Carbon dioxide fixation method, method for manufacturing a cement hardened body for carbon dioxide fixation, and carbon dioxide absorbent liquid

Abstract

In this carbon dioxide immobilization method, a cured cement body (10) is impregnated with a carbon-dioxide-absorbing liquid containing a carbon dioxide absorbent (20) in order to support the carbon dioxide absorbent (20) on the cured cement body (10) and obtain a cured cement body (1) for carbon dioxide immobilization; and the cured cement body (1) for carbon dioxide immobilization is brought into contact with the atmosphere and the carbon dioxide contained in the atmosphere is immobilized in the cured cement body (1) for carbon dioxide immobilization.

Description

[Technical Field]

[0001] This invention relates to a method for carbon dioxide fixation and a cement hardened body for carbon dioxide fixation. This application claims priority based on Japanese Patent Application No. 2022-042454, filed in Japan on March 17, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] To combat global warming, there is a worldwide demand for reducing carbon dioxide (hereinafter also referred to as CO2) emissions. In the field of construction materials, methods have been proposed to reduce the amount of CO2 generated during concrete production by reducing the amount of cement, as well as technologies related to concrete that can fix (absorb) CO2 (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent No. 4822373 [Patent Document 2] Japanese Patent Application Publication No. 2015-54806 [Patent Document 3] Japanese Patent Publication No. 2016-84258 [Overview of the project] [Problems that the invention aims to solve]

[0004] The prior art described above is intended for application in new construction projects. On the other hand, the amount of cement-hardened concrete structures and other existing structures is enormous compared to the number of newly constructed structures. Therefore, technologies for fixing CO2 in existing cement-hardened structures are expected to make a significant contribution to reducing CO2 emissions.

[0005] Therefore, the present invention aims to provide a carbon dioxide fixation method and a carbon dioxide fixation cement body that can fix carbon dioxide in existing cement bodies. [Means for solving the problem]

[0006] To solve the above problems, the present invention has the following aspects. [1] A method for carbon dioxide fixation, comprising impregnating a cement hardened body with a carbon dioxide absorbing liquid containing a carbon dioxide absorbent to obtain a cement hardened body for carbon dioxide fixation in which the carbon dioxide absorbent is supported on the cement hardened body, and bringing the cement hardened body for carbon dioxide fixation into contact with the atmosphere to fix the carbon dioxide contained in the atmosphere to the cement hardened body for carbon dioxide fixation. [2] The carbon dioxide fixation method according to [1], wherein carbon dioxide contained in the atmosphere is fixed as calcium carbonate to the carbon dioxide fixation cement hardened body. [3] The carbon dioxide fixation method according to [1] or [2], wherein the carbon dioxide absorbent is an alkaline compound. [4] The carbon dioxide fixation method according to any one of [1] to [3], wherein the pH of the carbon dioxide absorbent solution at 20°C is 10.0 or higher. [5] The carbon dioxide fixation method according to any one of [1] to [4], wherein the carbon dioxide absorbent does not contain an organosilicon compound. [6] The carbon dioxide fixation method according to any one of [1] to [5], wherein the cement hardened body is concrete. [7] The method for carbon dioxide fixation according to any one of [1] to [6], wherein the cement hardened body comprises recycled aggregate. [8] The carbon dioxide fixation method according to any one of [1] to [7], wherein the carbon dioxide absorbent is an amine compound. [9] The carbon dioxide fixation method according to any one of [1] to [8], wherein the carbon dioxide absorbent is both or either a secondary amine and a tertiary amine.

[10] The carbon dioxide fixation method according to any one of [1] to [9], wherein the carbon dioxide absorbent is either N-methylethanolamine or N-methyldiethanolamine.

[11] The carbon dioxide fixation method according to any one of [1] to

[10] , wherein the content of the carbon dioxide absorbent in the carbon dioxide absorbent solution is 0.01 to 75% by mass with respect to the total mass of the carbon dioxide absorbent solution.

[12] The carbon dioxide fixation method according to any one of [1] to

[11] , wherein the viscosity of the carbon dioxide absorbent at 25°C is 0.1 to 50 mPa·s.

[13] When the carbon dioxide absorbing liquid is applied to the surface of the cement hardened body, the amount of carbon dioxide absorbing liquid applied is 100 to 400 g / m². 2 The carbon dioxide fixation method described in any of [1] to

[12] .

[14] When the carbon dioxide absorbent liquid is sprayed onto the surface of the cement hardened body, the amount of carbon dioxide absorbent liquid sprayed is 100 to 400 g / m 2 The carbon dioxide fixation method described in any of [1] to

[13] .

[15] The carbon dioxide fixation method according to any one of [1] to

[14] , wherein the temperature at which the carbon dioxide fixation cement hardened body is brought into contact with the atmosphere is 0 to 50°C.

[0007]

[16] A cementite for carbon dioxide fixation, in which a carbon dioxide absorbent is supported on a cementite.

[17] The carbon dioxide absorbent is an alkaline compound, the carbon dioxide fixation cement hardened body according to

[16] .

[18] The carbon dioxide absorbent content is 5 to 20 parts by mass per 100 parts by mass of the cement hardened body, as described in

[16] or

[17] .

[19] A cement hardened body for carbon dioxide fixation according to any of

[16] to

[18] , which does not contain organosilicon compounds.

