JP2006335610A - Hydrogen generating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen generating apparatus having a high hydrogen production efficiency even though it is a compact apparatus, excellent in durability, and capable of lowering the cost. <P>SOLUTION: The hydrogen generating apparatus can obtain hydrogen from a raw material gas by being provided with a reforming catalyst, a CO shift catalyst, and a zeolite membrane in a gas passageway in this order in the gas flow direction in the gas passageway. Wherein the reforming catalyst produces a reforming gas containing at least hydrogen by reforming the raw material gas, the CO shift catalyst reduces the concentration of the carbon monoxide contained in the reforming gas, and the zeolite membrane permeates hydrogen contained in the reforming gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrogen generator for producing hydrogen from a raw material gas, and more particularly to a hydrogen generator for producing a reformed gas having a low carbon monoxide concentration and a high hydrogen concentration from the raw material gas. In particular, the present invention relates to a low-cost and small-sized hydrogen generator suitable for automobiles, and high hydrogen production efficiency and durability.

Conventionally, hydrogen has been generated by reforming hydrocarbon fuels such as natural gas, liquefied petroleum gas (LPG), gasoline, etc., and the generated hydrogen is used as fuel gas for fuel cells. Yes.
Although depending on the type of fuel used, the reformed gas obtained by the reforming includes carbon dioxide, carbon monoxide and the like in addition to hydrogen. In particular, when gasoline is used as a fuel, it is known that the reforming reaction needs to be performed at a high temperature, so that the concentration of carbon monoxide in the resulting reformed gas is known to increase.

In addition, when such a reformed gas is used as a fuel gas for a polymer electrolyte fuel cell, for example, it is known that the electrode catalyst of the fuel cell is poisoned by carbon monoxide contained in the reformed gas. Yes.
For this reason, attempts have been made to reduce the concentration of carbon monoxide contained in the reformed gas. In order to obtain a reformed gas having a low carbon monoxide concentration, for example, two types of fuel modification as shown below are used. A genitalia is being considered.

  The first fuel reformer includes a reforming section that performs a reforming reaction, a CO shift reaction section that performs a CO shift reaction using carbon monoxide as carbon dioxide, and the like, to further reduce the concentration of carbon monoxide. This is a selective oxidation reformer composed of a CO selective oxidation unit.

The second fuel reformer is a hydrogen permeable membrane reformer composed of a reforming section that performs a reforming reaction and a hydrogen separation section that includes a hydrogen permeable membrane that allows only hydrogen to permeate (non- (See Patent Document 1).
“Introduction to Automotive Environmental Technology”, Ryohei Matsudaira, Grand Prix Publishing, p278

However, in the conventional selective oxidation reformer, it is usually necessary to provide a high temperature CO shift reaction unit and a low temperature shift reaction unit as the CO shift reaction unit in order to sufficiently reduce the carbon monoxide concentration. Of these, the low-temperature CO shift reaction unit requires a larger amount of catalyst because it requires a catalyst amount.
Thus, in order to sufficiently reduce the concentration of carbon monoxide, there has been a problem that the reformer becomes large.

  Further, in the conventional hydrogen permeable membrane type reformer, since the hydrogen permeable membrane is made of palladium or an alloy thereof, hydrogen embrittlement easily occurs and there is a problem in durability. Furthermore, since palladium or an alloy thereof is used, there is a problem in terms of cost.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to have high hydrogen production efficiency, excellent durability, and low cost even if it is small. The object is to provide a hydrogen generator.

  As a result of intensive studies to achieve the above object, the present inventor has found that the reforming catalyst, the CO shift catalyst, and the zeolite are introduced into the gas channel from the upstream side in the gas flow direction of the gas channel. The inventors have found that the above-mentioned object can be achieved by arranging the films in this order, and have completed the present invention.

That is, the hydrogen generator of the present invention includes a reforming catalyst, a CO shift catalyst, and a zeolite membrane in this order from the upstream side with respect to the gas flow direction of the gas flow path in the gas flow path. From which hydrogen is obtained.
The reforming catalyst reforms the raw material gas to generate a reformed gas containing at least hydrogen, the CO shift catalyst reduces the concentration of carbon monoxide contained in the reformed gas, and the zeolite membrane Permeates hydrogen contained in the reformed gas.

