JPH07309603A - Production of hydrogen-containing gas for fuel cell - Google Patents

Abstract

PURPOSE:To develop a technique for easily reducing the CO concn. to a low value of 100ppm or lower while leaving a fixed amt. of oxygen by catalytically oxidizing the CO in a reformed gas consisting essentially of hydrogen and obtained by the steam reforming of various hydrogen producing fuels with an oxygen-contg. gas and so on with good selectivity to CO2 which is harmless to the electrode of a fuel cell. CONSTITUTION:A hydrogen producing fuel is reformed into a gaseous fuel contg. at least hydrogen. The obtained reformed gas consisting essentially of hydrogen and contg. CO2 and CO is mixed with an oxygen-contg. gas, the gaseous mixture is brought into contact with a catalyst to selectively oxidize and remove the CO, and a hydrogen-contg. gas for a fuel cell is produced. In this case, the oxygen concn. of the gas discharged from the reaction system is controlled to 0.2 to 2vol.% and the CO concn. to <=100ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen-containing gas for a fuel cell, and more specifically to various hydrogen producing fuels such as methane or natural gas (LN).
G), propane, butane or petroleum gas (LPG),
CO is selectively catalytically oxidized from reformed gas obtained by steam reforming of hydrocarbon fuels such as naphtha, kerosene, light oil, synthetic petroleum, alcohol fuels such as methanol and mixed alcohols, or city gas. The present invention relates to a method for efficiently producing a hydrogen-containing gas that can be removed and can be advantageously used as a fuel for a fuel cell that can prevent poisoning of electrodes of a fuel cell even if CO cannot be completely removed.

The hydrogen-containing gas production process according to the method of the present invention can be suitably used in the form of being incorporated into a fuel cell power generation system together with the reforming process.

[0003]

2. Description of the Related Art Power generation by a fuel cell has various advantages such as low pollution, low energy loss, selection of installation place, expansion, operability, etc. There is. Various types of fuel cells are known depending on the type of fuel or electrolyte, operating temperature, etc. Among them, hydrogen is used as a reducing agent (active material) and oxygen (air, etc.) is used as an oxidizing agent. Hydrogen-oxygen fuel cells (low-temperature operation fuel cells) have been most developed and put into practical use, and are expected to become even more popular in the future.

There are various types of such hydrogen-oxygen fuel cells depending on the type of electrolyte and the structure of the electrodes. Typical examples thereof include phosphoric acid fuel cells, KOH type fuel cells, and solid state fuel cells. There are polymer electrolyte fuel cells and the like. In such a fuel cell, especially in the case of a low temperature operation type fuel cell, platinum (platinum catalyst) is used for the electrode. However, the platinum (platinum catalyst) used for the electrodes is C
Since CO is liable to be poisoned by O, if CO is contained in the fuel at a certain level or more, the power generation performance is lowered, or depending on the concentration, power generation cannot be performed at all, which is a serious problem. The deterioration of catalytic activity due to this CO poisoning is
This problem is particularly serious in the case of a fuel cell that operates at a low temperature, since the problem is remarkable at a low temperature.

Therefore, pure hydrogen is preferable as a fuel for a fuel cell using such a platinum-based electrode catalyst.
From a practical point of view, various fuels that are cheap and have excellent storage properties, or have already been equipped with a public supply system [eg, methane or natural gas (LNG), petroleum gas (LPG) such as propane, butane, etc.] , Hydrocarbons such as naphtha, kerosene, and light oil, alcohol-based fuels such as methanol, city gas, and other fuels for hydrogen production] The fuel cell power generation system incorporating such a reforming facility is being widely spread. However, since such reformed gas generally contains a considerable concentration of CO in addition to hydrogen, this CO is converted into CO ₂ which is harmless to the platinum-based electrode catalyst, and the CO concentration in the fuel is reduced. There is a strong demand for the development of a technology for reducing this. At that time, the concentration of CO is usually 100 ppm
It is said that it is desirable to reduce the concentration to the low level below.

In order to solve the above problems, as one of means for reducing the concentration of CO in fuel gas (hydrogen-containing gas such as reformed gas), a shift reaction represented by the following formula (1) A technique utilizing (water gas shift reaction) has been proposed.

CO + H ₂ O = CO ₂ + H ₂ (1) However, in the method based only on this shift reaction, there is a limit to the reduction of the CO concentration due to restrictions on chemical equilibrium, and the CO concentration is generally 1%. It is difficult to

Therefore, as a means for reducing the CO concentration to a lower concentration, oxygen or a gas containing oxygen (such as air) is introduced (added) into the reformed gas, and a C is selectively used by using a catalyst.
Method for converting O to CO ₂ (CO selective oxidation removal method)
Is proposed. However, in this case, since a large amount of hydrogen is present in the reformed gas, when attempting to oxidize CO, hydrogen is also oxidized, and the CO concentration may not be sufficiently reduced.

