JP2022049431A - Acidic gas absorbent, acidic gas removing method, and acidic gas removing device - Google Patents

Abstract

To provide an acidic gas absorbent that can recover high volumes of an acidic gas such as carbon dioxide, and an acidic gas removing device and an acidic gas removing method employing the same.SOLUTION: An acidic gas absorbent contains at least one diamine compound represented by general formula (1): R1R2 N-(CR3R4)n-NR5R6 formula [where, R1, R2, R5, R6 each denote a C3-6 substituted or unsubstituted branched alkyl group, a hydrogen atom, a C1-4 alkyl group, or a hydroxyalkyl group, provided that at least one of R1 and R2 denotes a C3-6 substituted or unsubstituted branched alkyl group, and at least one of R5 and R6 denotes a hydroxyalkyl group. R3 and R4 each denote a hydrogen atom, a methyl group, or an ethyl group. n is an integer of from 1 to 6].SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to an acid gas absorbent, an acid gas removing device using the acid gas absorbent, and an acid gas removing method.

In recent years, the greenhouse effect due to an increase in carbon dioxide (CO ₂ ) concentration has been pointed out as one of the causes of the global warming phenomenon, 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 its emissions is increasing.

Technologies for suppressing the increase in the concentration of acid gas such as CO ₂ include the development of energy-saving products, the separation and recovery technology for acid gas to be discharged, the technology for using and storing acid gas as a resource, and the acid gas. There are conversions to alternative energies such as acid gas that does not emit acid gas and nuclear energy.

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

Therefore, for facilities such as thermal power plants that use fossil fuels, the exhaust gas generated when burning fossil fuels (coal, oil, natural gas, etc.) is brought into contact with chemical absorbers, and CO ₂ in the combustion exhaust gas is produced. There are methods all over the world to remove and recover the recovered CO ₂ and to store the recovered CO 2. It has also been proposed to use a chemical absorbent to remove acid gases such as hydrogen sulfide ( _H2S ) in addition to CO ₂ .

Generally, alkanolamines typified by monoethanolamine (MEA) have been developed as chemical absorbents used in the absorption method since the 1930s, and are still in use today. This method is economical and the removal device can be easily increased in size.

Widely used alkanolamines include monoethanolamine, methyldiethanolamine, diethanolamine, triethanolamine, diisopropanolamine, 3-amino-1-propanol, 2-amino-2-methylpropanol, ethyldiethanolamine, 2-methylamino. There are ethanol, 2-isopropylaminoethanol, 2-dimethylaminoethanol (DMAE), 2-diethylaminoethanol, ethylenediamine and the like.

In particular, secondary amines such as methylethanolamine and diethylethanolamine have been widely used because of their high reaction rates. However, these compounds have problems that they are corrosive, easily deteriorated, and require high energy for regeneration. On the other hand, methyldiethanolamine has low corrosiveness and low energy required for regeneration, but has a drawback of low absorption rate. Therefore, the development of a new adsorbent that improves these points is required.

In recent years, among amine compounds, studies on alkanolamines having structural steric hindrance have been actively attempted as acid gas absorbers. In general, alkanolamines having steric hindrance have the advantages that the selectivity of acid gas is very high and the energy required for regeneration is low.

Further, the diamine compound having a specific structure has an advantage that it can react with carbon dioxide with a low reaction heat while having a higher absorption / release performance than a known carbon dioxide absorber.

The reaction rate of an amine compound with steric hindrance depends on the degree of reaction hindrance determined by its steric structure. The reaction rate of amine compounds having steric hindrance is lower than that of secondary amines such as methylethanolamine and diethanolamine, but higher than that of tertiary amines. Further, as the alkanolamine to be blended in the absorbent, 2-amino-2-methylpropanol, 2-piperidineethanol and the like are known.

On the other hand, a method of using a cyclic amine as an absorbent is also known as an amine compound having a structure different from that of alkanolamines.

Japanese Unexamined Patent Publication No. 2008-307519 Japanese Patent No. 5039276 Japanese Patent No. 2871334 Japanese Patent No. 5688335 U.S. Pat. No. 4112052

However, even with 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 acid gas absorbent having a large recovery amount of an acid gas such as carbon dioxide and a small recovery energy, and an acid gas removing device and an acid gas removing method using the same. be.

