Compound for use as carbon dioxide absorbent, carbon dioxide absorbent, method for separating carbon dioxide, method for separating and recovering carbon dioxide, and device using carbon dioxide absorbent

Abstract

Provided are a compound for use as a carbon dioxide absorbent and a carbon dioxide absorbent exhibiting excellent carbon dioxide absorption performance. Furthermore, in addition to the carbon dioxide absorption performance, the carbon dioxide absorbent can easily release the carbon dioxide when reusing the absorbent. Further provided are a method for separating carbon dioxide by using the carbon dioxide absorbent, a method for separating and recovering carbon dioxide by using the carbon dioxide absorbent, and a device using the carbon dioxide absorbent. The present invention relates to a phosphine compound for use as a carbon dioxide absorbent, the compound being represented by general formula (1) (in the formula, a, b, and c independently represent an integer of 1-10).

Description

Compounds for carbon dioxide absorbents, carbon dioxide absorbents, carbon dioxide separation methods, carbon dioxide separation and recovery methods, and apparatus using carbon dioxide absorbents.

[0001] The present invention relates to a compound for carbon dioxide absorbent, a carbon dioxide absorbent, a method for separating carbon dioxide, a method for separating and recovering carbon dioxide, and an apparatus using a carbon dioxide absorbent.

[0002] In recent years, increased consumption of fossil fuels such as oil and coal due to industrial activities, as well as deforestation, has led to a continuous increase in the concentration of greenhouse gases such as carbon dioxide and methane in the atmosphere, resulting in global warming. If this warming continues at this rate, it is believed that serious consequences will appear in various aspects of life, including desertification of the Earth's surface, rising sea levels, and changes in ecosystems.

[0003] In this context, technologies for reducing carbon dioxide emissions and capturing carbon dioxide are attracting attention as a way to prevent global warming and reduce greenhouse gas emissions. Technologies for capturing carbon dioxide include chemical absorption, physical absorption, solid absorption, and membrane separation, but chemical absorption is mainly used because it can handle a wide range of concentrations. This chemical absorption method involves absorbing carbon dioxide into a liquid through a chemical reaction, and then releasing and capturing the carbon dioxide by heating the absorbent liquid.

[0004] As a liquid used to absorb carbon dioxide, for example, Patent Document 1 discloses an ionic liquid having one or more primary or secondary amino groups in the cation and an ethylenediamine or propylenediamine skeleton of amino acid.

[0005] Japanese Patent Publication No. 2016-10760

[0006] Although the acidic gas chemical absorbent described in Patent Document 1 can absorb a large amount of carbon dioxide at room temperature, there is room for further improvement in its carbon dioxide absorption performance.

[0007] Accordingly, the object of the present invention is to provide a carbon dioxide absorbent compound and carbon dioxide absorbent that have excellent carbon dioxide absorption performance, a carbon dioxide absorbent that, in addition to the above carbon dioxide absorption performance, allows for easy desorption of carbon dioxide when the absorbent is regenerated, a carbon dioxide separation method using the carbon dioxide absorbent, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorbent.

[0008] In view of the above circumstances, the inventors conducted extensive research and, as a result, discovered that the phosphine compound represented by the following general formula (1) has superior carbon dioxide absorption performance compared to conventional compounds, and furthermore, carbon dioxide can be easily removed when the carbon dioxide absorbent is regenerated, thus completing the present invention.

[0009]

[0010] (In the formula, a, b, and c represent integers between 1 and 10, inclusive.)

[0011] In other words, the present invention (1) is the following general formula (1):

[0012]

[0013] The present invention provides a compound for carbon dioxide absorbent characterized by being a phosphine compound represented by the formula (wherein a, b, and c represent integers between 1 and 10).

[0014] Furthermore, the present invention (2) provides a carbon dioxide absorbent characterized by containing the carbon dioxide absorbent compound of the present invention (1).

[0015] Furthermore, the present invention (3) provides a carbon dioxide separation method characterized by having a carbon dioxide separation step of separating carbon dioxide from a mixed gas by contacting the carbon dioxide absorbent of the present invention (2) with a mixed gas containing carbon dioxide, thereby causing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas.

[0016] Furthermore, the present invention (4) provides a carbon dioxide separation and recovery method characterized by comprising: a carbon dioxide separation step of separating carbon dioxide from a mixed gas by contacting the carbon dioxide absorbent of the present invention (2) with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas; and a carbon dioxide recovery step of regenerating the carbon dioxide absorbent and recovering the carbon dioxide that has absorbed carbon dioxide in the carbon dioxide separation step by heating the carbon dioxide absorbent that has absorbed carbon dioxide at a temperature of 50°C to 150°C, thereby desorbing carbon dioxide from the carbon dioxide absorbent.

