JPH09875A - Absorption liquid of carbon dioxide and method for absorbing carbon dioxide in gas to be treated using the absorption liquid - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress oxidative deterioration of alkanolamine, which is a CO ₂ absorbent, by O ₂ in a gas to be treated. [Structure] A gas to be treated containing CO ₂ and O ₂ is brought into contact with an alkanolamine absorbing solution in an absorption tower to form a solution rich in CO ₂ , and then the solution is circulated in a regeneration tower to produce CO ₂ As a solution depleted in CO ₂ by heating
In order to reduce the oxidative deterioration of the absorption liquid of the CO ₂ absorption liquid recycled in the absorption tower, it is selected from mercaptoimidazoles represented by (A) and mercaptobenzimidazoles represented by (B). One or more organic sulfur compounds are added to the absorption liquid before use. Embedded image

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of carbon dioxide (CO ₂ ) which is said to cause global warming, and particularly suppresses the oxidation of an absorbent for treating CO ₂ contained in combustion furnace exhaust gas. It is about doing.

[0002]

_2. Description of the Related Art There is a concern about global warming due to an increase in CO ₂ concentration, and in consideration of future increase in energy demand, it is an urgent need to develop a CO ₂ removal / recovery technique. Various techniques for removing CO ₂ using alkanolamines are known (FC Riesenfeld and ALK
ohl: 'Gad Purification', 2nd ed. Gulf Publishing C
omp., Houston, Texas. (1974); G. Sartori, WSHo, D.
W.Savage, GRChludzinski, and S.Wiechert: 'Steric
ally-Hindered Amines for Acid-Gas Absorption ', Sep
arationand Purification Methods, 16 (2), pp171-200
(1987) and Japanese Examined Patent Publication No. 1-34092).

When oxygen (O ₂ ) is contained in addition to CO ₂ as in the combustion furnace exhaust gas, alkanolamine is oxidized by O ₂ . The degree of oxidation is the smallest for primary alkanolamines, and increases in the order of secondary and tertiary. In particular, in the case of an alkanolamine in which a hydrogen atom attached to a nitrogen atom is substituted with an alkyl group, oxidation proceeds as the number of alkyl groups increases. Also, when a hydrogen atom attached to a carbon atom is replaced with an alkyl group, the number of substituents increases to form secondary or tertiary carbon, and thus oxidation progresses (Ryohei Oda, "Oxidation", Chemical Industry Co., Ltd. (1963)). Therefore, CO ₂ and / or H ₂ under a reducing gas atmosphere
The use of alkanolamine, which is not a problem when used for the treatment of S, causes the problem of oxidation of the amine when CO ₂ is recovered from the combustion gas containing O ₂ gas.

When oxidation occurs with monoethanolamine (MEA), at least NH ₃ and oxalic acid are produced as shown in formula (1). H ₂ NCH ₂ CH ₂ OH + 2O ₂ → NH ₃ + (COOH) ₂ + H ₂ O (1) If the NH ₃ produced by the formula (1) is released to the atmosphere, it is environmentally unfavorable. In addition, the production of oxalic acid is not preferable because it causes deterioration of the absorbing solution and corrosion of structural materials.

On the other hand, in the gas to be treated, CO ₂ , O ₂
In addition to SO ₂ , it has been pointed out that the use of a secondary alkanolamine significantly suppresses the oxidation (Japanese Patent Application No. 6-233387). Also,
The addition of an oxidation inhibitor is also under consideration. For example, JP-A-5
According to 3-67686, organic acid metal salt, copper naphthenate, Cr / Mn, Cr / Co, Mn / Fe, Mn / C
2 to 20 wt% of u, Fe / Co and Co / Cu are added. Further, according to JP-A-5-277342, F
The addition of oxides of e, Co, Ni or organic acids is being studied. All of these use organic acids and metal compounds.

Further, inventions relating to the inhibition of corrosion of structural materials are disclosed in JP-A-53-119739 and JP-A-54-66349.
And JP-A-54-69586.

