WO2024242452A1 - Absorbent for capturing carbon dioxide - Google Patents

Abstract

The present invention relates to an absorbent for capturing carbon dioxide and, more specifically, to an absorbent for capturing carbon dioxide, the absorbent comprising a first amine-based compound, a second amine-based compound, and an activating agent, wherein: the first amine-based compound is 1,4-diazabicyclo(2.2.2)octane; the activating agent is a piperazine-based compound; and the second amine-based compound is a tertiary amine-based compound, which is methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA), so that the crystal formation is prevented in a high-temperature environment during the removal of the absorbent or in a cooling process after the removal thereof, and the gas-liquid exchange is smoothly facilitated in an absorption part and a regeneration part through viscosity lowering.

Description

Absorbent for carbon dioxide capture

The present invention relates to an absorbent for capturing carbon dioxide, and more particularly, to an absorbent for capturing carbon dioxide, the absorbent comprising a first amine compound, a second amine compound, and an activator, wherein the first amine compound is 1,4-diazabicyclo(2.2.2)octane, the activator is a piperazine compound, and the second amine compound is a tertiary amine compound such as methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA), thereby preventing crystal formation in a high temperature environment during stripping of the absorbent or during the cooling process after stripping, and lowering the viscosity so that gas-liquid exchange is smooth in an absorption section and a regeneration section.

The exhaust gases emitted from various industries such as thermal power plants contain a large amount of air pollutants such as carbon dioxide, sulfur oxides, nitrogen oxides, and fine dust. The technology for separating and processing harmful substances in these exhaust gases is becoming increasingly important not only in academic and industrial aspects, but also for the sustainable development of mankind. In particular, it is important to reduce the emission of carbon dioxide into the atmosphere, which is the main cause of the greenhouse effect.

Many technologies, such as chemical absorption, adsorption, membrane separation, and deep-freezing, are being developed to reduce carbon dioxide, an acidic gas in exhaust gas. The chemical absorption method uses an absorbent to absorb and capture carbon dioxide, and is the most widely used due to its high efficiency and stable process.

To remove the acid gas, a scrubbing step using an absorbent of an inorganic or organic base can be performed. The acid gas including carbon dioxide can be dissolved in the absorbent, and the absorbent including carbon dioxide can be regenerated by expansion in a low pressure environment and/or stripping by heat, and the ionic species can be re-reacted to form an acid gas, which can then be removed by steam.

The carbon dioxide capture system according to Fig. 1 includes an absorption unit (91) for removing carbon dioxide from exhaust gas by combining it with an absorbent, a heat exchanger (93) for receiving the absorbent that has absorbed carbon dioxide through a pump (P) and performing heat exchange, and a regeneration unit (92) for removing carbon dioxide chemically bound to the heat-exchanged absorbent. Accordingly, the carbon dioxide absorption and removal device performs a carbon dioxide absorption process and an absorption liquid regeneration process (removal process) using the above components, and the regenerated absorption liquid is resupplied to the absorption unit (91).

The synthesis of carbon dioxide and absorbent performed in the absorption unit (91) is an exothermic reaction, so that a secondary cooling method is forced on the absorption unit for continuous reaction, and the removal of carbon dioxide performed in the regeneration unit is an endothermic reaction, so the energy required for the regeneration of the absorbent to remove carbon dioxide from the absorbent accounts for a significant portion of the energy required for the entire carbon capture system.

Conventionally, the absorbent used for carbon dioxide capture is monoethanolamine (MEA), and the MEA is mixed with water and used as an absorbent. In the absorption section, MEA and carbon dioxide are combined to remove carbon dioxide in the exhaust gas, and the absorbent that has absorbed the carbon dioxide is regenerated in the regeneration section by heating, etc. Conventional amine absorbents can recover carbon dioxide with an efficiency of about 75 to 90%, but there is a problem that the carbon dioxide absorbed in the absorption section is not smoothly removed in the regeneration section. The difference in carbon dioxide concentration between the carbon dioxide rich absorbent and the lean absorbent can be defined as the circulation capacity. The circulation capacity is expressed in units of gCO2/kg or mol/L, and indicates how smoothly the absorbed carbon dioxide is removed in the regeneration section. Conventional absorbents have a low circulation capacity, so that the carbon dioxide absorption capacity is relatively reduced when the absorbent is used after regeneration.

When trying to absorb carbon dioxide from gas emitted from a means of transportation such as a ship, first, substances such as sulfur oxides are absorbed from the exhaust gas, and then carbon dioxide is absorbed from the remaining exhaust gas. A scrubber can be operated to absorb substances such as sulfur oxides, and a low-temperature liquid such as seawater is used as the wash water to lower the temperature of the exhaust gas. When supplying an absorbent before absorbing carbon dioxide, there is a problem that the absorbent crystallizes if the temperature is low, making normal carbon dioxide absorption impossible. In addition, the absorption section and the regeneration section have a structure similar to a packing for gas-liquid exchange, and if the viscosity of the absorbent is high, there is a problem that the gas-liquid exchange efficiency is low.

Therefore, an absorbent that does not crystallize even at low temperatures when supplying the absorbent and has low viscosity to facilitate smooth gas-liquid exchange in the absorption and regeneration sections is required.

(Patent Document 1) Korean Patent Publication No. 10-2013-0002828 (January 8, 2013)

The present invention has been devised to solve the above problems.

The purpose of the present invention is to provide a carbon dioxide capture absorbent comprising a first amine compound, a second amine compound, and an activator, wherein the activator comprises a piperazine compound, and the circulation capacity and absorption rate of a tertiary amine compound are improved.

The purpose of the present invention is to provide an absorbent for capturing carbon dioxide, which can smoothly activate a tertiary amine compound even when a relatively small amount of piperazine, which is a solid amine compound, is used, by making the first amine compound be 1,4-diazabicyclo(2.2.2)octane (DABCO).

