Carbon dioxide absorbent

Abstract

A carbon dioxide absorbent comprising a polyamine compound (A) having an alicyclic hydrocarbon structure, the content of the polyamine compound (A) being 60% by mass or more.

Description

Technical Field

[0001] This invention relates to carbon dioxide absorbents. Background Technology

[0002] From the perspective of global warming, there is a demand to reduce carbon dioxide emissions.

[0003] One method for reducing carbon dioxide is the technology of effectively recovering high concentrations (approximately 10-30% by volume) of carbon dioxide from exhaust gases emitted from thermal power plants and storing it underground or in the sea (CCS: Carbon Dioxide Capture and Storage). Technologies involving carbon dioxide absorbents used in CCS include, for example, those described in Patent Documents 1-4.

[0004] Patent document 1 describes a method for recovering carbon dioxide using specific alkanolamines as carbon dioxide absorbents.

[0005] Patent document 2 describes the use of a carbon dioxide absorbent containing a carbon dioxide chemically absorbent amine having nitrogen-hydrogen bonds and a tertiary amine solvent without nitrogen-hydrogen bonds as a carbon dioxide absorbent.

[0006] Patent document 3 describes a method for removing acidic gases using sterically hindered amines and amino acids.

[0007] Patent document 4 describes an acidic gas absorbent containing a diamine compound having a hydroxyalkyl group.

[0008] Patent document 5 describes an air carbon dioxide absorbent comprising an alkylamine that has been substituted with a hydroxyl group or an amino group that can be substituted.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2008-13400

[0012] Patent Document 2: Japanese Patent Application Publication No. 2017-104776

[0013] Patent Document 3: Japanese Patent Application Publication No. 53-81490

[0014] Patent Document 4: Japanese Patent Application Publication No. 2015-27647

[0015] Patent Document 5: Japanese Patent Application Publication No. 2017-031046 Summary of the Invention

[0016] The problem the invention aims to solve

[0017] In recent years, the technology of directly recovering low concentrations of carbon dioxide (approximately 0.04% by volume) from the air (DAC: Direct Air Capture) has attracted attention. The carbon dioxide absorbent used in DAC requires a higher carbon dioxide absorption capacity than that used in CCS.

[0018] Here, the carbon dioxide absorbent described in Patent Documents 1-4 is not sufficient as an absorbent for DAC.

[0019] Furthermore, according to the research of the inventors, there is room for improvement in the absorption rate of carbon dioxide in the air by the carbon dioxide absorbent described in Patent Document 5.

[0020] The present invention was made in view of the above circumstances, and provides a carbon dioxide absorbent that improves the ability to absorb carbon dioxide from the air.

[0021] Solution for solving the problem

[0022] The inventors conducted repeated and in-depth research to solve the aforementioned problems. As a result, they discovered that a carbon dioxide absorbent containing a specific amount of a polyamine compound (A) with an alicyclic hydrocarbon structure can improve the absorption capacity of carbon dioxide in the air, thus completing the present invention.

[0023] That is, according to the present invention, a carbon dioxide absorbent as shown below is provided. [1]

[0025] A carbon dioxide absorbent comprising a polyamine compound (A) having an alicyclic hydrocarbon structure.

[0026] The content of the above-mentioned polyamine compound (A) is 60% by mass or more. [2]

[0028] According to the carbon dioxide absorbent described above [1], the polyamine compound (A) is a compound represented by the following formula (1).

[0029]

[0030] In the above formula (1), R 1 ~R 4 Each independently represents a hydrogen atom, or optionally a hydrocarbon group having 1 or more but less than 10 carbon atoms and having at least one substituent selected from amino, cyano, and phenyl; R 5 ~R 10 Each of them independently represents a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and less than 4 carbon atoms; x and y each independently represent an integer greater than 0 and less than 6, and x+y is greater than 1 and less than 6; p and q each independently represent an integer greater than 0 and less than 4. [3]

[0032] According to the carbon dioxide absorbent described in [1] or [2] above, the maximum carbon dioxide dissociation temperature of the polyamine compound (A) is below 140°C, as determined by the following method.

