(19)
(11)EP 3 501 632 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
26.06.2019 Bulletin 2019/26

(21)Application number: 18206947.6

(22)Date of filing:  19.11.2018
(51)International Patent Classification (IPC): 
B01J 7/00(2006.01)
B01J 12/00(2006.01)
C10L 3/08(2006.01)
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(30)Priority: 18.12.2017 JP 2017241970

(71)Applicant: Kabushiki Kaisha Toyota Chuo Kenkyusho
Nagakute-shi, Aichi 480-1192 (JP)

(72)Inventors:
  • ITOH, Yoshihiko
    Nagakute-shi, Aichi 480-1192 (JP)
  • SAKAI, Masatoshi
    Nagakute-shi, Aichi 480-1192 (JP)
  • IMAGAWA, Haruo
    Nagakute-shi, Aichi 480-1192 (JP)
  • SAYAMA, Shogo
    Nagakute-shi, Aichi 480-1192 (JP)
  • BABA, Naoki
    Nagakute-shi, Aichi 480-1192 (JP)

(74)Representative: Kramer Barske Schmidtchen Patentanwälte PartG mbB 
European Patent Attorneys Landsberger Strasse 300
80687 München
80687 München (DE)

  


(54)APPARATUS OF PRODUCING METHANE AND METHOD FOR PRODUCING METHANE USING THE SAME


(57) An apparatus of producing methane from a CO2-containing gas comprises:
at least two first reactors with a CO2 storage-reduction catalyst having a CO2 storage capacity and a methane generation ability disposed in parallel;
at least one second reactor provided with a methanation catalyst;
means for supplying purge gas; and
means for supplying reducing gas, wherein
the means for supplying purge gas and for supplying reducing gas are disposed upstream of the first reactors,
the second reactor is disposed downstream of the first reactors, and
a gas outlet of one of the first reactors is connected to a gas inlet of at least one different one of the first reactors via a purge gas recirculation line which supplies a purge gas emitted from the gas outlet of the one first reactor into the gas inlet of the different first reactor.




Description

BACKGROUND OF THE INVENTION


Field of the Invention



[0001] The present invention relates to an apparatus of producing methane and a method for producing methane using the same, in particular to an apparatus of producing methane from a CO2-containing gas and a method for producing methane from a CO2-containing gas using the same.

Related Background Art



[0002] Methods for producing methane using CO2 as a raw material and using a methanation catalyst such as Ru or Ni have been drawing attention in terms of the reduction of CO2 emissions in the global warming problems. However, production of methane which uses as a raw material a gas containing CO2 and O2 such as combustion exhaust gas or biogas makes it necessary to increase the purity of CO2 upstream of the methanation catalyst and remove reaction inhibiting components such as O2. Additionally, practically-used examples of the method for producing methane using a CO2-containig gas as a raw material include a method which individually combines a CO2 separation and recovery apparatus (chemical adsorption method, physical adsorption method, etc.) with a methanation catalyst apparatus. However, the method requires heat when separating and recovering CO2. This makes it necessary to supply external energy to the apparatuses and poses a problem of complex and large apparatuses.

[0003] In light of the above, Japanese Unexamined Patent Application Publication No. Hei 5-193920 (Patent Document 1) proposes a method which precipitates carbon on the ferrite surface by passing CO2 and H2 through the ferrite within a temperature range of 300°C to 400°C, and then converts the carbon, precipitated on the ferrite, to methane by raising the temperature of the ferrite to 600°C in H2 without the supply of CO2. However, although this method makes it possible to precipitate carbon from CO2 within a temperature range of 300°C to 400°C, it is necessary to provide external energy because this method requires raising the temperature to 600°C or more in the methanation of the carbon. Moreover, it is necessary to remove O2 in advance prior to supplying CO2 to the ferrite.

[0004] Additionally, Japanese Unexamined Patent Application Publication No. Hei 9-110731 (Patent Document 2) proposes a method for producing methane which alternately repeats the carbon dioxide decomposition step of bringing a CO2-containig gas into contact with an active ferritic iron oxide obtained by removing oxygen in a ferrite-based iron oxide crystal and the methane production step of bringing an H2-containing gas into contact with the active ferritic iron oxide obtained in the carbon dioxide decomposition step. However, this method requires removing O2 in advance prior to bringing the CO2-containing gas into contact with the active ferritic iron oxide. In addition, it is difficult to continuously produce methane using a CO2-containing gas as a raw material.

[0005] Furthermore, International Publication No. WO2006/007825 (Patent Document 3), Applied Catalysis B: Environmental, 168 and 169 (2015), 370 to 376 (Non-Patent Document 1), and Catalysts, 2017, 7, 88 (Non-Patent Document 2) propose a method which allows a CO2 storage-reduction catalyst, having CO2 storage capacity and methane generation ability, to store CO2 and then supplies H2 to reduce the stored CO2 for conversion into methane. Since this method is capable of separation/recovery of CO2 and methanation reaction with a single catalyst, it is possible to simplify and downsize the apparatus. Furthermore, since this method is capable of using heat generated in the methanation reaction for separation/recovery of CO2, it is possible to separate/recover CO2 and to carry out methanation reaction at a temperature of 250 to 400°C without supplying external energy. However, in the methods of Patent Document 3 and Non-Patent Documents 1 and 2, it is difficult to continuously produce methane using a CO2-containing gas as a raw material because the methods require alternate separation/recovery of CO2 and methanation reaction.

SUMMARY OF THE INVENTION



[0006] The present inventors have found a problem of the methods described in Patent Document 3 and Non-Patent Documents 1 and 2 that, in supplying a purge gas to remove oxygen in the catalytic reactor after the storage of CO2 or in supplying H2 for reduction reaction, the stored CO2 is desorbed from the catalyst, resulting in the decrease in the concentration and the purity of methane generated.

[0007] The present invention has been made in view of the above problem of the conventional techniques, and an object thereof is to provide an apparatus and a method for producing methane which can continuously produce methane using a CO2-containing gas as a raw material and which can further enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0008] The present inventors have made earnest studies for the purpose of achieving the above object and completed the present invention as a result. The findings are as follows: It is possible to continuously produce methane using a CO2-containing gas as a raw material when two or more reactors provided with a CO2 storage-reduction catalyst are disposed in parallel, each of the reactors alternately stores CO2 into the CO2 storage-reduction catalyst and reduces the stored CO2, and at least one of the reactors stores CO2 and simultaneously a remaining reactor reduces the stored CO2. In addition, it is possible to prevent emission of CO2 to the outside of the system by supplying a purge gas, supplied to the reactor after the storage of CO2, to the reactor after the reduction reaction and by storing the CO2 contained in the purge gas into the CO2 storage-reduction catalyst after the reduction reaction. Furthermore, it is possible to enhance the concentration and the purity of methane in the methane-containing gas to be obtained by reducing the CO2, contained in the reaction-produced gas obtained by reduction of the CO2, using a methanation catalyst disposed downstream.

