WO2023140336A1

WO2023140336A1 - Carbon dioxide fixation method and fixation system, and carbonate production method

Info

Publication number: WO2023140336A1
Application number: PCT/JP2023/001590
Authority: WO
Inventors: 剛安元; 美奈廣瀬; 聡勝又; 植田直幸牟田; 賢司森安; 道生鈴木
Original assignee: 学校法人北里研究所; 出光興産株式会社; 国立大学法人東京大学; 株式会社日本海水
Priority date: 2022-01-20
Filing date: 2023-01-19
Publication date: 2023-07-27

Abstract

Provided is a carbon dioxide fixation method in which a Group II element ion-containing aqueous solution (B) (the Group II element ion-containing aqueous solution (B) comprising at least an alkaline earth metal ion) is brought into contact with a carbon dioxide-derived carbonic acid ion in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of the foregoing amines to generate a carbonate of an alkaline earth metal. The carbon fixation method comprises a step (S) for using a carbon dioxide-containing gas (C) to suppress the increase in pH of the Group II element ion-containing aqueous solution (B) caused by the amine compound (A).

Description

Carbon dioxide fixation method and fixation system, and carbonate production method

The present disclosure relates to a method and system for fixing carbon dioxide, and a method for producing carbonate using the method for fixing carbon dioxide.

Among the greenhouse gases that are said to cause global warming, carbon dioxide (carbon dioxide gas) has a particularly large impact, and preventing an increase in the concentration of carbon dioxide in the atmosphere can be one means of curbing global warming. Therefore, research is being conducted on techniques for limiting the use of fossil resources and reducing the amount of carbon dioxide released into the atmosphere. In addition, many countries, including Japan, are actively researching technologies to absorb and fix carbon dioxide that has already been released into the atmosphere, and technologies to absorb and fix carbon dioxide from burning fossil resources without releasing it into the atmosphere or while suppressing its release into the atmosphere.

In recent years, as one method of absorbing and fixing carbon dioxide, the idea of fixing carbon dioxide as a carbonate by a chemical reaction has been proposed.
For example, Patent Document 1 proposes a method of contacting a gas containing carbon dioxide with an aqueous solution obtained from water and an alkaline earth metal-containing substance (e.g., steel slag) with a weak base and a salt of a strong acid to generate an alkaline earth metal carbonate.

Japanese Patent Application Laid-Open No. 2005-097072

However, the method described in Patent Document 1 has a problem that the carbon dioxide fixation efficiency is not sufficient.

The present disclosure has been made in view of such problems, and aims to provide a carbon dioxide fixation method and a fixation system that are excellent in carbon dioxide fixation efficiency, and a carbonate production method using the carbon dioxide fixation method.

According to the present disclosure, the following [1] to [5] are provided.
[1] A method for immobilizing carbon dioxide, wherein an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions) is brought into contact with carbon dioxide-derived carbonate ions in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, to produce an alkaline earth metal carbonate,
A step (S) of suppressing a pH increase of the group 2 element ion-containing aqueous solution (B) caused by the amine compound (A) by using a gas (C) containing carbon dioxide.
A method for immobilizing carbon dioxide, comprising:
[2] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
Aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, amines artificially synthesized, and polymers containing groups derived from these amines is brought into contact with a gas (C) containing carbon dioxide to prepare an amine aqueous solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C) (P1-1);
The aqueous amine solution (A2) and the aqueous solution (B) containing group 2 element ions (wherein the aqueous solution (B) containing group 2 element ions contains at least alkaline earth metal ions) are brought into contact with each other to deposit an alkaline earth metal carbonate in a second contact part (P1-2), and a carbonate recovery part (Q) in which the alkaline earth metal carbonate is recovered.
A carbon dioxide fixation system comprising at least
[3] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
At least one amine compound (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, a Group 2 element ion-containing aqueous solution (B) (wherein the Group 2 element ion-containing aqueous solution (B) contains at least alkaline earth metal ions) and a gas (C) containing carbon dioxide are brought into contact simultaneously with a carbon dioxide-containing gas (C) to deposit an alkaline earth metal carbonate, and a carbonate recovery for recovering the alkaline earth metal carbonate. Part (Q)
A carbon dioxide fixation system comprising at least
[4] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
A first contact part (P3-1) for preparing a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions);
A second contact part (P3-2) for bringing the mixed solution (AB) into contact with a gas (C) containing carbon dioxide to deposit an alkaline earth metal carbonate, and a carbonate recovery part (Q) for recovering the alkaline earth metal carbonate,
A carbon dioxide fixation system comprising at least
[5] A method for producing a carbonate using the method for immobilizing carbon dioxide according to [1] above.

According to the present disclosure, it is possible to provide a carbon dioxide fixation method and a fixation system with excellent carbon dioxide fixation efficiency, and a carbonate production method using the carbon dioxide fixation method.

BRIEF DESCRIPTION OF THE DRAWINGS It is a process schematic which shows an example of the fixing method of the carbon dioxide of 1st embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a process schematic which shows an example of the preferable aspect of the fixing method of the carbon dioxide of 1st embodiment. 1 is a schematic diagram showing an example of a carbon dioxide fixation system according to a first embodiment; FIG. 1 is a schematic diagram showing an example of a preferred aspect of the carbon dioxide fixation system of the first embodiment; FIG. FIG. 4 is a schematic diagram showing another preferred embodiment of the carbon dioxide fixation system of the first embodiment. FIG. 2 is a schematic diagram showing an example of a more preferred aspect of the carbon dioxide fixation system of the first embodiment; It is a process schematic which shows an example of the fixing method of the carbon dioxide of 2nd embodiment. It is a process schematic which shows an example of the preferable aspect of the fixing method of the carbon dioxide of 2nd embodiment. FIG. 2 is a schematic diagram showing an example of a carbon dioxide fixation system according to a second embodiment; FIG. 4 is a schematic diagram showing an example of a preferred aspect of the carbon dioxide fixation system of the second embodiment. It is a process schematic which shows an example of the fixing method of the carbon dioxide of 3rd embodiment. It is a process schematic which shows an example of the preferable aspect of the fixing method of the carbon dioxide of 3rd embodiment. FIG. 3 is a schematic diagram showing an example of a carbon dioxide fixation system according to a third embodiment; FIG. 4 is a schematic diagram showing an example of a preferred aspect of the carbon dioxide fixation system of the third embodiment. FIG. 4 is a diagram showing the results of examining calcium carbonate formation rates using seawater and various bases. FIG. 4 is a graph showing changes in pH over time when examining calcium carbonate formation rates using seawater and various bases. FIG. 2 is a diagram showing the results of examining the effect of base concentration on the calcium carbonate formation rate using demagnesium-free seawater produced by adding lime milk to seawater (natural seawater) and then removing the produced magnesium hydroxide slurry. [ Fig. 10] Fig. 10 is a diagram showing the results of examining the influence of base species on the calcium carbonate formation rate using the demagnesium-removed seawater. FIG. 4 is a graph showing changes over time in pH when the effect of basic species on the formation rate of calcium carbonate was studied using the demagnesium-free seawater. [ Fig. 10] Fig. 10 is a diagram showing the results of further examination of the influence of base species on the calcium carbonate formation rate using the demagnesium-removed seawater. FIG. 4 is a diagram showing the results of examining calcium carbonate formation rate using brackish water. FIG. 3 is a graph showing changes in pH over time when examining the rate of calcium carbonate formation using brackish water.

The upper and lower limits of the numerical ranges described herein can be arbitrarily combined. For example, if "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of this disclosure.
In addition, the numerical range "lower limit to upper limit" described in this specification means from the lower limit to the upper limit, unless otherwise specified.
Further, "amines" and "polyamines" as used herein, unless otherwise specified, refer to amines selected from amines synthesized in vivo and artificially synthesized amines.

As used herein, "group 2 element" means Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and radium (Rd).
Moreover, in this specification, "alkaline earth metal" means Ca (calcium), Sr (strontium), and Ba (barium).

[Fixation method of carbon dioxide]
The carbon dioxide immobilization method of the present embodiment is a carbon dioxide immobilization method in which an alkaline earth metal carbonate is produced by contacting an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions) and carbon dioxide-derived carbonate ions in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, wherein the amine compound. A step (S) of suppressing the pH increase of the group 2 element ion-containing aqueous solution (B) caused by (A) by using a gas (C) containing carbon dioxide.
Hereinafter, as specific examples of the method for immobilizing carbon dioxide according to the present embodiment, the first embodiment to the third embodiment will be described in detail below.

[First embodiment]
FIG. 1 shows an example of the carbon dioxide immobilization method of the first embodiment.
In the method for immobilizing carbon dioxide shown in FIG. 1, the step (S) (hereinafter sometimes abbreviated as “step (S)”) of suppressing the pH increase of the aqueous solution (B) containing group 2 element ions caused by the amine compound (A) by using the gas (C) containing carbon dioxide (hereinafter sometimes abbreviated as “step (S)”) is an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and a gas containing carbon dioxide ( C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the gas (C) (S1-1).
In addition, the method for immobilizing carbon dioxide shown in FIG. 1 includes, as a step (S), a second contact step (S1-2) of contacting the amine aqueous solution (A2) with the Group 2 element ion-containing aqueous solution (B) after the step (S1-1).
Furthermore, the carbon dioxide fixation method shown in FIG. 1 further includes a recovery step (T) for recovering the alkaline earth metal carbonate after the step (S).

FIG. 2 shows an example of a preferred mode of the method for immobilizing carbon dioxide according to the first embodiment.
In addition to the step (S) and the recovery step (T), the carbon dioxide immobilization method shown in FIG. 2 further includes an amine compound recovery/supply step (U) in which the amine compound (A) is recovered from the liquid phase after the alkaline earth metal carbonate has precipitated and is supplied as at least a part of the amine compound (A) used in the step (S).

