Modified polyalkyleneimine and carbon dioxide absorbent

Abstract

Provided is a novel modified polyalkyleneimine.　This modified polyalkyleneimine comprises: a structural unit (I) derived from a polyalkyleneimine; and a substituent (A) represented by general formula (1) of *-C(-R1)(-R2)-C(-R3)(-OH)-C(-R4)(-R5)-O-X (in general formula (1), X is an organic group having at most 7 carbon atoms, R1-R5 are the same as or different from one another and are each a hydrogen atom or an organic group having at most 7 carbon atoms, and * (asterisk) is directly bonded to a nitrogen atom contained in an amino group in the structural unit (I)), wherein the molar ratio [substituent (A) / primary amino group in structural unit (I)] of the substituent (A) to a primary amino group contained in the structural unit (I) in said modified polyalkyleneimine is at most 40 / 60.

Description

Modified polyalkyleneimines and carbon dioxide absorbers

[0001] This invention relates to a modified polyalkyleneimine. Furthermore, this invention relates to a carbon dioxide absorbent using the above-mentioned modified polyalkyleneimine.

[0002] In recent years, a technology called DAC (Direct Air Capture) has been considered as a way to achieve carbon neutrality. This technology captures dilute carbon dioxide in the atmosphere using a carbon dioxide absorbent, thereby concentrating and fixing the carbon dioxide within the absorbent. The fixed carbon dioxide can then be desorbed from the absorbent by heat treatment or vacuum treatment, allowing the carbon dioxide captured from the atmosphere to be stored underground or used as a raw material for chemical products.

[0003] Various chemicals have been considered as carbon dioxide absorbers (Patent Documents 1-8).

[0004] U.S. Patent No. 1,0010861, U.S. Patent No. 1,1027256, International Publication No. 2023 / 196800, International Publication No. 2023 / 215873, International Publication No. 2024 / 104700, International Publication No. 2024 / 124198, Japanese Patent Publication No. 2018-509280, Japanese Patent Publication No. 2012-011333

[0005] The object of the present invention is to provide a novel modified polyalkyleneimine. In one aspect of the present invention, the novel modified polyalkyleneimine exhibits excellent initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate, and its degradation is suppressed.

[0006] As a result of diligent research to achieve the above objective, the inventors of the present invention have found that modified polyalkyleneimines, in which some of the amino groups in the structural units derived from polyalkyleneimines are modified by specific substituents, exhibit excellent initial carbon dioxide desorption ability and carbon dioxide desorption ability retention, and that degradation can be suppressed. The present invention was completed based on these findings.

[0007] In other words, 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). *-C(-R １ ) (-R ２ )-C(-R ３ )(-OH)-C(-R ４ ) (-R ５ )-O-X (1) (In general formula (1), X is an organic group having 7 or fewer carbon atoms, and R １ ~R ５ These may be the same or different atoms, and are either a hydrogen atom or an organic group with 7 or fewer carbon atoms. *(Asterisk) indicates that it is directly bonded to the nitrogen atom contained in the amino group in the structural unit (I).

[0008] The molar ratio of the substituent (A) to the primary amino group contained in the structural unit (I) in the modified polyalkylene imine [substituent (A) / primary amino group in structural unit (I)] is preferably 40 / 60 or less.

[0009] The molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkylene imine [substituent (A) / amine hydrogen in structural unit (I)] is preferably 14 / 86 or less.

[0010] X is preferably at least one selected from the group consisting of an allyl group, a butyl group, an isopropyl group, and a benzyl group.

[0011] The number-average molecular weight of the above structural unit (I) is preferably 250 to 3000.

[0012] The above structural unit (I) preferably has structural units derived from polyethyleneimine.

[0013] Furthermore, the present invention provides a carbon dioxide absorbent containing the above-mentioned modified polyalkyleneimine.

[0014] The carbon dioxide absorbent preferably comprises a carrier and the modified polyalkylene imine supported on the carrier.

[0015] Further, the present invention provides a method for separating carbon dioxide, which includes a step of bringing carbon dioxide in a gas into contact with the above carbon dioxide absorbent.

[0016] Further, the present invention provides a method for recovering carbon dioxide, which includes a step of desorbing the above carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide.

[0017] According to the present invention, a novel modified polyalkyleneimine can be provided. In one aspect of the present invention, the novel modified polyalkyleneimine is excellent in the initial carbon dioxide desorption ability and the carbon dioxide desorption ability maintenance rate, and deterioration is suppressed.

[0018] [Modified polyalkyleneimine] The modified polyalkyleneimine of the present invention is a modified polyalkyleneimine having a structural unit (I) derived from polyalkyleneimine and a substituent (A) represented by the following general formula (1). The modified polyalkyleneimine of the present invention has such a structure, so that it is excellent in the initial carbon dioxide desorption ability and the carbon dioxide desorption ability maintenance rate, and deterioration is suppressed. Therefore, it can be suitably used, for example, in the carbon dioxide absorbent described later.

[0019] *-C(-R １ )(-R ２ )-C(-R ３ )(-OH)-C(-R ４ )(-R ５ ​​​​​​​​​​In the modified polyalkylene imine of the present invention, the molar ratio of the substituent (A) to the amine hydrogen contained in the structural unit (I) in the modified polyalkylene imine [substituent (A) / amine hydrogen in structural unit (I)] is preferably 14 / 86 or less, more preferably 12 / 88 or less, even more preferably 10 / 90 or less, and particularly preferably 8 / 92 or less. Furthermore, the above 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 above molar ratio is within the above range, the initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate are excellent, and degradation tends to be suppressed. In this specification, "amine hydrogen" refers to a primary amino group (-NH ２ This refers to hydrogen directly bonded to the nitrogen atom in the ) and hydrogen directly bonded to the nitrogen atom in the secondary amino group (-NH-).

[0022] The above molar ratio [substituent (A) / amine hydrogen in structural unit (I)] can be calculated stoichiometrically, for example, based on the synthesis method of the modified polyalkyleneimine of the present invention, as follows. Specifically, when the modified polyalkyleneimine of the present invention is obtained by forming substituent (A) derived from the glycidyl ether group-containing compound by an addition reaction between the pre-addition polyalkyleneimine and the glycidyl ether group-containing compound described later, the amount of substituent (A) and the amount of amine hydrogen contained in the structural unit (I) of the modified polyalkyleneimine can be determined by applying the amount and molecular weight of the glycidyl ether group-containing compound and the amount of amine hydrogen of the pre-addition polyalkyleneimine to the following formula. Then, the above molar ratio [substituent (A) / amine hydrogen in structural unit (I)] can be calculated from these amounts. [Amount of substituent (A) (mol)] = W Ｖ / M Ｖ [Amount of amine hydrogen in structural unit (I) (mol)] = (H × W) Ｐ )-(W Ｖ / M Ｖ ) W Ｖ : Amount of glycidyl ether group-containing compound (g) M Ｖ: Molecular weight of the glycidyl ether group-containing compound (g / mol) H: Amount of amine hydrogen per 1 g of pre-addition polyalkylene imine (mol / g) W Ｐ : Amount of polyalkylene imine before addition (g)

[0023] Furthermore, the above molar ratio may be determined by performing known measurements on the modified polyalkylene imine of the present invention, such as nuclear magnetic resonance (NMR) spectroscopy. In this case, for example, the peaks originating from substituent (A) and the peaks originating from amine hydrogens in structural unit (I) may be identified, and the above molar ratio may be calculated from the intensity ratio of these peaks.

[0024] In this specification, "pre-addition polyalkyleneimine" means a polyalkyleneimine that does not have a structure derived from the glycidyl ether group-containing compound, that is, a polyalkyleneimine before the addition of the glycidyl ether group-containing compound. This "pre-addition polyalkyleneimine" may be an unmodified polyalkyleneimine (unmodified polyalkyleneimine), or, as described later, a polyalkyleneimine modified with a compound other than the glycidyl ether group-containing compound. In this specification, unless otherwise specified, "polyalkyleneimine" includes "unmodified polyalkyleneimine" and "modified polyalkyleneimine." In this specification, unless otherwise specified, "polyethyleneimine" includes "unmodified polyethyleneimine" and "modified polyethyleneimine."