[0017] Furthermore, the present invention (5) provides an apparatus characterized in that the carbon dioxide absorbent of the present invention (2) is used.

[0018] According to the present invention, it is possible to provide a carbon dioxide absorbent compound and carbon dioxide absorbent with excellent carbon dioxide absorption performance, a carbon dioxide absorbent liquid that, in addition to the above carbon dioxide absorption performance, allows for easy desorption of carbon dioxide when the absorbent liquid is regenerated, a carbon dioxide separation method using the carbon dioxide absorbent liquid of the present invention, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorbent liquid of the present invention.

[0019] The present invention will be described below based on preferred embodiments. The carbon dioxide absorbent compound of the present invention is given by the following general formula (1):

[0020]

[0021] It is a phosphine compound represented by the formula (wherein a, b, and c represent integers between 1 and 10).

[0022] In general formula (1), a, b, and c represent integers between 1 and 10, preferably between 1 and 4, and more preferably between 3 and 4. The numbers a, b, and c may be the same or different, but it is preferable that they be the same from the viewpoint of facilitating synthesis. In the present invention, it is particularly preferable that a, b, and c are each 3 from the viewpoint of industrial availability.

[0023] All three groups bonded to P in general formula (1) have an amino group.

[0024] The carbon dioxide absorbent compound of the present invention can absorb carbon dioxide when the amino group of the phosphine compound represented by general formula (1) reacts with carbon dioxide. In other words, the carbon dioxide absorbent compound of the present invention is a compound used as a substance for absorbing carbon dioxide in a carbon dioxide absorbent.

[0025] The carbon dioxide absorbent of the present invention is characterized by containing the carbon dioxide absorbent compound of the present invention. In other words, the carbon dioxide absorbent of the present invention is characterized by containing a phosphine compound represented by general formula (1). In the carbon dioxide absorbent of the present invention, the phosphine compound represented by general formula (1) absorbs carbon dioxide. The phosphine compound represented by general formula (1) in the carbon dioxide absorbent of the present invention is the same as the phosphine compound represented by general formula (1) in the carbon dioxide absorbent compound of the present invention.

[0026] In the carbon dioxide absorbent of the present invention, the form in which the phosphine compound represented by general formula (1) exists is not particularly limited, and may, for example, be supported on a carrier, dissolved in a solvent, or a mixture with a soluble organic solvent or amine compound.

[0027] The first embodiment of the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by comprising a porous carrier and a carbon dioxide absorbent compound of the present invention supported on the porous carrier. In other words, the first embodiment of the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by comprising a porous carrier and a phosphine compound represented by general formula (1) supported on the porous carrier. In the first embodiment of the carbon dioxide absorbent of the present invention, the liquid phosphine compound represented by general formula (1) is taken into the pores of the porous carrier and physically adsorbed, so that the phosphine compound represented by general formula (1) is supported on the porous carrier.

[0028] The porous carrier according to the first embodiment of the carbon dioxide absorbent of the present invention is not particularly limited as long as it has a porous structure having many pores inside and can take in a phosphine compound represented by general formula (1) into its internal pores and physically adsorb and retain the phosphine compound represented by general formula (1) within the pores. Examples of porous carriers include activated carbon, silica gel, layered silicates, mesoporous silica, zeolites, vermiculite, molecular sieves, porous silica, diatomaceous earth, porous resins, porous fibers, porous metal-organic structures, porous alumina, porous ceramics, porous concrete, activated clay, clay minerals, or composites thereof. Activated carbon, silica gel, mesoporous silica, zeolites, molecular sieves, a composite of alumina and silica gel, and a composite of alumina and mesoporous silica are preferred in that they can carry a large amount of the phosphine compound represented by general formula (1). Furthermore, if the porous support is a porous material capable of retaining water within its pores, such as activated carbon, silica gel, mesoporous silica, zeolite, molecular sieve, alumina-silica gel composite, or alumina-mesoporous silica composite, then when the gas to be treated containing carbon dioxide also contains moisture, the moisture in the gas is adsorbed into the pores of the porous material. This prevents the carbon dioxide absorbent compound from leaching out of the porous support, thus improving the carbon dioxide absorption performance of the carbon dioxide absorbent. The porous material capable of retaining water within its pores is not particularly limited as long as it can retain water within its pores, but examples include materials that can contain water at a water content of 5 to 30% by mass, preferably 10 to 25% by mass.