Next, FIG. 3 shows an example of a carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the first embodiment.
The carbon dioxide fixation system 1a shown in FIG. 3 includes at least a first contact portion (P1-1), a second contact portion (P1-2), and a carbonate recovery portion (Q).
In the first contact part (P1-1), an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is brought into contact with a gas (C) containing carbon dioxide to prepare an aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C) containing carbon dioxide.
In the second contact portion (P1-2), the aqueous amine solution (A2) and the aqueous solution (B) containing group 2 element ions (wherein the aqueous solution (B) containing group 2 element ions contains at least alkaline earth metal ions) are brought into contact with each other to precipitate an alkaline earth metal carbonate.
The carbonate recovery section (Q) recovers carbonates of alkaline earth metals.

FIG. 4 shows an example of a preferred mode of a carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the first embodiment.
A carbon dioxide fixation system 1a′ shown in FIG. 4 includes a plurality of first contact portions. Although two first contact portions are provided in FIG. 4 (references (P1-1) and (P1-1)'), the number of first contact portions may be three or more.
Further, the carbon dioxide fixation system 1a' shown in FIG. 4 includes a plurality of second contact portions. Although two second contact portions are provided in FIG. 4 (references (P1-2) and (P1-2)′), the number of second contact portions may be three or more.
Note that the carbon dioxide fixation system in the first embodiment is not limited to a mode in which a plurality of both the first contact portion and the second contact portion are provided, and may be a mode in which a plurality of the first contact portions are provided and only one second contact portion is provided. Alternatively, a plurality of second contact portions may be provided and only one first contact portion may be provided.

Furthermore, FIG. 5 shows another example of a preferred embodiment of the carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the first embodiment.
The carbon dioxide immobilization system 1a'' shown in FIG. 5 does not include a second contact portion (P1-2), and the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact at the first contact portion (P1-1).
Although not shown, the carbon dioxide fixation system 1a'' shown in FIG. 5 may also have a plurality of first contact portions.

FIG. 6 shows an example of a more preferable aspect of the carbon dioxide fixation system of the present embodiment for carrying out the carbon dioxide fixation method of the first embodiment.
In addition to the first contact portion (P1-1), the second contact portion (P1-2), and the carbonate recovery portion (Q), the carbon dioxide fixation system 11a shown in FIG. 6 further includes an amine compound recovery/supply portion (R) that recovers the amine compound (A) from the liquid phase after the carbonate of the alkaline earth metal has precipitated and supplies it as at least part of the amine compound (A) used in the first contact portion (P1-1).
Although the carbon dioxide fixation system 11a shown in FIG. 6 further includes an amine compound recovery/supply unit (R) in addition to the carbon dioxide fixation system 1a shown in FIG. 3, it is not necessarily limited to such an aspect.
For example, the carbon dioxide fixation system 1a′ shown in FIG. 4 may further include an amine compound recovery/supply unit (R). In addition, the carbon dioxide fixation system 1a'' shown in FIG. 5 may further include an amine compound recovery/supply unit (R).

Hereinafter, the carbon dioxide fixation method of the first embodiment will be described in detail while explaining the configuration of the carbon dioxide fixation system for carrying out the method.

<First contact step (S1-1)>
In the first contact step (S1-1), an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, amines artificially synthesized, and polymers containing groups derived from these amines is brought into contact with a gas (C) containing carbon dioxide to prepare an aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C). By bringing an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group into contact with a gas (C) containing carbon dioxide, carbon dioxide in the gas (C) is efficiently absorbed by the aqueous amine solution (A1), and an aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C) is efficiently prepared. Carbon dioxide-derived carbonate ions contained in the aqueous amine solution (A2) function as a carbonate ion source for precipitating alkaline earth metal carbonate in the second contacting step (S1-2).

The amine aqueous solution (A1), the carbon dioxide-containing gas (C), and the method of contacting the amine aqueous solution (A1) with the carbon dioxide-containing gas (C) will be described in detail below.

(Amine aqueous solution (A1))
The aqueous amine solution (A1) contains one or more amine compounds selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines.

The present inventors have been conducting research on marine bacteria that form calcium carbonate granules as part of research to clarify calcium carbonate formation in marine organisms. When this marine bacterium is cultured in an artificial medium containing calcium, it forms dumbbell-shaped or spherical calcium carbonate (calcite) outside the cell. In the process of researching this mechanism, the present inventors have found that amines produced by marine bacteria play a major role.
In other words, the dumbbells and spherical calcium carbonate granules found in the culture of marine bacteria promote the crystallization of calcium carbonate by increasing the concentration of carbonate ions in the medium due to the amines that increase in the medium as the marine bacteria proliferate.
The amines in the culture solution of marine bacteria in which calcium carbonate granules were observed were derivatized with dansyl chloride according to the "analysis of non-volatile putrefactive amines in food" in the food hygiene inspection guidelines, and analyzed by HPLC. As a result, amines such as 1,3-propanediamine, putrescine, cataverine, spermine, spermidine, norspermidine, and norspermine were detected.
From the above, it was found that amines produced by marine bacteria combine with carbon dioxide in the air and are then hydrolyzed, increasing the concentration of carbonate ions in the medium and causing the precipitation of calcium carbonate. Precipitation of calcium carbonate was also confirmed when amine and calcium chloride were mixed in an aqueous solution free of marine bacteria and allowed to stand. From this, it was found that precipitation of calcium carbonate occurs even in the absence of marine bacteria. In other words, it was found that amines produced by marine bacteria can efficiently produce carbonate ions by forming salts with carbon dioxide even in the absence of marine bacteria.

However, as a result of further intensive studies by the present disclosure persons, it was found that when amines such as polyamines are mixed with seawater, calcium carbonate cannot be generated sufficiently efficiently. It is speculated that the reason for this is that when amines are added to seawater, the pH of seawater temporarily rises, and magnesium ions present in seawater in an amount three times as large as calcium ions become magnesium hydroxide, which inhibits the formation of calcium carbonate.

Therefore, in the carbon dioxide immobilization method of the first embodiment, in the first contacting step (S1-1), an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is brought into contact with a gas (C) containing carbon dioxide. As a result, carbonate ions for precipitating alkaline earth metal carbonate in the second contact step (S1-2) are efficiently generated in the aqueous amine solution (A2). Moreover, since carbonate ions for precipitating carbonates of alkaline earth metals are efficiently generated in the aqueous amine solution (A2), an increase in the pH of the aqueous amine solution (A2) can be suppressed. Therefore, when the amine aqueous solution (A2) is brought into contact with the group 2 element ion-containing aqueous solution (B), the increase in the pH of the group 2 element ion-containing aqueous solution (B) (the pH of the mixture of the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B)) is also suppressed. Therefore, even if magnesium ions are contained in the Group 2 element ion-containing aqueous solution (B), the inhibition of calcium carbonate formation due to the formation of magnesium hydroxide is also suppressed. Therefore, in the second contacting step (S1-2), calcium carbonate is produced very efficiently.

As the amine compound (A), amines (monoamines and polyamines) synthesized in vivo (for example, in vivo of marine bacteria) can be used without particular limitation. Among the amines, 1,3-propanediamine, putrescine (butane-1,4-diamine), cataverine (pentane-1,4-diamine), spermine (1,11-diamino-4,9-diazaundecane), spermidine (1,8-diamino-4-azaoctane), norspermidine (3,3′-iminobis(propane- 1-amine)) and norspermine (3,3′-[(propane-1,3-diyl)bisimino]bis(propan-1-amine)) is preferably used.
Further, according to experiments by the present inventors, it has been confirmed that even when an artificially synthesized amine is used as the amine compound (A), the same effects as those of an amine synthesized in vivo can be obtained. Therefore, artificially synthesized amines can also be used. Examples of artificially synthesized amines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), diglycolamine (DGA), methyldiethanolamine (MDEA), and diamines such as piperazine and ethylenediamine.
Further, as the amine compound (A), a polymer containing a group derived from the above amine (a polymer containing a group derived from an amine synthesized in vivo, a polymer containing a group derived from an artificially synthesized amine) may be used.
As the polymer containing a group derived from the amine, a polymer containing at least a terminal group derived from the amine is preferable. Such a polymer includes, for example, a polymer having a structural unit derived from a compound having an ethylenically unsaturated double bond and a group derived from the above amine, a polyalkyleneimine, and the like, preferably a polyalkyleneimine.
The number of carbon atoms in the alkylene group of the polyalkyleneimine is preferably 2-4, more preferably 2-3, still more preferably 2. The term “group derived from the above amine” means a monovalent or higher group excluding at least one hydrogen atom of the above amine (amine synthesized in vivo, amine synthesized artificially). For example, the group derived from ethylenediamine includes -NHCH ₂ CH ₂ NH ₂ which is a monovalent group.
The number average molecular weight of the polymer containing a group derived from the amine as measured by boiling point elevation method is preferably 500 to 50,000, more preferably 500 to 40,000, still more preferably 500 to 35,000.
The amine compound (A) may be used alone or in combination of two or more.

An amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is brought into contact with a gas (C) containing carbon dioxide. When the carbon dioxide is absorbed into the amine aqueous solution (A1), the carbon dioxide reacts with the amine compound (A) in the amine aqueous solution (A1) to produce carbonate ions in the amine aqueous solution (A1), and the amine compound (A) becomes a cation.
A presumed reaction formula for the case where the amine compound (A) is putrescine is shown below.

The content of the amine compound (A) in the amine aqueous solution (A1) is preferably 1% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and still more preferably 25% by mass to 35% by mass, based on the total amount of the amine aqueous solution (A1), from the viewpoint of facilitating efficient absorption of carbon dioxide into the amine aqueous solution (A1).

