Carbon dioxide absorbing liquid, method for separating carbon dioxide, method for separating and recovering carbon dioxide, and device using carbon dioxide absorbing liquid

Abstract

The present invention provides: a carbon dioxide absorbing liquid which has excellent carbon dioxide absorbing performance; a carbon dioxide absorbing liquid which is capable of easily desorbing carbon dioxide when the absorbing liquid is regenerated in addition to having the above-described carbon dioxide absorbing performance; a method for separating carbon dioxide and a method for separating and recovering carbon dioxide, each using the carbon dioxide absorbing liquid; and a device using the carbon dioxide absorbing liquid. The present invention relates to a carbon dioxide absorbing liquid which contains a solvent and a phosphine oxide compound represented by general formula (1) (wherein a, b, and c each represent an integer of 1 to 10, R1, R2, and R3 each independently represent an amino group or a hydroxy group, and at least one of R1, R2, and R3 is an amino group).

Description

Carbon dioxide absorbent solution, carbon dioxide separation method, carbon dioxide separation and recovery method, and apparatus using carbon dioxide absorbent solution

[0001] The present invention relates to a carbon dioxide absorption liquid, a carbon dioxide separation method, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorption liquid.

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

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

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

[0005] Japanese Patent Publication No. 2016-10760

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

[0007] Therefore, an object of the present invention is to provide a carbon dioxide absorption liquid having excellent carbon dioxide absorption performance, and further, in addition to the above carbon dioxide absorption performance, a carbon dioxide absorption liquid capable of easily desorbing carbon dioxide when regenerating the absorption liquid, a carbon dioxide separation method using the carbon dioxide absorption liquid, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorption liquid.

[0008] As a result of intensive studies in view of the above circumstances, the present inventors have found that a carbon dioxide absorption liquid containing a phosphine oxide compound represented by the following general formula (1) has superior oxidation resistance and heat resistance compared to the prior art, and also has excellent carbon dioxide absorption performance, and further, carbon dioxide can be easily desorbed when regenerating the carbon dioxide absorption liquid, thus completing the present invention.

[0009]

[0010] (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 an amino group or a hydroxy group, and at least one of R １ , R ２ and R ３ is an amino group.)

[0011] That is, the present invention (1) provides a carbon dioxide absorption liquid containing a phosphine oxide compound represented by the following general formula (1):

[0012]

[0013] (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 an amino group or a hydroxy group, and at least one of R １ , R ２ and R ３ is an amino group.)

[0014] Further, the present invention (2) 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 absorption liquid of the present invention (1) to absorb the carbon dioxide in the mixed gas into the carbon dioxide absorption liquid, thereby separating carbon dioxide from the mixed gas.

[0015] Further, the present invention (3) 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 absorption liquid of the present invention (1) to absorb the carbon dioxide in the mixed gas into the carbon dioxide absorption liquid, thereby separating carbon dioxide from the mixed gas, and a carbon dioxide recovery step of heating the carbon dioxide absorption liquid that has absorbed carbon dioxide in the carbon dioxide separation step at a temperature of 50°C or higher and 150°C or lower to desorb carbon dioxide from the carbon dioxide absorption liquid that has absorbed carbon dioxide, thereby regenerating the carbon dioxide absorption liquid and recovering the desorbed carbon dioxide.

[0016] Further, the present invention (4) provides an apparatus characterized by using the carbon dioxide absorption liquid of the present invention (1).

[0017] According to the present invention, it is possible to provide a carbon dioxide absorption liquid having excellent carbon dioxide absorption performance, a carbon dioxide absorption liquid that can easily desorb carbon dioxide when regenerating the absorption liquid in addition to the above carbon dioxide absorption performance, a carbon dioxide separation method using the carbon dioxide absorption liquid of the present invention, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorption liquid of the present invention.

[0018] Hereinafter, the present invention will be described based on preferred embodiments. The carbon dioxide absorption liquid of the present invention has the following general formula (1):

[0019]

[0020] (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 an amino group or a hydroxy group, and R １ , R ２ and R３ It is a carbon dioxide absorption liquid containing a phosphine oxide compound represented by (at least one of them is an amino group.) and a solvent.

[0021] In the carbon dioxide absorption liquid of the present invention, the phosphine oxide compound represented by the general formula (1) is water-soluble. That is, the carbon dioxide absorption liquid of the present invention is in the form of a solution containing the phosphine oxide compound represented by the general formula (1).

