JP2015071136A - Acidic gas absorbent, acidic gas removal method and acidic gas removal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acidic gas absorbent that is excellent in the collection amount and absorption rate of acidic gas such as carbon dioxide, particularly excellent in acidic gas desorption performance at high temperature, and an acidic gas removal device and acidic gas removal method using the same .SOLUTION: An acidic gas absorbent according to an embodiment comprises at least one of secondary amine compounds represented by general formula (1), and an additive comprising surfactant and/or alcohol. In the formula (1), a ring A represents a ring structure having carbon atoms of 3 or more and 10 or less, and Rrepresents a hydroxyalkyl group.

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 in use. 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, research has been actively conducted on alkanolamines having structurally steric hindrance, among amine compounds, as acid gas absorbents.
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.

In addition, it is known that the steric hindrance possessed by the amine compound has a large influence on the product upon absorption of carbon dioxide, and works favorably on the production of bicarbonate ions exhibiting a low heat of reaction. For example, 2- (2-butylamino) ethanol is known as an amine compound that can reduce the heat of reaction due to steric hindrance. 2- (2-butylamino) ethanol has a branched structure in which two alkyl groups are bonded to one carbon atom bonded to a nitrogen atom. Due to its steric hindrance, carbon dioxide (CO ₂ ) and the like There is an advantage that high reactivity can be obtained with respect to the acid gas, and a high amount of acid gas absorption can be obtained.

  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.

JP 2008-307519 A Japanese Patent No. 2871334 JP 2012-143745 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.

  Further, the acid gas absorbent is recovered after the acid gas is desorbed by heating after the acid gas absorption step. However, the absorbent using the amine compound having a large steric hindrance as described above does not sufficiently desorb the absorbed acid gas even when heated after absorption of the acid gas, and the recovery amount of the acid gas is sufficient. There is a problem that it cannot be raised. For this reason, there is a demand for an acid gas absorbent that is excellent not only in acid gas absorbability but also in acid gas detachability.

  The problem to be solved by the present invention is that the recovery amount and absorption rate of acidic gas such as carbon dioxide are high, and in particular, the acidic gas absorbent excellent in the detachability of acidic gas at high temperature, and the use thereof The present invention provides an acid gas removing device and an acid gas removing method.

  The acidic gas absorbent of the embodiment contains at least one secondary amine compound represented by the following general formula (1) and an additive composed of a surfactant and / or an alcohol.

・・・（１）
（上記式（１）中、環Ａは炭素数３以上１０以下の環構造を表し、Ｒ^１はヒドロキシアルキル基を表す。）

... (1)
(In the above formula (1), ring A represents a ring structure having 3 to 10 carbon atoms, and R ¹ represents a hydroxyalkyl group.)

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

Hereinafter, embodiments will be described in detail.
The acidic gas absorbent of the embodiment contains at least one secondary amine compound represented by the following general formula (1) and an additive composed of a surfactant and / or an alcohol.

・・・（１）
（上記式（１）中、環Ａは炭素数３以上１０以下の環構造を表し、Ｒ^１はヒドロキシアルキル基を表す。）

... (1)
(In the above formula (1), ring A represents a ring structure having 3 to 10 carbon atoms, and R ¹ represents a hydroxyalkyl group.)

The present inventors use an acidic gas absorbent containing a compound represented by the general formula (1) (for example, 2- (cyclopentylamino) ethanol) and an additive composed of a surfactant and / or an alcohol. In the desorption process performed after the acid gas absorption process, a high acid gas absorption amount and absorption rate can be obtained in the acid gas absorption process than the conventional acid gas absorbent using an amino compound having a branched structure. It was found that higher acid gas desorption amount can be obtained.
As a result, the amount of acid gas recovered per cycle comprising the acid gas absorption step and the desorption step is increased, and the energy required for the entire process of separating and recovering the acid gas such as carbon dioxide can be reduced. The present invention has been completed.

That is, the secondary amine compound represented by the general formula (1) (hereinafter referred to as secondary amine compound (1)) has a hydroxyalkyl group (R ¹ ) bonded to a nitrogen atom. Furthermore, it has a structure in which a cyclic structure is bonded to this nitrogen atom.

Thus, the secondary amine compound (1) in which the cyclic structure 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.

