JP2014036933A - Liquid absorbent and separation-recovery method for separating-recovering carbon dioxide from gas flow containing high pressure carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance liquid absorbent capable of attaining carbon dioxide separation-recovery from a gas flow containing high pressure carbon dioxide having carbon dioxide partial pressure of 1.5 bar or more in the gas flow, at a higher carbon dioxide recovery quantity, lower carbon dioxide absorption reaction heat, a higher carbon dioxide absorption speed and/or a higher carbon dioxide desorption speed than an advanced technology, under pressure equal to or higher than high carbon dioxide partial pressure of the gas flow containing the high pressure carbon dioxide.SOLUTION: The liquid absorbent is provided for separating-recovering carbon dioxide from the gas flow containing the high pressure carbon dioxide having a carbon dioxide partial pressure of 1.5 bar or more in the gas flow. The liquid absorbent includes (a) tertiary amine of at least one kind selected from a group composed of tertiary alkanolamine, tertiary alkyl diamine, tertiary alkyl triamine and tertiary alkyl tetra amine, having carbon dioxide separation-recovery performance as an aqueous solution in an area where the carbon dioxide partial pressure is 1.5 bar or more, (b) a water solvent of the molar concentration of 0.5 time or more of an amino group possessed by the tertiary amine and (c) an organic solvent of at least one kind.

Description

  The present invention relates to a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure in the gas stream of 1.5 bar or more, particularly a liquid absorbent for separating and recovering carbon dioxide from coal gasification product gas or mined natural gas, and The present invention relates to a method for separating and recovering carbon dioxide using the liquid absorbent.

  In recent years, the rapid increase in greenhouse gas emissions such as carbon dioxide and methane associated with human social activities has been cited as one of the causes of global warming. In particular, carbon dioxide is the most important greenhouse gas, and in accordance with the Kyoto Protocol entered into force in 2005, measures to reduce carbon dioxide emissions are urgently needed.

  Today, CO2 contained in mixed gas is targeted for mixed gas discharged from thermal power plants, boilers in steelworks, kilns in cement factories, etc. that use coal, heavy oil, natural gas, etc., which are the sources of carbon dioxide as fuel. A series of carbon dioxide capture & storage (CCS) technology that separates and collects carbon, compresses it, and injects it after transportation is a bridging technology to develop alternative energy to replace fossil fuels. Attention has been paid.

  In order to put this storage technology into practical use, it is necessary to reduce the cost as much as possible. In order to reduce these costs, the cost of separation / recovery and compression in the first stage accounts for more than 70% of the total storage cost in the series of processes of carbon dioxide separation / recovery, compression, transportation, and injection. Technology development is important. Therefore, in recent years, the development of carbon dioxide separation and recovery technology by chemical absorption method mainly composed of alkanolamine aqueous solution has been vigorously promoted for atmospheric pressure exhaust gas from power plants and ironworks.

  Patent Document 1 discloses a method for removing carbon dioxide from a gas stream in which the partial pressure of carbon dioxide in the gas stream is less than 0.2 bar. In this method, this gas stream is expressed as (A) molecule. It is described in contact with a liquid absorbent comprising an amine compound having at least two tertiary amino groups therein and an aqueous solution of an active agent selected from (B) primary amine and secondary amine.

  In contrast, carbon dioxide separation and recovery technology by chemical absorption from high-pressure carbon dioxide-containing gas streams such as coal gasification product gas and mining natural gas is compared with separation and recovery techniques from atmospheric-pressure carbon dioxide-containing gas streams. There are relatively few research examples. However, since the pressure energy of the gas itself can be used for the separation recovery and compression of carbon dioxide, the cost during the carbon dioxide storage process, particularly in the separation recovery process and the compression process, may be significantly reduced. Therefore, the development of a chemical absorbent that can be applied to the separation and recovery of carbon dioxide from a high-pressure carbon dioxide-containing gas stream is the focus.

  Until now, a physical absorption method has attracted attention as a method for removing an acidic gas containing carbon dioxide from a gas having a high pressure. In the physical absorption method, it is known that the higher the partial pressure of the target gas component is, the larger the acid gas absorption amount per unit absorption liquid is compared to the chemical absorption method. Typical absorbents include cyclotetramethylene sulfone (sulfolane) and derivatives thereof, and absorbents composed of aliphatic amides, methanol, and polyethylene glycol dialkyl ethers (SELEXOL, Union Carbide). However, in any carbon dioxide separation / recovery method using any of the absorbing liquids, a decompression operation is required in the process of dissipating the absorbed carbon dioxide and regenerating the absorbing liquid, which increases the energy required for the subsequent compression process. become.

  On the other hand, Patent Document 2 relates to an acid gas regeneration method which is performed under a pressure exceeding 3.5 bar absolute pressure and not exceeding 20 bar absolute pressure, and the recovered gas stream generated from the regenerator is compressed and underground. It is described that it is press-fitted during storage. Examples of acidic gas-absorbing chemical agents include triethanolamine (TEA). The absorbent illustrated in the examples consists of 43% by weight N-methyldiethanolamine (MDEA) and 57% by weight water.

  An aqueous solution of an amine compound having at least two tertiary amino groups in the molecule, TEA, and MDEA proposed in Patent Documents 1 and 2 above is generally used at a concentration of 30 to 50% by weight. In areas where the partial pressure of carbon dioxide assumed in coal gasification product gas, mining natural gas, etc. is high, the dispersibility is low, so the efficiency of carbon dioxide recovery and amine regeneration is low, and the energy and cost of carbon dioxide recovery are high. Become. Furthermore, when MDEA proposed in Patent Document 2 is used in an amount of 60% by weight or more, it is difficult to put it to practical use because the handling property deteriorates due to the increase in viscosity and the absorption rate decreases.

  On the other hand, Patent Document 3 describes a method for removing acid gas from a gas supply stream including a regeneration method in which an absorbing liquid containing acid gas at a high concentration is heated at a pressure higher than atmospheric pressure. . The absorbing solution is an aqueous solution of a tertiary alkylamine selected from diamine, triamine and tetramine. It is described that the aqueous amine solution can be regenerated at a high pressure by using a high concentration (60 to 90% by weight).