[0025] In the modified polyalkylene imine of the present invention, it is preferable that some or all of the substituents (A) are directly bonded to the nitrogen atom contained in the secondary amino group in the structural unit (I). In the modified polyalkylene imine of the present invention, the molar ratio of substituents (A) to primary amino groups contained in the structural unit (I) [substituents (A) / primary amino group in structural unit (I)] is preferably 40 / 60 or less, more preferably 35 / 65 or less, even more preferably 30 / 70 or less, and particularly preferably 24 / 76 or less. Furthermore, the above 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 above molar ratio is within the above range, the initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate are excellent, and degradation tends to be suppressed.

[0026] The above molar ratio [substituent (A) / primary amino group in structural unit (I)] can be calculated stoichiometrically, for example, based on the synthesis method of the modified polyalkyleneimine of the present invention, as follows. First, we will explain the case in which the modified polyalkyleneimine of the present invention is obtained by an addition reaction between the pre-addition polyalkyleneimine and a glycidyl ether group-containing compound to form substituent (A) derived from the glycidyl ether group-containing compound, and it can be assumed that all of the glycidyl ether group-containing compound has been added to the primary amino groups of the pre-addition polyalkyleneimine. In this case, when the amine ratio of the pre-addition polyalkyleneimine is set to primary amino group:secondary amino group = a:b, the amount of primary amino groups (N) per gram of pre-addition polyalkyleneimine can be calculated from a and b. N = H × [a / (2a + b)] N: Amount of primary amino groups per gram of polyalkyleneimine before addition (mol / g) H: Amount of amine hydrogens per gram of polyalkyleneimine before addition (mol / g)

[0027] Next, the amount of substituent (A) and the amount of primary amino groups contained in structural unit (I) in the modified polyalkylene imine can be determined from the following relational equations, and from these amounts, the above molar ratio [substituent (A) / primary amino groups in structural unit (I)] can be calculated. [Amount of substituent (A) (mol)] = W Ｖ / M Ｖ [Amount of primary amino groups in structural unit (I) (mol)] = (N × W) Ｐ )-(W Ｖ / M Ｖ ) W Ｖ : Amount of glycidyl ether group-containing compound (g) M Ｖ : Molecular weight of the glycidyl ether group-containing compound (g / mol) N: Amount of primary amino groups per gram of pre-addition polyalkyleneimine (mol / g) W Ｐ : Amount of polyalkylene imine before addition (g)

[0028] Furthermore, even if the glycidyl ether group-containing compound is thought to have been added to an amino group other than the primary amino group of the pre-addition polyalkylene imine (i.e., a secondary amino group and / or a tertiary amino group), the stoichiometric calculation can be performed by considering the reaction ratio with each amino group.

[0029] Furthermore, the above molar ratio may be determined by performing known measurements, such as nuclear magnetic resonance spectroscopy, on the modified polyalkylene imine of the present invention. In this case, for example, the peak originating from substituent (A) and the peak originating from the primary amino group in structural unit (I) may be identified, and the above molar ratio may be calculated from the intensity ratio of these peaks.

[0030] The modified polyalkylene imines of the present invention can absorb and desorb carbon dioxide (adsorption-desorption) because the amino groups within the molecule undergo a chemical reaction with carbon dioxide to reversibly form carbamates and bicarbonates. In this specification, "absorption" is used to include adsorption, and may also be referred to as sorption.

[0031] The modified polyalkyleneimine of the present invention has structural units (I) derived from polyalkyleneimine. The structural units (I) are not particularly limited, but examples include structural units (Ia) represented by the following general formula (2), structural units (Ib) represented by the following general formula (3), etc. The structural units (I) may be the same as or different from each other.

[0032]

[0033] In general formula (2), R ６ R represents an alkylene group. ６ Preferably, the alkylene group has 2 to 6 carbon atoms, and more preferably, a linear alkylene group has 2 to 6 carbon atoms, and a branched alkylene group has 3 to 6 carbon atoms. Among these, the ethylene group is particularly preferred as the linear alkylene group with 2 to 6 carbon atoms, and the 1,2-propylene group is particularly preferred as the branched alkylene group with 3 to 6 carbon atoms. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B".

[0034]

[0035] In general formula (3), R ６ R represents an alkylene group. ６ Preferably, the alkylene group has 2 to 6 carbon atoms, and more preferably, a linear alkylene group has 2 to 6 carbon atoms and a branched alkylene group has 3 to 6 carbon atoms. Among these, the ethylene group is particularly preferred as the linear alkylene group having 2 to 6 carbon atoms, and the 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 it is bonded to another structural unit (I) via an alkylene group through a branched structure.

[0036] The above structural unit (I) preferably has a structural unit (Ia) represented by the above general formula (2) and / or a structural unit (Ib) represented by the above general formula (3), and more preferably has a structural unit (Ia) represented by the above general formula (2) and a structural unit (Ib) represented by the above general formula (3).

[0037] The above 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 preferable to have structural units derived from NH-).

[0038] The number of nitrogen atoms in one molecule of the above 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 most preferably 12 to 45. Furthermore, the number of nitrogen atoms derived from the amino group in one molecule of the above structural unit (I) is preferably within the above range.

[0039] The number-average molecular weight (Mn) of the above structural unit (I) is preferably 250 to 3000 from the viewpoint of superior oxidation stability and superior low volatility and support 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 3000, even more preferably 2000, and particularly preferably 1500.

[0040] The modified polyalkyleneimine of the present invention has a primary amino group, a secondary amino group, or a tertiary amino group (-N<) in the above structural unit (I). Preferably, the modified polyalkyleneimine has at least a primary amino group in the above structural unit (I), more preferably a primary amino group and a secondary amino group and / or a tertiary amino group in the above structural unit (I), and even more preferably a primary amino group, a secondary amino group and a tertiary amino group in the above structural unit (I).

[0041] The modified polyalkyleneimine of the present invention may be linear or branched. Preferably, the modified polyalkyleneimine of the present invention has a branched structure, i.e., it has tertiary amino groups. The degree of branching of the above 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. Furthermore, the degree of branching is preferably 65% ​​or less, more preferably 55% or less, and even more preferably 50% or less. When the degree of branching is greater than 0%, the content of primary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide. Furthermore, when the degree of branching is 65% or less, the total content of primary and secondary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide.

[0042] The degree of branching described above is the same as that of the modified polyalkyleneimine. １３ By measuring 13C-NMR and determining the intensity ratio between carbon atoms directly bonded to secondary amino groups and carbon atoms directly bonded to tertiary amino groups from the resulting chart, the number of secondary amino groups b and the number of tertiary amino groups c can be calculated. These values ​​of b and c can then be applied to the following formula to determine the degree of branching. Specifically, linear modified polyalkyleneimines have no tertiary amino groups, so their branching degree is 0%. Modified polyalkyleneimines where all nitrogen atoms are tertiary amino groups, i.e., those that are maximally branched, have a branching degree of 100%. Branching degree (%) = [c / (b + c)] × 100

[0043] In general formula (1), X is an organic group having 1 to 7 carbon atoms. The organic group is preferably a hydrocarbon group which may be hydrogen-substituted, more preferably a linear or branched alkyl group, alkenyl group, alkynyl group or aryl group which may be hydrogen-substituted, and even more preferably an unhydrogen-substituted linear or branched alkyl group, alkenyl group, alkynyl group or aryl group. For example, an alcohol group, an amino group, etc., can substitute for the hydrogen of the hydrocarbon group. When X is as described above, the substituent (A) is easily formed by epoxy addition reaction, and the initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate are excellent, and degradation tends to be suppressed.

[0044] In general formula (1), R １ ~R ５ These may be the same or different, and are a hydrogen atom or an organic group having 7 or fewer carbon atoms. １ ~R ５ The number of carbon atoms is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2. The organic group is preferably a hydrocarbon group which may be hydrogen-substituted, more preferably a linear or branched alkyl group, alkenyl group, alkynyl group, or aryl group which may be hydrogen-substituted, and even more preferably an unhydrogen-unsubstituted linear or branched alkyl group, alkenyl group, alkynyl group, or aryl group. For example, an alcohol group, an amino group, etc., can substitute for the hydrogen atoms of the hydrocarbon group. １ ~R ５ Preferably, all of them are hydrogen atoms. １ ~R ５ In this case, it exhibits excellent initial carbon dioxide desorption capacity and carbon dioxide desorption capacity retention rate, and tends to suppress degradation.

