Carbon dioxide adsorbing / desorbing material

Abstract

Provided is a carbon dioxide adsorbing / desorbing material having a high desorption rate.　This carbon dioxide adsorbing / desorbing material contains a carrier and an alkylene imine polymer supported on the carrier, wherein the alkylene imine polymer contains structural units (A) represented by general formula (1), has a number-average molecular weight (Mn) of 200-6000, and has a degree of branching of greater than 0% and no greater than 35%.

Description

Carbon dioxide adsorbent / desorbent

[0001] This invention relates to a carbon dioxide adsorbent / desorbent.

[0002] Ethyleneimine polymers are widely used in fields such as paper processing agents, adhesives, sealants, paints, inks, textile processing agents, flocculants, cosmetics, toiletries, and dispersants. Generally, ethyleneimine polymers, which have secondary amino groups in the main chain and tertiary amino groups at the branching points, are sometimes expressed as having a degree of branching, which is the ratio of tertiary amino groups to the sum of the number of secondary and tertiary amino groups. A higher degree of branching indicates a higher proportion of tertiary amino groups and more branching, while a lower degree of branching indicates a higher proportion of secondary amino groups and less branching.

[0003] For example, Patent Document 1 discloses an ethyleneimine polymer with a branching degree of 30% or less, and Patent Document 2 discloses an ethyleneimine polymer containing 40 to 60% secondary nitrogen atoms.

[0004] In recent years, ethyleneimine polymers focusing on number-average molecular weight and degree of branching have been disclosed. For example, Patent Document 3 discloses an ethyleneimine polymer having a number-average molecular weight of 200 to 6000 and a degree of branching greater than 0% and less than or equal to 20%. On the other hand, Patent Document 4 focuses on ethyleneimine polymers with a larger number-average molecular weight compared to Patent Document 3, and in the examples, the number-average molecular weight exceeds 10000.

[0005] On the other hand, in recent years, a technology called DAC (Direct Air Capture) has been considered as a technology for achieving carbon neutrality. This technology captures dilute carbon dioxide in the atmosphere using a carbon dioxide absorbent, thereby concentrating and fixing the carbon dioxide within the absorbent. The fixed carbon dioxide can then be desorbed from the absorbent by heat treatment or vacuum treatment, allowing the carbon dioxide captured from the atmosphere to be stored underground or used as a raw material for chemical products.

[0006] Various chemicals have been considered as such carbon dioxide absorbers (Patent Documents 5-12).

[0007] Japanese Patent Publication No. 11-158271, Japanese Patent Publication No. 2000-501757, Japanese Patent Publication No. 2021-155570, Japanese Patent Publication No. 2021-155571, U.S. Patent No. 10010861, U.S. Patent No. 11027256, International Publication No. 2023 / 196800, International Publication No. 2023 / 215873, International Publication No. 2024 / 104700, International Publication No. 2024 / 124198, Japanese Patent Publication No. 2018-509280, Japanese Patent Publication No. 2012-011333

[0008] To date, the carbon dioxide separation ability of alkyleneimine polymers with low number-average molecular weight and branching degree has not been studied.

[0009] The inventors have revealed that in materials used for separating carbon dioxide from the atmosphere, such as the carbon dioxide absorbent, if the desorption rate is slow, the desorption of adsorbed carbon dioxide takes a long time, resulting in reduced productivity in carbon dioxide separation and low durability due to the heat load.

[0010] The present invention has been made in view of the above-mentioned problems, and its objective is to provide a carbon dioxide adsorption / desorption material with a fast desorption rate.

[0011] As a result of diligent research to achieve the above objective, the inventors of the present invention have found that alkylene imine polymers with a small number-average molecular weight and low degree of branching are useful as carbon dioxide adsorbents and desorbents when supported on a carrier, due to their rapid carbon dioxide desorption rate. The present invention was completed based on these findings.

[0012] In other words, the present invention comprises a carrier and an alkyleneimine polymer supported on the carrier, wherein the alkyleneimine polymer comprises a structural unit (A) represented by the following general formula (1), The present invention provides a carbon dioxide adsorbent / desorbent material that is an alkylene imine polymer having a number-average molecular weight (Mn) of 200 to 6000 and a branching degree of more than 0% and less than or equal to 35%.

[0013] Furthermore, the present invention provides a method for desorbing carbon dioxide, which includes the step of heating or reducing the pressure of the carbon dioxide adsorption / desorption material on which carbon dioxide is adsorbed.

[0014] Furthermore, the present invention provides a method for separating carbon dioxide, which includes the step of contacting the carbon dioxide adsorbent / desorbent with carbon dioxide in a gas.

[0015] Furthermore, the present invention provides a method for recovering carbon dioxide, which includes the step of desorbing carbon dioxide from the carbon dioxide adsorption / desorption material that has adsorbed carbon dioxide.

[0016] According to the present invention, it is possible to provide a carbon dioxide adsorption / desorption material with a fast desorption rate. A fast desorption rate shortens the desorption time of adsorbed carbon dioxide, improves the productivity of carbon dioxide separation, reduces the heat load, improves durability, and can further contribute to carbon neutrality.

[0017] Preferred embodiments of the present invention will be described below in detail, but the present invention is not limited to the following descriptions and can be modified and applied as appropriate without changing the gist of the invention. Furthermore, embodiments combining two or more of the individual preferred embodiments of the present invention described below also fall under the category of preferred embodiments of the present invention. In this specification, "X to Y" indicating a range means "X or more and Y or less," and "weight" and "mass," "weight%" and "mass%," and "parts by weight" and "parts by mass" are treated as synonyms. Unless otherwise specified, operations and measurements of physical properties, etc., are performed under conditions of room temperature (20-25°C) / relative humidity 40-50%.

[0018] <Carbon Dioxide Adsorbing and Desorbing Material> The present invention comprises a carrier and an alkyleneimine polymer supported on the carrier, wherein the alkyleneimine polymer comprises a structural unit (A) represented by the following general formula (1), The present invention provides a carbon dioxide adsorbent / desorbent material that is an alkylene imine polymer having a number-average molecular weight (Mn) of 200 to 6000 and a branching degree of more than 0% and less than or equal to 35%.

