Carbon dioxide absorbent and carbon dioxide separation / recovery method

Abstract

To provide an absorbent which can separate and recover carbon dioxide from a carbon dioxide-containing gas.SOLUTION: An absorbent for separating and recovering carbon dioxide from a carbon dioxide-containing gas may contain at lest one kind of alkanolamine compound represented by a general formula, at least one kind of tertiary amine compound such as 1-[2-(2-hidroxyethoxy)ethyl] piperazine or the like, and water. (In the formula, R1 is 1 to 5 C alkyl group or hydrogen atom, R2 and R3 are each independent 1 or 2 alkyl group or hydrogen atom, and n is 2 or 3).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an absorbent for efficiently separating and recovering carbon dioxide from a gas containing carbon dioxide, and a method for separating and recovering carbon dioxide using the absorbent. [Background technology]

[0002] In recent years, climate change and natural disasters believed to be caused by global warming have had a significant impact on agricultural production, living environments, energy consumption, etc. Global warming is believed to be caused by the increase in greenhouse gases in the atmosphere, such as carbon dioxide, methane, nitrous oxide, and fluorocarbons, which are increasing as a result of intensified human social activities. Carbon dioxide in the atmosphere is cited as the most important of these greenhouse gases, and measures to reduce carbon dioxide emissions into the atmosphere have become a global issue.

[0003] Sources of carbon dioxide include thermal power plants that use coal, heavy oil, natural gas, etc. as fuel, blast furnaces in steelworks that reduce iron oxide with coke, converters in steelworks that burn carbon in pig iron to make steel, boilers in various manufacturing plants, kilns in cement plants, and even transportation equipment such as automobiles, ships, and aircraft that use gasoline, heavy oil, light oil, etc. Carbon dioxide Capture and Storage (CCS), a series of technologies that target the mixed gas emitted from these sources and separate and capture the carbon dioxide contained in the mixed gas, compress it, transport it, and then inject it, is attracting attention as a technology to reduce carbon dioxide emissions into the atmosphere.

[0004] Among the processes of carbon dioxide separation and capture storage technology, the process of separating and capturing carbon dioxide is particularly costly, and therefore a technology for reducing the cost is required.In recent years, therefore, a method for separating and capturing carbon dioxide from a mixed gas has been considered in which a gas containing carbon dioxide is brought into contact with an aqueous solution of an amine compound in an absorption tower to allow the amine compound to absorb the carbon dioxide.

[0005] Known amine compounds include primary alkanolamines such as monoethanolamine (MEA), diglycolamine (DGA), and 2-amino-2-methyl-1-propanol (AMP); secondary alkanolamines such as 2-(methylamino)ethanol (MAE), 2-(ethylamino)ethanol (EAE), 2-(isopropylamino)ethanol (IPAE), 3-(isopropylamino)propanol (IPAP), diethanolamine (DEA), and diisopropanolamine (DIPA); tertiary alkanolamines such as N-methyldiethanolamine (MDEA), 2-(dimethylamino)ethanol (DMAE), and triethanolamine (TEA); and tertiary alkylamines such as N,N,N',N'-tetramethyl-1,6-diaminohexane (TMDAH), N,N,N',N'-tetramethyl-1,4-diaminobutane (TMDAB), and bis(2-dimethylaminoethyl)ether (BDER). Among these, monoethanolamine (MEA) is widely used.

[0006] For example, Patent Document 1 proposes a method for efficiently removing carbon dioxide from combustion exhaust gas under atmospheric pressure by using an aqueous solution of AMP, MAE, EAE, or the like as an absorbing solution. Patent Document 2 proposes a method for efficiently separating and recovering carbon dioxide with low energy consumption by using an aqueous solution containing IPAE as an absorbing solution. Patent Document 2 describes the result that when the concentration of IPAE in the aqueous solution is increased to 60 mass% or more in order to make the recovery of carbon dioxide more efficient, the absorption rate of carbon dioxide and the amount of carbon dioxide emitted are significantly reduced.

[0007] Patent Document 3 proposes a method for removing and recovering absorbed acid gas from an aqueous treatment fluid containing chemically absorbed acid gas and at least one acid gas absorbing chemical agent, and for regenerating the acid gas absorbing chemical agent. Examples of the acid gas absorbing chemical agent include MEA, DEA, DIPA, TEA, and MDEA.

