JP2003277018A - Hydrogen purification apparatus and method of manufacturing co removing catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen purification apparatus or the like having high CO removing efficiency through a long period. <P>SOLUTION: The hydrogen removing catalyst is manufactured by supporting at least one kind of a noble metal selected from Pt, Ru and Pd on a catalyst support formed from an oxide or a compound oxide contaning at least one kind of an element selected from Al, Si, Ti, Zr and Ce into a spherical form so that the difference between maximum and minimum diameters is ≤20% of the average diameter. The catalyst body 1 is a spherical structural body and the difference between the maximum diameter and the minimum diameter is controlled to ≤20% of the average diameter. Further the difference between the maximum diameter and the minimum diameter is controlled to ≥2% of the diameter. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen purifier for purifying a reformed gas containing hydrogen as a main component and containing carbon monoxide (hereinafter referred to as CO) to provide high purity hydrogen gas.

[0002]

2. Description of the Related Art As a hydrogen source for a fuel cell or the like, a reformed gas obtained by reforming a hydrocarbon or alcohol or ether is used. In the case of a polymer electrolyte fuel cell operating at a low temperature of 100 ° C. or lower, The Pt catalyst used for the fuel cell electrode may be poisoned by CO contained in the reformed gas. When the Pt catalyst is poisoned, the reaction of hydrogen is hindered and the power generation efficiency of the fuel cell is significantly reduced. Therefore, using a hydrogen purification device, CO
It is necessary to remove to below ppm, preferably below 10 ppm.

[0003] Usually, in order to remove CO, CO and steam are shifted in a CO shift section in which a CO shift catalyst is installed in a hydrogen purifier to convert them into carbon dioxide and hydrogen, and then several thousand ppm. CO concentration is reduced to a concentration of about 1% by volume.

Then, a small amount of air is used to add oxygen, and the CO selective oxidation catalyst removes CO to a level of several ppm which does not adversely affect the fuel cell.

Conventionally, as the CO conversion catalyst, an iron-chromium catalyst or a copper-zinc catalyst formed into a cylindrical pellet shape or a cordierite honeycomb surface coated with a catalyst having an activity for a conversion reaction is used. Was there.

[0006]

However, when the reforming gas is supplied before the catalyst body is sufficiently heated at the time of starting the apparatus, the steam in the reforming gas is condensed on the catalyst body, and this condensation occurs. Occasionally, when the water was evaporated again, cracking or pulverization of the catalyst body was sometimes induced. In addition, heat shock due to temperature rise and vibration may be applied to the reactor depending on the application, and similarly cracking or pulverization may occur. Due to the cracks in the catalyst body, the reformed gas flow path is blocked, and the pressure loss of the apparatus is increased to increase the load of the pump or the like for supplying the raw material.

For this reason, the temperature of the catalyst body is gradually raised, or an inert gas such as nitrogen heated before the reformed gas is supplied to the hydrogen purifier is supplied to sufficiently raise the temperature of the catalyst body and the reaction chamber. The method of supplying the reformed gas containing steam after warming was adopted. When a honeycomb such as cordierite is used, the strength is high and the coefficient of thermal expansion is small, so the possibility of cracking is reduced, but it is difficult to make the reforming gas flow and the temperature of the catalyst uniform, and In order to obtain very high CO removal characteristics, it was necessary to increase the volume of the reactor. For this reason, there have been problems that it takes time to raise the temperature of the reactor, and the amount of catalyst increases and the cost increases.

As described above, the conventional technique has a problem that it cannot be sufficiently applied to, for example, a time-consuming start-up of the hydrogen purifier or a frequent use of repeated start-stop.

The present invention has been made in view of the above problems, and an object thereof is to provide a hydrogen purifier having a high CO purification efficiency for a long period of time.

[0010]

The first aspect of the present invention relates to hydrogen,
A hydrogen purifying apparatus comprising a catalyst body for removing carbon monoxide from a reformed gas containing carbon monoxide and steam by a CO shift conversion reaction, wherein the catalyst body is a spherical structure,
The difference between the maximum diameter and the minimum diameter in the catalyst body is 20% of the diameter.
It is characterized by the following.

The second aspect of the present invention is characterized in that the difference between the maximum diameter and the minimum diameter in the catalyst body is 3% or more of the diameter.

According to a third aspect of the present invention, the catalyst body is packed in a reactor, and the geometric surface area of the catalyst body per cubic centimeter of volume occupied by the catalyst body packed in the reactor is 7 to 7. It is characterized by being 45 square centimeters.

A fourth aspect of the present invention is characterized in that the particle size of the catalyst filled in the upstream part in the flow direction of the reformed gas is larger than the particle size in the downstream part.