[0033] (method)

[0034] The polyamine compound (A) that has absorbed carbon dioxide was heated from 23°C to 250°C at a heating rate of 10°C / min. The temperature at which the heat of heat absorption accompanying the removal of carbon dioxide reached its maximum was measured, and this temperature was taken as the maximum dissociation temperature of carbon dioxide. [4]

[0036] According to any one of the carbon dioxide absorbents [1] to [3] above, the acid dissociation constant (pKa) of the polyamine compound (A) is 8.0 or more and 12.0 or less. [5]

[0038] According to any one of the carbon dioxide absorbents [1] to [4] above, the molecular weight of the polyamine compound (A) is 140 or more and 1000 or less. [6]

[0040] According to any one of the carbon dioxide absorbents [1] to [5] above, the maximum endothermic temperature of the polyamine compound (A) determined by the following method is 130°C or higher and 300°C or lower.

[0041] (method)

[0042] The polyamine compound (A) was heated from 23°C to 350°C at a heating rate of 10°C / min. The temperature at which the heat absorption accompanying the volatilization of the polyamine compound (A) reached its maximum was measured, and this temperature was taken as the maximum heat absorption temperature of the polyamine compound (A). [7]

[0044] According to any one of the above [1] to [6], the carbon dioxide absorbent has an amine value of 500 mg KOH / g or more and 1500 mg KOH / g or less. [8]

[0046] According to any one of the carbon dioxide absorbents [1] to [7] above, the number of amino groups in the polyamine compound (A) is 2 or more and 6 or less. [9]

[0048] The carbon dioxide absorbent according to any one of [1] to [8] above, wherein the alicyclic hydrocarbon structure comprises at least one selected from 5-membered rings and 6-membered rings.

[10]

[0050] The carbon dioxide absorbent according to any one of [1] to [9] above, wherein the polyamine compound (A) contains at least one selected from bis(aminomethyl)cyclohexane and its derivatives, limonene diamine and its derivatives, and isophorone diamine and its derivatives.

[11]

[0052] The carbon dioxide absorbent according to any one of [1] to

[10] above, wherein the water content is 30% by mass or less.

[12]

[0054] The carbon dioxide absorbent according to any one of [1] to

[11] above is characterized in that it is used to directly absorb carbon dioxide in the air.

[0055] The effects of the invention

[0056] According to the present invention, a carbon dioxide absorbent that improves the ability to absorb carbon dioxide from the air can be provided. Detailed Implementation

[0057] The embodiments for carrying out the present invention (hereinafter referred to as "this embodiment") will be described in detail below. The following embodiments are illustrative of the present invention and do not limit the scope of the invention. The present invention can be implemented with appropriate modifications within its spirit. In this embodiment, preferred provisions can be adopted arbitrarily, and combinations of preferred provisions are even more preferred. In this embodiment, the description "XX~YY" means "XX or more and YY or less".

[0058] The carbon dioxide absorbent of this embodiment contains a polyamine compound (A) having an alicyclic hydrocarbon structure, and the content of polyamine compound (A) is 60% by mass or more. Here, in this embodiment, an alicyclic hydrocarbon structure refers to a ring structure composed of saturated or unsaturated carbon and hydrogen that does not have aromaticity, and heterocyclic structures containing heteroatoms in the ring are excluded.

[0059] In addition, the polyamine compound (A) having an alicyclic hydrocarbon structure can be any of the cis, trans, or mixtures of cis and trans.

[0060] The carbon dioxide absorbent of this embodiment contains a specific amount of polyamine compound (A) and is an absorbent that improves the ability to absorb carbon dioxide from the air. Furthermore, the carbon dioxide absorbent of this embodiment also exhibits excellent reusability.

[0061] In this embodiment, "improved carbon dioxide absorption capacity" means that when comparing the concentrations of amine compounds in the carbon dioxide absorbent at a consistent rate, the absorption rate for low concentrations (approximately 0.04% by volume) of carbon dioxide in the air is faster, resulting in a greater amount of carbon dioxide absorbed. Furthermore, in this embodiment, "excellent reusability" means that during cyclic tests of carbon dioxide absorption and dissociation, it is difficult to cause weight loss or a decrease in carbon dioxide absorption capacity.

[0062] The carbon dioxide absorbent of this embodiment contains a specific amount of a polyamine compound (A) having an alicyclic hydrocarbon structure. By containing a specific amount of polyamine compound (A), the absorption capacity and reusability of carbon dioxide in the air can be improved. The reason for this is uncertain, but the following can be considered.