[20] The cementite for carbon dioxide fixation according to any one of

[16] to

[19] , wherein the cementite is concrete. The cement hardened body according to any one of

[16] to

[20] , wherein the cement hardened body contains recycled aggregate. The cement hardened body for carbon dioxide fixation according to any one of

[16] to

[21] , wherein the carbon dioxide absorbent is an amine compound. The cement hardened body for carbon dioxide fixation according to any one of

[16] to

[22] , wherein the carbon dioxide absorbent is both or either one of a secondary amine and a tertiary amine. The cement hardened body for carbon dioxide fixation according to any one of

[16] to

[23] , wherein the carbon dioxide absorbent is both or either one of N-methylethanolamine and N-methyldiethanolamine. [Effects of the Invention]

[0008] According to the carbon dioxide fixation method and the cement hardened body for carbon dioxide fixation of the present invention, carbon dioxide can also be fixed in an existing cement hardened body. [Brief Description of the Drawings]

[0009] [Figure 1] It is a cross-sectional view schematically showing a cement hardened body for carbon dioxide fixation according to an embodiment of the present invention. [Figure 2] It is a schematic diagram showing the flow of a carbon dioxide fixation method according to an embodiment of the present invention. [Figure 3] It is a graph showing the results of thermal decomposition GC / MS of a cement hardened body for carbon dioxide fixation according to an embodiment of the present invention. [Figure 4] It is a graph showing the ratio of the carbon dioxide fixation amount of a cement hardened body for carbon dioxide fixation according to an embodiment of the present invention. [Figure 5] It is a graph showing the results of TG / DTA of a cement hardened body for carbon dioxide fixation according to an embodiment of the present invention. [Figure 6] It is a graph showing a comparison of the production amounts of calcium carbonate in a cement hardened body for carbon dioxide fixation according to an embodiment of the present invention. [Figure 7]This graph shows the relationship between the concentration and pH of a carbon dioxide absorbent solution according to one embodiment of the present invention. [Figure 8] This is a schematic plan view showing the structure of the measuring jig used in the model test. [Figure 9] This is a cross-sectional view of line AA in Figure 8. [Figure 10] This graph shows the impedance spectrum of steel in a model test. [Figure 11] This graph shows the polarization resistance of steel in a model test. [Modes for carrying out the invention]

[0010] ≪Cement hardened material for carbon dioxide fixation≫ The present invention relates to a cementite-hardened body for carbon dioxide fixation, which is a carbon dioxide absorbent-carrying body in which a carbon dioxide absorbent is supported on a cementite-hardened body. In this specification, "supported" means that the carbon dioxide absorbent is attached to both the interior and / or surface of the cementitious body. In this specification, the hardened cement serves as a so-called carrier.

[0011] The following description of a cement hardened body for carbon dioxide fixation according to one embodiment of the present invention will be made with reference to the drawings. As shown in Figure 1, the carbon dioxide fixation cement body 1 of this embodiment is a carbon dioxide absorbent carrier in which a carbon dioxide absorbent 20 is supported on a cement body 10. The carbon dioxide absorbent 20 may be attached to the voids inside the cement body 10, or it may be attached to the surface of the cement body 10. The gradient in Figure 1 represents the degree of impregnation of the cement hardened body 10 with the carbon dioxide absorbing solution. Specifically, the dark areas of the cement hardened body 10 in Figure 1 indicate a high amount of carbon dioxide absorbing solution impregnation, while the light areas indicate a low amount of carbon dioxide absorbing solution impregnation.

[0012] <Hardened cement> The cement hardened body 10 is a hardened product of a cement-containing composition that contains cement and water. In this specification, "cured material" refers to a material that has hardened to the extent that it does not deform when pressed with a finger. Examples of cement-containing compositions include concrete (ready-mix concrete), mortar (paste mortar), cement milk (cement paste), and the like. In this specification, concrete refers to a mixture of cement, fine aggregate (sand), and coarse aggregate (gravel (crushed stone)) mixed with water. In this specification, mortar refers to a mixture of cement and fine aggregate (sand) mixed with water. In this specification, cement milk refers to a mixture of cement and water. In this specification, cement refers to a powder that hardens through a chemical reaction with water, primarily composed of limestone, clay, silica, iron oxide, and other raw materials. In this specification, fine aggregate refers to sand with a diameter of 5 mm or less. In this specification, coarse aggregate refers to gravel (crushed stone) with a diameter of more than 5 mm, and the diameter of the coarse aggregate is preferably 25 mm or less.

[0013] The water content (moisture content) in the hardened cement body 10 is not particularly limited, but can be adjusted, for example, by the ratio of cement to water in the cement-containing composition (water-cement ratio (W / C)) and the number of days required for hardening (curing period).

[0014] The mixing ratio of cement, fine aggregate, and coarse aggregate in concrete can be appropriately determined according to the required strength of the concrete. The mixing ratio of cement, fine aggregate, and coarse aggregate is preferably expressed by mass as follows: for example, 1 part cement to 2-3 parts fine aggregate and 4-6 parts coarse aggregate.

[0015] The mixing ratio of cement to fine aggregate in mortar can be appropriately determined according to the required strength of the mortar. The mixing ratio of cement to fine aggregate is preferably expressed by mass, for example, 1 part cement to 2 to 4 parts fine aggregate.

[0016] The cement hardened body 10 is not particularly limited, but concrete is preferred, and reinforced concrete is more preferred, given its high proportion in existing structures. Furthermore, the size and shape of the cement hardened body 10 are not particularly limited, and existing structures can be used as the cement hardened body 10. In addition, the cementitious body 10 may also be a cementitious body containing recycled aggregate (aggregate with hardened cement attached to its surface). Applying a cementitious body containing recycled aggregate contributes to further reducing the environmental burden.

[0017] <Carbon dioxide absorbent> The carbon dioxide absorbent 20 is supported in the cement hardened body 10 and absorbs carbon dioxide from the atmosphere. Therefore, the carbon dioxide in the atmosphere is incorporated into the carbon dioxide fixation cement hardened body 1, reducing the carbon dioxide concentration in the atmosphere. In addition, the carbon dioxide absorbent 20 absorbs carbon dioxide from the atmosphere and generates carbonate ions. These carbonate ions then react with calcium ions in the cement hardened body 10 to produce calcium carbonate. In this way, the carbon dioxide in the atmosphere is fixed as calcium carbonate in the cement hardened body 10 by the action of the carbon dioxide absorbent 20. That is, carbon dioxide from the atmosphere can be fixed into the carbon dioxide fixation cement hardened body 1. The carbon dioxide absorbent 20 may be a solid or a liquid at room temperature and pressure. In this specification, "room temperature" refers to the standard temperature of the atmosphere, for example, 15-25°C. "Normal pressure" refers to the standard pressure of the atmosphere, for example, 1 atmosphere (1013 hPa).

