JP2012005926A - Ammonia-decomposing catalyst and ammonia-decomposing method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ammonia-decomposing catalyst which stably, efficiently decomposes ammonia into hydrogen and nitrogen at a high temperature for long period of time, the ammonia being contained in a reaction gas at a high concentration; and to provide an ammonia-decomposing method.SOLUTION: The ammonia-decomposing catalyst is used to decompose, at a reaction temperature of 100-1,200°C, ammonia in a reaction gas which contains 1-100 vol.% of ammonia, 0-10 vol.% of hydrogen, 0-20 vol.% of oxygen, 0-80 vol.% of nitrogen, and the remainder (the total of the ammonia, hydrogen, oxygen, nitrogen and remainder is 100% in volume). In this case, the catalyst concerned is obtained by coating a honeycomb-like ceramic molding with a catalyst component. Further, the ammonia-decomposing method using the catalyst thus obtained is provided herein.

Description

  The present invention relates to an ammonia decomposition catalyst for decomposing ammonia to obtain hydrogen and a method for decomposing ammonia using the catalyst.

  Many techniques for decomposing ammonia and obtaining hydrogen have been proposed. For example, as an ammonia decomposition catalyst, an ammonia reforming catalyst composed of a composite of iron and an oxide of rare earth has been proposed (see Patent Document 1 (Claim 1)). By using metallic iron, the catalyst occludes nitrogen in the catalyst and exhibits a catalytic action. The catalyst is used as a powder when used in an ammonia decomposition reaction. In addition, as an example of using a composite in which a catalyst component is supported on a carrier, for example, a composite catalyst in which one element selected from the group consisting of an alkaline earth metal and a transition metal is supported on a carbon-based substrate. There has been proposed a technique (see Patent Document 2 (Claims 1 and 2)) in which ammonia is decomposed at 500 ° C. to 1200 ° C. to obtain hydrogen using powder and pellets. Further, a technology for obtaining hydrogen by decomposing ammonia at a low temperature (500 ° C. to 700 ° C.) using an ammonia decomposition catalyst in which ruthenium and an alkali metal are supported on an alumina particle carrier (Patent Document 3 (Claims 1 and 13)). Paragraph [0049])) has also been proposed.

  In addition, as an example of using a composite in which a catalyst component is supported on a carrier, a technique for decomposing ammonia into hydrogen and nitrogen at a reaction temperature of 300 ° C. to 800 ° C. by supporting ruthenium as a catalyst component on α-alumina is disclosed. (Patent Document 4 (Claims 1 and 3)). In the said patent document 4, spherical shape and a cylindrical shape are proposed about the shape of a catalyst.

  By the way, when an actual reactor is filled with a catalyst and used, particularly in the case of a powdery catalyst, there is a problem that the amount of catalyst filling is limited because the pressure loss becomes high. Furthermore, in the case of a powdery catalyst, there is a problem that the powdery catalyst is scattered from the reactor. On the other hand, in the case of a catalyst formed into a spherical shape or a cylindrical shape, if the packed state in the reactor is insufficient, the packed catalyst itself will vibrate in the reactor during the reaction, and these vibrations cause the catalyst. There is a problem that the reaction rate decreases due to wear. In addition, there are many practical limitations in selecting the reactor shape and efficient and stable operating conditions when trying to fill a powdery, spherical and cylindrical catalyst as proposed so far. .

JP 2001-300314 A JP 2001-261302 A JP-A-10-85601 JP-A-08-84910

  In the prior art as proposed in the above-mentioned patent documents and the like, the ammonia concentration, the reaction temperature, the space velocity at the time of supplying the raw material, the gas linear velocity, and the continuous reaction for a long time are not sufficiently satisfactory in practice.

  Here, the metal molding base material is excellent in thermal conductivity, has good reaction responsiveness, and has favorable properties in a situation where the reaction temperature and gas concentration change. It is expected to be used as The inventors of the present invention decompose ammonia using a catalyst in which a gas containing ammonia, hydrogen and oxygen is coated with a ferrite or austenitic stainless steel molded body, which is one of the metal molded body base materials. The reaction to obtain hydrogen was conducted. According to the reaction, the ammonia decomposition reaction can be continued without problems at low temperatures and in a short time. However, if the decomposition reaction is continued at a reaction temperature of 500 ° C. or higher, the molded body deteriorates, and molding for the catalyst. It turned out that it becomes a state unpreferable as a body.

  In addition, when the powdered catalyst used as the above prior art is used, there is no problem in steady use, but under the conditions where the reaction temperature, gas concentration and gas linear velocity change, a certain performance in reaction activity can be obtained. It was difficult to apply the prior art.

