Carbon dioxide absorbent and method for recovering carbon dioxide

Abstract

Provided is a carbon dioxide absorbent that absorbs CO2 in a gas with a low CO2 concentration and separates into an aqueous phase and an organic phase. 【Solution Means】The carbon dioxide absorbent contains at least one amine compound, water, and at least one organic solvent. Ra defined by the following formula Ra=[4(δDa·Ca / 100+δDw·Cw / 100-δDs) 2 +(δPa·Ca / 100+δPw·Cw / 100-δPs) 2 +(δHa·Ca / 100+δHw·Cw / 100-δHs) 2 1 / 2 (In the formula, δDa, δPa, and δHa represent the dispersion term, polar term, and hydrogen bonding term of the Hansen Solubility Parameter (HSP) of the at least one amine compound; δDw, δPw, and δHw represent the dispersion term, polar term, and hydrogen bonding term of the HSP of water; δDs, δPs, and δHs represent the dispersion term, polar term, and hydrogen bonding term of the HSP of the at least one organic solvent; Ca and Cw represent the total content (wt%) of the at least one amine compound and the water content (wt%) in the carbon dioxide absorbent, respectively.) is 14.6 to 17 MPa 1 / 2 .​

Description

[Technical Field]

[0001] This disclosure relates to carbon dioxide absorbents and methods for recovering carbon dioxide. [Background technology]

[0002] Patent Document 1 describes an absorbent capable of reversibly absorbing and desorbing acidic compounds, comprising water, an amine compound, and an organic solvent, wherein the solubility parameter of the amine compound minus the solubility parameter of the organic solvent is 1.1 (cal / cm³). 3 ) 1 / 2 More than 4.2(cal / cm 3 ) 1 / 2 The following features of an absorbent are described. Patent Document 1 describes that when an acidic compound is absorbed by the above absorbent, it naturally separates into two phases: a phase with a high content of the acidic compound and a phase with a low content of the acidic compound, and that the acidic compound can be recovered with relatively little energy consumption by performing a separation treatment of the acidic compound only on the phase with a high content of the acidic compound. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-113672 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] When absorbing carbon dioxide from a gas with a low carbon dioxide concentration (e.g., air), the absorbent described in Patent Document 1 may not be able to absorb carbon dioxide sufficiently, or it may not separate the carbon dioxide into two phases, one with a high carbon dioxide content and the other with a low carbon dioxide content, after absorption. This disclosure provides a carbon dioxide absorbent that absorbs carbon dioxide from a gas with a low carbon dioxide concentration, such as air, and separates it into two phases, an aqueous phase and an organic phase, and a method for recovering carbon dioxide using the same. Since the aqueous phase has a high carbon dioxide content, the carbon dioxide can be released and recovered by removing the aqueous phase and heating it, thereby saving energy for carbon dioxide recovery. [Means for solving the problem]

