Absorption liquid and separation and recovery method

Abstract

To provide an absorption liquid for carbon dioxide, containing a surfactant of the type that can stably function in an aqueous solution containing an amine component.SOLUTION: The present invention discloses an absorption liquid for separating and recovering carbon dioxide from a gas, the absorption liquid containing an amine component containing at least one selected from a primary amine, a secondary amine and a tertiary amine, and a nonionic surfactant that is at least one selected from amine oxide-based, alkanol amide-based, ester-based and ester ether-based ones.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an absorbing liquid and a method for separating and recovering carbon dioxide. [Background technology]

[0002] In order to suppress global warming, carbon dioxide capture and storage technology has been attracting attention. In particular, as a method for separating and capturing carbon dioxide from gas containing carbon dioxide emitted from thermal power plants, etc., an absorbing solution containing an amine component including at least one selected from the group consisting of primary amines, secondary amines, and tertiary amines has been actively researched.

[0003] For example, Patent Document 1 discloses a method for separating and recovering carbon dioxide in combustion exhaust gas under atmospheric pressure using a mixed aqueous solution of a secondary amine and a tertiary amine, while Patent Document 2 discloses a technology for absorbing and recovering carbon dioxide in exhaust gas using an aqueous solution containing a secondary amine compound and a surfactant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-252430 [Patent Document 2] JP 2012-11309 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 2 suggests that the addition of a surfactant to an aqueous solution containing a high concentration (e.g., 60% by weight) of a secondary amine compound may contribute to improving the absorption rate of carbon dioxide. However, there are many types of surfactants, and it is known that the physical properties differ depending on the type. It is unclear what type of surfactant is suitable for addition to an aqueous solution containing an amine component.

[0006] One aspect of the present invention aims to provide a carbon dioxide absorbing liquid or the like that contains a type of surfactant that can function stably in an aqueous solution containing an amine component. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, an absorption liquid according to one embodiment of the present invention is an absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide, and includes an amine component including at least one amine selected from the group consisting of primary amines, secondary amines and tertiary amines, and at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type and ester-ether type.

[0008] In the absorbing liquid according to one embodiment of the present invention, the nonionic surfactant may be a surfactant derived from at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines.

[0009] In the absorbing liquid according to one aspect of the present invention, the nonionic surfactant may be a surfactant derived from a tertiary amine.

[0010] The absorbing liquid according to one aspect of the present invention may contain 30% by mass or more of the amine component.

[0011] In the absorbing liquid according to one embodiment of the present invention, the amine components may include a tertiary amine and at least one of a primary amine and a secondary amine, and a total amount of the primary amine and the secondary amine may be 10 mass% or less of a total amount of the amine components.

[0012] In order to solve the above-mentioned problems, a separation and recovery method according to one embodiment of the present invention is a method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising: a separation step of contacting an absorption liquid with a gas containing carbon dioxide to separate carbon dioxide from the gas; and a recovery step of heating the absorption liquid having absorbed carbon dioxide obtained in the separation step to recover carbon dioxide from the absorption liquid, wherein the absorption liquid comprises an amine component including at least one amine selected from the group consisting of primary amines, secondary amines and tertiary amines, and at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type and ester-ether type.

[0013] In the separation and recovery method according to one aspect of the present invention, the absorbing liquid that has absorbed carbon dioxide may be heated to 80° C. or higher and 120° C. or lower in the recovery step. Effect of the Invention

[0014] According to one aspect of the present invention, it is possible to provide a carbon dioxide absorbing liquid or the like, which contains a type of surfactant that can function stably in an aqueous solution containing an amine component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. In addition, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic documents and patent documents described in this specification are incorporated herein by reference.

[0016] [Outline of the present invention] A chemical absorption method using an absorbing solution containing an amine component has been known as a carbon dioxide separation and capture technology. In this chemical absorption method, the carbon dioxide in the gas is absorbed into the absorbing solution through a chemical reaction with the amine component, and the absorbing solution is heated to release the carbon dioxide, thereby capturing the carbon dioxide in the gas.

[0017] The higher the content of the amine component in the absorbing liquid, the more improved the amount of carbon dioxide absorbed can be expected. However, it is empirically known that the rate of carbon dioxide absorption decreases as the content of the amine component in the absorbing liquid increases. This is thought to be due in part to the fact that the higher the concentration of the amine component, the higher the surface tension of the absorbing liquid becomes, and the lower the efficiency of gas-liquid contact between the absorbing liquid and carbon dioxide becomes.

