Carbon dioxide gas absorbing material, carbon dioxide gas absorbing method, carbon dioxide gas absorbing device, and method for regenerating carbon dioxide gas absorbing material

Abstract

This carbon dioxide gas absorbing material contains a composite metal oxide which is represented by formula (1) NaATiBMCOD (wherein 5 ≤ A ≤ 11, 4 ≤ B ≤ 6, 0 ≤ C ≤ 2, 10.5 ≤ D ≤ 17.5, and M is selected from among transition elements and typical elements), and / or this carbon dioxide gas absorbing material contains a composite metal oxide which contains sodium and titanium. The composite metal oxide shows peaks at diffraction angles 2θ of 12.0° ± 0.5° and 12.6° ± 0.5°, respectively, and also shows one or two peaks in the range from 39.1° ± 0.5° to 41.0° ± 0.5° in a powder X-ray diffraction pattern obtained using CuKα rays.

Description

Carbon dioxide absorbent, carbon dioxide absorption method, carbon dioxide absorption device, and method for regenerating carbon dioxide absorbent.

[0001] The present invention relates to a carbon dioxide absorbent using a composite metal oxide, a carbon dioxide absorption method, a carbon dioxide absorption apparatus, and a method for regenerating a carbon dioxide absorbent.

[0002] Conventionally, in light of social issues such as reducing greenhouse gas emissions, the practical application of technologies for recovering carbon dioxide from carbon dioxide-containing gases has been proposed. For example, carbon dioxide absorption technologies using organic absorbents such as amine liquids have good reactivity with gases and have been put into practical use in factories, etc. However, amine liquids have problems such as being harmful to the human body, and because they are liquids, they must be filled into enclosed spaces such as containers, which limits their uses. Furthermore, in recent years, there has been a demand for innovative technologies that can reduce carbon dioxide (carbon dioxide) emitted into the atmosphere in the past (beyond zero), but conventional carbon dioxide absorbents have not been able to efficiently absorb carbon dioxide at low concentrations in the atmosphere.

[0003] Therefore, the inventors have worked on developing inorganic absorbents and have proposed a technology relating to a carbon dioxide absorbent using α-sodium ferrites (hereinafter also referred to as Conventional Technology 1) (see Patent Document 1 below). Sodium ferrite is highly safe, has a high carbon dioxide absorption rate, and can be handled as a powder, making it suitable for various applications.

[0004] Japanese Patent Publication No. 2016-3156

[0005] However, in order to reuse α-sodium ferrites that have absorbed carbon dioxide as carbon dioxide absorbents, a regeneration reaction must be carried out by heating at high temperatures exceeding 400°C, which presented challenges in terms of thermal efficiency.

[0006] The present invention has been made in view of the above-mentioned background, and specifically proposes a carbon dioxide absorbent that has a good carbon dioxide absorption rate and allows for the regeneration of the carbon dioxide absorbent after use at a low temperature of 400°C or less, a carbon dioxide absorption method and apparatus using the carbon dioxide absorbent, and a method for regenerating the carbon dioxide absorbent.

[0007] The first carbon dioxide absorbent of the present invention is characterized by containing a composite metal oxide represented by the following formula (1) (wherein formula (1) is 5 ≤ ​​A ≤ 11, 4 ≤ B ≤ 6, 0 ≤ C ≤ 2, 10.5 ≤ D ≤ 17.5, and M is selected from transition elements and main group elements). [Formula 1] Na Ａ Ti Ｂ M Ｃ O Ｄ ... (1)

[0008] The second carbon dioxide absorbent of the present invention contains a composite metal oxide containing sodium and titanium, characterized in that, in a powder X-ray diffraction pattern using CuKα rays, the composite metal oxide shows peaks in the ranges of diffraction angle 2θ of 12.0°±0.5° and 12.6°±0.5°, and shows one or two peaks in the range of 39.1°±0.5° to 41.0°±0.5°.

[0009] The carbon dioxide absorption method of the present invention comprises a storage step of storing the carbon dioxide absorbent of the present invention in a reaction vessel; a reaction step of introducing a carbon dioxide-containing gas into the reaction vessel and bringing the carbon dioxide-containing gas into contact with the composite metal oxide to cause a reaction; and a discharge step of discharging the gas that has undergone the reaction step from the reaction vessel.

[0010] The carbon dioxide absorption device of the present invention is characterized by comprising a storage section for housing the carbon dioxide absorption material of the present invention, a gas inlet for introducing carbon dioxide-containing gas into the storage section, and a gas outlet for discharging the gas from the storage section to the outside.

[0011] The present invention provides a method for regenerating a carbon dioxide absorbent, characterized by heating the reaction product, which is the carbon dioxide absorbent after the carbon dioxide absorption reaction, at a temperature of 400°C or lower under air, an inert gas, or a vacuum.

[0012] The carbon dioxide absorbent of the present invention exhibits a carbon dioxide absorption capacity equal to or higher than that of a carbon dioxide absorbent using sodium ferrite, and can be regenerated at a low temperature of 400 ° C or lower after carbon dioxide absorption. Therefore, the carbon dioxide absorbent of the present invention can be recycled with good thermal efficiency and has a high contribution to environmental problems in a series of processes from carbon dioxide absorption to recycling. Also, the carbon dioxide absorption method and the carbon dioxide absorption apparatus of the present invention enjoy the effects of the carbon dioxide absorbent of the present invention. For example, the carbon dioxide absorption method and the carbon dioxide absorption apparatus of the present invention can absorb carbon dioxide in a temperature range from room temperature to a relatively low temperature. Also, the regeneration method of the carbon dioxide absorbent of the present invention can regenerate the used carbon dioxide absorbent at a low temperature as compared with the conventional carbon dioxide absorbent containing sodium ferrite, and is excellent in thermal efficiency.