[0063] Firstly, it is believed that because the polyamine compound (A) with an alicyclic hydrocarbon structure has a highly sterically hindered structure, the heat of reaction during carbon dioxide absorption is low, and the absorption rate of carbon dioxide is fast. Furthermore, it is believed that the polyamine compound (A) with an alicyclic hydrocarbon structure is strongly basic and contains multiple amino groups in its molecule, thus resulting in a large amount of carbon dioxide absorbed.

[0064] Furthermore, due to the steric hindrance of the alicyclic hydrocarbon structure, polyamine compound (A) exhibits excellent dissociation properties for carbon dioxide. Moreover, the relatively large molecular weight of polyamine compound (A) during carbon dioxide dissociation via heating makes oxidation and weight loss unlikely. Therefore, polyamine compound (A) with an alicyclic hydrocarbon structure is considered to have excellent reusability. It should be noted that non-cyclic aliphatic amines are prone to cyclization, oxidation, and weight loss upon heating, thus exhibiting poor reusability.

[0065] Based on the above reasons, it is believed that the carbon dioxide absorbent of this embodiment can improve the carbon dioxide absorption capacity and reusability in the air.

[0066] The carbon dioxide absorbent of this embodiment can improve the absorption capacity of carbon dioxide in the air, and therefore can be suitable for use in direct absorption of carbon dioxide from the air (DAC) technology.

[0067] In addition, the carbon dioxide absorbent of this embodiment can be suitably used, for example, to recover low concentrations of carbon dioxide of 0.01% to 1% by volume or more.

[0068] From the viewpoint of further improving the ability to absorb carbon dioxide from the air and its reusability, the alicyclic hydrocarbon structure of the polyamine compound (A) preferably includes at least one selected from 5-membered rings and 6-membered rings, more preferably including a 6-membered ring.

[0069] Examples of alicyclic hydrocarbon structures for the polyamine compound (A) include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane rings. Among these ring structures, cyclopentane and cyclohexane rings are preferred, cyclohexane rings are more preferred, and 1,3-substituted cyclohexane rings are even more preferred.

[0070] From the viewpoint of further improving the ability to absorb carbon dioxide in the air and reusability, the number of amino groups in the polyamine compound (A) is preferably 2 or more and 6 or less, more preferably 2 or more and 4 or less, even more preferably 2 or more and 3 or less, and even more preferably 2.

[0071] Furthermore, from the viewpoint of further improving the absorption of carbon dioxide from the air, amino groups having nitrogen-hydrogen bonds are preferred, and primary amino groups are more preferred.

[0072] More specifically, the polyamine compound (A) is preferably a compound represented by the following formula (1).

[0073]

[0074] In the above formula (1), R 1 ~R 4 Each independently represents a hydrogen atom, or optionally a hydrocarbon group having 1 or more but less than 10 carbon atoms and having at least one substituent selected from amino, cyano, and phenyl; R 5 ~R 10 Each of them independently represents a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and less than 4 carbon atoms; x and y each independently represent an integer greater than 0 and less than 6, and x+y is greater than 1 and less than 6; p and q each independently represent an integer greater than 0 and less than 4.

[0075] R 1 ~R 4 Each of the following is independently a hydrogen atom, or optionally a hydrocarbon group having 1 or more but less than 10 carbon atoms with at least one substituent selected from amino, cyano, and phenyl; preferably a hydrogen atom, or optionally an alkyl group having 1 or more but less than 4 carbon atoms with at least one substituent selected from amino, cyano, and phenyl; more preferably a hydrogen atom, or optionally an alkyl group having 1 or more but less than 4 carbon atoms with at least one substituent selected from amino and cyano; and even more preferably a hydrogen atom, or optionally an alkyl group having 2 or more but less than 4 carbon atoms with at least one substituent selected from amino and cyano.

[0076] R 1 ~R 4 The number of carbon atoms in each hydrocarbon group is 1 or more, preferably 2 or more, further preferably 10 or less, preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

[0077] R5 ~R 10 Each of the components is independently a hydrogen atom or a hydrocarbon group having 1 or more but less than 4 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 or more but less than 4 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 or more but less than 3 carbon atoms, further preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom.

[0078] R 5 ~R 10 The number of carbon atoms in each hydrocarbon group is independently 1 or more and 4 or less, preferably 1 or 2, and more preferably 1.

[0079] p and q are each independently 0 or more, preferably 1 or more, and further 4 or less, preferably 2 or less, and more preferably 1. In addition, at least one of p and q is preferably 1 or more, further 4 or less, preferably 2 or less, and more preferably 1.