[0007]

When CO ₂ in a combustion furnace exhaust gas is treated with an alkanolamine, suppressing the oxidization of the alkanolamine by O _{2 in} the exhaust gas is an absorption due to deterioration of the liquid. It is important not only to reduce the amount of liquid replenishment, but also to use environmentally or inexpensive structural materials.

An object of the present invention is to prevent the alkanolamine, which is a CO ₂ absorbent, from being oxidized and deteriorated by O ₂ in the gas to be treated.

[0009]

The above object of the present invention is achieved by the following constitution. That is, a gas to be treated containing CO ₂ and O ₂ is brought into contact with an alkanolamine absorption liquid in an absorption tower to form a solution rich in CO ₂ , and then the solution is circulated in a regeneration tower to remove CO ₂ by heating discharged as a solution poor in CO _2, in order to reduce the oxidative degradation of the absorbent in the absorption liquid CO ₂ to be recycled into the absorption column, expressed mercapto imidazoles by structural formula (a), the structural formula An oxidation inhibitor characterized by using one or more organic sulfur compounds selected from mercaptobenzimidazoles represented by (B).

Embedded image Here, R ₁ , R ₂ and R ₃ are hydrogen atoms or C ₁ -C
_{3 is} an alkyl group, a phenyl group or a benzyl group, R ₄ is a hydrogen atom or a C _{1 to} C ₃ alkyl group, and n is an integer of 1 to 3.

The above object of the present invention is achieved by the following constitution. That is, a gas to be treated containing CO ₂ and O ₂ is brought into contact with an alkanolamine absorption liquid in an absorption tower to form a solution rich in CO ₂ , and then the solution is circulated in a regeneration tower to remove CO ₂ by heating discharged as a solution poor in CO _2, CO ₂ to be recycled into the absorption tower
In the absorbing liquid of No. 1, as an oxidation inhibitor for reducing the oxidative deterioration of the absorbing liquid, one or more organic sulfur compounds selected from the mercaptoimidazoles or mercaptobenzimidazoles described in the structural formula above are included. It is an absorption liquid of carbon dioxide characterized by the above.

The above object of the present invention can be achieved by the following constitution. That is, a gas to be treated containing CO ₂ and O ₂ is brought into contact with an alkanolamine absorption liquid in an absorption tower to form a solution rich in CO ₂ , and then the solution is circulated in a regeneration tower to remove CO ₂ by heating discharged as a solution poor in CO _2, CO ₂ to be recycled into the absorption tower
A method for absorbing CO ₂ in a gas to be treated using an absorbing solution, wherein as an oxidation inhibitor for reducing oxidative deterioration of the absorbing solution, among the mercaptoimidazoles or mercaptobenzimidazoles described in the structural formula above, A method for absorbing carbon dioxide in a gas to be treated, which comprises using one or more organic sulfur compounds.

It is desirable to use an absorbing solution containing 100 to 10,000 ppm of an organic sulfur compound based on the weight of the total volume of the absorbing solution. When the content of the organic sulfur compound in the absorption liquid is less than 100 ppm, the amount of decomposed amine is almost the same as that when the inhibitor is not added. Moreover, when it exceeded 10,000 ppm, the amount of decomposed amine did not change so much. Further, the content of the organic sulfur compound in the absorption liquid is preferably 1,000 to 5,000 ppm for the reason of effective dissolution suppression with the dissolution liquid of the compound.

The absorption liquid of the present invention is not particularly limited, but a low utility liquid is preferred. For example, N-methylethanolamine, N-ethylethanolamine,
N-isopropylethanolamine, N-methyl-2-
Methylethanolamine, N-methyl-2-ethylethanolamine, N-methyl-2-isopropylethanolamine, N-ethyl-2-methylethanolamine,
N-ethyl-2-ethylethanolamine, N-ethyl-2-isopropylethanolamine, monoethanolamine and 2-amino-2-methyl-1-propanol are preferably used.

As the mercaptoimidazoles of the organic acid sulfur compound, 2-mercaptoimidazole,
2-mercapto-1-methylimidazole, 2-mercapto-4-methylimidazole, 2-mercapto-5
Methylimidazole, 2-mercapto-1,4-dimethylimidazole, 2-mercapto-1,5-dimethylimidazole, 2-mercapto-1-phenylimidazole, 2-mercapto-4-phenylimidazole, 2-
Examples thereof include mercapto-1-benzylimidazole.

