Carbon dioxide absorbent and method for recovering carbon dioxide

Abstract

To provide a carbon dioxide absorbent exhibiting excellent carbon dioxide absorption capability as well as excellent desorption capability of absorbed carbon dioxide, and a method for recovering carbon dioxide using the carbon dioxide absorbent.SOLUTION: A carbon dioxide absorbent comprises a solid material composed of a porous substance having pores on a surface, and a cyclic diamine and a polyamine supported in the pores, wherein the weight ratio of the polyamine relative to the total amount of the cyclic diamine and the polyamine is 60% or less.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide absorbent and a method for capturing carbon dioxide. [Background technology]

[0002] In recent years, in order to reduce the concentration of carbon dioxide in the atmosphere, technologies have been considered for directly absorbing carbon dioxide in the atmosphere and for separating and recovering carbon dioxide contained in the combustion exhaust gas of fossil fuels and the like.

[0003] In carbon dioxide recovery, a method has been proposed in which carbon dioxide is absorbed into an absorbent and the absorbed carbon dioxide is desorbed from the absorbent. For example, Patent Document 1 listed below describes a method in which carbon dioxide is separated from combustion exhaust gas using an amine-containing solution as an absorbent, and then the solution is heated to desorb and recover the carbon dioxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-245339 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in order to desorb and recover the absorbed carbon dioxide from a carbon dioxide absorbent, it is necessary to input energy such as heating. If the energy required for this desorption is large, the cost of carbon dioxide recovery increases. If it is not possible to desorb and recover the carbon dioxide absorbed by the absorbent with low energy after absorbing carbon dioxide with the absorbent, it becomes difficult to comprehensively reduce carbon dioxide emissions. For example, if a large amount of electricity is consumed to desorb carbon dioxide, carbon dioxide will be released to generate this electricity. In addition, problems may arise regarding the handling of the absorbent after carbon dioxide has been absorbed.

[0006] On the other hand, as mentioned above, if high energy is required to desorb and capture carbon dioxide from absorbents that have already absorbed it, the running costs associated with operating the system become a concern. This is an obstacle to the introduction and widespread use of carbon dioxide capture systems. At present, the problem of global warming is considered one of the issues that must be resolved worldwide. Reducing carbon dioxide emissions, which are considered one of the main causes of global warming, and ultimately reducing the carbon dioxide concentration in the atmosphere, can be said to be an urgent issue.

[0007] In light of the above, in order to promote efforts to reduce the concentration of carbon dioxide in the atmosphere, there is a need to develop a system that can absorb carbon dioxide into an absorbent material and then desorb and capture the carbon dioxide from the absorbent material at low cost and with low energy consumption.

[0008] In order to construct such a system, it is particularly important to realize a carbon dioxide absorbent material that has excellent carbon dioxide absorption capacity and excellent ability to desorb the absorbed carbon dioxide.

[0009] In view of the above circumstances, an object of the present invention is to provide a carbon dioxide absorbent having excellent carbon dioxide absorption capacity and excellent carbon dioxide desorption capacity, and to provide a carbon dioxide recovery method using the carbon dioxide absorbent. [Means for solving the problem]

[0010] The carbon dioxide absorbent according to the present invention comprises: a solid material made of a porous substance having pores on its surface; a cyclic diamine and a polyamine supported in the pores; The weight ratio of the polyamine to the total amount of the cyclic diamine and polyamine is 60% or less.

[0011] In this specification, the term "pore" refers to a minute hole with a diameter of about several nm to several tens of μm, and the term "porous material" refers to a material having numerous pores on its surface.

[0012] By supporting an amine capable of absorbing carbon dioxide in the pores of the porous material, it is possible to increase the area over which the carbon dioxide contained in the gas to be treated comes into contact with the amine, thereby enabling efficient absorption of carbon dioxide. In the above configuration, the amine includes a cyclic diamine and a polyamine.

[0013] As mentioned above, in order to construct a system that can capture carbon dioxide at low cost and with low energy consumption, it is important to realize a carbon dioxide absorbent that has excellent carbon dioxide absorption capacity and also excellent desorption capacity of the absorbed carbon dioxide.

[0014] In view of this, the present inventors have focused on cyclic diamines. A cyclic diamine is a cyclic compound having two primary or secondary amino groups in the molecule. An example of the reaction in which a cyclic diamine absorbs carbon dioxide is shown below. Formula (1) corresponds to the reaction between 4,4'-methylenebis(2-methylcyclohexylamine) and carbon dioxide, and formula (2) corresponds to the reaction between isophoronediamine and carbon dioxide. [ka]

[0015] As shown in formulas (1) and (2), cyclic diamines are characterized by producing carbamic acid when they absorb carbon dioxide. The carbamic acid precipitates as a solid phase from the carbon dioxide absorbing solution and separates from the liquid phase. In other words, in the reaction of absorbing carbon dioxide, the produced carbamic acid is sequentially removed from the reaction system (liquid phase). For this reason, cyclic diamines are characterized by the fact that the concentration of the product carbamic acid in the reaction system is less likely to increase, and therefore the carbon dioxide absorption reaction easily proceeds.

[0016] Furthermore, the absorbed carbon dioxide can be desorbed by providing energy to the cyclic diamine that has absorbed carbon dioxide through heat supply, causing the reverse reaction of the reactions represented by formulas (1) and (2). In the desorption reaction of absorbed carbon dioxide, the temperature of the liquid phase containing the cyclic diamine is increased by the supply of heat. This increases the solubility of the solid carbamic acid, causing it to dissolve in the liquid phase. The carbamic acid is stable in the solid phase, and in the unstable liquid phase, the energy required for the reaction is thought to be reduced. In other words, cyclic diamines have excellent desorption capabilities for absorbed carbon dioxide. Cyclic diamines can desorb absorbed carbon dioxide even in a relatively low temperature environment, such as 60°C. While the above formulas (1) and (2) use 4,4'-methylenebis(2-methylcyclohexylamine) or isophoronediamine as examples of the cyclic diamine, the reaction with carbon dioxide to produce solid carbamic acid is similar for other cyclic diamines.

[0017] As a result of extensive research aimed at further improving the carbon dioxide absorbent, the present inventors have newly discovered that, according to the above-mentioned configuration, the absorption capacity of the carbon dioxide absorbent can be further increased while maintaining the characteristic of the cyclic diamine, namely, excellent carbon dioxide desorption capacity. As will be described in detail later, the above-mentioned configuration realizes a carbon dioxide absorbent that has excellent carbon dioxide absorption capacity and also excellent desorption capacity of absorbed carbon dioxide.

[0018] Examples of cyclic diamines include 4,4'-methylenebis(2-methylcyclohexylamine), 4,4'-methylenebis(cyclohexylamine), isophoronediamine, cyclohexane-1,2-diamine, cyclohexane-1,3-diamine, metaxylenediamine, and derivatives thereof. The cyclic diamines can be used alone or in combination.

[0019] Examples of polyamines include polyethylene polyamines such as polyethylene imine, diamines such as ethylene diamine and N,N-dimethylethylene diamine, and triamines such as diethylene triamine. The polyamines can be used alone or as a mixture.

[0020] In the carbon dioxide absorbent, The porous material has an average particle size of 1 mm to 5 mm and a specific surface area of ​​50 m 2 / g~700m 2 / g is also acceptable.

[0021] The specific surface area of ​​a porous material is 10m 2 / g or more, and 2 / g or more is more preferable. The specific surface area of ​​the porous substance can be measured, for example, by a method conforming to JIS Z 8830 (method for measuring the specific surface area of ​​powder (solid) by gas adsorption).

[0022] The average particle size of the porous material can be measured, for example, by an image analysis type particle size distribution measurement method.