[0080] x and y each independently represent an integer greater than 0 and less than 6, and x+y is greater than 1 and less than 6. From the viewpoint of further increasing the overall steric hindrance of the molecule and further improving the ability to absorb carbon dioxide from the air, x+y is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more. From the viewpoint of improving the amount of carbon dioxide absorbed, it is preferably 5 or less, and more preferably 4. That is, the alicyclic hydrocarbon structure is preferably a 5-membered ring or a 6-membered ring, and more preferably a 6-membered ring. When x+y is 4, it is preferable that x is 1 and y is 3.

[0081] As the polyamine compound (A), from the viewpoint of further improving the ability to absorb carbon dioxide in the air and its reusability, it is preferably selected from at least one of bis(aminomethyl)cyclohexane and its derivatives, limonene diamine and its derivatives, and isophorone diamine and its derivatives, more preferably bis(aminomethyl)cyclohexane and its derivatives, even more preferably 1,3-bis(aminomethyl)cyclohexane and its derivatives, even more preferably derivatives of 1,3-bis(aminomethyl)cyclohexane, and even more preferably derivatives of 1,3-bis(aminomethyl)cyclohexane as shown in formula (2) or formula (3) below.

[0082] Here, as derivatives of bis(aminomethyl)cyclohexane, derivatives of limonene diamine, or derivatives of isophorone diamine, examples include compounds in which at least one hydrogen atom of the amino group is optionally substituted with a hydrocarbon group having 1 or more and 10 or less carbon atoms, preferably with an alkyl group having 1 or more and 4 or less carbon atoms, more preferably with an alkyl group having 1 or more and 4 or less carbon atoms, more preferably with an alkyl group having 1 or more and 4 or less carbon atoms, and even more preferably with an alkyl group having 2 or more and 4 or less carbon atoms, substituted with at least one substituent from amino and cyano.

[0083]

[0084] These polyamine compounds (A) can be used alone or in combination of two or more.

[0085] From the viewpoint of improving the absorption capacity and reusability of carbon dioxide in the air, when the total amount of carbon dioxide absorbent is set to 100% by mass, the content of polyamine compound (A) in the carbon dioxide absorbent of this embodiment is 60% by mass or more, preferably 70% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, further preferably 85% by mass or more, further preferably 90% by mass or more, further preferably 95% by mass or more, further preferably 98% by mass or more, and even more preferably 100% by mass or less.

[0086] Furthermore, from the viewpoint of improving the absorption capacity and reusability of carbon dioxide in the air, when the total amount of amine compounds contained in the carbon dioxide absorbent is set to 100 parts by mass, the content of polyamine compound (A) in the carbon dioxide absorbent of this embodiment is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and preferably 100 parts by mass or less.

[0087] From the viewpoint of improving the absorption capacity of carbon dioxide in the air and its reusability, the water content in the carbon dioxide absorbent of this embodiment is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less. The carbon dioxide absorbent of this embodiment is further preferably substantially free of water. Here, "substantially free of water" means that water is not intentionally added, but the presence of a small amount of water as an impurity is not excluded.

[0088] From the viewpoint of improving the carbon dissociation properties of carbon dioxide and further improving its reusability, the maximum carbon dioxide dissociation temperature of the polyamine compound (A), as determined by the following method, is preferably 140°C or lower, more preferably 130°C or lower, even more preferably 120°C or lower, even more preferably 110°C or lower, and even more preferably 100°C or lower. The lower limit of the above-mentioned maximum carbon dioxide dissociation temperature is not particularly limited, for example, it is 40°C or higher.

[0089] (method)

[0090] The polyamine compound (A) that has absorbed carbon dioxide was heated from 23°C to 250°C at a heating rate of 10°C / min. The temperature at which the endothermic heat accompanying the removal of carbon dioxide reaches its maximum was measured and taken as the maximum dissociation temperature of carbon dioxide. Here, the polyamine compound (A) that has absorbed carbon dioxide can be prepared, for example, by allowing 5 mmol of the polyamine compound (A) to stand in air at 23°C and 50% RH for 24 hours.

[0091] From the viewpoint of further improving the ability to absorb carbon dioxide from the air, the acid dissociation constant (pKa) of the polyamine compound (A) is preferably 8.0 or more, more preferably 9.0 or more, and even more preferably 9.3 or more. Furthermore, from the viewpoint of improving the dissociation of carbon dioxide and further enhancing reusability, it is preferably 12.0 or less.

