Modified polyalkyleneimine, and carbon dioxide absorbent

Abstract

Provided is a modified polyalkyleneimine that exhibits an excellent durability and an excellent carbon dioxide adsorption / desorption capability.　The modified polyalkyleneimine has a structural unit (I) derived from a polyalkyleneimine and has a substituent (A) represented by general formula (1). The molar ratio [substituent (A) / primary amino group in the structural unit (I)] of the substituent (A) to the primary amino group contained in the structural unit (I) in the modified polyalkyleneimine is not greater than 20 / 80.　(1) *– CH2 – CH ( – R1) – X (In general formula (1), X represents a monovalent group having 1 to 30 carbons, a nitro group, or a halogen atom; R1 represents a hydrogen atom or methyl group; and the * (asterisk) denotes a direct bond to a nitrogen atom contained in an amino group in the structural unit (I).)

Description

Modified polyalkyleneimine and carbon dioxide absorbent

[0001] The present invention relates to a modified polyalkyleneimine. The present invention also relates to a carbon dioxide absorbent using the modified polyalkyleneimine.

[0002] In recent years, a technology called DAC (Direct Air Capture) has been considered as a technology for achieving carbon neutrality. This technology involves capturing dilute carbon dioxide in the atmosphere using a carbon dioxide absorbent, thereby concentrating and fixing the carbon dioxide in the absorbent. The fixed carbon dioxide can then be desorbed (desorbed) from the absorbent by heating, depressurizing, or the like, so that the carbon dioxide captured from the atmosphere can be stored underground or used as a raw material for chemicals, etc.

[0003] Various chemicals have been investigated as such carbon dioxide absorbents, and one example is one that uses polyethyleneimine. However, it is known that such polyethyleneimine usually requires heating at around 100°C to desorb the fixed carbon dioxide. For this reason, modified polyethyleneimine in which a specific vinyl group-containing compound is added to the amino group of polyethyleneimine has been investigated, with the aim of shifting the desorption temperature to a lower temperature and proceeding with the desorption process with less energy (Patent Document 1).

[0004] International Publication No. 2023 / 237579

[0005] However, when using a carbon dioxide adsorbent using the modified polyethyleneimine disclosed in Patent Document 1, the addition rate of the vinyl group-containing compound to the amino group of the polyethyleneimine is high, which causes a problem that the amount of carbon dioxide adsorption itself is reduced, resulting in poor carbon dioxide adsorption and desorption ability. Furthermore, the durability of the modified polyalkyleneimine against deterioration factors such as heating and oxidation has not been fully investigated.

[0006] Therefore, an object of the present invention is to provide a modified polyalkyleneimine having excellent carbon dioxide adsorption / desorption ability and durability. Another object of the present invention is to provide a carbon dioxide absorbent containing the modified polyalkyleneimine.

[0007] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that a modified polyalkyleneimine having a structure in which some of the amino groups in the structural units derived from polyalkyleneimine are modified with substituents has excellent carbon dioxide adsorption / desorption ability and durability.

[0008] Furthermore, the present inventors have found that modified polyalkyleneimines, which have a structure in which some of the amine hydrogens in the structural units derived from polyalkyleneimines are substituted with substituents, have excellent carbon dioxide adsorption / desorption ability and durability. The present invention was completed based on these findings.

[0009] That is, the present invention provides a modified polyalkyleneimine having a structural unit (I) derived from a polyalkyleneimine and a substituent (A) represented by the following general formula (1): wherein the molar ratio of the substituent (A) to the primary amino group contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / primary amino group in the structural unit (I)] is 20 / 80 or less. ２ -CH(-R １ )-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) directly bonds to the nitrogen atom contained in the amino group in the structural unit (I).

[0010] The present invention also provides a modified polyalkyleneimine having a structural unit (I) derived from a polyalkyleneimine and a substituent (A) represented by the following general formula (1): wherein the molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / amine hydrogen in structural unit (I)] is 7 / 93 or less. ２ -CH(-R１ )-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) directly bonds to the nitrogen atom contained in the amino group in the structural unit (I).

[0011] The above X preferably includes at least one selected from the group consisting of a cyano group, an amide group, a salt of a carboxyl group, an N-alkylamide group, and an N-dialkylamide group.

[0012] The number average molecular weight of the structural unit (I) is preferably 250 to 3,000.

[0013] The structural unit (I) preferably has a structural unit derived from polyethyleneimine.

[0014] The present invention also provides a carbon dioxide absorbent containing the modified polyalkyleneimine.

[0015] The carbon dioxide absorbent preferably includes a carrier and the modified polyalkyleneimine supported on the carrier.

[0016] The present invention also provides a method for separating carbon dioxide, which comprises a step of contacting carbon dioxide in a gaseous state with the carbon dioxide absorbent.

[0017] The present invention also provides a method for recovering carbon dioxide, which includes a step of desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide.

[0018] The modified polyalkyleneimine of the present invention has excellent carbon dioxide adsorption / desorption capacity and durability.

[0019] [Modified Polyalkyleneimine] The modified polyalkyleneimine of the first aspect of the present invention is a modified polyalkyleneimine having a structural unit (I) derived from a polyalkyleneimine and a substituent (A) represented by the following general formula (1): Furthermore, the molar ratio of the substituent (A) to the primary amino group contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / primary amino group in structural unit (I)] is 20 / 80 or less. The modified polyalkyleneimine of the first aspect of the present invention has such a structure, and therefore has excellent carbon dioxide adsorption / desorption ability and durability, and can be suitably used, for example, as a carbon dioxide absorbent, as described below.

[0020] *-CH ２ -CH(-R １ ) -X (1)

[0021] In the general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group (—NO ２ ), or a halogen atom, R １ represents a hydrogen atom or a methyl group. * (asterisk) is directly bonded to the nitrogen atom contained in the amino group in the structural unit (I). In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0022] In general formula (1), some or all of the nitrogen atoms bonded with * (asterisk) are nitrogen atoms contained in the secondary amino group in the structural unit (I). In general formula (1), some of the nitrogen atoms bonded with * (asterisk) may be nitrogen atoms contained in the tertiary amino group in the structural unit (I).

[0023] In the modified polyalkyleneimine of the first aspect, the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] is preferably 15 / 85 or less, more preferably 12 / 88 or less, and even more preferably 10 / 90 or less. Moreover, the molar ratio is greater than 0, preferably 0.3 / 99.7 or more, more preferably 1 / 99 or more, even more preferably 1.5 / 98.5 or more, even more preferably 3 / 97 or more, and particularly preferably 6 / 94 or more. When the molar ratio is within the above range, stability and reactivity with carbon dioxide are more easily made appropriate, and durability and carbon dioxide adsorption / desorption ability can be further improved.

[0024] In this specification, the proportion of the substituent (A) based on the molar amount of the primary amino group may be referred to as the "addition rate (mol %) relative to the primary amino group." The addition rate relative to the primary amino group is obtained by interpreting the molar ratio of the substituent (A) relative to the primary amino group in the structural unit (I). For example, when the molar ratio is 15 / 85, the addition rate relative to the primary amino group can be interpreted as 15 mol %.

[0025] The molar ratio [substituent (A) / primary amino group in structural unit (I)] can be calculated stoichiometrically, for example, based on the synthesis method of modified polyalkyleneimine of the present invention as follows. First, the modified polyalkyleneimine of the present invention is obtained by forming a substituent (A) derived from the vinyl group-containing compound through the addition reaction of the pre-addition polyalkyleneimine and a vinyl group-containing compound described below, and it can be assumed that all of the vinyl group-containing compound is added to the primary amino group of the pre-addition polyalkyleneimine. In this case, when the amine ratio of the pre-addition polyalkyleneimine is primary amino group: secondary amino group = a:b, by applying these a and b and the amount of amine hydrogen (H) per 1 g of pre-addition polyalkyleneimine to the following relational formula, the amount of primary amino group (N) per 1 g of pre-addition polyalkyleneimine can be calculated. N=H×[a / (2a+b)] N: Amount of primary amino groups per 1 g of polyalkyleneimine before addition (mol / g) H: Amount of amine hydrogen per 1 g of polyalkyleneimine before addition (mol / g)

[0026] Next, the amount of the substituent (A) and the amount of primary amino groups contained in the structural unit (I) in the modified polyalkyleneimine can be calculated from the following relational expressions, and the molar ratio [substituent (A) / primary amino groups in structural unit (I)] can be calculated from these amounts: [amount of substituent (A) (mol)] = W Ｖ / M Ｖ [Amount (mol) of primary amino groups in structural unit (I)] = (N × W Ｐ )-(W Ｖ / M Ｖ ) W Ｖ M: Amount of vinyl group-containing compound (g) Ｖ W: molecular weight of vinyl group-containing compound (g / mol) N: amount of primary amino groups per 1 g of polyalkyleneimine before addition (mol / g) Ｐ : Amount of polyalkyleneimine before addition (g)

[0027] Even in cases where the vinyl group-containing compound is considered to have added to an amino group other than the primary amino group of the pre-addition polyalkyleneimine (i.e., a secondary amino group and / or a tertiary amino group), the amount can be calculated stoichiometrically by taking into account the proportion of reaction with each amino group.

[0028] The molar ratio may be determined by subjecting the modified polyalkyleneimine of the present invention to known measurements such as nuclear magnetic resonance (NMR) spectroscopy. In this case, for example, the peak derived from the substituent (A) and the peak derived from the primary amino group in the structural unit (I) may be identified, and the molar ratio may be calculated from the intensity ratio of these peaks.