[0029] The BET specific surface area of ​​the porous carrier is preferably 1.0 × 10⁻⁶. １ ~5.0 x 10 ３ I understand ２ / g, preferably 5.0 × 10 １ ~2.0 x 10 ３ I understand ２ The value is / g. Furthermore, the pore volume of the porous carrier obtained by gas adsorption is preferably 0.1 to 2.0 cm³. ３ / g, preferably 0.3 to 1.5 cm ３ It is / g.

[0030] Examples of the shape of the porous carrier include granular, powdery, fibrous, plate-like, columnar, honeycomb-like, dice-like, and rectangular parallelepiped-like shapes. Among these, from the viewpoints of contact with a mixed gas containing carbon dioxide and filling properties in filling equipment such as columns and towers, it is preferably granular or powdery. Note that the porous carrier may be a molded body.

[0031] Among the porous carriers, from the viewpoints of ease of handling and the ability to easily support the liquid phosphine compound represented by the general formula (1), activated carbon, silica gel, mesoporous silica, zeolite, molecular sieve, a composite of alumina and silica gel, and a composite of alumina and mesoporous silica are preferable, and activated carbon and silica gel are particularly preferable.

[0032] As the activated carbon used in the present invention, various activated carbons can be used. Examples include activated carbons made from raw materials such as wood, coconut shell, coal, petroleum pitch, coke, and coal tar. The activated carbon may be a molded body. In addition to the characteristics of the porous carrier described above, as physical property values measured by JIS K1474 (Test method for activated carbon), the loss on drying is preferably 0.1 to 5.0%, the ignited residue is preferably 0.1 to 5.0%, the bulk density is preferably 0.25 to 0.85 g / ml, the acetone adsorption performance is preferably 14.0 to 41.0%, the iodine adsorption performance is preferably 600 to 2600 mg / g, and the hardness is preferably 90.0 to 100.0%.

[0033] Examples of the silica gel used in the present invention include various silica gels. For example, those containing 99% by mass or more, particularly 99.9% by mass or more of silicon oxide are preferable. The silica gel may be a molded body. In addition to the characteristics of the porous carrier described above, the average particle diameter measured by a scanning electron microscope is preferably 0.005 to 10 mm, and the loss on drying is preferably 10% or less.

[0034] Various types of zeolites can be used in the present invention, including LTA-type zeolite, FER-type zeolite, MWW-type zeolite, MFI-type zeolite, MOR-type zeolite, LTL-type zeolite, FAU-type zeolite, BEA-type zeolite, and the like. The zeolite may also be a molded body. In addition to the porous carrier properties described above, it is preferable that the zeolite has an average particle size of 0.01 to 15 mm as measured by a scanning electron microscope.

[0035] In the first embodiment of the carbon dioxide absorbent of the present invention, when two or more phosphine compounds represented by general formula (1) are supported on a porous carrier, the two or more phosphine compounds represented by general formula (1) may be supported in the form of a mixed solution, or each of the two or more phosphine compounds represented by general formula (1) may be supported on a different part of the porous carrier. That is, for example, when supporting two phosphine compounds represented by general formula (1) on a porous carrier, the two phosphine compounds represented by general formula (1) may be mixed first, and the resulting mixed solution may be incorporated into the pores of the porous carrier and supported, or one of the two phosphine compounds represented by general formula (1) may be incorporated into the pores of the porous carrier first, and then the other phosphine compound represented by general formula (1) may be incorporated into the pores of the porous carrier to support the two phosphine compounds represented by general formula (1). The same applies when supporting three or more phosphine compounds represented by general formula (1) on a porous carrier.

[0036] The impregnation rate (content) of the phosphine compound represented by general formula (1) in the carbon dioxide absorbent of the first embodiment of the present invention is not particularly limited, but is preferably 5 to 60% by mass, more preferably 5 to 55% by mass, and particularly preferably 10 to 55% by mass, relative to the total carbon dioxide absorbent. By having the amount of phosphine compound represented by general formula (1) impregnated in the carbon dioxide absorbent within the above range, it can be uniformly present on the inner surface of the pores of the porous carrier, thereby enabling efficient absorption of carbon dioxide.