  According to the present invention, the reforming catalyst, the CO shift catalyst, and the zeolite membrane are arranged in this order from the upstream side with respect to the gas flow direction of the gas flow path. In addition, it is possible to provide a hydrogen generator that is low in cost and has high hydrogen production efficiency and durability.

Hereinafter, the hydrogen generator of the present invention will be described in more detail.
As described above, the hydrogen generator of the present invention includes a reforming catalyst, a CO shift catalyst, and a zeolite membrane in this order from the upstream side with respect to the gas flow direction of the gas passage in the gas passage. Hydrogen is obtained from the source gas.
Such a reforming catalyst reforms the raw material gas to produce a reformed gas containing at least hydrogen, the CO shift catalyst reduces the concentration of carbon monoxide contained in the reformed gas, and the zeolite membrane is modified. Permeates hydrogen contained in the gas.

By adopting such a configuration, more specifically, by using a conventional CO selective oxidation catalyst as a zeolite membrane, high hydrogen production efficiency can be achieved even if it is small. And it is possible to reduce to a practical carbon monoxide concentration (about 50 ppm or less).
In addition, since the conventional hydrogen permeable membrane used palladium or an alloy thereof as a material, hydrogen embrittlement easily occurred and there was a problem in terms of durability and cost. However, in the present invention, a zeolite membrane is used. Therefore, the durability can be further improved and the cost can be reduced.

Furthermore, in the case of using a CO selective oxidation catalyst, the startup time is long until the catalyst reaches the activation temperature (typically about 200 ° C.) and exhibits the effect of removing carbon monoxide by the reaction. However, when a zeolite membrane is used, carbon monoxide is removed by molecular sieving, so that there is almost no temperature dependence, start-up time can be shortened, and hydrogen production efficiency can be improved.
And such a hydrogen generator with a short starting time is especially preferable as what is mounted in a motor vehicle.

Furthermore, by arranging the reforming catalyst and the CO shift catalyst in this order in front of the zeolite membrane,
CO + H ₂ O⇔CO ₂ + H ₂ (1)
The following equation (2) that proceeds by a CO shift catalyst with respect to the equilibrium reaction represented by
CO + H ₂ O → CO ₂ + H ₂ (2)
Therefore, hydrogen can be efficiently generated. That is, the reformed gas after passing through the reforming catalyst reduces the concentration of carbon monoxide in the reformed gas that reaches the zeolite membrane with the equilibrium in the formula (1) tilted to the right by the reaction of the formula (2), Hydrogen concentration can be improved.

  FIG. 1 shows the temperature and conversion rate (hydrogen generation amount / theoretical hydrogen generation amount) when such a reforming catalyst and a CO shift catalyst are arranged upstream of the zeolite membrane and when only a conventional reforming catalyst is arranged. It is a graph which shows the relationship of (x100). From the figure, it can be seen that the hydrogen generation amount is improved when the CO shift catalyst is arranged.

The reforming catalyst, CO shift catalyst and zeolite membrane used in the hydrogen generator of the present invention will be specifically described.
First, the reforming catalyst will be described. The reforming catalyst used in the present invention is particularly limited as long as it can reform a raw material gas containing a hydrocarbon-based gas and / or an oxygen-containing hydrocarbon-based gas or a raw material gas further containing water vapor into a reformed gas containing at least hydrogen. For example, a reforming catalyst that promotes steam reforming is desirable.

  An example of such a reforming catalyst is a catalyst containing rhodium. As a production method, rhodium nitrate is used, and this solution is impregnated with high specific surface area alumina, dried and fired to prepare a powder. The prepared powder, boehmite alumina and nitric acid solution are mixed and pulverized with a ball mill to prepare a slurry. The slurry is coated on the honeycomb. The catalyst volume is 1.5L. Although it can be created in this way, it is not limited thereto.