[0092] In this embodiment, the acid dissociation constant of the polyamine compound (A) is determined by the following determination method based on acid-base titration.

[0093] (1) Dissolve 0.2g of polyamine compound (A) in 30mL of purified water.

[0094] (2) Using an automatic potentiometric titration apparatus (e.g., AT-610 manufactured by Kyoto Electronics Industries, Ltd.), the acid dissociation constant (pKa) is calculated by titrating the solution obtained in (1) above with a 0.1N perchloric acid-acetic acid solution.

[0095] It should be noted that the temperature during the measurement was 25±2℃.

[0096] From the viewpoint of suppressing weight reduction during heat treatment when carbon dioxide dissociates and further improving reusability, the molecular weight of the polyamine compound (A) is preferably 140 or more, more preferably 150 or more, even more preferably 160 or more, and even more preferably 180 or more. From the viewpoint of further improving the ability to absorb carbon dioxide from the air, it is preferably 1000 or less, more preferably 500 or less, even more preferably 300 or less, even more preferably 250 or less, and even more preferably 220 or less.

[0097] From the viewpoint of suppressing weight reduction during heat treatment when carbon dioxide dissociates and further improving reusability, the maximum endothermic temperature of the polyamine compound (A) determined by the following method is preferably 130°C or higher, more preferably 150°C or higher, even more preferably 160°C or higher, even more preferably 180°C or higher, even more preferably 200°C or higher, even more preferably 220°C or higher. From the viewpoint of further improving the ability to absorb carbon dioxide from the air, it is preferably 300°C or lower, more preferably 280°C or lower, even more preferably 260°C or lower.

[0098] (method)

[0099] Polyamine compound (A) was heated from 23°C to 350°C at a heating rate of 10°C / min. The temperature at which the heat absorption accompanying the volatilization of polyamine compound (A) reached its maximum was measured, and this temperature was taken as the maximum heat absorption temperature of polyamine compound (A).

[0100] From the viewpoint of further improving the absorption capacity of carbon dioxide in the air and its reusability, the amine value of the polyamine compound (A) is preferably 500 mg KOH / g or more, more preferably 550 mg KOH / g or more, and preferably 1500 mg KOH / g or less, more preferably 1200 mg KOH / g or less, even more preferably 1000 mg KOH / g or less, and even more preferably 900 mg KOH / g or less. The amine value indicates the amount of amine in the compound, referring to the number of mg of acid and equivalent potassium hydroxide (KOH) required to neutralize 1 g of the compound.

[0101] The amine value can be determined based on JIS K7237-1995 by the following method.

[0102] (1) Dissolve 0.1g of polyamine compound (A) in 20ml of acetic acid.

[0103] (2) The amine value is calculated by titrating the solution obtained in (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration device (e.g., AT-610 manufactured by Kyoto Electronics Industry Co., Ltd.).

[0104] The carbon dioxide absorbent of this embodiment may appropriately contain components other than the polyamine compound (A) without impairing the effect of the invention. Examples of components other than the polyamine compound (A) include compounds capable of absorbing carbon dioxide (e.g., methanol, polyethylene glycol, etc.), water, organic solvents, degradation inhibitors, defoamers, viscosity modifiers, antioxidants, and desiccants for removing moisture (e.g., magnesium sulfate, molecular sieves, etc.).

[0105] Examples of organic solvents include alcohols, dimethylacetamide, N-methylpyrrolidone, and dimethylformamide.

[0106] Example

[0107] The present invention will now be described through embodiments, but the invention is not limited to the scope of these embodiments. It should be noted that in these embodiments, various measurements and evaluations are performed using the following methods.

[0108] (Acid dissociation constant (pKa) of amine compounds)

[0109] The acid dissociation constant of amine compounds is determined by the following method.

[0110] (1) Dissolve 0.2g of the amine compound in 30ml of purified water.

[0111] (2) Using an automatic potentiometric titration apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., AT-610), the solution obtained in (1) above was titrated with a 0.1N perchloric acid-acetic acid solution, and the acid dissociation constant (pKa) was calculated.

[0112] It should be noted that the temperature during the measurement was 25±2℃.

[0113] (Amine value of amine compounds)

[0114] The amine value was determined using the following method based on JIS K7237-1995.