[0018] Examples of carbon dioxide absorbents 20 include alkaline compounds. Here, "alkaline compounds" refer to compounds whose pH becomes greater than 7 when dissolved in water. The alkaline compound may be an inorganic compound, an organic compound, or a mixture thereof. Examples of inorganic alkaline compounds include calcium hydroxide, magnesium hydroxide, sodium silicate, potassium silicate, lithium silicate, lithium nitrite, and calcium nitrite. Examples of organic alkaline compounds include arginine, lysine, urea, sodium acetate, potassium acetate, and amine compounds. The carbon dioxide absorbent 20 may be used alone or in combination of two or more types.

[0019] Examples of amine compounds include aliphatic amines and aromatic amines. As for amine compounds, aliphatic amines are preferred because they are readily soluble in water. Examples of aliphatic amines include alkylamines and alkanolamines. Examples of alkylamines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, and butylamine. Examples of alkanolamines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), monoisopropanolamine (MIPA), diisopropanolamine (DIPA), triisopropanolamine (TIPA), N-methylethanolamine (2-methylaminoethanol, MAE), and N-methyldiethanolamine (MDEA).

[0020] The amine compound may be a primary amine, secondary amine, tertiary amine, or quaternary ammonium salt, and may have a cyclic structure. Examples of amine compounds, in addition to those mentioned above, include dicyclohexylamine (DCHA), dimethylcyclohexylamine (DMCHA), polyetheramine (PEA), diglycolamine (DGA), 2-amino-2-methyl-1-propanol (AMP90), n-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), pyrrolidine, piperidine, piperazine, and morpholine. These amine compounds may be used individually or in combination of two or more.

[0021] As for amine compounds, secondary amines and tertiary amines are preferred because they readily generate carbonate ions in the hardened cement body 10. Examples of secondary amines include DEA, DIPA, and MAE, as mentioned above. MAE is preferred as a secondary amine because it is superior in its carbon dioxide fixation effect. Examples of tertiary amines include the aforementioned TEA, TIPA, and MDEA. Among the tertiary amines, MDEA is preferred because it exhibits superior carbon dioxide fixation effects.

[0022] Alkaline compounds have the effect of suppressing the corrosion of steel materials such as carbon steel. Therefore, when the cement hardened body 10 is reinforced concrete, alkaline compounds can suppress the corrosion of the reinforcing steel in the reinforced concrete. It is generally known that when reinforced concrete absorbs carbon dioxide, neutralization progresses, and there is a risk that the reinforcing steel will corrode due to a decrease in pH. By impregnating the cement hardened body 10 with an alkaline compound, the above risk can be reduced. From the above viewpoint, alkaline compounds are preferred as the carbon dioxide absorbent 20.

[0023] The amount of carbon dioxide absorbent 20 in the carbon dioxide fixation cement hardened body 1 (the amount of carbon dioxide absorbent 20 carried in the carbon dioxide fixation cement hardened body 1) is preferably 5 to 20 parts by mass per 100 parts by mass of the cement hardened body 10 that serves as the carrier. If the amount of carbon dioxide absorbent 20 carried in the carbon dioxide fixation cement hardened body 1 is above the lower limit, the amount of carbon dioxide that can be fixed can be increased. If the amount of carbon dioxide absorbent 20 carried in the carbon dioxide fixation cement hardened body 1 is below the upper limit, the amount of carbon dioxide absorbent 20 adhering to the cement hardened body 10 can be maintained. The amount of carbon dioxide absorbent 20 supported in the cement hardened body 1 for carbon dioxide fixation can be determined, for example, by pyrolysis gas chromatography-mass spectrometry (pyrolysis GC / MS), thermogravimetric differential thermal analysis (TG / DTA), Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ( 1 It can be determined by methods such as 1H NMR and Raman spectroscopy. The amount of carbon dioxide absorbent 20 supported on the cement hardened body 1 for carbon dioxide fixation can be adjusted by the type of cement hardened body 10, the type of carbon dioxide absorbent 20, the content of carbon dioxide absorbent 20 in the carbon dioxide absorption solution (concentration of carbon dioxide absorbent 20 in the carbon dioxide absorption solution), the amount of carbon dioxide absorption solution, and combinations thereof.

[0024] ≪Method for manufacturing cement hardened bodies for carbon dioxide fixation≫ The carbon dioxide fixation cementite of the present invention is obtained by impregnating a cementite with a carbon dioxide absorbing liquid containing a carbon dioxide absorbent, thereby supporting the carbon dioxide absorbent on the cementite. By impregnating the cementite with the carbon dioxide absorbing liquid, the carbon dioxide absorbing liquid seeps into the interior (pores) of the cementite, and the carbon dioxide absorbent in the carbon dioxide absorbing liquid is supported on the cementite. Furthermore, the solvent may be dried after impregnation with the carbon dioxide absorbent solution. Also, even if moisture such as rain penetrates the cement hardened body for carbon dioxide fixation from the outside, it is sufficient as long as the carbon dioxide absorbent is supported.

[0025] <Carbon dioxide absorbent liquid> A carbon dioxide absorbent is a liquid containing a carbon dioxide absorbent that can absorb carbon dioxide. The carbon dioxide absorbent has physical properties such as viscosity that allow it to penetrate hardened cement. If the carbon dioxide absorbent is a liquid, the carbon dioxide absorbent does not necessarily need to contain the solvent described later.