  In addition, US Pat. No. 6,047,089 discloses an absorbent and absorption for removing carbon dioxide from a gas stream having a high carbon dioxide partial pressure of 2 bar or more, in particular for removing carbon dioxide from exhaust gas from a coal gasification process. And recovery methods are described. The absorbent is a tertiary aliphatic diamine aqueous solution having no hydrogen bonding group and having an ether group. By using the aqueous amine solution at a high concentration (60 to 90% by weight), in a region where the partial pressure of carbon dioxide is high, a high carbon dioxide recovery amount that surpasses the performance of the aqueous tertiary alkylamine solution described in Patent Document 3 above. At the same time, it is described that a high carbon dioxide absorption rate and a high carbon dioxide emission rate can be obtained, and the target carbon dioxide can be separated and recovered.

However, in Japan, the goal of achieving CCS costs is set at 3000 yen / t-CO ₂ by 2015 and 2000 yen / t-CO _{2 by} 2020. To achieve these goals, it is applicable to the separation and recovery of carbon dioxide from high pressure carbon dioxide-containing gas streams, and more sophisticated chemical absorption liquids, particularly carbon dioxide components in carbon dioxide-containing gas streams. In selective separation and recovery of carbon dioxide from a high-pressure carbon dioxide-containing gas stream having a pressure of 1.5 bar or higher, a high carbon dioxide recovery amount under a pressure higher than the high carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream, There is a need for the development of liquid absorbents that have low heat of carbon dioxide absorption, high carbon dioxide absorption rate, and / or high carbon dioxide emission rate.

  In addition, in the said patent documents 1 to 4, about the form for implementing the invention, as components other than the tertiary amine used as the main ingredient of a carbon dioxide absorber, antioxidant, stabilizer, corrosion inhibitor, or It is described that it may contain an additive such as a physical absorbent, which itself is known to have carbon dioxide absorption performance. As examples of additives, Patent Document 4 discloses dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), sodium erythorbate, sodium sulfite, and sulfur dioxide as antioxidants, and physical absorbers. Cyclotetramethylene sulfone (sulfolane) and its derivatives, aliphatic acid amides (acetylmorpholine, N-formylmorpholine), N-alkylated pyrrolidones and corresponding piperidones such as N-methylpyrrolidone (NMP), propylene carbonate, methanol, and Polyethylene glycol is mentioned. However, in Patent Documents 1 to 4, it is noted that no mention is made of the effect of improving the carbon dioxide separation and recovery performance by these additives. Here, the carbon dioxide separation and recovery performance refers to the performance of absorbing carbon dioxide and the performance of releasing carbon dioxide, and the same applies to the following.

  Patent Documents 5 to 8 disclose, as a method for removing carbon dioxide from a carbon dioxide-containing gas stream, a liquid absorbent containing an organic compound other than an amine compound in an amine compound aqueous solution, and carbon dioxide produced by the liquid absorbent. A separation and recovery method is described.

  Patent Document 5 discloses a method of deoxidizing a gaseous effluent containing an acidic compound, wherein an absorbing solution containing an acidic compound is fractionated into a fraction rich in acidic compounds and a fraction low in acidic compounds. In addition, a method is described in which only the fraction rich in acidic compounds is distilled and regenerated to reduce the energy required for regeneration. The absorbing solution contains a reactive compound with carbon dioxide selected from amines, amino acids, amides and the like as an aqueous phase, and, in addition, a salt for promoting the formation of a separable phase with the aqueous phase. And / or containing organic compounds such as amines, alcohols and ketones.

  Patent Document 6 describes a method of deoxidation from a mixed gas containing an acidic gas, similar to Patent Document 5, in which the absorbent that absorbs the acidic gas is an incompatible organic phase and a hydrophilic carrier phase. A method is described in which, by including two phases, a rich acid gas phase and a poor acid gas phase are formed, and only the rich acid gas phase is supplied to the regeneration unit to separate the acid gas. It is described that the absorbent contains an amine solution dissolved in a hydrocarbon, alcohol, glycol, ether or the like as an organic phase, and contains an aqueous solution of an amine salt, an alkali salt, an amino acid salt or the like as a hydrophilic carrier phase. .

  Patent Documents 5 and 6 are inventions that provide a method for reducing the regeneration energy of an absorbent using a phase separation phenomenon between an aqueous phase and an organic phase, and the organic compound contained in the absorbent contains It is added for the purpose of ensuring or promoting phase separation, and there is no mention of the improvement effect on the carbon dioxide separation and recovery performance of the tertiary amine by the organic solvent provided by the present invention.

  Patent Document 7 discloses a hybrid absorption liquid that includes both a chemical absorption liquid and a physical absorption liquid for separating acid gas components with high efficiency, and has both chemical absorption and physical absorption capabilities, and the absorption liquid. A gas separation method using is described. The chemical absorption liquid is an amine absorption liquid having chemical absorption performance, and the physical absorption liquid is an absorption liquid composed of an ionic liquid, an organic solvent, or a compound having a hydroxyl group having physical absorption performance. It is described. Patent Document 7 is an invention that provides a reduction in the amount of physical absorption liquid and a reduction in the required thermal energy in chemical absorption by separating and purifying the acidic gas component by both chemical absorption and physical absorption mechanisms. The organic compound contained in the hybrid absorbent is added as an absorbent having physical absorption performance itself, and the carbon dioxide separation and recovery performance of the tertiary amine by the organic solvent provided by the present invention is achieved. There is no mention of any improvement effect.

  Patent Document 8 discloses a method for recovering carbon dioxide from a carbon dioxide-containing gas supply stream that also contains oxygen, by absorbing carbon dioxide and oxygen in an aqueous amine solution that also contains another organic component, and removing oxygen. A method for recovering carbon dioxide in a concentrated state by recovering carbon dioxide from an absorbing solution is described. It is described that the amine solution contains alcohol, glycol, glycol ether, glycerol and the like as another organic component. The organic component contained in the amine solution is added for the purpose of reducing the latent heat of liquid evaporation by reducing the relative content of water and reducing the sensible heat of liquid temperature by reducing the heat capacity of the entire amine solution. No mention is made of the effect of improving the carbon dioxide separation and recovery performance of the tertiary amine by the organic solvent provided by the present invention.

Special table 2007-527790 gazette JP 2006-528062 A International Publication No. 2004/082809 International Publication No. 2011-071150 Special table 2009-529420 Special table 2012-505077 gazette JP 2011-230056 Special table 2009-521313

  The present invention provides for the separation and recovery of carbon dioxide from a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure of 1.5 bar or more in the gas stream at a pressure higher than the high carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream. Provided below are high performance liquid absorbents and separation and recovery methods that can be achieved with higher carbon dioxide recovery, lower carbon dioxide absorption reaction heat, higher carbon dioxide absorption rate, and / or higher carbon dioxide emission rate than the prior art. For the purpose.