The purpose of the present invention is to provide a carbon dioxide capturing absorbent in which the first amine compound is incorporated in an amount of 20 to 30 wt%, preferably 25 wt%, and the piperazine compound is incorporated in an amount of 10 to 20 wt%, preferably 15 wt%, with respect to the carbon dioxide capturing absorbent, thereby improving the carbon dioxide absorption capacity of the tertiary amine compound and reducing the crystallization possibility of the absorbent.

The purpose of the present invention is to provide an absorbent for capturing carbon dioxide, in which the second amine compound is a tertiary amine compound, but is methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA), so that crystallization does not occur within the absorbent, thereby enabling normal carbon dioxide capturing function to be exhibited.

The purpose of the present invention is to provide a carbon dioxide capturing absorbent having low viscosity and preventing crystal formation during the stripping process of the absorbent by mixing 27 wt% to 30 wt% of the second amine compound into the absorbent for carbon dioxide capture.

The purpose of the present invention is to provide a carbon dioxide capturing absorbent having low viscosity and preventing crystal formation during the stripping process of the absorbent by mixing 9 wt% to 18 wt% of the second amine compound, wherein the dimethylethanolamine is dimethylethanolamine.

The purpose of the present invention is to provide a carbon dioxide capture absorbent that facilitates gas-liquid exchange within an absorption unit and a regeneration unit by making the viscosity value at 40°C after stripping the carbon dioxide capture absorbent 30 cP or less.

In order to achieve the above-mentioned purpose, the present invention is implemented by an embodiment having the following configuration.

According to one embodiment of the present invention, an absorbent for capturing carbon dioxide according to the present invention comprises a first amine-based compound, a second amine-based compound, and an activator, and is characterized in that the activator is a piperazine-based compound.

According to one embodiment of the present invention, the first amine compound is characterized by being 1,4-diazabicyclo(2.2.2)octane (DABCO).

According to one embodiment of the present invention, the first amine compound is incorporated in an amount of 20 to 30 wt%, preferably 25 wt%, of the absorbent for capturing carbon dioxide, and the piperazine compound is incorporated in an amount of 10 to 20 wt%, preferably 15 wt%, of the absorbent for capturing carbon dioxide.

According to one embodiment of the present invention, the second amine compound is characterized in that it is a tertiary amine compound.

According to one embodiment of the present invention, the tertiary amine compound is characterized in that it is methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA).

According to one embodiment of the present invention, the second amine compound is methyldiethanolamine (MDEA), and the methyldiethanolamine is characterized in that it is incorporated in an amount of 27 wt% to 30 wt% with respect to the carbon dioxide capturing absorbent.

According to one embodiment of the present invention, the second amine compound is dimethylethanolamine (DMEA), and the dimethylethanolamine is characterized in that it is incorporated in an amount of 9 wt% to 18 wt% with respect to the absorbent for capturing carbon dioxide.

According to one embodiment of the present invention, the viscosity value at 40°C after stripping of the carbon dioxide capturing absorbent is characterized by being 30 cP or less.

The present invention can obtain the following effects by combining the above-described embodiments with the configuration and usage relationship described below.

The present invention comprises a first amine compound, a second amine compound and an activator, wherein the activator is a carbon dioxide absorbent comprising a piperazine compound, and the circulation capacity and absorption rate of a tertiary amine compound are improved.

The present invention enables smooth activation of a tertiary amine compound even when a relatively small amount of piperazine, which is a solid amine compound, is used, by making the first amine compound 1,4-diazabicyclo(2.2.2)octane (DABCO).

The present invention has the effect of improving the carbon dioxide absorption capacity of the tertiary amine compound and reducing the crystallization possibility of the absorbent by mixing the first amine compound in an amount of 20 to 30 wt%, preferably 25 wt%, with respect to the carbon dioxide capturing absorbent, and mixing the piperazine compound in an amount of 10 to 20 wt%, preferably 15 wt%, with respect to the carbon dioxide capturing absorbent.

In the present invention, the second amine compound is a tertiary amine compound, but is methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA), so that crystallization does not occur within the absorbent, and thus a normal carbon dioxide capture function can be exhibited.

The present invention provides an absorbent for capturing carbon dioxide, wherein the second amine compound is methyldiethanolamine (MDEA), and the methyldiethanolamine is incorporated in an amount of 27 wt% to 30 wt% into the absorbent for capturing carbon dioxide, thereby preventing crystal formation during the stripping process of the absorbent and providing an absorbent for capturing carbon dioxide with low viscosity.

The present invention provides a carbon dioxide capturing absorbent having low viscosity and preventing crystal formation during the stripping process of the absorbent by allowing the second amine compound to be dimethylethanolamine (DMEA), and mixing the dimethylethanolamine in an amount of 9 wt% to 18 wt% with respect to the carbon dioxide capturing absorbent.

The present invention has the effect of providing a carbon dioxide capture absorbent that facilitates gas-liquid exchange within an absorption unit and a regeneration unit by making the viscosity value at 40°C after stripping the carbon dioxide capture absorbent 30 cP or less.

Figure 1 is a drawing illustrating a carbon dioxide capture system according to one embodiment of the present invention.

Figure 2 is a block diagram of an experimental device for evaluating the performance of an absorbent according to one embodiment of the present invention.

Figure 3 is an actual photograph of the experimental device of Figure 2.

Figure 4 is a carbon dioxide absorption and removal curve showing the absorption rate, minimum absorption amount, maximum absorption amount, and circulation capacity of a carbon dioxide absorbent.

Figure 5 is a photograph of an absorbent in which a gel has been formed at room temperature after the regeneration process is completed.