As the mercaptobenzimidazoles, 2-mercaptobenzimidazole, 4-methyl-2-mercaptobenzimidazole, 5-methyl-2.
-Mercaptobenzimidazole and the like.

According to the present invention, since the organic acid used in the prior art is not used, there is no corrosion of the structural material due to the addition of the oxidation inhibitor. In addition, since metal ions that are easily hydrolyzed are not used, there is no clogging in the liquid circulation line due to precipitation. Furthermore, the gas to be treated does not have to contain SO ₂ and is not limited to the gas to be treated.

[0017]

As the gas to be treated of the effects of the present invention method, in removing the CO ₂ from the combustion furnace exhaust gas containing other O ₂ in CO _2, for example in the case of using MEA as the alkanolamines, as described above formula ( According to 1), the absorbing solution is oxidized to produce NH ₃ and oxalic acid.

Although the detailed mechanism of the oxidation of the formula (1) has not been clarified yet, it is said to proceed radically. Therefore, the reaction mechanism of formula (1) was considered. First, the hydrogen atom attached to the second carbon counted from N is desorbed and a radical is generated as shown in formula (2). O ₂ reacts with this to form a peroxide as shown in formula (3).

Embedded image

Next, the hydrogen radical reacts with the peroxide of formula (3) to produce glycine as shown in formula (4). Further, the hydrogen atom of glycine is desorbed to generate a radical as shown in formula (5).

Embedded image

Further, this reacts with O ₂ to give formula (6), which reacts with hydrogen radicals to give ammonia and oxalic acid as shown in formula (7).

Embedded image

It is easily understood that the formula (1) is obtained from the formulas (2) to (7). Therefore, O _{2 in the} gas to be treated is
It can be seen that the absorption liquid is subject to oxidative deterioration.

On the other hand, the so-called secondary oxidation inhibitor having the structural formulas (A) and (B) is effective in preventing the deterioration due to the decomposition of peroxide generated by radical oxidation. Met.

On the other hand, a so-called radical scavenger composed of a phenolic compound or an amine compound was not effective in suppressing oxidation. Therefore, the deterioration prevention mechanism is considered as follows. However, peroxide is abbreviated as ROOH.

That is, the compounds having the structural formulas (A) and (B) and ROOH react with each other to form the formulas (8), (9),
Persulfoxides like (10) and (11) are generated to decompose ROOH (Nippon Kagaku ed., Chemistry of reactive oxygen species, Academic Publishing Center (1990)). This gives R
It is considered that the decomposition of OOH progresses and the generation of ammonia can be suppressed.

Embedded image

[0025]

An embodiment of the present invention will be described. FIG. 1 shows the flow of the CO ₂ absorption process of this example. After introducing the absorbing liquid from the liquid supply line 8, the gas to be treated containing O ₂ in addition to CO ₂ is a combustion furnace 1, a denitration device 2, a dust removing device 3 (a desulfurization device when SO ₂ is contained in the gas to be treated). 4 is required) and a gas gas heater (GGH) 5 to lead to a CO ₂ absorption facility from a blower 6 through a line 11 and a gas cooler 50. At this time, part of the exhaust gas is bypassed and the line 7
May be discharged from the stack 10. The gas to be treated comes into contact with the absorbing liquid flowing down from the top of the absorption tower 40 while being absorbed, and enters the water washing section 42 installed at the upper part of the tower. In the washing section 42, the cooler 48 is driven by the power of the pump 47.
By the cleaning water circulated and supplied from the water circulation line 51 through, the vapor mainly scattered from the absorption part is collected. Further, the mist is collected by the mist catcher 52, and the exhaust gas is guided to the gas outlet line 12 and discharged from the chimney 10 to the atmosphere.

In this embodiment, the water circulation line 51 is provided with a bypass line 80, and a part of the washing water is introduced to the line 80.
A detector 90 is provided for quantifying the decomposed amine and / or the alkanolamine in the absorption liquid. The cleaning liquid introduced into the bypass line 80 is decomposed amine and / or
Or line 8 after quantitative analysis of alkanolamine in the absorption liquid
Emitted from 1. Here, as the detector 90, a commercially available analyzer such as an ion chromatograph can be used.