  As described above, Patent Documents 2 and 3 show that a high carbon dioxide recovery amount can be obtained in a region where the partial pressure of carbon dioxide is high by using an aqueous solution of a tertiary amine having a specific structure. Document 4 describes that a high carbon dioxide recovery amount, a high carbon dioxide absorption rate, and a high carbon dioxide emission rate can be obtained.

  Furthermore, the present inventors have provided a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure is 1.5 bar or higher, and an aqueous solvent having a molar concentration of 0.5 times or more of the amino group of the tertiary amine. In the carbon dioxide separation and recovery from the high-pressure carbon dioxide-containing gas stream in which the partial pressure of carbon dioxide in the gas stream is 1.5 bar or more by mixing a specific organic solvent, the high-pressure carbon dioxide-containing gas stream has a high A liquid absorbent having a high carbon dioxide recovery, a low carbon dioxide absorption reaction heat, a high carbon dioxide absorption rate, and / or a high carbon dioxide emission rate under a pressure of carbon dioxide partial pressure or higher, The knowledge that the purpose can be achieved was obtained.

  The present invention has been completed based on these findings, and has been completed. The present invention provides a liquid absorbent and a separation and recovery method for separating and recovering the following carbon dioxide.

Item 1. A liquid absorbent for separating and recovering carbon dioxide from a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure in the gas stream of 1.5 bar or more,
(a) Selected from the group consisting of tertiary alkanolamines, tertiary alkyldiamines, tertiary alkyltriamines, and tertiary alkyltetramines that have carbon dioxide separation and recovery performance as aqueous solutions in the region where the partial pressure of carbon dioxide is 1.5 bar or higher. At least one tertiary amine,
(b) a water solvent having a molar concentration of 0.5 times or more of the amino group of the tertiary amine, and
(c) A liquid absorbent containing at least one organic solvent.

  Item 2. Item 2. The liquid absorbent according to Item 1, wherein the concentration of the tertiary amine is 30 to 80% by weight.

  Item 3. Item 3. The liquid absorbent according to Item 1 or 2, wherein the concentration of the organic solvent is 1 to 60% by weight.

  Item 4. Item 4. The liquid absorbent according to any one of Items 1 to 3, wherein the organic solvent is at least one aprotic polar solvent.

  Item 5. Item 5. The liquid absorbent according to Item 4, wherein the acid dissociation constant pKa in an aqueous solution of the aprotic polar solvent is 10 or more.

  Item 6. Item 6. The liquid absorbent according to Item 5, wherein the aprotic polar solvent is at least one selected from the group consisting of ether solvents, ester solvents, and ketone solvents.

  Item 7. The ether solvent is at least one selected from the group consisting of diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, the ester solvent is γ-butyrolactone, and the ketone solvent is Item 7. The liquid absorbent according to Item 6, which is at least one selected from the group consisting of acetone, methyl ethyl ketone, and cyclohexanone.

  Item 8. Item 8. The liquid absorbent according to any one of Items 1 to 7, wherein the tertiary amine is bis (2-dimethylaminoethyl) ether.

Item 9. (1) By bringing the liquid absorbent according to any one of Items 1 to 8 into contact with a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure of 1.5 bar or more in the gas stream, the high-pressure carbon dioxide-containing gas stream A step of absorbing and separating carbon dioxide from, and (2) a step of heating the liquid absorbent that has absorbed carbon dioxide obtained in the step (1) to dissipate and recover the carbon dioxide,
A method for separating and recovering carbon dioxide containing.

  Item 10. Item 10. The method according to Item 9, wherein the step (1) is performed at a temperature of 25 to 60 ° C, and the step (2) is performed at a temperature of 70 to 150 ° C.

  Item 11. Item 11. The method according to Item 9 or 10, wherein the step (2) is performed under a pressure equal to or higher than a carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream in the step (1).

  According to the liquid absorbent of the present invention, since it has a high carbon dioxide recovery amount and a low carbon dioxide absorption reaction heat, the energy required for the carbon dioxide separation and recovery process is reduced, and carbon dioxide can be separated and recovered with low energy. Become. In addition, pure or high-concentration carbon dioxide with a pressure higher than the high carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream is recovered, greatly reducing the energy required for the compression process after carbon dioxide separation and recovery. Is done. Furthermore, since it has a high carbon dioxide absorption rate and a high carbon dioxide emission rate, it is possible to design a more compact carbon dioxide separation and recovery facility, thereby reducing the initial cost.

6 is a graph showing the results of Examples 1, 2, 5, and 6 in Test Examples 1, 2, and 3 as a rate of change with respect to the results of Comparative Example 1. The increase rate is shown for the carbon dioxide recovery amount, the carbon dioxide absorption rate, the carbon dioxide emission rate, and the carbon dioxide dissolution amount difference, and the reduction rate is shown for the carbon dioxide absorption reaction heat. It is a graph which shows the value of the carbon dioxide collection amount in a test example 6, the carbon dioxide absorption rate, and the carbon dioxide emission rate.

  Hereinafter, the liquid absorbent for separating and collecting carbon dioxide and the method for separating and collecting carbon dioxide of the present invention will be described in detail.

Liquid absorbent for separating and recovering carbon dioxide The liquid absorbent for separating and recovering carbon dioxide of the present invention is carbon dioxide from a high-pressure carbon dioxide-containing gas stream in which the partial pressure of carbon dioxide in the gas stream is 1.5 bar or more. (A) tertiary alkanolamine, tertiary alkyl diamine, tertiary alkyl having a carbon dioxide separation and recovery performance as an aqueous solution in a region where the partial pressure of carbon dioxide is 1.5 bar or more. At least one tertiary amine selected from the group consisting of triamine and tertiary alkyltetramine, (b) an aqueous solvent having a molar concentration of 0.5 or more times the amino group of the tertiary amine, and (c) at least one kind The organic solvent is characterized by including.

  The concentration of the tertiary amine in the liquid absorbent of the present invention is preferably 30 to 80% by weight. Within this range, the liquid absorbent is excellent in carbon dioxide separation and recovery performance in a region where the carbon dioxide partial pressure is high. More preferably, it is 40 to 70% by weight.