[0018] Patent Document 2 discloses that, for example, when a surfactant is added to an aqueous solution containing 60% by weight of 2-isopropylaminoethanol, which is a secondary amine, the surface tension of the aqueous solution decreases and the absorption rate of carbon dioxide increases. In this study, attempts were made to add a nonionic or amphoteric perfluoro compound, or Triton X, which is a nonionic ether surfactant, as the surfactant.

[0019] However, there are many other types of surfactants. It is not preferable for the surfactant added to the carbon dioxide absorption liquid to inhibit the absorption of carbon dioxide due to properties other than lowering the surface tension of the absorption liquid. In addition, since the absorption liquid becomes relatively hot during the carbon dioxide absorption process, the surfactant is required to be resistant to deterioration and function stably even under such conditions. It was previously unknown what type of surfactant would meet these requirements.

[0020] The present inventors have found that at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type, and ester-ether type is resistant to deterioration and can function stably in an absorbing liquid containing an amine component. The absorbing liquid according to one embodiment of the present invention will be described below.

[0021] [Absorption liquid] An absorbing liquid according to one embodiment of the present invention (hereinafter referred to as "the absorbing liquid of the present embodiment") is an absorbing liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide, and contains an amine component including at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines, and at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type, and ester-ether type.

[0022] (amine component) The absorbing liquid of the present embodiment includes an amine component. The amine component includes at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. The amine included in the amine component is not particularly limited, and amines of any structure may be used, and the number of carbon atoms of the amine is not particularly limited.

[0023] Examples of primary amines include primary amines having a heterocycle such as 2-methylpiperidine; primary alkanolamines such as monomethanolamine, monoethanolamine, monopropanolamine, and monobutanolamine. When used as an absorbing liquid, the primary amine is preferably monomethanolamine, since it has a high carbon dioxide absorption rate and can absorb a large amount of carbon dioxide. The primary amines may be used alone or in combination of two or more.

[0024] Examples of secondary amines include secondary alkanolamines such as 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, and 2-n-butylaminoethanol; and secondary amines having heterocycles such as piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, and 2-piperidinoethanol. When used as an absorbing liquid, secondary alkanolamines are preferred among these secondary amines because they absorb a large amount of carbon dioxide and have a fast absorption rate, and 2-isopropylaminoethanol is particularly preferred. In addition, when the amine component contains a primary amine and / or a tertiary amine in addition to a secondary amine, the secondary amine is preferably piperazine. In this case, the concentration of piperazine in the absorbing liquid of this embodiment is preferably 3% by mass or more and 7% by mass or less, and more preferably 5% by mass. The secondary amine may be used alone or in combination of two or more types.

[0025] Examples of tertiary amines include tertiary alkanolamines such as methyldiethanolamine, diethylaminopropanol, diethylaminoethanol, dimethylaminoethanol, dimethylaminomethylpropanol, N-ethyl-N-methylethanolamine, 3-(dimethylamino)propanol, 4-(dimethylamino)butanol, 4-(diethylamino)butanol, 2-(2-diethylaminoethoxy)ethanol, and 2-(2-dimethylaminoethoxy)ethanol; and tertiary amines having a heterocycle such as 1-methyl-2-piperidinemethanol, 1-ethyl-3-piperidinemethanol, and 1-(2-hydroxyethyl)piperidine. When used as an absorbing liquid, the tertiary amine is preferably a tertiary alkanolamine, and particularly preferably methyldiethanolamine, in that it can reduce the dissipation energy of carbon dioxide. The dissipation energy is the energy required to separate carbon dioxide from the absorbing liquid. The tertiary amine may be used alone or in combination of two or more types.

[0026] The concentration of the amine component in the absorbing solution is not particularly limited. However, generally, the higher the concentration of the amine component, the greater the absorption amount, absorption rate, desorption amount and desorption rate of carbon dioxide per unit liquid volume in the absorbing solution. Therefore, from the viewpoints of reducing energy consumption, reducing the scale of plant equipment, and carbon dioxide treatment efficiency, the concentration of the amine component in the absorbing solution of this embodiment is preferably 10 mass% or more.

