Phosphine oxide compounds, carbon dioxide absorbent compounds, carbon dioxide absorbents, carbon dioxide separation methods, carbon dioxide separation and recovery methods, and apparatus using carbon dioxide absorbents.

Abstract

To provide a novel trialkylphosphine oxide having an alkyl group to which an amino group is bonded. 【Solution means】The following general formula (1): TIFF2026086685000014.tif60148 (In the formula, a, b, and c are integers of 1 or more and 10 or less, and R 1 , R 2 and R 3 each independently represent a primary amino group, a secondary amino group, or a tertiary amino group, and at least one of R 1 , R 2 and R 3 is a secondary or tertiary amino group.) A phosphine oxide compound represented by the formula.

Description

[Technical Field]

[0001] The present invention relates to phosphine oxide compounds, compounds for carbon dioxide absorbents, carbon dioxide absorbents, carbon dioxide separation methods, carbon dioxide separation and recovery methods, and apparatus using carbon dioxide absorbents. [Background technology]

[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. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-10760 [Patent Document 2] Japanese Patent Application Publication No. 4-39324 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, although the carbon dioxide absorbent described in Patent Document 1 can absorb carbon dioxide at room temperature, there is room for further improvement in its carbon dioxide absorption performance. Furthermore, since it is necessary to recover the absorbed carbon dioxide after it has been absorbed by the carbon dioxide absorbent, good desorption properties of the absorbed carbon dioxide are also required.

[0007] Incidentally, trialkylphosphine oxides having an alkyl group to which a primary amino group is bonded are used, for example, as curing agents for epoxy resins. Patent Document 2 discloses a curing agent for epoxy resins containing an aminoalkylphosphine oxide as an active ingredient.

[0008] Because such trialkylphosphine oxides have a phosphine oxide structure (α3P=O, where α is more alkyl even if it has substituents) and an amino group (-NH2) within their molecule, they are expected to have various applications other than as curing agents for epoxy resins.

[0009] Furthermore, when developing trialkylphosphine oxides, which have an alkyl group to which a primary amino group is bonded, for various applications, specific effects derived from the amino group can be expected. On the other hand, it is also anticipated that problems caused by the amino group may arise depending on the application. Therefore, the development of novel trialkylphosphine oxides tailored to specific applications is desired, along with the development of applications for trialkylphosphine oxides.

[0010] Furthermore, depending on the application of trialkylphosphine oxide, oxidation stability may be required. Generally, amino groups (-NH2) are easily oxidized, so it is presumed that trialkylphosphine oxides with enhanced oxidation resistance will be required in such applications.

[0011] Therefore, the objective of the present invention is to solve at least one of the following problems. In other words, the object of the present invention is to provide a novel trialkylphosphine oxide having an alkyl group to which an amino group is bonded. Furthermore, an object of the present invention is to provide a compound for carbon dioxide absorbent and a carbon dioxide absorbent that exhibits excellent carbon dioxide absorption performance. Furthermore, an object of the present invention is to provide a carbon dioxide separation method, a carbon dioxide separation and recovery method using the above-mentioned carbon dioxide absorbent, and an apparatus using the carbon dioxide absorbent. [Means for solving the problem]

[0012] In view of the above circumstances, the present inventors conducted extensive research and found that by using an alkyl group in trialkylphosphine oxide to which a secondary or tertiary amino group is attached, that is, by using a phosphine oxide compound represented by the following general formula (1), (1) it exhibits superior carbon dioxide absorption performance compared to conventional compounds, (2) it has good carbon dioxide desorption properties after absorption, and (3) it has excellent heat resistance, thus completing the present invention.

[0013] [ka]

[0014] (In the formula, a, b, and c represent integers between 1 and 10, and R 1 , R 2 and R 3 Each of these independently represents a primary amino group, a secondary amino group, or a tertiary amino group, and R 1 , R 2 and R 3 At least one of them is a secondary or tertiary amino group.

[0015] In other words, the present invention (1) is the following general formula (1):

[0016] [ka]

[0017] (In the formula, a, b, and c represent integers of 1 or more and 10 or less, and R 1 , R 2 and R 3 each independently represent a primary amino group, a secondary amino group, or a tertiary amino group, and at least one of R 1 , R 2 and R 3 is a secondary amino group or a tertiary amino group.) The present invention provides a phosphine oxide compound characterized by being represented by

[0018] Further, the present invention (2) provides a compound for a carbon dioxide absorbent, characterized by being the phosphine oxide compound of the present invention (1).

[0019] Further, the present invention (3) provides a carbon dioxide absorbent characterized by containing the compound for a carbon dioxide absorbent of the present invention (2).

[0020] Further, the present invention (4) provides a carbon dioxide separation method characterized by having a carbon dioxide separation step of bringing a mixed gas containing carbon dioxide into contact with the carbon dioxide absorbent of the present invention (3) to absorb carbon dioxide in the mixed gas into the carbon dioxide absorbent, thereby separating carbon dioxide from the mixed gas.

[0021] Further, the present invention (5) provides a carbon dioxide separation and recovery method characterized by having a carbon dioxide separation step of bringing a mixed gas containing carbon dioxide into contact with the carbon dioxide absorbent of the present invention (3) to absorb carbon dioxide in the mixed gas into the carbon dioxide absorbent, thereby separating carbon dioxide from 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 30°C or higher and 150°C or lower to desorb carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

