JP7843719B2 - Methanation Reaction Apparatus and Methanation Reaction Method - Google Patents

Description

This invention relates to a methanation reaction apparatus and a methanation reaction method.

Currently, there is a global surge in the commercialization and development of carbon dioxide ( _CO2 ) capture technologies from a carbon neutrality perspective. Furthermore, there is also a surge in the commercialization and development of hydrogen production technologies using electrolysis derived from renewable energy sources. The demand for methanation systems that utilize these carbon dioxide ( _CO2 ) and hydrogen ( _H2 ) to produce methane ( _CH4 ) is expected to increase in the future.

Development of methanation technology for carbon dioxide using catalysts is progressing in various places. A common challenge in this methanation technology is controlling the rapid exothermic reaction. This exothermic reaction can cause the catalyst layer to rise uncontrollably, leading to concerns about catalyst degradation and requiring high-temperature resistant materials when designing catalytic reactors (hereinafter also referred to as "reactors").

In particular, in reactors, there is a problem in that the temperature of the catalyst layer rises sharply due to the exothermic reaction near the inlet.

To address this, one proposed solution involves alternately filling the reaction zone where a rapid temperature rise in the catalyst layer is expected with methanation catalyst and alumina balls (inert to the methanation reaction), or by mixing the catalyst and alumina balls and filling the zone with these materials. This suppresses the rate of the exothermic reaction and mitigates the rapid temperature rise in the catalyst layer (Patent Document 1).

Japanese Patent Publication No. 2003-321400

However, Patent Document 1 merely dilutes the methanation catalyst with alumina balls that do not contribute to catalytic activity. This presents problems because it makes it difficult to secure a heat dissipation outlet for the generated heat, and also requires wasted volume due to the alumina balls, making it unsuitable for miniaturizing the reactor.

Typically, to mitigate the rapid temperature rise of the catalyst layer within such a methanation reactor, a separate cooling system is often incorporated to remove reaction heat. However, this presents the problem of increasing the overall size of the methanation system.

This invention was made to solve the problems of the prior art, and its objective is to provide a methanation reactor and a methanation reaction method that can mitigate the rapid temperature rise of the catalyst layer in the methanation reactor due to the heat of reaction.

One embodiment of the present invention is a methanation reactor characterized by filling a reactor, into which a raw material gas containing carbon dioxide and hydrogen is introduced, with a mixed catalyst obtained by mixing a methanation catalyst for methane conversion of the carbon dioxide and a reverse shift catalyst (hereinafter also referred to as "reverse shift catalyst") in a predetermined ratio.

Furthermore, one embodiment of the methanation reaction method according to the present invention is characterized by a reaction step in which a mixed catalyst, obtained by mixing a methanation catalyst and a reverse shift catalyst in a predetermined ratio, is packed from the gas inlet side to the gas outlet side of the reactor, the introduced carbon dioxide is converted to methane by the methanation catalyst, and the introduced carbon dioxide is converted to carbon monoxide by a reverse shift reaction, which absorbs a portion of the heat generated by the methanation reaction.

According to the present invention, by mixing a methanation catalyst and a reverse shift catalyst in a single reaction field, a portion of the heat generated by the methanation reaction can be utilized through the endothermic reaction of the reverse shift reaction, thereby exhibiting a kind of thermal cancellation effect.

This is a schematic diagram of a methanation reactor according to the first embodiment of the present invention. This is a schematic diagram of a methanation reactor according to the first embodiment of the present invention. This is a schematic diagram of a methanation reactor according to a second embodiment of the present invention. This is a schematic diagram of a methanation reactor according to a second embodiment of the present invention. This graph shows the test results of the second embodiment of the present invention. This graph shows the test results related to the conventional technology.

The embodiments of the present invention will be described in detail below with reference to the drawings. In the embodiments described herein, the same reference numerals are used for the same components throughout.

[First Embodiment]
Figures 1(A) to 1(C) are schematic diagrams of a methanation reactor according to the first embodiment of the present invention.
As shown in Figure 1(A), the methanation reactor according to this embodiment is packed with a mixed catalyst 22 in a predetermined ratio within a reactor 11 into which a raw material gas G1 containing carbon dioxide ( _CO2 ) and hydrogen ( _H2 ) is introduced. This mixed catalyst 22 is obtained by mixing a methanation catalyst 20, which converts carbon dioxide into methane, and a reverse shift catalyst 21, which reacts by endothermically releasing some of the heat generated by the methanation reaction.
Here, the mixing ratio (volume %) of the reverse shift catalyst 21 and the methanation catalyst 20 is preferably, for example, 90:10 to 40:60.