  An object of the present invention is an ammonia decomposing catalyst that has high temperature durability in a technology for decomposing ammonia to obtain hydrogen, and that can overcome practical problems in conventionally proposed powdery, spherical and cylindrical catalysts, And a method of decomposing ammonia using the catalyst.

  In order to solve the above-mentioned problems, the present inventors have found the following constitution as a result of intensive studies and completed the invention.

In the first invention, the amount of ammonia (NH ₃ ) is 1 to 100% by volume, the amount of hydrogen (H ₂ ) is 0 to 10% by volume, the amount of oxygen (O ₂ ) is 0 to 20% by volume, and the amount of nitrogen (N ₂ ) Is a catalyst used for decomposing ammonia in a reaction gas of 0 to 80% by volume and the balance (a total amount of ammonia, hydrogen, oxygen, nitrogen and the balance is 100% by volume) at a reaction temperature of 100 to 1200 ° C. The catalyst is an ammonia decomposition catalyst characterized in that a honeycomb ceramic molded body is coated with a catalyst component. Preferably, the honeycomb ceramic formed body is mainly composed of cordierite, mullite or silicon carbide, and the cross-sectional shape of the through hole is preferably a square, hexagon or corrugated shape. Further, the coating amount of the catalyst component is preferably 0.1 to 600 g per liter of the ammonia decomposition catalyst.

  2nd invention uses the said catalyst, ammonia amount is 1-100 volume%, hydrogen amount is 0-10 volume%, oxygen amount is 0-20 volume%, nitrogen amount is 0-80 volume%, and remainder (ammonia The ammonia decomposition method is characterized by decomposing ammonia in a reaction gas having a total amount of hydrogen, oxygen, nitrogen and the balance of 100% by volume into hydrogen and nitrogen at a reaction temperature of 100 to 1200 ° C.

  According to the present invention, a gas containing ammonia, hydrogen, and oxygen is obtained by stably decomposing ammonia in the gas over a long period of time under conditions where the gas concentration and the amount of gas change at high temperatures. be able to.

  In the first invention, the amount of ammonia is 1 to 100% by volume, the amount of hydrogen is 0 to 10% by volume, the amount of oxygen is 0 to 20% by volume, the amount of nitrogen is 0 to 80% by volume, and the balance (ammonia, hydrogen, oxygen, nitrogen And a catalyst used for decomposing ammonia in the reaction gas at a reaction temperature of 100 to 1200 ° C., and the catalyst coats the honeycomb ceramic molded body with a catalyst component. This is an ammonia decomposition catalyst.

  The reaction gas used in the first invention has an ammonia amount of 1 to 100% by volume, a hydrogen amount of 0 to 10% by volume, an oxygen amount of 0 to 20% by volume, a nitrogen amount of 0 to 80% by volume and the balance (ammonia, hydrogen , Oxygen, nitrogen and the balance are 100% by volume).

  The amount of ammonia in the reaction gas is 1 to 100% by volume, preferably 10 to 90% by volume, more preferably 20 to 80% by volume. The amount of hydrogen is 0 to 10% by volume, preferably 0 to 5% by volume in the reaction gas. The oxygen concentration in the reaction gas is 0 to 20% by volume, preferably 4 to 16% by volume, and more preferably 6 to 12% by volume. The nitrogen concentration in the reaction gas is 0 to 80% by volume, preferably 0 to 50% by volume, and more preferably 0 to 40% by volume. However, in this case, the total amount of ammonia, hydrogen, oxygen, nitrogen and the balance is 100% by volume. The volume ratio of oxygen to ammonia (oxygen / ammonia) is less than 0.75, preferably 0.1 or more and 0.5 or less, more preferably 0.12 or more and 0.3 or less.

  Examples of the remainder include water vapor, argon, helium, carbon dioxide, carbon monoxide, nitrogen monoxide, nitrogen dioxide, and nitrous oxide. The amount of these remaining components is 0 to 5% by volume in the reaction gas.

The reaction temperature for decomposing ammonia in the reaction gas is 100 to 1200 ° C, preferably 100 to 1000 ° C. The reaction gas has a space velocity (SV) of 500 to 500,000 hr ⁻¹ , preferably 5000 to 150,000 hr ⁻¹ with respect to the catalyst. The gas linear velocity (LV) is 0.2 to 80 Nm (normal meter) / second.

  The molded product used in the present invention is made of ceramics having through holes, and is preferably cordierite, mullite, or silicon carbide. The cross-sectional shape of the through hole of the ceramic molded body is preferably a square, hexagon or corrugated shape.

