JP7117867B2 - Methane removal system and methane removal method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a methane removal system and a methane removal method for removing methane in a gas to be treated containing methane.

As catalysts for removing hydrocarbons by oxidation, catalysts supporting platinum group metals such as platinum and palladium are known to exhibit high performance. However, even if such a catalyst is used, when the main component of the hydrocarbons contained is methane, such as in methane fermentation gas and combustion exhaust gas of natural gas, methane has high chemical stability. , the problem is that sufficient methane removal is not achieved.

In recent years, the problem of global warming has come to be strongly recognized, and the fact that a large amount of gas containing dilute methane (about 0.1 to 1%) such as coal mine ventilation gas is diffused is regarded as a problem. , and its economic treatment is also an issue. In removing methane, a highly active methane treatment system capable of treating at the lowest possible temperature is required.

A method for treating unburned methane described in Patent Document 1 has been proposed as a solution to such problems. The treatment method described in Patent Document 1 is a method for treating methane remaining in the mixed gas, and includes a step of introducing a mixed gas containing methane into a plasma reactor, generating plasma in the plasma reactor, and a plasma reaction. A step of introducing the mixed gas introduced into the vessel into the catalyst device is performed.

According to the treatment method described in Patent Document 1, by combining plasma and catalytic oxidation, the mixed gas containing unburned methane is not heated to the activation temperature of the catalyst or higher for purification. Gas can be purified.

JP 2008-168284 A

As described above, according to the method for treating unburned methane described in Patent Document 1, even when the temperature of the gas to be treated is lower than the activation temperature of the catalyst, the combined use of plasma and catalytic oxidation results in unburned methane. Methane removal rate can be increased.

However, since plasma is used to remove unburned methane, a large amount of power must be supplied to generate plasma, and there is a problem that power consumption cannot be suppressed.

Therefore, the inventors of the present application conducted intensive research on a method for efficiently removing unburned methane while suppressing the power input, and as a result, by applying a voltage and a weak current to the catalyst for removing methane, the plasma and the catalyst are separated. We have found new knowledge that unburned methane can be efficiently removed while reducing power input compared to the case of using both.

The present invention has been made based on the above findings, and it is an object of the present invention to provide a methane removal system and a methane removal method capable of efficiently removing methane from a gas to be treated containing methane while suppressing power input. and

A characteristic configuration of a methane removal system according to the present invention for achieving the above object is a methane removal system for removing methane in a gas to be treated containing methane,
a methane removal catalyst that has the electrical conductivity of a semiconductor region and removes the methane in the gas to be treated;
electric field applying means for applying a voltage of 0.1 to 2 kV and a current of 1 to 15 mA to the methane removal catalyst so that the input power is 0.1 to 10 W ;
and a control means for controlling the operation of the electric field applying means,
The methane removal catalyst is characterized in that at least one of Pt, Pd and Rh is supported on cerium oxide as a carrier .

Further, a methane removal method according to the present invention for achieving the above object is characterized in that the methane removal method removes methane from a gas to be treated containing methane,
An electric field applying means applies a voltage of 0.1 to 2 kV and a current of 1 to 15 mA so that the input power is 0.1 to 10 W to the methane removal catalyst having electrical conductivity in the semiconductor region. Performing a process to remove the methane in the process gas,
The methane removal catalyst is characterized in that at least one of Pt, Pd and Rh is supported on cerium oxide as a carrier .

According to the above two characteristic configurations, the catalyst having electrical conductivity in the semiconductor region is used as the methane removal catalyst, and the power applied to the methane removal catalyst is 0.1 to 2 kV so that the power is 0.1 to 10 W. and a current of 1 to 15 mA activates the methane removal catalyst and the molecules in the gas to be treated that are in contact with it, and the methane contained in the gas to be treated is efficiently removed by the methane removal catalyst. be. In addition, since a voltage of 0.1 to 2 kV and a current of 1 to 15 mA are applied so that the input power is 0.1 to 10 W, the input power can be suppressed compared to the case of using plasma. can be done.
In addition, since the methane removal catalyst is obtained by supporting at least one of Pt, Pd, and Rh on cerium oxide as a carrier, the methane removal catalyst sufficiently exhibits the methane removal ability. ing.

The case where the input power can be suppressed as compared with the case of using plasma is, specifically, the case of applying a voltage that does not generate the discharge necessary for plasma generation.

That is, a further characteristic configuration of the methane removal system according to the present invention is that the electric field applying means applies a voltage lower than the minimum discharge forming voltage.

A further characteristic configuration of the methane removal system according to the present invention is that the voltage and current are applied while the electric field applying means is in direct contact with the methane removal catalyst.