The acid gas absorbent of the embodiment contains at least one diamine compound represented by the following general formula (1).

R ¹ R ² N- (CR ³ R ⁴ ) _n -NR ⁵ R ⁶ formula (1)

[In the above formula (1), R ¹ , R ² , R ⁵ , and R ⁶ are substituted or unsubstituted branched alkyl groups having 3 to 6 carbon atoms, hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, and hydroxy. Represents one of the alkyl groups. However, at least one of R ¹ and R ² is a substituted or unsubstituted branched alkyl group having 3 to 6 carbon atoms, and at least one of R ⁵ and R ⁶ is a hydroxy alkyl group. R ³ and R ⁴ are any of a hydrogen atom, a methyl group, and an ethyl group. n is an integer from 1 to 6. ]

The acid gas removing method of the embodiment is to bring the gas containing the acid gas into contact with the acid gas adsorbent according to the above-described embodiment to remove the acid gas from the gas containing the acid gas.

The acid gas removing device of the embodiment has an absorption tower that removes the acid gas from the gas by bringing the gas containing the acid gas into contact with the acid gas adsorbent, and the acid gas from the acid gas adsorbent that has absorbed the acid gas. An acid gas removing device for reusing the acid gas adsorbent regenerated in the regenerating tower and the acid gas adsorbent regenerated in the regenerating tower, using the acid gas adsorbent according to the above-described embodiment. It will be.

According to the present invention, an acid gas absorber having a large recovery amount of acid gas such as carbon oxide and low recovery energy is provided, and an acid gas removing method and an acid gas removing device having improved acid gas recovery efficiency can be obtained. ..

FIG. 1 is a schematic view of an acid gas removing device according to an embodiment.

Hereinafter, embodiments will be described in detail.
The acid gas absorbent of the embodiment is characterized by containing at least one diamine compound represented by the following general formula (1).

R ¹ R ² N- (CR ³ R ⁴ ) _n -NR ⁵ R ⁶ formula (1)

[In the above formula (1), R ¹ , R ² , R ⁵ , and R ⁶ are substituted or unsubstituted branched alkyl groups having 3 to 6 carbon atoms, hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, and hydroxy. Represents one of the alkyl groups. However, at least one of R ¹ and R ² is a substituted or unsubstituted branched alkyl group having 3 to 6 carbon atoms, and at least one of R ⁵ and R ⁶ is a hydroxy alkyl group. R ³ and R ⁴ are any of a hydrogen atom, a methyl group, and an ethyl group. n is an integer from 1 to 6. ]

Conventionally, it has been known that the steric hindrance of an amino compound has a large effect on the product during carbon dioxide absorption and is advantageous for the production of bicarbonate ion showing a low heat of reaction.
For example, N-isopropylaminoethanol having a branched structure has been reported to exhibit low endothermic reaction to the endothermic reaction of carbon dioxide.

Based on such findings, as a result of examination by the inventor of the present application in order to further obtain the effect of steric hindrance, the compound represented by the above general formula (1) (for example, N-isopropyl-N'-(2-hydroxypropyl) ethylenediamine). However, it has been found that the amount of CO ₂ absorbed is larger and the heat of reaction is smaller than that of the conventional amino compound having a branched structure.

That is, in the diamine compound of the above general formula (1), a branched alkyl group (R ¹ ) having 3 to 6 carbon atoms is bonded to one of the two nitrogen atoms, and a branched alcohol group is bonded to the other nitrogen atom. Are combined.

As described above, the diamine compound of the above general formula (1) in which the branched alkyl group and the branched alcohol group are directly bonded to the respective nitrogen atoms has a structure having a large steric hindrance, and thus has a structure of carbon dioxide (CO ₂ ). It is considered that in the reaction, bicarbonate ions are generated and the heat of reaction is reduced, and at the same time, CO ₂ is easily released due to the presence of branched alcohol groups.

