Alkyleneimine polymer, method for producing same, and carbon dioxide absorbent material

Abstract

The present invention provides: an alkyleneimine polymer which has little coloration, high solubility in water, and excellent storage stability in an aqueous solution, and has reduced deterioration; and a method for producing the same. The present invention also provides a carbon dioxide absorbent material which is excellent in terms of carbon dioxide adsorption / desorption capacity (especially, carbon dioxide adsorption / desorption capacity retention rate and carbon dioxide desorption rate).　This alkyleneimine polymer comprises a structural unit (A) represented by general formula (1) (in general formula (1), either N is a primary amine) and a structural unit (B) represented by general formula (2), and has a number average molecular weight (Mn) of 250 to 50,000. (In general formula (2), X represents an organic group having 3 to 20 carbon atoms.)

Description

Alkyleneimine polymer, its production method, and carbon dioxide absorbent

[0001] The present invention relates to an alkyleneimine polymer and a method for producing the same, and also to a carbon dioxide absorbent using the alkyleneimine polymer.

[0002] Ethyleneimine polymers are widely used in fields such as paper processing agents, adhesives, pressure-sensitive adhesives, paints, inks, fiber treatment agents, flocculating and separating agents, cosmetics, toiletries, and dispersants. Generally, ethyleneimine polymers, which are polymers having a secondary amine in the main chain, are produced by ring-opening polymerization of ethyleneimine in the presence of an acid catalyst such as hydrochloric acid or sulfuric acid. Patent Document 1 discloses that ethyleneimine is dropped into an acid catalyst and an amine such as ethylenediamine to polymerize, and the molecular weight of the polymer is controlled by changing the molar ratio of the amine to the ethyleneimine. Patent Document 2 discloses that ethyleneimine is polymerized in the presence of a polymetallooxoacid salt to produce an ethyleneimine polymer with little branching, specifically an ethyleneimine polymer with a branching degree exceeding 0 and 30% or less. Patent Document 3 discloses that polyethyleneimine is supported on a carrier and then subjected to CO ２ There are many other reports on polyamines (for example, Patent Documents 4 and 5).

[0003] Japanese Patent Publication No. 49-33120 Japanese Patent Application Laid-Open No. 11-158271 Japanese Patent Application Laid-Open No. 2020-168624 International Publication No. 2022-13802 International Publication No. 2023-181676

[0004] However, ethyleneimine polymers have a problem in that they tend to yellow or even brown over time during the production process, storage, transportation, use, etc. Therefore, the use of ethyleneimine polymers has been restricted in some applications where appearance is important, such as food packaging films, detergent raw materials, inks, and paints. Furthermore, when an aqueous solution of polyethyleneimine is stored for a long period of time or when stored in a refrigerator, it may become cloudy or precipitate, and it has become clear that there are handling issues, such as the need to remove the precipitate by heating, stirring, or filtration to redissolve the solution uniformly.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an alkyleneimine polymer that has little coloration, high solubility in water, excellent storage stability in an aqueous solution, and suppressed deterioration, and a method for producing the same, which is an industrially applicable method. Another object of the present invention is to provide a carbon dioxide absorbent that uses the alkyleneimine polymer and has excellent carbon dioxide adsorption and desorption capacity (particularly, carbon dioxide adsorption and desorption capacity retention rate and carbon dioxide desorption rate).

[0006] The present inventors have conducted extensive research on various alkyleneimine polymers, including polyethyleneimine, and have discovered that by introducing an organic group having 3 or more carbon atoms as a base amine when synthesizing the alkyleneimine polymer and polymerizing ethyleneimine, an alkyleneimine polymer can be produced by an industrially applicable method, which has little coloration, high solubility in water, excellent storage stability in an aqueous solution, or is inhibited from deteriorating. They have also found that use of the alkyleneimine polymer results in excellent carbon dioxide adsorption / desorption capacity (particularly, carbon dioxide adsorption / desorption capacity retention rate and carbon dioxide desorption rate), and have conceived that the above-mentioned problems can be solved in an excellent manner, thereby completing the present invention.

[0007] That is, the present invention includes the following inventions: [1] A structural unit (A) represented by the following general formula (1), and

[0008] (However, any N in the general formula (1) is a primary amine.) An alkyleneimine polymer comprising a structural unit (B) represented by the following general formula (2), and having a number average molecular weight (Mn) of 250 to 50,000:

[0009] (In the general formula (2), X represents an organic group having 3 to 20 carbon atoms.) [2] Structural unit (C) represented by the following general formula (3): (wherein each N in the general formula (3) is independently a secondary amine or a tertiary amine.) [3] The alkyleneimine polymer according to claim 1, further comprising a structural unit (A) represented by the general formula (1) and / or a structural unit (C) represented by the following general formula (3): (wherein both N in general formula (3) are independently a secondary amine or a tertiary amine).) [4] The alkyleneimine polymer according to any one of the above [1] to [3], which has two or more primary amines and one or more secondary amines or tertiary amines. [5] An amino group-containing compound having a structural unit represented by the following general formula (4),

[0010] (In general formula (4), X represents an organic group having 3 to 20 carbon atoms.) A method for producing an alkyleneimine polymer, comprising a step of subjecting ethyleneimine to a ring-opening addition reaction. [6] A carbon dioxide absorbent comprising the alkyleneimine polymer described in any of [1] to [4] above. [7] The carbon dioxide absorbent described in [6] above, comprising: a carrier; and the alkyleneimine polymer supported on the carrier. [8] A method for separating carbon dioxide, comprising a step of contacting gaseous carbon dioxide with the carbon dioxide absorbent described in [6] or [7] above. [9] A method for recovering carbon dioxide, comprising a step of desorbing the carbon dioxide from the carbon dioxide absorbent described in [6] or [7] above that has absorbed the carbon dioxide.

[0011] The alkyleneimine polymer of the present invention has the above-mentioned configuration, exhibits little coloration, high solubility in water, excellent storage stability in aqueous solution, and inhibits deterioration. Therefore, it can be suitably used in a variety of applications, such as paper processing agents, adhesives, pressure-sensitive adhesives, paints, inks, fiber treatment agents, flocculation / separation agents, cosmetics, toiletries, dispersants, metal surface treatment agents, polishing / cleaning agents for semiconductor manufacturing processes, and carbon dioxide absorbents. Furthermore, a carbon dioxide absorbent containing the alkyleneimine polymer of the present invention has excellent carbon dioxide adsorption / desorption capacity (particularly, carbon dioxide adsorption / desorption capacity retention rate and carbon dioxide desorption rate). Furthermore, a carbon dioxide absorbent containing the alkyleneimine polymer of the present invention preferably tends to have a low moisture absorption amount, and is expected to reduce the energy required to heat the absorbent to the temperature required for carbon dioxide desorption.

[0012] 1 shows the results of measuring the absorbance at each wavelength (300 to 500 nm) of 4% by mass aqueous solutions of the alkyleneimine polymers obtained in Examples 1 to 5 and Comparative Examples 1 to 4. It can be seen that the absorbances of Examples 1 to 3 tend to be lower than the absorbances of Comparative Examples 1 to 3.

[0013] Preferred embodiments of the present invention are specifically described below, but the present invention is not limited to the following description and can be appropriately modified and applied within the scope of the present invention. A combination of two or more of the individual preferred embodiments of the present invention described below also falls within the scope of preferred embodiments of the present invention. Furthermore, in this specification, the term "X to Y" indicating a range means "X or more and Y or less," and "weight" and "mass," "wt %" and "mass %," and "parts by weight" and "parts by mass" are treated as synonyms. Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20 to 25°C) and a relative humidity of 40 to 50%.

[0014] <Alkyleneimine Polymer> The alkyleneimine polymer of the present invention is preferably a polymer obtained by ring-opening addition polymerization of ethyleneimine to a base amine, and is preferably a polymer compound having a branched structure containing primary, secondary, and tertiary amines.