When the electric field applying means and the methane removal catalyst are not in contact with each other, that is, when a gap is formed between them, the voltage and current are applied by the electric field applying means due to the spatial resistance of the gap. Since the resistance at the time increases, it becomes necessary to supply more power than necessary.

However, according to this characteristic configuration, the electric field applying means is in direct contact with the methane removal catalyst, and no gap is formed between the two. Electricity can be saved.

A further characteristic configuration of the methane removal system according to the present invention is that the gas to be treated contains oxygen, and the methane in the gas to be treated is removed in an oxidizing atmosphere.

For example, the gas discharged from HCCI engines and gas engines that use natural gas as fuel contains oxygen in addition to unburned methane. Methane is removed under an oxidizing atmosphere.

By the way, since a general methane removal catalyst has an activation temperature of 400° C. or higher, in order to remove methane in the gas to be treated, the methane removal catalyst must be exposed to the gas to be treated of 400° C. or higher. , it is necessary to raise the temperature to a temperature equal to or higher than the activation temperature.

However, according to the knowledge obtained by the inventors of the present application through research, when a voltage and a weak current are applied to the methane removal catalyst, methane is efficiently removed even if the temperature of the methane removal catalyst is below the activation temperature. .

Therefore, a further characteristic configuration of the methane removal system according to the present invention is that the temperature of the gas to be treated is room temperature or higher.

A further characteristic configuration of the methane removal system according to the present invention is that the temperature of the gas to be treated is in the range of room temperature to 300°C.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structural example of the methane removal system which concerns on 1st Embodiment. 4 is a graph showing the relationship between the temperature of the catalyst layer and the conversion rate of methane.

Hereinafter, with reference to the drawings, the methane removal system according to one embodiment is applied to combustion exhaust gas such as methane fermentation gas and natural gas city gas, gas containing methane such as coal mine ventilation gas and various process gases (to be treated). An example of a gas) will be described using an embodiment used for removing methane in the gas.

[Methane removal system]
FIG. 1 is a schematic configuration diagram of a methane removal system according to one embodiment. As shown in the figure, the methane removal system 1 is housed in layers in a gas channel 7 for discharging gas Eg from a gas source 10, and flows through the gas channel 7. A methane removal catalyst 2 for removing methane in the gas Eg to be treated, an electric field application means 3 for applying a voltage and a weak current to the methane removal catalyst 2, and a control means 6 for controlling the operation. .

[Catalyst for removing methane]
The methane removal catalyst 2 preferably uses an oxide catalyst, more preferably Pt on a carrier made of at least one selected from the group consisting of cerium oxide, zirconia oxide, and cerium-zirconium solid solution oxide. , Pd, and Rh are used. In addition, the carrier and the active metal are not limited to the above, but when an insulating material is used as the carrier, dielectric breakdown occurs when a voltage and a weak current are applied, spark discharge occurs, and the gas to be treated Since the removal of methane in Eg cannot be adequately performed, it is necessary to use a material with electrical conductivity in the semiconducting region as the carrier. In addition, the methane removal catalyst 2 may contain additive components that are additionally added.

[Electric field applying means]
The electric field applying means 3 is a pair of electric field applying means 3 which are arranged in direct contact with the surface of the catalyst layer 2a at positions opposed to each other with the layer of the catalyst 2 for removing methane (hereinafter also referred to as "catalyst layer 2a") interposed therebetween. It comprises electrodes 4a, 4b and a power source 5 connected to the electrodes 4a, 4b by electrical wiring. That is, the electric field applying means 3 is a means for applying an electric field to the methane removal catalyst 2 by applying a predetermined current to the catalyst layer 2a and applying a predetermined voltage to the catalyst layer 2a.

[Control means]
The control means 6 controls the strength of the current and the magnitude of the voltage applied by the electric field applying means 3 so that the power to be applied (input power) becomes a predetermined power. In the methane removal system 1 of the present embodiment, the control means 6 controls the operation of the electric field application means 3 so as to apply a voltage lower than the discharge formation minimum voltage. It is preferable to control the operation of the electric field applying means 3 by the control means 6 so that the voltage is 15 mA or 0.1 to 2 kV and the input power is 0.1 to 10 W. If the input power is within the above range, the input power is greatly reduced compared to the case of plasma generation.

The removal of methane in the methane-containing gas to be treated Eg by the methane removal system 1 having the above configuration is performed as follows.