The reactor 11 is equipped with a gas introduction pipe 12A for introducing the raw material gas G1 and a gas discharge pipe 12B for discharging the exhaust gas G2, both on the upper and lower sides.

It is preferable to introduce raw material gas G1 consisting of carbon dioxide ( _CO₂ ) and hydrogen ( _H₂ ) in a ratio of 1:4.
The reaction start temperature of reactor 11 is set to 200 to 400°C, preferably 270 to 300°C.
Carbon dioxide ( _CO₂ ) and hydrogen ( _H₂ ) introduced from the gas introduction pipe 12A are converted into methane ( _CH₄ ) and water ( _H₂O ) by the methanation catalyst 20, as shown in equation (1) below.

[Chemical formula 1]
CO ₂ +4H ₂ →CH ₄ +2H ₂ O…(1)

In this process, the reverse-shift catalyst 21 adjacent to the methanation catalyst 20 converts the introduced carbon dioxide ( _CO₂ ) and hydrogen ( _H₂ ) into carbon monoxide (CO) and water (H₂O), as shown in equation ( ₂ ) below.

[Case 2]
CO ₂ + H ₂ →CO + H ₂ O…(2)

In other words, the introduced carbon dioxide generates heat (+165.0 kJ/mol) through the methanation reaction of formula (1) on the methanation catalyst 20.
Furthermore, on the adjacent reverse-shift catalyst 21, a portion of the heat generated in the methanation catalyst 20 is absorbed (-41.2 kJ/mol), and the reverse-shift reaction proceeds as shown in equation (2) above.

Thus, if the exothermic reaction in the methanation reaction of equation (1) is thermally offset or nearly offset by the endothermic reaction in the reverse shift reaction of equation (2), the rapid temperature rise in the catalyst layer near the inlet of reactor 11, for example to 600°C or higher, will be mitigated.

Therefore, according to this embodiment, a portion of the heat generated by the methanation reaction of formula (1) is utilized in the endothermic reaction by the reverse shift reaction of formula (2), thereby exhibiting a kind of heat cancellation effect and mitigating the rapid temperature rise of the catalyst layer.

Furthermore, by mixing the methanation catalyst 20 and the reverse-shift catalyst 21 (which is produced by an endothermic reaction) within the reactor 11 of a single reaction field, a portion of the heat generated by the methanation reaction can be utilized in the endothermic reaction of the reverse-shift reaction, thereby exhibiting a kind of heat cancellation effect.

Figure 2 shows an example of a schematic diagram of a methanation reactor, but the present invention is not limited thereto. As shown in Figure 2, the methanation reactor 10A of this embodiment consists of a gas introduction pipe 12A for introducing a raw material gas G1 consisting of carbon dioxide ( _CO2 ), hydrogen ( _H2 ), and purging nitrogen ( _N2 ), a reactor 11 filled with a methanation catalyst 20 and a reverse shift catalyst 21 in a predetermined ratio, a preheater 31 for preheating the raw material gas G1 before introducing it into the reactor 11, a heater 32 for heating the inside of the reactor 11, and a gas meter 33. Pressure gauges P are also installed in various places (not all are shown). A reaction tube thermometer (not shown) for measuring the internal temperature is provided inside the reactor 11.

Here, in the present invention, a methanation catalyst refers to a catalyst that converts carbon dioxide ( _CO₂ ) and hydrogen ( _H₂ ) into methane ( _CH₄ ) and water ( _H₂O ) through a catalytic reaction, as shown in formula (1) above. A methanation catalyst can be exemplified by one in which at least one catalytically active component, such as Pt, Ru, Ni, or Pd, is supported on a carrier such as alumina, but the present invention is not limited thereto.

Furthermore, in this invention, a reverse shift catalyst refers to a catalyst that converts carbon dioxide ( _CO₂ ) and hydrogen ( _H₂ ) into carbon monoxide (CO) and water ( _H₂O ) through a catalytic reaction. Examples of reverse shift catalysts include those in which at least one catalytically active component, such as Mn or Pd, is supported on a carrier such as alumina, or those made of oxides of Fe or Cr, but this invention is not limited to these.

Furthermore, as shown in Figure 1(B), when mixing the methanation catalyst 20 and the reverse-shift catalyst 21, an endothermic region consisting only of the reverse-shift catalyst 21 may be provided in a region perpendicular to the gas flow direction, spaced at a predetermined interval from the inlet side, to further suppress heat generation. The height ratio (thickness) of the reverse-shift catalyst 21-only packed layer may be appropriately changed depending on the degree of heat cancellation. In this way, by using a packed layer consisting only of the reverse-shift catalyst 21, it is expected that the heat cancellation effect will be further improved.