[0015] The alkyleneimine polymer of the present invention contains a structural unit (A) represented by the following general formula (1).

[0016] The structural unit (A) is a structural unit derived from ethyleneimine. Because ethyleneimine is an amine compound with a small molecular weight, the amino group concentration can be increased when the alkyleneimine polymer is polymerized, thereby more significantly enhancing the characteristics of the amino group contained in the alkyleneimine polymer. Furthermore, since ethyleneimine can undergo cycloaddition polymerization, it is easier to achieve a high molecular weight than polycondensation of diamines, etc., and no by-products such as ammonia are produced by polycondensation, resulting in a low environmental impact in terms of element efficiency. Furthermore, since special conditions or equipment such as a transition metal catalyst are not required for the polymerization reaction, industrial productivity is excellent. Additionally, industrial availability is higher than that of other monomers capable of cycloaddition polymerization, such as propyleneamine and azetidine. It is also preferable that the alkyleneimine polymer of the present invention contains two or more structural units (A) represented by the general formula (1). The alkyleneimine polymer of the present invention preferably contains two or more structural units (A), because the solubility of the alkyleneimine polymer of the present invention in water is improved when dissolved in water. In addition, embodiments other than the case where two different bonds of N in the general formula (1) form the same ring are included.

[0017] The alkyleneimine polymer of the present invention also contains a structural unit (B) represented by the following general formula (2).

[0018] (In general formula (2), X represents an organic group having 3 to 20 carbon atoms.) The general formula (2) is preferably a structural unit derived from a base amine.

[0019] As described above, the alkyleneimine polymer of the present invention is preferably a polymer obtained by ring-opening addition polymerization of ethyleneimine to a base amine. The base amine has an organic group having 3 to 20 carbon atoms. Furthermore, the base amine is preferably one or more types selected from compounds having two or more amines selected from primary amines and secondary amines.

[0020] X in the general formula (2) is not particularly limited as long as it is an organic group having 3 to 20 carbon atoms, and when it does not contain a heteroatom, it is preferably an organic group having 3 to 15 carbon atoms, more preferably an organic group having 3 to 10 carbon atoms, and even more preferably an organic group having 3 to 8 carbon atoms (e.g., a trimethylene group (propylene group), a tetramethylene group (butylene group), a pentamethylene group (pentylene group), a hexamethylene group (hexylene group), a heptamethylene group (heptylene group), an octamethylene group (octylene group), an m-xylylene group, or a p-xylylene group). When X in the general formula (2) contains a heteroatom, it is preferably an organic group having 3 to 15 carbon atoms, more preferably an organic group having 3 to 10 carbon atoms, and even more preferably an organic group having 3 to 8 carbon atoms, per heteroatom. Specifically, X is, for example, a compound given as an example of a base amine to be described later (for example, 1,4-bis(3-aminopropyl)piperazine, etc.) in which NH ２ It is preferable that the number of carbon atoms in X in the general formula (2) is within the above-mentioned range, because the solubility in water of the alkyleneimine polymer of the present invention is improved when the alkyleneimine polymer is dissolved in water.

[0021] The organic group is preferably a hydrocarbon group. More preferably, it is a linear, branched, or cyclic alkyl group, alkenyl group, alkynyl group, aryl group, or aralkyl group. Still more preferably, it is a linear, branched, or cyclic alkyl group, which may contain a heteroatom such as an oxygen atom, sulfur atom, nitrogen atom, or phosphorus atom. When a heteroatom is contained, it is preferably a hydrocarbon group having an amino group.

[0022] As described above, the alkyleneimine polymer of the present invention has a linear structure, and preferably further has a branched structure, a cyclic structure, or a branched structure and a cyclic structure. Furthermore, the terminal of each polymer chain constituting the alkyleneimine polymer of the present invention is a primary amine. Therefore, it is preferable that any N in general formula (1) is a primary amine.

[0023] When any N in the general formula (1) is a primary amine, the alkyleneimine polymer of the present invention further contains a structural unit (C) represented by the following general formula (3): (However, both N's in general formula (3) are independently a secondary amine or a tertiary amine.) The structural unit (C) is a structural unit derived from ethyleneimine. Because ethyleneimine is an amine compound with a small molecular weight, the amino group concentration can be increased when the alkyleneimine polymer is polymerized, thereby more significantly bringing out the characteristics of the amino group contained in the alkyleneimine polymer. Furthermore, since ethyleneimine can undergo cycloaddition polymerization, it is easier to achieve a high molecular weight than polycondensation of diamines, etc., and there are no by-products due to polycondensation such as ammonia, which reduces the environmental impact in terms of element efficiency. Furthermore, since special conditions or equipment such as a transition metal catalyst are not required for the polymerization reaction, it is excellent in industrial productivity. In addition, it is more industrially available than other monomers capable of cycloaddition polymerization, such as propyleneamine and azetidine. Furthermore, the alkyleneimine polymer of the present invention preferably contains two or more structural units (C) represented by general formula (3). The alkyleneimine polymer of the present invention preferably contains two or more of the structural units (C), because the solubility of the alkyleneimine polymer of the present invention in water is improved when the alkyleneimine polymer is dissolved in water. This also includes embodiments other than the case where two different N bonds in the general formula (3) form the same ring.

[0024] The alkyleneimine polymer of the present invention preferably contains two or more structural units (A) represented by the general formula (1) and / or two or more structural units (C) represented by the general formula (3).

[0025] The alkyleneimine polymer of the present invention preferably has a structure having two or more primary amines and one or more secondary or tertiary amines.

[0026] The base amine can be expressed as an amino group-containing compound having a structural unit represented by the following general formula (4).

[0027] (In the general formula (4), X represents an organic group having 3 to 20 carbon atoms.) X in the general formula (4) is the same as in the general formula (2), and the preferred embodiments are also the same.

[0028] The base amine is not particularly limited as long as it is an amino group-containing compound having a structural unit represented by the general formula (4). Specific examples of the base amine include alkylene diamines such as trimethylenediamine, 1,4-butanediamine (putrescine), 1,5-pentanediamine (cadaverine), hexamethylenediamine, heptamethylenediamine, octamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 1,2-diaminopropane, 2-ethylaminoethylamine, 3-methylaminopropylamine, 1,2-diaminobutane, N,N'-di-tert-butylethylenediamine, and m-xylylenediamine. Examples of base amines include alkylene polyamines such as iminobispropylamine (dipropylenetriamine), methyliminobispropylamine, N,N'-bis(2-aminoethyl)-1,3-propanediamine, N,N'-bis(3-aminopropyl)-ethylenediamine, N,N'-bis(3-aminopropyl)-1,3-propylenediamine, N,N'-bis(3-aminopropyl)1,4-butylenediamine, and dihexylenetriamine. Examples of the base amine also include ring-containing amines such as 1,4,7-triazacyclononane, 1,4,8,12-tetraazacyclopentadecane, 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,7,10-tetraazacyclododecane (cyclen), 1,4-bis(3-aminopropyl)piperazine, 2-aminomethylpiperazine, metaxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, norbornanediamine, isophoronediamine, phenylenediamine, 4,4'-methylenebis(cyclohexylamine), and 4,4'-methylenebis(2-methylcyclohexylamine). Examples of the base amine also include oxygen-containing amines such as 3-(2-hydroxyethylamino)propylamine, bis(3-aminopropyl)ether, and 1,2-bis(3-aminopropoxy)ethane.