The electric field applying means 3 applies a current of a predetermined strength to the layer of the methane removal catalyst 2 and a voltage of a predetermined magnitude. As a result, the methane removal catalyst 2 is activated by electrical action. As described above, in the methane removal system 1 of the present embodiment, the carrier of the methane removal catalyst 2 is made of a material having electrical conductivity in the semiconductor region. Application of voltage and weak current to the removal catalyst 2 is performed appropriately.

When the gas to be treated Eg introduced from the gas to be treated discharge source 10 into the gas path 7 to be treated contacts the methane removal catalyst 2, unburned methane contained therein is removed by the methane removal catalyst 2. It is catalytically oxidized and converted to carbon dioxide. Since the gas to be treated Eg from the gas to be treated emission source 10 contains not only unburned methane but also oxygen, the catalytic oxidation of unburned methane by the methane removal catalyst 2 is performed in an oxidizing atmosphere.

Here, in the methane removal system 1 of this embodiment, as described above, the methane removal catalyst 2 is activated by applying a voltage and a weak current to the methane removal catalyst 2 . Generally, the activation temperature of the methane removal catalyst 2 is 400° C. or higher, but since the methane removal catalyst 2 is activated, the temperature of the catalyst layer 2a is lower than the activation temperature (from room temperature to about 300° C.). range), the unburned methane can be efficiently converted into carbon dioxide by the methane removal catalyst 2 .

Furthermore, when the temperature of the gas to be treated Eg is low, the temperature of the catalyst layer 2a cannot be sufficiently raised only by contact with the gas to be treated Eg, and the removal rate of unburned methane may be extremely lowered. . However, in the methane removal system 1 of the present embodiment, by applying an electric field to the methane removal catalyst 2, the methane removal ability of the methane removal catalyst 2 is improved even when the temperature of the gas to be treated Eg is low. can be reduced and the unburned methane removal rate can be maintained. Further, even in the case of auxiliary heating of the catalyst layer 2a using an electric heater or the like, the methane removal ability can be improved by applying a voltage and a weak current. can also be suppressed.

As described above, according to the methane removal system 1 according to the present embodiment, the methane removal catalyst 2 is activated by applying a voltage and a weak current to the methane removal catalyst 2 . Therefore, in a state in which the temperature of the catalyst layer 2a is lower than the activation temperature of the methane removal catalyst 2, the methane removal catalyst 2 efficiently converts unburned methane into carbon dioxide, thereby removing methane in the gas to be treated Eg. can do.

Furthermore, according to the methane removal system 1, by applying voltage and weak current, the methane removal ability of the methane removal catalyst 2 can be improved, and the removal rate of unburned methane can be maintained. Further, even when the catalyst layer 2a is supplementarily heated by using an electric heater or the like, it is possible to reduce the electric power supplied to the electric heater or the like.

The effects of the present invention will be shown below with specific experimental examples.

As the methane removal catalyst, a carrier made of cerium oxide (CeO ₂ ) on which platinum (Pt) as an active metal is supported so that the weight percentage is 1% by weight is used, and this methane removal catalyst is used. 200 mg is filled in the flow channel so that the layer height is 4 mm, and nitrogen is the main component, the methane concentration is 3000 ppm, and the oxygen concentration is 8%. It was introduced into the channel so as to be 50,000 h ⁻¹ and the methane conversion rate was calculated.

In the examples, an electrode was brought into contact with the surface of the catalyst layer to form an electric field with an input power of 4 W (current: 5 mA, voltage: 0.8 kV). In Example 1, an electric field was formed without using an electric heater, in Example 2, an electric field was formed in a state where the temperature of the catalyst layer was stabilized at 100 ° C. by an electric heater, and in Example 3, An electric field was formed while the temperature of the catalyst layer was stabilized at 200° C. by an electric heater. On the other hand, in the comparative examples, the temperature was about 300° C. (Comparative Example 1), 330° C. (Comparative Example 2), 350° C. (Comparative Example 3), and 380° C. (Comparative Example 4) without applying an electric field to the catalyst layer. , 400° C. (Comparative Example 5).

Experimental results are shown in Table 1 below. The "methane conversion rate" in Table 1 is a value calculated based on the amount of methane input and discharged. Moreover, FIG. 2 is a graph showing the relationship between the temperature of the catalyst layer and the methane conversion rate calculated based on the amount of input and output of methane.

As shown in Table 1 and FIG. 2, in Comparative Examples 1-5, the temperatures of the catalyst layers were 311° C., 333° C., 352° C., 381° C. and 405° C., respectively, and the methane conversion rates were 7.8% and 12° C. .5%, 17.9%, 30.6% and 40.4%. From these results, when no electric field is applied to the methane removal catalyst, catalytic oxidation of methane by the methane removal catalyst is sufficient when the temperature of the catalyst layer is lower than the activation temperature (about 400°C) of the methane removal catalyst. It can be seen that the temperature of the catalyst layer must be raised to 400° C. or higher in order to prevent the occurrence of methane inversion and increase the methane conversion rate to 40% or higher.