[0009] Specifically, an apparatus of producing methane of the present invention is an apparatus of producing methane from a CO2-containing gas, comprising:

a reactor which is provided with a CO2 storage-reduction catalyst having a CO2 storage capacity and a methane generation ability;

at least one reactor which is provided with a methanation catalyst;

at least one means for supplying purge gas; and

at least one means for supplying reducing gas, wherein

two or more of the reactors provided with the CO2 storage-reduction catalyst are disposed in parallel,

the means for supplying purge gas and the means for supplying reducing gas are disposed upstream of the reactors provided with the CO2 storage-reduction catalyst on gas flow paths,

the reactor provided with the methanation catalyst is disposed downstream of the reactors provided with the CO2 storage-reduction catalyst on the gas flow paths, and

a gas outlet of one of the reactors provided with the CO2 storage-reduction catalyst is connected to a gas inlet of at least one different reactor provided with the CO2 storage-reduction catalyst, other than the one reactor, via a purge gas recirculation line which supplies a purge gas emitted from the gas outlet of the one reactor into the gas inlet of the different reactor.



[0010] In the apparatus of producing methane of the present invention, at least one gas storage container, which stores a reaction-produced gas emitted from gas outlets of the reactors provided with the CO2 storage-reduction catalyst, is preferably further disposed between the reactors provided with the CO2 storage-reduction catalyst (more preferably, each of the reactors provided with the CO2 storage-reduction catalyst) and the reactor provided with the methanation catalyst.

[0011] A method for producing methane of the present invention is a method for producing methane from a CO2-containing gas using the apparatus of producing methane of the present invention, the method comprising the steps of:

allowing the CO2 storage-reduction catalyst to store CO2 by supplying a CO2-containing gas to one of the reactors provided with the CO2 storage-reduction catalyst;

reducing the CO2 by supplying a reducing gas to the one reactor provided with the CO2 storage-reduction catalyst having stored the CO2;

supplying a reaction-produced gas obtained by reduction of the CO2 to the reactor provided with the methanation catalyst;

supplying a purge gas to the one reactor after the storage of the CO2 and supplying the purge gas emitted from the one reactor to the one reactor after the reduction reaction; and

reducing residual CO2 in the reaction-produced gas supplied to the reactor provided with the methanation catalyst, wherein

each of the reactors provided with the CO2 storage-reduction catalyst alternately carries out the storing of CO2 and the reducing of CO2, and

at least one of the reactors provided with the CO2 storage-reduction catalyst carries out the storing of CO2 and simultaneously a remaining reactor provided with the CO2 storage-reduction catalyst carries out the reducing of CO2.



[0012] In the method for producing methane of the present invention, it is preferable to store the reaction-produced gas obtained by reduction of CO2 in the gas storage container and then to supply the reaction-produced gas to the reactor provided with the methanation catalyst by
using the apparatus of producing methane in which the at least one gas storage container is further disposed between the reactors provided with the CO2 storage-reduction catalyst (more preferably, each of the reactors provided with the CO2 storage-reduction catalyst) and the reactor provided with the methanation catalyst.

[0013] The present invention makes it possible to continuously produce methane using a CO2-containing gas as a raw material and further to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS



[0014] 

FIG. 1 is a schematic diagram illustrating a preferred embodiment of an apparatus of producing methane of the present invention.

FIG. 2 is a schematic diagram illustrating another preferred embodiment of the apparatus of producing methane of the present invention.

FIG. 3 is a schematic diagram illustrating another preferred embodiment of the apparatus of producing methane of the present invention.

FIG. 4 is a schematic diagram illustrating another preferred embodiment of the apparatus of producing methane of the present invention.

FIG. 5 is a schematic diagram illustrating another preferred embodiment of the apparatus of producing methane of the present invention.

FIG. 6A is a flowchart for a reactor A1 which is provided with a CO2 storage-reduction catalyst in the production of methane carried out in Example 1.

FIG. 6B is a flowchart for a reactor A2 which is provided with a CO2 storage-reduction catalyst in the production of methane carried out in Example 1.

FIG. 6C is a flowchart for a reactor B which is provided with a methanation catalyst in the production of methane carried out in Example 1.

FIG. 7A is a flowchart for a gas storage container C1 and the reactor A1 provided with a CO2 storage-reduction catalyst in the production of methane carried out in Example 2.

FIG. 7B is a flowchart for a gas storage container C2 and the reactor A2 provided with a CO2 storage-reduction catalyst in the production of methane carried out in Example 2.

FIG. 7C is a flowchart for the reactor B provided with a methanation catalyst in the production of methane carried out in Example 2.

FIG. 8 is a graph illustrating the amount of CO2 removed per hour in the production of methane carried out in Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 9 is a graph illustrating the amount of CO2 emitted per hour in the production of methane carried out in Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 10 is a graph illustrating the amount of methane generated per hour in the production of methane carried out in Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 11 is a schematic diagram illustrating an apparatus of producing methane used in Comparative Example 1.

FIG. 12 is a schematic diagram illustrating an apparatus of producing methane used in Comparative Example 2.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS



[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the drawings. Note that in the following description and drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant explanations may be omitted.

[0016] First, a description is provided for a CO2 storage-reduction catalyst, a methanation catalyst, a CO2-containing gas, a reducing gas, and a purge gas used in the present invention.

[0017] The CO2 storage-reduction catalyst is not particularly limited as long as it is a catalyst having a CO2 storage capacity and a methane generation ability. Examples thereof include a catalyst supporting a component having a methanation catalytic ability and a component having a CO2 storage capacity on a catalytic support. The component having the methanation catalytic ability is not particularly limited, and examples thereof include Ru, Ni, Pt, Pd, Rh, Co, Fe, and Mn. These methanation catalytic components may be used singly or used in combination of two or more kinds. The component having the CO2 storage capacity is not particularly limited, and examples thereof include alkali metal compounds, alkaline earth metal compounds, and rare earth compounds. These components having the CO2 storage capacity may be used singly or used in combination of two or more kinds. In addition, the components having the methanation catalytic ability and the components having the CO2 storage capacity are preferably supported on a catalytic support (more preferably, a porous catalytic support). The component constituting the catalytic support is preferably alumina, silica, silica-alumina, titania, zirconia, ceria, ceria-zirconia, and the like.

