JP7839328B2 - Carbon dioxide absorbent, carbon dioxide separation method, carbon dioxide separation and recovery method, and apparatus using carbon dioxide absorbent - Google Patents

Description

This invention relates to a compound for carbon dioxide absorbent, a carbon dioxide absorbent, a carbon dioxide separation method, a carbon dioxide separation and recovery method, and an apparatus using a carbon dioxide absorbent.

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 emerge in various areas, including desertification of the Earth's surface, rising sea levels, and changes in ecosystems.

In this context, technologies for reducing carbon dioxide emissions and capturing carbon dioxide are attracting attention as a means of preventing global warming. While there are various carbon dioxide capture technologies, including chemical absorption, physical absorption, solid absorption, and membrane separation, chemical absorption is primarily used due to its ability to handle a wide range of concentrations. This method involves absorbing carbon dioxide into a liquid through a chemical reaction, and then releasing the carbon dioxide by heating the absorbent liquid.

As a liquid used for absorbing 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.

Japanese Patent Publication No. 2016-10760

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

Therefore, the object of the present invention is to provide a carbon dioxide absorbent compound and carbon dioxide absorbent with 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 during regeneration of the absorbent, 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.

In view of the above circumstances, the inventors of this invention conducted extensive research and, as a result, discovered that the phosphine oxide 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. Based on these findings, the inventors have completed the present invention.

(In the formula, a, b, and c represent integers between 1 and 10, ^R1 , ^R2 , and ^R3 each independently represent an amino group or a hydroxyl group, and at least one of ^R1 , ^R2 , and ^R3 is an amino group.)

In other words, the present invention (1) is based on the following general formula (1):

(In the formula, a, b, and c represent integers between 1 and 10, ^R1 , ^R2 , and ^R3 each independently represent an amino group or a hydroxyl group, and at least one of ^R1 , ^R2 , and ^R3 is an amino group.)
This invention provides a compound for carbon dioxide absorbers, characterized by being a phosphine oxide compound represented by [formula].

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

Furthermore, the present invention (3) provides a carbon dioxide separation method characterized by having a carbon dioxide separation step in which a carbon dioxide-containing mixed gas is brought into contact with the carbon dioxide absorbent of the present invention (2), causing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas, thereby separating the carbon dioxide from the mixed gas.

Furthermore, the present invention (4) provides a carbon dioxide separation and recovery method characterized by comprising: a carbon dioxide separation step of contacting the carbon dioxide absorbent of the present invention (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, thereby desorbing carbon dioxide from the carbon dioxide absorbent, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

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

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 that, in addition to the above carbon dioxide absorption performance, allows for easy desorption of carbon dioxide during regeneration of the absorbent, a carbon dioxide separation method using the carbon dioxide absorbent of the present invention, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorbent of the present invention.

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):

(In the formula, a, b, and c represent integers between 1 and 10, ^R1 , ^R2 , and ^R3 each independently represent an amino group or a hydroxyl group, and at least one of ^R1 , ^R2 , and ^R3 is an amino group.)
It is a phosphine oxide compound represented by [formula].

The phosphine oxide compound represented by general formula (1) has a phosphine oxide structure ( _α3P =O), which gives it high heat resistance, a low vapor pressure in the heating temperature range during regeneration after carbon dioxide absorption of the carbon dioxide absorbent, for example, in the heating temperature range of 50°C to 150°C, and it has almost no volatility.

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 this invention, it is particularly preferable that a, b, and c are each 3, from the viewpoint of industrial availability.

In general formula (1), ^R1 , ^R2 , and ^R3 each independently represent an amino group ( _-NH2 ) or a hydroxyl group (-OH). ^R1 , ^R2 , and ^R3 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, from the viewpoint of carbon dioxide absorption performance, it is preferable that at least one of ^R1 , ^R2 , and ^R3 is an amino group, and all of them are amino groups.

The carbon dioxide absorbent compound of the present invention can absorb carbon dioxide through the reaction of the amino group of the phosphine oxide compound represented by general formula (1) 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.