The absorption liquid rich in CO ₂ (rich absorption liquid) that flows out from the absorption tower 40 is supplied from the liquid outlet line 13 to the absorption tower 4
Exit 0. Here, an additional inhibitor replenishment line 100
Is provided. The rich absorbing liquid exits the pump 70, is guided from the line 14 to the heat exchanger 53 and is heated, and then reaches the regeneration tower 41 via the line 15. Here, the rich absorbing liquid comes into contact with the heated steam rising in the regeneration tower 41 and CO
Release ₂ The released CO ₂ is recovered from the product line 17 through the tower top outlet line 16 of the regeneration tower 41, the condenser 54 and the gas-liquid separator 55.

The condensate is returned to the regeneration tower 41 by the pump 49 via the line 18. Part of the lean absorbent that released CO ₂ while flowing down the regeneration tower 41
It is guided from 9 to the reboiler 60, heated and becomes steam,
It is introduced into the regeneration tower 41 through the line 20. Also, most of the lean liquid passes through the bottom of the regeneration tower 41 to the line 21.
From the pump 71 to the heat exchanger 53, where
The rich absorbent is heat-exchanged and cooled, and the line 22
And is led to the amine cooler 56. Then the absorption tower 40
Recirculated to Part of the above-mentioned persulfoxide accumulated in the absorbing solution is transferred from the line 24 to the reclaimer 61 together with the absorbing solution. The aqueous alkanolamine solution is returned to the regeneration tower 41 through the line 25 by distillation, substantially using the alkanolamine and water as overhead products.

The residue containing persulfoxide in the reclaimer 61 can be removed from the discharge line 31. When the gas to be treated contains SO ₂ , an inorganic alkali such as sodium carbonate or potassium carbonate is added through the line 30 to remove it from the residue discharge line 31 as inorganic sulfate of sodium sulfate or potassium sulfate, respectively. be able to.

In the present embodiment, an alkanolamine aqueous solution containing an oxidation inhibitor is used and the concentration of decomposed amine in the water washing section 42 is controlled and operated. The addition of the oxidation inhibitor is carried out when the concentration of the decomposed amine exceeds a certain concentration. This is added from line 100 as a solid or dissolved in the absorbent.

As the gas to be treated according to the method of the present invention, CO ₂ is contained in an amount of about 5 to 16 vol%, and O ₂ is added in an amount of about ₃ to 1.
It contains 5 vol%. As the mercaptoimidazoles as the oxidation inhibitor added to the absorption liquid, one or more organic sulfur compounds selected from the above group are used. The concentration of the inhibitor is 100 to 10,000 based on the weight of the total volume of the absorbing solution.
ppm, preferably 1,000-5,000 ppm.

The absorbing liquid is not particularly limited, but it is selected from the above-mentioned alkanolamines and used.
Also, a mixture of the alkanolamines can be used. The concentration of the absorbing liquid is 30 to 60 wt%, preferably 40
Operate in the concentration range of up to 55 wt%.

The CO ₂ -containing gas is absorbed in the absorption tower 40 by bringing it into gas-liquid contact at 40 to 80 ° C. When the absorption temperature is as low as 40 ° C. or lower, a large amount of energy needs to be consumed. Also, if the temperature is higher than 80 ° C, C
O ₂ absorption decreases.

The absorption pressure may be atmospheric pressure or pressurization, and may be atmospheric pressure as long as the CO ₂ partial pressure is 0.05 atm or more.

The regeneration temperature is in the range of about 106 to 130 ° C., preferably 110 to 125 ° C., and the regeneration pressure for desorbing CO ₂ gas is in the range of atmospheric pressure to 1 kg / cm ² .

As described above, the gas to be treated containing CO ₂ and O ₂ is brought into contact with the alkanolamine absorbing solution to produce CO ₂
When removing and collecting, the mercaptoimidazoles,
It was found that the oxidation of the absorption liquid was effectively suppressed by using the absorption liquid containing one or more organic sulfur compounds selected from mercaptobenzimidazoles.