[0029] In this specification, "pre-addition polyalkyleneimine" means a polyalkyleneimine that does not have a structure derived from the vinyl group-containing compound, i.e., a polyalkyleneimine before the vinyl group-containing compound is added. This "pre-addition polyalkyleneimine" may be an unmodified polyalkyleneimine (unmodified polyalkyleneimine), or, as described below, may be a polyalkyleneimine modified with a compound other than the vinyl group-containing compound. In this specification, unless otherwise specified, "polyalkyleneimine" includes "unmodified polyalkyleneimine" and "modified polyalkyleneimine." The same applies to "polyethyleneimine."

[0030] In the modified polyalkyleneimine of the first aspect, the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] is preferably 7 / 93 or less, more preferably 5 / 95 or less, even more preferably 4 / 96 or less, and particularly preferably 3.3 / 96.7 or less. The molar ratio is greater than 0, and is preferably 0.1 / 99.9 or more, more preferably 0.3 / 99.7 or more, even more preferably 0.5 / 99.5 or more, even more preferably 1 / 99 or more, and particularly preferably 2 / 98 or more. When the molar ratio is within the above range, stability and reactivity with carbon dioxide are more likely to be appropriate, and durability and carbon dioxide adsorption / desorption ability can be further improved. In this specification, "amine hydrogen" refers to a primary amino group (-NH ２ ) and the hydrogen bonded directly to the nitrogen atom in a secondary amino group (—NH—).

[0031] In this specification, the proportion of the substituent (A) based on the molar amount of amine hydrogen is sometimes referred to as the "degree of substitution of amine hydrogen (mol %)." The degree of substitution of amine hydrogen is obtained by interpreting the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I). For example, when the molar ratio is 7 / 93, the degree of substitution of amine hydrogen can be interpreted as 7 mol %.

[0032] The molar ratio [substituent (A) / amine hydrogen in structural unit (I)] can be stoichiometrically calculated, for example, based on the synthesis method of modified polyalkyleneimine of the present invention as follows. Specifically, when the modified polyalkyleneimine of the present invention is obtained by forming a substituent (A) derived from the vinyl group-containing compound through an addition reaction between a pre-addition polyalkyleneimine and a vinyl group-containing compound, the amount of the substituent (A) and the amount of amine hydrogen contained in the structural unit (I) in the modified polyalkyleneimine can be determined by applying the blending amount and molecular weight of the vinyl group-containing compound and the blending amount and amount of amine hydrogen per 1 g of pre-addition polyalkyleneimine to the following relational formula. Then, the molar ratio [substituent (A) / amine hydrogen in structural unit (I)] can be calculated from these amounts. [Amount (mol) of substituent (A)] = W Ｖ / M Ｖ [Amount of amine hydrogen in structural unit (I) (mol)] = (H × W Ｐ )-(W Ｖ / M Ｖ ) W Ｖ M: Amount of vinyl group-containing compound (g) Ｖ W: Molecular weight of vinyl group-containing compound (g / mol) H: Amount of amine hydrogen per 1 g of polyalkyleneimine before addition (mol / g) Ｐ : Amount of polyalkyleneimine before addition (g)

[0033] The molar ratio may be determined by subjecting the modified polyalkyleneimine of the present invention to known measurements such as nuclear magnetic resonance spectroscopy. In this case, for example, the peak derived from the substituent (A) and the peak derived from the amine hydrogen in the structural unit (I) may be identified, and the molar ratio may be calculated from the intensity ratio of these peaks.

[0034] The modified polyalkyleneimine of the second aspect of the present invention is a modified polyalkyleneimine having a structural unit (I) derived from a polyalkyleneimine and a substituent (A) represented by the following general formula (1): wherein the molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / amine hydrogen in structural unit (I)] is 7 / 93 or less. The modified polyalkyleneimine of the second aspect of the present invention has such a structure, and therefore has excellent carbon dioxide adsorption / desorption ability and durability, and can be suitably used, for example, as a carbon dioxide absorbent, as described below.

[0035] *-CH ２ -CH(-R １ ) -X (1)

[0036] In the general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom; １ represents a hydrogen atom or a methyl group. * (asterisk) directly bonds to the nitrogen atom contained in the amino group in the structural unit (I).

[0037] In general formula (1), it is preferred that at least some or all of the nitrogen atoms to which * (asterisk) is bonded are nitrogen atoms contained in the secondary amino group in the structural unit (I).

[0038] In the modified polyalkyleneimine of the second aspect, the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] is preferably 20 / 80 or less, more preferably 15 / 85 or less, even more preferably 12 / 88 or less, and particularly preferably 10 / 90 or less. Moreover, the molar ratio is greater than 0, preferably 0.3 / 99.7 or more, more preferably 1 / 99 or more, even more preferably 1.5 / 98.5 or more, even more preferably 3 / 97 or more, and particularly preferably 6 / 94 or more. When the molar ratio is within the above range, stability and reactivity with carbon dioxide are more likely to be appropriate, and durability and carbon dioxide adsorption / desorption ability can be further improved.

[0039] In the modified polyalkyleneimine of the second aspect, the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] is preferably 5 / 95 or less, more preferably 4 / 96 or less, and even more preferably 3.3 / 96.7 or less. Furthermore, the molar ratio is greater than 0, preferably 0.1 / 99.9 or more, more preferably 0.3 / 99.7 or more, even more preferably 0.5 / 99.5 or more, even more preferably 1 / 99 or more, and particularly preferably 2 / 98 or more. When the molar ratio is within the above range, stability and reactivity with carbon dioxide are more easily made appropriate, and durability and carbon dioxide adsorption / desorption ability can be further improved.

[0040] In this specification, the "modified polyalkyleneimine of the present invention" is a general term that includes the modified polyalkyleneimine of the first embodiment and the modified polyalkyleneimine of the second embodiment.

[0041] The modified polyalkyleneimine of the present invention can absorb and desorb (adsorb / desorb) carbon dioxide because the amino groups in the molecule undergo a chemical reaction with carbon dioxide to reversibly form carbamates or bicarbonates. In this specification, the term "absorption" is used in a sense that includes adsorption, and can also be referred to as "sorption."

[0042] The modified polyalkyleneimine of the present invention has a structural unit (I) derived from a polyalkyleneimine. The structural unit (I) is not particularly limited, but examples thereof include a structural unit (Ia) represented by the following general formula (2) and a structural unit (Ib) represented by the following general formula (3). The structural units (I) may be the same or different from each other.

[0043]

[0044] In general formula (2), R ２ represents an alkylene group. ２As the alkylene group, an alkylene group having 2 to 6 carbon atoms is preferred, and a linear alkylene group having 2 to 6 carbon atoms and a branched alkylene group having 3 to 6 carbon atoms are more preferred. Of these, an ethylene group is particularly preferred as the linear alkylene group having 2 to 6 carbon atoms, and a 1,2-propylene group is particularly preferred as the branched alkylene group having 3 to 6 carbon atoms.

[0045]

[0046] In general formula (3), R ２ represents an alkylene group. ２ is preferably an alkylene group having 2 to 6 carbon atoms, more preferably a linear alkylene group having 2 to 6 carbon atoms, or a branched alkylene group having 3 to 6 carbon atoms. Of these, an ethylene group is particularly preferred as the linear alkylene group having 2 to 6 carbon atoms, and a 1,2-propylene group is particularly preferred as the branched alkylene group having 3 to 6 carbon atoms. In general formula (3), P indicates that the structural unit (I) is bonded to another structural unit (I) via an alkylene group due to a branched structure.

[0047] The structural unit (I) preferably has a structural unit (Ia) represented by the general formula (2) and / or a structural unit (Ib) represented by the general formula (3), and more preferably has a structural unit (Ia) represented by the general formula (2) and a structural unit (Ib) represented by the general formula (3).

[0048] The structural unit (I) preferably has a structural unit derived from an alkyleneimine having 2 to 6 carbon atoms, and among these, polyethyleneimine (—CH ２ CH ２ It is more preferred that the alkyl group has a structural unit derived from NH—.

[0049] The number of nitrogen atoms contained in one molecule of the structural unit (I) is not particularly limited, but is preferably 4 to 100, more preferably 5 to 75, even more preferably 10 to 50, and particularly preferably 12 to 45. In addition, the number of nitrogen atoms derived from amino groups contained in one molecule of the structural unit (I) is preferably within the above range.

[0050] The number average molecular weight (Mn) of the structural unit (I) is preferably 250 to 3000 from the viewpoint of superior oxidation stability and superior supportability on a carrier due to low volatility. The lower limit of the number average molecular weight is more preferably 400, and even more preferably 600. The upper limit of the number average molecular weight is more preferably 2000, even more preferably 1500, and particularly preferably 1000.

[0051] The modified polyalkyleneimine of the present invention has a primary amino group, a secondary amino group, or a tertiary amino group (-N<) in the structural unit (I). The modified polyalkyleneimine preferably has at least a primary amino group in the structural unit (I), more preferably has a primary amino group, a secondary amino group, and / or a tertiary amino group in the structural unit (I), and even more preferably has a primary amino group, a secondary amino group, and a tertiary amino group in the structural unit (I).

[0052] The modified polyalkyleneimine of the present invention may be linear or may have a branched structure. The modified polyalkyleneimine of the present invention preferably has a branched structure, i.e., has a tertiary amino group. The branching degree of the modified polyalkyleneimine is preferably greater than 0%, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, even more preferably 20% or more, and particularly preferably 30% or more. The branching degree is preferably 65% ​​or less, more preferably 55% or less, and even more preferably 50% or less. When the branching degree is greater than 0%, the content ratio of primary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide. When the branching degree is 65% or less, the total content ratio of primary amino groups and secondary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide.