[0023] Materials that can be used as the porous substance include ceramic materials such as silica, alumina, and zirconia; engineering plastic materials such as polypropylene, polyacetal, polyamide, and polycarbonate; carbon materials such as activated carbon and carbon fiber; and resins containing cellulose. The shape of the porous substance is not particularly limited. Examples of the shape of the porous substance include granular, plate-like, tubular, honeycomb, and pellet-like shapes.

[0024] The average pore diameter of the porous material is preferably in the range of 10 nm to 0.5 μm, more preferably 30 nm to 0.1 μm. The average pore diameter of the porous material (also expressed as "4V / A") can be measured by a known gas adsorption method in accordance with JIS Z 8831-2 (Powder (Solid) Pore Size Distribution and Pore Characteristics). Here, V is the pore volume, and A is the specific surface area.

[0025] In the carbon dioxide absorbent, The cyclic diamine may be 4,4'-methylenebis(2-methylcyclohexylamine), and the polyamine may be polyethyleneimine.

[0026] The carbon dioxide absorbent is It may also contain polyethylene glycol supported in the pores.

[0027] The carbon dioxide recovery method according to the present invention comprises: A step (a) of preparing a first absorbent material that is an absorbent material before absorbing carbon dioxide by causing a carbon dioxide absorbing liquid to be supported in the pores of a solid material made of a porous substance having pores on the surface; (b) a step of absorbing carbon dioxide into the first absorbent material to prepare a second absorbent material that has absorbed carbon dioxide; (c) providing heat to the second absorbent material; and a step (d) of recovering the carbon dioxide desorbed from the second absorbent material after the step (c), The carbon dioxide absorbing solution contains a cyclic diamine and a polyamine, and is characterized in that the weight ratio of the polyamine to the total amount of the cyclic diamine and the polyamine is 60% or less.

[0028] In this specification, the term "first absorbent" refers to the state of the carbon dioxide absorbent before it absorbs carbon dioxide. Furthermore, the term "second absorbent" refers to the state of the carbon dioxide absorbent after it has absorbed carbon dioxide. Note that the term "first absorbent" also includes the state in which, after the absorbent has absorbed carbon dioxide and become the second absorbent, it has been supplied with thermal energy and desorbed the carbon dioxide.

[0029] In addition, in this specification, "recovery" means transferring carbon dioxide desorbed from the absorbent material from the area where the absorbent material is placed to another area. For example, the carbon dioxide may be stored in a storage tank such as a cylinder, or may be sent via piping to a carbon dioxide utilization facility. Examples of such utilization facilities include a plant factory.

[0030] In the carbon dioxide recovery method, The cyclic diamine may be 4,4'-methylenebis(2-methylcyclohexylamine), and the polyamine may be polyethyleneimine.

[0031] In the carbon dioxide recovery method, The carbon dioxide absorbing liquid may contain polyethylene glycol. [Effects of the Invention]

[0032] According to the present invention, there is provided a carbon dioxide absorbent having excellent carbon dioxide absorption capacity and excellent carbon dioxide desorption capacity. Furthermore, according to the present invention, there is provided a carbon dioxide recovery method using the carbon dioxide absorbent. [Brief explanation of the drawings]

[0033] [Figure 1A] 1 is a cross-sectional view schematically showing the configuration of a first embodiment of a carbon dioxide recovery system. [Figure 1B] 1B is a view showing a different scene from that of FIG. 1A in the recovery system according to FIG. 1A; [Figure 2] 1B is a view of the collection system of FIG. 1A from a different angle. [Figure 3] FIG. 1 is a flow chart showing an example of a recovery method according to the present invention. [Figure 4A] FIG. 2 is a cross-sectional view schematically showing the structure of a porous material that supports a carbon dioxide absorbing liquid. [Figure 4B] FIG. 2 is a cross-sectional view schematically showing the structure of a first absorbent material. [Figure 4C] FIG. 4 is a cross-sectional view schematically showing another example of the structure of the first absorbent material. [Figure 5A] 1 is a graph showing the amount of carbon dioxide absorbed by a first absorbent material in each example. [Figure 5B] 1 is a graph showing the amount of carbon dioxide absorbed after 12 hours in each example. [Figure 6A]1 is a graph showing the amount of carbon dioxide desorbed from a second absorbent material in each example. [Figure 6B] 1 is a graph showing the desorption rate after 2 hours in each example. [Figure 7] 6B is a graph showing the results of verification 2. [Figure 8] 10 is a diagram schematically illustrating the configuration of a second embodiment of a recovery system. [Figure 9] FIG. 10 is a cross-sectional view schematically showing the structure of a reaction vessel according to a second embodiment. [Figure 10] 10 is a view showing a different scene from that of FIG. 9 in the reaction vessel according to FIG. 9. [Figure 11] FIG. 10 is a cross-sectional view schematically showing the structure of a heat source according to a second embodiment. [Figure 12] 12 is a view of the heat source according to FIG. 11 as seen from the Z direction. [Figure 13] 10 is a diagram schematically illustrating the configuration of another embodiment of the recovery system. [Figure 14] 14 is a diagram showing a different scene from that of FIG. 13 in the recovery system according to FIG. 13. [Figure 15] 10 is a diagram schematically illustrating another configuration example of the recovery system. [Figure 16A] FIG. 16 is a perspective view schematically showing the configuration of a heat source in FIG. [Figure 16B] 16B is a ZY cross-sectional view of the heat source of FIG. 16A when viewed from the X direction. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, a carbon dioxide capture method according to the present invention (hereinafter simply referred to as the "capture method") will be described with reference to a carbon dioxide capture system capable of carrying out the capture method. After that, the configuration of the carbon dioxide absorbent according to the present invention will be described. Note that the drawings below are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily match the actual dimensional ratios and numbers.

[0035] [First embodiment] (Carbon dioxide capture system) 1A and 1B are cross-sectional views showing a schematic configuration of a carbon dioxide recovery system (hereinafter simply referred to as "recovery system") capable of carrying out the recovery method of the present invention. FIG. 1A corresponds to a scene in which a step of absorbing carbon dioxide contained in a gas G1 to be treated, such as the atmosphere (step S2 described below) is carried out, and FIG. 1B corresponds to a scene in which a step of desorbing the absorbed carbon dioxide (step S3 described below) is carried out. Furthermore, FIG. 2 is a drawing showing the recovery system of FIG. 1A viewed from a different direction.

[0036] In each of the following figures, an XYZ coordinate system consisting of mutually orthogonal X, Y, and Z directions is also shown as appropriate. Typically, the Z direction is the vertical direction. Based on this definition, FIG. 2 corresponds to a drawing of the recovery system according to FIG. 1A as seen from the Z direction. Note that, as will be described later, part of the configuration of the reaction tank 2 is omitted in FIG. 2.

[0037] As shown in FIG. 1A, the recovery system 1 includes a reaction tank 2, a carbon dioxide absorbent (hereinafter, sometimes simply referred to as "absorbent 3") located inside the reaction tank 2 and exhibiting carbon dioxide absorption properties, and a heat source 4 that supplies thermal energy to the absorbent 3.

[0038] As described above, the absorbent 3 is configured to contain a carbon dioxide absorbing liquid that has the property of absorbing carbon dioxide and the property of desorbing the absorbed carbon dioxide by supplying heat H1. The absorbent 3 is made of a granular porous substance having pores on its surface, and the carbon dioxide absorbing liquid is supported in the pores. The configuration of the absorbent 3 will be described later.

[0039] The reaction vessel 2 accommodates therein an absorber 3, a solar heat collecting member 15 (hereinafter simply referred to as "heat collecting member 15") as a heat source 4, and a heat transfer member 19 for efficiently transferring heat H1 from the heat collecting member 15 to the absorber 3. The reaction vessel 2 also has a light-transmitting part 20 made of a glass material such as quartz glass on the +Z side so that the heat collecting member 15 can receive solar light C2 (see also FIG. 1B).