As said raw material gas, conventionally well-known gasoline, light oil, hydrocarbon type gas, such as methane containing gas, oxygen-containing hydrocarbon type gas, such as alcohol, and these arbitrary mixtures can be used. Further, water vapor may be included.
In the present invention, it is desirable to use a raw material gas containing water vapor because steam reforming of a hydrocarbon gas or an oxygen-containing hydrocarbon gas with a reforming catalyst is excellent in hydrogen production efficiency.

  Next, the CO shift catalyst will be described. The CO shift catalyst used in the present invention is not particularly limited as long as the concentration of carbon monoxide in the reformed gas is reduced by a CO shift reaction. More specifically, the CO shift catalyst contains an oxygen storage / release material, It is desirable that the noble metal or the like is a catalyst supported on the oxygen storage / release material.

Examples of the oxygen storage / release material include perovskite oxides, cerium-zirconium composite oxides, and cerium oxides. From the viewpoint of improving CO shift performance, it is desirable to contain cerium.
When the CO shift catalyst contains an oxygen storage / release material, the source gas supplied at startup and the oxygen in the oxygen storage / release material react to generate heat, so the catalyst temperature rises early and the startup time is shortened. can do.

Moreover, since it is not necessary to arrange another catalyst temperature raising apparatus separately, cost reduction can be achieved.
Furthermore, since the oxygen storage / release material from which oxygen has been released exhibits CO shift performance more remarkably, it is possible to increase the hydrogen production efficiency.
The noble metal is not particularly limited as long as it promotes the CO shift reaction. For example, platinum, palladium, rhodium or iridium, and any of these noble metals can be used in combination. It is particularly preferable to use platinum from the viewpoint of improving the reaction efficiency of the CO shift reaction.

  Examples of such a CO shift catalyst include a catalyst containing a powder in which platinum is supported on ceria. When coating a honeycomb or a support, the content of ceria is set to 50% or more, boehmite alumina and nitric acid are mixed, pulverized with a ball mill, a slurry is prepared, and the honeycomb is coated. The volume of the honeycomb is 2.5L. Although an example was given as a manufacturing method, it is not limited to this.

Next, the zeolite membrane will be described. The zeolite membrane used in the present invention is not particularly limited as long as hydrogen contained in the reformed gas permeates with good selectivity. For example, LTA zeolite, MFI zeolite, MOR zeolite, or the like can be used.
In particular, in MFI zeolite, MOR zeolite, etc., the pore diameter is such that anything other than hydrogen passes as it is, so use metal ions to deposit inside the pores by ion exchange or the like, and control the pore diameter. It is also possible to use the zeolite. The kind of element is not limited for the control.

Further, in the present invention, the zeolite membrane used as necessary may be provided on a support, and such a support is particularly limited as long as gas permeability is secured to some extent and the zeolite membrane can be supported. For example, porous alumina, silicon nitride, silica, or the like can be used. Such zeolite membrane, in order to obtain a conventional equal or carbon monoxide concentration reduction effect, typically may be the area 0.5m ² ~100m ^2.

As such a zeolite membrane, for example, A-type zeolite is preferable. The use area of zeolite is preferably 0.5 m ² or more. The thickness may be 10 nm or more.
As a manufacturing method, sodium hydroxide is dissolved in water, and Al powder is stirred and dissolved. On the other hand, tetramethylammonium hydroxide aqueous solution is added to HS-30 colloidal silica and stirred at room temperature to obtain a white suspension. Next, these solutions are mixed and stirred at room temperature for 30 minutes, followed by hydrothermal synthesis at 90 ° C. for 6 hours. Centrifugation is performed, hydrothermal synthesis is again performed on the supernatant, and zeolite A type is obtained through centrifugation, washing with water and drying.

In the present invention, a CO selective oxidation catalyst may be provided on the downstream side of the zeolite membrane in the gas flow path, and an oxygen supply means may be provided between the zeolite membrane and the CO selective oxidation catalyst in the gas flow path.
A hydrogen generator equipped with a CO selective oxidation catalyst leads to an increase in size as described above, but when used in combination with a zeolite membrane, further increases the hydrogen production efficiency while suppressing an increase in the size of the CO selective oxidation catalyst to be used. Can do.