In the fifth aspect of the present invention, the breaking strength of the catalyst body is 1
It is characterized by being 5 to 180 N.

A sixth aspect of the present invention is Al, Si, Ti, Z.
For a catalyst carrier in which an oxide or a composite oxide containing at least one element selected from r and Ce is formed into a spherical shape in which the difference between the maximum diameter and the minimum diameter is 20% or less of the average diameter, The method for producing a hydrogen removal catalyst is characterized in that it is produced by supporting at least one noble metal selected from Pt, Ru, Rh, and Pd on.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) First, with reference to FIG. 1, the structure of the hydrogen purifier according to the present embodiment will be described. Note that FIG. 1 is a schematic vertical cross-sectional view showing the configuration of the hydrogen purifier according to the present embodiment.

In FIG. 1, reference numeral 1 is a catalyst body, which is installed inside the reaction chamber 2. The catalyst body 1 is obtained by supporting Pt on a zirconia-ceria composite oxide formed into a true sphere having a diameter of 3 mm.

Reference numeral 3 is a reformed gas inlet from which reformed gas is introduced. The reformed gas reacted with the catalyst body 1 is discharged from the reformed gas outlet 4.

A diffusion plate 5 is installed on the upstream side of the catalyst body 1 so that the reformed gas flows uniformly. Further, in order to keep the reaction chamber 2 at a constant temperature, the outer periphery of a necessary portion is covered with a heat insulating material 6 made of ceramic wool.

Next, the operation of the hydrogen purifier according to this embodiment will be described.

As the fuel used to generate the reformed gas to be supplied to the hydrogen purifier, there are natural gas, methanol, gasoline and the like, and the reforming method is also a steam reforming in which steam is added, or a portion in which air is added. There is reforming and the like, but here, a case where a reformed gas is obtained by steam reforming natural gas containing methane as a main component will be described.

The composition of the reformed gas when steam is reformed from natural gas varies somewhat depending on the temperature of the reforming catalyst,
About 80% of hydrogen, about 10% of carbon dioxide and about 10% of carbon monoxide are contained as an average value excluding water vapor.

The steam reforming reaction of natural gas is carried out at about 500 to 800 ° C. by mixing 2.5 to 3.5 times as many steams as the number of carbon atoms in natural gas, whereas CO and steam are carried out. Since the transformation reaction in which the reaction is performed is performed at about 150 to 400 ° C., the reformed gas is supplied after being cooled before the reformed gas inlet 3.

The CO concentration after passing through the CO conversion catalyst body 1 is reduced to about 0.5% and discharged from the reformed gas outlet 4. In this example, the reformed gas temperature was adjusted to 400 ° C. and the reformed gas was supplied to the hydrogen purifier.

When the hydrogen purifier is started, the catalytic body 1 and the reaction chamber 2 are heated from room temperature to a predetermined operating temperature by the sensible heat of the reformed gas. 10 in the reformed gas or unreacted gas (methane in this example) supplied at the time of starting the apparatus.
~ 80% water vapor is included, so catalyst body 1 and reaction chamber 2
If the temperature is not sufficiently raised, the steam in the reformed gas is condensed. More specifically, when the reformed gas containing steam is supplied to the reaction chamber 2 at room temperature, the catalyst body 1 is
First, water is condensed on the wall surface of the catalyst, and then the condensed water is evaporated as the temperature rises. At this time, the water impregnated in the catalyst body may destroy the catalyst body due to volume expansion when becoming water vapor. Further, the catalytic reaction may be hindered by covering the surface of the catalyst with water.

Therefore, the catalyst body 1 and the reaction chamber 2 are heated by using an electric heater, a burner, or the like, or an inert gas such as heated nitrogen is supplied before the reformed gas is supplied, and the catalyst body is sufficiently supplied. In the past, it was necessary to supply the reformed gas after raising the temperature of the reaction chamber.

On the other hand, in the hydrogen purifying apparatus according to the embodiment of the present invention, since the catalyst body 1 has a spherical shape, an external force is evenly applied, so that the corners of the pellet are less likely to be chipped or cracked. Further, since the number of contact points between the catalyst bodies is larger than that of the cylindrical pellet, heat conduction is improved and heat shock is alleviated.

The shape of the catalyst body 1 is preferably closer to a true sphere, and the difference between the maximum diameter and the minimum diameter (hereinafter referred to as the degree of strain) with respect to the average diameter is preferably 20% or less. When the degree of strain becomes larger than 20% and the shape of the CO shift catalyst body deviates greatly from the true sphere, the above effect is significantly reduced (see Table 1).