[0037] The carbon dioxide absorbent of the first embodiment of the present invention is a phosphine compound represented by general formula (1) that is capable of chemical adsorption of carbon dioxide, supported on a porous carrier. As a result, carbon dioxide can be absorbed more efficiently when the temperature of the carbon dioxide absorbent is between -20°C and 60°C, and the carbon dioxide is easily desorbed, making it easy to regenerate the carbon dioxide absorbent.

[0038] The carbon dioxide absorbent of the first embodiment of the present invention is spread out on the surface of a porous carrier with a large surface area, thereby increasing the contact area between the phosphine compound represented by general formula (1) and carbon dioxide. Therefore, the carbon dioxide absorbent of the first embodiment of the present invention can achieve high carbon dioxide absorption efficiency.

[0039] The first embodiment of the carbon dioxide absorbent of the present invention is supported on a solid carrier and can be used by packing it into columns or reaction towers. Furthermore, compared to liquid carbon dioxide absorbents, the first embodiment of the present invention allows for more efficient contact with carbon dioxide or carbon dioxide-containing gases because appropriate gaps are formed when it is packed into columns or reaction towers.

[0040] A second embodiment of the present invention is a carbon dioxide absorbent characterized by comprising the carbon dioxide absorbent compound of the present invention, that is, a phosphine compound represented by general formula (1), and a solvent (hereinafter also referred to as "carbon dioxide absorbent solution"). The phosphine compound represented by general formula (1) is water-soluble, and the second embodiment of the present invention is in the form of a solution containing the phosphine compound represented by general formula (1).

[0041] In the second embodiment of the carbon dioxide absorbent of the present invention, the solvent can be water, glycol-based solvents, alcohol-based solvents, amine compounds, alkanolamine compounds, etc. Among these, water, glycol-based solvents, and alcohol-based solvents are preferred because the viscosity of the carbon dioxide absorbent does not increase easily after absorbing carbon dioxide and it has good handling properties.

[0042] Examples of glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin.

[0043] These solvents may be used individually or in mixtures of two or more types.

[0044] In the second embodiment of the carbon dioxide absorbent of the present invention, the content of the phosphine compound represented by general formula (1) in the carbon dioxide absorbent is 5 to 80% by mass, preferably 10 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. Because the content of the phosphine compound represented by general formula (1) in the carbon dioxide absorbent is within the above range, the viscosity of the carbon dioxide absorbent after absorbing carbon dioxide does not increase easily, resulting in good handling properties.

[0045] The second embodiment of the carbon dioxide absorbent of the present invention is in solution form, and therefore, from the viewpoint of ease of acquisition and safety, is suitably used for separating and recovering carbon dioxide emitted from large-scale carbon dioxide sources such as power plants such as coal-fired power plants and natural gas-fired power plants, chemical plants, waste treatment plants, and steel mills. Because the second embodiment of the carbon dioxide absorbent of the present invention is a solution, it can be used in existing carbon dioxide absorption equipment in large-scale facilities and factories where the concentration of carbon dioxide is high and large-scale processing is required. Furthermore, because the second embodiment of the carbon dioxide absorbent of the present invention is a solution, it is easy to transport to and fill into large-scale carbon dioxide separation and recovery equipment, or to remove from equipment.

[0046] The carbon dioxide absorbent of the present invention can separate and recover carbon dioxide from a mixed gas containing carbon dioxide. The other components of the mixed gas are not particularly limited, as long as the gas contains carbon dioxide. Examples of the other components include oxygen, nitrogen, carbon monoxide, nitric oxide, nitrogen dioxide, dinitrogen monoxide, dinitrogen trioxide, dinitrogen tetroxide, dinitrogen pentoxide, sulfur monoxide, sulfur dioxide, sulfur trioxide, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, water, etc. The concentration of carbon dioxide in the mixed gas is not particularly limited and may be a high concentration with a purity of about 100%, or it may be a concentration similar to that found in the atmosphere.

[0047] The carbon dioxide absorbent of the present invention is useful as an absorbent liquid for separating and recovering carbon dioxide from mixed gases containing carbon dioxide emitted from, for example, power plants such as coal-fired power plants and natural gas-fired power plants, factories such as chemical plants, waste treatment plants and steel mills, and transportation equipment such as automobiles, aircraft and ships. It is also useful as an absorbent liquid used in DAC (Direct Air Capture) devices that directly separate and recover carbon dioxide from the atmosphere. In other words, the carbon dioxide absorbent of the present invention is suitable as a carbon dioxide absorbent or absorbent liquid used in various devices such as devices used in power plants, factories and transportation equipment, and DAC devices.