[0022] The phosphine oxide compound represented by the general formula (1) has a high heat resistance due to having a phosphine oxide structure (α ３ P=O). Also, the vapor pressure in the heating temperature range during regeneration after carbon dioxide absorption, for example, in the heating temperature range of 50°C or higher and 150°C or lower, is low, and it has almost no volatility.

[0023] In the general formula (1), a, b, and c represent integers of 1 or more and 10 or less, preferably 1 or more and 4 or less, more preferably 3 or more and 4 or less. The numbers of a, b, and c may be the same or different from each other, but from the viewpoint of easy synthesis, it is preferable that they are the same. In the present invention, from the viewpoint of easy industrial availability, it is particularly preferable that a, b, and c are each 3.

[0024] R in the general formula (1) １ , R ２ and R ３ each independently represent an amino group (—NH ２ ) or a hydroxy group (—OH). R １ , R ２ and R ３ may be the same or different from each other, but from the viewpoint of easy synthesis, it is preferable that they are the same. In the present invention, from the viewpoint of the carbon dioxide absorption performance, R １ , R ２ and R ３ at least one of them is an amino group, and it is preferable that all of them are amino groups.

[0025] The amino group of the phosphine oxide compound represented by general formula (1) reacts with carbon dioxide, thereby absorbing carbon dioxide. In other words, the phosphine oxide compound represented by general formula (1) is a compound used as a substance for absorbing carbon dioxide in the carbon dioxide absorption solution of the present invention.

[0026] In the carbon dioxide absorbent of the present invention, the phosphine oxide compound represented by general formula (1) is dissolved in the solvent. That is, the carbon dioxide absorbent of the present invention is in the form of a solution containing the phosphine oxide compound represented by general formula (1) and a solvent. Since the phosphine oxide compound represented by general formula (1) has a high boiling point, when heating is performed to desorb carbon dioxide from the carbon dioxide absorbent of the present invention after it has absorbed carbon dioxide, the phosphine oxide compound represented by general formula (1) is unlikely to evaporate from the carbon dioxide absorbent of the present invention. Therefore, even when the carbon dioxide absorbent of the present invention is heated under atmospheric conditions, the phosphine oxide compound represented by general formula (1) is unlikely to come into contact with the gas phase containing oxygen. As a result, in the carbon dioxide absorbent of the present invention, even when heating is performed under atmospheric conditions to desorb carbon dioxide from the carbon dioxide absorbent of the present invention after it has absorbed carbon dioxide, the phosphine oxide compound represented by general formula (1) is unlikely to be oxidized.

[0027] Furthermore, because the solvent in the carbon dioxide absorbent of the present invention has a boiling point that is the same as or lower than the heating temperature used to desorb carbon dioxide from the carbon dioxide absorbent of the present invention, the gas phase is filled with solvent vapor during heating, making it less likely for the phosphine oxide compound represented by general formula (1) to come into contact with the gas phase containing oxygen. As a result, even if the heating to desorb carbon dioxide from the carbon dioxide absorbent of the present invention after carbon dioxide absorption is performed under atmospheric conditions, the phosphine oxide compound represented by general formula (1) is less likely to be oxidized, thus enhancing the effect of making it less likely for the phosphine oxide compound represented by general formula (1) to be oxidized.

[0028] In the carbon dioxide absorbent liquid of the present invention, the solvents include water, glycol-based solvents, alcohol-based solvents, amine compounds, alkanolamine compounds, and the like. Among these, water, glycol-based solvents, and alcohol-based solvents are preferred, and water and glycol-based solvents are more preferred, because the viscosity of the carbon dioxide absorbent liquid does not increase easily after absorbing carbon dioxide and it has good handling properties.

[0029] Examples of glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin. Examples of alcohol-based solvents include ethanol.

[0030] These solvents may be used individually or in mixtures of two or more types.

[0031] In the carbon dioxide absorbent solution of the present invention, the solvent is particularly preferably water. The solvent being water in the carbon dioxide absorbent solution of the present invention significantly enhances the effect of making the phosphine oxide compound represented by general formula (1) less susceptible to oxidation, even when heating is performed to remove carbon dioxide from the absorbent solution after it has absorbed carbon dioxide, under atmospheric or oxidizing gas conditions.

