Carbon dioxide adsorbent

Abstract

Provided is a carbon dioxide adsorbent comprising: a fiber structure formed from fibers; and a carbon dioxide adsorption compound supported on the fibers. The fiber diameter of the fibers supporting the carbon dioxide adsorption compound is 0.3-30 μm, the pore diameter of the fibers supporting the carbon dioxide adsorption compound is 2.0 nm or greater, and the supported amount of the carbon dioxide adsorption compound is 20-70 mass% relative to 100 mass% of the carbon dioxide adsorbent.

Description

Carbon dioxide adsorbent

[0001] The present invention relates to a carbon dioxide adsorbent that efficiently adsorbs carbon dioxide in a gas to be treated, such as the atmosphere.

[0002] As a measure against recent global warming and climate change, carbon neutrality, which means reducing greenhouse gas emissions to zero by 2050, is the goal. However, it is difficult to completely reduce greenhouse gas emissions to zero, and negative carbon dioxide emission technologies and offsets are needed to make up for shortfalls in emission reductions. Negative emission technologies include fixation in minerals and seaweed, and a technology called Direct Air Capture (DAC), which directly captures carbon dioxide from the atmosphere.

[0003] There are several DAC technologies, including chemical absorption, chemical adsorption, membrane separation, and cryogenic separation, but all of these methods have significant issues with equipment and running costs. Of these, chemical adsorption is expected to be able to reduce costs, as it can desorb the captured carbon dioxide at a relatively low temperature by heating.

[0004] However, cost improvements are still required, and a multifaceted approach to solving the problem is required. Examples include reducing installation costs by making the equipment more compact and reducing the power required for carbon dioxide adsorption. To achieve this, it is necessary to adsorb a large amount of carbon dioxide in a short period of time and operate it with low pressure loss.

[0005] In the chemical adsorption method, it is widely known that a porous substrate can be used as a carbon dioxide adsorbent by supporting amines as carbon dioxide adsorption compounds, and porous particles with amines supported on them are widely used. However, the high pressure loss (pressure drop) is an issue with the prior art, and evaluation systems that can output a constant flow rate even with high pressure drop have been proposed, and there has been discussion about the carbon dioxide adsorption amount using evaluation methods that involve adsorption treatment over a long period of time.

[0006] For example, in Patent Document 1, a carbon dioxide absorbing fiber is obtained by extruding an aqueous solution of polyvinyl alcohol and an amine polymer, which is a carbon dioxide adsorption compound, into the air through a nozzle, thereby obtaining a carbon dioxide absorbing fiber in which up to 40 mass% of the adsorption compound is unevenly distributed on the fiber surface. Furthermore, the carbon dioxide adsorption amount is evaluated by leaving the fiber to stand for up to one week in an environment of 400 ppm, 20°C, and 60% RH.

[0007] For example, in Patent Document 2, a fiber serving as a carbon dioxide adsorbent is obtained by spinning an aqueous solution containing a mixture of polyvinyl alcohol and an amine prepolymer, which is a carbon dioxide adsorbing compound, while applying a voltage of 10 kV, and the amount of carbon dioxide adsorbed is evaluated by contacting the membrane with a constant pressure gas for up to 15 hours.

[0008] For example, in Patent Document 3, activated carbon fibers that have been heat-treated in a non-oxidizing atmosphere that does not contain activating gases such as water vapor or carbon dioxide to make them hydrophobic are impregnated with an aqueous solution or alcohol solution of an amine compound, which is an adsorbent compound, and then the water and alcohol are removed to support the amine compound, thereby obtaining a carbon dioxide adsorbent. The carbon dioxide adsorption capacity is evaluated by feeding a gas of 200 ppm, 30°C, and 0 to 60% RH at a constant pressure.

[0009] For example, in Patent Document 4, porous particles of a hypercrosslinked polymer are prepared by Friedel-Crafts catalytic polymerization, and a liquid containing an amine, which is an adsorption compound and acts as an acid gas absorbent, is impregnated into the porous particles to form a carbon dioxide adsorbent. The amount of carbon dioxide adsorption is evaluated by flowing a constant flow rate of gas using a thermal mass flow controller.

[0010] International Publication No. 2021 / 200348 International Publication No. 2022 / 202152 Japanese Patent Application Laid-Open No. 2019-209293 Special Publication No. 2024-500705

[0011] When a large amount of carbon dioxide adsorption compound is unevenly distributed on the surface of a non-porous fiber, such as the carbon dioxide absorption fiber described in Patent Document 1, the adsorption compound forms a thick layer, and carbon dioxide is adsorbed onto the outermost surface of the fiber. Since adsorption then proceeds through internal diffusion, it takes a long time to adsorb carbon dioxide. In fact, the carbon dioxide absorption amount is evaluated over a period of 12 hours or one week, and there is no concept of adsorption in a short period of time. Furthermore, the evaluation is performed in a static environment, and there is no concept of achieving low pressure loss.

[0012] The fiber described in Patent Document 2 is a nanoscale fiber, so it has a relatively high specific surface area, but when spun by electrospinning, no pores remain on the fiber surface. Therefore, after carbon dioxide is adsorbed to the adsorbent compounds present on the fiber surface, it is adsorbed by the adsorbent compounds present inside the fiber via internal diffusion, requiring time for carbon dioxide adsorption. The carbon dioxide adsorption amount was also evaluated over a period of 15 hours, indicating that adsorption takes time. In addition, the production of nonwoven fabrics using the electrospinning method generally poses many challenges in terms of cost and productivity, making it unsuitable for the production of DAC substrates. Furthermore, Patent Document 2 does not disclose an evaluation of carbon dioxide adsorption when the carbon dioxide adsorbent has a honeycomb structure, nor does it disclose low pressure loss.

[0013] The activated carbon fiber described in Patent Document 3 is a relatively thin fiber having pores, but the amount of amine compound supported is kept low so as not to impair the porosity, so a high amount of carbon dioxide adsorption cannot be expected, and no technology for increasing the amount of amine compound supported is disclosed. Furthermore, Patent Document 3 does not disclose that the carbon dioxide adsorbent described in this document is a fiber structure with low pressure loss.

[0014] The hypercrosslinked polymer contained in the composition described in Patent Document 4 is porous and achieves the loading of a considerable amount of amine as an acid gas adsorbent, but on the other hand, it is presumed that the pores of the polymer are completely filled with the amine. In such a structure, after carbon dioxide is adsorbed to the amine on the outermost surface of the porous particle, the adsorption of carbon dioxide to the amine inside the porous particle proceeds by internal diffusion, requiring a long period of time for adsorption. Furthermore, Patent Document 4 does not disclose that the composition described is a material that achieves both high adsorption and low pressure drop.

[0015] In view of the above-mentioned conventional techniques, the problem to be solved by the present invention is to provide a carbon dioxide adsorbent that can adsorb a large amount of carbon dioxide in a short time and has a low pressure loss.

[0016] The gist of the present invention is as follows. [1] A carbon dioxide adsorbent comprising a fiber structure composed of fibers and a carbon dioxide adsorbent compound supported on the fibers, wherein the fibers supporting the carbon dioxide adsorbent have a fiber diameter of 0.3 μm to 30 μm, a pore diameter of the fibers supporting the carbon dioxide adsorbent being 2.0 nm or more, and the amount of the carbon dioxide adsorbent supported is 20 mass% to 70 mass% relative to 100 mass% of the carbon dioxide adsorbent. [2] The carbon dioxide adsorbent according to [1] above, wherein the fibers are cellulose or polyketone. [3] The carbon dioxide adsorbent according to [1] or [2] above, wherein the average C / N ratio of the cross section of the fibers supporting the carbon dioxide adsorbent is 3.8 to 16.0. [4] The carbon dioxide adsorbent according to any of [1] to [3] above, wherein the carbon dioxide adsorbent compound is an amine-based compound and is liquid. [5] The carbon dioxide adsorbent according to any of [1] to [4] above, wherein the fibers are cellulose. [6] The carbon dioxide adsorbent according to [5] above, wherein the cellulose is regenerated cellulose. [7] The carbon dioxide adsorbent according to [6] above, wherein the regenerated cellulose is cupra. [8] The carbon dioxide adsorbent according to any one of [1] to [7] above, wherein the fiber structure is a nonwoven fabric. [9] The carbon dioxide adsorbent according to any one of [1] to [8] above, wherein the fibers are continuous long fibers.

[10] The carbon dioxide adsorbent according to any one of [1] to [9] above, wherein the pore size of the fibers carrying the carbon dioxide adsorbing compound is 20.0 nm or less.

[11] The carbon dioxide adsorbent according to any one of [1] to

[10] above, wherein the amount of the carbon dioxide adsorbing compound carried is 30 mass% or more relative to 100 mass% of the carbon dioxide adsorbent.

[0017] According to the present invention, there is provided a material that has a small pressure loss during carbon dioxide adsorption and is capable of adsorbing a large amount of carbon dioxide in a short period of time.

