Carbon dioxide separation composition

Abstract

The present disclosure pertains to a carbon dioxide separation composition comprising a carbonic anhydrase and at least one selected from the group consisting of amino acids and salts thereof.

Description

Composition for carbon dioxide separation

[0001] The present disclosure relates to a composition for carbon dioxide separation.

[0002] In the past, amines such as ethanolamine and metal hydroxides such as sodium hydroxide have been used as carbon dioxide absorbents for separating and capturing carbon dioxide. However, these conventional carbon dioxide absorbents have been noted to be corrosive to the equipment and toxic when leaked into the environment. Furthermore, because these conventional carbon dioxide absorbents have a strong bond with carbon dioxide, the energy input required to capture the absorbed carbon dioxide and regenerate the absorbent is high. In particular, metal hydroxides, which are commonly used for direct carbon dioxide capture from the atmosphere, require high temperatures of 900°C or higher to regenerate the absorbent after carbon dioxide absorption. While amines can be regenerated at relatively low temperatures of around 100°C, they have low chemical stability and suffer from decomposition and degradation due to repeated absorption and regeneration.

[0003] To solve the above-mentioned problems, amino acids have recently attracted attention as absorbents with high carbon dioxide absorption rates. As an example, Brethome et al. have proposed a carbon dioxide separation and recovery method that includes the steps of: absorbing atmospheric carbon dioxide into glycine or sarcosine; contacting the glycine or sarcosine with a compound having a guanidide group to regenerate the glycine or sarcosine while precipitating the guanidide group as a carbonate hydrate; and heating the precipitate at a relatively low temperature of 80 to 120 °C to regenerate the guanidide compound while recovering carbon dioxide (Non-Patent Document 1). Sarlak et al. have also reported that high carbon dioxide absorption was achieved by using methyldiethanolamine (MDEA), which has high chemical stability but a low carbon dioxide absorption rate, in combination with arginine (Non-Patent Document 2). Carbon dioxide recovery using a gas separation membrane containing an ionic liquid containing an amino acid as a component has also been reported (Patent Documents 1 to 4). Furthermore, it has been reported that potassium carbonate, which can release carbon dioxide at a relatively low temperature but has a slow carbon dioxide absorption rate, can be regenerated at a relatively low temperature of around 80°C by using it in combination with carbonic anhydrase (Non-Patent Documents 3 and 4).

[0004] Japanese Patent Application Laid-Open No. 2010-214324 Japanese Patent Application Laid-Open No. 2015-025057 Japanese Patent Application Laid-Open No. 2015-027654 Japanese Patent Application Laid-Open No. 2017-213563 International Publication No. 2011 / 066304 International Publication No. 2011 / 041011 U.S. Patent No. 8,569,031

[0005] Nat. Energy, 3 (2018), 553-559. Energy, 239 (2022), 122349. Appl. Energy, 209 (2018), 180-189. PNAS, 111 (2014), 16436-16441. J. CO2 Util. , 47 (2021), 101475. Vought Biochemistry (1st edition) 1st edition 2nd printing, published by Tokyo Kagaku Dojin Co., Ltd., October 20, 1992, p50.

[0006] An object of one aspect of the present disclosure is to provide a composition for carbon dioxide separation that has an excellent carbon dioxide absorption rate.

[0007] Some aspects of the present disclosure provide the following [1] to [6].

[0008] [1] A composition for carbon dioxide separation comprising at least one amino acid selected from the group consisting of amino acids and salts thereof, and carbonic anhydrase. [2] The composition for carbon dioxide separation according to [1], wherein the amino acid is at least one amino acid selected from the group consisting of glycine, arginine, histidine, aspartic acid, glutamic acid, lysine, and cysteine. [3] The amino acid is represented by the general formula (1): wherein R is a group having a hydrophilic group, and the pKa of the amino group of the amino acid is 9.4 or higher. [4] The carbon dioxide separation composition according to [1] or [2], wherein the amino acid is at least one selected from the group consisting of aspartic acid, glutamic acid, lysine, and cysteine. [5] The carbon dioxide separation composition according to any of [1] to [4], wherein the carbonic anhydrase is a carbonic anhydrase derived from Thermosulfurimonas dismutans. [6] A method for separating carbon dioxide, comprising the steps of: contacting a gas containing carbon dioxide with the carbon dioxide separation composition according to any of [1] to [5], thereby allowing the carbon dioxide contained in the gas to be absorbed into the carbon dioxide separation composition; and releasing the carbon dioxide from the carbon dioxide separation composition into which the carbon dioxide has been absorbed.

[0009] According to the present disclosure, it is possible to provide a carbon dioxide separation composition that has an excellent carbon dioxide absorption rate.

[0010] It is a schematic diagram of a carbon dioxide absorption rate measuring device used in Examples and Comparative Examples. It is a diagram comparing the carbon dioxide absorption rate due to differences in carbon dioxide separating compositions. It is a diagram comparing the carbon dioxide absorption rate due to differences in carbon dioxide separating compositions.

[0011] In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Furthermore, unless specifically stated otherwise, the units of the numerical values ​​before and after "to" are the same. In numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of a numerical range of another stage. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. Furthermore, the upper and lower limits individually described can be arbitrarily combined. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. Unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more types.

[0012] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to the following embodiments.