[0032] In the carbon dioxide absorbent liquid of the present invention, the content of the phosphine oxide compound represented by general formula (1) in the carbon dioxide absorbent liquid is 5 to 80% by mass, preferably 10 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. Because the content of the phosphine oxide compound represented by general formula (1) in the carbon dioxide absorbent liquid is within the above range, the viscosity of the carbon dioxide absorbent liquid does not increase easily after absorbing carbon dioxide, resulting in good handling properties.

[0033] Because the carbon dioxide absorbent of the present invention is in the form of a solution, it is suitably used for separating and recovering carbon dioxide emitted from large-scale carbon dioxide sources such as power plants (including coal-fired and natural gas-fired power plants), chemical plants, waste treatment plants, and steel mills, from the viewpoint of ease of acquisition and safety. Because the carbon dioxide absorbent of the present invention is a solution, it can be used in existing carbon dioxide absorbent equipment in large-scale facilities and factories where high concentrations of carbon dioxide are present and large-scale processing is required. Furthermore, because the carbon dioxide absorbent of the present invention is a solution, it is easy to transport to and fill into large-scale carbon dioxide separation and recovery equipment, or to remove from equipment.

[0034] The carbon dioxide absorbent liquid 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.

[0035] 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 and natural gas-fired), 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.

[0036] Next, a method for separating carbon dioxide and a method for separating and recovering carbon dioxide using the carbon dioxide absorption liquid of the present invention will be described.

[0037] The present invention relates to a carbon dioxide separation method characterized by having a carbon dioxide separation step (A) in which a mixed gas containing carbon dioxide is brought into contact with a carbon dioxide absorption liquid of the present invention, and the carbon dioxide in the mixed gas is absorbed by the carbon dioxide absorption liquid, thereby separating the carbon dioxide from the mixed gas.

[0038] The present invention provides a carbon dioxide separation and recovery method comprising: a carbon dioxide separation step (A) in which a mixed gas containing carbon dioxide is brought into contact with a carbon dioxide absorption liquid of the present invention, and the carbon dioxide in the mixed gas is absorbed by the carbon dioxide absorption liquid, thereby separating the carbon dioxide from the mixed gas; and a carbon dioxide recovery step (B) in which the carbon dioxide absorption liquid that has absorbed carbon dioxide in the carbon dioxide separation step is heated at a temperature of 50°C to 150°C, thereby decarbonizing the carbon dioxide that has absorbed carbon dioxide, thereby regenerating the carbon dioxide absorption liquid and recovering the decarbonized carbon dioxide.

[0039] In the carbon dioxide separation method and the carbon dioxide separation and recovery method of the present invention, the step of separating carbon dioxide from a mixed gas containing carbon dioxide is the carbon dioxide separation step (A) in both cases and is the same.

[0040] The carbon dioxide separation step (A) is a step in which the carbon dioxide absorption liquid of the present invention is brought into contact with a mixed gas containing carbon dioxide, thereby causing the carbon dioxide absorption liquid of the present invention to absorb the carbon dioxide in the mixed gas.

[0041] One example of the carbon dioxide separation process (A) is to supply a mixed gas containing carbon dioxide to an absorption tower filled with the carbon dioxide absorption liquid of the present invention, bring the mixed gas into contact with the carbon dioxide absorption liquid, and separate the carbon dioxide from the mixed gas by allowing the carbon dioxide absorption liquid 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 absorption liquid by supplying the mixed gas to the absorption tower, and the mixed gas that has been in contact with the carbon dioxide absorption liquid inside the absorption tower is discharged from the absorption tower. Furthermore, the method of filling the absorption tower with the carbon dioxide absorption liquid of the present invention is not particularly limited and can be carried out under atmospheric pressure or reduced pressure.

[0042] The temperature of the carbon dioxide absorbent in the carbon dioxide separation step (A) is not limited as long as the carbon dioxide absorbent can perform its function, but a temperature of -20°C to 60°C, and particularly 0°C to 40°C, is preferable from the viewpoint of more efficient carbon dioxide absorption.

[0043] The pressure (absolute pressure) in the carbon dioxide separation process (A) is not particularly limited and can be carried out under atmospheric pressure.

[0044] In the carbon dioxide separation step (A), the carbon dioxide-containing mixed gas comes into contact with the carbon dioxide absorbent, 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.

[0045] The carbon dioxide separation and recovery method of the present invention includes a carbon dioxide recovery step (B) in which carbon dioxide is recovered while regenerating the carbon dioxide absorbent liquid that absorbed carbon dioxide in the carbon dioxide separation step. The carbon dioxide recovery step (B) is a step in which carbon dioxide is removed from the carbon dioxide absorbent liquid that absorbed carbon dioxide in the carbon dioxide separation step (A) by heating the carbon dioxide absorbent liquid.