[0008] Patent Document 4 proposes a water-containing liquid absorbent containing a tertiary aliphatic amine that has no hydrogen bonding group and has an ether group, as an absorbent that achieves a high absorption rate, a high diffusion rate, and a high carbon dioxide recovery amount in a region where the carbon dioxide partial pressure is high.

[0009] Patent Documents 5 to 7 propose absorbents using an amine compound in combination, which can recover high-purity carbon dioxide efficiently and with low energy consumption. The absorbent in Patent Document 5 is an aqueous solution containing an aminoalcohol compound and an amine compound such as TMDAH or TMDAB, and the absorbent in Patent Document 6 is a liquid containing a secondary amine compound such as IPAE having a specific structure, a polyamine compound having a specific structure, and water. Patent Document 7 proposes an absorbent containing an alkanolamine compound having a specific structure, a tertiary aliphatic amine compound such as BDER having an ether group, and water. Patent Document 7 describes that the absorbent shows high performance when the total mass concentration of the amine compounds contained in the absorbent is in the range of more than 60% and less than 85%, and the performance decreases when the total mass concentration of the amine compounds is 85% or more. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 5-301023 [Patent Document 2] JP 2009-6275 A [Patent Document 3] International Publication No. 2005 / 009592 [Patent Document 4] International Publication No. 2011 / 071150 [Patent Document 5] International Publication No. 2013 / 118819 [Patent Document 6] International Publication No. 2014 / 129400 [Patent Document 7] International Publication No. 2019 / 163867 Summary of the Invention [Problem to be solved by the invention]

[0011] In today's world, where reductions in the amount of carbon dioxide generated and energy and resource conservation are required, reductions in energy consumption in carbon dioxide separation and capture are important for the practical application of separation and capture technology. Therefore, in carbon dioxide separation and capture technology, there is a need for an absorbent that can separate and capture carbon dioxide from a gas containing carbon dioxide as efficiently as possible. [Means for solving the problem]

[0012] One aspect of the present invention is an absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, At least one alkanolamine compound represented by general formula (1), At least one tertiary amine compound represented by general formula (2), The present invention relates to an absorbent which may contain water. General formula (1): [ka] (In the formula, R 1 represents an alkyl group having 1 to 5 carbon atoms or a hydrogen atom; R 2 and R 3 each independently represents an alkyl group having 1 or 2 carbon atoms or a hydrogen atom, and n represents 2 or 3. General formula (2): [ka] (In the formula, R 4 represents a hydroxyalkyl group having 1 to 4 carbon atoms.

[0013] Another aspect of the present invention is a process for producing an absorbent by contacting the absorbent with a gas containing carbon dioxide, the absorbent having absorbed carbon dioxide from the gas containing carbon dioxide; and a step B of heating the absorbent having absorbed carbon dioxide obtained in the step A to desorb and release the carbon dioxide, and recovering the released carbon dioxide. Effect of the Invention

[0014] According to the present invention, it is possible to improve the absorption performance while maintaining high carbon dioxide diffusion performance, and to efficiently separate and recover carbon dioxide from a gas containing carbon dioxide. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram of a carbon dioxide absorption experimental apparatus used in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The absorbent according to the embodiment of the present invention will be described below, but the absorbent is not limited to the following embodiment. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less". In the following description, when a lower limit and an upper limit of a numerical value related to a specific physical property or condition are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them may be selected and used alone, or two or more may be used in combination.

[0017] <Absorbent> The absorbent of the present invention (hereinafter also referred to as "absorbent (AS)" or simply "absorbent") is an absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, and is a liquid containing at least one alkanolamine compound represented by general formula (1) and at least one tertiary amine compound represented by general formula (2), and may be referred to as an "absorption liquid". The absorbent may contain water, but since water has a large specific heat, it is desirable for the water content to be low. By reducing the mass concentration of water contained in the absorbent, the dielectric constant of the absorbent is reduced, and the solvation energy in the reaction with carbon dioxide is reduced. As a result, the heat of carbon dioxide absorption can be reduced. Furthermore, the specific heat of the absorbent is also reduced. General formula (1): [ka] General formula (2): [ka]

[0018] In the general formula (1), R 1 represents an alkyl group having 1 to 5 carbon atoms or a hydrogen atom. The alkyl group having 1 to 5 carbon atoms may be either linear or branched, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, and a 3-pentyl group. R 1 may be a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a tert-pentyl group, or a 3-pentyl group, or may be a hydrogen atom, a methyl group, an ethyl group, or an isopropyl group.