[0018] 1 shows a scanning electron microscope (SEM) image (field of view size: 0.63 mm x 0.48 mm and magnification: 200x) of a carbon dioxide adsorbent of this embodiment. 2 shows an SEM image (field of view size: 0.63 mm x 0.48 mm and magnification: 200x) of a carbon dioxide adsorbent carrying an excess amine compound. 3 shows an SEM image (field of view size: 4.2 μm x 3.2 μm and magnification: 30,000x) of a cross section of supercritically dried fiber. 4 shows a conceptual diagram of the measurement points of SEM-EDS of this embodiment. The vertical and horizontal axes indicate the points where line analysis was performed. 5 shows a conceptual diagram of an evaluation system for the carbon dioxide adsorption amount using the constant flow rate method of this embodiment. 6 shows a conceptual diagram of an evaluation system for the carbon dioxide adsorption amount using the constant flow rate air blowing method of this embodiment. 7 shows a conceptual diagram of the reference points when calculating the carbon dioxide adsorption amount.

[0019] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter referred to as the present embodiment). Note that the present embodiment is not limited to the embodiment described below, and various combinations can be used within the scope of the description.

[0020] <Carbon Dioxide Adsorbent> The carbon dioxide adsorbent of this embodiment adsorbs carbon dioxide (CO ) from the gas to be treated. ２ It is sufficient if the carbon dioxide adsorbent can adsorb carbon dioxide, and it is preferable to adsorb carbon dioxide from process exhaust gases from factories, power plants, etc., the atmosphere, or a mixture of these gases, and it is particularly preferable to adsorb carbon dioxide from the atmosphere. Furthermore, techniques for recovering carbon dioxide from the atmosphere include a solid adsorption method in which carbon dioxide is adsorbed onto a solid substrate and a liquid adsorption method in which carbon dioxide is adsorbed onto a liquid. The carbon dioxide adsorbent of this embodiment can be used in a solid adsorption method.

[0021] The carbon dioxide adsorbing material of this embodiment includes a carbon dioxide adsorption compound and a fiber structure composed of fibers. In the carbon dioxide adsorbing material of this embodiment, the carbon dioxide adsorption compound is supported on the surface or the interior of the fibers that make up the fiber structure, or both.

[0022] In the carbon dioxide adsorbent according to this embodiment, by reducing the fiber diameter of the fibers constituting the fiber structure, the gas to be treated can diffuse into the interior of the fibers in a short time even if the pore diameter of the fibers constituting the fiber structure is small, and therefore a large amount of carbon dioxide adsorption compound can be supported.

[0023] In the present disclosure, "supported" refers to being immobilized on a carrier by physical adsorption, electrostatic adsorption, chemical bonding, etc. Furthermore, in the present disclosure, "carrier" refers to a substance that serves as a carrier for immobilizing a compound.

[0024] <Fiber Diameter> The fiber diameter in this embodiment refers to the value of the fiber diameter measured in a dry state of fibers carrying a carbon dioxide adsorption compound, and refers to the number average value. There are various methods for measuring the fiber diameter, and for example, the fiber can be observed and measured using an electron microscope or an optical microscope. Furthermore, in the case of a fiber structure made up of multiple fibers, a method in which both the front and back surfaces of the structure are observed using an electron microscope or the like and the fiber diameter is calculated is preferred. The fiber diameter of the fibers carrying a carbon dioxide adsorption compound in this embodiment is measured by the method described in the Examples.

[0025] The fiber diameter of the fiber carrying the carbon dioxide adsorbing compound of this embodiment is 0.3 μm or more and 30.0 μm or less. If the fiber diameter is 30.0 μm or less, the number of times the fiber comes into contact with the gas to be treated (e.g., a gas containing carbon dioxide) can be increased, and the diffusion distance of carbon dioxide into the fiber can also be shortened. The fiber diameter is preferably 20 μm or less, and more preferably 15 μm or less. On the other hand, if the fiber diameter is 0.3 μm or more, there is little aggregation between the fibers, and the gas to be treated can easily pass through the gaps between the fibers, so the gas to be treated is easily diffused throughout the carbon dioxide adsorbent. The fiber diameter is preferably 0.5 μm or more, and more preferably 1 μm or more. If the fiber diameter of the fiber carrying the carbon dioxide adsorbing compound of this embodiment is within a predetermined range, the accessibility of carbon dioxide to the carbon dioxide adsorbing compound is increased, and a large amount of carbon dioxide can be adsorbed by the carbon dioxide adsorbing compound efficiently and in a short time.

[0026] <Pore diameter> In the present disclosure, the term "pore diameter" refers to the pore diameter of the voids inside the porous fibers or porous particles, and does not include the voids between fibers or particles. The pore diameter can be measured by gas adsorption, mercury porosimetry, gas permeation spectroscopy, or the like, and the pore diameter in this embodiment refers to the number average value measured by these methods. The pore diameter of the fiber carrying the carbon dioxide adsorption compound of this embodiment is measured by the method described in the Examples.

[0027] The pore diameter of the fiber carrying the carbon dioxide adsorbent compound of this embodiment is 2.0 nm or more. If the fiber diameter of the fiber carrying the carbon dioxide adsorbent compound is within the above-mentioned specified range and the pore diameter is 2.0 nm or more, the accessibility of carbon dioxide to the carbon dioxide adsorbent compound present inside the fiber is excellent. The pore diameter of the fiber carrying the carbon dioxide adsorbent compound is preferably 2.1 nm or more, more preferably 2.5 nm or more, even more preferably 3.0 nm or more, particularly preferably 5.0 nm or more, and most preferably 10.0 nm or more. If the pore diameter is too large, the pore depth tends to increase, which may result in poor accessibility of carbon dioxide to the carbon dioxide adsorbent compound carried in the pores. Therefore, the pore diameter of the fiber carrying the carbon dioxide adsorbent compound is preferably 100.0 nm or less, more preferably 50.0 nm or less, and most preferably 20.0 nm or less. When the pore size of the fiber carrying the carbon dioxide adsorption compound of this embodiment is within a predetermined range, the accessibility of carbon dioxide to the carbon dioxide adsorption compound increases, and a large amount of carbon dioxide can be adsorbed by the carbon dioxide adsorption compound efficiently and in a short time.

[0028] <Specific surface area> In the present disclosure, the specific surface area refers to the BET specific surface area. In one aspect, the specific surface area of ​​the carbon dioxide adsorbent of the present embodiment is 0.1 m ２ / g or more 20m ２ The specific surface area of ​​the carbon dioxide adsorbent of this embodiment is preferably 0.1 m / g or less. ２ / g or more 15m ２ The specific surface area of ​​the carbon dioxide adsorbent of this embodiment is measured by the method described in the Examples.

[0029] <Pore Volume> In one aspect, the pore volume of the carbon dioxide adsorbent of the present embodiment is 0.001 cm ３ / g or more 0.9cm ３ The upper limit of the pore volume of the carbon dioxide adsorbent of this embodiment is preferably 0.5 cm ３ / g or less is more preferable, and 0.3 cm ３ / g or less is more preferable, and 0.1 cm ３ / g or less is particularly preferred, and 0.08 cm ３ The pore volume of the carbon dioxide adsorbent of this embodiment is measured by the method described in the Examples.

[0030] The proportion of the carbon dioxide carbon adsorbent in the space (in one embodiment, the adsorption column) in which the carbon dioxide adsorbent of this embodiment is present (hereinafter referred to as the space occupancy rate) is preferably 5 to 40 volume % and more preferably 7 to 35 volume % when the total space volume is taken as 100 volume % from the viewpoints of the carbon dioxide adsorption amount and pressure loss. Note that, as an example of calculating the space occupancy rate, the value converted into the volume of the carbon dioxide adsorbent from the weight and specific gravity of the carbon dioxide adsorbent is divided by the volume of the space (in one embodiment, the adsorption column) in which the carbon dioxide adsorbent is present; specifically, it can be calculated by the method described in the Examples.

[0031] Furthermore, in the carbon dioxide adsorbent of this embodiment, from the viewpoint of efficiently exerting adsorption performance all the way to the inside of the fiber structure, the air resistance in the thickness direction of the carbon dioxide adsorbent at a thickness of 1 mm is preferably 20 kPa·s / m or less, more preferably 10 kPa·s / m or less, even more preferably 5 kPa·s / m or less, particularly preferably 3 kPa·s / m or less, and most preferably 1 kPa·s / m or less.

[0032] The airflow resistance of a carbon dioxide adsorbent is measured as follows: Using a KES-F8 air permeability tester (manufactured by Kato Tech Co., Ltd.), measurements are taken at 20 locations evenly spaced across the width of the carbon dioxide adsorbent and 10 locations evenly spaced across the length of the adsorbent, for a total of 200 locations, within an area of ​​1 m width x 50 cm length, and the average value and standard deviation are taken as the airflow resistance and standard deviation of the airflow resistance of the carbon dioxide adsorbent (measurement area 0.2π cm). ２ (Diameter: 8.9 mm). The thickness of the carbon dioxide adsorbent is measured at a total of 200 locations, 20 locations equally spaced across the width and 10 locations equally spaced across the length, using a thickness measuring meter (JAN-257, manufactured by PEACOCK), in the same manner as in the measurement of the airflow resistance value. The average value is taken as the average thickness (unit: mm), and the calculated airflow resistance value is divided by the average thickness to calculate the airflow resistance value at a thickness of 1 mm. The calculated airflow resistance value of the carbon dioxide adsorbent is divided by the average thickness of the carbon dioxide adsorbent to calculate the airflow resistance value of the carbon dioxide adsorbent at a thickness of 1 mm.