[0046] Examples of carbon dioxide recovery processes (B) include a method in which, after performing the carbon dioxide separation process (A), the carbon dioxide absorbent liquid filled in the absorption tower is heated to regenerate the carbon dioxide absorbent liquid and recover the desorbed carbon dioxide; and a method in which, after performing the carbon dioxide separation process (A), the carbon dioxide absorbent liquid that has absorbed carbon dioxide is transported to a regeneration tower, where the carbon dioxide absorbent liquid is heated to regenerate the carbon dioxide absorbent liquid and recover the desorbed carbon dioxide.

[0047] In the carbon dioxide recovery step (B), the heating temperature of the carbon dioxide absorbent is 50°C to 150°C, preferably 80°C to 145°C, and preferably 80°C to 140°C. Generally, the higher the heating temperature, the easier it is for carbon dioxide to be released from the carbon dioxide absorbent. 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 145°C, and preferably 80°C to 140°C, and at a temperature equivalent to or higher than the temperature in the carbon dioxide separation step (A).

[0048] In carbon dioxide recovery step (B), the pressure (absolute pressure) is not particularly limited, and the carbon dioxide absorbent liquid that has absorbed carbon dioxide may be heated under atmospheric pressure or under reduced pressure. When heated 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 liquid, and further preferably 50 kPa or less, particularly 10 kPa or less, from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent liquid. In addition, in carbon dioxide recovery step (B), the heating temperature may be set to a temperature above the boiling point of the solvent, and the carbon dioxide absorbent liquid that has absorbed carbon dioxide may be heated under reflux of the solvent. In addition, in carbon dioxide recovery step (B), the carbon dioxide absorbent liquid that has absorbed carbon dioxide may be heated while bubbling air, an inert gas, water vapor, etc. into the carbon dioxide absorbent liquid.

[0049] In the carbon dioxide separation and recovery method of the present invention, the carbon dioxide separation step (A) and the carbon dioxide recovery step (B) can be repeated two or more times by using the regenerated carbon dioxide absorbent obtained in the carbon dioxide recovery step (B) as the carbon dioxide absorbent to which a mixed gas containing carbon dioxide is contacted in the carbon dioxide separation step (A). 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.

[0050] In the carbon dioxide separation method and carbon dioxide separation and recovery method of the present invention, the carbon dioxide absorption solution 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.

[0051] 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.

[0052] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0053] (Synthesis Example 1: Tris(3-aminopropyl)phosphine oxide) In a 1L stainless steel autoclave equipped with a stirrer, thermometer, injection pump, safety valve, and gas inlet pipe, 150ml of toluene and 133g (2.33 mol) of allylamine were charged, and the mixture was replaced three times with nitrogen gas and vacuum. Then, 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, 1.06g (0.006 mol) of azobisisobutyronitrile was dissolved in 150ml 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 overnight maturation, the mixture was cooled to room temperature, the remaining gas was evacuated into a removal system, and the system was further purged with nitrogen gas and vacuum. The mixture was then extracted into a reduced-pressure round-bottom flask to obtain 585 g of a colorless, transparent liquid. Next, the obtained 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 heated further (gauge pressure 0.2 kPa (absolute pressure 101.5 kPa), 160°C). Heating was stopped when the initial distillate began to appear, and the residue was used as the product. After cooling the obtained product to room temperature, it was purged with nitrogen gas to obtain 120 g of a colorless, transparent liquid. The NMR identification data for the obtained colorless, transparent liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); -29.73ppm 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.

[0054] 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. 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 hydrogen peroxide, the mixture was cooled to room temperature and concentrated under reduced pressure using an evaporator to remove water, yielding 100.8 g of a colorless, transparent liquid. The NMR identification data of the obtained colorless, transparent liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); 60.77ppm １ H-NMR (D ２ O); 1.50 to 1.58 ppm (m, 6H, -CH ２ -), 1.71 to 1.77 ppm (m, 6H, P-CH ２ -), 2.57 to 2.60 ppm (t, 6H, -CH ２ -NH ２ ), 4.70ppm (s, 6H, -NH ２ As a result, it was confirmed to be tris(3-aminopropyl)phosphine oxide.

