalyst reduces ruthenium to a metal by a reducing agent. Hydrogen is effective as the reducing agent. Reduction with organic compounds such as formalin and hydrazine is also effective. It is effective that the reduction operation is performed in the gas phase. It is also effective to be performed in a liquid phase such as in an aqueous solution. The reduction temperature may be that the ruthenium compound becomes a metal, but ruthenium sintering occurs at an excessively high temperature. The temperature varies depending on the preparation method of the catalyst, but usually room temperature to about 700 ° C. is used. Preferably, it is carried out at room temperature to 500 ° C.
[0016]
In a normal oxidation reaction, the halogen on the catalyst surface is easily desorbed by the oxidizing agent. Therefore, it can be removed from the reaction system in which the oxidation reaction proceeds and at an initial stage without any special operation. For this reason, halogen is not a problem in the oxidation reaction. However, when a halogen-containing catalyst is used in this reaction, it is difficult to oxidize and remove carbon monoxide, and there is no elimination of halogen in the reaction system, and the halogen on the catalyst is not lost. . In order to use a catalyst containing substantially no halogen, which is a feature of the present invention, it is necessary to remove the halogen used in the ruthenium raw material in the stage of preparing the catalyst in advance. There are several methods for removing the halogen on the catalyst. A commonly used method is reduction removal with hydrogen. However, in order to completely remove the halogen, a high temperature operation is required, which causes sintering of ruthenium used in this reaction, and it is not preferable to remove the halogen only by this operation. Many methods using oxidation with an oxygen-containing gas are also performed. Also in this method, sintering is likely to occur in the case of a ruthenium catalyst, and the particle diameter of ruthenium increases. In the present invention, a method for removing halogen with an alkaline agent is preferred. This halogen removal operation is preferably performed after ruthenium is supported on the catalyst or after reduction with hydrogen or the like. Further, depending on the preparation method, it is carried out during handling in a liquid phase such as during the precipitation operation. It is also preferably performed during the reduction in water. These removal operations are preferably performed in an aqueous solution. As long as it can remove the halogen as an alkali agent used, for example, an alkali metal such as Lithium, oxide or hydroxide of alkaline earth metals such as magnesium and the like. A catalyst subjected to the above-described halogen removal treatment is provided for the present invention.
[0017]
On the other hand, a carrier that is usually used industrially, for example, alumina contains 10 to several tens of ppm of chlorine, and in some cases, contains more. In the above operation, chlorine in this carrier is not removed, but halogen in these carriers is not affected in this reaction, and the effect of the present invention is not impaired. The catalyst used in the present invention is substantially free of halogen. The catalyst used in the present invention has a halogen content of 500 ppm or less, preferably 200 ppm or less, more preferably 100 ppm or less.
[0018]
The catalyst of the present invention is preferably pretreated in a gas containing hydrogen as a main component and then used without being exposed to air. The gas containing hydrogen as a main component may contain hydrocarbons such as carbon dioxide, water vapor, nitrogen, methanol and methane in addition to hydrogen as long as the hydrogen content is 50 mol% or more. A small amount of carbon monoxide may be included. In addition, it is preferable that the gas containing hydrogen as a main component in the pretreatment stage does not substantially contain oxygen. The pretreatment temperature is usually from room temperature to 600 ° C, preferably from 50 ° C to 400 ° C, more preferably from 70 ° C to 300 ° C.
