JP5659128B2 - Acid gas absorbent, acid gas removal method, and acid gas removal apparatus - Google Patents

Description

  Embodiments described herein relate generally to an acidic gas absorbent, and an acidic gas removing device and an acidic gas removing method using the same.

In recent years, the greenhouse effect due to an increase in carbon dioxide (CO ₂ ) concentration has been pointed out as a cause of global warming, and international measures to protect the environment on a global scale are urgently needed. The source of CO ₂ is largely due to industrial activities, and the momentum for controlling emissions is increasing.

Techniques for suppressing the increase in the concentration of acid gases, including CO _2, the development of energy-saving products, separation and recovery techniques acid gas to be discharged, a technique for utilizing and capture and storage as a resource acid gas, acid gases There is a shift to alternative energy such as natural energy and nuclear energy that does not emit energy.

  Acid gas separation techniques that have been studied to date include absorption methods, adsorption methods, membrane separation methods, and cryogenic methods. In particular, the absorption method is suitable for processing a large amount of gas, and its application to factories and power plants is being studied.

Therefore, for facilities such as thermal power plants that use fossil fuel, the exhaust gas generated when burning fossil fuel (coal, petroleum, natural gas, etc.) is brought into contact with the chemical absorbent, and CO ₂ in the combustion exhaust gas A method for removing and recovering CO ₂ and a method for storing the recovered CO ₂ are performed all over the world. Further, it has been proposed to remove an acidic gas such as hydrogen sulfide (H ₂ S) in addition to CO ₂ using a chemical absorbent.

  In general, alkanolamines typified by monoethanolamine (MEA) have been developed since the 1930s as chemical absorbents used in the absorption method and are still used (see, for example, Patent Document 1). This method is economical and the removal apparatus can be easily increased in size.

  Examples of alkanolamines widely used in the past include monoethanolamine, 2-amino-2-methylpropanolamine, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, Examples include triethanolamine and dimethylamino-1-methylethanol.

  In particular, primary monoethanolamine has been widely used because of its high reaction rate. However, this compound has a problem that it is corrosive, easily deteriorates, and requires high energy for regeneration. On the other hand, tertiary methyldiethanolamine has low corrosivity and low energy required for regeneration, but has a disadvantage of low absorption rate. Therefore, development of a new adsorbent that improves these points is required.

  In recent years, researches on alkanolamines having structurally steric hindrance, among amine compounds, have been actively attempted as acid gas absorbents (see, for example, Patent Document 2). The alkanolamine having steric hindrance has the advantages that the selectivity of the acid gas is very high and the energy required for regeneration is small.

  The reaction rate of an amine compound having steric hindrance depends on the degree of reaction hindrance determined by its steric structure.

  On the other hand, as an amine compound having a structure different from that of alkanolamines, a method using a cyclic amine as an absorbent is also known (see Patent Document 1 and Patent Document 4).

JP 2008-307519 A Japanese Patent No. 2871334 JP 2009-6275 A U.S. Pat. No. 4,120,052

  However, even in these techniques, the acid gas absorption capacity such as the acid gas absorption amount and the acid gas absorption rate is still insufficient, and further improvement of the gas absorption capacity is required.

  The problem to be solved by the present invention is to provide an acidic gas absorbent having a high recovery amount of acidic gas such as carbon dioxide, and an acidic gas removing device and an acidic gas removing method using the same.

・・・（１）
（上記式（１）中、Ｒ ^１０ 、Ｒ ^１１ は、これらが結合して炭素数３〜５の環式構造を形成する。Ｒ ^１０ 、Ｒ ^１１ は、それぞれ、炭素数１〜５の置換または非置換のアルキル基を表す。Ｒ^１２はヒドロキシアルキル基を表す。） The acidic gas absorbent according to the embodiment is an aqueous solution containing at least one secondary amine compound represented by the following general formula (1).

... (1)
(In the above formula (1), R ¹⁰ and R ¹¹ are combined to form a cyclic structure having 3 to 5 carbon atoms. R ¹⁰ and R ¹¹ are each substituted or substituted with 1 to 5 carbon atoms. Represents an unsubstituted alkyl group, and R ¹² represents a hydroxyalkyl group .

Acid gas removal method embodiment, a gas containing acid gases, by contacting the acid gas absorption agent according to the above-described embodiment is intended to remove acid gases from a gas containing the acid gases.

Acid gas removal apparatus embodiments, an absorption tower for removing acid gas from the gas by contacting the gas and the acid gas absorption agent containing acid gases, from the acid gas absorption agent which has absorbed acid gases It has a regenerator for reproducing the acid gas absorption agent to remove acid gases, and the acid gas absorption agent reproduced by the regenerator an acid gas removal system to recycle in the absorption tower it is obtained by using the acid gas absorption agent according to the above embodiment.

It is the schematic of the acidic gas removal apparatus of embodiment.

Hereinafter, embodiments will be described in detail.
The acidic gas absorbent according to the embodiment includes at least one secondary amine compound represented by the following general formula (1).