[0029] Preferred base amines are 1,2-diaminopropane, trimethylenediamine, hexamethylenediamine, bis(3-aminopropyl)ether, iminobispropylamine, methyliminobispropylamine, N,N'-bis(2-aminoethyl)-1,3-propanediamine, N,N'-bis(3-aminopropyl)-ethylenediamine, N,N'-bis(3-aminopropyl)-1,3-propylenediamine, N,N'-bis(3-aminopropyl)1,4-butylenediamine, 1,4-bis(3-aminopropyl)piperazine, 2-aminomethylpiperazine, metaxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, norbornanediamine, isophoronediamine, dihexylenetriamine, 4,4'-methylenebis(cyclohexylamine), and 4,4'-methylenebis(2-methylcyclohexylamine). It is preferable that these amine compounds are precursors of the general formula (2) because they prevent a decrease in the amino group concentration of the alkyleneimine polymer and do not significantly impair the properties inherent to the alkyleneimine polymer (adhesion, cationicity, coagulation, reactivity, etc.) Furthermore, it is preferable that these amine compounds are precursors of the general formula (2) because they improve the solubility in water when the alkyleneimine polymer of the present invention is dissolved in water.

[0030] As described above, the alkyleneimine polymer of the present invention is usually a polymer obtained by ring-opening addition polymerization of ethyleneimine to the base amine. For example, the base amine may be a methyl group having a structure of NH ２ The alkyleneimine polymer of the present invention is a compound having an NH group (primary amine) or an NH group (secondary amine), and the alkyleneimine polymer of the present invention can be obtained by ring-opening addition polymerization of ethyleneimine to the amino group. However, the alkyleneimine polymer of the present invention is not limited to a production method other than the ring-opening addition polymerization of ethyleneimine to the base amine, and may be a polymer obtained by a condensation reaction or other reaction.

[0031] In the method for ring-opening addition polymerization of ethyleneimine to the base amine, the base amine is ２When the compound has an NH ２ In some cases, only one ethyleneimine group undergoes an addition reaction with ethyleneimine, and in other cases, both ethyleneimine groups undergo an addition reaction with NH ２ At the end of the group, a new NH ２ The NH group is generated. ２ Similarly, one or two ethyleneimines can be added to the NH group. ２ Ethyleneimine can also undergo an addition reaction with an NH group generated by an addition reaction with a group (primary amine) or an NH group (secondary amine) contained in a base amine. Therefore, the alkyleneimine polymer of the present invention can have a branched structure. The alkyleneimine polymer of the present invention may contain at least one structural unit derived from the base amine and represented by the general formula (4), or may contain two or more structural units.

[0032] As mentioned above, the terminal structure produced by the addition reaction of ethyleneimine is NH ２ It is a group. Furthermore, as mentioned above, since ethyleneimine can also undergo an addition reaction with NH groups, it is preferable that the alkyleneimine polymer of the present invention contains a polyalkyleneamine structure with a linear structure and a polyalkyleneamine structure with a branched structure. Therefore, it is preferable that the alkyleneimine polymer of the present invention contains a primary amine, a secondary amine, and a tertiary amine. When the base amine of the structural unit (B) constituting the alkyleneimine polymer of the present invention is the alkylenediamine or alkylenepolyamine, the total number of nitrogen atoms (N ｔ ) to the number of primary amines (N １ ) ratio [(N １ / N ｔ ) × 100] is 20 to 65 mol %, and the number of secondary amines (N ２ ) ratio [(N ２ / N ｔ ) × 100] is 20 to 65 mol %, and the number of tertiary amines (N ３ ) ratio [(N ３ / N ｔ) × 100] is preferably 10 to 60 mol %, and the ratio (molar ratio) of the number of primary amines / secondary amines / tertiary amines is preferably 25 to 60 / 25 to 60 / 15 to 50, and more preferably 30 to 60 / 30 to 60 / 10 to 40.

[0033] When any N in the general formula (1) is a primary amine, the ratio of the structural unit (A) and / or the structural unit (C) to the structural unit (B) is preferably 2 to 1,000 mol, more preferably 2 to 500 mol, and even more preferably 3 to 200 mol of the structural unit (A) and / or the structural unit (C) per 1 mol of the structural unit (B).

[0034] The alkyleneimine polymer of the present invention is an alkyleneimine polymer having a narrow molecular weight distribution, and the dispersity (Mw / Mn ratio), which indicates the degree of broadness of the molecular weight distribution, is preferably 1.0 to 3.0 (measured by gel permeation chromatography (GPC), converted into pullulan). The number average molecular weight (Mn) of the alkyleneimine polymer of the present invention is not particularly limited as long as it is 250 to 50,000. It is more preferably 300 to 30,000, and even more preferably 300 to 20,000. When the number average molecular weight (Mn) of the alkyleneimine polymer of the present invention is in the above-mentioned range, this is preferred because the solubility in water of the alkyleneimine polymer of the present invention is improved when dissolved in water.

[0035] The weight-average molecular weight and number-average molecular weight in the present invention can be measured by a known method using gel permeation chromatography (GPC) with pullulan as a standard substance. The following conditions are adopted as GPC measurement conditions in the present invention: Measurement apparatus: manufactured by Shimadzu Corporation; Columns used: Shodex OHpak SB-807HQ (two columns) + SB-806M / HQ (two columns) manufactured by Resonaq; Eluent: 0.5 mol% sodium nitrate, 0.5 mol% acetic acid; Standard substance: Shodex STANDARD P-82 (manufactured by Resonaq Corporation); Detector: Differential refractometer (manufactured by Shimadzu Corporation).

[0036] The alkyleneimine polymer of the present invention is more reactive than other polymer compounds, and can be chemically modified depending on the intended use by reacting it with an aldehyde compound, an alkyl halide compound, an isocyanate compound, an epoxy compound such as epichlorohydrin, a cyanamide compound, a guanidine compound, urea, a carboxylic acid compound, a cyclic acid anhydride compound, or an acyl halide compound.

[0037] The alkyleneimine polymer and modified products thereof according to the present invention can be industrially used in a variety of applications, including papermaking agents, anchor agents for laminating paper, cloth, OPP or PET films, heavy metal chelating agents, metal plating additives, fire extinguishing foams, adhesion improvers for vinyl chloride sol adhesives, crosslinking agents for epoxy resins, adhesion improvers for ethylene vinyl acetate copolymers (EVA), polyvinyl acetate (PVAc) or polyvinyl alcohol (PVA), pressure-sensitive adhesive modifiers, adhesion promoters for film printing inks, adhesion improvers for paints, dispersants for pigments and the like, enzyme immobilization agents, cement for oil drilling, water treatment agents (coagulants), scale inhibitors, It can be widely used in applications such as surface modifiers for glass or carbon fibers, dye fixing agents, textile or dishwashing detergents, metal corrosion inhibitors, wood preservatives, polishing / cleaning agents for semiconductor manufacturing processes, hair care products, absorbents for carbon dioxide, chlorine, nitrogen oxides, sulfur oxides, hydrogen sulfide, or aldehydes, antislip agents for polyvinyl acetal films, agents for improving the heat or oil resistance of thermoplastic polymers such as polyamides, polyacetals, polyolefins, polyesters, PVC, or polycarbonates, antistatic agents for polyolefins, crosslinking agents for polymers containing acid anhydride groups, and surface modifiers for water-absorbing resins. Among these, preferred applications are anchoring agents, adhesion improvers, dispersants, polishing / cleaning agents for semiconductor manufacturing processes, and carbon dioxide absorbents (carbon dioxide absorbers).

[0038] <Method for producing alkyleneimine polymer> The method for producing an alkyleneimine polymer of the present invention is not particularly limited and may be carried out under general reaction conditions. The method for producing an alkyleneimine polymer of the present invention may be referred to as the "production method of the present invention." The production method of the present invention preferably includes a step of subjecting ethyleneimine to a ring-opening addition reaction with an amino group-containing compound having a structural unit represented by the following general formula (4). The ring-opening addition reaction can also be referred to as polymerization.

[0039] (In general formula (4), X represents an organic group having 3 to 20 carbon atoms.)

[0040] In a more preferred production method, ethyleneimine is polymerized in an atmosphere having an oxygen concentration of 2% by volume or less, so that the temperature of the reaction solution during polymerization is 80 to 160°C, and the temperature of the heat medium for removing the reaction heat during polymerization is 40°C or higher.