[0013] [Composition for Carbon Dioxide Separation] One embodiment of the present disclosure is a composition for carbon dioxide separation, comprising at least one selected from the group consisting of amino acids and salts thereof, and carbonic anhydrase.

[0014] The carbon dioxide separation composition is a composition that can absorb carbon dioxide by contacting with a gas containing carbon dioxide and can release carbon dioxide after absorbing it. The carbon dioxide separation composition can be used as a carbon dioxide absorption / release agent in a carbon dioxide chemical absorption method.

[0015] As used herein, an "amino acid" refers to an amino group (-NH ２) and a carboxy group (—COOH). The amino acid may be an α-amino acid, in which both the amino group and the carboxy group are bound to the same carbon atom, or an amino acid in which the amino group and the carboxy group are bound to different carbon atoms (e.g., a β-amino acid). When the amino acid is an α-amino acid containing an asymmetric carbon, the amino acid may be any of the L-, D-, and DL-configurations. The amino acid may be a naturally occurring amino acid, or a non-natural amino acid that does not occur in nature.

[0016] In this specification, the amino group is a primary amino group (-NH ２ ) in the present specification. The amino group does not include those that form a resonance structure with an adjacent functional group. For example, the guanidino group (—NH—C(═NH)—NH ２ ) contained in -NH ２ is not included in the amino group in this specification.

[0017] The amino acid may be an α-amino acid represented by the general formula (1). [In general formula (1), R represents the side chain of an amino acid.]

[0018] Examples of α-amino acids include glycine, arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, histidine, isoleucine, leucine, lysine (lysine), methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine.

[0019] The α-amino acid may be an amino acid in which R is a group having a hydrophilic group and the pKa (acid dissociation constant) of the amino group is 9.4 or higher, which further increases the rate of carbon dioxide absorption.

[0020] In this specification, the term "hydrophilic group" refers to a functional group that is not a hydrogen atom (-H) and has the property of easily interacting with water. Examples of hydrophilic groups include a thiol group, a thioether group, a hydroxyl group, an amino group, and an amide group (-CONH ２), a carboxy group, a guanidino group, and an imidazole group. R may be a group consisting of a hydrophilic group and a linking group that links the hydrophilic group and the α-carbon. The linking group may be, for example, an alkanediyl group. The number of carbon atoms in the alkanediyl group may be, for example, 1 to 6. Examples of the alkanediyl group include a methylene group, an ethylene group, a propane-1,2-diyl group, a propane-1,3-diyl group, and a butane-1,4-diyl group.

[0021] In the present specification, the "pKa of the amino group" refers to the higher pKa value when the side chain R of the amino acid contains an amino group. For example, lysine has two amino groups in its side chain, and when the pKa values ​​of the two amino groups are compared, the pKa value of the amino group in the side chain is higher, so the pKa value of the amino group of lysine is 10.79. The pKa value of the amino group of an amino acid may be 9.4 to 10.8.

[0022] For the pKa of the amino group of each amino acid, see "Table 4.2 pKa values ​​(25°C) of dissociable groups of standard amino acids" on page 50 of Non-Patent Document 6. For the pKa of amino groups not listed in Non-Patent Document 6, the pKa measured in water at 25°C is used.

[0023] Specific examples of amino acids whose side chains have hydrophilic groups and whose amino group pKa is 9.4 or higher include aspartic acid (pKa: 9.90), glutamic acid (pKa: 9.47), lysine (pKa: 10.79), and cysteine ​​(pKa: 10.78).

[0024] Examples of amino acid salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; and amine salts such as ammonium salts, guanidine salts, and tertiary amine salts.

[0025] At least one selected from the group consisting of amino acids and salts thereof has high solubility. Therefore, a carbon dioxide separation composition containing at least one selected from the group consisting of amino acids and salts thereof at a high concentration can be easily obtained. The at least one selected from the group consisting of amino acids and salts thereof may be at least one selected from the group consisting of glycine, arginine, histidine, aspartic acid, glutamic acid, lysine, cysteine, and salts thereof, or may be at least one selected from the group consisting of aspartic acid, glutamic acid, lysine, cysteine, and salts thereof.

[0026] The total content of at least one selected from the group consisting of amino acids and salts thereof may be 0.10 mol / L or more, 0.20 mol / L or more, 0.40 mol / L or more, 0.60 mol / L or more, 0.80 mol / L or more, or 0.95 mol / L or more, based on the total amount of the carbon dioxide separation composition, and may be a saturated concentration or less, 3.0 mol / L or less, 2.0 mol / L or less, 1.5 mol / L or less, or 1.2 mol / L or less. The total content of at least one selected from the group consisting of amino acids and salts thereof may be 0.10 mol / L or more, 0.20 mol / L or more, 0.40 mol / L or more, 0.60 mol / L or more, 0.80 mol / L or more, or 0.95 mol / L or more, based on the total amount of the carbon dioxide separation composition, and may be the saturated concentration or less, and may be 0.10 to 3.0 mol / L, 0.20 to 3.0 mol / L, 0.40 to 3.0 mol / L, 0.60 to 3.0 mol / L, 0.80 to 3.0 mol / L, or 0.95 to 3.0 mol / L, and may be 0.10 to 2.0 mol / L, 0.20 to 3.0 mol / L, 0.40 to 3.0 mol / L, 0.60 to 3.0 mol / L, 0.80 to 3.0 mol / L, or 0.95 to 3.0 mol / L. The concentration may be 2.0 mol / L, 0.40 to 2.0 mol / L, 0.60 to 2.0 mol / L, 0.80 to 2.0 mol / L, or 0.95 to 2.0 mol / L; may be 0.10 to 1.5 mol / L, 0.20 to 1.5 mol / L, 0.40 to 1.5 mol / L, 0.60 to 1.5 mol / L, 0.80 to 1.5 mol / L, or 0.95 to 1.5 mol / L; may be 0.10 to 1.2 mol / L, 0.20 to 1.2 mol / L, 0.40 to 1.2 mol / L, 0.60 to 1.2 mol / L, 0.80 to 1.2 mol / L, or 0.95 to 1.2 mol / L.