By dissolving the diamine compound represented by the above general formula (1) in a solvent such as water, an acid gas absorbent having a high acid gas absorbing ability can be obtained. In the following embodiment, the case where the acidic gas is carbon dioxide will be described as an example, but the acid gas absorbent according to the embodiment of the present invention can obtain the same effect on other acidic gases such as hydrogen sulfide. Can be done.

In the above formula (1), R ¹ , R ² , R ⁵ , and R ⁶ are substituted or unsubstituted branched alkyl groups having 3 to 6 carbon atoms, hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, and hydroxyalkyl. Represents one of the groups. However, at least one of R ¹ and R ² is a substituted or unsubstituted branched alkyl group having 3 to 6 carbon atoms, and at least one of R ⁵ and R ⁶ is a hydroxy alkyl group. R ³ and R ⁴ are any of a hydrogen atom, a methyl group, and an ethyl group. n is an integer from 1 to 6.

Examples of the substituted or unsubstituted branched alkyl group having 3 to 6 carbon atoms include an isopropyl group, a 2-butyl group, a t-butyl group, a 2-pentyl group, a 3-pentyl group, and a 2-methyl-2-pentyl group. , 3-Methyl-3-butyl group, 2-hexyl group, 3-hexyl group, 4-methyl-2-pentyl group, 2-methyl-2-pentyl group, 3-methyl-2-pentyl group and the like. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an n-butyl group and a sec-butyl group. From the viewpoint of the reactivity of the compound of the above formula (1) with carbon dioxide, a methyl group or an ethyl group is preferable among these alkyl groups, and a methyl group is more preferable.

Examples of the branched hydroxyalkyl group include a 2-hydroxypropyl group, a 3-hydroxypropyl group, a 2-hydroxybutyl group, a 3-hydroxybutyl group, and a 4-hydroxybutyl group. From the viewpoint of solubility, a 2-hydroxypropyl group is preferable as the branched hydroxyalkyl group.

R ³ and R ⁴ are any of a hydrogen atom, a methyl group, and an ethyl group. A methyl group is preferable as the alkyl group from the viewpoint of reactivity with carbon dioxide of the above formula (1).

Further, the alkyl groups of R ¹ to R ⁶ may contain heteroatoms such as Si, O, N and S.
In addition, n is preferably 2 to 6.

In addition, since the diamine compound of the above formula (1) is suppressed in volatility by having a branched structure, acid gas removal in which the amount of amine components released into the atmosphere is reduced in the process of treating the exhaust gas. Can be an agent. Among the above-mentioned branched structures, an isopropyl group is preferable from the viewpoint of solubility.

Preferred specific examples of the diamine compound (1) include, for example, the following.
N-isopropyl-N'-(2-hydrokipropyl) ethylenediamine,
N-isopropyl-N'-(2-hydroxypropyl) trimethylenediamine,
N-isopropyl-N'-(2-hydroxypropyl) tetramethylenediamine,
N-isopropyl-N'-(2-hydroxypropyl) pentamethylenediamine,
N-isopropyl-N'-(2-hydroxypropyl) hexamethylenediamine,
N-2-butyl-N'-(2-hydrokipropyl) ethylenediamine,
N-2-butyl-N'-(2-hydroxypropyl) trimethylenediamine,
N-2-butyl-N'-(2-hydroxypropyl) tetramethylenediamine,
N-2-butyl-N'-(2-hydroxypropyl) pentamethylenediamine,
N-2-butyl-N'-(2-hydroxypropyl) hexamethylenediamine,
N-isopropyl-N'-(2-hydrokibutyl) ethylenediamine,
N-isopropyl-N'-(2-hydroxybutyl) trimethylenediamine,
N-isopropyl-N'-(2-hydroxybutyl) tetramethylenediamine,
N-isopropyl-N'-(2-hydroxybutyl) pentamethylenediamine,
N-isopropyl-N'-(2-hydroxybutyl) hexamethylenediamine,
N-2-butyl-N'-(2-hydrokibutyl) ethylenediamine,
N-2-butyl-N'-(2-hydroxybutyl) trimethylenediamine,
N-2-butyl-N'-(2-hydroxybutyl) tetramethylenediamine,
N-2-butyl-N'-(2-hydroxybutyl) pentamethylenediamine,
N-2-butyl-N'-(2-hydroxybutyl) hexamethylenediamine,
And so on.