[0018] The methanation catalyst is not particularly limited as long as it has a catalytic ability of generating methane by reducing CO2. Examples thereof include catalysts which support the methanation catalytic component such as Ru, Ni, Pt, Pd, Rh, Co, Fe, and Mn on the porous catalytic support. These methanation catalysts may be used singly or used in combination of two or more kinds.

[0019] The CO2-containing gas is not particularly limited as long as it contains CO2. However, the CO2-containing gas is preferably a gas at least containing CO2 and O2 from the viewpoint that use of the production apparatus and the production method for methane of the present invention makes it possible to continuously produce methane using the CO2-containing gas as a raw material and further to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0020] The reducing gas is not particularly limited as long as it can reduce CO2 to methane. Examples thereof include H2 gas, NH3 gas, hydrazine gas, and a gas containing these gases. In addition, examples of the purge gas include noble gases such as He and inert gases such as N2.

[0021] Next, a description is provided for the apparatus of producing methane of the present invention. FIG. 1 to FIG. 5 are each a schematic diagram illustrating a preferred embodiment of the apparatus of producing methane of the present invention. As illustrated in FIG. 1 to FIG. 5, the apparatus of producing methane of the present invention is an apparatus of producing methane from a CO2-containing gas, including a reactor A which is provided with the CO2 storage-reduction catalyst having the CO2 storage capacity and the methane generation ability, a reactor B which is provided with the methanation catalyst, a means 1 for supplying purge gas, and a means 2 for supplying reducing gas.

[0022] The reactor A provided with the CO2 storage-reduction catalyst used in the present invention is not particularly limited. Examples thereof include a catalytic reactor packed with powder of the CO2 storage-reduction catalyst, a catalytic reactor packed with pellets of the CO2 storage-reduction catalyst, and a catalytic reactor packed with a honeycomb or foam coated with the CO2 storage-reduction catalyst. In the apparatus of producing methane of the present invention, two or more of the reactors A provided with the CO2 storage-reduction catalyst as described above are disposed in parallel. For example, in the apparatuses of producing methane of the present invention illustrated in FIG. 1 to FIG. 5, two reactors A provided with the CO2 storage-reduction catalyst are disposed in parallel. In addition, the apparatus of producing methane of the present invention is not limited to this. Three or more reactors A provided with the CO2 storage-reduction catalyst may be disposed in parallel. By disposing two or more reactors A provided with the CO2 storage-reduction catalyst in parallel as described above, it is possible to alternately store and reduce CO2 in each of the reactors A, and to store CO2 in some reactors A and simultaneously to reduce CO2 in the remaining reactors A, making it possible to continuously produce methane using the CO2-containing gas as a raw material. Moreover, the gas inlet of each of the two or more reactors A provided with the CO2 storage-reduction catalyst is connected to a corresponding gas supply line 3 for supplying the CO2-containing gas. Furthermore, the gas outlet of each of the reactors A provided with the CO2 storage-reduction catalyst is connected to a corresponding gas transfer line 4 for transferring the reaction-produced gas obtained in the reactors A provided with the CO2 storage-reduction catalyst to a reactor B provided with the methanation catalyst.

[0023] The reactor B provided with the methanation catalyst used in the present invention is not particularly limited. Examples thereof include a catalytic reactor packed with powder of the methanation catalyst, a catalytic reactor packed with pellets of the methanation catalyst, and a catalytic reactor packed with a honeycomb or foam coated with the methanation catalyst. In the apparatus of producing methane of the present invention, at least one reactor B provided with the methanation catalyst as described above is disposed downstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths, specifically, the gas transfer lines 4 are connected to the gas inlet of the reactor B provided with the methanation catalyst. For example, in the apparatuses of producing methane of the present invention illustrated in FIG. 1 to FIG. 5, one reactor B provided with the methanation catalyst is disposed downstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths. In addition, the apparatus of producing methane of the present invention is not limited to this. Two or more reactors B provided with the methanation catalyst may be disposed as long as they are disposed downstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths. By disposing at least one reactor B provided with the methanation catalyst downstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths as described above, it is possible to generate methane by reducing CO2 contained in the reaction-produced gas obtained in the reactors A provided with the CO2 storage-reduction catalyst and to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0024] No particular limitation is imposed on the means 1 for supplying purge gas used in the present invention. Examples thereof include a gas cylinder filled with the purge gas, an N2 gas production unit which removes oxygen from the atmosphere using a porous film, a separation membrane or a freezer, and a unit for gasifying liquid nitrogen. In the apparatus of producing methane of the present invention, at least one means 1 for supplying purge gas as described above is disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths (specifically, at least one means 1 for supplying purge gas is connected to the gas supply line 3). For example, in the apparatuses of producing methane of the present invention illustrated in FIG. 1 to FIG. 5, one means 1 for supplying purge gas is disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths (specifically, one means 1 for supplying purge gas is connected to all of the gas supply lines 3). In addition, the apparatus of producing methane of the present invention is not limited to this. Two or more means 1 for supplying purge gas may be each disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on two or more gas flow paths (specifically, the means 1 for supplying purge gas may be each connected to the gas supply lines 3 which are connected to the respective two or more reactors A provided with the CO2 storage-reduction catalyst).

[0025] No particular limitation is imposed on the means 2 for supplying reducing gas used in the present invention. Examples thereof include a gas cylinder filled with the reducing gas, a water electrolyzer, a pyrolysis apparatus for ammonia or methylcyclohexane, an H2 gas generation unit which desorbs hydrogen from a hydrogen storage material, and a unit for gasifying liquid hydrogen. In the apparatus of producing methane of the present invention, at least one means 2 for supplying reducing gas as described above is disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths (specifically, at least one means 2 for supplying reducing gas is connected to the gas supply line 3). For example, in the apparatuses of producing methane of the present invention illustrated in FIG. 1 to FIG. 5, one means 2 for supplying reducing gas is disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on the gas flow paths (specifically, one means 2 for supplying reducing gas is connected to all of the gas supply lines 3). In addition, the apparatus of producing methane of the present invention is not limited to this. Two or more means 2 for supplying reducing gas may be each disposed upstream of the reactors A provided with the CO2 storage-reduction catalyst on two or more gas flow paths (specifically, the means 2 for supplying reducing gas may be each connected to the gas supply lines 3 which are connected to the respective two or more reactors A provided with the CO2 storage-reduction catalyst).