[0013] (1A) is a graph showing the weight increase rate at room temperature by thermogravimetric measurement (TG) of one embodiment (Na ８ Ti ５ O １４ ) of the carbon dioxide absorbent of the present invention and sodium titanate (Na ４ Ti ５ O １２ ) which is a comparative example having the same composition but different composition ratios during the carbon dioxide absorption reaction. (1B) is a graph showing the amounts of carbon dioxide and moisture absorbed by the reaction shown in (1A). It is basic data showing the powder X-ray diffraction pattern using the CuKα ray of Na ８ Ti ５ O １４ . It is basic data showing the powder X-ray diffraction pattern using the CuKα ray of Na ８ Ti ５ O １４This is a process diagram showing an example of a manufacturing method. This is an explanatory diagram showing one embodiment of the carbon dioxide absorption apparatus of the present invention. This chart shows the powder X-ray diffraction patterns using CuKα rays for Examples 1 to 5 before carbon dioxide absorption. This chart shows the powder X-ray diffraction patterns using CuKα rays for Examples 1 to 5 after carbon dioxide absorption. This chart shows the powder X-ray diffraction pattern using CuKα rays for Example 1-1 after regeneration. This graph shows the results of simultaneous differential thermal and thermogravimetric analysis (TG-DTA) during the regeneration reaction of Example 1-1 after carbon dioxide absorption. This graph shows the results of calculating the carbon dioxide and water content of the sample of Example 1 after carrying out the carbon dioxide absorption reaction at different ambient temperatures (ambient temperatures: 25°C, 50°C, 100°C).

[0014] The first carbon dioxide absorbent, the second carbon dioxide absorbent, the carbon dioxide absorption method, the carbon dioxide absorption apparatus, and the method for regenerating the used carbon dioxide absorbent of the present invention will be described below in order. In the following description, the first carbon dioxide absorbent and the second carbon dioxide absorbent of the present invention may be collectively referred to as the carbon dioxide absorbent of the present invention. The present invention encompasses carbon dioxide absorbents containing a composite metal oxide that combines the characteristics of the composite metal oxide in the first carbon dioxide absorbent and the composite metal oxide in the second carbon dioxide absorbent. Furthermore, in relation to the present invention, carbon dioxide absorption means that the carbon dioxide absorbent absorbs at least a portion of the carbon dioxide contained in the gas subjected to the reaction, thereby reducing the concentration of carbon dioxide in the gas after the reaction. Furthermore, in relation to the present invention, the used carbon dioxide absorbent used in the carbon dioxide absorption reaction may be referred to as the reaction product.

[0015] [First Carbon Dioxide Absorbent] The first carbon dioxide absorbent of the present invention contains a composite metal oxide represented by the following formula (1). [Formula 2] Na Ａ Ti Ｂ M Ｃ O Ｄ... (1) However, in formula (1), M is selected from transition elements and main group elements, and 5 ≤ A ≤ 11, 4 ≤ B ≤ 6, 0 ≤ C ≤ 2, and 10.5 ≤ D ≤ 17.5. Furthermore, composite metal compounds containing two or more M selected from transition elements and main group elements (hereinafter also simply referred to as "element M") are also included in the present invention. For example, Na where M is two types, M1 and M2. Ａ Ti Ｂ M1 Ｃ１ M2 Ｃ２ O Ｄ Therefore, the sum of C1 and C2 must be within the range of C mentioned above.

[0016] The composite metal oxide represented by formula (1) was discovered by the inventors as sodium titanate with high carbon dioxide absorption capacity. For example, as shown in Figure 1A, the weight increase rate at room temperature due to contact reaction with air is Na, which is one of the composite metal oxides of the present invention. ８ Ti ５ O １４ However, other composite metal oxides with similar compositions but different compositional ratios include Na ４ Ti ５ O １２ It is significantly higher compared to [another factor]. Furthermore, as shown in Figure 1B, in the above contact reaction, CO in 1 g of sample (composite metal oxide) 18 hours after the start of contact with air. ２ and H ２ Upon checking the amount of O absorbed, Na ８ Ti ５ O １４ Na ４ Ti ５ O １２ Compared to CO ２ It absorbs a large amount of CO, and the absorbed CO ２ and H ２ In the sum of O, CO ２ It is confirmed that the proportion exceeds 50%. In other words, the composite metal oxide shown in formula (1) above has a significantly higher carbon dioxide absorption capacity compared to other sodium titanates. The details of the carbon dioxide absorption reaction shown in Figure 1 will be explained in the examples described later.

[0017] From the viewpoint of providing a composite metal oxide with higher carbon dioxide absorption capacity, it is preferable that A in formula (1) is 6 ≤ A ≤ 10, and more preferably 7 ≤ A ≤ 9. Also from a similar viewpoint, the composition ratio in formula (1) is preferably A = 8, 4.5 ≤ B ≤ 5.5, 0 ≤ C ≤ 1, and D is a value where the charge in formula (1) is ±0, and more preferably A = 8, 4.5 ≤ B ≤ 5.0, 0 ≤ C ≤ 0.5, and D is a value where the charge in formula (1) is ±0. Also from a similar viewpoint, when C in formula (1) is greater than 0 and less than or equal to 1, M is selected from transition elements and main group elements, and is preferably Si, Zr, Mn, or Fe, and among these, Si, Zr, and Mn, which exhibit a tetravalent positive charge, are more preferred. Formula (1) is Na ８ Ti ５ O １４ It is particularly preferable that this be the case.