Hereinafter, an absorbent for capturing carbon dioxide according to the present invention will be described in detail with reference to the attached drawings. In addition, a detailed description of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted. It should be noted that the same components in the drawings are represented by the same reference numerals wherever possible. In addition, a detailed description of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted. Unless otherwise defined, all terms in this specification have the same general meaning as those terms understood by a person skilled in the art to which the present invention pertains, and if there is a conflict with the meaning of a term used in this specification, the definitions used in this specification shall apply. Terms such as "first ~", "second ~" may be used to indicate the same or substantially same configuration in a different order, and may be interpreted as a configuration that is substantially the same as a configuration that is not indicated as "first", "second", etc.

The carbon dioxide capturing absorbent according to the present invention is characterized in that the absorbent, which is an aqueous solution containing a liquid amine compound and a solid amine compound, is brought into contact with a gas flow such as exhaust gas to absorb carbon dioxide in the gas flow, and after sending the rich absorbent containing carbon dioxide from an absorption unit (91) to a regeneration unit, the carbon dioxide is removed through a process such as stripping, thereby regenerating it into a lean absorbent, and since the viscosity is low, gas-liquid exchange is easy in the absorption unit and the regeneration unit, and since the absorbent is supplied to the absorption unit in a low temperature environment, no crystallization phenomenon occurs in the absorbent, so that a normal carbon dioxide capturing function can be exhibited. In addition, since the removal of carbon dioxide is easy, the cyclic capacity is large, and thus the absorbent can be regenerated using a small amount of regeneration energy.

The 'absorption amount (mol/l)' referred to in this application is a term indicating the capacity to absorb carbon dioxide, and is expressed in moles, for example, the amount of carbon dioxide absorbed by 1L of absorbent. In addition, the 'absorption amount' in the state where the absorbent absorbs the maximum amount of carbon dioxide, i.e., the 'rich state', is expressed as the 'maximum absorption amount', while the 'absorption amount' in the state where it absorbs the minimum amount, i.e., the 'lean state', is called the 'minimum absorption amount', and the value obtained by subtracting the 'minimum absorption amount' from the 'maximum absorption amount' is called the 'circulation capacity'. In other words, the 'maximum absorption amount' indicates the amount of carbon dioxide absorbed by the absorbent up to the maximum after the completion of the absorption process and before the start of the regeneration process, so it means the value in the state where carbon dioxide can no longer be absorbed, and the 'minimum absorption amount' indicates the amount of absorbent that is not removed after the completion of regeneration and remains in the absorbent. Therefore, an absorbent from which carbon dioxide removal is complete has the ability to absorb carbon dioxide starting from the 'minimum absorption amount' to the 'maximum absorption amount', and the difference between them becomes the 'circulation capacity'. And, 'absorption rate (mol/l·s)' is the rate at which the absorbent absorbs carbon dioxide, and is expressed as the amount absorbed per hour. And, in this invention, 'absorption rate' and 'absorption amount' are expressed as 'absorption capacity'. Therefore, an absorbent with excellent 'absorption capacity' means that both the 'absorption rate' and 'absorption amount' are excellent, and conversely, an absorbent with poor 'absorption capacity' means that at least one of the 'absorption rate' and 'absorption amount' is poor.

The carbon dioxide capturing absorbent according to the present invention can be used in a carbon dioxide capturing system having an absorption unit (91) and a regeneration unit (92), preferably in a carbon dioxide capturing system in which a rich absorbent, which absorbs carbon dioxide through contact between the absorbent and carbon dioxide in the absorption unit, is transported to the regeneration unit to separate it from the carbon dioxide and regenerate it, and then the regenerated lean absorbent is recycled back to the absorption unit to be used for carbon dioxide absorption. The preferred temperature when absorbing carbon dioxide in the absorption unit (91) is in the range of about 0°C to about 80°C, particularly in the range of about 20°C to about 60°C, and the preferred pressure is in the range of 1 atm to 30 atm, particularly in the range of normal pressure to 20 atm. It will be understood by those skilled in the art that the lower the temperature and the higher the pressure when absorbing carbon dioxide, the more the amount of carbon dioxide absorbed increases.

In the carbon dioxide absorption process that occurs within the above absorption section, the amount of carbon dioxide absorbed can increase depending on the amount of absorbent. On the other hand, the initial speed at which carbon dioxide is absorbed, i.e. the absorption rate, varies depending on the type and composition of the absorbent.

The absorbent that has absorbed carbon dioxide is regenerated by decomposing carbamate in the regeneration unit, thereby desorbing carbon dioxide (stripping, degassing, or separating) from the absorbent. In one embodiment, the regeneration unit may use a distillation tower, which may efficiently perform the regeneration of the carbon dioxide absorbent. More specifically, the distillation tower may use a distillation tower having a packing material inside, and preferably, packing may be provided inside the distillation tower to maximize the contact area between the gas and the liquid.

In the carbon dioxide removal process that occurs within the above regeneration unit, the amount of carbon dioxide removed from the absorbent may vary depending on the end of the absorbent and the composition ratio, and as described above, an absorbent in which carbon dioxide is removed smoothly during the regeneration process exhibits a large cyclic capacity. The preferred temperature for removing carbon dioxide within the regeneration unit (92) is in the range of about 6°C to about 120°C, particularly in the range of about 80°C to about 110°C, and the preferred pressure is in the range of 1 to 30 atm, particularly in the range of normal pressure to 10 atm.

In general, when carbon dioxide is absorbed in an aqueous absorbent solution containing alkanolamine, the reaction equation is as follows.

Reaction formula 1

CO ₂ (g) ↔ CO ₂ (aq) (1)

CO ₂ (aq) + 2H ₂ O ↔ HCO ₃ ^- + H ₃ O ⁺ (2)

HCO ₃ ^- + H ₂ O ↔ CO ₃ ^2- + H ₃ O (3)

Amine + H ₂ O ↔ Amine H ⁺ + OH ^- (4)

Amine H ⁺ + H ₂ O ↔ Amine + H ₃ O ⁺ (5)

Amine + CO ₂ (aq) + H ₂ O ↔ Amine COO ^- + H ₃ O ⁺ (6)

Monoethanolamine (MEA) has a fast reaction rate, but is highly corrosive to equipment and requires a lot of heat to regenerate.