[0026] Furthermore, in the apparatus of producing methane of the present invention, the gas outlet of a reactor A provided with the CO2 storage-reduction catalyst and the gas inlet of at least one different reactor A, other than that reactor, provided with the CO2 storage-reduction catalyst are connected together via a purge gas recirculation line 5 which supply the purge gas emitted from the gas outlet of the reactor A into the gas inlet of the different reactor A. For example, in the apparatuses of producing methane of the present invention each of which includes the two reactors A1 and A2 each provided with the CO2 storage-reduction catalyst, as illustrated in FIG. 1 to FIG. 5, the gas outlet of the reactor A1 and the gas inlet of the reactor A2 are connected together via the purge gas recirculation line 5, and the gas outlet of the reactor A2 and the gas inlet of the reactor A1 are connected together via the purge gas recirculation line 5. In addition, in an apparatus of producing methane of the present invention which includes three reactors A1, A2, and A3 each provided with the CO2 storage-reduction catalyst (not illustrated), the gas outlet of the reactor A1 and the gas inlet of the reactor A2 are connected together via the purge gas recirculation line 5, the gas outlet of the reactor A2 and the gas inlet of the reactor A3 are connected together via the purge gas recirculation line 5, and the gas outlet of the reactor A3 and the gas inlet of the reactor A1 are connected together via the purge gas recirculation line 5. The connection between the gas outlet of an arbitrary reactor A provided with the CO2 storage-reduction catalyst and the gas inlet of a different reactor A provided with the CO2 storage-reduction catalyst via the purge gas recirculation line 5 as described above makes it possible to prevent emission of CO2 to the outside of the system by supplying the purge gas emitted from the reactor A after the storage of CO2 to the reactor A after the reduction reaction and then allowing the CO2 storage-reduction catalyst to store the CO2 contained in the purge gas during the removal of reaction-inhibiting components such as O2 by supplying a purge gas to a reactor A after the storage of CO2. As a result, it is possible to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0027] In addition, in the apparatus of producing methane of the present invention, at least one gas storage container C for storing the reaction-produced gas emitted from the gas outlets of the reactors A provided with the CO2 storage-reduction catalyst is further preferably disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). For example, in the apparatus of producing methane of the present invention illustrated in FIG. 2, one gas storage container C is disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). In the apparatuses of producing methane of the present invention illustrated in FIG. 3 and FIG. 5, two gas storage containers C are disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). Additionally, the apparatus of producing methane of the present invention is not limited to these. Three or more gas storage containers C may be disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). This makes it easy to control the reaction-produced gas to be supplied to the reactor B provided with the methanation catalyst and to supply at a suitable ratio the desorbed CO2 and unreacted H2 to the reactor B provided with the methanation catalyst. Thus, it is possible to further enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0028] Moreover, in the apparatus of producing methane of the present invention, at least one means 2 for supplying reducing gas is further preferably disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer line 4). For example, in the apparatus of producing methane of the present invention illustrated in FIG. 4, one means 2 for supplying reducing gas is disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer line 4). In addition, the apparatus of producing methane of the present invention is not limited to this. Two or more means 2 for supplying reducing gas may be disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). This makes it possible to supply at a suitable ratio CO2 and the reducing gas to the reactor B provided with the methanation catalyst. Thus, it is possible to further enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0029] In addition, in the apparatus of producing methane of the present invention, at least one means 6 for removing moisture in gas is further preferably disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer line 4). For example, in the apparatus of producing methane of the present invention illustrated in FIG. 5, two means 6 for removing moisture in gas are disposed between the reactors A provided with the CO2 storage-reduction catalyst and the gas storage containers C (specifically, in the gas transfer lines 4). In addition, the apparatus of producing methane of the present invention is not limited to this. One or three or more means 6 for removing moisture in gas may be disposed between the reactors A provided with the CO2 storage-reduction catalyst and the reactor B provided with the methanation catalyst (specifically, in the gas transfer lines 4). This removes water, an inhibitory factor of methanation reaction, and enhances methanation activity. In addition, the apparatus of producing methane of the present invention illustrated in FIG. 5 can reduce the amount of reaction-produced gas supplied to the reactor B provided with the methanation catalyst. This makes it possible to reduce the volume of the gas storage container C and thus to downsize the apparatus.

[0030] Next, a description is provided for the method for producing methane of the present invention. The method for producing methane of the present invention is a method for producing methane from the CO2-containing gas using the apparatus of producing methane of the present invention, comprising the steps of: allowing the CO2 storage-reduction catalyst to store CO2 by supplying the CO2-containing gas to the reactor A provided with the CO2 storage-reduction catalyst [CO2 storage step]; reducing the CO2 by supplying the reducing gas to the reactor A provided with the CO2 storage-reduction catalyst having stored the CO2 [CO2 reduction step]; supplying a reaction-produced gas obtained by reduction of the CO2 to the reactor B provided with the methanation catalyst [reaction-produced gas supply step]; supplying a purge gas to the reactor A after the storage of the CO2 and supplying the purge gas emitted from the reactor A to the reactor A after the reduction reaction [purge gas recirculation step]; and reducing residual CO2 in the reaction-produced gas supplied to the reactor B provided with the methanation catalyst [methanation reaction step].

[0031] In addition, in the method for producing methane of the present invention, each of the reactors A provided with the CO2 storage-reduction catalyst alternately carries out the CO2 storage step and the CO2 reduction step, and at least one of the reactors A provided with the CO2 storage-reduction catalyst carries out the CO2 storage step and simultaneously a remaining reactor A provided with the CO2 storage-reduction catalyst carries out the CO2 reduction step.

[0032] Moreover, in the method for producing methane of the present invention, it is preferable to store the reaction-produced gas obtained by reduction of CO2 in the gas storage container C and then to supply the reaction-produced gas to the reactor B provided with the methanation catalyst.

[0033] Hereinafter, a description is provided for the method for producing methane of the present invention taking as an example the case of using the apparatuses of producing methane illustrated in FIG. 1 to FIG. 5 each of which includes two reactors A1 and A2 provided with the CO2 storage-reduction catalyst. However, the method for producing methane of the present invention is not limited to these.