[0018] A preferred example of the first carbon dioxide absorbent of the present invention is, for example, Na ８ Ti ５ O １４ Na ８ Ti ４．７５ Si ０．２５ O １４ Na ８ Ti ４．７５ Zr ０．２５ O １４ Na ８ Ti ４．７５ Mn ０．２５ O １４ Na ８ Ti ４．７５ Fe ０．２５ O １４ One example is Na ８ Ti ５ O １４ Na ８ Ti ４．７５ Si ０．２５ O １４ Na ８ Ti ４．７５ Zr ０．２５ O １４ Na ８ Ti ４．７５ Mn ０．２５ O １４ , among others, Na ８ Ti５ O １４ This is preferable because it exhibits particularly high carbon dioxide absorption capacity.

[0019] [Second Carbon Dioxide Absorbent] The second carbon dioxide absorbent of the present invention relates to sodium titanate, which has high carbon dioxide absorption capacity, similar to the first carbon dioxide absorbent described above. The second carbon dioxide absorbent is identified by a large peak that appears in a predetermined range of diffraction angle 2θ in a powder X-ray diffraction pattern using CuKα rays. That is, the second carbon dioxide absorbent of the present invention contains a composite metal oxide containing sodium and titanium, and the composite metal oxide shows peaks in the ranges of 12.0°±0.5° and 12.6°±0.5°, respectively, in a powder X-ray diffraction pattern using CuKα rays, and shows one or two peaks in the range from 39.1°±0.5° to 41.0°±0.5°. From the viewpoint of providing a carbon dioxide absorbent with higher carbon dioxide absorption capacity, the second carbon dioxide absorbent of the present invention preferably contains a composite metal oxide that, in a powder X-ray diffraction pattern using CuKα rays, shows peaks in the ranges of 12.0°±0.5° and 12.6°±0.5°, and one peak each in the ranges of 39.1°±0.5° and 41.0°±0.5°.

[0020] To explain the second carbon dioxide absorber, Na ８ Ti ５ O １４ The basic data of the powder X-ray diffraction pattern using CuKα rays is shown in Figure 2. ８ Ti ５ O １４As shown in Figure 2, the diffraction angle 2θ shows large peaks at 12.0°, 12.6°, 39.1°, and 41.0°. The second carbon dioxide absorbent of the present invention includes a composite metal oxide in which, in addition to sodium and titanium, elements selected from transition elements and main group elements are substituted for a portion of the titanium, and the powder X-ray diffraction pattern of the composite metal oxide using CuKα rays shows a pattern that is generally similar to the four large peaks shown in Figure 2. Here, a pattern that is generally similar means a pattern that has large peaks detected within ±0.5° of the diffraction angle 2θ of the four large peaks shown in Figure 2, and a pattern that shows one or two large peaks among the four large peaks in Figure 2 in the diffraction angle 2θ range from 39.1°±0.5° to 41.0°±0.5°. In other words, the present invention also includes configurations that exhibit an X-ray diffraction pattern in which a peak at a diffraction angle 2θ of 39.1°±0.5° and a peak at 41.0°±0.5° overlap to form a single peak.

[0021] The first and second carbon dioxide absorbents of the present invention both contain sodium titanate, a composite metal oxide that satisfies predetermined conditions, and exhibit excellent carbon dioxide absorption. The carbon dioxide absorbents of the present invention can absorb carbon dioxide not only from gases with high carbon dioxide concentrations, but also from gases with low carbon dioxide concentrations. More specifically, the carbon dioxide absorbents of the present invention can absorb carbon dioxide from gases with a carbon dioxide content of more than 10% by volume and 100% by volume or less, as well as from gases with a carbon dioxide content of 10% by volume or less, and even from air with a carbon dioxide content of approximately 0.04% by volume. The reason why the carbon dioxide absorbents of the present invention have excellent absorption capacity for low concentrations of carbon dioxide is not clear, but it is presumed that the composite metal oxide contained in the carbon dioxide absorbents of the present invention contains many sodium atoms, and as a result, can efficiently absorb carbon dioxide from gases with low carbon dioxide concentrations, such as air.

[0022] Furthermore, the first and second carbon dioxide absorbents of the present invention have the advantage of being regenerative at lower temperatures compared to conventional carbon dioxide absorbents using sodium ferrite after the carbon dioxide absorption reaction. More specifically, for example, at a low temperature of 400°C or less, the absorbed carbon dioxide can be desorbed from the carbon dioxide absorbent of the present invention after carbon dioxide absorption, and it can be regenerated to a degree that makes it reusable as a carbon dioxide absorbent. The lower limit of the temperature during regeneration is not particularly limited, but from the viewpoint of rapid regeneration, it is preferable to be 200°C or higher. Therefore, the carbon dioxide absorbent of the present invention has good thermal efficiency for recycling. The regeneration of used composite metal oxides can be confirmed by performing the carbon dioxide absorption reaction again using the sample after the regeneration reaction, or by checking the powder X-ray diffraction pattern using CuKα rays of the sample after the regeneration reaction to confirm the second feature of the present invention described above.

[0023] Currently, waste heat generated in factories at temperatures above medium temperature (above 400°C) has established uses. On the other hand, waste heat at temperatures below medium temperature (below 400°C, and even below 350°C) has no established uses, and there is a need for proposals for effective applications. Therefore, using waste heat such as exhaust gas discharged from factories as a heat source for the regeneration reaction of the carbon dioxide absorbent of the present invention is desirable from the viewpoint of energy recycling, and also proposes new applications for waste heat at temperatures below medium temperature or even lower temperatures from factories.

[0024] Although the reason why the carbon dioxide absorbent of the present invention can be regenerated at lower temperatures than conventional materials is not clear, the carbon dioxide absorbent of the present invention tends to absorb less water along with carbon dioxide than conventional carbon dioxide absorbents such as sodium ferrite. Therefore, it is presumed that the reduced energy required for the evaporation of water generated simultaneously when separating the absorbed carbon dioxide from the carbon dioxide absorbent is one of the factors that enables low-temperature regeneration.