[0055] (Example 1) Tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in pure water to obtain a carbon dioxide absorbent solution prepared so that the tris(3-aminopropyl)phosphine oxide content was 40% by mass. The obtained carbon dioxide absorbent solution was evaluated in regeneration test 1 and regeneration test 2 described later.

[0056] (Example 2) Tris(3-aminopropyl)phosphine oxide obtained in Synthesis Example 1 was dissolved in ethylene glycol to obtain a carbon dioxide absorbent solution prepared so that the tris(3-aminopropyl)phosphine oxide content was 40% by mass. The obtained carbon dioxide absorbent solution was evaluated by viscosity measurement and regeneration test 3 described later.

[0057] (Comparative Example 1) Diethylenetriamine was dissolved in pure water to obtain a carbon dioxide absorbent solution with a diethylenetriamine content of 40% by mass. The obtained carbon dioxide absorbent solution was evaluated in regeneration test 2 described later.

[0058] (Comparative Example 2) Diethylenetriamine was dissolved in ethylene glycol to obtain a carbon dioxide absorbent solution with a diethylenetriamine content of 40% by mass. The obtained carbon dioxide absorbent solution was evaluated by viscosity measurement and regeneration test 3 described later.

[0059] (Evaluation) (Regeneration Test 1) The carbon dioxide absorbent obtained in Example 1 was placed in a 50 ml Erlenmeyer flask, and 99.995% pure carbon dioxide gas was blown in at a flow rate of 1 L / min at room temperature (25°C). After 15 minutes, the weight was accurately measured to a sensitivity of 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. Next, the carbon dioxide absorbent that had absorbed carbon dioxide was heated in an oil bath while stirring. After the liquid temperature reached 100°C, it was heated for 2 hours, and carbon dioxide was expelled by refluxing water in a condenser, and regeneration was performed. Then, pure water was added to the carbon dioxide absorbent so that the weight was the same as the water lost during heating, and the carbon dioxide absorption and regeneration process was repeated multiple times. The regeneration rate was calculated using the following formula based on the number of moles of carbon dioxide absorbed. The results are shown in Table 1. Regeneration rate (%) = (Number of moles of carbon dioxide absorbed during regeneration / Number of moles of carbon dioxide absorbed initially) × 100

[0060]

[0061] As shown in Table 1, the carbon dioxide absorbent solution of Example 1 exhibited excellent carbon dioxide absorption performance, and it was confirmed that its absorption capacity did not easily decrease even after repeated carbon dioxide absorption and regeneration cycles.

[0062] (Regeneration Test 2) The carbon dioxide absorption solutions obtained in Example 1 and Comparative Example 1 were placed in 50 ml Erlenmeyer flasks, and 99.995% pure carbon dioxide gas was blown in at a flow rate of 1 L / min at room temperature (25°C). After 15 minutes, the weight was accurately measured to a sensitivity of 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 absorption solution. Next, carbon dioxide absorption solutions, which had absorbed carbon dioxide by blowing gas into the flask at a flow rate of 2 L / min from an air pump, were heated in an oil bath while being stirred. The solution was heated for 2 hours starting when the liquid temperature reached 100°C, and carbon dioxide was expelled by refluxing water in a condenser to regenerate it. Then, pure water was added to the carbon dioxide absorption solution to make it the same weight as the water lost during heating, and the carbon dioxide absorption and regeneration process was repeated multiple times. The regeneration rate was calculated using the following formula based on the number of moles of carbon dioxide absorbed. The results are shown in Tables 2 and 3. Regeneration rate (%) = (Number of moles of carbon dioxide absorbed during regeneration / Number of moles of carbon dioxide absorbed initially) × 100

[0063]

[0064]

[0065] The results shown in Tables 2 and 3 confirm that the carbon dioxide absorbent solution of Example 1 exhibited superior oxidation resistance and less reduction in absorption capacity even after multiple cycles of carbon dioxide absorption and regeneration, compared to the carbon dioxide absorbent solution of Comparative Example 1. Furthermore, the carbon dioxide absorbent solution of Comparative Example 1 was found to have deteriorated, turning yellow during the test.