In general, a compound in which a hydrogen atom of an amino group is substituted with an alkyl group, such as a hindered amine, has a structure having a large steric hindrance, and therefore has low hydrophilicity. Viscosity tends to increase with the absorption of carbon (CO ₂ ) and the increase in blending amount. In particular, the secondary amine compound of the above general formula (1) has a structure having a large steric hindrance in which a cyclic alkyl group is bonded to a nitrogen atom, so that the acid gas absorption rate decreases as the viscosity of the absorbing liquid increases. In addition, phenomena such as degradation of acid gas desorption performance tend to occur.

As a result of intensive studies by the present inventors, the absorbent is obtained by mixing the secondary amine compound (1) with an additive comprising a surfactant and / or an alcohol described in detail below. The effect of increasing the viscosity of the gas is suppressed, and when the secondary amine compound (1) having a cyclic alkyl group is used, the absorption performance and desorption performance of acidic gas such as carbon dioxide (CO ₂ ) are improved. I found it.

  That is, by using the secondary amine compound (1) having a cyclic alkyl group, the acid gas absorption performance such as the absorption performance and absorption speed of the acid gas can be enhanced, and the secondary amine compound (1) By mixing with an additive comprising a surfactant and / or an alcohol, the acid gas desorption performance is enhanced. For this reason, the secondary amine compound (1) is dissolved in a solvent such as water together with the above-described additives, so that a loading amount of one cycle consisting of an absorption step and a desorption step (absorption step in a low temperature region). An acidic gas absorbent having a large acid gas absorption amount-acid acid absorption amount in a desorption step at a high temperature range) can be obtained. By using such an acid gas absorbent, it becomes possible to recover high-purity carbon dioxide with lower energy than before, and excellent acid gas recovery performance can be obtained.

  Ring A represents a ring structure having 3 to 10 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group.

By setting it as the structure which the cyclic structure (ring A) couple | bonded with the nitrogen atom, the volatility of a 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. In addition, by the nitrogen atom in the cyclic structure (the ring A) are bonded structure by the steric hindrance, the heat of reaction with acidic gases carbon dioxide (CO ₂₎ or the like of the secondary amine compound (1) is It is reduced, and high reactivity can be obtained with respect to acidic gas.

An acidic gas absorbent that has absorbed an acidic gas such as carbon dioxide (CO ₂ ) is regenerated by heating in a high temperature range of about 120 ° C. For this reason, as the acidic gas absorbent, it is preferable to use a high-boiling amine compound that is difficult to be released from the regeneration tower when heated. In the secondary amine compound (1), from the viewpoint of obtaining a higher boiling point, it is preferable to have a cyclic alkyl group having a larger number of carbon atoms. There is a possibility that solubility may be lowered. From the viewpoint of obtaining good solubility while suppressing volatility, among the above cyclic structures, a cyclopentyl group and a cyclohexyl group are more preferable.

R ¹ 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. When the number of carbon atoms of R ¹ exceeds 4, the reactivity of the secondary amine compound (1) with an acidic gas may be lowered. As the hydroxyalkyl group for R ¹ , for example, a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 4-hydroxybutyl group, or the like can be used. In these hydroxyalkyl groups, a part of hydrogen atoms may be substituted with a methyl group or an ethyl group within a range not exceeding 4 carbon atoms.
Among these, the 2-hydroxyethyl group is more preferable because it can obtain the greatest hydrophilicity and does not reduce the solubility of the secondary amine compound (1).

  Specific examples of the secondary amine compound (1) include the following compounds. That is, as the secondary amine compound (1), 2- (cyclopropylamino) ethanol, 2- (cyclobutylamino) ethanol, 2- (cyclopentylamino) ethanol, 2- (cyclohexylamino) ethanol, 2- ( Cycloheptylamino) ethanol, 2- (cyclooctylamino) ethanol, 3- (cyclopropylamino) propanol, 3- (cyclobutylamino) propanol, 3- (cyclopentylamino) propanol, 3- (cyclohexylamino) propanol, 3 -(Cycloheptylamino) propanol, 3- (cyclooctylamino) propanol, 4- (cyclopropylamino) butanol, 4- (cyclobutylamino) butanol, 4- (cyclopentylamino) butanol, 4- (cyclohexyl) Arylamino) butanol, 4- (cycloheptyl amino) butanol, 4- (cyclooctyl amino) butanol.