[0040] In this embodiment, as shown in Fig. 2, a plurality of plate-shaped heat transfer members 19 are arranged in the X direction. In addition, from the viewpoint of efficiently transferring heat from the heat collecting member 15 to the absorption material 3, the heat transfer members 19 are connected on the +Z side and arranged directly with respect to the heat collecting member 15 (see Fig. 1B). Note that, for convenience of illustration, Fig. 2 does not show the connection portions between the light transmitting portion 20, the heat collecting member 15, and the heat transfer members 19.

[0041] In this embodiment, an example is shown in which the heat source 4 is disposed inside the reaction vessel 2, but as will be described later with reference to a second embodiment, the arrangement of the heat source 4 is not limited to this example.

[0042] Next, an example of a collection method that can be performed by the collection system 1 will be described.

[0043] 3 is a flow diagram showing an example of a recovery method according to the present invention. This recovery method 1a includes a step S1 of preparing an absorbent 3 in a state before absorbing carbon dioxide (hereinafter referred to as a "first absorbent 3a" for convenience), a step S2 of making the first absorbent 3a absorb carbon dioxide and preparing an absorbent 3 in a state in which carbon dioxide has been absorbed (hereinafter referred to as a "second absorbent 3b" for convenience), a step S3 of supplying heat to the second absorbent 3b, and a step S4 of recovering a gas containing carbon dioxide desorbed from the second absorbent 3b by carrying out step S3 (hereinafter referred to as a "recovered gas G2" for convenience).

[0044] By performing step S3, the second absorbent 3b desorbs the absorbed carbon dioxide and then becomes the first absorbent 3a. That is, in the recovery method 1a, step S2 and subsequent steps can be repeated after performing step S4.

[0045] (Step S1: Preparation of first absorbent material) First, an absorbent (first absorbent 3a) is prepared before absorbing carbon dioxide. The first absorbent 3a is prepared by supporting a carbon dioxide absorbing liquid on a porous material having pores on the surface.

[0046] FIG. 4A is a cross-sectional view schematically showing the structure of a porous material 10. As shown in FIG. 4A, the porous material 10 is a solid material having numerous pores 11 on its surface. A carbon dioxide absorbing liquid is brought into contact with this porous material 10, and the carbon dioxide absorbing liquid is supported in the pores 11. FIG. 4B is a cross-sectional view schematically showing the structure of a first absorbent 3a prepared through the above-described operation. In FIG. 4B, the average pore diameter D2 of the porous material 10 is schematically shown. As an example, the average pore diameter D2 is 100 nm or less. Note that in FIGS. 4A and 4B, the average pore diameter D2 is exaggerated relative to the particle diameter D1 of the porous material 10 for ease of illustration.

[0047] 4C is a cross-sectional view, similar to FIG. 4B, that schematically illustrates the structure of the first absorbent 3a when the average pore diameter D2 is relatively large (for example, about several μm). The average pore diameter D2 is appropriately designed depending on, for example, the surface tension of the carbon dioxide absorbing liquid 12 supported in the pores 11 and the carbon dioxide absorption capacity. Note that, from the viewpoint of preventing the supported carbon dioxide absorbing liquid 12 from peeling off from the pores 11, the average pore diameter D2 may be set to 0.5 μm or less.

[0048] The porous material 10 may be a ceramic material such as silica, alumina, or zirconia; an engineering plastic material such as polypropylene, polyacetal, polyamide, or polycarbonate; a carbon material such as activated carbon or carbon fiber; or a resin containing cellulose.

[0049] The carbon dioxide absorbing liquid 12 contains a cyclic diamine and a polyamine as amines that absorb carbon dioxide. As the cyclic diamine, for example, 4,4'-methylenebis(2-methylcyclohexylamine) is preferably used. Hereinafter, for convenience, 4,4'-methylenebis(2-methylcyclohexylamine) is abbreviated as "MBMCA." Furthermore, as the polyamine, polyethyleneimine (hereinafter abbreviated as "PEI") is preferably used.

[0050] MBMCA is characterized by a large molecular weight of approximately 238 g / mol and a relatively high boiling point of approximately 340° C. It is conceivable that the supply of heat H1 will cause a small amount of carbon dioxide absorbing solution to evaporate from the absorbent 3, but MBMCA is preferable because its high boiling point can suppress such evaporation of the carbon dioxide absorbing solution.

[0051] The carbon dioxide absorbing solution may contain water or an alcohol such as methanol in advance depending on the viscosity of the cyclic diamine and polyamine, etc. For example, by mixing methanol, the viscosity of the carbon dioxide absorbing solution in which the cyclic diamine and polyamine are mixed can be reduced.

[0052] By adding methanol or the like to the carbon dioxide absorbing liquid 12, the viscosity of the carbon dioxide absorbing liquid 12 is reduced, and as a result, the carbon dioxide absorbing liquid 12 can be suitably introduced into the pores 11. In this case, after the carbon dioxide absorbing liquid 12 is supported on the porous material 10, the porous material 10 is preferably heated to evaporate the alcohol. For example, the heating condition when methanol is used is about 60°C. When evaporating the alcohol, the porous material 10 is preferably placed in a reduced pressure atmosphere of, for example, about 60 kPa or less.

[0053] Furthermore, the carbon dioxide absorbing liquid 12 may be mixed with an additive such as polyethylene glycol (hereinafter abbreviated as "PEG"), for example. PEG has many oxygen bonds in its molecule. Since cyclic diamines and polyamines have hydrogen atoms at their terminals, it is thought that a bonding force resulting from hydrogen bonds is generated between the oxygen atoms of the PEG and the hydrogen atoms of the amine. In other words, by adding PEG when supporting the carbon dioxide absorbing liquid 12 on the porous material 10, the carbon dioxide absorbing liquid 12 can be preferably supported on the porous material 10. In view of this, it is preferable that the carbon dioxide absorbing liquid 12 contains PEG as an additive.

[0054] Furthermore, before the porous material 10 is made to support the carbon dioxide absorbing liquid 12, the porous material 10 may be sprayed with plasma gas or irradiated with ultraviolet rays. This can improve the hydrophilicity of the surfaces of the pores 11 contained in the porous material 10, allowing the carbon dioxide absorbing liquid 12 to be favorably supported. More specifically, when the plasma gas is sprayed onto the pores 11, nitrogen molecules or oxygen molecules in the atmosphere are converted into plasma, and the plasmatized active species form hydrophilic functional groups (hydroxyl groups, carbonyl groups, carboxy groups, etc.) on the surfaces of the pores 11. When ultraviolet rays are used, radicals (mainly oxygen radicals in the case of air) are generated in the atmosphere by the ultraviolet rays, and at the same time, the ultraviolet rays irradiate the porous material 10 to break the bonds between molecules that constitute the surfaces of the pores 11, and the radicals react with the broken sites, resulting in the formation of hydrophilic functional groups on the surfaces of the pores 11.

[0055] The first absorbent material 3a obtained through the above-mentioned operations is placed inside the reaction vessel 2 (see FIG. 1A).

[0056] Thus, the step S1 of preparing the first absorbent material 3a corresponds to the step (a).

[0057] (Step S2: Carbon dioxide absorption step) As shown in FIG. 1A, a gas to be treated G1 containing carbon dioxide is introduced into a reaction vessel 2, inside which a first absorbent 3a is located, through an inlet 5 and brought into contact with the first absorbent 3a. FIG. 2 schematically shows a manner in which the gas to be treated G1 flows through the reaction vessel 2. As a result, the first absorbent 3a absorbs carbon dioxide in the gas to be treated G1, and a second absorbent 3b is obtained that has absorbed carbon dioxide. Note that, to facilitate understanding, the second absorbent 3b that has absorbed carbon dioxide is hatched in each drawing (see FIG. 1B, etc.). The gas to be treated G1, whose carbon dioxide concentration has been reduced by the absorption of carbon dioxide, is discharged through an outlet 6, for example, to the outside space.