The pH of the aqueous amine solution (A1) before contact with the gas (C) containing carbon dioxide is determined in consideration of the amount of carbon dioxide to be absorbed and the reactivity in the second contact step (S1-2). Specifically, the pH of the amine aqueous solution (A1) before contact with the carbon dioxide-containing gas (C) is adjusted so that the pH of the amine aqueous solution (A2) containing carbon dioxide-derived carbonate ions after contact with the carbon dioxide-containing gas (C) is preferably 6 or higher, more preferably 7 or higher, and still more preferably 8 or higher.
Further, the pH of the aqueous amine solution (A1) before contacting with the gas (C) containing carbon dioxide may be adjusted according to the carbonate species to be precipitated in the second contacting step (S1-2). For example, from the viewpoint of facilitating the precipitation of calcium carbonate, the pH of the aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide after contact with the carbon dioxide-containing gas (C) is preferably 7 to 12, more preferably 7 to 9, so that the pH of the amine aqueous solution (A1) before contact with the carbon dioxide-containing gas (C) may be adjusted. Further, from the viewpoint of facilitating precipitation of calcium carbonate, the pH of the aqueous amine solution (A1) before contact with the gas (C) containing carbon dioxide may be adjusted so that the pH of the mixed solution when the aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions and the aqueous solution (B) containing group 2 element ions are brought into contact in the second contacting step (S1-2) is preferably 8 to 9.

The temperature of the amine aqueous solution (A1) when the amine aqueous solution (A1) and the carbon dioxide-containing gas (C) are brought into contact is preferably 10°C or higher, more preferably 30°C to 50°C, from the viewpoint of efficiently absorbing carbon dioxide and easily increasing the carbonate ion concentration in the amine aqueous solution (A2). In order to suppress the loss of the bond between the amine and carbon dioxide in this step, the temperature of the aqueous amine solution (A1) when the aqueous amine solution (A1) and the gas (C) containing carbon dioxide are brought into contact is preferably maintained at 50°C or lower.

The time for contacting the aqueous amine solution (A1) with the gas (C) containing carbon dioxide is appropriately set according to the contact method, the temperature of the aqueous amine solution (A1), the content of the amine compound (A) in the aqueous amine solution (A1), the temperature of the gas (C) containing carbon dioxide, the carbon dioxide concentration, the gas flow rate of carbon dioxide, and the size of the container (reaction tank). It is generally 30 minutes to 3 hours, preferably 1 hour to 24 hours.

(Gas (C) containing carbon dioxide)
Examples of the gas (C) containing carbon dioxide include air and flue gas.
Examples of flue gas include flue gas emitted from various factories such as steelworks, flue gas emitted from LNG-fired power plants, flue gas emitted from coal-fired power plants, and off-gases emitted from hydrogen production equipment in refineries. From the viewpoint of making it easier to improve the carbon dioxide fixation efficiency, among these, the flue gas (carbon dioxide concentration is 11 to 15% by volume) discharged from a coal-fired power plant and a refinery. Also, when the carbon dioxide concentration in the air is 0.04% by volume or more, air may be used.

(Method of contacting amine aqueous solution (A1) with carbon dioxide-containing gas (C))
The method of contacting the aqueous amine solution (A1) with the gas (C) containing carbon dioxide is not particularly limited as long as it is a method capable of efficiently absorbing carbon dioxide into the aqueous amine solution (A1).

Here, an example of a method for contacting the amine aqueous solution (A1) and the carbon dioxide-containing gas (C) will be described based on the carbon dioxide immobilization system in the first embodiment.
In the carbon dioxide fixation systems 1a, 1a′, 1a″, and 11a of the first embodiment, the first contacting step (S1-1) is to bring an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines into contact with a gas (C) containing carbon dioxide to prepare an amine aqueous solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C). It is performed at the first contact (P1-1).
An aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is stored in a storage tank 21 and supplied to the first contact portion (P1-1) through a supply line 21a.
On the other hand, the gas (C) containing carbon dioxide, for example, is supplied from a cylinder or equipment (for example, a coal-fired power plant, etc.) not shown, and is supplied to the first contact portion (P1-1) via the supply line 22a by the blower 22.
Here, when the gas (C) containing carbon dioxide is a high-temperature gas such as combustion exhaust gas, the combustion exhaust gas is cooled to an appropriate temperature, and then contacted with the aqueous amine solution (A1). A method of cooling the flue gas includes, for example, a method using a heat exchanger.
In addition, the flue gas may be subjected to one or more treatments selected from denitrification, dust collection, and desulfurization, if necessary.

Methods of contacting the aqueous amine solution (A1) and the gas (C) containing carbon dioxide in the first contact portion (P1-1) include, for example, the following methods (1) to (4), but are not limited thereto, and various methods for dissolving the gas into a liquid may be used.
(1) Aqueous amine solution (A1) is placed in a reaction tank, and gas (C) containing carbon dioxide is blown near the surface of the aqueous amine solution (A1) while stirring the aqueous amine solution (A1) with a stirring blade or the like.
(2) An aqueous amine solution (A1) is placed in a reaction tank, and a gas (C) containing carbon dioxide is directly blown into the aqueous amine solution (A1).
(3) A carbon dioxide-containing gas (C) is introduced from the bottom of a closed reaction tower and raised, and an amine aqueous solution (A1) is sprayed from the top of the reaction tower with a nozzle or the like to bring the carbon dioxide-containing gas (C) and the amine aqueous solution (A1) into countercurrent contact.
(4) The gas (C) containing carbon dioxide is fine-bubbled and introduced into the aqueous amine solution (A1). Thereby, the contact area between the aqueous amine solution (A1) and the gas (C) containing carbon dioxide can be increased, and carbon dioxide can be more efficiently absorbed into the aqueous amine solution (A1).
The contact between the amine aqueous solution (A1) and the carbon dioxide-containing gas (C) in the first contact portion (P1-1) is preferably carried out at 50° C. or less and under normal pressure, more preferably at normal temperature (25±15° C.) and under normal pressure.

The amine aqueous solution (A2) rich in carbonate ions derived from carbon dioxide prepared in the first contacting step (S1-1) is supplied to the second contacting step (S1-2).
Since the aqueous amine solution (A2) contains a large amount of carbon dioxide-derived carbonate ions, the alkaline earth metal carbonate is likely to precipitate in the second contacting step (S1-2). In addition, since the amine aqueous solution (A2) abundantly contains carbonate ions derived from carbon dioxide, in the second contacting step (S1-2), when the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact, a rapid increase in the pH of the mixed solution can be suppressed. Therefore, in the second contacting step (S1-2), when the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact with each other, the alkaline earth metal carbonate can be readily precipitated easily. In other words, carbon dioxide can be efficiently immobilized.
In addition, since the aqueous amine solution (A2) contains abundant carbonate ions derived from carbon dioxide, even if the alkaline earth metal ion concentration of the group 2 element ion-containing aqueous solution (B) is low, the carbonate can be precipitated. For example, carbonate (calcium carbonate) can be precipitated even when the group 2 element ion-containing aqueous solution (B) having a calcium ion concentration of 300 mass ppm (further 400 mass ppm) is used.

In the above-described method, the gas (C) containing carbon dioxide is supplied from a cylinder or equipment (for example, a coal-fired power plant, etc.) not shown, and is supplied to the first contact portion (P1-1) via the supply line 22a by the blower 22. However, these may be omitted, and the aqueous amine solution (A1) may be stirred with a stirring blade or the like while air is brought into contact with the liquid surface of the aqueous amine solution (A1), so that carbon dioxide in the air is absorbed into the aqueous amine solution (A1).

<Second contact step (S1-2)>
In the second contacting step (S1-2), the aqueous amine solution (A2) prepared in the first contacting step (S1-1) is brought into contact with the group 2 element ion-containing aqueous solution (B) (wherein the group 2 element ion-containing aqueous solution (B) contains at least alkaline earth metal ions) to precipitate an alkaline earth metal carbonate.
By bringing the aqueous amine solution (A2) prepared in the first contact step (S1-1) into contact with the aqueous solution (B) containing Group 2 element ions, the carbonate ions in the aqueous amine solution (A2) react with the alkaline earth metal ions in the aqueous solution (B) containing Group 2 element ions, and an alkaline earth metal carbonate is precipitated. Since the carbonate ions in the amine aqueous solution (A2) are produced from the carbon dioxide in the gas (C) as a raw material, the carbon dioxide is fixed as an alkaline earth metal carbonate.

The method of contacting the group 2 element ion-containing aqueous solution (B) and the amine aqueous solution (A2) used in the second contact step (S1-2) with the group 2 element ion-containing aqueous solution (B) will be described in detail below.

(Group 2 element ion-containing aqueous solution (B))
The Group 2 element ion-containing aqueous solution (B) contains Group 2 element ions. However, the second group element ion-containing aqueous solution (B) contains at least alkaline earth metal ions.
As used herein, “group 2 element ion” means beryllium ion (Be ²⁺ ), magnesium ion (Mg ²⁺ ), calcium ion (Ca ²⁺ ), strontium ion (Sr ²⁺ ), barium ion (Ba ²⁺ ), and radium ion (Rd ²⁺ ).
In addition, the term "alkaline earth metal ion" as used herein means calcium ion (Ca ²⁺ ), strontium ion (Sr ²⁺ ), and barium ion (Ba ²⁺ ).
Among these, the alkaline earth metal ions contained in the second group element ion-containing aqueous solution (B) are preferably calcium ions. This is because calcium carbonate produced from calcium ions has various industrial uses.

Here, the Group 2 element ion-containing aqueous solution (B) may contain at least magnesium ions and calcium ions.
In the first embodiment, in the first contacting step (S1-1), one or more selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines. An aqueous amine solution (A1) containing one or more amine compounds (A) is brought into contact with a gas (C) containing carbon dioxide. As a result, an increase in the pH of the aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the gas (C) is suppressed, so that when the aqueous amine solution (A2) is brought into contact with the aqueous solution containing Group 2 element ions (B), the increase in pH of the mixture of the aqueous amine solution (A) and the aqueous solution containing Group 2 element ions (B) is also suppressed. Therefore, even if magnesium ions are contained in the Group 2 element ion-containing aqueous solution (B), the inhibition of calcium carbonate formation due to the formation of magnesium hydroxide is also suppressed. Therefore, calcium carbonate is produced very efficiently in the second contacting step (S1-2).