・・・（１）
（上記式（１）中、Ｒ^１０、Ｒ^１１は、いずれか一方が炭素数２〜５の置換又は非置換のアルキル基を表し、他方が炭素数１〜５の置換又は非置換のアルキル基を表す。Ｒ^１２はヒドロキシアルキル基を表す。Ｒ^１０、Ｒ^１１はそれぞれ同一あっても異なっていてもよく、これらが結合して環式構造を形成していてもよい。Ｒ^１０、Ｒ^１１が環式構造を形成する場合、Ｒ^１０、Ｒ^１１は炭素数１〜５の置換または非置換のアルキル基を表す。）

... (1)
(In the formula (1), one of R ¹⁰ and R ¹¹ represents a substituted or unsubstituted alkyl group having 2 to 5 carbon atoms, and the other represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. ^{.R 12} is ^{.R 10, R 11} each may be different, even the same, optionally they are bonded to form a cyclic structure ^.R 10 representing a hydroxyalkyl group ^{representing, R 11} When R ¹⁰ forms a cyclic structure, R ¹⁰ and R ¹¹ represent a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.)

Conventionally, it is known that the steric hindrance of an amino compound has a large influence on a product upon absorption of carbon dioxide, and works favorably for the production of bicarbonate ions exhibiting a low heat of reaction.
Based on these findings, the inventors of the present application have studied to obtain a greater steric hindrance effect. As a result, the compound represented by the general formula (1) (for example, 2- (cyclopentylamino) ethanol) has a conventional branched structure. It has been found that a lower reaction heat property can be obtained and the amount of carbon dioxide absorption can be increased than the amino compound possessed.

That is, in the secondary amine compound of the general formula (1), a hydroxyalkyl group (R ¹² ) is bonded to a nitrogen atom, and two alkyl groups (R) are bonded to one carbon atom bonded to the nitrogen atom. ¹⁰ and R ¹¹ ) have a branched structure.

Thus, the secondary amine compound of the above general formula (1) in which the branched alkyl group is directly bonded to the nitrogen atom has a structure with a large steric hindrance. For this reason, it has high reactivity with respect to acidic gas such as carbon dioxide (CO ₂ ), and a high amount of absorbed acidic gas can be obtained.

By dissolving the secondary amine compound represented by the above general formula (1) (hereinafter referred to as secondary amine compound (1)) in a solvent such as water, the acid gas absorption capacity can be improved. A high acid gas absorbent can be obtained.
In the following embodiments, the case where the acidic gas is carbon dioxide will be described as an example. However, the acidic gas absorbent according to the embodiment of the present invention obtains the same effect with respect to other acidic gases such as hydrogen sulfide. Can do.

In said formula (1), R < ¹⁰ >, R < ¹¹ > is group couple | bonded with the carbon atom couple | bonded with the nitrogen atom. One of R ¹⁰ and R ¹¹ represents a substituted or unsubstituted alkyl group having 2 to 5 carbon atoms, and the other represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. R ¹⁰ and R ¹¹ may be the same or different.
As the substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, for example, a branched or linear hydrocarbon group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, or a s-butyl group is used. These hydrocarbon groups may contain heteroatoms such as Si, O, N, and S.
The substituted or unsubstituted alkyl group having 1 to 5 carbon atoms is more preferably a methyl group or an ethyl group.

As the substituted or unsubstituted alkyl group having 2 to 5 carbon atoms, for example, a branched or linear hydrocarbon group such as an ethyl group, a propyl group, an isopropyl group, a butyl group, and an s-butyl group can be used. These hydrocarbon groups may contain heteroatoms such as Si, O, N, and S.
The substituted or unsubstituted alkyl group having 2 to 5 carbon atoms is more preferably an ethyl group.

The secondary amine compound (1) in which at least one of R ¹⁰ and R ¹¹ is an alkyl group having 2 or more carbon atoms has a small reaction heat in the reaction with the acid gas, and is superior to the acid gas. Has reactivity.
In addition, the secondary amine compound (1) in which either one of R ¹⁰ and R ¹¹ is an alkyl group having 2 or more carbon atoms is a secondary amine compound in which both R ¹⁰ and R ¹¹ are methyl groups. Compared with the boiling point, it is difficult to cause volatilization from the absorbent.

R ¹⁰ and R ¹¹ may be linked to form a cyclic structure. When R < ¹⁰ >, R < ¹¹ > forms a cyclic structure, R < ¹⁰ >, R < ¹¹ > represents a C1-C5 substituted or unsubstituted alkyl group.
Examples of such a cyclic structure include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclononyl group.

When R ¹⁰ and R ¹¹ form a cyclic structure, the volatility of the secondary amine compound (1) is suppressed. For this reason, in the process which processes exhaust gas, it can be set as the acidic gas removal agent by which the quantity of the amine component discharge | released in air | atmosphere was reduced. Moreover, the reaction heat at the time of reaction with the acidic gas of the secondary amine compound of the said Formula (1) is reduced because R < ¹⁰ >, R < ¹¹ > forms cyclic structure.
Among the above cyclic structures, a cyclopentyl group and a cyclohexyl group are more preferable from the viewpoint of solubility.

R ¹² is a hydroxyalkyl group. From the viewpoint of improving the reactivity with carbon dioxide, a hydroxyalkyl group having 2 to 4 carbon atoms is preferred. The hydroxyalkyl group for R ¹² is more preferably a 2-hydroxyethyl group.

