Absorbent for seawater-derived carbon dioxide

Abstract

The purpose of the present invention is to provide a carbon dioxide absorbent for efficiently absorbing carbon dioxide contained in seawater. The present invention relates to a novel polymer including a guanidino group or a cyclic guanidino group. The present invention also relates to a carbon dioxide absorbent for absorbing carbon dioxide contained in seawater, the carbon dioxide absorbent including the polymer.

Description

Seawater-derived carbon dioxide absorbent

[0001] The present invention relates to a novel polymer containing a guanidino group or a cyclic guanidino group. The present invention also relates to a carbon dioxide absorbent containing the polymer for absorbing carbon dioxide in seawater and recovering it from the ocean.

[0002] Carbon dioxide (hereinafter referred to as "CO ２ In recent years, active research has been conducted into technologies for capturing carbon dioxide (CO2) and storing it underground or on the seabed. These technologies are called CCS (Carbon dioxide-Capture-and-Storage) (Non-Patent Document 1) and DAC (Direct-Air-Capture) (Non-Patent Document 2, Non-Patent Document 3). ２ Recently, direct ocean capture (DOC), a technology that directly captures carbon dioxide from the ocean, has been attracting attention. The reason for this is that the CO ２ Increased concentrations of CO in the ocean ２ If the concentration continues to rise, there are concerns that the pH of the ocean will change, resulting in an impact on the ecosystem.

[0003] As a conventional carbon dioxide absorbent, a water-soluble amine compound such as ethylenediamine is generally used. ２ In DOC conducted in the ocean, where carbon dioxide concentrations are low, it has been difficult to use existing water-soluble amine compounds as carbon dioxide absorbents because they are miscible with water and cause marine pollution. Furthermore, because the carbon dioxide concentration in seawater is lower than in the atmosphere, compounds with high carbon dioxide absorption capacity are required.

[0004] Recently, the present inventors have discovered that alkylamines incorporating a hydrophobic phenyl group near the amino group can selectively and efficiently absorb and release atmospheric carbon dioxide (Patent Documents 1 to 4, Non-Patent Documents 4 and 5). This method, whether the alkylamine is used alone or in aqueous solution as a carbon dioxide absorbent, results in a solid containing almost no water after carbon dioxide absorption, enabling solid-liquid separation. This method has the advantage of eliminating the need for water heating energy when releasing the absorbed carbon dioxide and allowing efficient carbon dioxide generation under mild temperature conditions. However, it is unclear whether the alkylamine can absorb low concentrations of carbon dioxide in seawater, which contains large amounts of various salts. Even if it can absorb carbon dioxide, the alkylamine compound disperses in the ocean after carbon dioxide absorption, making separation and recovery from the ocean difficult, and therefore may not be suitable for use in seawater.

[0005] On the other hand, molecular sieves are also known as adsorbents for carbon dioxide from exhaust gases (Patent Document 5), but they also adsorb water vapor, so they are not suitable for CO ２ Furthermore, Patent Document 6 describes that a carbon dioxide absorbent obtained by physically supporting or impregnating (spraying and then drying) a cyclic guanidine compound on inorganic particles such as silica or activated carbon, or on fibers, can absorb carbon dioxide in various organic solvents, but does not even suggest use in water, and therefore it is unclear whether the absorbent can withstand use in water, particularly in seawater which is rich in various salts.

[0006] As mentioned above, there have been no reports to date of chemical absorbents that can efficiently capture carbon dioxide in seawater and recover it from the ocean.

[0007] Japanese Patent Application Laid-Open No. 2017-31046 Japanese Patent Application Laid-Open No. 2017-31062 Japanese Patent Application Laid-Open No. 2019-127417 International Publication No. 2022 / 176534 Japanese Patent Application Laid-Open No. 2002-519188 Japanese Patent Application Laid-Open No. 2011-206671

[0008] Iijima, M. and Nakatani, S., Kagaku Kogaku, 2013, Vol.77, pages 300-303.Baciocchi, R., Storti, G., and Mazzotti, M. Chemical Engineering and Processing, 2006, Vol.45, pages 1047-1058.Kiani, A., Jiang, K., and Feron, P., frontiers in Energy Research, 2020, Vol.8, Article 92.Inagaki, F., Matsumoto, C., Iwata, T., and Mukai, C., J. Am. Chem. Soc., 2017, Vol.139, pages 4639-4642.Murakami, R., Kawamitsu, H., Otsuka, R., Tanishima, H., and Inagaki, F., Adv. Mater. Interfaces., 2024, Vol.11, 2300881.

[0009] An object of the present invention is to provide a compound that can efficiently absorb carbon dioxide at low concentrations in seawater and that can be easily recovered from the ocean after absorbing carbon dioxide.

[0010] Under these circumstances, the present inventors have conducted extensive research and have found that by using a polymer having a guanidino group in the side chain, particularly a polymer having a polystyrene main chain, as a carbon dioxide absorbent, it is possible to absorb carbon dioxide in a low CO concentration such as in seawater. ２ The present inventors have found that high carbon dioxide absorption performance can be achieved even in this concentration range, and that carbon dioxide can be easily recovered from the ocean after absorption, leading to the completion of the present invention.

[0011] That is, the present invention is as follows: [1] Formula (1):

[0012]

[0013] [In the formula, R １ and R ２ each independently represents a hydrogen atom or an optionally substituted alkyl group, or R１ and R ２ are bonded to each other to form, together with the nitrogen atom to which they are attached, an optionally substituted 5- to 8-membered ring; and R ３ represents a hydrogen atom or an optionally substituted alkyl group.] and a repeating structural unit (1) represented by formula (2):

[0014]

[0015] [2] A polymer according to the above item [1], which comprises a repeating structural unit (1) and a repeating structural unit (2), and each repeating unit is contained randomly or in a block (hereinafter, this may be referred to as the "polymer of the present invention"). [3] R １ , R ２ and R ３ are each independently a hydrogen atom or a methyl group. １ and R ２ are bonded to each other to form imidazoline or 1,4,5,6-tetrahydropyrimidine together with the nitrogen atoms to which they are bonded. [5] The polymer according to any one of [1] to [4] above, which is a random copolymer in which, of all the structural units of the polymer, the repeating structural unit (1) accounts for 50 to 99 mol % and the repeating structural unit (2) accounts for 1 to 50 mol %. [2'] The polymer is represented by formula (3):

[0016]

[0017] wherein R is a group represented by the following formula:

[0018]

[0019] (In the formula, the wavy line indicates the bonding position with the main chain, and R ４ is C １－６ [3'] R represents an alkyl group, and n represents an integer of 1 to 10. [3'] R represents a group selected from the group consisting of １ , R ２and R ３ are each independently a hydrogen atom or a methyl group. １ and R ２ are bonded to each other to form imidazoline or 1,4,5,6-tetrahydropyrimidine together with the nitrogen atoms to which they are bonded. [5'] The polymer according to any of [2'] to [4'] above, which is a random copolymer in which, of all the structural units of the polymer, the repeating structural unit (1) accounts for 35 to 96 mol%, the repeating structural unit (2) accounts for 2 to 63 mol%, and the repeating structural unit (3) accounts for 2 to 63 mol%. [6] A carbon dioxide absorbent containing a polymer according to any of [1] to [5] and [2'] to [5'] above (hereinafter, sometimes referred to as the "carbon dioxide absorbent of the present invention"). [7] The carbon dioxide absorbent according to [6] above, for absorbing carbon dioxide in seawater. [8] A carbon dioxide absorbent according to formula (I):

[0020]

[0021] [wherein each symbol has the same meaning as defined above], and a compound represented by formula (II):

[0022]

[0023] [9] The method according to [8] above, wherein the polymerization initiator is 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) or azobisisobutyronitrile (AIBN). [8'] A compound represented by formula (I):

[0024]

[0025] [wherein each symbol has the same meaning as defined above], a compound represented by formula (II):

[0026]

[0027] and a compound represented by formula (III):

[0028]

[0029] [wherein each symbol has the same meaning as defined above.], with a polymerization initiator under heating. [9'] The method according to [8'] above, wherein the polymerization initiator is 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) or azobisisobutyronitrile (AIBN).