[0025] The following further describes matters common to the composite metal oxides in the first and second carbon dioxide absorbents of the present invention. The carbon dioxide absorbents of the present invention include the composite metal oxides in the first carbon dioxide absorbent and / or the composite metal oxides in the second carbon dioxide absorbent described above, but may further include any other components without departing from the spirit of the present invention, or the carbon dioxide absorbent of the present invention may consist substantially only of the composite metal oxides described above. In this specification, preferred numerical ranges of the present invention may be indicated as appropriate. In this case, preferred ranges, more preferred ranges, and particularly preferred ranges regarding the upper and lower limits of the numerical range can be determined from all combinations of the upper and lower limits.

[0026] (Porrosion of Composite Metal Oxides) The porosity of the composite metal oxide used in the present invention is not particularly limited, but from the viewpoint of providing a carbon dioxide absorbent that absorbs carbon dioxide more effectively, the porosity is preferably 39.0% or more, more preferably 39.1% or more, even more preferably 39.2% or more, and even more preferably 39.3% or more. On the other hand, the upper limit of the porosity is preferably 41.5% or less, and more preferably 41.0% or less. A composite metal oxide having a large amount of sodium atoms in its composition and a moderately high porosity as described above, with a sparse unit cell structure of the compound, is presumed to readily absorb carbon dioxide from a gas containing low concentrations of carbon dioxide and to enable good regeneration at low temperatures. Specifically, a large amount of sodium atoms in its composition refers to 5 ≤ A ≤ 11, more preferably 6 ≤ A ≤ 10, and even more preferably 7 ≤ A ≤ 9, as shown in formula (1) above.

[0027] The porosity of a composite metal oxide is calculated using the following formula (2): [Formula 1] Porosity (%) = 100 - [(Sum of spherical volumes of all ions contained in the unit cell) / Unit cell volume) × 100] ... (2) Here, the spherical volume of an ion refers to the volume of a sphere calculated by the radius of the atomic sphere, assuming that the atomic sphere of each atom is an immovable sphere.

[0028] (Form of composite metal oxide) The shape of the composite metal oxide used in the present invention is not particularly limited, and for example, it may be a powder or a porous body solidified with a binder. The composite metal oxide in the form of a powder is preferable from the viewpoint of increasing the total contact area with the gas and thus accelerating the absorption rate of carbon dioxide gas. Further, the composite metal oxide in the form of a porous body is preferable in terms of excellent handleability. Examples of the method for forming the composite metal oxide into a porous body include, but are not limited to, granulation and extrusion methods. The above porous body may be adjusted to an average particle size of about 0.1 mm to 10.0 mm, and various shapes such as granular, cylindrical, disk-shaped, honeycomb-shaped, etc. can be adopted for its shape.

[0029] When forming the composite metal oxide into the above-mentioned porous body, a binder material (binder) for binding the powdery composite metal oxide can be used. Either an inorganic material or an organic material can be used as the binder material. Examples of the above inorganic material include clay, minerals, lime milk, etc. Examples of the above organic material include starch, methyl cellulose, polyvinyl alcohol, paraffin, etc.

[0030] (Method for producing composite metal oxide) The method for producing the composite metal oxide used in the present invention is not particularly limited, and it can conform to a general method for producing a composite metal oxide. An example of the method for producing the composite metal oxide used in the present invention will be described with reference to FIG. 3. Specifically, in FIG. 3, Na ８ Ti ５ O １４Shows the steps of the manufacturing method. First, sodium carbonate and titanium dioxide are blended to obtain a blend. This blending ratio is adjusted so as to be the same as the composition ratio of sodium and titanium in the finally obtained composite metal oxide. Next, ion-exchanged water is poured into the above blend, and then it is stirred for 1 hour using an ultrasonic stirrer. After stirring, the blend is heated at 80 °C and evaporated to dryness until no moisture is visually recognized in the container or the blend, and then dried overnight in a constant temperature bath adjusted to 120 °C. The obtained dried product is pulverized and mixed using an agate mortar for 30 minutes to obtain a mixed powder. The above mixed powder is placed in a tubular furnace and heated at 700 °C for 5 hours under air flow, and then cooled to 100 °C or lower by natural cooling under argon gas flow, whereby powdery Na ８ Ti ５ O １４ is obtained.

[0031] Na ８ Ti ５ O １４ When producing a composite metal oxide in which a part of titanium of Na Ａ Ti Ｂ M Ｃ O Ｄ in the above formula (1) is substituted with another element (M in the above formula (1)), sodium carbonate, titanium dioxide, and an element M-containing material are blended to obtain a blend. This blending ratio is adjusted so as to be the same as the composition ratio of sodium, titanium, and element M in the finally obtained composite metal oxide, as described above. Using the blend thus obtained, Na Ａ Ti Ｂ M Ｃ O Ｄ shown in the formula (1) can be produced in the same manner as the above-described manufacturing method.

[0032] [Carbon Dioxide Absorption Method] The carbon dioxide absorbent of the present invention described above reacts by contacting with a gas containing carbon dioxide and absorbs the carbon dioxide in the gas. Hereinafter, as a preferred example of the carbon dioxide absorption method using the carbon dioxide absorbent of the present invention, the carbon dioxide absorption method of the present invention will be described.