[0045] In this specification, examples of linear or branched alkyl groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group (amyl group), n-hexyl group, n-heptyl group, i-propyl group, sec-butyl group, i-butyl group, t-butyl group, 1-methylbutyl group, 1-ethylpropyl group, 2-methylbutyl group, i-amyl group, neopentyl group, 1,2-dimethylpropyl group, 1,1-dimethylpropyl group, t-amyl group, 1,3-dimethylbutyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, 2-ethyl-2-methylpropyl group, 2-methylhexyl group, 3-methylhexyl group, 1,2-dimethylpentyl group, cyclohexyl group, and the like.

[0046] In the present invention, examples of linear or branched alkenyl groups include vinyl groups, allyl groups, 1-butenyl groups, 2-butenyl groups, pentenyl groups, hexenyl groups, and heptenyl groups.

[0047] In the present invention, examples of linear or branched alkynyl groups include ethynyl group, 1-propynyl group, 2-propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, and the like.

[0048] In the present invention, examples of linear or branched aryl groups include phenyl groups, benzyl groups, methylphenyl groups, and the like.

[0049] When the modified polyalkyleneimine of the present invention has a plurality of X, the plurality of X may be the same as or different from each other.

[0050] [Method for Producing Modified Polyalkyleneimine] The method for producing the modified polyalkyleneimine of the present invention is not particularly limited, but for example, it can be obtained by forming a substituent (A) on the amino group in the polyalkyleneimine. More specifically, it can be produced by mixing the above-mentioned pre-addition polyalkyleneimine with the above-mentioned glycidyl ether group-containing compound and reacting them. The above method for producing the modified polyalkyleneimine may be referred to as "the method for producing the present invention." As the method for producing the present invention, it is preferable to include a step of epoxy adding the above-mentioned glycidyl ether group-containing compound to the above-mentioned pre-addition polyalkyleneimine, from the viewpoint of excellent reactivity and suppression of adverse effects (such as contamination with impurities and generation of by-products). Note that the modified polyalkyleneimine of the present invention may be produced by methods other than the method for producing the present invention.

[0051] The manufacturing method of the present invention preferably includes a step of mixing the above-mentioned pre-addition polyalkyleneimine and the above-mentioned glycidyl ether group-containing compound (mixing step). In the above mixing step, the method of mixing each component is not particularly limited; for example, all components may be mixed at once, or any of the components may be added later and mixed. In the above mixing step, the method of adding each component is not particularly limited, and known or conventional methods can be applied. For example, they may be added at once to the reaction system, continuously (added over a certain period of time), or intermittently (added in multiple installments). Furthermore, the rate of addition may be changed once or more during the addition process. In particular, from the viewpoint of excellent reactivity, it is preferable to continuously or intermittently add and mix the above-mentioned pre-addition polyalkyleneimine. As a method of continuous addition, known or conventional methods can be applied, for example, a method of addition using a microtube pump, a dropping funnel, etc. Methods for intermittent addition include known or conventional methods, such as a method of continuous addition in which the addition can be stopped and restarted manually or automatically. Furthermore, a solvent may be used in the mixing step as needed, and a solvent may or may not be used for any of the components.

[0052] (Pre-addition polyalkyleneimine) The pre-addition polyalkyleneimine is a compound having structural units derived from alkyleneimine and not having structures derived from the glycidyl ether group-containing compound. The modified polyalkyleneimine of the present invention can typically be obtained by reacting the pre-addition polyalkyleneimine with the glycidyl ether group-containing compound. However, the modified polyalkyleneimine of the present invention is not limited to these substrate combinations.

[0053] The above-mentioned pre-addition polyalkyleneimine is a compound having structural units derived from alkyleneimine. The structural units derived from alkyleneimine are not particularly limited, but structural units derived from alkyleneimine having 2 to 6 carbon atoms are preferred. The above-mentioned pre-addition polyalkyleneimine may be used alone or two or more types may be used.

[0054] The polyalkylene imine before addition described above may be modified with a compound other than the glycidyl ether group-containing compound described above (other compounds). Examples of these other compounds include alkylene oxides having 2 to 30 carbon atoms (e.g., ethylene oxide, propylene oxide, butylene oxide, etc.), vinyl group-containing compounds, isocyanate group-containing compounds, or acid anhydrides.

[0055] Examples of the polyalkyleneimines before addition include polymers of alkyleneimines and polymers of polyamines. Examples of the alkyleneimines 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, or two or more types may be used. That is, the polyalkyleneimines before addition may be homopolymers or copolymers of alkyleneimines.

[0056] Examples of the polyamines mentioned above include ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, which are polyamines having 2 to 6 carbon atoms. One type of polyamine may be used, or two or more types may be used. That is, the polyalkyleneimine before addition may be a homopolymer of polyamines, a copolymer of polyamines, or a copolymer of polyamines and alkyleneimines.

[0057] Among the above-mentioned polyalkyleneimines before addition, polyethyleneimine (PEI) having ethyleneimine structural units is preferred. The above-mentioned polyalkyleneimines before addition are not particularly limited, and commercially available products may be used, or products manufactured by known manufacturing methods may be used.

[0058] The above pre-addition polyalkyleneimine contains at least a primary amino group (-NH ２ It has either a primary amino group or a secondary amino group (-NH-). The above pre-addition polyalkyleneimine preferably has a primary amino group and a secondary amino group, and more preferably has a primary amino group, a secondary amino group, and a tertiary amino group (-N<).

[0059] Generally, the reactivity of primary amino groups is considered to be higher than that of secondary amino groups. Therefore, when obtaining the modified polyalkyleneimine of the present invention by reacting the above-mentioned pre-addition polyalkyleneimine with a glycidyl ether group-containing compound, the glycidyl ether group-containing compound is usually considered to preferentially add to the primary amino group. However, the glycidyl ether group-containing compound may also add to the secondary amino group.

[0060] The amount of amine hydrogen per gram of the polyalkyleneimine before addition is preferably 5 mmol / g or more, more preferably 10 mmol / g or more, and even more preferably 15 mmol / g or more. Furthermore, the amount of amine hydrogen is preferably 45 mmol / g or less, more preferably 40 mmol / g or less, and even more preferably 35 mmol / g or less.

[0061] The amount of amine hydrogen per gram of the pre-addition polyalkyleneimine can be calculated stoichiometrically from the substrate used in the synthesis of the pre-addition polyalkyleneimine. For example, if the pre-addition polyalkyleneimine is obtained by adding x moles of alkyleneamine, which has 1 amine hydrogen per molecule, to 1 mole of polyamine, which has 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 gram of pre-addition polyalkyleneimine (mol / g) = [(p + x) / number-average molecular weight of pre-addition polyalkyleneimine (g / mol)] × 1000

[0062] The number-average molecular weight (Mn) of the polyalkylene imine before addition is preferably 250 to 3000, from the viewpoint of superior oxidation stability and superior support 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 3000, even more preferably 2000, and particularly preferably 1500.

[0063] The above number-average molecular weight can be measured by a known method using pullulan as a standard substance in gel permeation chromatography (GPC). In this invention, the following conditions are adopted for GPC measurement: Measurement apparatus: GPC apparatus (manufactured by Shimadzu Corporation) Column used: Shodex OHpak SB-807HQ (2 tubes) + SB-806M / HQ (2 tubes) manufactured by Resonaq 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 volume: 50 μL Standard substance: Shodex STANDARD P-82 (manufactured by Resonaq Corporation) Detector: Differential refractometer (manufactured by Shimadzu Corporation)

[0064] The molar ratio (amine ratio) of primary amino groups, secondary amino groups, and tertiary amino groups in the polyalkyleneimine before addition is preferably 10-60:10-60:10-50 (total 100) for primary amino groups:secondary amino groups:tertiary amino groups, more preferably 20-50:20-55:10-40 (total 100), and even more preferably 25-45:30-50:20-35 (total 100).