[0005] The forms of this disclosure include the following: [Aspect 1] It is a carbon dioxide absorbent, At least one type of amine compound, Water and, At least one type of organic solvent, Includes, Ra is defined by the following formula Ra=[4(δDa·Ca / 100+δDw·Cw / 100-δDs) 2 +(δPa·Ca / 100+δPw·Cw / 100-δPs) 2 +(δHa·Ca / 100+δHw·Cw / 100-δHs) 2 ] 1 / 2 (In the formula, Ca represents the total content (by weight) of at least one amine compound in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. Cw represents the water content (by weight) in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. δDa represents the dispersion force term of the Hansen solubility parameter of at least one amine compound, δDw represents the dispersion force term of the Hansen solubility parameter for water, δDs represents the dispersion force term of the Hansen solubility parameter of at least one organic solvent, δPa represents the polar term of the Hansen solubility parameter of at least one amine compound, δPw represents the polar term of the Hansen solubility parameter of water, δPs represents the polar term of the Hansen solubility parameter of at least one organic solvent, δHa represents the hydrogen bonding term of the Hansen solubility parameter of at least one amine compound, δHw represents the hydrogen bonding term of the Hansen solubility parameter of water, δHs represents the hydrogen bonding term of the Hansen solubility parameter of at least one organic solvent.) is 14.6 to 17 MPa 1 / 2 in the range, the carbon dioxide absorbent. [Aspect 2] The carbon dioxide absorbent according to Aspect 1, wherein the at least one amine compound is selected from the group consisting of primary amines, cyclic secondary amines, and acyclic secondary amines, which may optionally contain at least one group selected from the group consisting of a hydroxy group and an ether group. [Aspect 3] The total content of the at least one amine compound in the carbon dioxide absorbent is 10 to 50 wt% based on the total weight of the carbon dioxide absorbent, the content of water in the carbon dioxide absorbent is 5 to 20 wt% based on the total weight of the carbon dioxide absorbent, the total content of the at least one organic solvent in the carbon dioxide absorbent is 45 to 85 wt% based on the total weight of the carbon dioxide absorbent, the carbon dioxide absorbent according to Aspect 1 or 2. [Aspect 4] A method for recovering carbon dioxide, comprising: causing the carbon dioxide absorbent according to any one of Aspects 1 to 3 to absorb carbon dioxide, and separating the carbon dioxide absorbent into an aqueous phase and an organic phase; heating the aqueous phase to release and recover carbon dioxide from the aqueous phase; a method comprising. [Aspect 5] The method according to aspect 4, further comprising mixing the organic phase with the aqueous phase from which carbon dioxide has been released to regenerate the carbon dioxide absorbent. [Effects of the Invention]

[0006] The carbon dioxide absorbent of the present disclosure absorbs carbon dioxide in a gas having a low carbon dioxide concentration and separates into two phases, an aqueous phase and an organic phase. In the carbon dioxide recovery method of the present disclosure, since the aqueous phase is taken out and heated to release and recover carbon dioxide, the energy required for carbon dioxide recovery can be reduced. [Brief Description of the Drawings]

[0007] [Figure 1] This is a flowchart showing the carbon dioxide recovery method according to the embodiment. [Figure 2] This is a schematic diagram of a carbon dioxide recovery apparatus used in the carbon dioxide recovery method according to the embodiment. [Modes for Carrying Out the Invention]

[0008] Hereinafter, embodiments will be described with appropriate reference to the drawings, but the present disclosure is not limited to the following embodiments. Various modifications, alterations, additions, omissions, and / or combinations of the embodiments described below are possible without departing from the technical scope described in the claims.

[0009] In the present application, a numerical range represented using the symbol "~" includes the numerical values stated before and after the symbol "~" as the lower limit and upper limit, respectively, unless otherwise specified. The upper limits and lower limits described in the present application may be used alone or in any arbitrary combination.

[0010] In this application, "contains" means that additional components or elements may be included unless otherwise specified, and encompasses "essentially made of" and "consisting of." "Essentially made of" means that additional components or elements may be included that do not substantially adversely affect the product. "Consisting of" means that only the described material or element is included, but does not exclude the inclusion of unavoidable impurities.

[0011] I. Carbon dioxide absorbers The carbon dioxide absorbent according to this embodiment comprises at least one amine compound, water, and at least one organic solvent.

