JPH10261425A - Method and apparatus for removing carbon monoxide - Google Patents

Abstract

[PROBLEMS] To provide a high-performance carbon monoxide removal apparatus capable of selectively oxidizing carbon monoxide in a reformed gas obtained by reforming a hydrocarbon-based raw material with as little oxygen as possible. The challenge to say. SOLUTION: A detector 1 for detecting carbon monoxide in a reformed gas obtained by reforming a hydrocarbon-based raw material, an oxidation reactor 2 filled with an oxidation catalyst 3, and introduced into the oxidation catalyst 3 together with the reformed gas. An electronic control unit 6 and a flow rate regulator 7 for temporally changing the ratio of oxygen to be generated and carbon monoxide in the reformed gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be used to selectively oxidize and remove, for example, carbon monoxide (CO), in particular, trace amounts of CO in a reformed gas that poisons the anode of a fuel cell. And a method for removing carbon monoxide.

[0002]

2. Description of the Related Art Conventionally, polymer electrolyte fuel cells (hereinafter referred to as PE
Expressed by FC. As the fuel in (1), city gas or reformed gas obtained by steam reforming methanol is usually used. This reformed gas is, of course, a hydrogen-rich mixed gas. However, the fuel electrode of PEFC is usually
Since a platinum catalyst is used, there has been a problem that the platinum catalyst is poisoned by a trace amount of CO contained in the reformed gas, and the battery performance is greatly deteriorated.

Therefore, conventionally, as a method for removing CO in a reformed gas, a hydrogen separation method using a Pd thin film or the like has been known. This is a method in which a constant pressure is applied to one side of a hydrogen separation membrane to selectively permeate only hydrogen. When this method is used, gas other than hydrogen does not permeate, so that only pure hydrogen is obtained, and can be used as a fuel for PEFC. This method has been put to practical use in semiconductor manufacturing plants and the like, and has been partially developed for PEFC.

[0004] As another method for reducing the CO concentration in the reformed gas, there is CO conversion. In this method, a reformed gas obtained by steam reforming methanol or city gas is subjected to a CO shift reaction (CO + H ₂ O → CO ₂ + H) using a CO shift catalyst.
₂ ) to reduce the CO concentration in the gas to 0.4 to 1.5%. If CO can be reduced to this extent,
A phosphoric acid fuel cell (hereinafter referred to as PA) using the same Pt electrode catalyst
Expressed by FC. ) Can be used as fuel.

However, in order to prevent the poisoning of the platinum catalyst at the fuel electrode of the PEFC, the operating temperature of the PEFC (room temperature to 100 ° C.) is lower than the operating temperature of the PAFC (about 170 ° C.). It is necessary to reach at least several tens of ppm level.
Is not enough to be used as a fuel gas for fuels.

[0006] Therefore, oxygen (air) is introduced into the gas after CO conversion, and at 200 to 300 ° C using an oxidizing catalyst, C is introduced.
Development to oxidize and remove O is underway. For this oxidation catalyst, studies have been made to use an alumina catalyst or the like carrying a noble metal, but a large amount of CO in a large amount of hydrogen is removed.
It is very difficult to selectively oxidize completely. Usually, oxidation is performed by introducing an oxygen amount larger than the stoichiometric ratio.

[0007]

The above-mentioned method using a metal hydride film such as the above-mentioned conventional Pd film is most suitable as a fuel for PEFC because high-purity hydrogen can be obtained. However, since an extremely expensive Pd film is used, there is a problem that the cost increases. In addition, since a structure for obtaining hydrogen by a pressure difference is basically required, there is also a problem that the structure of the apparatus becomes complicated.

On the other hand, there is a problem that the CO concentration cannot be sufficiently reduced to the extent that it can be used as a fuel for PEFC even if the above-mentioned conventional CO conversion is used.

On the other hand, the conventional CO oxidation removal can be made relatively simple in structure, and may be inexpensive as compared with the method using a hydrogen separation membrane. However, in the above-described oxidation removal method which has been conventionally studied,
Much more oxygen must be introduced than the stoichiometric ratio,
At this time, the amount of hydrogen that is simultaneously oxidized becomes very large, and there is a problem that the efficiency is reduced. Therefore, in order to remove CO by oxidation, it has been desired to realize a high-performance carbon monoxide removal method capable of selectively oxidizing a trace amount of CO contained in a large amount of hydrogen with a minimum amount of oxygen. .

The present invention has been made in consideration of such problems of the conventional carbon monoxide removal method, and can reduce the amount of oxygen necessary for removing or reducing carbon monoxide contained in a gas. An object of the present invention is to provide a method for removing carbon oxide and a device for removing carbon monoxide.