On the other hand, researches for improving the CO resistance of polymer electrolyte fuel cells have also been conducted, and for example, Japanese Patent Laid-Open No.
JP-A-208135 describes that the electrode catalyst is alloyed to make it less susceptible to the CO concentration in the fuel gas.

Further, in US Pat. No. 4,910,099, by mixing an oxygen-containing gas into a fuel gas supplied to a fuel cell, CO up to about 100 ppm can be obtained.
It can be operated without reducing the voltage even when the fuel cell is in the fuel gas. Further, by mixing air or oxygen into the fuel gas immediately before the fuel cell until the oxygen concentration reaches 6 to 13%, it is possible to operate without lowering the voltage even with the fuel gas having a CO concentration up to about 1000 ppm. It is shown. However, if a large amount of air is mixed with the hydrogen-containing gas in this way, the mixed gas enters the explosion range, which increases the risk.It is usually impossible to supply oxygen, but air is supplied. Since a large amount of nitrogen is mixed with the fuel gas at the same time as oxygen, the partial pressure of hydrogen in the fuel gas is reduced, which lowers the voltage of the fuel cell, and the oxidation of hydrogen or CO occurs on the electrodes of the fuel cell. The heat of combustion raises the temperature of the electrodes of the fuel cell, which may cause fatal damage such as deterioration of the catalyst and melting of the electrolyte membrane, resulting in holes, and wasting hydrogen for power generation. There were problems such as leading to consumption.

For these reasons, it is practically difficult to mix a large amount of air into the fuel gas supplied to the fuel cell. That is, even if a method of mixing air into the fuel gas immediately before the fuel cell is used, it is impossible to directly supply the reformed gas discharged from the reformer or the shift reactor to the fuel cell. It can be seen that it is essential to pass a CO reduction device such as an oxidizer.

Journal of Power So
urces 29 (1990) p. 251-264, the CO concentration in the fuel gas supplied to the fuel cell is 100.
If it is up to ppm, the mixing ratio of the air mixed as the oxygen-containing gas is 2% by volume (the oxygen concentration after mixing is 0.1.
It is described that the fuel gas polymer electrolyte fuel cell can be operated without lowering the voltage even if it is reduced to about 4% by volume). If the amount of the mixed air is as small as about 2% by volume, the problem due to the large amount of air described above does not pose a problem. Further, if the CO resistance of the fuel cell is improved to about 100 ppm, the operating pressure of the CO oxidizer can be lowered, and the range of the optimum operating temperature is widened, which facilitates temperature control of the catalyst layer, which is advantageous in system construction. Become. However, in this method, at the inlet of the CO selective oxidation reactor, C
The air for the O selective oxidation reaction is mixed, and further the air is mixed in the path from the outlet of the CO selective oxidation reactor to the fuel electrode inlet of the fuel cell, and it is necessary to install two air mixing devices. The control of the entire fuel cell system becomes complicated, which causes a cost increase. In addition, when air is newly mixed, nitrogen mixed with oxygen causes a problem that the partial pressure of hydrogen in the fuel gas is reduced and the voltage of the fuel cell is lowered.

Prior arts relating to the selective oxidation of CO in the production of fuel gas for a fuel cell include the following ones. In all of them, the path from the outlet of the CO selective oxidation reactor to the fuel electrode inlet of the fuel cell is used. No consideration is given to the inclusion of air, including the inclusion of air, and no mention is made of the oxygen concentration at the CO selective oxidation reactor outlet. This is because generally when the oxidation reaction of CO is performed under normal conditions, the total amount of oxygen mixed in is consumed for the oxidation of CO or hydrogen, and it is unlikely that oxygen will remain at the outlet.

As a prior art relating to the selective oxidation of CO, for example, JP-A-3-276577 describes that an oxygen introduction device and a CO oxidation device are installed between a reformer and a fuel cell. There is. However, in this publication, there is no clear explanation about the selective oxidation method of CO, that is, what kind of conditions (catalyst, reaction conditions, etc.) should actually be used for the oxidation.

Further, Japanese Patent Application Laid-Open No. 2-153801 discloses a technique in which the oxidation removal reaction of CO is carried out using an Au catalyst at a reaction temperature of 200 ° C. or lower. However, in the case of this conventional technique, the catalyst activity is insufficient and the conditions such as the reaction pressure are also inadequate, so it is necessary to lower the space velocity (SV) in order to obtain a high CO conversion rate. Moreover, since the selectivity of CO oxidation is not sufficient, the CO concentration cannot be sufficiently reduced if hydrogen oxidation is suppressed.