[0027] Here, it is known that when the absorbing liquid contains a high concentration (e.g., 30 mass % or more) of an amine component, the absorption rate of carbon dioxide by the absorbing liquid decreases. One of the reasons for this is believed to be that the high concentration of the amine component increases the surface tension of the absorbing liquid. In this regard, the absorbing liquid of this embodiment contains a surfactant, which will be described later. When the absorbing liquid contains a surfactant, the surface tension of the absorbing liquid decreases. Therefore, when the absorbing liquid contains a surfactant, it is believed that the gas-liquid contact efficiency between the absorbing liquid and carbon dioxide is improved.

[0028] According to this configuration, the absorbing liquid of the present embodiment can prevent a decrease in the carbon dioxide absorption rate while containing a high concentration of the amine component. Therefore, the concentration of the amine component in the absorbing liquid of the present embodiment may be 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, or 70 mass% or more.

[0029] On the other hand, if the concentration of the amine component in the absorbing liquid is too high, even if the absorbing liquid contains a surfactant, problems such as a decrease in the amount of carbon dioxide absorbed per unit liquid volume in the absorbing liquid, a decrease in the miscibility of the amine component, an increase in viscosity, etc. Therefore, the concentration of the amine component in the absorbing liquid of this embodiment is preferably 80 mass% or less.

[0030] The amine component preferably contains a tertiary amine. If the amine component contains a tertiary amine, corrosion of the carbon dioxide absorption equipment is less likely to occur. Tertiary amines are known to be less corrosive to carbon dioxide absorption equipment than primary amines and secondary amines. This is thought to be because primary amines and secondary amines undergo a carbamate formation reaction in the absorption reaction with carbon dioxide, but tertiary amines do not, resulting in different reaction products.

[0031] In addition, when the absorbing solution contains a tertiary amine, carbonate ions are generated by the absorption reaction between the tertiary amine and carbon dioxide. The carbonate ions can react with iron or calcium in the environment to become carbonates such as iron carbonate or calcium carbonate. It is known that the presence of iron carbonate or calcium carbonate in a high-temperature absorbing solution provides high protection against corrosion. This knowledge is disclosed, for example, in the reference (Shimizu et al., Materials and the Environment, 65, 365-368, 2016).

[0032] In addition, the amine component preferably contains a primary amine and / or a secondary amine in addition to a tertiary amine. Compared with primary amines and secondary amines, tertiary amines tend to have a smaller dissipation energy of absorbed carbon dioxide, but also a smaller amount of carbon dioxide absorbed. If the amine component contains a primary amine and / or a secondary amine, it is easy to maintain the amount of carbon dioxide absorbed and reduce the dissipation energy in the absorbing solution of this embodiment.

[0033] The ratio of the tertiary amine when the amine component is taken as 100% by mass is preferably 90% by mass or more and 99% by mass or less, more preferably 93% by mass or more and 99% by mass or less, and may be 100% by mass. Furthermore, the ratio of the primary amine and / or secondary amine when the amine component is taken as 100% by mass is preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 7% by mass or less. With such a ratio, a carbon dioxide absorbing solution that satisfies both maintaining the amount of carbon dioxide absorbed and reducing the energy emitted, and reducing corrosiveness, can be obtained.

[0034] However, the respective proportions of primary amine, secondary amine and tertiary amine in the amine component are not limited to these, and may be appropriately determined depending on the corrosiveness, the amount of carbon dioxide absorbed and the amount of dissipated energy, and the like.

[0035] (Surfactant) The absorbing liquid of this embodiment contains a surfactant. This surfactant is at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type, and ester-ether type (hereinafter referred to as "surfactant of this embodiment"). As described above, the surfactant reduces the surface tension of the absorbing liquid containing an amine component. This improves the efficiency of gas-liquid contact between carbon dioxide and the absorbing liquid, and can improve the absorption rate of carbon dioxide by the absorbing liquid.

[0036] Surfactants are broadly classified into nonionic and ionic based on their properties in an aqueous solution. Ionic surfactants are further classified into cationic, anionic and amphoteric. The surfactant contained in the absorbing liquid of this embodiment is a nonionic surfactant.

[0037] Ionic surfactants are more reactive than nonionic surfactants because they are ionized in an aqueous solution, and may have a negative effect on the amount and rate of carbon dioxide absorption by the absorbing solution. In addition, ionic surfactants are prone to deterioration due to changes in chemical structure such as decomposition due to their high reactivity. The absorbing solution of this embodiment may come into contact with a gas containing carbon dioxide at a high temperature, and is heated during separation of carbon dioxide. Therefore, in order to withstand repeated absorption and release of carbon dioxide, the surfactant added to the absorbing solution of this embodiment is also required to be stable.