[0033] <Carbon dioxide adsorption compound> The carbon dioxide adsorption compound supported on the fiber according to this embodiment is not particularly limited as long as it can adsorb carbon dioxide. The carbon dioxide adsorption compound according to this embodiment is preferably an amine compound and is liquid. If the amine compound serving as the carbon dioxide adsorption compound is liquid, carbon dioxide adsorbed to the amine compound on the surface of the fiber can be easily diffused to the amine compound inside the fiber, thereby improving adsorption performance.

[0034] <Amount of Carbon Dioxide Adsorbing Compound Supported> The amount of carbon dioxide adsorbing compound supported on the carbon dioxide adsorbent according to this embodiment can be calculated by a known method or simply by measuring the change in weight.

[0035] For example, when the carbon dioxide adsorption compound is supported by coating it on a support, the weight of the carbon dioxide adsorption compound coated on the support is measured, the carbon dioxide adsorption compound is extracted with a solvent for the carbon dioxide adsorption compound, and the weight of the support is then measured. The amount of the supported carbon dioxide adsorption compound is then calculated from the weight difference, and divided by the weight of the carbon dioxide adsorbent, thereby calculating the amount of the carbon dioxide adsorption compound supported per 100% by mass of the carbon dioxide adsorbent.

[0036] Furthermore, when an additive or the like other than the carbon dioxide adsorption compound is supported on the carrier, the weight change can be evaluated by extracting the additive with a solvent in the same manner as described above, and the composition of the extract can be analyzed by the Kjeldahl method or the combustion method.

[0037] When the carbon dioxide adsorbing compound is polymerized on a carrier, the carbon dioxide adsorbing compound can be extracted and the weight change evaluated in the same manner as described above. For example, the carbon dioxide adsorbing compound can be extracted with a depolymerizable cleaning solution, and for example, silane-based or ester-based polymers can be extracted with an alkaline cleaning solution. More specifically, the amount of carbon dioxide adsorbing compound supported on the carbon dioxide adsorbent of this embodiment is measured by the method described in the Examples.

[0038] The amount of carbon dioxide adsorption compound supported in the carbon dioxide adsorbent of this embodiment is 20% by mass or more and 70% by mass or less, relative to 100% by mass of the carbon dioxide adsorbent. When the amount of carbon dioxide adsorption compound supported is 70% by mass or less, relative to 100% by mass of the carbon dioxide adsorbent of this embodiment, a large amount of carbon dioxide can be adsorbed efficiently and in a short time. The amount of carbon dioxide adsorption compound supported is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less. When the amount of carbon dioxide adsorption compound supported is 20% by mass or more, relative to 100% by mass of the carbon dioxide adsorbent of this embodiment, a large amount of carbon dioxide can be adsorbed. The amount of carbon dioxide adsorption compound supported is preferably 21% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more. When the fiber diameter and pore diameter of the carbon dioxide adsorbent satisfy the specified ranges, supporting the carbon dioxide adsorption compound on the fibers within the specified amount ranges allows the carbon dioxide adsorption compound to be supported thinly and widely on the pore surfaces of the fibers constituting the fiber structure. As a result, the proportion of carbon dioxide adsorbing compounds involved in carbon dioxide adsorption increases, making it possible to efficiently adsorb a large amount of carbon dioxide in a short period of time.

[0039] The carbon dioxide adsorption amount of the carbon dioxide adsorbent of this embodiment can be measured by flowing air through the adsorption column using two methods: a constant flow rate method and a constant flow rate air blowing method. ２ The system 1 for evaluating the amount of carbon dioxide adsorption using a constant flow rate method is shown, and includes a pump 5 that is a power source for drawing in air and on which a sensor 2 is installed, an adsorption column 3 containing a carbon dioxide adsorbing compound that adsorbs carbon dioxide in the drawn-in air, and a flow meter 4 that measures the flow rate of the air with carbon dioxide adsorbed. In the present disclosure, the constant flow rate method is a technique in which air is drawn in by installing a pump 5 on the outlet side of the adsorption column 3 as shown in Fig. 5, and the amount of air passing through the carbon dioxide adsorbent is constant regardless of the carbon dioxide adsorbent without being affected by pressure loss of the carbon dioxide adsorbent. Fig. 6 shows a system 1 for evaluating the amount of carbon dioxide adsorption using a constant flow rate method, which includes a blower 6 and a CO 2 adsorbent at the inlet and outlet through which the air passes. ２Illustrated is a system 7 for evaluating the amount of carbon dioxide adsorption using a constant flow rate blowing method, which includes an adsorption column 3 equipped with a sensor 2 and containing a carbon dioxide adsorption compound that adsorbs carbon dioxide in the drawn-in atmosphere, and a flow meter 4 that measures the flow rate of the atmosphere with adsorbed carbon dioxide. In the present disclosure, the constant flow rate blowing method is a technique in which a blower 6 is installed on the inlet side of the adsorption column 3 to blow air, as shown in FIG. 6 , and the amount of air passing through the carbon dioxide adsorbent is affected by the pressure loss of the carbon dioxide adsorbent. In particular, the carbon dioxide adsorption amount of the carbon dioxide adsorbent of this embodiment is measured by the method described in the Examples.

[0040] From the viewpoint of adsorbing a large amount of carbon dioxide in a short period of time, the carbon dioxide adsorption capacity of the carbon dioxide adsorbent of this embodiment is preferably 1.0 mmol / g or more per unit weight of the carbon dioxide adsorbent, and more preferably the carbon dioxide adsorption capacity measured by the constant flow rate air blowing method is 1.0 mmol / g or more per unit weight of the carbon dioxide adsorbent.

[0041] <Amine Compound> The amine compound of the present embodiment may be any compound as long as it can adsorb and desorb carbon dioxide and has at least one primary, secondary, or tertiary amino group. Two or more types of amine compounds may be used in combination.

[0042] From the viewpoint of adsorbing a large amount of carbon dioxide in a short time, the amine compound of this embodiment is preferably an amine compound having a carbon dioxide adsorption capacity of 1.4 mmol / g or more per unit weight of the amine compound, and more preferably an amine compound having a carbon dioxide adsorption capacity of 1.4 mmol / g or more per unit weight of the amine compound as measured by a constant flow rate air blowing method. Although a larger upper limit of the carbon dioxide adsorption capacity is preferable, an amine compound having a carbon dioxide adsorption capacity of 16.0 mmol / g or less per unit weight of the amine compound is preferred, and more preferably an amine compound having a carbon dioxide adsorption capacity of 16.0 mmol / g or less per unit weight of the amine compound as measured by a constant flow rate air blowing method.

[0043] Examples of the amine-based compound of this embodiment include isobutylamine, aziridine, ethylenediamine (EDA), diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N,N-dimethyl-1,3-propanediamine, polyallylamine, polyethyleneimine (PEI), aniline, nitroaniline, octadecylamine, N,N-dimethylacrylamide, 4-acryloylmorpholine, acrylamide monomer, N-butylacrylamide, N,N-diethylacrylamide, N-[2-(dimethylacrylamide)] ... Examples of suitable amine compounds include 3-(2-aminoethylamino)propyl]acrylamide, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propyldimethoxymethylsilane, 3-aminopropyldimethoxymethylsilane, 3-aminopropyltrimethoxymethylsilane, 3-aminopropyldiethoxymethylsilane, trimethoxy[3-(methylamino)propyl]silane, [3-(N,N-dimethylamino)propyl]trimethoxysilane, and N-[3-(trimethoxysilyl)propyl]butan-1-amine. The amine compounds may be used alone or in combination of two or more. When a polyamine is used, its molecular weight is not limited, but a low molecular weight is preferred from the viewpoint of carbon dioxide permeability into the amine compound layer.

[0044] Furthermore, methods for supporting an amine compound by physical adsorption or electrostatic adsorption include applying a solution of isobutylamine, aziridine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N,N-dimethyl-1,3-propanediamine, polyallylamine, polyethyleneimine, aniline, nitroaniline, octadecylamine, or the like in a solvent and then evaporating the solvent, or directly applying the compound without using a solvent. Furthermore, these amine compounds may be fixed to the fiber structure by crosslinking using a crosslinking agent. Examples of crosslinking agents include epichlorohydrin (EP) and dimethylolhydroxyethyleneurea.

[0045] Furthermore, an amine compound may be supported on a support by polymerizing N,N-dimethylacrylamide, 4-acryloylmorpholine, an acrylamide monomer, N-butylacrylamide, N,N-diethylacrylamide, N-[2-(dimethylamino)ethyl]acrylamide, or the like.