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 oxide compound represented by general formula (1). In the carbon dioxide absorbent of the present invention, the phosphine oxide represented by general formula (1) absorbs carbon dioxide. The phosphine oxide compound represented by general formula (1) in the carbon dioxide absorbent of the present invention is the same as the phosphine oxide compound represented by general formula (1) in the carbon dioxide absorbent compound of the present invention.

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

The carbon dioxide absorbent of the present invention is 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 carbon dioxide absorbent of the present invention is characterized by comprising a porous carrier and a phosphine oxide compound represented by general formula (1) supported on the porous carrier. Furthermore, in the carbon dioxide absorbent of the present invention, the liquid phosphine oxide compound represented by general formula (1) is incorporated into the pores of the porous carrier and physically adsorbed, thereby enabling the phosphine oxide compound represented by general formula (1) to be supported on the porous carrier.

The porous carrier for 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 oxide compound represented by general formula (1) into its internal pores and physically adsorb and retain the phosphine oxide 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, composites of alumina and silica gel, and composites of alumina and mesoporous silica are preferred in that they can support a large amount of the phosphine oxide 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 treated gas containing carbon dioxide also contains moisture, the moisture in the treated 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, but examples include materials capable of containing water at a water content of 5 to 30% by mass, preferably 10 to 25% by mass.

The BET specific surface area of the porous carrier is preferably 1.0 × ^10¹ to 5.0 × ^{10³ m²} /g, and more preferably 5.0 × ^10¹ to 2.0 × ^{10³ m²} /g. Furthermore, the pore volume of the porous carrier by gas adsorption method is preferably 0.1 to 2.0 ^cm³ /g, and more preferably 0.3 to 1.5 ^cm³ /g.

The porous carrier can take the form of, for example, granular, powdery, fibrous, plate-like, cylindrical, honeycomb-like, die-like, or rectangular parallelepiped. Of these, granular or powdery forms are preferred from the viewpoint of contact with mixed gases containing carbon dioxide and packing into packing equipment such as columns and towers. The porous carrier may also be a molded body.

Among porous supports, activated carbon, silica gel, mesoporous silica, zeolite, molecular sieve, alumina-silica gel composites, and alumina-mesoporous silica composites are preferred from the viewpoint of ease of handling and the ability to easily support liquid phosphine oxide compounds represented by general formula (1). Activated carbon, silica gel, mesoporous silica, alumina-silica gel composites, and alumina-mesoporous silica composites are particularly preferred.

In this invention, various types of activated carbon can be used, including, for example, activated carbon made from wood, coconut shells, coal, petroleum pitch, coke, coal tar, etc. The activated carbon may also be in molded form. Furthermore, in addition to the characteristics of the porous carrier described above, the activated carbon preferably has the following physical properties, as measured according to JIS K1474 (Activated Carbon Test Method): a loss on drying of 0.1 to 5.0%, a residue on ignition of 0.1 to 5.0%, a packing density of 0.25 to 0.85 g/ml, an acetone adsorption capacity of 14.0 to 41.0%, an iodine adsorption capacity of 600 to 2600 mg/g, and a hardness of 90.0 to 100.0%.

Various types of silica gel can be used in this invention, and for example, those containing 99% or more by mass of silicon dioxide, particularly 99.9% or more by mass, are preferred. The silica gel may also be a molded body. Furthermore, in addition to the porous carrier properties described above, the silica gel preferably has an average particle size of 0.005 to 10 mm as measured by a scanning electron microscope, and preferably a drying loss of 10% or less.

Various types of zeolites can be used in this invention, including, for example, LTA-type zeolite, FER-type zeolite, MWW-type zeolite, MFI-type zeolite, MOR-type zeolite, LTL-type zeolite, FAU-type zeolite, and BEA-type zeolite. The zeolite may also be a molded body. Furthermore, 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.