[0019]
In the present invention, hydrogen gas containing carbon monoxide produced by a reforming reaction of an organic compound is used. Here, examples of the organic compound include methanol, ethanol, methane, ethane, and the like. The organic compound reforming reaction is partial oxidation reforming with water vapor and / or oxygen gas. The gas containing hydrogen as a main component in the method of the present invention preferably contains substantially no oxygen.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
(Production Example 1)
80 ml of an aqueous solution containing 2.6 g of ruthenium chloride was added to 25 g of an alumina carrier manufactured by JGC Chemical Co., Ltd., and evaporated to dryness on a hot water bath. 10 g of this was immersed in 50 ml of 0.05 N aqueous sodium bicarbonate solution, left standing for 2 hours with stirring, and then filtered off. After repeating this operation once more, it was repeatedly washed with water until the cleaning solution showed neutrality. Then, it was dried and treated in a hydrogen stream at 300 ° C. for 3 hours. The mixture was cooled to room temperature under a nitrogen atmosphere and taken out. The catalyst was subjected to elemental analysis using a fluorescent X-ray analyzer (RIX-3000, manufactured by Rigaku Corporation). As a result, the chloro content was 25 ppm. Further, the content of chloro in the alumina used as a simple substance was 14 ppm. (The detection limit of chlor in this device is 10 ppm)
[0021]
(Production Example 2)
80 ml of an aqueous solution containing 2.6 g of ruthenium chloride was added to 25 g of zeolite Y carrier manufactured by Tosoh Corporation, and evaporated to dryness on a hot water bath. 10 g of this was immersed in 50 ml of 0.05N aqueous sodium hydroxide solution, left standing for 2 hours with stirring, and then filtered off. After repeating this operation once more, it was repeatedly washed with water until the cleaning solution showed neutrality. Then, it was dried and treated in a hydrogen stream at 400 ° C. for 1 hour. The mixture was cooled to room temperature under a nitrogen atmosphere and taken out. The chloro content of this catalyst was 20 ppm.
[0022]
(Production Example 3)
80 ml of an aqueous solution containing 2.6 g of ruthenium chloride was added to 25 g of a silica gel carrier manufactured by JGC Chemical Co., Ltd., and evaporated to dryness on a hot water bath. 10 g of this was immersed in 50 ml of 0.05N aqueous sodium hydroxide solution, left standing for 2 hours with stirring, and then filtered off. After repeating this operation once more, it was put into 100 g of water, and reduced in water at 120 ° C. for 2 hours in an autoclave under a hydrogen pressure of 100 kg / cm ₂ . The catalyst thus taken out was filtered off and washed repeatedly with water until the washing solution became neutral. The chloro content of this catalyst was 20 ppm.
[0023]
(Production Example 4)
80 ml of an aqueous solution containing 2.6 g of ruthenium chloride was added to 25 g of an alumina carrier manufactured by JGC Chemical Co., Ltd., and evaporated to dryness on a hot water bath. 10 g of this was taken and treated in a hydrogen stream at 400 ° C. for 3 hours. The mixture was cooled to room temperature under a nitrogen atmosphere and taken out. The catalyst had a chloro content of 10,000 ppm (a portion of this catalyst was used in Comparative Example 1). Of this, 5 g was immersed in 25 ml of 0.05N aqueous sodium bicarbonate solution, allowed to stand for 2 hours with stirring, and then filtered off. After repeating this operation once more, it was repeatedly washed with water until the cleaning solution showed neutrality. After this operation, it was dried. The chloro content of this catalyst was 20 ppm.
[0024]
(Production Example 5)
The same operation as in Production Example 4 was performed except that the treatment in a hydrogen stream was carried out at 740 ° C. for 3 hours. The resulting catalyst had a chloro content of 1,000 ppm (a portion of this catalyst was used in Comparative Example 2). Further, the same operation as in Production Example 4 was performed to obtain a catalyst. The catalyst had a chloro content of 18 ppm.
[0025]
(Production Example 6)
The same operation as in Production Example 4 was performed, except that silica gel manufactured by JGC Chemical was used as the carrier. The resulting catalyst had a chloro content of 6,000 ppm. Further, the same operation as in Production Example 4 was performed to obtain a catalyst. The chloro content of this catalyst was 25 ppm.
[0026]
Example 1
0.9 ml of the catalyst prepared in Production Example 1 was charged into a carbon monoxide removal test reactor, and pretreated for 1 hour at 70 ° C. in a hydrogen stream. After cooling to room temperature in a hydrogen stream, hydrogen is changed to hydrogen, and a mixed gas of hydrogen: carbon dioxide: carbon monoxide: air = 3: 1: 0.001: 0.03 is used at a space velocity of 20,000 ml / ml / catalyst / sent to the reactor in hr. An exotherm was observed in the reactor, and the temperature of the outer wall of the reactor rose to 23 ° C and the temperature of the catalyst rose to 33 ° C. When carbon monoxide in the reactor outlet gas was analyzed, it could not be detected. Carbon monoxide was analyzed using a PID (photoionization detector) gas chromatograph (manufactured by Hitachi). The lower limit of detection of carbon monoxide in this analyzer was 0.5 ppm.