[0027] Carbonic anhydrase (CA) is an enzyme that catalyzes the hydration of carbon dioxide and its reverse reaction. CA has a reaction rate of 10 ６ s －１ The carbon dioxide separation composition has such a high catalytic activity that the diffusion rate of carbon dioxide into the carbon dioxide separation composition can be improved by including a CA.

[0028] CAs are classified into α-, β-, γ-, δ-, and ζ-types based on amino acid sequence homology. α-, β-, and δ-types have a zinc ion at the active center. γ-type has an iron ion. ζ-type has a cadmium ion or zinc ion. CAs that have catalytic activity at 70°C or below can be used, for example.

[0029] The origin of CA may be, for example, animals, plants, or microorganisms. Examples of animals include mammals, birds, and seafood. Examples of mammals include cows, pigs, sheep, and humans. Examples of birds include chickens, geese, ducks, and wild goats. Examples of seafood include shrimp. Examples of plants include grains and fruits. Examples of microorganisms include microalgae, Escherichia coli, Bacillus subtilis, yeast, filamentous fungi, and archaea. Examples of microorganisms may be, for example, microorganisms classified into the genus Thermosulfurimonas, such as Thermosulfurimonas dismutans.

[0030] CA may be obtained, for example, by separation and purification from a sample derived from an animal, plant, or microorganism, or by culturing a microorganism with the primary purpose of obtaining CA.

[0031] The source of animal-derived CA may be a blood sample containing red blood cells. The blood sample as the source of CA may be, for example, livestock by-products, which are inexpensively available, or medical waste. Examples of medical waste include donated blood specimens, human placenta, and excised organs.

[0032] The source of plant-derived CA may be, for example, the inedible parts of agricultural products such as the leaves of grains and fruits.

[0033] Examples of sources for isolating microbial CA include filtration residues containing yeast cells after sake and beer brewing.

[0034] The CA separation source may be used as is as a component of the carbon dioxide separation composition, or may be processed as necessary to efficiently separate carbon dioxide. The CA separation source may be used, for example, by extraction with a solvent. The solvent used for extraction may be water or a buffer solution containing dissolved salts. The solvent used for extraction may contain, for example, an organic solvent such as ethanol or acetone, and a denaturant such as urea or guanidine hydrochloride, within a range that does not significantly inhibit CA activity.

[0035] The extract containing CA may be used as is as a component of the carbon dioxide separation composition, or may be purified to any desired purity before use. CA can be purified using existing methods. Examples of purification methods that can be used include ammonium sulfate salting out, solvent fractionation, various types of chromatography, and any combination of these.

[0036] CA can also be obtained by a method including, for example, introducing a polynucleotide encoding a CA protein (hereinafter also referred to as "CA gene") into a microorganism and culturing the resulting recombinant. The microorganism may be an easily cultivable microorganism such as Escherichia coli. The CA gene may be obtained from the various isolation sources mentioned above. When a recombinant is used, CA with improved properties such as heat resistance, alkali resistance, and specific activity can be obtained by modifying the introduced CA gene.

[0037] Known modified CAs (modified CAs) include a modified β-class CA derived from Desulfovibrio vulgaris (Non-Patent Document 4), a modified β-class CA derived from Methabacterium thermoautotrophicus DeltaH (Patent Document 4), and a modified γ-class CA derived from Methanosarcina thermophila (Patent Document 6).

[0038] The CA may be a chemically modified CA. A known example of a chemically modified CA is human CAII, an α-class CA, which has been chemically crosslinked and stabilized (Patent Document 7).

[0039] The CA may be immobilized on an insoluble carrier by physical adsorption or covalent bonding. An example of a CA immobilized on an insoluble carrier is the immobilized CA disclosed by Cristian Molina-Fernandez et al. (Non-Patent Document 5).

[0040] The material of the insoluble carrier is not particularly limited as long as it can maintain stability under the conditions (temperature, solvent atmosphere, etc.) used in the carbon dioxide separation method, and examples include silica, alumina, magnesia, porous glass, activated carbon, polymethyl methacrylate-based porous resin, or fiber. When silica is used as the insoluble carrier, there are no particular limitations on the silica used, and it may be crystalline silica, non-crystalline (amorphous) silica, zeolite-like silica having pores, mesoporous silica, or industrially available silica may be used as is. The silica used as the insoluble carrier may be silica with a large surface area.

[0041] The content of CA may be 0.06 parts by mass or more, 0.13 parts by mass or more, or 0.19 parts by mass or more, and may be 13.3 parts by mass or less, 6.65 parts by mass or less, 2.66 parts by mass or less, 1.33 parts by mass or less, 0.99 parts by mass or less, 0.66 parts by mass or less, or 0.33 parts by mass or less, relative to 100 parts by mass of the total content of at least one kind selected from the group consisting of amino acids and salts thereof.