[0058] As will be described later, it is assumed that the reaction vessel 2 will be irradiated with sunlight C2 (step S3). On the other hand, from the viewpoint of efficiently absorbing carbon dioxide by the first absorbent 3a, it is preferable to keep the atmosphere in the reaction vessel 2 at a low temperature. Therefore, in step S2, the sunlight C2 irradiated onto the reaction vessel 2 may be blocked by an arbitrary shielding member (not shown). Furthermore, step S2 may be performed during a time period when there is no or little sunlight C2 irradiation, such as at night.

[0059] Examples of the gas G1 to be treated include the atmosphere, exhaust gas from a factory, etc. In particular, when the gas G1 to be treated is an exhaust gas, the gas G1 to be treated may be subjected to pretreatment such as cooling the gas G1 to be treated or screening for substances contained in the gas G1 to be treated that inhibit the absorption of carbon dioxide before being introduced into the reaction tank 2.

[0060] In this way, step S2 of preparing the second absorbent material 3b by causing the first absorbent material 3a to absorb carbon dioxide corresponds to step (b).

[0061] (Step S3: Supplying heat to the second absorbent material 3b) As described above, energy is required to desorb the absorbed carbon dioxide from the second absorbent 3b. For this reason, heat H1 is supplied to the second absorbent 3b. In this embodiment, the heat H1 is obtained by converting sunlight C2.

[0062] As shown in FIG. 1B, the heat source 4 is composed of a heat collecting member 15 disposed vertically above (on the +Z side of) the reaction vessel 2. The heat collecting member 15 is heated by absorbing sunlight C2 taken in through the light-transmitting portion 20. For example, the heat collecting member 15 is typically made of a metal such as aluminum or copper that is coated with a black color in order to efficiently absorb sunlight C2. Alternatively, the heat collecting member 15 may be coated with a black body material such as graphite that exhibits high light absorption.

[0063] In the example of FIG. 1B , the light-transmitting section 20 is made up of a plurality of transparent members 21 made of a glass material such as quartz glass. Furthermore, a reduced-pressure space 22 is formed between these transparent members 21. The pressure in the low-pressure space 22 is, for example, 10 kPa or less, and is typically approximately 0 atmospheres. The low-pressure space 22 is provided to make it difficult for the heat H1 converted by the heat collecting member 15 to be transmitted to the +Z side, but the present invention is not limited to whether or not the low-pressure space 22 is formed.

[0064] The heat H1 obtained by the heat collecting member 15 is supplied to the second absorption material 3b. As shown in FIG. 1B, the reaction vessel 2 has a heat transfer member 19 for efficiently supplying the heat H1 from the heat collecting member 15 to the second absorption material 3b. Typically, the heat transfer member 19 is disposed directly relative to the heat collecting member 15 and is heated by the heat from the heat collecting member 15. For example, a material with a high thermal conductivity, such as aluminum, copper, or ceramics, can be used as the heat transfer member 19. Note that the heat transfer member 19 may be formed integrally with the heat collecting member 15 using the same material.

[0065] 1B, heat H1 radiated from the heat transfer member 19 that has reached a high temperature is supplied to the second absorption material 3b, and the second absorption material 3b is heated. That is, in this embodiment, the sunlight C2 is converted into heat H1, and at the same time, the heat H1 is supplied to the second absorption material 3b.

[0066] Furthermore, the carbon dioxide concentration increases locally near the second absorbent where the carbon dioxide desorption reaction progresses. To efficiently promote the carbon dioxide desorption reaction, it is preferable to lower the carbon dioxide concentration near the second absorbent. This is because, in the carbon dioxide desorption reaction, lowering the carbon dioxide concentration in the carbon dioxide production (desorption) system makes it easier for the reaction system to proceed toward the carbon dioxide production side. For this reason, as shown in FIG. 1B, a desorption-promoting gas B1, such as air or nitrogen gas, may be introduced into the reaction vessel 2 through an inlet 5 simultaneously with the supply of heat H1.

[0067] As will be described later, a heat transfer medium made of a fluid may be used to supply the heat H1 to the second absorbent material 3b, and this configuration will be described in detail in the second embodiment below.

[0068] In this way, the step S3 of supplying the heat H1 to the second absorbent material 3b corresponds to the step (c).

[0069] (Step S4: Recovering desorbed carbon dioxide) The recovered gas G2 containing the carbon dioxide desorbed in step S3 is sent to a carbon dioxide utilization facility such as a plant factory through a pipe (not shown) via the outlet 6. However, in the present invention, the destination of the recovered gas G2 is not limited.

[0070] Thus, step S4 of recovering carbon dioxide corresponds to step (d).

[0071] [Verification 1] The carbon dioxide recovery capacity of the carbon dioxide absorbent according to the present invention was verified, and will be described below.

[0072] Example 1 First, 10 g of methanol was weighed out, and MBMCA, PEI, and a predetermined amount of PEG were mixed with the methanol to prepare a mixture. The mixture was stirred for 1 hour using a stirrer. Specifically, the MBMCA and PEI amounts were 0.35 g and 0.07 g, respectively.

[0073] Then, 1 g of silica was added as a solid material to the mixed solution, and the mixture was stirred for about 1 hour using a stirrer.

[0074] The solid material used was granular silica manufactured by Fuji Silysia. This silica has an average particle size of 1 mm to 5 mm and a specific surface area of ​​50 m 2 / g~700m 2 The average pore size of the silica was 50 nm.

[0075] After adding silica, the mixture was stirred while being heated at about 60°C in a reduced pressure atmosphere of about 50 kPa. A rotary evaporator was used for the stirring. The solid material removed from the rotary evaporator was then heated and dried at about 70°C in an atmospheric pressure atmosphere replaced with nitrogen gas. By the above operation, the methanol contained in the mixture impregnated into the solid material was evaporated. In this way, a first absorbent 3a in which the carbon dioxide absorbing liquid was supported on the solid material was obtained (step S1).

[0076] A few grams of the first absorbent material 3a obtained through the above-mentioned operation was placed inside the reaction vessel 2. A stainless steel pipe was used as the reaction vessel 2 for the test. The diameter of the pipe was approximately 9 mm. The reaction vessel 2 was placed in a thermostatic bath whose temperature inside the bath could be changed.

[0077] First, in order to desorb carbon dioxide absorbed during the preparation of the first absorbent material 3a, the first absorbent material 3a was heated at 70°C for several hours while nitrogen gas (purity 99.9%) was passed through at 75 mL / min.

[0078] Then, after the temperature inside the thermostatic chamber was maintained at 25° C., air (carbon dioxide concentration: approximately 400 pm) was introduced into the reaction chamber 2 as the gas to be treated G1 at a flow rate of 200 mL / min.

[0079] Because carbon dioxide is absorbed by the first absorbent 3a, the carbon dioxide concentration of the gas to be treated G1 after contact with the first absorbent 3a decreases. In this example, the absorption amount of the first absorbent 3a was evaluated from the carbon dioxide concentrations measured at a position upstream of the inlet 5 and a position downstream of the outlet 6 of the reaction vessel 2. This step yields a second absorbent 3b that has absorbed carbon dioxide (step S2).

[0080] Next, the temperature inside the thermostatic chamber was set to 60°C, and heat was supplied to the second absorbent 3b (step S3). At that time, nitrogen gas (purity 99.9%) was passed through the reaction vessel 2 at a rate of 75 mL / min. Then, based on the carbon dioxide concentration measured at a position downstream of the outlet 6 of the reaction vessel 2, the amount of carbon dioxide desorbed from the second absorbent 3b was obtained.

[0081] Example 2 Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amines contained in the mixed solution were 0.35 g of MBMCA and 0.07 g of PEI.