[0033] The carbon dioxide absorption method of the present invention comprises a storage step of storing the carbon dioxide absorbent of the present invention in a reaction vessel; a reaction step of introducing a carbon dioxide-containing gas into the reaction vessel and bringing the carbon dioxide-containing gas into contact with the composite metal oxide to cause a reaction; and a discharge step of discharging the gas that has undergone the reaction step from the reaction vessel. This carbon dioxide absorption method of the present invention can absorb carbon dioxide in a very simple manner and can discharge a gas with a lower carbon dioxide concentration than before the reaction. Furthermore, the carbon dioxide absorption method of the present invention may further include a recovery step of recovering the gas with a lower carbon dioxide concentration that has been discharged from the discharge step.

[0034] The carbon dioxide absorption method of the present invention benefits from the effects of the carbon dioxide absorbent of the present invention described above. Therefore, it is possible to absorb carbon dioxide not only from gases with a high concentration of carbon dioxide, but also from gases with a low concentration of carbon dioxide. For example, in the carbon dioxide absorption method of the present invention, the carbon dioxide concentration of the carbon dioxide-containing gas introduced into the reaction vessel in the above reaction step may be 10% or less, 1% or less, 0.1% or less, or 0.05% or less.

[0035] The carbon dioxide absorption method of the present invention can be carried out at high temperatures or at room temperature. More specifically, from the viewpoint of better carbon dioxide absorption, the temperature environment of the reaction step is preferably 5°C or higher, more preferably 15°C or higher, and even more preferably 25°C or higher. From the viewpoint of exhibiting good thermal efficiency, it is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 100°C or lower, and particularly preferably 50°C or lower. For example, room temperature air can be directly subjected to the reaction step and carbon dioxide can be absorbed from the air. Alternatively, relatively high-temperature exhaust gas discharged from a factory can be directly subjected to the reaction step. Furthermore, a heating step to raise the carbon dioxide-containing gas to a predetermined temperature before the reaction step or during the reaction step may be carried out.

[0036] The atmospheric gas in the reaction process is not particularly limited, but may be, for example, air, or an inert gas such as nitrogen or argon.

[0037] The carbon dioxide absorption rate of the carbon dioxide absorbent of the present invention can be improved by increasing the humidity of the carbon dioxide-containing gas used in the reaction. Therefore, a "humidity adjustment step" to increase the humidity of the carbon dioxide-containing gas used in the reaction step may be performed before the reaction step. The humidity adjustment step can be performed as appropriate within a range that can increase the humidity of the carbon dioxide-containing gas, but for example, it can be performed by preparing an environment with a humidity relatively higher than the humidity of the carbon dioxide-containing gas being introduced and passing the carbon dioxide-containing gas through that environment. More specifically, examples include, but are not limited to, methods such as installing a water tank in the flow path of the carbon dioxide-containing gas and passing the carbon dioxide-containing gas through the water, or bringing the carbon dioxide-containing gas into contact with the surface of the water. From the viewpoint of increasing the carbon dioxide absorption rate, the humidity of the carbon dioxide-containing gas used in the reaction step is preferably a relative humidity (RH) of 18% or higher, more preferably 40% or higher, even more preferably 60% or higher, and even more preferably 70% or higher.

[0038] The flow rate and pressure of the carbon dioxide-containing gas passing through the reaction process are not particularly limited. For example, the flow rate can be adjusted to approximately 50 ml / min to 200 ml / min. The pressure can also be adjusted to 0.1 MPa or higher, or 0.1 MPa or lower. The carbon dioxide-containing gas introduced into the reaction vessel may be continuously discharged from the reaction vessel, or it may be stored in the reaction vessel for a predetermined time before being discharged.

[0039] [Carbon Dioxide Absorbing Device] Next, the carbon dioxide absorbing device of the present invention will be described. Figure 4 shows a carbon dioxide absorbing device 100, which is one embodiment of the present invention. In the description of the carbon dioxide absorbing device 100, the upstream and downstream sides refer to the upstream and downstream sides of the gas flow in the device, relative to any position in the gas flow. The carbon dioxide absorbing device 100 includes a storage section 10 for housing the carbon dioxide absorbing material 20 of the present invention described above, a gas inlet 30 for introducing carbon dioxide-containing gas into the storage section 10, and a gas outlet 40 for discharging the gas from the storage section 10 to the outside. In this embodiment, the gas inlet 30 and the gas outlet 40 are provided at both ends of the tubular storage section 10. The carbon dioxide absorbing device 100 can enjoy the effects of the carbon dioxide absorbing material of the present invention, absorb carbon dioxide well, and discharge gas with reduced carbon dioxide concentration. Although not shown, a recovery section for recovering the discharged gas may be provided downstream of the gas outlet 40.

[0040] In this embodiment, the carbon dioxide-containing gas introduced into the storage section 10 is shown as air with a low carbon dioxide concentration, but the present invention is not limited to this, and a carbon dioxide-containing gas with a high carbon dioxide concentration can be introduced into the storage section 10, and the carbon dioxide can be absorbed by the carbon dioxide absorbent material 20 stored in the storage section 10.