[0030] The carbon dioxide absorbent of the present invention is easy to synthesize, stable and easy to handle even in water, particularly seawater containing various salts, and has a high carbon dioxide absorption capacity. Therefore, it has the advantage of being able to efficiently absorb and immobilize carbon dioxide, even at room temperature and atmospheric pressure, even when carbon dioxide is diluted and present in the ocean at low concentrations. Furthermore, the carbon dioxide absorbent of the present invention not only facilitates recovery after immobilization of carbon dioxide, but also allows the immobilized carbon dioxide to be released under mild conditions and effectively utilized as a carbon source. Therefore, the present invention can provide a novel and effective method for direct ocean capture (DOC).

[0031] FIG. 1a shows the change in carbon dioxide concentration (mg / L) over time in distilled water at room temperature and atmospheric pressure due to the addition of a polymer of the present invention (compound (1-1) or compound (1-2)), a molecular sieve 3 Å, and a molecular sieve 4 Å. FIG. 1b shows the results of an experiment conducted on a scale 10 times larger than that of FIG. 1a using a polymer of the present invention (compound (1-2)) and a molecular sieve 4 Å. FIG. 2a shows the change in carbon dioxide concentration (mg / L) over time in seawater at room temperature and atmospheric pressure due to the addition of a polymer of the present invention (compound (1-2)) and a molecular sieve 4 Å. FIG. 2b shows the results of an experiment conducted on a scale 10 times larger than that of FIG. 2a using a polymer of the present invention (compound (1-2)) and a molecular sieve 4 Å. FIG. 3 shows the change in the amount of carbon dioxide released (ppm) over time from a polymer of the present invention (compound (1-2)) after carbon dioxide absorption due to heating. FIG. 4 shows the change in carbon dioxide concentration (mg / L) over time due to the addition of a polymer of the present invention (compound (1-2), compound (1-3), compound (1-4), compound (1-5), or compound (1-6)) to seawater (50 mL) at room temperature and atmospheric pressure. FIG. 5 shows the change in carbon dioxide concentration (mg / L) over time due to the addition of a polymer of the present invention (compound (1-2) or compound (1-7)) to seawater (500 mL) at room temperature and atmospheric pressure. FIG. 6 is a schematic diagram of an experimental apparatus for investigating the amount of carbon dioxide released over time from a polymer of the present invention after carbon dioxide absorption by heating. FIG. 7 shows the change in the amount of carbon dioxide released (ppm) over time from a polymer of the present invention (compound (1-2) or compound (1-7)) after carbon dioxide absorption by heating.

[0032] The present invention will be described in detail below.

[0033] (Definitions) In this specification, "room temperature" means about 15°C to about 25°C.

[0034] In this specification, "normal pressure" means 1 atmosphere (1013 hPa).

[0035] As used herein, "about" is defined as ±5°C for temperature, ±10 minutes for time, and ±10% for weight, volume, and concentration.

[0036] As used herein, the term "bicarbonate" refers to a hydrogen carbonate salt of a substituted guanidine or cyclic guanidine formed by reacting a substituted guanidino group or cyclic guanidino group contained in the polymer of the present invention with carbon dioxide.

[0037] In this specification, "absorption" means a state in which a substituted guanidino group or a cyclic guanidino group contained in the polymer of the present invention chemically reacts with carbon dioxide to form a substituted guanidine or a cyclic guanidine bicarbonate, which is then incorporated into the polymer of the present invention. The carbon dioxide absorbed into the polymer of the present invention is easily desorbed and released from the polymer of the present invention by applying conditions such as heating.

[0038] In this specification, the term "adsorption" refers to a state in which carbon dioxide is physically taken in by van der Waals forces or the like.

[0039] The polymer (guanidino group-containing polymer) of the present invention is a random copolymer or block copolymer containing repeating structural units (1) and (2), preferably a random copolymer. In the copolymer, the repeating structural units (1) and (2) may each be of one type or two or more types. Furthermore, the copolymer may contain structural units other than the structural units (1) and (2). Hereinafter, the groups contained in the repeating structural units will be described in order.

[0040] In the present specification, the term "alkyl group" in "optionally substituted alkyl group" means a linear or branched alkyl group having 1 or more carbon atoms, and when there is no particular limitation on the range of the carbon number, １－２０ It means an alkyl group. １－６ Alkyl groups are more preferred, and C １－３ Alkyl groups are particularly preferred.

[0041] In this specification, "C １－２０The term "alkyl group" means a straight-chain or branched-chain alkyl group having 1 to 20 carbon atoms, and examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, 1-ethylpropyl, hexyl, isohexyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, and eicosyl.

[0042] In this specification, "C １－６ The term "alkyl group" means a straight-chain or branched-chain alkyl group having 1 to 6 carbon atoms, and examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, 1-ethylpropyl, hexyl, isohexyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, and 2-ethylbutyl.

[0043] In this specification, "C １－３ The term "alkyl group" refers to a straight or branched chain alkyl group having 1 to 3 carbon atoms, and includes, for example, methyl, ethyl, propyl, or isopropyl.

[0044] In this specification, R １ and R ２ Examples of "an optionally substituted 5- to 8-membered ring which may be formed by bonding together with the nitrogen atom to which they are bonded" include the following formula:

[0045]

[0046] (In the formula, the wavy line indicates the bonding site with the NH group, and R ３ has the same meaning as defined above.) Among them, imidazoline or 1,4,5,6-tetrahydropyrimidine is preferred, and imidazoline is particularly preferred.

[0047] In this specification, unless otherwise specified, the term "optionally substituted" means that the compound may have one or more substituents, and examples of the "substituents" include (1) a halogen atom, (2) a nitro group, (3) a cyano group, (4) a hydroxy group, (5) an amino group which may be substituted with a protecting group, (6) a C ３－８ cycloalkyl group, (7) C １－６ Alkoxy group, (8) C １－６ Alkoxy-C １－６ Alkoxy group, (9) C ６－１４ aryl group, (10) C ６－１４ (11) an aryloxy group, (12) a formyl group, (13) a C １－６ (13) a carbamoyl group optionally substituted by an alkyl group; (14) a carbamoyl group optionally substituted by an alkyl group; (15) a carbamoyl group optionally substituted by an alkyl group; (16) a carbamoyl group optionally substituted by an alkyl group; (17) a carbamoyl group optionally substituted by an alkyl group; (18) a carbamoyl group optionally substituted by an alkyl group; (19) a carbamoyl group optionally substituted by an alkyl group; ( １－６ (14) a sulfamoyl group optionally substituted with an alkyl group; １－６ Alkyl-carbonyl group, (15) C １－６ Alkoxy-carbonyl group, (16) C ３－８ cycloalkyl-carbonyl group, (17) C ６－１４ (18) an aryl-carbonyl group, (19) a 3- to 14-membered heterocyclylcarbonyl group, (20) a C １－６ Alkylsulfonyl group, (21) C ６－１４ (21) an arylsulfonyl group, (22) a 5- to 10-membered heteroarylsulfonyl group, (23) a 3- to 14-membered heterocyclylsulfonyl group, (24) an azido group, (25) a trisubstituted silyl group, (26) a trisubstituted silyloxy group, (27) a 5- to 10-membered heteroaryl group, and (28) a 3- to 14-membered heterocyclyl group. Among these, halogen, cyano, hydroxy, amino, C １－６ Alkoxy, C １－６ Alkyl-carbonyl, C １－６ Alkoxy-carbonyl, C ６－１０ An aryl, carbamoyl, sulfamoyl or 5- to 10-membered heteroaryl group is preferred. When a plurality of substituents are present, the respective substituents may be the same or different.

[0048] The above-mentioned substituents may be further substituted with the above-mentioned substituents. The number of substituents is not particularly limited as long as it is a substitutable number, but is preferably 1 to 5, more preferably 1 to 3. When a plurality of substituents are present, the respective substituents may be the same or different.

[0049] In this specification, "C １－６ Unless otherwise specified, the term "alkoxy group" refers to a straight-chain or branched-chain alkoxy group having 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, or tert-butoxy.

[0050] In this specification, "C ３－８ The term "cycloalkyl group" means a monocyclic saturated hydrocarbon ring group having 3 to 8 carbon atoms, and examples thereof include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and the like.

[0051] In this specification, "C ６－１４ The term "aryl group" refers to a monocyclic or polycyclic (fused) aromatic hydrocarbon group, and examples thereof include phenyl, naphthyl, anthryl, phenanthryl, acenaphthylenyl, biphenylyl, and the like. ６－１４ The "aryl group" may be condensed with another ring, and examples thereof include fluorenyl, dihydronaphthyl, and tetrahydronaphthyl. ６－１０ Aryl groups are preferred, with phenyl groups being particularly preferred.