[0082] Example 3 Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amines contained in the mixed solution were 0.27 g of MBMCA and 0.15 g of PEI.

[0083] Example 4 Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amines contained in the mixed solution were 0.21 g of MBMCA and 0.21 g of PEI.

[0084] Comparative Example 1 Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amines contained in the mixed solution were 0.15 g of MBMCA and 0.27 g of PEI.

[0085] Comparative Example 2 Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amines contained in the mixed solution were 0.10 g of MBMCA and 0.32 g of PEI.

[0086] <Reference Example 1> Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amine contained in the mixed solution was 0.42 g of MBMCA, and no PEI was contained.

[0087] <Reference Example 2> Except for the change in the composition of the mixed solution used to prepare the carbon dioxide absorbent, the experiment was carried out under the same conditions as in Example 1. The amine contained in the mixed solution was 0.35 g of PEI, and did not contain MBMCA.

[0088] Table 1 below shows the experimental conditions for Examples 1 to 4, Comparative Examples 1 and 2, and Reference Examples 1 and 2. Table 1 also shows the weight ratio of PEI to the total weight of amines, and the weight ratio of PEI to the total weight of the first absorbent material 3a at the time of preparation. [Table 1]

[0089] FIG. 5A is a graph showing the amount of carbon dioxide absorbed by the first absorbent 3a in each example. FIG. 5A shows the amount of carbon dioxide absorbed over time. The amount of carbon dioxide absorbed is an integrated value of the contact time between the first absorbent 3a and the gas G1 to be treated. Note that FIG. 5A does not show Comparative Examples 1 and 2. FIG. 5B is a graph extracting the amount of absorption after 12 hours in each example. In FIG. 5B, the horizontal axis shows the weight ratio of PEI to the total weight of amine in each example, and the vertical axis shows the amount of carbon dioxide absorbed.

[0090] Furthermore, Fig. 6A is a graph showing the amount of carbon dioxide desorption from the second absorbent 3b in each example. Fig. 6A shows the ratio of the amount of carbon dioxide desorption to the amount of carbon dioxide absorbed (hereinafter sometimes referred to as the "desorption ratio") over time. The horizontal axis of Fig. 6A corresponds to the time for which heat is supplied for desorption. Furthermore, Fig. 6B is a graph showing the desorption ratio after two hours have elapsed in each example.

[0091] 5B, it can be seen that the carbon dioxide absorption capacity of the carbon dioxide absorbent improves as the weight ratio of PEI to the total weight of amine increases. This is because PEI has a higher carbon dioxide absorption capacity than MBMCA (Reference Examples 1 and 2). In other words, Reference Example 2 has superior results in terms of carbon dioxide absorption capacity.

[0092] 5B, from the viewpoint of absorbing a larger amount of carbon dioxide, it seems preferable to use only PEI as the amine. However, in order to desorb the absorbed carbon dioxide and use the first absorbent 3a to absorb carbon dioxide again, it is necessary to supply heat to desorb the absorbed carbon dioxide. In other words, in order to recover carbon dioxide from the gas G1 to be treated more efficiently, the carbon dioxide absorption capacity of the first absorbent 3a and the carbon dioxide desorption capacity of the second absorbent 3b are important indicators.

[0093] In this regard, in Reference Example 2, as shown in Figure 6A, it takes a relatively long time for the absorbed carbon dioxide to desorb. Specifically, the desorption rate after 2 hours was less than 50% (see Figure 6B). In light of this, it can be seen that when the amine is composed only of PEI, a large amount of energy is required to desorb the absorbed carbon dioxide.

[0094] On the other hand, in Reference Example 1, the desorption of absorbed carbon dioxide is significantly faster (see FIG. 6A). As mentioned above, this is presumably because MBMCA produces carbamic acid by absorbing carbon dioxide. However, the amount of carbon dioxide absorbed in Reference Example 1 is about 50% of the amount absorbed in Reference Example 2, and Reference Example 1 also has issues in terms of carbon dioxide absorption capacity.

[0095] In contrast to this, as shown in FIG. 5B, in Examples 1 to 4 and Comparative Examples 1 and 2, mixing MBMCA and PEI makes it possible to increase the carbon dioxide absorption capacity.

[0096] 5B and 6B, it was found that in Examples 1 to 4, the carbon dioxide absorption capacity was approximately 1.4 times or more that of Reference Example 1, and the desorption rate after 2 hours was at least 50%. On the other hand, in Comparative Examples 1 and 2, although the carbon dioxide absorption capacity was increased, the carbon dioxide desorption capacity was similar to that of Reference Example 2 (see FIG. 6B).

[0097] The present inventors consider these results as follows: First, according to Reference Example 2, although PEI has a high absorption capacity, it also requires a large amount of energy to desorb the absorbed carbon dioxide. On the other hand, according to Reference Example 1, MBMCA has an absorption capacity inferior to PEI, but has a superior carbon dioxide desorption capacity.

[0098] As mentioned above, the superior desorption ability of MBMCA is due to the fact that carbamic acid produced by carbon dioxide absorption is unstable in the liquid phase. Therefore, in Examples 1 to 4, when heat is supplied to desorb the absorbed carbon dioxide, it is believed that MBMCA in the carbon dioxide absorbent first desorbs carbon dioxide before PEI. Here, since the PEI retains carbon dioxide, it can be said that carbon dioxide is localized in the PEI in the carbon dioxide absorbent, more specifically, in the amine supported in the pores. The localized state of carbon dioxide is an unstable state, and it is believed that the carbon dioxide is extracted from the PEI by MBMCA, which previously desorbed carbon dioxide. Then, upon receiving heat, MBMCA desorbs the carbon dioxide extracted from the PEI. As mentioned above, MBMCA has an excellent desorption ability for absorbed carbon dioxide. Therefore, it is believed that the desorption of carbon dioxide absorbed by PEI via MBMCA accelerates the rate of carbon dioxide desorption compared to the rate at which carbon dioxide is desorbed by PEI.

[0099] As mentioned above, the absorption of carbon dioxide to generate solid-phase carbamic acid is not limited to MBMCA, but is also true for other cyclic diamines. In other words, even when PEI is mixed with other cyclic diamines, such as isophorone diamine, it is believed that the desorption of carbon dioxide can be accelerated more quickly than the desorption of carbon dioxide by PEI. Furthermore, based on the above, it can be seen that the carbon dioxide absorption capacity can be increased by mixing PEI, which has a higher carbon dioxide absorption capacity than MBMCA. In other words, it is important that the polyamine mixed with the cyclic diamine has a higher carbon dioxide absorption capacity than the cyclic diamine, and the polyamine is not limited to PEI.

[0100] In Comparative Examples 1 and 2, the weight ratio of PEI to the total weight of amines was high, so absorption and desorption of carbon dioxide by PEI became dominant, and it is thought that the carbon dioxide desorption capacity was not improved compared to Reference Example 2 (see FIG. 6B). In other words, it is thought that the high weight ratio of PEI may have inhibited desorption of carbon dioxide from MBMCA.

[0101] In view of the above, it is preferable that the weight ratio of PEI to the total weight of amines is 60% or less.

[0102] Furthermore, when the weight ratio of PEI to the total weight of amines was in the range of 50% or less, the carbon dioxide absorption capacity was increased compared to Reference Example 1, and the desorption rate after 2 hours was 60% or more, due to the inclusion of PEI in the carbon dioxide absorbent. In addition, when the weight ratio of PEI to the total weight of amines was in the range of 20% or less, the carbon dioxide absorption capacity was increased compared to Reference Example 1, and the desorption rate after 2 hours reached 80% or more. In light of this, the weight ratio of PEI to the total weight of amines is more preferably 50% or less, and particularly preferably 20% or less.