[0053] The degree of branching of the modified polyalkyleneimine １３From the chart obtained by measuring C-NMR, the number of secondary amino groups b and the number of tertiary amino groups c can be calculated by determining the intensity ratio between the carbon atoms directly bonded to secondary amino groups and the carbon atoms directly bonded to tertiary amino groups, and then applying b and c to the following formula. That is, a linear modified polyalkyleneimine has no tertiary amino groups and therefore has a branching degree of 0%. Furthermore, a modified polyalkyleneimine in which all nitrogen atoms are tertiary amino groups, i.e., which is maximally branched, has a branching degree of 100%. Branching degree (%) = [c / (b+c)] × 100

[0054] In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom. In this specification, the term "monovalent group having 1 to 30 carbon atoms" refers to a functional group having 1 to 30 carbon atoms. Examples of the monovalent group having 1 to 30 carbon atoms include a cyano group (-CN), an amide group (-C(=O)-NH ２ ), N-alkylamide group (—C(═O)—NH-Alkyl), N-dialkylamide group (—C(═O)—N(-Alkyl) ２ a monovalent group having a carbonyl group (—C(═O)—), a sulfonyl group (—SO ) represented by the following general formula (4): ２ The above X preferably contains a monovalent electron-withdrawing group having 1 to 30 carbon atoms, such as a cyano group, an amide group, or a salt of a carboxyl group (—COO － M ＋ It is more preferable that X contains at least one selected from the group consisting of an N-alkylamide group, an N-dialkylamide group, and a cyano group and an amide group, and it is even more preferable that X contains at least one selected from the group consisting of a cyano group and an amide group. Of these, it is particularly preferable that X is a cyano group. When X is the above, the substituent (A) is easily and efficiently formed by a Michael addition reaction, and durability and carbon dioxide adsorption / desorption ability can be further improved.

[0055] In addition, in the general formula (1), when X is a cyano group, R １ may be a methyl group.

[0056] *-SO ２-Y １ (4)

[0057] In general formula (4), Y １ represents a monovalent group having 1 to 30 carbon atoms. * (asterisk) represents R １ The carbon atom bonded to the above Y １ As the alkyl group, a hydrocarbon group such as an alkyl group or an aryl group is preferred, and a methyl group, an ethyl group, an n-propyl group, or an i-propyl group is more preferred.

[0058] The alkyl group contained in the N-alkylamide group is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group, among which a methyl group is preferred.

[0059] The two alkyl groups in the N-dialkylamide group may be the same or different. Examples of the alkyl group include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group. Of these, a methyl group is preferred.

[0060] In the general formula (1), when X is a monovalent group having a carbonyl group, specific examples of the monovalent group having a carbonyl group include a carboxyl group and its salts, an aldehyde group (-CH(=O)), a monovalent group having an ester group represented by the following general formula (5), and a monovalent group having a ketone group represented by the following general formula (6). As the monovalent group having a carbonyl group, from the viewpoints of compatibility with polyalkyleneimine and stability, a carboxyl group and / or its salt is preferred, and a salt of a carboxyl group is more preferred. In this specification, "carboxyl group" means a carboxylic acid group (-COOH), and "salt of a carboxyl group" means a hydrogen ion (H ＋ ) is a salt-derived cation (M ＋ ) substituted with a functional group (—COO － M ＋ ) means

[0061] *-C(=O)-O-Y ２ (5)

[0062] In general formula (5), Y ２ represents a monovalent group having 1 to 29 carbon atoms. * (asterisk) represents R １ The carbon atom bonded to the above Y ２ As the alkyl group, a hydrocarbon group such as an alkyl group or an aryl group is preferred.

[0063] *-C(=O)-C-Y ３ (6)

[0064] In general formula (6), Y ３ represents a monovalent group having 1 to 28 carbon atoms. * (asterisk) represents R １ The carbon atom bonded to the above Y ３ As the alkyl group, a hydrocarbon group such as an alkyl group or an aryl group is preferred.

[0065] When the modified polyalkyleneimine of the present invention has a plurality of Xs, the plurality of Xs may be the same or different. １ , Y １ , Y ２ , and Y ３ The same applies when they have the same structure, and they may be the same or different.

[0066] Examples of the salt include inorganic salts and organic salts. Examples of the inorganic salt include alkali metals such as sodium and potassium; alkaline earth metals such as magnesium and calcium; and the like. Examples of the organic salt include ammonium; (mono-, di-, tri-) alkylamines such as (mono-, di-, tri-) methylamine and (mono-, di-, tri-) ethylamine; and (mono-, di-, tri-) alkanolamines such as (mono-, di-, tri-) methanolamine and (mono-, di-, tri-) ethanolamine. Organic salts are preferred as the salt. One or more of the above salts may be used.

[0067] [Method for Producing Modified Polyalkyleneimine] The method for producing the modified polyalkyleneimine of the present invention is not particularly limited, and can be obtained, for example, by forming a substituent (A) on an amino group in the polyalkyleneimine. More specifically, the modified polyalkyleneimine can be produced by mixing the pre-addition polyalkyleneimine with the vinyl group-containing compound and reacting them. The method for producing the modified polyalkyleneimine may be referred to as the "production method of the present invention." As the production method of the present invention, from the viewpoint of excellent reactivity and suppressing adverse effects (such as the incorporation of impurities or the generation of by-products), it is preferable to subject the vinyl group-containing compound to Michael addition to the pre-addition polyalkyleneimine. Note that the modified polyalkyleneimine of the present invention may also be produced by a method other than the production method of the present invention.

[0068] The production method of the present invention preferably includes a step (mixing step) of mixing the pre-addition polyalkyleneimine with the vinyl group-containing compound. In the mixing step, the method of mixing the components is not particularly limited. For example, all components may be mixed at once, or any component may be added later and mixed. In the mixing step, the method of adding the components is not particularly limited, and known or conventional methods can be applied. For example, the components may be added to the reaction system all at once, continuously (added over a certain period of time), or intermittently (added in multiple portions). In addition, the addition rate, etc. may be changed once or more during the addition. In particular, from the viewpoint of excellent reactivity, it is preferable to add the vinyl group-containing compound to the pre-addition polyalkyleneimine continuously or intermittently and mix them. As the method of continuous addition, known or conventional methods can be applied, for example, a method of adding using a microtube pump, a dropping funnel, etc. As a method for intermittently adding, a known or conventional method can be applied, for example, a method in which addition is stopped and restarted manually or automatically in a continuous addition method. In addition, a solvent can be used in the above mixing step as necessary, and a solvent may or may not be used for any of the components.

[0069] (Pre-addition polyalkyleneimine) The pre-addition polyalkyleneimine is a compound having a structural unit derived from alkyleneimine and not having a structure derived from the vinyl group-containing compound. The modified polyalkyleneimine of the present invention can be typically obtained by reacting the pre-addition polyalkyleneimine with the vinyl group-containing compound. However, the present invention is not limited to the combination of these substrates.

[0070] The pre-addition polyalkyleneimine is a compound having a structural unit derived from an alkyleneimine. The structural unit derived from the alkyleneimine is not particularly limited, but a structural unit derived from an alkyleneimine having 2 to 6 carbon atoms is preferred. The pre-addition polyalkyleneimine may be used alone or in combination of two or more types.

[0071] The pre-addition polyalkyleneimine may be modified with a compound (other compound) other than the vinyl group-containing compound, such as an alkylene oxide having 2 to 30 carbon atoms (e.g., ethylene oxide, propylene oxide, butylene oxide, etc.), a glycidyl ether compound, an isocyanate group-containing compound, or an acid anhydride.

[0072] Examples of the pre-addition polyalkyleneimine include alkyleneimine polymers and polyamine polymers. Examples of the alkyleneimine include alkyleneimines having 2 to 6 carbon atoms, such as aziridine, 2-methylaziridine, azetidine, 1,2-butyleneimine, 2,3-butyleneimine, and 1,1-dimethylethyleneimine. One type of alkyleneimine may be used alone, or two or more types may be used. That is, the pre-addition polyalkyleneimine may be a homopolymer or copolymer of alkyleneimine.

[0073] Examples of the polyamine include polyamines having 2 to 6 carbon atoms, such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. The polyamines may be used singly or in combination. That is, the pre-addition polyalkyleneimine may be a homopolymer or copolymer of polyamine, or a copolymer of polyamine and alkyleneimine.

[0074] Among them, the pre-addition polyalkyleneimine is preferably polyethyleneimine (PEI) having an ethyleneimine structural unit. The pre-addition polyalkyleneimine is not particularly limited, and for example, a commercially available product or one produced by a known production method may be used.

[0075] The polyalkyleneimine before addition in the modified polyalkyleneimine of the first aspect has at least a primary amino group (—NH ２ The pre-addition polyalkyleneimine preferably further has a secondary amino group (—NH—) and / or a tertiary amino group (—N<), and more preferably has a secondary amino group and a tertiary amino group.

[0076] The pre-addition polyalkyleneimine in the modified polyalkyleneimine of the second aspect has at least a primary amino group or a secondary amino group, preferably a primary amino group and a secondary amino group, and more preferably a primary amino group, a secondary amino group, and a tertiary amino group.

[0077] Regarding the reactivity of amino group, it is generally considered that the reactivity of primary amino group is higher than that of secondary amino group.Therefore, when the pre-addition polyalkyleneimine and vinyl group-containing compound are reacted to obtain the modified polyalkyleneimine of the present invention, it is considered that the vinyl group-containing compound usually preferentially adds to the primary amino group.In addition, the vinyl group-containing compound may also add to the secondary amino group.

[0078] The amount of amine hydrogen per gram of the pre-addition polyalkyleneimine is preferably 5 mmol / g or more, more preferably 10 mmol / g or more, and even more preferably 15 mmol / g or more, and is preferably 45 mmol / g or less, more preferably 40 mmol / g or less, and even more preferably 35 mmol / g or less.