[0019] The carbon dioxide adsorbent / desorbent may be referred to as "the carbon dioxide adsorbent / desorbent of the present invention". The carbon dioxide adsorbent / desorbent of the present invention may consist of an alkyleneimine polymer and a carrier, or may be, for example, a material in which an alkyleneimine polymer and other components are supported on a carrier. By including the alkyleneimine polymer, the carbon dioxide adsorbent / desorbent of the present invention has a high carbon dioxide desorption rate, a shortened desorption time of the adsorbed carbon dioxide, improved productivity related to carbon dioxide separation, reduced heat load, and improved durability.

[0020] The carbon dioxide adsorbent / desorbent may be in a liquid state or a solid state, but is preferably in a solid state.

[0021] <Alkyleneimine polymer> The alkyleneimine polymer contains a structural unit (A) represented by the following general formula (1).

[0022]

[0023] The structural unit (A) is a structural unit derived from alkyleneimine. Since alkyleneimine is an amine compound with a small molecular weight, the amine concentration when it is polymerized into an alkyleneimine polymer can be increased, and the characteristics of the amine contained in the alkyleneimine polymer can be more prominently exhibited. In addition, since ring-opening polymerization is possible, it is easier to increase the molecular weight than polycondensation such as diamine, there are no by-products due to polycondensation such as ammonia, and the environmental load is small in terms of elemental efficiency. Furthermore, since special conditions and equipment such as transition metal catalysts are not required for the polymerization reaction, it has excellent industrial productivity. In addition, it has a higher industrial availability than other monomers capable of ring-opening polymerization such as propyleneamine and azetidine. It is also preferable that two or more structural units (A) represented by the general formula (1) are included.

[0024] The alkyleneimine polymer has a linear structure and a branched structure, and may further have a cyclic structure. The terminal of each polymer chain constituting the alkyleneimine polymer may be a primary amino group (NH ２ group), and the hydrogen atom of the primary amino group may be substituted with another substituent (for example, a group derived from glycidyl ether, etc.).

[0025] The alkyleneimine polymer preferably has a structure having two or more primary amino groups and one or more secondary and tertiary amino groups.

[0026] The number average molecular weight (Mn) of the alkyleneimine polymer is not particularly limited as long as it is from 200 to 6000. The number average molecular weight (Mn) of the alkyleneimine polymer is preferably less than 4000, 3500 or less, 3000 or less, 2500 or less, 2000 or less, 1500 or less, etc. The number average molecular weight (Mn) of the alkyleneimine polymer is preferably 300 or more, 400 or more, etc. In the present invention, all combinations of the above upper limit value and the above lower limit value are included. When the number average molecular weight (Mn) of the alkyleneimine polymer is within the above range, an increase in viscosity during carbon dioxide adsorption can be suppressed, and a decrease in the carbon dioxide adsorption amount due to the increase in viscosity can be prevented. [[ID=,6]]

[0027] The number average molecular weight can be measured by a known method using pullulan as a standard substance by gel permeation chromatography (GPC). As the measurement conditions of GPC, in the present invention, the following conditions are adopted. Measuring device: manufactured by Shimadzu Corporation. Columns used: Shodex OHpak SB-807HQ (2 columns) + SB-806M / HQ (2 columns) manufactured by Resonac Co., Ltd. Eluent: prepared with 0.5 mol% - sodium nitrate and 0.5 mol% - acetic acid. Standard substance: pullulan P-82 (manufactured by Fujifilm Wako Pure Chemical Corporation). Detector: differential refractometer (manufactured by Shimadzu Corporation)

[0028] The alkyleneimine polymer is rich in reactivity compared to other polymer compounds, and those chemically modified by reacting 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, an acyl halide compound can also be used.

[0029] The degree of branching of the alkyleneimine polymer is not particularly limited as long as it is more than 0% and 35% or less. The degree of branching of the alkyleneimine polymer is preferably 30% or less, 25% or less, 23% or less, etc. The degree of branching of the alkyleneimine polymer is preferably 0.1% or more, 0.2% or more, etc. In the present invention, all combinations of the above upper limit value and the above lower limit value are included.

[0030] The degree of branching of the alkyleneimine polymer is calculated from the following formula by calculating the number a of tertiary amino groups and the number b of secondary amino groups. Degree of branching (%) = [a / (a + b)] × 100

[0031] When the degree of branching of the alkyleneimine polymer is within the above range, the proportion of secondary amino groups is larger than the proportion of tertiary amino groups, which contributes to an improvement in the carbon dioxide desorption rate.

[0032] The above degree of branching can be determined by performing measurement by the method of nuclear magnetic resonance (NMR) on the alkyleneimine polymer. For example, １３ From the chart obtained by measuring 13C-NMR, when the carbon atom directly bonded to the nitrogen atom in the secondary amino group and the carbon atom directly bonded to the nitrogen atom in the tertiary amino group can be identified, it can be calculated by obtaining the intensity ratio of the peaks derived from each carbon atom. Incidentally, when the analysis is difficult only by the measurement of the above １３ 13C-NMR, the characteristic atomic-derived peaks such as the peaks derived from each carbon atom may be identified by a known method as appropriate, and the amine ratio may be calculated by obtaining the intensity ratio of each peak. Examples of the method suitable for the above analysis include, for example,​​​​​​​​​​​​​​​​​C HMBC (Heteronuclear Multiple Bond Connectivity), １ H- １３ C HMQC-TOCSY (TOtally Correlated Spectroscopy), １ H- １５ Examples include heterogeneous nuclear correlation two-dimensional NMR using HMBs and other fluorocarbons.

[0033] (Method for producing alkyleneimine polymers) The method for producing alkyleneimine polymers may include a step of ring-opening polymerization of alkyleneimine in the presence of an amine additive and a strong acid, or it may include a condensation reaction step or other reaction steps.