Furthermore, in the carbon dioxide absorbent of the present invention, when two or more phosphine oxide compounds represented by general formula (1) are supported on a porous carrier, the two or more phosphine oxide compounds represented by general formula (1) may be supported in the form of a mixed solution, or each of the two or more phosphine oxide 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 oxide compounds represented by general formula (1) on a porous carrier, the two phosphine oxide 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 oxide compounds represented by general formula (1) may be incorporated into the pores of the porous carrier first, and then the other phosphine oxide compound represented by general formula (1) may be incorporated into the pores of the porous carrier to support the two phosphine oxide compounds represented by general formula (1). The same applies when three or more phosphine oxide compounds represented by general formula (1) are supported on a porous carrier.

The deposition rate (content) of the phosphine oxide compound represented by general formula (1) in the carbon dioxide absorbent 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 oxide compound represented by general formula (1) deposited in the carbon dioxide absorbent within this range, it can be uniformly present on the inner surface of the pores of the porous carrier, thereby enabling efficient absorption of carbon dioxide.

The carbon dioxide absorbent of the present invention is a phosphine oxide compound represented by general formula (1) that is capable of chemical adsorption of carbon dioxide, supported on a porous carrier. This allows for more efficient absorption of carbon dioxide when the carbon dioxide absorbent's temperature is between -20°C and 60°C, and facilitates the desorption of carbon dioxide, thus facilitating the regeneration of the carbon dioxide absorbent.

Because the carbon dioxide absorbent of the present invention is spread across the surface of a porous carrier with a large surface area, the contact area between the phosphine oxide compound represented by general formula (1) and carbon dioxide can be increased. Therefore, the carbon dioxide absorbent of the present invention can achieve high carbon dioxide absorption efficiency.

The carbon dioxide absorbent of the present invention, being supported on a solid carrier, can be used by filling columns and reaction towers. Furthermore, compared to liquid carbon dioxide absorbents, the carbon dioxide absorbent of the present invention forms appropriate gaps when filled into columns and reaction towers, allowing for more efficient contact with carbon dioxide or carbon dioxide-containing gases.

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 these 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, and water. The concentration of carbon dioxide in the mixed gas is not particularly limited; it may be a high concentration with a purity of about 100%, or it may be at a concentration similar to that found in the atmosphere.

The carbon dioxide absorbent of the present invention is useful as an absorbent for separating and recovering carbon dioxide from mixed gases containing carbon dioxide emitted from sources such as power plants (coal-fired power plants, natural gas-fired power plants, etc.), factories (chemical plants, waste treatment plants, steel mills, etc.), and transportation equipment (automobiles, aircraft, ships, etc.). It is also useful as an absorbent used in DAC (Direct Air Capture) systems 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 used in various devices such as equipment used in power plants, factories, and transportation equipment, as well as DAC devices.

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.

The present invention relates to a carbon dioxide separation method characterized by having 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, and the carbon dioxide absorbent absorbs the carbon dioxide in the mixed gas, thereby separating the carbon dioxide from the mixed gas.

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.

In both 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), and is the same in both cases.

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.

One example of the carbon dioxide separation process (A) is to supply a mixed gas containing carbon dioxide to an absorbent-packed column or absorbent-packed 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 brought into contact with the carbon dioxide absorbent by supplying the mixed gas to the absorbent-packed column or absorbent-packed tower, and the mixed gas that has been in contact with the carbon dioxide absorbent within the absorbent-packed column or absorbent-packed tower is discharged from the absorbent-packed column or absorbent-packed tower. Furthermore, the method of packing the carbon dioxide absorbent of the present invention into the absorbent-packed column or absorbent-packed tower is not particularly limited and can be carried out under atmospheric pressure or reduced pressure.

The temperature of the carbon dioxide absorbent in the carbon dioxide separation process (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.

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

In the carbon dioxide separation step (A), the carbon dioxide absorbent comes into contact with a mixed gas containing carbon dioxide. The carbon dioxide absorbent of the present invention absorbs the carbon dioxide from the mixed gas, thereby separating the carbon dioxide from the mixed gas. Furthermore, the carbon dioxide separation step (A) yields a carbon dioxide absorbent that has absorbed carbon dioxide.