[0052] In the present specification, the term "heteroaryl (group)" refers to an aromatic heterocycle (group), and examples thereof include 5- to 10-membered (preferably 5- or 6-membered) monocyclic heteroaryl groups and fused heteroaryl groups each containing, as ring-constituting atoms other than carbon atoms, 1 to 4 heteroatoms selected from oxygen atoms, sulfur atoms, and nitrogen atoms. Examples of the fused heteroaryl groups include groups derived from a ring corresponding to these 5- or 6-membered monocyclic heteroaryl groups fused with one or two rings selected from a 5- or 6-membered monocyclic heteroaryl ring containing one or two nitrogen atoms (e.g., pyrrole, imidazole, pyrazole, pyrazine, pyridine, pyrimidine, etc.), a 5-membered heteroaryl ring containing one sulfur atom (e.g., thiophene), and a benzene ring.

[0053] Preferable examples of the heteroaryl group include 5- or 6-membered monocyclic heteroaryl groups such as furyl, thienyl, pyridyl, pyrimidinyl, pyridazinyl, pyrazinyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, oxadiazolyl, thiadiazolyl, triazolyl, tetrazolyl, and triazinyl; Examples thereof include 8- to 10-membered fused heteroaryl groups such as quinolyl, isoquinolyl, quinazolyl, quinoxalyl, benzofuranyl, benzothienyl, benzoxazolyl, benzisoxazolyl, benzothiazolyl, benzimidazolyl, benzotriazolyl, indolyl, indazolyl, carbazolyl, pyrrolopyrazinyl, imidazopyridyl, thienopyridyl, imidazopyrazinyl, pyrazolopyridyl, pyrazolothienyl, pyrazolotriazinyl, pyridopyridyl, and thienopyridyl.

[0054]

[0023] In the present specification, the term "heterocyclyl (group)" refers to a non-aromatic heterocycle (group), and examples thereof include 3- to 8-membered (preferably 5- or 6-membered) monocyclic heterocyclyl groups and fused heterocyclyl groups, and 7- to 14-membered bridged heterocyclyl groups, each containing, in addition to carbon atoms, 1 to 4 heteroatoms selected from oxygen, sulfur, and nitrogen atoms as ring-constituting atoms. Examples of the fused heterocyclyl groups include groups derived from rings formed by fusing a ring corresponding to these 3- to 8-membered monocyclic heterocyclyl groups with one or two rings selected from a 5- or 6-membered monocyclic heteroaryl ring containing one or two nitrogen atoms (e.g., pyrrole, imidazole, pyrazole, pyrazine, pyridine, pyrimidine, etc.), a 5-membered monocyclic heteroaryl ring containing one sulfur atom (e.g., thiophene), and a benzene ring, as well as groups obtained by partial saturation of such groups.

[0055] Preferable examples of the heterocyclyl group include 3- to 7-membered monocyclic heterocyclyl groups such as aziridinyl, azetidinyl, pyrrolidinyl, piperidyl, morpholinyl, thiomorpholinyl, piperazinyl, hexamethyleneiminyl, oxazolidinyl, thiazolidinyl, imidazolidinyl, oxazolinyl, thiazolinyl, imidazolinyl, dioxolyl, dioxolanyl, dihydrooxadiazolyl, pyranyl, tetrahydropyranyl, thiopyranyl, tetrahydrothiopyranyl, tetrahydrofuryl, pyrazolidinyl, pyrazolinyl, tetrahydropyrimidinyl, dihydrotriazolyl, and tetrahydrotriazolyl; 9- to 14-membered fused heterocyclyl groups such as dihydroindolyl, dihydroisoindolyl, dihydrobenzofuranyl, dihydrobenzodioxenyl, dihydrobenzodioxepinyl, tetrahydrobenzofuranyl, chromenyl, dihydrochromenyl, dihydroquinolyl, tetrahydroquinolyl, dihydroisoquinolyl, tetrahydroisoquinolyl, dihydrophthalazinyl, and the like; and the like.

[0056]

[0033] In the present specification, examples of the "7- to 14-membered bridged heterocyclyl group" include quinuclidinyl, 7-azabicyclo[2.2.1]heptanyl and the like.

[0057] As used herein, the term "tri-substituted silyl group" refers to a group having three identical or different substituents (e.g., C １－６ Alkyl group, C ６－１４ The term "silyl group substituted with a silyl group" refers to a silyl group substituted with a trialkylsilyl group (preferably a triC group) such as a trimethylsilyl group, a triethylsilyl group, a triisopropylsilyl group, or a tert-butyldimethylsilyl group. １－６ alkylsilyl group), tert-butyldiphenylsilyl group, triphenylsilyl group, etc. are preferred.

[0058] In this specification, the term "tri-substituted silyloxy group" refers to a group in which a tri-substituted silyl group is bonded to an oxygen atom. Examples of such a group include a trimethylsiloxy group, a triethylsiloxy group, a triisopropylsiloxy group, and a tert-butyldimethylsiloxy group.

[0059] As used herein, the term "amino group optionally substituted with a protecting group" refers to an amino group in which one or two hydrogen atoms of the amino group may be substituted with a "protecting group." As the "protecting group," for example, the amino protecting groups described in "Protective Groups in Organic Synthesis" by P.G. Wuts, 5th Edition, Wiley, 2014, can be used. Specific examples of the amino protecting group include methyl, acetyl, trifluoroacetyl, pivaloyl, benzoyl, tert-butoxycarbonyl, benzyloxycarbonyl, etc.

[0060] In this specification, the term "structural unit derived from a styrene derivative" refers to a structural unit formed by polymerization of the carbon-carbon double bond of a styrene derivative which may be substituted with one or more substituents other than an amidino group or a cyclic amidino group (for example, a hydroxy group, a sulfanyl group, an amino group, a polyethylene glycol (PEG) group, a triethylene glycol (TEG) group, an alkyl group, etc.). The "structural unit derived from a styrene derivative" may be composed of only one type of styrene derivative, or may be composed of two or more types of styrene derivatives. By selecting the substituents of the styrene derivative, it is possible to adjust the swelling degree of the polymer of the present invention as needed.

[0061] In this specification, "structural units derived from acrylic acid derivatives" refers to structural units formed by polymerization of carbon-carbon double bonds of acrylic acid derivatives (for example, acrylic acid esters, acrylonitrile, acrylamide, methacrylic acid esters, methacrylic acid amides, etc.). The "structural units derived from acrylic acid derivatives" may be composed of only one type of acrylic acid derivative, or may be composed of two or more types of acrylic acid derivatives. Among these, structural units derived from acrylic acid derivatives represented by formula (3):

[0062]

[0063] wherein R is a group represented by the following formula:

[0064]

[0065] (In the formula, the wavy line indicates the bonding position with the main chain, and R ４ is C １－６ represents an alkyl group, and n represents an integer of 1 to 10.) and R′ represents a hydrogen atom or a methyl group.] is preferred.

[0066] In this specification, the term "structural unit derived from a diacrylic acid derivative" refers to a crosslinkable structural unit formed by polymerization of two carbon-carbon double bonds of a diacrylic acid derivative.

[0067] In this specification, examples of the "diacrylic acid derivative" include di(meth)acrylates such as methylene di(meth)acrylate, ethylene di(meth)acrylate, propylene di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropyleneethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, and nonanediol di(meth)acrylate; methylene di(meth)acrylamide, ethylene di(meth)acrylamide, propylene di(meth)acrylamide, ethylene glycol Examples of suitable di(meth)acrylamide include diethylene glycol di(meth)acrylamide, triethylene glycol di(meth)acrylamide, tetraethylene glycol di(meth)acrylamide, polyethylene glycol di(meth)acrylamide, propylene glycol di(meth)acrylamide, dipropyleneethylene glycol di(meth)acrylamide, tripropylene glycol di(meth)acrylamide, polypropylene glycol di(meth)acrylamide, butanediol di(meth)acrylamide, hexanediol di(meth)acrylamide, nonanediol di(meth)acrylamide, etc. The "structural unit derived from a diacrylic acid derivative" may be composed of only one type of diacrylic acid derivative, or may be composed of two or more types of diacrylic acid derivatives.

[0068] In this specification, the term "structural unit derived from a vinyl derivative" refers to a structural unit formed by polymerization of the carbon-carbon double bond of a vinyl derivative (for example, vinyl halide, N-vinylamides, vinyl ethers, vinylidene halide, α-olefins, etc.). The "structural unit derived from a vinyl derivative" may be composed of only one type of vinyl derivative, or may be composed of two or more types of vinyl derivatives.