[0038] In this respect, nonionic surfactants are more stable than ionic surfactants because they do not ionize even in an aqueous solution, and therefore the nonionic surfactants tend to function stably and continuously even if the absorbing solution of the present embodiment is repeatedly heated to high temperatures.

[0039] In addition, nonionic surfactants are less likely to foam than ionic surfactants, which is undesirable because foaming in the absorbing solution inhibits contact between the carbon dioxide and the absorbing solution, reducing the efficiency of carbon dioxide absorption.

[0040] Nonionic surfactants can be further classified into several types based on their chemical structure. The surfactant of the present embodiment is at least one of an amine oxide type, an alkanolamide type, an ester type, and an ester-ether type. As the nonionic surfactant, an ether type is generally and widely used. However, an ether type nonionic surfactant is not preferable as the surfactant of the present embodiment.

[0041] The ether-type nonionic surfactant is made from higher alcohols and the like, and when it decomposes due to deterioration or the like, an organic acid is generated. The organic acid may cause corrosion of carbon dioxide absorption equipment. In addition, the organic acid may also cause foaming. Therefore, the advantageous effect of the nonionic surfactant, that is, "frothing is unlikely to occur," cannot be fully exhibited with the ether-type. In addition, from the viewpoint of preventing foaming, fluorine-based surfactants such as perfluoro-type surfactants are also used as foaming agents, and therefore are not preferable as the surfactant of this embodiment.

[0042] Nonionic surfactants of the amine oxide type, alkanolamide type, ester type, or ester-ether type are less likely to cause the problems associated with the ether type, and can therefore be suitably used for addition to the absorbing liquid. Thus, the present inventors have found that nonionic surfactants are preferable as surfactants to be added to the carbon dioxide absorbing liquid, and that nonionic surfactants other than ether type are even more preferable.

[0043] In addition, the surfactant of the present embodiment is preferably a surfactant derived from at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. If the surfactant of the present embodiment is such an amine-derived surfactant, it is considered that the negative effect that the surfactant may have on the absorption of carbon dioxide by the amine component can be minimized. In addition, even if the amine-derived surfactant is decomposed due to deterioration or the like, a part of it can function as the amine component.

[0044] When the surfactant of the present embodiment is an amine-derived type, it is particularly preferred that the surfactant is derived from a tertiary amine. As described above, in the case of a tertiary amine, carbonate ions generated during the absorption of carbon dioxide react with molecules in the environment to become carbonates, and the carbonates exhibit protective properties against corrosion. If the surfactant of the present embodiment is a surfactant derived from a tertiary amine, it can exhibit protective properties against corrosion in the same way as a tertiary amine. From the viewpoint of reducing the corrosiveness of the absorbing solution of the present embodiment, it is most preferred that the amine component of the present embodiment is made of a tertiary amine, and the surfactant of the present embodiment is a surfactant derived from a tertiary amine.

[0045] In addition, some nonionic surfactants are known to function as defoamers. If the surfactant of the present embodiment also functions as a defoamer, it is preferable because foaming of the absorbing liquid can be more reliably prevented. Examples of such nonionic surfactants include, but are not limited to, those having a polyoxyethylene-polyoxypropylene group in the hydrophilic group. Note that there are several known mechanisms for the defoaming action of defoamers. Examples of the defoaming action include a "foam breaking action" that reduces the elasticity of the generated bubbles to break them, a "foam suppression action" that suppresses foaming itself, and a "degassing action" that makes foamed bubbles bond together to make them easier to break. The surfactant of the present embodiment may have any of these defoaming actions.

[0046] Examples of amine oxide type nonionic surfactants include fatty acid amine oxides derived from tertiary amines. When the pH of the solution is acidic, the amine oxide type surfactant may exhibit the properties of a cationic surfactant. However, since the absorbing liquid of this embodiment contains an amine component, the pH is basic. When the pH of the solution is basic, the amine oxide type surfactant exhibits the properties of a nonionic surfactant. Therefore, when used in the absorbing liquid of this embodiment, the amine oxide type surfactant can be said to be a nonionic surfactant.

[0047] Examples of alkanolamide-type nonionic surfactants include fatty acid alkanolamides such as fatty acid diethanolamides. Examples of ester-type nonionic surfactants include glycerin fatty acid esters, sorbitan fatty acid esters, and sucrose fatty acid esters. Examples of ether-ester-type nonionic surfactants include fatty acid polyethylene glycols and fatty acid polyoxyethylene sorbitans.