[0034] The amine additive is added as a base amine that serves as the starting point for polymerization. The amine additive is, for example, NH ２ The compound has a primary amino group and / or an NH group (secondary amino group), and an alkyleneimine polymer can be obtained by ring-opening addition polymerization of alkylene to these groups. ２ If it is a compound having a group, NH ２ In some cases, only one alkylene imine undergoes an addition reaction, while in other cases, both alkylene imines undergo an addition reaction. Also, when alkylene imine is added to NH ２ A new NH at the end of the base ２ The group is generated, but its NH ２ Similarly, one or two alkylenes can be added to the base. ２Alkyleneimines can also undergo addition reactions to NH groups (secondary amino groups) generated by addition reactions to primary amino groups, as well as to NH groups (secondary amino groups) contained in amine additives. Therefore, alkyleneimine polymers can have a branched structure. The molecular weight of the amine additive can be, for example, in the range of 31 to 1000. Specifically, ethylenediamine, diethylenetriamine, iminobispropylamine (dipropylenetriamine), dihexylentriamine, m-xylylenediamine, and 1,4-bis(3-aminopropyl)piperazine are preferably used as amine additives. These amine additives may be used individually or in combination of two or more. By adding amine additives, the rapid increase in molecular weight of the resulting alkyleneimine polymer can be suppressed, and the molecular weight can be controlled.

[0035] From the viewpoint of more efficiently suppressing the high molecular weight of the resulting polyalkyleneimine, the amount of amine additive added in the reaction system is preferably 0.1 mol% or more, more preferably 1 mol% or more, and even more preferably 10 mol% or more. From the viewpoint of controlling the molecular weight of the more favorably obtained polyalkyleneimine, the upper limit of the amount of amine additive added in the reaction system is preferably 30 mol% or less, more preferably 25 mol% or less, and even more preferably 20 mol% or less.

[0036] The strong acid is added as a catalyst in the polymerization reaction of alkyleneimines. By using a strong acid, it is possible to react the primary amino group relatively preferentially in the polymerization reaction even at low temperatures, making it possible to produce alkyleneimine polymers with a desired degree of branching. Examples of strong acids include oxoacids containing chlorine such as perchloric acid and chloric acid, hydrochloric acid, hydrogen bromide, hydrogen iodide, sulfuric acid, nitric acid, tetrafluoroboric acid, hexafluorophosphate, etc. These strong acids may be used individually or in combination of two or more.

[0037] From the viewpoint of more efficiently obtaining alkylene imine polymers with the desired degree of branching, the amount of strong acid added in the reaction system is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and even more preferably 0.5 mol% or more. From the viewpoint of more efficiently obtaining alkylene imine polymers with the desired degree of branching, the upper limit of the amount of strong acid added in the reaction system is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less.

[0038] Suitable alkyleneimines include, for example, ethyleneimine and propyleneimine (2-methylaziridine), which may be produced by synthesis or commercially available. Methods for synthesizing ethyleneimine include, for example, intramolecular cyclization of ethylamine halogenated with concentrated alkali in the liquid phase, intramolecular cyclization of monoethanolamine sulfate ester with hot concentrated alkali, or catalytic gas-phase intramolecular dehydration of monoethanolamine.

[0039] Suitable solvents for the production of alkyleneimine polymers include, but are not limited to, water; alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and cyclohexane; and halogenated hydrocarbons such as dichloromethane and chloroform. These solvents may be used individually or in combination of two or more. Of the solvents exemplified above, water, isopropyl alcohol, and mixtures thereof are more preferably used.

[0040] In the method for producing alkyleneimine polymers, the polymerization reaction temperature is preferably 80°C or lower, 70°C or lower, 65°C or lower, etc. In the method for producing alkyleneimine polymers, the polymerization reaction temperature is preferably, for example, -10°C or higher, 0°C or higher, 10°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, 55°C or higher, etc. In the present invention, all combinations of the above upper and lower limits are included. By adjusting the temperature, an alkyleneimine polymer having a desired degree of branching can be obtained.

[0041] In the method for producing alkyleneimine polymers, the polymerization reaction time is not particularly limited, but may be, for example, 4 hours or more, 5 hours or more, 8 hours or less, or 7 hours or less.

[0042] In the method for producing alkyleneimine polymers, the polymerization reaction may be carried out under either atmospheric pressure or pressurized pressure, and may be performed at 0 to 10 MPaG, 0 to 2 MPaG, etc.

[0043] In a method for producing alkyleneimine polymers, a maturation step may be included following the polymerization reaction step. Maturation refers to polymerization after the polymerization of alkyleneimine is complete, preferably after 95% or more of the supplied alkyleneimine has been consumed, and the reaction solution is matured at 80 to 160°C, preferably 110 to 130°C. At temperatures above 100°C, maturation does not require a long time. At temperatures below 150°C, thermal decomposition of the generated alkyleneimine polymer is less likely to occur, and a high-quality polymer can be obtained. The maturation time is usually 1 to 20 hours, preferably 2 to 10 hours. The time required to raise the reaction solution to the maturation temperature is usually 0.2 to 5 hours, preferably 0.5 to 3 hours.

[0044] In a method for producing alkylene imine polymers, a step of concentrating the polymerization reaction solution may be included following the polymerization reaction step or the maturation step, for the purpose of removing the solvent in the polymerization reaction solution obtained, if desired. The concentration may be, for example, reduced-pressure concentration. Furthermore, the concentration conditions are not particularly limited and can be any reduced-pressure conditions, and the concentration may be carried out at a temperature of, for example, 60 to 120°C.

[0045] The concentration of impurities in the alkyleneimine polymer is preferably 0.1 ppm or less, 0.05 ppm or less, or 0.01 ppm or less relative to the mass of the alkyleneimine polymer. The concentration of impurities can be measured by gas chromatography.

[0046] The concentration of unreacted alkylene in the alkylene polymer is preferably 0.1 ppm or less, 0.01 ppm or less, etc., relative to the mass of the alkylene polymer. The amount of unreacted alkylene can be reduced by sufficient maturation. The concentration of unreacted alkylene can be measured by gas chromatography.

[0047] The resin concentration of the alkyleneimine polymer is preferably 90 to 99.9% by mass, 95 to 99.8% by mass, etc., relative to the mass of the alkyleneimine polymer.

[0048] The viscosity of the alkyleneimine polymer varies depending on the resin concentration, but for example, when the resin concentration is 99.0% by mass, it is preferably 200 to 300,000 mPa·s / 25°C. When the alkyleneimine polymer has the above-mentioned physical properties and / or composition, it exhibits little discoloration during storage, low volatility, and good handling properties.

[0049] <Carrier> From the viewpoint of improving carbon dioxide adsorption and desorption capacity, the carrier is preferably porous carrier particles. Examples of materials constituting the carrier include inorganic materials and polymer materials. Specifically, the carrier is preferably porous carrier particles composed of inorganic materials and / or polymer materials.