[0069] In this specification, the term "α-olefins" refers to alkenes in which the carbon-carbon double bond is at the α-position, that is, at the terminal.

[0070] In this specification, "structural units derived from 1,3-diene derivatives" refers to crosslinkable structural units formed by polymerization of the carbon-carbon double bonds of 1,3-diene derivatives (for example, 1,3-butadiene, isoprene, chloroprene, etc.). The "structural units derived from 1,3-diene derivatives" may be composed of only one type of 1,3-diene derivative, or may be composed of two or more types of 1,3-diene derivatives.

[0071] In the present specification, the "polymerization initiator" is not particularly limited, but is preferably a compound that generates radical species when heated. Specific examples thereof include azo compounds such as 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 2-(carbamoylazo)isobutyronitrile; dibenzoyl peroxide, dilauroyl peroxide, distearoyl peroxide, and 1,1-di(tert-butylperionitrile). Examples of peroxides include 1,1-di(tert-hexylperoxy)-2-methylcyclohexane, 1,1-di(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-hexylperoxy)cyclohexane, 1,1-di(tert-butylperoxy)cyclohexane, di-tert-hexyl peroxide, tert-butylcumyl peroxide, di-tert-butyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, and tert-butylperoxyisopropyl monocarbonate. Among these, ADVN and AIBN are preferred. The amount of polymerization initiator to be added is not particularly limited, and a person skilled in the art can select an appropriate amount.

[0072] (Polymer of the Invention) The polymer of the invention is a polymer represented by formula (1):

[0073]

[0074] [In the formula, R １ and R ２ each independently represents a hydrogen atom or an optionally substituted alkyl group, or R １ and R ２ are bonded to each other to form, together with the nitrogen atom to which they are attached, an optionally substituted 5- to 8-membered ring; and R ３represents a hydrogen atom or an optionally substituted alkyl group.] and a repeating structural unit (1) represented by formula (2):

[0075]

[0076] The polymer contains repeating units (2) represented by the following formula (1): wherein the repeating units are contained randomly or in blocks.

[0077] Each group in the repeating structural unit (1) (i.e., formula (1)) of the polymer of the present invention will be explained below.

[0078] R １ and R ２ represents a hydrogen atom or an optionally substituted alkyl group, or R １ and R ２ are bonded to each other and together with the nitrogen atom to which they are attached form an optionally substituted 5- to 8-membered ring.

[0079] R １ and R ２ are preferably each independently a hydrogen atom or C １－４ It is preferably an alkyl group, more preferably each independently a hydrogen atom or a methyl group, and particularly preferably both are hydrogen atoms.

[0080] R １ and R ２ Another preferred embodiment of R １ and R ２ are bonded to each other and, together with the nitrogen atom to which they are bonded, form an optionally substituted 5- or 6-membered ring (e.g., imidazoline or 1,4,5,6-tetrahydropyrimidine), more preferably an unsubstituted imidazoline.

[0081] R ３ represents a hydrogen atom or an optionally substituted alkyl group.

[0082] R ３ is preferably a hydrogen atom or C １－４ It is an alkyl group, more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom.

[0083] As the structural unit (1), the following are preferred.

[0084] [Structural unit (1A)] R １ and R ２ are each independently a hydrogen atom or C １－４ is an alkyl group; and R ３ is a hydrogen atom or C １－４ The structural unit (1) is an alkyl group.

[0085] [Structural unit (1B)] R １ and R ２ are joined to each other, together with the nitrogen atom to which they are attached, to form an optionally substituted 5- or 6-membered ring (e.g., imidazoline or 1,4,5,6-tetrahydropyrimidine); and R ３ is a hydrogen atom or C １－４ The structural unit (1) is an alkyl group.

[0086] [Structural unit (1C)] R １ and R ２ are each independently a hydrogen atom or a methyl group; and R ３ is a hydrogen atom or a methyl group.

[0087] [Structural unit (1D)] R １ and R ２ are joined together to form, together with the nitrogen atom to which they are attached, an imidazoline or a 1,4,5,6-tetrahydropyrimidine; and R ３ is a hydrogen atom or a methyl group.

[0088] [Structural unit (1E)] R １ and R ２ are both hydrogen atoms; and R ３ is a hydrogen atom.

[0089] [Structural unit (1F)] R １ and R ２ are bonded to each other and together with the nitrogen atom to which they are attached form an imidazoline; and R ３ is a hydrogen atom.

[0090] The monomer corresponding to the structural unit (1) used in the method for producing the polymer of the present invention described below is represented by the formula (I):

[0091]

[0092] wherein each symbol has the same meaning as defined above.] (hereinafter referred to as compound (I)).

[0093] Suitable compounds (I) include monomer compounds in which the groups in the formula (I) correspond to the groups shown in the structural units (1A), (1B), (1C), (1D), (1E), and (1F). Only one type of compound (I) may be used, or two or more types may be used in combination.

[0094] Particularly preferred specific examples of compound (I) include compound (I-1) and compound (I-2) described in the examples below.

[0095] The structural unit (2) is represented by the formula (2):

[0096]

[0097] Among these, examples of the structural unit (2) include repeating structural units represented by the following formula (2A):

[0098] or the following formula (2B):

[0099]

[0100] The repeating structural unit (2) represented by the following formula is preferred.

[0101] The monomer corresponding to the structural unit (2) used in the method for producing the polymer of the present invention described below is represented by the formula (II):

[0102]

[0103] The compound is represented by the formula (hereinafter referred to as compound (II)).

[0104] Suitable examples of compound (II) include monomer compounds corresponding to the structural unit (2A) or structural unit (2B) described above. As compound (II), a single compound may be used, or two or more compounds may be used in combination.

[0105] A particularly preferred specific example of compound (II) is p-divinylbenzene or m-divinylbenzene, and specific examples include a mixture of p-divinylbenzene and m-divinylbenzene (compound (II-1)), which is a commercially available product used in the examples described later.

[0106] The polymer of the present invention is preferably a random copolymer comprising the structural unit (1) and the structural unit (2).

[0107] When the polymer of the present invention is composed of the structural unit (1) and the structural unit (2), the amount of the structural unit (1) is 50 to 99 mol %, preferably 70 to 97 mol %, and more preferably 80 to 95 mol %, relative to 100 mol % of the total amount of all structural units, in order to maintain high absorption capacity as a carbon dioxide absorbent in seawater.

[0108] When the polymer of the present invention is composed of the structural unit (1) and the structural unit (2), the amount of the structural unit (2) is 1 to 50 mol %, preferably 3 to 30 mol %, and more preferably 5 to 20 mol %, relative to 100 mol % of the total amount of all structural units, in order to improve affinity for water.

[0109] The polymer of the present invention can have its affinity for water and carbon dioxide absorption capacity adjusted by adjusting the ratio of each structural unit.

[0110] The polymer of the present invention may contain repeating structural units other than the structural units (1) and (2) in order to adjust the degree of swelling, etc., as necessary, within a range that does not impair its carbon dioxide absorption capacity. The content of structural units other than the structural units (1) and (2) is preferably 63 mol % or less, relative to 100 mol % as the total amount of all structural units of the polymer of the present invention.

[0111] The structural units other than the structural units (1) and (2) are not particularly limited, but for example, the above-mentioned structural units derived from styrene derivatives, structural units derived from acrylic acid derivatives, structural units derived from diacrylic acid derivatives, structural units derived from vinyl derivatives, structural units derived from 1,3-diene derivatives, etc. are preferably used. As the structural units other than the structural units (1) and (2), structural units derived from acrylic acid derivatives are preferred, and are represented by the formula (3):

[0112]

[0113] wherein R is a group represented by the following formula:

[0114]

[0115] (In the formula, the wavy line indicates the bonding position with the main chain, and R ４ is C １－６ represents an alkyl group, and n represents an integer of 1 to 10.) and R′ represents a hydrogen atom or a methyl group.] is more preferred.

[0116] The structural unit (3) is represented by the following formula (3A):

[0117]

[0118] , the following formula (3B):

[0119]

[0120] , the following formula (3C):

[0121]

[0122] , or the following formula (3D):

[0123]

[0124] The repeating structural unit (3) represented by the following formula is particularly preferred.