  Examples of the secondary amine compound (1) in which a branched alkyl group is bonded to a nitrogen atom include the following compounds. That is, as the secondary amine compound (1), 2- (2-butylamino) ethanol, 2- (2-pentylamino) ethanol, 2- (2-hexylamino) ethanol, 2- (3-pentylamino) ) Ethanol, 2- (3-hexylamino) ethanol, 2- (3-heptylamino) ethanol, 2- (4-heptylamino) ethanol, 2- (4-octylamino) ethanol, 2- (5-nonylamino) Ethanol, 3- (2-butylamino) propanol, 3- (2-pentylamino) propanol, 3- (2-hexylamino) propanol, 3- (3-pentylamino) propanol, 3- (3-hexylamino) Propanol, 3- (3-heptylamino) propanol, 3- (4-heptylamino) propanol, 3- ( -Octylamino) propanol, 3- (5-nonylamino) propanol, 4- (2-butylamino) butanol, 4- (2-pentylamino) butanol, 4- (2-hexylamino) butanol, 4- (3- Pentylamino) butanol, 4- (3-hexylamino) butanol, 4- (3-heptylamino) butanol, 4- (4-heptylamino) butanol, 4- (4-octylamino) butanol, 4- (5- Nonylamino) butanol, 2- (cyclopropylamino) ethanol, 2- (cyclobutylamino) ethanol, 2- (cyclopentylamino) ethanol, 2- (cyclohexylamino) ethanol, 2- (cycloheptylamino) ethanol, 2- ( Cyclooctylamino) ethanol, 3- (cyclopropi Amino) propanol, 3- (cyclobutylamino) propanol, 3- (cyclopentylamino) propanol, 3- (cyclohexylamino) propanol, 3- (cycloheptylamino) propanol, 3- (cyclooctylamino) propanol, 4- ( Cyclopropylamino) propanol, 4- (cyclobutylamino) butanol, 4- (cyclopentylamino) butanol, 4- (cyclohexylamino) butanol, 4- (cycloheptylamino) butanol, 4- (cyclooctylamino) butanol and the like. Can be mentioned. As the secondary amine compound (1), one compound selected from the above group or a mixture of two or more compounds can be used.

As the secondary amine compound (1), the secondary amine compounds (secondary amino alcohols) having the above-mentioned high boiling point are preferable. The acidic gas absorbent that has absorbed CO ₂ is regenerated by heating in a high temperature range of about 120 ° C. For this reason, as the secondary amine compound (1), it is preferable to use a secondary amine compound having a high boiling point that is not easily released from the regeneration tower when heated. For this reason, it is preferable to use an alkyl group having a large number of carbon atoms as the secondary amine compound (1). In particular, a secondary amine compound having a cyclic structure is preferable.

  As the secondary amine compound (1), one compound selected from the above group can be used, or a mixture of two or more compounds selected from the above group can be used. Is also possible.

The content of the secondary amine compound (1) contained in the acidic gas adsorbent is preferably 10 to 55% by mass.
In general, the higher the concentration of the amine component, the greater the amount of carbon dioxide absorbed and desorbed per unit volume, and the higher the carbon dioxide absorption rate and desorption rate. In terms of processing efficiency, it is preferable.
However, if the concentration of the amine component in the absorbing solution is too high, the water contained in the absorbing solution cannot sufficiently function as an activator for carbon dioxide absorption. Moreover, if the concentration of the amine component in the absorbing solution is too high, defects such as an increase in the viscosity of the absorbing solution cannot be ignored.

  When the content of the secondary amine compound (1) is 55% by mass or less, phenomena such as an increase in the viscosity of the absorbing solution and a decrease in the function of water as an activator are not observed. Further, by setting the content of the secondary amine compound (1) to 10% by mass or more, a sufficient amount of carbon dioxide absorbed and absorption rate can be obtained, and excellent processing efficiency can be obtained.

When the acidic gas absorbent having a secondary amine compound (1) content in the range of 10 to 55% by mass is used for carbon dioxide recovery, it not only has a high carbon dioxide absorption and carbon dioxide absorption rate. Also, the carbon dioxide desorption amount and carbon dioxide desorption rate are high. For this reason, it is advantageous in that carbon dioxide can be efficiently recovered.
The content of the secondary amine compound (1) is more preferably 20 to 50% by mass.

  The secondary amine compound (1) is a reaction accelerator comprising an alkanolamine and / or a heterocyclic amine compound represented by the following general formula (2) (hereinafter referred to as a heterocyclic amine compound (2)). It is preferable to use a mixture.

・・・（２）

... (2)

In the above formula (2), R ⁵ represents a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ⁶ represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms bonded to the carbon atom. Represents. n represents an integer of 1 to 3, m represents an integer of 1 to 4, and p represents an integer of 0 to 12. When n is 2 to 3, nitrogen atoms are not directly bonded to each other.