[0103] 5B, when the weight ratio of PEI to the total weight of amines is 10% or more, the amount of carbon dioxide absorbed is approximately 1.1 to 1.6 times or more compared to Reference Example 1. In view of this, it is preferable that the weight ratio of PEI to the total weight of amines is 10% or more.

[0104] The weight ratio of PEI to the total weight of amines can be set when preparing the carbon dioxide absorbent. Furthermore, in the prepared carbon dioxide absorbent, the weight ratio of PEI to the total weight of amines supported in the pores can be measured, for example, by solvent extraction of the substance supported in the pores of the carbon dioxide absorbent, followed by liquid chromatography mass spectrometry (LS / MS). This allows the weight ratio of PEI to the total weight of amines supported in the pores of the carbon dioxide absorbent to be obtained. It is also possible to obtain the weight ratio of MBMCA to the total weight of the amines using a similar method.

[0105] According to Table 1, the weight ratio of PEI to the total weight of the carbon dioxide absorbent is preferably 15% or less, and more preferably 10% or less.

[0106] The weight ratio of PEI to the total weight of amines may also be expressed as the volume ratio of PEI to the total volume of amines, using the density of MBMCA (0.95 g / ml) and the density of PEI (1.05 g / ml) at room temperature and normal pressure.

[0107] The above verification 1 showed that a carbon dioxide absorbent containing MBMCA and PEI, with the weight ratio of PEI to the total weight of amines being 60% or less, can increase the carbon dioxide absorption capacity while desorbing absorbed carbon dioxide with less energy, thereby enabling efficient carbon dioxide capture.

[0108] As mentioned above, this result is obtained by mixing a cyclic diamine, which has particularly excellent desorption ability for absorbed carbon dioxide, with a polyamine, which has relatively high carbon dioxide absorption ability. In other words, the inclusion of a polyamine in the amines supported in the pores enhances the carbon dioxide absorption capacity. Furthermore, when the weight ratio of polyamine to the total weight of amines is high, the fact that carbon dioxide absorption and desorption by the polyamine become dominant is presumed to be not limited to the fact that the polyamine is PEI. In other words, although the cyclic diamine is MBMCA and the polyamine is PEI in the above example, even if other amines are used, it is believed that a carbon dioxide absorbent with excellent carbon dioxide desorption capacity can be realized while enhancing the carbon dioxide absorption capacity of the cyclic diamine. In light of the above, it is presumed that the weight ratio of polyamine to the total weight of amines is preferably 60% or less, more preferably 50% or less, and particularly preferably 20% or less. The weight ratio of polyamine to the total weight of the carbon dioxide absorbent and the volume ratio of polyamine to the total weight of amines are also presumed to be similar to those described above.

[0109] In this verification, heat was supplied to the second absorption material 3b using a thermostatic bath, but the present invention is not limited to a specific method for supplying heat. For example, sunlight may be used as described in the first configuration example above.

[0110] In the above examples, silica is used as the porous material constituting the solid material, but the present invention is not limited to this. The solid material may be composed of, for example, a ceramic material such as alumina, an engineering plastic material such as polypropylene, a carbon material such as activated carbon, or a resin containing cellulose.

[0111] As an example, it is believed that carbon materials such as activated carbon can more suitably support a carbon dioxide absorbing solution containing a cyclic diamine. In carbon materials such as activated carbon, six-membered or five-membered ring structures composed of carbon atoms are stacked irregularly. On the other hand, cyclic diamines are also cyclic compounds and have ring structures within their structures. Because both the carbon material and the cyclic diamine have ring structures, it is presumed that a bonding force resulting from π-electron interaction is generated between the two ring structures.

[0112] Furthermore, even if the solid material is a resin containing cellulose, it is believed that it can more effectively support a carbon dioxide absorbing liquid containing a cyclic diamine. Because cellulose has a six-membered ring structure containing carbon atoms, it is believed that it bonds more strongly with the cyclic diamine through π-electron interactions. Furthermore, because cellulose has many hydroxyl groups, an increase in the bonding strength between cellulose and the cyclic diamine due to dipole-dipole interactions can be expected.

[0113] [Verification 2] In order to examine the absorption capacity of the carbon dioxide absorbent in more detail, a test was carried out in which the amount of PEG added to the carbon dioxide absorbent was varied, and this is explained below.

[0114] Example 5 The carbon dioxide absorbent was prepared under the same conditions as in Example 1, except that the amount of PEG added to the mixed solution was 0.04 g.

[0115] Example 6 The carbon dioxide absorbent was prepared under the same conditions as in Example 1, except that the amount of PEG added to the mixed solution was 0.06 g.

[0116] Example 7 The carbon dioxide absorbent was prepared under the same conditions as in Example 1, except that the amount of PEG added to the mixed solution was 0.10 g.

[0117] Example 8 The carbon dioxide absorbent was prepared under the same conditions as in Example 1, except that the amount of PEG added to the mixed solution was 0.12 g.

[0118] Table 2 below shows the experimental conditions for Example 1 and Examples 5 to 8. Table 2 also shows the ratio of PEG added to the total weight of amine, and the weight ratio of PEG to the total weight of the first absorbent material 3a at the time of preparation. [Table 2]

[0119] Fig. 7 is a graph, similar to Fig. 6B, showing the amount of carbon dioxide absorbed after 12 hours in Example 1 and Examples 5 to 8. In Fig. 7, the horizontal axis shows the ratio of PEG added to the total weight of amine in each Example, and the vertical axis shows the amount of carbon dioxide absorbed.

[0120] According to Figure 7, when the ratio of PEG added to the total weight of the amine was in the range of approximately 10% to 20%, the amount of carbon dioxide absorbed after 12 hours was approximately 60 mg, and no significant change was observed in this absorption amount compared to Example 1. On the other hand, when the ratio of PEG added exceeded 20%, the amount of carbon dioxide absorbed tended to decrease. This is presumably because when the ratio of PEG in the pores becomes too large, it becomes difficult for the amine and carbon dioxide to come into contact with each other. In light of this, it is presumed that a ratio of PEG added to the total weight of the amine in the range of 10% to 20% is more preferable.

[0121] The ratio of PEG to the total weight of amines can be set when preparing the carbon dioxide absorbent. In addition, the ratio of PEG to the total weight of amines supported in the pores of the prepared carbon dioxide absorbent can be measured by the above-mentioned liquid chromatography mass spectrometry (LS / MS).

[0122] Furthermore, according to Table 2, the weight ratio of PEG to the total weight of the carbon dioxide absorbent is preferably 3% to 6%.

[0123] As described above, the present invention makes it possible to increase the efficiency of carbon dioxide capture while reducing the amount of energy input compared to conventional methods. This will also greatly contribute to Goal 13 of the United Nations' Sustainable Development Goals (SDGs), which is to "take urgent action to combat climate change and its impacts."

[0124] [Second embodiment] Hereinafter, the second embodiment of the carbon dioxide recovery system will be described, focusing on the differences from the first embodiment.

[0125] In the first embodiment described above, the heat source 4 is disposed inside the reaction tank 2, but the heat source 4 can also be disposed outside the reaction tank 2 at a position independent of the reaction tank 2. That is, in this embodiment, a heat transfer medium heated by the heat source 4 is introduced into the reaction tank 2 and supplies heat H1 to the second absorbent 3b inside the reaction tank 2.

[0126] 8 is a diagram schematically illustrating the configuration of a second embodiment of the recovery system 1, with some components shown in block diagram form. As shown in FIG. 8, the recovery system 1 according to this embodiment includes a reaction vessel 2, a heat source 4, a first flow path 31 connecting the heat source 4 and the reaction vessel 2, a second flow path 32 introducing the gas to be treated G1 into the reaction vessel 2, and a third flow path 33 located downstream of the reaction vessel 2 in the flow direction of the gas to be treated G1, etc. FIG. 8 illustrates a scene of step S4 (see FIG. 3), in which air as a heat transfer medium A1 is introduced into the reaction vessel 2 from the first flow path 31.