[0125] The monomer corresponding to the structural unit (3) used in the method for producing the polymer of the present invention described below is a monomer represented by the formula (III):

[0126]

[0127] [wherein each symbol has the same meaning as defined above] (hereinafter referred to as compound (III)).

[0128] Suitable examples of the compound (III) include the monomer compounds corresponding to the structural units (3A) to (3D) described above. As the compound (III), one type may be used alone, or two or more types may be used in combination.

[0129] Particularly preferred specific examples of compound (III) include, for example, commercially available products used in the examples described below: methyl methacrylate (III-1), acrylamide (III-2), and N,N-dimethylacrylamide (III-3), and poly(ethylene glycol) monomethyl ether monomethacrylate (III-4).

[0130] When the polymer of the present invention is composed of the structural unit (1), the structural unit (2), and the structural unit (3), the amount of the structural unit (1) is 35 to 96 mol %, and preferably 40 to 92 mol %, relative to 100 mol % of the total amount of all structural units, in order to maintain high absorption capacity as a carbon dioxide absorbent in seawater.

[0131] When the polymer of the present invention is composed of the structural unit (1), the structural unit (2), and the structural unit (3), the amount of the structural unit (2) is 2 to 63 mol %, and preferably 4 to 56 mol %, relative to 100 mol % of the total amount of all structural units, in order to improve affinity for water.

[0132] When the polymer of the present invention is composed of the structural unit (1), the structural unit (2), and the structural unit (3), the amount of the structural unit (3) is 2 to 63 mol %, and preferably 4 to 56 mol %, relative to 100 mol % of the total amount of all structural units, in order to improve affinity for water.

[0133] The molecular weight of the polymer of the present invention is not particularly limited, but the weight average molecular weight (Mw) is preferably in the range of 10,000 to 1,000,000. The weight average molecular weight (Mw) can be measured using high temperature gel permeation chromatography (GPC) / size exclusion chromatography (SEC) and a refractive index (RI) detector.

[0134] The proportion of guanidino groups or cyclic guanidino groups supported per 1 g of polymer is, for example, about 5.2 meq / g (milliequivalents of guanidino groups or cyclic guanidino groups per 1 g of polymer) when structural units (1) and (2) are polymerized in a ratio of 10:1. In another embodiment, when structural units (1), (2), and (3) are polymerized in a ratio of 10:1:10, the proportion is about 2.0 to 3.5 meq / g (milliequivalents of guanidino groups or cyclic guanidino groups per 1 g of polymer). Here, the milliequivalents of guanidino groups or cyclic guanidino groups per 1 g of polymer (meq / g) correspond to the number of millimoles of guanidino groups or cyclic guanidino groups per 1 g of polymer.

[0135] (Method for Producing the Polymer of the Present Invention) The polymer of the present invention can be produced by thermal radical polymerization (radical suspension polymerization) of commercially available monomers, or the compound (I) and the compound (II), which are monomers produced according to the methods described in the Examples below or methods similar thereto, and, if necessary, other monomers such as the styrene derivatives, acrylic acid derivatives, diacrylic acid derivatives, vinyl derivatives, α-olefins, and 1,3-diene derivatives (preferably the compound (III)), in the presence of a polymerization initiator in a solvent that does not affect the reaction. The polymer of the present invention is obtained as a solid.

[0136] Examples of the polymerization initiator used in producing the polymer of the present invention include those mentioned above, with 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) or 2,2'-azobisisobutyronitrile (AIBN) being particularly preferred. The amount of the polymerization initiator added is not particularly limited, but when ADVN is used, for example, it is preferably 0.1 to 20 mol %, more preferably 0.5 to 10 mol %, and even more preferably 1 to 5 mol %, based on the total amount of all the monomers used.

[0137] The solvent used in producing the polymer of the present invention is not particularly limited, and solvents commonly used in the field of thermal radical polymerization can also be used in the present invention. Specific examples include ethers such as 1,4-dioxane, diethyl ether, and cyclopentyl methyl ether; amides such as dimethylformamide; nitriles such as acetonitrile; halogenated hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride; aromatic hydrocarbons such as benzene and toluene; water; and mixed solvents thereof, with water being preferred.

[0138] The temperature during the polymerization reaction is usually 60° C. to 120° C., preferably 65° C. to 90° C., more preferably 70° C. to 80° C. The reaction time is usually 1 to 24 hours.

[0139] (Carbon dioxide absorbent of the present invention and carbon dioxide absorption method using the same) Since the polymer of the present invention is obtained as a solid, the polymer can be used alone as a carbon dioxide absorbent in water or seawater. Furthermore, the carbon dioxide absorbent of the present invention may contain additives and the like in addition to the polymer of the present invention, or may be used in combination with other carbon dioxide absorbents.

[0140] In a carbon dioxide absorbent containing the polymer of the present invention, a substituted guanidino group or cyclic guanidino group contained in the polymer reacts with carbon dioxide in water or seawater to form a bicarbonate of a substituted guanidine or cyclic guanidine, thereby immobilizing carbon dioxide on the polymer of the present invention.

[0141] The carbon dioxide absorbent containing the polymer of the present invention is stable and easy to handle, and can be easily scaled up. Furthermore, recovery of the polymer after carbon dioxide absorption can be easily carried out by solid-liquid separation. Furthermore, since the polymer exhibits high carbon dioxide absorption capacity even in seawater, which is rich in various salts (cations, anions, etc.) in addition to carbon dioxide, it is expected that the absorbent will be suitable for use not only at a laboratory level as described in the test examples below, but also on a pilot scale in the ocean by a similar method.

[0142] By using the carbon dioxide absorbent of the present invention, it is possible to reduce the carbon dioxide concentration per unit volume in seawater to approximately 1 / 5 at maximum.

[0143] The carbon dioxide absorbent of the present invention can be used not only in water, particularly seawater, but also in waste liquids or waste gases containing high concentrations of carbon dioxide, or in the atmosphere.

[0144] (Method for Releasing Carbon Dioxide Absorbed (Immobilized) in the Carbon Dioxide Absorbent of the Present Invention) The bicarbonate of the polymer of the present invention, obtained by absorbing (immobilizing) carbon dioxide in a carbon dioxide absorbent containing the polymer of the present invention, can be easily regenerated by heating it in water (distilled water or seawater) at about 100 to 120°C according to or in accordance with the method described in Test Example 2 below, thereby easily releasing (desorbing) the immobilized carbon dioxide. The regenerated polymer of the present invention can be used again as a carbon dioxide absorbent in water, particularly seawater.

[0145] Generally, compared to conventional methods that require heating conditions at a high temperature of 900°C (specifically, conventional techniques that use an aqueous sodium hydroxide solution or an aqueous hydroxyethylamine solution as a carbon dioxide absorbent), the method for releasing carbon dioxide of the present invention uses the carbon dioxide again in water, particularly seawater, after releasing (desorbing) the carbon dioxide, so there is no need to remove water, and carbon dioxide can be released under extremely mild conditions, making it possible to regenerate the polymer of the present invention with high energy efficiency.

[0146] By repeatedly carrying out the above series of processes (the carbon dioxide absorption step (a carbon dioxide absorption method using the polymer of the present invention), the carbon dioxide generation step (a method for releasing carbon dioxide absorbed (immobilized) in the carbon dioxide absorbent of the present invention), and the regeneration step of the carbon dioxide absorbent of the present invention), it is possible to improve the efficiency of absorption of carbon dioxide from seawater, and to realize an environmentally friendly process that can significantly reduce the amount of external energy used when utilizing the absorbed and immobilized carbon dioxide.

[0147] The present invention will be explained in more detail below with reference to the following examples, examples, and test examples. However, the present invention is not limited to these examples, and may be changed within the scope of the present invention. % indicates mol / mol% for yield, and other values ​​indicate % by weight unless otherwise specified. Furthermore, room temperature indicates a temperature of 15°C to 30°C unless otherwise specified.