[0022] Furthermore, the present invention (6) provides an apparatus characterized in that the carbon dioxide absorbent of the present invention (3) is used. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a novel trialkylphosphine oxide having an alkyl group to which an amino group is bonded. Furthermore, according to the present invention, it is possible to provide a novel trialkylphosphine oxide having an alkyl group to which an amino group is bonded, and exhibiting excellent oxidation resistance. Furthermore, according to the present invention, it is possible to provide a compound for carbon dioxide absorbent and a carbon dioxide absorbent that have excellent carbon dioxide absorption performance. Furthermore, according to the present invention, in addition to the carbon dioxide absorption performance described above, it is possible to provide a carbon dioxide absorbent compound and a carbon dioxide absorbent that have excellent oxidation resistance and thus excellent durability for repeated absorption and regeneration. Furthermore, according to the present invention, in addition to the carbon dioxide absorption performance described above, it is possible to provide a carbon dioxide absorbent that can easily release carbon dioxide when the absorbent is regenerated. Furthermore, according to the present invention, it is possible to provide a carbon dioxide separation method using the above-mentioned carbon dioxide absorbent, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorbent. [Modes for carrying out the invention]

[0024] The present invention will be described below based on preferred embodiments. The phosphine oxide compound of the present invention is given by the following general formula (1):

[0025] [ka]

[0026] (In the formula, a, b, and c represent integers between 1 and 10, and R 1 , R 2and R 3 Each of these independently represents a primary amino group, a secondary amino group, or a tertiary amino group, and R 1 , R 2 and R 3 At least one of them is a secondary or tertiary amino group. It is a phosphine oxide compound represented by [formula].

[0027] The phosphine oxide compound represented by general formula (1) has three alkyl groups to which an amino group is bonded at the P of the phosphine oxide structure (P=O). At least one of these three alkyl groups to which an amino group is bonded is an alkyl group to which a secondary or tertiary amino group is bonded. Alkyl groups to which a secondary or tertiary amino group is bonded have superior oxidation resistance compared to alkyl groups to which a primary amino group is bonded. Furthermore, when phosphine oxide compounds represented by general formula (1) are used for carbon dioxide absorption, alkyl groups to which secondary or tertiary amino groups are attached exhibit superior desorption of absorbed carbon dioxide compared to alkyl groups to which primary amino groups are attached, enabling desorption of carbon dioxide at low temperatures. In addition, phosphine oxide compounds represented by general formula (1) have a phosphine oxide structure (P=O), resulting in high heat resistance. When used as a carbon dioxide absorbent, the vapor pressure is low in the heating temperature range during regeneration after carbon dioxide absorption, for example, in the heating temperature range of 30°C to 150°C, and they have almost no volatility.

[0028] 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 composition. In the present invention, it is particularly preferable that a, b, and c are each 3 from the viewpoint of industrial availability.

[0029] R in general formula (1) 1 , R 2 and R 3Each independently represents a primary amino group (-NH2), a secondary amino group (-NH-β, where β represents an optionally substituted alkyl group), or a tertiary amino group (-Nβ2, where β represents an optionally substituted alkyl group). And R 1 , R 2 and R 3 At least one of them is a secondary amino group or a tertiary amino group. 1 , R 2 and R 3 In terms of excellent oxidation resistance, and when used as a carbon dioxide absorbent, further, in terms of excellent desorption of absorbed carbon dioxide, a secondary amino group or a tertiary amino group is preferred, with a secondary amino group being particularly preferred. Also, in general formula (1), in terms of excellent oxidation resistance, and when used as a carbon dioxide absorbent, further, in terms of excellent desorption of absorbed carbon dioxide, R 1 , R 2 and R 3 Preferably, all of them are secondary or tertiary amino groups, R 1 , R 2 and R 3 It is particularly preferable that all of them be secondary amino groups. Also, in general formula (1), R 1 , R 2 and R 3 One or two of these may be primary amino groups, but the phosphine oxide compound represented by general formula (1) is preferable to have fewer primary amino groups, and is particularly preferable to have no primary amino groups, in terms of excellent oxidation resistance and, when used as a carbon dioxide absorbent, even better in terms of excellent desorption of absorbed carbon dioxide. 1 , R 2 and R 3 These components may be identical or different, but it is preferable that they be identical from the viewpoint of facilitating synthesis.

[0030] R 1 , R 2 and R 3A secondary amino group is an amino group to which one hydrogen atom and one substituent are bonded, and a tertiary amino group is an amino group to which two substituents are bonded. Substituents bonded to a secondary or tertiary amino group include alkyl groups, alkyl groups with functional groups, cycloalkyl groups, alkyl halides, alkoxy groups, halogen atoms, and other substituents. A cyclic amino group is also included in the tertiary amino group. Functional groups in alkyl groups with functional groups include hydroxyl groups, amino groups, carboxyl groups, mercapto groups, amide groups, carboxymethyl groups, carboxyethyl groups, sulfonic acid groups, and the like. In the present invention, from the viewpoint of oxidation resistance, R 1 , R 2 and R 3 The secondary or tertiary amino group relating to this is preferably an amino group whose substituent is an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 10 carbon atoms with a hydroxyl group, and more preferably an amino group whose substituent is an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms with a hydroxyl group. Note that alkyl groups include linear alkyl groups, branched alkyl groups and cyclic alkyl groups.

[0031] Examples of branched alkyl groups having 1 to 10 carbon atoms include isopropyl group, isobutyl group, s-butyl group, t-butyl group, isopentyl group, s-pentyl group, t-pentyl group, isohexyl group, s-hexyl group, t-hexyl group, and ethylhexyl group. In the present invention, isopropyl group is more preferred from the viewpoint of ease of synthesis.

[0032] Examples of the cyclic alkyl group having 1 to 10 carbon atoms include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, 2-methylcyclopentyl group, 3-methylcyclopentyl group, cycloheptyl group, 2-methylcyclohexyl group, 3-methylcyclohexyl group, 4-methylcyclohexyl group, cyclooctyl group, 2-methylcycloheptyl group, 3-methylcycloheptyl group, 4-methylcycloheptyl group, and 5-methylcycloheptyl group. In the present invention, the cyclohexyl group is more preferred from the viewpoint of ease of synthesis.