[0019] In the general formula (1), R 2 and R 3 Each independently represents an alkyl group having 1 or 2 carbon atoms or a hydrogen atom. Examples of the alkyl group having 1 or 2 carbon atoms include a methyl group and an ethyl group. R2 and R 3 may each be a hydrogen atom or a methyl group.

[0020] In the general formula (1), n ​​represents 2 or 3, and may be 2.

[0021] Specific examples of the alkanolamine compound represented by the general formula (1) include monoethanolamine, 2-amino-2-methyl-1-propanol, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol, 3-(isopropylamino)propanol, etc. The alkanolamine compound may be 2-amino-2-methyl-1-propanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol, 3-(isopropylamino)propanol. The absorbent (AS) may contain one type of alkanolamine compound represented by the general formula (1) alone, or two or more types in combination.

[0022] The compounds exemplified as the alkanolamine compound represented by the general formula (1) are all commercially available, or can be easily produced by known methods.

[0023] In the general formula (2), R 4 R represents a hydroxyalkyl group having 1 to 4 carbon atoms. Examples of the hydroxyalkyl group having 1 to 4 carbon atoms include a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, and a hydroxybutyl group. 4 may be a hydroxyethyl group.

[0024] Specific examples of the tertiary amine compound represented by general formula (2) include 1-[2-(2-hydroxymethoxy)ethyl]piperazine, 1-[2-(2-hydroxyethoxy)ethyl]piperazine, 1-[2-(2-hydroxypropoxy)ethyl]piperazine, 1-[2-(2-hydroxybutoxy)ethyl]piperazine, etc. The tertiary amine compound may be 1-[2-(2-hydroxyethoxy)ethyl]. The absorbent (AS) may contain one type of tertiary amine compound represented by general formula (2) alone, or two or more types in combination.

[0025] The compounds exemplified as the tertiary amine compound represented by the general formula (2) are all commercially available, or can be easily produced by known methods.

[0026] The water that can be contained in the absorbent (AS) is not particularly limited, and distilled water, ion-exchanged water, tap water, groundwater, etc. can be used appropriately.

[0027] The alkanolamine compound represented by the general formula (1) has high carbon dioxide absorption, while the tertiary amine compound represented by the general formula (2) has low viscosity and is capable of absorbing and releasing carbon dioxide.

[0028] The sum of the mass concentrations of the alkanolamine compound represented by general formula (1) and the tertiary amine compound represented by general formula (2) contained in the absorbent (AS) may be 65% to 100%. By making the sum of the mass concentrations of the alkanolamine compound and the tertiary amine compound 65% or more, the mass concentration of water can be made less than 35%. The sum of the mass concentrations of the alkanolamine compound and the tertiary amine compound may be 80% to 100%, and by making it within this concentration range, the absorption speed can be made faster.

[0029] Conventional carbon dioxide absorbents containing an aqueous solution of an amine compound show a significant decrease in performance when the concentration of the amine compound increases. This is mainly because the viscosity of the aqueous solution increases significantly with increasing concentration of the amine compound, suppressing the diffusion of substances in the aqueous solution.

[0030] Tertiary amine compounds having an ether group generally have low viscosity. However, when a tertiary amine compound having a hydroxyl group is included in an absorbent together with water, the viscosity of the absorbent increases due to the high hydration of the hydroxyl group. On the other hand, a tertiary amine compound having a piperazine ring, an ether group, and a hydroxyl group, as represented by general formula (2), has low viscosity, so that even if the concentration of the tertiary amine compound increases, the diffusion of the substance in the aqueous solution is not significantly suppressed, and the carbon dioxide absorption performance can be maintained. It is considered that the piperazine ring has the effect of increasing the absorption rate of carbon dioxide by the tertiary amine compound, the ether group has the effect of decreasing the viscosity of the tertiary amine compound, and the hydroxyl group has the effect of increasing the boiling point of the tertiary amine compound and suppressing evaporation.

