JP7637524B2 - Absorption liquid and separation and recovery method - Google Patents

Description

The present invention relates to a carbon dioxide absorption solution and a method for separating and recovering carbon dioxide.

In order to curb global warming, carbon dioxide capture and storage technology has been attracting increasing attention. In particular, as a method for separating and capturing carbon dioxide from gases containing carbon dioxide emitted from thermal power plants and the like, 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.

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. 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.

Japanese Patent Application Publication No. 8-252430 JP 2012-11309 A

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 rate of carbon dioxide absorption. 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.

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.

In order to solve the above 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.

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

In one embodiment of the present invention, the nonionic surfactant in the absorbing liquid may be a surfactant derived from a tertiary amine.

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

In one embodiment of the present invention, the amine component of the absorbing liquid includes a tertiary amine and at least one of a primary amine and a secondary amine, and the total amount of the primary amine and the secondary amine may be 10 mass% or less of the total amount of the amine component.

In order to solve the above 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, 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 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.

In one embodiment of the separation and recovery method of the present invention, the absorption liquid that has absorbed carbon dioxide may be heated to 80°C or higher and 120°C or lower in the recovery process.

According to one aspect of the present invention, it is possible 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.

One embodiment of the present invention is described below, but the present invention is not limited to this. 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 literature and patent documents described in this specification are incorporated herein by reference.

[Outline of the present invention]
Conventionally, 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, carbon dioxide in a 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.

The higher the amine component content in the absorbing liquid, the greater the amount of carbon dioxide absorbed can be expected. However, it is empirically known that as the amine component content in the absorbing liquid increases, the carbon dioxide absorption rate decreases. 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, reducing the efficiency of gas-liquid contact between the absorbing liquid and carbon dioxide.

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

However, there are many other types of surfactants. It is undesirable 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 to function stably even under such conditions. It was previously unknown what type of surfactant would meet these requirements.

The 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 is described below.

[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.

(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 a primary amine, a secondary amine, and a tertiary amine. 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.

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

Examples of secondary amines include secondary alkanolamines such as 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, and 2-n-butylaminoethanol; and secondary amines having a heterocycle such as piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, and 2-piperidinoethanol. When used as an absorbing liquid, among these secondary amines, secondary alkanolamines are preferred, and 2-isopropylaminoethanol is particularly preferred, in that they absorb a large amount of carbon dioxide and have a fast absorption rate. 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.

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.

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

Here, it is known that when the absorbing liquid contains a high concentration (e.g., 30 mass % or more) of amine components, the rate at which carbon dioxide is absorbed by the absorbing liquid decreases. One of the reasons for this is thought to be that the high concentration of amine components 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 thought that the gas-liquid contact efficiency between the absorbing liquid and carbon dioxide improves.

With this configuration, the absorbing solution of this embodiment can prevent a decrease in the carbon dioxide absorption rate while containing a high concentration of amine components. Therefore, the concentration of the amine components in the absorbing solution of this embodiment may be 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more.

On the other hand, if the concentration of the amine component in the absorption liquid is too high, problems such as a decrease in the amount of carbon dioxide absorbed per unit volume of the absorption liquid, a decrease in the mixability of the amine component, and an increase in viscosity may occur, even if the absorption liquid contains a surfactant. Therefore, the concentration of the amine component in the absorption liquid of this embodiment is preferably 80% by mass or less.

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 and secondary amines undergo a carbamate formation reaction in the absorption reaction with carbon dioxide, but such a reaction does not occur with tertiary amines, resulting in different reaction products.

In addition, when the absorption 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 absorption 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).

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 absorption liquid of this embodiment.

The proportion of tertiary amines 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 proportion of primary amines and/or secondary amines 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 proportion, a carbon dioxide absorbing liquid can be obtained that satisfies both the maintenance of the amount of carbon dioxide absorbed and the reduction of dissipated energy, as well as the reduction of corrosiveness.

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

(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.

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

Ionic surfactants are more reactive than nonionic surfactants because they ionize in an aqueous solution, and can have a negative effect on the amount and rate of carbon dioxide absorption by the absorbing solution. In addition, due to their high reactivity, ionic surfactants are prone to deterioration due to changes in chemical structure such as decomposition. The absorbing solution of this embodiment may come into contact with high-temperature gas containing carbon dioxide, 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.

In this respect, nonionic surfactants are more stable than ionic surfactants because they do not ionize even in an aqueous solution. Therefore, even if the absorption liquid of this embodiment is repeatedly heated to high temperatures, the nonionic surfactant is likely to function stably and continuously.