  The concentration of the aqueous solvent in the liquid absorbent of the present invention is 0.5 or more times the molar concentration of the amino group of the tertiary amine, preferably 1 to 2 times the molar concentration of the amino group of the tertiary amine. It is. If it is this range, the amount of water solvent required in the carbon dioxide absorption reaction by the tertiary amine will be contained in the liquid absorbent. More preferably, the molar concentration is equal to the molar concentration of the amino group of the tertiary amine.

  The organic solvent in the liquid absorbent of the present invention is contained as a component other than the tertiary amine and the water solvent, and the concentration in the liquid absorbent is preferably 1 to 60% by weight. If it is this range, the improvement effect with respect to the carbon dioxide separation-and-recovery performance by this tertiary amine will be exhibited. More preferably, it is 10 to 50% by weight.

  A preferable solvent as an organic solvent contained in the liquid absorbent of the present invention is an aprotic polar solvent or a protic polar solvent that is miscible with an aqueous solution composed of the tertiary amine and the aqueous solvent, and more preferably. An aprotic polar solvent, more preferably an aprotic polar solvent having an acid dissociation constant pKa of 10 or more in an aqueous solution.

  Examples of the aprotic polar solvent include ether solvents such as diethyl ether, 1,2-dimethoxyethane, diglyme, tetrahydrofuran, tetrahydropyran, 1,4-dioxane, 2-methyltetrahydrofuran, ethyl acetate, ethyl formate, Ester solvents such as γ-butyrolactone, ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, amide solvents such as formamide, N-methylformamide, N, N-dimethylformamide, N-methylacetamide, N, N-dimethylacetamide And nitrile solvents such as acetonitrile and succinonitrile.

  Examples of the protic polar solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, cyclohexanol, ethylene glycol, propion glycol, and 2-methoxyethanol. And alcohol solvents such as 2-ethoxyethanol, phenol, benzyl alcohol, diethylene glycol, triethylene glycol and glycerin, and amine solvents such as ethylenediamine, pyridine, piperidine and morpholine.

  These aprotic polar solvents and protic polar solvents can be used alone or in combination as the organic solvent contained in the liquid absorbent of the present invention.

  As the organic solvent, a solvent that does or does not have carbon dioxide separation / recovery performance can be used.

  The water solubility of the organic solvent is preferably 50 g / L or more. If it is this range, the minimum miscibility is obtained with respect to the aqueous solution which consists of the said tertiary amine and a water solvent. More preferably, it is 150 g / L or more, and further preferably 250 g / L or more.

  The organic solvent preferably has a hydrogen ion exponent pH of 7 or more in a 20% by weight aqueous solution. Within this range, carbon dioxide separation and recovery by the liquid absorbent of the present invention is not hindered. More preferably, the hydrogen ion exponent pH is 7-10.

  The boiling point of the organic solvent is preferably as high as possible in order to avoid volatilization loss in step (2) in the carbon dioxide separation and recovery method described later, and is preferably 30 ° C. or higher. If it is this range, volatilization loss can be suppressed little under the pressure more than the high carbon dioxide partial pressure which a high pressure carbon dioxide containing gas flow has. More preferably, it is 70 ° C or higher, and further preferably 100 ° C or higher.

  The viscosity of the organic solvent at 25 ° C. is preferably 10 mPa · s or less. Within this range, carbon dioxide separation and recovery by the liquid absorbent of the present invention is not hindered. More preferably, it is 5 mPa · s or less, and further preferably 2 mPa · s or less.

  The tertiary amine contained in the liquid absorbent of the present invention has a carbon dioxide separation and recovery performance as an aqueous solution in a region where the partial pressure of carbon dioxide is 1.5 bar or more, a tertiary alkanolamine, a tertiary alkyldiamine, a tertiary alkyltriamine, And at least one selected from the group consisting of tertiary alkyltetramines. Examples of the tertiary amine include tertiary alkanolamines such as TEA and MDEA, and tertiary alkyl diamines such as tetramethylethylenediamine, pentamethyldiethylenetriamine, hexamethyltriethylenetetramine, bis (2-dimethylaminoethyl) ether, 3 Examples include tertiary alkyl triamines and tertiary alkyl tetramines.

  These tertiary amines can be used alone or in combination as the tertiary amine contained in the liquid absorbent of the present invention.

The tertiary amine desirably has a heat of carbon dioxide absorption reaction in a 60% by weight aqueous solution of 70 kJ / mol-CO ₂ or less, and is desirably as low as possible. Here, the carbon dioxide absorption heat of reaction is used to mean the amount of heat generated when 1 mol of carbon dioxide is absorbed by the tertiary amine under the conditions of 40 ° C. and 1 atm.

  The tertiary amine desirably has a carbon dioxide solubility difference in a 60% by weight aqueous solution of 100 g / L or more, and is desirably as high as possible. Here, the carbon dioxide solubility difference is used as the meaning of a value obtained by subtracting the carbon dioxide saturation dissolution amount at 120 ° C. from the carbon dioxide saturation dissolution amount at 40 ° C., and is a value serving as a standard for the carbon dioxide recovery amount.

  The tertiary amine desirably has a carbon dioxide absorption rate and a carbon dioxide emission rate in a 60% by weight aqueous solution that are equal to or higher than those of MDEA, and the higher the tertiary amine, the more desirable.

  The liquid absorbent of the present invention may also contain an antioxidant, a corrosion inhibitor, and / or a physical absorbent as components other than the tertiary amine, water solvent, and organic solvent.

  Examples of the antioxidant include dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), sodium erythorbate, sodium sulfite, sulfur dioxide and the like.

  The physical absorbents include cyclotetramethylene sulfone (sulfolane) and its derivatives, aliphatic acid amides (e.g. acetylmorpholine or N-formylmorpholine), N-alkylated pyrrolidones and corresponding piperidones (e.g. N-methylpyrrolidone (NMP )), Dialkyl ethers such as propylene carbonate, methanol, and polyethylene glycol.

  The partial pressure of carbon dioxide in the high-pressure carbon dioxide-containing gas stream from which the liquid absorbent of the present invention separates and recovers carbon dioxide is 1.5 bar or more. Within this range, the liquid absorbent is excellent in carbon dioxide recovery, carbon dioxide absorption rate, and carbon dioxide emission rate. Preferably it is 10 bar or more, More preferably, it is 10-40 bar.