[0034] The method for producing methane of the present invention supplies the CO2-containing gas to the reactor A1 provided with the CO2 storage-reduction catalyst after the reduction reaction and simultaneously allows the means 1 for supplying purge gas to supply the purge gas to the reactor A2 provided with the CO2 storage-reduction catalyst after the storage of CO2. This allows the reactor A1 to store the CO2 contained in the CO2-containing gas into the CO2 storage-reduction catalyst and allows the reactor A2 to remove the reaction-inhibiting components such as O2. In addition, the purge gas emitted from the reactor A2 is also supplied to the reactor A1 via the purge gas recirculation line 5. This allows the reactor A1 to store the CO2 which is contained in the purge gas emitted from the reactor A2 into the CO2 storage-reduction catalyst, making it possible to prevent emission of CO2 to the outside of the system and to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0035] Next, the reactor A1 is supplied only with the CO2-containing gas, and simultaneously, the reactor A2 is supplied with a reducing gas from the means 2 for supplying reducing gas. This subsequently allows the reactor A1 to store the CO2 contained in the CO2-containing gas into the CO2 storage-reduction catalyst and allows the reactor A2 to reduce the CO2 stored in the CO2 storage-reduction catalyst. Consequently, a reaction-produced gas, containing methane, CO2 desorbed from the CO2 storage-reduction catalyst, and an unreacted reducing gas, is obtained. This reaction-produced gas is supplied via the gas transfer lines 4 to the reactor B provided with the methanation catalyst. In the reactor B, the residual CO2 is reduced for production of methane. This enhances the concentration and the purity of methane in the methane-containing gas to be obtained.

[0036] Next, the reactor A2 after the reduction reaction is supplied with a purge gas from the means 1 for supplying purge gas to remove reaction-inhibiting components such as O2 in the reactor A2. After that, the reactor A2 is supplied with the CO2-containing gas, and simultaneously, the reactor A1 after the storage of CO2 is supplied with the purge gas from the means 1 for supplying purge gas. This allows the reactor A2 to store the CO2 contained in the CO2-containing gas into the CO2 storage-reduction catalyst and allows the reactor A1 to remove the reaction-inhibiting components such as O2. In addition, the purge gas emitted from the reactor A1 is also supplied to the reactor A2 via the purge gas recirculation line 5. This allows the reactor A2 to store the CO2 which is contained in the purge gas emitted from the reactor A1 into the CO2 storage-reduction catalyst, making it possible to prevent emission of CO2 to the outside of the system and to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0037] Next, the reactor A2 is supplied only with the CO2-containing gas, and simultaneously, the reactor A1 is supplied with the reducing gas from the means 2 for supplying reducing gas. This subsequently allows the reactor A2 to store the CO2 contained in the CO2-containing gas into the CO2 storage-reduction catalyst and allows the reactor A1 to reduce the CO2 stored in the CO2 storage-reduction catalyst. Consequently, a reaction-produced gas, containing methane, CO2 desorbed from the CO2 storage-reduction catalyst, and an unreacted reducing gas, is obtained. This reaction-produced gas is also supplied via the gas transfer lines 4 to the reactor B provided with the methanation catalyst. In the reactor B, the residual CO2 is reduced for production of methane. This enhances the concentration and the purity of methane in the methane-containing gas to be obtained.

[0038] Once the method for producing methane of the present invention repeats the series of operations described above, the reactors A1 and A2 provided with the CO2 storage-reduction catalyst alternately repeat the CO2 storage step and the CO2 reduction step, making it possible to continuously produce methane using the CO2-containing gas as a raw material.

[0039] In addition, in the method for producing methane of the present invention, it is preferable to store the reaction-produced gas obtained in the reactors A1 and A2 into the gas storage container C by using the apparatuses of producing methane provided with the gas storage container C illustrated in FIG. 2, FIG. 3, and FIG. 5 and then to supply the reaction-produced gas to the reactor B. This makes it easy to control the reaction-produced gas to be supplied to the reactor B and to supply at a suitable ratio the desorbed CO2 and unreacted H2 to the reactor B. Thus, it is possible to further enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0040] Moreover, in the method for producing methane of the present invention, it is preferable to supply a reducing gas to the reaction-produced gas obtained in the reactors A1 and A2 by using the apparatus of producing methane illustrated in FIG. 4 which includes the means 2 for supplying the reducing gas to the reactor B provided with the methanation catalyst. This makes it possible to supply at a suitable ratio CO2 and the reducing gas to the reactor B, further enhancing the concentration and the purity of methane in the methane-containing gas to be obtained.

[0041] In addition, in the method for producing methane of the present invention, it is preferable to remove moisture, an inhibitory factor of methanation reaction, from the reaction-produced gas obtained in the reactors A1 and A2 by using the apparatus of producing methane provided with the means 6 for removing moisture in gas, illustrated in FIG. 5. This enhances the methanation activity and also makes it possible to reduce the amount of reaction-produced gas supplied to the reactor B. Consequently, it is possible to reduce the volume of the gas storage container C and thus to downsize the apparatus.

[0042] In the method for producing methane of the present invention, no particular limitation is imposed on the method for controlling the steps described above. For example, the supply gases may be switched over time, or the supply gases may be switched when a predetermined gas concentration is reached, with the gas concentration measured with a gas sensor attached to the gas outlet of the reactor A, reactor B, or the gas storage container C.

[0043] As above, a description has been provided for preferred embodiments of the method for producing methane of the present invention taking as an example the case of using the apparatus of producing methane which includes two reactors provided with the CO2 storage-reduction catalyst. However, the method for producing methane of the present invention is not limited to the embodiments described above. For example, also in the case of using an apparatus of producing methane which includes three or more reactors provided with the CO2 storage-reduction catalyst, it is possible to continuously produce methane using the CO2-containing gas as a raw material when these reactors are used in parallel, each of the reactors alternately stores CO2 into the CO2 storage-reduction catalyst and reduces the stored CO2, and at least one of the reactors stores CO2 and simultaneously a remaining reactor reduces the stored CO2. In addition, it is possible to prevent emission of CO2 to the outside of the system by supplying the purge gas, supplied to the reactor after the storage of CO2, to the reactor after the reduction reaction and then storing the CO2 contained in the purge gas into the CO2 storage-reduction catalyst after the reduction reaction. Furthermore, it is possible to enhance the concentration and the purity of methane in the methane-containing gas to be obtained by reducing the CO2, contained in the reaction-produced gas obtained by reduction of the CO2, using the methanation catalyst disposed downstream.

[Examples]



[0044] Hereinafter, the present invention is described more specifically based on Examples and Comparative Examples. However, the present invention is not limited to the examples below.

(Example 1)



[0045] Methane was continuously produced with a gas containing CO2 and O2 as a raw material by using the apparatus of producing methane illustrated in FIG. 1 and in accordance with the flowcharts described in FIG. 6A to FIG. 6C and with the time settings described in Table 1. In the apparatus of producing methane illustrated in FIG. 1, two reactors A1 and A2 provided with a CO2 storage-reduction catalyst were disposed in parallel. The gas inlet of each of the reactors A1 and A2 was connected to the gas supply line 3 for supplying a CO2-containing gas. The gas supply line 3 was connected to the means 1 for supplying purge gas and the means 2 for supplying reducing gas. In addition, the gas outlet of each of the reactors A1 and A2 was connected to the gas transfer line 4 for transferring the obtained reaction-produced gas to the reactor B provided with a methanation catalyst. Moreover, the gas outlet of the reactor A1 and the gas inlet of the reactor A2 were connected together via the purge gas recirculation line 5. Simultaneously, the gas outlet of the reactor A2 and the gas inlet of the reactor A1 were connected together via the purge gas recirculation line 5.