Methyldiethanolamine (MDEA) has a relatively low heat of reaction compared to MEA, which can reduce some of the heat of regeneration. However, methyldiethanolamine (MDEA) is a tertiary alkanolamine in which all of the hydrogens in _NH3 are replaced by hydrocarbon groups, and has the disadvantage of a low initial absorption rate when carbon dioxide is absorbed in the absorption section.

Primary and secondary amines, such as monoethanolamine (MEA) and diethanolamine (DEA), are known to undergo two reactions in aqueous solutions: a carbon dioxide reaction by water and a carbon dioxide reaction by the amine's carbamate, and stoichiometrically, 0.5 mol of carbon dioxide can be absorbed per mol of amine. However, tertiary amines, such as triethanolamine (TEA) and methyldiethanolamine (MDEA), only undergo absorption reactions from (1) to (5) in the above reaction scheme 1, and absorption by carbamate does not occur. On the other hand, tertiary amines, such as methyldiethanolamine (MDEA), can easily remove carbon dioxide by heat during the regeneration of the absorbent.

First, the activator is a compound that promotes the reaction between an amine compound and carbon dioxide, and the carbon dioxide absorption capacity, such as the maximum carbon dioxide absorption amount and absorption speed, can be improved through an absorbent that mixes an amine compound and an activator.

The above activator may include at least one selected from the group consisting of piperazine compounds, such as piperazine, morpholine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,3-dimethylpiperazine, 2,4-dimethylpiperazine, 2-ethanolpiperazine, 2,5-diethanolpiperazine, and 2-aminoethylpiperazine. In a preferred embodiment, the activator may be piperazine.

Piperazine has the advantage of high reactivity toward carbon dioxide, high carbon dioxide absorption capacity, and low volatility, but it must go through a process of dissolving in an absorbent aqueous solution in a solid state at room temperature. When dissolving piperazine in an absorbent, it can be first dissolved in methyldiethanolamine (MDEA), a liquid amine compound, and then the absorbent can be formed.

However, if piperazine is excessively mixed in the absorbent, the absorbent may crystallize at room temperature or low temperature and change into a gel form. If the absorbent crystallizes into a gel form, normal absorption and removal of carbon dioxide are impossible. Therefore, in order to reduce the amount of piperazine in the absorbent and improve the carbon dioxide absorption capacity, a first amine compound may be prepared together with piperazine at a reduced weight ratio.

According to one embodiment of the present invention, the carbon dioxide capture absorbent may have a piperazine concentration of 10 wt% or more and 20 wt% or less with respect to the absorbent. If the concentration of piperazine with respect to the absorbent is too high, piperazine, which is a solid amine compound, may not dissolve, or even if dissolved, may exist in a gel state with excessively high viscosity. In this case, gas-liquid exchange between the absorbent and the exhaust gas stream is insufficient, making normal absorption of carbon dioxide impossible. In one embodiment, the concentration of piperazine with respect to the absorbent may preferably be 15 wt%.

The first amine compound can enhance the carbon dioxide absorption of other amine compounds together with piperazine, and the first amine compound can be a compound with a tertiary amine, such as 1,4-diazabicyclo(2.2.2)octane.

1,4-Diazabicyclo(2.2.2)octane, also known as Dabco or TEDA, is an amine compound that exists in a solid state as a white crystalline powder at room temperature. 1,4-Diazabicyclo(2.2.2)octane can absorb carbon dioxide by reacting with carbon oxide to form carbamates, solid compounds that can be easily removed from gas streams.

As a first amine compound, 1,4-diazabicyclo(2.2.2)octane may have a concentration of 10 to 20 wt% with respect to the absorbent. If the concentration of 1,4-diazabicyclo(2.2.2)octane with respect to the absorbent is too high, 1,4-diazabicyclo(2.2.2)octane, which is a solid amine compound, may not dissolve, or even if it dissolves, it may exist in a gel state with excessively high viscosity. In this case, gas-liquid exchange between the absorbent and the exhaust gas stream is insufficient, making normal absorption of carbon dioxide impossible. In one embodiment, the concentration of 1,4-diazabicyclo(2.2.2)octane with respect to the absorbent may preferably be 25 wt%.

The above Dabco is preferably used together with piperazine. When forming an absorbent by mixing with another amine compound, for example, a second amine compound described below, if only Dabco is used with the other amine compound without piperazine, there is a problem that the carbon dioxide absorption capacity is reduced because Dabco does not normally activate the amine compound.

Next, a secondary amine compound, piperazine as an activator, can be used together with 1,4-diazabicyclo(2.2.2)octane as a primary amine compound, incorporated into the absorbent. The secondary amine compound may be a tertiary amine compound. For the same amount of absorbent, the use of a tertiary amine compound together with piperazine as an activator and 1,4-diazabicyclo(2.2.2)octane, a tertiary amine compound, as a primary amine compound is advantageous in terms of maximum carbon dioxide absorption compared to the use of a primary amine compound such as methylethanolamine (MEA) or a secondary amine compound such as 2-amino-2-methylpropanol (AMP) or (2-aminoethyl)ethanol.

However, as described above, when a secondary amine compound is used as a tertiary amine compound, crystallization of the absorbent is problematic. After the absorbent absorbs carbon dioxide, the temperature of the lean absorbent is raised to 80 degrees in the regeneration unit (92) to remove the carbon dioxide, but in the environment of the regeneration unit having a temperature of 80 degrees, the absorbent crystallizes and the carbon dioxide is not removed in some cases. In addition, even if the removal is completed in the regeneration unit, the absorbent crystallizes in the process of cooling the absorbent to room temperature, 40 degrees, after the removal, and the absorbent cannot be used in the next cycle.