Here, the average diameter is the average value of the diameter of one catalyst body measured at several points, and the maximum and minimum diameters are the maximum and minimum diameters of one catalyst body. It shows the degree of distortion of the medium 1 from a true sphere. In addition,
Since the reaction chamber 2 is filled with a large number of catalyst bodies 1, the degree of strain has a distribution, but usually 90% or more of the catalyst bodies 2
If the strain degree is 0% or less, the above effect can be obtained.

On the other hand, however, the shape of the catalyst body 1 is not a true sphere itself, but the degree of strain (difference between the maximum diameter and the minimum diameter with respect to the average diameter) is preferably 2% or more. When the shape of the catalyst body is distorted from a true sphere, the flow of the reformed gas is disturbed, and the reformed gas can be made to react efficiently on the surface of the catalyst body.
This is because the O concentration can be reduced to a low concentration (see Table 1).

In this case as well, the reaction chamber is filled with a large number of catalyst bodies, but if the average value of the strain degree of these many catalyst bodies is 3% or more, the above-mentioned effect can be obtained.

The geometric surface area of the catalyst body per cubic centimeter of volume occupied by the catalyst body is preferably 7 to 45 square centimeters. When the diameter of the catalyst body is almost uniform without distribution, for example, 10
The geometric surface area per volume of the catalyst body can be easily calculated from the number of the catalyst bodies and the average diameter in a cube of 00 cubic centimeter. At this time, the diameter of the catalyst body is 1 to 6 m
It becomes the range of m.

The smaller the diameter of the catalyst body, the higher the contact efficiency between the catalyst body and the reformed gas and the higher the reactivity, but the frequency with which the steam contained in the reformed gas condenses on the surface of the catalyst body when the apparatus is started. Increase. For this reason, when the diameter of the catalyst body becomes smaller than 1 mm, the water condensed at the time of starting the device poisons the catalyst (water covers the catalyst surface and the reaction gas cannot be adsorbed) and inhibits the reaction. Water impregnated into the medium is more likely to induce cracking of the catalyst body.

Further, the pressure loss when the reformed gas passes through the reaction chamber also becomes large, and the power consumption of the pump for supplying the raw material becomes large. On the other hand, when the diameter of the catalyst body is larger than 5 mm, the reactivity is slightly lowered, but the water condensed on the surface of the catalyst body is quickly evaporated, and the poisoning of the water on the catalyst body and the cracking of the catalyst body are reduced.

In the present embodiment, a catalyst body having a substantially uniform average diameter is used, but the diameter of the catalyst body is, for example, 2 to 4 m.
The same effect can be obtained by providing a distribution of m.

Further, in the present embodiment, the catalyst body in which Pt is supported on the zirconia-ceria composite oxide is used.
As long as it is a catalyst component which is active in the O conversion reaction, spherical pellets made of oxides such as alumina, zirconia, titanium, and silica-alumina carrying Pt or other noble metal may be used. An active ingredient such as cerium may be carried only on the surface of these pellets.

Further, the breaking strength of the catalyst body is 15 to 180 N.
Is preferred. The breaking strength of the catalyst body is generally measured by using a Chatillon type hardness meter, and gradually applying a load from above to the catalyst body to measure the force at which the catalyst body breaks. In the case of a columnar catalyst body, it may be expressed by the strength per cross-sectional area of the bottom surface (N / cm ² ).

When the breaking strength of the catalyst body is less than 15 N, the probability of cracking of the catalyst body in the step of supporting Pt increases, and the yield decreases. The breaking strength is 1
When it is larger than 80 N, the particle size of the noble metal particles becomes large at the stage of supporting the noble metal, and the catalytic activity decreases. The breaking strength of the catalyst body can be changed by the temperature at which the catalyst body is fired, and the higher the temperature at which the catalyst body is fired, the higher the strength can be. It can also be changed depending on the type and addition amount of an inorganic binder such as alumina, zirconia, or silica used for molding. Further, the larger the diameter of the catalyst body, the higher the fracture strength.

(Second Embodiment) Next, a second embodiment of the present invention will be described. This embodiment is similar to the first embodiment except that the first catalyst body 11 and the second catalyst body 12 are installed on the downstream side as shown in FIG. Therefore, the present embodiment will be described focusing on different points. In addition, as the first catalyst body 11, a zirconia-ceria composite oxide formed into a spherical shape having a diameter of 3 mm and Pt supported thereon was used, and as the second catalyst body 12, a zirconia formed into a spherical shape having a diameter of 1 mm was used. -A ceria composite oxide supporting Pt was used.