[0065] The above amine ratio can be determined by performing a measurement on the polyalkylene imine before addition using nuclear magnetic resonance (NMR) spectroscopy. For example, １３ If the carbon atoms directly bonded to the nitrogen atom in the primary amino group, the secondary amino group, and the tertiary amino group can be identified from the chart obtained by measuring C-NMR, the amine ratio can be calculated by determining the intensity ratio of the peaks originating from each of these carbon atoms. Specifically, the number of primary amino groups a, the number of secondary amino groups b, and the number of tertiary amino groups c are calculated, and the ratio of a, b, and c is taken as the amine ratio, so that primary amino group:secondary amino group:tertiary amino group = a:b:c. Note that if the structure of the polyalkylene imine before addition is complex, the above １３ If analysis is difficult using only C-NMR measurements, the amine ratio may be calculated by identifying characteristic atom-derived peaks, such as those originating from each carbon atom, using known methods, and determining the intensity ratio of each peak. Suitable methods for the above analysis include, for example, １ H-NMR, １３ C-NMR, １５ One-dimensional NMR such as N-NMR, １ H- １ H₂COSY (Correlation Spectroscopy) and other homogeneous nuclear correlation two-dimensional NMR, １ H- １３ C HMQC (Heteronuclear Multiple Quantum Coherence), １ H- １３C HMBC (Heteronuclear Multiple Bond Connectivity), １ H- １３ C HMQC-TOCSY (TOtally Correlated Spectroscopy), １ H- １５ Examples include heterogeneous nuclear correlation two-dimensional NMR using HMBs and other fluorocarbons.

[0066] The primary amino group content 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, based on 100 mol% of the total amount of alkyleneimine constituting the polyalkyleneimine before addition. Furthermore, the above content 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.

[0067] The content of secondary amino groups in the polyalkyleneimine before addition is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, based on 100 mol% of the total amount of alkyleneimines constituting the polyalkyleneimine before addition. Furthermore, the above content is preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less.

[0068] The content of tertiary amino groups in the polyalkyleneimine before addition is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, based on 100 mol% of the total amount of alkyleneimines constituting the polyalkyleneimine before addition. Furthermore, the above content is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less.

[0069] The above-mentioned polyalkyleneimine before addition may be linear or branched, that is, it may have a tertiary amino group. It is preferable that the above-mentioned polyalkyleneimine before addition has a branched structure. The degree of branching of the above-mentioned polyalkyleneimine before addition 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. Furthermore, the degree of branching is preferably 65% ​​or less, more preferably 55% or less, and even more preferably 50% or less. When the degree of branching is greater than 0%, the content of primary amino groups becomes moderately high, which is preferable from the viewpoint of excellent reactivity with carbon dioxide. Furthermore, when the degree of branching is 65% or less, the total content of primary and secondary amino groups becomes moderately high, which is preferable from the viewpoint of even better reactivity with carbon dioxide.

[0070] The above degree of branching is the same as that of the polyalkyleneimine before addition. １３ By measuring C-NMR and obtaining a chart, the intensity ratio of carbon atoms directly bonded to secondary amino groups to carbon atoms directly bonded to tertiary amino groups can be determined. This allows for the calculation of the number of secondary amino groups (b) and the number of tertiary amino groups (c). These values ​​(b and c) can then be applied to the following formula: That is, the linear pre-addition polyalkyleneimine has no tertiary amino groups, so its branching degree is 0%. Furthermore, the pre-addition polyalkyleneimine, where all nitrogen atoms are tertiary amino groups, i.e., maximally branched, has a branching degree of 100%. Branching degree (%) = [c / (b + c)] × 100

[0071] The amine value per unit of nonvolatile content of the polyalkylene imine before addition is preferably 5 or higher, more preferably 10 or higher, and even more preferably 15 or higher. Furthermore, the amine value is preferably 30 or lower, more preferably 27 or lower, and even more preferably 25 or lower.

[0072] The above non-volatile content (resin content) can be measured by the Karl Fischer method or the dry weight method. The specific measurement methods are described below. • Karl Fischer method: Measuring instrument; Karl Fischer moisture meter; Solvent; methanol 20-30 ml; Amine neutralizer; acetic acid 7 ml; Formula: Resin content (wt%) = 100 - V × F / S × 100; V = KF titration volume (ml); F = KF titer (mg / ml); S = Sample volume (mg) • Dry weight method: Approximately 1 g of the sample is placed in an aluminum dish and dried in a hot air circulating dryer at 150 ± 5°C for 1 hour, then allowed to cool in a desiccator for 10 minutes. Formula: Resin content (wt%) = W / S × 100; W: Residual weight after drying (g); S: Sample weight before drying (g)

[0073] The amine value mentioned above is the number of moles (moles) of amino groups contained in 1 g of the non-volatile content of the polyalkylene imine before addition. The amine value can be calculated by potentiometric titration using a 0.5 mol / L p-toluenesulfonic acid standard solution in methanol solution.

[0074] (Glycidyl ether group-containing compounds) Glycidyl ether group-containing compounds can be suitably used because they react with the amino group of polyalkyleneimines under relatively mild conditions, forming a stable structure, and exhibiting excellent manufacturing efficiency and product stability (oxidation resistance, heat resistance).The above glycidyl ether group-containing compounds include methyl glycidyl ether, ethyl glycidyl ether, n-propyl glycidyl ether, n-butyl glycidyl ether, n-pentyl glycidyl ether, n-hexyl glycidyl ether, n-heptyl glycidyl ether, i-propyl glycidyl ether, sec-butyl glycidyl ether, i-butyl glycidyl ether, t-butyl glycidyl ether, 1-methylbutyl glycidyl ether, 1-ethylpropyl glycidyl ether, 2-methylbutyl glycidyl ether, i-amyl glycidyl ether, neopentyl glycidyl ether, 1,2-dimethylpropyl glycidyl ether, 1,1-dimethylpropyl glycidyl ether, t-amyl glycidyl ether, 1,3-dimethylbutyl glycidyl ether, 3,3-dimethylbutyl glycidyl ether, 2-ethylbutyl glycidyl ether, 2-ethyl-2-methylpropyl glycidyl ether, 2-methylhexyl glycidyl ether, and 3-methylhexyl glycidyl ether. It is more preferable to include at least one selected from the group consisting of ether, 1,2-dimethylpentyl glycidyl ether, cyclohexyl glycidyl ether, vinyl glycidyl ether, allyl glycidyl ether, 1-butenyl glycidyl ether, 2-butenyl glycidyl ether, pentenyl glycidyl ether, hexenyl glycidyl ether, heptenyl glycidyl ether, ethinyl glycidyl ether, 1-propynyl glycidyl ether, 2-propynyl glycidyl ether, butynyl glycidyl ether, pentynyl glycidyl ether, hexynyl glycidyl ether, heptynyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether; it is even more preferable to include at least one selected from the group consisting of allyl glycidyl ether, butyl glycidyl ether, i-propyl glycidyl ether, and benzyl glycidyl ether; and it is particularly preferable to include allyl glycidyl ether, i-propyl glycidyl ether, and benzyl glycidyl ether.In particular, using allyl glycidyl ether, i-propyl glycidyl ether, or benzyl glycidyl ether results in excellent initial carbon dioxide desorption ability and retention rate, as well as a tendency to suppress degradation. The above glycidyl ether group-containing compounds may be used individually or in combination of two or more.

[0075] The modified polyalkylene imine of the present invention has a structure in which a specific amount of amine hydrogen is substituted with the specific glycidyl ether group-containing compound described above, resulting in excellent initial carbon dioxide desorption ability and retention rate of carbon dioxide desorption ability, and a tendency to suppress degradation. Generally, amino groups having amine hydrogen in polyalkylene imines can react with carbon dioxide and adsorb or desorb it. Among them, primary amino groups and secondary amino groups have excellent reactivity with carbon dioxide. However, carbon dioxide absorbents containing polyalkylene imines have the problem of being prone to degradation due to heating, repeated use, side reactions, etc. For example, H is abstracted from the C-H bond of the α-carbon of the amino group, generating a C radical, followed by O ２It is known that the O radical generated by the addition of a certain group acts as a starting point for the cleavage of the C-N bond, thereby generating a carbonyl group. Modifying the amino group can suppress the above degradation, but a trade-off occurs where a decrease in amine concentration due to modification leads to a decrease in carbon dioxide desorption ability. The modified polyalkylene imine of the present invention can improve the stability of the amino group while suppressing the decrease in carbon dioxide absorption by modifying a specific amount of amino group with the specific glycidyl ether group-containing compound described above. In particular, by modifying with a glycidyl ether group-containing compound that has a structure with a small C-H bond energy, such as an allyl group, i-propyl group, or benzyl group, a weak C-H bond can be introduced near the amino group. Therefore, it is thought that the C-H bond with a smaller bond energy is removed preferentially (sacrificed) over the C-H bond at the α position of the amino group, resulting in the C-H bond at the α position of the amino group being more likely to remain, thereby suppressing amine degradation and improving the maintenance rate of carbon dioxide desorption ability. In this way, it is estimated that the modified polyalkylene imines of the present invention exhibit superior initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rates compared to the unmodified polyalkylene imines, and that degradation can be suppressed.