[0026] The content of the carbon dioxide absorbent in the carbon dioxide absorbent solution is preferably, for example, 0.01 to 75% by mass, more preferably 1 to 50% by mass, and even more preferably 5 to 25% by mass, relative to the total mass of the carbon dioxide absorbent solution. If the content of the carbon dioxide absorbent is above the lower limit, the amount of carbon dioxide that can be immobilized can be increased. If the content of the carbon dioxide absorbent is below the upper limit, the amount of carbon dioxide absorbent solution impregnated into the cement hardened body can be increased.

[0027] When the carbon dioxide absorbent contains a solvent, its viscosity can be reduced, allowing for a greater amount of the absorbent to impregnate the cementitious body. As a result, the amount of carbon dioxide absorbent supported on the cementitious body can be increased, and the amount of carbon dioxide that can be immobilized can be further increased. For this reason, it is preferable that the carbon dioxide absorbent contains a solvent. Examples of solvents include water or organic solvents such as ethanol. Water is preferred as the solvent because it does not volatilize easily at room temperature and readily dissolves carbon dioxide absorbents. These solvents may be used individually or in combination of two or more.

[0028] The solvent content is preferably 25 to 99.99% by mass, more preferably 50 to 99% by mass, and even more preferably 75 to 95% by mass, relative to the total mass of the carbon dioxide absorbent. If the solvent content is above the lower limit, the amount of carbon dioxide absorbent impregnated into the cement hardened body can be increased. If the solvent content is below the upper limit, the carbon dioxide absorbent content can be increased. Therefore, the amount of carbon dioxide that can be immobilized can be increased.

[0029] The viscosity of the carbon dioxide absorbent at 25°C is preferably, for example, 0.1 to 50 mPa·s, more preferably 0.5 to 25 mPa·s, and even more preferably 0.5 to 10 mPa·s. If the viscosity of the carbon dioxide absorbent at 25°C is above the lower limit, the amount of carbon dioxide absorbent supported on the cement hardened body can be increased. If the viscosity of the carbon dioxide absorbent at 25°C is below the upper limit, the amount of carbon dioxide absorbent impregnated into the cement hardened body can be increased. The viscosity of a carbon dioxide absorbent at 25°C can be determined, for example, by setting the temperature of the sample to 25°C, using the second rotor of a Type B viscometer, and reading the value 30 seconds after the rotor starts rotating at a rotation speed of 60 rpm.

[0030] The pH of the carbon dioxide absorbent at 20°C is preferably 10.0 or higher, more preferably 10.2 or higher, and even more preferably 10.5 or higher. If the pH of the carbon dioxide absorbent at 20°C is above the lower limit mentioned above, the rate of carbon dioxide absorption can be increased. The upper limit of the pH of the carbon dioxide absorbent at 20°C is not particularly limited, but considering ease of handling, it is set to, for example, 14.0. The pH of the carbon dioxide absorption solution at 20°C can be measured by adjusting the temperature of the sample to 20°C and using a pH meter (for example, the Horiba Multi-Digital Water Quality Meter WQ-330J).

[0031] If the carbon dioxide absorbent contains organosilicon compounds, a silicon film forms on the surface and inside (pore surface) of the hardened cement, making it difficult for the water-solvent carbon dioxide absorbent to penetrate the hardened cement. As a result, the amount of carbon dioxide absorbent supported on the hardened cement is reduced, and the amount of carbon dioxide that can be immobilized is reduced. For this reason, it is preferable that the carbon dioxide absorbent does not contain organosilicon compounds. Examples of organosilicon compounds include silane compounds such as methoxysilane and ethoxysilane.

[0032] The method for impregnating the cementitious body with a carbon dioxide absorbent is not particularly limited, and one example is to bring the carbon dioxide absorbent into contact with the surface of the cementitious body. Methods for bringing a carbon dioxide absorbent into contact with the surface of a hardened cement include, for example, applying the carbon dioxide absorbent to the surface of the hardened cement, spraying the carbon dioxide absorbent to the surface of the hardened cement, attaching a sheet material containing the carbon dioxide absorbent to the surface of the hardened cement, and immersing the hardened cement in the carbon dioxide absorbent. Because it offers superior work efficiency, the preferred method for bringing the carbon dioxide absorbing solution into contact with the surface of the hardened cement is to spray the carbon dioxide absorbing solution onto the surface of the hardened cement. Examples of devices for spraying carbon dioxide absorption liquid onto the surface of a hardened cement include pressurized sprayers and electric sprayers.

[0033] When applying a carbon dioxide absorbent to the surface of a hardened cement body, the amount of carbon dioxide absorbent applied should be, for example, 100 to 400 g / m². 2 Preferably, 200-400 g / m 2 This is more preferable. If the amount of carbon dioxide absorbent applied is above the lower limit, the amount of carbon dioxide that can be fixed by the cement hardened body for carbon dioxide fixation can be increased. If the amount of carbon dioxide absorbent applied is below the upper limit, the amount of carbon dioxide absorbent used can be reduced, and work efficiency can be increased. In addition, it is advantageous in terms of cost. Note that the amount of carbon dioxide absorbent applied may be the amount applied in a single application, or it may be the cumulative amount applied by multiple applications.

[0034] When spraying a carbon dioxide absorbent solution onto the surface of a hardened cement body, the amount of carbon dioxide absorbent solution to spray should be, for example, 100 to 400 g / m². 2 Preferably, 200-400 g / m 2This is more preferable. If the amount of carbon dioxide absorbent solution sprayed is above the lower limit, the amount of carbon dioxide that can be fixed by the cement hardened body for carbon dioxide fixation can be increased. If the amount of carbon dioxide absorbent solution sprayed is below the upper limit, the amount of carbon dioxide absorbent solution used can be reduced, and work efficiency can be increased. In addition, it is advantageous in terms of cost. Note that the amount of carbon dioxide absorbent solution sprayed may be the amount sprayed in a single application, or it may be the cumulative amount sprayed by multiple applications.