  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 used by mixing with an additive comprising a surfactant and / or alcohol.

By using the secondary amine compound (1) mixed with an additive composed of a surfactant and / or alcohol, the surface tension of the acidic gas absorbent is reduced, and the acidic gas accompanying an increase in the viscosity of the absorbent. Phenomena such as a decrease in the absorption rate and a decrease in acid gas desorption performance can be suppressed. Therefore, not only the absorption performance of acidic gas such as carbon dioxide (CO ₂ ) but also the desorption performance of acidic gas can be improved, and the recovery efficiency of acidic gas can be increased.

  As the surfactant, an anionic fluorosurfactant having an anionic group, a cationic fluorosurfactant having a cationic group, an amphoteric fluorosurfactant having both an anionic group and a cationic group, Or nonionic fluorine-type surfactant is mentioned. As the surfactant, any of the above can be used, and known ones can be used without any particular limitation.

  Known anionic surfactants can be used, such as primary higher fatty acid salts, secondary higher fatty acid salts, primary higher alcohol sulfates, and secondary higher alcohol sulfates. Salt, primary higher alkyl sulfonate, secondary higher alkyl sulfonate, higher alkyl disulfonate, sulfonated higher fatty acid salt, higher fatty acid sulfate ester salt, higher fatty acid sulfate sulfonate salt, higher alcohol ether Examples include sulfuric acid sulfonates, higher alcohol ether sulfonates, higher fatty acid amide alkylol sulfates, alkylbenzene sulfonates, alkylphenol sulfonates, alkylnaphthalene sulfonates, and alkylbenzimidazole sulfonates. .

  Among these anionic surfactants, particularly preferred are higher fatty acid salts, particularly alkali metal salts of saturated or unsaturated higher fatty acids having 10 to 20 carbon atoms, such as capric acid, Unsaturated fatty acids such as undecanoic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, etc. Mention may be made of alkali metal salts of fatty acids or mixtures thereof.

  Known cationic surfactants can be used, and examples thereof include alkyltrimethylammonium salts.

  As the nonionic surfactant, known ones can be used. For example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene fatty acid amide ether, polyhydric alcohol fatty acid Examples include esters, polyoxyethylene polyhydric alcohol fatty acid esters, fatty acid sucrose esters, alkylolamides, polyoxyalkylene block copolymers, and the like.

  Among these, nonionic surfactants are less active against metal materials than cationic surfactants and anionic surfactants, and reduce the corrosion resistance as acidic gas absorbents. In addition, the acid gas absorption performance and desorption performance can be improved, which is preferable.

  As the surfactant, a fluorine-based surfactant having a fluorine atom can also be used. Examples of the fluorosurfactant include an anionic fluorosurfactant, a cationic fluorosurfactant, an amphoteric fluorosurfactant, and a nonionic fluorosurfactant, as described above. Can also be used.

As the fluorine-based surfactant, specifically, compounds having a perfluoroalkyl group such as perfluoroalkyl alcohol and perfluoroalkylsulfonic acid can be suitably used. Here, the perfluoroalkyl group is a group represented by (CF ₃ (CF ₂ ) n-), and is a group in which all hydrogen atoms of the alkyl group are substituted with fluorine atoms.

  The fluorosurfactant having a perfluoroalkyl group has a very small intermolecular force between perfluoroalkyl groups, and the surface tension of water can be significantly reduced by dissolving or dispersing a very small amount in water. For this reason, since the detachability | desorption property of acidic gas after absorption of acidic gas can be improved efficiently, and the outstanding acidic gas recovery performance can be obtained, it is preferable.

  In particular, the nonionic fluorosurfactant having a perfluoroalkyl group has suppressed activity against metal materials, and the acid gas in the desorption process can be reduced without reducing the corrosion resistance as an acid gas absorbent. This is preferable because the acid gas desorption performance of the absorbent can be improved efficiently.

  Specific examples of the fluorosurfactant having a nonionic perfluoroalkyl group include “Surflon S-141” (product name, manufactured by Seimi Chemical Co., Ltd.), “Surflon S-211” (product name, Sey Chemical Co., Ltd.) is preferably used.