Even if only a CO selective oxidation catalyst is arranged on the downstream side, a slight carbon monoxide concentration reducing effect is exhibited, but by providing an oxygen supply means between the zeolite membrane and the CO selective oxidation catalyst, and supplying oxygen as appropriate, The concentration of carbon monoxide can be further reduced.
At this time, the oxygen supply amount may be appropriately adjusted based on the concentration of carbon monoxide permeated with hydrogen.
For example, a separate flow path that joins the gas flow path may be provided, and a control valve may be provided at the supply port of the separate flow path. However, the present invention is not limited to this.
The oxygen supplied by the oxygen supply means is not limited to oxygen, and may be a mixed gas depending on the system in which the hydrogen generator is incorporated. For example, air can be suitably used.

An example of such a CO selective oxidation catalyst is a catalyst containing platinum. As a manufacturing method, dinitrodiaminoplatinum is impregnated with alumina, and powder is obtained through drying and baking. This powder is pulverized with boehmite alumina and nitric acid to obtain a slurry. This is coated on a honeycomb and dried and fired to form a catalyst.
In addition, when only a CO selective oxidation catalyst is arranged without using a zeolite membrane as in the prior art, it was necessary to use a CO selective oxidation catalyst having a volume of 2.0 L or more. When obtaining the hydrogen production efficiency, the volume of the CO selective oxidation catalyst to be used can be suppressed to 1.0 L or less.

In the present invention, it is desirable that the reforming catalyst, the CO shift catalyst, and the zeolite membrane have a layer structure. In the case of a layer structure, it is desirable to ensure gas permeability to some extent also for the reforming catalyst layer and the CO shift catalyst.
By adopting a layer structure in which the reforming catalyst, the CO shift catalyst, and the zeolite membrane are integrated, the equilibrium reaction as described above tends to decrease in the direction of decreasing the carbon monoxide concentration and increasing the hydrogen concentration.
In addition, the conventional reforming catalyst and CO shift catalyst were coated on the ceramic honeycomb. However, since the layered structure eliminates the need for a honeycomb catalyst dedicated to the reforming catalyst and CO shift catalyst, the startup time is shortened. can do.
In the case of a layer structure, the reforming catalyst typically has an area of 0.5 m ² or more, and the CO shift catalyst typically has an area of 0.5 m ² or more.
Thereby, not only the start-up time can be shortened, but also the cost can be reduced.

FIG. 2 is an explanatory diagram conceptually showing an example of the hydrogen generator of the present invention. As shown in the figure, the reforming catalyst layer 12, the CO shift catalyst layer 14 and the zeolite laminated on the support 30 from the upstream side in the gas flow path 18 indicated by the phantom line in the gas flow direction indicated by the arrow F. A membrane 16 is disposed, and a CO selective oxidation catalyst 20 is disposed further downstream thereof.
Such a hydrogen generator 10 reforms the raw material gas containing gasoline and water vapor by the reforming catalyst layer 12 to generate a reformed gas containing at least hydrogen, and the CO shift catalyst layer 14 is contained in the reformed gas. The concentration of carbon monoxide contained is reduced and the concentration of hydrogen is increased, and the zeolite membrane 16 permeates the hydrogen contained in the reformed gas. In addition, the CO selective oxidation catalyst 20 disposed on the downstream side oxidizes carbon monoxide that is slightly permeated with hydrogen with high selectivity. Thereby, the concentration of carbon monoxide can be further reduced to a practical concentration.
An oxygen supply means (not shown) may be provided between the zeolite membrane 16 and the CO selective oxidation catalyst 20, and the oxygen selective means appropriately supplies oxygen to further improve the catalytic performance of the CO selective oxidation catalyst 20. Thus, the carbon monoxide concentration can be further reduced.