Examples of the high-pressure carbon dioxide-containing gas stream include coal gasification product gas, mining natural gas, and the like, and the carbon dioxide concentration in the high-pressure carbon dioxide-containing gas stream is usually 20 to 50% by volume, particularly 30-40% by volume. If it is this range, the carbon dioxide separation-and-recovery performance by the liquid absorbent of this invention will be exhibited especially suitably. The high-pressure carbon dioxide-containing gas stream may contain gas components such as water vapor, CO, H ₂ S, COS, and H ₂ as components other than carbon dioxide.

Carbon dioxide separation and recovery method The carbon dioxide separation and recovery method of the present invention comprises (1) contacting the liquid absorbent of the present invention with a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure of 1.5 bar or more in the gas stream. A step of absorbing and separating carbon dioxide from the high-pressure carbon dioxide-containing gas stream, and (2) heating the carbon dioxide-absorbed liquid absorbent obtained in the step (1) to It includes a step of dissipating and collecting.

  In addition, the liquid absorbent after releasing the carbon dioxide is returned again to the step (1) and recycled. In the circulation process, the heat applied in the step (2) is utilized for increasing the temperature of the liquid absorbent by heat exchange with the liquid absorbent that has absorbed carbon dioxide. The heat exchange can reduce the energy of the entire carbon dioxide separation and recovery process.

  Carbon dioxide separated and recovered through the carbon dioxide separation and recovery step usually has a concentration of 95 to 99.9% by volume, and pure or high concentration carbon dioxide is recovered with high pressure. The separated and recovered carbon dioxide can be used for sequestration and storage in the ground or on the seabed where the technology is currently being developed. In this case, the energy required for the compression process required in the isolated storage is reduced because the carbon dioxide separated and recovered has a high pressure and a high concentration. In addition, the use application of the separated and recovered carbon dioxide is not particularly limited. For example, synthetic raw materials such as chemical products, cooling agents for freezing foods, and the like can be mentioned.

Process (1)
In step (1), the liquid absorbent of the present invention is brought into contact with the high-pressure carbon dioxide-containing gas stream to absorb and separate carbon dioxide in the high-pressure carbon dioxide-containing gas stream.

  The temperature at which carbon dioxide is absorbed and separated by the liquid absorbent of the present invention is preferably 25 to 60 ° C. Within this range, the liquid absorbent is excellent in carbon dioxide recovery and carbon dioxide absorption rate. More preferably, it is 25-50 degreeC, More preferably, it is 25-40 degreeC.

  The partial pressure of carbon dioxide in the high-pressure carbon dioxide-containing gas stream is 1.5 bar or more. If it is this range, the said liquid absorbent is excellent in a carbon dioxide recovery amount and a carbon dioxide absorption rate. Preferably it is 10 bar or more.

  The method for absorbing and separating carbon dioxide by bringing the liquid absorbent of the present invention into contact with a high-pressure carbon dioxide-containing gas stream is not particularly limited. For example, a method of bubbling a high-pressure carbon dioxide-containing gas stream in the liquid absorbent, a method of spraying the liquid absorbent in a high-pressure carbon dioxide-containing gas stream (spraying or spraying method), magnetic or metal mesh And a method in which the high-pressure carbon dioxide-containing gas stream and the liquid absorbent are brought into countercurrent contact in an absorption tower containing the above filler.

Step (2)
In the step (2), the liquid absorbent obtained by absorbing the carbon dioxide obtained in the step (1) is heated to dissipate and collect the carbon dioxide.

  The temperature at which carbon dioxide is diffused and recovered from the liquid absorbent of the present invention is preferably 70 to 150 ° C. Within this range, the liquid absorbent is excellent in carbon dioxide recovery and carbon dioxide emission rate. More preferably, it is 100-120 degreeC.

  Step (2) is preferably performed under a pressure equal to or higher than the carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream of step (1).

  The partial pressure of carbon dioxide diffused and recovered from the liquid absorbent of the present invention is preferably a pressure equal to or higher than the partial pressure of carbon dioxide possessed by the high-pressure carbon dioxide-containing gas stream in the step (1). If it is this range, the energy required for the compression process after the separation and recovery of carbon dioxide can be reduced. More preferably, the pressure is higher than or equal to the carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream to 40 bar.

  There is no particular limitation on the method of heating and recovering the pure or high concentration carbon dioxide by heating the liquid absorbent that has absorbed the carbon dioxide. Just like distillation, heating the absorbent and bubbling it in a kettle, removing it from a plate tower, spray tower, diffusion tower containing a magnetic or metal mesh filler, heating the liquid interface, etc. Is mentioned.

  Examples are given below to illustrate the present invention in more detail. However, the present invention is not limited to these examples.

The reagents and gas types used in the reagent examples and comparative examples are shown in Tables 1 and 2.

Test method 1
Measurement of carbon dioxide recovery, carbon dioxide absorption rate, and carbon dioxide emission rate with respect to the liquid absorbent in Test Examples 1, 2, 5, and 6 is performed by measuring carbon dioxide gas cylinder and nitrogen gas cylinder, carbon dioxide gas flow controller and nitrogen gas flow rate controller, This was carried out using a carbon dioxide absorption / dissipation device (not shown) in which a high-pressure vessel (600 mL), a condenser, a back pressure control valve, a flow meter, and a carbon dioxide concentration meter were connected in sequence.

  Around the high-pressure vessel, heat transfer oil sent from two oil baths whose temperatures were controlled at 40 ° C and 120 ° C circulated, so that the temperature of the liquid absorbent in the high-pressure vessel was controlled.

  After adding 300 mL of liquid absorbent in the high-pressure vessel, the gas in the high-pressure vessel was replaced with nitrogen gas under atmospheric pressure.

  The back pressure adjustment valve was adjusted so that the pressure in the high-pressure vessel was 35 bar, and the pressure was increased with nitrogen gas at a flow rate of 3 L / min.

  A heat transfer oil at 40 ° C. was circulated around the high-pressure vessel, and the temperature of the liquid absorbent in the high-pressure vessel was kept at 40 ° C.

  The condenser temperature was maintained at 5 ° C, and the volatilized liquid absorbent was returned to the high-pressure vessel.