[0031] The absorbent (AS) can reduce the mass concentration of water by containing a tertiary amine compound represented by general formula (2), and can reduce the heat of carbon dioxide absorption and the specific heat while maintaining the carbon dioxide absorption performance. As a result, separation and recovery of carbon dioxide can be performed, for example, under conditions of low temperature or low pressure compared to the conventional conditions, and the energy required for separation and recovery of carbon dioxide can be significantly reduced. The mass concentration of the tertiary amine compound represented by general formula (2) may be 1% to 64%, or may be 5% to 50%. More preferably, it is 25% to 45%. In the above concentration range, the increase in the viscosity of the absorbent is effectively suppressed, and the carbon dioxide absorption performance is further improved. In addition, the tertiary amine compound has the ability to absorb and release carbon dioxide, and also contributes to an increase in the amount of carbon dioxide recovered by the absorbent.

[0032] The water contained in the absorbent (AS) plays a role in decreasing the viscosity of the absorbent when absorbing carbon dioxide, but at the same time, it increases the specific heat of the absorbent. Usually, the amount of water used is determined by the balance between the viscosity, the specific heat, and the like. In the case of the present invention, the viscosity does not increase significantly even when a tertiary amine compound represented by the general formula (2) is used, so the amount of water can be reduced. The mass concentration of water used in the absorbent (AS) is preferably 35% or less. More preferably, it is 20% or less.

[0033] The sum of the mass concentrations of the alkanolamine compound represented by general formula (1) and the tertiary amine compound represented by general formula (2) in the absorbent (AS) is, for example, within the range of 65% to 100%, and the mass concentration of the alkanolamine compound represented by general formula (1) is equal to or less than the amount obtained by subtracting the mass concentration of the tertiary amine compound represented by general formula (2) and the mass concentration of water from 100%. The mass concentration of the alkanolamine compound represented by general formula (1) may usually be 30% to 90%, preferably 30% to 70%, and more preferably 50% to 55%. Since the alkanolamine compound has high carbon dioxide absorption, the amount of carbon dioxide recovered by the absorbent is increased within the above range.

[0034] The absorbent (AS) may contain components other than the alkanolamine compound, the tertiary amine compound, and water, as necessary. Examples of such components include stabilizers (such as antioxidants that suppress side reactions) for ensuring the chemical or physical stability of the absorbent, inhibitors (such as corrosion inhibitors) for preventing deterioration of the materials of the device or facility that uses the absorbent, and physical absorbents for carbon dioxide for supplementing the absorption and dissipation of carbon dioxide by the absorbent (AS). There are no particular limitations on the content of these components as long as they do not impair the effects of the present invention, and the content may be 5% or less by mass concentration.

[0035] Examples of the antioxidant include dibutylhydroxytoluene, butylhydroxyanisole, sodium erythorbate, sodium sulfite, and sulfur dioxide.

[0036] Examples of corrosion inhibitors include 1-hydroxyethane-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-phosphonopropane-2,3-dicarboxylic acid, phosphonosuccinic acid, 2-hydroxyphosphonoacetic acid, and maleic acid-based polymers (e.g., copolymers of maleic acid and amylene, terpolymers of maleic acid, acrylic acid, and styrene, etc.).

[0037] Examples of physical absorbents include cyclotetramethylene sulfone and its derivatives, aliphatic acid amides (e.g., acetylmorpholine or N-formylmorpholine), N-alkylated pyrrolidones and the corresponding piperidones (e.g., N-methylpyrrolidone or N-methylpiperidone), propylene carbonate, methanol, dialkyl ethers of polyethylene glycol, and the like.

[0038] The absorbent (AS) is used when separating and recovering carbon dioxide from a gas containing carbon dioxide. Examples of the gas containing carbon dioxide include exhaust gas from a thermal power plant using coal, heavy oil, natural gas, etc. as fuel, a boiler in a manufacturing plant, a kiln in a cement factory, a steelmaking blast furnace that reduces iron oxide with coke, a steelmaking converter that burns carbon in pig iron to make steel, a coal gasification combined cycle power generation facility, natural gas during mining, reformed gas, etc. The carbon dioxide concentration in the gas may be usually about 5% to 50%, particularly about 10% to 40%, in volume concentration. In this carbon dioxide concentration range, the action and effect of the present invention are suitably exhibited. The gas containing carbon dioxide may contain gases such as N2, H2O, CO, H2S, COS, SO2, NO2, CH4, and H2 in addition to carbon dioxide.