[0148] １ H (500MHz)-NMR, １３ C (125 MHz)-NMR spectra were measured on an AVANCE III 500 manufactured by Bruker BioSpin Inc. １ H and １３ Chemical shift values ​​for C-NMR spectra are referenced to tetramethylsilane. Chemical shifts are reported in δ ppm. IR spectra were measured on a Nicoleti STM5FT-IR (Thermo Scientific). High-resolution mass spectra were measured on a Bruker micrOTOF-Q mass spectrometer. TLC analysis was performed on a Merck Silicagel 60F. ２５４ The experiments were carried out on a commercially available glass plate with a 0.25 mm layer of CO ２ ​The concentration was measured using a CGP-31 (DKK-TOA Corporation) (closed space). The oil-free air compressor used was an SA2000S manufactured by SILENTAIR, and the mass flow controller used was an FCS-T1000L manufactured by Fujikin. The commercially available products used in the examples were potassium phthalimide (Tokyo Chemical Industry Co., Ltd.), 4-vinylbenzyl chloride (Tokyo Chemical Industry Co., Ltd.), divinylbenzene (Tokyo Chemical Industry Co., Ltd.), thiourea (Fujifilm Wako Pure Chemical Industries, Ltd.), ethylene thiourea (Tokyo Chemical Industry Co., Ltd.), iodomethane (Fujifilm Wako Pure Chemical Industries, Ltd.), hydrazine monohydrate (Tokyo Chemical Industry Co., Ltd.), and polystyrene resin (crosslinking agent: 1% divinylbenzene) (Tokyo Chemical Industry Co., Ltd.). The molecular sieve 4 Å powder and molecular sieve 3 Å powder (manufactured by Nacalai Tesque) used in the test examples were commercially available products that were dried at 130°C for 6 hours before use. All other reagents and solvents were purchased commercially and used as they were. ２ The seawater used in the absorption experiment was collected from the surface layer of Kobe Port.

[0149] Other abbreviations used in the text have the following meanings: THF: tetrahydrofuran CDCl ３ : deuterated chloroform DMSO-d ６ : deuterated dimethyl sulfoxide DMF: N,N-dimethylformamide MS: molecular sieves

[0150] Reference Example 1: Synthesis of 4-vinylbenzylamine (4)

[0151]

[0152] 4-Vinylbenzyl chloride (1) (28 mL, 200 mmol) was dissolved in DMF (200 mL) with potassium phthalimide (2) (37 g, 200 mmol) and potassium carbonate (K ２ CO ３) (33 g, 240 mmol), and the mixture was stirred at room temperature for 12 hours. Then, ethyl acetate / hexane and water were added to the reaction mixture, and the aqueous phase was separated and extracted with ethyl acetate. The combined organic phase was washed successively with water (3 x 100 mL) and saturated brine, dried over magnesium sulfate, filtered, and concentrated under reduced pressure using an evaporator. The residue was dried in vacuum at room temperature for 12 hours to obtain N-(4-vinylbenzyl)phthalimide (3):

[0153]

[0154] (45.4 g, 172 mmol, yield: 86%) was obtained as a white powder. 1 H NMR (500 MHz, CDCl3, 25℃): δ 4.83 (s, 2H), 5.22 (d, 1H, J cis = 10.9 Hz), 5.71 (d, 1H, J trans = 17.6 Hz), 6.67 (dd, 1H, J cis = 10.9 Hz, J trans = 17.6 Hz), 7.35 (d, 2H, J = 8.2 Hz), 7.40 (d, 2H, J = 8.0 Hz), 7.70-7.85 (m, 4H); 13 C NMR (125 MHz, CDCl3, 25℃): δ 41.5, 114.3, 123.5, 126.6, 129.0, 132.2, 134.1, 136.0, 136.4, 137.3, 168.2.

[0155] The obtained N-(4-vinylbenzyl)phthalimide (3) (26.3 g, 100 mmol), hydrazine monohydrate (12.7 mL, 400 mmol), and ethanol (200 mL) were placed in a 500 mL eggplant-shaped flask equipped with a stirrer and stirred overnight under reflux (70°C), after which the solvent was removed under reduced pressure. The residue was filtered through a glass filter and dried under vacuum at room temperature for 12 hours to obtain 4-vinylbenzylamine (4) (9.5 g, 71 mmol, yield: 71%) as a yellow oil. 1 H NMR (500 MHz, CDCl3, 25℃): δ 3.73 (s, 2H), 5.11 (dd, 1H, Jgem = 0.8 Hz, J cis = 10.9 Hz), 5.62 (dd, 1H, J gem = 0.8, J trans = 17.6 Hz), 6.60 (dd, 1H, J cis = 10.9 Hz, J trans = 17.6 Hz), 7.15 (d, 2H, J = 8.1 Hz), 7.27 (d, 2H, J = 8.2 Hz); 13 C NMR (125 MHz, CDCl3, 25℃): δ 46.3, 113.5, 126.4, 127.3, 136.3, 136.6, 143.0.

[0156] Reference Example 2: Synthesis of isothiouronium iodide (6)

[0157]

[0158] (The symbols in the formula are as defined above.)

[0159] According to the literature method (Aoyagi, N. et al., Synlett, 2014, 25(07), 983; Aoyagi, N. and Endo, T., Synth Commun., 2017, 47, 442.), a solution of methyl iodide (1.46 mL, 120 mmol) was added dropwise to a solution of thiourea (5) (100 mmol) in methanol (100 mL) at room temperature over approximately 5 minutes with stirring. The mixture was stirred at room temperature for 12 hours and then concentrated under reduced pressure using an evaporator. The residue was washed with diethyl ether (3 × 50 mL), filtered, and dried under vacuum at room temperature to obtain the isothiouronium iodide derivative (6).

[0160] (1) As the thiourea (5), compound (5a) (in the above formula 5, R １ , R ２ and R ３ are all hydrogen atoms), S-methylisothiouronium iodide (6a):

[0161]

[0162] was obtained as a pale yellow powder (20.7 g, 95 mmol, 95%). 1 H NMR (500 MHz, DMSO-d6, 25℃): δ 8.88 (brs, 4H), 2.56 (s, 3H); 13 C NMR (125 MHz, DMSO-d6, 25℃): δ 13.4, 171.1.

[0163] (2) As the thiourea (5), compound (5b) (in the above formula 5, R ３ is a hydrogen atom, and R １ and R ２ together form a bond to form a dihydroimidazole ring with the nitrogen atom to which they are attached), 2-methylthio-4,5-dihydro-1H-imidazole hydroiodide (6b):

[0164]

[0165] was obtained as a white powder (22.0 g, 90 mmol, 90%). 1 H NMR (500 MHz, DMSO-d6, 25℃): δ 2.62 (s, 3H), 3.86 (s, 4H), 9.98 (brs, 2H); 13 C NMR (125 MHz, DMSO-d6, 25℃): δ 13.5, 45.2, 170.5.

[0166] Reference Example 3: Synthesis of 4-vinylbenzylguanidine (I)

[0167]

[0168] (The symbols in the formula are as defined above.)

[0169] According to the method described in the literature (Aoyagi, N. et al., Synlett, 2014, 25(07), 983; Aoyagi, N. and Endo, T., Synth Commun., 2017, 47, 442), 4-vinylbenzylamine (4) (100 mmol) synthesized in Reference Example 1, isothiouronium iodide (6) (100 mmol) synthesized in Reference Example 2, and THF (100 mL) were placed in a flask (200 mL) equipped with a stirrer, and the mixture was stirred overnight under reflux (70°C). The solvent was removed from the reaction mixture under reduced pressure. The residue was washed with diethyl ether and dried under vacuum at room temperature. The resulting solid was then neutralized with aqueous sodium hydroxide (40 wt%) to obtain 4-vinylbenzylguanidine (I).

[0170] (1) When S-methylisothiouronium iodide (6a) obtained in Reference Example 2(1) was used as isothiouronium iodide (6), 4-vinylbenzylguanidine (I-1):

[0171]

[0172] was obtained as a white powder (yield: 72%). 1 H NMR (500 MHz, CDCl3, 25℃): δ 4.21(s, 2H), 5.22 (d, 1H, J cis = 10.9 Hz), 5.72 (d, 1H, J trans = 17.6 Hz), 6.68 (dd, 1H, J cis = 10.9 Hz, J trans = 17.6 Hz), 7.24 (d, 2H, J = 8.0 Hz), 7.35 (d, 2H, J = 8.1 Hz); 13 C NMR (125 MHz, CDCl3, 25℃): δ 46.3, 77.4, 113.9, 126.6, 127.6, 136.5, 136.8, 138.5.