[0127] In this embodiment, the air sent into the reaction tank 2 by a ventilation mechanism such as a blower fan (not shown) is used as the heat transfer medium A1. Furthermore, in this embodiment, the gas G1 to be treated is air. Therefore, the recovery system 1 includes a first valve V1 capable of controlling the flow rate of air flowing through the second flow path 32, a second valve V2 capable of controlling the flow rate of air flowing through the first flow path 31, and a control unit 8 that controls the open / closed states of the valves (V1, V2). In FIG. 8, the first valve V1 is in a closed state and the second valve V2 is in an open state. To schematically represent the open / closed states of the valves, the valves are depicted at different positions relative to the piping.

[0128] The reaction tank 2 also has a thermometer 9 that measures the temperature of the internal space of the reaction tank 2. As will be described later, the control unit 8 can send signals (d1, d2) to each valve (V1, V2) to adjust the valve opening based on temperature information d0 inside the reaction tank 2 from the thermometer 9.

[0129] The configuration of this embodiment will be described below with reference to Figs. 9 to 12. Figs. 9 and 10 are cross-sectional views schematically showing the structure of the reaction vessel 2, with Fig. 9 corresponding to a scene in step S2 and Fig. 10 corresponding to a scene in step S3 (see Fig. 3). Figs. 11 and 12 are cross-sectional views schematically showing the structure of the heat source 4, with Fig. 12 being a drawing of the heat source 4 of Fig. 11 as viewed from the Z direction, following Fig. 2.

[0130] 9, the first absorbent 3a prepared through the above-mentioned step S1 is placed inside the reaction tank 2. Then, the second valve V2 is closed and the first valve V1 is open, and air as the gas to be treated G1 is introduced into the reaction tank 2 through the inlet 5b. The first absorbent 3a absorbs carbon dioxide contained in the gas to be treated G1, thereby obtaining the second absorbent 3b (step S2).

[0131] Next, step S3 is performed by the heat source 4. As shown in Fig. 11, the heat source 4 has a heating tank 4a, a heat collecting member 15 arranged vertically above (on the +Z side of) the heating tank 4a, a heat transfer member 19 arranged directly on the heat collecting member 15, and a light-transmitting portion 20 for taking in solar light C2 inside. Note that, for convenience of illustration, Fig. 12 omits some of the light-transmitting portion 20, the heat collecting member 15, and the heat transfer member 19. The heat source 4 has a structure common to the reaction tank 2 according to the first embodiment, and therefore, description of the common parts will be simplified.

[0132] 11, air as a heat transfer medium A1 is introduced into the heating tank 4a through the inlet 5. Then, the heat transfer medium A1 comes into contact with the heat transfer member 19, which has been heated to a high temperature by heat H1 obtained by converting sunlight C2 by the heat collecting member 15, and is heated. Thereafter, the heat transfer medium A1 is discharged from the outlet 6 and sent into the reaction tank 2 through the first flow path 31. Note that the same discussion as in the first embodiment can be applied to the light transmitting portion 20.

[0133] 12, the heat transfer member 19 may be formed of, for example, a plate-like member and arranged so that its main surface is substantially perpendicular to the flow direction of the heat transfer medium A1. From a similar perspective, a flow passage 25 may be positioned between the inner wall of the heating tank 4a and the heat transfer member 19 in the Y direction, through which the heat transfer medium A1 passes, and may overlap with the main surface of the heat transfer member 19 located downstream in the flow direction of the heat transfer medium A1 when viewed in the X direction (flow direction). Note that the "main surface" here refers to a surface of the plate-like heat transfer member 19 that has a much larger area than the other surfaces.

[0134] As shown in Fig. 10, air as a heat transfer medium A1 heated by a heat source 4 is introduced into the reaction vessel 2 where the second absorbent 3b is located through an inlet 5a. At this time, typically, the second valve V2 is opened and the first valve V1 is closed. In this manner, the high-temperature heat transfer medium A1 is brought into contact with the second absorbent 3b, and heat H1 is supplied to the second absorbent 3b (step S4).

[0135] The recovered gas G2 containing carbon dioxide desorbed from the second absorbent 3b by the supply of heat H1 is recovered via the outlet 6a (step S4).

[0136] In this embodiment, the air is used as the heat transfer medium A1, and therefore the carbon dioxide concentration in the vicinity of the second absorbent 3b can be reduced by introducing the heat transfer medium A1 into the reaction vessel 2. In other words, the air used as the heat transfer medium A1 also functions as a desorption-promoting gas B1 that promotes desorption of carbon dioxide.

[0137] By heating the second absorbent 3b using air as the heat transfer medium A1, the absorbed carbon dioxide is desorbed. However, from the perspective of repeatedly using the absorbent 3 (see FIG. 3), it is preferable to reduce the thermal impact on the second absorbent 3b. For this reason, the control unit 8 receives temperature information d0 from the thermometer 9 and, if the temperature in the reaction vessel 2 is equal to or higher than a predetermined value, transmits a signal d1 to the first valve V1 to adjust the aperture. By adjusting the aperture of the first valve V1, air at a lower temperature than the heat transfer medium A1 can be introduced, thereby lowering the temperature in the reaction vessel 2 and reducing the thermal impact on the second absorbent 3b. In other words, the air in this case corresponds to a "cooling gas." Furthermore, from the perspective of promoting cooling of the temperature in the reaction vessel 2, a signal d2 may be transmitted to the second valve V2 to adjust the aperture of the second valve V2. Note that the predetermined value is determined, for example, taking into consideration the thermal resistance, such as the boiling point, of the carbon dioxide absorbent constituting the absorbent 3. The predetermined value may be, for example, 100°C or less, preferably 80°C or less, and more preferably 60°C or less.

[0138] In this embodiment, an example has been described in which the control unit 8 adjusts the opening of each valve (V1, V2) based on the temperature information d0 from the thermometer 9 to lower the temperature inside the reaction tank 2 in step S4. However, the control unit 8 may also be configured to control the first valve V1 to be in an open state and the second valve V2 to be in a closed state for a predetermined time, for example, when the accumulated time during which V2 has been in an open state reaches a preset time.

[0139] In this embodiment, a configuration for heating the heat transfer medium A1 introduced into the reaction tank 2 is shown, but as described with reference to Figure 1, a configuration of a heat source 4 that is placed in the reaction tank 2 and heats the heat transfer medium A1 and the second absorbent 3b may also be used in combination.

[0140] [Another embodiment] 13 and 14 are diagrams schematically illustrating the configuration of another embodiment of the collection system 1, with a portion of the configuration shown in block diagram form. Fig. 13 corresponds to a scene in which step S2 is performed, and Fig. 14 corresponds to a scene in which steps S3 and S4 are performed.

[0141] This embodiment includes a heat exchanger 36 that exchanges heat between the air as a heat transfer medium A1 and a recovered gas G2 containing carbon dioxide recovered from the reaction tank 2 (see FIG. 14). The recovery system 1 also includes a fourth flow path 34 (see FIG. 13) that branches off from the third flow path 33 and through which the gas to be treated G1 flows after passing through the reaction tank 2, and a fourth valve V4 that is disposed in the fourth flow path 34. Note that the configurations of the reaction tank 2 and the heat source 4 can be discussed in the same manner as those described with reference to FIGS. 9 to 12.

[0142] 13, when step S2 is performed, the first valve V1 and the fourth valve V4 arranged in the second flow path 32 are opened, and a flow mechanism such as a fan (not shown) introduces the gas to be treated G1 into the reaction tank 2. In the reaction tank 2, the gas to be treated G1 from which carbon dioxide has been absorbed by the first absorbent 3a is discharged via the fourth flow path 34, for example, to the outside space.