[0027]
(Example 2)
0.9 ml of the catalyst prepared in Production Example 2 was charged into a carbon monoxide removal test reactor, and pretreated at 140 ° C. for 2 hours in a hydrogen stream. After cooling to 70 ° C. in a hydrogen stream, hydrogen is changed to hydrogen, and a mixed gas of hydrogen: carbon dioxide: carbon monoxide: air = 3: 1: 0.001: 0.03 is used at a space velocity of 20,000 ml / g catalyst / In hr, water was further added at a water vapor conversion space velocity of 1,500 ml / g catalyst / hr and sent to the reactor. An exotherm was observed in the reactor and the catalyst temperature rose to 82 ° C. When carbon monoxide in the reactor outlet gas was analyzed, it could not be detected.
[0028]
(Example 3)
The same operation as in Example 2 was performed except that the catalyst prepared in Production Example 3 was used. As a result, the carbon monoxide concentration in the reactor outlet gas was 1 ppm.
(Example 4)
The same operation as in Example 2 was performed except that the catalyst prepared in Production Example 4 was used. As a result, the carbon monoxide concentration in the reactor outlet gas was 1 ppm.
[0029]
(Example 5)
The same operation as in Example 2 was performed except that the catalyst prepared in Production Example 5 was used. As a result, the carbon monoxide concentration in the reactor outlet gas was 1 ppm.
(Example 6)
The same operation as in Example 1 was performed except that the catalyst prepared in Production Example 6 was used. As a result, the carbon monoxide concentration in the reactor outlet gas was 1 ppm.
[0030]
(Example 7)
0.9 ml of the catalyst prepared in Production Example 2 was charged into a carbon monoxide removal test reactor, and a mixed gas of hydrogen: carbon dioxide: carbon monoxide: = 3: 1: 0.001: space velocity of 20,000 ml / g Pre-treatment for 2 hours at 140 ° C. during catalyst / hr flow. After cooling to 70 ° C. as it was, 3 times the amount of carbon monoxide air was added to the mixed gas, and water vapor was further added at a space velocity of 1,500 ml / g catalyst / hr, and sent to the reactor. An exotherm was observed in the reactor and the temperature of the catalyst rose to 81 ° C. When carbon monoxide in the reactor outlet gas was analyzed, the carbon monoxide concentration in the outlet gas was 2 ppm.
[0031]
(Comparative Example 1)
Exactly the same operation as in Example 2 was performed, except that 0.9 ml of the chloro-containing catalyst prepared in Production Example 4 was charged into the carbon monoxide removal test reactor. There was little heat generation in the reactor, and the temperature of the catalyst was 74 ° C. When carbon monoxide in the reactor outlet gas was analyzed, it was 800 ppm. Therefore, the experiment was continued by heating the reactor and setting the temperature of the catalyst to 82 ° C. When carbon monoxide in the reactor outlet gas at this time was analyzed, it was 760 ppm. Further, after the reaction, the chloro content in the catalyst was measured and found to be 10,000 ppm.
[0032]
(Comparative Example 2)
Exactly the same operation as in Example 1 was performed, except that 0.9 ml of the chloro-containing catalyst prepared in Production Example 5 was charged into the carbon monoxide removal test reactor. There was little heat generation in the reactor, and the temperature of the catalyst was 25 ° C. When carbon monoxide in the reactor outlet gas was analyzed, it was 780 ppm. Further, after the reaction, the chloro content in this catalyst was measured and found to be 1,000 ppm.
[0033]
【The invention's effect】
By reducing the concentration of carbon monoxide in hydrogen gas containing carbon monoxide, the fuel cell can be operated efficiently.

Claims (1)

A method for purifying hydrogen for a fuel cell, wherein a mixed gas obtained by adding a gas containing oxygen to hydrogen gas containing carbon monoxide produced by a reforming reaction of an organic compound is brought into contact with a carbon monoxide oxidation reaction catalyst. And the purification method comprises:
(1) A ruthenium catalyst obtained by treating ruthenium halide with at least one alkaline agent selected from alkali metal, alkaline earth metal hydroxide, and bicarbonate,
(2) After filling in the reactor, and subsequently pre-treating in a gas mainly containing hydrogen in a temperature range of room temperature to 600 ° C.,
(3) A method for purifying hydrogen for a fuel cell, wherein the ruthenium catalyst is brought into contact with the mixed gas without being brought into contact with air.