[0115] (1) Dissolve 0.1g of the amine compound in 20mL of acetic acid.

[0116] (2) The amine value is calculated by titrating the solution obtained in (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration device (e.g., AT-610 manufactured by Kyoto Electronics Industry Co., Ltd.).

[0117] (Maximum endothermic temperature of amine compounds)

[0118] The amine compounds used in the examples and comparative examples were subjected to DSC measurements as follows to determine the maximum endothermic temperature of the amine compounds. First, for the amine compounds, differential scanning calorimetry (DSC) was performed using a differential thermogravimetric analyzer (product name: DTG-60, manufactured by Shimadzu Corporation) under the conditions of a measurement temperature range of 23–350°C, a heating rate of 10°C / min, and a nitrogen atmosphere. Based on the resulting DSC curves, the temperature at which the endothermic heat accompanying the volatilization of the amine compound reaches its maximum was calculated, and this temperature was taken as the maximum endothermic temperature of the amine compound.

[0119] (Evaluation of the ability to absorb carbon dioxide from the air)

[0120] A carbon dioxide concentration meter and a petri dish were placed inside a closable desiccator (internal dimensions: 370mm × 260mm × 272mm). Then, an amine compound (5 mmol) was added to the petri dish inside the desiccator, the door was immediately closed, and the carbon dioxide concentration inside the desiccator was measured after 24 hours in an air environment of 23°C and 50% RH. It should be noted that the initial carbon dioxide concentration was adjusted to approximately 400 ppm. The changes in carbon dioxide concentration inside the desiccator 2 hours and 24 hours after the amine compound was placed inside are shown in Table 1. Here, a greater change in carbon dioxide concentration inside the desiccator indicates a greater amount of carbon dioxide absorbed by the carbon dioxide absorbent.

[0121] (Cyclical evaluation)

[0122] After the evaluation of the carbon dioxide absorption capacity was completed, the amine compound was removed from the desiccator and heated at 100°C for 1 hour to dissociate the absorbed carbon dioxide and regenerate the amine compound. At this time, the weight of the amine compound before and after the heat treatment was measured, and the weight retention rate (first time) was calculated.

[0123] Next, the carbon dioxide absorption capacity of the regenerated amine compound was evaluated again, and the changes in carbon dioxide concentration in the dryer were measured after 2 hours and 24 hours (second time).

[0124] Next, the amine compound was removed from the desiccator, and the amine compound that had absorbed carbon dioxide was heated at 100°C for 1 hour to dissociate the absorbed carbon dioxide, thus regenerating the amine compound. At this time, the weight of the amine compound before and after the heat treatment was measured, and the weight retention rate (second time) was calculated.

[0125] Next, the carbon dioxide absorption capacity of the regenerated amine compound was evaluated again, and the changes in carbon dioxide concentration in the dryer after 2 hours and 24 hours were measured (for the third time).

[0126] (Maximum dissociation temperature of amine compounds by carbon dioxide (CO2))

[0127] After evaluating the carbon dioxide absorption capacity as described above, the amine compound was removed from the desiccator, yielding the amine compound that had absorbed carbon dioxide. For the amine compound that had absorbed carbon dioxide, DSC determination was performed as follows to determine the maximum carbon dioxide dissociation temperature of the amine compound. First, for the amine compound, differential scanning calorimetry (DSC) was performed using a differential thermogravimetric analyzer (product name: DTG-60, manufactured by Shimadzu Corporation) under the conditions of a measurement temperature range of 23–250 °C, a heating rate of 10 °C / min, and a nitrogen atmosphere. Based on the resulting DSC curve, the temperature at which the heat of heat absorption accompanying the release of carbon dioxide reached its maximum was calculated, and this temperature was taken as the maximum carbon dioxide dissociation temperature of the amine compound.

[0128] In the examples and comparative examples, the following were used as amine compounds.

[0129] (amine compounds)

[0130] 1,3-BAC: 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.)

[0131] 1,4-BAC (40 mol% trans, 60 mol% cis): 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.)

[0132] 1,4-BACT (trans-iso 85 mol%, cis-iso 15 mol%): 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.)

[0133] 1,3-BAC-AN: A 1:1 (molar ratio) reactant of 1,3-BAC and acrylonitrile (prepared according to Synthesis Example 1 below).