As the diamine 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 also be used. be.

The content of the diamine compound (1) contained in the acid gas adsorbent is preferably 10 to 55% by mass.
Generally, the higher the concentration of the amine component, the larger the amount of carbon dioxide absorbed and desorbed per unit capacity, and the faster the carbon dioxide absorption rate and desorption rate, so that the energy consumption and the size of the plant equipment are large. , It is preferable in terms of processing efficiency.

However, if the concentration of the amine component is too high, the drawbacks such as the fact that water as an activator for absorbing carbon dioxide does not function sufficiently and the viscosity of the absorbing liquid increases cannot be ignored. When the content of the diamine compound (1) is 55% by mass or less, no such deterioration in performance is observed. Further, by setting the content of the diamine compound (1) to 10% by mass or more, a sufficient absorption amount and absorption rate of carbon dioxide can be obtained, and excellent treatment efficiency can be obtained.

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

The diamine compound (1) is composed of alkanolamines and / or a heterocyclic amine compound represented by the following general formula (2) or (3) (hereinafter referred to as heterocyclic amine compound (2) (3)). It is preferable to use it by mixing it with a reaction accelerator.

[In equation (2),
R ⁷ represents a hydrogen atom, a hydroxyl group, and a hydroxyalkyl group having 1 to 8 carbon atoms.
R ⁸ independently represents a hydrogen atom, a hydroxyl group, a hydroxyalkyl group having 1 to 8 carbon atoms, or an aminoalkyl group.
At least one of R ⁷ and R ⁸ is a hydroxyalkyl group having 1 to 8 carbon atoms.
p is an integer of 2 to 4 independently of each other.
The cyclic skeleton in the formula (2) may contain oxygen as a member. ]
Examples of the hydroxyalkyl group include a hydroxyethyl group, a hydroxypropyl group, a hydroxypentyl group, a hydroxyhexyl group, a hydroxyheptyl group, and a hydroxyoctyl group, and among these, a hydroxyethyl group and a hydroxypropyl group are preferable.

p is an integer of 2 to 4 independently. Therefore, the compound of the general formula (2) contains a complex cyclic skeleton having 6 to 10 members.

The complex cyclic skeleton may further contain oxygen as a member.

The other specific cyclic secondary amine compound is represented by the following general formula (3).

[In equation (3),
R ⁹ independently represents a hydrogen atom, a hydroxyl group, and a hydroxyalkyl group having 1 to 8 carbon atoms.
At least one of R ⁹ is a hydroxyalkyl group having 1 to 8 carbon atoms.
q is an integer of 3 to 8 and
The cyclic skeleton in the formula (3) may contain oxygen as a member. ]
Examples of the hydroxyalkyl group include a hydroxyethyl group, a hydroxypropyl group, a hydroxypentyl group, a hydroxyhexyl group, a hydroxyheptyl group, and a hydroxyoctyl group, and among these, a hydroxyethyl group and a hydroxypropyl group are preferable.

q is an integer of 3 to 8. Therefore, the compound of the general formula (3) contains a complex cyclic skeleton having 4 to 9 members.
The complex cyclic skeleton may further contain oxygen as a member.

As an example of the cyclic secondary amine compound represented by the general formula (2) or (3),
2-Azetidine methanol, 2-pyrrolidin methanol, 2-piperidine methanol, 3-piperidine ethanol, 1- (2-hydroxyethyl) piperazine, 2- (hydroxymethyl) piperazine, 3-hydroxypyrrolidin, 3-pyrrolidin methanol, 2 -(2-Hydroxyethyl) pyrrolidine, 4-piperidineethanol, 3-hydroxypiperidine, 4-hydroxypiperidine, 4- (hydroxymethyl) piperidine, and the like can be mentioned.

Of these, it consists of 2-azetidine methanol, 2-pyrrolidin methanol, 4-hydroxypiperidine, 2-piperidine methanol, 3-piperidine ethanol, 1- (2-hydroxyethyl) piperazine, and 2- (hydroxymethyl) piperazine. Those selected from the group are preferred.
The cyclic amine compound represented by the general formula (2) and the cyclic amine compound represented by the general formula (3) can be used in combination.