[0039] <Method of separating and capturing carbon dioxide using absorbent (AS)> The method for separating and recovering carbon dioxide using an absorbent (AS) is a method for separating and recovering carbon dioxide in a gas containing carbon dioxide, and includes step A of contacting the absorbent (AS) with a gas containing carbon dioxide to obtain an absorbent that has absorbed carbon dioxide from the gas containing carbon dioxide, and step B of heating the absorbent that has absorbed carbon dioxide obtained in step A to desorb and release the carbon dioxide from the absorbent, and recovering the released carbon dioxide.

[0040] (Process A) In step A, the absorbent is brought into contact with a gas containing carbon dioxide, whereby carbon dioxide in the gas containing carbon dioxide is absorbed into the absorbent and separated.

[0041] In step A, the method of contacting the absorbent with the gas containing carbon dioxide is not particularly limited. For example, there may be mentioned a method of bubbling the gas containing carbon dioxide in the absorbent, a method of dropping the absorbent in the form of mist into the gas containing carbon dioxide (atomization or spray method), a method of countercurrently contacting the gas containing high pressure carbon dioxide with the absorbent in an absorption tower containing a porcelain or metal mesh filler, and the like.

[0042] The temperature in step A can be 25° C. to 60° C. Within the above range, the amount of carbon dioxide recovered by the absorbent increases, and the carbon dioxide absorption rate also increases. The temperature in step A may be 25° C. to 50° C., or may be 25° C. to 40° C.

[0043] The pressure in step A is usually 1.0 bar or more, and may be 1.0 bar to 3.5 bar. By contacting the absorbent with the gas containing carbon dioxide at a higher pressure, the carbon dioxide absorption performance of the absorbent is improved.

[0044] (Process B) In step B, the absorbent having absorbed the carbon dioxide obtained in step A is heated to desorb and release the carbon dioxide from the absorbent, and the released carbon dioxide is recovered.

[0045] The temperature in step B can be 70°C to 150°C. Within the above range, the carbon dioxide dissipation rate of the absorbent increases. The temperature in step B may be 70°C to 120°C, or may be 70°C to 100°C.

[0046] The pressure in step B is usually 3.5 bar or less, and may be 1.0 bar to 3.5 bar. By lowering the pressure, the carbon dioxide dissipation performance is improved. In addition, the lower the mass concentration of water contained in the absorbent, the lower the temperature and pressure at which steps A and B can be carried out, thereby improving the energy efficiency of the process.

[0047] The method of heating the absorbent that has absorbed carbon dioxide to desorb and dissipate the carbon dioxide and recover the carbon dioxide is not particularly limited. For example, the absorbent may be heated and bubbled in a vessel to desorb the carbon dioxide, as in distillation, or the liquid interface may be expanded and heated in a plate tower, spray tower, or a stripping tower containing a filler made of porcelain, metal mesh, or the like. These methods can recover pure or very high-concentration carbon dioxide.

[0048] In step B, the absorbent after dissipating carbon dioxide can be returned to step A and recycled. In the recycling process, the heat added in step B is used to raise the temperature of the absorbent through heat exchange with the absorbent that has absorbed carbon dioxide. This heat exchange also makes it possible to reduce the energy required for the entire carbon dioxide separation and capture process.

[0049] Carbon dioxide separated and captured by the carbon dioxide separation and capture method using an absorbent (AS) usually has a volume concentration of 95% to 100%, and can be pure or very highly concentrated. The separated and captured carbon dioxide can be used for underground or seabed sequestration and storage (CCS) and enhanced oil recovery (EOR).

[0050] The separated and recovered carbon dioxide may be used for any purpose, including, but not limited to, a raw material for synthesizing chemical products, a cooling agent for freezing food, and the like.

[0051] [Example] Next, the present disclosure will be described more specifically using experimental examples.

[0052] Example 1 (Preparation of absorbent) An absorbent was prepared containing the alkanolamine compound 2-isopropylaminoethanol (IPAE), the tertiary amine compound 1-[2-(2-hydroxyethoxy)ethyl]piperazine (HEOPZ), and water. The mass concentrations of each compound in the absorbent were 55% IPAE, 10% HEOPZ, and 35% water.

[0053] (evaluation) The prepared absorbents were evaluated for carbon dioxide absorption performance (absorption amount and absorption rate) at 40°C, carbon dioxide desorption performance (emission amount) at 90°C, and emission rate (emission amount / absorption amount). FIG. 1 shows a schematic diagram of a carbon dioxide absorption test apparatus 1 used in the evaluation.