[0046] Additionally, the amine compound may be supported by chemical bonding by reacting an aminoalkylsilane such as 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propyldimethoxymethylsilane, 3-aminopropyldimethoxymethylsilane, 3-aminopropyltrimethoxymethylsilane, 3-aminopropyldiethoxymethylsilane, trimethoxy[3-(methylamino)-propyl]silane, [3-(N,N-dimethylamino)-propyl]trimethoxysilane, and N-[3-(trimethoxysilyl)-propyl]butan-1-amine with the support.

[0047] The amine compound is not particularly limited, but from the viewpoint of improving the diffusibility of carbon dioxide into the amine compound layer, amines that are liquid at 20°C or higher, such as isobutylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N,N-dimethyl-1,3-propanediamine, polyallylamine, polyethyleneimine, or aniline, are preferred, and polyethyleneimine is more preferred from the viewpoint of ease of preparation.

[0048] From the viewpoint of allowing the carbon dioxide adsorbent to adsorb a large amount of carbon dioxide, the loading density of the amine compound contained in the carbon dioxide adsorbent is preferably 0.01 mmol / g or more, more preferably 0.10 mmol / g or more, still more preferably 0.74 mmol / g or more, and particularly preferably 4.00 mmol / g or more, per unit weight of the carbon dioxide adsorbent. From the viewpoint of allowing the carbon dioxide adsorbent to efficiently adsorb carbon dioxide in a short period of time, the upper limit of the loading density of the amine compound contained in the carbon dioxide adsorbent is preferably 50.0 mmol / g or less, more preferably 30.0 mmol / g or less, and even more preferably 20.0 mmol / g or less, per unit weight of the carbon dioxide adsorbent.

[0049] <Fiber structure> In the carbon dioxide adsorbent of this embodiment, it is preferable to use a fiber structure as the base material rather than particles, from the viewpoints of being able to adsorb carbon dioxide with low pressure loss, being able to be molded into any shape, and having excellent handling properties when replacing the carbon dioxide adsorbent in a DAC system.

[0050] The fiber structure of this embodiment is a substrate (in one embodiment, a sheet substrate) made of fibers. The fiber structure of this embodiment is a carrier for a carbon dioxide adsorption compound.

[0051] The material of the fiber structure of this embodiment is not particularly limited, and hydrophobic fibers, hydrophilic fibers, and hydrophobic fibers that have been hydrophilized, including thermoplastic resins, can be used.

[0052] Hydrophobic fibers include fibers made of polyacrylic, polyester, polyethylene, polypropylene, etc. Hydrophilic fibers include fibers made of polyvinyl alcohol, polyamides such as 6-nylon and 6,6-nylon, cellulose derivatives and regenerated cellulose, and polyketones.

[0053] "Cellulose" includes cotton, silk, and wood pulp. "Cellulose derivatives" include carboxymethyl cellulose, TEMPO-oxidized cellulose, cellulose acetate, and hydroxyethyl cellulose. "Regenerated cellulose" includes cupra, viscose rayon, and lyocell.

[0054] Methods for hydrophilizing hydrophobic fibers include plasma treatment and chemical modification. Plasma treatment breaks some of the polymer bonds in the fibers, which then bond with the generated oxygen radicals and introduce polar functional groups such as hydroxyl groups and carbonyl groups, making them hydrophilic. Alternatively, the fiber surface can be chemically modified with hydrophilic substances such as hydroxyl groups and carbonyl groups to make it hydrophilic. Plasma treatment has drawbacks, such as the tendency for unevenness in the treatment to occur, so chemical modification is preferred for hydrophilization.

[0055] The fiber structure of this embodiment is not particularly limited, but is preferably a porous fiber from the viewpoint of being able to support a large amount of carbon dioxide adsorption compound inside the fiber. As the porous fiber, cellulose, polyketone, polyvinylidene fluoride, etc. are preferred, and among them, cellulose or polyketone, which have excellent porosity, are more preferred, and cellulose is particularly preferred. Furthermore, from the viewpoint of ease of coating with the carbon dioxide adsorption compound, cellulose fiber is preferred, regenerated cellulose fiber is more preferred, and cupra fiber is most preferred.

[0056] From the viewpoint of further improving handleability, the fiber structure is preferably a nonwoven fabric. A nonwoven fabric is a fiber structure formed into a sheet shape by intertwining fibers without weaving, and examples of such a nonwoven fabric include spunlace, spunbond, meltblowing, electrospinning, and needlepunching. Of these, spunlace is preferred, and spunbond is particularly preferred.

[0057] The fibers constituting the fiber structure of the present embodiment are preferably long fibers, and more preferably continuous long fibers.

[0058] Among cupra fibers that constitute a fiber structure that satisfies these conditions, continuous long cupra fibers are most preferred.

[0059] In this disclosure, porous is not limited to either the surface or the internal voids of the fiber.

[0060] <Crystalline structure of cellulose> In the present disclosure, the "crystalline structure of cellulose" is not particularly limited, and may be type I, type II, type III, or type IV cellulose. From the viewpoint of making the interior of the fiber porous, type II, type III, or type IV cellulose is preferred, and type II cellulose is most preferred.

[0061] <Additives> The carbon dioxide adsorbent of this embodiment may contain an additive in addition to the fiber structure and the carbon dioxide adsorption compound. Examples of the additive include a surfactant and a diffusing agent. The diffusing agent may be any agent that can improve the carbon dioxide permeability to the carbon dioxide adsorption compound layer and promote the reversible adsorption and desorption of carbon dioxide, and may have an ionic functional group such as an amino group or a carbonyl group.

[0062] Examples of the diffusing agent include polyethylene glycol (PEG), polyethylene oxide, polypropylene glycol, glycerin, silicone, polyoxyethylene sorbitan monostearate, polyoxyethylene 23 lauryl ether, and sorbitan monostearate.

[0063] The diffusing agent can be used alone or in combination of two or more kinds. When a polymer is used as the diffusing agent, its molecular weight (in one embodiment, weight average molecular weight) is not limited.

[0064] From the viewpoint of maximizing its effect, the amount of diffusing agent contained in the carbon dioxide adsorbent should be 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and most preferably 4% by mass or more, per 100% by mass of the carbon dioxide adsorbent. On the other hand, if the amount of diffusing agent contained in the carbon dioxide adsorbent is too large, the amount of carbon dioxide adsorption compound supported by the carbon dioxide adsorbent will relatively decrease, and a high amount of carbon dioxide adsorption cannot be expected, so the amount of diffusing agent supported per 100% by mass of the carbon dioxide adsorbent is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and most preferably 10% by mass or less.

[0065] <Average C / N Value of Cross Section> The average C / N value of the cross section of the fiber on which the carbon dioxide adsorption compound is supported can be calculated based on elemental information of the cross section obtained by energy dispersive X-ray spectroscopy (EDS or EDX), X-ray photoelectron spectroscopy (XPS), solid nebulizer ICP / MS, etc. More specifically, the average C / N value of the cross section of the fiber on which the carbon dioxide adsorption compound of this embodiment is supported is measured by the method described in the Examples.

[0066] It is desirable that the carbon dioxide adsorbing compound is uniformly distributed across the cross section of the fiber on which it is supported, and when the carrier is an organic material, the average C / N value is preferably 3.8 or more, more preferably 4.5 or more, and even more preferably 5.5 or more. When the carbon dioxide adsorbing compound is not distributed inside the fiber on which it is supported, the average C / N value will be high, so the average C / N value is preferably 16.0 or less, more preferably 14.0 or less, and even more preferably 10.0 or less.

[0067] From the viewpoint of enabling the carbon dioxide adsorption compound to be uniformly distributed in the fibers, the average C / N value of the cross section of the fibers carrying the carbon dioxide adsorption compound is preferably 3.8 or more and 16.0 or less, more preferably 4.5 or more and 14.0 or less, and even more preferably 5.5 or more and 10.0 or less.

[0068] [Method for manufacturing a carbon dioxide adsorbing material] The method for manufacturing a carbon dioxide adsorbing material according to this embodiment includes a step of manufacturing a fiber structure made of fibers and a step of supporting a carbon dioxide adsorbing compound on the manufactured fiber structure.

[0069] (Process for Producing a Fiber Structure) In the process for producing a fiber structure, when polyacrylic, polyester, polyethylene, polypropylene, polyvinyl alcohol, polyamide, polyketone, cellulose, cellulose derivatives, etc. are used as raw materials, the fiber structure can be obtained by a known method, such as a spunlace method, a spunbond method, a meltblowing method, or an electrospinning method.

[0070] In the spunlace method, a sheet of fibers is formed and a high-pressure water jet is applied to entangle the fibers to obtain a nonwoven fabric.

[0071] In the spunbonding method, for example, a nonwoven fabric can be obtained by spinning a molten raw resin in an extruder, depositing the discharged polymer on a net, and then bonding it onto a sheet.