According to one embodiment of the present invention, an absorbent for capturing carbon dioxide is prepared by mixing methyldiethanolamine (MDEA), 1,4-diazabicyclo(2.2.2)octane, and piperazine among tertiary amine compounds at an appropriate concentration, thereby preventing crystallization of the absorbent during the process of stripping the absorbent or after stripping the absorbent, and lowering the viscosity of the absorbent to enable active gas-liquid exchange to be performed within an absorption section and a regeneration section.

In one embodiment, the molar concentration of methyldiethanolamine may be 2.3 to 2.5 molar concentration for the carbon dioxide absorbent. For an absorbent containing 15 wt% of piperazine and 25 wt% of 1,4-diazabicyclo(2.2.2)octane, it was observed that when the concentration of methyldiethanolamine was 27 wt% to 30 wt%, it exhibited advantageous effects on the carbon dioxide absorption rate, circulation capacity, viscosity, and maximum carbon dioxide absorption amount. When the molar concentration of methyldiethanolamine is too high, the maximum carbon dioxide absorption amount decreases, and when the molar concentration of methyldiethanolamine is too low, there is a problem that the circulation capacity decreases.

According to another embodiment of the present invention, an absorbent for capturing carbon dioxide is prepared by mixing dimethylethanolamine (DMEA), 1,4-diazabicyclo(2.2.2)octane, and piperazine among tertiary amine compounds at an appropriate concentration, thereby preventing crystallization of the absorbent during or after the absorbent stripping process and lowering the viscosity of the absorbent to enable active gas-liquid exchange within the absorption unit and the regeneration unit. However, in the case of dimethylethanolamine (DMEA), the absorbent crystallizes and changes into a gel form after carbon dioxide stripping at a predetermined concentration, so the change in the concentration of dimethylethanolamine (DMEA) in the absorbent must be monitored.

In one embodiment, the viscosity value at 40° C. after stripping of the absorbent for capturing carbon dioxide may be 30 cP or less. cP (cPoisson) may be used as the viscosity of the absorbent, and when the viscosity is high, the gas-liquid exchange between the absorbent and the gas stream or the gas stream rising by heating within the absorption unit or the regeneration unit is reduced. In one embodiment of the present invention, the viscosity of the absorbent may be measured at a temperature of 40° C. and atmospheric pressure after stripping of the absorbent.

(Example 1)

Under the experimental conditions described below, 200 g of absorbent was prepared by mixing 39 wt% of methyldiethanolamine (MDEA, Acros), 25 wt% of 1,4-diazabicyclo(2.2.2)octane (Dabco), 15 wt% of piperazine (Pz, BASF), and 21 wt% of water.

(Example 2)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 33 wt% of MDEA and 27 wt% of water without changing the concentration of other compounds.

(Example 3)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 30 wt% of MDEA and 30 wt% of water without changing the concentration of other compounds.

(Example 4)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 27 wt% of MDEA and 33 wt% of water without changing the concentration of other compounds.

(Example 5)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 24 wt% of MDEA and 36 wt% of water without changing the concentration of other compounds.

(Example 6)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 21 wt% of MDEA and 39 wt% of water without changing the concentration of other compounds.

(Example 7)

Under the experimental conditions of Example 1, 200 g of an absorbent was prepared by mixing 36 wt% of dimethylethanolamine (DMEA), 25 wt% of 1,4-diazabicyclo(2.2.2)octane (Dabco), 15 wt% of piperazine (Pz, BASF), and 24 wt% of water.

(Example 8)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 27 wt% of DMEA, 25 wt% of Dabco, 15 wt% of piperazine, and 33 wt% of water.

(Example 9)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 18 wt% DMEA, 25 wt% Dabco, 15 wt% piperazine, and 42 wt% water.

(Example 10)

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 9 wt% DMEA, 25 wt% Dabco, 15 wt% piperazine, and 51 wt% water.

Comparative Example 1 is an absorbent containing commonly used MEA, and Comparative Examples 2 to 19 are absorbents that do not contain MEA and use other amine compounds as secondary amine compounds.

<Comparative Example 1>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 30 wt% of MEA and 70 wt% of water.

<Comparative Example 2>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 25 wt% of Dabco, 15 wt% of piperazine, and 60 wt% of water.

<Comparative Example 3>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 39 wt% of MDEA, 25 wt% of Dabco, and 36 wt% of water.

<Comparative Example 4>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 33 wt% of MDEA, 25 wt% of Dabco, and 42 wt% of water.

<Comparative Example 5>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 27 wt% of MDEA, 25 wt% of Dabco, and 48 wt% of water.

<Comparative Example 6>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 21 wt% of MDEA, 25 wt% of Dabco, and 54 wt% of water.

<Comparative Example 7>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 39 wt% of MDEA, 15 wt% of piperazine, and 46 wt% of water.

<Comparative Example 8>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 33 wt% of MDEA, 15 wt% of piperazine, and 52 wt% of water.

<Comparative Example 9>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 27 wt% of MDEA, 15 wt% of piperazine, and 58 wt% of water.

<Comparative Example 10>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 21 wt% of MDEA, 15 wt% of piperazine, and 64 wt% of water.

<Comparative Example 11>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 44 wt% of triethylenetetramine (TETA), 25 wt% of Dabco, 15 wt% of piperazine, and 16 wt% of water.

<Comparative Example 12>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 29 wt% of TETA, 25 wt% of Dabco, 15 wt% of piperazine, and 31 wt% of water.

<Comparative Example 13>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 15 wt% of TETA, 25 wt% of Dabco, 15 wt% of piperazine, and 45 wt% of water.

<Comparative Example 14>

Under the experimental conditions of Example 1, 200 g of an absorbent was prepared by mixing 39 wt% of 3,3-diaminodipropylamine (DDPA), 25 wt% of Dabco, 15 wt% of piperazine, and 21 wt% of water.