[0050] 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 structures, with silica and / or alumina being more preferred, and silica even more preferred. The silica is not particularly limited, and known silicas such as fumed silica produced by a dry method, precipitated silica produced by a wet method, silica gel, and silica sol can be used as appropriate. The inorganic material may be used by one or more types.

[0051] Examples of the polymer material include ether sulfone (PES), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose mixed ester, nitrocellulose (NC), polyolefin, polyethylene, polypropylene, polymethylpentene, polyketone, polyimide, polystyrene, polymethyl methacrylate, polydimethylsiloxane, polyester, nylon, polycaprolactone, polylactic acid, polyvinyl alcohol, and polyglycolic acid. One type of polymer material may be used, or two or more types may be used.

[0052] The specific surface area of ​​the aforementioned carrier is set at 70 m² from the viewpoint of having excellent carbon dioxide adsorption and desorption capabilities. ２ Preferably 80 m / g or more, and more preferably 80 m ２ / g or more, more preferably 100m ２ It is 1 / g or more. Furthermore, the specific surface area is 800 m². ２ It may be less than / g, and 650m ２ It may be less than / g, and 500m ２ It may be less than / g.

[0053] From the viewpoint of excellent carbon dioxide adsorption / desorption ability, the content of alkyleneimine polymer in the carbon dioxide adsorption / desorption material is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the total amount of the carrier. Furthermore, from the viewpoint of excellent carbon dioxide adsorption / desorption ability and support, the content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less, per 100 parts by mass of the total amount of the carrier.

[0054] The carrier may contain metals as impurities. Examples of the metals include those described and illustrated as other metal components that may be included in the carbon dioxide adsorption / desorption material of the present invention, as described later. From the viewpoint of excellent durability, the content ratio of the metal-containing component in the carrier is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, even more preferably 3,000 ppm or less, and particularly preferably 2,000 ppm or less, based on 100% by mass of the total amount of the carrier. Furthermore, from the viewpoint of industrial applicability (productivity), the content ratio may be 10 ppm or more, 30 ppm or more, or 50 ppm or more, based on 100% by mass of the total amount of the carrier. More specifically, the total content ratio of each component containing chromium, manganese, iron, cobalt, nickel, and copper in the carrier is preferably within the above range, based on 100% by mass of the total amount of the carrier. The content ratio can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0055] <Other Components> The carbon dioxide adsorbent / desorbent of the present invention may contain components other than the alkyleneimine polymer and the carrier (hereinafter referred to as "other components").

[0056] The aforementioned other components may be used individually or in combination of two or more. Examples of the aforementioned other components include the strong acid that can be added as a catalyst in the polymerization reaction of the alkyleneimine, solvents (e.g., water; organic solvents such as methanol and ethanol), surfactants (anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants), antioxidants, antioxidant aids, crystallization inhibitors, etc. Other components may also include impurities such as metals that are not intentionally included. The aforementioned other components may be used individually or in combination of two or more. The HLB (hydrophilic-lipophilic balance) of the surfactant is preferably 10 or more, more preferably 12 or more, and even more preferably 15 or more.

[0057] The amount of the strong acid relative to 100% by mass of the alkyleneimine polymer in the carbon dioxide adsorption / desorption material of the present invention can be determined by known or conventional analytical methods such as ion chromatography. The conditions for ion chromatography can be found in the examples described below.

[0058] From the viewpoint of further improving the heat resistance of the carbon dioxide adsorbent / desorbent, it is preferable that the amount of the strong acid in the carbon dioxide adsorbent / desorbent of the present invention relative to 100% by mass of the alkyleneimine polymer is small, for example, 15,000 ppm by mass or less, 10,000 ppm by mass or less, 5,000 ppm by mass or less, 4,000 ppm by mass or less, 1,000 ppm by mass or less, 100 ppm by mass or less, etc.

[0059] Methods for reducing the amount of strong acid include, for example, a method of neutralizing strong acid ions and removing the salt (neutralization and salt removal method), and a method of adsorbing strong acid ions onto an ion exchange resin (adsorption method).

[0060] As the neutralization method, known or conventional methods can be employed. For the neutralization, for example, an alkaline aqueous solution containing one or more bases selected from the group consisting of alkali metal ions hydroxide and alkoxylated compounds, alkaline earth metal ions hydroxide and alkoxylated compounds, salts of alkali metal ions with a conjugate base of a weak acid, and salts of alkaline earth metal ions with a conjugate base of a weak acid may be used.

[0061] Examples of alkali metal ion hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide, with sodium hydroxide being preferred. Examples of alkali metal ion alkoxyides include sodium methoxide. Examples of alkaline earth metal hydroxides include beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, and radium hydroxide, with magnesium hydroxide being preferred. Examples of alkaline earth metal ion alkoxyides include magnesium methoxide.

[0062] Examples of salts of alkali metal ions and conjugate bases of weak acids include salts of alkali metals such as sodium and potassium with weak acids such as citric acid, acetic acid, carbonic acid, and phosphoric acid, specifically sodium bicarbonate, tripotassium phosphate, and trisodium citrate. Examples of salts of alkaline earth metal ions and conjugate bases of weak acids include salts of alkaline earth metals such as magnesium and calcium with weak acids such as citric acid, acetic acid, carbonic acid, and phosphoric acid, specifically magnesium acetate, calcium acetate, and magnesium citrate.

[0063] As a method for removing the salt, known or conventional methods can be employed, such as recovering the target product in an organic solvent layer by liquid-liquid separation with an organic solvent such as isopropanol, and then further removing the organic solvent by distillation.

[0064] In the adsorption method described above, an anion exchange resin is preferred as the ion exchange resin. Examples of anion exchange resins include Diaion (registered trademark) SH10AOH (manufactured by Mitsubishi Chemical Corporation) having a trimethylamine functional group, a strongly basic anion exchange resin which is the OH form of a styrene-ethylstyrene-divinylbenzene copolymer having a triethylamine functional group, a strongly basic anion exchange resin having a quaternary ammonium group, and a weakly basic anion exchange resin having a primary or secondary amine. The method for adsorbing halogen ions onto the ion exchange resin may be a known or conventional method. After adsorption, it is preferable to further remove the solvent by distillation.

[0065] Furthermore, the amount of the strong acid in the carbon dioxide adsorption / desorption material of the present invention relative to 100% by mass of the alkyleneimine polymer may be, for example, 50 ppm by mass or more.