[0033] When the phosphine oxide compound of the present invention is used as a carbon dioxide absorbent, it can exhibit excellent carbon dioxide absorption performance. Furthermore, even when the absorbent is regenerated by desorbing the absorbent carbon dioxide, its carbon dioxide absorption capacity is restored, resulting in a regenerated carbon dioxide absorbent with excellent carbon dioxide absorption performance. Therefore, in the general formula (1), R 1 , R 2 and R 3 It is preferable that the substituent is an amino group having a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an ethanol group, an n-propanol group, or an isopropanol group, and it is particularly preferable that the substituent is an amino group having a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an ethanol group, or an isopropanol group.

[0034] Examples of phosphine oxide compounds represented by general formula (1) include tris(3-(N-ethylaminopropyl))phosphine oxide, tris(3-(N-methylaminopropyl))phosphine oxide, tris(3-(N-(n-propyl)aminopropyl))phosphine oxide, tris(3-(N-isopropylaminopropyl))phosphine oxide, tris(3-(N-ethanolaminopropyl))phosphine oxide, and tris(3-(N-(n-propanol)aminopropyl) Examples include tris(3-(N-isopropanolaminopropyl))phosphine oxide, bis(3-(N-ethylaminopropyl))(3-aminopropyl)phosphine oxide, bis(3-aminopropyl)(3-(N-ethylaminopropyl))phosphine oxide, bis(3-(N-methylaminopropyl))(3-aminopropyl)phosphine oxide, and bis(3-aminopropyl)(3-(N-methylaminopropyl))phosphine oxide.

[0035] The carbon dioxide absorbent compound of the present invention is given by the following general formula (1):

[0036] [ka]

[0037] (In the formula, a, b, and c represent integers between 1 and 10, and R 1 , R 2 and R 3 Each of these independently represents a primary amino group, a secondary amino group, or a tertiary amino group, and R 1 , R 2 and R 3 At least one of them is a secondary or tertiary amino group. This compound for carbon dioxide absorbers is characterized by being a phosphine oxide compound represented by [formula].

[0038] The carbon dioxide absorbent compound of the present invention can absorb carbon dioxide through the reaction of a primary, secondary, or tertiary amino group of a phosphine oxide compound represented by general formula (1) with carbon dioxide. In other words, the phosphine oxide compound of the present invention is a carbon dioxide absorbent compound used as a substance for absorbing carbon dioxide in a carbon dioxide absorbent. The phosphine oxide compound represented by general formula (1) relating to the carbon dioxide absorbent compound of the present invention is the same as the phosphine oxide compound represented by general formula (1) relating to the phosphine oxide compound of the present invention, except as described below.

[0039] 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 phosphine oxide compound of the present invention.

[0040] Examples of phosphine oxide compounds represented by general formula (1) used in the carbon dioxide absorbent of the present invention include tris(3-(N-ethylaminopropyl))phosphine oxide, tris(3-(N-methylaminopropyl))phosphine oxide, tris(3-(N-(n-propyl)aminopropyl))phosphine oxide, tris(3-(N-isopropylaminopropyl))phosphine oxide, tris(3-(N-ethanolaminopropyl))phosphine oxide, and tris(3-(N-(n-propano Examples include (3-(N-isopropanolaminopropyl))phosphine oxide, tris(3-(N-ethylaminopropyl))(3-aminopropyl)phosphine oxide, bis(3-(3-(N-ethylaminopropyl))(3-(3-)ethylaminopropyl))phosphine oxide, bis(3-(N-methylaminopropyl))(3-aminopropyl)phosphine oxide, and bis(3-aminopropyl)(3-(N-methylaminopropyl))phosphine oxide.

[0041] The phosphine oxide compound represented by general formula (1) used in the carbon dioxide absorbent of the present invention is R 1 , R 2 and R 3 A compound in which both of the groups are secondary amino groups is preferable because it has excellent oxidation resistance, is highly durable in repeated absorption and desorption of carbon dioxide, and is highly effective in desorbing absorbed carbon dioxide. Among the phosphine oxide compounds represented by general formula (1), R 1 , R 2 and R 3 Examples of compounds in which all of the groups are secondary amino groups include tris(3-(N-ethylaminopropyl))phosphine oxide, tris(3-(N-methylaminopropyl))phosphine oxide, tris(3-(N-(n-propyl)aminopropyl))phosphine oxide, tris(3-(N-isopropylaminopropyl))phosphine oxide, tris(3-(N-ethanolaminopropyl))phosphine oxide, tris(3-(N-propanol)aminopropyl))phosphine oxide, and tris(3-(N-isopropanolaminopropyl))phosphine oxide.

[0042] The carbon dioxide absorbent of the present invention may contain two or more compounds for carbon dioxide absorbent of the present invention. That is, the carbon dioxide absorbent of the present invention may contain two or more phosphine oxide compounds represented by general formula (1). For example, the carbon dioxide absorbent of the present invention may contain, among the phosphine oxide compounds represented by general formula (1), R 1 , R 2 and R 3 Both of these have secondary amino groups, and R 1 , R 2 and R 3 A mixture of two secondary amino groups and one primary amino group, or a phosphine oxide compound represented by general formula (1), R 1 , R 2 and R 3 Both of these have secondary amino groups, and R 1 , R 2 and R 3 Two of them are secondary amino groups and one is a primary amino group, and R 1 , R 2 and R 3 A mixture in which one of the groups is a secondary amino group and the other two are primary amino groups, or R 1 , R 2 and R 3Examples include mixtures in which one or all of a, b, and c are different from the others, or mixtures in which one or all of a, b, and c are different from the others. Examples of mixtures of two or more phosphine oxide compounds represented by general formula (1) include tris(3-(N-ethylaminopropyl))phosphine oxide, tris(3-(N-methylaminopropyl))phosphine oxide, tris(3-(N-(n-propyl)aminopropyl))phosphine oxide, tris(3-(N-isopropylaminopropyl))phosphine oxide, tris(3-(N-ethanolaminopropyl))phosphine oxide, and tris(3-(N-(n-propanol)aminopropyl)) Examples include mixtures of two or more substances selected from the group consisting of sphingoxide, tris(3-(N-isopropanolaminopropyl))phosphine oxide, bis(3-(N-ethylaminopropyl))(3-aminopropyl)phosphine oxide, bis(3-aminopropyl)(3-(N-ethylaminopropyl))phosphine oxide, bis(3-(N-methylaminopropyl))(3-aminopropyl)phosphine oxide, and bis(3-aminopropyl)(3-(N-methylaminopropyl))phosphine oxide.