The number of the through holes (hereinafter sometimes referred to as “cells”) is preferably 100 to 900 per 1 square inch (6.45 cm ² ) in which the reaction gas passes through the molded body, and more preferably. There are 100 to 600 per square inch. If the number of through-holes per square inch is 100 cells or more, the geometric surface area of the molded body increases, so that the reaction efficiency is further improved. If it is 900 cells or less, individual cells do not become too small. Further, the clogging of the cell opening when the catalyst component is coated is further suppressed. The thickness of the partition wall of each through hole is 2 to 20 mil (50.8 to 508 μm), preferably 2 to 15 mil (50.8 to 381 μm).

  Any catalyst component may be used as long as it can decompose ammonia into hydrogen. The catalyst component preferably contains a transition metal element such as platinum, palladium, rhodium, ruthenium, iron, cobalt, nickel, molybdenum, tungsten, manganese, lanthanum, cerium, or neodymium. Among these, noble metal elements such as platinum, palladium, rhodium, and ruthenium are more preferable. These catalyst components can be used alone or in combination as appropriate. The catalyst component is preferably 0.1 to 600 g per liter of catalyst, more preferably 5 to 600 g, and still more preferably 50 to 500 g (hereinafter sometimes referred to as “g / liter”).

  The catalyst component can be used by being supported on a refractory inorganic oxide having a high specific surface area such as alumina, silica, zirconia or titania. The refractory inorganic oxide is preferably 0 to 300 g per liter of the catalyst, particularly preferably 0 to 100 g when a transition metal oxide is used as a catalyst component, and more preferably 10 to 300 g when a noble metal is included as a catalyst component. Preferred (hereinafter sometimes referred to as “g / liter”).

  The catalyst can be prepared by any conventional means. For example, (1) a method in which a slurry obtained by wet-grinding a metal or an oxide as a catalyst component is coated on the molded body, and (2) an aqueous catalyst component. A method of coating the molded body with a liquid, and optionally drying and firing; (3) a method of coating the molded body with a slurry obtained by wet-grinding a powder carrying a catalyst component on a refractory inorganic oxide; (4) A method of coating the molded body with a slurry obtained by wet pulverizing a metal or oxide as a catalyst component and a refractory inorganic oxide, and (5) wet pulverizing the refractory inorganic oxide and molding. There is a method of coating the body and then further coating the catalyst component.

  In the second invention, the catalyst is installed in the flow of the reaction gas, and ammonia is decomposed by the temperature, space velocity, etc., to obtain nitrogen and hydrogen. The said catalyst is not limited to a single thing, A some catalyst can also be used depending on the case. When using a plurality of catalysts, a single molded article can be used by coating a plurality of catalyst components, and individual catalysts can be used in series or in parallel with the reaction gas.

  Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples as long as it has the effects of the present invention.

1. Production of catalyst 1-1. Catalyst A1 (Example 1)
A powder (catalyst component A) carrying 5% by mass of platinum on γ-alumina was wet pulverized with a ball mill to obtain an aqueous dispersion slurry. A cordierite honeycomb (having 400 gas flow cells per square inch) was immersed in the slurry, and then the excess slurry was blown off with compressed air. Subsequently, after drying at 150 degreeC for 5 hours, it baked at 500 degreeC for 1 hour, and obtained catalyst A1. The catalyst A1 supported 200 g of catalyst component A per liter of catalyst.

1-2. Catalyst B1 (Example 2)
A powder (catalyst component B) in which 5% by mass of ruthenium was supported on γ-alumina was wet-ground by a ball mill to obtain an aqueous dispersion slurry. A cordierite honeycomb (having 400 gas flow cells per square inch) was immersed in the slurry, and then the excess slurry was blown off with compressed air. Next, after drying at 150 ° C. for 5 hours, firing was performed at 450 ° C. for 1 hour to obtain a honeycomb coated with the catalyst component B. Subsequently, reduction treatment was performed at 600 ° C. for 1 hour in a hydrogen (5% by volume) / nitrogen atmosphere to obtain catalyst B1. The catalyst B1 supported 250 g of catalyst component B per liter of catalyst.

1-3. Catalyst a1 (Comparative Example 1)
In Example 1, the catalyst A1 was used except that the cordierite honeycomb carrier was changed to a metal honeycomb carrier made of Fe-20Cr-5Al (having 400 gas flow cells per square inch in cross section). The catalyst a1 coated with the catalyst component A was obtained in the same manner as in the production of Example 1 (Example 1). The catalyst a1 was loaded with 180 g of catalyst component A per liter of catalyst.