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 the carbon dioxide separation step is regenerated and carbon dioxide is recovered.
The carbon dioxide recovery process (B) is a process in which carbon dioxide is removed from the carbon dioxide absorbent that absorbed carbon dioxide in the carbon dioxide separation process (A) by heating the absorbent.

The carbon dioxide recovery process (B) may involve, for example, heating the carbon dioxide absorbent packed in the absorbent-packed column or tower after the carbon dioxide separation process (A) to regenerate the absorbent and recover the desorbed carbon dioxide.

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 absorbent. 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 in the carbon dioxide separation process (A). For example, if the carbon dioxide absorbent is the carbon dioxide absorbent of the present invention, the heating temperature is preferably 80 to 120°C.

In the carbon dioxide recovery process (B), the pressure (absolute pressure) 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. Furthermore, from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent, it is more preferably 50 kPa or less, more preferably 10 kPa or less, and particularly preferably 4 kPa or less.

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 the carbon dioxide absorbent to which the carbon dioxide-containing mixed gas 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.

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 oxide compound represented by general formula (1) that exhibits excellent chemical absorption, is used for carbon dioxide absorption, thereby increasing the efficiency of carbon dioxide removal from the mixed gas.

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.

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

(Synthesis Example 1: Tris(3-aminopropyl)phosphine oxide)
In a 1L stainless steel autoclave equipped with a stirrer, thermometer, inlet pump, safety valve, and gas inlet pipe, 150ml of toluene and 133g (2.33 mol) of allylamine were charged. The autoclave was then purged three times with nitrogen gas and vacuum, and 22g (0.65 mol) of phosphine gas manufactured by Nippon Chemical Industrial Co., Ltd. with a purity of 99.9% was charged. At this time, when the temperature was raised to 80°C using a water bath, the gauge pressure was 0.93 MPa (absolute pressure 1.03 MPa).
Next, 1.06 g (0.006 mol) of azobisisobutyronitrile was dissolved in 150 ml of toluene, injected in stages over 6 hours, and aged overnight at 80°C. At this time, the gauge pressure was 0.01 MPa (absolute pressure 0.11 MPa). After aging overnight, the mixture was cooled to room temperature, the remaining gas was exhausted into a decontamination system, and the system was further purged with nitrogen gas and vacuum. Finally, 585 g of a colorless, transparent liquid was obtained by withdrawing it into a vacuum-reduced round-bottom flask.
Next, the resulting colorless, transparent liquid was heated under reduced pressure (gauge pressure 4 kPa (absolute pressure 105.3 kPa), 80°C) to remove excess allylamine and toluene. The vacuum and temperature were then increased and the mixture was heated further (gauge pressure 0.2 kPa (absolute pressure 101.5 kPa), 160°C). When the initial distillate began to form, the heating was stopped, and the residue in the pot was used as the product.
The obtained product was cooled to room temperature and then purged with nitrogen gas to obtain 120 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); -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 ), 4.67ppm (s, 6H, -NH ₂ )
As a result, it was confirmed to be tris(3-aminopropyl)phosphine.

Next, a 1 L four-necked flask equipped with a stirrer and thermometer was purged with nitrogen gas, and 92.4 g (0.45 mol) of the obtained tris(3-aminopropyl)phosphine and 500 ml of pure water were charged in. 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 following the addition of the solution, it 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); 60.77 ppm
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.