[0134] 1,3-BAC-BisAP: A hydride of the 1:2 (molar ratio) reactive adduct of 1,3-bis(aminomethyl)cyclohexane and acrylonitrile (prepared according to Synthetic Example 2 below)

[0135] IPDA: Isophorone diamine (manufactured by Evonik)

[0136] LDA: Limonene diamine (prepared according to Synthesis Example 3 below).

[0137] MXDA: m-xylylenediamine (manufactured by Mitsubishi Gas Chemical Co., Ltd.)

[0138] TETA: Triethylenetetramine (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0139] (Synthetic Example 1: Preparation of 1,3-BAC-AN)

[0140] In a 100 mL round-bottom flask equipped with a stirrer, thermometer, argon inlet tube, dropping funnel, and cooling tube, 10.0 g of 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added. After thorough stirring under an argon gas flow, 3.73 g of acrylonitrile (manufactured by Sigma-Aldrich) was added dropwise over 10 minutes. After the addition was complete, the temperature was raised to 65 °C and maintained for 1 hour, then cooled to room temperature to obtain 1,3-BAC-AN.

[0141] (Synthetic Example 2: Preparation of 1,3-BAC-BisAP)

[0142] (1) In a 100 mL round-bottom flask equipped with a stirrer, thermometer, argon inlet tube, dropping funnel, and cooling tube, 10.0 g of 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and 20.0 g of 2-propanol (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added. After stirring thoroughly under an argon gas flow, 7.5 g of acrylonitrile (manufactured by Sigma-Aldrich) was added dropwise over 10 minutes. After the addition was completed, the temperature was raised to 65 °C and maintained for 1 hour, then cooled to room temperature to obtain reaction solution (1).

[0143] (2) In a tubular vertical hydrogenation reactor (glass, 10 mm φ inner diameter), 7.0 g of a hydrogenation catalyst (trilobite type, 1.2 mm φ diameter, Johnson Matthey Japan; HTCCo2000) with a cobalt content of 15% by mass was filled. After maintaining the temperature at 120°C for 1 hour under a hydrogen gas flow, the temperature was raised to 240°C and maintained for more than 4 hours for reduction and activation. After cooling, 14.8 g of 2-propanol, the above catalyst, and the reaction liquid (1) were fully added to a high-pressure vessel (150 mL capacity, material: SUS316L) equipped with a stirrer and heater to replace the gas phase with hydrogen. After pressurizing to 3.5 MPaG with hydrogen, the temperature was raised while stirring. After 20 minutes, the liquid temperature was raised to 80°C, and the pressure was adjusted to 8.0 MPaG. Then, the reaction was continued for 3 hours while maintaining the liquid temperature at 80°C and the pressure at 8.0 MPaG, with hydrogen supplied continuously. The reaction solution was completely concentrated under vacuum to obtain 1,3-BAC-BisAP17.5 g.

[0144] (Synthesis Example 3: Manufacturing of LDA)

[0145] 20.0 g (102 mmol) of limonene dialdehyde, 100 g of 1-butanol, and 5 ml of sponge cobalt catalyst (the sponge cobalt catalyst was replaced with 1-butanol solvent and then decanted to remove the 1-butanol before use) were added to a 300 ml stainless steel autoclave. Next, 52 g (3053 mmol) of liquid ammonia was added, and hydrogen was added at room temperature until the internal pressure reached 2.5 MPa. Nitrogen was then added to adjust the internal pressure to 5.0 MPa. The autoclave was heated to 90 °C while stirring. Once 90 °C was reached, hydrogen was added appropriately at an internal pressure of 6 MPa, and the reaction was carried out for 3 hours (hydrogen / nitrogen molar ratio = 1). After cooling, the reaction solution was purged with hydrogen and ammonia and filtered to remove the sponge cobalt catalyst. Gas chromatography analysis of the resulting reaction solution confirmed the presence of 19.2 g (97 mmol) of limonene diamine and 0.6 g (3 mmol) of limonene monoamine monoaldehyde. Next, vacuum distillation was performed under a nitrogen atmosphere using a distillation apparatus equipped with a distillation column filled with Dixon packing and a nitrogen inlet capillary. 15.7 g of the target limonene diamine (99% by mass purity) was obtained as the main fraction.

[0146] (Examples 1-7 and Comparative Examples 1-2)

[0147] In Examples 1-7 and Comparative Examples 1-2, carbon dioxide absorbents containing 100% by mass of the amine compounds shown in Table 1 were used for the above evaluations. The results are shown in Table 1. Examples 4, 5, and Comparative Example 2 were subjected to cyclic evaluations. The results are shown in Table 2.