In addition, nonionic surfactants are less likely to foam than ionic surfactants. If foaming occurs in the absorbing liquid, contact between the carbon dioxide and the absorbing liquid is hindered, which reduces the efficiency of carbon dioxide absorption, which is undesirable.

Nonionic surfactants can be further classified into several types based on their chemical structure. The surfactants of this embodiment are at least one of amine oxide type, alkanolamide type, ester type, and ester-ether type. As nonionic surfactants, ether type is generally widely used. However, ether type nonionic surfactants are not preferred as surfactants of this embodiment.

Ether-type nonionic surfactants are made from higher alcohols and the like, and when they decompose due to deterioration or the like, organic acids are generated. Organic acids can cause corrosion of carbon dioxide absorption equipment. In addition, organic acids can also cause foaming. Therefore, the advantageous effect of nonionic surfactants, that is, "frothing is less likely to occur," cannot be fully achieved with ether-type surfactants. 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 preferred as surfactants for this embodiment.

Amine oxide, alkanolamide, ester or ester-ether type nonionic surfactants are less likely to cause the problems associated with ether types, and are therefore suitable for addition to the absorbing liquid. In this way, the present inventors have discovered that nonionic surfactants are preferred as surfactants to be added to the carbon dioxide absorbing liquid, and that nonionic surfactants that are not ether types are even more preferred.

The surfactant of this 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 this embodiment is such an amine-derived surfactant, it is believed that the negative effect that the surfactant may have on the absorption of carbon dioxide by the amine component can be minimized. Furthermore, even if the amine-derived surfactant decomposes due to deterioration or the like, a part of it can still function as the amine component.

When the surfactant of this embodiment is an amine-derived type, it is particularly preferable that the surfactant is derived from a tertiary amine. As described above, in 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 this 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 absorption liquid of this embodiment, it is most preferable that the amine component of this embodiment is made of a tertiary amine, and the surfactant of this embodiment is a surfactant derived from a tertiary amine.

In addition, some nonionic surfactants are known to function as defoamers. If the surfactant of this embodiment also functions as a defoamer, it is preferable because it can more reliably prevent foaming of the absorbing liquid. 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 easier to break by bonding them together. The surfactant of this embodiment may have any of these defoaming actions.

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

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 sorbitan.

When the surfactant of this embodiment is a surfactant derived from a tertiary amine, such as a fatty acid amine oxide, examples of the tertiary amine used as a raw material include coconut alkylamine, dimethyl coconut amine, dimethyl octylamine, dimethyl decylamine, dimethyl laurylamine, dimethyl myristylamine, dimethyl palmitylamine, dimethyl stearylamine, and dimethyl behenylamine. The surfactant of this embodiment is not limited to the above examples.

The concentration of the surfactant of this embodiment in the absorption 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 absorption liquid.

The surface tension of the absorbing solution 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 solution. Since the absorbing solution of this embodiment contains a surfactant as described above, such a surface tension can be easily maintained even if it contains a high concentration of amine components of 30 mass% or more. Therefore, the absorbing solution 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.

(solvent)
The solvent of the absorbing solution of this embodiment is not particularly limited as long as it does not impair the effects of the present invention. An example of the solvent is water. Among the reactions of absorbing carbon dioxide by the amine component, water is required for the reaction accompanying the production of bicarbonate ions, so that the absorption of carbon dioxide by the amine component proceeds efficiently by including water in the absorbing solution of this embodiment.

In addition, the solvent preferably contains an organic solvent in addition to water, since it can reduce the dissipation energy. The organic solvent is more preferably a hydrophilic organic solvent, since it can reduce the heating temperature when separating carbon dioxide from the absorbing liquid and reduce the dissipation energy. In addition, since the absorbing liquid contains a hydrophilic organic solvent, the amount of carbon dioxide absorbed by the absorbing liquid can be increased. Furthermore, since 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.

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

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. 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.

The boiling point of the organic solvent used in the absorption 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 absorption 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 absorption liquid reacts with carbon dioxide, and the organic solvent may not function as a solvent for the absorption 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 including an organic solvent with a boiling point lower than that of water in the absorption liquid, the heating temperature when separating carbon dioxide from the absorption liquid can be reduced. Therefore, the dissipation energy can be reduced.

The absorbing solution of this embodiment may contain components other than those described above, as necessary, to the extent that the effects of the present invention are not impaired. Examples of such components include corrosion inhibitors, deterioration inhibitors, and antifoaming agents of a type different from the surfactant of this embodiment. The concentrations of these components are not particularly limited as long as they are within the range that does not impair the effects of the present invention.

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

[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 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.

(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.

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 stream containing carbon dioxide, and countercurrent gas-liquid contact between the absorbing liquid and the gas containing carbon dioxide. Absorption of carbon dioxide by the absorbing liquid can be carried out, for example, in boilers at thermal power plants and in absorption towers installed in power plants, etc.