  As the surfactant, one of the compounds listed above can be used, or two or more of the compounds listed above can be used in combination.

The content of the surfactant contained in the acidic gas adsorbent is appropriately selected depending on the type of the surfactant and the like, but is preferably 1 to 2000 ppm by mass.
If the content of the surfactant contained in the acid gas adsorbent is less than 1 ppm, the effect of improving the detachability of the acid gas may not be sufficiently obtained. On the other hand, when the content of the surfactant contained in the acidic gas adsorbent exceeds 2000 ppm, foaming is likely to occur in the acidic gas absorbent. The content of the surfactant contained in the acid gas adsorbent is mass%, more preferably 10 to 1500 ppm, and still more preferably 10 to 1000 ppm.

  The surfactant may be added to the acidic gas absorbent as it is, or as a solution added to a solvent that does not affect the absorption or desorption of the acidic gas, such as alcohol, It may be added to the agent.

  As the alcohol, linear or branched ones having 1 to 20 carbon atoms can be used, and those having one hydroxyl group or polyols having two or more hydroxyl groups may be used. .

  The polyol is not particularly limited. For example, ethylene glycol, propylene glycol, glycerol, ethylene glycol oligomer, polyethylene glycol, polyethylene oxide, ethylene glycol oligomer ether, polyethylene glycol ether, polyethylene oxide ether, polytetrahydrofuran, etc. These oligomers and polymers of cyclic ethers, and derivatives thereof can be used. As a polyol, 1 type selected from said group may be used, or 2 or more types selected from said group may be mixed and used.

  From the viewpoint of solubility in water, the polyol preferably has a molecular weight of less than 10,000, more preferably a molecular weight of less than 1,000.

The acid gas absorbent that has absorbed carbon dioxide (CO ₂ ) is regenerated by heating in a regeneration tower in a high temperature range of about 120 ° C. For this reason, it is preferable that the alcohol used as an additive has a boiling point of 150 ° C. or higher. When the boiling point of the alcohol is less than 150 ° C., when the acidic gas absorbent is heated, the alcohol is easily released from the regeneration tower, which may increase the cost required for the entire recovery process of the acidic gas.

  The content of alcohol contained in the acidic gas adsorbent is preferably 0.1 to 20% by mass. If the content of the alcohol contained in the acid gas adsorbent is less than 0.1% by mass, the effect of improving the detachability of the acid gas may not be sufficiently obtained. When the content of the alcohol contained in the acid gas adsorbent exceeds 20% by mass, the viscosity of the absorbent becomes excessively high, and the reactivity with the acid gas may be lowered. The content of alcohol contained in the acidic gas adsorbent is more preferably 0.5 to 10% by mass.

  The secondary amine compound (1) includes a reaction accelerator composed of alkanolamines 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 formula (2), ^{R 2} is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ³ represents a C 1-4 alkyl group bonded to a 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 not directly bonded to each other. When m is 2, n is an integer of 1 or 2. Further, a part of hydrogen atoms of the alkyl group having 1 to 4 carbon atoms of R ² and a part of hydrogen atoms of the alkyl group having 1 to 4 carbon atoms of R ³ are respectively substituted with a hydroxyl group and an amino group. Also good.

In this 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) mixed 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.
Further, the secondary amine compound (1) is mixed with the alkanolamines and / or the heterocyclic amine compound (2) and used to separate the acid gas after absorbing carbon dioxide (acid gas desorption energy). And the energy for regenerating the acidic gas absorbent can be reduced.

  As the alkanolamine as the reaction accelerator, for example, alkanolamines having no steric hindrance due to a cyclic structure as shown below can be used. Here, alkanolamine means a compound having an amino group and a hydroxyl group in one molecule. Specific examples of the alkanolamine as the reaction accelerator include, for example, alkanolamines such as monoethanolamine, 2-amino-2-methylpropanolamine, 2-amino-2-methyl-1,3-di Propanolamine, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, bis (2-hydroxy-1-methylethyl) amine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, dimethylamino-1- Methylethanol, 2-methylaminoethanol, 2-ethylaminoethanol, 2-propylaminoethanol, n-butylaminoethanol, 2- (isopropylamino) ethanol, 3-ethylamino Propanol, triethanolamine, diethanolamine and the like.