[0048] Next, a method for separating carbon dioxide and a method for separating and recovering carbon dioxide using the carbon dioxide absorbent of the present invention will be described.

[0049] The present invention provides a carbon dioxide separation method characterized by having a carbon dioxide separation step (A) in which carbon dioxide is separated from a mixed gas by contacting a carbon dioxide absorbent of the present invention with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas.

[0050] The present invention provides a carbon dioxide separation and recovery method comprising: a carbon dioxide separation step (A) in which a carbon dioxide absorbent of the present invention is brought into contact with a mixed gas containing carbon dioxide, thereby separating carbon dioxide from the mixed gas by allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas; and a carbon dioxide recovery step (B) in which the carbon dioxide absorbent that has absorbed carbon dioxide in the carbon dioxide separation step is heated at a temperature of 50°C to 150°C to desorb carbon dioxide from the carbon dioxide absorbent, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

[0051] In the carbon dioxide separation method and the carbon dioxide separation and recovery method of the present invention, the step of separating carbon dioxide from a mixed gas containing carbon dioxide is the carbon dioxide separation step (A) in both cases and is the same.

[0052] The carbon dioxide separation step (A) is a step in which the carbon dioxide absorbent of the present invention is brought into contact with a mixed gas containing carbon dioxide, thereby causing the carbon dioxide absorbent of the present invention to absorb the carbon dioxide in the mixed gas.

[0053] One example of the carbon dioxide separation process (A) is to supply a mixed gas containing carbon dioxide to an absorption tower filled with the carbon dioxide absorbent of the present invention, bring the mixed gas into contact with the carbon dioxide absorbent, and separate the carbon dioxide from the mixed gas by allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas. In this form of carbon dioxide separation process (A), the mixed gas is supplied to the absorption tower to bring the mixed gas into contact with the carbon dioxide absorbent, and the mixed gas that has come into contact with the carbon dioxide absorbent inside the absorption tower is discharged from the absorption tower. Furthermore, the method of filling the absorption tower with the carbon dioxide absorbent of the present invention is not particularly limited and can be carried out under atmospheric pressure or reduced pressure.

[0054] The temperature of the carbon dioxide absorbent in the carbon dioxide separation step (A) is not limited as long as the carbon dioxide absorbent can perform its function, but a temperature of -20°C to 60°C, and particularly 0°C to 40°C, is preferable from the viewpoint of more efficient carbon dioxide absorption.

[0055] The pressure (absolute pressure) in the carbon dioxide separation process (A) is not particularly limited and can be carried out under atmospheric pressure.

[0056] In the carbon dioxide separation step (A), the carbon dioxide absorbent comes into contact with a mixed gas containing carbon dioxide, causing the carbon dioxide in the mixed gas to be absorbed by the carbon dioxide absorbent of the present invention, thereby separating the carbon dioxide from the mixed gas. In addition, the carbon dioxide separation step (A) yields a carbon dioxide absorbent that has absorbed carbon dioxide.

[0057] The carbon dioxide separation and recovery method of the present invention includes a carbon dioxide recovery step (B) in which a carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step is regenerated and carbon dioxide is recovered. The carbon dioxide recovery step (B) is a step in which carbon dioxide is removed from the carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step (A) by heating the carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step (A).

[0058] The carbon dioxide recovery process (B) may involve, for example, heating the carbon dioxide absorbent packed in the absorption tower after the carbon dioxide separation process (A) to regenerate the carbon dioxide absorbent and recover the desorbed carbon dioxide. Alternatively, if the carbon dioxide absorbent is in the form of a solution, for example, after the carbon dioxide separation process (A), the carbon dioxide absorbent solution that has absorbed carbon dioxide may be transported to a regeneration tower, where it is heated to regenerate the carbon dioxide absorbent solution and recover the desorbed carbon dioxide.

[0059] In the carbon dioxide recovery process (B), the heating temperature of the carbon dioxide absorbent is 50°C to 150°C, preferably 80°C to 140°C. Generally, the higher the heating temperature, the easier it is for carbon dioxide to be released from the carbon dioxide absorbent that has absorbed it. In the carbon dioxide absorbent of the present invention, carbon dioxide can be released at a temperature of 50°C to 150°C, preferably 80°C to 140°C, and at a temperature equivalent to or higher than the temperature of the carbon dioxide separation process (A).