[0054] The carbon dioxide absorption experimental apparatus 1 comprises a glass gas absorption bottle 2, a glass filter 3 connected to a gas inlet 4, and a gas outlet 5, and the gas outlet 5 is connected to a carbon dioxide analyzer 7 via a trap 6. Although not shown in FIG. 1, stirring can be performed using a magnetic stirrer.

[0055] A gas absorption bottle 2 was immersed in a thermostatic water bath 8 for absorption, which was set so that the temperature of the absorbent used in the experiment was 40° C., and 100 g of absorbent was filled into the gas absorption bottle 2. A mixed gas adjusted with nitrogen to a carbon dioxide concentration of 20% was bubbled into the absorbent at 0.7 liters / minute through a glass filter 3 with a mesh size of 100 μm and a diameter of 13 mm, which was connected to a gas inlet 4, and the carbon dioxide was absorbed into the absorbent for 120 minutes at a stirring speed of 700 rpm.

[0056] In the desorption step, the carbon dioxide absorption experimental apparatus 1 was transferred into a thermostatic water bath 9 for desorption, in which the temperature of the absorbent was set to 90°C, and carbon dioxide was released from the absorbent for 120 minutes at a stirring speed of 700 rpm. During the experiment, the absorbent remained as a homogeneous solution.

[0057] The amount of carbon dioxide absorbed for 120 minutes at 40°C (g-CO2 / kg-absorbent), the absorption rate calculated at 50% of the absorption amount ((g-CO2 / kg-absorbent) / min), the emission amount (g-CO2 / kg-absorbent) which is the difference between the absorption amount at 40°C and the absorption amount at 90°C, and the emission rate (%) which is the value calculated by the emission amount / absorption amount were calculated. The results are shown in Table 1 together with the results of Examples 2 to 8, Comparative Examples 1 to 6, and Reference Example 1.

[0058] Furthermore, the specific heat of each absorbent was measured using a liquid specific heat meter (SHA-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The results are shown in Table 1 together with the results of Examples 2 to 8, Comparative Examples 1 to 6, and Reference Example 1.

[0059] Example 2 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of HEOPZ in the absorbent was changed to 15% and the mass concentration of water was changed to 30%.

[0060] Example 3 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of HEOPZ in the absorbent was changed to 20% and the mass concentration of water was changed to 25%.

[0061] Example 4 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of HEOPZ in the absorbent was changed to 25% and the mass concentration of water was changed to 20%.

[0062] Example 5 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of HEOPZ in the absorbent was changed to 35% and the mass concentration of water was changed to 10%.

[0063] Example 6 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of HEOPZ in the absorbent was changed to 45% and the mass concentration of water was changed to 0%.

[0064] Example 7 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of IPAE in the absorbent was changed to 50% and the mass concentration of HEOPZ was changed to 15%.

[0065] Example 8 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the mass concentration of IPAE in the absorbent was changed to 50%, the mass concentration of HEOPZ was changed to 20%, and the mass concentration of water was changed to 30%.

[0066] Comparative Example 1 An absorbent was prepared and evaluated in the same manner as in Example 1, except that HEOPZ in the absorbent was replaced with bis(2-dimethylaminoethyl) ether (BDER). Note that BDER has an ether group like HEOPZ, but does not have a piperazine ring or a hydroxyl group.

[0067] Comparative Example 2 An absorbent was prepared and evaluated in the same manner as in Example 2, except that HEOPZ in the absorbent was replaced with BDER.

[0068] Comparative Example 3 An absorbent was prepared and evaluated in the same manner as in Comparative Example 2, except that the mass concentration of IPAE in the absorbent was changed to 50% and the mass concentration of BDER was changed to 20%.

[0069] Comparative Example 4 An absorbent was prepared and evaluated in the same manner as in Example 1, except that HEOPZ in the absorbent was replaced with 1-methylimidazole (1MIm). Note that 1MIm does not have an ether group, a piperazine ring, or a hydroxy group.

[0070] Comparative Example 5 An absorbent was prepared and evaluated in the same manner as in Example 2, except that the amount of HEOPZ in the absorbent was changed to 1MIm.

[0071] Comparative Example 6 An absorbent was prepared and evaluated in the same manner as in Example 4, except that the amount of HEOPZ in the absorbent was changed to 1MIm.