[0042] The content of CA is not particularly specified, but can be determined taking into consideration the range in which sufficient activity is exhibited and economic efficiency. For example, in the case of carbonic anhydrase derived from Thermosulfurimonas dismutans, the content of CA may be 0.05 mg / mL or more, 0.10 mg / mL or more, or 0.15 mg / mL or more, and may be 10.0 mg / mL or less, 5.0 mg / mL or less, 2.0 mg / mL or less, 1.0 mg / mL or less, 0.75 mg / mL or less, 0.50 mg / mL or less, or 0.25 mg / mL or less, based on the total amount of the carbon dioxide separation composition. The content of the CA may be 0.05 to 10.0 mg / mL, 0.10 to 10.0 mg / mL, or 0.15 to 10.0 mg / mL, or 0.05 to 5.0 mg / mL, 0.10 to 5.0 mg / mL, or 0.15 to 5.0 mg / mL, or 0.05 to 2.0 mg / mL, 0.10 to 2.0 mg / mL, or 0.15 to 2.0 mg / mL, or 0.05 to 1.0 mg / mL, based on the total amount of the carbon dioxide separation composition. L, 0.10-1.0 mg / mL, or 0.15-1.0 mg / mL, optionally 0.05-0.75 mg / mL, 0.10-0.75 mg / mL, or 0.15-0.75 mg / mL, optionally 0.05-0.50 mg / mL, 0.10-0.50 mg / mL, or 0.15-0.50 mg / mL, and optionally 0.05-0.25 mg / mL, 0.10-0.25 mg / mL, or 0.15-0.25 mg / mL.

[0043] From the viewpoint of operability, the carbon dioxide separation composition may further contain a solvent. The solvent is not particularly limited, but examples thereof include water, alcohols (monohydric alcohols and polyhydric alcohols), and mixtures thereof. Examples of polyhydric alcohols include ethylene glycol, glycerin, and polyethylene glycol.

[0044] The solvent may be water, because it is more efficient in absorbing and separating carbon dioxide gas as bicarbonate, more effective in suppressing an increase in the viscosity of the carbon dioxide separation composition and the generation of solids, and more effective in suppressing the energy emitted by carbon dioxide.

[0045] When a solvent is contained, the total content of the solvent may be 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, or 75% by mass or more, relative to the total amount of the carbon dioxide separation composition, since the operability of the carbon dioxide separation composition is superior, and may be 99% by mass or less, 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less. When a solvent is contained, the total content of the solvent may be 30 to 99% by mass, 40 to 99% by mass, 50 to 99% by mass, 60 to 99% by mass, 70 to 99% by mass, or 75 to 99% by mass, relative to the total amount of the carbon dioxide separation composition, since the operability of the carbon dioxide separation composition is superior. It may be 30 to 90 mass%, 40 to 90 mass%, 50 to 90 mass%, 60 to 90 mass%, 70 to 90 mass%, or 75 to 90 mass%, 30 to 85 mass%, 40 to 85 mass%, 50 to 85 mass%, 60 to 85 mass%, 70 to 85 mass%, or 75 to 85 mass%, 30 to 80 mass%, 40 to 80 mass%, 50 to 80 mass%, 60 to 80 mass%, 70 to 80 mass%, or 75 to 80 mass%.

[0046] The carbon dioxide separation composition may further contain a pH adjuster. Examples of pH adjusters include potassium hydroxide, sodium hydroxide, and aqueous ammonia. The pH of the carbon dioxide separation composition may be, for example, 9.5 or higher, 10.0 or higher, or 10.5 or higher, and may be 12.0 or lower, 11.5 or lower, or 11.0 or lower. The pH of the carbon dioxide separation composition may be, for example, 9.5 to 12.0, 10.0 to 12.0, or 10.5 to 12.0, 9.5 to 11.5, 10.0 to 11.5, or 10.5 to 11.5, or 9.5 to 11.0, 10.0 to 11.0, or 10.5 to 11.0.

[0047] The carbon dioxide separation composition may further contain other components in addition to the components described above, such as buffer components such as trishydroxymethylaminomethane and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid, ethylene glycol diglycidyl ether, and water-soluble polymers such as polyethyleneimine and sodium polyacrylate.

[0048] The carbon dioxide separation composition of the present disclosure contains at least one selected from the group consisting of amino acids and their salts, and carbonic anhydrase, and therefore has an excellent carbon dioxide absorption rate. Because amino acids are significantly less corrosive and toxic than amines and other non-amino acids, the carbon dioxide separation composition of the present disclosure inhibits corrosion of equipment and reduces the environmental impact in the event of a leak. Therefore, the carbon dioxide separation composition of the present disclosure enables the construction of a carbon dioxide capture process with a low environmental impact.

[0049] [Method for producing a composition for carbon dioxide separation] The above-mentioned composition for carbon dioxide separation can be obtained, for example, by a method including mixing at least one selected from the group consisting of amino acids and salts thereof with carbonic anhydrase in the presence of a solvent.