Further, in Japanese Unexamined Patent Publication No. 5-201102, the oxidation removal reaction of CO is carried out by using a catalyst composed of Rh and Ru at a reaction temperature of 120 ° C. or lower and oxygen / C of feed gas.
It is described that the O ratio is smaller than 1, but
There is a description about the reaction temperature, the reaction pressure and the oxygen / CO ratio, but there is no description about the oxygen concentration of the outlet gas.

[0017]

The object of the present invention is to provide a fuel electrode.
H type that uses platinum (platinum catalyst) for the (negative electrode) electrode
₂Combustion fuel cell (phosphoric acid fuel cell, KOH fuel cell
Low temperature operation including ponds and solid polymer electrolyte fuel cells
When used as fuel for a dynamic fuel cell, etc.
Control the poisoning and deterioration of the electrode catalyst to reduce the voltage of the fuel cell.
Can be prevented and can be used as fuel for fuel cells.
For efficiently producing hydrogen-containing gas
To provide.

[0018]

The present inventor has conducted extensive studies to achieve the above object, and as a result, CO in the reformed gas
Depending on the reaction conditions of the CO oxidation-removal reaction in which CO is oxidized to CO ₂ to remove CO, some oxygen remains at the outlet of the oxidation reactor, and the CO concentration remaining in the gas discharged from the reaction system and It was found that a hydrogen-containing gas suitable as a fuel for a low temperature operation type fuel cell using a platinum electrode catalyst can be efficiently obtained by controlling the oxidation removal reaction of CO so that the oxygen concentration falls within a specific range. It was Based on these findings, the present inventor has completed the present invention.

That is, the present invention is a reformed gas obtained by reforming a fuel for hydrogen production which can be converted into a fuel gas containing at least hydrogen by a reforming reaction, the reformed gas containing hydrogen as a main component and CO. A hydrogen-containing gas for a fuel cell is produced by bringing a mixed gas obtained by mixing a reformed gas containing ₂ and CO with an oxygen-containing gas into contact with a catalyst to selectively oxidize CO and convert it into CO _2. In the above method, the reaction conditions of the selective oxidation reaction of CO are controlled so that the oxygen concentration remaining in the gas discharged from the reaction system is 0.2 vol% or more and less than 2 vol% and the CO concentration is 100 ppm or less. The present invention provides a method for producing a hydrogen-containing gas for a fuel cell, which comprises:

1. Reforming Step of Fuel In the method of the present invention, a reformed gas (containing hydrogen as a main component and CO
CO contained in the fuel gas containing hydrogen) is selectively oxidized using a catalyst to produce a desired hydrogen-containing gas in which the CO concentration is sufficiently reduced. A reforming step for obtaining the reformed gas The (reforming reaction) can be performed by an arbitrary method such as a method implemented or proposed in a conventional fuel cell system, as shown below. Therefore, in a fuel cell system equipped with a reforming device in advance, the reformed gas may be prepared in the same manner by using it as it is.

The fuel used as a raw material for this reforming reaction contains hydrogen as a main component and C by a suitable reforming reaction.
Various types and compositions of hydrogen-producing fuels that can be converted to a fuel gas containing O can be used, and specifically, for example, hydrocarbons such as methane, ethane, propane, butane (either alone or as a mixture). , Or natural gas (L
NG), petroleum gas (LPG), naphtha, kerosene, light oil, hydrocarbon fuels such as synthetic petroleum, methanol, ethanol,
Alcohols such as propanol and butanol (may be used alone or as a mixture), as well as various city gases, syngas,
Coal or the like can be used as appropriate. Of these,
What kind of fuel for hydrogen production should be used may be determined in consideration of various conditions such as the scale of the fuel cell system and the circumstances of fuel supply, but normally, methanol, methane or LNG, propane or LPG is used. , Naphtha or lower saturated hydrocarbon, city gas containing methane, etc. are preferably used.

The steam reforming reaction (steam reforming) is the most common reforming reaction, but depending on the raw material, a more general reforming reaction (for example, thermal reforming reaction such as thermal decomposition or catalytic cracking). And various catalytic reforming reactions such as shift reaction, partial oxidation reforming, etc.) can be appropriately applied.
At that time, different types of reforming reactions may be appropriately combined and used. For example, since the steam reforming reaction is generally an endothermic reaction, the steam reforming reaction and partial oxidation may be combined to supplement this endothermic amount, or the CO generated by the steam reforming reaction (by-product) may be subjected to a shift reaction. Use H ₂ O
Various combinations are possible, such as reacting with and partially converting it into CO ₂ and H ₂ in advance.