[0076] When the above glycidyl ether group-containing compound is reacted with the above pre-addition polyalkyleneimine, it is presumed that an epoxy addition reaction will proceed between the amino group of the pre-addition polyalkyleneimine and the above glycidyl ether group-containing compound, thereby yielding a modified polyalkyleneimine having a terminal structure in which the amine hydrogen is substituted by the above glycidyl ether group-containing compound. Specifically, for example, using allyl glycidyl ether, which is the above glycidyl ether group-containing compound, the primary amino group (-NH) of the pre-addition polyalkyleneimine is reacted. ２ When an epoxy addition reaction proceeds with a primary amino group (-NH-), the primary amino group is modified by allyl glycidyl ether to form a terminal structure (-NH-CH ２ -CH(-OH)-CH ２ -O-CH ２ -CH=CH ２ ) or terminal structures in which the above secondary amino group is modified by allyl glycidyl ether (>N-CH２ -CH(-OH)-CH ２ -O-CH ２ -CH=CH ２ It is presumed that a modified polyalkylene imine having the above-mentioned glycidyl ether group-containing compound will be obtained. The modified polyalkylene imine of the present invention preferably has a structure in which the above-mentioned glycidyl ether group-containing compound is added to at least a primary amino group.

[0077] Examples of solvents used in the above mixing step include water and organic solvents. Polar solvents are preferred as organic solvents. Alcohols such as methanol and ethanol are preferred as polar solvents.

[0078] The reaction temperature in the above mixing step can be adjusted as appropriate depending on the reactivity of the glycidyl ether group-containing compound, for example, preferably 0°C to 100°C, more preferably 20°C to 95°C, and even more preferably 20°C to 90°C.

[0079] The reaction time in the above mixing step can be appropriately adjusted according to the reactivity of the glycidyl ether group-containing compound, for example, preferably 0.1 to 200 hours, more preferably 0.2 to 100 hours, even more preferably 0.5 to 24 hours, and most preferably 0.5 to 12 hours.

[0080] [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, by containing the modified polyalkyleneimine of the present invention, exhibits excellent initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate, and tends to suppress degradation. In other words, the above composition is preferably a carbon dioxide absorbent composition.

[0081] The above composition may be liquid or solid. When the above composition is used as a carbon dioxide absorbent as described later, it is preferable that the composition be liquid from the viewpoint of superior handling and support properties. Examples of liquid compositions include compositions 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 liquid compositions include compositions that do not contain a solvent such as water, in which the modified polyalkyleneimine of the present invention is in liquid form. Examples of solid compositions include solvent-free compositions containing the modified polyalkyleneimine of the present invention.

[0082] (Other Components) The compositions of the present invention can be produced, for example, by adding various components to the modified polyalkyleneimine of the present invention. Other components other than the modified polyalkyleneimine of the present invention can be used as appropriate. Examples of 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 aids, crystallization inhibitors, etc. Other components may also include impurities such as metals that are not intentionally included. 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 preferably 10 or more, more preferably 12 or more, and even more preferably 15 or more.

[0083] As the above-mentioned antioxidant, radical scavengers, peroxide decomposers, etc., can be used. As the above-mentioned radical scavengers, phenolic antioxidants, amineic antioxidants, etc., can be used, and amineic antioxidants are preferred. As the above-mentioned peroxide decomposers, there are no particular limitations as long as they can effectively decompose peroxides, but sulfuric antioxidants, phosphorusic antioxidants, phenolic antioxidants, hindered amineic antioxidants, etc., can be used. Examples of the above sulfur-based antioxidants include 2-hydroxyethyl disulfide, 1,2-bis[(2-hydroxyethyl)thio]ethane, thiodipropionic acid, dilauryl thiodipropionate, distearyl thiodipropionate, lauryl stearyl 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, dodecanethiol, etc., with 2-hydroxyethyl disulfide and 1,2-bis[(2-hydroxyethyl)thio]ethane being more preferred.Examples of the phosphorus-based antioxidants mentioned above include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris(nonylphenyl) phosphite, diisodecylpentaerythritol phosphite, tris(2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis(octadecyl) phosphite, cyclic neopentanetetraylbis(2,4-di-t-butylphenyl) phosphite, and cyclic neopentanetetraylbis(2,4-di-t- Phosphates such as butyl-4-methylphenyl) phosphite and bis[2-t-butyl-6-methyl-4-{2-(octadecyloxycarbonyl)ethyl}phenyl]hydrogen phosphite (phosphite-based antioxidants); 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 are examples.Examples of the above-mentioned phenolic antioxidants 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} Examples include bisphenols such as ethyl[2,4,8,10-tetraoxaspiro[5.5]undecane; 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 high molecular weight phenols such as tocopherol. Examples of the above-mentioned hindered amine antioxidants include bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, methyl-1,2,2,6,6-pentamethyl-4-piperidyl sebacate, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, and 4-hydroxy-2,2,6,6-tetramethylpiperidine.

[0084] Examples of the crystallization inhibitors mentioned above include water-soluble polymers such as polyvinylpyrrolidone, polyvinyl alcohol, and hydroxyethylcellulose. By using water-soluble polymers as crystallization inhibitors, it is possible to suppress the secondary interaction between carbamic acid, which is produced by the reaction of the oligoamine compound with carbon dioxide, and the oligoamine compound, which can lead to the formation of insoluble salts.

[0085] Examples of the metal impurities mentioned above include elemental metals and components containing metals (e.g., metal oxides). Examples of the metals mentioned above include transition metals. The transition metals are elements from groups 3 to 12 of the periodic table, and more 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.

[0086] From the viewpoint of excellent durability, the content of metal-containing components in the above composition is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less, based on 100% by mass of the total amount of the composition. Furthermore, it is particularly preferable that the above composition substantially does not contain any metal-containing components. The above content may also be 0.5 ppm or more, or 1 ppm or more, based on 100% by mass of the total amount of the composition. More specifically, the total content of each component containing chromium, manganese, iron, cobalt, nickel, and copper in the above composition is preferably within the above range based on 100% by mass of the total amount of the composition. The above content can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0087] The above composition can be produced by known or conventional methods. For example, it can be produced by mixing the above-mentioned other components with the modified polyalkylene imine of the present invention and stirring.

[0088] [Carbon Dioxide Absorbent] A carbon dioxide absorbent can be prepared using the modified polyalkyleneimine of the present invention or the above 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, by containing the modified polyalkyleneimine of the present invention, exhibits excellent initial carbon dioxide desorption ability and carbon dioxide desorption ability retention rate, and tends to suppress degradation.

[0089] 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 it may be manufactured, for example, by adding various components to the modified polyalkyleneimine of the present invention. Examples of the various components include carriers and other components that may be included in the composition of the present invention as described above. From the viewpoint of ease of handling, 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 may be used.

[0090] From the viewpoint of improving carbon dioxide adsorption and desorption capacity, the above-mentioned carrier is preferably a porous carrier particle. Furthermore, examples of materials constituting the above-mentioned carrier include inorganic materials and polymer materials. In other words, the above-mentioned carrier is preferably a porous carrier particle composed of an inorganic material and / or a polymer material.

[0091] The inorganic material may preferably include 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 structures, with silica and / or alumina being more preferred, and silica being even more preferred. The silica is not particularly limited, and known silicas such as fumed silica produced by a dry method, precipitated silica produced by a wet method, silica gel, and silica sol can be used as appropriate. The inorganic material may be used by one or more types.

[0092] Examples of the above polymer materials include ether sulfone (PES), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose mixed ester or nitrocellulose (NC), polyolefin, polyethylene, polypropylene, polymethylpentene, polyketone, polyimide, polystyrene, polymethyl methacrylate, polydimethylsiloxane, polyester, nylon, polycaprolactone, polylactic acid, polyvinyl alcohol, and polyglycolic acid. One type of the above polymer material may be used, or two or more types may be used.