[0048] When the surfactant of the present embodiment is a surfactant derived from a tertiary amine, such as fatty acid amine oxide, the tertiary amine as a raw material may be, for example, coconut alkylamine, dimethyl coconut amine, dimethyl octylamine, dimethyl decylamine, dimethyl laurylamine, dimethyl myristylamine, dimethyl palmitylamine, dimethyl stearylamine, and dimethyl behenylamine. Note that the surfactant of the present embodiment is not limited to the above examples.

[0049] The concentration of the surfactant of this embodiment in the absorbing liquid is preferably 0.01% by mass or more, may be 0.03% by mass or more, may be 0.05% by mass or more, may be 0.1% by mass or more, may be 0.25% by mass or more, or may be 0.5% by mass or more, from the viewpoint of improving the amount of carbon dioxide absorbed and the absorption speed. In addition, the concentration of the surfactant of this embodiment is preferably 5% by mass or less, may be 2.5% by mass or less, may be 1% by mass or less, or may be 0.5% by mass or less, from the viewpoint of not inhibiting the absorption of carbon dioxide by the amine component. In addition, the concentration of the surfactant of this embodiment is preferably 10 times or less of the critical micelle concentration, from the viewpoint of preventing foaming of the absorbing liquid.

[0050] The surface tension of the absorbing liquid of this embodiment at 25°C is preferably 100 mN / m or less, more preferably 70 mN / m or less, more preferably 50 mN / m or less, more preferably 30 mN / m or less, more preferably 25 mN / m or less, and more preferably 20 mN / m or less, for efficient gas-liquid contact between carbon dioxide and the absorbing liquid. Since the absorbing liquid of this embodiment contains a surfactant as described above, even if it contains a high concentration of amine components of 30 mass% or more, it can easily maintain such a surface tension. Therefore, the absorbing liquid of this embodiment can achieve both a high absorption amount due to a high concentration of amine components and a high absorption rate due to efficient gas-liquid contact at low surface tension in absorbing carbon dioxide.

[0051] (solvent) The solvent of the absorbing liquid in this embodiment is not particularly limited as long as it does not impair the effects of the present invention. An example of the water-containing gas is water. Among the reactions of absorbing carbon dioxide by the amine component, the reaction involving the production of bicarbonate ions requires water. Therefore, by including water in the absorbing solution of the present embodiment, the absorption of carbon dioxide by the amine component proceeds efficiently.

[0052] In addition, the solvent preferably contains an organic solvent in addition to water, in that it can reduce the dissipation energy. The organic solvent is more preferably a hydrophilic organic solvent, in that it can reduce the heating temperature when separating carbon dioxide from the absorbing liquid and reduce the dissipation energy. In addition, when the absorbing liquid contains a hydrophilic organic solvent, the amount of carbon dioxide absorbed by the absorbing liquid can be increased. Furthermore, when the absorbing liquid contains a hydrophilic organic solvent, the surface tension of the absorbing liquid can be reduced. Therefore, the efficiency of gas-liquid contact between the absorbing liquid and the gas containing carbon dioxide is improved, and the absorption rate of carbon dioxide by the absorbing liquid can be improved.

[0053] The organic solvent is not particularly limited, and examples thereof include alcohols, ethers, ketones, and nitriles. Examples of the alcohols include methanol, ethanol, propanol, isopropyl alcohol, and tertiary butyl alcohol. Examples of the ethers include dimethoxyethane and tetrahydrofuran. Examples of the ketones include acetone. Examples of the nitriles include acetonitrile. The organic solvent may be used alone or in combination of two or more kinds.

[0054] The concentration of the organic solvent contained in the absorbing liquid may be 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more. Also, the concentration of the organic solvent contained in the absorbing liquid may be 60% by mass or less, 50% by mass or less, or 40% by mass or less.

[0055] The boiling point of the organic solvent used in the absorbing liquid is not particularly limited, but is preferably 40°C or higher and lower than 100°C. In general, the temperature when carbon dioxide in a gas containing carbon dioxide is absorbed into the absorbing liquid is, for example, 20°C or higher and 40°C or lower. Therefore, if the boiling point of the organic solvent is lower than 40°C, the organic solvent may become gas when the absorbing liquid reacts with carbon dioxide, and the organic solvent may not function as a solvent for the absorbing liquid. In addition, if the boiling point of the organic solvent is lower than 100°C, the boiling point of the organic solvent is lower than the boiling point of water. By containing an organic solvent with a boiling point lower than water in the absorbing liquid, the heating temperature when separating carbon dioxide from the absorbing liquid can be reduced. Therefore, the dissipation energy can be reduced.