The invention is explained in greater detail by the examples below, without being restricted to the examples below.

Example 1 The oxidative decomposition and gas absorption / desorption characteristics of the absorbing liquid were examined by using the test apparatus shown in FIG. The equipment is absorption tower 101 and regeneration tower 1
The column diameter was φ50 mm, and the packed bed height was 1.4 m. Reflux condensers 103 and 10 at the top of the tower
4 were attached to each and cooling water having a constant temperature was circulated.

The experiment was conducted by raising the temperature of the absorption tower and the reflux condenser as shown in Table 1 in order to clarify the degree of the inhibitory effect of the decomposition amine by the oxidation inhibitor.

[Table 1]

A gas having a predetermined composition was supplied at a predetermined flow rate by CO ₂ , O ₂ and N ₂ gas. The supply gas was led to the absorption tower 101 through the humidifier 106 having a predetermined temperature. The gas comes into countercurrent contact with the absorbing liquid flowing down from the absorption tower 101 and is partially absorbed. Exhaust gas that is not absorbed is the reflux condenser 1
It is led from 03 to the analyzer or the exhaust gas line. CO
_The liquid rich in ₂ is adjusted in temperature from the bottom of the absorption tower 101 by the circulation pump 107 at a predetermined flow rate through the heat exchanger 109 by the preheater 110 and sent to the regeneration tower 102.

In the regeneration tower 102, the vapor heated by the heater 111 and the absorbing liquid come into contact with each other, so that CO
₂ is desorbed and the gas is discharged from the analyzer or CO ₂ product line. The absorption liquid from which most of the CO ₂ has been desorbed is sent from the bottom of the regeneration tower 102 to the heat exchanger 109 at a predetermined flow rate by the circulation pump 113, and further recirculated to the absorption tower 101 through the amine cooler 114. To be done.

In this example, N was used as the alkanolamine.
A substituted alkyl ethanolamine was used. As the alkyl group, one having methyl, ethyl and isopropyl was selected. 50 mol of the ethanolamine and 306 mo of water
and 10 g of 2-mercaptobenzimidazole as an oxidation inhibitor (concentration = 1,000 ppm) were charged into a 10 liter container to prepare a uniform solution. 7.5 liters of this aqueous solution was put into the kettle parts of the absorption tower 101 and the regeneration tower 102, respectively, and the pump was operated to fill the inside of the system. Next, N ₂ supply gas containing 13% CO ₂ and 16% O ₂ was used, and the ratio L / G of the liquid circulation amount (L) and the gas circulation amount (G) was set to 2.5 liters / Nm ^3. Gas absorption was performed.

It took about 3 hours until the CO ₂ removal rate was settled. Then, the exhaust gas emitted from the outlet of the absorption tower 101 is treated with a 0.05 mol / liter HCl aqueous solution of 200 m.
It was bubbled into an absorption bottle containing 1 for 1 hour.

The amount of aeration gas is 2 liter / m.
in. After aeration for 1 hour, methylamine, ethylamine and isopropylamine in the aqueous HCl solution were measured using an ion chromatograph. As a result, the amounts of methylamine, ethylamine and isopropylamine methylamine were 10, 40 and 160 mg / liter, respectively. In addition, 1 g of 2-mercaptobenzimidazole
If the inhibitor concentration is (100 ppm) or more and less than 10 g (1,000 ppm), the amount of the decomposed amine decreases as the inhibitor concentration increases.

Example 2 The same experiment as in Example 1 was carried out except that the concentration of the oxidation inhibitor was 5,000 ppm. The amounts of methylamine, ethylamine and isopropylamine were 2, 8 and 3, respectively.
It was 4 mg / liter, which was smaller than that of Example 1. It can be seen that the oxidation of the alkanolamine was further suppressed because the inhibitor concentration was increased by 5 times.