[0041] The ethyleneimine used in the production method of the present invention is not particularly limited, and for example, ethyleneimine obtained by a method of intramolecularly cyclizing a halogenated ethylamine in a liquid phase with a concentrated alkali, a method of intramolecularly cyclizing a monoethanolamine sulfate with a hot concentrated alkali (hereinafter also referred to as a liquid phase method), or a method of catalytically intramolecularly dehydrating monoethanolamine in a gas phase (hereinafter also referred to as a gas phase method) can be used.

[0042] As the polymerization catalyst, those generally used in the polymerization of ethyleneimine can be used, and inorganic acids, organic acids, carbon dioxide, or Lewis acids are suitable. Examples of inorganic acids include hydrochloric acid, sulfuric acid, hydrobromic acid, and phosphoric acid. Examples of organic acids include p-toluenesulfonic acid, trichloroacetic acid, and trifluoroacetic acid. Examples of Lewis acids include aluminum chloride, and acetic acid, hydrochloric acid, sulfuric acid, and carbon dioxide are particularly preferred. The amount of catalyst is preferably 0.1 to 1% by mass relative to the ethyleneimine in order to produce the product at an adjustable reaction rate.

[0043] In the production method of the present invention, the base amine serving as the starting point for polymerization is as described above, and is not particularly limited as long as it is a compound represented by an amino group-containing compound having a structural unit represented by the following general formula (4):

[0044] In the general formula (4), X represents an organic group having 3 to 20 carbon atoms. X in the general formula (4) is the same as X in the general formula (2), and the preferred form is also the same. The amount of base amine used can be appropriately selected depending on the molecular weight of the target alkyleneimine polymer; however, it is preferable to increase the ratio of base amine when obtaining a low-molecular-weight alkyleneimine polymer and decrease the ratio of base amine when obtaining a high-molecular-weight alkyleneimine polymer, and it is preferable to use the base amine in an amount within the range of 1% by mass to 40% by mass relative to the weight (100% by mass) of the alkyleneimine polymer obtained after the polymerization reaction. This base amine may be charged into a reaction vessel and serve as a solvent when initiating polymerization.

[0045] In the production method of the present invention, polymerization of ethyleneimine is preferably carried out in an inert gas atmosphere with an oxygen concentration of 2% by volume or less. More preferably, the oxygen concentration is 1% by volume or less, and even more preferably, 0.5% by volume or less. When the oxygen concentration is 2% by volume or less, the alkyleneimine polymer is less colored, and coloration during storage or preservation is reduced. The inert gas is not particularly limited, and any gas that is reactively inert to ethyleneimine may be used. For example, nitrogen, helium, carbon dioxide, or argon may be used, with nitrogen being preferred.

[0046] In the production method of the present invention, the reaction solution temperature during polymerization of ethyleneimine is preferably 80 to 160°C, more preferably 110 to 130°C. At a temperature of 160°C or less, an alkyleneimine polymer of stable quality can be obtained. At a temperature of 80°C or more, the polymerization time is shortened, which is economical.

[0047] In the production method of the present invention, it is preferable to carry out polymerization while maintaining the temperature of the heat medium used to remove the heat of reaction at 40° C. or higher. It is preferably 45° C. or higher, more preferably 50° C. or higher. When the temperature of the heat medium is 40° C. or higher, coloration of the aqueous alkyleneimine polymer solution tends to be reduced. There is no particular restriction on the upper limit temperature of the heat medium, and it is sufficient if it is lower than the reaction solution temperature and can control the reaction temperature. However, if the difference with the reaction solution temperature is small, the reaction time will be extended and productivity will decrease.

[0048] By maintaining the temperature of the heat medium, the reaction solution is prevented from becoming locally highly viscous during the ethyleneimine reaction, and highly efficient stirring allows for uniform polymerization without localized retention, making it possible to carry out the ethyleneimine reaction uniformly and efficiently. As the heat medium, hot water, steam, heated oil, etc. can be used, and hot water and steam are preferably used industrially.

[0049] In the production method of the present invention, the ring-opening addition reaction step (polymerization) may include an aging step. "Aging" refers to polymerization after the completion of polymerization of ethyleneimine, preferably after 95% or more of the supplied ethyleneimine has been consumed, and the reaction solution is aged at 80 to 160°C, preferably 110 to 130°C. At temperatures of 80°C or higher, aging does not require a long period of time. Furthermore, at temperatures of 160°C or lower, thermal decomposition of the produced alkyleneimine polymer is unlikely to occur, resulting in a high-quality polymer. The aging time is typically 1 to 20 hours, preferably 2 to 10 hours. Furthermore, the time required to raise the temperature of the reaction solution to the aging temperature is typically 0.2 to 5 hours, preferably 0.5 to 3 hours.

[0050] During the polymerization reaction of ethyleneimine in the production method of the present invention, the polymerization catalyst and ethyleneimine may be added all at once, but since it is an exothermic reaction, it is better to feed them continuously while controlling the temperature.

[0051] The polymerization reaction may be carried out at normal pressure or under pressure, and is usually carried out at 0 to 10 MPaG, preferably 0 to 2 MPaG. The reaction solution is aged usually at 0 to 10 MPaG, preferably 0 to 2 MPaG. Here, MPaG (megapascal gauge) refers to gauge pressure.

[0052] The polymerization reaction and aging treatment can be carried out by any reaction system, such as a batch system, a semi-batch system, or a continuous flow system. When an alkyleneimine polymer is produced continuously, such as in a continuous flow system, a tubular reactor or the like is used, while in the case of a batch reaction, a reactor or the like is used. As the reactor used in the present invention, a cylindrical reactor equipped with a thermometer, a stirrer, a cooling device, etc. is preferably used.

[0053] In the case of a batch reaction, the viscosity of the polymer increases during the polymerization reaction, so that a paddle blade or a high-viscosity agitator blade, such as the Max Blend Blade (manufactured by Sumitomo Heavy Industries, Ltd.), is industrially used as an agitator for heat removal, diffusion, and reaction promotion, with the Max Blend Blade being preferred. Furthermore, a reactor equipped with a cooling device for passing a heat medium so as to remove the reaction heat generated by the polymerization, such as an externally jacketed reactor, is preferably used. A vertical tube cooler can also be used to improve the efficiency of jacket-type heat removal, and it is preferred to polymerize ethyleneimine under reflux.

[0054] In the production method of the present invention, the final liquid volume of the reaction liquid (m ３ ), that is, the PV value (agitation power / final liquid volume) is set to 5kW / m ３ It is recommended to use a power of 8kW / m or more. ３ More than 15kW / m is preferable. ３ If the temperature is below this, the energy cost is low and it is economical.

[0055] A preferred embodiment of the production method of the present invention includes a step of further purifying the obtained alkyleneimine polymer by any one of the following procedures (A) to (C). The procedures (A) to (C) are explained below.

[0056] Operation (A) involves bubbling an inert gas into the alkyleneimine polymer. Specifically, for example, after the polymerization reaction is complete, the inert gas is bubbled into the polymer in the reactor. Gases inert to the amine, such as nitrogen gas, helium gas, and argon gas, are used as the inert gas, but nitrogen gas is preferred from an economical standpoint. The temperature of the polymer during bubbling should not exceed 150°C, and is preferably maintained in the range of 110 to 130°C. The amount of inert gas is typically 0.01 to 10 Nl / min, preferably 0.1 to 2 Nl / min, per kg of polymer. The bubbling time is typically 0.5 to 100 hours, preferably 1 to 20 hours. The operation may be performed under either atmospheric pressure or reduced pressure. When performed under reduced pressure, the pressure inside the reactor is preferably 10 to 700 mmHg. By the procedure (A), a high purity alkyleneimine polymer having a content of light amines, acetonitrile, etc. of 1 ppm or less can be obtained.