[0173] (2) When 2-methylthio-4,5-dihydro-1H-imidazole hydroiodide (6b) obtained in Reference Example 2(2) was used as isothiouronium iodide (6), 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2):

[0174]

[0175] was obtained as a white powder (yield: 77%). 1 H NMR (500 MHz, CDCl3, 25℃): δ 3.50 (s, 4H), 4.31 (s, 2H), 5.22 (dd, 1H, J gem = 0.7 Hz, J cis = 10.9 Hz), 5.71 (dd, 1H, J gem = 0.8, J trans = 17.6 Hz), 6.68 (dd, 1H, J cis = 10.9 Hz, J trans = 17.6 Hz), 7.25 (d, 2H, J = 8.5 Hz), 7.35 (d, 2H, J = 8.1 Hz); 13 C NMR (125 MHz, CDCl3, 25℃): δ 47.5, 77.36, 133.8, 126.5, 127.72, 136.54, 136.7, 139.1, 161.7.

[0176] Example 1: Synthesis of guanidino group-containing polystyrene (compound (1-1)) An aqueous solution of acacia gum (6.3 g) and sodium chloride (7.9 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 4-vinylbenzylguanidine (I-1) (20 mmol) obtained in Reference Example 3(1), divinylbenzene (II-1) (2 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (0.27 mmol) were added, and the mixture was stirred at 70°C for 18 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 60°C for 12 hours to obtain compound (1-1) (2.3 g, yield: 60%) as a pale yellow bead-like solid. IR (ATR): 3340, 2918, 1683, 1653, 1559, 1457, 1322 cm -1

[0177] Example 2: Synthesis of cyclic guanidino group-containing polystyrene (compound (1-2)) An aqueous solution of acacia gum (6.3 g) and sodium chloride (7.9 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) (20 mmol) obtained in Reference Example 3(2), divinylbenzene (II-1) (2 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (0.27 mmol) were added, and the mixture was stirred at 70°C for 18 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 60°C for 12 hours to obtain compound (1-2) (3.0 g, yield: 69%) as a pale yellow bead-like solid. IR (ATR): 3293, 2919, 1663, 1654, 1559, 1508, 1457, 1285 cm -1

[0178] Example 3: Synthesis of cyclic guanidino group-containing copolymer (compound (1-3)) An aqueous solution (30 mL) of gum acacia (0.45 g) and sodium chloride (1.35 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) (15 mmol) obtained in Reference Example 3(2), divinylbenzene (II-1) (0.2 g; 1.5 mmol), methyl methacrylate (III-1) (1.6 mL; 15 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (74.5 mg; 0.3 mmol) were added, and the mixture was stirred under a nitrogen atmosphere at 70°C for 18 hours. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 40°C for 12 hours to obtain compound (1-3) (4.48 g, yield: 94%) as a pale yellow solid. IR (ATR): 3648, 3177, 1670, 1558, 1507, 1287 cm -1

[0179] Example 4: Synthesis of cyclic guanidino group-containing copolymer (compound (1-4)) An aqueous solution (30 mL) of gum acacia (0.45 g) and sodium chloride (1.35 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) (15 mmol) obtained in Reference Example 3(2), divinylbenzene (II-1) (0.2 g; 1.5 mmol), acrylamide (III-2) (1.07 g; 15 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (74.5 mg; 0.3 mmol) were added, and the mixture was stirred at 70°C for 18 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 40°C for 12 hours to obtain compound (1-4) (2.76 g, yield: 64%) as a pale yellow solid. IR (ATR): 1653, 1569, 1558, 1395 cm -1

[0180] Example 5: Synthesis of cyclic guanidino group-containing copolymer (compound (1-5)) An aqueous solution (18 mL) of gum acacia (0.27 g) and sodium chloride (0.81 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) (9 mmol) obtained in Reference Example 3(2), divinylbenzene (II-1) (0.12 g; 0.9 mmol), N,N-dimethylacrylamide (III-3) (0.89 g; 9 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (44.7 mg; 0.18 mmol) were added, and the mixture was stirred at 70°C for 18 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 40°C for 12 hours to obtain compound (1-5) (1.71 g, yield: 44%) as a pale yellow solid. IR (ATR): 2911, 1653, 1576, 1558, 1507, 1395 cm -1

[0181] Example 6: Synthesis of cyclic guanidino group-containing copolymer (compound (1-6)) An aqueous solution (30 mL) of gum acacia (0.45 g) and sodium chloride (1.35 g) was placed in a round-bottom flask equipped with a stirrer, and nitrogen gas was bubbled through for 30 minutes to deoxygenate the mixture. After deoxygenation, 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) (15 mmol) obtained in Reference Example 3(2), divinylbenzene (II-1) (0.2 g; 1.5 mmol), poly(ethylene glycol) monomethyl ether monomethacrylate (III-4) (n = 4) (3.9 mL; 15 mmol), and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) (74.5 mg; 0.3 mmol) were added, and the mixture was stirred at 70°C for 18 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered through a glass filter, washed successively with water, methanol, toluene, and THF, and dried under vacuum at 40°C for 12 hours to obtain compound (1-6) (5.15 g, yield: 69%) as a pale yellow solid. IR (ATR): 3157, 2892, 1670, 1558, 1457, 1398, 1287 cm -1

[0182] Example 7: Synthesis of cyclic guanidino group-containing copolymer (compound (1-7)) A suspension polymerization reaction was carried out under the same conditions as in Example 5, except that the amounts of 2-(4-vinylbenzylamino)-4,5-dihydro-1H-imidazole (I-2) were changed to 10 mmol, divinylbenzene (II-1) to 1 mmol, N,N-dimethylacrylamide (III-3) to 1 mmol, and 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) to 0.2 mmol. Compound (1-7) (2.49 g, yield: >99%) was obtained as a pale yellow solid. IR (ATR): 3689, 3156, 1868, 1663, 1541, 1507, 1287 cm -1

[0183] Test Example 1: CO in distilled water using the polymer and molecular sieve of the present invention ２Absorption experiment (Experimental procedure) (1) A stirrer and distilled water (50 mL) were added to a dedicated cell with a capacity of 50 mL, and a carbon dioxide gas concentration meter was immersed in the solution and allowed to stabilize for about 10 minutes. After numerical stabilization, the polymers of the present invention (compound (1-1), compound (1-2)), molecular sieve 3 Å powder, and molecular sieve 4 Å powder were added to separate cells, and the CO 2 in each cell was measured. ２ The amount of the polymer used in the present invention was calculated as the amino group equivalent of the CO concentration in the cell. ２ The amount of the molecular sieve powder used was 100 equivalents of the amount of the polymer of the present invention. The polymer of the present invention was vacuum dried at 60°C for about 12 hours before use to completely remove the solvent. (2) The amount was scaled up to 10 times the amount of (1) above, and a 500 ml Erlenmeyer flask was used instead of the dedicated cell with a capacity of 50 mL. The amount of the polymer of the present invention used was calculated based on the amount of CO in the cell in terms of amino groups. ２ The same procedure as in (1) above was followed except that the amount was 10 equivalents, and the polymer of the present invention (compound (1-2)) and molecular sieve 4 Å powder were added to CO 2 ２ The change in concentration was measured over time.

[0184] (Experimental Results) CO of each sample ２ The results of the change in concentration over time are shown in Table 1 (volume 50 mL), Table 2 (volume 500 mL), Figure 1a (volume 50 mL), and Figure 1b (volume 500 mL) below. Figure 1 confirms that in distilled water, the polymers of the present invention (compound (1-1) and compound (1-2)), molecular sieve 3 Å powder, and molecular sieve 4 Å powder all exhibit good carbon dioxide absorption capacity, and a similar tendency was observed when the experiment was scaled up.

[0185]

[0186]

[0187] Test Example 2: CO in seawater using the polymer and molecular sieve of the present invention ２Absorption experiment (experimental procedure) (1) A stirrer and seawater (50 mL) were added to a dedicated cell with a capacity of 50 mL, and a carbon dioxide gas concentration meter was immersed in the solution and allowed to stabilize for about 10 minutes. After numerical stabilization, the polymer of the present invention (compound (1-2)) and molecular sieve 4Å powder were added to separate cells, and the CO 2 concentration in each cell was measured. ２ The amount of the polymer used in the present invention was calculated as the amino group equivalent of the CO concentration in the cell. ２ The amount of the molecular sieve powder used was 100 equivalents of the amount of the polymer of the present invention. The polymer of the present invention was vacuum dried at 60°C for about 12 hours before use to completely remove the solvent. (2) The amount was scaled up to 10 times the amount of (1) above, and a 500 ml Erlenmeyer flask was used instead of the dedicated cell with a capacity of 50 mL. The amount of the polymer of the present invention used was calculated based on the amount of CO in the cell in terms of amino groups. ２ The same procedure as in (1) above was followed except that the amount was 10 equivalents, and the polymer of the present invention (compound (1-2)) and molecular sieve 4 Å powder were added to CO 2 ２ The change in concentration was measured over time.