[0043] In the carbon dioxide absorbent of the present invention, the proportion of primary amino groups among the total amino groups of the phosphine oxide compound represented by general formula (1) is preferably 50 mol% or less, more preferably 30 mol% or less, and particularly preferably 0.0 mol%, in terms of excellent oxidation resistance. 1 It can be determined by 1H-NMR.

[0044] 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 exist supported on a carrier, dissolved in an aqueous solvent, or as a mixture with a soluble organic solvent or amine compound.

[0045] 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. In the carbon dioxide absorbent of the present invention, the liquid phosphine oxide compound represented by general formula (1) is taken into the pores of the porous carrier and physically adsorbed, so that the phosphine oxide compound represented by general formula (1) is supported on the porous carrier.

[0046] 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, a composite of alumina and silica gel, and a composite 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 carrier 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 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 carrier, 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 capable of containing water at a water content of 5 to 30% by mass, preferably 10 to 25% by mass.

[0047] The BET specific surface area of ​​the porous carrier is preferably 1.0 × 10⁻⁶. 1 ~5.0×10 3 m 2 / g, preferably 1.0 × 10 2 ~2.0×10 3 m 2 The volume is / g. Furthermore, the pore volume of the porous carrier obtained by gas adsorption is preferably 0.1 to 2.0 mL / g, and preferably 0.3 to 1.5 mL / g.

[0048] 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.

[0049] Among porous supports, activated carbon, silica gel, mesoporous silica, zeolite, molecular sieve, alumina-silica gel composite, and alumina-mesoporous silica composite are preferred from the viewpoint of ease of handling and the ability to easily support liquid phosphine oxide compounds represented by general formula (1), with activated carbon and silica gel being particularly preferred.

[0050] Various types of activated carbon can be used as the activated carbon in the present invention, for example, activated carbon made from wood, coconut shells, coal, petroleum pitch, coke, coal tar, etc. The activated carbon may also be a molded body. In addition to the characteristics of the porous carrier described above, the activated carbon preferably has the following physical properties 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 performance of 14.0 to 41.0%, an iodine adsorption performance of 600 to 2600 mg / g, and a hardness of 90.0 to 100.0%.

[0051] Various types of silica gel can be used in the present invention, and for example, those containing 99% by mass or more, and particularly 99.9% by mass or more, of silicon dioxide are preferred. The silica gel may be a molded body. In addition to the porous carrier properties described above, the silica gel preferably has an average particle size of 0.01 to 10 mm as measured by a scanning electron microscope, and preferably has a drying loss of 10% or less.

[0052] 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, and BEA-type zeolite. 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.

[0053] 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.

[0054] The impregnation 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 50% by mass, more preferably 20 to 40% by mass, relative to the total carbon dioxide absorbent. By having the amount of phosphine oxide 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.

[0055] 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. As a result, carbon dioxide can be absorbed more efficiently when the temperature of the carbon dioxide absorbent is between -20°C and 50°C, and the carbon dioxide is easily desorbed, making it easy to regenerate the carbon dioxide absorbent.

[0056] Because the carbon dioxide absorbent of the present invention is spread out on 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.

[0057] Since the carbon dioxide absorbent of the present invention is supported on a solid carrier, it can be used by filling columns or reaction towers. Furthermore, compared to liquid carbon dioxide absorbents, the carbon dioxide absorbent of the present invention forms appropriate gaps when filled into columns or reaction towers, allowing for more efficient contact with carbon dioxide or carbon dioxide-containing gases.

[0058] 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.

[0059] 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) 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 used in various devices such as equipment used in power plants, factories, and transportation equipment, as well as DAC devices.

[0060] 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.

[0061] The present invention relates to 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 causing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas.

[0062] 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 30°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.

[0063] 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 same carbon dioxide separation step (A) in both cases.

[0064] 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.

[0065] 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.

[0066] 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 from the viewpoint of more efficient carbon dioxide absorption, it is preferable that the temperature be between -20°C and 50°C, preferably between -10°C and 30°C, and more preferably around room temperature of 25°C.

[0067] The pressure (absolute pressure) in the carbon dioxide separation process (A) is not particularly limited and can be carried out under atmospheric pressure.

[0068] 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.

[0069] 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.

[0070] The carbon dioxide recovery process (B) may include, for example, a method in which, after performing the carbon dioxide separation process (A), the carbon dioxide absorbent packed in the absorbent-packed column or absorbent-packed tower is heated to regenerate the carbon dioxide absorbent and recover the desorbed carbon dioxide.

[0071] In the carbon dioxide recovery process (B), the heating temperature of the carbon dioxide absorbent is 30°C to 150°C, preferably 30°C to 120°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 30°C to 150°C, preferably 30°C to 120°C, and at a temperature equivalent to or higher than the temperature of the carbon dioxide separation process (A). For example, if the carbon dioxide absorbent is the carbon dioxide absorbent of the present invention, carbon dioxide can be released even if the heating temperature is 30°C to 80°C, preferably 30°C to 70°C, and more preferably 30°C to 60°C. Therefore, the required thermal energy can be reduced. Furthermore, waste heat from factories such as chemical plants, waste treatment facilities, and steel mills can be utilized.