[0066] The neutralization and desalting, and adsorption may be performed individually or in combination. In the latter case, the adsorption may be performed after the neutralization and desalting, or after the adsorption.

[0067] As the antioxidant, radical scavengers, peroxide decomposers, etc., can be used. As the radical scavenger, phenolic antioxidants, amine antioxidants, etc., can be used, and amine antioxidants are preferred. As the peroxide decomposer, there are no particular limitations as long as it can effectively decompose peroxides, but sulfur-based antioxidants, phosphorus-based antioxidants, phenolic antioxidants, hindered amine antioxidants, etc., can be used. Examples of the sulfur-based antioxidants include 2-hydroxyethyl disulfide, 1,2-bis[(2-hydroxyethyl)thio]ethane, thiodipropionic acid, dilauryl thiodipropionate, distearyl thiodipropionate, lauryl stearyl thiodipropionate, dimyristyl thiodipropionate, distearyl-β,β'-thiodibutyrate, thiobis(β-naphthol), thiobis(N-phenyl-β-naphthylamine), 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, dodecyl mercaptan, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, nickel dibutyldithiocarbamate, nickel isopropyl xanthate, dodecanethiol, and the like, with 2-hydroxyethyl disulfide and 1,2-bis[(2-hydroxyethyl)thio]ethane being more preferred.Examples of the phosphorus-based antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenyldiisodecyl phosphite, tris(nonylphenyl) phosphite, diisodecylpentaerythritol phosphite, tris(2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis(octadecyl) phosphite, cyclic neopentanetetraylbis(2,4-di-t-butylphenyl) phosphite, and cyclic neopentanetetraylbis(2,4-di-t- Phosphates such as butyl-4-methylphenyl) phosphite and bis[2-t-butyl-6-methyl-4-{2-(octadecyloxycarbonyl)ethyl}phenyl]hydrogen phosphite (phosphite-based antioxidants); oxaphosphaphenanthrene oxides such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are examples.Examples of the phenolic antioxidants include monophenols such as 4-methoxyphenol, hydroquinone, 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-p-ethylphenol, and stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), and 3,9-bis[1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy} Examples include bisphenols such as ethyl[2,4,8,10-tetraoxaspiro[5.5]undecane; 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane; 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene; tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane; bis[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid]glycol ester; 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione; and high molecular weight phenols such as tocopherol. Examples of the hindered amine antioxidants include bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, methyl-1,2,2,6,6-pentamethyl-4-piperidyl sebacate, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, and 4-hydroxy-2,2,6,6-tetramethylpiperidine.

[0068] Examples of crystallization inhibitors include water-soluble polymers such as polyvinylpyrrolidone, polyvinyl alcohol, and hydroxyethylcellulose. By using water-soluble polymers as crystallization inhibitors, it is possible to suppress the secondary interaction between carbamic acid, which is produced by the reaction of the oligoamine compound with carbon dioxide, and the oligoamine compound, which can lead to the formation of insoluble salts.

[0069] Examples of the metal impurity include elemental metals and components containing metals (e.g., metal oxides). Examples of the metal include transition metals. The transition metal is an element from any of groups 3 to 12 of the periodic table, and more specifically, at least one selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, and more specifically, at least one selected from the group consisting of chromium, manganese, iron, cobalt, nickel, and copper.

[0070] From the viewpoint of excellent durability, the content ratio of metal-containing components in the carbon dioxide adsorbent / desorbent is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less, based on 100% by mass of the total amount of the carbon dioxide adsorbent / desorbent. Furthermore, it is particularly preferable that the carbon dioxide adsorbent / desorbent substantially does not contain any metal-containing components. The content ratio may also be 0.5 ppm or more, or 1 ppm or more, based on 100% by mass of the total amount of the carbon dioxide adsorbent / desorbent. More specifically, the total content ratio of each component containing chromium, manganese, iron, cobalt, nickel, and copper in the carbon dioxide adsorbent / desorbent is preferably within the above range, based on 100% by mass of the total amount of the carbon dioxide adsorbent / desorbent. The content ratio can be measured, for example, by X-ray fluorescence (XRF) analysis.

[0071] <Method for Manufacturing Carbon Dioxide Adsorbing and Desorbing Material> The carbon dioxide adsorbing and desorbing material can be manufactured by known or conventional methods, except that the alkyleneimine polymer is used. Here, the carbon dioxide adsorbing and desorbing material can be manufactured, for example, by mixing and stirring the above-mentioned components. Specifically, the method for manufacturing the carbon dioxide adsorbing and desorbing material preferably includes a step of mixing and stirring the alkyleneimine polymer and the carrier to support the alkyleneimine polymer on the carrier (supporting step). From the viewpoint of excellent handling and supportability, the method for manufacturing the carbon dioxide adsorbing and desorbing material preferably includes a step of mixing and stirring a composition containing at least the alkyleneimine polymer and a solvent with the carrier to support the alkyleneimine polymer on the carrier (supporting step). When using the composition, the supporting step may be a step of adding the composition to the carrier and supporting it (step (a)), or a step of adding each component contained in the composition separately to the carrier and supporting it (step (b)). Of the aforementioned loading steps, step (a) is preferred from the viewpoint of superior manufacturing efficiency. In step (b), the order in which each component is added is not particularly limited.

[0072] The aforementioned supporting step can employ known or conventional methods. For example, the alkyleneimine polymer may be supported by impregnating the carrier (impregnation), by dropping the alkyleneimine polymer onto the carrier (dropping), or by filling the carrier into a container such as a column and then passing the alkyleneimine polymer through it (liquid passage). Among these, the impregnation method is preferred from the viewpoint of ease of operation and equipment.

[0073] The pressure conditions in the loading process are not particularly limited and can be arbitrarily selected from atmospheric pressure, reduced pressure, or increased pressure. If the carrier has pores, it is preferable to process it under reduced pressure from the viewpoint of removing air bubbles in the pores and efficiently loading it onto the carrier. The specific processing pressure is preferably 1 Pa to 100 Pa, more preferably 1 Pa to 50 Pa, and even more preferably 10 Pa to 30 Pa.