<Comparative Example 15>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 26 wt% of DDPA, 25 wt% of Dabco, 15 wt% of piperazine, and 34 wt% of water.

<Comparative Example 16>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 13 wt% of DDPA, 25 wt% of Dabco, 15 wt% of piperazine, and 47 wt% of water.

<Comparative Example 17>

Under the experimental conditions of Example 1, 200 g of an absorbent was prepared by mixing 31 wt% of diethylenetriamine (DETA), 25 wt% of Dabco, 15 wt% of piperazine, and 29 wt% of water.

<Comparative Example 18>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 21 wt% of DETA, 25 wt% of Dabco, 15 wt% of piperazine, and 39 wt% of water.

<Comparative Example 19>

Under the experimental conditions of Example 1, 200 g of absorbent was prepared by mixing 10 wt% of DETA, 25 wt% of Dabco, 15 wt% of piperazine, and 50 wt% of water.

experiment

(1) Experimental equipment

Fig. 2 is a block diagram of an experimental device for evaluating the performance of an absorbent, and Fig. 3 is a photograph of the actual experimental device. According to Figs. 2 and 3, the experimental device is composed of a pipe (21) through which a gas composed of carbon dioxide (CO2) and nitrogen (N2) flows in, a mixer (22) for uniformly mixing nitrogen and carbon dioxide, an absorption unit (91) for absorbing carbon dioxide, a regeneration unit (92) for removing carbon dioxide, silica gel (27) for removing moisture contained in the gas, and a carbon dioxide analyzer (28, Fuji NDIR Gas Analyzer, ZPA) for measuring the concentration of carbon dioxide in the gas. The above absorption unit (91) and regeneration unit (93) are composed of a reaction tank (23) in which an absorbent is contained and gas is introduced to perform an absorption reaction to absorb carbon dioxide and a regeneration process to remove carbon dioxide from the absorbent, a cooler (26) connected to the reaction tank to cool water vapor and return it to the reaction tank and send the gas to a carbon dioxide analyzer, a water bath (24) in which the reaction tank (23) is located and contains water at 40°C, and a water bath (23) in which the reaction tank (23) is located and contains water at 80°C.

In order to obtain rapid experimental results, the applicant prepared a total of four sets, including a 40°C water container (24) and an 80°C water container (25), as shown in Fig. 3, and installed four carbon dioxide analyzers (28) dedicated to measuring the carbon dioxide concentration of gas flowing from each set. This made it possible to conduct experiments on four types of absorbents simultaneously.

(2) Reliability evaluation of experimental equipment

The absorbent of the reactor (23) is initially in a 'lean state', so the amount of carbon dioxide absorbed increases rapidly as shown in Fig. 4, but as time passes, the slope becomes gentle and the maximum amount of absorption is reached, and the absorption process is completed. In the analyzer, the concentration of carbon dioxide that has escaped the absorbent without being absorbed by the absorbent is measured, so it initially shows a low value but increases over time and converges to a certain value (since the absorbent is initially in a 'lean state', the absorption rate is fast, so the concentration of carbon dioxide measured by the carbon dioxide analyzer is low at the beginning, but as time passes, the absorbent converges to a saturated state, so the concentration of carbon dioxide measured by the analyzer increases). The measurement value of the analyzer is reverse-calculated using a given formula to calculate the absorption amount of the absorbent over time.

A gas of 2000 ml/min consisting of 1700 ml/min of nitrogen and 300 ml/min of carbon dioxide is supplied to a reactor (23) located in a water container (24) of an absorption section containing water at 40°C. The reactor (23) contains 500 ml of a reference solution, a monoethanolamine aqueous solution (30 wt% of monoethanolamine, 70 wt% of water). The gas is supplied to an absorbent in the reactor, and carbon dioxide in the gas is absorbed by the absorbent, and the remaining gas (nitrogen and unabsorbed carbon dioxide) passing through the absorbent is continuously introduced into a carbon dioxide analyzer (28), and the concentration of carbon dioxide remaining in the gas is measured by the analyzer at 30-second intervals and calculated inversely according to a given formula. After a certain period of time, it was confirmed that the maximum absorption amount reached 0.511 mol/l. It was confirmed that this is within the range of 0.5 to 0.55 mol/l, which is the reliability evaluation criterion of this equipment.

(2) Absorption measurement

The experiments below were conducted with 200 g of the absorbents of the previous examples and comparative examples placed in a reactor.

1) Measurement of absorption process

Nitrogen gas is supplied and used to remove carbon dioxide remaining in the reactor and pipe. Next, 2000 ml/min of gas consisting of 1900 ml/min of nitrogen and 100 ml/min (5 v/v%) of carbon dioxide is supplied to the reactor (23) located in the water container (24) of the absorption section containing water at 40°C. The temperature of the water container (24) containing the reactor (23) is maintained at 40°C to implement the temperature of the normal absorption section. The gas is continuously supplied to the reactor (23), and as the gas passes through the absorbent, some of the carbon dioxide is absorbed and the remaining gas (unabsorbed carbon dioxide and nitrogen gas) exits the absorbent and flows into a carbon dioxide analyzer (28). The concentration of carbon dioxide is measured in the analyzer at 30-second intervals. As seen above, since the absorbent is initially in a 'lean state', the concentration of carbon dioxide measured in the carbon dioxide analyzer (28) is low for the first certain period of time. However, as time passes, the carbon dioxide absorption capacity of the absorbent decreases, so the concentration of carbon dioxide measured in the analyzer gradually increases. Then, the absorption process is terminated when the absorbent reaches the saturation state where it can no longer absorb the absorbent. That is, the analyzer measures the carbon dioxide concentration at 30-second intervals, and when the absorbent reaches the saturation state, 100 ml/min of carbon dioxide flows directly into the carbon dioxide analyzer, so when the carbon dioxide concentration in the analyzer reaches 100 ml/min, the gas injection is stopped and the absorption process is terminated. Then, the values measured for each time period are reverse-calculated, and the total concentration of carbon dioxide absorbed up to that measurement time is displayed for each time period (the 'absorption process' section illustrated in Figure 4).