(Synthesis example 2: Tributyl(3-aminopropyl)phosphonium/β-alanine)
1500 ml of ion exchange resin (Organo Corporation, Amberlite IRA400J Cl, exchange capacity 1.4 equivalents/resin volume L) was packed into a glass column (inner diameter 65 mmφ x length 500 mm), and 1000 ml of an aqueous solution containing 80 g (2.0 mol) of sodium hydroxide was flowed from above using a tube pump at a rate of SV = 1.0. Pure water was then flowed until the effluent became neutral.
Next, an aqueous solution of 140.0 g (0.41 mol) of tributyl(3-aminopropyl)phosphonium bromide dissolved in 500 ml of pure water was flowed from the top of the column at a rate of SV = 1.0, and then 1000 ml of pure water was flowed through it to obtain 1550 g of an aqueous solution of tributyl(3-aminopropyl)phosphonium hydroxide. Neutralization titration was performed with 1/10 N hydrochloric acid titration solution, resulting in a concentration of 6.5% and a yield of 89.0%.
500 g (0.12 mol) of the obtained aqueous solution of tributyl(3-aminopropyl)phosphonium hydroxide was dissolved in 10.7 g (0.12 mol) of β-alanine at room temperature. The resulting mixed aqueous solution was concentrated under reduced pressure using an evaporator, and the methanol solution, which was mixed with methanol, was dehydrated overnight with anhydrous magnesium sulfate. The dehydrated methanol solution was then concentrated under reduced pressure using an evaporator to obtain 41.4 g (crude yield 99.0%) of a colorless, transparent viscous liquid with a viscosity (25°C) of 288 cP. The NMR identification data of the obtained colorless, transparent viscous liquid is as follows.
(Identification data)
^31P -NMR; 34.34ppm
¹ H-NMR; 0.80 ppm (t, 9H, -CH ₃ ), 1.31 to 1.45 ppm (m, 12H, -CH ₂ -), 1.54 to 1.59 ppm (m, 2H, -CH ₂ -) 2.03 to 2.08 ppm (m, 8H, P-CH ₂ -), 2.19ppm (t, 2H, -CH ₂ -COO), 2.58, 2.69ppm (t, 2H, -CH ₂ -NH ₂ ), 3.20, 3.21ppm (s, -NH ₂ )
As a result, it was confirmed to be tributyl(3-aminopropyl)phosphonium β-alanine.

(Example 1)
38.0 g (0.172 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 70.0 g of silica gel (CARiACT Q-30, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 ^m² /g, average pore size 30 nm) was added. The mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 108.9 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1, carbon dioxide absorption test 2, and regeneration test 1, which will be described later.

(Example 2)
28.7 g (0.13 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 85.0 g of silica gel (CARiACT Q-30, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 ^m² /g, average pore size 30 nm) was added. The mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 114.3 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 25.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 3)
33.2 g (0.15 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 40.6 g of silica gel (CARiACT Q-30, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 ^m² /g, average pore size 30 nm) was added. The mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 74.3 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 45.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 4)
33.2 g (0.15 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 54.2 g of silica gel (CARiACT Q-30, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 ^m² /g, average pore size 30 nm) was added. The mixture was left to stand at room temperature until the silica gel was permeable to moisture. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 87.4 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 38.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 5)
33.2 g (0.15 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 61.7 g of silica gel (CARiACT Q-50, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 80 ^m² /g, average pore size 50 nm) was added. The mixture was left to stand at room temperature until the silica gel was permeable to moisture. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 95.0 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 6)
33.2 g (0.15 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 54.2 g of silica gel (CARiACT Q-50, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 80 ^m² /g, average pore size 50 nm) was added. The mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 87.5 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 38.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 7)
33.2 g (0.15 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 300 ml of pure water, and 49.8 g of silica gel (CARiACT Q-50, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 80 ^m² /g, average pore size 50 nm) was added. The mixture was left to stand at room temperature until the silica gel was permeable to moisture. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 83.2 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 40.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2, which will be described later.

(Example 8)
22.1 g (0.1 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 200 ml of pure water and added to 192.5 g of granular activated carbon Shirasagi G2c (manufactured by Osaka Gas Chemical Co., Ltd.) with a particle size of 4-8 mesh at room temperature. While rotating in an evaporator, the vacuum was gradually increased and the water was completely removed until the weight became constant, yielding 214.6 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the activated carbon. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 10.3% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1 described later.

(Example 9)
22.1 g (0.1 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 100 ml of pure water. Then, 51.6 g of powdered silica gel (CARPLEX BS-510BX, manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 m²/g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) was added, and the mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 74.0 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 30.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 3, which will be described later.