[0057] In operation (B), water is added to and mixed with an alkyleneimine polymer, and the mixture is then heated to evaporate and remove the water. Specifically, for example, after the polymerization reaction is complete, water is added to the polymer in the reactor, the mixture is thoroughly mixed, and the mixture is then heated to evaporate and remove the water. The amount of water added is usually 1 to 95% by mass of the polymer, and preferably 5 to 30% by mass. During the evaporative removal of water, it is preferable to prevent the temperature of the polymer from exceeding 160°C, and it is preferable to maintain the temperature in the range of 100 to 150°C. The operation may be performed under either atmospheric pressure or reduced pressure. When performed under reduced pressure, the pressure inside the reactor is preferably 10 to 700 mmHg. By evaporating and removing at least 15% by mass of the added water, a high-purity alkyleneimine polymer having a content of light amines, acetonitrile, and the like of 1 ppm or less can be obtained.

[0058] The procedure (C) is a combination of the procedures (A) and (B), and enables a high-purity alkyleneimine polymer to be obtained in a shorter operation time. Specifically, for example, after the reaction is completed, water is added to the polymer in the reactor, and the water is evaporated and removed while bubbling an inert gas into the mixture.

[0059] There are no particular limitations on the degree of bubbling or evaporation and removal of water (degree of concentration of the aqueous solution). However, as will be described later, the concentration range of the alkyleneimine polymer (resin component) excluding the solvent and water is 30 to 99.99 mass%, preferably 90 to 99.9 mass%, relative to the total mass of the alkyleneimine polymer of the present invention, and therefore the solvent and water may be removed by evaporation so as to fall within this range.

[0060] The alkyleneimine polymer of the present invention is preferably a high-purity polymer with few impurities. The raw material ethyleneimine is not particularly limited, but the impurities contained therein vary depending on the type of production method for the raw material ethyleneimine. When using ethyleneimine obtained by the gas-phase method, impurities include, for example, heavy impurities such as the raw material monoethanolamine, ethyleneimine oligomers, ketones such as acetaldehyde, Schiff bases formed by the reaction of acetaldehyde with the raw material monoethanolamine, light amines such as ammonia, methylamine, and ethylamine, and light impurities such as acetonitrile, each of which is 0.1 ppm or less, preferably 0.05 ppm or less, and more preferably 0.01 ppm or less, based on the weight of the alkyleneimine polymer. High impurity content may adversely affect the coloration and viscosity changes over time, as described below. These impurities can be measured by gas chromatography.

[0061] The alkyleneimine polymer of the present invention contains unreacted ethyleneimine at a concentration of 0.1 ppm or less, preferably 0.01 ppm or less. The unreacted ethyleneimine can be reduced by sufficient aging, but it can also be removed simultaneously during any of the purification methods (A) to (C) described above. The unreacted ethyleneimine can be measured by gas chromatography.

[0062] The resin concentration of the alkyleneimine polymer obtained by the production method of the present invention is usually from 90 to 99.9% by mass, preferably from 95 to 99.8% by mass, based on the total mass of the alkyleneimine polymer.

[0063] The viscosity of the alkyleneimine polymer of the present invention varies depending on the resin content concentration, but when the resin content concentration is 99.0 mass %, for example, it is 200 to 300,000 mPa·s / 25° C. When the alkyleneimine polymer of the present invention has the above-mentioned physical properties and / or composition, it undergoes little change in color during storage or preservation, and has a narrow molecular weight distribution.

[0064] <Composition> A composition can be prepared using the alkyleneimine polymer of the present invention. A composition containing the alkyleneimine polymer of the present invention may be referred to as the "composition of the present invention." By including the alkyleneimine polymer of the present invention, the composition of the present invention has excellent carbon dioxide adsorption / desorption ability and durability. In other words, the composition is preferably a composition for a carbon dioxide absorbent.

[0065] The composition may be liquid or solid. From the viewpoint of superior handling and supportability when the composition is used in a carbon dioxide absorbent described below, the composition is preferably liquid. Examples of the liquid composition include a composition containing a solvent such as water, in which the alkyleneimine polymer 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 alkyleneimine polymer of the present invention is liquid. Examples of the solid composition include a solvent-free composition containing the alkyleneimine polymer of the present invention.

[0066] (Other Components) The composition of the present invention can be produced, for example, by adding various components to the alkyleneimine polymer of the present invention. As the various components, components other than the alkyleneimine polymer 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, and crystallization inhibitors. Examples of the other components also include metals that are not intentionally incorporated as impurities. Only one type of the other components may be used, or two or more types 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.

[0067] The antioxidant may be a radical scavenger, a peroxide decomposer, or the like. The radical scavenger may be a phenol-based antioxidant, an amine-based antioxidant, or the like, with an amine-based antioxidant being preferred. The peroxide decomposer may be any agent capable of effectively decomposing peroxides, and may be a sulfur-based antioxidant, a phosphorus-based antioxidant, a phenol-based 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.

[0068] 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 between the oligoamine compound and carbon dioxide.

[0069] 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 an element of any 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.

[0070] 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-mentioned ranges, relative to 100% by mass of the total composition. The content can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0071] The composition can be produced by a known or conventional method, for example, by mixing the alkyleneimine polymer of the present invention with the other components described above and stirring the mixture.

[0072] <Carbon dioxide absorbent> A carbon dioxide absorbent can be produced using the alkyleneimine polymer of the present invention or the composition. A carbon dioxide absorbent containing the alkyleneimine polymer of the present invention may be referred to as the "carbon dioxide absorbent of the present invention." By containing the alkyleneimine polymer of the present invention, the carbon dioxide absorbent of the present invention has excellent carbon dioxide adsorption / desorption ability and durability.

[0073] The carbon dioxide absorbent of the present invention may contain other components besides the alkyleneimine polymer of the present invention. The carbon dioxide absorbent of the present invention may be the alkyleneimine polymer of the present invention itself, or may be one produced by adding various components to the alkyleneimine polymer 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, it is preferable that the carbon dioxide absorbent contains the alkyleneimine polymer of the present invention and the carrier, and the alkyleneimine polymer of the present invention is supported on the carrier. Only one of the various components may be used, or two or more of them may be used.

[0074] The carrier is preferably a porous carrier particle from the viewpoint of improving the carbon dioxide adsorption / desorption ability. 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.

[0075] The inorganic material is preferably 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 type of the inorganic material may be used, or two or more types may be used.

[0076] 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 polymeric materials may be used, or two or more of them may be used.

[0077] 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. ２ / g or less, and ２ / g or less, and ２ / g or less.

[0078] From the viewpoint of excellent carbon dioxide adsorption / desorption ability, the content of the alkyleneimine polymer 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. Moreover, 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. Moreover, 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.

[0079] The support 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 support 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 support. 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 support. More specifically, the total content of the components containing chromium, manganese, iron, cobalt, nickel, and copper in the support is preferably within the above-mentioned ranges, relative to 100% by mass of the total amount of the support. The content can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0080] 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 and desorption capacity even after repeated carbon dioxide absorption and desorption.

[0081] 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 alkyleneimine polymer or the composition of the present invention and the carrier, the method for producing the carbon dioxide absorbent preferably includes a step of mixing and stirring the alkyleneimine polymer or the composition of the present invention with the carrier, thereby supporting the alkyleneimine polymer or the composition of the present invention on the carrier (supporting step). From the viewpoint of excellent handleability and supportability, the method for producing the carbon dioxide absorbent more preferably includes a step of mixing and stirring the composition containing at least the alkyleneimine polymer of the present invention and a solvent with the carrier, thereby supporting the alkyleneimine polymer of the present invention on the carrier (supporting step). 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.

[0082] For example, the alkyleneimine polymer of the present invention or the composition may be loaded by impregnating the carrier with the alkyleneimine polymer of the present invention or the composition (impregnation), or the alkyleneimine polymer of the present invention or the composition may be added dropwise to the carrier (dropping), or the carrier may be filled in a container such as a column and then the alkyleneimine polymer of the present invention or the composition may be passed through the carrier (passing). Of these, the impregnation method is preferred from the viewpoint of simplicity of operation and equipment.