In the present embodiment, for example, a diamine compound (1) and a reaction accelerator composed of an alkanolamine and / or a heterocyclic amine compound (2) or (3) are mixed, and a mixture thereof is used as, for example, an aqueous solution. , Can be used as an acid gas absorber.

By using the diamine compound (1) in combination with alkanolamines and / or the heterocyclic amine compound (2) or (3), the amount of carbon dioxide absorbed per unit mol of the diamine compound (1) and acidity can be obtained. The amount of carbon dioxide absorbed per unit volume of the gas absorber and the rate of carbon dioxide absorption can be further improved.

Further, by using the diamine compound (1) in combination with alkanolamines and / or the heterocyclic amine compound (2), the energy for separating acid gas after absorption of carbon dioxide (acid gas desorption energy) is also reduced. , The energy required to regenerate the acid gas absorber can be reduced.

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

Among these, as alkanolamines, 2- (isopropylamino) ethanol, 2- (ethylamino) ethanol and 2-amino-2-- from the viewpoint of further improving the reactivity between the tertiary amine and the acid gas. It is preferably at least one selected from the group consisting of methyl-1-propanol.
Among these, the piperazine derivative is particularly desirable from the viewpoint of improving the carbon dioxide absorption amount and absorption rate of the acid gas absorber.

The piperazine derivative is a secondary amine compound, and generally, the nitrogen atom of the secondary amino group binds to carbon dioxide to form a carbamate ion, which contributes to the improvement of the absorption rate in the initial stage of the reaction. Furthermore, the nitrogen atom of the secondary amino group plays a role of converting the carbon dioxide bonded to it into bicarbonate ion (HCO _3- ⁾ , which contributes to the speed improvement in the latter half of the reaction.

The piperazine derivative is more preferably 1- (2-hydroxyethyl) piperazine.

The content of the reaction accelerator (alkanolamines and / or heterocyclic amine compounds (2) (3)) contained in the acid gas adsorbent is preferably 5 to 50% by mass. If the content of the reaction accelerator contained in the acid gas adsorbent is less than 5% by mass, the effect of improving the carbon dioxide absorption rate may not be sufficiently obtained. If the content of the reaction accelerator contained in the acid gas adsorbent exceeds 50% by mass, the viscosity of the absorbent becomes excessively high, and the reactivity may rather decrease. The content of the reaction accelerator (alkanolamines and / or heterocyclic amine compounds (2) (3)) is more preferably 10 to 50% by mass.

Acid gas absorbers include, in addition to the above amine compounds and reaction accelerators, anticorrosive agents such as phosphoric acid to prevent corrosion of plant equipment, and antifoaming agents such as silicone to prevent foaming. , An antioxidant or the like for preventing deterioration of the acid gas absorber may be contained.

In the acid gas removing method according to the present embodiment, an acid gas-containing exhaust gas is brought into contact with an acid gas absorber obtained by dissolving the amine compound described in the above embodiment in a solvent, and the acid gas-containing exhaust gas is contained. It absorbs and separates acid gas from the gas and removes it.

The basic configuration of the carbon dioxide absorption and separation step is a step of contacting an acid gas absorber with an exhaust gas containing carbon dioxide to allow the acid gas absorber to absorb carbon dioxide (carbon dioxide absorption step). It includes a step (carbon dioxide separation step) of heating an acid gas absorber that has absorbed carbon dioxide and desorbing and recovering the carbon dioxide obtained in the carbon dioxide absorption step.

The method of contacting the gas containing carbon dioxide with the above-mentioned aqueous solution containing the acid gas absorber is not particularly limited. For example, a method of bubbling a gas containing carbon dioxide in an acid gas absorber to absorb carbon dioxide. A method of atomizing an acid gas absorber into a gas stream containing it (spray or spray method), or a gas containing carbon dioxide and an acid gas absorber in an absorption tower containing a filler made of porcelain or metal mesh. This can be done by a method of making countercurrent contact.

The temperature of the acid gas absorbent when absorbing a gas containing carbon dioxide into an aqueous solution is usually carried out at room temperature to 60 ° C. or lower. It is preferably performed at 50 ° C. or lower, more preferably about 20 to 45 ° C.