[0041] In this embodiment, the carbon dioxide absorption device 100 is provided with a humidity control unit 50 upstream of the gas inlet 30. The humidity control unit 50 is a means for increasing the relative humidity of the carbon dioxide-containing gas introduced into the storage unit 10, and its configuration is not particularly limited as long as it can increase the relative humidity of the carbon dioxide-containing gas. In this embodiment shown in Figure 4, the humidity control unit 50 increases the humidity of the carbon dioxide-containing gas by passing the carbon dioxide-containing gas under the water surface 58 or by bringing the carbon dioxide-containing gas into contact with the water surface 58. More specifically, the container 52 in this embodiment is provided with a first inlet passage 32 for introducing external gas into the container 52, and a second inlet passage 34 for introducing the gas inside the container 52 into the storage unit 10. The gas that enters the container 52 through the first inlet passage 32 passes through an introduction pipe 54 provided inside the container 52 and is discharged from the downstream opening 321 of the introduction pipe 54. The discharged gas, after coming into contact with water, is introduced to the outside through a discharge pipe 56 provided inside the container 52, and then introduced into the storage section 10 through a second inlet passage 34 that is continuous with the discharge pipe. At this time, the humidity of the carbon dioxide-containing gas can be adjusted, for example, by adjusting the distance between the downstream opening 321 of the inlet pipe 54 and the water surface 58. In other words, if the downstream opening 321 is below the water surface 58, the carbon dioxide-containing gas passes through the water, so the humidity of the carbon dioxide-containing gas can be made sufficiently high. Alternatively, by positioning the downstream opening 321 above the water surface 58, the increase in the humidity of the carbon dioxide-containing gas can be kept relatively small. Humidity can also be adjusted by adjusting the flow velocity of the carbon dioxide-containing gas passing through the container 52.

[0042] Although not shown in the diagram, the carbon dioxide absorption device 100 may be configured with a heating means either upstream of the storage section 10 or within the storage section 10 itself, to react the carbon dioxide-containing gas with the carbon dioxide absorbent material 20 in a temperature environment higher than room temperature. Alternatively, the storage section 10 may be heated using a heating means prepared outside the storage section 10 to react the carbon dioxide-containing gas with the carbon dioxide absorbent material 20. Furthermore, the carbon dioxide absorbent material 20 may be filled into the entire internal space of the storage section 10.

[0043] [Method for Regenerating Carbon Dioxide Absorbent Material] The carbon dioxide absorbent material of the present invention can be regenerated to a state where it can absorb carbon dioxide again by desorbing the absorbed carbon dioxide through heating. A preferred example of such a regeneration method is the carbon dioxide absorbent material regeneration method of the present invention, in which the reaction product after the carbon dioxide absorption reaction (used carbon dioxide absorbent material) is heated at a temperature of 400°C or lower in the presence of air or an inert gas. The carbon dioxide absorbent material regeneration method of the present invention can regenerate used carbon dioxide absorbent material at a significantly lower temperature compared to the regeneration temperature of conventional sodium ferrite, and has good thermal efficiency.

[0044] In the carbon dioxide absorbent regeneration method of the present invention, the reason why the carbon dioxide absorbent can be regenerated at low temperatures is not clear, but the following factors are considered to be the cause. The first factor is that the composite metal oxide used in the present invention has a high sodium composition ratio and tends to have a large porosity in the unit cell. The second factor is that the reactivity of the titanium compound in the used carbon dioxide absorbent of the present invention is higher than that of the iron oxide in conventional used sodium ferrite. The third factor is that the composite metal oxide used in the present invention absorbs less water simultaneously with carbon dioxide during the absorption reaction than sodium ferrite, so less energy (heat) is required to desorb carbon dioxide and water during the regeneration reaction.

[0045] In the carbon dioxide absorbent regeneration method of the present invention, the heating temperature is preferably 350°C or lower, more preferably 300°C or lower, and even more preferably 270°C or lower, from an economic standpoint. Furthermore, from the viewpoint of rapid regeneration, the lower limit of the above heating temperature is preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 230°C or higher.

[0046] The carbon dioxide absorbent regeneration method of the present invention involves, for example, placing used carbon dioxide absorbent in a container filled with air or an inert gas such as argon or nitrogen, and heating it at a temperature within the range described above for about 12 to 24 hours. This removes carbon dioxide and moisture from the used carbon dioxide absorbent (particularly composite metal oxide), yielding reusable carbon dioxide absorbent. The removed carbon dioxide may also be recovered and provided for industrial use.

[0047] The present invention will be described in detail below with reference to examples. Table 1 shows the manufacturing conditions for the carbon dioxide absorbent in each example and comparative example. However, the present invention is not limited to the examples described below.

[0048] [Example 1] Sodium carbonate (Na ２ CO ３ ) and titanium dioxide (TiO ２ Using ), the molar ratio Na:Ti was adjusted to 8:5 to obtain a mixed powder. 100 ml of deionized water was added to the above mixed powder and stirred with an ultrasonic stirrer for 1 hour. Then, it was evaporated to dryness on a hot stirrer and the dried mixed powder was placed in a constant temperature bath at 120°C and dried overnight. The mixed powder removed from the constant temperature bath was ground and mixed in an agate mortar for 30 minutes. The resulting pulverized mixture was heated in a tubular furnace under air circulation at 700°C for 5 hours. After heating, argon gas was circulated to cool it down to room temperature, thereby removing Na ８ Ti ５ O １４ This was obtained and designated as Example 1.

[0049] [Examples 2-5, Comparative Example 1] Examples 2-5 and Comparative Example 1 were manufactured in the same manner as Example 1 described above, except that the carbon dioxide absorbent manufacturing conditions shown in Table 1 were changed.

[0050] [Comparative Example 2] Sodium nitrate (NaNO) ３Using β-NaFeO₂ and iron oxide (Fe₂O₃), the mixture was adjusted to a molar ratio of Na:Fe = 1:1 to obtain a mixed powder. 100 ml of deionized water was added to the mixed powder and stirred with an ultrasonic stirrer for 1 hour. Then, it was evaporated to dryness on a hot stirrer, and the dried mixed powder was placed in a constant temperature bath at 120°C and dried overnight. The mixed powder removed from the constant temperature bath was ground and mixed in an agate mortar for 30 minutes, and the resulting pulverized mixture was heated in a tubular furnace under air circulation at 800°C for 15 hours. After heating, argon gas was circulated to cool it down to room temperature, thereby converting it to β-NaFeO₂. ２ This was obtained and designated as Comparative Example 2.