[0012] In the carbon dioxide absorbent according to the embodiment, Ra defined by the following formula (1) Ra=[4(δDa·Ca / 100+δDw·Cw / 100-δDs) 2 +(δPa·Ca / 100+δPw·Cw / 100-δPs) 2 +(δHa·Ca / 100+δHw·Cw / 100-δHs) 2 ] 1 / 2 ...(1) (In the formula, Ca represents the total content (by weight) of at least one amine compound in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. Cw represents the water content (by weight) in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. δDa represents the dispersion force term of the Hansen solubility parameter (HSP) of at least one amine compound, δDw represents the dispersion force term of the HSP of water, δDs represents the dispersion force term of the HSP of at least one organic solvent, δPa represents the polar term of the HSP of at least one amine compound, δPw represents the polarity term of the HSP of water, δPs represents the polarity term of the HSP of at least one organic solvent, δHa represents the hydrogen bonding term of the HSP of at least one amine compound, δHw represents the hydrogen bonding term of the water HSP, δHs represents the hydrogen bonding term of the HSP of at least one organic solvent. The pressure is 14.6-17 MPa. 1 / 2 It is within this range. As a result, the carbon dioxide absorbent is single-phase before carbon dioxide absorption and can absorb carbon dioxide even from gases with low carbon dioxide concentrations (for example, gases with carbon dioxide concentrations in the range of 0.01 vol% to 20 vol%) and separate into an aqueous phase and an organic phase. Note that Ra represents the distance between the HSP of the amine compound aqueous solution and the HSP of the organic solvent in the Hansen space.

[0013] The dispersion force term δDa, polarity term δPa, and hydrogen bonding term δHa of the HSP of at least one amine compound are given by the following formula

number

[0014] The dispersion force term δDs, polarity term δPs, and hydrogen bonding term δHs of HSP in at least one organic solvent are given by the following formula

number

[0015] The definitions and calculation methods for the dispersion force term, polarity term, and hydrogen bonding term of HSP are described in Charles M. Hansen's *Hansen Solubility Parameters: A Users Handbook*, CRC Press, 2007. For compounds for which literature values ​​are unknown, the dispersion force term, polarity term, and hydrogen bonding term of HSP can be estimated from their chemical structure using commercially available computer software such as *Hansen Solubility Parameters in Practice* (HSPiP).

[0016] The total content of at least one amine compound in the carbon dioxide absorbent may be 10 to 50% by weight based on the total weight of the carbon dioxide absorbent. When the total content of at least one amine compound is 10% by weight or more, the carbon dioxide absorbent can have a high carbon dioxide absorption capacity. When the total content of at least one amine compound is 50% by weight or less, when the carbon dioxide absorbent absorbs carbon dioxide and separates into an aqueous phase and an organic phase, the aqueous phase can have a high carbon dioxide content, thus significantly reducing the energy required for carbon dioxide recovery. The total content of at least one amine compound in the carbon dioxide absorbent may also be 30 to 40% by weight based on the total weight of the carbon dioxide absorbent.

[0017] The total content of at least one organic solvent in the carbon dioxide absorbent may be 45 to 85% by weight based on the total weight of the carbon dioxide absorbent. When the total content of at least one organic solvent is 45% by weight or more, the carbon dioxide absorbent readily separates into an aqueous phase and an organic phase when it absorbs carbon dioxide. When the total content of at least one organic solvent is 85% by weight or less, the carbon dioxide absorbent can have a high carbon dioxide absorption capacity. The total content of at least one organic solvent in the carbon dioxide absorbent may be 50 to 55% by weight based on the total weight of the carbon dioxide absorbent.

[0018] The water content in the carbon dioxide absorbent may be 5 to 20% by weight, based on the total weight of the carbon dioxide absorbent.

[0019] At least one type of amine compound has an Ra of 14.6-17 MPa. 1 / 2 The range is not particularly limited. For example, at least one amine compound may be selected from the group consisting of primary amines, cyclic secondary amines, and acyclic secondary amines, and may optionally contain at least one group selected from the group consisting of hydroxyl groups and ether groups. Examples of primary amines include 2-(2-aminoethoxy)ethanol, 2-aminoethanol, DL-2-amino-1-propanol, (R)-4-amino-2-methyl-1-butanol, and 1,3-diaminopropane. Examples of cyclic secondary amines include morpholine and DL-3-pyrrolidinol. Examples of acyclic secondary amines include 2-(methylamino)ethanol, 2-(ethylamino)ethanol, and 2-(butylamino)ethanol.

[0020] At least one type of organic solvent has an Ra of 14.6-17 MPa. 1 / 2 The range is not particularly limited. For example, at least one organic solvent may be selected from ether compounds. Examples of ether compounds include diethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol monomethyl ether, and diethylene glycol diethyl ether.