[0079] The amount of amine hydrogen per 1 g of the pre-addition polyalkyleneimine can be stoichiometrically calculated from the substrate used in the synthesis of the pre-addition polyalkyleneimine. For example, when the pre-addition polyalkyleneimine is obtained by adding x moles of alkyleneimine having one amine hydrogen per molecule to 1 mole of polyamine having p amine hydrogens per molecule, the amount of amine hydrogen can be calculated from the following formula. In this specification, the amount of amine hydrogen calculated from the following formula may be referred to as the amount of amine hydrogen (theoretical value). Amount of amine hydrogen per 1 g of pre-addition polyalkyleneimine (mmol / g) = [(p + x) / number average molecular weight of pre-addition polyalkyleneimine (g / mol)] × 1000

[0080] The number average molecular weight (Mn) of the pre-addition polyalkyleneimine is preferably 250 to 3000 from the viewpoints of superior oxidation stability and low volatility, resulting in superior supportability on a carrier. The lower limit of the number average molecular weight is more preferably 400, and even more preferably 600. The upper limit of the number average molecular weight is more preferably 2000, even more preferably 1500, and particularly preferably 1000.

[0081] The number average molecular weight can be measured by a known method using gel permeation chromatography (GPC) with pullulan as a standard substance. The following conditions are used as GPC measurement conditions in the present invention. Measurement apparatus: GPC apparatus (manufactured by Shimadzu Corporation) Columns used: Shodex OHpak SB-807HQ (two columns) + SB-806M / HQ (two columns) manufactured by Resonac Corporation Column temperature: 40°C Eluent: aqueous solution prepared with 0.5 mol% sodium nitrate and 0.5 mol% acetic acid Flow rate: 0.4 mL / min Sample concentration: 0.5 mass% Sample injection amount: 50 μL Standard substance: Shodex STANDARD P-82 (manufactured by Resonac Corporation) Detector: differential refractometer (manufactured by Shimadzu Corporation)

[0082] The molar ratio (amine ratio) of primary amino groups, secondary amino groups, and tertiary amino groups in the pre-addition polyalkyleneimine is preferably 10-60:10-60:10-50 (total 100), more preferably 20-50:20-55:10-40 (total 100), and even more preferably 25-45:30-50:20-35 (total 100), where primary amino groups:secondary amino groups:tertiary amino groups.

[0083] The amine ratio can be determined by measuring the polyalkyleneimine before addition by a nuclear magnetic resonance method. For example, １３ When the carbon atom directly bonded to the nitrogen atom in the primary amino group, the carbon atom directly bonded to the nitrogen atom in the secondary amino group, and the carbon atom directly bonded to the nitrogen atom in the tertiary amino group can be identified from the chart obtained by measuring C-NMR, the ratio of the intensities of the peaks derived from the respective carbon atoms can be calculated. Specifically, the number a of primary amino groups, the number b of secondary amino groups, and the number c of tertiary amino groups are calculated, and the ratio of a, b, and c can be taken as the amine ratio, where primary amino groups:secondary amino groups:tertiary amino groups=a:b:c. Note that when the structure of the pre-addition polyalkyleneimine is complicated, etc., the above １３When analysis is difficult using only C-NMR measurement, the amine ratio may be calculated by appropriately identifying peaks derived from characteristic atoms, such as the peaks derived from each carbon atom, using a known method and determining the intensity ratio of each peak. １ H-NMR, １３ C-NMR, １５ One-dimensional NMR such as N-NMR, １ H- １ Homonuclear correlation two-dimensional NMR such as H COSY (COrrelation SpectroscopY), １ H- １３ C HMQC (Heteronuclear Multiple Quantum Coherence), １ H- １３ C HMBC (Heteronuclear Multiple Bond Connectivity), １ H- １３ C HMQC-TOCSY (TOtally Correlated Spectroscopy), １ H- １５ and heteronuclear correlation two-dimensional NMR such as N HMBC.

[0084] The content of primary amino groups in the polyalkyleneimine before addition is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and particularly preferably 27 mol% or more, relative to 100 mol% of the total amount of alkyleneimines constituting the polyalkyleneimine before addition, and is preferably 60 mol% or less, more preferably 50 mol% or less, even more preferably 45 mol% or less, and particularly preferably 37 mol% or less.

[0085] The content of secondary amino groups in the pre-addition polyalkyleneimine is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, relative to 100 mol% of the total amount of alkyleneimines constituting the pre-addition polyalkyleneimine, and is preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less.

[0086] The content of tertiary amino groups in the pre-addition polyalkyleneimine is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, relative to 100 mol% of the total amount of alkyleneimines constituting the pre-addition polyalkyleneimine, and is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less.

[0087] The pre-addition polyalkyleneimine may be linear or may have a branched structure, i.e., may have a tertiary amino group. The pre-addition polyalkyleneimine preferably has a branched structure. The branching degree of the pre-addition polyalkyleneimine is preferably more than 0%, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, even more preferably 20% or more, and particularly preferably 30% or more. The branching degree is preferably 65% ​​or less, more preferably 55% or less, and even more preferably 50% or less. When the branching degree is more than 0%, the content ratio of primary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide. When the branching degree is 65% or less, the total content ratio of primary amino groups and secondary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide.

[0088] The degree of branching is determined by the polyalkyleneimine before addition. １３ From the chart obtained by measuring C-NMR, the number b of secondary amino groups and the number c of tertiary amino groups can be calculated by determining the intensity ratio between the carbon atoms directly bonded to secondary amino groups and the carbon atoms directly bonded to tertiary amino groups, and the degree of branching can be calculated by applying b and c to the following formula. That is, the linear pre-addition polyalkyleneimine does not have any tertiary amino groups, so the degree of branching is 0%. Furthermore, the pre-addition polyalkyleneimine in which all nitrogen atoms are tertiary amino groups, i.e., which is maximally branched, has a degree of branching of 100%. Degree of branching (%) = [c / (b+c)] × 100

[0089] The amine value per nonvolatile content of the pre-addition polyalkyleneimine is preferably 5 or more, more preferably 10 or more, and even more preferably 15 or more. The amine value is preferably 30 or less, more preferably 27 or less, and even more preferably 25 or less.

[0090] The nonvolatile content (resin content) can be measured by the Karl Fischer method or the dry weight method. The specific measurement method is described below. Karl Fischer method: Measurement equipment: Karl Fischer moisture meter Solvent: Methanol 20-30 ml Amine neutralizer: Acetic acid 7 ml Calculation formula: Resin content (wt%) = 100 - V x F / S x 100 V = KF titer (ml) F = KF titer (mg / ml) S = sample amount (mg) Dry weight method: Approximately 1 g of sample is placed on an aluminum dish and dried in a hot air circulation dryer at 150 ± 5°C for 1 hour, then allowed to cool in a desiccator for 10 minutes. Calculation formula: Resin content (wt%) = W / S x 100 W: Residual weight after drying (g) S: Sample weight before drying (g)

[0091] The amine value is the number of moles (mmol) of amino groups contained in 1 g of the nonvolatile content of the pre-addition polyalkyleneimine and can be calculated by potentiometric titration in a methanol solution using a 0.5 mol / L standard solution of p-toluenesulfonic acid.

[0092] (Vinyl Group-Containing Compound) The vinyl group-containing compound is a compound having a terminal carbon-carbon double bond (C═C bond). The vinyl group-containing compound can react with the amino group of the polyalkyleneimine under relatively mild conditions to form a stable structure, resulting in excellent production efficiency and product stability (oxidation resistance, heat resistance), making it suitable for use. Generally, the amino group in the polyalkyleneimine reacts with carbon dioxide. Therefore, adding the vinyl group-containing compound to the amino group usually reduces the activity of the amino group, potentially reducing the reactivity of the amino group with carbon dioxide. However, it has been found that the modified polyalkyleneimine of the present invention can improve carbon dioxide adsorption / desorption capacity and durability when the vinyl group-containing compound is added to the polyalkyleneimine in a specific ratio. While the reason for this is unclear, the following may be considered: First, primary and secondary amino groups may also cause undesirable side reactions. In particular, primary amino groups are more likely to cause undesirable side reactions due to their high reactivity. For this reason, primary amino groups and secondary amino groups may cause a decrease in carbon dioxide adsorption / desorption capacity and durability due to side reactions, etc. In particular, although primary amino groups have excellent reactivity with carbon dioxide, they are more likely to cause a decrease in carbon dioxide adsorption / desorption capacity and durability due to side reactions, etc. For this reason, it is presumed that by adding the above-mentioned vinyl group-containing compound to some primary amino groups or secondary amino groups (particularly primary amino groups), the decrease in carbon dioxide adsorption / desorption capacity can be suppressed while the above-mentioned side reactions can be efficiently suppressed, and as a result, the carbon dioxide adsorption / desorption capacity and durability can be improved.

[0093] The vinyl group-containing compound is not particularly limited, but from the viewpoint of efficiently proceeding with the pre-addition polyalkyleneimine through the Michael addition reaction, a vinyl group-containing compound having an electron-withdrawing group is preferred. Examples of the electron-withdrawing group include a cyano group, an amide group, an N-alkylamide group, an N-dialkylamide group, a group having a carbonyl group, a nitro group, and a group having a sulfonyl group. Among these, the electron-withdrawing group is preferably a cyano group, an amide group, an N-alkylamide group, or a group having a carbonyl group, with a cyano group, an amide group, or an N-alkylamide group being more preferred. As the vinyl group-containing compound having an electron-withdrawing group, a compound known as a Michael acceptor in a Michael addition reaction may be used. One or more of the vinyl group-containing compounds may be used.

[0094] The vinyl group-containing compound is preferably a compound represented by the following general formula (7): CH ２ = C (-R １ ) -X (7)

[0095] In general formula (7), R １ and X is R in general formula (1). １ and similar to X.