The temperature of the absorbing liquid when it 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, 20°C or higher and 40°C or lower. The contact between the absorbing liquid and the gas containing carbon dioxide may be carried out under atmospheric pressure or under pressure.

(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.

Methods for recovering carbon dioxide from the absorption liquid after the separation process include heating and bubbling the absorption liquid after the separation process, and absorbing carbon dioxide using a packing material, etc. Carbon dioxide can be recovered from the absorption liquid after the separation process, for example, in a stripping tower (regeneration tower) installed in a boiler at a thermal power plant or in a power plant, etc.

In the case of a conventional absorption liquid that uses water as a solvent, the temperature of the absorption liquid when recovering carbon dioxide in the recovery process 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 this embodiment, the temperature of the absorption liquid when recovering carbon dioxide in the recovery process may be lower than 130°C, for example, may be 80°C or higher and 120°C or lower. In the separation and recovery method of this embodiment, since the absorption liquid contains a hydrophilic organic solvent, carbon dioxide can be dissipated from the absorption liquid under temperature conditions that are lower than the heating temperature in the conventional recovery process. Therefore, the dissipation energy in the recovery process can be reduced.

(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.

The captured carbon dioxide can be used as a raw material for chemicals and as a refrigerant for freezing food.

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 details are possible.

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 and final times.

[Measurement of _CO2 absorption amount 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 by mixing the gas through a flow rate regulator so that the carbon dioxide content was 15% by volume and the nitrogen content was 85% by 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.

The carbon dioxide concentration at the inlet and outlet of the glass container was measured using a Shimadzu total organic carbon (TOC) meter. The amount of carbon dioxide absorbed by the absorbing solution was estimated from the amount of carbon dioxide flowing over 60 minutes and the difference in carbon dioxide concentration at the inlet and outlet of the glass container.

[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 for 60 minutes was measured and integrated using a gas flow meter manufactured by Keyence.

The method for preparing the absorbing liquid for each Example and Comparative Example is described below. The composition of the absorbing liquid for each Example and Comparative Example is summarized in Table 1 below. The proportion of the surfactant is shown as an external number when the total amount of the amine component and water is 100 mass%.

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.

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.

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.

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.

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.

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.

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 (Stahome (registered trademark) F: alkanolamide 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.

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.

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.

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.

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.

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.) Then, 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.

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.) Then, 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.

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.) Then, 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.

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 Seikagaku Co., Ltd.) Then, 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.

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),
Viewlite 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.).

Table 2 below shows the amount of carbon dioxide absorbed and released by the absorbing solution according to each Example and Comparative Example. In Table 2, " _CO2 absorption amount" is the amount of carbon dioxide absorbed (g) per kg of absorbing solution at 40°C. Also, " _CO2 release amount" is the amount of carbon dioxide released (g) per kg of absorbing solution at 100°C. "Release rate" is the ratio of the amount of _CO2 released to the amount of _CO2 absorbed ( _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 solution was repeated.

As shown in Table 2, the absorption and release amounts of carbon dioxide were superior in the absorbing liquid according to each Example to Comparative Example 1, which did not contain a surfactant. This tendency was particularly noticeable 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 absorption and release amounts of carbon dioxide was observed even after the absorption and release of carbon dioxide by the absorbing liquid was repeated 10 times.

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), which 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. In addition, the absorption amount, desorption amount, and desorption rate of carbon dioxide in the absorption liquid at the end of the repetitions were clearly lower than those at the initial time.

These results show that the surfactant of this embodiment is effective in improving the amount of carbon dioxide absorbed and released in the absorption liquid. In addition, the surfactant of this embodiment is shown to have excellent stability in the absorption liquid.

The present invention can be used as an absorption liquid for separating and recovering carbon dioxide from a gas that contains carbon dioxide.

Claims (7)

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. The absorbing liquid according to claim 1, wherein the nonionic surfactant is a surfactant derived from at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. The absorbing liquid according to claim 2, wherein the nonionic surfactant is a surfactant derived from a tertiary amine. The absorbing solution according to any one of claims 1 to 3, containing 30% by mass or more of the amine component. The absorbing liquid according to any one of claims 1 to 4, wherein the amine component includes a tertiary amine and at least one of a primary amine and a secondary amine, and the total amount of the primary amine and the secondary amine is 10 mass% or less of the total amount of the amine component. 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 the 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. The separation and recovery method according to claim 6, wherein in the recovery step, the absorption liquid having absorbed carbon dioxide is heated at a temperature of 80°C or higher and 120°C or lower.