(Example 10)
22.1 g (0.1 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 100 ml of pure water. Then, 33.2 g of powdered silica gel (CARPLEX BS-510BX, manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 ^m² /g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) was added, and the mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 55.9 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 40.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 3, which will be described later.

(Example 11)
22.1 g (0.1 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 100 ml of pure water. Then, 27.0 g of powdered silica gel (CARPLEX BS-510BX, manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 ^m² /g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) was added, and the mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 49.8 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 45.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 3, which will be described later.

(Example 12)
22.1 g (0.1 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in 100 ml of pure water. Then, 18.1 g of powdered silica gel (CARPLEX BS-510BX, manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 ^m² /g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) was added, and the mixture was left to stand at room temperature until moisture permeated the silica gel. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 40.5 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 55.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 3, which will be described later.

(Example 13)
The tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in pure water to obtain a 40% aqueous solution of tris(3-aminopropyl)phosphine oxide.
Next, a mixture of 52% by mass of powdered silica gel (CARPLEX BS-510BX manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 ^m² /g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) used in Example 9 and 48% by mass of clay mineral containing alumina was uniformly kneaded, then cut into 5 mm square dies and fired at 500°C to obtain die-shaped pellets which are composites of alumina and mesoporous silica.
4.97 g of the obtained diced pellets were immersed in a 40% aqueous solution of tris(3-aminopropyl)phosphine oxide (6.73 g), and then the water was completely removed using an evaporator to obtain 7.66 g of carbon dioxide absorbent in which tris(3-aminopropyl)phosphine oxide was impregnated onto a composite of alumina and mesoporous silica. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 4, which will be described later.

(Example 14)
The tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in pure water to obtain a 35% aqueous solution of tris(3-aminopropyl)phosphine oxide.
Next, a mixture of 52% by mass of powdered silica gel (CARPLEX BS-510BX manufactured by Evonik Japan Co., Ltd., average particle size 10.5 μm, BET specific surface area 290 ^m² /g, average pore diameter 10 nm, pore volume 1.5 ^cm³ /g) used in Example 9 and 48% by mass of clay mineral containing alumina was uniformly kneaded. The mixture was then extruded using a φ3 mm 200-cell mold (lattice 1.4 mm, slit width 0.4 mm, pitch 1.8 mm) and fired at 500°C to obtain a honeycomb-shaped molded product with a diameter of φ30 × t15 mm, which is a composite of alumina and mesoporous silica.
The resulting honeycomb-shaped molded product (3.93 g per piece) was immersed overnight in a 35% aqueous solution of tris(3-aminopropyl)phosphine oxide, and then vacuum-dried at 100°C using a vacuum oven to completely remove moisture, thereby obtaining 5.89 g of carbon dioxide absorbent in which tris(3-aminopropyl)phosphine oxide was impregnated onto a composite of alumina and mesoporous silica. The impregnation rate of tris(3-aminopropyl)phosphine oxide relative to the total mass of the carbon dioxide absorbent was 33.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 5 and regeneration test 2, which will be described later.

(Reference example 1)
30.2 g (0.086 mol) of tributyl(3-aminopropyl)phosphonium-β-alanine obtained in Synthesis Example 2 was dissolved in 300 ml of pure water, and 55.9 g of silica gel (CARiACT Q-30, manufactured by Fuji Silysia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 ^m² /g, average pore size 30 nm) was added. The mixture was left to stand at room temperature until the silica gel was permeable to moisture. The mixture was concentrated under reduced pressure using an evaporator, and the added water was completely removed by distillation to obtain 86.3 g of carbon dioxide absorbent with tributyl(3-aminopropyl)phosphonium-β-alanine impregnated onto the silica gel. The impregnation rate of tributyl(3-aminopropyl)phosphonium-β-alanine relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1 and carbon dioxide absorption test 2, which will be described later.