[0072] Reference example 1 An absorbent was prepared and evaluated in the same manner as in Example 1, except that the absorbent did not contain HEOPZ, the mass concentration of IPAE was 55%, and the mass concentration of water was 45%.

[0073] [Table 1]

[0074] As shown in Table 1, the absorbents of the present invention prepared in Examples 1 to 8 had a higher carbon dioxide absorption rate than the absorbents of Comparative Examples 1 to 6 that did not contain HEOPZ. The absorbent of Comparative Example 1 containing BDER and Comparative Example 4 containing 1MIm had a lower absorption rate than the absorbent of Reference Example 1 that did not contain HEOPZ, BDER, and 1MIm, but the absorbent of Example 1 containing HEOPZ did not show a lower absorption rate compared to the absorbent of Reference Example 1.

[0075] In addition, from the results of Examples 1 to 6 in which the mass concentration of HEOPZ was changed, it was confirmed that the absorption rate did not decrease even if the sum of the mass concentrations of IPAE and HEOPZ increased. In particular, the absorption rate increased significantly in the absorbent of Example 6, which does not contain water and has a sum of the mass concentrations of IPAE and HEOPZ of 100%. This is thought to be because the viscosity of the absorbent did not increase significantly by using HEOPZ. In addition, from Examples 1 to 6, it was found that the specific heat decreases when the amount of water contained in the absorbent is reduced. In other words, it was revealed that by using the absorbent of the present invention, it is possible to reduce the amount of water contained in the absorbent and suppress the energy consumption required for separating and capturing carbon dioxide without reducing the absorption rate. [Industrial Applicability]

[0076] The absorbent of the present invention enables separation and recovery of carbon dioxide from a gas containing carbon dioxide to be performed with low energy, and therefore can be used in a process for absorbing and recovering carbon dioxide from a gas containing carbon dioxide emitted from various sources. [Explanation of symbols]

[0077] 1 Carbon dioxide absorption experiment equipment 2 Gas absorption bottles 3 Glass Filter 4 Gas inlet 5 Gas exhaust passage 6. Trap 7 Carbon Dioxide Analyzer 8. Absorption thermostatic bath 9. Thermostatic water bath for dissipation

Claims

1. An absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, At least one alkanolamine compound represented by general formula (1), At least one tertiary amine compound represented by general formula (2), An absorbent that may contain water. General formula (1): 【Chemistry 1】 (In the formula, R １ represents an alkyl group having 1 to 5 carbon atoms or a hydrogen atom; R ２ and R ３ each independently represents an alkyl group having 1 or 2 carbon atoms or a hydrogen atom, and n represents 2 or 3. General formula (2): 【Chemistry 2】 (In the formula, R ４ represents a hydroxyalkyl group having 1 to 4 carbon atoms.

2. The absorbent according to claim 1, wherein the sum of the mass concentrations of the alkanolamine compound and the tertiary amine compound contained in the absorbent is 65% to 100%.

3. The absorbent according to claim 1 or 2, wherein the alkanolamine compound is at least one selected from the group consisting of monoethanolamine, 2-amino-2-methyl-1-propanol, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol and 3-(isopropylamino)propanol.

4. The absorbent according to claim 1 or 2, wherein the alkanolamine compound is at least one selected from the group consisting of 2-amino-2-methyl-1-propanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol and 3-(isopropylamino)propanol.

5. 3. The absorbent according to claim 1, wherein the tertiary amine compound is 1-[2-(2-hydroxyethoxy)ethyl]piperazine.

6. A step A of contacting the absorbent according to claim 1 with a gas containing carbon dioxide to obtain an absorbent having absorbed carbon dioxide from the gas containing carbon dioxide; A method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising: a step B of heating the absorbent that has absorbed the carbon dioxide obtained in the step A to desorb and release the carbon dioxide, and recovering the released carbon dioxide.

7. The method for separating and recovering carbon dioxide according to claim 6, wherein the step A is carried out at a temperature of 25°C to 60°C, and the step B is carried out at a temperature of 70°C to 150°C.

8. 8. The method for separating and recovering carbon dioxide according to claim 6 or 7, wherein the step A is carried out under a pressure of 1.0 bar or more, and the step B is carried out under a pressure of 3.5 bar or less.

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