[0051] [Comparative Example 3] Sodium nitrate (NaNO) ３ ) and manganese nitrate (Mn(NO) ３ ) 2 Using ), the molar ratio Na:Mn was adjusted to 0.70:1 to obtain a mixed powder. 100 ml of deionized water was added to the above mixed powder and stirred with an ultrasonic stirrer for 1 hour. Then, it was evaporated to dryness on a hot stirrer and the dried mixed powder was placed in a constant temperature bath at 120°C and dried overnight. The mixed powder removed from the constant temperature bath was ground and mixed in an agate mortar for 30 minutes. The resulting pulverized mixture was heated in a tubular furnace under air circulation at 650°C for 3 hours. After heating, argon gas was circulated to cool it down to room temperature, thereby removing Na ０．７ MnO ２．０５ This was obtained and designated as Comparative Example 3.

[0052] [Carbon Dioxide Absorption Reaction] The carbon dioxide absorption reaction of the carbon dioxide absorbent of Example 1 obtained as described above was confirmed as follows using the carbon dioxide absorption apparatus (100) shown in Figure 4. The reaction conditions for the carbon dioxide absorption reaction are shown in Table 2. Specifically, first, 100 mg of the carbon dioxide absorbent (20) of Example 1 was placed in a tubular furnace (container section (10)) with a volume of approximately 0.2 L, and 1 ml of water was filled into a 200 ml Erlenmeyer flask (container (50)) in the humidity control section (50). Then, at an ambient temperature of 25°C, air was introduced into the container (50) from the first inlet passage (32 (30)) at a flow rate of 100 ml / min, and the air was discharged into the container (50) from the downstream opening (321) of the introduction pipe (54). Then, after bringing the air and water into contact inside the container (50), the humidified air was discharged through the discharge pipe (56) and introduced into the tubular furnace (container section (10)) through the second flow path (34) connecting the container (50) and the tubular furnace (container section (10)). The air that flowed into the tubular furnace (container section (10)) came into contact with the carbon dioxide absorbent (20) and was then discharged to the outside through the gas outlet (40). The above series of processes was carried out continuously for 18 hours.

[0053] Furthermore, in order to adjust the humidity of the air flowing into the tubular furnace (container (10)), the distance between the downstream opening (321) of the inlet pipe (54) and the water surface (58) was adjusted. Specifically, in Example 1-1, the downstream opening (321) was positioned below the water surface (58) so that the air could pass through the water, thereby adjusting the humidity to a high level (humidity (RH) of 77%). In Example 1-2, the humidity (RH) was adjusted to 67% by circulating air with the downstream opening (321) closer to the water surface (18). In Example 1-3, the humidity (RH) was adjusted to 41% by circulating air with the downstream opening (321) further away from the water surface (58) than in Example 1-2.

[0054] [Analysis of the carbon absorbent after the reaction] After completing the series of steps as described above, elemental analysis was performed on 1 mg of the used carbon dioxide absorbent (reaction product) in the tubular furnace to confirm the carbon (C) content (mass%) and hydrogen (H) content (mass%) in 100% mass of the sample, which are shown in Table 1. The above elemental analysis was performed using an elemental analyzer (product name FlashSmart) manufactured by Thermo Scientific. Furthermore, the amount of carbon dioxide and water actually absorbed was calculated from the carbon and hydrogen content (mass%) confirmed by this elemental analysis and the amount of carbon dioxide absorbent set in the tubular furnace, and is shown in Table 2.

[0055] As described above, the carbon dioxide absorption reaction was carried out in the same manner as in Example 1, except that the carbon dioxide absorption reaction conditions were changed to those shown in Table 2, using Examples 2 to 5 and Comparative Examples 1 to 3. In addition, in Examples 2 to 5 and Comparative Examples 1 to 3, the humidity was adjusted by adjusting the position of the downstream opening (321) of the introduction pipe (54) relative to the water surface (58), as in Examples 1-1 to 1-3. For Comparative Example 2, the carbon dioxide absorption reaction was carried out in air with a humidity (RH) of 76% as Comparative Example 2-1, and in air with a humidity (RH) of 39% as Comparative Example 2-2. Furthermore, the carbon dioxide and water content in the reaction products of Examples 2 to 5 and Comparative Examples 1, 2-1, 2-2, and 3, which were the reaction products after the absorption reaction, were analyzed in the same manner as in Example 1. The analysis results are shown in Table 2.

[0056] Figure 9 shows the results of calculating the carbon dioxide and water content of each sample after carrying out the carbon dioxide absorption reaction using the sample from Example 1 at ambient temperatures of 25°C, 50°C, and 100°C. From Figure 9, it was confirmed that increasing the ambient temperature from 25°C to 50°C and then to 100°C significantly increased the amount of carbon dioxide absorbed, and also significantly increased the ratio of carbon dioxide to absorbed water.

[0057] [Confirmation of crystal density, lattice volume, and porosity] For Example 1 and Comparative Example 1 described above, the crystal density (g / cm³) was determined by powder X-ray diffraction using CuKα rays. ３ ), unit cell volume ( Å３ The unit cell volume (Å) obtained as described above was calculated. ３ The porosity (%) was calculated using the following formula (2). The crystal density, unit cell volume, and porosity obtained as described above are all shown in Table 3. [Formula 2] Porosity (%) = 100 - [(Sum of spherical volumes of all ions contained in the unit cell) / Unit cell volume) × 100] ... (2) Here, the spherical volume of an ion refers to the volume of a sphere calculated by the radius of the atomic sphere, assuming that the atomic sphere of each atom is an immovable sphere.