[0050] [Method for Separating Carbon Dioxide] One embodiment of the present disclosure is a method for separating carbon dioxide using a carbon dioxide separation composition. The separation method includes a step of bringing a gas containing carbon dioxide into contact with the carbon dioxide separation composition to absorb the carbon dioxide contained in the gas (absorption step), and a step of releasing the carbon dioxide from the carbon dioxide separation composition that has absorbed the carbon dioxide (release step).

[0051] In the absorption step, a gas containing carbon dioxide is brought into contact with a carbon dioxide separating composition, and the carbon dioxide contained in the gas is absorbed into the carbon dioxide separating composition.

[0052] The carbon dioxide-containing gas may be pure carbon dioxide gas or a mixed gas containing carbon dioxide and other gases. The other gases are not particularly limited, and examples thereof include air, nitrogen, oxygen, hydrogen, argon, neon, helium, carbon monoxide, water vapor, methane, and nitrogen oxides (NOx). Considering the improvement of the separation performance between carbon dioxide and other gases, the concentration of carbon dioxide contained in the mixed gas may be 5% or more, or 10% or more, based on the total amount of the mixed gas.

[0053] The method for contacting a carbon dioxide-containing gas with the carbon dioxide separation composition is not particularly limited, and known methods such as a bubbling method and a head-on contact method using a packed column or a plate column can be used.

[0054] The temperature (absorption temperature) when a gas containing carbon dioxide is absorbed into the carbon dioxide separation composition may be, for example, 50°C or lower, or 45°C or lower, or may be 0°C or higher, 10°C or higher, 20°C or higher, 30°C or higher, or 35°C or higher. The absorption temperature may be, for example, 0°C or higher and 50°C or lower. The absorption temperature may be constant throughout the absorption step, or may be changed stepwise or continuously.

[0055] In the desorption step, carbon dioxide is desorbed from the carbon dioxide separation composition that has absorbed carbon dioxide in the absorption step. The desorption step allows the carbon dioxide chemically adsorbed in the carbon dioxide separation composition to be desorbed.

[0056] As a method for releasing the absorbed carbon dioxide, for example, a method of heating the carbon dioxide separating composition in which carbon dioxide has been absorbed and / or exposing it to a reduced pressure environment can be used.

[0057] The temperature (dissipation temperature) at which carbon dioxide is dissipated from the carbon dioxide separation composition may be, for example, 150°C or less, 120°C or less, 100°C or less, 80°C or less, or 70°C or less, or may be 60°C or more, or 65°C or more. The dissipation temperature may be, for example, 60 to 150°C. From the viewpoint of energy conservation, the dissipation temperature may be 100°C or less. The dissipation temperature may be constant throughout the dissipation step, or may be changed stepwise or continuously.

[0058] The separation method may further include other steps that are commonly performed in carbon dioxide separation in addition to the absorption step and the desorption step. Examples of such other steps include a cooling step, a heating step, a washing step, an extraction step, an ultrasonic treatment step, a distillation step, and a chemical treatment step.

[0059] The separation method can be applied to applications such as separation of carbon dioxide from combustion exhaust gas generated in thermal power plants, steel plants, cement factories, etc., and separation of carbon dioxide from steam reformed gas obtained in a steam reforming process.

[0060] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0061] The apparatus used to measure the carbon dioxide absorption rate in this example and this comparative example is shown in Figure 1. The apparatus shown in Figure 1 includes a bottle 11 containing an absorbing liquid 2 (carbon dioxide separation composition), an agitator 10 equipped with an agitator blade 12 and a band heater 13, a thermocouple 14 and a pH electrode 15 installed in the bottle 11 of the agitator, mass flow controllers 20a and 20b controlling the flow rates of air 1a and carbon dioxide 1b, respectively, a mist trap 40 connected to the bottle 11, a carbon dioxide analyzer 61 measuring the carbon dioxide concentration contained in the flue gas 3, a data logger 62 collecting the output from the carbon dioxide analyzer 61, a three-way valve 31 arranged in the flow path between the bottle 11 and the mass flow controllers 20a and 20b, a three-way valve 32 arranged in the flow path between the mist trap 40 and the carbon dioxide analyzer 61, an air filter 51 arranged in the flow path between the mass flow controllers 20a and 20b and the three-way valve 31, and an air filter 52 arranged in the flow path between the carbon dioxide analyzer 61 and the three-way valve 32. The three-way valves 31 and 32 can switch the gas vent path to a path into the bottle 11 or a bypass path 100 for discharging the gas outside the flow path without passing through the bottle 11.

[0062] Example 1 Carbon Dioxide Absorption into Aqueous Glycine Solution (with Addition of Carbonic Anhydrase (CA)) (1) Preparation of Carbonic Anhydrase (1-1) A polynucleotide was synthesized by adding an oligonucleotide (CAT) for cleavage with the restriction enzyme NdeI to the 5'-end of a polynucleotide (SEQ ID NO: 3) encoding a polypeptide (SEQ ID NO: 2) in which the amino acid residues from the second lysine (K) to the 20th alanine (A), which correspond to the signal peptide, of the amino acid sequence (GenBank No. OAQ21602, SEQ ID NO: 1) of wild-type Thermosulfurimonas dismutans-derived carbonic anhydrase (hereinafter also referred to as tdCA) were deleted, and adding an oligonucleotide (CAT) for cleavage with the restriction enzyme NdeI to the 3'-end of the polynucleotide, and adding an oligonucleotide (SEQ ID NO: 4) encoding six histidine residues (histidine tag) and an oligonucleotide (TAAGCTT) corresponding to a stop codon and a cleavage site for the restriction enzyme HindIII to the 3'-end of the polynucleotide.