(Reference example 2)
34.9 g (0.1 mol) of tributyl(3-aminopropyl)phosphonium-β-alanine obtained in Synthesis Example 2 was dissolved in 150 ml of pure water and added to 287.1 g of granular activated carbon Shirasagi G2c (manufactured by Osaka Gas Chemical Co., Ltd.) with a particle size of 4-8 mesh at room temperature. While rotating in an evaporator, the vacuum was gradually increased and the water was completely removed until the weight became constant, yielding 332.7 g of carbon dioxide absorbent with tributyl(3-aminopropyl)phosphonium-β-alanine impregnated onto the activated carbon. The impregnation rate of tributyl(3-aminopropyl)phosphonium-β-alanine relative to the total mass of the carbon dioxide absorbent was 10.8% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1 described later.

(evaluation)
(Carbon dioxide absorption test 1)
90 ml of the carbon dioxide absorbent obtained in Example 1 and Reference Example 1 was packed into a glass column with an inner diameter of 20 mm and a length of 300 mm, and air (room temperature 25°C, average carbon dioxide concentration: 450 ppm) was passed through it at a flow rate of 100 ml/min using an air pump. The carbon dioxide concentration at the outlet of the glass column was measured and recorded using a data logger carbon dioxide meter (TR-76Ui-S, T&D Corporation), and the time until saturation occurred and the carbon dioxide concentration began to rise (breakthrough time) was determined. The number of moles of absorbed carbon dioxide was calculated by taking the difference between the average carbon dioxide concentration in the room and the average carbon dioxide concentration at the outlet as the amount of carbon dioxide absorbed. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent. The results are shown in Table 1.
The same procedure was also performed on the carbon dioxide absorbents obtained in Example 8 and Reference Example 2, and the results are shown in Table 2.

The results shown in Table 1 indicate that the carbon dioxide absorbent of Example 1 has superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.
Furthermore, the results shown in Table 2 indicate that the carbon dioxide absorbent of Example 8 has superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 2.

(Carbon dioxide absorption test 2)
The carbon dioxide absorbents obtained in Examples 1-7 and Reference Example 1 were placed in 35 ml Erlenmeyer flasks, and their weight was accurately measured 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 measured to the nearest 0.1 mg every 10 minutes. Gas blowing was stopped when the weight became constant . The increase in 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 results are shown in Table 3.

The results shown in Table 3 demonstrate that the carbon dioxide absorbents of Examples 1 to 7 exhibit superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.

(Carbon dioxide absorption test 3)
The carbon dioxide absorbents obtained in Examples 9-12 were placed in 35 ml Erlenmeyer flasks, and the amount was accurately measured to a sensitivity of 0.1 mg. Cotton wool was placed inside to prevent the powdered sample from being carried out of the system by the airflow. 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 measured to a sensitivity of 0.1 mg every 10 minutes. Gas blowing was stopped when the weight became constant . The increase in 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. Furthermore, any remaining carbon dioxide in the cotton wool was expelled with nitrogen gas. The results are shown in Table 4.

The results shown in Table 4 indicate that the carbon dioxide absorbents of Examples 9 to 12 have excellent carbon dioxide absorption performance.

(Carbon dioxide absorption test 4)
The carbon dioxide absorbent obtained in Example 13 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 into the flask at a flow rate of 100 ml/min at room temperature (25°C) for 10 minutes, and the weight was accurately weighed 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. The results are shown in Table 5.

The results shown in Table 5 indicate that the carbon dioxide absorbent of Example 13 exhibits excellent carbon dioxide absorption performance.

(Carbon dioxide absorption test 5)
The carbon dioxide absorbent obtained in Example 14 was placed in a 100 ml glass screw-top bottle, and its weight was accurately measured to the nearest 0.1 mg. 99.995% pure carbon dioxide gas was then blown into the bottle at a flow rate of 100 ml/min at room temperature (25°C) for 10 minutes, and the weight was accurately measured to the nearest 0.1 mg. Furthermore, any remaining carbon dioxide in the screw-top bottle was expelled with nitrogen gas. 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 results are shown in Table 6.