In such a reforming reaction, a catalyst or reaction conditions are generally selected so that the yield of hydrogen is as large as possible, but it is difficult to completely suppress the CO by-product, and even if the shift reaction However, there is a limit to the reduction of CO concentration in the reformed gas.

In fact, in the steam reforming reaction of hydrocarbons such as methane, the following formula (2) or (3): CH ₄ + 2H _{2 is used in} order to obtain the yield of hydrogen and suppress the by-product of CO. O → 4H ₂ + CO ₂ (2) C _n H _m + 2nH ₂ O → (2n + m / 2) H ₂ + nCO ₂ (3) The conditions should be selected so that the reaction represented by the formula is as selective as possible. preferable.

Similarly, for the steam reforming reaction of methanol, the reaction represented by the following formula (4): CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ (4) is as selective as possible. It is preferred to choose the conditions to occur.

Further, even if CO is modified and modified by utilizing the shift reaction represented by the above formula (1), a considerable concentration of CO remains because the shift reaction is an equilibrium reaction. Therefore, the reformed gas produced by such a reaction contains CO ₂ and unreacted water vapor and a small amount of CO in addition to a large amount of hydrogen.

As the catalyst effective for the reforming reaction, there are known various catalysts depending on the type of raw material (fuel), the type of reaction, the reaction conditions and the like. Specific examples of some of them include, for example, Cu-Zn as an effective catalyst for steam reforming of hydrocarbons and methanol.
O-based catalyst, Cu-Cr ₂ O ₃ -based catalyst, supported Ni-based catalyst, C
u-Ni-ZnO-based catalyst, Cu-Ni-MgO-based catalyst,
Examples thereof include Pd-ZnO-based catalysts, and examples of the catalyst effective for catalytic reforming reaction and partial oxidation of hydrocarbons include supported Pt-based catalysts and supported Ni-based catalysts. Of course, the catalyst that can be used in the reforming reaction in the method of the present invention is not limited to the above-exemplified catalysts, and may be any suitable catalyst depending on the type of raw material (fuel), the type of reaction, the reaction conditions, etc. May be appropriately selected and used. That is, also in the method of the present invention, as the reforming reaction catalyst, various known catalysts such as various known steam reforming catalysts and catalytic reforming catalysts including those exemplified above can be applied.

The reforming device is not particularly limited, and any type such as a device commonly used in a conventional fuel cell system can be applied, but many reforming processes such as steam reforming reaction and decomposition reaction are possible. Since the reaction is an endothermic reaction, generally, a reaction device or a reactor (heat exchanger type reaction device or the like) having a good heat supply property is preferably used. Examples of such a reaction device include a multi-tube reactor and a plate fin reactor, and examples of the heat supply method include heating by a burner or the like, a method using a heating medium, and a catalyst utilizing partial oxidation. The heating includes, but is not limited to, heating by combustion.

The reaction conditions of the reforming reaction differ depending on other conditions such as the raw material used, the reforming reaction, the catalyst, the type of the reaction apparatus, the reaction system, etc., and may be appropriately determined. In any case, the conversion rate of the raw material (fuel) is sufficient (preferably 10%).
It is desirable to select various conditions such that the hydrogen yield rate is as high as possible and the hydrogen yield rate is as high as possible. Further, if necessary, a method of separating unreacted hydrocarbons and alcohols and recycling may be adopted. Further, if necessary, the generated or unreacted CO ₂ or water may be appropriately removed.

Thus, a desired reformed gas having a high hydrogen content and sufficiently reduced fuel components other than hydrogen, such as hydrocarbons and alcohols, is obtained. The CO concentration in the obtained reformed gas is usually
It is suitable to keep it at 0.02 mol or less, preferably 0.01 mol or less, and the CO concentration is adjusted to such a relatively low concentration at the stage of this reforming process to thereby prevent the subsequent oxidation. The burden of reaction becomes lighter.