Example 3 The concentration of the oxidation inhibitor was 2,000, 3,000, 4,000.
An experiment similar to that in Example 1 was conducted except that the concentration was 0 ppm, and the inhibitor concentrations were 2,000, 3,000, and 4000 p.
In the case of pm, the amounts of methylamine, ethylamine and isopropylamine are 6, 24, 100 mg / l and 4, 16, 68 mg / l and 2.
The amount of decomposed amine decreased as the inhibitor concentration increased to 4, 9.6 and 40 mg / liter. Further, even when the inhibitor concentration was 10,000 ppm or more, there was not much change.

Comparative Example 1 The same experiment as in Example 2 was carried out except that 2-mercaptobenzimidazole was contained as an oxidation inhibitor in an amount of 0 to less than 100 ppm, and the amounts of methylamine, ethylamine and isopropylamine were the same. It was about 10 times more than the case containing. Further, as the N-substituted alkyl became larger, oxidative decomposition proceeded.

Example 4 The same experiment as in Example 2 was carried out except that 3,000 ppm of 2-mercapto-1-methylimidazole was added as an inhibitor in the experiment of Example 2, and methylamine, ethylamine and The amounts of isopropylamine were 4.5, 18 and 67 mg / liter, respectively.

Example 5 The same experiment as in Example 4 was conducted except that 5,000 ppm of 2-mercapto-4-phenylimidazole was added as an inhibitor in the experiment of Example 4, and methylamine, ethylamine and isopropyl were added. The amount of amine was 2, 8 and 34 mg / liter, respectively.

Example 6 In the experiment of Example 2, the same experiment as in Example 2 was conducted except that monoethanolamine was used as the absorbent and 5,000 ppm was used as the inhibitor concentration. It was 1 mg / liter.

Example 7 In the experiment of Example 6, as an inhibitor, 2-mercapto-1-methylimidazole, 2-mercapto-4-methylimidazole, 2-mercapto-5-phenylimidazole or 5-methyl-2- The same experiment as in Example 7 was conducted except that mercaptobenzimidazole was used, and the amounts of ammonia were 1, 1, 2 and 1 respectively.
mg / liter.

Comparative Example 2 When the same experiment as in Example 6 was conducted except that no inhibitor was used, the amount of ammonia was 9 times that in Example 6. From Example 6 and Comparative Example 2, it can be seen that the present oxidation inhibitor has the same effect not only on the secondary alkanolamine but also on the primary alkanolamine. In addition, SO ₂ coexisted with the primary alkanolamine, but this did not affect the oxidative deterioration.

Example 8 In the experiment of Example 2, methyldiethanolamine was used as the absorbent and the inhibitor concentration was 5,000 pp.
The same experiment as in Example 2 was carried out except that m was used, and the amount of methylamine was 2.5 mg / liter.

Example 9 As an absorbing liquid, CO ₂ and O ₂ as well as SO ₂ were added to the gas to be treated.
The same experiment as in Example 8 was carried out except that the amount of methylamine was 40 ppm, and the amount of methylamine was similar to that in Example 9.

Comparative Example 3 The same experiment as in Example 8 was carried out except that no inhibitor was used, and the amount of methylamine was 15 as compared with Example 8.
Doubled. From Example 8 and Comparative Example 3, it can be seen that the present oxidation inhibitor has a similar effect on the tertiary alkanolamine. Also, from Example 8 and Example 9, in the tertiary alkanolamine, SO ₂ may coexist, but there was no effect on oxidative deterioration.

Comparative Example 4 2,5-di-butyl-4-methylphenol, which is a phenolic antioxidant, was used in place of the oxidation inhibitor of the present invention.
When the same experiment as in Example 6 was conducted except that 000 ppm was added, the amount of ammonia was 20 mg / liter.

Comparative Example 5 In Example 6, the amine antioxidant dioctyldiphenylamine was replaced by 1,000 instead of the oxidation inhibitor of the present invention.
When an experiment similar to that of Example 6 was performed except that ppm was added, the amount of ammonia was 19.8 mg / liter.

Example 10 SS400 and SUS304L which are often used as structural steel in the kettle section of the absorption tower 101 and the regeneration tower 102 of Example 2.
And the corrosion rate was investigated. The corrosion rate in the absorption tower pot was 0.05 g / m ² h for SS400 and 0.
01 g / m ² h or less, and S in the kettle part of the regeneration tower 102
0.08 g / m ² h for S400, 0.0 for SUS304
It is advantageous since it is small as 1 g / m ² h or less and an inexpensive structural material can be used. An ethyl substitution product was used as the alkanolamine. As a result, the oxidation inhibitor had no effect on the corrosion of the structural material.