  After the temperature and pressure stabilize at 40 ° C and 35 bar, respectively, carbon dioxide with a flow rate of 1.4 L / min and nitrogen gas with a flow rate of 1.6 L / min are blown into the liquid absorbent in the high-pressure vessel, and the The carbon dioxide absorption process was continued for 2 hours at a carbon partial pressure of about 16 bar.

  After the carbon dioxide absorption process is completed, the temperature of the liquid absorbent in the high-pressure vessel is raised to 120 ° C by replacing the 40 ° C heat transfer oil circulating around the high-pressure vessel with the 120 ° C heat transfer oil. The carbon dioxide emission process was performed.

  The exhaust gas from the high-pressure vessel in the carbon dioxide absorption process and the emission process was analyzed by a carbon dioxide concentration meter (IR100 manufactured by Yokogawa).

The amount of carbon dioxide dissolved in the liquid absorbent S _c [g / L] was determined from the carbon dioxide concentration C [volume%] obtained from the carbon dioxide concentration meter using the following equation (1).

  The amount of carbon dioxide recovered by the liquid absorbent was defined as a value obtained by subtracting the amount of carbon dioxide dissolved 2 hours after the start of the carbon dioxide releasing step from the amount of carbon dioxide dissolved 2 hours after the start of the carbon dioxide absorbing step.

  The rate of carbon dioxide absorption into the liquid absorbent was defined as the change in the amount of carbon dioxide dissolved per unit time at the start of the carbon dioxide absorption process.

  The carbon dioxide emission rate from the liquid absorbent was defined as the maximum value of the absolute change in the amount of dissolved carbon dioxide per unit time in the carbon dioxide emission process.

Test method 2
Measurement of the carbon dioxide absorption reaction heat with respect to the liquid absorbent in Test Example 3 was performed using a suggested thermal reaction calorimeter (DRC manufactured by SETARAM) (not shown).

  150 mL of the liquid absorbent was added to each of the measurement-side and control-side reaction vessels (Pyrex (registered trademark) double shell flask: 500 mL).

  Each reaction container is kept at 40 ° C, carbon dioxide gas is flowed into the measurement side reaction container at a flow rate of 224 mL / min, and nitrogen gas of the same flow rate is blown into the control side reaction container, and carbon dioxide absorption reaction at atmospheric pressure. The calorific value due to was measured.

Test method 3
The difference in the amount of carbon dioxide dissolved in the liquid absorbent in Test Example 4 is as follows: carbon dioxide cylinder and nitrogen gas cylinder, carbon dioxide flow controller and nitrogen gas flow controller, high pressure vessel (450 mL), condenser, back pressure regulating valve, carbon dioxide concentration The measurement was performed using a carbon dioxide gas-liquid equilibration apparatus (not shown) in which a meter was sequentially connected.

  The periphery of the high-pressure vessel was covered with an electric heater, and the liquid absorbent in the high-pressure vessel was controlled to an arbitrary temperature.

  After adding 250 mL of the liquid aqueous solution in the high-pressure vessel, the gas in the high-pressure vessel was replaced with nitrogen gas under atmospheric pressure.

  Adjust the back pressure adjustment valve so that the pressure in the high pressure vessel becomes 40 bar, blow carbon dioxide with a flow rate of 0.4 L / min and nitrogen gas with a flow rate of 0.6 L / min into the liquid absorbent in the high pressure vessel, The partial pressure of carbon dioxide in the high-pressure vessel was about 16 bar.

  The temperature of the liquid absorbent in the high-pressure vessel was maintained at 40 ° C., and the liquid absorbent absorbed carbon dioxide.

  The condenser temperature was maintained at 5 ° C, and the volatilized liquid absorbent was returned to the high-pressure vessel.

  The exhaust gas from the high-pressure vessel was analyzed with a carbon dioxide concentration meter (IR100 manufactured by Yokogawa).

  Equilibrate when the carbon dioxide concentration of the exhaust gas from the high-pressure vessel is stable, collect a small amount of liquid absorbent in the high-pressure vessel, and measure the organic carbon concentration in the liquid absorbent with a carbon concentration meter (TOC-V CSH manufactured by SHIMADZU) And the inorganic carbon concentration was analyzed.

  The same test as described above was performed under the conditions of a carbon dioxide partial pressure of 16 bar and a temperature of 120 ° C., and a carbon dioxide partial pressure of 40 bar and a temperature of 120 ° C.

The carbon dioxide saturated dissolution amount S _cs [g / L] in the liquid absorbent is calculated from the following formula based on the organic carbon concentration C _o [g / L] and the inorganic carbon concentration C _i [g / L] obtained from the carbon concentration meter. Obtained using (2).

Here, _Co ′ is the organic carbon concentration [g / L] in the liquid absorbent before the test, and was obtained by analyzing the liquid absorbent before the test with a carbon densitometer.

  The difference in carbon dioxide solubility relative to the liquid absorbent was defined as the value obtained by subtracting the carbon dioxide saturation dissolution at 120 ° C. from the carbon dioxide saturation dissolution at 40 ° C.

Test example 1
By the method described in Test Method 1, the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate with respect to the liquid absorbent were measured using a carbon dioxide absorption and emission device. In this test example, BDER was employed as a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure was 1.5 bar or higher. The composition of the liquid absorbent used in the examples in this test example was BDER: 60% by weight, water: 13.5% by weight, and the organic solvent shown in Table 1: 26.5% by weight. The composition of the liquid absorbent used in the comparative example in this test example was BDER: 60% by weight and water: 40% by weight. The test conditions in the carbon dioxide absorption step and the emission step in this test example were a temperature of 40 ° C .: carbon dioxide partial pressure of 16 bar and a temperature of 120 ° C .: carbon dioxide partial pressure of 16 bar, respectively. Table 3 shows the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate for the liquid absorbent obtained as a result of this test example.

  As shown in Table 3, with the addition of an organic solvent, the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and / or the carbon dioxide emission rate under a pressure higher than the high carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream. Improved. Especially when an aprotic polar solvent such as an ether solvent, ester solvent, ketone solvent or the like is added, the improvement effect is remarkable, and when DME, THF, MTHF, GBL, ACTN, or CHN is added, In all the performance of carbon dioxide recovery, carbon dioxide absorption rate, and carbon dioxide emission rate, it surpassed the liquid absorbent without adding organic solvent. In addition, DME has a relatively significant improvement in all of the performance of carbon dioxide recovery, carbon dioxide absorption rate, and carbon dioxide emission rate, ACTN is carbon dioxide absorption rate and carbon dioxide emission rate, and GBL is carbon dioxide. There was a relatively significant improvement in carbon recovery and carbon dioxide emission rate.