[0046] The CO2 storage-reduction catalyst used was 2 g of catalyst supporting 10% by mass of calcium acetate in terms of CaO and 5% by mass of Ru on an alumina catalytic support. In addition, the methanation catalyst used was 1 g of a commercially available methanation catalyst supporting 2% by mass of Ru in terms of metal Ru on titania. The temperatures of the reactors A1 and A2 and the reactor B were set to 320°C. The CO2-containing gas used was a mixture gas of 10% of CO2 + 3% of O2 + He (balance), and its flow rate was set to 20 ml/min. The purge gas used was a 100% He gas, and its flow rate was set to 20 ml/min. The reducing gas used was a 100% H2 gas, and its flow rate was set to 10.5 ml/min.
[Table 1]
Time [sec]Reactor A1Reactor A2Reactor B
7.5 T11 T21 T31
140.5 --- T22 T32
148.0 T13 T23 ---
155.5 T14 T24 T34
288.5 T15 --- T35
296.0 T16 T26 T36


[0047] As shown in FIG. 6A to FIG. 6C and Table 1, the reactor A1 after the reduction reaction (excluding the first cycle) was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A2 after the storage of CO2 (excluding the first cycle) was supplied with the purge gas for 7.5 seconds. In addition, in this period of time (for 7.5 seconds), the purge gas emitted from the reactor A2 was supplied to the reactor A1 via the purge gas recirculation lines 5. This allowed the reactor A1 to store CO2 into the CO2 storage-reduction catalyst and allowed the reactor A2 to remove reaction-inhibiting components such as O2. Note that the reactor B was closed in this period of time.

[0048] Next, methane was generated (excluding the first cycle) by supplying the reactor A2 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. A methane-containing gas was obtained (excluding the first cycle) by supplying the reactor B with the obtained reaction-produced gas (considered to contain methane as well as CO2 desorbed from the CO2 storage-reduction catalyst and an unreacted reducing gas) and reducing the residual CO2 in the reactor B for generation of methane. Note that the reduction time of CO2 in the reactor B was 133 seconds, and the reactor B was closed after the emission of the methane-containing gas. After that, the reactor A2 was supplied with the purge gas for 7.5 seconds followed by emission as it was. On the other hand, in this period of time (140.5 seconds), the reactor A1 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst.

[0049] Next, the reactor A2 was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A1 after the storage of CO2 was supplied with the purge gas for 7.5 seconds. In addition, the purge gas emitted from the reactor A1 was supplied to the reactor A2 via the purge gas recirculation lines 5. This allowed the reactor A2 to store CO2 into the CO2 storage-reduction catalyst and allowed the reactor A1 to remove the reaction-inhibiting components such as O2. Note that the reactor B was successively closed (15 seconds in total).

[0050] Next, methane was generated by supplying the reactor A1 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. A methane-containing gas was obtained by supplying the reactor B with the obtained reaction-produced gas (considered to contain methane as well as CO2 desorbed from the CO2 storage-reduction catalyst and an unreacted reducing gas) and reducing the residual CO2 in the reactor B for generation of methane. Note that the reduction time of CO2 in the reactor B was 133 seconds, and the reactor B was closed after the emission of the methane-containing gas. After that, the reactor A1 was supplied with the purge gas for 7.5 seconds followed by emission as it was. On the other hand, in this period of time (140.5 seconds), the reactor A2 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst.

[0051] The series of operations described above was repeated until a steady state was reached. A mass spectrometer was used to measure the CO2 concentrations and methane concentrations in the incoming gas (CO2-containing gas) and the outgoing gas (methane-containing gas) into/from the apparatus in the steady state. Determined were the amount of CO2 removed, the amount of CO2 emitted, and the amount of methane generated per hour based on the obtained measurement results. Table 3 and FIG. 8 to FIG. 10 show the results.

(Example 2)



[0052] Methane was continuously produced with a gas containing CO2 and O2 as a raw material by using the apparatus of producing methane illustrated in FIG. 3 and in accordance with the flowcharts described in FIG. 7A to FIG. 7C and with the time settings described in Table 2. In the apparatus of producing methane illustrated in FIG. 3, two reactors A1 and A2 provided with a CO2 storage-reduction catalyst were disposed in parallel. The gas inlet of each of the reactors A1 and A2 was connected to the gas supply line 3 for supplying a CO2-containing gas. The gas supply line 3 was connected to the means 1 for supplying purge gas and the means 2 for supplying reducing gas. In addition, the gas outlet of each of the reactors A1 and A2 was connected to the gas transfer line 4 for transferring the obtained reaction-produced gas to the reactor B provided with a methanation catalyst. The gas storage containers C1 and C2 were disposed on the gas transfer lines 4. Moreover, the gas outlet of the reactor A1 and the gas inlet of the reactor A2 were connected together via the purge gas recirculation line 5. Simultaneously, the gas outlet of the reactor A2 and the gas inlet of the reactor A1 were connected together via the purge gas recirculation line 5.

[0053] The CO2 storage-reduction catalyst, the methanation catalyst, the CO2-containing gas, the purge gas, and the reducing gas used were the same as those used in Example 1. In addition, the same conditions as those in Example 1 were set for the temperatures of the reactors A1 and A2 and the reactor B and the flow rates of the CO2-containing gas, the purge gas, and the reducing gas.
[Table 2]
Time [sec]Reactor A1Reactor A2Gas Storage Container C1Gas Storage Container C2Reactor B
7.5 T11 T21 --- T51 ---
140.5 --- T22 --- T52 ---
148.0 T13 T23 T43 T53 T63
155.5 T14 T24 T44 --- ---
288.5 T15 --- T45 --- ---
296.0 T16 T26 T46 T56 T66


[0054] As shown in FIG. 7A to FIG. 7C and Table 2, the reactor A1 after the reduction reaction (excluding the first cycle) was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A2 after the storage of CO2 (excluding the first cycle) was supplied with the purge gas for 7.5 seconds. In addition, in this period of time (for 7.5 seconds), the purge gas emitted from the reactor A2 was supplied to the reactor A1 via the purge gas recirculation lines 5. This allowed the reactor A1 to store CO2 into the CO2 storage-reduction catalyst and allowed the reactor A2 to remove reaction-inhibiting components such as O2. Moreover, in this period of time, a methane-containing gas was obtained (excluding the first cycle) by supplying the reactor B with the reaction-produced gas stored in the gas storage container C1 and reducing the residual CO2 in the reactor B for generation of methane. Note that the gas storage container C2 was closed in this period of time (for 7.5 seconds).