[0093] The specific surface area of ​​the above carrier is set at 70 m² from the viewpoint of having excellent carbon dioxide adsorption and desorption capacity. ２ Preferably 80 m / g or more, and more preferably 80 m ２ / g or more, more preferably 100m ２ It is 1 / g or more. Furthermore, the specific surface area is 800 m². ２ It may be less than / g, and 650m ２ It may be less than / g, and 500m ２ It may be less than / g.

[0094] From the viewpoint of excellent carbon dioxide adsorption / desorption ability, the content of the modified polyalkylene imine 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, per 100 parts by mass of the total amount of the carrier. Furthermore, from the viewpoint of excellent carbon dioxide adsorption / desorption ability and support, 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, per 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 per 100 parts by mass of the total amount of the carrier.

[0095] The above-mentioned carrier may contain metals as impurities. Examples of the above-mentioned metals are those exemplified and described as other metal components that may be contained in the composition of the present invention described above. From the viewpoint of excellent durability, the content ratio of the metal-containing component in the above-mentioned 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, based on 100% by mass of the total amount of the above-mentioned carrier. Furthermore, from the viewpoint of industrial applicability (productivity), the above-mentioned content ratio may be 10 ppm or more, 30 ppm or more, or 50 ppm or more, based on 100% by mass of the total amount of the above-mentioned carrier. More specifically, the total content ratio of each component containing chromium, manganese, iron, cobalt, nickel, and copper in the above-mentioned carrier is preferably within the above range, based on 100% by mass of the total amount of the above-mentioned carrier. The above-mentioned content ratio can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0096] The above-mentioned carbon dioxide absorbent can separate carbon dioxide not only from gases containing high concentrations of carbon dioxide, but also from dilute carbon dioxide in conditioned air and the atmosphere. Furthermore, by going through a process of desorption (removal) of the absorbed carbon dioxide, the carbon dioxide can be recovered, and it becomes possible to absorb carbon dioxide again. Therefore, by using the above-mentioned carbon dioxide absorbent, it is possible to suppress the decrease in carbon dioxide absorption and desorption capacity even after repeated absorption and desorption of carbon dioxide.

[0097] The carbon dioxide absorbent described above can be manufactured by known or conventional methods. Here, the carbon dioxide absorbent can be manufactured, for example, by mixing and stirring the above-mentioned components. Specifically, when the carbon dioxide absorbent contains the modified polyalkylene imine of the present invention or the above composition and the above carrier, the method for manufacturing the carbon dioxide absorbent preferably includes a step of mixing and stirring the modified polyalkylene imine of the present invention or the above composition and the above carrier to support the modified polyalkylene imine of the present invention or the above composition on the carrier (supporting step). From the viewpoint of excellent handling and supportability, it is more preferable that the method for manufacturing the carbon dioxide absorbent includes a step of mixing and stirring the above composition, which contains at least the modified polyalkylene imine of the present invention and a solvent, and the above carrier to support the modified polyalkylene imine of the present invention on the carrier (supporting step). When using the above composition, the supporting step may be a step of adding the above composition to the carrier and supporting it (step (a)), or a step of adding each component contained in the above composition separately to the carrier and supporting it (step (b)). Of the above-mentioned loading process, process (a) is preferred from the viewpoint of superior manufacturing efficiency. In addition, the order in which each component is added in process (b) is not particularly limited.

[0098] The above-mentioned loading process can employ known or conventional methods. For example, the modified polyalkyleneimine or composition of the present invention may be loaded by impregnating the carrier (impregnation), or the modified polyalkyleneimine or composition of the present invention may be loaded by dropwise adding it to the carrier (dropwise adding), or the carrier may be loaded by filling a container such as a column and then passing the modified polyalkyleneimine or composition of the present invention through it (liquid passing). Among these, the impregnation method is preferred from the viewpoint of ease of operation and equipment.

[0099] The pressure conditions in the above loading process are not particularly limited and can be arbitrarily selected from atmospheric pressure, reduced pressure, or increased pressure. If the carrier has pores, it is preferable to process it under reduced pressure from the viewpoint of removing air bubbles in the pores and efficiently loading it onto the carrier. The specific pressure during processing is preferably 1 Pa to 100 Pa, more preferably 1 Pa to 50 Pa, and even more preferably 10 Pa to 30 Pa.

[0100] The temperature conditions in the above loading process are not particularly limited, but from the viewpoint of excellent loading performance, 20°C to 90°C is preferred, more preferably 30°C to 80°C, and even more preferably 40°C to 70°C.

[0101] Furthermore, the method for producing the carbon dioxide absorbent may, if necessary, include a step of separating the excess solvent from the carrier on which the composition is supported (separation step), and / or a step of removing the solvent from the carrier (drying step).

[0102] The above separation process can employ known or conventional methods, such as filtration, decantation, or centrifugation. Among these, filtration is preferred due to its ease of procedure.

[0103] The temperature conditions in the above drying process 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 most preferably 50°C to 90°C.

[0104] The processing time in the above drying process 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.

[0105] The pressure conditions in the above drying process are not particularly limited and can be arbitrarily selected from atmospheric pressure, reduced pressure, or increased pressure. Among these, atmospheric pressure is preferred from the viewpoint of maintaining the state in which the modified polyalkylene imine of the present invention is supported on the carrier.

[0106] The above-mentioned carbon dioxide absorbent can be installed and used in a device (carbon dioxide recovery device) 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 other gases. Examples of the gas to be treated include the atmosphere, or high-concentration gases with a higher carbon dioxide concentration than the atmosphere. Such high-concentration gases are, for example, those emitted from internal combustion engines or factories.

[0107] Methods for using the above-mentioned carbon dioxide absorbent include a carbon dioxide separation method that includes a step of contacting the carbon dioxide absorbent with carbon dioxide in a gas (contact step), and a carbon dioxide recovery method that includes 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 carbon dioxide can be removed (separated) from the gas. In the desorption step, carbon dioxide can be recovered by desorbing the carbon dioxide from the carbon dioxide absorbent.

[0108] The pressure conditions for the above contact process may be, for example, 0.8 atmospheres to 1.1 atmospheres. The temperature conditions for the above contact process may be, for example, -40°C to 50°C.

[0109] The pressure conditions for the above-mentioned attachment / detachment process may be, for example, under reduced pressure, or between 0.02 atmospheres and 0.5 atmospheres, or between 0.1 atmospheres and 0.3 atmospheres. The temperature conditions for the above-mentioned attachment / detachment process may be, for example, under heating, or between 50°C and 130°C.

[0110] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "mass percent," and the blending amounts and mass ratios described in the examples mean the blending amount and mass ratio of each component (i.e., the blending amount and mass ratio of the solid content in each raw material).

[0111] Synthesis Example 1 (Preparation of Modified Polyethyleneimine 1) 5.0 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 content 27.6 mmol / g (theoretical value)), which is the polyalkyleneimine before addition, was charged into the reactor. Then, 0.95 g of allyl glycidyl ether (AGE, molecular weight 114.14) was added dropwise while stirring at 23°C, and the mixture was continued to stir at 23°C for 1 hour. After stirring, the mixture was reacted at 50°C for 4 days, １ ¹H-NMR analysis confirmed the loss of the peaks attributed to the C-H of the glycidyl group of AGE, thus confirming the acquisition of modified polyethyleneimine 1. Modified polyethyleneimine 1 has a structural unit (I) derived from polyethyleneimine and a substituent (A) derived from AGE (*-CH ２ -CH(-OH)-CH ２ -O-CH ２ -CH=CH ２ ) possessed.