[0063] (1-2) The polynucleotide synthesized in (1-1) (previously digested with NdeI and HindIII) was inserted into a pET26b(+) plasmid vector (Novagen) previously digested with NdeI and HindIII to prepare a wild-type tdCA expression plasmid, pET-tdCA_WT.

[0064] (1-3) The plasmid capable of expressing pET-tdCA_WT prepared in (1-2) was used to transform Escherichia coli BL21 (DE3) strain (Nippon Gene Co., Ltd.) to prepare tdCA-expressing Escherichia coli (transformant).

[0065] (1-4) The tdCA-expressing E. coli prepared in (1-3) was inoculated into test tubes containing 100 mL of antibiotic-containing 2xYT medium (16 g / L tryptone, 10 g / L yeast extract, 5 g / L sodium chloride), and then pre-cultured overnight at 37°C and 150 rpm with shaking.

[0066] (1-5) 10 mL of the preculture solution from (1-4) was inoculated into a baffled flask containing 1,000 mL of antibiotic-containing 2xYT medium, and cultured with shaking at 37°C and 130 rpm for 3 hours. IPTG (isopropyl β-D-thiogalactopyranoside) was then added to a final concentration of 50 μmol / L, and the culture was further cultured at 25°C and 150 rpm for 24 hours to induce tdCA expression.

[0067] (1-6) The culture solution of (1-5) was centrifuged at 4°C and 15,000 rpm for 30 minutes, and the supernatant was removed to recover wet bacterial cells. The recovered wet bacterial cells were stored at -30°C until use.

[0068] (1-7) 5 mL of extraction buffer containing BugBuster reagent (Merck) was added per 1 g of wet bacterial cells recovered in (1-6), and the mixture was stirred at 25°C and 150 rpm for 30 minutes. Then, the mixture was centrifuged at 4°C and 10,000 rpm for 30 minutes, and the supernatant was recovered to prepare a bacterial cell extract.

[0069] (1-8) The bacterial cell extract prepared in (1-7) was sterilized using a filter with a pore size of 0.22 μm, and then added to an open column packed with 5 mL of Ni-NTA agarose (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The column was washed with 100 mL of a buffer solution containing 20 mmol / L of imidazole, and then eluted with 30 mL of a buffer solution containing 300 mmol / L of imidazole.

[0070] (1-9) The purified tdCA contained in the fraction obtained in (1-8) was quantified using a NanoDrop microspectrophotometer (manufactured by Thermo Fisher Scientific) and adjusted to a concentration of 1 mg / mL.

[0071] (2) Preparation of Absorption Solution (2-1) 15.0 g (approximately 200 mmol) of glycine (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) was weighed and dissolved in a small amount of pure water. Potassium hydroxide was added to adjust the pH to 11, and pure water was further added to prepare 200 g of absorption solution.

[0072] (2-2) 100 g of the absorption solution prepared in (2-1) was placed in a 250 mL bottle 11. After being equipped with a stirring blade 12, a band heater 13, a thermocouple 14, and a pH electrode 15, the bottle was placed in a stirring device 10 (Able Bio Jr. 8 culture device) and stirred at 40°C and 200 rpm using the stirring blade 12 to condition the absorption solution.

[0073] (3) Measurement of Carbon Dioxide Absorption Rate (3-1) After switching the flow path using three-way valves 31 and 32 so that gas would flow through bypass path 100, mass flow controllers 20a and 20b were used to ventilate air 1a at 450 mL / min and carbon dioxide 1b at 50 mL / min. The carbon dioxide concentration contained in exhaust gas 3 was measured for 5 minutes using a carbon dioxide analyzer 61 (an infrared exhaust gas analyzer OFF-GAS Jr. DEX-2562A manufactured by ABLE). The output from the analyzer 61 was collected at 5-second intervals using a data logger 62 (a midi Logger GL220 manufactured by GRAPHETC).

[0074] (3-2) After switching the flow path with the three-way valves 31 and 32 so that the gas would flow into the bottle 11 containing the absorbing liquid 2, the carbon dioxide concentration contained in the exhaust gas 3 was measured for 5 minutes with the carbon dioxide analyzer 61. During the measurement, the temperature and pH of the absorbing liquid 2 were obtained from the thermocouple 14 and pH electrode 15 and recorded by the control computer 16. Taking into account the dead volume of the piping, the carbon dioxide absorption rate in the absence of CA was calculated based on the average value of the carbon dioxide concentration measured from 2 minutes to 5 minutes after the start of aeration, according to the following formula 1, and was found to be 38.6 mL / min. v=(CO ２ (in)-CO ２ (out))×F...Formula 1 v: Carbon dioxide absorption rate (mL / min) CO ２ (in): Carbon dioxide concentration in the supply gas (mL / mL) CO ２ (out): carbon dioxide concentration in exhaust gas (mL / mL) F: supply gas flow rate (mL / min)

[0075] (3-3) 20 mL of the 1 mg / mL tdCA aqueous solution prepared in (1) was added to bottle 11 (final concentration: 167 mg / L), and the carbon dioxide absorption rate in the presence of CA was calculated using the above formula 1 from the average carbon dioxide concentration measured from 2 minutes to 4 minutes after addition.