[0096] In general formula (7), examples of X include the same groups as those exemplified in the description of general formula (1). Among these, X preferably contains a monovalent electron-withdrawing group having 1 to 30 carbon atoms, more preferably contains at least one selected from the group consisting of a cyano group, an amide group, a salt of a carboxyl group, an N-alkylamide group, and an N-dialkylamide group, and even more preferably contains at least one selected from the group consisting of a cyano group and an amide group. It is particularly preferable that X is a cyano group. When X is the above group, the substituent (A) is easily formed efficiently by a Michael addition reaction, and durability and carbon dioxide adsorption / desorption ability can be further improved.

[0097] In addition, in the general formula (7), when X is a cyano group, R １ may be a methyl group.

[0098] When such a vinyl group-containing compound is used, it is presumed that a Michael addition reaction between the amino group of the pre-addition polyalkyleneimine and the vinyl group-containing compound proceeds, thereby obtaining a modified polyalkyleneimine having a terminal structure in which the amino group is modified with the vinyl group-containing compound. Specifically, the primary amino group (—NH ２ ) or a secondary amino group (—NH—) and the vinyl group-containing compound (CH ２ = C (-R １ When the Michael addition reaction with the vinyl group-containing compound proceeds, the primary amino group is modified with the vinyl group-containing compound to form a terminal structure (—NH—CH ２ -CH(-R １ )-X) or a terminal structure in which the secondary amino group is modified with the vinyl group-containing compound (>N-CH ２ -CH(-R １ The modified polyalkyleneimine of the present invention is presumed to have a structure (—NH—CH)-X) in which the vinyl group-containing compound is added to at least a primary amino group. ２ -CH(-R １ )-X).

[0099] The alkyl group contained in the N-alkylamide group is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group, among which a methyl group is preferred.

[0100] The two alkyl groups in the N-dialkylamide group may be the same or different. Examples of the alkyl group include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group. Of these, a methyl group is preferred.

[0101] In general formula (5), when X is a group having a carbonyl group, more specific examples of the group having a carbonyl group include a carboxyl group and its salts, a ketone group (a group having a carbonyl group between carbon atoms), an aldehyde group, an ester group, etc. As the group having a carbonyl group, from the viewpoints of compatibility with polyalkyleneimine and stability, a carboxyl group and / or a salt thereof is preferred, and a salt of a carboxyl group is more preferred.

[0102] Examples of the salt include inorganic salts and organic salts. Examples of the inorganic salt include alkali metals such as sodium and potassium; alkaline earth metals such as magnesium and calcium; and the like. Examples of the organic salt include ammonium; (mono-, di-, tri-) alkylamines such as (mono-, di-, tri-) methylamine and (mono-, di-, tri-) ethylamine; and (mono-, di-, tri-) alkanolamines such as (mono-, di-, tri-) methanolamine and (mono-, di-, tri-) ethanolamine. Organic salts are preferred as the salt. One or more of the above salts may be used.

[0103] Specifically, the vinyl group-containing compound preferably contains at least one selected from the group consisting of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N-dialkylacrylamide, N-dialkylmethacrylamide, acrylates, and methacrylates, more preferably contains at least one selected from the group consisting of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide, and even more preferably contains acrylonitrile and / or methacrylonitrile. Of these, it is particularly preferred that the vinyl group-containing compound is acrylonitrile.

[0104] The salts of the acrylate and methacrylate include those exemplified and explained above as salts of the carboxy group. The salts are preferably organic salts.

[0105] Examples of the solvent used in the mixing step include water and organic solvents. The organic solvent is preferably a polar solvent. The polar solvent is preferably an alcohol such as methanol or ethanol.

[0106] The reaction temperature in the mixing step may be adjusted appropriately depending on the reactivity of the vinyl group-containing compound, and is, for example, preferably 0°C to 100°C, more preferably 20°C to 95°C, and even more preferably 20°C to 90°C.

[0107] The reaction time in the mixing step may be adjusted appropriately depending on the reactivity of the vinyl group-containing compound, and is, for example, preferably 0.1 to 200 hours, more preferably 0.2 to 100 hours, and even more preferably 0.5 to 48 hours.

[0108] [Composition] A composition can be prepared using the modified polyalkyleneimine of the present invention. A composition containing the modified polyalkyleneimine of the present invention may be referred to as the "composition of the present invention." The composition of the present invention is excellent in carbon dioxide adsorption / desorption ability and durability due to the inclusion of the modified polyalkyleneimine of the present invention. In other words, the composition is preferably a composition for a carbon dioxide absorbent.

[0109] The composition may be liquid or solid. When the composition is used in a carbon dioxide absorbent described below, the composition is preferably liquid from the viewpoint of superior handling and supportability. Examples of the liquid composition include a composition containing a solvent such as water, in which the modified polyalkyleneimine of the present invention is dissolved or dispersed in the solvent. Other examples of the liquid composition include a composition that does not contain a solvent such as water, in which the modified polyalkyleneimine of the present invention is liquid. Examples of the solid composition include a solvent-free composition containing the modified polyalkyleneimine of the present invention.

[0110] (Other Components) The composition of the present invention can be produced, for example, by adding various components to the modified polyalkyleneimine of the present invention. As the various components, components other than the modified polyalkyleneimine of the present invention can be used as appropriate. Examples of the other components include solvents (e.g., water; organic solvents such as methanol and ethanol), surfactants (anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants), antioxidants, antioxidant assistants, crystallization inhibitors, and the like. Other components also include metals that are not intentionally incorporated as impurities. Only one of the other components may be used, or two or more may be used. The HLB (hydrophilic-lipophilic balance) of the surfactant is, for example, preferably 10 or more, more preferably 12 or more, and even more preferably 15 or more.

[0111] The antioxidant may be a radical scavenger, a peroxide decomposer, or the like. The radical scavenger may be a phenolic antioxidant, an amine antioxidant, or the like, with an amine antioxidant being preferred. The peroxide decomposer may be any agent capable of effectively decomposing peroxides, but may be a sulfur-based antioxidant, a phosphorus-based antioxidant, a phenolic antioxidant, a hindered amine-based antioxidant, or the like. Examples of the sulfur-based antioxidant include 2-hydroxyethyl disulfide, 1,2-bis[(2-hydroxyethyl)thio]ethane, thiodipropionic acid, dilauryl thiodipropionate, distearyl thiodipropionate, laurylstearyl thiodipropionate, dimyristyl thiodipropionate, distearyl-β,β'-thiodibutyrate, thiobis(β-naphthol), thiobis(N-phenyl-β-naphthylamine), 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, dodecyl mercaptan, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, nickel dibutyldithiocarbamate, nickel isopropyl xanthate, and dodecanethiol, with 2-hydroxyethyl disulfide and 1,2-bis[(2-hydroxyethyl)thio]ethane being more preferred.Examples of the phosphorus-based antioxidant include triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, tris(nonylphenyl) phosphite, diisodecyl pentaerythritol phosphite, tris(2,4-di-t-butylphenyl) phosphite, cyclic neopentane tetrayl bis(octadecyl) phosphite, cyclic neopentane tetrayl bis(2,4-di-t-butylphenyl) phosphite, cyclic neopentane tetrayl bis(2,4-di-t-butylphenyl) phosphite, and cyclic neopentane tetrayl bis(2,4-di-t-butylphenyl) phosphite. phosphites (phosphite antioxidants) such as bis[2-t-butyl-4-methylphenyl]phosphite and bis[2-t-butyl-6-methyl-4-{2-(octadecyloxycarbonyl)ethyl}phenyl]hydrogenphosphite; and oxaphosphaphenanthrene oxides such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.Examples of the phenolic antioxidant include monophenols such as 4-methoxyphenol, hydroquinone, 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-p-ethylphenol, and stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), and 3,9-bis[1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy} bisphenols such as 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, bis[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid]glycol ester, 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione, and polymeric phenols such as tocophenol. Examples of the hindered amine antioxidant include bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl-1,2,2,6,6-pentamethyl-4-piperidylsebacate, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, and 4-hydroxy-2,2,6,6-tetramethylpiperidine.

[0112] Examples of the crystallization inhibitor include water-soluble polymers such as polyvinylpyrrolidone, polyvinyl alcohol, hydroxyethyl cellulose, etc. By using a water-soluble polymer as a crystallization inhibitor, it is possible to suppress the formation of an insoluble salt due to a secondary interaction between the oligoamine compound and carbamic acid generated by the reaction of the oligoamine compound with carbon dioxide.

[0113] Examples of the metal impurity include a simple metal and a component containing a metal (e.g., a metal oxide). Examples of the metal include a transition metal. The transition metal is any element of Groups 3 to 12 of the periodic table of the elements, specifically at least one selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, and more specifically at least one selected from the group consisting of chromium, manganese, iron, cobalt, nickel, and copper.

[0114] From the viewpoint of excellent durability, the content of metal-containing components in the composition is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less, relative to 100% by mass of the total composition. It is particularly preferable that the composition is substantially free of metal-containing components. The content may be 0.5 ppm or more, or even 1 ppm or more, relative to 100% by mass of the total composition. More specifically, the total content of the components containing chromium, manganese, iron, cobalt, nickel, and copper in the composition is preferably within the above range, relative to 100% by mass of the total composition. The content can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0115] The composition can be produced by a known or conventional method, for example, by mixing the modified polyalkyleneimine of the present invention with the other components described above and stirring the mixture.

[0116] [Carbon dioxide absorbent] A carbon dioxide absorbent can be prepared using the modified polyalkyleneimine of the present invention or the above-mentioned composition. A carbon dioxide absorbent containing the modified polyalkyleneimine of the present invention may be referred to as the "carbon dioxide absorbent of the present invention." The carbon dioxide absorbent of the present invention has excellent carbon dioxide adsorption / desorption ability and durability due to the inclusion of the modified polyalkyleneimine of the present invention.