[0060] When using the carbon dioxide absorbent of the first embodiment of the present invention as the carbon dioxide absorbent, the pressure (absolute pressure) in the carbon dioxide recovery step (B) is not particularly limited and may be carried out under atmospheric pressure or under reduced pressure. When carried out under reduced pressure, the pressure (absolute pressure) is preferably 85 kPa or less, more preferably 60 kPa or less, from the viewpoint of preventing oxidation of the carbon dioxide absorbent, and further preferably 50 kPa or less, particularly 10 kPa or less, from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent.

[0061] When using the carbon dioxide absorbent of the second embodiment of the present invention as the carbon dioxide absorbent, the pressure (absolute pressure) in the carbon dioxide recovery step (B) is not particularly limited, and the heating of the carbon dioxide absorbent that has absorbed carbon dioxide may be carried out under atmospheric pressure or under reduced pressure. When carried out under reduced pressure, the pressure (absolute pressure) is preferably 85 kPa or less, more preferably 60 kPa or less, from the viewpoint of preventing oxidation of the carbon dioxide absorbent solution, and further preferably 50 kPa or less, particularly 10 kPa or less, from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent. Also, when using the carbon dioxide absorbent of the second embodiment of the present invention as the carbon dioxide absorbent, the heating temperature in the carbon dioxide recovery step (B) may be set to a temperature above the boiling point of the solvent, and the heating of the carbon dioxide absorbent that has absorbed carbon dioxide may be carried out under reflux of the solvent. Also, when using the carbon dioxide absorbent of the second embodiment of the present invention as the carbon dioxide absorbent, the heating of the carbon dioxide absorbent that has absorbed carbon dioxide may be carried out in the carbon dioxide recovery step (B) while bubbling air, an inert gas, water vapor, etc. through the carbon dioxide absorbent.

[0062] In the carbon dioxide separation and recovery method of the present invention, by using the recycled carbon dioxide absorbent obtained in the carbon dioxide recovery step (B) as a carbon dioxide absorbent to which a mixed gas containing carbon dioxide is contacted in the carbon dioxide separation step (A), the carbon dioxide separation step (A) and the carbon dioxide recovery step (B) can be repeated two or more times. For example, when repeating the carbon dioxide separation step (A) and the carbon dioxide recovery step (B) twice, the process is carried out as follows: "carbon dioxide separation step (A) → carbon dioxide recovery step (B) → carbon dioxide separation step (A) → carbon dioxide recovery step (B)". The carbon dioxide separation step (A) and the carbon dioxide recovery step (B) can be repeated as long as the carbon dioxide absorption performance is sustained.

[0063] In the carbon dioxide separation method and carbon dioxide separation and recovery method of the present invention, the carbon dioxide absorbent of the present invention, which contains a phosphine compound represented by general formula (1) that has excellent chemical absorption properties, is used for carbon dioxide absorption, thereby increasing the efficiency of carbon dioxide removal from the mixed gas.

[0064] The carbon dioxide separation method and carbon dioxide separation and recovery method of the present invention are suitably used when separating or recovering carbon dioxide from mixed gases containing carbon dioxide emitted from, for example, power plants such as coal-fired power plants and natural gas-fired power plants, factories such as chemical plants, waste treatment facilities and steel mills, and transportation equipment such as automobiles, aircraft and ships. They are also suitably used when separating or recovering carbon dioxide directly from the atmosphere.