The results shown in Table 6 indicate that the carbon dioxide absorbent of Example 14 exhibits excellent carbon dioxide absorption performance.

(Regeneration Test 1)
The carbon dioxide absorbent obtained in Example 1 was filled into a 190 ml stainless steel clean pipe, and 99.995% pure carbon dioxide gas was passed through it at a flow rate of 500 ml/min for 10 minutes to absorb the carbon dioxide. The weight was measured before and after the gas was passed through, and the increase in weight was taken 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, which had absorbed carbon dioxide, was placed entirely into a 200 mm diameter petri dish and heated for 90 minutes at 120°C and a gauge pressure of 0.2 kPa (absolute pressure of 101 kPa) to expel the carbon dioxide and regenerate the absorbent.
Next, the recycled carbon dioxide absorbent was refilled into the stainless steel clean pipe, and the carbon dioxide absorption and recycling process was repeated five times. The recycling rate was calculated based on the following formula. The results are shown in Table 7.
Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

As shown in Table 7, the carbon dioxide absorbent, after being heated following the initial carbon dioxide absorption test to remove carbon dioxide, regained its carbon dioxide absorption capacity. This demonstrates that even recycled carbon dioxide absorbents exhibit superior absorption performance and a high regeneration rate.

(Regeneration Test 2)
Using the carbon dioxide absorbent obtained in Example 14, carbon dioxide was absorbed by performing the same procedure as in carbon dioxide absorption test 5. The weight was measured before and after ventilation, and the increase in weight was taken 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 was removed from the carbon dioxide absorbent and placed in a stainless steel tray. It was then heated in a vacuum oven at 100°C and a gauge pressure of -0.1 MPa (absolute pressure of 0.001 MPa) for 90 minutes to expel the carbon dioxide and regenerate the absorbent.
Next, the recycled carbon dioxide absorbent was placed back into a 100 ml glass screw-top bottle, and the carbon dioxide absorption and recycling process was repeated twice. The recycling rate was calculated based on the following formula. The results are shown in Table 8.
Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

As shown in Table 8, the results indicate that when carbon dioxide absorbent material is heated after the initial carbon dioxide absorption test to remove carbon dioxide, the regenerated carbon dioxide absorbent material regains its carbon dioxide absorption capacity. This demonstrates that even regenerated carbon dioxide absorbent material exhibits excellent absorption performance and a high regeneration rate.

Claims (8)

The following general formula (1):

(In the formula, a, b, and c represent integers between 1 and 10, and ^R1 , ^R2 , and ^R3 are all amino groups .)
A phosphine oxide compound represented by,
A porous carrier supporting the phosphine oxide compound,
A carbon dioxide absorbent characterized by being composed of the following: The carbon dioxide absorbent according to claim 1, 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 . A method for separating carbon dioxide, characterized by comprising a carbon dioxide separation step of contacting a carbon dioxide absorbent according to claim 1 or 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. A carbon dioxide separation step in which a carbon dioxide absorbent according to claim 1 or 2 is brought into contact 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;
The carbon dioxide absorption process involves heating the carbon dioxide absorption agent that has absorbed carbon dioxide in the carbon dioxide separation process at a temperature of 50°C to 150°C to remove carbon dioxide from the carbon dioxide absorption agent, thereby regenerating the carbon dioxide absorption agent and recovering the removed carbon dioxide.
A method for separating and recovering carbon dioxide, characterized by having the following features. The carbon dioxide separation and recovery method according to claim 4, 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 carbon dioxide is contacted in the carbon dioxide separation step, thereby repeating the carbon dioxide separation step and the carbon dioxide recovery step two or more times. An apparatus characterized by using the carbon dioxide absorbent described in claim 1 or 2. The apparatus according to claim 6 , characterized in that the apparatus is used in a power plant, factory, or transportation equipment. The apparatus according to claim 6 , characterized in that the apparatus is a DAC (Direct Air Capture) apparatus that directly separates and recovers carbon dioxide from the atmosphere .