The lower the temperature, the more the amount of acid gas absorbed increases, but the lower limit of the treatment temperature is determined by the gas temperature on the process, the heat recovery target, and the like. The pressure at the time of carbon dioxide absorption is usually almost atmospheric pressure. Although it is possible to pressurize to a higher pressure in order to improve the absorption performance, it is preferable to perform the pressurization under atmospheric pressure in order to suppress the energy consumption required for compression.

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

As a method of separating carbon dioxide from the acid gas absorbent that has absorbed carbon dioxide and recovering pure or high-concentration carbon dioxide, the method of heating the acid gas absorbent and whipping it in a kettle to remove it is the same as distillation. , A method of heating by expanding the liquid interface in a shelf tower, a spray tower, and a regeneration tower containing a filler made of porcelain or metal mesh. As a result, carbon dioxide is liberated and released from the carbamic acid anion and bicarbonate ion.

The acid gas absorbent temperature at the time of carbon dioxide separation is usually 70 ° C. or higher, preferably 80 ° C. or higher, and more preferably 90 to 120 ° C. or higher. The higher the temperature, the higher the amount of absorption, but as the temperature rises, the energy required to heat the absorption liquid increases, so the temperature is determined by the gas temperature in the process, the heat recovery target, and the like. The pressure at the time of carbon dioxide desorption is usually almost atmospheric pressure. It is possible to reduce the pressure to a lower pressure in order to improve the desorption performance, but it is preferable to reduce the pressure under atmospheric pressure in order to reduce the energy consumption required for the decompression.

After separating the carbon dioxide, the acid gas absorbent is sent to the carbon dioxide absorption process again for recycling. Further, the heat generated during the absorption of carbon dioxide is generally cooled by heat exchange in a heat exchanger for the preheating of the aqueous solution injected into the regeneration tower in the process of recycling the aqueous solution.

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

Of the above-mentioned steps, the step of separating carbon dioxide from the acid gas absorbent and regenerating the acid gas absorbent is the part that consumes the largest amount of energy. Therefore, by reducing the energy consumption in the acid gas absorber regeneration step, the cost of the carbon dioxide absorption / separation step can be reduced, and the acid gas can be economically removed from the exhaust gas.

According to this embodiment, the energy required for carbon dioxide desorption (regeneration step) can be reduced by using the acid gas absorbent of the above embodiment. Therefore, the carbon dioxide absorption / separation step can be performed under economically advantageous conditions.

Further, the amine compound according to the above-described embodiment has significantly higher corrosion resistance to metal materials such as carbon steel as compared with alkanolamines such as 2-aminoethanol which have been conventionally used as acid gas absorbers. have. Therefore, by adopting such an acid gas removing method using an acid gas absorbent, for example, in plant construction, it is not necessary to use high-cost high-grade corrosion-resistant steel, which is advantageous in terms of cost.

The acid gas removing device according to the present embodiment is composed of an absorption tower that removes an acid gas from the gas by bringing the gas containing the acid gas into contact with the acid gas adsorbent and the acid gas adsorbent that has absorbed the acid gas. An acid gas removing device having a regeneration tower that removes and regenerates acid gas and reuses the acid gas adsorbent regenerated in the regeneration tower in the absorption tower, as the acid gas adsorbent. For example, the acid gas absorber according to the above embodiment is used.

FIG. 1 is a schematic view of an acid gas removing device according to an embodiment. The acid gas removing device 1 has an absorption tower 2 that brings a gas containing an acidic gas (hereinafter referred to as an exhaust gas) into contact with an acid gas adsorbent and absorbs and removes the acid gas from the exhaust gas, and an acidic gas. It is provided with a regeneration tower 3 that separates the acid gas from the acid gas adsorbent that has absorbed the gas and regenerates the acid gas adsorbent.

Hereinafter, the case where the acid 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 an 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 acid gas absorber supplied from the acid gas absorber supply port 5 at the upper part of the absorption tower 2. As the acid gas absorbent, the acid gas absorbent according to the above-described embodiment is used.

The pH value of the acid gas absorber may be adjusted to at least 9 or more, but the optimum conditions may be appropriately selected depending on the type, concentration, flow rate and the like of the harmful gas contained in the exhaust gas.