[0074] The temperature conditions in the loading process are not particularly limited, but from the viewpoint of excellent loading performance, 20°C to 90°C is preferred, more preferably 30°C to 80°C, and even more preferably 40°C to 70°C.

[0075] Furthermore, the method for producing the carbon dioxide adsorbent / desorbent may optionally include a step of separating the excess solvent from the support on which the alkyleneimine polymer is supported (separation step), and / or a step of removing the solvent from the support (drying step).

[0076] The separation step can employ known or conventional methods, such as filtration, decantation, or centrifugation. Among these, filtration is preferred due to its ease of procedure.

[0077] The temperature conditions in the drying process are not particularly limited, but are preferably 30°C to 100°C, more preferably 40°C to 98°C, even more preferably 50°C to 95°C, and most preferably 50°C to 90°C.

[0078] The processing 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.

[0079] The pressure conditions in the drying process are not particularly limited and can be arbitrarily selected from atmospheric pressure, reduced pressure, or increased pressure. Among these, atmospheric pressure is preferred from the viewpoint of maintaining the state in which the alkylene imine polymer is supported on the carrier.

[0080] <Method of using carbon dioxide adsorption / desorption material> The carbon dioxide adsorption / desorption material can separate carbon dioxide not only from gases containing high concentrations of carbon dioxide, but also from dilute carbon dioxide in conditioned air and the atmosphere by adsorbing it. Furthermore, by going through a process of desorption (removal) of the adsorbed carbon dioxide, the carbon dioxide can be recovered, and it is also possible to adsorb carbon dioxide again. For this reason, by using the carbon dioxide adsorption / desorption material, it is possible to suppress the decrease in carbon dioxide adsorption / desorption capacity even after repeated adsorption and desorption of carbon dioxide.

[0081] The carbon dioxide adsorbent / desorbent can be installed and used in a device (carbon dioxide recovery device) that separates and recovers carbon dioxide from a gas to be treated that contains carbon dioxide. The gas to be treated is a carbon dioxide-containing gas that contains at least carbon dioxide, but may also contain other gases. Examples of the gas to be treated include the atmosphere, or high-concentration gases with a higher carbon dioxide concentration than the atmosphere. Such high-concentration gases are, for example, those emitted from internal combustion engines or factories.

[0082] Methods for using the carbon dioxide adsorbent / desorbent include a carbon dioxide separation method that includes a step of contacting the carbon dioxide adsorbent / desorbent with carbon dioxide in a gas (contact step), a desorption method that includes a step of heating or depressurizing the carbon dioxide adsorbent / desorbent on which carbon dioxide has been adsorbed, and a carbon dioxide recovery method that includes a step of desorbing the carbon dioxide from the carbon dioxide adsorbent / desorbent that has adsorbed carbon dioxide (desorption step). In the contact step, the carbon dioxide adsorbent / desorbent adsorbent adsorbs carbon dioxide in the gas, so carbon dioxide can be removed (separated) from the gas. In the desorption step, carbon dioxide can be recovered by desorbing carbon dioxide from the carbon dioxide adsorbent / desorbent. Therefore, the carbon dioxide adsorbent / desorbent may be referred to as a carbon dioxide absorbent.

[0083] The pressure conditions for the separation method may be, for example, 0.8 atmospheres to 1.1 atmospheres. The adsorption temperature conditions for the separation method may be, for example, -40°C to 50°C, or 30°C to 40°C.

[0084] The pressure conditions for the recovery method and the desorption method may, for example, be under reduced pressure, or between 0.02 atmospheres and 1.1 atmospheres, or between 0.1 atmospheres and 0.3 atmospheres. The temperature conditions for the recovery method and the desorption method may, for example, be under heating, or between 50°C and 130°C, or between 70°C and 80°C.

[0085] The amount of carbon dioxide adsorbed and desorbed can be measured, for example, by referring to the carbon dioxide adsorption / desorption test method in the example described later. Specifically, a TG-DTA (TG-DTA8120, 8122 manufactured by Rigaku Corporation) is used to measure the mass at the adsorption temperature (35°C) and the desorption temperature (75°C). The material is held at the adsorption temperature for 150 minutes and at the desorption temperature for 60 minutes. Using a mass flow controller, a carbon dioxide-containing gas with adjusted nitrogen and carbon dioxide flow rates is supplied to the TG-DTA oven at 200 ml / min. The carbon dioxide concentration of the simulated gas is kept constant at approximately 400 ppm, and the humidity of the supplied gas is kept constant at an absolute humidity of 2 g / kg. From the TG-DTA measurements, the amount of carbon dioxide adsorbed and desorbed material during carbon dioxide adsorption at each temperature and the amount of carbon dioxide adsorbed and desorbed material during carbon dioxide desorption by heating are measured, and the amount of carbon dioxide adsorbed and desorbed is calculated from the following formula: Amount of carbon dioxide adsorbed and desorbed (g / g) = (W Ａ -W Ｄ ) / W １ W Ａ : Mass (g) of carbon dioxide adsorbent / desorbent at adsorption temperature W Ｄ : Mass (g) of carbon dioxide adsorbent / desorbent at the desorption temperature W １ : Mass (g) of the carbon dioxide adsorbent / desorbent used in the test

[0086] For example, the carbon dioxide desorption rate (g / g / min) when heating from 35°C to 75°C can be determined by measuring the time taken for desorption when heating from the adsorption temperature (35°C) to the desorption temperature (75°C), and dividing the amount of carbon dioxide adsorbed and desorbed (g / g) by that time (minutes). The time taken for desorption refers to, for example, the time until 98% or more of the carbon dioxide is desorbed during 60 minutes of holding at the desorption temperature (75°C).

[0087] The rapid desorption rate of carbon dioxide by a carbon dioxide adsorbent / desorbent can be determined, for example, as follows: A carbon dioxide adsorbent / desorbent that has adsorbed carbon dioxide is heated to 75°C at atmospheric pressure at a rate of 10°C / min, and then maintained at 75°C. The time from which heating begins at 35°C is set to 0 minutes (reference time). If the amount of carbon dioxide desorbed in the first 20 minutes after heating begins is X (g / g) and the amount of carbon dioxide desorbed in the first 40 minutes after heating begins is Y (g / g), then if X / Y is between 0.93 and 1.00, it can be determined that the carbon dioxide desorption rate is rapid.

[0088] 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 below, "ppm", "%", and "parts" in this specification refer to "mass ppm", "mass %", and "mass parts".