2. CO Selective Oxidation Removal Step In the method of the present invention, the reformed gas obtained as described above is mixed with an oxygen-containing gas, and the mixed gas is brought into contact with a catalyst to selectively remove CO in the reformed gas. In this case, the reaction conditions of the selective oxidation reaction of CO are set so that the oxygen concentration remaining in the gas discharged from the reaction system, that is, the outlet oxygen concentration is 0.2% by volume or more and less than 2.0% by volume, CO concentration is 1
It is important to control the concentration to be 00 ppm or less. If the outlet oxygen concentration is less than 0.2% by volume, there is no effect of increasing the CO allowable concentration of the fuel cell, and if it is 2% by volume or more, the fuel gas enters the explosive range, hydrogen at the fuel electrode of the fuel cell, The heat of CO oxidation reaction causes problems such as damage to the electrodes and the electrolyte membrane, and wasted consumption of hydrogen for power generation on the fuel electrode. The preferable range of the outlet oxygen concentration is 0.2% by volume or more and less than 1.5% by volume, and the more preferable range is 0.3% by volume or more and less than 1.0% by volume. Also,
When the CO concentration exceeds 100 ppm, the effect of preventing poisoning of the electrode of the fuel cell is not exhibited even if oxygen is left as the oxygen-containing gas to be added and mixed with the reformed gas, usually pure oxygen (O ₂ ), Air or oxygen enriched air is preferably used. The addition amount of the oxygen-containing gas is oxygen / CO
The (molar ratio) is preferably adjusted to 0.5 to 10, and more preferably 1 to 5. If this ratio is small, the CO removal rate will be low, and if it is large, the hydrogen consumption will be too large, which is not preferable. If the oxygen concentration is too low, oxygen will not remain in the gas discharged from the reaction system, which is not preferable.

As described above, the mixed gas obtained by mixing the reformed gas and the oxygen-containing gas is brought into contact with the catalyst to carry out the selective oxidation reaction of CO. The reactor used for this selective oxidation reaction is not particularly limited, and various types can be applied as long as they satisfy the above reaction conditions, but since this oxidation reaction is an exothermic reaction, temperature control is required. In order to facilitate the reaction, it is desirable to use a reaction device or a reactor having a good removal of reaction heat. Specifically, for example, a multi-tube type or a plate fin type heat exchange type reactor is preferably used.

The catalyst used in the method of the present invention is not particularly limited and is preferably Pt, Au or Rh.
A catalyst containing at least one metal selected from Ru and Ru is preferably used. Among these, a gold-containing catalyst is preferably used. As this gold-containing catalyst, a catalyst composed of gold and a suitable metal oxide is preferably used, and this catalyst is a mixture of gold and a metal oxide, or gold is immobilized or supported on a suitable metal oxide. (Hereinafter, this form is referred to as a gold-immobilized metal oxide, the metal oxide used for immobilizing or supporting the gold is referred to as a gold-immobilizing metal oxide), and further, gold and a metal oxide. It can be used as a catalyst in various forms such as a mixture of products and / or the gold-immobilized metal oxide supported on another carrier.

The gold in such a gold-containing catalyst is preferably in the form of ultrafine particles (in a highly dispersed state), and particularly, the particle diameter is 10 nm or less, and further, the particle diameter is 1 to 5 nm.
It is preferable that they are carried (immobilized) or contained in the above state. Here, since large gold particles having a particle size of more than 10 nm generally do not show sufficient catalytic activity for a predetermined oxidation reaction, those containing only such large gold particles have insufficient catalytic activity. However, even if the catalyst containing a large amount of such large gold particles satisfies the catalytic activity, expensive gold is wasted and the catalyst cost increases.

The metal oxide for immobilizing gold or the metal oxide used as a mixture or composition with gold (ultrafine particles, etc.) is itself inert to hydrogen oxidation under the above-mentioned predetermined reaction conditions. Or, those having an activity but exhibiting no extreme activity are preferably used, and specific examples thereof include iron oxide, manganese oxide, cobalt oxide, zinc oxide, nickel oxide, magnesium oxide, magnesium hydroxide, tin oxide. , Oxides of single metals such as titanium oxide, aluminum oxide, beryllium oxide, zirconium oxide, silicon oxide, lanthanum oxide, or iron, manganese, cobalt, zinc, nickel, magnesium, tin, titanium, aluminum, beryllium, zirconium Oxides consisting of two or more metal elements such as nickel, silicon and lanthanum Etc. can be mentioned. Further, these single metal oxides and complex oxides may be mixed or used as a complex, if necessary.

In the present invention, among the various types of gold-containing catalysts described above, a catalyst comprising a gold-immobilized metal oxide as described above (that is, a gold-immobilized metal oxide catalyst or other catalysts which will be described later). A catalyst supported on a suitable carrier or support is preferably used. This is because gold immobilized on metal oxide (supported) is supported on the metal oxide surface in ultrafine particle form with good dispersibility as compared to that prepared by mixing gold and metal oxide. This is because it is easy to carry out, the effective surface area of gold becomes large, and the contact area between the gold particles and the metal oxide also becomes large, so that excellent catalytic performance is exhibited.