Therefore, it is preferable to use seawater as the Group 2 element ion-containing aqueous solution (B). Although seawater is readily available, it contains more magnesium ions than calcium ions together with calcium ions. As a result, there is a problem that the formation of calcium carbonate is inhibited as described above. However, according to the carbon dioxide immobilization method of the first embodiment, even when seawater is used as the group 2 element ion-containing aqueous solution (B), the inhibition of calcium carbonate production due to the formation of magnesium hydroxide is suppressed. Therefore, calcium carbonate is produced extremely efficiently even when readily available seawater is used as the group 2 element ion-containing aqueous solution (B).

As the group 2 element ion-containing aqueous solution (B), in addition to seawater, for example, waste seawater obtained when seawater is desalinated; concentrated seawater generated when salt or bittern is produced; salt lake brine; underground brine; and brine such as brackish water can be used.
Brine water is water containing salt such as sodium chloride, and usually contains one or more alkaline earth metal ions (especially calcium ions) selected from the group consisting of calcium ions, strontium ions, and barium ions. Therefore, by using brackish water as the Group 2 element ion-containing aqueous solution (B), it is possible to easily supply alkaline earth metal ions for producing alkaline earth metal carbonates.
Here, since the concentrated seawater contains alkaline earth metal ions (especially calcium ions) at a high concentration, in the second contacting step (S1-2), alkaline earth metal ions that serve as a source of alkaline earth metal carbonate can be efficiently supplied. Therefore, the carbon dioxide fixation efficiency can be further improved, and the yield of alkaline earth metal carbonate can be improved. Also, the second contact portion (P1-2) for performing the second contact step (S1-2) can be made compact to reduce the size of the manufacturing system. Salt lake brine such as the Uyuni Salt Lake and hot water brine such as the Salton Lake in the United States are also preferable because they have high concentrations of alkaline earth metal ions. In recent years, geothermal power generation has been actively developed as a renewable energy. These underground hot water brines are preferred as well.
Therefore, as the Group 2 element ion-containing aqueous solution (B), the calcium ion concentration is preferably 400 mass ppm or more, more preferably 600 mass ppm or more, still more preferably 800 mass ppm or more, still more preferably 1,000 mass ppm or more, still more preferably 1,500 mass ppm or more, and still more preferably 1,800 mass ppm or more.
In addition, what was illustrated as group 2 element ion containing aqueous solution (B) may be used individually by 1 type, and may be used in combination of 2 or more type.

The concentrated seawater can be produced using seawater as a raw material by known methods such as ion exchange membrane method, evaporation method, and reverse osmosis method.

Further, as the Group 2 element ion-containing aqueous solution (B), alkaline earth metal ion-containing water (preferably calcium ion-containing water) having a magnesium ion concentration of 500 mass ppm or less (preferably 400 mass ppm or less, more preferably 300 mass ppm or less) may be used.
For example, in an industrial process for producing magnesium hydroxide from seawater, alkaline earth metal ion-containing water having a magnesium ion concentration of 500 ppm by mass or less is produced as a by-product. In the first embodiment, it is also possible to effectively utilize such by-products.
Further, in an industrial magnesium hydroxide production process from seawater, by adding lime milk to seawater, after extracting the produced magnesium hydroxide slurry, alkaline earth metal ion-containing water having a magnesium ion concentration of 500 ppm by mass or less is produced as a by-product. By adding milk of lime to seawater, such a by-product has a calcium ion concentration higher than that of seawater containing alkaline earth metal ions (for example, preferably 400 mass ppm or more, more preferably 600 mass ppm or more, still more preferably 800 mass ppm or more, even more preferably 1,000 mass ppm or more, still more preferably 1,500 mass ppm or more, and still more preferably 1,800 mass ppm or more). Therefore, in order to recover all the calcium ions from the by-product alkaline earth metal ion-containing water, it is necessary to increase the concentration of the amine compound in the aqueous amine solution (A1). When the concentration of the amine compound (A) in the aqueous amine solution (A1) is increased, the pH of the aqueous amine solution (A1) increases, making it difficult for the reaction to generate calcium carbonate to proceed. However, in the first embodiment, by bringing the gas (C) containing carbon dioxide into contact with the amine aqueous solution (A1), even if the alkaline earth metal ion-containing water having a higher calcium ion concentration than seawater is used as the group 2 element ion-containing aqueous solution (B), the pH increase can be suppressed and calcium carbonate can be efficiently produced.

(Method of Contacting Amine Aqueous Solution (A2) and Group 2 Element Ion-Containing Aqueous Solution (B))
The method of contacting the amine aqueous solution (A2) with the group 2 element ion-containing aqueous solution (B) is not particularly limited as long as it is a method capable of efficiently producing an alkaline earth metal carbonate.

Here, an example of a method for contacting the amine aqueous solution (A2) and the Group 2 element ion-containing aqueous solution (B) will be described based on the carbon dioxide immobilization system in the first embodiment.
In the carbon dioxide fixation systems 1a, 1a′, and 11a of the first embodiment, the second contacting step (S1-2) is carried out in the second contacting portion (P1-2) where the amine aqueous solution (A2) and the Group 2 element ion-containing aqueous solution (B) are brought into contact with each other to precipitate an alkaline earth metal carbonate.
The aqueous amine solution (A2) is supplied from the first contact portion (P1-1) to the second contact portion (P1-2) through the supply line 2a.
On the other hand, the group 2 element ion-containing aqueous solution (B) is stored in the storage tank 31 and supplied to the second contact portion (P1-2) through the supply line 31a.

Examples of methods for contacting the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) in the second contact portion (P1-2) include the following methods (5) and (6).
(5) The amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are introduced into the reaction tank, and stirred and mixed using a stirring blade or the like.
(6) The amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are introduced into a line mixer or the like, and mixed by turbulent stirring or the like without stirring using a stirring blade or the like.
Here, in the method (5), it is preferable to use, as the reaction tank, a thickener sedimentation apparatus capable of sedimenting and separating from the liquid phase the alkaline earth metal carbonate precipitated and dispersed in the liquid phase by the action of gravity. In this case, the second contact portion (P1-2) can also function as a carbonate recovery portion (Q), which will be described later.
The temperature of each solution during contact between the aqueous amine solution (A2) and the aqueous solution containing group 2 element ions (B) in the second contact portion (P1-2) is 10°C to 45°C, preferably 25°C to 40°C.
In addition, the ratio of the supply amount of the aqueous amine solution (A2) to the second contact portion (P1-2) and the supply amount of the group 2 element ion-containing aqueous solution (B) is appropriately adjusted so that the molar amount of carbon dioxide (carbonate ions) and the molar amount of calcium ions in the aqueous amine solution (A2) are approximately equivalent.
It should be noted that precipitation of alkaline earth metal carbonate occurs in a short period of time. In addition, since the use of the above polyamine can prevent an increase in pH, there is also an advantage that calcium carbonate can be easily precipitated while suppressing precipitation of magnesium hydroxide.

<Preferred Embodiments of First Contacting Step (S1-1) and Second Contacting Step (S1-2)>
The first contacting step (S1-1) is preferably performed at a plurality of first contacting portions, as shown in FIG.
Also, the second contacting step (S1-2) is preferably performed at a plurality of second contacting portions, as shown in FIG.
Specifically, in the first unit (first contact portion (P1-1)), an amine aqueous solution (A1) is produced and brought into contact with a carbon dioxide-containing gas (C) to prepare an amine aqueous solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C). Then, by preparing the already prepared amine aqueous solution (A2) in the second unit (first contact portion (P1-1)′), while the amine aqueous solution (A2) is being prepared in the first unit, the amine aqueous solution (A2) can be supplied from the second unit to the second contact portion, and the second contact step (S1-2) can be performed.
Similarly, in the second contact portion, the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact with each other at the first contact portion (second contact portion (P1-2)) to precipitate an alkaline earth metal carbonate. In the meantime, the second base (second contact portion (P1-2)') can receive the aqueous amine solution (A2). Alternatively, the alkaline earth metal carbonate can be discharged to the recovery section.

Also, as shown in FIG. 5, the first contact step (S1-1) and the second contact step (S1-2) can be performed at the first contact portion (P1-1) without providing the second contact portion (P1-2). Also in this case, by providing a plurality of first contact portions (P1-1), continuous supply of alkaline earth metal carbonate to the carbonate recovery portion (Q) becomes possible.

Whether the number of the first contact portion (P1-1) and the second contact portion (P1-2) is plural or singular, or whether the first contact step (S1-1) and the second contact step (S1-2) are carried out at the first contact portion can be selected according to conditions and requirements such as the target fixed amount of carbon dioxide.

In addition, the first contact part (P1-1) is an AC contact method using a closed reaction tower, and the second contact part (P1-2) is a continuous stirred tank reactor or line mixer, so that the entire process can be made continuous.

<Recovery step (T)>
In the recovery step (T), the alkaline earth metal carbonate produced in the second contact step (S1-2) is recovered.
Since the alkaline earth metal carbonate precipitates and precipitates, it can be separated and recovered by one or more solid-liquid separation treatments selected from filtration, centrifugation, and the like.
The alkaline earth metal carbonate is recovered in the carbonate recovery section (Q). In the carbon dioxide fixation systems 1a, 1a′, 1a″, and 11a shown in FIGS. 3 to 6, the carbonate recovery unit (Q) is, for example, a sub-tank, and the liquid phase containing the alkaline earth metal carbonate obtained in the second contact step (S1-2) is transferred to a sub-tank or the like, and solid-liquid separation is performed in the sub-tank to recover the alkaline earth metal carbonate.
As described above, when a thickener sedimentation separation device is used as a reaction tank in the second contact portion (P1-2), the second contact portion (P1-2) can also function as the carbonate recovery portion (Q).

The recovered alkaline earth metal carbonate can be washed with water and dried as necessary to make a product.