In the present embodiment, for example, a secondary amine compound (1) and a reaction accelerator composed of an alkanolamine and / or a heterocyclic amine compound (2) are mixed, and the mixture is made into an aqueous solution, for example. It can be used as an acid gas absorbent.
By using the secondary amine compound (1) in a mixture with the alkanolamines and / or the heterocyclic amine compound (2), the amount of carbon dioxide absorbed per unit mole of the secondary amine compound (1), The amount of carbon dioxide absorbed and the carbon dioxide absorption rate per unit volume of the acid gas absorbent can be further improved.
In addition, the secondary amine compound (1) is mixed with the alkanolamines and / or the heterocyclic amine compound (2) and used to separate the acidic gas after carbon dioxide absorption (acid gas desorption energy). And the energy for regenerating the acidic gas absorbent can be reduced.

  Examples of the alkanolamine include monoethanolamine, 2-amino-2-methylpropanolamine, 2-amino-2-methyl-1,3-dipropanolamine, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, Bis (2-hydroxy-1-methylethyl) amine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, dimethylamino-1-methylethanol, 2-methylaminoethanol, 2-ethylaminoethanol, 2- Examples include propylaminoethanol, n-butylaminoethanol, 2- (isopropylamino) ethanol, 3-ethylaminopropanol, triethanolamine, and diethanolamine.

  Among these, alkanolamines include 2- (isopropylamino) ethanol, 2- (ethylamino) ethanol and 2-amino-2-, from the viewpoint of further improving the reactivity between the tertiary amine and the acidic gas. It is preferably at least one selected from the group consisting of methyl-1-propanol.

  Examples of the heterocyclic amine compound (2) include azetidine, 1-methylazetidine, 1-ethylazetidine, 2-methylazetidine, 2-azetidylmethanol, 2- (2-aminoethyl) azetidine, pyrrolidine, 1- Methylpyrrolidine, 2-methylpyrrolidine, 2-butylpyrrolidine, 2-pyrrolidylmethanol, 2- (2-aminoethyl) pyrrolidine, piperidine, 1-methylpiperidine, 2-ethylpiperidine, 3-propylpiperidine, 4-ethylpiperidine 2-piperidylmethanol, 3-piperidylethanol, 2- (2-aminoethyl) pyrrolidine, hexahydro-1H-azepine, hexamethylenetetramine, piperazine, piperazine derivatives and the like.

Among these, piperazine derivatives are particularly desirable from the viewpoint of improving the carbon dioxide absorption amount and absorption rate of the acidic gas absorbent.
A piperazine derivative is a secondary amine compound, and generally, a nitrogen atom of a secondary amino group is bonded to carbon dioxide to form a carbamate ion, thereby contributing to an improvement in the absorption rate in the initial stage of the reaction. Further, the nitrogen atom of the secondary amino group plays a role of converting carbon dioxide bonded thereto to bicarbonate ion (HCO ₃ ⁻ ), and contributes to the speed increase in the latter half of the reaction.

  The piperazine derivative is more preferably at least one of 2-methylpiperazine, 2,5-dimethylpiperazine, and 2,6-dimethylpiperazine.

  The content of the reaction accelerator (alkanolamines and / or heterocyclic amine compound (2)) contained in the acid gas adsorbent is preferably 1 to 20% by mass. If the content of the reaction accelerator contained in the acidic gas adsorbent is less than 1% by mass, the effect of improving the carbon dioxide absorption rate may not be sufficiently obtained. When the content of the reaction accelerator contained in the acidic gas adsorbent exceeds 20% by mass, the viscosity of the absorbent becomes excessively high, and the reactivity may be lowered. The content of the reaction accelerator (alkanolamines and / or heterocyclic amine compound (2)) is more preferably 5 to 15% by mass.

  In addition to the above amine compounds and reaction accelerators, acid gas absorbents include anticorrosives such as phosphoric acid to prevent corrosion of plant equipment, antifoaming agents such as silicone to prevent foaming, Further, an antioxidant for preventing deterioration of the acid gas absorbent may be contained.

  The acid gas removal method according to the present embodiment is an exhaust gas containing an acid gas by bringing an exhaust gas containing the acid gas into contact with an acid gas absorbent obtained by dissolving the amine compound described in the above embodiment in a solvent. The acid gas is absorbed and separated from the gas and removed.

  The basic structure of the carbon dioxide absorption and separation step is a step of bringing an acid gas absorbent into contact with an exhaust gas containing carbon dioxide and causing the acid gas absorbent to absorb carbon dioxide (carbon dioxide absorption step); Heating the acidic gas absorbent in which carbon dioxide has been absorbed obtained in the carbon dioxide absorption step, and desorbing and collecting carbon dioxide (carbon dioxide separation step).

  A method of bringing a gas containing carbon dioxide into contact with the aqueous solution containing the acid gas absorbent is not particularly limited. For example, a method of absorbing gas by bubbling a gas containing carbon dioxide in the acid gas absorbent; A method of spraying an acid gas absorbent into a gas stream containing gas (a spray or spray method), or a gas containing carbon dioxide and an acid gas absorbent in an absorption tower containing a magnetic or metal mesh filler It is performed by a method of making a countercurrent contact.