[0083] 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 1 Pa to 100 Pa, more preferably 1 Pa to 50 Pa, and even more preferably 10 Pa to 30 Pa.

[0084] The temperature conditions in the supporting step are not particularly limited, but from the viewpoint of excellent supporting ability, the temperature is preferably 20°C to 90°C, more preferably 30°C to 80°C, and even more preferably 40°C to 70°C.

[0085] 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).

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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 alkyleneimine polymer of the present invention is supported on the support.

[0090] The carbon dioxide absorbent can be installed and used in an apparatus (carbon dioxide capture apparatus) that separates and captures 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.

[0091] 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 the desorption step, the carbon dioxide can be recovered by desorbing the carbon dioxide from the carbon dioxide absorbent.

[0092] The pressure condition in the separation step may be, for example, 0.8 to 1.1 atmospheres, and the temperature condition in the separation step may be, for example, −40° C. to 50° C.

[0093] The pressure conditions in the recovery step may be, for example, reduced pressure, 0.02 to 0.5 atmospheres, or 0.1 to 0.3 atmospheres, and the temperature conditions in the recovery step may be, for example, heated, 50°C to 130°C.

[0094] The alkyleneimine polymer of the present invention, where X in general formula (2) is an organic group having 3 to 20 carbon atoms, tends to have little coloration, high solubility in water, excellent storage stability in aqueous solution, excellent carbon dioxide adsorption / desorption ability (particularly, carbon dioxide desorption ability retention rate and carbon dioxide desorption rate), low moisture absorption, or suppressed deterioration. These are presumably related to the fact that the nitrogen-nitrogen bond in X has 3 or more carbon atoms, which improves the hydrophobicity of the group derived from the base amine and increases the C—H bond energy present in the alkyleneimine polymer, and also to the fact that the introduction of a structure other than general formula (1) reduces the structural regularity of the alkyleneimine polymer. The appearance, water solubility, storage stability, carbon dioxide adsorption / desorption ability (particularly, carbon dioxide desorption ability retention rate and carbon dioxide desorption rate), moisture absorption, or suppression of deterioration of the alkyleneimine polymer or a carbon dioxide absorbent containing the same can be confirmed, for example, by the methods in the Examples described below.

[0095] The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples. Unless otherwise specified, "ppm" and "%" described in this specification refer to "ppm by mass" and "% by mass".

[0096] <Viscosity> Viscosity was measured using an E-type viscometer TV-100 (manufactured by Toki Sangyo Co., Ltd.) with a standard cone rotor (1°34' x R24) at a measurement range of 2.5M and 25°C. Examples 1 and 2 and Comparative Examples 1 and 2 were measured at a rotation speed of 0.5 rpm, and Examples 3 and 4 and Comparative Examples 3 and 4 were measured at a rotation speed of 1.0 rpm. For Example 5, viscosity was measured using an E-type viscometer TV-35 (manufactured by Toki Sangyo Co., Ltd.) with a cone rotor (3° x R9.7) at a measurement range of H, a rotation speed of 20 rpm, and 25°C. The results are shown in Table 1.

[0097] <Appearance> 3 g of each alkyleneimine polymer was placed in a 20 ml glass screw tube, and the color was visually observed. The results are shown in Table 1.

[0098] <Absorbance> Each alkyleneimine polymer was diluted with ion-exchanged water to prepare a 4% by mass aqueous solution. Each aqueous solution was placed in a 1 cm quartz cell, and the absorbance was measured in the range of 300 to 1100 nm using a UV-3600 ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation). The region of 300 to 500 nm where absorption was confirmed is shown in Figure 1, and the values ​​for the region of 360 to 450 nm, which corresponds to the visible light region, are shown in Table 1.

[0099] <Solubility Evaluation 1> 0.2 g of each alkyleneimine polymer was weighed into a 20 ml glass screw tube and diluted with ion-exchanged water to prepare a 4 mass% aqueous solution. Subsequently, the solution was left to stand overnight in a refrigerator at 5°C, and the presence or absence of cloudiness (precipitation / sediment) was visually confirmed.

[0100] <Solubility Evaluation 2> 0.2 g of each alkyleneimine polymer was weighed into a 5 ml glass screw tube and diluted with ion-exchanged water to prepare a 20 mass % aqueous solution. Subsequently, the solution was allowed to stand at room temperature for 2 weeks, and then visually inspected for the presence or absence of cloudiness (precipitation / sediment).

[0101] Example 1 A 45 ml pressure reactor was charged with 3.2 g of dipropylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 12.1 g of ethyleneimine was then added dropwise with stirring at 120° C., followed by ring-opening polymerization for 6 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding an alkyleneimine polymer (1).

[0102] Example 2: A 45 ml pressure reactor was charged with 3.2 g of dipropylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 100° C., followed by ring-opening polymerization for 10 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding an alkyleneimine polymer (2).

[0103] Example 3: A 45 ml pressure reactor was charged with 6.4 g of dipropylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 9.6 g of ethyleneimine was then added dropwise with stirring at 100° C., followed by ring-opening polymerization for 10 hours. Subsequently, remaining impurities were removed under reduced pressure, yielding an alkyleneimine polymer (3).

[0104] Example 4: A 45 ml pressure reactor was charged with 6.4 g of dipropylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 9.6 g of ethyleneimine was then added dropwise with stirring at 120° C., followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure, yielding an alkyleneimine polymer (4).

[0105] Example 5: A 45 ml pressure reactor was charged with 1.6 g of dipropylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 13.3 g of ethyleneimine was then added dropwise with stirring at 120° C., followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure, yielding an alkyleneimine polymer (5).

[0106] Comparative Example 1: A 45 ml pressure reactor was charged with 2.5 g of diethylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 12.1 g of ethyleneimine was then added dropwise with stirring at 120° C., followed by ring-opening polymerization for 6 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding a comparative alkyleneimine polymer (1).

[0107] Comparative Example 2: A 45 ml pressure reactor was charged with 2.5 g of diethylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 12.1 g of ethyleneimine was then added dropwise with stirring at 100° C., followed by ring-opening polymerization for 10 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding a comparative alkyleneimine polymer (2).

[0108] Comparative Example 3: A 45 ml pressure reactor was charged with 5.0 g of diethylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 9.6 g of ethyleneimine was then added dropwise with stirring at 100° C., followed by ring-opening polymerization for 10 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding a comparative alkyleneimine polymer (3).

[0109] Comparative Example 4: A 45 ml pressure reactor was charged with 5.0 g of diethylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. 9.6 g of ethyleneimine was then added dropwise with stirring at 120° C., followed by ring-opening polymerization for 6 hours. Thereafter, remaining impurities were removed under reduced pressure, yielding a comparative alkyleneimine polymer (4).

[0110] 1 , it was found that the alkyleneimine polymers of the Examples have the same viscosity as those of the Comparative Examples, and there is no significant difference in handleability as alkyleneimine polymers, but they are less colored, and therefore have excellent appearance when used as anchor agents or adhesion promoters, and are expected to improve color development when used as pigment dispersants, etc. Furthermore, they have excellent solubility in water, do not become cloudy or precipitate even during storage, and have excellent storage stability in aqueous solution, so that concentration distribution in the aqueous solution does not occur and removal of precipitates by filtration, etc. is not necessary, which leads to a reduction in the workload of the work process.

[0111]

[0112] DPTA: Dipropylenetriamine DETA: Diethylenetriamine

[0113] Example 6 Preparation and Evaluation of Carbon Dioxide Absorbent Using Alkyleneimine Polymer (3) 0.5 parts of alkyleneimine polymer (3) and 5.0 parts of ion-exchanged water were mixed to prepare a homogeneous solution. Next, 1.0 parts of CARIACT G-10 (manufactured by Fuji Silysia Chemical Ltd.) as a carrier was added to the 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 to obtain a carbon dioxide absorbent in which alkyleneimine polymer (3) was supported on the carrier.