In contrast, in Examples 1-3, the methane conversion rate exceeded 40% regardless of the temperature of the catalyst layer. As described above, when no electric field is applied, the catalyst layer needs to be heated to 400° C. or higher in order to achieve a methane conversion rate of 40% or higher, whereas when an electric field is applied, the catalyst layer Even in Example 1 in which the temperature is 239° C., the methane conversion rate is 48.6, and it can be seen that high activity is exhibited even at a low temperature by applying an electric field. In Comparative Example 2, the temperature of the catalyst layer was 352° C. and the methane conversion rate was 17.9%. shows an extremely high value of 77.5%, which indicates that the application of an electric field results in a higher methane conversion rate even at the same temperature of the catalyst layer.

In addition, it was confirmed that the methane conversion rate calculated based on the amount of methane input and emitted was approximately the same as the methane conversion rate calculated based on the amount of carbon dioxide emitted. It was also found that most of the oxidized methane was converted to carbon dioxide.

[Another embodiment]
[1]
In the above embodiment, the configuration of the methane removal system 1 has been described with a specific example, but the configuration can be changed as appropriate. For example, the electrodes 4a and 4b are brought into direct contact with the surface of the catalyst layer 2a, but the present invention is not limited to this. For example, there may be a gap between the surface of the catalyst layer 2a and the electrodes 4a and 4b. From the viewpoint of minimizing the input power, it is preferable to bring the electrodes 4a and 4b into contact with the surface of the catalyst layer 2a.

[2]
In the above embodiment, the methane is removed from the gas to be treated Eg containing methane and oxygen. However, the present invention is not limited to this. It is also possible to remove methane in the gas to be treated.

[3]
In the above embodiment, when the temperature of the gas to be treated is low and the temperature of the catalyst layer 2a is only lower than the activation temperature (in the range of room temperature to about 300° C.), unburned methane is converted to carbon dioxide. However, according to the methane removal system of the present invention, when the temperature of the gas to be treated is high and the temperature of the catalyst layer 2a rises to a temperature equal to or higher than the activation temperature, that is, the temperature of the gas to be treated is activated. Above temperature, of course, unburned methane can be converted to carbon dioxide.

It should be noted that the configurations disclosed in the above embodiments (including other embodiments, the same shall apply hereinafter) can be applied in combination with configurations disclosed in other embodiments as long as there is no contradiction. The embodiments disclosed in this specification are exemplifications, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be used for a methane removal system and a methane removal method capable of efficiently removing methane from a gas to be treated containing methane while suppressing input power.

Reference Signs List 1 methane removal system 2 methane removal catalyst 3 electric field applying means 4a, 4b electrode 5 power supply 6 control means 7 gas passage 10 gas discharge source Eg gas to be treated

Claims (7)

A methane removal system for removing methane in a gas to be treated containing methane,
a methane removal catalyst that has the electrical conductivity of a semiconductor region and removes the methane in the gas to be treated;
electric field applying means for applying a voltage of 0.1 to 2 kV and a current of 1 to 15 mA to the methane removal catalyst so that the input power is 0.1 to 10 W ;
and a control means for controlling the operation of the electric field applying means,
The methane removal system, wherein the methane removal catalyst comprises at least one of Pt, Pd, and Rh supported on cerium oxide as a carrier . 2. The methane removal system according to claim 1, wherein said electric field applying means applies a voltage less than a minimum discharge forming voltage. 3. The methane removal system according to claim 1, wherein said electric field applying means applies said voltage and current while being in direct contact with said methane removal catalyst. The methane removal system according to any one of claims 1 to 3, wherein the gas to be treated contains oxygen, and the methane in the gas to be treated is removed under an oxidizing atmosphere. The methane removal system according to any one of claims 1 to 4 , wherein the temperature of the gas to be treated is room temperature or higher. The methane removal system according to any one of claims 1 to 4 , wherein the temperature of the gas to be treated ranges from room temperature to 300°C. A methane removal method for removing methane in a gas to be treated containing methane,
An electric field applying means applies a voltage of 0.1 to 2 kV and a current of 1 to 15 mA so that the input power is 0.1 to 10 W to the methane removal catalyst having electrical conductivity in the semiconductor region. Performing a process to remove the methane in the process gas,
The method for removing methane, wherein the catalyst for removing methane comprises at least one of Pt, Pd and Rh supported on cerium oxide as a carrier .

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