[0056] The absorbing liquid of the present embodiment may contain components other than those described above, if necessary, within a range that does not impair the effects of the present invention. Examples of such components include corrosion inhibitors, deterioration inhibitors, and antifoaming agents that are different from the surfactant of the present embodiment. The concentrations of these components are not particularly limited as long as they do not impair the effects of the present invention.

[0057] The absorbing liquid of the present embodiment can be prepared by adding the amine component of the present embodiment and the surfactant of the present embodiment to a solvent. The amine in the amine component and the surfactant may be commercially available or may be synthesized by a known method.

[0058] [Method for separating and capturing carbon dioxide] A separation and recovery method according to one embodiment of the present invention (hereinafter referred to as "the separation and recovery method of the present embodiment") is a separation and recovery method for separating and recovering carbon dioxide from a gas containing carbon dioxide, and includes a separation step of contacting an absorption liquid with a gas containing carbon dioxide to separate carbon dioxide from the gas, and a recovery step of heating the absorption liquid that has absorbed carbon dioxide and is obtained in the separation step to recover carbon dioxide from the absorption liquid, wherein the absorption liquid includes an amine component including at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines, and at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type, and ester-ether type.

[0059] (separation process) In the separation step, the absorbing liquid to be brought into contact with the gas containing carbon dioxide is the absorbing liquid of the present embodiment described in the above section [Absorbing Liquid]. The absorbing liquid is brought into contact with the gas containing carbon dioxide, and the carbon dioxide is absorbed into the absorbing liquid, whereby the carbon dioxide is separated from the gas.

[0060] Methods for contacting the absorbing liquid with carbon dioxide include bubbling the gas containing carbon dioxide in the absorbing liquid, misting or spraying the absorbing liquid into a gas flow containing carbon dioxide, and countercurrent gas-liquid contact between the absorbing liquid and the gas containing carbon dioxide, etc. Absorption of carbon dioxide by the absorbing liquid can be carried out, for example, in an absorption tower provided in a boiler of a thermal power plant or a power plant.

[0061] The temperature of the absorbing liquid when the absorbing liquid is brought into contact with the gas containing carbon dioxide can be appropriately selected depending on the composition of the absorbing liquid, and may be, for example, from 20° C. to 40° C. The contact between the absorbing liquid and the gas containing carbon dioxide may be carried out under atmospheric pressure or under pressure.

[0062] (Recovery process) In the recovery step, the absorbing liquid that has absorbed the carbon dioxide obtained in the separation step is heated to recover the carbon dioxide from the absorbing liquid. The separation and recovery method of this embodiment can reduce the energy dissipated in the recovery step by using an absorbing liquid that contains a hydrophilic organic solvent. Furthermore, since carbon dioxide can also be absorbed by a hydrophilic organic solvent, the amount of carbon dioxide absorbed in the separation step can be increased by making the absorbing liquid contain a hydrophilic organic solvent.

[0063] Methods for recovering carbon dioxide from the absorption liquid after the separation step include heating and bubbling the absorption liquid after the separation step, and absorbing carbon dioxide with a packing material, etc. Recovery of carbon dioxide from the absorption liquid after the separation step can be carried out, for example, in a boiler at a thermal power plant and a stripper tower (regenerator) provided at the power plant, etc.

[0064] In the case of a conventional absorption liquid using water as a solvent, the temperature of the absorption liquid when recovering carbon dioxide in the recovery step had to be raised to about 130°C in order to evaporate the solvent. On the other hand, in the separation and recovery method of the present embodiment, the temperature of the absorption liquid when recovering carbon dioxide in the recovery step may be lower than 130°C, and may be, for example, 80°C or higher and 120°C or lower. In the separation and recovery method of the present embodiment, since the absorption liquid contains a hydrophilic organic solvent, carbon dioxide can be dissipated from the absorption liquid under temperature conditions lower than the heating temperature in the conventional recovery step. Therefore, the dissipation energy in the recovery step can be reduced.

[0065] (Other processes) The separation and recovery method of the present embodiment may further include other steps in addition to the steps described above, as long as the effects of the present embodiment can be obtained. Examples of the other steps include a storage step of storing the carbon dioxide recovered in the recovery step.

[0066] The captured carbon dioxide can be used as a raw material for chemicals, a refrigerant for freezing food, and the like.