[0076] (3-4) The stirring speed by the stirring blades 12 was increased to 300 rpm. The carbon dioxide absorption rate at 300 rpm was calculated using the above formula 1 from the average value of the carbon dioxide concentration measurements from 2 minutes to 3 minutes after setting the speed at 300 rpm.

[0077] (3-5) The stirring speed by the stirring blades 12 was increased to 400 rpm. The carbon dioxide absorption rate at 400 rpm was calculated using the above formula 1 from the average value of the carbon dioxide concentration measurements from 120 seconds (2 minutes) to 150 seconds after setting the speed at 300 rpm.

[0078] Comparative Example 1 Carbon dioxide absorption into aqueous glycine solution (no addition of CA) (1) An absorbing solution was prepared by the method described in Example 1(2).

[0079] (2) After measuring the carbon dioxide concentration contained in the gas introduced into the absorbing solution by the method described in Example 1 (3-1), the carbon dioxide absorption rate at 200 rpm was calculated by the method described in Example 1 (3-2).

[0080] (3) After the stirring speed of the stirring blades 12 was increased to 300 rpm (without adding the tdCA solution) as it was, the carbon dioxide absorption rate at 300 rpm was calculated by the method described in Example 1 (3-4).

[0081] (4) After the stirring speed of the stirring blades 12 was increased to 400 rpm (without adding the tdCA solution) as it was, the carbon dioxide absorption rate at 400 rpm was calculated by the method described in Example 1 (3-5).

[0082] Example 2 Carbon dioxide absorption into arginine aqueous solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (pH 10.5) prepared by dissolving 17.5 g (100 mmol) of arginine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) in pure water was used as the absorption solution (water was added until the total amount reached 100 g). The carbon dioxide absorption rate in the absence of CA (corresponding to Example 1 (3-2)) was 29.4 mL / min.

[0083] Comparative Example 2 Carbon dioxide absorption into arginine aqueous solution (no addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the arginine aqueous solution (pH 10.5) prepared in Example 2 was used as the absorbing liquid.

[0084] Comparative Example 3 Carbon dioxide absorption into potassium carbonate aqueous solution (no CA added) (1) 38.7 g of potassium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) and 3.44 g of potassium bicarbonate (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) were weighed and dissolved in a small amount of pure water, and further pure water was added to prepare 210 g of an absorbing solution. The pH of the absorbing solution was 10.8.

[0085] (2) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that 100 g of the absorbing solution prepared in (1) was used.

[0086] Comparative Example 4 Carbon dioxide absorption with aqueous potassium carbonate solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that 100 g of the absorbing solution prepared in Comparative Example 3 (1) was used as the absorbing solution. The carbon dioxide absorption rate in the absence of CA (corresponding to Example 1 (3-2)) was 3.9 mL / min.

[0087] The carbon dioxide absorption rates and pH of the absorbing solutions calculated in Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1. The carbon dioxide absorption rates at 200 rpm in the examples where CA was added (Examples 1 and 2 and Comparative Example 4) are values ​​in the presence of CA (corresponding to Example 1 (3-3)). Of the carbon dioxide absorption rates shown in Table 1, a comparison of the carbon dioxide absorption rates at 200 rpm is shown in Figure 2.

[0088] 2, the results of Examples 1 and 2 and Comparative Examples 1 and 2 show that the addition of CA to an aqueous amino acid solution (Examples 1 and 2) improves the carbon dioxide absorption rate compared to the aqueous amino acid solution alone (Comparative Examples 1 and 2). The addition of CA to an aqueous potassium carbonate solution (Comparative Example 4) also improved the amount of carbon dioxide absorbed compared to the aqueous potassium carbonate solution alone (Comparative Example 3), but the carbon dioxide absorption rate was lower than in the systems in which CA was added to an aqueous amino acid solution (Examples 1 and 2).

[0089] In summary, it can be seen that a carbon dioxide separation composition containing an amino acid and carbonic anhydrase has an improved carbon dioxide absorption rate compared to conventional carbon dioxide separation compositions, such as a composition containing potassium carbonate and carbonic anhydrase, amino acids alone, and potassium carbonate alone.

[0090] A carbon dioxide separation composition containing an amino acid and carbonic anhydrase uses components with a low environmental impact, and yet has an improved carbon dioxide absorption rate compared to a composition containing potassium carbonate and carbonic anhydrase. Therefore, the use of a carbon dioxide separation composition containing an amino acid and carbonic anhydrase can provide a carbon dioxide separation process with a lower environmental impact.

[0091] Example 3 Carbon dioxide absorption into histidine aqueous solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (water was added until the total amount reached 100 g) (pH 11.0) prepared by dissolving 15.6 g (100 mmol) of L-histidine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) in pure water was used as the absorption solution.

[0092] Comparative Example 5 Carbon Dioxide Absorption into Aqueous Histidine Solution (No CA Added) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the L-histidine aqueous solution (pH 11.0) prepared in Example 3 was used as the absorbing solution.

[0093] Example 4 Carbon dioxide absorption into aspartic acid aqueous solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (pH 10.9) prepared by dissolving 13.4 g (100 mmol) of L-aspartic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) in pure water (water was added until the total amount reached 100 g) was used as the absorption solution.