[0072] In the melt-blowing method, for example, a nonwoven fabric can be obtained by extruding a molten raw resin material from a nozzle while spraying high-temperature air onto the material, thereby depositing fibers onto a net.

[0073] In the electrospinning method, for example, a high voltage is applied to a nozzle, and a voltage is applied to a polymer solution to spin the polymer into fibers, which are then deposited on a net to obtain a nonwoven fabric.

[0074] Methods for producing nonwoven fabrics using staple fibers include dry and wet methods. In the dry method, for example, staple fibers are arranged in a fixed direction or randomly using a machine called a card or an air flow called an air laying. In the wet method, for example, staple fibers are dispersed in water and then laid on a mesh net to obtain a nonwoven fabric.

[0075] An example of a method for producing cellulose fibers according to this embodiment will be described below, but this embodiment is not limited to this production method.

[0076] A nonwoven fabric made of long cellulose fibers can be produced by dissolving cellulose and spinning it, and can be obtained by a known method. The solvent for dissolving cellulose is not particularly limited, and various known solvents can be used. Examples include aqueous solutions of acids, alkalis, and inorganic salts such as zinc chloride at limited concentrations, copper-ammonia solutions, viscose solutions, and ionic liquids such as N-methylmorpholine N-oxide. Examples of spinning methods include a down-flow tension spinning method in which a solution is extruded in the form of a thread from a nozzle and flows into a funnel together with a coagulating liquid to coagulate, and an air-gap spinning method in which the solution is extruded into air.

[0077] (Step of Supporting Carbon Dioxide Adsorbing Compound on Fiber Structure) The step of supporting the carbon dioxide adsorbing compound on the fiber structure can be carried out by a known method.

[0078] For example, the carbon dioxide adsorption compound can be supported on the fibers constituting the fiber structure by a method in which a solution prepared by dissolving a stock solution of the carbon dioxide adsorption compound in a solvent is continuously sprayed onto the fiber structure with a sprayer and then dried, or by a method in which the fiber structure is immersed in a tank containing the above solution and then dried. Examples of the "solvent" used in this embodiment include water, methanol, ethanol, propanol, t-butyl alcohol, and acetone.

[0079] Furthermore, the carbon dioxide adsorption compound can be supported on the fiber structure by adding the fiber structure to a solution in which an amine monomer or aminoalkylsilane is dissolved in a solvent, and then polymerizing the resulting mixture with heat or light.

[0080] The step of supporting a carbon dioxide adsorbing compound on a fiber structure is not particularly limited, but from the viewpoint of maintaining the porosity of the carbon dioxide adsorbent obtained after this step, freeze-drying or supercritical drying is preferred, and supercritical drying is more preferred. Freeze-drying preferably uses water or t-butyl alcohol as a solvent, and t-butyl alcohol is most preferred. Furthermore, supercritical drying preferably uses ethanol or carbon dioxide as a solvent, and carbon dioxide is most preferred. Furthermore, by using a crosslinking agent to suppress drying aggregation of the fiber structure and then supporting a carbon dioxide adsorbing compound on the fibers, the porosity of the fiber structure can be maintained.

[0081] Freeze drying can be performed using water, t-butyl alcohol, or the like, depending on the solvent used. For example, in water freeze drying, a fiber structure swollen with water is frozen at −70° C. or lower and then freeze-dried for 72 to 168 hours. For example, in t-butyl alcohol freeze drying, the solvent contained in the water-swollen fiber structure is replaced from water to ethanol, and then the solvent is replaced with t-butyl alcohol. The fiber structure swollen with t-butyl alcohol is then frozen at −77° C. or lower and freeze-dried. For example, in supercritical drying, a water-swollen fiber structure is subjected to solvent replacement with ethanol about five times, and then the ethanol-swollen fiber structure is dried in a carbon dioxide atmosphere.

[0082] When the fiber structure according to this embodiment is to be loaded with a diffusing agent, this may be done before the carbon dioxide-adsorbing compound is loaded, or the diffusing agent may be dissolved in a co-solvent with the carbon dioxide-adsorbing compound and loaded by the method described above. From the viewpoint of uniformly mixing the carbon dioxide-adsorbing compound and the diffusing agent, it is preferable to use a co-solvent for coating.

[0083] <<Uses of Carbon Dioxide Adsorbent>> The carbon dioxide adsorbent of the present embodiment is a material that has a small pressure drop, supports an appropriate amount of a carbon dioxide adsorbing compound, and has a small number of pores on the surface of the material. Therefore, the carbon dioxide adsorbent can efficiently capture carbon dioxide in a short period of time, and is particularly suitable for use in directly capturing carbon dioxide from the atmosphere.

[0084] In the present disclosure, the presence of a small number of pores in the carbon dioxide adsorbent of the present embodiment means that the proportion of pores that do not carry a carbon dioxide adsorption compound among the pores present in the porous fibers of the fiber structure contained in the carbon dioxide adsorbent is 5% or more. Although there are slight differences depending on the size of the pores present in the carbon dioxide adsorbent of the present embodiment, in the present disclosure, when the amount of carbon dioxide adsorption compound carried on the fiber of the present embodiment exceeds 70 mass%, the pores present in the fiber structure are completely filled with the carbon dioxide adsorption compound.

[0085] Hereinafter, examples of using the carbon dioxide adsorbent of this embodiment will be described, but this embodiment is not limited to these examples.

[0086] The present embodiment will be specifically described below with reference to examples, but the present embodiment is not limited to these examples.

[0087] <Fiber Diameter> The fiber diameter of the fibers carrying the carbon dioxide adsorbing compound was measured as follows. A carbon dioxide adsorbent having a fibrous structure as a carrier was coated with gold / palladium to prepare an observation sample. The observation sample was observed from the fiber surface side using a tabletop electron microscope (Hitachi High-Tech, TM-4000) with a field of view size of 0.032 mm x 0.024 mm to 2.5 μm x 1.9 μm and a magnification of 4,000 to 50,000 times, and an image was obtained. A diagonal line was drawn on the obtained image, and the average value of 30 fibers on that line was taken as the fiber diameter (μm) of the fibers carrying the carbon dioxide adsorbing compound.

[0088] <Particle diameter> The particle diameter according to the present embodiment refers to the average value of the major axis and minor axis of a particle measured in a dry state of a carbon dioxide adsorbing material in which the carrier is a particle, and refers to the number average value.

[0089] The particle diameter of the carbon dioxide adsorbent was measured as follows. A carbon dioxide adsorbent with a particle carrier was coated with gold / palladium to prepare an observation sample. The observation sample was observed from the particle surface side using a tabletop microscope (Hitachi High-Tech, TM-4000) with a field of view of 0.032 mm x 0.024 mm and a magnification of 4000 times, and an image was obtained. 30 random particles in the obtained image were measured, and the average value was taken as the particle diameter (μm).

[0090] <Amount of Carbon Dioxide Adsorbent Supported> Using the solvents (t-butyl alcohol or water) listed in Tables 1, 2, 4, and 5, carbon dioxide adsorbent compounds were extracted from 1.0 g of the carbon dioxide adsorbent of Examples 1 to 12, 14, and 16 to 18, and Comparative Examples 1 to 15. Subsequently, 1.0 g of the carbon dioxide adsorbent from which the carbon dioxide adsorbent compounds had been extracted was placed in 200 mL of pure water, stirred for 30 minutes, and then decanted. This process was repeated three times, after which the adsorbent was heated and dried in a constant temperature dryer at 100°C or less for 24 hours. The weight of the carbon dioxide adsorbent before and after solvent extraction was measured, and the amount of carbon dioxide adsorbent supported was calculated by applying the following formula (1). The solvent used to extract the carbon dioxide adsorbent compounds from the carbon dioxide adsorbent was the same as the solvent used to prepare the carbon dioxide adsorbents of the above Examples and Comparative Examples. Furthermore, in Examples 7 and 8, in which no solvent was used to prepare the carbon dioxide adsorbent, and Comparative Example 8, the carbon dioxide adsorbent compounds were extracted using ethanol, ethanol, and t-butyl alcohol, respectively.

[0091] The carbon dioxide adsorption compound was extracted from 1.0 g of the carbon dioxide adsorbent of Example 15 using the solvent (t-butyl alcohol) shown in Table 4. The extract was analyzed by the Kjeldahl method to calculate the ratio of polyethyleneimine to polyethylene glycol in the extract, and the amount of the carbon dioxide adsorption compound supported was determined.