[0089] Synthesis Example 1: 8 g of a water-IPA (isopropyl alcohol) mixed solution (water:IPA = 1:1 by mass) was charged into a 40 mL pressure reactor as the solvent, 0.0389 g of 60% perchloric acid as the catalyst, and 0.2940 g of diethylenetriamine as the amine additive. 2 g of ethyleneimine was slowly added dropwise. The temperature was raised to 60°C, and ring-opening polymerization was carried out with stirring for 6 hours. The temperature was then further raised to 120°C and aged for 6 hours. After aging, the remaining ethyleneimine and solvent were removed at 100°C under reduced pressure to obtain the target polyethyleneimine. NMR analysis of the obtained polyethyleneimine under the following conditions showed a branching degree of 22%, confirming a high proportion of secondary amino groups. GPC analysis of the obtained polyethyleneimine under the following conditions showed a number-average molecular weight (Mn) of 750.

[0090] Synthesis Example 2 In a 40 mL pressure reactor, 1.4 g of pure water was charged as the solvent, 0.078 g of 60% perchloric acid as the catalyst, and 0.208 g of diethylenetriamine as the amine additive. 2 g of ethyleneimine was slowly added dropwise. The temperature was raised to 65°C, and ring-opening polymerization was carried out with stirring for 6 hours. The temperature was then raised to 120°C and aged for 6 hours. After aging, the remaining ethyleneimine and solvent were removed at 100°C under reduced pressure to obtain the target polyethyleneimine. NMR analysis of the obtained polyethyleneimine under the following conditions showed a branching degree of 27%, confirming a high proportion of secondary amino groups. GPC analysis of the obtained polyethyleneimine under the following conditions showed a number-average molecular weight (Mn) of 1,000. The amount of perchlorate ions per 100% by mass of polyethyleneimine in the composition containing the polyethyleneimine obtained in Synthesis Example 2 was 12,700 ppm by mass.

[0091] Synthesis Example 3 Ten parts of a 20% aqueous solution of polyethyleneimine obtained in Synthesis Example 2 were mixed with 1.5 parts of strongly basic anion exchange resin No. 8 (OH form) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., the OH form of a copolymer of styrene-ethylstyrene-divinylbenzene having a triethylamine functional group). After stirring for 1 hour, the ion exchange resin was filtered off. The resulting liquid was concentrated to produce a composition containing polyethyleneimine with a reduced amount of perchlorate ions. The amount of perchlorate ions per 100% by mass of polyethyleneimine in the polyethyleneimine-containing composition obtained in Synthesis Example 3 was 70 ppm by mass.

[0092] NMR analysis: 10% by mass of polyethyleneimine was dissolved in heavy water containing 30% by mass of biacetic acid, and NMR (400 MHz) analysis was performed. １３By measuring C-NMR and obtaining a chart, the intensity ratio of carbon atoms directly bonded to secondary amino groups to carbon atoms directly bonded to tertiary amino groups can be determined. This allows for the calculation of the number of tertiary amino groups (a) and the number of secondary amino groups (b). These values ​​(a) and (b) can then be applied to the following formula. Specifically, linear modified polyalkyleneimines have no tertiary amino groups, so their branching degree is 0%. Modified polyalkyleneimines where all nitrogen atoms are tertiary amino groups, i.e., those with maximum branching, have a branching degree of 100%. Branching degree (%) = [a / (a ​​+ b)] × 100

[0093] The number-average molecular weight of polyethyleneimine was measured under the following conditions for GPC analysis: • Measuring instrument: Shimadzu Corporation • Columns used: SHODEX OHpak SB-807HQ (x2 columns) + SB-806M / HQ (x2 columns) manufactured by Resonaq Corporation • Eluent: 0.5 mol% sodium nitrate / 0.5 mol% aqueous acetic acid solution • Standard substance: Pullulan P-82 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) • Detector: Differential refractometer (manufactured by Shimadzu Corporation)

[0094] Analysis of Perchloric Acid (Ion) Content (Ion Chromatography) Ion chromatography was performed under the following conditions to calculate the perchloric acid (ion) content (ppm) in the polyethyleneimine-containing compositions obtained in Synthesis Examples 2 and 3. Apparatus: Dionex® ICS-2000 (manufactured by Thermo Fisher Scientific Co., Ltd.) Detector: Conductivity detector Column: Dionex® IonPac® AS-18 (manufactured by Thermo Fisher Scientific Co., Ltd.) Guard column: Dionex® IonPac® AG-18 (manufactured by Thermo Fisher Scientific Co., Ltd.) Column temperature: 30°C Eluent: KOH aqueous solution (15 mmol / L) Flow rate: 0.9 mL / min Injection volume: 25 μL

[0095] Example 1 0.25 parts of polyethyleneimine with a high proportion of secondary amino groups obtained in Synthesis Example 1 and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of a silica-containing carrier (product name "CARiACT G-10", manufactured by Fuji Silicia Chemical Co., Ltd.) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material on which polyethyleneimine with a high proportion of secondary amino groups (referred to as secondary richPEI in Table 1 below) was supported.

[0096] Example 2 0.25 parts of polyethyleneimine with a high proportion of secondary amino groups obtained in Synthesis Example 1 and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of a silica-containing carrier (product name "HI-SIL-915", manufactured by PPG Industries) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material on which polyethyleneimine with a high proportion of secondary amino groups (referred to as secondary richPEI in Table 1 below) was supported on a porous material.

[0097] Example 3 0.25 parts of polyethyleneimine with a high proportion of secondary amino groups obtained in Synthesis Example 2 and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of silica-containing carrier (product name "CARiACT G-10", manufactured by Fuji Silicia Chemical Co., Ltd.) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material in which polyethyleneimine with a high proportion of secondary amino groups (referred to as secondary richPEI in Table 1 below) was supported on a porous material.

[0098] Example 4 0.25 parts of polyethyleneimine with a high proportion of secondary amino groups obtained in Synthesis Example 3 and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of silica-containing carrier (product name "CARiACT G-10", manufactured by Fuji Silicia Chemical Co., Ltd.) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material on which polyethyleneimine with a high proportion of secondary amino groups (referred to as secondary richPEI in Table 1 below) was supported on a porous material.