The temperature of the acidic gas absorbent when the gas containing carbon dioxide is absorbed in the aqueous solution is usually from room temperature to 60 ° C. or less. Preferably it is 50 degrees C or less, More preferably, it is performed at about 20-45 degreeC.
As the temperature is lowered, the amount of acid gas absorbed increases, but the lower limit of the processing temperature is determined by the gas temperature in the process, the heat recovery target, and the like. The pressure during carbon dioxide absorption is usually about atmospheric pressure. Although it is possible to pressurize to a higher pressure in order to enhance the absorption performance, it is preferable to carry out under atmospheric pressure in order to suppress energy consumption required for compression.

  In the carbon dioxide absorption step, the amount of carbon dioxide absorbed at the time of carbon dioxide absorption (40 ° C.) of the acidic gas absorbent containing 10 to 55% by mass of the amine compound according to the embodiment described above is based on 1 mol of amine contained in the absorbent. It is about 0.26 to 0.62 mol, and the carbon dioxide absorption rate after a lapse of several minutes from the time when the absorption of carbon dioxide is started is about 0.029 to 0.038 mol / L / min.

  Here, the carbon dioxide saturated absorption amount is a value obtained by measuring the amount of inorganic carbon in the acid gas absorbent with an infrared gas concentration measuring device, and the carbon dioxide absorption rate is from the time when absorption of carbon dioxide is started. It is a value measured using an infrared carbon dioxide meter when several minutes have passed.

  The method of separating carbon dioxide from the acid gas absorbent that has absorbed carbon dioxide and recovering pure or high-concentration carbon dioxide is the same as distillation, in which the acid gas absorbent is heated and bubbled in a kettle and desorbed. And a heating method in which a liquid interface is expanded in a regenerator tower containing a plate tower, a spray tower, or a magnetic or metal mesh filler. Thereby, carbon dioxide is liberated and released from the carbamate anion and bicarbonate ion.

  The acidic gas absorbent temperature at the time of carbon dioxide separation is usually 70 ° C. or higher, preferably 80 ° C. or higher, more preferably about 90 to 120 ° C. The higher the temperature, the greater the amount of absorption, but the higher the temperature, the greater the energy required to heat the absorbent, so the temperature is determined by the process gas temperature, heat recovery target, etc. The pressure during carbon dioxide desorption is usually about atmospheric pressure. Although the pressure can be reduced to a lower pressure in order to enhance the desorption performance, it is preferably performed under atmospheric pressure in order to suppress energy consumption required for the pressure reduction.

  The amount of carbon dioxide desorbed at the time of carbon dioxide desorption (80 ° C.) of the aqueous solution containing 10 to 55% by mass of the amine compound according to the embodiment described above is 0.15 to 0.47 mol per mol of amine contained in the absorbent. Degree.

  The acidic gas absorbent after separating the carbon dioxide is sent again to the carbon dioxide absorption step and recycled (recycled). In addition, heat generated during carbon dioxide absorption is generally cooled by heat exchange in a heat exchanger in order to preheat the aqueous solution injected into the regeneration tower in the aqueous solution recycling process.

  The purity of the carbon dioxide recovered in this manner is usually as high as about 95 to 99% by volume. This pure carbon dioxide or high-concentration carbon dioxide is used as a chemical, a synthetic raw material for a polymer substance, a cooling agent for freezing foods, or the like. In addition, it is possible to sequester and store the recovered carbon dioxide in the underground, where technology is currently being developed.

  Of the steps described above, the step of separating the carbon dioxide from the acid gas absorbent to regenerate the acid gas absorbent is the portion that consumes the most amount of energy. In this step, about 50 to 80% of the entire process is consumed. A certain amount of energy is consumed. Therefore, by reducing the energy consumption in the regeneration process of the acidic gas absorbent, the cost of the carbon dioxide absorption and separation process can be reduced, and the acidic gas removal from the exhaust gas can be performed economically advantageously.

  According to this embodiment, the energy required for carbon dioxide desorption (regeneration process) can be reduced by using the acidic gas absorbent of the above embodiment. For this reason, the absorption separation process of carbon dioxide can be performed on economically advantageous conditions.

  In addition, the amine compound according to the above-described embodiment is significantly higher in corrosion resistance than metal materials such as carbon steel as compared with alkanolamines such as 2-aminoethanol which has been conventionally used as an acid gas absorbent. It has sex. Therefore, the acid gas removal method using such an acid gas absorbent eliminates the need to use high-cost high-grade corrosion-resistant steel in, for example, plant construction, which is advantageous in terms of cost.

  The acidic gas removal apparatus according to the present embodiment includes an absorption tower that removes acidic gas from the gas by bringing a gas containing acidic gas into contact with the acidic gas adsorbent, and the acidic gas adsorbent that has absorbed the acidic gas. A regeneration tower that removes the acid gas and regenerates the acid gas adsorbent, and the acid gas adsorber that regenerates the acid gas adsorbent regenerated in the regeneration tower in the absorption tower, As the acidic gas adsorbent, for example, the acidic gas absorbent according to the above embodiment is used.

  FIG. 1 is a schematic view of an acidic gas removal apparatus according to an embodiment. The acidic gas removing device 1 includes an absorption tower 2 for contacting a gas containing an acidic gas (hereinafter referred to as exhaust gas) with an acidic gas adsorbent and absorbing and removing the acidic gas from the exhaust gas. A regenerating tower 3 for separating the acid gas from the acid gas adsorbent that has absorbed the gas and regenerating the acid gas adsorbent. Hereinafter, the case where the acidic gas is carbon dioxide will be described as an example.