1-4. Catalyst b1 (Comparative Example 2)
In Example 2, the catalyst B1 was used except that the cordierite honeycomb support was changed to a metal honeycomb support made of Fe-20Cr-5Al (having 400 gas flow cells per square inch in cross section). A catalyst b1 coated with the catalyst component B was obtained in the same manner as in the production of Example 2 (Example 2). The catalyst b1 supported 200 g of catalyst component B per liter of catalyst.

2-1. Ammonia decomposition reaction 1 (catalyst evaluation 1)
The reactor is charged so that the catalyst A1 is on the gas inlet side and the catalyst B1 is on the outlet side, 57.1% by volume of ammonia (NH ₃ ), 33.3% by volume of nitrogen (N ₂ ), oxygen (O ₂ ) The reaction test was continued for 30 hours using a gas consisting of 8.9% by volume and the balance argon (Ar). The ammonia decomposition reaction was performed at a catalyst inlet temperature of 200 ° C., a gas SV of 36221 hr ⁻¹ , and a volume ratio (A1 / B1) of catalyst A1 to catalyst B1 of 1/3. Table 1 shows the H ₂ yield at the initial stage and after the reaction for 30 hours. The H ₂ yield after the reaction for 30 hours was the same as that at the beginning of the reaction. The maximum catalyst layer temperature was 1000 ° C. and the catalyst layer outlet temperature was 470 ° C., and there was no change during the reaction for 30 hours. The H ₂ yield was determined by the following formula. Further, when the cordierite honeycomb catalyst after the reaction for 30 hours was taken out from the reactor and observed, structural deterioration such as deformation and collapse of the cell shape did not occur at all.

2-2. Ammonia decomposition reaction 2 (catalyst evaluation 2)
The reactor is charged so that the catalyst a1 is on the gas inlet side and the catalyst b1 is on the outlet side, ammonia is 57.1% by volume, nitrogen is 33.3% by volume, oxygen is 8.9% by volume, and the remainder from argon The reaction test was continued for 30 hours using The ammonia decomposition reaction was performed at a catalyst inlet temperature of 200 ° C., an SV of 34996 hr ⁻¹ , and a volume ratio (a1 / b1) of the catalyst a1 to the catalyst b1 of 1/5. Table 2 shows the H ₂ yield at the initial stage and after the reaction for 30 hours. When the metal honeycomb catalyst was used, the H ₂ yield after the reaction for 30 hours was clearly reduced as compared with that at the beginning of the reaction. The catalyst layer maximum temperature and catalyst layer outlet temperature were 1000 ° C. and 500 ° C. at the beginning of the reaction, respectively, but changed to 1000 ° C. and 565 ° C. after the reaction for 30 hours, respectively. Further, when the metal honeycomb catalyst after the reaction for 30 hours was taken out from the reactor and observed, remarkable structural deterioration such as deformation and collapse of the cell shape was observed.

  The present invention can be applied to an ammonia decomposition reaction, and can be used in a technique for decomposing ammonia to obtain hydrogen.

Claims (5)

1 to 100% by volume of ammonia, 0 to 10% by volume of hydrogen, 0 to 20% by volume of oxygen, 0 to 80% by volume of nitrogen and the balance (total amount of ammonia, hydrogen, oxygen, nitrogen and the balance Is a catalyst used for decomposing ammonia in a reaction gas having a reaction temperature of 100 to 1200 ° C.
An ammonia decomposing catalyst, wherein the catalyst comprises a honeycomb ceramic molded body coated with a catalyst component.   The ammonia-decomposing catalyst according to claim 1, wherein the honeycomb ceramic formed body is mainly composed of cordierite, mullite or silicon carbide.   The ammonia decomposition catalyst according to claim 1 or 2, wherein a cross-sectional shape of the through hole of the honeycomb ceramic formed body is a square, a hexagon or a corrugated shape.   The ammonia decomposition catalyst according to any one of claims 1 to 3, wherein a coating amount of the catalyst component is 0.1 to 600 g per liter of the ammonia decomposition catalyst. Using the ammonia decomposition catalyst according to any one of claims 1 to 4,
1 to 100% by volume of ammonia, 0 to 10% by volume of hydrogen, 0 to 20% by volume of oxygen, 0 to 80% by volume of nitrogen and the balance (total amount of ammonia, hydrogen, oxygen, nitrogen and the balance Is decomposed into hydrogen and nitrogen at a reaction temperature of 100 to 1200 ° C.