Further, in addition to the above-mentioned amine compound and a solvent such as water, the acid gas absorber may include any other compound such as a nitrogen-containing compound, an antioxidant, a pH adjuster, etc. that improve the absorption performance of carbon dioxide. It may be contained in the ratio of.

In this way, when the exhaust gas comes into contact with the acid gas absorber, the carbon dioxide in the exhaust gas is absorbed and removed by the acid gas absorber. The exhaust gas after the carbon dioxide is removed is discharged to the outside of the absorption tower 2 from the gas discharge port 6.

The acid gas absorber 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 acid gas absorber sent into the regeneration tower 3 moves from the upper part to the lower part of the regeneration tower 3, during which time carbon dioxide in the acid gas absorber is desorbed and the acid gas absorber is regenerated.

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

On the other hand, the carbon dioxide separated from the acid gas absorber comes into contact with the reflux water supplied from the reflux drum 11 at the upper part 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 condenser 12, and then separated from the condensed liquid component of water vapor accompanied by carbon dioxide in the reflux drum 11, and this liquid component is distilled by the recovered carbon dioxide line 13. Guided to the carbon recovery process. On the other hand, the recirculated water from which carbon dioxide is separated is sent to the regeneration tower 3 by the recirculation water pump 14.

According to the acid gas removing device 1 of the present embodiment, by using an acid gas absorbent having excellent carbon dioxide absorption characteristics and desorption characteristics, it is possible to efficiently absorb and remove carbon dioxide.

Although the embodiments of the present invention have been described above with reference to specific examples, the above-mentioned examples are given as an example of the present invention and do not limit the present invention.

Further, in the description of each of the above embodiments, the description of the parts which are not directly required in the description of the present invention in the acid gas absorber, the acid gas removing device and the acid gas removing method 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 removing devices, and acid gas removing methods that have the elements of the present invention and can be appropriately redesigned by those skilled in the art within the scope of the present invention are within the scope of the present invention. Be included. The scope of the invention is defined by the scope of claims and their equivalents.

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>
Dissolve N- (2-butyl) -N'-(2-hydroxypropyl) ethylenediamine in 30% by mass and 1- (2-hydroxyethyl) piperazine in 30% by mass, and add 50 ml of an aqueous solution (hereinafter referred to as "." , Shown as an absorbent solution.) This absorbent 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 aerated at a flow rate of 500 mL / min to the test tube. The carbon dioxide (CO ₂ ) concentration in the gas at the outlet was measured using an infrared gas concentration measuring device (manufactured by Shimadzu Corporation, trade name "CGT-700"), and the absorption performance was evaluated. A 1/8 inch Teflon (registered trademark) tube (inner diameter: 1.59 mm, outer diameter: 3.17 mm) was used for the gas introduction port to the amine aqueous solution in the test tube.

Further, as described above, the aqueous solution after absorbing the mixed gas at 40 ° C. is heated to 70 ° C., 100% nitrogen (N ₂ ) gas is aerated at a flow rate of 500 mL / min, and the CO ₂ concentration in the absorbing liquid is adjusted. The recovery performance was evaluated by measuring using an infrared gas concentration measuring device.
The recovered amount obtained from the difference between the carbon dioxide absorption amount of the absorption liquid at 40 ° C. and the carbon dioxide absorption amount of the absorption liquid at 70 ° C. was compared with Comparative Example 1. The heat of reaction was also compared relative to Comparative Example 1 in the same manner.

<Example 2>
Same as Example 1 except that N-isopropyl-N'-(2-hydroxypropyl) ethylenediamine was used instead of N- (2-butyl) -N'-(2-hydroxypropyl) ethylenediamine. An absorbent solution (aqueous solution) was prepared and evaluated using the same apparatus as in Example 1.

<Example 3>
An absorbent solution (aqueous solution) was prepared in the same manner as in Example 2 except that N- (2-aminoethyl) piperazine was used instead of N- (2-hydroxyethyl) piperazine, and the same as in Example 1. It was evaluated using the device of.