[0058] [X-ray Diffraction] Powder X-ray diffraction using CuKα rays was performed on the obtained Examples 1 to 5 as described above, and the differences in the XRD patterns were confirmed. The results are shown in Figure 5. Similarly, the changes in the XRD patterns were confirmed for the used Examples 1-1 and Examples 2 to 5 after carbon dioxide absorption. The results are shown in Figure 6. Note that Na is included in Figure 6 for confirmation. ２ CO ３ ・H ２ Basic data showing the powder X-ray diffraction pattern of O using CuKα radiation is also included.

[0059] As shown by the XRD pattern changes in Figure 5, it was confirmed that in all of Examples 1 to 5, the diffraction angle 2θ showed peaks in the ranges of 12.0°±0.5° and 12.6°±0.5°, and one or two peaks in the range from 39.1°±0.5° to 41.0°±0.5°. In particular, it was confirmed that in Examples 1 to 4, the diffraction angle 2θ showed peaks in the ranges of 12.0°±0.5° and 12.6°±0.5°, and peaks in the ranges of 39.1°±0.5° and 41.0°±0.5°. Furthermore, as shown by the XRD pattern changes in Figure 6, in all of Examples 1-1 to 5 after the carbon dioxide absorption reaction, Na ２ CO ３ ・H ２ A peak characteristic of O was observed, confirming that carbon dioxide was absorbed through a carbon dioxide absorption reaction.

[0060] [Regeneration of Carbon Dioxide Absorbent] The used Example 1-1, which was used in the carbon dioxide absorption reaction, was regenerated as follows. 10 mg of the reaction product from Example 1-1 was used as a sample, and the sample was placed in the sample chamber of a heated X-ray diffractometer in air. The sample was then left in the sample chamber of the apparatus at room temperature, 50°C, 100°C, 150°C, 200°C, 250°C, and 300°C for 5 minutes to carry out the regeneration reaction and obtain a regenerated product.

[0061] As described above, the regenerated materials obtained at each temperature were used as samples, and powder X-ray diffraction using CuKα rays was performed to confirm the change in the crystalline phase due to the regeneration reaction. The powder X-ray diffraction patterns are shown in Figure 7. For confirmation, Figure 7 also shows the basic data of the powder X-ray diffraction pattern of Example 1 before the carbon dioxide absorption reaction, as well as Na ２ CO ３ ・H ２ O and Na ２ CO ３ Basic data showing the respective powder X-ray diffraction patterns are also shown. As can be seen in frames 60 and 62 in Figure 7, in the regeneration reactions where the regeneration temperatures were 200°C, 250°C, and 300°C, Na ８ Ti ５ O １４ Four large peaks characteristic of this material were observed, confirming that the carbon dioxide absorbent had been regenerated.

[0062] Also, the Na used in Example 1-1 ８ Ti ５ O １４ Approximately 5 mg of the reaction product was used as a sample, and the thermal decomposition behavior was observed by heating it from room temperature to 300°C using differential thermal and thermogravimetric analysis (TG-DTA). The results of the differential thermal and thermogravimetric analysis are shown in Figure 8. It was inferred that the dehydration reaction of sodium carbonate hydrate occurred due to the endothermic reaction in frame 64 shown in Figure 8. By further heating to a higher temperature, another endothermic reaction occurred in frame 66, which caused carbon dioxide to be removed, and Na ８ Ti ５ O １４ It was confirmed that it had been played back.

[0063]

[0064]

[0065]

[0066] 10...Tubular furnace 20...Carbon dioxide absorbent 30...Gas inlet 32...First inlet passage 321...Downstream opening 34...Second inlet passage 40...Gas outlet 50...Humidity control section 52...Container 54...Inlet pipe 56...Outlet pipe 58...Water surface 60, 62, 64, 66...Frame 100...Carbon dioxide absorber

Claims

A carbon dioxide absorbent characterized by containing a composite metal oxide represented by the following formula (1) (wherein formula (1) is 5 ≤ ​​A ≤ 11, 4 ≤ B ≤ 6, 0 ≤ C ≤ 2, 10.5 ≤ D ≤ 17.5, and M is selected from transition elements and main group elements). [Formula 1] Na Ａ Ti Ｂ 7. Ｃ 9 Ｄ ・・・・・(1) It contains a composite metal oxide including sodium and titanium, The aforementioned composite metal oxide, in a powder X-ray diffraction pattern using CuKα rays, A carbon dioxide absorbent characterized in that the diffraction angle 2θ shows peaks in the ranges of 12.0°±0.5° and 12.6°±0.5°, and one or two peaks in the range from 39.1°±0.5° to 41.0°±0.5°. The carbon dioxide absorbent according to claim 1 or 2, wherein the porosity of the composite metal oxide is 39.0% or more. The aforementioned composite metal oxide is Na ８ Ti ５ O １４ A carbon dioxide absorbent according to claim 1 or 2, comprising: A storage step of storing the carbon dioxide absorbent according to claim 1 or 2 in a reaction vessel, A reaction step comprising introducing a carbon dioxide-containing gas into the reaction vessel and bringing the carbon dioxide-containing gas into contact with the composite metal oxide to cause a reaction, A method for absorbing carbon dioxide, comprising a discharge step of discharging the gas obtained through the reaction step from the reaction vessel. A storage section for storing the carbon dioxide absorbent according to claim 1 or 2, The storage section includes a gas inlet for introducing carbon dioxide-containing gas, A gas outlet for discharging gas from the storage compartment to the outside A carbon dioxide absorption device characterized by being equipped with the following features. A method for regenerating a carbon dioxide absorbent according to claim 1 or 2, The reaction product after the carbon dioxide absorption reaction is A method for regenerating carbon dioxide absorbent, characterized by heating at a temperature of 400°C or less under air, an inert gas, or a vacuum.

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