[0148] [Table 1]

[0149]

[0150] [Table 2]

[0151]

[0152] (Example 8 and Comparative Example 3)

[0153] Except for changing the carbon dioxide absorbent to an aqueous solution of an amine compound with the concentrations shown in Table 3, the above evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

[0154] (Example 9 and Comparative Example 4)

[0155] Except for changing the carbon dioxide absorbent to an aqueous solution of an amine compound with the concentrations shown in Table 3, the above evaluations were performed in the same manner as in Example 4. The results are shown in Table 3.

[0156] (Example 10 and Comparative Example 5)

[0157] Except for changing the carbon dioxide absorbent to an aqueous solution of an amine compound with the concentrations shown in Table 3, the above evaluations were performed in the same manner as in Example 6. The results are shown in Table 3.

[0158] [Table 3]

[0159]

[0160] As shown in Tables 1-3, the carbon dioxide absorbent of the examples containing a specific amount of polyamine compound (A) with an alicyclic hydrocarbon structure absorbs low concentrations of carbon dioxide from the air quickly, resulting in a large amount of carbon dioxide absorbed. That is, it can be seen that the carbon dioxide absorbent of the present invention can efficiently absorb carbon dioxide from the air. In contrast, it can be seen that the carbon dioxide absorbent of the comparative examples absorbs low concentrations of carbon dioxide from the air more slowly than that of the examples.

Claims

1. A carbon dioxide absorbent comprising a polyamine compound (A) having an alicyclic hydrocarbon structure. The content of the polyamine compound (A) is 70% by mass or more. The polyamine compound (A) is a compound represented by the following formula (1). In the above formula (1), R 1 ~R 4 Each independently represents a hydrogen atom, or optionally a hydrocarbon group having 1 or more but less than 10 carbon atoms and having at least one substituent selected from amino, cyano, and phenyl; R 5 ~R 10 Each of the following independently represents a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and less than 4 carbon atoms; x and y each independently represent an integer greater than or equal to 0 and less than 6, and x+y is greater than or equal to 1 and less than 6; p and q each independently represent an integer greater than or equal to 0 and less than 4. The water content in the carbon dioxide absorbent is less than 1% by mass. The carbon dioxide absorbent is used to directly absorb carbon dioxide from the air.

2. The carbon dioxide absorbent according to claim 1, wherein, The maximum carbon dioxide dissociation temperature of the polyamine compound (A), as determined by the following method, is below 140°C. method: The polyamine compound (A) that has absorbed carbon dioxide is heated from 23°C to 250°C at a heating rate of 10°C / min. The temperature at which the heat absorption accompanying the removal of the carbon dioxide reaches its maximum is measured and taken as the maximum dissociation temperature of the carbon dioxide.

3. The carbon dioxide absorbent according to claim 1 or 2, wherein, The acid dissociation constant (pKa) of the polyamine compound (A) is greater than 8.0 and less than 12.

0.

4. The carbon dioxide absorbent according to claim 1 or 2, wherein, The polyamine compound (A) has a molecular weight of 140 or more and 1000 or less.

5. The carbon dioxide absorbent according to claim 1 or 2, wherein, The maximum endothermic temperature of the polyamine compound (A), as determined by the following method, is above 130°C and below 300°C. method: The polyamine compound (A) was heated from 23°C to 350°C at a heating rate of 10°C / min. The temperature at which the heat absorption accompanying the volatilization of the polyamine compound (A) reached its maximum was measured, and this temperature was taken as the maximum heat absorption temperature of the polyamine compound (A).

6. The carbon dioxide absorbent according to claim 1 or 2, wherein, The polyamine compound (A) has an amine value of 500 mg KOH / g or more and 1500 mg KOH / g or less.

7. The carbon dioxide absorbent according to claim 1 or 2, wherein, The polyamine compound (A) has 2 or more but less than 6 amino groups.

8. The carbon dioxide absorbent according to claim 1 or 2, wherein, The alicyclic hydrocarbon structure comprises at least one selected from 5-membered and 6-membered rings.

9. The carbon dioxide absorbent according to claim 1 or 2, wherein, The polyamine compound (A) contains at least one selected from bis(aminomethyl)cyclohexane and its derivatives, limonene diamine and its derivatives, and isophorone diamine and its derivatives.

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