[0011]

According to the present invention, when removing or reducing carbon monoxide contained in a gas, the amount of oxygen introduced into the oxidation catalyst together with the gas is determined. This is a carbon monoxide removal method in which the ratio to the amount of carbon monoxide in a gas is temporally or spatially changed.

According to a second aspect of the present invention, there is provided a method for removing carbon monoxide, wherein the gas is a reformed gas obtained by reforming a hydrocarbon-based raw material.

According to a third aspect of the present invention, a detector for detecting carbon monoxide contained in a gas, an oxidation reactor filled with an oxidation catalyst, and a detection result of the detector are used.
A carbon monoxide removing apparatus comprising: a changing unit that changes a ratio of an amount of oxygen introduced into the oxidation catalyst together with the gas to an amount of carbon monoxide in the gas with time or space.

According to a fourth aspect of the present invention, there is provided the carbon monoxide removing apparatus, wherein the gas is a reformed gas obtained by reforming a hydrocarbon-based raw material.

According to a fifth aspect of the present invention, the oxidation catalyst temperature of the oxidation catalyst when the reformed gas passes is from 20 ° C. to 20 ° C.
It is a carbon monoxide removing device at 200 ° C.

According to a sixth aspect of the present invention, there is provided the above-mentioned oxidation catalyst, wherein the at least one metal selected from the group consisting of Pt, Pd, Ru, Au, Rh and Ir is supported.
It is a carbon monoxide removal device that is a type zeolite.

With the above configuration, for example, the same amount of carbon monoxide is removed by changing the ratio of the required amount of oxygen to the amount of carbon monoxide in the reformed gas temporally or spatially. The amount of oxygen required for this is reduced compared to the prior art. Also,
The amount of hydrogen oxidized simultaneously with CO can be reduced, and the efficiency can be increased.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows a configuration diagram of a carbon monoxide removing apparatus according to an embodiment of the present invention.

Referring to FIG. 1, the configuration and operation of this embodiment will be described together. An embodiment of the method for removing carbon monoxide of the present invention will be described at the same time.

As shown in FIG. 1, the CO detector 1 is a detector for detecting the amount of carbon monoxide contained in the reformed gas described later. The stainless steel container 2 is an oxidation reactor filled with an oxidation catalyst 3. The flow regulator 7 is a means for temporally changing the ratio between the amount of oxygen introduced into the oxidation catalyst 3 together with the reformed gas and the amount of carbon monoxide in the reformed gas.
The electronic control unit 6 is a means for controlling the operation of the flow regulator 7. Incidentally, the changing means of the present invention includes the electronic control unit 6 and the flow rate regulator 7.

That is, the reformed gas after reforming the city gas and converting it into CO passes through the CO detector 1 and is introduced into the oxidation catalyst 3 filled in the stainless steel vessel 2. As the oxidation catalyst 3, a Pt-supported alumina catalyst was used.
The value (flow rate / catalyst volume) was 5000 h ⁻¹ , and the reformed gas was introduced. A heater 5 is provided outside the stainless steel container 2.
The temperature is detected by a thermocouple 4 installed in the oxidation catalyst, and the operating temperature can be adjusted based on the temperature. The container 2 made of stainless steel has a double-pipe structure, in which air is supplied from a fan to the outside, and when the oxidation temperature rises, the container 2 is cooled to control the temperature. The output signal from the CO detector is input to the electronic control unit 6. Here, a signal obtained by giving an amplitude of 0.2 and a frequency of 2 Hz with respect to a predetermined O ₂ / CO ratio is output to the flow regulator 7, the air is adjusted to a predetermined flow, and introduced into the oxidation catalyst 3. I do.

Here, for a given O ₂ / CO ratio, 0.1.
When an amplitude of 2 and a vibration of a frequency of 2 Hz are given, for example,
In O ₂ /CO=1.0, Given the vibration, O ₂
The value of / CO fluctuates ± 20% around 1.0.

That is, in this case, the value of O ₂ / CO is 0.
With a width of 8 to 1.2, a periodic vibration change at a frequency of 2 Hz is performed. Therefore, in the case of this example, the average value of the O ₂ / CO ratio coincides with the center value of the vibration, and is obviously 1.0.

In this way, the O ₂ / CO ratio was oscillated by changing the amount of O ₂ in the air. The gas composition in the processing gas after passing through the carbon monoxide removing device was measured by gas chromatography, and the CO conversion was calculated.