FIG. 2 is a schematic sectional view showing the structure of the hydrogen purifying apparatus according to this embodiment. The reformed gas of about 400 ° C. supplied from the reformed gas inlet 14 is reacted with the first catalyst body 11 and then supplied to the second catalyst body 12.

The temperature of the second catalyst body 12 is set to about 250 ° C. by radiating heat by reducing the thickness of the heat insulating material. The CO conversion reaction has a high reaction rate at high temperatures,
Since it is an equilibrium reaction and an exothermic reaction, the lower the temperature, the more the CO concentration can be reduced. For this reason, a method such as providing a cooling unit in the middle is usually used so that the temperature of the catalyst body becomes lower as it goes downstream.

Since there is a temperature difference of 100 ° C. or more between the upstream part and the downstream part of the reaction chamber 2, the volume of the reformed gas is larger in the upstream part than in the downstream part, the shift reaction speed is faster, and the inside of the catalyst body is higher. The gas diffusion rate is different. Further, since the CO conversion reaction consumes water vapor, the ratio of water vapor is higher in the upstream portion, and water is more likely to be condensed in the upstream portion when the apparatus is started.

Therefore, by making the diameter of the catalyst body in the downstream portion smaller than that in the upstream portion, the reactivity can be enhanced without increasing the pressure loss. In addition, by increasing the size of the catalyst body on the upstream side where water easily condenses, it is possible to reduce the influence of cracking and poisoning when water condenses. Further, the gas diffusion rate is high in the upstream part of high temperature, and even if the diameter of the catalyst body is large, the inside of the catalyst body can be effectively functioned.

In the present embodiment, the reformed gas is cooled by simply radiating heat, but a method of using heat to preheat the water or the raw material gas used for producing the reformed gas may be adopted. In this case, the efficiency of the device can be improved as compared with the case of simply dissipating heat and dissipating the heat.

[0046]

Example 1 Pure water and methylcellulose were added to a powder made of a complex oxide of zirconia and ceria, and the mixture was kneaded and then molded into a spherical shape having a diameter of 3 mm by a granulator to prepare a catalyst carrier. By selecting those having a degree of strain of the catalyst carrier (ratio of maximum diameter to minimum diameter to average diameter) of 0% to 40%, impregnating each with a nitric acid aqueous solution of dinitrodiamine platinum complex nitrate, and calcining at 500 ° C.,
A catalyst body was prepared. The catalyst body having each strain degree was filled as the catalyst body 1 in the reaction chamber 2 of the hydrogen purifier shown in FIG.

From the reformed gas inlet 3, a reformed gas containing 8% of carbon monoxide, 8% of carbon dioxide, 20% of steam and the balance of hydrogen was introduced at a flow rate of 10 liters per minute. After reacting with the catalyst body 1, the CO concentration in the gas discharged from the reformed gas outlet 4 was measured using a CO measuring device. By changing the temperature of the catalyst body, CO at the temperature where the CO concentration becomes the lowest
The concentration was measured to compare the activities of the catalyst bodies. Further, after operating for 1 hour, the supply of the reformed gas was stopped, the temperature was cooled to room temperature, and the same starting and stopping was repeated 50 times, and the rate of cracking of the catalyst body was measured. The results are also shown in Table 1.

[0048]

[Table 1] The experimental results shown in Table 1 support the following facts described above. When the degree of strain of the catalyst body is 20% or less, the rate at which the catalyst body is destroyed due to the start and stop of the device decreases. Also, when the degree of strain is 3% or more, C after the reaction
Although the O concentration becomes low, the strain degree does not affect the CO concentration more than that.

Example 2 In Example 1, only the diameter of the catalyst body was changed to prepare a catalyst body having a diameter of 0.8 mm to 10 mm. A strain having a degree of 3% was used. The prepared catalyst body was filled in the reaction chamber 2 as the catalyst body 1 in the same manner as in Example 1, and the start and stop were repeated to measure the CO concentration after the reaction and the ratio of the broken catalyst body. The results are shown in Table 2.

[0050]

[Table 2] The experimental results shown in Table 2 support the following facts described above. If the geometric surface area of the catalyst body per cubic centimeter is smaller than 7 square centimeters, the CO concentration after the reaction is high. On the other hand, if it is larger than 45 square centimeters, the rate of cracking of the catalyst body due to start-up and stop increases.