[0112] The above unmodified polyethyleneimine was obtained by a known manufacturing method. The amount of amine hydrogen per gram of the above unmodified polyethyleneimine was calculated to be 27.6 mmol / g from the substrate used in the synthesis of the above unmodified polyethyleneimine and the following formula: Amount of amine hydrogen per gram of unmodified polyalkyleneimine (mol / g) = [(p + x) / number average molecular weight of unmodified polyalkyleneimine (g / mol)] × 1000 p: number of amine hydrogens per molecule of polyamine x: number of moles of alkyleneamine having one amine hydrogen per molecule

[0113] The degree of amine hydrogen substitution in modified polyethyleneimine 1 was calculated to be 6.0 mol% by applying the amount and molecular weight of the epoxy group-containing compound AGE, the amount of unmodified polyethyleneimine, and the amount of amine hydrogen per gram of unmodified polyethyleneimine calculated above to the following formula: Degree of amine hydrogen substitution (mol%) = [(W Ｖ / M Ｖ ) / (H×W Ｐ)〕×100 W Ｖ : The blending amount (g) of the glycidyl ether group-containing compound M Ｖ : The molecular weight (g / mol) of the glycidyl ether group-containing compound H: The amount of amine hydrogen per 1 g of unmodified polyethyleneimine (mol / g) W Ｐ : The blending amount (g) of unmodified polyethyleneimine

[0114] The addition rate of the glycidyl ether group-containing compound to the primary amino group of modified polyethyleneimine 1 was calculated to be 18 mol% by applying the molar ratio of the primary amino group and secondary amino group in the above unmodified polyethyleneimine as primary amino group: secondary amino group = a:b, and these a and b and the substitution degree of the above amine hydrogen to the following formula. In addition, it was assumed that all AGE was added to the primary amino group of unmodified polyethyleneimine. Addition rate (mol%) of vinyl group-containing compound to primary amino group = [substitution degree of amine hydrogen (mol%)] × [(2a + b) / a]

[0115] 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 structural unit (I)] was calculated to be 18 / 82 by the above method. Similarly, the molar ratio of the substituent (A) to the amine hydrogen in the structural unit (I) [substituent (A) / amine hydrogen in structural unit (I)] was calculated to be 6 / 94 by the above method.

[0116] Synthesis Example 2 (Preparation of Modified Polyethyleneimine 2) A modified polyethyleneimine 2 of Synthesis Example 2 was obtained in the same manner as in Synthesis Example 1, except that 1.1 g of butyl glycidyl ether (BGE, molecular weight 130.19) was dropped instead of AGE. Here, in the modified polyethyleneimine 2, 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, 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. The modified polyethyleneimine 2 has a structural unit derived from polyethyleneimine as the structural unit (I), and a structure (*-CH ２ -CH(-OH)-CH ２ -O-CH ２ -CH ２ -CH ２ -CH ３ ) derived from BGE as the substituent (A).

[0117] Synthesis Example 3 (Preparation of Modified Polyethyleneimine 3) Unmodified polyethyleneimine (trade name "SP-012", manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 1200 (GPC method), primary amino group: secondary amino group: tertiary amino group = 35:35:30 (catalog value), amine hydrogen amount 25.4 mmol / g (theoretical value)) was used, and a modified polyethyleneimine-3 of Synthesis Example 3 was obtained in the same manner as in Synthesis Example 1, except that the dropping amount of AGE was 0.48 g. Here, in the modified polyethyleneimine 3, 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 9.1 / 90.9, 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 3 / 97. The modified polyethyleneimine 3 has a structural unit derived from polyethyleneimine as the structural unit (I), and a structure (*-CH ２ -CH(-OH)-CH ２ -O-CH ２ -CH=CH ２ ) derived from AGE as the substituent (A).

[0118] 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 0.58 g of isopropyl glycidyl ether (iPrGE, molecular weight 116.16) was added dropwise instead of AGE. Here, 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 18 / 82, 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. Modified polyethyleneimine 4 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from iPrGE as substituent (A). ２ -CH(-OH)-CH ２ -O-CH(-CH ３ )CH ３ ) possessed.

[0119] 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 0.82 g of benzyl glycidyl ether (BnGE, molecular weight 164.2) was added dropwise instead of AGE. Here, 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 18 / 82, 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. Modified polyethyleneimine 5 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from BnGE as substituent (A). ２ -CH(-OH)-CH ２ -O-CH ２ It had -Ph).

[0120] 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 2, except that the amount of BGE added was 3.2 g. Here, in modified polyethyleneimine 6, 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 53 / 47, 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. Modified polyethyleneimine 6 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from BGE as substituent (A). ２ -CH(-OH)-CH ２ -O-CH ２ -CH ２ -CH ２ -CH ３ ) possessed.

[0121] 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 1.1 g of 1,2-epoxyoctane (12EO, molecular weight 128.22) was added dropwise instead of AGE. Here, 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 18 / 82, 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. Modified polyethyleneimine 7 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from 12EO as substituent (A). ２ -CH(-OH)-CH ２ -CH ２ -CH ２ -CH ２ -CH ２ -CH ３ ) possessed.

[0122] 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 6, except that the amount of 12EO added was 3.2 g. Here, 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 53 / 47, 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. Modified polyethyleneimine 8 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from 12EO as substituent (A). ２ -CH(-OH)-CH ２ -CH ２ -CH ２ -CH ２ -CH ２ -CH ３ ) possessed.

[0123] 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 1.5 g of 2-ethylhexylglycidyl ether (2EHGE, molecular weight 186.30) was added dropwise instead of AGE. Here, in modified polyethyleneimine 9, 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, 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. Modified polyethyleneimine 9 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from 2EHGE as substituent (A). ２ -CH(-OH)-CH ２ -O-CH ２ -CH (-CH ２ CH ３ ) - CH ２ -CH ２ -CH ２ -CH ３ ) possessed.

[0124] Synthesis Example 10 (Preparation of Modified Polyethyleneimine 10) Modified polyethyleneimine 10 of Synthesis Example 10 was obtained in the same manner as in Synthesis Example 8, except that the amount of 2EHGE added was 4.5 g. Here, 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 53 / 47, 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. Modified polyethyleneimine 10 has a structural unit derived from polyethyleneimine as structural unit (I), and a structure (*-CH) derived from 2EHGE as substituent (A). ２ -CH(-OH)-CH ２ -O-CH ２ -CH (-CH ２ CH ３ ) - CH ２ -CH ２ -CH ２ -CH ３ ) possessed.

[0125] Example 1 Modified polyethyleneimine 1 (0.5 parts) from Synthesis Example 1 and water (5.0 parts) were mixed to obtain a homogeneous solution. Next, 1.0 part of CARIACT G-10 (manufactured by Fuji Silysia Chemical Co., Ltd.) as a carrier was added to the above solution and impregnated while stirring for 30 minutes. Then, after being treated under reduced pressure at 60°C and 20 Pa, the solution was heated and dried in an oven at 80°C for 2 hours to obtain the carbon dioxide absorbent of Example 1 in which modified polyethyleneimine 1 was supported on the carrier.

[0126] Examples 2-5 and Comparative Examples 1-6: Carbon dioxide absorbents for Examples 2-5 and Comparative Examples 1-6 were obtained in the same manner as in Example 1, except that, as shown in Table 1, each modified polyethyleneimine or unmodified polyethyleneimine (product names "SP-006" and "SP-012", manufactured by Nippon Shokubai Co., Ltd.) obtained in each synthesis example were used instead of modified polyethyleneimine 1.

[0127] <Evaluation> The carbon dioxide absorbents obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0128] (1) Carbon dioxide adsorption and desorption capacity The carbon dioxide adsorption and desorption capacity of the carbon dioxide absorbents obtained in Examples 1 to 5 and Comparative Examples 1 to 6 was measured by the following test. Then, using the obtained carbon dioxide adsorption and desorption capacity, the blank retention rate was calculated from the following formula and evaluated according to the following criteria. Note that the carbon dioxide adsorption and desorption capacity at this time is the "initial CO2" in Table 1. ２ This is shown in the item "Adsorption / Desorption Amount [g / g]".

[0129] [Carbon Dioxide Adsorption / Desorption Test] A differential thermal-thermogravimetric (TG-DTA) thermogravimetric (TG-DTA) analyzer (manufactured by Rigaku Corporation, TG-DTA8120, 8122) was used to measure the mass of carbon dioxide absorbent at the absorption temperature (40°C) and desorption temperature (110°C), and the amount of carbon dioxide adsorbed and desorbed 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 approximately 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 : Mass (g) of carbon dioxide absorbent at absorption temperature W Ｄ : Mass (g) of carbon dioxide absorbent at desorption temperature W １ : Mass (g) of carbon dioxide absorbent used in the test

[0130] [Formula for calculating blank retention rate] Blank retention rate (%) = [(Initial carbon dioxide adsorption / desorption amount in each example or comparative example) / (Initial carbon dioxide adsorption / desorption amount in comparative example 1)] × 100

[0131] [Evaluation Criteria for Initial Carbon Dioxide Adsorption / Desorption Ability] ○: Blank retention rate exceeds 80% ×: Blank retention rate is 80% or less

[0132] (2) Carbon Dioxide Desorption Ability Retention Rate The carbon dioxide absorbents obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were subjected to the degradation treatment described below, and then the carbon dioxide adsorption and desorption tests described above were carried out to measure the amount of carbon dioxide adsorbed and desorbed. Using the obtained amount of carbon dioxide adsorption and desorption, the retention rate after degradation treatment at 100°C for 48 hours was calculated from the calculation formula below and evaluated according to the criteria below. The amount of carbon dioxide adsorption and desorption at this time is shown in Table 1 as "CO2 after degradation treatment at 100°C for 48 hours". ２ This is shown in the item "Adsorption / Desorption Amount [g / g]".