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0066] (Synthesis Example 1: Tris(3-aminopropyl)phosphine) 150 ml of toluene and 133 g (2.33 mol) of allylamine were charged into a 1 L stainless steel autoclave equipped with a stirrer, thermometer, pressure injection pump, safety valve, and gas introduction tube. The autoclave was purged three times with nitrogen gas and vacuum, and then 22 g (0.65 mol) of phosphine gas manufactured by Nippon Chemical Industry Co., Ltd. with a purity of 99.9% was charged. At this time, when the temperature was raised to 80°C by a hot water bath, the gauge pressure showed 0.93 MPa (absolute pressure 1.03 MPa). Next, 1.06 g (0.006 mol) of azobisisobutyronitrile was dissolved in 150 ml of toluene, and it was divided and pressure-injected over 6 hours, and aged overnight at 80°C. At this time, the gauge pressure showed 0.01 MPa (absolute pressure 0.11 MPa). After aging overnight, it was cooled to room temperature, the residual gas was exhausted to an exhaust facility, and the system was replaced with nitrogen gas and vacuum again. Then, by extracting it into a reduced-pressure eggplant-shaped flask, 585 g of a colorless transparent liquid was obtained. Next, the obtained colorless transparent liquid was heated under reduced pressure (gauge pressure 4 kPa (absolute pressure 105.3 kPa), 80°C) to distill off excess allylamine and toluene. Further, the degree of vacuum and temperature were increased and heated (gauge pressure 0.2 kPa (absolute pressure 101.5 kPa), 160°C). When the initial distillate began to appear, the heating was stopped, and the residue in the kettle was used as the product. After cooling the obtained product to room temperature and replacing it with nitrogen gas, 120 g of a colorless transparent liquid was obtained. The NMR identification data of the obtained colorless transparent liquid is as follows. (Identification data) ３１ P-NMR (D ２ O); -29.73 ppm １ H-NMR (D ２ O); 1.40 to 1.46 ppm (m, 6H, -CH ２ -), 1.52 to 1.61 ppm (m, 6H, P-CH ２ -), 2.63 to 2.71 ppm (m, 6H, -CH ２ -NH ２ ), 4.67 ppm (s, 6H, -NH ２ ) As a result, it was confirmed that it was tris(3-aminopropyl)phosphine.

[0067] (Synthesis Example 2: Tris(3-aminopropyl)phosphine oxide) A 1 L four-necked flask equipped with a stirrer and thermometer was purged with nitrogen gas. 92.4 g (0.45 mol) of tris(3-aminopropyl)phosphine obtained in Synthesis Example 1 and 500 ml of pure water were charged, and 56.1 g (0.495 mol) of 30% hydrogen peroxide diluted with 100 ml of pure water was added dropwise over 1 hour while maintaining the temperature at 70-75°C. After aging for 1 hour, the mixture was cooled to room temperature and concentrated under reduced pressure using an evaporator to remove water, yielding 100.8 g of a colorless, transparent liquid. The NMR identification data of the obtained colorless, transparent liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); 60.77ppm １ H-NMR (D ２ O); 1.50 to 1.58 ppm (m, 6H, -CH ２ -), 1.71 to 1.77 ppm (m, 6H, P-CH ２ -), 2.57 to 2.60 ppm (t, 6H, -CH ２ -NH ２ ), 4.70ppm (s, 6H, -NH ２ As a result, it was confirmed to be tris(3-aminopropyl)phosphine oxide.

[0068] (Example 1) Dissolve 20.5 g (0.1 mol) of tris(3-aminopropyl)phosphine obtained in Synthesis Example 1 in 300 ml of pure water, and silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²) ２ 38.1 g of (average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure in an evaporator and completely removing the added water, 58.9 g of a carbon dioxide absorbent with tris(3-aminopropyl)phosphine impregnated onto the silica gel was obtained. The impregnation rate of tris(3-aminopropyl)phosphine relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in regeneration test 1 described later.

[0069] (Example 2) Tris(3-aminopropyl)phosphine obtained in Synthesis Example 1 was dissolved in pure water to obtain a carbon dioxide absorbent solution prepared so that the tris(3-aminopropyl)phosphine content was 40% by mass. The obtained carbon dioxide absorbent solution was evaluated in regeneration test 2 described later.

[0070] (Reference Example 1) Tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 was dissolved in pure water to obtain a carbon dioxide absorbent solution prepared so that the tris(3-aminopropyl)phosphine oxide content was 40% by mass. The obtained carbon dioxide absorbent solution was evaluated in regeneration test 2 described later.

[0071] (Evaluation) (Regeneration Test 1) The carbon dioxide absorbent obtained in Example 1 was placed in a 35 ml Erlenmeyer flask and accurately weighed to the nearest 0.1 mg. 99.995% pure carbon dioxide gas was blown in at a flow rate of 200 ml / min at room temperature (25°C), and the weight was accurately weighed to the nearest 0.1 mg every 10 minutes. Gas blowing was stopped when the weight reached the weighing point. The increased weight was used as the amount of carbon dioxide absorbed, and the number of moles was calculated. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent. The carbon dioxide absorbent from Example 1, which had absorbed carbon dioxide to saturation, was transferred to a 50 mm diameter petri dish and regenerated by static heating in a vacuum dryer maintained at 120°C under full vacuum using a vacuum pump for 1 hour to remove carbon dioxide. Next, the carbon dioxide absorbent regenerated by removing carbon dioxide was again filled into a 35 ml Erlenmeyer flask, and the absorption and regeneration of carbon dioxide was repeated multiple times. The regeneration rate was calculated based on the following formula. The results are shown in Table 1. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

[0072]

[0073] The results shown in Table 1 confirm that the carbon dioxide absorbent of Example 1 has excellent carbon dioxide absorption performance, and that its absorption capacity does not decrease even after repeated carbon dioxide absorption and regeneration cycles.