[0021] The carbon dioxide absorbent may further contain additives such as absorption enhancers, antioxidants, and corrosion inhibitors.

[0022] II. Methods for capturing carbon dioxide As shown in Figure 1, the carbon dioxide recovery method according to the embodiment includes: absorbing carbon dioxide with the carbon dioxide absorbent according to the embodiment and separating the carbon dioxide absorbent into an aqueous phase and an organic phase (S1); releasing and recovering carbon dioxide from the aqueous phase by heating the aqueous phase (S2); and regenerating the carbon dioxide absorbent by mixing the organic phase with the aqueous phase from which carbon dioxide has been released (S3). Note that regenerating the carbon dioxide absorbent by mixing the organic phase and the aqueous phase is an optional step.

[0023] The carbon dioxide recovery method according to this embodiment can be carried out, for example, using the carbon dioxide recovery device 10 shown in Figure 2.

[0024] The carbon dioxide recovery device 10 includes an absorber 1 that brings a carbon dioxide absorbent into contact with a carbon dioxide-containing gas, a liquid separator 2 that separates the aqueous phase and organic phase produced in the absorber 1, a desorber 3 that heats the aqueous phase from the liquid separator 2 to release (desorb) carbon dioxide, and a circulation mechanism 4 that combines the organic phase from the liquid separator 2 and the aqueous phase from the desorber 3 and returns them to the absorber 1.

[0025] Examples of carbon dioxide-containing gases include air and exhaust gas. The carbon dioxide concentration of the carbon dioxide-containing gas is not particularly limited and may be any concentration including the carbon dioxide concentration in the atmosphere (approximately 0.04 vol%), for example, from 0.01 vol% to 20 vol%, and particularly from 0.01 vol% to 0.1 vol%.

[0026] Absorber 1 absorbs carbon dioxide by bringing the carbon dioxide absorbent into contact with a carbon dioxide-containing gas, and then discharges the gas from which the carbon dioxide has been removed or reduced. Absorber 1 can be any device that can continuously bring the carbon dioxide absorbent and the carbon dioxide-containing gas into contact. Examples of devices used as absorber 1 include a device that sprays the carbon dioxide absorbent into a flow path of carbon dioxide-containing gas, a device that causes the carbon dioxide absorbent to flow down through a packing material placed in the flow path of carbon dioxide-containing gas, and a device that merges a number of fine flow paths into which carbon dioxide-containing gas and carbon dioxide absorbent are introduced, respectively.

[0027] Liquid separator 2 can be any device that promotes phase separation of the carbon dioxide absorbent and separates the aqueous phase, which has a high carbon dioxide content, from the organic phase, which has a low carbon dioxide content. Examples of devices used as liquid separator 2 include devices that separate the aqueous phase and the organic phase by specific gravity, and devices that separate the aqueous phase and the organic phase by centrifugal separation.

[0028] Desorber 3 releases carbon dioxide from the aqueous phase by heating the aqueous phase. Desorber 3 has a reboiler 5 that heats the aqueous phase. When the aqueous phase is heated, not only is carbon dioxide released, but water also evaporates. Therefore, desorber 3 has a condenser 6 that cools the mixed gas containing water vapor and carbon dioxide released from the aqueous phase, condensing and separating the water vapor. The water condensed in condenser 6 recirculates within desorber 3, and the carbon dioxide is discharged outside the system and recovered.

[0029] The circulation mechanism 4 includes a first channel L1 that supplies the carbon dioxide absorbent from the absorber 1 to the liquid separator 2, a second channel L2 that supplies the aqueous phase extracted from the liquid separator 2 to the desorber 3, a third channel L3 that recirculates the aqueous phase treated in the desorber 3 back to the absorber 1, and a fourth channel L4 that introduces the organic phase extracted from the liquid separator 2 into the third channel L3 and recirculates it back to the absorber 1.