Alternatively, as shown in Figure 1(C), a mixed catalyst may be packed into the common carrier 23, in which the catalytically active component 20a of the methanation catalyst 20 and the catalytically active component 21a of the reverse-shift catalyst 21 are supported on the common carrier 23 in a predetermined ratio.
In this way, by supporting the catalytic active components 20a and 21a of the methanation catalyst and the reverse shift catalyst on the common carrier 23, the catalyst packing efficiency is improved. The mixing ratio of the catalytic active component 21a of the reverse shift catalyst 21 and the catalytic active component 20a of the methanation catalyst 20 supported on the common carrier 23 is preferably a mixing ratio calculated from 90:10 to 40:60, the same as when each catalyst is mixed individually.

As described above, according to the present invention, in temperature control in the methanation reactor, by providing a reactor 11 filled with a methanation catalyst 20 and a reverse-shift catalyst 21 in a predetermined ratio, the rapid exothermic reaction of the raw material gas G1 can be mitigated.

This allows for the reduction or simplification of the cooling function in the methanation device, resulting in a simpler device configuration and cost reduction.

[Second Embodiment]
Figure 3 (Figures 3(A) to 3(D)) is a schematic diagram of a methanation reactor according to a second embodiment of the present invention.

As shown in Figure 3(A), the methanation reactor of the second embodiment is divided into a first reaction region 11A and a second reaction region 11B from the gas inlet side to the gas outlet side of the reactor 11. The first reaction region 11A is filled with a mixed catalyst 22, which is a mixture of the methanation catalyst 20 and the reverse-shift catalyst 21 in a predetermined ratio, while the second reaction region 11B is filled with only the methanation catalyst 20.

According to this embodiment, carbon dioxide introduced into the first reaction region 11A of the reactor 11 is exothermic (+165.0 kJ/mol) by the methanation reaction of formula (1) on the methanation catalyst 20.
Furthermore, on the adjacent reverse-shift catalyst 21, a portion of the heat generated in the methanation catalyst 20 is absorbed (-41.2 kJ/mol), and the reverse-shift reaction from carbon dioxide to carbon monoxide in equation (2) above proceeds.

Thus, if the heat generated by the methanation reaction in equation (1) is thermally offset or nearly offset by the heat absorbed by the reverse shift reaction in equation (2), the rapid temperature rise of the catalyst layer near the inlet of reactor 11, for example to 600°C or higher, will be mitigated.

If the methanation reaction does not proceed sufficiently in the first reaction region 11A, the unreacted carbon dioxide in the outlet gas of the first reaction region is converted into methane ( _CH₄ ) and water ( _H₂O ) by the methanation catalyst 20 by the second reaction region 11B, as shown in formula (1) above.
Furthermore, the carbon monoxide (CO) produced by the reverse shift reaction is converted into methane ( _CH₄ ) and water ( _H₂O ) by the methanation catalyst 20 in the second reaction region 11B, as shown in equation (3) below. Thus, almost all of the carbon dioxide in the introduced raw material gas G1 is converted into methane.

[Chemical 3]
CO+3H ₂ →CH ₄ +H ₂ O…(3)+206.2kJ/mol

When reaction equations (2) and (3) are combined, the carbon monoxide (CO) produced cancels out, and the total reaction is the same as that in equation (1).

Thus, comparing reaction equation (1) with the sum of reaction equations (2) and (3), while the total amount of heat generated in the reaction remains the same, if the reactions in equations (1) and (2) in the first reaction region 11A are thermally canceled out or nearly so, the rapid temperature rise in the catalyst layer near the inlet of reactor 11, for example to 600°C or higher, will be mitigated.

Therefore, according to this embodiment, a portion of the heat generated by the methanation reaction of formula (1) is utilized in the endothermic reaction by the reverse shift reaction of formula (2), thereby exhibiting a kind of heat cancellation effect and mitigating a rapid rise in the catalyst layer temperature.

Here, the volume ratio of the first reaction region 11A to the second reaction region 11B is preferably 95:5 to 30:70, more preferably 80:20 to 30:70.

Furthermore, the methanation reactor shown in Figure 3(B) has a second reaction region 11B downstream of the first reaction region 11A in Figure 1(B), similar to that in Figure 3(A). As a result, the methanation reaction of formula (1) and the reverse shift reaction of formula (2) occur in the first reaction region, and in the second reaction region, the carbon monoxide (CO) and unreacted carbon dioxide ( _CO2 ) generated by the reverse shift reaction are converted into methane ( _CH4 ) and water ( _H2O ) by the methanation catalyst 20 in the second reaction region 11B, as shown in formulas (1) and (3), and almost all of the carbon dioxide in the raw material gas G1 is converted into methane.