[0072] In the carbon dioxide recovery process (B), the pressure (absolute pressure) is not particularly limited and may be carried out in air (at atmospheric pressure) or under reduced pressure. Carrying it out in air (at atmospheric pressure) eliminates the need for a degassing device. When carried out under reduced pressure, the pressure (absolute pressure) is preferably 150 kPa or less, more preferably 110 kPa or less, from the viewpoint of more easily preventing oxidation of the carbon dioxide absorbent, and further preferably 50 kPa or less, particularly 30 kPa or less, from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent.

[0073] 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.

[0074] In the carbon dioxide separation and recovery method of the present invention, by using a carbon dioxide absorbent in which the carbon dioxide absorbent compound of the present invention is supported on a porous carrier, the carbon dioxide recovery step (B) can be performed in air (at atmospheric pressure) at a heating temperature of 30°C to 80°C, preferably 30°C to 70°C, and more preferably 30°C to 60°C. Therefore, it is extremely useful in that it can reduce the energy costs required for carbon dioxide recovery. Furthermore, since carbon dioxide can be degassed in air, a degassing device is unnecessary, and since carbon dioxide can be degassed at a relatively low temperature, waste heat from factories such as chemical plants, waste treatment facilities, and steel mills can be utilized.

[0075] 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 has excellent chemical absorption properties, is used for carbon dioxide absorption, thereby increasing the efficiency of carbon dioxide removal from the mixed gas.

[0076] 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. [Examples]

[0077] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0078] (Synthesis example 1: 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 × 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) 31 P-NMR; 34.34 ppm 1 H-NMR;0.80ppm(t,9H,-CH3),1.31~1.45ppm(m,12H,-CH2-),1.54~1.59ppm(m,2H,-CH2-),2.03~2.08p pm(m,8H,P-CH2-),2.19ppm(t,2H,-CH2-COO),2.58,2.69ppm(t,2H,-CH2-NH2),3.20,3.21ppm(s,-NH2) As a result, it was confirmed to be tributyl(3-aminopropyl)phosphonium·β-alanine.

[0079] (Synthesis example 2: 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 added. 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, and it was divided and press-fitted over 6 hours and aged overnight at 80°C. At this time, the pressure showed a gauge pressure of 0.01 MPa (absolute pressure 0.11 MPa). After aging overnight, it was cooled to room temperature, the residual gas was exhausted to the exhaust equipment, and the system was further purged with nitrogen gas and vacuum. 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, and the degree of vacuum and temperature were further 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 bottom residue was used as the product. After cooling the obtained product to room temperature and purging 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 (D2O); -29.73 ppm 1 H-NMR (D2O); 1.40~1.46 ppm (m, 6H, -CH2-), 1.52~1.61 ppm (m, 6H, P-CH2-), 2.63~2.71 ppm (m, 6H, -CH2-NH2), 4.67 ppm (s, 6H, -NH2) As a result, it was confirmed to be tris(3-aminopropyl)phosphine. Next, a 1 L four-necked flask equipped with a stirrer and a 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, 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 after the dropwise addition, it was cooled to room temperature and concentrated under reduced pressure with an evaporator to remove water, and 100.8 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 (D2O); 60.77 ppm 1 H-NMR(D2O); 1.50~1.58ppm(m, 6H, -CH2-), 1.71~1.77ppm(m, 6H, P-CH2-), 2.57~2.60ppm(t, 6H, -CH2-NH2), 4.70ppm(s, 6H, -NH2) As a result, it was confirmed to be tris(3-aminopropyl)phosphine oxide.

[0080] (Example 1) Synthesis of Tris(3-(N-ethylaminopropyl))phosphine oxide In a 1 L four-necked flask equipped with a stirrer, thermometer, and dropping funnel, 44.3 g (0.2 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 and 200 ml of pure water were charged and heated to 60-65°C. Furthermore, 98.1 g (0.9 mol) of ethyl bromide was gradually added dropwise, taking care not to cause excessive reflux. After aging for 1 hour, the mixture was cooled to room temperature, and the pH was confirmed to be neutral using pH test paper. By concentrating under reduced pressure using an evaporator to remove water, 108.0 g (crude yield 98.5%) of a slightly yellowish transparent liquid was obtained. The NMR identification data of the obtained slightly yellowish transparent liquid is as follows. (Identification data) 31 P-NMR (D2O); 57.06 ppm 1 H-NMR(D2O); 1.12~1.14ppm(t, 9H, -CH3), 1.75~1.85ppm(m, 6H, -CH2-), 1.85~1.93ppm(m, 6H, P-CH2-), 2.94~3.12ppm(m, 12H, -CH2-N + H2-CH2-), 4.65ppm(s, 6H, -N + H2-) As a result, it was confirmed to be tris(3-(N-ethylaminopropyl))phosphine oxide 3-hydrobromide. Next, 82.2 g (0.15 mol) of tris(3-(N-ethylaminopropyl))phosphine oxide·3 hydrobromide and 200 ml of ethanol were charged into a 1 L four-necked flask equipped with a stirrer and a thermometer, and 153.1 g (0.45 mol) of sodium ethylate (20% ethanol solution) was added and stirred at room temperature. Gradually, a white precipitate formed and the solution became turbid. After stirring for 1 hour, it was filtered off with a Buchner funnel lined with a ethanol slurry of filter aid celite (Hyflo Supercel, Fujifilm Wako Pure Chemical Corporation), and the ethanol was concentrated with an evaporator to obtain 43.5 g of a slightly yellow liquid (crude yield 95.0%). The NMR identification data of the obtained slightly yellow transparent liquid is as follows. (Identification data) 31 P-NMR (D2O); 60.61 ppm 1 H-NMR (D2O); 0.89~0.93 ppm (m, 9H, -CH3), 1.50~1.60 ppm (m, 6H, -CH2-), 1.65~1.68 ppm (m, 6H, P-CH2-), 2.40~2.58 ppm (m, 12H, -CH2-NH-CH2-), 4.68 ppm (s, 6H, -NH-) As a result, it was confirmed that it was tris(3-(N-ethylaminopropyl))phosphine oxide.