Various methods are known as a method for preparing such a gold-immobilized metal oxide catalyst or a method for immobilizing gold in the form of ultrafine particles on a metal oxide. Specifically, for example, (1) Coprecipitation method (method described in Japanese Patent Publication No. 12934/1993), (2) Uniform precipitation method (JP-A-62-1
155937), (3) drop neutralization precipitation method (method described in JP-A-63-252908), (4) pH control neutralization precipitation method (JP-A 63- 25
2908), (5) carboxylic acid metal salt addition method (such as the method described in JP-A-2-252610), and (6) reducing agent addition method (JP-A-63-25290).
8), (7) precipitation-precipitation method (method described in JP-A-3-97623, etc.), and (8) impregnation method.

The catalyst composed of the various kinds of gold-immobilized metal oxides used in the oxidation reaction in the method of the present invention can be suitably prepared by various methods including these known methods. That is, for the various types of gold-immobilized metal oxides, a metal oxide for gold immobilization is prepared or prepared in advance, and a predetermined gold compound (eg, chloroauric acid) is added to the metal oxide (catalyst carrier). Is used as a gold raw material to immobilize (carry) ultrafine gold particles, or a predetermined gold compound and an appropriate metal compound that is a raw material of a predetermined metal oxide for immobilizing gold are used as preparation raw materials. It can be prepared by various methods such as a method of obtaining a metal oxide in which ultrafine gold particles are immobilized (supported) by a precipitation method, or a method of a combination thereof.

Chloroauric acid is usually most widely used as the gold raw material used as the catalyst preparation raw material, but the gold raw material is not limited to this, and depending on the case, gold halide such as gold chloride or oxidation may be used. Various gold compounds such as gold, gold hydroxide and gold cyanide complex, gold colloid and the like are appropriately used. As a raw material of the metal oxide for immobilizing gold, for example, various compounds of a predetermined metal such as nitrate, sulfate, chloride and acetate can be used. These preparation raw materials are appropriately selected according to the preparation method and the like.

The shape of the metal oxide for fixing gold (catalyst carrier) used in the preparation of the catalyst is not particularly limited, and for example, it can be formed into a specific shape such as powder, gel or sol. Or not, or beads, pellets,
It can be used in various shapes or forms such as granules or the like which are molded in a desired shape in advance.

In the above catalyst preparation, gold-immobilized metal oxide (precipitate, etc.) deposited by the above coprecipitation method or gold-immobilized metal supported by gold-immobilization The metal oxide (supported material, etc.) is usually subjected to post-treatments such as washing, drying, and calcination, and if necessary, appropriately shaped to obtain a catalyst in a desired shape. Post-treatments such as drying and calcination can be performed according to a conventional method such as a known method. The firing temperature at that time is usually 2
It is suitable to select in the range of about 00 to 600 ° C, preferably 300 to 400 ° C.

The content of gold in the gold-containing catalyst such as the gold-immobilized metal oxide catalyst thus obtained is usually, relative to the total amount of gold and metal oxide (metal oxide for gold immobilization).
It is suitable to select in the range of 0.1 to 30% by weight, preferably 0.3 to 1.0% by weight. If the content of gold is too small, the oxidation activity of CO will be insufficient. On the other hand, if the supporting rate is too high, the amount of gold used will be unnecessarily excessive and the catalyst cost will increase. It may be difficult to stably fix it in the form of ultrafine particles, which may cause problems.

As described above, various desired metal oxides for immobilizing gold can be suitably obtained. The catalyst thus obtained can be preferably used as the catalyst for the oxidation reaction in the present invention, but as described above, this gold-immobilized metal oxide may be further used in another suitable carrier (or support), if necessary. It may be used by supporting it on the body. From a more practical point of view, a method in which the gold-immobilized metal oxide is supported on a carrier or support having an appropriate shape and excellent structural stability is widely used.

As such a carrier (or support), a wide variety of metal oxide carriers, metal carriers, or composites thereof are preferably used. Examples of the material of the metal oxide-based carrier include a single oxide-based material or a composite oxide-based material such as alumina, silica, titania, silica alumina, silica magnesia, alumina titania, cordierite, mullite, or zeolite. Can be illustrated. Examples of the metal-based carrier include stainless steel, iron, lead, copper, and aluminum-based single metal-based carriers and alloy-based carriers. The shape and size of these carriers (or supports) are not particularly limited, and for example, generally used such as powder, sphere, granule, honeycomb, foam, fiber, cloth, plate and ring. Various shapes and structures are available.

The gold-immobilized metal oxide catalyst supported on such a carrier or support can be obtained by various methods. For example, a gold-immobilized metal oxide is prepared in the above catalyst preparation. It may be obtained by previously supporting it on another suitable carrier as a carrier, or alternatively, a gold-immobilized metal oxide prepared in advance or its precursor in the preparation stage may be used as the predetermined carrier or support. For example,
It can also be suitably obtained by carrying it by various carrying methods such as a deposition method, a wash coat method and a spray coat method.