[0099] Comparative Example 1: 0.25 parts of polyethyleneimine (SP-012; manufactured by Nippon Shokubai Co., Ltd.; number average molecular weight 1200 (catalog value, boiling point elevation method)) and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of silica-containing carrier (product name "CARiACT G-10" manufactured by Fuji Silicia Chemical Co., Ltd.) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material on which the polyethyleneimine (referred to as PEI in Table 1 below) was supported. The branching degree of SP-012 was 46%.

[0100] Comparative Example 2: 0.25 parts of polyethyleneimine (SP-012; manufactured by Nippon Shokubai Co., Ltd.; branching degree 46%, number average molecular weight 1200 (catalog value, boiling point elevation method)) and 2.5 parts of water were mixed to make a homogeneous solution. Subsequently, 0.50 parts of silica-containing carrier (product name "HI-SIL-915" manufactured by PPG Industries) were added and impregnated while stirring for 30 minutes. Subsequently, the material 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 adsorbent / desorbent material on which the polyethyleneimine (referred to as PEI in Table 1 below) was supported.

[0101] [Carbon Dioxide Adsorption and Desorption Test Using Carbon Dioxide-Containing Gas Simulating Dry Atmosphere] To measure the amount of carbon dioxide adsorbed and desorbed, a TG-DTA (TG-DTA8120, 8122, manufactured by Rigaku Corporation) was used, and the mass at the adsorption temperature (35°C) and desorption temperature (75°C) was measured. The material was held for 150 minutes at the adsorption temperature and for 60 minutes at the desorption temperature. Using a mass flow controller, a carbon dioxide-containing gas with adjusted nitrogen and carbon dioxide flow rates was supplied to the TG-DTA oven at 200 ml / min. The carbon dioxide concentration of the simulated gas was kept constant at approximately 400 ppm, and the humidity of the supplied gas was kept constant at an absolute humidity of 2 g / kg. From the TG-DTA measurements, the amount of carbon dioxide adsorbed and desorbed material during carbon dioxide adsorption at each temperature and the amount of carbon dioxide adsorbed and desorbed material during carbon dioxide desorption by heating were measured, and the amount of carbon dioxide adsorbed and desorbed was calculated using the following formula: Amount of carbon dioxide adsorbed and desorbed (g / g) = (W Ａ -W Ｄ ) / W １ W Ａ : Mass (g) of carbon dioxide adsorbent / desorbent at adsorption temperature W Ｄ : Mass (g) of carbon dioxide adsorbent / desorbent at the desorption temperature W １ : Mass (g) of the carbon dioxide adsorbent / desorbent used in the test. The results are shown in Table 1.

[0102] Of the amount of carbon dioxide desorbed during 60 minutes at the desorption temperature (75°C), the time until 98% or more of the carbon dioxide was desorbed was measured as the time taken for desorption. The amount of carbon dioxide adsorbed and desorbed (g / g) was then divided by this time (minutes) to determine the CO2 adsorption / desorption rate when heating from 35°C to 75°C. ２ The desorption / desorption rate ((g / g) / min) * 1000 was calculated. The results are shown in Table 1.

[0103] A carbon dioxide adsorbent / desorbent material that had adsorbed carbon dioxide was heated at atmospheric pressure from 35°C to 75°C at a rate of 10°C / min, and then held at 75°C. The time from when heating started at 35°C was set to 0 minutes (reference time). The amount of carbon dioxide desorbed in the first 20 minutes after heating started was X (g / g), and the amount of carbon dioxide desorbed in the first 40 minutes after heating started was Y (g / g). The ratio X / Y was then calculated. The results are shown in Table 1.

[0104]

[0105] Table 1 shows that the carbon dioxide desorption rate of the example was faster than that of the comparative example. Furthermore, the ratio of the amount of desorption in the first 20 minutes after heating to the amount of desorption in the first 40 minutes after heating was 0.93 or higher in the example, indicating that desorption was almost complete within 20 minutes of heating, further demonstrating the fast carbon dioxide desorption rate. In addition, it was found that there was almost no difference in the amount of carbon dioxide adsorption and desorption per cycle between the example and the comparative example. From these findings, it was confirmed that the example can improve productivity as a carbon dioxide adsorption and desorption material that repeats adsorption and desorption cycles, reduce thermal load, and consequently improve durability.

[0106] [Degradation Treatment] 0.03 g each of the carbon dioxide absorbent obtained in Example 4 and Comparative Example 1 was weighed into 10 mL vials. The top of each vial was protected with weighing paper that had several holes punched in it to prevent contamination with foreign matter while allowing air to pass through. After standing in a 100°C oven for 24 hours, the vials were cooled to obtain carbon dioxide adsorbents that had undergone degradation treatment. This treatment causes the carbon dioxide adsorbents to undergo oxidative degradation, thus mimicking adsorbents that have undergone heating or repeated adsorption / desorption treatments. The carbon dioxide adsorption and desorption amounts (carbon dioxide adsorption and desorption amounts (g / g) after heating at 100°C for 24 hours) of each carbon dioxide adsorption and desorption material obtained in Example 4 and Comparative Example 1 after treatment by the degradation treatment were 0.036 and 0.025, respectively. It was found that the carbon dioxide absorbent obtained in Example 4, which used a composition containing polyethyleneimine obtained in Synthesis Example 3 as a raw material, which has a low amount of perchlorate ions relative to 100% by mass of polyethyleneimine, also exhibits excellent heat resistance (oxidation resistance).

Claims

1. The material comprises a carrier and an alkyleneimine polymer supported on the carrier, wherein the alkyleneimine polymer contains a structural unit (A) represented by the following general formula (1), A carbon dioxide adsorbent / desorbent that is an alkylene imine polymer having a number-average molecular weight (Mn) of 200 to 6000 and a branching degree of more than 0% and less than or equal to 35%.

2. A method for desorbing carbon dioxide, comprising the step of heating or reducing the pressure of a carbon dioxide adsorbent / desorbent material according to claim 1, which has carbon dioxide adsorbed onto it.

3. A method for separating carbon dioxide, comprising the step of contacting a carbon dioxide adsorbent / desorbent material according to claim 1 with carbon dioxide in a gas.

4. A method for recovering carbon dioxide, comprising the step of desorbing carbon dioxide from a carbon dioxide adsorbent / desorbent material according to claim 1 that has adsorbed carbon dioxide.

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