[0117] The carbon dioxide absorbent of the present invention may contain other components besides the modified polyalkyleneimine of the present invention. The carbon dioxide absorbent of the present invention may be the modified polyalkyleneimine of the present invention itself, or may be one produced by adding various components to the modified polyalkyleneimine of the present invention, for example. Examples of the various components include a carrier and those exemplified and explained as other components that may be contained in the composition of the present invention described above. From the viewpoint of excellent handleability, the carbon dioxide absorbent preferably contains at least a carrier. That is, the carbon dioxide absorbent preferably contains the modified polyalkyleneimine of the present invention and the carrier, and the modified polyalkyleneimine of the present invention is preferably supported on the carrier. Only one of the various components may be used, or two or more of them may be used.

[0118] The carrier is preferably a porous carrier particle from the viewpoint of improving the carbon dioxide adsorption / desorption capacity. Furthermore, examples of materials constituting the carrier include inorganic materials and polymeric materials. That is, the carrier is preferably a porous carrier particle composed of an inorganic material and / or a polymeric material.

[0119] The inorganic material preferably includes at least one selected from the group consisting of bentonite, attapulgite, kaolinite, montmorillonite, ball clay, fuller's earth, hectorite, palygorskite, saponite, sepiolite, halloysite, silica, calcium sulfate, zeolite, alumina, activated carbon, and metal-organic frameworks, more preferably silica and / or alumina, and even more preferably silica. The silica is not particularly limited, and known silicas such as fumed silica produced by a dry process, precipitated silica produced by a wet process, silica gel, and silica sol can be used as appropriate. Only one of the inorganic materials may be used, or two or more may be used.

[0120] Examples of the polymeric material include ether sulfone (PES), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), mixed cellulose esters or nitrocellulose (NC), polyolefin, polyethylene, polypropylene, polymethylpentene, polyketone, polyimide, polystyrene, polymethyl methacrylate, polydimethylsiloxane, polyester, nylon, polycaprolactone, polylactic acid, polyvinyl alcohol, polyglycolic acid, etc. Only one of the above polymeric materials may be used, or two or more thereof may be used.

[0121] The specific surface area of ​​the carrier is set to 70 m from the viewpoint of excellent carbon dioxide adsorption / desorption ability. ２ / g or more is preferable, and 80m ２ / g or more, more preferably 100m ２ / g or more. The specific surface area is 800 m ２ / g or less, and ２ / g or less, and ２ / g or less.

[0122] From the viewpoint of excellent carbon dioxide adsorption / desorption ability, the content of the modified polyalkyleneimine of the present invention in the carbon dioxide absorbent is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, relative to 100 parts by mass of the total amount of the carrier. Furthermore, from the viewpoint of excellent carbon dioxide adsorption / desorption ability and supportability, the content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less, relative to 100 parts by mass of the total amount of the carrier. Furthermore, the content of the composition in the carbon dioxide absorbent is preferably within the above range, relative to 100 parts by mass of the total amount of the carrier.

[0123] The carrier may contain metals as impurities. Examples of such metals include those exemplified and described as other metal components that may be contained in the composition of the present invention. From the viewpoint of excellent durability, the content of the metal-containing components in the carrier is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, even more preferably 3,000 ppm or less, and particularly preferably 2,000 ppm or less, relative to 100% by mass of the total amount of the carrier. Furthermore, from the viewpoint of industrial applicability (productivity), the content may be 10 ppm or more, 30 ppm or more, or even 50 ppm or more, relative to 100% by mass of the total amount of the carrier. More specifically, the total content of the components containing chromium, manganese, iron, cobalt, nickel, and copper in the carrier is preferably within the above range, relative to 100% by mass of the total amount of the carrier. The content can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0124] The carbon dioxide absorbent can separate carbon dioxide by absorbing not only carbon dioxide in gases containing high concentrations of carbon dioxide, but also dilute carbon dioxide in conditioned air or the atmosphere. Furthermore, by undergoing a step of desorbing (desorbing) the absorbed carbon dioxide, the carbon dioxide can be recovered and further absorbed again. Therefore, by using the carbon dioxide absorbent, it is possible to suppress a decrease in carbon dioxide adsorption / desorption ability even after repeated carbon dioxide absorption / desorption.

[0125] The carbon dioxide absorbent can be produced by a known or conventional method. Here, the carbon dioxide absorbent can be produced, for example, by mixing and stirring the above-mentioned components. Specifically, when the carbon dioxide absorbent contains the modified polyalkyleneimine of the present invention or the composition and the carrier, the production method of the carbon dioxide absorbent preferably includes a step of mixing and stirring the modified polyalkyleneimine of the present invention or the composition with the carrier, and supporting the modified polyalkyleneimine of the present invention or the composition on the carrier (supporting step). From the viewpoint of excellent handleability and supportability, the production method of the carbon dioxide absorbent more preferably includes a step of mixing and stirring the composition containing at least the modified polyalkyleneimine of the present invention and a solvent with the carrier, and supporting the modified polyalkyleneimine of the present invention on the carrier (supporting step). Note that when the composition is used, the supporting step may be a step of adding the composition to the carrier and supporting it (step (a)), or a step of separately adding each component contained in the composition to the carrier and supporting it (step (b)). As the supporting step, the step (a) is preferred from the viewpoint of excellent production efficiency. In the step (b), the order of adding each component is not particularly limited.

[0126] For example, the carrier may be impregnated with the modified polyalkyleneimine or the composition of the present invention (impregnation), the carrier may be loaded with the modified polyalkyleneimine or the composition of the present invention by dropping the modified polyalkyleneimine or the composition onto the carrier (dropping), or the carrier may be filled in a container such as a column and then the modified polyalkyleneimine or the composition of the present invention is passed through the carrier (passing). Among these, the impregnation method is preferred from the viewpoint of simplicity of operation and equipment.

[0127] The pressure conditions in the loading step are not particularly limited and can be arbitrarily selected from normal pressure, reduced pressure, increased pressure, etc. When the support has pores, the treatment is preferably carried out under reduced pressure from the viewpoint of removing bubbles in the pores and efficiently loading the support. Specifically, the pressure during the treatment is preferably −0.08 MPaG to −0.004 MPaG, more preferably −0.07 MPaG to −0.01 MPaG, and even more preferably −0.06 MPaG to −0.02 MPaG.

[0128] The temperature conditions in the above-mentioned supporting step are not particularly limited, but from the viewpoint of excellent supporting ability, it is preferably 20°C to 90°C, more preferably 30°C to 80°C, and even more preferably 40°C to 70°C.

[0129] Furthermore, the method for producing the carbon dioxide absorbent may include, as necessary, a step of separating the excess solvent from the carrier carrying the composition (separation step), and / or a step of removing the solvent from the carrier (drying step).

[0130] For the separation step, any known or conventional method can be used, such as filtration, decantation, centrifugation, or other solid-liquid separation technique. Among these, filtration is preferred from the viewpoint of excellent procedural simplicity.

[0131] The temperature conditions in the drying step are not particularly limited, but are preferably 30°C to 100°C, more preferably 40°C to 98°C, even more preferably 50°C to 95°C, and particularly preferably 50°C to 90°C.

[0132] The treatment time in the drying step is not particularly limited, but is preferably 0.1 to 48 hours, more preferably 0.2 to 24 hours, and even more preferably 0.5 to 12 hours.

[0133] The pressure conditions in the drying step are not particularly limited and can be arbitrarily selected from normal pressure, reduced pressure, increased pressure, etc. Among these, normal pressure is preferred from the viewpoint of maintaining the state in which the modified polyalkyleneimine of the present invention is supported on the carrier.

[0134] The carbon dioxide absorbent can be installed and used in an apparatus (carbon dioxide recovery apparatus) that separates and recovers carbon dioxide from a gas to be treated that contains carbon dioxide. The gas to be treated is a carbon dioxide-containing gas that contains at least carbon dioxide, but may also contain gases other than carbon dioxide. Examples of the gas to be treated include the atmosphere and high-concentration gases that contain carbon dioxide at a higher concentration than the atmosphere. Such high-concentration gases are, for example, those emitted from internal combustion engines or factories.

[0135] Examples of methods for using the carbon dioxide absorbent include a carbon dioxide separation method including a step of contacting carbon dioxide in a gas with the carbon dioxide absorbent (contact step), and a carbon dioxide recovery method including a step of desorbing the carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide (desorption step). In the contact step, the carbon dioxide absorbent absorbs carbon dioxide in the gas, so that the carbon dioxide can be removed (separated) from the gas. In addition, in the desorption step, the carbon dioxide can be recovered by desorbing the carbon dioxide from the carbon dioxide absorbent.

[0136] The pressure condition of the contact step may be, for example, 0.8 to 1.1 atmospheres, and the temperature condition of the contact step may be, for example, −40° C. to 50° C.

[0137] The pressure conditions for the desorption step may be, for example, reduced pressure, 0.02 to 0.5 atmospheres, or 0.1 to 0.3 atmospheres, and the temperature conditions for the desorption step may be, for example, heated, 50 to 130°C.

[0138] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass," and the blending amounts and mass ratios described in the examples mean the blending amounts and mass ratios of each component (i.e., the blending amounts and mass ratios of the solid content in each raw material).

[0139] Synthesis Example 1 (Preparation of Modified Polyethyleneimine 1) A reactor was charged with 10.0 g of unmodified polyethyleneimine (trade name "SP-006", manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 600 (GPC method), primary amino group: secondary amino group: tertiary amino group = 35:35:30 (catalog value), amine hydrogen amount 27.6 mmol / g (theoretical value)), which is a pre-addition polyalkyleneimine, and then 0.22 g of acrylonitrile (AN, molecular weight 53.06) was added dropwise with stirring at 23°C, followed by reaction for 4 hours at 23°C. After the reaction, the mixture was left to stand at room temperature for 24 hours, and then １ H-NMR analysis confirmed the disappearance of the shift due to hydrogen on the carbon having the double bond of acrylonitrile, confirming that modified polyethyleneimine 1 was obtained. Modified polyethyleneimine 1 has a structural unit derived from polyethyleneimine as the structural unit (I) and a structure (*-CH) derived from acrylonitrile as the substituent (A). ２ -CH ２ -CN).