<Amine compound recovery/supply step (U)>
In the amine compound recovery step (U), the amine compound (A) is recovered from the liquid phase after the alkaline earth metal carbonate has precipitated, and supplied as at least part of the amine compound (A) in the aqueous amine solution (A1) used in the first contact step (S1-1).
The amine recovery/supply step (U) makes it possible to repeatedly use the amine compound (A) in the carbon dioxide immobilization method and system, thereby reducing the cost of the amine compound (A).

The method for collecting the amine compound (A) and the method for supplying the collected amine compound (A), which are performed in the amine compound collection/supply step (U), will be described in detail below.

(Method for recovering amine compound)
The amine compound (A) can be recovered from the liquid phase after the alkaline earth metal carbonate has precipitated, for example, by a method using an adsorbent, which will be described below. The method described here is equivalent to the principle and method of ion exchange chromatography. Recovery of the amine compound (A) may be performed using a known method, and is not limited to the method using an adsorbent. Specifically, an electrodialysis method, a dialysis membrane method, and an ultrafiltration method can be used.

-adsorbent-
As the adsorbent, a solid adsorbent capable of recovering the amine compound (A) is used by contacting the liquid phase after the carbonate of the alkaline earth metal has precipitated.
As the solid adsorbent, for example, one having a substituent represented by —SO ₃ M (M represents a hydrogen atom or an alkali metal) is used.
Alkali metals that can be selected for M are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or francium (Fr).
From the viewpoint of water solubility and operability, M is preferably Na or a hydrogen atom.
In addition, one solid adsorbent may be used alone, or two or more solid adsorbents having different M values may be used in combination.

The solid adsorbent exhibits a function of collecting the amine compound (A) by binding the substituent to the carrier. The carrier is not particularly limited as long as the above substituent can be bonded thereto, but examples thereof include silica gel, alumina, glass, kaolin, mica, talc, clay, hydrated alumina, wollastonite, iron powder, potassium titanate, titanium oxide, zinc oxide, silicon carbide, silicon nitride, calcium carbonate, carbon, barium sulfate, boron, ferrite, cellulose, and activated carbon.
One carrier may be used alone, or two or more carriers may be used in combination.

The shape of the solid adsorbent is not particularly limited, and may be, for example, powdery, granular, or sheet-like. It may also be a cartridge, column, funnel, or the like filled with solid adsorbent powder or particles.

-Contact between liquid phase and solid adsorbent-
The amine compound (A) is recovered by the solid adsorbent by bringing the liquid phase after the precipitation of the alkaline earth metal carbonate into contact with the solid adsorbent. At this time, the pH of the liquid phase is preferably 1-7. Although the temperature of the liquid phase is not particularly limited, it is preferably 20°C to 40°C.

The method of contacting the liquid phase after the carbonate of the alkaline earth metal precipitates with the solid adsorbent is not particularly limited, but from the viewpoint of ease of handling, it is preferable to use a cartridge, column, or funnel filled with powder or particles of the solid adsorbent, and circulate the liquid phase through this.

-Elution of amine compound (A)-
The amine compound (A) recovered by the solid adsorbent can be eluted into the eluate and recovered by bringing the eluate into contact with the solid adsorbent.
The eluent includes an aqueous solution containing a basic compound (including those to which an organic solvent has been added or partially substituted).
A basic compound that does not substantially cause a chemical reaction with the amine compound (A) to be recovered and that is soluble or miscible with water can be appropriately used. Preferred basic compounds include, for example, ammonia, sodium hydroxide, ammonium hydroxide, triethylamine, pyridine, histidine, diazabicycloundecene, and mixtures thereof.

From the viewpoint of improving the elution efficiency of the amine compound (A), the concentration of the basic compound is preferably 0.5% by mass to 10% by mass based on the total 100% by mass of the basic compound and the organic solvent.

As the organic solvent, a general organic solvent that dissolves the amine compound (A) to be recovered and the basic compound can be used, but from the viewpoint of operability, etc., a low-viscosity, low-boiling organic solvent is preferred, and more preferably one that mixes uniformly with water. Examples thereof include lower alcohols having 1 to 3 carbon atoms such as methanol, ethanol and 2-propanol; acetone; acetonitrile and the like.
A small amount of the organic solvent may be added or mixed to adjust the aqueous solution containing the basic compound, but the aqueous solution containing the basic compound preferably does not contain the organic solvent.

The temperature of the eluent when eluting the amine compound (A) into the eluate is not particularly limited, but is generally 20 to 40°C.

The method of eluting the amine compound (A) recovered from the solid adsorbent is not particularly limited, but from the viewpoint of ease of handling, etc., when a cartridge, column, or funnel filled with powder or particles of the solid adsorbent is used, the liquid phase after the precipitation of the alkaline earth metal carbonate is circulated through the cartridge to recover the amine, and then the eluate is circulated through the solid adsorbent in which the amine compound (A) has been recovered to elute and recover the amine compound (A) in the eluate. method.
Therefore, the amine compound recovery means constituting the amine compound recovery/supply unit (R) includes, for example, a configuration including a cartridge, column, or funnel filled with powder or particles of a solid adsorbent for recovering the amine compound (A) by circulating the liquid phase supplied from the supply line 51a, and a supply line (not shown) for circulating the eluate through the cartridge, column, or funnel.

(Method for supplying amine compound (A))
The amine compound (A) recovered in the eluate is supplied to the storage tank 21 through the supply line 51b. As a result, the amine compound (A) is recycled within the system in the carbon dioxide immobilization method and system of the first embodiment.
The amine compound (A) recovered in the eluate may be supplied to the storage tank 21 together with the eluate, or at least part of the eluate may be separated to concentrate the amine compound (A) and then supplied to the storage tank 21.

In the amine compound recovery/supply step (U) described above, an example of recovering the amine compound (A) using a solid adsorbent has been described, but the recovery of the amine compound (A) is not limited to this method.
Therefore, the carbon dioxide immobilization system of the first embodiment may include an ion-exchange membrane electrolysis device, a reverse osmosis membrane device, an electrodialysis device, a diffusion dialysis device, or a device provided with an ion exchange resin as the amine compound recovery/supply unit (R) for carrying out the amine compound recovery/supply step (U).
When a polymer containing a group derived from a biogenic amine or a polymer containing a group derived from an artificial amine is used as the amine compound (A), the amine compound may be recovered with an ultrafiltration membrane (UF membrane).

[Second embodiment]
FIG. 7 shows an example of the carbon dioxide immobilization method of the second embodiment.
The method for immobilizing carbon dioxide shown in FIG. 7 includes, as step (S), a contacting step (S2) of simultaneously contacting one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions), and a gas (C) containing carbon dioxide.
Furthermore, the carbon dioxide fixation method shown in FIG. 7 includes a recovery step (T) of recovering the alkaline earth metal carbonate after the step (S).

In the carbon dioxide immobilization method of the second embodiment, in the contacting step (S2), the amine compound (A), the group 2 element ion-containing aqueous solution (B), and the gas containing carbon dioxide (C) are brought into contact at the same time. Therefore, an alkaline earth metal carbonate can be efficiently produced while suppressing the increase in pH of the group 2 element ion-containing aqueous solution (B) caused by the amine compound (A) by the carbon dioxide-derived carbonate ions in the gas (C) generated in the group 2 element ion-containing aqueous solution (B).

Also, in the carbon dioxide immobilization method of the second embodiment, as shown in FIG. 8, it is preferable to further include an amine compound recovery/supply step (U) in which the amine compound (A) is recovered from the liquid phase after the carbonate of the alkaline earth metal has precipitated and is supplied as at least part of the amine compound (A) used in the step (S).

Next, FIG. 9 shows an example of a carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the second embodiment.
A carbon dioxide fixation system 1b shown in FIG. 9 includes at least a contact section (P2) and a carbonate recovery section (Q).
In the contact portion (P2), one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions) and a gas (C) containing carbon dioxide are simultaneously brought into contact with each other to precipitate an alkaline earth metal carbonate.
The carbonate recovery section (Q) recovers carbonates of alkaline earth metals.

In the carbon dioxide fixation system 1b shown in FIG. 9, the amine compound (A) is stored in the storage tank 21 as an amine aqueous solution (A1), and the amine aqueous solution (A1) is supplied to the contact portion (P2) through the supply line 21a.
The group 2 element ion-containing aqueous solution (B) is stored in the storage tank 31 and supplied to the contact portion (P2) through the supply line 31a.
A gas (C) containing carbon dioxide is supplied from, for example, a cylinder (not shown) or equipment (for example, a coal-fired power plant, etc.), and is supplied to the contact portion (P2) via a supply line 22a by a blower 22.
The amine compound (A) in the amine aqueous solution (A1), the Group 2 element ion-containing aqueous solution (B), and the carbon dioxide-containing gas (C) are brought into contact at the contact portion (P2) at the same time to form an alkaline earth metal carbonate.
In addition, the amine compound (A) is not limited to a mode in which it is supplied to the contact portion (P2) as an aqueous amine solution (A1), and may be a mode in which the amine compound (A) is directly supplied to the contact portion (P2).

Although illustration is omitted, in the carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the second embodiment, a plurality of contact parts (P2) may be provided.

FIG. 10 shows an example of a preferable mode of the carbon dioxide fixation system of the present embodiment for carrying out the carbon dioxide fixation method of the second embodiment.
In addition to the contact part (P2) and the carbonate recovery part Q, the carbon dioxide fixation system 11b shown in FIG. 10 further includes an amine compound recovery/supply part (R) that recovers the amine compound (A) from the liquid phase after the carbonate of the alkaline earth metal precipitates and supplies it as at least a part of the amine compound (A) used in the contact part (P2).

In addition, in the second embodiment, regarding aspects and configurations common to the first embodiment, preferred aspects and configurations are also the same as in the first embodiment, and description thereof is omitted.
For example, the amine compound (A), the amine aqueous solution (A1), the group 2 element ion-containing aqueous solution (B), and the carbon dioxide-containing gas (C) used in the second embodiment are the same as in the first embodiment, and the preferred aspects and the like are also the same as in the first embodiment.
The recovery step (T), the amine compound recovery/supply step (U), the carbonate recovery section (Q), and the amine compound recovery/supply section (R) are also the same as in the first embodiment, and the preferred aspects and the like are also the same as in the first embodiment.