  As shown in FIG. 1, exhaust gas containing carbon dioxide, such as combustion exhaust gas discharged from a thermal power plant, is guided to the lower part of the absorption tower 2 through a gas supply port 4. This exhaust gas is pushed into the absorption tower 2 and comes into contact with the acidic gas absorbent supplied from the acidic gas absorbent supply port 5 at the top of the absorption tower 2. As the acidic gas absorbent, the acidic gas absorbent according to the above-described embodiment is used.

The pH value of the acid gas absorbent may be adjusted to at least 9 or more, but the optimum conditions may be appropriately selected depending on the type, concentration, flow rate, etc. of harmful gas contained in the exhaust gas.
In addition to the above amine compound and a solvent such as water, the acidic gas absorbent may be any other compound such as a nitrogen-containing compound that improves the absorption performance of carbon dioxide, an antioxidant, and a pH adjuster. You may contain in the ratio.

  Thus, when the exhaust gas comes into contact with the acidic gas absorbent, carbon dioxide in the exhaust gas is absorbed by the acidic gas absorbent and removed. The exhaust gas after the carbon dioxide is removed is discharged from the gas outlet 6 to the outside of the absorption tower 2.

  The acidic gas absorbent that has absorbed carbon dioxide is sent to the heat exchanger 7 and the heater 8, heated, and then sent to the regeneration tower 3. The acidic gas absorbent sent to the inside of the regeneration tower 3 moves from the upper part to the lower part of the regeneration tower 3, and during this time, carbon dioxide in the acidic gas absorbent is desorbed and the acidic gas absorbent is regenerated.

  The acid gas absorbent regenerated in the regeneration tower 3 is sent to the heat exchanger 7 and the absorption liquid cooler 10 by the pump 9 and returned to the absorption tower 2 from the acid gas absorbent supply port 5.

On the other hand, the carbon dioxide separated from the acidic gas absorbent comes into contact with the reflux water supplied from the reflux drum 11 at the top of the regeneration tower 3 and is discharged to the outside of the regeneration tower 3.
The reflux water in which carbon dioxide is dissolved is cooled by the reflux cooler 12 and then separated from the liquid component in which the water vapor accompanied with carbon dioxide is condensed in the reflux drum 11. This liquid component is guided to the carbon dioxide recovery process by the recovery carbon dioxide line 13. On the other hand, the reflux water from which carbon dioxide has been separated is sent to the regeneration tower 3 by the reflux water pump 14.

  According to the acidic gas removal device 1 of the present embodiment, it is possible to perform highly efficient absorption and removal of carbon dioxide by using an acidic gas absorbent excellent in carbon dioxide absorption characteristics and desorption characteristics.

As mentioned above, although embodiment of this invention was described referring a specific example, said Example is mentioned as an example of this invention and does not limit this invention.
In addition, in the description of each of the above embodiments, in the acidic gas absorbent, the acidic gas removal device, and the acidic gas removal method, the description of the portions that are not directly required for the explanation of the present invention is omitted, but these are necessary. Each element to be used can be appropriately selected and used.

  In addition, all acid gas absorbents, acid gas removal devices, and acid gas removal methods that include elements of the present invention and that can be appropriately modified by those skilled in the art without departing from the spirit of the present invention are within the scope of the present invention. Is included. The scope of the present invention is defined by the appended claims and equivalents thereof.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1
2- (Cyclopentylamino) ethanol was dissolved in water so that 45 mass% and piperazine were 5 mass%, and it was set as a 50 ml aqueous solution (henceforth an absorption liquid). The absorption liquid is filled in a test tube and heated to 40 ° C., and a mixed gas containing 10% by volume of carbon dioxide (CO ₂ ) and 90% by volume of nitrogen (N ₂ ) gas is vented at a flow rate of 500 mL / min. The carbon dioxide (CO ₂ ) concentration in the gas at the outlet was measured using an infrared gas concentration measuring apparatus (manufactured by Shimadzu Corporation, trade name “CGT-700”) to evaluate the absorption performance. A 1/8 inch Teflon (registered trademark) tube (inner diameter: 1.59 mm, outer diameter: 3.17 mm) was used as a gas inlet to the amine aqueous solution in the test tube.
Further, the aqueous solution after absorbing the mixed gas at 40 ° C. as described above is heated to 80 ° C., 100% nitrogen (N ₂ ) gas is vented at a flow rate of 500 mL / min, and the CO ₂ concentration in the absorbing solution is reduced. The emission performance was evaluated by measurement using an infrared gas concentration measuring device.

The carbon dioxide absorption rate of the absorbing solution was the rate measured at a point two minutes after the start of carbon dioxide absorption.
The heat of reaction was measured using a calorimeter “DRC Evolution” (product name, manufactured by SETRAM).

  The diffusibility of the amine compound was evaluated as follows. That is, the absorbent was put into a flask with a cooling tube, and then the whole flask was heated to 120 ° C. And the gaseous component diffused from a cooling pipe was collect | recovered, and the quantity of the amine compound contained in the collect | recovered gas was measured.