[0140] The unmodified polyethyleneimine was obtained by a known production method. The amount of amine hydrogen per 1 g of the unmodified polyethyleneimine was calculated to be 27.6 mmol / g from the substrate used in the synthesis of the unmodified polyethyleneimine and the following formula: Amount of amine hydrogen per 1 g of unmodified polyalkyleneimine (mmol / g) = [(p + x) / number average molecular weight of unmodified polyalkyleneimine (g / mol)] × 1000, where p: number of amine hydrogens per molecule of polyamine, and x: number of moles of alkyleneamine having one amine hydrogen per molecule.

[0141] In modified polyethyleneimine 1, the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] was calculated by the above-mentioned method to be 4.5 / 95.5 (4.5 mol% as the addition rate to the primary amino group). Similarly, the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] was calculated by the above-mentioned method to be 1.5 / 98.5 (1.5 mol% as the substitution degree of amine hydrogen).

[0142] Synthesis Example 2 (Preparation of Modified Polyethyleneimine 2) Except for changing the amount of acrylonitrile from 0.22 g to 0.44 g, modified polyethyleneimine 2 of Synthesis Example 2 was obtained in the same manner as in Synthesis Example 1. In modified polyethyleneimine 2, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 9 / 91 (9.0 mol% as addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 3 / 97 (3.0 mol% as substitution degree of amine hydrogen).

[0143] Synthesis Example 3 (Preparation of Modified Polyethyleneimine 3) Modified polyethyleneimine 3 of Synthesis Example 3 was obtained in the same manner as in Synthesis Example 1, except that the amount of acrylonitrile was changed from 0.22 g to 0.88 g and the reaction conditions were changed from a 4-hour reaction at 23° C. to a 4-hour reaction at 40° C. In modified polyethyleneimine 3, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 18 / 82 (18.0 mol% as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 6 / 94 (6.0 mol% as the substitution degree of amine hydrogen).

[0144] Synthesis Example 4 (Preparation of Modified Polyethyleneimine 4) Modified polyethyleneimine 4 of Synthesis Example 4 was obtained in the same manner as in Synthesis Example 1, except that the amount of acrylonitrile was changed from 0.22 g to 2.65 g and the reaction conditions were changed from a 4-hour reaction at 23° C. to a 4-hour reaction at 40° C. In modified polyethyleneimine 4, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 54.3 / 45.7 (54.3 mol% as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 18.1 / 81.9 (18.1 mol% as the substitution degree of amine hydrogen).

[0145] Synthesis Example 5 (Preparation of Modified Polyethyleneimine 5) Modified polyethyleneimine 5 of Synthesis Example 5 was obtained in the same manner as in Synthesis Example 1, except that the amount of acrylonitrile was changed from 0.22 g to 4.42 g and the reaction conditions were changed from a 4-hour reaction at 23° C. to a 4-hour reaction at 40° C. In modified polyethyleneimine 5, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 90.5 / 9.5 (90.5 mol% as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 30.2 / 69.8 (30.2 mol% as the substitution degree of amine hydrogen).

[0146] Synthesis Example 6 (Preparation of Modified Polyethyleneimine 6) Modified polyethyleneimine 6 of Synthesis Example 6 was obtained in the same manner as in Synthesis Example 1, except that 0.28 g of methacrylonitrile (MAN, molecular weight 67.09) was used instead of 0.22 g of acrylonitrile, and the reaction conditions were changed from a reaction at 23° C. for 4 hours to a reaction at 80° C. for 6 hours. Modified polyethyleneimine 6 has a structural unit derived from polyethyleneimine as the structural unit (I), and a structure (*-CH ２ -CH(-CH ３In modified polyethyleneimine 6, the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] was calculated to be 4.5 / 95.5 (4.5 mol % as the addition rate to the primary amino group), and the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] was calculated to be 1.5 / 98.5 (1.5 mol % as the substitution degree of amine hydrogen).

[0147] Synthesis Example 7 (Preparation of Modified Polyethyleneimine 7) Modified polyethyleneimine 7 of Synthesis Example 7 was obtained in the same manner as in Synthesis Example 1, except that 0.56 g of methacrylonitrile (MAN) was used instead of 0.22 g of acrylonitrile and the reaction conditions were changed from a 4-hour reaction at 23° C. to a 6-hour reaction at 80° C. In modified polyethyleneimine 7, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 9.1 / 90.9 (9.1 mol % as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 3 / 97 (3.0 mol % as the substitution degree of amine hydrogen).

[0148] Synthesis Example 8 (Preparation of Modified Polyethyleneimine 8) Modified polyethyleneimine 8 of Synthesis Example 8 was obtained in the same manner as in Synthesis Example 1, except that 1.12 g of methacrylonitrile (MAN) was used instead of 0.22 g of acrylonitrile, and the reaction conditions were changed from a 4-hour reaction at 23° C. condition to a 8-hour reaction at 80° C. condition, followed by a 24-hour reaction at 50° C. condition. In modified polyethyleneimine 8, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 18.1 / 81.9 (18.1 mol% as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 6 / 94 (6.0 mol% as the substitution degree of amine hydrogen).

[0149] Synthesis Example 9 (Preparation of Modified Polyethyleneimine 9) Modified polyethyleneimine 9 of Synthesis Example 9 was obtained in the same manner as in Synthesis Example 1, except that a solution of 1.18 g of acrylamide (AAm, molecular weight 71.08) dissolved in 10 g of ethanol was used instead of 0.22 g of acrylonitrile, and the reaction conditions were changed from a reaction at 23° C. for 4 hours to a reaction at 50° C. for 1 hour. Modified polyethyleneimine 9 has a structural unit derived from polyethyleneimine as the structural unit (I), and a structure (*-CH ２ -CH ２ —C(═O)—NH ２ In modified polyethyleneimine 9, the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] was calculated to be 18 / 82 (18.0 mol % as the addition rate to the primary amino group), and the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] was calculated to be 6 / 94 (6.0 mol % as the substitution degree of amine hydrogen).

[0150] Synthesis Example 10 (Preparation of Modified Polyethyleneimine 10) A reactor was charged with 10.0 g of unmodified polyethyleneimine (trade name "SP-006", manufactured by Nippon Shokubai Co., Ltd.), and then a solution of 3.55 g of acrylamide (AAm) dissolved in 10 g of ethanol was added dropwise at 23°C with stirring, followed by reaction at 50°C for 1 hour. After the reaction, the mixture was allowed to stand at room temperature for 24 hours. Thereafter, a sample was taken, and the ethanol was removed under reduced pressure. The resulting liquid was １H-NMR measurement confirmed the disappearance of the shift due to hydrogen on the carbon bearing the double bond of acrylamide, confirming that modified polyethyleneimine 10 (polyethyleneimine acrylamide adduct) was obtained. In modified polyethyleneimine 10, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 54 / 46 (54.0 mol% as the addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 18 / 82 (18.0 mol% as the degree of substitution of amine hydrogen).

[0151] Synthesis Example 11 (Preparation of Modified Polyethyleneimine 11) Modified polyethyleneimine 11 of Synthesis Example 11 was obtained in the same manner as in Synthesis Example 10, except that the amount of acrylamide was changed from 3.55 g to 5.92 g. In modified polyethyleneimine 11, the molar ratio of substituent (A) to primary amino group in structural unit (I) [substituent (A) / primary amino group in structural unit (I)] was calculated to be 90 / 10 (90.0 mol% as addition rate to primary amino group), and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 30 / 70 (30.0 mol% as substitution degree of amine hydrogen).

[0152] Example 1 The modified polyethyleneimine 1 (0.5 parts) of Synthesis Example 1 and water (5.0 parts) were mixed to prepare a homogeneous solution. Next, 1.0 part of HI-SIL-250 (manufactured by PPG Industries) as a carrier was added to the above solution, and the mixture was impregnated with stirring for 30 minutes. Next, the mixture was treated under reduced pressure at 60°C and 20 Pa, and then heated and dried in an oven at 80°C for 2 hours, thereby obtaining a carbon dioxide absorbent of Example 1 in which the modified polyethyleneimine 1 was supported on the carrier.

[0153] Examples 2 to 7 and Comparative Examples 1 to 5 Carbon dioxide absorbents of Examples 2 to 7 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that, instead of modified polyethyleneimine 1, each modified polyethyleneimine obtained in each Synthesis Example or unmodified polyethyleneimine (trade name "SP-006", manufactured by Nippon Shokubai Co., Ltd.) was used, as shown in Table 1.

[0154] <Evaluation> The carbon dioxide absorbents obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0155] (1) Carbon dioxide adsorption / desorption ability The carbon dioxide adsorption / desorption amounts of the carbon dioxide absorbents obtained in Examples 1 to 7 and Comparative Examples 1 to 5 were measured by the following test. Then, using the obtained carbon dioxide adsorption / desorption amounts, the blank retention rate was calculated from the following calculation formula, and evaluation was performed according to the following criteria. The carbon dioxide adsorption / desorption amounts at this time are shown in the item "Initial carbon dioxide adsorption / desorption amount [g / g]" in Table 1.