[0066] (Viscosity Measurement and Regeneration Test 3) For the carbon dioxide absorbent liquids obtained in Example 2 and Comparative Example 2, a rheometer (Thermo Fisher Scientific HAAKE MARS 60) was used to measure the viscosity at a shear rate of 1 s. －１After measuring the viscosity at 25°C, the solution was placed in a 50 ml Erlenmeyer flask, and 99.995% pure carbon dioxide gas was blown in at a flow rate of 1 L / min at room temperature (25°C). After 15 minutes, the weight was accurately measured to a sensitivity of 0.1 mg. The increased weight was used as the amount of carbon dioxide absorbed, and the number of moles was calculated. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent solution. The viscosity of the carbon dioxide absorbent solution at 25°C after carbon dioxide absorption was measured only during the first regeneration test 3. Next, the carbon dioxide absorbent solution after carbon dioxide absorption was heated in an oil bath while stirring. After heating for 2 hours from the point when the liquid temperature reached 140°C, carbon dioxide was expelled by refluxing water in a condenser, and regeneration was performed. Then, pure water was added to the carbon dioxide absorbent solution to make it the same weight as the water lost during heating, and carbon dioxide absorption and regeneration were repeated multiple times. The regeneration rate was calculated using the following formula based on the number of moles of carbon dioxide absorbed. The viscosity measurement results are shown in Table 4, and the results of regeneration test 3 are shown in Tables 5 and 6. Regeneration rate (%) = (Number of moles of carbon dioxide absorbed during regeneration / Number of moles of carbon dioxide absorbed initially) × 100

[0067]

[0068]

[0069]

[0070] From the results shown in Tables 4, 5, and 6, it was confirmed that the carbon dioxide absorbent solution of Example 2 showed less viscosity increase even after carbon dioxide absorption compared to the carbon dioxide absorbent solution of Comparative Example 2. Therefore, even when carbon dioxide absorption and regeneration were repeated multiple times, the contact efficiency with carbon dioxide did not decrease easily, meaning that the absorption capacity did not decrease easily, and it was confirmed to have excellent heat resistance. In addition, the carbon dioxide absorbent solution of Comparative Example 2 turned yellow during the test, indicating thermal degradation. Furthermore, when the diethylenetriamine used in Comparative Example 2 was heated to 140°C and the headspace gas was analyzed using a gas chromatography mass spectrometer GCMS-QP2020 (manufactured by Shimadzu Corporation), H ２ NCH ２ CH ２A fragment (M / Z = 44) was observed, suggesting that the N-C bond was undergoing thermal decomposition.

Claims

1. The following general formula (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 an amino group or a hydroxyl group, R １ , R ２ and R ３ A carbon dioxide absorbent containing a phosphine oxide compound represented by (where at least one of the groups is an amino group) and a solvent.

2. In the formula of general formula (1), R １ , R ２ and R ３ The carbon dioxide absorption liquid according to claim 1, wherein all of them are amino groups.

3. The carbon dioxide absorbent liquid according to claim 1 or 2, characterized in that the solvent comprises at least one selected from the group consisting of water, glycol-based solvents, and alcohol-based solvents.

4. The carbon dioxide absorbent liquid according to claim 1 or 2, characterized in that the solvent comprises at least one selected from the group consisting of water and glycol-based solvents.

5. The carbon dioxide absorbent liquid according to claim 1 or 2, characterized in that the content of the phosphine oxide compound in the carbon dioxide absorbent liquid is 5% by mass or more and 80% by mass or less.

6. A method for separating carbon dioxide, characterized by comprising a carbon dioxide separation step of contacting a mixed gas containing carbon dioxide with a carbon dioxide absorbing liquid according to claim 1 or 2, thereby allowing the carbon dioxide absorbing liquid to absorb the carbon dioxide in the mixed gas and separating the carbon dioxide from the mixed gas.

7. A method for separating and recovering carbon dioxide, comprising: a carbon dioxide separation step of contacting a carbon dioxide absorption liquid according to claim 1 or 2 with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorption liquid to absorb the carbon dioxide in the mixed gas and separating the carbon dioxide from the mixed gas; and a carbon dioxide recovery step of heating the carbon dioxide absorption liquid that has absorbed carbon dioxide in the carbon dioxide separation step at a temperature of 50°C to 150°C, thereby decarbonizing the carbon dioxide absorption liquid and recovering the decarbonized carbon dioxide.

8. The carbon dioxide separation and recovery method according to claim 7, 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 brought into contact in the carbon dioxide separation step, thereby repeating the carbon dioxide separation step and the carbon dioxide recovery step two or more times.

9. An apparatus characterized in that it uses the carbon dioxide absorption liquid described in claim 1 or 2.

10. The apparatus according to claim 9, characterized in that the apparatus is used in a power plant, factory, or transportation equipment.

11. The apparatus according to claim 9, characterized in that the apparatus is a DAC apparatus.

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