Furthermore, the methanation reactor shown in Figure 3(C) has a second reaction region 11B downstream of the first reaction region 11A in Figure 1(C), similar to that in Figure 3(A). As a result, the methanation reaction (1) and the reverse shift reaction (2) described above occur in the first reaction region, and in the second reaction region, the carbon monoxide (CO) and unreacted carbon dioxide ( _CO₂ ) generated by the reverse shift reaction are converted into methane ( _CH₄ ) and water ( _H₂O ) by the methanation catalyst 20 in the second reaction region 11B, as shown in equations (1) and (3), and almost all of the carbon dioxide in the raw material gas G1 is converted into methane.

An example of the methanation reactor of this embodiment is shown in Figure 4. As shown in Figure 4, the configuration of the methanation reactor 10B of this embodiment is the same as that of the methanation reactor 10A shown in Figure 2, so details are omitted. The methanation reactor 10B of this embodiment has a first reaction region 11A and a second reaction region 11B within the reactor 11. The reactor 11 is the one shown in Figures 3(A) to 3(C) above.

The methanation reaction method involves dividing the reactor 11 into a first reaction region 11A and a second reaction region 11B, extending from the gas inlet side to the gas outlet side. The first reaction region 11A is filled with a mixed catalyst 22, a mixture of a methanation catalyst 20 and a reverse shift catalyst 21 in a predetermined ratio. The first reaction step involves converting the introduced carbon dioxide into methane using the methanation catalyst 20, and simultaneously converting the introduced carbon dioxide into carbon monoxide through a reverse shift reaction that absorbs some of the heat generated by the methanation reaction. The second reaction step involves filling the second reaction region with only the methanation catalyst 20, converting unreacted carbon dioxide into methane, and converting the carbon monoxide produced by the reverse shift reaction into methane.

In this methanation reaction method, in the first reaction region 11A, the methanation catalyst 20 converts carbon dioxide in the raw material gas G1 into methane, and the reverse shift catalyst 21 converts carbon dioxide into carbon monoxide. In the second reaction region 11B, the methanation catalyst 20 converts carbon monoxide and unreacted carbon dioxide into methane ( _CH4 ), so that almost all of the carbon dioxide in the raw material gas G1 can be converted into methane.
As described above, according to the present invention, when a methanation reaction occurs between carbon dioxide and hydrogen introduced into a reactor 11 using a methanation catalyst 20, a rapid rise in the catalyst layer temperature can be mitigated by a simple method.

(Example test)
The following describes test examples demonstrating the effects of the present invention.
In this test example, as shown in Figure 3(D), the reactor 11, which has a diameter of 20 mm, was divided into two parts: a first reaction region 11A and a second reaction region 11B. 15 ml of mixed catalyst was packed into the first reaction region 11A, and 15 ml of methanation catalyst was packed into the second reaction region 11B.
The mixing ratio of the mixed catalyst layer was 70% by volume of the reverse-shift catalyst and 30% by volume of the methanation catalyst (note that the illustration of the mixing ratio is simplified in the figure).

In contrast, a control was used in which the reaction vessel was not divided into a first reaction region 11A and a second reaction region 11B, but instead filled only with a 30 ml catalyst layer of methanation catalyst 20. In both cases, the catalyst was used after reduction at a predetermined temperature.

The preheating temperature in the preheater 31 was set to 200°C, the reaction temperature in the reactor 11 was set to 300°C, and the reaction pressure was set to 0.1 MPaG and 0 MPaG. A carbon dioxide methanation test was performed by supplying 2 NL/min of hydrogen, followed by 0.5 NL/min of carbon dioxide. The catalyst layer temperature distribution at this time is shown in Figures 5 and 6 (Figure 5 shows the catalyst layer temperature distribution in Figure 2(D), and Figure 6 shows the temperature distribution in the methanation catalyst 20 only).
Furthermore, plot A in the figure represents a reaction pressure of 0.1 MPaG, and plot B represents a reaction pressure of 0 MPaG. Plot C in the figure represents a state without the introduction of carbon dioxide. In Figures 5 and 6, the catalyst height on the horizontal axis is the distance from the gas inlet of the test apparatus in the direction of gas flow (downward in this example).
Furthermore, the reaction pressure inside the reactor 11 is preferably in the range of 0 MPaG (atmospheric pressure) to less than 1 MPaG.