The amount of carbon dioxide absorbed by the absorbing solution at 40 ° C. was 0.56 mol per 1 mol of amino compound in the absorbing solution. Also, the absorbing solution at 80 ° C. carbon dioxide (CO ₂₎ absorption was 1mol per 0.25mol amino compounds. In the process of absorbing carbon dioxide (CO ₂ ) at 40 ° C. and desorbing carbon dioxide (CO ₂ ) at 80 ° C., 0.31 mol of CO ₂ was recovered per 1 mol of amino compound. The carbon dioxide absorption rate was 0.036 mol / L / min.

(Example 2)
An absorbent solution was prepared in the same manner as in Example 1 except that 2- (2-butylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same apparatus as in Example 1 was used. Under the conditions, carbon dioxide absorption and carbon dioxide absorption rate were measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.57 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.24 mol, and 0.33 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.036 mol / L / min.

Example 3
An absorbent solution was prepared in the same manner as in Example 1 except that 2- (2-pentylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same apparatus as in Example 1 was used. Under the conditions, carbon dioxide absorption and carbon dioxide absorption rate were measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.55 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.25 mol, and 0.30 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.036 mol / L / min.

Example 4
An absorbent solution was prepared in the same manner as in Example 1 except that 2- (3-pentylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same apparatus as in Example 1 was used. Under the conditions, carbon dioxide absorption and carbon dioxide absorption rate were measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.53 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.25 mol, and 0.28 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.036 mol / L / min.

(Example 5)
An absorbing solution was prepared in the same manner as in Example 1 except that 2- (2-hexylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same apparatus as in Example 1 was used. Under the conditions, carbon dioxide absorption and carbon dioxide absorption rate were measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.51 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.26 mol, and 0.25 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.036 mol / L / min.

(Example 6)
An absorbing solution was prepared in the same manner as in Example 1 except that 2- (3-hexylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same apparatus as in Example 1 was used. Under the conditions, carbon dioxide absorption and carbon dioxide absorption rate were measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.50 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.27 mol, and 0.23 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.034 mol / L / min.

(Example 7)
An absorbent solution was prepared in the same manner as in Example 1 except that the amount of 2- (cyclopentylamino) ethanol was changed from 45% by mass to 30% by mass. The carbon dioxide absorption and carbon dioxide absorption rate were measured below.
The amount of carbon dioxide absorbed at 40 ° C. per mol of amino compound in the absorbing solution is 0.56 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.24 mol, and 0.32 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.037 mol / L / min.

(Example 8)
An absorbing solution was prepared in the same manner as in Example 1 except that 2- (cyclobutylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same conditions were used using the same apparatus as in Example 1. The carbon dioxide absorption and carbon dioxide absorption rate were measured below.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.56 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.25 mol, and 0.31 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.037 mol / L / min.

Example 9
An absorbent solution was prepared in the same manner as in Example 1 except that 2- (cyclopentylamino) -1-propanol was used instead of 2- (cyclopentylamino) ethanol, and piperidine was used instead of piperazine. The amount of carbon dioxide absorption and the carbon dioxide absorption rate were measured under the same conditions using the same apparatus as in 1.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.54 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.24 mol, and 0.30 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.034 mol / L / min.

(Example 10)
An absorbent solution was prepared in the same manner as in Example 1 except that 3- (cyclohexylamino) ethanol was used instead of 2- (cyclopentylamino) ethanol, and the same conditions were used under the same conditions as in Example 1. The carbon dioxide absorption and the carbon dioxide absorption rate were measured by
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.50 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.24 mol, and 0.26 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.034 mol / L / min.

(Example 11)
An absorbing solution was prepared in the same manner as in Example 1 except that 2.5% by mass of piperazine and 2.5% by mass of 2-amino-2-methyl-1-propanol were used instead of 5% by mass of piperazine. Using the same apparatus as in Example 1, the carbon dioxide absorption and the carbon dioxide absorption rate were measured under the same conditions.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.58 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.26 mol, and 0.32 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.037 mol / L / min.

(Example 12)
An absorbent solution was prepared in the same manner as in Example 1 except that the amount of 2- (cyclopentylamino) ethanol was changed from 45% by mass to 30% by mass and piperazine was not used. The carbon dioxide absorption and the carbon dioxide absorption rate were measured under the same conditions.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.59 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.25 mol, and 0.34 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.038 mol / L / min.

(Example 13)
Example 1 except that the blending amount of 2- (cyclopentylamino) ethanol is changed from 45% by mass to 30% by mass, and 5% by mass of 2-amino-2-methyl-1-propanol is used instead of piperazine. Similarly, an absorbing solution was prepared, and the carbon dioxide absorption amount and the carbon dioxide absorption rate were measured under the same conditions using the same apparatus as in Example 1.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.61 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.28 mol, and 0.33 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.038 mol / L / min.