[0092] 1.0 g of the carbon dioxide adsorbent of Example 13 was added to 200 mL of a 20% by mass aqueous sodium hydroxide solution to extract the carbon dioxide adsorption compounds. The carbon dioxide adsorbent from which the carbon dioxide adsorption compounds had been extracted was then stirred for 30 minutes and decanted. This process was repeated 10 times, and then the adsorbent was heated and dried in a constant temperature dryer at 100°C or less for 24 hours. After drying, the weight was measured, and the amount of carbon dioxide adsorption compounds supported was calculated by applying the following formula (1) to the weight change of the carbon dioxide adsorbent:

[0093] Amount of carbon dioxide adsorbing compound supported [mass%] = (weight change [g] of carbon dioxide adsorbent before and after extraction) / (weight [g] of carbon dioxide adsorbent) × 100 Formula (1)

[0094] <Specific Surface Area, Pore Diameter, and Pore Volume> The specific surface area, pore diameter, and pore volume of the carbon dioxide adsorbent were measured as follows. The specific surface area was measured using a specific surface area / pore distribution measuring device (Nova-4200e, manufactured by Quantachrome Instruments). 1 g of the dry carbon dioxide adsorbent was dried under vacuum at 105°C for 4 hours, and then the adsorption amount of nitrogen gas at the boiling point of liquid nitrogen was measured at 5 points in the range of relative vapor pressure (P / P0) of 0.05 to 0.2 (multipoint method). Then, the BET specific surface area (m ２ Furthermore, 1 g of the dry carbon dioxide adsorbent was dried under vacuum at 105°C for 4 hours, and then the adsorption and desorption amounts of nitrogen gas at the boiling point of liquid nitrogen were measured in a range where the relative vapor pressure (P / P0) was 1.0 or less, and the pore diameter (nm) and pore volume (cm ３ In this disclosure, the term "pore size" refers to the mode of the measured pore size distribution, and the term "pore volume" refers to the volume excluding inter-fiber gaps and inter-particle gaps.

[0095] <Average C / N value> The ratio of the main elements present in the fiber cross section of the carbon dioxide adsorbent was calculated by the following method. In this example, an amine compound was supported on an organic substance such as cellulose, so the ratio of carbon to nitrogen as the main elements was calculated.

[0096] A slice of the carbon dioxide adsorbent supporting the amine compound was coated with gold / palladium, and the fiber cross section of the carbon dioxide adsorbent was observed under an acceleration voltage of 5 kV using a low-vacuum scanning electron microscope equipped with EDS (JSM-IT500LA, JEOL Ltd.) to perform line analysis. The line analysis was performed twice, and measurements were performed so that each line was slightly longer than the fiber diameter of the carbon dioxide adsorbent and the two lines were perpendicular to each other, as shown in FIG. 4 . In this disclosure, the fiber diameter of the carbon dioxide adsorbent is the minor axis of the ellipse. The average value of the elemental peak intensities of each obtained line was determined, and the C / N was calculated according to the following formula. This measurement was performed on 20 fibers of the carbon dioxide adsorbent, and the average value of the 20 fibers was taken as the average C / N value.

[0097] C / N average value of the cross section of the fiber carrying the carbon dioxide adsorption compound=(average value of carbon peak intensity) / (average value of nitrogen peak intensity)...formula

[0098] The carbon dioxide adsorption step was carried out as follows, and the amount of carbon dioxide adsorbed and the adsorption efficiency were determined.

[0099] <Pretreatment Step> The carbon dioxide adsorbents (samples) obtained in the Examples and Comparative Examples were packed into an adsorption column and heat-treated at a relative humidity of 100% and a temperature of 80°C under vacuum for 24 hours to desorb the carbon dioxide adsorbed into the samples during sample preparation.

[0100] <Adsorption step> Next, the temperature was lowered to 30°C or lower, and air with a relative humidity of 50% and a carbon dioxide concentration of 450 ppm was passed through the adsorption column packed with the carbon dioxide adsorbent at a flow rate of 250 mL / min. The carbon dioxide adsorption amount was evaluated continuously for 24 hours by tracking the carbon dioxide concentrations of the air taken into the adsorption column and the air discharged from the adsorption column.

[0101] In addition, the adsorption process of the carbon dioxide adsorbent according to this embodiment was evaluated by flowing atmospheric air through the adsorption column using two methods: a constant flow rate method and a constant flow rate air blowing method. In the constant flow rate method, a pump was installed on the outlet side of the adsorption column to draw in atmospheric air. In the constant flow rate method, the amount of atmospheric air passing through the carbon dioxide adsorbent is constant regardless of the carbon dioxide adsorbent, so pressure loss is not taken into account. In the constant flow rate air blowing method, a blower was installed on the inlet side of the adsorption column to blow atmospheric air. The flow rate of the blower was set to 250 mL / min without the carbon dioxide adsorbent in the adsorption column, and then the carbon dioxide adsorbent was placed in the adsorption column, and atmospheric air was blown at the flow rate of the blower set without the carbon dioxide adsorbent in the adsorption column. In the constant flow rate air blowing method, the amount of atmospheric air passing through the carbon dioxide adsorbent is affected by the carbon dioxide adsorbent, so the results take pressure loss into account.

[0102] <Saturated adsorption amount> The saturated adsorption amount of carbon dioxide was evaluated by flowing air through an adsorption column using a constant flow rate method. The total adsorption amount of carbon dioxide (mmol) was calculated by integrating 24-hour data of the difference between the carbon dioxide concentration of the air taken into the adsorption column and the carbon dioxide concentration of the air discharged from the adsorption column. The saturated adsorption amount of carbon dioxide [mmol / g] was calculated by dividing the obtained total adsorption amount of carbon dioxide by the weight of the carbon dioxide adsorbent packed in the adsorption column. The evaluation of the saturated adsorption amount is less affected by pressure loss and the adsorption rate of carbon dioxide to the amine compound.

[0103] <Constant flow rate adsorption amount> The total carbon dioxide adsorption amount was calculated by integrating five hours' worth of data on the difference between the carbon dioxide concentration of the air taken into the adsorption column using the constant flow rate method and the carbon dioxide concentration of the air discharged from the adsorption column. This was divided by the weight of the carbon dioxide adsorbent to obtain the constant flow rate adsorption amount [mmol / g]. The evaluation of the constant flow rate adsorption amount is less affected by pressure loss, but is greatly influenced by the carbon dioxide adsorption rate.

[0104] <Constant flow rate airflow adsorption amount> The total carbon dioxide adsorption amount was calculated by integrating five hours' worth of data on the difference between the carbon dioxide concentration of the air taken into the adsorption column subjected to the constant flow rate airflow method and the carbon dioxide concentration of the air discharged from the adsorption column. This was divided by the weight of the carbon dioxide adsorbent to obtain the constant flow rate airflow adsorption amount [mmol / g]. The evaluation of the constant flow rate airflow adsorption amount is greatly influenced by the pressure loss and the carbon dioxide adsorption rate.

[0105] If the constant flow rate air adsorption capacity is 1.0 mmol / g or more, it can be suitably used as the carbon dioxide adsorbent of this embodiment.

[0106] <Adsorption efficiency> The adsorption efficiency was calculated by applying the carbon dioxide adsorption amount calculated by the above-mentioned method, the amount of the amine compound supported on the carbon dioxide adsorbent, and the molar mass of the amine compound to the following formula (2). The adsorption efficiency is the ratio of the amount of CO adsorbed to the total amount of the amine compound supported on the carbon dioxide adsorbent. ２ This shows the ratio of amine compounds involved in adsorption. If the adsorption efficiency is high, the amine compounds will efficiently absorb CO ２This means that the carbon dioxide is involved in adsorption, making it a suitable carbon dioxide adsorbent.

[0107] Adsorption efficiency [%] = (saturated adsorption amount of carbon dioxide [mmol / g]) ÷ {(supported amount of amine compound [mass %] ÷ 100) × (molar mass of amine compound [g / mmol])} × 100 Equation (2)

[0108] If the adsorption efficiency at a constant flow rate of air blown and adsorbed is 15% or more, 20% or more, or 25% or more, it can be suitably used as the carbon dioxide adsorbing material of this embodiment.

[0109] <Space Occupancy Rate> The space occupancy rate, which is the rate at which the carbon dioxide adsorbents produced in Examples 16 to 18 occupy a space where they are present, was determined by the following method. The rate at which the carbon dioxide adsorbent occupied a space (adsorption column) was calculated was as follows: the weight of the carbon dioxide adsorbent was measured using an electronic balance, and then the total weight of the fiber structure and the carbon dioxide adsorption compound was calculated using the weight rates of the fiber structure and the carbon dioxide adsorption compound in the carbon dioxide adsorbent. The volume value of the carbon dioxide adsorbent, converted from the specific gravity of each, was divided by the volume of the adsorption column to calculate the rate.

[0110] The carbon dioxide adsorbents were prepared according to the following procedures, and the carbon dioxide adsorption amounts of the prepared carbon dioxide adsorbents were evaluated.

[0111] Example 1 Polyethyleneimine (PEI) having a weight-average molecular weight of 600 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in t-butyl alcohol (t-BuOH) (manufactured by Kanto Chemical Co., Inc.) as a carbon dioxide adsorption compound to prepare a solution with a polyethyleneimine concentration of 4.9% by mass.