[0055] Next, methane was generated (excluding the first cycle) by supplying the reactor A2 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. The obtained reaction-produced gas (considered to contain methane as well as CO2 desorbed from the CO2 storage-reduction catalyst and an unreacted reducing gas) was supplied to the gas storage container C2. After that, the reactor A2 was supplied with the purge gas for 7.5 seconds followed by emission as it was. In this period of time (for 7.5 seconds), the gas storage container C2 was closed and stored the reaction-produced gas. On the other hand, in this period of time (140.5 seconds), the reactor A1 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst. In addition, a methane-containing gas was obtained (excluding the first cycle) by subsequently supplying the reactor B with the reaction-produced gas stored in the gas storage container C1 and reducing the residual CO2 in the reactor B for generation of methane. Note that the supply time taken to supply the reaction-produced gas from the gas storage container C1 to the reactor B was 148 seconds in total (in other words, the reduction time of CO2 in the reactor B). Next, the reactor A2 was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A1 after the storage of CO2 was supplied with the purge gas for 7.5 seconds. In addition, the purge gas emitted from the reactor A1 was supplied to the reactor A2 via the purge gas recirculation lines 5. This allowed the reactor A2 to store CO2 into the CO2 storage-reduction catalyst and allowed the reactor A1 to remove the reaction-inhibiting components such as O2. Moreover, in this period of time, a methane-containing gas was obtained by supplying the reactor B with the reaction-produced gas stored in the gas storage container C2 and reducing the residual CO2 in the reactor B for generation of methane. Note that the gas storage container C1 was closed in this period of time (for 7.5 seconds).

[0056] Next, methane was generated by supplying the reactor A1 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. The obtained reaction-produced gas (considered to contain methane as well as CO2 desorbed from the CO2 storage-reduction catalyst and an unreacted reducing gas) was supplied to the gas storage container C1. After that, the reactor A1 was supplied with the purge gas for 7.5 seconds followed by emission as it was. In this period of time (for 7.5 seconds), the gas storage container C1 was closed and stored the reaction-produced gas. On the other hand, in this period of time (140.5 seconds), the reactor A2 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst. In addition, a methane-containing gas was obtained by subsequently supplying the reactor B with the reaction-produced gas stored in the gas storage container C2 and reducing the residual CO2 in the reactor B for generation of methane. Note that the supply time taken to supply the reaction-produced gas from the gas storage container C2 to the reactor B was 148 seconds in total (in other words, the reduction time of CO2 in the reactor B).

[0057] The series of operations described above was repeated until a steady state was reached. A mass spectrometer was used to measure the CO2 concentrations and methane concentrations in the incoming gas (CO2-containing gas) and the outgoing gas (methane-containing gas) into/from the apparatus in the steady state. Determined were the amount of CO2 removed, the amount of CO2 emitted, and the amount of methane generated per hour based on the obtained measurement results. Table 3 and FIG. 8 to FIG. 10 show the results.

(Comparative Example 1)



[0058] Methane was continuously produced with a gas containing CO2 and O2 as a raw material by using the apparatus of producing methane illustrated in FIG. 11. In the apparatus of producing methane illustrated in FIG. 11, one reactor A1 provided with a CO2 storage-reduction catalyst was disposed. The gas inlet of the reactor A1 was connected to the gas supply line 3 for supplying a CO2-containing gas. The gas supply line 3 was connected to the means 1 for supplying purge gas and the means 2 for supplying reducing gas.

[0059] The CO2 storage-reduction catalyst, the CO2-containing gas, the purge gas, and the reducing gas used were the same as those used in Example 1. In addition, the same conditions as those in Example 1 were set for the temperatures of the reactor A1 and the reactor B and the flow rates of the CO2-containing gas, the purge gas, and the reducing gas.

[0060] The reactor A1 after the reduction reaction (excluding the first cycle) was supplied with the CO2-containing gas for 148 seconds. This allowed the reactor A1 to store CO2 into the CO2 storage-reduction catalyst. Next, the reactor A1 after the storage of CO2 was supplied with the purge gas for 7.5 seconds followed by emission as it was. This allowed the reactor A1 to remove reaction-inhibiting components such as O2. Next, methane was generated by supplying the reactor A1 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. As a result, a methane-containing gas was obtained. After that, the reactor A1 was supplied with the purge gas for 7.5 seconds followed by emission as it was.

[0061] The series of operations described above was repeated until a steady state was reached. A mass spectrometer was used to measure the CO2 concentrations and methane concentrations in the incoming gas (CO2-containing gas) and the outgoing gas (methane-containing gas) into/from the apparatus in the steady state. Determined were the amount of CO2 removed, the amount of CO2 emitted, and the amount of methane generated per hour based on the obtained measurement results. Table 3 and FIG. 8 to FIG. 10 show the results.

(Comparative Example 2)



[0062] Methane was continuously produced with a gas containing CO2 and O2 as a raw material by using the apparatus of producing methane illustrated in FIG. 12. In the apparatus of producing methane illustrated in FIG. 12, two reactors A1 and A2 provided with a CO2 storage-reduction catalyst were disposed in parallel. The gas inlet of each of the reactors A1 and A2 was connected to the gas supply line 3 for supplying a CO2-containing gas. The gas supply line 3 was connected to the means 1 for supplying purge gas and the means 2 for supplying reducing gas.

[0063] The CO2 storage-reduction catalyst, the CO2-containing gas, the purge gas, and the reducing gas used were the same as those used in Example 1. In addition, the same conditions as those in Example 1 were set for the temperatures of the reactors A1 and A2 and the flow rates of the CO2-containing gas, the purge gas, and the reducing gas.

[0064] The reactor A1 after the reduction reaction (excluding the first cycle) was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A2 after the storage of CO2 (excluding the first cycle) was supplied with the purge gas for 7.5 seconds. This allowed the reactor A1 to storage CO2 into the CO2 storage-reduction catalyst and allowed the reactor A2 to remove reaction-inhibiting components such as O2.

[0065] Next, methane was generated (excluding the first cycle) by supplying the reactor A2 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. As a result, a methane-containing gas was obtained. After that, the reactor A2 was supplied with the purge gas for 7.5 seconds followed by emission as it was. On the other hand, in this period of time (140.5 seconds), the reactor A1 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst.