In the CO selective oxidation reaction of the present invention, the reaction conditions for setting the oxygen concentration and CO concentration in the gas discharged from the reaction system to predetermined values are the mixed amount of the oxygen-containing gas, the reaction temperature, the reaction pressure, GHSV (supply volume velocity in standard state of supply gas and apparent volume-based space velocity of oxidation catalyst layer to be used) and the like, and by appropriately controlling these, hydrogen for fuel cell having predetermined oxygen concentration and CO concentration A containing gas is obtained. As an example, the reaction conditions when Au / Fe ₂ O ₃ is used as the catalyst will be described.

The reaction pressure is usually ^{2 to} 10 kg / cm ² G
Perform in the pressure range of. Here, if the reaction pressure is 2 kg /
If it is less than cm ² G, CO cannot be oxidized with sufficient selectivity to a sufficiently low concentration. That is, in such a reaction at a low pressure, the consumption of hydrogen is sufficiently suppressed, and then C
It becomes difficult to reduce the O concentration to a sufficiently low concentration of 100 ppm or less. On the other hand, if the reaction pressure is set too high, it is economically disadvantageous because the power for increasing the pressure needs to be increased by that amount.
If it exceeds kg / cm ² G, there is a problem that the high-pressure gas control law is regulated and the explosion limit is widened so that the safety is lowered. Preferably, 2 to 5 kg / cm ² G
Pressure range. Even if the GHSV is the same, when the pressure is reduced, the residence time decreases, so the outlet oxygen concentration increases and the outlet CO concentration also increases. CO concentration at the outlet is 100 ppm
In order to maintain the temperature below and allow oxygen to remain at the outlet, it is desirable to carry out the reaction within the above pressure range.

The oxidation reaction is usually carried out at 45 to 200 ° C.
Preferably, it can be suitably carried out at a temperature of 50 to 90 ° C. If the reaction temperature is lower than 45 ° C., the reaction rate becomes slow, so that the CO removal rate (conversion rate) tends to be insufficient in a practical SV (space velocity) range. When the temperature of the catalyst increases, the rate of hydrogen oxidation reaction increases, so that the outlet oxygen concentration decreases. In order to keep the outlet oxygen concentration while keeping the outlet CO concentration at 100 ppm or less, the reaction temperature is more preferably maintained at 55 to 85 ° C.

Since the reaction in the process of selective oxidation of CO is exothermic, the temperature of the catalyst rises. Since the temperature increase of the catalyst deteriorates the selectivity of CO, it is necessary to control the temperature of the catalyst layer to the optimum temperature as described above. Usually, the cooling medium is circulated to cool the catalyst layer. When the temperature of the cooling medium used for this cooling is close to the temperature of the cooling medium of the fuel cell body used, the cooling medium supply line installed in the CO selective oxidation reactor is connected to the cooling medium circulation line of the fuel cell body. However, it is also possible to share the circulation line, which is advantageous in terms of cost and compactness as compared with the case of separately circulating.

The oxidation reaction is usually performed by GHSV.
(Supply volume velocity in standard state of feed gas and apparent space-based space velocity of oxidation catalyst layer used) is 500
It is preferable to select it in the range of 0 to 50,000 h ⁻¹ . Here, when GHSV is made small, the outlet oxygen concentration is reduced by the oxidation of hydrogen, while when GHSV is made too large, the CO removal rate is lowered. Preferably 6000-
Select within the range of 16000h ^-1 .

As described above, the hydrogen-containing gas produced by the method of the present invention has a sufficiently low CO concentration and contains a predetermined amount of oxygen. Therefore, poisoning and deterioration of the platinum electrode catalyst of the fuel cell are prevented. It can be sufficiently reduced, and its life and power generation efficiency / power generation performance can be greatly improved. In addition, by operating the CO selective oxidation reactor using the method of the present invention, it is possible to raise the allowable CO concentration of the fuel cell without using the step of mixing air in front of the fuel cell fuel electrode inlet.

The hydrogen-containing gas obtained by the present invention can be suitably used as a fuel for various H ₂ combustion type fuel cells, and in particular, platinum (platinum catalyst) is used as at least the electrode of the fuel electrode (negative electrode). It is advantageously used as a fuel supply to various types of H ₂ combustion fuel cells of the type used (phosphoric acid fuel cells, KOH fuel cells, low-temperature fuel cells such as solid polymer electrolyte fuel cells). be able to.