[0067] The following examples are provided to further explain the embodiments of the present invention. Of course, the present invention is not limited to the following examples, and various modifications are possible in terms of details. EXAMPLES

[0068] The amount of carbon dioxide absorbed and released was examined using an absorbing solution according to an embodiment of the present invention and an absorbing solution according to a comparative example. In order to confirm the stability of the absorbing solution, absorption and release were repeated multiple times. The repetition was stopped when the absorbing solution became cloudy or foaming was confirmed, and the repetition was repeated up to 10 times. The amount of carbon dioxide absorbed and released was measured at the first time and at the end.

[0069] [Measurement of CO2 absorption by absorbing solution] A glass container containing 100 g of the absorbing solution according to each Example or Comparative Example was placed in a thermostatic water bath and the temperature was adjusted to 40° C. After adjusting the simulated gas mixed through a flow regulator so that the carbon dioxide content was 15 volume % and the nitrogen content was 85 volume %, the simulated gas was introduced into the glass container containing the absorbing solution at a flow rate of 0.9 L / min for 60 minutes.

[0070] The carbon dioxide concentrations at the inlet and outlet of the glass container were measured using a total organic carbon (TOC) meter manufactured by Shimadzu Corporation. The amount of carbon dioxide absorbed by the absorbing solution was estimated from the amount of carbon dioxide flowed in 60 minutes and the difference in the carbon dioxide concentrations at the inlet and outlet of the glass container.

[0071] [Measurement of CO2 emission from the absorbing solution after CO2 absorption] The temperature of the thermostatic bath containing the glass container containing the absorbing liquid after absorbing carbon dioxide was set to 100°C, and the amount of carbon dioxide emitted over 60 minutes was measured and integrated using a Keyence gas flow meter.

[0072] The method of preparing the absorbing liquid according to each of the Examples and Comparative Examples will be described below. The compositions of the absorbing liquid according to each of the Examples and Comparative Examples are summarized in Table 1 below. The proportion of the surfactant is shown as an outside number when the total amount of the amine component and water is 100 mass%.

[0073] Example 1 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.005% by mass of a nonionic surfactant (UNISAFE (registered trademark) A-LM: amine oxide type, manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0074] Example 2 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0075] Example 3 A mixed liquid was prepared by mixing 30% by mass of 2-isopropylaminoethanol, 70% by mass of water, and 0.05% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0076] Example 4 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 1.0% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0077] Example 5 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 5% by mass of piperazine, 65% by mass of water, and 0.005% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type, manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0078] Example 6 A mixed liquid was prepared by mixing 60% by mass of monoethanolamine, 40% by mass of water, and 0.1% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type, manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0079] Example 7 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.005% by mass of a nonionic surfactant (NOF Corporation's Stahome (registered trademark) F: alkanolamide type). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0080] Example 8 A mixed liquid was prepared by mixing 2% by mass of piperazine, 60% by mass of methyldiethanolamine, 38% by mass of water, and 0.1% by mass of a nonionic surfactant (Cadenax (registered trademark) DM12D-W (C): tertiary amine-derived amine oxide type, manufactured by Lion Specialty Chemicals Co., Ltd.). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0081] Example 9 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 10% by mass of a nonionic surfactant (UNISAFE A-LM: amine oxide type manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0082] Comparative Example 1 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine and 70% by mass of water. Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0083] Comparative Example 2 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of a nonionic surfactant (Nonion E-202: ether type, manufactured by NOF Corporation). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0084] Comparative Example 3 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of an anionic surfactant (Viewlite (registered trademark) SHAA manufactured by Sanyo Chemical Industries, Ltd.). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0085] Comparative Example 4 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of an amphoteric surfactant (Revon (registered trademark) 101H manufactured by Sanyo Chemical Industries, Ltd.). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0086] Comparative Example 5 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of a cationic surfactant (Cation G-50 manufactured by Sanyo Chemical Industries, Ltd.). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0087] Comparative Example 6 A mixed liquid was prepared by mixing 30% by mass of monoethanolamine, 70% by mass of water, and 0.05% by mass of a fluorosurfactant (Amine oxide type S-241 manufactured by AGC Seiko Chemical Co., Ltd.). Next, a gas containing 15% by volume of carbon dioxide and 85% by volume of nitrogen was blown into the mixed liquid at a pressure of 101 kPa to obtain an absorption liquid.