[0114] Comparative Example 5 Preparation and Evaluation of Carbon Dioxide Absorbent Using Comparative Alkyleneimine Polymer (3) 0.5 parts of the comparative alkyleneimine polymer (3) and 5.0 parts of ion-exchanged water were mixed to prepare a homogeneous solution. Next, 1.0 parts of CARIACT G-10 (manufactured by Fuji Silysia Chemical Ltd.) as a carrier was added to the 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 to obtain a carbon dioxide absorbent in which the comparative alkyleneimine (3) was supported on the carrier.

[0115] <Carbon dioxide adsorption / desorption capacity> The carbon dioxide adsorption / desorption amounts of the carbon dioxide absorbents obtained in Example 6 and Comparative Example 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 2.

[0116] [Carbon dioxide adsorption / desorption test] Using a simultaneous differential thermal / thermogravimetric analyzer (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

[0117] The carbon dioxide absorbents obtained in Example 6 and Comparative Example 5 were subjected to the following degradation treatment, and then the carbon dioxide adsorption / desorption test was carried out to measure the carbon dioxide adsorption / desorption amounts. 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 2.

[0118] [Deterioration Treatment] 0.03 g of the carbon dioxide absorbents obtained in Example 6 and Comparative Example 5 were weighed into 10 mL vials. The top of each vial was protected with a paper wrapper with multiple holes punched in it to prevent the inclusion of foreign matter while allowing air to pass through. This was left in an oven at 100°C for 12 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 and desorption treatments.

[0119] [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

[0120]

[0121] From Table 2, it was found that the alkyleneimine polymers of the Examples exhibited superior carbon dioxide adsorption / desorption amount retention rates compared to the alkyleneimine polymers of the Comparative Examples.

[0122] Example 7 Using the alkyleneimine polymer (1) obtained in Example 1, a degradation index analysis was carried out by an accelerated test as described below.

[0123] Example 8: A 45 ml pressure reactor was charged with 3.2 g of dihexylenetriamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was purged with nitrogen gas to an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120°C, followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure to obtain an alkyleneimine polymer (6). The obtained alkyleneimine polymer (6) was used to carry out a degradation index analysis using the accelerated test described below.

[0124] Example 9: A 45 ml pressure reactor was charged with 3.2 g of m-xylylenediamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120°C, followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure to obtain an alkyleneimine polymer (7). Using the obtained alkyleneimine polymer (7), a degradation index analysis was performed using the accelerated test described below.

[0125] Example 10: A 45 ml pressure reactor was charged with 3.2 g of 1,4-bis(3-aminopropyl)piperazine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to create an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120°C, followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure to obtain an alkyleneimine polymer (8). Using the obtained alkyleneimine polymer (8), a degradation index analysis was performed using the accelerated test described below.

[0126] Comparative Example 6 Using the comparative alkyleneimine polymer (1) obtained in Comparative Example 1, a degradation index analysis was carried out by an accelerated test described below.

[0127] <Analysis of Deterioration Indicators by Accelerated Testing> 0.5 g of each of the alkyleneimine polymers obtained in Examples 7 to 10 or Comparative Example 6 was weighed into an aluminum cup. Each aluminum cup was left to stand in an oven at 120°C for 4 hours to obtain an alkyleneimine polymer that had been subjected to a degradation treatment. Such an accelerated test allows the alkyleneimine polymer to be simulated in a short period of time as the alkyleneimine polymer is subject to degradation due to heating and oxidation, and therefore the alkyleneimine polymer in a carbon dioxide absorbent that has been subjected to heating and repeated adsorption and desorption treatments.

[0128] [IR Measurement] The alkyleneimine polymer obtained above and subjected to the degradation treatment was measured by the diamond ATR method using a Fourier transform infrared spectrophotometer (NEXUS670, manufactured by Thermo Fisher Scientific Co., Ltd.). The intensity ratios of (1) / (3) and (2) / (3) were calculated for the absorbances attributed below, and the results are shown in Table 3. Due to oxidative degradation of the alkyleneimine polymer, the absorbances of (1) and (2) increase, so the lower the ratios of (1) / (3) and (2) / (3), the more stable it is against the degradation treatment. (1) 1660 cm －１ Carbonyl C=O stretching vibration (2) 1680 cm －１ Imine C=N stretching vibration (3) 2810 cm －１ C-H stretching vibration of alkanes

[0129] [Evaluation criteria for structural deterioration after accelerated testing] (1) / (3) change rate ○: Less than 80% ×: 80% or more (2) / (3) change rate ○: Less than 55% ×: 55% or more

[0130] The results of solubility (Solubility Evaluation 2) and degradation index analysis are shown in Table 3. The alkyleneimine polymers of the Examples did not precipitate even in aqueous solution and had excellent storage stability. Furthermore, the results of IR measurement showed that all of the alkyleneimine polymers of the Examples were stable against degradation treatment, i.e., degradation was suppressed.

[0131]

[0132] DPTA: Dipropylenetriamine DHTA: Dihexylenetriamine XDA: m-xylylenediamine APP: 1,4-bis(3-aminopropyl)piperazine DETA: Diethylenetriamine

[0133] Example 11 A carbon dioxide absorbent was prepared using alkyleneimine polymer (6) in the same manner as in Example 6, and the hygroscopicity, carbon dioxide desorption rate, deterioration index in a 100°C 24-hour accelerated heating test, and carbon dioxide adsorption / desorption test (40-75°C) were evaluated as described below.

[0134] Example 12 A carbon dioxide absorbent was prepared using alkyleneimine polymer (7) in the same manner as in Example 6, and the hygroscopicity and carbon dioxide desorption rate, which will be described later, were evaluated.

[0135] Example 13 A carbon dioxide absorbent was prepared using the alkyleneimine polymer (8) in the same manner as in Example 6, and the hygroscopicity and carbon dioxide desorption rate, which will be described later, were evaluated.

[0136] Comparative Example 7 A carbon dioxide absorbent was prepared using the comparative polymer (1) in the same manner as in Comparative Example 5, and the hygroscopicity, carbon dioxide desorption rate, deterioration index in a 100°C 24 hour accelerated heating test, and carbon dioxide adsorption / desorption test (40-75°C), which will be described later, were evaluated.

[0137] Example 14 A carbon dioxide absorbent was prepared using alkyleneimine polymer (3) in the same manner as in Example 6, and the hygroscopicity and carbon dioxide desorption rate, which will be described later, were evaluated.

[0138] Example 15: A 45 ml pressure reactor was charged with 4.1 g of isophoronediamine and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120°C, followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure conditions to obtain an alkyleneimine polymer (9). Using the obtained alkyleneimine polymer (9), a carbon dioxide absorbent was prepared in the same manner as in Example 6, and the hygroscopicity, carbon dioxide desorption rate, and degradation index in a 100°C 24-hour accelerated heating test (described below) were evaluated, as well as a carbon dioxide adsorption / desorption test (40-75°C).

[0139] Example 16: A 45 ml pressure reactor was charged with 5.1 g of 4,4'-methylenebis(cyclohexylamine) and 0.2 g of 35% hydrochloric acid, and the atmosphere was then purged with nitrogen gas to an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120 ° C., followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure conditions to obtain an alkyleneimine polymer (10). Using the obtained alkyleneimine polymer (10), a carbon dioxide absorbent was prepared in the same manner as in Example 6, and the hygroscopicity and carbon dioxide desorption rate, a deterioration index in a 24-hour accelerated heating test at 100 ° C., and a carbon dioxide adsorption / desorption test (40-75 ° C.), as described below, were evaluated.