<Comparative Example 1>
Same as Example 1 except that N-methyl-N'-(2-hydroxyethyl) ethylenediamine was used instead of N- (2-butyl) -N'-(2-hydroxypropyl) ethylenediamine. An absorbent solution (aqueous solution) was prepared and evaluated using the same apparatus as in Example 1.

It was confirmed that in Examples 1 to 23, the amount of CO ₂ recovered was large and the heat of reaction was small as compared with the comparative examples.

According to the above-described embodiment, the recovery amount of acid gas such as carbon dioxide can be increased.

1 ... acid gas absorber, 2 ... absorption tower, 3 ... regeneration tower, 4 ... gas supply port, 5 ... acid gas absorber supply port, 6 ... gas discharge port, 7 ... heat exchanger, 8 ... heater, 9 ... pump, 10 ... acid gas cooler, 11 ... reflux drum, 12 ... reflux condenser, 13 ... recovered carbon dioxide line, 14 ... reflux water pump

Claims (9)

An acid gas absorbent comprising at least one diamine compound represented by the following general formula (1).

R ¹ R ² N- (CR ³ R ⁴ ) _n -NR ⁵ R ⁶ formula (1)

[In the above formula (1), R ¹ , R ² , R ⁵ , and R ⁶ are substituted or unsubstituted branched alkyl groups having 3 to 6 carbon atoms, hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, and hydroxy. Represents one of the alkyl groups. However, at least one of R ¹ and R ² is a substituted or unsubstituted branched alkyl group having 3 to 6 carbon atoms, and at least one of R ⁵ and R ⁶ is a hydroxy alkyl group. R ³ and R ⁴ are any of a hydrogen atom, a methyl group, and an ethyl group. n is an integer from 1 to 6. ] The acid gas absorbent according to claim 1, wherein in the diamine compound represented by the general formula (1), ^R4 is a 2-hydroxypropyl group. The acid gas adsorbent according to claim 1 or 2, wherein the content of the diamine compound represented by the general formula (1) is 10 to 50% by mass. The reaction comprises a diamine compound represented by the general formula (1) and a reaction accelerator composed of alkanolamines and / or a heterocyclic amine compound represented by the following general formulas (2) and (3). The acid gas absorber according to any one of claims 1 to 3, wherein the content of the accelerator is 5 to 50% by mass.

[In equation (2),
R ⁷ represents a hydrogen atom, a hydroxyl group, and a hydroxyalkyl group having 1 to 8 carbon atoms.
R ⁸ independently represents a hydrogen atom, a hydroxyl group, a hydroxyalkyl group having 1 to 8 carbon atoms, or an aminoalkyl group.
At least one of R ⁷ and R ⁸ is a hydroxyalkyl group having 1 to 8 carbon atoms.
p is an integer of 2 to 4 independently of each other.
The cyclic skeleton in the formula (2) may contain oxygen as a member. ]

[In equation (3),
R ⁹ independently represents a hydrogen atom, a hydroxyl group, a hydroxyalkyl group having 1 to 8 carbon atoms, or an aminoalkyl group.
At least one of R ⁹ is a hydroxyalkyl group having 1 to 8 carbon atoms.
q is an integer of 3 to 8 and
The cyclic skeleton in the formula (3) may contain oxygen as a member. ] The acid gas absorbent according to claim 4, wherein the heterocyclic amine compound comprises at least one selected from the group consisting of piperazines. The acid gas absorbent according to claim 5, wherein the piperazines are N- (2-hydroxyethyl) piperazine. The acid gas absorbent according to any one of claims 1 to 6, wherein R ¹ of the general formula (1) is an isopropyl group. An acid gas, which comprises contacting a gas containing an acid gas with the acid gas adsorbent according to any one of claims 1 to 7 to remove the acid gas from the gas containing the acid gas. Removal method. An absorption tower that removes acid gas from the gas by contacting a gas containing acid gas with an acid gas adsorbent, and a regeneration tower that removes acid gas from the acid gas adsorbent that has absorbed acid gas and regenerates it. The acid gas removing device for reusing the acid gas adsorbent regenerated in the regenerating tower in the absorbing tower, using the acid gas adsorbent according to any one of claims 1 to 8. An acid gas removing device characterized by being made of.

Images