[0074] (Regeneration Test 2) The carbon dioxide absorbent solutions obtained in Example 2 and Comparative Example 1 were placed in a 50 ml Erlenmeyer flask, and 99.995% pure carbon dioxide gas was blown in at a flow rate of 1 L / min at room temperature (25°C). After 15 minutes, the weight was accurately measured to the nearest 0.1 mg. The increased weight was used as the amount of carbon dioxide absorbed, and the number of moles was calculated. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent solution. Next, the carbon dioxide absorbent solution that had absorbed carbon dioxide was heated in an oil bath while being stirred. After heating for 2 hours from the point when the liquid temperature reached 100°C, carbon dioxide was expelled by refluxing water in a condenser, and regeneration was performed. Then, pure water was added to the carbon dioxide absorbent solution to make it the same weight as the water lost during heating, and the carbon dioxide absorption and regeneration process was repeated multiple times. The regeneration rate was calculated using the following formula based on the number of moles of carbon dioxide absorbed. The results are shown in Tables 2 and 3. Regeneration rate (%) = (Number of moles of carbon dioxide absorbed during regeneration / Number of moles of carbon dioxide absorbed initially) × 100

[0075]

[0076]

[0077] The results of regeneration test 2 confirmed that the carbon dioxide absorbent solution of Example 2 exhibited excellent regeneration rates even after repeated carbon dioxide absorption and regeneration cycles.

Claims

1. The following general formula (1): A compound for carbon dioxide absorbent, characterized by being a phosphine compound represented by the formula (wherein a, b, and c represent integers between 1 and 10).

2. A carbon dioxide absorbent characterized by containing the carbon dioxide absorbent compound described in claim 1.

3. The carbon dioxide absorbent according to claim 2, characterized by comprising a porous carrier and the carbon dioxide absorbent compound according to claim 1 supported on the porous carrier.

4. The carbon dioxide absorbent according to claim 3, characterized in that the porous carrier is activated carbon, silica gel, layered silicate, mesoporous silica, zeolite, vermiculite, molecular sieve, porous silica, diatomaceous earth, porous resin, porous fiber, porous metal-organic structure, porous alumina, porous ceramic, porous concrete, activated clay, clay mineral, or a composite thereof.

5. The carbon dioxide absorbent according to claim 2, characterized by comprising the carbon dioxide absorbent compound and solvent according to claim 1.

6. The carbon dioxide absorbent according to claim 5, characterized in that the solvent comprises at least one selected from the group consisting of water, glycol-based solvents, and alcohol-based solvents.

7. The carbon dioxide absorbent according to claim 5, characterized in that the content of the carbon dioxide absorbent compound described in claim 1 is 5% by mass or more and 80% by mass or less.

8. A method for separating carbon dioxide, characterized by comprising a carbon dioxide separation step of contacting a carbon dioxide absorbent described in claim 2 with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas and separating the carbon dioxide from the mixed gas.

9. A carbon dioxide separation and recovery method characterized by comprising: a carbon dioxide separation step of contacting a carbon dioxide absorbent described in claim 2 with a mixed gas containing carbon dioxide, thereby separating carbon dioxide from the mixed gas by allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas; and a carbon dioxide recovery step of heating the carbon dioxide absorbent that has absorbed carbon dioxide in the carbon dioxide separation step at a temperature of 50°C to 150°C to desorb carbon dioxide from the carbon dioxide absorbent, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

10. The carbon dioxide separation and recovery method according to claim 9, characterized in that the recycled carbon dioxide absorbent obtained by the carbon dioxide recovery step is used as the carbon dioxide absorbent to which the mixed gas containing the carbon dioxide is brought into contact in the carbon dioxide separation step, thereby repeating the carbon dioxide separation step and the carbon dioxide recovery step two or more times.

11. An apparatus characterized in that it uses the carbon dioxide absorbent described in claim 2.

12. The apparatus according to claim 11, characterized in that the apparatus is used in a power plant, factory, or transportation equipment.

13. The apparatus according to claim 11, characterized in that the apparatus is a DAC apparatus.

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