[0035] When a sheet material containing a carbon dioxide absorbent is applied to the surface of a hardened cement body, examples of alkali-resistant materials for the sheet material include polypropylene and polyvinyl alcohol. The water retention capacity of the sheet material (amount of carbon dioxide absorbent liquid in the sheet material) is preferably 50% by mass or more, and more preferably 100% by mass or more, relative to the dry mass of the sheet material. If the water retention capacity of the sheet material is above the lower limit, the amount of carbon dioxide absorbent liquid impregnated into the cement hardened body can be increased. The upper limit of the water retention capacity of the sheet material is not particularly limited, but for example, 500% by mass is preferred. The time for applying the sheet material is not particularly limited, but for example, 24 hours or more is preferred. If the time for applying the sheet material is greater than or equal to the lower limit mentioned above, the amount of carbon dioxide absorbent liquid impregnated into the hardened cement can be increased.

[0036] When immersing a hardened cement in a carbon dioxide absorbent solution, the immersion time (immersion period) is preferably, for example, 6 hours to 50 days, and more preferably 12 hours to 30 days. If the immersion time of the hardened cement in the carbon dioxide absorbent solution is greater than or equal to the lower limit, a sufficient amount of carbon dioxide absorbent solution can be impregnated into the hardened cement. If the immersion time of the hardened cement in the carbon dioxide absorbent solution is less than or equal to the upper limit, the productivity of the hardened cement for carbon dioxide fixation can be further increased.

[0037] The amount of carbon dioxide absorbent supported on the cementitious body (carbon dioxide absorbent content) is preferably 5 to 20 parts by mass per 100 parts by mass of the cementitious body. If the carbon dioxide absorbent content is above the lower limit, the amount of carbon dioxide that can be immobilized can be increased. If the carbon dioxide absorbent content is below the upper limit, the amount of carbon dioxide absorbent adhering to the cementitious body can be maintained.

[0038] ≪Carbon dioxide fixation method≫ The carbon dioxide fixation method of the present invention comprises the steps of: impregnating a cement hardened body with a carbon dioxide absorbing liquid containing a carbon dioxide absorbent to obtain a cement hardened body for carbon dioxide fixation (Step I); and bringing the obtained cement hardened body for carbon dioxide fixation into contact with the atmosphere to fix carbon dioxide contained in the atmosphere to the cement hardened body for carbon dioxide fixation (Step II). In other words, the carbon dioxide fixation method 100 according to one embodiment of the present invention has a step I (S1) and a step II (S2), as shown in Figure 2.

[0039] In step I, a cementite is impregnated with a carbon dioxide absorbing solution containing a carbon dioxide absorbent, thereby obtaining a cementite for carbon dioxide fixation that supports the carbon dioxide absorbent. The method for impregnating the cementitious body with carbon dioxide absorbing liquid is the same as the method described in the method for manufacturing cementitious body for carbon dioxide fixation.

[0040] In step II, the carbon dioxide-fixing cement is brought into contact with the atmosphere, causing the carbon dioxide in the atmosphere to be absorbed by the carbon dioxide absorbent contained in the cement. Some or all of the carbon dioxide absorbed by the carbon dioxide absorbent reacts with calcium ions in the cement to form calcium carbonate as carbonate ions. In this way, some or all of the carbon dioxide in the atmosphere is fixed as calcium carbonate in the cement through the action of the carbon dioxide absorbent. Therefore, carbon dioxide can be fixed in the cement for carbon dioxide fixation.

[0041] The method for exposing the carbon dioxide-fixing cement to the atmosphere is not particularly limited; for example, the carbon dioxide-fixing cement may be exposed to the atmosphere. The temperature at which the cement hardened body for carbon dioxide fixation is brought into contact with the atmosphere is not particularly limited, but is preferably 0 to 50°C, and more preferably 5 to 40°C. If the temperature at which the cement hardened body for carbon dioxide fixation is brought into contact with the atmosphere is above the lower limit, the amount of carbon dioxide that can be fixed can be increased. If the temperature at which the cement hardened body for carbon dioxide fixation is brought into contact with the atmosphere is below the upper limit, deterioration of the cement hardened body for carbon dioxide fixation can be suppressed.

[0042] The time for exposing the carbon dioxide-fixing cement to the atmosphere is not particularly limited, but is preferably 1 hour or more, and more preferably 24 hours or more. If the time for exposing the carbon dioxide-fixing cement to the atmosphere is greater than or equal to the lower limit mentioned above, the amount of carbon dioxide that can be fixed can be increased. The upper limit for the time for exposing the carbon dioxide-fixing cement to the atmosphere is not particularly limited, but is preferably 3 months, for example, because the carbon dioxide absorbent liquid in the carbon dioxide-fixing cement is more easily retained.

[0043] The amount of carbon dioxide fixed to the cement hardened material for carbon dioxide fixation can be measured, for example, by pyrolysis gas chromatography-mass spectrometry (pyrolysis GC / MS), thermogravimetric differential thermal analysis (TG / DTA), etc.

[0044] The carbon dioxide-fixing cementitious body of the present invention can absorb (fix) carbon dioxide from the atmosphere because it has a carbon dioxide absorbent supported on it. As a result, the concentration of carbon dioxide in the atmosphere can be reduced. The carbon dioxide fixation method of the present invention can be applied to hardened cement bodies, not to cement-containing compositions in the process of manufacturing. Therefore, it can be applied to existing hardened cement bodies and contribute to reducing the concentration of carbon dioxide in the atmosphere. The carbon dioxide fixation method of the present invention can fix carbon dioxide using a simple impregnation method, thus eliminating the need for large-scale equipment or construction work. The carbon dioxide fixation method of the present invention can fix carbon dioxide in a simple manner and can therefore be repeatedly applied to existing cement hardened bodies.