[0081] (Example 2) Synthesis of a mixture mainly composed of tris(3-(N-ethylaminopropyl))phosphine oxide 44.3 g (0.2 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 and 200 ml of ethanol were charged into a 1 L four-necked flask equipped with a stirrer, a thermometer, and a dropping funnel, and heated to 60~65 °C. Further, 98.1 g (0.9 mol) of ethyl bromide was gradually dropped so that the reflux did not become violent. After aging for 1 hour, it was cooled to room temperature, and it was confirmed with pH test paper that the pH was weakly basic. Ethanol was removed by concentrating under reduced pressure with an evaporator to obtain 97.6 g of tris(3-(N-ethylaminopropyl))phosphine oxide·3 hydrobromide, which is a slightly yellow transparent liquid (crude yield 89.0%). Next, 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 × 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. Then, pure water was flowed until the effluent became neutral. 54.8 g (0.1 mol) of the obtained tris(3-(N-ethylaminopropyl))phosphine oxide-3 hydrobromide was dissolved in 500 ml of pure water and flowed through the column from the top at a rate of SV=1.0. Another 1000 ml of pure water was then flowed through to obtain 1450 ml of a basic aqueous solution. The solution was concentrated using an evaporator to remove the water and obtain 28.7 g (crude yield 94.0%) of a slightly yellowish liquid. The NMR identification data of the obtained slightly yellowish liquid is as follows. (Identification data) 31 P-NMR (CD3OD); 55.34 ppm 1 H-NMR(CD3OD); 1.03~1.10ppm(m, 6.3H, -CH3), 1.65~1.84ppm(m, 12H, P-CH2-CH2-), 2.52~2.73ppm(m, 10.2H, -CH2-NH-CH2-), 4.76ppm(s, 5.7H, -NH-) As a result, the mixture is mainly composed of tris(3-(N-ethylaminopropyl))phosphine oxide, and further 1 ¹H-NMR analysis revealed that 70% of the total amino groups in the mixture were N-ethylated, while the remaining 30% remained as amino groups.

[0082] (Example 3) Synthesis of Tris(3-(N-methylaminopropyl))phosphine oxide In a 1 L four-necked flask equipped with a stirrer, thermometer, and dropping funnel, 44.3 g (0.2 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 and 200 ml of methanol were charged. 85.2 g (0.6 mol) of methyl iodide was gradually added dropwise at room temperature, and the liquid temperature rose to 36.1°C. After addition, the solution was aged at room temperature for 1 hour, and the pH was confirmed to be neutral using pH test paper. By concentrating under reduced pressure using an evaporator to remove methanol, 129.4 g of slightly yellowish flaky crystals (melting point 62.5~64.5°C, crude yield 100.0%) were obtained. The NMR identification data of the obtained slightly yellowish flaky crystals is as follows. (Identification data) 31 P-NMR (D2O); 57.06 ppm 1 H-NMR(D2O); 1.81~1.93ppm(m, 6H, -CH2-), 1.86~2.01ppm(m, 6H, P-CH2-), 3.03~3.10ppm(m, 15H, -CH2-N + H2-CH3), 4.66 ppm (s, 6H, -N + H2-) As a result, it was confirmed to be tris(3-(N-methylaminopropyl))phosphine oxide-3-hydroiodide. 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 × 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. 64.7 g (0.1 mol) of the obtained tris(3-(N-methylaminopropyl))phosphine oxide-3-hydroiodide was dissolved in 500 ml of pure water and flowed through the column from the top at a rate of SV=1.0. Another 1000 ml of pure water was then flowed through to obtain 1450 ml of a basic aqueous solution. The solution was concentrated using an evaporator to remove the water and obtain 25.8 g (crude yield 98.0%) of a slightly yellowish liquid. The NMR identification data of the obtained slightly yellowish liquid is as follows. (Identification data) 31 P-NMR (D2O); 59.38 ppm 1 H-NMR(D2O); 1.49~1.58ppm(m, 6H, -CH2-), 1.68~1.78ppm(m, 6H, P-CH2-), 2.50~2.54ppm(m, 6H, -CH2-NH-), 3.00ppm(s, 9H, -NH-CH3), 4.69ppm(s, 3H, -NH-) As a result, it was confirmed to be tris(3-(N-methylaminopropyl))phosphine oxide.

[0083] (Example 4) Synthesis of Tris(3-(N-isopropylaminopropyl))phosphine oxide In a 1 L four-necked flask equipped with a stirrer, thermometer, and dropping funnel, 44.3 g (0.2 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2, 200 ml of isopropyl alcohol, and 86.1 g (0.7 mol) of isopropyl bromide were charged and heated and stirred at reflux temperature for 12 hours. After cooling, the pH of the reaction solution was confirmed to be neutral using pH test paper. 50 ml of 24.0 g (0.6 mol) aqueous solution of sodium hydroxide was added and the mixture was concentrated under reduced pressure using an evaporator. 150 ml of isopropyl alcohol and anhydrous sodium sulfate were added and the mixture was allowed to stand for 12 hours. The precipitate was filtered off using a Buchner funnel lined with Celite filter aid and filter paper, and the solvent was concentrated under reduced pressure using an evaporator to obtain 61.2 g (crude yield 88.1%) of a slightly yellowish liquid. The NMR identification data of the obtained slightly yellowish liquid is as follows. (Identification data) 31 P-NMR (D2O); 60.78 ppm 1 H-NMR(D2O); 0.91ppm(d, 18H, -CH3), 1.50~1.61ppm(m, 6H, -CH2-), 1.72~1.78ppm(m, 6H, P- CH2-), 2.52~2.58ppm(m, 6H, -CH2-NH-), 2.68~2.73ppm(m, 3H, -CH-), 4.68ppm(s, 3H, -NH-) As a result, it was confirmed to be tris(3-(N-isopropylaminopropyl))phosphine oxide.