FIG. 3 is an explanatory view conceptually showing the cross-sectional shape of another example of the hydrogen generator of the present invention. As shown in the figure, a support 30 which is a bottomed cylindrical porous alumina tube is provided in a gas flow path 18 indicated by an imaginary line, and a zeolite membrane 16 and a CO shift catalyst are provided on the porous alumina tube. The layer 14 and the reforming catalyst layer 12 are provided.
In the hydrogen generator 10 having such a structure, CO exists in the gas that has reached equilibrium with the reforming catalyst, but the CO is reduced and H ₂ is increased by the shift reaction, and the H ₂ separation ratio of the zeolite is the same. However, the total H ₂ separation ratio is preferably increased when the CO shift catalyst is brought into contact.
In the reforming catalyst layer, a reformed gas containing at least hydrogen is generated by steam reforming from the supplied hydrocarbon and steam-containing raw material gas, and the carbon monoxide concentration in the reformed gas is generated in the CO shift catalyst layer. Is reduced by the CO shift reaction, and hydrogen is selectively separated in the zeolite membrane. Carbon monoxide partially permeates with hydrogen.

  Hereinafter, the present invention will be described in more detail with reference to some examples, but the present invention is not limited to such examples.

Example 1
(Creation of zeolite membrane)
Sodium hydroxide was dissolved in water, and Al powder was stirred and dissolved. A tetramethylammonium hydroxide aqueous solution was added to HS-30 colloidal silica and stirred at room temperature to obtain a white suspension.
Next, these solutions were mixed and stirred at room temperature for 30 minutes, followed by hydrothermal synthesis at 90 ° C. for 6 hours. Centrifugation was performed, hydrothermal synthesis was again performed on the supernatant, and after centrifugation, washing with water and drying, a zeolite A type seed crystal was obtained.
The alumina tube with the tip sealed was immersed in a solution containing the zeolite A type crystal and sucked to attach the zeolite seed crystal to the surface of the alumina tube. This was repeated to form a zeolite membrane.

(Creation of CO shift catalyst layer)
Dinitrodiaminoplatinum was impregnated with alumina, dried and fired to obtain a powder. This powder was pulverized with boehmite alumina and nitric acid by a ball mill to prepare a slurry. This slurry was coated on the zeolite layer and sucked from the alumina tube.

(Creation of reforming catalyst layer)
Using rhodium nitrate, this solution was impregnated with high specific surface area alumina, dried and fired to prepare a powder.
The prepared powder, boehmite alumina and nitric acid solution were mixed and pulverized with a ball mill to prepare a slurry. This slurry was coated on an alumina tube on which a zeolite layer and a CO shift catalyst layer were formed, and sucked from the inside of the alumina tube.
This was placed in the gas flow path to obtain the hydrogen generator of this example.

It is a graph which shows the relationship between temperature and a conversion rate. It is explanatory drawing which shows an example of the hydrogen generator of this invention notionally. It is explanatory drawing which shows notionally the cross-sectional shape of the other example of the hydrogen generator of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydrogen generator 12 Reforming catalyst layer 14 CO shift catalyst layer 16 Zeolite layer 18 Gas flow path 20 CO selective oxidation catalyst 30 Support body

Claims (4)

A hydrogen generation apparatus comprising a reforming catalyst, a CO shift catalyst, and a zeolite membrane in this order in the gas flow path from the upstream side with respect to the gas flow direction of the gas flow path, and obtaining hydrogen from a raw material gas. ,
The reforming catalyst reforms the raw material gas to generate a reformed gas containing at least hydrogen,
The CO shift catalyst reduces the concentration of carbon monoxide contained in the reformed gas,
The hydrogen generating apparatus, wherein the zeolite membrane permeates hydrogen contained in the reformed gas.   The CO selective oxidation catalyst is provided downstream of the zeolite membrane in the gas flow path, and an oxygen supply means is provided between the zeolite membrane and the CO selective oxidation catalyst in the gas flow path. 2. The hydrogen generator according to 1.   The hydrogen generator according to claim 1 or 2, wherein the reforming catalyst, the CO shift catalyst, and the zeolite membrane have a layer structure. The hydrogen generator according to any one of claims 1 to 3, wherein the CO shift catalyst contains at least an oxygen storage / release material.

Images