[Third embodiment]
FIG. 11 shows an example of the carbon dioxide immobilization method of the third embodiment.
The carbon dioxide immobilization method shown in FIG. 11 includes, as the step (S), a first contacting step (S3-1) in which one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines are brought into contact with the group 2 element ion-containing aqueous solution (B) to prepare a mixed solution (AB) of the amine compound (A) and the group 2 element ion-containing aqueous solution (B), and after the first contacting step (S3-1). 2 includes a second contacting step (S3-2) of contacting the mixture (AB) with the gas (C) containing carbon dioxide.
Furthermore, the carbon dioxide fixation method shown in FIG. 11 includes a recovery step (T) of recovering the alkaline earth metal carbonate after the step (S).

By bringing the gas (C) containing carbon dioxide into contact with the mixed solution (AB) of the amine compound (A) and the group 2 element ion-containing aqueous solution (B), alkaline earth metal carbonate can be efficiently produced while suppressing the pH increase of the group 2 element ion-containing aqueous solution (B) caused by the amine compound (A).
However, from the viewpoint of making it easier to suppress the pH increase and more efficiently producing alkaline earth metal carbonates, it is preferable to bring the mixture (AB) into contact with the gas (C) containing carbon dioxide as soon as possible after preparation.

Also, in the carbon dioxide immobilization method of the third embodiment, as shown in FIG. 12, it is preferable to further include an amine compound recovery/supply step (U) of recovering the amine compound (A) from the liquid phase after the precipitation of the alkaline earth metal carbonate and supplying the amine compound (A) as at least part of the amine compound (A) used in the first contact step (S3-1).

Next, FIG. 13 shows an example of a carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the third embodiment.
A carbon dioxide fixation system 1c shown in FIG. 13 includes at least a first contact portion (P3-1), a second contact portion (P3-2), and a carbonate recovery portion (Q).
In the first contact part (P3-1), a mixed solution (AB) is prepared of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions).
In the second contact portion (P3-2), the mixed liquid (AB) and the gas (C) containing carbon dioxide are brought into contact with each other to precipitate an alkaline earth metal carbonate.
The carbonate recovery section (Q) recovers carbonates of alkaline earth metals.

In the carbon dioxide fixation system 1c shown in FIG. 13, the amine compound (A) is stored in the storage tank 21 as an amine aqueous solution (A1), and the amine aqueous solution (A1) is supplied to the first contact portion (P3-1) through the supply line 21a.
A group 2 element ion-containing aqueous solution (B) is stored in a storage tank 31 and supplied to the first contact portion (P3-1) through a supply line 31a.
The amine compound (A) in the amine aqueous solution (A1) and the group 2 element ion-containing aqueous solution (B) are contacted and mixed at the first contact portion (P3-1) to prepare a mixed solution (AB).
The mixed liquid (AB) is supplied to the second contact portion (P3-2) through the supply line 2a. The mixed liquid (AB) in the second contact portion (P3-2) is supplied from a cylinder or equipment (for example, a coal-fired power plant, etc.) not shown, and is brought into contact with the carbon dioxide-containing gas (C) supplied to the second contact portion (P3-2) via the supply line 22a by the blower 22 to generate an alkaline earth metal carbonate.
In addition, the amine compound (A) is not limited to the aspect in which it is supplied to the first contact portion (P3-1) as an amine aqueous solution (A1), and the amine compound (A) may be directly supplied to the first contact portion (P3-1).

Further, although not shown, in the carbon dioxide fixation system for carrying out the carbon dioxide fixation method of the second embodiment, one first contact part (P3-1) may be provided, or a plurality of the first contact parts (P3-1) may be provided. In addition, one second contact portion (P3-2) may be provided, or a plurality thereof may be provided.
Further, although not shown, the carbon dioxide immobilization system 1c shown in FIG. 13 preferably does not include the second contact portion (P3-2), and the mixed liquid (AB) and the carbon dioxide-containing gas (C) are brought into contact with each other at the first contact portion (P3-1). By adopting such a configuration, after the mixed liquid (AB) is prepared in the first contact portion (P3-1), it is easy to quickly contact the gas (C) containing carbon dioxide, and the production efficiency of the alkaline earth metal carbonate is easily improved.

FIG. 14 shows an example of a preferable mode of the carbon dioxide fixation system of the present embodiment for carrying out the carbon dioxide fixation method of the third embodiment.
In addition to the first contact portion (P3-1), the second contact portion (P3-2), and the carbonate recovery portion (Q), the carbon dioxide fixation system 11c shown in FIG. 14 further includes an amine compound recovery/supply portion (R) that recovers the amine compound (A) from the liquid phase after the carbonate of the alkaline earth metal has precipitated and supplies it as at least part of the amine compound (A) used in the first contact portion (P3-1).

In addition, in the third embodiment, regarding aspects and configurations common to the first embodiment, preferred aspects and configurations are also the same as those in the first embodiment, and description thereof will be omitted.
For example, the amine compound (A), the amine aqueous solution (A1), the group 2 element ion-containing aqueous solution (B), and the carbon dioxide-containing gas (C) used in the third embodiment are the same as in the first embodiment, and the preferred aspects and the like are also the same as in the first embodiment.
The recovery step (T), the amine compound recovery/supply step (U), the carbonate recovery section (Q), and the amine compound recovery/supply section (R) are also the same as in the first embodiment, and the preferred aspects and the like are also the same as in the first embodiment.

[Method for producing carbonate]
As described above, according to the carbon dioxide immobilization methods of the first to third embodiments, alkaline earth metal carbonate can be recovered. Therefore, according to the present disclosure, there is also provided a method for producing carbonate using the carbon dioxide fixation methods of the first to third embodiments.
Alkaline earth metal carbonates are useful in a variety of applications.
For example, calcium carbonate can be used as a filler, pigment, extender, etc. in a wide range of industrial fields such as papermaking, rubber, plastics, food, and cosmetics.
Strontium carbonate can also be used as a raw material for Braun tubes and ferrite magnets.
Furthermore, barium carbonate can be used as a raw material for electronic materials.

[One aspect of the present disclosure provided]
According to one aspect of the present disclosure, the following [1] to [21] are provided.
[1] A method for immobilizing carbon dioxide, wherein an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions) is brought into contact with carbon dioxide-derived carbonate ions in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, to produce an alkaline earth metal carbonate,
A step (S) of suppressing a pH increase of the group 2 element ion-containing aqueous solution (B) caused by the amine compound (A) by using a gas (C) containing carbon dioxide.
A method for immobilizing carbon dioxide, comprising:
[2] The step (S) is
A first contact step (S1-1) of bringing an aqueous amine solution (A1) containing the amine compound (A) into contact with the gas (C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the gas (C).
The method for immobilizing carbon dioxide according to [1] above, comprising:
[3] The step (S) is
After the step (S1-1),
A second contacting step (S1-2) of bringing the aqueous amine solution (A2) into contact with the aqueous solution (B) containing Group 2 element ions
The method for immobilizing carbon dioxide according to [2] above, comprising:
[4] The step (S) is
A contacting step (S2) of simultaneously contacting the amine compound (A), the group 2 element ion-containing aqueous solution (B), and the gas (C)
The method for immobilizing carbon dioxide according to [1] above, comprising:
[5] The step (S) is
A first contacting step (S3-1) of contacting the amine compound (A) and the aqueous solution (B) containing group 2 element ions to prepare a mixed solution (AB) of the amine compound (A) and the aqueous solution (B) containing group 2 element ions, and a second contacting step (S3-2) of contacting the mixed solution (AB) with the gas (C) after the first contacting step (S3-1).
The method for immobilizing carbon dioxide according to [1] above, comprising:
[6] The method for immobilizing carbon dioxide according to any one of [1] to [5] above, wherein the amine synthesized in vivo is one or more selected from the biogenic amine group consisting of 1,3-propanediamine, putrescine, cadaverine, spermidine, spermine, norspermidine, and norspermine.
[7] The method for immobilizing carbon dioxide according to any one of [1] to [6] above, wherein the artificially synthesized amine is one or more selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, diisopropanolamine, diglycolamine, methyldiethanolamine, piperazine, and ethylenediamine.
[8] The method for immobilizing carbon dioxide according to any one of [1] to [7] above, wherein the Group 2 element ion-containing aqueous solution (B) contains at least magnesium ions and calcium ions.
[9] The method for immobilizing carbon dioxide according to any one of the above [1] to [8], wherein the Group 2 element ion-containing aqueous solution (B) is seawater.
[10] The method for immobilizing carbon dioxide according to any one of [1] to [8] above, wherein the Group 2 element ion-containing aqueous solution (B) has a calcium ion concentration of 400 ppm by mass or more.
[11] The method for immobilizing carbon dioxide according to any one of [1] to [8] and [10] above, wherein the Group 2 element ion-containing aqueous solution (B) has a magnesium ion concentration of 500 ppm by mass or less.
[12] The carbon dioxide fixation method according to any one of [1] to [11] above, further comprising a recovery step (T) of recovering the alkaline earth metal carbonate after the step (S).
[13] The method for immobilizing carbon dioxide according to any one of the above [1] to [12], further comprising an amine compound recovery/supply step (U) of recovering the amine compound (A) from the liquid phase after the alkaline earth metal carbonate has precipitated and supplying it as at least part of the amine compound (A) used in the step (S).
[14] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
A first contact part (P1-1) for preparing an aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C) by bringing an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines into contact with a gas (C) containing carbon dioxide;
The aqueous amine solution (A2) and the aqueous solution (B) containing group 2 element ions (wherein the aqueous solution (B) containing group 2 element ions contains at least alkaline earth metal ions) are brought into contact with each other to deposit an alkaline earth metal carbonate in a second contact part (P1-2), and a carbonate recovery part (Q) in which the alkaline earth metal carbonate is recovered.
A carbon dioxide fixation system comprising at least
[15] The carbon dioxide fixation system according to [14] above, comprising a plurality of the first contact portions (P1-1).
[16] The carbon dioxide fixation system according to [14] or [15] above, comprising a plurality of second contact portions (P1-2).
[17] In the carbon dioxide fixation system according to [14] or [15] above,
A carbon dioxide immobilization system in which the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact at the first contact portion (P1-1) without the second contact portion (P1-2).
[18] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
At least one amine compound (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines, a Group 2 element ion-containing aqueous solution (B) (wherein the Group 2 element ion-containing aqueous solution (B) contains at least alkaline earth metal ions) and a gas (C) containing carbon dioxide are simultaneously brought into contact with each other to deposit an alkaline earth metal carbonate, and a carbonate recovery unit (Q) for recovering the alkaline earth metal carbonate.
A carbon dioxide fixation system comprising at least
[19] A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to [1] above,
a first contact portion (P3-1) for preparing a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines, and an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions);
A second contact part (P3-2) for bringing the mixed solution (AB) into contact with a gas (C) containing carbon dioxide to deposit an alkaline earth metal carbonate, and a carbonate recovery part (Q) for recovering the alkaline earth metal carbonate,
A carbon dioxide fixation system comprising at least
[20] An amine compound recovery/supply unit (R) that recovers the amine compound (A) from the liquid phase after the alkaline earth metal carbonate has precipitated and supplies it as at least part of the amine compound (A) used in the first contact portion (P1-1), the contact portion (P2), or the first contact portion (P3-1);
The carbon dioxide fixation system according to any one of [14] to [19] above, further comprising:
[21] A method for producing a carbonate, using the method for immobilizing carbon dioxide according to any one of [1] to [13] above.