[0188] (Experimental Results) CO of each sample ２ The results of the change in concentration over time are shown in Table 3 (volume 50 mL), Table 4 (volume 500 mL), Figure 2a (volume 50 mL), and Figure 2b (volume 500 mL) below. Figure 2 shows that in seawater, the molecular sieve 4 Å powder hardly absorbed carbon dioxide, while the polymer of the present invention (compound (1-2)) exhibited good carbon dioxide absorption capacity similar to that in distilled water. It was also confirmed that the polymer of the present invention can maintain good carbon dioxide absorption capacity even when scaled up.

[0189]

[0190]

[0191] Test Example 3: Experiment on carbon dioxide release from the polymer of the present invention (compound (1-2)) after carbon dioxide absorption under heating (100°C) (Experimental procedure) The polymer of the present invention (compound (1-2)) (2 g) that had absorbed carbon dioxide in Test Example 1 was placed in a two-necked flask (100 mL), and heated in an oil bath (100°C) while flowing nitrogen gas into the two-necked flask at a rate of 100 mL / min using a mass flow controller (MFC). ２ The concentration was measured over time. The same experiment was repeated twice.

[0192] (Experimental results) CO ２ The results of the change in concentration (ppm) over time are shown in Table 5 below and Fig. 3. As shown in Fig. 3, it was confirmed that the polymer of the present invention (compound (1-2)) that had absorbed carbon dioxide efficiently released carbon dioxide in a short period of time under heated conditions, and the polymer of the present invention was regenerated with good reproducibility.

[0193]

[0194] Test Example 4: CO2 emission in seawater using the polymers of the present invention (compounds (1-2), (1-3), (1-4), (1-5), and (1-6)) ２ Absorption experiment (Experimental procedure) A stirrer and seawater (50 mL) were added to a dedicated cell with a capacity of 50 mL, and a carbon dioxide gas concentration meter was immersed in the solution and allowed to stabilize for about 10 minutes. After numerical stabilization, the polymers of the present invention (i.e., Compound (1-2), Compound (1-3), Compound (1-4), Compound (1-5), or Compound (1-6)) were added to separate cells, and the CO in each cell was measured. ２ The amount of the polymer used in the present invention was calculated as the amino group equivalent of the CO concentration in the cell. ２ The polymer of the present invention was vacuum dried at 40° C. for about 12 hours before use to completely remove the solvent before use.

[0195] (Experimental Results) CO of each sample ２The results of the change in concentration over time are shown in Table 6 below and Fig. 4. As shown in Fig. 4, it was confirmed that all of the polymers of the present invention exhibited good carbon dioxide absorption capacity in seawater. Among them, it was confirmed that compound (1-5) exhibited high carbon dioxide absorption capacity.

[0196]

[0197] Test Example 5: CO2 emission in seawater using the polymer of the present invention (compound (1-2) or compound (1-7)) ２ Absorption experiment (experimental procedure) A stirrer and seawater (500 mL) were added to a 500 mL Erlenmeyer flask, and a carbon dioxide gas concentration meter was immersed in the solution and allowed to stabilize for about 10 minutes. After numerical stabilization, 1 g of the polymer of the present invention (i.e., compound (1-2) or compound (1-7)) was added to each separate cell, and the CO 2 concentration in each cell was measured. ２ The amount of the polymer used in the present invention was calculated as the amino group equivalent of the CO concentration in the cell. ２ The polymer of the present invention was vacuum dried at 40° C. for about 12 hours before use to completely remove the solvent before use.

[0198] (Experimental Results) CO of each sample ２ The results of the change in concentration over time are shown in Table 7 below and Figure 5. Figure 5 confirms that in seawater, the polymers of the present invention can all maintain good carbon dioxide absorption capacity even when scaled up.

[0199]

[0200] Test Example 6: Experiment on carbon dioxide release from the polymer of the present invention (compound (1-2) or compound (1-7)) after carbon dioxide absorption under heating (100°C) (Experimental procedure) The compound (1-2) that had absorbed carbon dioxide in Test Example 2 or the compound (1-7) (1 g) that had absorbed carbon dioxide in Test Example 5 was placed in a two-necked flask (100 mL), and heated in an oil bath (100°C) while flowing nitrogen gas into the two-necked flask at a rate of 40 mL / min using a mass flow controller (MFC). ２ The concentration was measured over time and recorded every 30 seconds. A schematic diagram of the apparatus used for the carbon dioxide release experiment is shown in Figure 6.

[0201] (Experimental results) CO ２ The results of the change in concentration (ppm) over time are shown in Table 8 below and Fig. 7. As shown in Fig. 7, it was confirmed that the polymer of the present invention (compound (1-2) or compound (1-7)) that had absorbed carbon dioxide efficiently released carbon dioxide in a short period of time under heated conditions, and the polymer of the present invention was regenerated with good reproducibility.

[0202]

[0203] The carbon dioxide absorbent of the present invention is easy to synthesize, stable and easy to handle even in water, particularly seawater containing various salts, and has a high carbon dioxide absorption capacity. Therefore, it has the advantage of being able to efficiently absorb and immobilize carbon dioxide, even at room temperature and atmospheric pressure, even when carbon dioxide is diluted and present in the ocean at low concentrations. Furthermore, the carbon dioxide absorbent of the present invention not only facilitates recovery after immobilization of carbon dioxide, but also allows the immobilized carbon dioxide to be released under mild conditions and effectively utilized as a carbon source. Therefore, the present invention can provide a novel and effective method for direct ocean capture (DOC).

[0204] This application is based on Japanese Patent Application No. 2024-030458 filed on February 29, 2024 in Japan, the contents of which are incorporated in their entirety herein.

Claims

1. Formula (1): [In the formula, R １ and R ２ each independently represents a hydrogen atom or an optionally substituted alkyl group, or R １ and R ２ are bonded to each other to form, together with the nitrogen atom to which they are attached, an optionally substituted 5- to 8-membered ring; and R ３ represents a hydrogen atom or an optionally substituted alkyl group.] and a repeating structural unit (1) represented by formula (2): A polymer comprising a repeating structural unit (2) represented by the following formula: wherein each repeating unit is contained randomly or in blocks.

2. The polymer of claim 1, wherein the polymer consists of repeating structural units (1) and repeating structural units (2).

3. R １ , R ２ and R ３ The polymer according to claim 1 or 2, wherein each of is independently a hydrogen atom or a methyl group.

4. R １ and R ２ are linked to each other together with the nitrogen atoms to which they are attached to form an imidazoline or a 1,4,5,6-tetrahydropyrimidine.

5. The polymer has the formula (3): wherein R is a group represented by the following formula: (In the formula, the wavy line indicates the bonding position with the main chain, and R ４ is C １－６ and n is an integer of 1 to 10. ), and R' is a hydrogen atom or a methyl group.

6. R １ , R ２ and R ３ and each independently represent a hydrogen atom or a methyl group.

7. R １ and R ２ are linked to each other together with the nitrogen atoms to which they are attached to form an imidazoline or a 1,4,5,6-tetrahydropyrimidine.

8. The polymer according to any one of claims 5 to 7, which is a random copolymer in which, of all structural units of the polymer, the repeating structural unit (1) accounts for 35 to 96 mol%, the repeating structural unit (2) accounts for 2 to 63 mol%, and the repeating structural unit (3) accounts for 2 to 63 mol%.

9. A carbon dioxide absorbent containing the polymer according to any one of claims 1 to 8.

10. The carbon dioxide absorbent according to claim 9, for absorbing carbon dioxide in seawater.

11. Formula (I): [wherein each symbol has the same meaning as defined above], and a compound represented by formula (II):

2. A method for producing a polymer according to claim 1, characterized by reacting a compound represented by the following formula (I) with a polymerization initiator under heating.

12. The method of claim 8, wherein the polymerization initiator is 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) or azobisisobutyronitrile (AIBN).

13. Formula (I): [wherein each symbol has the same meaning as defined above], a compound represented by formula (II): and a compound represented by formula (III): The method for producing a polymer according to claim 5, characterized in that a compound represented by the formula: wherein each symbol has the same meaning as defined above is reacted with a polymerization initiator under heating.

14. The method of claim 13, wherein the polymerization initiator is 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) or azobisisobutyronitrile (AIBN).

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