[0094] Comparative Example 6 Carbon dioxide absorption into an aspartic acid aqueous solution (no addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the L-aspartic acid aqueous solution (pH 10.9) prepared in Example 4 was used as the absorbing liquid.

[0095] Example 5 Carbon dioxide absorption into aqueous glutamic acid solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (water was added until the total amount reached 100 g) (pH 11.2) prepared by dissolving 18.8 g (100 mmol) of sodium L-glutamate monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) in pure water was used as the absorption solution.

[0096] Comparative Example 7 Carbon dioxide absorption into aqueous glutamic acid solution (no addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the L-glutamic acid aqueous solution (pH 11.2) prepared in Example 5 was used as the absorbing solution.

[0097] Example 6 Carbon dioxide absorption into cysteine ​​aqueous solution (with addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (water was added until the total amount reached 100 g) (pH 10.8) prepared by dissolving 17.7 g (100 mmol) of L-cysteine ​​hydrochloride monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) in pure water was used as the absorption solution.

[0098] Comparative Example 8 Carbon Dioxide Absorption into Aqueous Cysteine ​​Solution (No CA Added) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the L-cysteine ​​aqueous solution (pH 10.8) prepared in Example 6 was used as the absorbing liquid.

[0099] Example 7 Carbon Dioxide Absorption into Aqueous Lysine Solution (with Addition of CA) The carbon dioxide absorption rate was calculated in the same manner as in Example 1, except that a solution (water was added until the total amount reached 100 g) (pH 10.8) prepared by dissolving 18.3 g (100 mmol) of L-lysine hydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) in pure water was used as the absorption solution.

[0100] Comparative Example 9 Carbon Dioxide Absorption into Aqueous Lysine Solution (No CA Added) The carbon dioxide absorption rate was calculated in the same manner as in Comparative Example 1, except that the L-lysine aqueous solution (pH 10.8) prepared in Example 7 was used as the absorbing solution. The carbon dioxide absorption rates calculated in Examples 3 to 7 and Comparative Examples 5 to 9 and the pH of the absorbing solution are shown in Table 2. The carbon dioxide absorption rate at 200 rpm in the examples where CA was added (Examples 3 to 7) is the value in the presence of CA (corresponding to Example 1 (3-3)). Among the carbon dioxide absorption rates shown in Table 2, a comparison of the carbon dioxide absorption rate at 200 rpm is shown in FIG. 3.

[0101] It can be seen that even when the type of amino acid is changed, the addition of CA (Examples 3 to 7) improves the carbon dioxide absorption rate compared to the use of an aqueous amino acid solution alone (Comparative Examples 5 to 9).

[0102] Table 3 shows the pKa values ​​of the amino groups of the amino acids used in this example (the higher pKa value when the side chain R contains an amino group) and the general formula (1) The pKa values ​​are based on the values ​​in Non-Patent Document 6.

[0103] 2 and 3, it can be seen that the carbon dioxide separation compositions containing any of the amino acids examined herein and CA have an improved carbon dioxide absorption rate compared to the aqueous solutions of each amino acid alone. In particular, it was found that the carbon dioxide separation compositions containing CA and an amino acid in which R in general formula (1) has a hydrophilic group and the pKa of the amino group is 9.4 or higher (among the amino acids examined herein, aspartic acid, glutamic acid, lysine, or cysteine) have a faster carbon dioxide absorption rate compared to the carbon dioxide separation compositions containing other amino acids and CA.

[0104] This application claims priority based on a Japanese patent application filed on May 31, 2024 (Patent Application No. 2024-088860) and a Japanese patent application filed on January 24, 2025 (Patent Application No. 2025-010783), the entire contents of which are incorporated by reference and incorporated as the disclosure of the specification of the present disclosure.

[0105] 1a...air, 1b...carbon dioxide, 2...absorption liquid, 3...exhaust gas, 10...agitator, 11...bottle, 12...agitator blade, 13...band heater, 14...thermocouple, 15...pH electrode, 16...control computer, 20a, 20b...mass flow controllers, 31, 32...three-way valve, 40...mist trap, 51, 52...air filter, 61...carbon dioxide analyzer, 62...data logger, 100...bypass path

Claims

1. A composition for separating carbon dioxide, comprising at least one member selected from the group consisting of amino acids and salts thereof, and carbonic anhydrase.

2. The carbon dioxide separation composition according to claim 1, wherein the amino acid is at least one selected from the group consisting of glycine, arginine, histidine, aspartic acid, glutamic acid, lysine and cysteine.

3. The amino acid is represented by the general formula (1):

2. The carbon dioxide separation composition according to claim 1, wherein R is a group having a hydrophilic group, and the pKa of the amino group of the amino acid is 9.4 or higher.

4. The carbon dioxide separation composition according to claim 1, wherein the amino acid is at least one selected from the group consisting of aspartic acid, glutamic acid, lysine and cysteine.

5. The carbon dioxide separation composition according to any one of claims 1 to 4, wherein the carbonic anhydrase is a carbonic anhydrase derived from Thermosulfurimonas dismutans.

6. A method for separating carbon dioxide, comprising the steps of: bringing a gas containing carbon dioxide into contact with the carbon dioxide separation composition according to any one of claims 1 to 4, thereby allowing the carbon dioxide contained in the gas to be absorbed into the carbon dioxide separation composition; and releasing the carbon dioxide from the carbon dioxide separation composition into which the carbon dioxide has been absorbed.

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