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

  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-mentioned amine compounds, reaction accelerators, and additives consisting of surfactants and / or alcohols, acid gas absorbents include anticorrosives such as phosphoric acid to prevent corrosion of plant equipment, It may contain an antifoaming agent such as silicone for preventing foaming, an antioxidant for preventing deterioration of the acid gas absorbent, and the like.

  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 method in which a liquid interface is expanded and heated in a plate tower, a spray tower, or a regeneration tower containing a magnetic or metal mesh filler. Thereby, carbon dioxide is liberated and released from the carbamate anion and bicarbonate ion.

  The acid gas absorbent temperature at the time of carbon dioxide separation is usually 70 ° C or higher. The temperature of the acidic gas absorbent at the time of carbon dioxide separation is preferably 80 ° C. or higher, more preferably about 90 to 120 ° C. The higher the temperature, the greater the amount of desorption, 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.
The exhaust gas is pushed into the absorption tower 2 and is brought into contact with the acidic gas absorbent that is supplied from the acidic gas absorbent supply port 5 at the top of the absorption tower 2 and accommodated inside 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 compounds and water and other solvents, the acidic gas absorbent may be any other compound such as a nitrogen-containing compound that improves carbon dioxide absorption performance, 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. 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 is dissolved in water at 45% by mass, piperazine at 5% by mass, and Surflon s-141 (surfactant) at 500 ppm, and 50 ml of an aqueous solution (hereinafter referred to as an absorbing solution). It was. 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 amount of carbon dioxide absorbed by the absorbing solution at 40 ° C. was 0.55 mol per 1 mol of the amine compound in the absorbing solution. Also, the absorbing solution at 80 ° C. carbon dioxide (CO ₂₎ absorption was amine compound 1mol per 0.22 mol. In the process of absorbing carbon dioxide (CO ₂ ) at 40 ° C. and desorbing carbon dioxide (CO ₂ ) at 80 ° C., 0.33 mol of CO ₂ was recovered per 1 mol of the amine compound. The carbon dioxide absorption rate was 0.036 mol / L / min.

The heat of reaction was measured as follows. The reaction heat of carbon dioxide absorption by the absorbing solution is measured using a differential thermal reaction calorimeter “DRC Evolution” (product name, manufactured by SETARAM) consisting of a glass reaction tank of the same shape and a reference tank installed in a thermostat. It was measured. Each of the reaction tank and the reference tank is filled with 150 mL of absorption liquid, and constant temperature water at 40 ° C. is circulated in the jacket portion of the tank. In this state, 100% carbon dioxide gas was blown into the absorption liquid in the reaction tank at 200 ml / min, and the temperature rise of the liquid was continuously recorded with a temperature recorder until the carbon dioxide absorption was completed, and measured in advance. The reaction heat was calculated using the overall heat transfer coefficient between the reaction vessel and the jacket water. The reaction heat of carbon dioxide absorption was 67 kJ / mol.
In Examples 1 and 2 and Comparative Example 1, the heat of reaction indicates the heat of reaction per 1 mol of carbon dioxide contained in the absorbing solution.

(Example 2)
An absorbent solution was prepared in the same manner as in Example 1 except that ethylene glycol was used instead of Surflon s-141 (surfactant). That is, 2- (cyclopentylamino) ethanol was dissolved in water such that 45% by mass, piperazine was 5% by mass, and ethylene glycol was 3% by mass to obtain a 50 ml absorbent solution. And the carbon dioxide absorption amount and the carbon dioxide absorption rate were measured on the same conditions using the apparatus similar to Example 1. FIG.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amine 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 amine compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.035 mol / L / min. The reaction heat of carbon dioxide absorption was 67 kJ / mol.

(Comparative Example 1)
Except not using a surfactant, an absorption liquid was prepared in the same manner as in Example 1, and using the same apparatus as in Example 1, the amount of carbon dioxide absorbed and the carbon dioxide absorption rate were the same as in Example 1. Was measured.
The amount of carbon dioxide absorbed at 40 ° C. per 1 mol of amine 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 amine compound in the absorbing solution. Of carbon dioxide was recovered. The carbon dioxide absorption rate was 0.036 mol / L / min. The reaction heat of carbon dioxide absorption was 69 kJ / mol.