[0112] A nonwoven fabric (Benliese (basis weight 40 g / m)) made of cellulose fibers spun from a cuprammonium cellulose solution containing 10.15 mass % of cellulose, 6.09 mass % of ammonia, 3.63 mass % of copper, and 80.13 mass % of water was used. ２A nonwoven fabric (0.35 mm thick, manufactured by Asahi Kasei Corporation) was swollen with water, and then ethanol, t-butyl alcohol, and a 4.9% by mass polyethyleneimine (PEI) solution were added in this order to perform stepwise solvent substitution. The nonwoven fabric swollen with the polyethyleneimine solution was frozen in a freezer at −77°C or below and then freeze-dried to prepare a carbon dioxide adsorbent.

[0113] Example 2 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the cellulose concentration of the cuprammonium cellulose solution was changed to 4.0 mass % and the copper concentration was changed to 1.4 mass %.

[0114] Example 3 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 1.1 μm and the concentration of the PEI solution was changed to 2.4 mass %.

[0115] Example 4 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 1.1 μm.

[0116] Example 5 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 1.0 μm and the concentration of the PEI solution was changed to 11.8 mass %.

[0117] Example 6 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 28.7 μm.

[0118] Example 7 An ethanol solution containing 12.4% by mass of PEI (PEI solution) was prepared. The cellulose nonwoven fabric prepared in Example 3 was used. The cellulose nonwoven fabric swollen with the PEI solution was placed in a supercritical dryer (manufactured by ITEC Co., Ltd.), and supercritical CO was added to the container of the supercritical dryer. ２ and subjected to supercritical drying (under a carbon dioxide atmosphere, at a temperature of 40° C., for a drying time of 2 hours) to prepare a carbon dioxide adsorbent carrying PEI.

[0119] Example 8 A carbon dioxide adsorbing material was produced in the same manner as in Example 7, except that the PEI concentration was set to 30.9 mass %.

[0120] Example 9 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the solvent of the PEI solution was changed from t-butyl alcohol (t-BuOH) to water, and the solvent substitution was performed in the order of water, then PEI solution.

[0121] Example 10 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the carrier for supporting PEI was changed to poly(1-oxotrimethylene) (polyketone, manufactured by Asahi Kasei Corporation) and the concentration of the PEI solution was changed to 37.7% by mass.

[0122] Example 11 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the carrier for supporting PEI was changed to viscose rayon (Kuraclean, manufactured by Kuraray Co., Ltd.).

[0123] (Example 12) A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the amine compound to be supported as the carbon dioxide adsorbing compound was changed from polyethyleneimine (PEI) to ethylenediamine (EDA) having a weight-average molecular weight of 60.

[0124] Example 13 A silane coupling agent having a primary amine (KBP-90, manufactured by Shin-Etsu Silicones Co., Ltd.) was dissolved in water to prepare a 45% by mass KBP-90 solution as a carbon dioxide adsorption compound. Bemliese fiber having a diameter of 6.1 μm was immersed in the 45% by mass KBP-90 solution, removed from the solution, and dried at 110°C to prepare a carbon dioxide adsorbent. The use of a silane coupling agent having a primary amine fixed the cellulose structure during drying.

[0125] Example 14 Bemliese having a fiber diameter of 6.4 μm was immersed in a 10% by mass aqueous sodium hydroxide solution containing epichlorohydrin (EP) as a crosslinking agent at a concentration of 10% by mass, and crosslinked at 60° C. for 3 hours to fix the cellulose structure with the epichlorohydrin. A carbon dioxide adsorbent was produced in the same manner as in Example 1, except that after crosslinking, the product was washed with water to remove unreacted epichlorohydrin.

[0126] Example 15 PEI and, as a diffusing agent, polyethylene glycol (PEG, manufactured by Tokyo Chemical Industry Co., Ltd.) having an average molecular weight of 400 were dissolved in t-butyl alcohol to prepare a solution containing PEI at a concentration of 5.5 mass% and PEG at a concentration of 2.0 mass%. A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the solution prepared as above was used to support a carbon dioxide adsorbing compound.

[0127] (Example 16) The basis weight of the cellulose nonwoven fabric was 38 g / m ２ A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the thickness was changed to 0.40 mm.

[0128] (Example 17) The basis weight of the cellulose nonwoven fabric was 97 g / m ２ A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the thickness was changed to 0.41 mm.

[0129] (Example 18) The basis weight of the cellulose nonwoven fabric was 151 g / m ２ A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the thickness was changed to 0.49 mm.

[0130] Comparative Example 1 A carbon dioxide adsorbing material was prepared in the same manner as in Example 1, except that the concentration of the PEI solution was changed to 0.5% by mass.

[0131] Comparative Example 2 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the carrier for supporting PEI was changed from Bemliese to silica particles (CARiACT Q-15) having a particle size of 90 μm, and the concentration of the PEI solution was changed to 2.5 mass%.

[0132] Comparative Example 3 A carbon dioxide adsorbing material was prepared in the same manner as in Comparative Example 2, except that the concentration of the PEI solution was changed to 21.0 mass %.

[0133] Comparative Example 4 A carbon dioxide adsorbing material was prepared in the same manner as in Example 1, except that the concentration of the PEI solution was changed to 1.1 mass %.

[0134] Comparative Example 5 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the concentration of the PEI solution was changed to 33.1% by mass.

[0135] Comparative Example 6 With reference to Patent Document 3, a carbon dioxide adsorbent was produced in the same manner as in Example 1, except that the carrier for supporting PEI was changed from Bemliese to the activated carbon fiber described in Patent Document 3, and the concentration of the PEI solution was changed to 35.1 mass%.

[0136] Comparative Example 7 A carbon dioxide adsorbing material was prepared in the same manner as in Comparative Example 6, except that the concentration of the PEI solution was changed to 99.5 mass %.

[0137] Comparative Example 8 A carbon dioxide adsorbent was prepared in the same manner as in Comparative Example 6, except that PEI was added at a concentration of 58.0% by mass relative to 100% by mass of the activated carbon fiber.

[0138] (Comparative Example 9) With reference to Patent Document 1, a carbon dioxide adsorbent was produced in the same manner as in Example 9, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 27.3 μm and that the drying after solvent substitution was changed to heat drying at 80°C.

[0139] Comparative Example 10 A carbon dioxide adsorbing material was produced in the same manner as in Example 2, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 0.1 μm.

[0140] Comparative Example 11 A carbon dioxide adsorbing material was produced in the same manner as in Example 1, except that the fiber diameter of the cellulose fibers forming the nonwoven fabric was changed to 43.5 μm.

[0141] (Comparative Example 12) With reference to Patent Document 4, a cuprammonium cellulose solution containing 1.0% by mass of cellulose, 4.0% by mass of ammonia, 0.4% by mass of copper, and 94.6% by mass of water was prepared. This solution was attached to a spray dryer GB210-A (manufactured by Yamato Scientific Co., Ltd.) using a disk atomizer as an atomizer, sprayed under conditions of a spray pressure of 0.3 MPa, a liquid supply rate of 1.4 kg / h, an inlet concentration of 130°C, and an outlet temperature of 65°C, granulated, and recovered. The recovered particles were placed in a 7.5% by mass aqueous sulfuric acid solution, stirred with a magnetic stirrer for 10 minutes, and then subjected to suction filtration. After performing the same operation again, the obtained particles were placed in pure water, stirred with a magnetic stirrer for 10 minutes, and subjected to suction filtration to produce cupra particles. Washing with pure water was performed until the pH of the filtrate became neutral. A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the cupra particles prepared above were used instead of the cupra fibers, and the PEI solution concentration was changed to 25.5 mass%.

[0142] (Comparative Example 13) With reference to Patent Document 2, a cuprammonium cellulose solution containing 3.0% by mass of cellulose, 3.8% by mass of PEI, 0.1% by mass of surfactant (Pegnol, manufactured by Toho Chemical Co., Ltd.), 3.6% by mass of copper, 6.1% by mass of ammonia, and 90.3% by mass of water was prepared. A solution was prepared by adding PEI to this cuprammonium cellulose solution at a concentration of 55.0% by mass relative to 100% by mass of cellulose. This solution was placed in a syringe and ejected at 2.63 ml / h from a metal nozzle with an inner diameter of 0.41 mm onto a metal substrate. A voltage of 20 kV was applied from a high-voltage power source with the distance between the metal nozzle and the metal substrate set to 10 cm, and electrospinning was performed to produce a carbon dioxide adsorbent.

[0143] Comparative Example 14 A carbon dioxide adsorbent was produced in the same manner as in Example 1, except that the carrier for supporting PEI was changed from Bemliese to Lyocell (Sontara, manufactured by Nissei Co., Ltd.).

[0144] Comparative Example 15 A carbon dioxide adsorbent was prepared in the same manner as in Example 1, except that the carrier for supporting PEI was changed from Bemliese to polypropylene (Eltas, manufactured by M.A. Life Materials, Inc.) and the concentration of the PEI solution was changed to 50.5% by mass.