The methanation catalyst used in the test was "Aeronite® agAl-NiPd" (product name), manufactured by Itochu Ceratec Co., Ltd.
Furthermore, the reverse shift catalyst is "Aeronite (registered trademark) agAl-MnPd" (product name) manufactured by Itochu Ceratec Co., Ltd.

Comparing Figure 5 and Figure 6, it can be seen that when the reaction vessel 11 is not divided into a first reaction region 11A and a second reaction region 11B, a rapid temperature increase is observed near the entrance.
In contrast, when the reaction vessel 11 was divided into a first reaction region 11A and a second reaction region 11B, the rapid temperature rise near the entrance was mitigated.
Furthermore, in plot A of Figure 5, the temperature rise near the inlet was less than 500°C (485°C) in the present invention, but it exceeded 500°C (515°C) in the conventional plot A shown in Figure 6.

As explained above, according to the present invention, by mixing a methanation catalyst and a reverse shift catalyst in a single reaction field, a portion of the heat generated by the methanation reaction can be utilized in the endothermic reaction of the reverse shift reaction, thereby exhibiting a kind of thermal cancellation effect.

Therefore, since the rapid temperature rise in this reaction can be mitigated without complex processes or complex reactor structures, the cost of the methanation apparatus can be reduced. Furthermore, because high temperatures are less likely to occur, the catalyst lifespan can be extended and the reactor cost can be reduced (by selecting general stainless steel instead of special materials such as heat-resistant steel).

Furthermore, by eliminating or simplifying conventional cooling functions, and by eliminating the need to fill the reactor with materials that do not contribute to the catalytic reaction, such as alumina balls, it is possible to mitigate the rapid rise in catalyst layer temperature in the methanation reactor, even with a simple configuration.

Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and can be appropriately modified within the scope of the gist of the invention.

The present invention can also be used in methanation reactors other than those shown in this embodiment.

10A, 10B Methanation reactor 11 Reactor 11A First reaction region 11B Second reaction region 12A Gas introduction piping 12B Gas discharge piping 20 Methanation catalyst 20a Methanation catalyst active component 21 Reverse shift catalyst 21a Reverse shift catalyst active component 22 Mixed catalyst 23 Common carrier G1 Raw material gas G2 Exhaust gas

Claims (8)

A methanation reactor characterized by filling a reactor, into which a raw material gas containing carbon dioxide and hydrogen is introduced, with a mixed catalyst comprising a methanation catalyst that converts carbon dioxide into methane and a reverse shift reaction catalyst that absorbs a portion of the heat generated by the methanation reaction, all in a predetermined ratio. The reactor is divided into a first reaction region and a second reaction region from the gas inlet side to the gas outlet side.
The first reaction region is filled with a mixed catalyst obtained by mixing the methanation catalyst and the reverse shift catalyst in a predetermined ratio,
The methanation reaction apparatus according to claim 1, characterized in that the second reaction region is filled only with the methanation catalyst. The methanation reactor according to claim 2, characterized in that the mixed catalyst comprises the catalytically active components of a methanation catalyst and a reverse-shift catalyst supported on a common carrier in predetermined proportions. The methanation reactor according to claim 2 or 3, characterized in that the mixing ratio of the reverse-shift catalyst and the methanation catalyst in the first reaction region is 90:10 to 40:60. The methanation reactor according to claim 2 or 3, characterized in that the volume ratio of the first reaction region and the second reaction region is 95:5 to 30:70. The methanation reactor according to claim 1 or 2, characterized in that the reaction pressure inside the reactor is in the range of 0 MPaG to less than 1 MPaG. A methanation reaction method characterized by a reaction step comprising: filling the reactor from the gas inlet side to the gas outlet side with a mixed catalyst, which is a mixture of a methanation catalyst and a reverse shift catalyst in a predetermined ratio; converting the introduced carbon dioxide into methane using the methanation catalyst; and converting the introduced carbon dioxide into carbon monoxide through a reverse shift reaction, which absorbs a portion of the heat generated by the methanation reaction. The reactor is divided into a first reaction region and a second reaction region from the gas inlet side to the gas outlet side.
The methanation reaction method according to claim 7, characterized in that a first reaction step is to fill the first reaction region with a mixed catalyst obtained by mixing a methanation catalyst and a reverse shift catalyst in a predetermined ratio, and a second reaction step is to fill the second reaction region with only the methanation catalyst to convert unreacted carbon dioxide in the first reaction region into methane and to convert carbon monoxide produced in the reverse shift reaction in the first reaction region into methane.