[0143] As shown in FIG. 14, when steps S3 and S4 are performed, a second valve V2 disposed in the first flow path 31 through which the air flows as the heat transfer medium A1, and a third valve V3 disposed in the third flow path 33 through which the recovered gas G2 flows, are opened. In this embodiment, as shown in FIG. 14, the air in the space where plants are grown in the plant factory 35 (hereinafter, for convenience, referred to as the "growth space 35a") is used as the heat transfer medium A1. Furthermore, the recovered gas G2 containing carbon dioxide desorbed from the second absorbent 3b in the reaction vessel 2 can be used in the growth space 35a. The recovered gas G2 contains carbon dioxide desorbed by heating the second absorbent 3b, and therefore has a higher temperature than the air used as the heat transfer medium A1. Therefore, it is preferable to perform heat exchange between the recovered gas G2 and the air used as the heat transfer medium A1.

[0144] Note that the supply of heat H1 may cause a small amount of amine contained in the second absorbent 3b to evaporate. Therefore, it is expected that the recovered gas G2 contains a small amount of amine-derived components that have evaporated due to the supply of heat H1. In light of this, it is preferable to cool the recovered gas G2 by performing heat exchange between the recovered gas G2 and hydroponic wastewater (not shown) in the plant factory 35. By cooling the recovered gas G2, the amine-derived components are cold-trapped, preventing them from flowing into the growth space 35a. Note that, in order to supply sufficient heat to the air serving as the heat transfer medium A1, it is preferable that the heat exchange as a cold trap be performed after heat exchange between the air and the recovered gas G2.

[0145] In the plant factory 35, it is assumed that the growth lights are turned on or off in accordance with the circadian rhythm specific to the plants. That is, while the lights are on, the carbon dioxide concentration in the growth space 35a decreases due to photosynthesis by the plants. Therefore, from the viewpoint of enhancing the effect of the desorption-promoting gas B1 described above, it is preferable to use the air in the growth space 35a as the heat transfer medium A1. When the carbon dioxide concentration in the growth space 35a is high due to plant respiration or the like (typically while the growth lights are off), the air in another space, such as an outdoor space, may be used as the heat transfer medium A1.

[0146] <2> In the second embodiment, in step S3, air is introduced as the heat transfer medium A1 into the internal space of the reaction tank 2. However, as shown in FIG. 15, heat exchange may be performed between the heat transfer medium A1 flowing outside the reaction tank 2 and the reaction tank 2 in which the second absorbent 3b is located. FIG. 15 is a diagram schematically illustrating a portion of another configuration example of the recovery system 1. FIG. 16A is a perspective view schematically illustrating the configuration of the heat source 4 in FIG. 15, and FIG. 16B is a ZY cross-sectional view of the heat source 4 in FIG. 16A when viewed from the X direction. In FIGS. 16A and 16B, the flow direction of the heat transfer medium A1 is the X direction.

[0147] The heat source 4 in FIG. 16A has an L-shaped cross section, as shown in FIG. 16B, for example, and contains water as a heat transfer medium A1 inside. The heat source 4 has a flat heat collecting member 15 on a part of its outer wall surface, and the heat collecting member 15 is heated by absorbing solar light C2, generating high-temperature water (hereinafter referred to as "hot water"). The heat source 4 is typically placed on an inclined surface such as a stand 41 so that the heat collecting member 15 can efficiently receive the solar light C2. The hot water is configured to flow through a flow path 40, and heat exchange occurs between the hot water as the heat transfer medium A1 and the reaction tank 2, thereby supplying heat H1 to the second absorbent 3b in the reaction tank 2.

[0148] At this time, in order to reduce the carbon dioxide concentration in the reaction tank 2 and promote desorption of absorbed carbon dioxide from the second absorbent 3b, it is acceptable to introduce air as desorption-promoting gas B1 into the reaction tank 2, for example, from the second flow path 32 (see Figure 15).

[0149] <3> In addition, Fig. 15 has described an example in which heat exchange is performed between hot water serving as heat transfer medium A1 flowing through flow path 40 and reaction vessel 2. However, heat exchange may also be performed between the hot water and air serving as heat transfer medium A1 flowing through first flow path 31 described with reference to Figs. 8 and 10. That is, air heated to a high temperature by the heat exchange is introduced into reaction vessel 2, whereby heat H1 is supplied to second absorbent 3b (see Fig. 10), and absorbed carbon dioxide is desorbed.

[0150] <4> The above-described embodiments can be combined as appropriate. For example, a heat source 4 may be additionally disposed inside the reaction vessel 2 shown in Fig. 8 or Fig. 15. The reaction vessel 2 may have the same configuration as that described with reference to Fig. 1.

[0151] <5> In the above description, the absorbent material 3 is described as being granular, but as mentioned above, the shape of the absorbent material 3 is not limited to this, and it may be, for example, plate-shaped.

[0152] <6> In the above, heat H1 obtained by converting solar light C2 is supplied to the second absorption material 3b, but the present invention is not limited to a method for supplying heat to the second absorption material 3b. For example, the second absorption material 3b may be heated using a heater or a boiler. Furthermore, heat emitted from various heat generating mechanisms may be taken in and used as a heat source. [Explanation of symbols]

[0153] 1: Collection system 1a: Collection method 2: Reactor 3: Absorbent material 3a: First absorbent material 3b: Secondary absorbent material 4: Heat source 4a: Heating tank 5,5a,5b: Inlet 6,6a: Outlet 8: Control section 9: Thermometer 10 : Porous material 11: Pore 12: Carbon dioxide absorbent 15: Heat collecting member 19: Heat transfer material 20 : Translucent part 21: Transparent material 22: Low pressure space 25: Flow section 30: Halogen lamp 31, 32, 33, 34, 40: Flow path 35: Plant factory 35a: Growth space 36 : Heat exchanger 41: Mounting stand A1: Heat transfer medium B1: Desorption promoting gas C1: Sun C2: Sunlight G1: Gas to be treated G2: Recovered gas

Claims

1. a solid material made of a porous substance having pores on its surface; a cyclic diamine and a polyamine supported in the pores; A carbon dioxide absorbent, characterized in that the weight ratio of polyamine to the total amount of cyclic diamine and polyamine is 60% or less.

2. 2. The carbon dioxide absorbent according to claim 1, wherein the cyclic diamine is 4,4'-methylenebis(2-methylcyclohexylamine) and the polyamine is polyethyleneimine.

3. The porous material has an average particle size of 1 mm to 5 mm and a specific surface area of ​​50 m 2 / g~700m 2 The carbon dioxide absorbent according to claim 1 or 2, wherein the carbon dioxide absorbent has a molecular weight of 1000 or more and a molecular weight of 1000 or more.

4. 3. The carbon dioxide absorbent according to claim 1, further comprising polyethylene glycol supported in the pores.

5. A step (a) of preparing a first absorbent material that is an absorbent material before absorbing carbon dioxide by causing a carbon dioxide absorbing liquid to be supported in the pores of a solid material made of a porous substance having pores on the surface; (b) a step of absorbing carbon dioxide into the first absorbent material to prepare a second absorbent material that has absorbed carbon dioxide; (c) providing heat to the second absorbent material; and a step (d) of recovering the carbon dioxide desorbed from the second absorbent material after the step (c), A method for recovering carbon dioxide, wherein the carbon dioxide absorbing solution contains a cyclic diamine and a polyamine, and the weight ratio of the polyamine to the total amount of the cyclic diamine and the polyamine is 60% or less.

6. 6. The method for recovering carbon dioxide according to claim 5, wherein the cyclic diamine is 4,4'-methylenebis(2-methylcyclohexylamine) and the polyamine is polyethyleneimine.

7. 7. The method for recovering carbon dioxide according to claim 5, wherein the carbon dioxide absorbing liquid contains polyethylene glycol.

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