Next, more specific experiments will be described with reference to FIGS. 2 and 3.

First, the oxidation temperature of the oxidation catalyst 3 is set to 1
An experiment was performed in which the O ₂ / CO ratio introduced at 50 ° C. was changed by the flow rate regulator 7 described above, and the CO removal characteristics were examined.

On the other hand, in addition to the above-described experiment, a case where the above-described vibration change was not performed, that is, an experiment using the same method as the conventional method was performed as a comparative example. FIG. 2 shows a case where the vibration is changed (in FIG. 2, the solid line is shown as Experimental Example 1) and a case where the vibration is not changed (in FIG. 2, the dotted line is shown as Comparative Example 1). FIG. 2 is a diagram showing the relationship between the O ₂ / CO ratio and the CO conversion (%).

That is, as shown in FIG. 2, in the case of Comparative Example 1 in which the vibration is not changed, the CO conversion extremely decreases when the O ₂ / CO ratio becomes 1.5 or less. In the case of Experimental Example 1 in which the vibration is changed at each O ₂ / CO ratio of
Even at a stoichiometric ratio of O ₂ / CO ratio of 0.5, CO conversion is 80%
Was found. Thus, when the O ₂ / CO ratio is changed by vibration, the amount of oxygen to be introduced can be reduced as compared with Comparative Example 1, and the amount of hydrogen that is oxidized and consumed simultaneously with CO is also minimized. be able to. This also increases overall efficiency.

Next, the Pt-supported alumina catalyst as the oxidation catalyst 3 was replaced with Pt-supported K / A type zeolite,
In the same manner as described above, Experimental Example 2 and Comparative Example 2 were performed, and the CO oxidation removal characteristics were examined.

FIG. 3 shows an experimental example 2 in which the above-mentioned vibration change was performed.
FIG. 7 is a diagram showing a relationship between an O ₂ / CO ratio and a CO conversion rate in Comparative Example 2 in which vibration is not changed. The oxidation temperature,
The conditions such as the SV value are the same as those described with reference to FIG.
That is, as shown in FIG. 3, in the case of Comparative Example 2, as in the case of the Pt / alumina catalyst, C decreases as the O ₂ / CO ratio decreases.
It was found that the O conversion was reduced.

However, each O ₂ / C of the present embodiment is
In Experimental Example 2 in which the vibration was changed by the O ratio, it was found that even when the O ₂ / CO ratio was 0.5, the CO conversion was 90% or more.

Therefore, from the experimental examples 1 and 2 and the comparative examples 1 and 2, when the O ₂ / CO ratio was changed by vibration, the use of the Pt-supported K / A type zeolite catalyst was
It was found that the t / alumina catalyst exhibited even higher CO conversion.

In the above, the value of the O ₂ / CO ratio is set to about 1.5 to
When the value of the O ₂ / CO ratio is changed to various values between about 1.5 and 2.0, and when the value is changed to various values between 2.0 and A comparison was made with the case where the value was changed by vibration centering on the value of the ratio. In both cases, the oxidation temperature of the oxidation catalyst 3 was fixed at 150 ° C.

Next, separately from this, the oxidation temperature of each oxidation catalyst 3 in Experimental Example 2 and Comparative Example 2 was set to 25 to 200.
Experiments 3 and Comparative Example 3 were conducted on the CO removal characteristics at each temperature when the temperature was changed to ° C. Note that, here, unlike the experimental example 2 and the comparative example 2, the O ₂ / CO ratio was set to 0.5. In the case of Experimental Example 3, it goes without saying that the O ₂ / CO ratio was subjected to the same vibration change as described above with the center value being 0.5. This result is shown in Table 1.
Shown in

[0035]

[Table 1]

As shown in (Table 1), the CO conversion was higher in Experimental Example 3 than in Comparative Example 3 regardless of the oxidation temperature.

Next, as Experimental Example 4 and Comparative Example 4, O ₂
With the / CO ratio set to 0.5 and the oxidation temperature set to 150 ° C., the oxidation catalyst 3 was divided into six types as shown below, including the Pt-supported K / A type zeolite catalyst, and the CO removal characteristics were examined for each catalyst. Was. In other words, the six types of oxidation catalysts are prepared by selecting the metals supported on the zeolite from the six types of metals, Pt, Pd, Ru, Au, Rh, and Ir, one at a time. The results are shown in (Table 2). Table 2 shows, as an example in which a Pt / alumina catalyst was used as the oxidation catalyst 3, the CO ₂ obtained when the O ₂ / CO ratio was 0.5 obtained in Comparative Example 1 and Experimental Example 1 described above. The conversion (40%, 80%) is shown in the upper and lower columns on the right end.