[Examination of calcium carbonate formation rate using seawater and various bases]
Using seawater and various bases, calcium carbonate formation rate was investigated.

<Base used>
"Base 1": An amine aqueous solution (A2) containing carbon dioxide-derived carbonate ions, obtained by using putrescine (1,4-butanediamine) as the amine compound (A) and introducing carbon dioxide into the amine aqueous solution (A1) in which the putrescine concentration was adjusted to 30% by mass.
Carbon dioxide was introduced by adding CO ₂ gas (99.9%) to 20 L of the amine aqueous solution (A1) through an air stone at 1 L/min for 2 hours.
- "Base 2": An aqueous amine solution (A1) in which putrescine was used as the amine compound (A) and the concentration of putrescine was adjusted to 30% by mass.
・ "Base 3": NaOH

<Example 1-1>
Base 1 (amine aqueous solution (A2)) was added to 500 mL of seawater (natural seawater).
The amount of base 1 added was adjusted so that the concentration of the amine compound in the mixture of seawater and base 1 was 10 mM.
Next, while keeping the mixture of seawater and base 1 at 40° C. in a water bath, air was continuously introduced at 1 L/min for 5 hours through an air stone, and the calcium ion concentration in the mixture was measured. The calcium ion concentration in the mixed liquid was measured before the introduction of air and immediately after the introduction of air (1 minute after the introduction of air was started), and then continued to be measured over time.
Also, the pH was measured over time.
The calcium ion concentration in the mixed solution was measured using LAQAtwin-Ca-11 manufactured by Horiba, Ltd.
The pH of the mixed solution was measured using F-72 manufactured by Horiba, Ltd.

<Example 1-2>
The calcium ion concentration and pH in the mixed solution of seawater and base 2 were measured in the same manner as in Example 1-1, except that base 1 was changed to base 2 (amine aqueous solution (A2)).

<Comparative Example 1-1>
The calcium ion concentration and pH in the mixed solution of seawater and base 3 were measured in the same manner as in Example 1-1, except that base 1 was changed to base 3 (NaOH).
The amount of base 3 added was adjusted so that the NaOH concentration of the mixture of seawater and base 3 was 10 mM.

FIG. 15 shows the measurement results of calcium ion concentration, and FIG. 16 shows the measurement results of pH.
The results shown in FIGS. 15 and 16 reveal the following.
In Example 1-1, when the base 1 (amine aqueous solution (A2)) was added to seawater, the calcium ion concentration immediately decreased. Also, no significant increase in pH was observed. From this, it can be seen that when base 1 (amine aqueous solution (A2)) was added to seawater, calcium carbonate precipitated immediately without a large increase in pH.
In contrast, as in Comparative Example 1-1, when base 3 (NaOH) was added to seawater, cloudiness of the mixed liquid was observed. Also, a significant increase in pH was observed. From this, it is considered that when the pH of seawater was raised by adding Base 3 to seawater, the magnesium ions present in the seawater in an amount three times as large as the calcium ions became magnesium hydroxide, inhibiting the formation of calcium carbonate.
In addition, as in Example 1-2, when base 2 (aqueous amine solution (A1)) was added, the calcium ion concentration did not decrease as quickly as in Example 1-1, but compared to Comparative Example 1-1, there was a clear tendency for the calcium ion concentration to decrease. From this, it can be seen that even when base 2 (aqueous amine solution (A1)) was added as in Example 1-2, calcium carbonate was produced efficiently, though not as efficiently as in Example 1-1.

From the above results, it became clear that calcium carbonate can be produced most efficiently by using base 1 (amine aqueous solution (A2)) as in Example 1-1.
It was also found that calcium carbonate can be efficiently produced by using base 2 (aqueous amine solution (A1)) as in Example 1-2.
The rate of decrease of the calcium ion concentration from the initial period (0 minutes) to the end period (300 minutes) is, as shown in FIG. 15, 86.2% in Example 1-1, 78.8% in Example 1-2, and 50.9% in Comparative Example 1-1.

[Investigation of influence of base concentration on calcium carbonate formation rate using demagnesium seawater]
Using demagnesium seawater and base 1, the influence of base concentration on calcium carbonate formation rate was investigated.

<Example 2-1>
Base 1 (amine aqueous solution (A2)) was added to 500 mL of demagnesium seawater.
Demagnesium-free seawater was produced by adding milk of lime to seawater (natural seawater) and then removing the produced magnesium hydroxide slurry. The magnesium concentration of the magnesium-free seawater is 500 ppm by mass or less.
The amount of base 1 to be added was adjusted so that the concentration of the amine compound in the mixed solution of Mg-free seawater and base 1 was 10 mM.
Next, air was continuously introduced at 1 L/min for 1 hour through an air stone while the mixture of demagnesium-free seawater and base 1 was kept at 40° C. in a water bath, and the calcium ion concentration in the mixture was measured. The calcium ion concentration in the mixed liquid was measured before introducing the air, immediately after the introduction of the air (1 minute after the introduction of the air started), and then continuously measured over time.

<Examples 2-2 to 2-7>
The amount of base 1 added was adjusted so that the amine compound concentrations in the mixture of demagnesium-free seawater and base 1 were as follows, respectively, and the calcium ion concentration in the mixture was measured in the same manner as in Example 2-1.
・Example 2-2: 20 mM
・Example 2-3: 30 mM
・Example 2-4: 40 mM
・Example 2-5: 50 mM
・Example 2-6: 60 mM
・Example 2-7: 70 mM

The results are shown in FIG.
The results shown in FIG. 17 reveal the following.
In any of Examples 2-1 to 2-7, the calcium ion concentration decreased immediately after adding base 1 (amine aqueous solution (A2)). Moreover, it was confirmed that the rate of decrease in calcium ion concentration increased as the amount of base 1 added increased.
In addition, in any of Examples 2-1 to 2-7, the calcium ion concentration did not change much after the calcium ion concentration greatly decreased immediately after the addition of Base 1.

[Examination of the influence of base species on calcium carbonate formation rate using demagnesium seawater 1]
Using demagnesium seawater and base 1 or 3, the effect of base species on the rate of calcium carbonate formation was investigated.

<Example 3-1>
The same test as in Examples 2-5 above was conducted for 180 minutes to measure changes over time in the calcium ion concentration in the mixed solution, and to measure changes over time in pH of the mixed solution.

<Comparative Example 3-1>
The same test as in Example 3-1 was performed by changing the base species from base 1 to base 3 (NaOH), and the change over time of the calcium ion concentration in the mixed solution was measured, and the change over time of the pH of the mixed solution was measured.

FIG. 18 shows the measurement results of calcium ion concentration, and FIG. 19 shows the measurement results of pH.
The results shown in FIG. 18 reveal the following.
In Example 3-1, the calcium ion concentration decreased immediately after the addition of base 1 (amine aqueous solution (A2)), and thereafter the calcium ion concentration remained low.
On the other hand, in Comparative Example 3-1, when the base 3 (NaOH) was added at the beginning, the calcium ion concentration gradually increased, and thereafter the calcium ion concentration gradually decreased. After 60 minutes from the start of the test, the calcium ion concentration did not change significantly and remained above 1,000 mass ppm.
Moreover, the following things are understood from the result shown in FIG.
In Example 3-1, the pH decreased immediately after the addition of the base 1 (amine aqueous solution (A2)), followed by a gradual increase in pH, but the pH was maintained at 8.5 or less.
On the other hand, in Comparative Example 3-1, the pH was maintained at 11 or higher over the entire test period.

From the above results, it became clear that calcium carbonate can be produced overwhelmingly more efficiently by using base 1 (amine aqueous solution (A2)) as in Example 3-1 than using base 3 (NaOH) as in Comparative Example 3-1.

[Examination of the influence of base species on the calcium carbonate formation rate using demagnesium seawater 2]
Using polyethylenimine as a base species, the rate of formation of calcium carbonate was investigated.

<Example 4-1>
Using polyethyleneimine 1 (manufactured by Nippon Shokubai Co., Ltd., product number "SP-006", molecular weight 600) as a base, the same test as in Example 3-1 was performed. Base concentration was 50 mM.