[0045] The carbon dioxide fixation method and the cement hardened body for carbon dioxide fixation of the present invention have been described above, but the present invention is not limited to the embodiments described above and can be modified as appropriate without departing from the spirit of the invention. For example, the cement hardened body for carbon dioxide fixation may be dried, and the carbon dioxide absorbent liquid may be dried. However, in carbon dioxide fixation methods, it is preferable not to dry the carbon dioxide absorbent liquid, as this can further improve the carbon dioxide absorption efficiency. For example, if the carbon dioxide absorption effect decreases, the effect can be restored by re-impregnating the hardened cement with a carbon dioxide absorbent solution. The carbon dioxide absorption effect can be determined by measuring the concentration of carbon dioxide in the atmosphere surrounding the hardened cement for carbon dioxide fixation. Alternatively, it can be determined by placing a sample of the hardened cement for carbon dioxide fixation in a container such as a sample bag filled with carbon dioxide and observing the decrease in the volume of the container as the sample absorbs carbon dioxide. [Examples]

[0046] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0047] [Experimental Example 1] As the cement hardened body, a powder obtained by hardening cement paste and grinding it in a ball mill was used. The composition of the cement paste was a water-cement ratio (W / C) of 60%. As a carbon dioxide absorbent, N-methyldiethanolamine (MDEA) was used, and carbon dioxide absorbent solutions were prepared with water as the solvent at concentrations of MDEA of 0% by mass (water), 5% by mass, 10% by mass, 25% by mass, 50% by mass, and 75% by mass. 250 mL of each concentration of carbon dioxide absorbent solution was measured into 400 mL resin containers, 10 g of the above powder was added, and the mixture was thoroughly mixed to impregnate the powder with the carbon dioxide absorbent solution and obtain carbon dioxide fixation cementitious bodies. A chamber atmosphere with a temperature of 20°C, humidity of 60% RH, and a CO2 concentration of 5% by mass was supplied to each resin container at a flow rate of 8 L / min for 12 hours to allow the carbon dioxide fixation cementitious bodies to absorb CO2. Subsequently, 10 mg of the carbon dioxide fixation cementitious body was taken from each example, and the mass of fixed CO2 was measured using a pyrolysis gas chromatography-mass spectrometry (pyrolysis GC / MS) apparatus. The results are shown in Figures 3 and 4.

[0048] In the graph in Figure 3, the vertical axis represents the mass loss (mass %) of the cementite used for carbon dioxide fixation. The mass loss of the cementite is due to the detachment of carbon dioxide that was fixed in the cementite. As shown in Figure 3, it was confirmed that when the MDEA concentration in the carbon dioxide absorbent solution was 5% by mass or higher, the mass reduction of the carbon dioxide-fixing cement hardened body was greater than when no carbon dioxide absorbent was included (water).

[0049] As shown in Figure 4, the mass reduction (mass%) of the cement hardened material for carbon dioxide fixation, i.e., the mass of carbon dioxide fixed to the cement hardened material, was greatest when the MDEA concentration was 10 mass%, and was more than twice that of the water-impregnated powder (cement hardened material). Furthermore, it was found that when the carbon dioxide absorbent solution had an MDEA concentration of 25 mass% or higher, the carbon dioxide absorbent solution was not sufficiently impregnated into the powder. This is thought to be because carbon dioxide absorbent solutions with an MDEA concentration of 25 mass% or higher have high viscosity and are difficult to impregnate into the cement hardened material.

[0050] [Experimental Example 2] A cement paste with a water-cement ratio (W / C) of 50% was sealed and cured at 20°C for 28 days, and the resulting granular material was used as a sample of hardened cement. At 20°C, 30 g of the sample was weighed out and immersed in 300 mL of water, 300 mL of a 10% by mass MDEA aqueous solution, or 300 mL of a 10% by mass N-methylethanolamine (MAE) aqueous solution. Carbonation was performed by bubbling CO2 gas into the water or aqueous solution (carbon dioxide absorbent). The CO2 gas concentration was 5% by volume, the flow rate was 2 L / min, and the bubbling time was 6 hours. After bubbling, each sample was filtered and dried at 40°C for 24 hours. The dried samples were pulverized into powder, 10 mg was taken out, and the amount of calcium carbonate produced was measured by simultaneous thermogravimetric differential thermal analysis (TG / DTA). The results are shown in Figures 5 and 6. The amount of calcium carbonate produced in TG / DTA is given by the mass difference (mass loss) between the mass at 500°C and the mass at 800°C.

[0051] In the graph in Figure 5, the vertical axis represents the ratio of the mass of the sample after heating with TG / DTA to the mass of the sample before TG / DTA. The sample loses mass due to the decomposition of the generated calcium carbonate. A larger decrease in the mass of calcium carbonate indicates a larger amount of carbon dioxide fixed in the sample (hardened cement body for carbon dioxide fixation). As shown in Figure 5, the mass loss of the sample from 500°C to 800°C was greatest in the order of MAE aqueous solution, MDEA aqueous solution, and water. It was confirmed that the mass loss of the carbon dioxide-fixing cement hardened body was greater when impregnated with the carbon dioxide absorbent than when it did not contain the carbon dioxide absorbent (water).

[0052] In the graph in Figure 6, the vertical axis represents the mass loss (mass %) of the sample from 500°C to 800°C relative to the total mass of the sample before TG / DTA. As shown in Figure 6, the mass loss of the sample from 500°C to 800°C was greatest in the order of MAE aqueous solution, MDEA aqueous solution, and water. This confirmed that the mass loss of the carbon dioxide-fixing cement hardened body was greater when impregnated with the carbon dioxide absorbent than when it did not contain the carbon dioxide absorbent (water).

[0053] [Experimental Example 3] To confirm the relationship between the concentration of the carbon dioxide absorbent and the pH of the carbon dioxide absorption solution, carbon dioxide absorption solutions were prepared using MDEA or MAE as the carbon dioxide absorbent and water as the solvent, at the concentrations listed in Table 1. The pH of each solution at 20°C was measured. A pH meter (Multi-Digital Water Quality Meter, WQ-330J) manufactured by Horiba, Ltd. was used to measure the pH. The results are shown in Table 1 and Figure 5.