(Comparative Example 1)
n-Butyldiethanolamine was dissolved in water so as to be 60% by mass and piperazine was 5% by mass to obtain a 50 ml aqueous solution (hereinafter referred to as an absorbing solution). Thereafter, using the same apparatus as in Example 1, the carbon dioxide absorption amount and the carbon dioxide absorption rate were measured under the same conditions as in Example 1.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amino compound in the absorbing solution is 0.20 mol, the amount of carbon dioxide absorbed at 80 ° C. is 0.08 mol, and 0.12 mol per mol of amino compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.023 mol / L / min.

  In Table 1, with respect to Examples 1 to 13 and Comparative Example 1, together with the contents of the amino compound and reaction accelerator in the absorption liquid, the carbon dioxide absorption at 40 ° C., the carbon dioxide absorption at 80 ° C., carbon dioxide The recovery amount, carbon dioxide absorption rate, and reaction heat measurement results are shown. In Table 1, the carbon dioxide absorption amount and the carbon dioxide recovery amount indicate the absorption amount and recovery amount per mole of the amine compound contained in the absorption liquid in terms of moles.

As is clear from Table 1, in the absorbing liquids of Examples 1 to 13 using the secondary amine compound having a branched alkyl group or a cyclic alkyl group, the carbon dioxide absorption amount and the carbon dioxide recovery amount were high. In Examples 1 to 13, the carbon dioxide absorption rate was high, and the carbon dioxide absorption performance was excellent.
In particular, Examples 1, 7, and 11 using a secondary amine compound having a cyclic alkyl group are more reactive than Examples 2 to 6 using a secondary amine compound having a branched alkyl group. Low heat was observed.
In addition, in Examples 2 to 6 in which secondary amine compounds having a branched alkyl group were used in the evaluation test for dispersibility, about 1% by mass of the amine compound was recovered, whereas the cyclic amine group was included. In Example 1 and Examples 7 to 13 using the secondary amine compound, the amine compound was hardly recovered. From this, it was recognized that the secondary amine compound having a cyclic alkyl group has low dispersibility and suppressed volatility. Furthermore, in Example 1 and Examples 7-13, it was recognized that the carbon dioxide recovery amount and carbon dioxide recovery rate equivalent to Examples 2-6 can be obtained.

  On the other hand, in Comparative Example 1 using an amine compound having no branched alkyl group or cyclic alkyl group, it was confirmed that the amount of carbon dioxide recovered was as low as 0.12 mol and the carbon dioxide absorption rate was small.

DESCRIPTION OF SYMBOLS 1 ... Acid gas removal apparatus, 2 ... Absorption tower, 3 ... Regeneration tower, 4 ... Gas supply port, 5 ... Acid gas absorbent supply port, 6 ... Gas discharge port, 7 ... Heat exchanger, 8 ... Heater, 9 ... Pump, 10 ... Absorbent liquid cooler, 11 ... Reflux drum, 12 ... Reflux cooler, 13 ... Recovered carbon dioxide line, 14 ... Reflux water pump

Claims (9)

An acidic gas absorbent, which is an aqueous solution containing at least one secondary amine compound represented by the following general formula (1).

... (1)
(In the above formula (1), R ¹⁰ and R ¹¹ are combined to form a cyclic structure having 3 to 5 carbon atoms. R ¹⁰ and R ¹¹ are each substituted or substituted with 1 to 5 carbon atoms. Represents an unsubstituted alkyl group, and R ¹² represents a hydroxyalkyl group . The acidic gas absorbent according to claim 1, wherein in the secondary amine compound represented by the general formula (1), R ¹² is a 2-hydroxyethyl group. Acid gas absorption agent according to claim 1 or 2, wherein the content of the secondary amine compound is 10 to 55 wt% represented by the general formula (1). A reaction accelerator comprising an alkanolamine and / or a heterocyclic amine compound represented by the following general formula (2) is further contained, and the content of the reaction accelerator is 1 to 20% by mass. The acid gas absorbent according to any one of the above.

... (2)
(In the above formula (2), R ⁵ represents a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ⁶ represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms bonded to the carbon atom. N represents an integer of 1 to 3, m represents an integer of 1 to 4, and p represents an integer of 0 to 12. When n is 2 to 3, nitrogen atoms are directly bonded to each other. Not.)   The acidic gas absorption according to claim 4, wherein the alkanolamines are at least one selected from the group consisting of 2- (isopropylamino) ethanol, 2- (ethylamino) ethanol and 2-amino-2-methyl-1-propanol. Agent.   The acidic gas absorbent according to claim 4 or 5, wherein the heterocyclic amine compound contains at least one selected from the group consisting of piperazines.   The acidic gas absorbent according to claim 6, wherein the piperazine is at least one selected from the group consisting of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, and 2,6-dimethylpiperazine. A gas containing acid gases, by contacting the acid gas absorption agent according to any one of claims 1 to 7, acid gases, and removing acid gases from a gas containing the acid gases Removal method. An absorption tower for removing acid gas from the gas by contacting the gas containing acid gas and the acid gas absorption agent, the acid gas to remove acidic gases from said acid gas absorption agent which has absorbed acid gases has a regenerator for reproducing absorption agent, and the acid gas absorption agent reproduced by the regenerator an acid gas removal system to recycle in the absorption tower, any one of claims 1 to 7 acid gas removal apparatus characterized by using the acid gas absorption agent according to 1, wherein.

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