[0038]

[Table 2]

That is, as can be seen from Table 2, Experimental Example 4
In each case of Comparative Example 4 and Comparative Example 4, a higher CO conversion rate is shown as compared with the case where the Pt / alumina catalyst is used as the oxidation catalyst 3. In addition, compared to the case where neither changes the vibration,
The CO conversion was higher when the vibration was changed.

From these results, it is possible to oxidize and remove the same amount of CO with a smaller amount of oxygen than in the prior art by using the method of the present invention in which the O ₂ / CO ratio is changed by oscillating with time. A simple CO removal device can be configured.

The oxidation catalyst may be any catalyst to which the present invention can be applied, in addition to the Pt / alumina catalyst used in the present embodiment and various metal-supported K / A-type zeolites.

The method of changing the O ₂ / CO ratio is not limited to the amplitude and frequency shown in the present embodiment, but may be any method as long as it can be changed with time. I do not care.

Further, the apparatus for removing carbon monoxide is also constructed,
The shape and the like are not limited to this embodiment, and any shape can be used as long as the O ₂ / CO ratio can be temporally changed. (Embodiment 2) Next, FIG. 4 shows a configuration diagram of a carbon monoxide removing apparatus according to a second embodiment of the present invention.

Referring to FIG. 4, the configuration and operation of this embodiment will be described together. The operation of another embodiment of the method for removing carbon monoxide of the present invention will be described at the same time.

As shown in the figure, the city gas is reformed and
After the reformed gas passes through the CO detector 1,
It is introduced into the oxidation catalyst 3 filled in a stainless steel container 2. As the oxidation catalyst 3, as in the first embodiment, P
Using a t-supported alumina catalyst, a reformed gas was introduced at an SV value of 5000 h ^-1 . A heater 5 is arranged outside the stainless steel vessel 2, and the temperature is detected by a thermocouple 4 installed in the oxidation catalyst, and the operating temperature can be adjusted based on the temperature. The container 2 made of stainless steel has a double-pipe structure, in which air is supplied from a fan to the outside, and when the oxidation temperature rises, the container 2 is cooled to control the temperature. The output signal from the CO detector is input to the electronic control unit 6. Here, the predetermined O ₂ / C
Calculate the O ratio and output signals to the flow controllers 7a to 7e,
The air is adjusted to a predetermined flow rate and introduced into the oxidation catalyst 3.
Here, the air is changed every 7 seconds from 7a to 7b to 7c.
The configuration is such that the introduction position is switched like 7d → 7e. However, temporally, the O ₂ amount in the air and the O ₂ / CO ratio in the reformed gas are set to be the same. The gas composition in the processing gas after passing through the carbon monoxide removing device configured as described above is measured by gas chromatography in the same manner as in the first embodiment, and the CO conversion is calculated to obtain C
The removal characteristics were examined.

Next, more specific experiments will be described with reference to FIGS. 5 and 6.

First, the oxidation temperature of the oxidation catalyst 3 is set to 1
At 50 ° C., CO removal characteristics were examined using the carbon monoxide removal apparatus shown in FIG. 4 (Experimental Example 5).

On the other hand, as Comparative Example 5, a different structure, that is, a carbon monoxide removing device (not shown) having only one air introduction point was used, and the other conditions were the same. The removal characteristics were investigated. FIG. 5 is a diagram showing the relationship between the O ₂ / CO ratio and the CO conversion based on both results.

That is, as shown in FIG. 5, when the air introduction point is one as in the conventional case (Comparative Example 5), when the O ₂ / CO ratio becomes 1.5 or less, the CO conversion rate becomes extremely high. On the other hand, when the number of introduction points is five (Experimental Example 5) as in the present embodiment, the CO conversion is 85 even if the O ₂ / CO ratio is 0.5 at the stoichiometric ratio. %. In this case, the amount of oxygen introduced to remove the same amount of CO is smaller in the case where the number of air introduction points is plural and the amount of oxygen is spatially changed, compared to the case where such a configuration is not used. can do. Further, the amount of hydrogen that is oxidized and consumed simultaneously with CO can be minimized. This also increases overall efficiency.

Next, the Pt-supported alumina catalyst as the oxidation catalyst 3 was replaced with a Pt-supported K / A type zeolite.
The other conditions were the same as above, and the experimental example 6 and the comparative example 6 were performed, and the CO oxidation removal characteristics were examined.