[0066] Next, the reactor A2 was supplied with the CO2-containing gas for 7.5 seconds, and simultaneously, the reactor A1 after the storage of CO2 was supplied with the purge gas for 7.5 seconds. This allowed the reactor A2 to store CO2 into the CO2 storage-reduction catalyst and allowed the reactor A1 to remove the reaction-inhibiting components such as O2.

[0067] Next, methane was generated by supplying the reactor A1 with the reducing gas for 133 seconds to reduce the CO2 stored in the CO2 storage-reduction catalyst. As a result, a methane-containing gas was obtained. After that, the reactor A1 was supplied with the purge gas for 7.5 seconds followed by emission as it was. On the other hand, in this period of time (140.5 seconds), the reactor A2 was supplied only with the CO2-containing gas to store CO2 in the CO2 storage-reduction catalyst.

[0068] The series of operations described above was repeated until a steady state was reached. A mass spectrometer was used to measure the CO2 concentrations and methane concentrations in the incoming gas (CO2-containing gas) and the outgoing gas (methane-containing gas) into/from the apparatus in the steady state. Determined were the amount of CO2 removed, the amount of CO2 emitted, and the amount of methane generated per hour based on the obtained measurement results. Table 3 and FIG. 8 to FIG. 10 show the results.
[Table 3]
[mmol/hr]Example 1Example 2Comparative Example 1Comparative Example 2
Amount of CO2 removed 2.68 2.68 1.13 2.26
Amount of CO2 emitted 0 0 0.21 0.42
Amount of methane generated 2.24 2.64 0.80 1.60


[0069] As shown in Table 3 and FIG. 8 to FIG. 10, each of the amount of CO2 removed and the amount of methane generated doubled in the case of continuously producing methane by disposing two reactors provided with the CO2 storage-reduction catalyst in parallel (Comparative Example 2) compared to the case of alternately storing and reducing CO2 by using one reactor provided with the CO2 storage-reduction catalyst (Comparative Example 1). However, since the amount of the purge gas emitted also doubled, the amount of CO2 emitted doubled, too.

[0070] On the other hand, even in comparison with Comparative Example 2, the amount of CO2 removed and the amount of methane generated increased, and furthermore, no emission of CO2 was detected in the cases (Examples 1 and 2) of using the apparatus of producing methane of the present invention in which the two reactors provided with the CO2 storage-reduction catalyst are disposed in parallel, their gas inlets and gas outlets are connected to each other via purge gas recirculation lines, and the reactor provided with the methanation catalyst is disposed downstream of the reactors provided with the CO2 storage-reduction catalyst on the gas flow paths. In addition, as is obvious from the results of Examples 1 and 2, it was found that the amount of methane generated increased by disposing the gas storage container between the reactors provided with the CO2 storage-reduction catalyst and the reactor provided with a methanation catalyst.

[0071] As described above, the present invention makes it possible to prevent emission of CO2 at the time of removing reaction-inhibiting components such as O2 contained in a CO2-containing gas and further to enhance the concentration and the purity of methane in the methane-containing gas to be obtained.

[0072] Therefore, the apparatus and the method for producing methane of the present invention are useful as e.g. an apparatus and a method which make it possible to continuously produce methane using, as a raw material, a gas such as a combustion exhaust gas or a biogas which contains CO2 and reaction-inhibiting components such as O2.

Reference Signs List



[0073] 

A, A1, A2: a reactor provided with a CO2 storage-reduction catalyst

B: a reactor provided with a methanation catalyst

C, C1, C2: a gas storage container

1: a means for supplying purge gas

2: a means for supplying reducing gas

3: a gas supply line

4: a gas transfer line

5: a purge gas recirculation line

6: a means for removing moisture in gas




Claims

1. An apparatus of producing methane from a CO2-containing gas, comprising:

a reactor which is provided with a CO2 storage-reduction catalyst having a CO2 storage capacity and a methane generation ability;

at least one reactor which is provided with a methanation catalyst;

at least one means for supplying purge gas; and

at least one means for supplying reducing gas,

wherein

two or more of the reactors provided with the CO2 storage-reduction catalyst are disposed in parallel,

the means for supplying purge gas and the means for supplying reducing gas are disposed upstream of the reactors provided with the CO2 storage-reduction catalyst on gas flow paths,

the reactor provided with the methanation catalyst is disposed downstream of the reactors provided with the CO2 storage-reduction catalyst on the gas flow paths, and

a gas outlet of one of the reactors provided with the CO2 storage-reduction catalyst is connected to a gas inlet of at least one different reactor provided with the CO2 storage-reduction catalyst, other than the one reactor, via a purge gas recirculation line which supplies a purge gas emitted from the gas outlet of the one reactor into the gas inlet of the different reactor.


 
2. The apparatus of producing methane according to claim 1, wherein

at least one gas storage container, which stores a reaction-produced gas emitted from gas outlets of the reactors provided with the CO2 storage-reduction catalyst, is further disposed between the reactors provided with the CO2 storage-reduction catalyst and the reactor provided with the methanation catalyst.


 
3. The apparatus of producing methane according to claim 2, wherein

the gas storage container is disposed between the reactor provided with the methanation catalyst and each of the reactors provided with the CO2 storage-reduction catalyst.


 
4. A method for producing methane from a CO2-containing gas using the apparatus of producing methane according to any one of claims 1 to 3, the method comprising the steps of:

allowing the CO2 storage-reduction catalyst to store CO2 by supplying a CO2-containing gas to one of the reactors provided with the CO2 storage-reduction catalyst;

reducing the CO2 by supplying a reducing gas to the one reactor provided with the CO2 storage-reduction catalyst having stored the CO2;

supplying a reaction-produced gas obtained by reduction of the CO2 to the reactor provided with the methanation catalyst;

supplying a purge gas to the one reactor after the storage of the CO2 and supplying the purge gas emitted from the one reactor to the one reactor after the reduction reaction; and

reducing residual CO2 in the reaction-produced gas supplied to the reactor provided with the methanation catalyst, wherein

each of the reactors provided with the CO2 storage-reduction catalyst alternately carries out the storing of CO2 and the reducing of CO2, and

at least one of the reactors provided with the CO2 storage-reduction catalyst carries out the storage of CO2 and simultaneously a remaining reactor provided with the CO2 storage-reduction catalyst carries out the reducing of CO2.


 
5. The method for producing methane from a CO2-containing gas according to claim 4 using the apparatus of producing methane according to claim 2 or 3, wherein

the reaction-produced gas obtained by reduction of CO2 is stored in the gas storage container and then is supplied to the reactor provided with the methanation catalyst.


 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description




Non-patent literature cited in the description