  Table 1 shows the absorption of carbon dioxide at 40 ° C. with respect to Examples 1 and 2 and Comparative Example 1, together with the contents of additives consisting of amine compounds, reaction accelerators, surfactants and / or alcohols in the absorption liquid. The measurement results of the amount, carbon dioxide absorption at 80 ° C., carbon dioxide recovery, carbon dioxide absorption rate, and reaction heat are shown. In Table 1, the amount of carbon dioxide absorbed and the amount of carbon dioxide recovered represent the amount of absorption and the amount recovered per mole of amine compound (including amine compound as a reaction accelerator) contained in the absorption liquid. Is.

As is apparent from Table 1, the absorbents of Examples 1 and 2 using an acidic gas absorbent containing a surfactant or alcohol have a high carbon dioxide absorption at 40 ° C., and CO _{2 at} 80 ° C. The amount released was large and a high carbon dioxide recovery was obtained. Moreover, in Examples 1-2, the carbon dioxide absorption rate was also high and it was excellent in the carbon dioxide absorption performance.

On the other hand, in Comparative Example 1 using an acidic gas absorbent that does not contain any surfactant or alcohol, the amount of CO ₂ released at 80 ° C. is not sufficiently increased. The recovered amount of ₂ was small.

According to the acid gas absorbent, the acid gas removal method, and the acid gas removal device of at least one embodiment described above, the absorption amount and absorption rate of acid gas such as carbon dioxide can be increased, and the acid gas absorption The reaction heat at the time can be lowered, the amount of acid gas desorbed at a high temperature can be increased, and the recovery performance of the acid gas can be improved.
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

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 (14)

An acidic gas absorbent comprising at least one secondary amine compound represented by the following general formula (1) and an additive comprising a surfactant and / or an alcohol.

... (1)
(In the above formula (1), ring A represents a ring structure having 3 to 10 carbon atoms, and R ¹ 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 ¹ is a 2-hydroxyethyl group.   The acidic gas absorbent according to claim 1 or 2, wherein in the secondary amine compound represented by the general formula (1), the ring structure represented by the ring A is a cyclopentyl group or a cyclohexyl group.   The acidic gas absorbent according to any one of claims 1 to 3, wherein a content of the secondary amine compound represented by the general formula (1) is 10 to 55 mass%.   The acidic gas absorbent according to any one of claims 1 to 4, wherein a content of the surfactant is 1 to 2000 ppm.   The acidic gas absorbent according to any one of claims 1 to 5, wherein the surfactant is a nonionic fluorosurfactant having a perfluoroalkyl group.   The acidic gas absorbent according to any one of claims 1 to 6, wherein the alcohol is a polyol.   The acidic gas absorbent according to any one of claims 1 to 7, wherein the alcohol has a boiling point of 150 ° C or higher. 9. 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 2} represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, ^{R 3} is a .n 1-3 represents an alkyl group having 1 to 4 carbon atoms bonded to carbon atoms Represents an integer, 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.   The acidic gas absorbent according to claim 9, wherein the alkanolamine is at least one selected from the group consisting of 2- (isopropylamino) ethanol and 2-amino-2-methyl-1-propanol. The acidic gas absorbent according to claim 9 or 10, wherein the heterocyclic amine compound contains at least one selected from the group consisting of piperazines.   The acidic gas absorbent according to claim 11, wherein the piperazine is at least one selected from the group consisting of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, and 2,6-dimethylpiperazine.   An acid gas removal comprising: bringing a gas containing an acid gas into contact with the acid gas adsorbent according to any one of claims 1 to 12 to remove the acid gas from the gas containing the acid gas. Method. An acid gas removing device for removing acid gas from gas containing acid gas,
An absorption tower for containing the acidic gas absorbent according to any one of claims 1 to 12, contacting the gas containing an acidic gas and the acidic gas adsorbent to remove the acidic gas from the gas,
A regeneration tower that contains an acid gas absorbent having an acid gas absorbed in the absorption tower, removes the acid gas from the acid gas adsorbent, and regenerates the acid gas adsorbent that is reused in the absorption tower; An acid gas removing device having

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