[0156] [Carbon dioxide adsorption / desorption test] Using a thermogravimetry-differential thermal analysis (TG-DTA) (manufactured by Rigaku Corporation, TG-DTA8120, 8122), the masses of the carbon dioxide absorbent at the absorption temperature (40°C) and the desorption temperature (110°C) were measured, and the carbon dioxide adsorption / desorption amount was calculated using the following formula. In this measurement, a carbon dioxide-containing gas simulating dry air was prepared by adjusting the flow rates of nitrogen and carbon dioxide using a mass flow controller, and supplied to the TG-DTA oven at 200 ml / min. At this time, the carbon dioxide concentration in the gas was set to about 400 ppm, and the humidity of the gas was kept constant at an absolute humidity of 2 g / kg. Carbon dioxide adsorption / desorption amount (g / g) = (W Ａ -W Ｄ ) / W １ W Ａ W: Mass (g) of carbon dioxide absorbent at absorption temperature Ｄ W: Mass (g) of carbon dioxide absorbent at desorption temperature １ : Mass (g) of carbon dioxide absorbent used in the test

[0157] [Calculation formula for blank retention rate] Blank retention rate (%) = [(amount of carbon dioxide adsorption / desorption in each Example or Comparative Example) / (amount of carbon dioxide adsorption / desorption in Comparative Example 1)] x 100

[0158] [Evaluation criteria for carbon dioxide adsorption / desorption capacity] ∘: Blank retention rate is 100% or more ×: Blank retention rate is less than 100%

[0159] (2) Durability The carbon dioxide absorbents obtained in Examples 1 to 7 and Comparative Examples 1 to 5 were subjected to the following degradation treatment, and then the above-mentioned carbon dioxide adsorption / desorption test was carried out to measure the amount of carbon dioxide adsorption / desorption. Using the obtained carbon dioxide adsorption / desorption amounts, the retention rate after degradation treatment was calculated according to the following calculation formula, and evaluation was carried out according to the following criteria. The carbon dioxide adsorption / desorption amounts at this time are shown in the item "Carbon dioxide adsorption / desorption amount after degradation treatment [g / g]" in Table 1.

[0160] [Deterioration Treatment] 0.03 g of each of the carbon dioxide absorbents obtained in Examples 1 to 7 and Comparative Examples 1 to 5 was weighed into a 10 mL vial. The top of each vial was protected with a piece of medicine paper with multiple holes punched in it to prevent the inclusion of foreign matter while allowing air to pass through. This was left to stand in an oven at 100°C for 24 hours and then cooled to obtain a carbon dioxide absorbent that had been subjected to a deterioration treatment. This treatment causes the carbon dioxide absorbent to deteriorate due to heating and oxidation, making it possible to simulate an absorbent that has undergone heating and repeated adsorption / desorption treatments.

[0161] [Calculation formula for retention rate] Retention rate (%) = [(amount of carbon dioxide adsorption / desorption after degradation treatment) / (initial amount of carbon dioxide adsorption / desorption)] x 100

[0162] [Durability evaluation criteria] ○: Maintenance rate is over 18% ×: Maintenance rate is 18% or less

[0163]

[0164] The blank retention rates when carbon dioxide absorbents containing modified polyethyleneimine in which the molar ratio of substituent (A) to primary amino groups in structural unit (I) [substituent (A) / primary amino groups in structural unit (I)] was 20 / 80 or less and the molar ratio of substituent (A) to amine hydrogen in structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was 7 / 93 or less were used were 100 to 122% (Examples 1 to 7). Therefore, it was found that the carbon dioxide absorbents of Examples 1 to 7 exhibited carbon dioxide adsorption / desorption capabilities equivalent to or greater than those of the carbon dioxide absorbent containing unmodified polyethyleneimine of Comparative Example 1.

[0165] Furthermore, the retention rates after the deterioration treatment when the carbon dioxide absorbents of Examples 1 to 7 were all 19% or more, which were higher values ​​than the retention rate of Comparative Example 1. Therefore, it was found that the carbon dioxide absorbents of Examples 1 to 7 had improved durability compared to the carbon dioxide absorbent of Comparative Example 1.

[0166] On the other hand, when a carbon dioxide absorbent containing a modified polyethyleneimine was used in which the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] was greater than 20 / 80 and the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] was greater than 7 / 93, the blank retention was 61 to 82%, and a significant decrease in carbon dioxide adsorption / desorption capacity was confirmed (Comparative Examples 2 and 3).

[0167] Furthermore, even when acrylamide was used as the vinyl group-containing compound, when a carbon dioxide absorbent containing a modified polyethyleneimine in which the molar ratio of the substituent (A) to the primary amino group in the structural unit (I) [substituent (A) / primary amino group in the structural unit (I)] was greater than 20 / 80 and the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in the structural unit (I)] was greater than 7 / 93 was used, the blank retention was 28 to 55%, and a significant decrease in carbon dioxide adsorption / desorption capacity was confirmed (Comparative Examples 4 and 5).

[0168] From the above, it was found that the modified polyethyleneimine of this example not only suppresses the decrease in carbon dioxide adsorption / desorption capacity that occurred in conventional modified polyethyleneimines, but also improves durability, thereby achieving both excellent carbon dioxide adsorption / desorption capacity and durability. The reasons for this are presumed to be, for example, the following: Primary amino groups and secondary amino groups have the desirable function of being able to adsorb and desorb carbon dioxide. On the other hand, primary amino groups and secondary amino groups have the undesirable effect of being highly reactive, which can lead to a decrease in carbon dioxide adsorption / desorption capacity and durability due to side reactions, etc. The modified polyethyleneimine of this example was obtained by reacting a small amount of a vinyl group-containing compound with unmodified polyethyleneimine, which is a pre-addition polyalkyleneimine, and it is therefore presumed that the particularly highly reactive amino groups have a structure modified by the vinyl group-containing compound. Therefore, since the molar ratio is below a certain level, it is possible to efficiently suppress the undesirable effects while maintaining the desired effects, thereby achieving both excellent carbon dioxide adsorption / desorption capacity and durability.

[0169] Variations of the present invention are described below. [Appendix 1] A compound comprising a structural unit (I) derived from polyalkyleneimine and a compound represented by the following general formula (1); *-CH ２ -CH(-R １ )-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) is directly bonded to a nitrogen atom contained in an amino group in the structural unit (I). A modified polyalkyleneimine having a substituent (A) represented by the following general formula (1); *-CH ２ -CH(-R １)-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) is directly bonded to the nitrogen atom contained in the amino group in the structural unit (I). A modified polyalkyleneimine having a substituent (A) represented by the following formula (I): wherein the molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / amine hydrogen in structural unit (I)] is 7 / 93 or less. [Appendix 3] The modified polyalkyleneimine according to Appendices 1 or 2, wherein X comprises at least one selected from the group consisting of a cyano group, an amide group, a salt of a carboxyl group, an N-alkylamide group, and an N-dialkylamide group. [Appendix 4] The modified polyalkyleneimine according to any one of Appendices 1 to 3, wherein the number-average molecular weight of the structural unit (I) is 250 to 3,000. [Appendix 5] The modified polyalkyleneimine according to any one of Appendices 1 to 4, wherein the structural unit (I) has a structural unit derived from polyethyleneimine. [Appendix 6] A carbon dioxide absorbent comprising the modified polyalkyleneimine according to any one of Appendices 1 to 5. [Appendix 7] The carbon dioxide absorbent according to Appendices 6, comprising: a carrier; and the modified polyalkyleneimine supported on the carrier. [Appendix 8] A method for separating carbon dioxide, comprising a step of contacting gaseous carbon dioxide with the carbon dioxide absorbent according to Appendices 6 or 7. [Appendix 9] A method for recovering carbon dioxide, comprising a step of desorbing the carbon dioxide from the carbon dioxide absorbent according to Appendices 6 or 7 that has absorbed carbon dioxide.

Claims

1. A structural unit (I) derived from polyalkyleneimine and a structural unit (I) represented by the following general formula (1); *-CH ２ -CH(-R １ )-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) is directly bonded to a nitrogen atom contained in an amino group in the structural unit (I). A modified polyalkyleneimine having a substituent (A) represented by the following formula (I): wherein the molar ratio of the substituent (A) to the primary amino groups contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / primary amino groups in the structural unit (I)] is 20 / 80 or less.

2. A structural unit (I) derived from polyalkyleneimine and a structural unit (I) represented by the following general formula (1); *-CH ２ -CH(-R １ )-X (1) (In general formula (1), X represents a monovalent group having 1 to 30 carbon atoms, a nitro group, or a halogen atom, and R １ represents a hydrogen atom or a methyl group. * (asterisk) is directly bonded to a nitrogen atom contained in the amino group in the structural unit (I). A modified polyalkyleneimine having a substituent (A) represented by the following formula: wherein the molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkyleneimine [substituent (A) / amine hydrogen in structural unit (I)] is 7 / 93 or less.

3. The modified polyalkyleneimine according to claim 1 or 2, wherein X comprises at least one selected from the group consisting of a cyano group, an amide group, a salt of a carboxyl group, an N-alkylamide group, and an N-dialkylamide group.

4. The modified polyalkyleneimine according to claim 1 or 2, wherein the structural unit (I) has a number average molecular weight of 250 to 3,000.

5. The modified polyalkyleneimine according to claim 1 or 2, wherein the structural unit (I) has a structural unit derived from polyethyleneimine.

6. A carbon dioxide absorbent comprising the modified polyalkyleneimine according to claim 1 or 2.

7. The carbon dioxide absorbent according to claim 6, comprising: a carrier; and the modified polyalkyleneimine supported on the carrier.

8. A method for separating carbon dioxide, comprising a step of contacting carbon dioxide in gaseous form with the carbon dioxide absorbent according to claim 6.

9. A method for recovering carbon dioxide, comprising a step of desorbing carbon dioxide from the carbon dioxide absorbent according to claim 6 which has absorbed carbon dioxide.

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