(2) Measurement of the regeneration process

After the absorption process is completed, the reactor (23) containing the absorbent in which carbon dioxide has been absorbed is transferred to a water container (25) containing water at 80°C, and while supplying only nitrogen gas at 1900 ml/min to the absorbent, carbon dioxide is removed, and the concentration of carbon dioxide in the gas flowing into the analyzer is measured. At the beginning of the removal process, the absorbent in the reactor (23) is in a 'rich state', that is, the state in which the carbon dioxide concentration is the highest, so that the removal progresses smoothly and the concentration of carbon dioxide measured in the analyzer is high, but as time passes, the concentration of carbon dioxide decreases. The applicant terminates the regeneration process when the concentration of carbon dioxide in the analyzer becomes 5 ml/min. Then, the carbon dioxide concentration values measured for each time period are reverse-calculated to show the concentration of carbon dioxide that was not removed at that measurement time and remained in a state absorbed in the absorbent for each time period ('regeneration process' section illustrated in FIG. 4).

(3) Absorption rate measurement

As shown in Figure 4, the slope of the graph at the point where the carbon dioxide concentration of the absorbent is at its minimum absorption amount, which is the point at which no further stripping occurs, i.e., the regeneration process is completed, is taken as the absorption rate.

(4) Whether gel phenomenon occurs

After the regeneration process is complete, transfer the absorbent to a designated container and store it at room temperature, and visually observe whether crystallization occurs.

Decision Formation Evaluation

In order to evaluate the crystallization phenomenon according to the type and concentration of the secondary amine compound in the carbon dioxide capture absorbent, the formation of crystals was compared for the absorbents formed by Examples 1 to 10 when stripped at 80°C in a regeneration tower and when cooled to 40°C at 1 atm after stripping. In addition, the carbon dioxide absorption rate and circulation capacity, which are the basic carbon dioxide absorption performances of the absorbents, were evaluated.

CO2 absorption rate*
10^5 (mol/L·s) Circulating capacity (mol/L) Whether or not a decision is formed during or after removal Example 1 9.754 1.294 Crystallization after removal Example 2 7.082 1.250 No crystals are formed at 55 degrees,
Crystallization when cooled to 18 degrees Example 3 7.848 1.223 - Example 4 8.431 1.268 - Example 5 5.928 1.193 - Example 6 2.205 0.893 - Example 7 11.493 1.373 Crystallization after removal Example 8 10.312 1.428 Crystallization after removal Example 9 9.158 1.207 - Example 10 8.457 1.213 -

In addition, for the absorbents formed by Comparative Examples 1 to 19, the formation of crystals was compared when stripped at 80°C in a regeneration tower and when cooled to 40°C at 1 atm after stripping. In addition, the basic carbon dioxide absorption performance of the absorbent, namely the carbon dioxide absorption rate and circulation capacity, were evaluated. In Table 2 below, the absence of the absorption rate and circulation capacity indicates a case in which the absorbent is crystallized and carbon dioxide absorption and stripping are impossible.

CO2 absorption rate*
10^5 (mol/L·s) Circulating capacity (mol/L) Whether or not a decision is formed during or after removal Comparative Example 1 8.574 0.740 Comparative Example 2 8.833 1.031 Comparative Example 3 0.869 0.087 Comparative Example 4 0.791 0.037 Comparative Example 5 1.426 0.044 Comparative Example 6 1.245 0.226 Comparative Example 7 4.643 0.858 Comparative Example 8 9.300 1.144 Comparative Example 9 9.664 1.167 Comparative Example 10 9.261 0.924 Comparative Example 11 - - Crystallized and cannot be removed Comparative Example 12 - - Crystallized and cannot be removed Comparative Example 13 4.527 1.302 Crystallization after removal Comparative Example 14 - - Crystallized and cannot be removed Comparative Example 15 - - Crystallized and cannot be removed Comparative Example 16 6.356 1.137 Comparative Example 17 - - Crystallized and cannot be removed Comparative Example 18 - - Crystallized and cannot be removed Comparative Example 19 4.021 1.135

Maximum carbon dioxide absorption assessment

The maximum carbon dioxide absorption amount was evaluated according to the type and concentration of the secondary amine compound in the carbon dioxide capture absorbent of Examples 1 to 10 and Comparative Examples 2 to 19. In Table 3 below, the case where the maximum carbon dioxide absorption amount is not indicated indicates a case where the absorbent is crystallized and carbon dioxide absorption and removal are impossible.

division Carbon dioxide
Maximum absorption
(mol/L) division Carbon dioxide
Maximum absorption
(mol/L) division Carbon dioxide
Maximum absorption
(mol/L) Example 1 1.831 Comparative Example 2 2.175 Comparative Example 11 - Example 2 1.891 Comparative Example 3 0.312 Comparative Example 12 - Example 3 2.132 Comparative Example 4 0.113 Comparative Example 13 4.239 Example 4 2.335 Comparative Example 5 0.106 Comparative Example 14 - Example 5 2.558 Comparative Example 6 0.352 Comparative Example 15 - Example 6 3.432 Comparative Example 7 2.490 Comparative Example 16 3.501 Example 7 2.215 Comparative Example 8 2.004 Comparative Example 17 - Example 8 2.206 Comparative Example 9 1.787 Comparative Example 18 - Example 9 2.483 Comparative Example 10 1.990 Comparative Example 19 4.222 Example 10 2.487