[0084] (Example 5) Synthesis of Tris(3-(N-isopropanolaminopropyl))phosphine oxide In a 100 ml two-necked flask equipped with a stirrer and thermometer, 10.0 g of a 40% aqueous solution of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 (4.03 g, 0.018 mol as tris(3-aminopropyl)phosphine oxide) and 3.17 g (0.055 mol) of propylene oxide were charged. The mixture was stirred at room temperature for 1 hour, and then heated at 60°C for 2 hours. After cooling, the reaction mixture was concentrated under reduced pressure using an evaporator to obtain 6.57 g of a colorless, transparent liquid (yield 92.3%). The NMR identification data of the obtained colorless, transparent liquid is as follows. (Identification data) 31 P-NMR (D2O); 60.39 ppm 1 H-NMR(D2O); 0.98~1.01ppm(m, 9H, -CH3), 1.46~1.73ppm(m, 12H, P-CH2-CH2-), 2. 26~2.54ppm(m, 12H, -CH2-NH-), 3.71~3.79ppm(m, 3H, -CH-), 4.68ppm(s, 3H, -NH-) As a result, it was confirmed to be tris(3-(N-isopropanolaminopropyl))phosphine oxide.

[0085] (Reference example 1) 30.2 g (0.086 mol) of tributyl(3-aminopropyl)phosphonium·β-alanine obtained in Synthesis Example 1 was dissolved 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) was used. 255.9 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 using an evaporator and completely removing the added water, 86.3 g of a carbon dioxide absorbent with tributyl(3-aminopropyl)phosphonium·β-alanine impregnated onto the silica gel was obtained. 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.

[0086] (Reference example 2) 38.0 g (0.172 mol) of tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 2 was dissolved 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) was used. 2 70.0 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 using an evaporator and completely removing the added water, 108.9 g of carbon dioxide absorbent with tris(3-aminopropyl)phosphine oxide impregnated onto the silica gel was obtained. 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 by carbon dioxide absorption test 2 and a heat stability test, which will be described later.

[0087] (Example 6) 30.5 g (0.1 mol) of tris(3-(N-ethylaminopropyl))phosphine oxide obtained in Example 1 was dissolved in 200 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) was used. 256.6 g of (average pore size 30 nm) was added and allowed 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 to obtain 87.9 g of carbon dioxide absorbent silica gel impregnated with tris(3-(N-ethylaminopropyl))phosphine oxide. The impregnation rate of tris(3-(N-ethylaminopropyl))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 the carbon dioxide absorption test 1, carbon dioxide absorption test 2, regeneration test 1, regeneration test 2, and heat stability test described below.

[0088] (Example 7) 30.5 g (0.1 mol) of a mixture mainly composed of tris(3-(N-ethylaminopropyl))phosphine oxide obtained in Example 2 was dissolved in 200 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) was used. 2 56.6 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, 87.4 g of carbon dioxide absorbent was obtained, in which a mixture mainly composed of tris(3-(N-ethylaminopropyl))phosphine oxide was impregnated onto the silica gel. The impregnation rate of tris(3-(N-ethylaminopropyl))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 and carbon dioxide absorption test 2, which will be described later.

[0089] (Example 8) 13.2 g (0.05 mol) of tris(3-(N-methylaminopropyl))phosphine oxide obtained in Example 3 was dissolved in 200 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) was used. 224.5 g of tris(3-(N-methylaminopropyl))phosphine oxide (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 using an evaporator and completely removing the added water, 38.2 g of carbon dioxide absorbent with tris(3-(N-methylaminopropyl))phosphine oxide impregnated onto silica gel was obtained. The impregnation rate of tris(3-(N-methylaminopropyl))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 described later.

[0090] (Example 9) 34.8 g (0.1 mol) of tris(3-(N-isopropylaminopropyl))phosphine oxide obtained in Example 4 was dissolved in 200 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) was used. 2 64.6 g of tris(3-(N-isopropylaminopropyl))phosphine oxide (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 using an evaporator and completely removing the added water, 100.1 g of carbon dioxide absorbent with tris(3-(N-isopropylaminopropyl))phosphine oxide impregnated onto the silica gel was obtained. The impregnation rate of tris(3-(N-isopropylaminopropyl))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 and carbon dioxide absorption test 2, which will be described later.

[0091] (Example 10) 6.57 g (0.016 mol) of tris(3-(N-isopropanolaminopropyl))phosphine oxide obtained in Example 5 was dissolved in isopropanol to make a 20% solution. 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) was added to this solution. 212.2 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 isopropanol, 18.65 g of carbon dioxide absorbent with tris(3-(N-isopropanolaminopropyl))phosphine oxide impregnated onto silica gel was obtained. The impregnation rate of tris(3-(N-isopropanolaminopropyl))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 regeneration test 3 described later.

[0092] (evaluation) (Carbon dioxide absorption test 1) The carbon dioxide absorbent obtained in Examples 6, 7, 9, and Reference Example 1 was packed into a glass column with an inner diameter of 20 mm and a length of 300 mm at a rate of 90 ml. Air (room temperature 25°C, average carbon dioxide concentration: 450 ppm) was passed through the column 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.

[0093] [Table 1]

[0094] The results shown in Table 1 indicate that the carbon dioxide absorbents of Examples 6, 7, and 9 have superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.

[0095] (Carbon dioxide absorption test 2) The carbon dioxide absorbents obtained in Examples 6-9, Reference Example 1, and Reference Example 2 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 2.

[0096] [Table 2]

[0097] The results shown in Table 2 indicate that the carbon dioxide absorbents of Examples 6-9 have superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.