[0054] [Table 1]

[0055] As shown in Table 1 and Figure 7, the pH of the carbon dioxide absorbent solution was 10.0 or higher when the concentration of the carbon dioxide absorbent was 1% by mass or higher. The pH of the carbon dioxide absorbent solution increased with increasing concentration of the carbon dioxide absorbent. The pH of the carbon dioxide absorbent solution with a MAE concentration of 100% by mass was 13.45.

[0056] [Experimental Example 4] As the cement-hardened body, a mortar made by mixing cement, fine aggregate, and water was hardened and molded into a cylindrical shape with a diameter of 50 mm and a height of 10 mm. The composition of the mortar was a water-cement ratio (W / C) of 50% and a mass ratio of cement to fine aggregate of 1:2.5. Using MDEA as the carbon dioxide absorbent and water as the solvent, carbon dioxide absorbent solutions were prepared with MDEA concentrations of 0% by mass (water), 5% by mass, 10% by mass, 25% by mass, 50% by mass, 75% by mass, and 100% by mass. The cylindrical cement hardened bodies described above were immersed in the carbon dioxide absorbent solution at a temperature of 20°C for 24 hours to impregnate them with the carbon dioxide absorbent solution and obtain cement hardened bodies for carbon dioxide fixation. After removal and drying, the surface hardness of the obtained cement hardened bodies for carbon dioxide fixation was evaluated using a scratch tester (manufactured by Linax Co., Ltd.) certified by the Japan Society for Architectural Finishing. The results are shown in Table 2. In Table 2, "bold1" and "bold2" represent the width (mm) of two scratches randomly selected from the thicker scratch. "bold ave" represents the average value of "bold1" and "bold2". "narrow1" and "narrow2" represent the width (mm) of two scratches randomly selected from the thinner scratch. "narrow ave" represents the average of "narrow1" and "narrow2".

[0057] [Table 2]

[0058] As shown in Table 2, a tendency was observed for the width of scratches to narrow as the concentration of MDEA increased. There was a correlation between the width of scratches and compressive strength, with a tendency for the compressive strength to be lower as the width of the scratches increased. In other words, the results in Table 2 show that impregnation with MDEA does not adversely affect compressive strength, regardless of the concentration of MDEA.

[0059] [Experimental Example 5] A model test was conducted to confirm that the carbon dioxide absorbent of this embodiment has corrosion resistance to reinforcing steel in reinforced concrete. A 25mm outer diameter, 2.5mm thick SS400 steel material is placed in the sample holder of the measuring jig shown in Figures 8 and 9, and the exposed surface of the steel material (1cm) is measured. 2)The cement paste with a water-cement ratio (W / C) of 50% was poured into it and cured in a sealed manner for 3 days. After curing, the cement hardened body together with the sample holder was left to carbonize for 35 days in an environment with a CO2 concentration of 5% by volume, a temperature of 20 °C, and a humidity of 60% RH. Then, the polarization resistance of the steel was obtained by the electrochemical impedance method in a 0.1 mol / L calcium nitrate aqueous solution. Further, the cement hardened body together with the sample holder was immersed in an MDEA aqueous solution with a concentration of 5% by mass, and the impedance and polarization resistance of the steel were measured by the electrochemical impedance method in the MDEA aqueous solution at 14 days and 28 days after immersion. The results are shown in FIGS. 10 and 11.

[0060] FIG. 10 is a graph showing the impedance spectrum of the steel. As shown in FIG. 10, the steel in the cement hardened body immersed in the carbon dioxide absorption liquid for 14 days had a larger impedance value compared to the steel in the cement hardened body at 0 days (before immersion) of the immersion period. A larger impedance value means that the corrosion current density flowing on the surface of the steel is small, which means that the corrosion rate of the steel is low, that is, the corrosion resistance of the steel is high. That is, it means that the anticorrosion performance of the cement hardened body is improved.

[0061] FIG. 11 is a graph showing the polarization resistance of each steel in three cases with different immersion periods. The polarization resistance can be calculated from the impedance value. As shown in FIG. 11, in the case of an immersion period of 28 days, it far exceeded the reference value of the corrosion rate that can be regarded as corrosion stop, 130,000 Ω·cm 2 (130 kΩ·cm 2 ) and was 200,000 Ω·cm 2 (200 kΩ·cm 2 ). Thus, the polarization resistance increases as the immersion period becomes longer, which means that the anticorrosion effect becomes higher due to the impregnation of the carbon dioxide absorption liquid.

[0062] From the above, it was found that according to the carbon dioxide fixation method of the present invention, carbon dioxide can be fixed in the cement hardened body for carbon dioxide fixation. In addition, it has been found that the carbon dioxide absorbing liquid according to the carbon dioxide fixation method of the present invention can further enhance the corrosion protection effect of the cement hardened body for carbon dioxide fixation.

[0063] Among the 17 international goals adopted at the UN Summit in September 2015 are the "Sustainable Development Goals (SDGs)." One embodiment of the carbon dioxide sequestration method can contribute to achieving some of these 17 SDGs, such as "11. Make cities and human settlements inclusive, safe, resilient and sustainable," "12. Responsible consumption and production," and "13. Take urgent action to combat climate change." [Explanation of Symbols]

[0064] 1...Cement hardened body for carbon dioxide fixation, 10...Cement hardened body, 20...Carbon dioxide absorbent, 100...Carbon dioxide fixation method, S1...Process I, S2...Process II

Claims

1. A method for carbon dioxide fixation, comprising: impregnating a carbon dioxide absorbent solution containing an aliphatic amine into the interior of a cement hardened body to obtain a cement hardened body for carbon dioxide fixation in which the aliphatic amine is supported inside the cement hardened body; bringing the cement hardened body for carbon dioxide fixation into contact with the atmosphere; and fixing the carbon dioxide contained in the atmosphere into the cement hardened body for carbon dioxide fixation, A carbon dioxide fixation method wherein the carbon dioxide absorbent solution contains water and 5 to 25% by mass of the aliphatic amine relative to the total mass of the carbon dioxide absorbent solution, does not contain organosilicon compounds, has a pH of 10.5 or higher at 20°C, and the viscosity measured at 25°C using a B-type viscometer (second rotor, rotation speed 60 rpm) is 0.5 to 25 mPa·s.