FIG. 6 is a diagram showing the relationship between the O ₂ / CO ratio and the CO conversion for Experimental Example 6 and Comparative Example 6. The conditions such as the oxidation temperature and the SV value are set the same as in the case described with reference to FIG.

That is, as shown in FIG.
In two places (Comparative Example 6), as in the case where the Pt / alumina catalyst was used, as the O ₂ / CO ratio became smaller, C
It was found that the O conversion was reduced. However, when the amount of oxygen is spatially changed at each O ₂ / CO ratio according to the present embodiment (Experimental Example 6), even if the O ₂ / CO ratio is 0.5, the CO conversion rate is 90% or more. I understood. From this, when the Pt-supported K / A type zeolite catalyst was used, P
It was found that the t / alumina catalyst exhibited a higher CO conversion than the case where the t / alumina catalyst was used.

Further, the CO removal characteristics when the O ₂ / CO ratio was set to 1.0 and the oxidation temperature was changed were also examined.
In each case, the CO conversion was higher than in the case where the introduction point was one.

From these results, by using the method of spatially changing the O ₂ / CO ratio of the present invention, the same amount of CO can be oxidized and removed with a smaller amount of oxygen than in the prior art, and high efficiency can be achieved. A carbon monoxide removing device can be configured. Also,
At the same time, the amount of hydrogen consumed by oxidation can be reduced, so that a carbon monoxide removing device with higher efficiency than before can be provided.

The oxidation catalyst is a Pt / alumina catalyst used in the present embodiment, a Pt-supported K / A type zeolite, or a K / A type catalyst supporting a metal such as Pd, Ru, Au, Rh, and Ir. Zeolites can also be used.

In addition, any other materials may be used as long as the present invention can be applied.

The air introduction method is not limited to this embodiment, and any method can be used as long as the O ₂ / CO ratio can be changed spatially.

[0058] The configuration also carbon monoxide oxidizer is not limited to the shape or the like the present embodiment, O ₂ / C
Anything can be used as long as the O ratio can be changed spatially.

Further, the gas of the present invention is the same as that of the above embodiment,
The reformed gas is not limited to the reformed gas obtained by reforming city gas, but may be, for example, a reformed gas obtained by steam reforming methanol.

Further, the gas of the present invention is the same as that of the above embodiment,
The mixed gas is not limited to the reformed gas obtained by reforming the city gas, and may be, for example, another type of mixed gas including carbon monoxide.

[0061]

As is apparent from the above description, the present invention has an advantage that the amount of oxygen required for removing or reducing carbon monoxide contained in a gas can be made smaller than before.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a carbon monoxide removing device used in a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the CO conversion rate and the O ₂ / CO ratio of the apparatus.

FIG. 3 is a diagram showing the relationship between the CO conversion and the O ₂ / CO ratio of the apparatus.

FIG. 4 is a longitudinal sectional view showing a configuration of a carbon monoxide removing device used in a second embodiment of the present invention.

FIG. 5 is a view showing the relationship between the CO conversion rate and the O ₂ / CO ratio of the apparatus.

FIG. 6 is a view showing the relationship between the CO conversion rate and the O ₂ / CO ratio of the apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CO detector 2 Stainless steel container 3 Oxidation catalyst 4 Thermocouple 5 Heater 6 Electronic control unit 7, 7a-7e Flow controller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Gamo 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] When removing or reducing carbon monoxide contained in a gas, the ratio of the amount of oxygen introduced into the oxidation catalyst together with the gas to the amount of the carbon monoxide in the gas is determined. A method for removing carbon monoxide, wherein the method is changed temporally or spatially. 2. The method according to claim 1, wherein the gas is a reformed gas obtained by reforming a hydrocarbon-based raw material. 3. A detector for detecting carbon monoxide contained in a gas, an oxidation reactor filled with an oxidation catalyst, and using the detection result of the detector to apply the gas to the oxidation catalyst together with the gas. A carbon monoxide removing device, comprising: changing means for temporally or spatially changing a ratio between an amount of oxygen introduced and an amount of carbon monoxide in the gas. 4. The carbon monoxide removing apparatus according to claim 3, wherein the gas is a reformed gas obtained by reforming a hydrocarbon-based raw material. 5. The carbon monoxide removing apparatus according to claim 4, wherein the oxidation catalyst temperature of the oxidation catalyst when the reformed gas passes is 20 ° C. to 200 ° C. 6. The oxidation catalyst comprises Pt, Pd, Ru, A
The carbon monoxide removal device according to claim 3, wherein the A-type zeolite supports at least one metal among a plurality of types of metals, u, Rh, and Ir.