[0030] The circulation mechanism 4 further includes a main heat exchanger 7 arranged across the second flow path L2 and the third flow path L3. The main heat exchanger 7 exchanges heat between the aqueous phase from the liquid separator 2 and the aqueous phase from which carbon dioxide has been released in the desorber 3. Any heat exchanger can be used as the main heat exchanger 7. Examples of heat exchangers used as the main heat exchanger 7 include plate heat exchangers and microchannel heat exchangers. Microchannel heat exchangers are highly energy efficient because they can exchange heat between fluids with relatively small temperature differences.

[0031] The circulation mechanism 4 further includes a cooler 8 located downstream of the confluence of the third channel L3 and the fourth channel L4. The cooler 8 cools the mixture of the aqueous phase from the desorber 3 and the organic phase from the liquid separator 2, i.e., the regenerated carbon dioxide absorbent. The cooler 8 keeps the temperature of the carbon dioxide absorbent in the absorber 1 low, thereby maintaining a high carbon dioxide absorption efficiency in the absorber 1. As the cooler 8, a heat exchanger using inexpensive cooling water, such as river water, can be used.

[0032] The carbon dioxide capture device 10 may further include appropriately arranged heat recovery means, thereby further reducing the energy consumed for carbon dioxide capture.

[0033] In the carbon dioxide recovery method according to this embodiment, the aqueous phase with a high carbon dioxide content is extracted and heated to release and recover carbon dioxide from the aqueous phase. Since the extracted aqueous phase is heated to release the carbon dioxide, it is not necessary to heat the entire amount of carbon dioxide absorbent, and therefore the energy consumption for carbon dioxide recovery is small. [Examples]

[0034] The present disclosure will be further described below with reference to examples. However, the scope of the present disclosure is not limited to these examples.

[0035] The following abbreviations are used in this example. DGA: 2-(2-aminoethoxy)ethanol MOR: Morpholine DL3P: DL-3-pyrrolidinol DEGEME: Diethylene glycol ethyl methyl ether DEGDME: Diethylene glycol dimethyl ether DEGMME: Diethylene glycol monomethyl ether

[0036] DGA, MOR, and DL3P were prepared as amine compounds. DEGEME, DEGDME, and DEGMME were prepared as organic solvents. The dispersion force term δD, polarity term δP, and hydrogen bonding term δH of these amine compounds and organic solvents are shown in Table 1.

[0037] [Table 1]

[0038] In Examples 1-5 and Comparative Examples 1-6, the materials listed in Table 2 were used as the amine compound and organic solvent. The compositions of Examples 1-5 and Comparative Examples 1-6 were prepared by mixing the amine compound, organic solvent, and water. The content of the amine compound, organic solvent, and water in the compositions, based on the total weight of the compositions, was as shown in Table 2.

[0039] In Examples 1-5 and Comparative Examples 1-6, Ra is defined by the following formula: Ra=[4(δDa·Ca / 100+δDw·Cw / 100-δDs) 2 +(δPa·Ca / 100+δPw·Cw / 100-δPs) 2 +(δHa·Ca / 100+δHw·Cw / 100-δHs) 2 ] 1 / 2 (In the formula, Ca represents the content (by weight) of the amine compound in the composition, based on the total weight of the composition. Cw represents the water content (by weight) in the composition, based on the total weight of the composition. δDa represents the dispersion force term of the HSP of the amine compound. δDw represents the dispersion force term of the HSP of water, δDs represents the dispersion force term of HSP in organic solvents. δPa represents the polarity term of the HSP of an amine compound. δPw represents the polarity term of the HSP of water, δPs represents the polarity term of the HSP of an organic solvent. δHa represents the hydrogen bonding term of the HSP of the amine compound. δHw represents the hydrogen bonding term of the water HSP, δHs represents the hydrogen bonding term of the HSP in organic solvents. The calculation was performed. The results are shown in Table 2.

[0040] The composition of Comparative Example 2 separated into two phases: an aqueous phase and an organic phase. The compositions of Examples 1-5 and Comparative Examples 1, 3-6 were single-phase.