2. The carbon dioxide fixation method according to claim 1, wherein the aliphatic amine is one or more selected from alkylamines and alkanolamines.

3. The carbon dioxide fixation method according to Claim 1, wherein the aliphatic amine is one or more selected from the group consisting of N-methylethanolamine (MAE), N-methyldiethanolamine (MDEA), monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP90), and piperazine.

4. The carbon dioxide fixation method according to claim 1, wherein the aliphatic amine is one or more selected from N-methylethanolamine (MAE) and N-methyldiethanolamine (MDEA).

5. The carbon dioxide fixation method according to claim 1, wherein the aliphatic amine is N-methylethanolamine (MAE).

6. The carbon dioxide fixation method according to claim 1, wherein the water content relative to the total mass of the carbon dioxide absorbent is 75 to 95% by mass.

7. The carbon dioxide fixation method according to claim 1, wherein the cement hardened body is concrete.

8. This is a method for manufacturing a cementite for carbon dioxide fixation in which an aliphatic amine is supported inside the cementite. This includes impregnating the interior of the cementitious body with a carbon dioxide absorbing solution containing the aliphatic amine, and supporting the aliphatic amine inside the cementitious body. A method for producing a cement hardened body for carbon dioxide fixation, wherein the carbon dioxide absorbent solution contains water and 5 to 25% by mass of the aliphatic amine relative to the total mass of the carbon dioxide absorbent solution, does not contain organosilicon compounds, has a pH of 10.5 or higher at 20°C, and has a viscosity of 0.5 to 25 mPa·s measured at 25°C using a B-type viscometer (second rotor, rotation speed 60 rpm).

9. The method for producing a cementite for carbon dioxide fixation according to claim 8, wherein the aliphatic amine is one or more selected from alkylamines and alkanolamines.

10. The method for producing a cement hardened body for carbon dioxide fixation according to claim 8, wherein the aliphatic amine is one or more selected from the group consisting of N-methylethanolamine (MAE), N-methyldiethanolamine (MDEA), monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP90), and piperazine.

11. The method for producing a cement hardened body for carbon dioxide fixation according to claim 8, wherein the aliphatic amine is one or more selected from N-methylethanolamine (MAE) and N-methyldiethanolamine (MDEA).

12. The method for producing a cement hardened body for carbon dioxide fixation according to claim 8, wherein the aliphatic amine is N-methylethanolamine (MAE).

13. The method for producing a cement hardened body for carbon dioxide fixation according to claim 8, wherein the water content relative to the total mass of the carbon dioxide absorbent is 75 to 95% by mass.

14. The method for manufacturing a cementite for carbon dioxide fixation according to claim 8, wherein the cementite is concrete.

15. A method for impregnating the interior of the cement hardened body with the carbon dioxide absorbing liquid is a method of spraying the carbon dioxide absorbing liquid onto the surface of the cement hardened body. The amount of carbon dioxide absorbent solution sprayed onto the hardened cement body is 100 to 400 g / m². ２ The method for producing a cement hardened body for carbon dioxide fixation according to claim 8.

16. The method for impregnating the inside of the cement hardened body with the carbon dioxide absorbing liquid is a method of applying the carbon dioxide absorbing liquid to the surface of the cement hardened body. The amount of carbon dioxide absorbent liquid applied to the hardened cement body is 100 to 400 g / m². ２ The method for producing a cement hardened body for carbon dioxide fixation according to claim 8.

17. The method for impregnating the interior of the cement hardened body with the carbon dioxide absorbing liquid is to attach a sheet material containing the carbon dioxide absorbing liquid to the surface of the cement hardened body. The amount of carbon dioxide absorbent liquid in the sheet material is 50 to 500% by mass relative to the dry mass of the sheet material. The method for manufacturing a cementite for carbon dioxide fixation according to claim 8, wherein the time for attaching the sheet material to the cementite is 24 hours or more.

18. The method for impregnating the hardened cement body with the carbon dioxide absorbing liquid is a method of immersing the hardened cement body in the carbon dioxide absorbing liquid. The method for producing a cementite for carbon dioxide fixation according to claim 8, wherein the time for immersing the cementite in the carbon dioxide absorbent is 6 hours or more and 50 days or less.

19. A carbon dioxide absorbent comprising an aliphatic amine, wherein the absorbent comprises water and 5 to 25% by mass of the aliphatic amine relative to the total mass of the carbon dioxide absorbent, is free of organosilicon compounds, has a pH of 10.5 or higher at 20°C, and has a viscosity of 0.5 to 25 mPa·s measured at 25°C using a B-type viscometer (second rotor, rotation speed 60 rpm).

20. The carbon dioxide absorbent according to claim 19, wherein the aliphatic amine is one or more selected from alkylamines and alkanolamines.

21. The carbon dioxide absorbent according to claim 19, wherein the aliphatic amine is one or more selected from the group consisting of N-methylethanolamine (MAE), N-methyldiethanolamine (MDEA), monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP90), and piperazine.

22. The carbon dioxide absorbent according to claim 19, wherein the aliphatic amine is one or more selected from N-methylethanolamine (MAE) and N-methyldiethanolamine (MDEA).

23. The carbon dioxide absorbent according to claim 19, wherein the aliphatic amine is N-methylethanolamine (MAE).

24. The carbon dioxide absorbent according to claim 19, wherein the water content relative to the total mass of the carbon dioxide absorbent is 75 to 95% by mass.

Images