[0145] [Evaluation of Carbon Dioxide Adsorption Amount] Table 1 compares the constant flow rate airflow adsorption amount, constant flow rate adsorption amount, and saturated adsorption amount to confirm the differences in results depending on the evaluation conditions. The carbon dioxide adsorption amounts for Example 1 were nearly 90% of the saturated adsorption amount for both the constant flow rate airflow adsorption amount and the constant flow rate adsorption amount. Even when the fibers constituting the carbon dioxide adsorbent support a certain amount of carbon dioxide adsorption compound, the presence of pores in the carbon dioxide adsorbent provides excellent accessibility of carbon dioxide to the carbon dioxide adsorbent. Furthermore, since the fiber diameter of the carbon dioxide adsorbent is relatively small, it is believed that the carbon dioxide diffusion distance is short, allowing a large amount of carbon dioxide to be adsorbed in a short period of time. Furthermore, since the carbon dioxide adsorbent of Example 1 is a material with low pressure loss, a high carbon dioxide adsorption amount was achieved even with the constant flow rate airflow method. On the other hand, in Comparative Examples 2 and 3, porous silica particles were used as the fiber structure of the carbon dioxide adsorbent, and therefore the saturated adsorption amount showed a high carbon dioxide adsorption amount depending on the amount of carbon dioxide adsorption compound supported, but the constant flow rate airflow method resulted in large pressure loss and made it impossible to adsorb a large amount of carbon dioxide in a short period of time.

[0146]

[0147] In Examples 2 to 18 and Comparative Examples 4 to 15, the amount of carbon dioxide adsorption (amount of adsorption by constant flow rate air blowing) was evaluated using the constant flow rate air blowing method in order to evaluate whether a large amount of carbon dioxide could be adsorbed in a short period of time.

[0148] Table 2 evaluates the influence of the fiber diameter, pore diameter, and amount of amine compound carried on the carbon dioxide adsorbent according to this embodiment.

[0149] When the carbon dioxide adsorbents of Examples 2 to 9 were evaluated, the constant flow rate airflow adsorption capacity was high because the fiber diameter was within the specified range. This is because when the fiber diameter of the carbon dioxide adsorbent is a specified fineness, the diffusion distance of carbon dioxide diffusing within the fibers is shortened. When the amount of PEI supported, which is the carbon dioxide adsorption compound, was changed, the constant flow rate airflow adsorption capacity increased as the amount supported increased. Generally, when a carbon dioxide adsorbent is supported in the pores of the porous fibers of a fiber structure, if a certain number of pores are to be left after the carbon dioxide adsorption compound is supported, the amount of carbon dioxide adsorption compound supported is limited. However, the results of the Examples suggest that even if the pores are filled to some extent with the carbon dioxide adsorption compound, as long as the fiber diameter of the carbon dioxide adsorbent is relatively small and only a few pores remain, carbon dioxide can be adsorbed to a saturated adsorption capacity in a short period of time. Furthermore, the results of Examples 7 and 8 showed that the amount of carbon dioxide adsorption compound supported could be further increased by using supercritical drying in the PEI support process.

[0150] In Comparative Examples 4 and 5, the amount of carbon dioxide adsorption compound supported was less than the predetermined range, and the amount supported was greater than the predetermined range, respectively, so it was not possible to achieve a large amount of carbon dioxide adsorption in a short period of time. In Comparative Examples 10 and 11, the fiber diameter was smaller than the predetermined range, and the fiber diameter was greater than the predetermined range, respectively, so it was not possible to achieve a large amount of carbon dioxide adsorption in a short period of time.

[0151]

[0152]

[0153] Table 3 shows the results of investigating the difference in fiber porosity due to different drying methods after 1 g of cupra fiber with a fiber diameter of 10 μm was swollen in water. For water heating drying, the water-swollen cupra fiber was dried in a constant temperature dryer at 80°C for 5 hours. For water freeze drying, the water-swollen cupra fiber was frozen at -70°C or below and then freeze-dried for 72 hours. For t-butyl alcohol freeze drying, the solvent contained in the water-swollen cupra fiber was replaced from water to ethanol, followed by solvent replacement with t-butyl alcohol. The fiber was then frozen at -77°C or below and freeze-dried for 72 hours. For supercritical drying, the water-swollen cupra fiber was subjected to solvent replacement with ethanol five times, followed by supercritical drying using carbon dioxide at 40°C for 2 hours.

[0154]

[0155] The results in Table 3 suggest that freeze-drying using water as a solvent (water freeze-drying) was able to suppress fiber aggregation to some extent. On the other hand, the results in Table 3 suggest that freeze-drying using t-butyl alcohol as a solvent (t-butyl alcohol freeze-drying) suppressed fiber aggregation and also maintained the voids inside the fibers without collapsing them. Furthermore, the results in Table 3 suggest that supercritical drying is even more effective at suppressing fiber aggregation than t-butyl alcohol freeze-drying.

[0156] In Comparative Examples 6 to 8, activated carbon fiber was used as the fiber structure, but when the amount of carbon dioxide adsorption compound supported was reduced in order to leave pores in the carbon dioxide adsorbent, the amount of carbon dioxide adsorbed was small, and on the other hand, when the amount of carbon dioxide adsorption compound supported was increased, the pores in the carbon dioxide adsorbent were filled, and it was not possible to achieve high carbon dioxide adsorption in a short period of time.

[0157] In Comparative Example 9, the carbon dioxide adsorbing compound was distributed in large quantities on the fiber surface of the carbon dioxide adsorbent. In Comparative Example 12, the carbon dioxide adsorbing compound was supported in an amount that completely filled the pores of the carbon dioxide adsorbent. In Comparative Example 13, a carbon dioxide adsorbent was produced from nanofibers whose pore size did not satisfy the specified range. In the carbon dioxide adsorbents of Comparative Examples 9, 12, and 13, not enough pores remained, and a large amount of carbon dioxide could not be adsorbed in a short period of time.

[0158] In Examples 10 and 11, the material of the fiber structure was changed to something other than cupra, but a large amount of carbon dioxide was able to be adsorbed in a short period of time.

[0159] In Examples 12 and 13, the carbon dioxide adsorbing compound was changed to a compound other than PEI. In Example 14, a crosslinking agent was added to the fiber surface before the carbon dioxide adsorbing compound was supported. In Example 15, a diffusing agent was added to the fiber surface before the carbon dioxide adsorbing compound was supported. In all of the above Examples, the carbon dioxide adsorbent of this embodiment could be suitably used.

[0160] The results of Examples 10 to 15 and Comparative Examples 14 and 15 are shown in Table 4.

[0161]

[0162] In order to investigate the relationship between the proportion of space occupied by the carbon dioxide adsorbent (space occupancy rate) and the amount of carbon dioxide adsorbed, adsorption evaluation was carried out for the carbon dioxide adsorbents of Examples 16 to 18. Table 5 shows the relationship between the space occupancy rate and the amount of carbon dioxide adsorbed for the carbon dioxide adsorbents of Examples 16 to 18.

[0163]

[0164] The present invention can be used in a wide range of industrial fields by adsorbing and recovering (DAC, etc.) carbon dioxide emitted from process exhaust gases such as those from factories and power plants, the atmosphere, or mixtures of these.

[0165] 1: Evaluation system for carbon dioxide adsorption amount using constant flow method 2: CO ２ Sensor 3: Adsorption column 4: Flow meter 5: Pump 6: Blower 7: Evaluation system for carbon dioxide adsorption amount using constant flow rate blowing method

Claims

1. A carbon dioxide adsorbent comprising a fiber structure composed of fibers and a carbon dioxide adsorbing compound supported on the fibers, wherein the fiber diameter of the fibers supporting the carbon dioxide adsorbing compound is 0.3 μm or more and 30 μm or less, the pore diameter of the fibers supporting the carbon dioxide adsorbing compound is 2.0 nm or more, and the amount of the carbon dioxide adsorbing compound supported is 20 mass% or more and 70 mass% or less, relative to 100 mass% of the carbon dioxide adsorbent.

2. The carbon dioxide adsorbent material according to claim 1, wherein the fibers are cellulose or polyketone.

3. The carbon dioxide adsorbing material according to claim 1 or 2, wherein the average C / N value of the cross section of the fiber carrying the carbon dioxide adsorbing compound is 3.8 or more and 16.0 or less.

4. The carbon dioxide adsorbing material according to claim 1 or 2, wherein the carbon dioxide adsorbing compound is an amine compound and is liquid.

5. The carbon dioxide adsorbent material according to claim 1, wherein the fibers are cellulose.

6. The carbon dioxide adsorbent material according to claim 5, wherein the cellulose is regenerated cellulose.

7. The carbon dioxide adsorbent material according to claim 6, wherein the regenerated cellulose is cupro.

8. The carbon dioxide adsorbing material according to claim 1 or 2, wherein the fiber structure is a nonwoven fabric.

9. The carbon dioxide adsorbent material according to claim 1 or 2, wherein the fibers are continuous long fibers.

10. The carbon dioxide adsorbent according to claim 1 or 2, wherein the pore size of the fibers carrying the carbon dioxide adsorbing compound is 20.0 nm or less.

11. The carbon dioxide adsorbing material according to claim 1 or 2, wherein the amount of the carbon dioxide adsorbing compound supported is 30 mass % or more relative to 100 mass % of the carbon dioxide adsorbing material.

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