[0140] Example 17: A 45 ml pressure reactor was charged with 3.3 g of 1,3-bis(aminomethyl)cyclohexane and 0.2 g of 35% hydrochloric acid, and the atmosphere was purged with nitrogen gas to an oxygen concentration of 0.5% by volume. Then, 12.1 g of ethyleneimine was added dropwise with stirring at 120°C, followed by ring-opening polymerization for 6 hours. Subsequently, remaining impurities were removed under reduced pressure to obtain an alkyleneimine polymer (11). Using the obtained alkyleneimine polymer (11), a carbon dioxide absorbent was prepared in the same manner as in Example 6, and the hygroscopicity and carbon dioxide desorption rate, a deterioration index in a 24-hour accelerated heating test at 100°C, and a carbon dioxide adsorption / desorption test (40-75°C), as described below, were evaluated.

[0141] [Hygroscopicity] Using a differential thermal-thermogravimetric simultaneous analyzer (TG-DTA) (TG-DTA8122, manufactured by Rigaku Corporation) and a water vapor generator (Precise dew point generator), the masses of a carbon dioxide absorbent from which adsorbed moisture had been removed by flowing dry nitrogen at 100°C for 30 minutes, and a carbon dioxide absorbent from which moisture had been adsorbed by flowing nitrogen containing water vapor adjusted to a dew point of 20°C at 35°C were measured, and the moisture absorption amount was calculated using the following formula. In this measurement, the flow rate of nitrogen was adjusted using a mass flow controller, and the nitrogen was supplied into the TG-DTA oven at 100 ml / min. Moisture absorption amount (g / g) = (W wet -W dry ) / W １ W wetW: Mass (g) of carbon dioxide absorbent with adsorbed water dry W: Mass (g) of carbon dioxide absorbent from which moisture has been removed １ : Mass (g) of carbon dioxide absorbent used in the test

[0142] [Carbon dioxide desorption rate] In the carbon dioxide adsorption / desorption test, the mass was measured at the absorption temperature (35°C) and the desorption temperature (75°C). The sample was held at the absorption temperature for 150 minutes, and at the desorption temperature for 40 minutes. The desorption time was defined as the time required for 98% or more of the carbon dioxide desorbed during the 40-minute holding period to be desorbed, and the desorption rate was calculated using the following formula: Carbon dioxide desorption rate [(g / g) / min x 10 ３ ] = {(W 35 -W 75 ) / W １ / T×10 ３ W 35 W: Mass (g) of carbon dioxide absorbent at absorption temperature 75 W: Mass (g) of carbon dioxide absorbent at desorption temperature １ : Mass (g) of the carbon dioxide absorbent used in the test T: Time (min) required for 98% or more of the carbon dioxide to be desorbed

[0143]

[0144] The results of the moisture absorption evaluation and carbon dioxide desorption rate for Examples 11 to 14 and Comparative Example 7 are shown in Table 4. The alkyleneimine polymers of the Examples have moisture absorption amounts equal to or less than those of the alkyleneimine polymers of the Comparative Examples, and therefore are expected to reduce the energy required to heat the absorbent to the temperature required for carbon dioxide desorption. Furthermore, the alkyleneimine polymers of the Examples also have excellent carbon dioxide desorption rates, and it was found that these contribute to improving the amount of carbon dioxide recovered per unit time (productivity) and reducing thermal history by shortening the heating time, thereby improving the life of the absorbent.

[0145] <Evaluation of Degradation Index by Accelerated Heating Test at 100°C for 24 Hours> 0.03 g of carbon dioxide absorbents using each alkyleneimine polymer obtained in Examples 11, 15-17, or Comparative Example 7 were weighed into 10 mL vials. The top of each vial was protected with a paper wrapper with multiple holes punched in it to prevent contamination while allowing air to pass through. This was left in an oven at 100°C for 24 hours and then cooled to obtain carbon dioxide absorbents that had been subjected to a 100°C 24 hour degradation treatment. This treatment causes the carbon dioxide absorbent to deteriorate due to heating and oxidation, making it possible to simulate an absorbent that had undergone heating and repeated adsorption / desorption treatments.

[0146] [IR Measurement] 2.5 mg of the carbon dioxide absorbent after the above-mentioned degradation treatment and 97.5 mg of potassium bromide for IR absorption measurement (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were ground in a mortar to prepare a KBr tablet. Using a KBr tablet prepared using only potassium bromide for IR absorption measurement as the background, IR measurement of the KBr tablet containing the carbon dioxide absorbent was performed by the transmission method using a Fourier transform infrared spectrophotometer (NEXUS670, manufactured by Thermo Fisher Scientific Co., Ltd.). For the absorbances assigned below, the intensity ratio of (1) / (2) was calculated, and the results are shown in Table 5. Due to oxidative degradation of the alkyleneimine polymer, the absorbance of (1) increases, so the lower the (1) / (2), the more stable the carbon dioxide absorbent is against degradation treatment. (1) 1662 cm －１ Carbonyl C=O stretching vibration (2) 806 cm －１ Si-O-Si in-plane deformation vibration of the support (silica)

[0147] [Evaluation criteria for structural deterioration after accelerated testing] (1) / (2) Change rate ○: Less than 130% ×: 160% or more

[0148] [Carbon dioxide adsorption / desorption test (40-75°C)] For the carbon dioxide absorbent before and after a 100°C 24-hour accelerated heating test, a simultaneous differential thermal / thermogravimetric analyzer (TG-DTA) (manufactured by Rigaku Corporation, TG-DTA8120, 8122) was used to measure the mass of the carbon dioxide absorbent at the absorption temperature (40°C) and the desorption temperature (75°C), 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 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 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

[0149]

[0150] DHTA: Dihexylenetriamine IPDA: Isophoronediamine MBCA: 4,4'-methylenebis(cyclohexylamine) BMAC: 1,3-bis(aminomethyl)cyclohexane DETA: Diethylenetriamine

[0151] Table 5 shows the results of the moisture absorption evaluation, the degradation index in a 24-hour accelerated heating test at 100°C, the carbon dioxide adsorption / desorption test (40-75°C), and the carbon dioxide desorption rate for Examples 11 and 15-17 and Comparative Example 7. Because the alkyleneimine polymers of the Examples absorb less moisture than the alkyleneimine polymers of the Comparative Examples, it is expected that the energy required to heat the absorbent to the temperature required for carbon dioxide desorption will be reduced. Furthermore, it was found that the alkyleneimine polymers of the Examples exhibited less degradation in a 24-hour accelerated heating test at 100°C than the alkyleneimine polymers of the Comparative Examples, and also exhibited superior carbon dioxide adsorption / desorption rate retention after degradation treatment. Furthermore, it was found that the alkyleneimine polymers of the Examples have a superior carbon dioxide desorption rate than the alkyleneimine polymers of the Comparative Examples, thereby contributing to improved carbon dioxide recovery (productivity) per unit time and reduced thermal history due to shorter heating times, thereby improving the lifespan of the absorbent.

Claims

1. A structural unit (A) represented by the following general formula (1), and (However, any N in the general formula (1) is a primary amine.) An alkyleneimine polymer comprising a structural unit (B) represented by the following general formula (2), and having a number average molecular weight (Mn) of 250 to 50,000: (In general formula (2), X represents an organic group having 3 to 20 carbon atoms.) 2. A structural unit (C) represented by the following general formula (3):

2. The alkyleneimine polymer of claim 1, further comprising: (wherein both N's in general formula (3) are independently a secondary amine or a tertiary amine).

3. A structural unit (A) represented by the general formula (1) and / or a structural unit (C) represented by the following general formula (3):

2. The alkyleneimine polymer according to claim 1, comprising two or more of the following: (wherein both N's in general formula (3) are independently a secondary amine or a tertiary amine).

4. The alkyleneimine polymer of claim 1 having two or more primary amines and one or more secondary or tertiary amines.

5. An amino group-containing compound having a structural unit represented by the following general formula (4): (In general formula (4), X represents an organic group having 3 to 20 carbon atoms.) A method for producing an alkyleneimine polymer, comprising the step of subjecting ethyleneimine to a ring-opening addition reaction.

6. A carbon dioxide absorbent comprising the alkyleneimine polymer of claim 1.

7. The carbon dioxide absorbent according to claim 6, comprising: a support; and the alkyleneimine polymer supported on the support.

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

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

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