[0133] [Degradation Treatment] 0.03 g each of the carbon dioxide absorbent obtained in Examples 1-5 and Comparative Examples 1-6 was weighed into 10 mL vials. The top of each vial was protected with weighing paper that had multiple holes punched in it to prevent contamination with foreign matter while allowing air to pass through. After standing in a 100°C oven for 48 hours, the vials were cooled to obtain carbon dioxide absorbent that had undergone degradation treatment. This treatment causes the carbon dioxide absorbent to degrade due to heating and oxidation, thus mimicking absorbent that has undergone heating and repeated adsorption / desorption treatments.

[0134] [Formula for calculating retention rate after degradation treatment] Retention rate after degradation treatment (%) = [(Amount of carbon dioxide adsorption / desorption after degradation treatment in each example or comparative example) / (Amount of carbon dioxide adsorption / desorption after degradation treatment in Comparative Example 1)] × 100

[0135] [Durability Evaluation Criteria] ○: Retention rate after degradation treatment exceeds 105% ×: Retention rate after degradation treatment is 105% or less

[0136] (3) Suppression of deterioration <Analysis of deterioration indicators by accelerated testing> 0.5 g each of the modified or unmodified polyethyleneimine obtained in each synthesis example was weighed into an aluminum cup. Each aluminum cup was left to stand in an oven at 120°C for 4 hours to obtain modified or unmodified polyethyleneimine that had undergone deterioration treatment. By such accelerated testing, polyethyleneimines undergo deterioration due to heating and oxidation, so it is possible to simulate polyethyleneimines in absorbents that have undergone heating and repeated adsorption / desorption treatment in a short time.

[0137] [IR Measurement] The polyethyleneimines that underwent the degradation treatment described above were measured using a Fourier transform infrared spectrophotometer (NEXUS670, Thermo Fisher Scientific) by the diamond ATR method. For the absorbances assigned below, the intensity ratios of (1) / (3) and (2) / (3) were calculated, and the results are shown in Table 1. Due to the oxidative degradation of polyethyleneimines, the absorbances of (1) and (2) increase, so the lower the ratio of (1) / (3) and (2) / (3), the more stable the material is against the degradation treatment. (1) 1660 cm －１ Carbonyl C=O stretching vibration (2) 1680 cm －１ Imin's C=N stretching vibration (3) 2810 cm －１ Alkane C-H stretching vibration

[0138] [Evaluation Criteria for Structural Degradation After Accelerated Testing] (1) / (3) Rate of Change ◎: Less than 50% ○: 50% or more and less than 60% ×: 60% or more (2) / (3) Rate of Change ◎: Less than 35% ○: 35% or more and less than 50% ×: 50% or more

[0139] [Appearance] The polyethyleneimines that had undergone the degradation treatment described above were collected in 5 ml glass screw tubes, and their color was observed visually.

[0140] [Evaluation criteria for deterioration of appearance after accelerated testing] ◎: Slightly yellowish ○: Pale yellow ×: Brownish

[0141] The results are shown in Table 1.

[0142]

[0143] All of the carbon dioxide absorbents in the examples had a blank retention rate of over 80% and a retention rate of over 105% after degradation treatment. On the other hand, none of the carbon dioxide absorbents in the comparative examples had a blank retention rate of over 80% and a retention rate of over 105% after degradation treatment. Therefore, it was found that all of the carbon dioxide absorbents in the examples were superior to the carbon dioxide absorbents in the comparative examples in terms of initial carbon dioxide desorption ability and retention rate of carbon dioxide desorption ability.

[0144] Furthermore, IR measurements revealed that all carbon dioxide absorbents in the examples were stable against degradation treatment, meaning that degradation was suppressed. In particular, the carbon dioxide absorbents in Examples 1, 3, 4, and 5 showed more suppressed degradation than the carbon dioxide absorbent in Example 2.

[0145] Furthermore, the carbon dioxide absorbent in the examples that underwent degradation treatment was slightly yellowish or pale yellow, indicating that degradation was suppressed based on its appearance.

[0146] The following describes variations of the invention according to the present invention. [Note 1] A structural unit (I) derived from a polyalkyleneimine and the following general formula (1); *-C(-R １ ) (-R ２ )-C(-R ３ )(-OH)-C(-R ４ ) (-R ５ )-O-X (1) (In general formula (1), X is an organic group having 7 or fewer carbon atoms, and R １ ~R ５ A modified polyalkyleneimine having a substituent (A) represented by * (asterisk), wherein the molar ratio of substituent (A) to primary amino groups contained in structural unit (I) in the modified polyalkyleneimine [substituent (A) / primary amino group in structural unit (I)] is 40 / 60 or less. [Note 2] A modified polyalkyleneimine having a structural unit (I) derived from polyalkyleneimine and the following general formula (1); *-C(-R １ ) (-R ２ )-C(-R ３ )(-OH)-C(-R ４ ) (-R ５ )-O-X (1) (In general formula (1), X is an organic group having 7 or fewer carbon atoms, and R １ ~R ５A modified polyalkyleneimine having a substituent (A) represented by * (asterisk), wherein 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 14 / 86 or less. [Note 3] X is at least one selected from the group consisting of an allyl group, a butyl group, an isopropyl group, and a benzyl group, as described in Note 1 or 2. [Note 4] The number average molecular weight of the structural unit (I) is 250 to 3000, as described in any one of Notes 1 to 3. [Note 5] The structural unit (I) is a modified polyalkyleneimine according to any one of Notes 1 to 4, having a structural unit derived from polyethyleneimine. [Note 6] A carbon dioxide absorbent comprising a modified polyalkyleneimine according to any one of Notes 1 to 5. [Note 7] A carbon dioxide absorbent according to Note 6, comprising a carrier and the modified polyalkyleneimine supported on the carrier. [Note 8] A method for separating carbon dioxide, comprising the step of contacting the carbon dioxide absorbent according to Note 6 or 7 with carbon dioxide in a gas. [Note 9] A method for recovering carbon dioxide, comprising the step of desorbing the carbon dioxide from the carbon dioxide absorbent according to Note 6 or 7 that has absorbed carbon dioxide.

Claims

1. A structural unit (I) derived from a polyalkyleneimine and the following general formula (1); *-C(-R １ ) (-R ２ )-C(-R ３ )(-OH)-C(-R ４ ) (-R ５ )-O-X (1) (In general formula (1), X is an organic group having 7 or fewer carbon atoms, and R １ ~R ５ A modified polyalkyleneimine having a substituent (A) represented by * (asterisk), wherein 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 40 / 60 or less.

2. A structural unit (I) derived from a polyalkyleneimine and the following general formula (1); *-C(-R １ )(-R ２ )-C(-R ３ )(-OH)-C(-R ４ )(-R ５ )-O-X (1) (In general formula (1), X is an organic group having 7 or fewer carbon atoms, and R １ to R ５ may be the same or different and are a hydrogen atom or an organic group having 7 or fewer carbon atoms. The asterisk (*) is directly bonded to the nitrogen atom contained in the amino group in the structural unit (I).), which is a modified polyalkyleneimine having a substituent (A) represented by the formula, and 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 14 / 86 or less, which is a modified polyalkyleneimine.

3. The modified polyalkylene imine according to claim 1 or 2, wherein X is at least one selected from the group consisting of an allyl group, a butyl group, an isopropyl group, and a benzyl group.

4. The modified polyalkylene imine according to claim 1 or 2, wherein the number-average molecular weight of the structural unit (I) is 250 to 3000.

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 polyalkylene imine described in 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 the step of contacting a carbon dioxide absorbent according to claim 6 with carbon dioxide in a gas.

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

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