Test example 2
By the method described in Test Method 1, the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate with respect to the liquid absorbent were measured using a carbon dioxide absorption and emission device. In this test example, as a tertiary amine, MDEA as a representative example of a tertiary alkanolamine in Patent Document 2 (Japanese Patent Publication No. 2006-528062), diamine, triamine and tetramine in Patent Document 3 (International Publication No. 2004/082809) Representative examples of tertiary alkylamines selected from PDTA and tertiary aliphatic diamines having no hydrogen bonding group and having an ether group in Patent Document 4 (International Publication No. 2011/071150) As BDER three kinds of tertiary amines were used.

  The composition of the liquid absorbent used in the examples in this test example was tertiary amine: 60% by weight, water: 13.5% by weight, and organic solvent: 26.5% by weight. The composition of the liquid absorbent used in the comparative example in this test example was tertiary amine: 60% by weight and water: 40% by weight. The organic solvent used in the examples in this test example was DME that showed a high carbon dioxide recovery, a high carbon dioxide absorption rate, and a high carbon dioxide emission rate in test example 1 above. The test conditions in the carbon dioxide absorption step and the emission step in this test example were a temperature of 40 ° C .: carbon dioxide partial pressure of 16 bar and a temperature of 120 ° C .: carbon dioxide partial pressure of 16 bar, respectively. Table 4 shows the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate for the liquid absorbent obtained as a result of this test example.

  As shown in Table 4, for any tertiary amine aqueous solution, the addition of an organic solvent showed a significant increase in carbon dioxide recovery, carbon dioxide absorption rate, and carbon dioxide emission rate. In Example 2 to which a solvent was added, the highest carbon dioxide separation and recovery performance was shown. Therefore, the organic solvent contained in the liquid absorbent of the present invention is an effect of improving the carbon dioxide separation and recovery performance with respect to the tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in the region where the carbon dioxide partial pressure is 1.5 bar or more. It was shown to exert.

Test example 3
By the method described in Test Method 2, the heat of carbon dioxide absorption reaction with respect to the liquid absorbent was measured using a suggested thermal reaction calorimeter. In this test example, BDER was employed as a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure was 1.5 bar or higher. The composition of the liquid absorbent used in the examples in this test example was BDER: 60% by weight, water: 13.5% by weight, and the organic solvent shown in Table 1: 26.5% by weight. The composition of the liquid absorbent used in the comparative example in this test example was BDER: 60% by weight and water: 40% by weight. The test condition in this test example was a temperature of 40 ° C .: atmospheric pressure. Table 5 shows carbon dioxide absorption reaction heat with respect to the liquid absorbent obtained as a result of this test example.

  As shown in Table 5, when DEE, DME, THF, GBL, ACTN, MEK, or EtOH was added, a decrease in heat of carbon dioxide absorption reaction was shown. In particular, DEE showed the highest effect of reducing the heat of carbon dioxide absorption reaction, and EtOH and ACTN also showed relatively high reduction effects. In general, the lower the molecular weight of the organic solvent, the higher the effect of decreasing the heat of carbon dioxide absorption reaction due to the addition.

Test example 4
By the method described in Test Method 3, the difference in the amount of carbon dioxide dissolved in the liquid absorbent was measured using a carbon dioxide gas-liquid equilibrium device. In this test example, BDER was employed as a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure was 1.5 bar or higher. The composition of the liquid absorbent used in the examples in this test example was BDER: 60% by weight, water: 13.5% by weight, and organic solvent: 26.5% by weight. The composition of the liquid absorbent used in the comparative example in this test example was BDER: 60% by weight and water: 40% by weight. The organic solvent used in the examples in this test example has a particularly high carbon dioxide recovery amount, a low carbon dioxide absorption reaction heat, a high carbon dioxide absorption rate, and / or a high carbon dioxide emission rate in the above test examples 1 and 3. The four organic solvents shown were DEE, DME, GBL, and ACTN. The test conditions in this test example were temperature 40 ° C .: carbon dioxide partial pressure 16 bar, temperature 120 ° C .: carbon dioxide partial pressure 16 bar, and temperature 120 ° C .: carbon dioxide partial pressure 40 bar. Table 6 shows the difference in the amount of carbon dioxide dissolved in the liquid absorbent obtained as a result of this test example.

  As shown in Table 6, the addition of DEE, DME, GBL, or ACTN shows a significant improvement in the carbon dioxide solubility difference, and the carbon dioxide partial pressure in the carbon dioxide emission process is lower than when no organic solvent is added. It improved by 10-40% at 16 bar and 80-150% at 40 bar. In addition, the higher the carbon dioxide partial pressure in the carbon dioxide emission step, the higher the effect of improving the difference in carbon dioxide solubility due to the addition of these organic solvents. Therefore, the liquid absorbent of the present invention has a high-pressure carbon dioxide-containing gas stream. It was shown to be effective for the selective separation and recovery of carbon dioxide under pressures higher than the high partial pressure of carbon dioxide.

  FIG. 1 is a graph showing the results of Examples 1, 2, 5, and 6 in Test Examples 1 and 3 and the test example in terms of the rate of change relative to the result of Comparative Example 1. The increase rate is shown for the carbon dioxide recovery, the carbon dioxide absorption rate, the carbon dioxide emission rate, and the carbon dioxide dissolution amount difference, and the decrease rate is shown for the carbon dioxide absorption reaction heat.

Test Example 5
By the method described in Test Method 1, the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate of the liquid absorbent containing no tertiary amine were measured using a carbon dioxide absorption and emission device. The composition of the liquid absorbent used in Comparative Examples 4 to 7 in this test example was organic solvent: 60% by weight and water: 40% by weight. The composition of the liquid absorbent used in Comparative Example 8 in this test example is water: 100% by weight, and the composition of the liquid absorbent used in Comparative Example 1 is BDER: 60% by weight and water: 40% by weight. %Met.