In the conventional fuel cell system, between the reformer (when the reformer is followed by the modifier, the modifier is also regarded as a part of the reformer) and the fuel cell, the present invention is used. By incorporating the oxygen introduction device and the oxidation reaction device according to the method of Example 1, or in the case where the oxygen introduction device and the oxidation reaction device are already provided, using the gold-containing catalyst as the oxidation catalyst and setting the reaction conditions as described above. It is possible to configure a fuel cell system far superior to the conventional one also by adjusting to.

[0054]

EXAMPLES The present invention will now be described more specifically by showing examples of the present invention, but the present invention is not limited to these examples.

Example 1 Fe ₂ O ₃ -supported alumina obtained by impregnating 100 g of alumina pellets having a particle diameter of 3 mm with a 0.5 M ferric nitrate aqueous solution at 400 ° C. for 5 hours was treated with chloroauric acid. It was immersed in 300 ml of an aqueous solution of 1 g of potassium carbonate having a pH of 10. 20 ml of 3.7% formalin aqueous solution
Was gradually added dropwise over 50 minutes. The obtained pellets were washed with water, dried under vacuum, and calcined in air at 400 ° C. to obtain a gold-containing catalyst (Au / Fe ₂ O ₃ catalyst). The gold content in the catalyst after calcination was 0.5% by weight, which corresponded to 4 g per liter of catalyst.

Gold-containing catalyst (catalyst A) 16 to 3 obtained above
1 cc of pulverized to 2 mesh was filled in a tubular reactor, and a mixed gas having the following composition was passed through the catalyst layer under the conditions of Table 1 to carry out a predetermined oxidation reaction.

Supply gas composition CO: 1% by volume,
O₂: 2% by volume, CO₂: 25% by volume, N ₂: 7.5 volume
%, H₂O: 0.7%, H₂: Balance

[0058]

[Table 1]

[0059]

Industrial Applicability The method for producing a hydrogen-containing gas for a fuel cell according to the method of the present invention is the same as that in the reformed gas containing hydrogen as a main component.
This is a method of performing a selective oxidation reaction of O so that the CO concentration is appropriately lowered and a predetermined amount of oxygen is left, and it is not necessary to set a postnatal device for mixing air into the fuel gas. Since the operating condition restrictions of the oxidation reactor are relaxed,
This is an extremely advantageous method for constructing a manufacturing system. Also,
In the hydrogen-containing gas for a fuel cell obtained by the method of the present invention, a sufficient amount of oxygen remains to suppress the poisoning and deterioration of the residual CO on the platinum-based electrode catalyst of the fuel cell due to the CO. Therefore, the power generation performance (efficiency and life) of the fuel cell can be significantly improved. Therefore, the hydrogen-containing gas for fuel cells obtained by the method of the present invention is advantageous as a fuel for various low-temperature fuel cells (phosphoric acid fuel cells, KOH fuel cells, solid polymer electrolyte fuel cells, etc.). It is possible to improve the performance and the like of the conventional fuel cell system.

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[Procedure amendment]

[Submission date] July 11, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0058

[Correction method] Change

[Correction content]

[0058]

[Table 1]

Claims (5)

[Claims] 1. A reformed gas obtained by reforming a hydrogen-producing fuel that can be converted into a fuel gas containing at least hydrogen by a reforming reaction, the reformed gas containing hydrogen as a main component and CO ₂ and CO. In a method for producing a hydrogen-containing gas for a fuel cell by mixing a reformed gas containing a mixed gas with an oxygen-containing gas with a catalyst to selectively oxidize CO and convert it into CO ₂ . The reaction conditions of the CO selective oxidation reaction are controlled such that the oxygen concentration remaining in the gas discharged from the reaction system is 0.2 vol% or more and less than 2 vol% and the CO concentration is 100 ppm or less. And a method for producing a hydrogen-containing gas for a fuel cell. 2. The method for producing a hydrogen-containing gas for a fuel cell according to claim 1, wherein the reaction conditions for the selective oxidation reaction of CO are a reaction temperature of 45 ° C. or higher and 200 ° C. or lower. 3. The method for producing a hydrogen-containing gas for a fuel cell according to claim 1, wherein GHSV of all gases is not less than 5000 h ^{−1 and} less than 50,000 h ^{−1 as} a reaction condition of the selective oxidation reaction of CO. 4. The method for producing a hydrogen-containing gas for a fuel cell according to claim 2, wherein the reaction condition of the selective oxidation reaction of CO is an operating pressure of 2 kg / cm ² G or more and 10 kgG / cm ² or less. 5. The method for producing a hydrogen-containing gas for a fuel cell according to claim 1, wherein the hydrogen-containing gas for a polymer electrolyte fuel cell is produced.