[0041] At an ambient temperature of 20°C, 15 g of each composition from Examples 1-5 and Comparative Examples 1-6 were bubbling with air containing 400-500 ppm of carbon dioxide at a flow rate of 1.5 L / min for 5 hours.

[0042] After bubbling, the compositions of Examples 1-5 and Comparative Example 2 separated into two phases: an aqueous phase and an organic phase. The compositions of Comparative Examples 1, 3-6 were single-phase.

[0043] [Table 2]

[0044] Ra is 14.6-17 MPa 1 / 2 Compositions within the specified range were confirmed to separate into two phases after air bubbling: an aqueous phase with a high carbon dioxide content and an organic phase with a low carbon dioxide content. When such compositions are used as carbon dioxide absorbents, the high-carbon dioxide aqueous phase can be extracted and heated to release the carbon dioxide. Since it is not necessary to heat the entire carbon dioxide absorbent, carbon dioxide can be recovered with minimal energy consumption. [Explanation of symbols]

[0045] 1: Absorber, 2: Liquid separator, 3: Desorber, 4: Circulation mechanism, 5: Reboiler, 6: Condenser, 7: Main heat exchanger, 8: Cooler, L1: First channel, L2: Second channel, L3: Third channel, L4: Fourth channel

Claims

1. It is a carbon dioxide absorbent, At least one type of amine compound, Water and, At least one type of organic solvent, Includes, Ra defined by the following formula Ra=[4(δDa・Ca / 100+δDw・Cw / 100-δDs) ２ +(δPa・Ca / 100+δPw・Cw / 100-δPs) ２ +(δHa・Ca / 100+δHw・Cw / 100-δHs) ２ ] １／２ (In the formula, Ca represents the total content (by weight) of at least one amine compound in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. Cw represents the water content (by weight) in the carbon dioxide absorbent, based on the total weight of the carbon dioxide absorbent. δDa represents the dispersion force term of the Hansen solubility parameter of at least one amine compound, δDw represents the dispersion force term of the Hansen solubility parameter for water, δDs represents the dispersion force term of the Hansen solubility parameter of at least one organic solvent, δPa represents the polarity term of the Hansen solubility parameter of at least one amine compound, δPw represents the polarity term of the Hansen solubility parameter for water. δPs represents the polarity term of the Hansen solubility parameter of at least one organic solvent, δHa represents the hydrogen bonding term of the Hansen solubility parameter of at least one amine compound, δHw represents the hydrogen bonding term of the Hansen solubility parameter for water. δHs represents the hydrogen bonding term of the Hansen solubility parameter of at least one organic solvent. However, 14.6-17 MPa １／２ A carbon dioxide absorbent that falls within the specified range.

2. The carbon dioxide absorbent according to claim 1, wherein at least one amine compound may optionally contain at least one group selected from the group consisting of a hydroxyl group and an ether group, and is selected from the group consisting of primary amines, cyclic secondary amines, and acyclic secondary amines.

3. The total content of at least one amine compound in the carbon dioxide absorbent is 10 to 50% by weight, based on the total weight of the carbon dioxide absorbent. The water content in the carbon dioxide absorbent is 5 to 20% by weight, based on the total weight of the carbon dioxide absorbent. The carbon dioxide absorbent according to claim 1, wherein the total content of at least one organic solvent in the carbon dioxide absorbent is 45 to 85% by weight based on the total weight of the carbon dioxide absorbent.

4. A method for capturing carbon dioxide, The carbon dioxide absorbent described in any one of claims 1 to 3 absorbs carbon dioxide, thereby separating the carbon dioxide absorbent into an aqueous phase and an organic phase, By heating the aqueous phase, carbon dioxide is released from the aqueous phase and recovered. A method that includes this.

5. The method according to claim 4, further comprising mixing the organic phase with the aqueous phase from which carbon dioxide has been released to regenerate the carbon dioxide absorbent.

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