  The organic solvents used in Comparative Examples 4 to 7 in this test example are the same as those in Test Examples 1 and 3, particularly high carbon dioxide recovery, low carbon dioxide absorption reaction heat, high carbon dioxide absorption rate, and / or high carbon dioxide. There were four types of organic solvents, DEE, DME, GBL, and ACTN, which showed the emission rate. The liquid absorbent containing DEE was subjected to the test in a separated state because it was not sufficiently mixed with DEE occupying 60% by weight and water occupying 40% by weight. The test conditions in the carbon dioxide absorption step and the emission step in this test example were a temperature of 40 ° C .: carbon dioxide partial pressure of 16 bar and a temperature of 120 ° C .: carbon dioxide partial pressure of 16 bar, respectively. Table 7 shows the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate for the liquid absorbent obtained as a result of this test example.

  As shown in Table 7, the carbon dioxide recovery amount of the liquid absorbent containing the organic solvent is lower than the carbon dioxide recovery amount when the organic solvent is not included, and is significantly lower than the result of Comparative Example 1. Indicated. The amount of carbon dioxide recovered observed when the organic solvent of Comparative Example 8 is not included is due to the physical absorption effect of carbon dioxide by the water solvent. Therefore, the physical absorption performance of carbon dioxide by the organic solvent is due to the water solvent. It was shown to be lower than the physical absorption performance of carbon dioxide. Further, no significant changes were observed in the carbon dioxide absorption rate and carbon dioxide emission rate of the liquid absorbent containing the organic solvent compared to the case where the organic solvent was not contained. Accordingly, the organic solvent contained in the liquid absorbent of the present invention is a carbon dioxide recovery amount of a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure is 1.5 bar or more, a carbon dioxide absorption rate, and It has been shown that the carbon dioxide emission rate is improved.

Test Example 6
For the liquid absorbent in which the concentration of the aqueous solvent contained in the liquid absorbent is changed by using the carbon dioxide absorption and desorption device by the method described in Test Method 1, the amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide The carbon emission rate was measured. In this test example, BDER was employed as a tertiary amine having carbon dioxide separation and recovery performance as an aqueous solution in a region where the carbon dioxide partial pressure was 1.5 bar or higher. The composition of the liquid absorbent used in Comparative Example 9 in this test example was BDER: 60% by weight and organic solvent: 40% by weight. The composition of the liquid absorbent used in the examples in this test example was BDER: 60% by weight, water was changed in concentration in the range of 0.5 to 2.0 in a molar ratio with respect to the amino group of BDER, It was components other than the said water. The composition of the liquid absorbent used in Comparative Example 1 in this test example was BDER: 60% by weight and water: 40% by weight. In this case, the molar ratio of water to amino groups was 3.0.

  The organic solvents used in Comparative Example 9 and Examples in this test example were the same as in Test Examples 1 and 3 above, high carbon dioxide recovery, low carbon dioxide absorption reaction heat, high carbon dioxide absorption rate, and high carbon dioxide emission rate. It was DME that showed. The test conditions in the carbon dioxide absorption step and the emission step in this test example were a temperature of 40 ° C .: carbon dioxide partial pressure of 16 bar and a temperature of 120 ° C .: carbon dioxide partial pressure of 16 bar, respectively. The amount of carbon dioxide recovered, the carbon dioxide absorption rate, and the carbon dioxide emission rate for the liquid absorbent obtained as a result of this test example are shown in Table 8 and FIG.

  As shown in Table 8 and FIG. 2, the amount of carbon dioxide recovered and the carbon dioxide emission rate showed the highest values when an aqueous solvent having a molar concentration equal to the amino group of the tertiary amine was included. Moreover, the carbon dioxide absorption rate showed a higher value as the relative content of the organic solvent increased. When the concentration of the aqueous solvent is lower than the molar concentration equal to the amino group possessed by the tertiary amine, a significant decrease in the amount of carbon dioxide recovered is observed. Therefore, the liquid absorbent of the present invention is an amino group possessed by the tertiary amine. It is desirable to contain 1 to 2 times the aqueous solvent with respect to the molar concentration. In addition, it is thought that the carbon dioxide recovery amount observed when the aqueous solvent of Comparative Example 9 is not included is due to the physical absorption effect of carbon dioxide by the tertiary amine that does not require the aqueous solvent.

Claims (11)

A liquid absorbent for separating and recovering carbon dioxide from a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure in the gas stream of 1.5 bar or more,
(a) Selected from the group consisting of tertiary alkanolamines, tertiary alkyldiamines, tertiary alkyltriamines, and tertiary alkyltetramines that have carbon dioxide separation and recovery performance as aqueous solutions in the region where the partial pressure of carbon dioxide is 1.5 bar or higher. At least one tertiary amine,
(b) a water solvent having a molar concentration of 0.5 times or more of the amino group of the tertiary amine, and
(c) A liquid absorbent containing at least one organic solvent.   The liquid absorbent according to claim 1, wherein the concentration of the tertiary amine is 30 to 80% by weight.   The liquid absorbent according to claim 1 or 2, wherein the concentration of the organic solvent is 1 to 60% by weight.   The liquid absorbent according to any one of claims 1 to 3, wherein the organic solvent is at least one aprotic polar solvent.   The liquid absorbent according to claim 4, wherein an acid dissociation constant pKa in an aqueous solution of the aprotic polar solvent is 10 or more.   The liquid absorbent according to claim 5, wherein the aprotic polar solvent is at least one selected from the group consisting of ether solvents, ester solvents, and ketone solvents.   The ether solvent is at least one selected from the group consisting of diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, the ester solvent is γ-butyrolactone, and the ketone solvent is The liquid absorbent according to claim 6, which is at least one selected from the group consisting of acetone, methyl ethyl ketone, and cyclohexanone.   The liquid absorbent according to any one of claims 1 to 7, wherein the tertiary amine is bis (2-dimethylaminoethyl) ether. (1) By bringing the liquid absorbent according to any one of claims 1 to 8 into contact with a high-pressure carbon dioxide-containing gas stream having a carbon dioxide partial pressure of 1.5 bar or more in the gas stream, the high-pressure carbon dioxide-containing gas A step of absorbing and separating carbon dioxide from the stream, and (2) heating the liquid absorbent that has absorbed carbon dioxide obtained in step (1) to dissipate and recover carbon dioxide.
A method for separating and recovering carbon dioxide containing.   The method according to claim 9, wherein the step (1) is performed at a temperature of 25 to 60 ° C, and the step (2) is performed at a temperature of 70 to 150 ° C.   The method according to claim 9 or 10, wherein the step (2) is performed under a pressure equal to or higher than a carbon dioxide partial pressure of the high-pressure carbon dioxide-containing gas stream of the step (1).

Images