[0098] (Regeneration Test 1) The carbon dioxide absorbent obtained in Example 6 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 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 carbon dioxide absorbent from Example 6, 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 50°C under full vacuum pressure using a vacuum pump, thereby removing carbon dioxide. Next, the carbon dioxide absorbent, regenerated by desorption, was refilled into a 35 ml Erlenmeyer flask, and the carbon dioxide absorption and regeneration process was repeated twice. The regeneration rate was calculated based on the following formula. The results are shown in Table 3. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

[0099] [Table 3]

[0100] (Regeneration Test 2) The carbon dioxide absorbent obtained in Example 6 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 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 carbon dioxide absorbent from Example 6, 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 30°C under full vacuum pressure using a vacuum pump, thereby removing carbon dioxide. Next, the carbon dioxide absorbent, regenerated by desorption, was refilled into a 35 ml Erlenmeyer flask, and the carbon dioxide absorption and regeneration process was repeated twice. The regeneration rate was calculated based on the following formula. The results are shown in Table 4. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

[0101] [Table 4]

[0102] The results shown in Tables 3 and 4 indicate that a carbon dioxide absorbent that has absorbed carbon dioxide to saturation can be regenerated by heating it in a vacuum (reduced pressure) at a predetermined heating temperature to remove the carbon dioxide. This regenerated carbon dioxide absorbent exhibits excellent absorption performance and a high regeneration rate.

[0103] (Regeneration Test 3) The carbon dioxide absorbent obtained in Example 10 was placed in a 35 ml Erlenmeyer flask, and its concentration was accurately measured 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), and the gas injection 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 carbon dioxide absorbent from Example 10, which had absorbed carbon dioxide to saturation, was transferred to a 30 mm diameter petri dish and regenerated by static heating in a constant temperature drying oven maintained at 70°C to remove carbon dioxide. Next, the carbon dioxide absorbent, regenerated by desorption, was refilled into a 35 ml Erlenmeyer flask, and the process of carbon dioxide absorption and regeneration was repeated five times. The regeneration rate was calculated based on the following formula. The results are shown in Table 5. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

[0104] [Table 5]

[0105] The results shown in Table 5 indicate that even in air (at atmospheric pressure) rather than in a vacuum (reduced pressure), the regenerated carbon dioxide absorbent, when heated at a predetermined temperature to remove carbon dioxide, regains its carbon dioxide absorption capacity. This demonstrates that even regenerated carbon dioxide absorbents exhibit excellent absorption performance and a high regeneration rate. This is extremely useful in reducing energy costs during carbon dioxide capture.

[0106] (Heating stability test) The carbon dioxide absorbent obtained in Example 6 was filled into a 190 ml capacity 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 in air at 120°C for 90 minutes to remove the carbon dioxide and regenerate the absorbent. Next, the carbon dioxide absorbent, which had been regenerated by decarbonizing it, was refilled into a stainless steel clean pipe to perform carbon dioxide absorption and regeneration again. The regeneration rate was calculated based on the following formula. The results are shown in Table 6. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100 Furthermore, the carbon dioxide absorbent obtained in Reference Example 2 was subjected to the same procedure, repeating carbon dioxide absorption and regeneration twice. The results are shown in Table 7.

[0107] [Table 6]

[0108] [Table 7]

[0109] The results shown in Table 6 indicate that the carbon dioxide absorbent from Example 6, which had absorbed carbon dioxide, was heated in air (under atmospheric pressure) at a predetermined heating temperature to remove the carbon dioxide. The regenerated carbon dioxide absorbent remained white in appearance, and its carbon dioxide absorption capacity was restored. This demonstrates that even as a regenerated carbon dioxide absorbent, it exhibits excellent absorption performance and a high regeneration rate. On the other hand, the results shown in Table 7 indicate that the carbon dioxide absorbent from Reference Example 2, which had absorbed carbon dioxide, was regenerated by heating it in air (under atmospheric pressure) at a predetermined heating temperature to remove the carbon dioxide, resulting in a brown appearance and further reduced absorption performance.

Claims

1. The following general formula (1): 【Chemistry 1】 (In the formula, a, b, and c represent integers between 1 and 10, and R １ , R ２ and R ３ Each of these independently represents a primary amino group, a secondary amino group, or a tertiary amino group, R １ , R ２ and R ３ At least one of them is a secondary or tertiary amino group. A phosphine oxide compound characterized by being represented by [a specific formula / method].

2. In the formula of the general formula (1), R １ , R ２ and R ３ are all secondary amino groups in which the substituent is an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 10 carbon atoms having a hydroxyl group, and the phosphine oxide compound according to claim 1 is characterized in that

3. The following general formula (1): 【Chemistry 1】 (In the formula, a, b, and c represent integers between 1 and 10, and R １ , R ２ and R ３ Each of these independently represents a primary amino group, a secondary amino group, or a tertiary amino group, R １ , R ２ and R ３ At least one of them is a secondary or tertiary amino group. A compound for carbon dioxide absorbers characterized by being a phosphine oxide compound represented by [formula].

4. A carbon dioxide absorbent characterized by containing the carbon dioxide absorbent compound described in claim 3.

5. The carbon dioxide absorbent according to claim 4, characterized by comprising a porous carrier and the carbon dioxide absorbent compound according to claim 3 supported on the porous carrier.

6. The carbon dioxide absorbent according to claim 5, 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.

7. A method for separating carbon dioxide, characterized by comprising a carbon dioxide separation step of contacting a carbon dioxide absorbent described in claim 5 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.

8. A carbon dioxide separation step is performed by contacting a carbon dioxide absorbent according to claim 5 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 30°C to 150°C to desorb carbon dioxide from the carbon dioxide absorption agent, thereby regenerating the carbon dioxide absorption agent and recovering the desorbed carbon dioxide. A method for separating and recovering carbon dioxide, characterized by having the following features.

9. The carbon dioxide separation and recovery method according to claim 8, 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.

10. An apparatus characterized in that it uses the carbon dioxide absorbent described in claim 4.

11. The apparatus according to claim 10, characterized in that the apparatus is used in a power plant, a factory, or transportation equipment.

12. The apparatus according to claim 10, characterized in that the apparatus is a DAC apparatus.

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