Referring to Examples 1 to 6 in which the second amine compound is MDEA, the carbon dioxide absorption rate and circulation capacity were excellent when the MDEA presented in Examples 3 and 4 was 2.3 to 2.5 mol/L for the carbon dioxide absorbent in which piperazine as an activator was incorporated at 15 wt% and Dabco as a first amine compound was incorporated at 25 wt%. Referring to Examples 1 and 2, it was confirmed that when MDEA was incorporated in excessive amounts, the absorption rate was high, but the absorbent crystallized and changed into a gel form. On the other hand, referring to Examples 5 and 6, when MDEA was incorporated in small amounts, the maximum carbon dioxide absorption amount increased, but there was a problem in that the carbon dioxide absorption rate and circulation capacity decreased. Referring to Examples 7 to 10 in which the second amine compound was DMEA, the carbon dioxide absorption rate and circulation capacity were excellent when DMEA was 24 wt% or less (which can be understood as a concentration of 2 mol/L or less). If DMEA is mixed in excessively, a crystallization phenomenon occurs after removing the absorbent, so there is a problem that attention should be paid to the change in the concentration of DMEA in the absorbent when using a secondary amine compound as DMEA. As the concentration of DMEA decreases, the circulation capacity decreases, so if a small amount of DMEA is mixed, there is a problem that it is difficult to achieve a circulation capacity of 1.2 mol/L or more.

In the case of Comparative Example 1, which is an absorbent prepared by mixing 30 wt% of MEA in water, the absorption rate is similar to that of the carbon dioxide absorbent of the present invention, but the circulation capacity is only 0.740 mol/L, which causes a problem in that the carbon dioxide absorption capacity is low when the absorbent is circulated within the carbon dioxide capture system.

In the case of Comparative Example 2, which mixed only 25 wt% of Dabco and 15 wt% of piperazine without using a secondary amine compound, the circulation capacity was lower than that of the carbon dioxide absorbent of the present invention.

In Comparative Examples 3 to 6 that did not use piperazine as an activator, it was confirmed that the carbon dioxide absorption capacity was significantly low. In Comparative Examples 7 to 10 that did not use Dabco as a first amine compound, when MDEA was mixed in at 36 wt% or less (which can be understood as 3 mol/L or less), the carbon dioxide absorption rate was excellent, but the maximum carbon dioxide absorption amount and circulation capacity were observed to be disadvantageous compared to the carbon dioxide absorbent of the present invention. Considering that piperazine as an activator activates the carbon dioxide absorption of MDEA, it may be thought that this can be solved by increasing the amount of piperazine as an activator, but piperazine exists as a solid compound, and when it is mixed in excessive amounts such as 20 wt% or 25 wt%, there was a problem that the absorbent crystallized during the cooling process after stripping or in a low-temperature environment.

When other tertiary amine compounds (TETA, DDPA, DETA) were used as secondary amine compounds, most of the absorbents crystallized, making it impossible to absorb and remove carbon dioxide. When a small amount was mixed, the maximum carbon dioxide absorption capacity was excellent, but there was a problem that the absorption rate was too low.

Therefore, the carbon dioxide capture absorbent according to the present invention adjusts the concentration of methyldiethanolamine (MDEA) relative to piperazine and Dabco so that the viscosity becomes 30 cP or less in an environment of 1 atm and 40°C after carbon dioxide stripping, thereby facilitating gas-liquid exchange between the absorbent and an exhaust gas stream containing carbon dioxide within a structure that assists gas-liquid exchange, such as packing in an absorption tower or a regeneration tower. As can be seen in Examples 3 and 4, the disclosed carbon dioxide capture absorbent has a maximum carbon dioxide absorption amount of 2 mol/L or more, excellent circulation capacity and carbon dioxide absorption rate, and is suitable for use as an absorbent in a carbon dioxide capture system in which no crystallization phenomenon occurs during stripping or in the process of cooling the absorbent after stripping.

The above detailed description is illustrative of the present invention. In addition, the above contents illustrate and explain the preferred embodiment of the present invention, and the present invention can be used in various other combinations, changes, and environments. That is, changes or modifications are possible within the scope of the inventive concept disclosed in this specification, the scope equivalent to the written disclosure, and/or the scope of technology or knowledge in the art. The above-described embodiments describe the best state for implementing the technical idea of the present invention, and various changes required for specific application fields and uses of the present invention are also possible. Therefore, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. In addition, the appended claims should be interpreted to include other embodiments.

Claims (8)

Contains a first amine compound, a second amine compound and an activator, An absorbent for capturing carbon dioxide, characterized in that the above activator is a piperazine-based compound. An absorbent for capturing carbon dioxide, characterized in that in claim 1, the first amine compound is 1,4-diazabicyclo(2.2.2)octane (DABCO). In the second paragraph, the first amine compound is incorporated in an amount of 20 to 30 wt%, preferably 25 wt%, of the absorbent for capturing carbon dioxide. An absorbent for capturing carbon dioxide, characterized in that the piperazine compound is incorporated in an amount of 10 to 20 wt%, preferably 15 wt%, of the absorbent for capturing carbon dioxide. An absorbent for capturing carbon dioxide, characterized in that in the third paragraph, the second amine compound is a tertiary amine compound. An absorbent for capturing carbon dioxide, characterized in that in claim 4, the tertiary amine compound is methyldiethanolamine (MDEA) or dimethylethanolamine (DMEA). An absorbent for capturing carbon dioxide, characterized in that in claim 5, the second amine compound is methyldiethanolamine (MDEA), and the methyldiethanolamine is mixed in an amount of 27 wt% to 30 wt%. An absorbent for capturing carbon dioxide, characterized in that in claim 5, the second amine compound is dimethylethanolamine (DMEA), and the dimethylethanolamine is mixed in an amount of 9 wt% to 18 wt%. In claim 5, a carbon dioxide capture absorbent, characterized in that the viscosity value at 40°C after stripping the carbon dioxide capture absorbent is 30 cP or less.

Images