[0088] [Table 1]

[0089] The abbreviations or surfactants in Table 1 respectively indicate the following: MEA: monoethanolamine; IPAE: 2-isopropylaminoethanol, PZ: piperazine; MDEA: methyldiethanolamine; Unisafe A-LM: Dimethyl lauryl-amine oxide aqueous solution (NOF Corporation), Stahome F: coconut fatty acid diethanolamide (NOF Corporation), Nonion E-202: Ether type surfactant (NOF Corporation), Viewlight SHAA: Anionic surfactant (Sanyo Chemical Industries, Ltd.), Levon 101H: amphoteric surfactant (Sanyo Chemical Industries, Ltd.), Cation G-50: Cationic surfactant (Sanyo Chemical Industries, Ltd.), S-241: Amine oxide surfactant (AGC Sei Chemical Co., Ltd.), Cadenax DM12D-W(C): Tertiary amine derived surfactant (Lion Specialty Chemicals Co., Ltd.).

[0090] Table 2 below shows the amounts of carbon dioxide absorbed and released by the absorbing liquid according to each of the examples and comparative examples. In Table 2, "CO2 absorption amount" is the amount of carbon dioxide absorbed (g) per 1 kg of absorbing liquid at 40°C. Also, "CO2 release amount" is the amount of carbon dioxide released (g) per 1 kg of absorbing liquid at 100°C. "Release rate" is the ratio of the CO2 release amount to the CO2 absorption amount (CO2 release amount / CO2 absorption amount). "Number of repetitions" is the number of times that the absorption and release of carbon dioxide by the same absorbing liquid was repeated.

[0091] [Table 2]

[0092] As shown in Table 2, the absorbing liquid according to each Example had a higher carbon dioxide absorption amount and release amount than Comparative Example 1, which did not contain a surfactant. This tendency was particularly remarkable when the concentration of the amine component was high (Example 6 and Comparative Example 1). Furthermore, in the absorbing liquid according to each Example, no decrease in the carbon dioxide absorption amount and release amount was observed even after the absorption and release of carbon dioxide by the absorbing liquid was repeated 10 times.

[0093] On the other hand, in the case of an ether-type nonionic surfactant (Comparative Example 2), an ionic surfactant (Comparative Examples 3 to 5), and a fluorochemical surfactant (Comparative Example 6) that are not included in the scope of this embodiment, the absorption liquid became cloudy or foamed after the absorption and desorption of carbon dioxide by the absorption liquid was repeated 5 to 8 times. Moreover, the absorption amount, desorption amount, and desorption rate of carbon dioxide in the absorption liquid at the end of the repetition were clearly lower than those at the initial time.

[0094] From the above results, it was shown that the surfactant of the present embodiment is effective in improving the amount of carbon dioxide absorbed and released in the absorbing liquid. It was also shown that the surfactant of the present embodiment has excellent stability in the absorbing liquid. [Industrial Applicability]

[0095] INDUSTRIAL APPLICABILITY The present invention can be used as an absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide.

Claims

1. An absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide, an amine component comprising at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines; and at least one nonionic surfactant selected from the group consisting of an amine oxide type, an alkanolamide type, an ester type, and an ester-ether type.

2. 2. The absorbing fluid of claim 1, wherein the non-ionic surfactant is a surfactant derived from at least one amine selected from the group consisting of primary amines, secondary amines and tertiary amines.

3. 3. The absorbing fluid of claim 2, wherein the non-ionic surfactant is a tertiary amine derived surfactant.

4. The absorbing solution according to claim 1 , comprising 30% by mass or more of the amine component.

5. 5. The absorbing solution according to claim 1, wherein the amine component includes a tertiary amine and at least one of a primary amine and a secondary amine, and a total amount of the primary amine and the secondary amine is 10 mass% or less of a total amount of the amine component.

6. A method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising the steps of: a separation step of contacting the absorption liquid with a gas containing carbon dioxide to separate carbon dioxide from the gas; A recovery step of heating the absorption liquid that has absorbed the carbon dioxide obtained in the separation step and recovering the carbon dioxide from the absorption liquid that has absorbed the carbon dioxide, the absorption liquid is an aqueous solution containing an amine component including at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines, and at least one nonionic surfactant selected from the group consisting of amine oxide type, alkanolamide type, ester type, and ester-ether type.

7. The separation and recovery method according to claim 6, wherein in the recovery step, the absorption liquid having absorbed carbon dioxide is heated at 80°C or higher and 120°C or lower.

Images