<Example 4-2>
Using polyethyleneimine 2 (manufactured by Nippon Shokubai Co., Ltd., product number “SP-018”, molecular weight 1,800) as a base, the same test as in Example 3-1 was performed. Base concentration was 50 mM.

<Example 4-3>
Polyethyleneimine 3 (manufactured by Nippon Shokubai Co., Ltd., product number "SP-200", molecular weight 10,000) was used as a base, and the same test as in Example 3-1 was performed. Base concentration was 50 mM.

<Example 4-4>
Polyethyleneimine 4 (manufactured by Nippon Shokubai Co., Ltd., product number "HM-2000", molecular weight 30,000) was used as a base, and the same test as in Example 3-1 was carried out. Base concentration was 50 mM.

The molecular weights of polyethyleneimines 1 to 4 are number average molecular weights determined by boiling point elevation method.

The results are shown in FIG.
FIG. 20 also shows the results of Example 3-1 and Comparative Example 3-1.
From the results shown in FIG. 20, it was clarified that calcium carbonate can be produced more efficiently when any of polyethyleneimine 1 to 4 is used as the base, compared to when NaOH is used as the base.

[Examination of calcium carbonate formation rate using brackish water]
Using brackish water and base 1, the rate of calcium carbonate formation was investigated.

<Example 5-1>
Base 1 (amine aqueous solution (A2)) was added to 500 mL of brine.
Waste seawater (calcium ion concentration: 800 ppm by mass) from a seawater desalination apparatus was used as brackish water.
The amount of base 1 added was adjusted so that the concentration of the amine compound in the mixed solution of brine and base 1 was 10 mM.
Next, while keeping the mixture of brine and base 1 at 40° C. in a water bath, air was continuously introduced at 1 L/min for 1 hour through an air stone, and the calcium ion concentration in the mixture was measured. The calcium ion concentration in the mixed liquid was measured before introducing the air, immediately after the introduction of the air (1 minute after the introduction of the air started), and then continuously measured over time.
Also, the pH was measured over time.

<Examples 5-2 to 5-4>
The amount of base 1 added was adjusted so that the amine compound concentrations in the mixture of brine and base 1 were as follows, respectively, and the calcium ion concentration and pH in the mixture were measured in the same manner as in Example 5-1.
・Example 5-2: 20 mM
・Example 5-3: 50 mM
・Example 5-4: 100 mM

FIG. 21 shows the measurement results of calcium ion concentration, and FIG. 22 shows the measurement results of pH.
From the results shown in FIG. 21, it was confirmed that even when brine was used, the use of Base 1 reduced the calcium ion concentration regardless of the amine compound concentration, and that the higher the amine compound concentration (particularly, when the amine compound concentration was 20 mM or more), the more pronounced the decrease in calcium ion concentration immediately after the addition of Base 1 was.
Moreover, from the results shown in FIG. 22, it was found that when the concentration of the amine compound was 20 mM or higher, the pH temporarily decreased 1 minute after the start of the experiment.
From the above results, it was found that even in the case of using brine, calcium carbonate can be efficiently produced by using Base 1, and the more Base 1 is added (particularly, when the amine compound concentration is 20 mM or more), the calcium carbonate formation rate increases significantly.

1a, 1a′, 1a″, 11a Carbon dioxide fixation systems 1b, 11b (in the second embodiment) Carbon dioxide fixation systems 1c, 11c (In the third embodiment) Carbon dioxide fixation systems (P1-1), (P1-1)′ (In the third embodiment) First contact portion (P2) (In the second embodiment) Contact portion (P3-1 in the second embodiment) First contact portion 2a (From the first contact portion to the second contact portion in the third embodiment) of) supply line 21 (of amine aqueous solution (A1)) storage tank 21a (of amine aqueous solution (A1)) supply line 22 blower 22a (of air (C) containing carbon dioxide) supply line (P1-2), (P1-2)' (in the first embodiment) second contact portion (P3-2) (in the third embodiment) second contact portion 31 (of group 2 element ion-containing aqueous solution (B)) storage tank 31a (of group 2 element ion-containing aqueous solution (B)) ) supply line (Q) carbonate recovery unit (R) amine compound recovery/supply unit 51a (from carbonate recovery unit to amine compound recovery/supply unit) supply line 51b (from amine compound recovery/supply unit to storage tank for amine aqueous solution (A1)) supply line

Claims

In the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, a group 2 element ion-containing aqueous solution (B) (wherein the group 2 element ion-containing aqueous solution (B) contains at least alkaline earth metal ions) is brought into contact with carbon dioxide-derived carbonate ions to form an alkaline earth metal carbonate.
A step (S) of suppressing a pH increase of the group 2 element ion-containing aqueous solution (B) caused by the amine compound (A) by using a gas (C) containing carbon dioxide.
A method for immobilizing carbon dioxide, comprising:
The step (S) is
A first contact step (S1-1) of bringing an aqueous amine solution (A1) containing the amine compound (A) into contact with the gas (C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the gas (C).
The method for immobilizing carbon dioxide according to claim 1, comprising:
The step (S) is
After the step (S1-1),
A second contacting step (S1-2) of bringing the aqueous amine solution (A2) into contact with the aqueous solution (B) containing Group 2 element ions
The method for immobilizing carbon dioxide according to claim 2, comprising:
The step (S) is
A contacting step (S2) of simultaneously contacting the amine compound (A), the group 2 element ion-containing aqueous solution (B), and the gas (C)
The method for immobilizing carbon dioxide according to claim 1, comprising:
The step (S) is
A first contacting step (S3-1) of contacting the amine compound (A) and the aqueous solution (B) containing group 2 element ions to prepare a mixed solution (AB) of the amine compound (A) and the aqueous solution (B) containing group 2 element ions, and a second contacting step (S3-2) of contacting the mixed solution (AB) with the gas (C) after the first contacting step (S3-1).
The method for immobilizing carbon dioxide according to claim 1, comprising:
The carbon dioxide immobilization method according to any one of claims 1 to 5, wherein the amine synthesized in vivo is one or more selected from the biogenic amine group consisting of 1,3-propanediamine, putrescine, cadaverine, spermidine, spermine, norspermidine, and norspermine.
The method for immobilizing carbon dioxide according to any one of claims 1 to 6, wherein the artificially synthesized amine is one or more selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, diisopropanolamine, diglycolamine, methyldiethanolamine, piperazine, and ethylenediamine.
The method for immobilizing carbon dioxide according to any one of claims 1 to 7, wherein the group 2 element ion-containing aqueous solution (B) contains at least magnesium ions and calcium ions.
The method for immobilizing carbon dioxide according to any one of claims 1 to 8, wherein the aqueous solution (B) containing group 2 element ions is seawater.
The method for immobilizing carbon dioxide according to any one of claims 1 to 8, wherein the second group element ion-containing aqueous solution (B) has a calcium ion concentration of 400 ppm by mass or more.
The method for immobilizing carbon dioxide according to any one of claims 1 to 8 and 10, wherein the group 2 element ion-containing aqueous solution (B) has a magnesium ion concentration of 500 ppm by mass or less.
The method for immobilizing carbon dioxide according to any one of claims 1 to 11, further comprising a recovery step (T) of recovering the alkaline earth metal carbonate after the step (S).
The carbon dioxide fixation method according to any one of claims 1 to 12, further comprising an amine compound recovery/supply step (U) of recovering the amine compound (A) from the liquid phase after the alkaline earth metal carbonate has precipitated and supplying it as at least part of the amine compound (A) used in the step (S).
A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to claim 1,
A first contact part (P1-1) for preparing an aqueous amine solution (A2) containing carbon dioxide-derived carbonate ions in the gas (C) by bringing an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines into contact with a gas (C) containing carbon dioxide;
The aqueous amine solution (A2) and the aqueous solution (B) containing group 2 element ions (wherein the aqueous solution (B) containing group 2 element ions contains at least alkaline earth metal ions) are brought into contact with each other to deposit an alkaline earth metal carbonate in a second contact part (P1-2), and a carbonate recovery part (Q) in which the alkaline earth metal carbonate is recovered.
A carbon dioxide fixation system comprising at least
The carbon dioxide fixation system according to claim 14, comprising a plurality of said first contact portions (P1-1).
The carbon dioxide fixation system according to claim 14 or 15, comprising a plurality of said second contact parts (P1-2).
In the carbon dioxide fixation system according to claim 14 or 15,
A carbon dioxide immobilization system in which the amine aqueous solution (A2) and the group 2 element ion-containing aqueous solution (B) are brought into contact at the first contact portion (P1-1) without the second contact portion (P1-2).
A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to claim 1,
At least one amine compound (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines, a Group 2 element ion-containing aqueous solution (B) (wherein the Group 2 element ion-containing aqueous solution (B) contains at least alkaline earth metal ions) and a gas (C) containing carbon dioxide are simultaneously brought into contact with each other to deposit an alkaline earth metal carbonate, and a carbonate recovery unit (Q) for recovering the alkaline earth metal carbonate.
A carbon dioxide fixation system comprising at least
A carbon dioxide fixation system for carrying out the carbon dioxide fixation method according to claim 1,
a first contact portion (P3-1) for preparing a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers of these amines, and an aqueous solution (B) containing Group 2 element ions (wherein the aqueous solution (B) containing Group 2 element ions contains at least alkaline earth metal ions);
A second contact part (P3-2) for bringing the mixed solution (AB) into contact with a gas (C) containing carbon dioxide to deposit an alkaline earth metal carbonate, and a carbonate recovery part (Q) for recovering the alkaline earth metal carbonate,
A carbon dioxide fixation system comprising at least
An amine compound recovery/supply unit (R) that recovers the amine compound (A) from the liquid phase after the alkaline earth metal carbonate has precipitated and supplies it as at least a part of the amine compound (A) used in the first contact portion (P1-1), the contact portion (P2), or the first contact portion (P3-1);
The carbon dioxide fixation system according to any one of claims 14 to 19, further comprising:
A method for producing a carbonate using the method for immobilizing carbon dioxide according to any one of claims 1 to 13.