Example 3 In Example 1, the heat treatment temperature of the catalyst carrier was changed to change the breaking strength from 10N to 250N. The breaking strength was measured using an ordinary Chatillon type hardness meter, and 25 samples were measured and the average value was taken. Moreover, the strain degree used was 3%. This catalyst carrier was impregnated with an aqueous nitric acid solution of a dinitrodiamine platinum complex in the same manner as in Example 1 and calcined at 500 ° C. The rate of cracking after this was measured. Further, in the same manner as in Example 1, the reaction chamber 2 was filled with the catalyst body 1, and the start and stop was repeated to measure the CO concentration after the reaction. The results are shown in Table 3.

[0052]

[Table 3] From the results shown in Table 3, when the breaking strength of the catalyst body is less than 15 N, the rate of cracking of the catalyst body in the Pt supporting step increases. Further, when the breaking strength is higher than 180 N, the CO concentration after the reaction becomes high.

(Example 4) The diameter used in Example 1 was 3 mm.
1 mm in diameter, the catalyst body having a diameter of 3 mm is filled as the first catalyst body 11 shown in FIG. 2, and the second catalyst body 12 having a diameter of 1 mm is provided downstream thereof. Filled. The start-up / shutdown was repeated in the same manner as in Example 1 to measure the CO concentration after the reaction and the ratio of cracked catalyst bodies. As a result, the CO concentration was 0.28%, and the proportion of cracked catalyst bodies was 0.16%.

(Comparative Example 1) Instead of the spherical catalyst body in Example 1, a cylindrical catalyst body having a diameter of 3 mm and a height of 3 mm was molded, and starting and stopping were repeated in the same manner as in Example 1 to prepare a catalyst body. The cracking ratio was measured and found to be 38%.

[0055]

As is apparent from the above description, the present invention can provide a hydrogen purifying apparatus which has a small number of cracks in the catalyst body and operates stably for a long period of time even under reaction conditions in which the ratio of steam is large.

Further, high CO removal performance can be obtained.

Further, the breaking strength of the catalyst body is set to 15N-18.
By setting it to 0 N, cracks in the noble metal supporting step at the time of catalyst preparation can be reduced to improve the yield in the manufacturing step, Pt can be supported in a highly dispersed manner, and the amount of the noble metal used can be reduced.

Further, by making the diameter of the catalyst body filled in the downstream portion of the reaction chamber smaller than that in the upstream portion, it is possible to improve the reactivity of the catalyst body without increasing the number of cracks in the catalyst body.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing the configuration of a hydrogen generator including a hydrogen purifier according to a first embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view showing the configuration of a hydrogen generator including a hydrogen purifier according to a second embodiment of the present invention.

[Explanation of symbols]

1 catalyst 2, 13 Reaction chamber 3, 14 Reformed gas inlet 4,15 Reformed gas outlet 5, 16 Diffuser 6,17 insulation 11 First catalyst body 12 Second catalyst body

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidenobu Wakita             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Seiji Fujiwara             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 4G069 AA03 AA08 BA01A BA02A                       BA04A BA05A BB04A BB06A                       BB06B BC43A BC43B BC51A                       BC51B BC70A BC71A BC72A                       BC75A BC75B CC26 DA06                       EA04X EA04Y EB18X EB18Y                       EC01X ED03 FA01 FB14                       FB30 FB61                 4G140 EB34                 5H027 AA02 BA01

Claims (6)

[Claims] 1. A hydrogen purification apparatus comprising a catalyst body for removing carbon monoxide from a reformed gas containing at least hydrogen, carbon monoxide and steam by a CO shift reaction, wherein the catalyst body has a spherical structure. And a difference between the maximum diameter and the minimum diameter in the catalyst body is 20% or less of the average diameter. 2. The hydrogen purifier according to claim 1, wherein the difference between the maximum diameter and the minimum diameter in the catalyst body is 2% or more of the diameter. 3. The reaction body is filled with the catalyst body,
The geometric surface area of the catalyst body per cubic centimeter volume occupied by the catalyst body filled in the reaction chamber is 7 to 45 square centimeters.
The hydrogen purification device described. 4. A first catalyst body is filled in an upstream portion and a second catalyst body is filled in a downstream portion with respect to a flow direction of the reformed gas, and a particle diameter of the first catalyst body is equal to the second catalyst body. The hydrogen purifier according to any one of claims 1 to 3, which is larger than the particle size of the medium. 5. The breaking strength of the catalyst body is 15 to 180.
The hydrogen purifier according to any one of claims 1 to 4, which is N. 6. An oxide or composite oxide containing at least one element selected from Al, Si, Ti, Zr, and Ce is formed into a spherical shape having a difference between the maximum diameter and the minimum diameter of 20% or less of the average diameter. A method for producing a hydrogen-removing catalyst, which is produced by supporting at least one precious metal selected from Pt, Ru, Rh, and Pd on the formed catalyst support.