[0059]

According to the present invention, CO ₂ is treated from a feed gas containing CO ₂ and O ₂ by using a primary alkanolamine, a secondary alkanolamine, a tertiary alkanolamine and a mixed aqueous solution thereof. In this case, if an organic sulfur oxide is used as an oxidation inhibitor for reducing the oxidative deterioration of the absorption liquid, the oxidative deterioration of the alkanolamine can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a CO ₂ absorption process according to an embodiment of the present invention.

FIG. 2 is a diagram showing a CO ₂ absorber used in one example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Combustion furnace 2 Denitration apparatus 3 Dust removal apparatus 4 Desulfurization apparatus 5 GGH 6 Blower 30 Inorganic alkali addition line 31 Residue discharge line 40, 101 Absorption tower 41, 102
Regeneration tower 42 Water washing section 48 Cooler 51 Water circulation line 52 Mist catcher 53 Heat exchanger 54 Condenser 55 Gas-liquid separator 56 Amine cooler 60 Reboiler 61 Reclaimer 80 Bypass line 90 Detector 101 Inhibitor supply port 103, 104
Reflux condenser 106 Humidifier 109 Heat exchanger 110 Preheater 111 Heater 114 Amine cooler

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C09K 15/30 B01D 53/34 ZAB (72) Inventor Naomi Oda 6-9 Takaracho, Kure-shi, Hiroshima Babcock Hitachi Co., Ltd. Kure Factory (72) Inventor Yoshio Tanaka 1-5, Shintomi, Chuo-ku, Tokyo Toho Kagaku Kogyo Co., Ltd. (72) Norio Takahashi 1-1-5, Shintomi, Chuo-ku, Tokyo Toho Chemical Industry Co., Ltd.

Claims (5)

[Claims] 1. A gas to be treated containing carbon dioxide and oxygen is brought into contact with an alkanolamine absorbing solution in an absorption tower to form a solution rich in carbon dioxide, and then the solution is circulated in a regeneration tower to oxidize carbon dioxide. A mercaptoimidazole represented by the following structural formula (A), in order to reduce the oxidative deterioration of the absorption liquid of carbon dioxide which is recirculated into the absorption tower as a carbon dioxide-poor solution by releasing carbon by heating An oxidation inhibitor comprising one or more organic sulfur compounds selected from mercaptobenzimidazoles represented by the formula (B). Embedded image Here, R ₁ , R ₂ and R ₃ are hydrogen atoms or C ₁ -C
_{3 is} an alkyl group, a phenyl group or a benzyl group, R ₄ is a hydrogen atom or a C _{1 to} C ₃ alkyl group, and n is an integer of 1 to 3. 2. A gas to be treated containing carbon dioxide and oxygen is brought into contact with an alkanolamine absorbing solution in an absorption tower to obtain a solution rich in carbon dioxide, and then the solution is circulated in a regeneration tower to oxidize carbon dioxide. As a carbon dioxide-poor solution that releases carbon by heating and is recirculated in the absorption tower, in an absorption liquid of carbon dioxide, as an oxidation inhibitor for reducing oxidative deterioration of the absorption liquid,
A carbon dioxide absorbing solution comprising one or more organic sulfur compounds selected from the mercaptoimidazoles or mercaptobenzimidazoles according to claim 1. 3. An organic sulfur compound in an amount of 100 to 10,000 ppm, preferably 1.00, based on the weight of the total volume.
The carbon dioxide absorbent according to claim 2, wherein the carbon dioxide absorbent is contained in an amount of 0 to 5,000 ppm. 4. A gas to be treated containing carbon dioxide and oxygen is brought into contact with an alkanolamine absorption liquid in an absorption tower to form a solution rich in carbon dioxide, and then the solution is circulated in a regeneration tower to oxidize carbon dioxide. A method for absorbing carbon dioxide in a gas to be treated, which uses a carbon dioxide absorbent to be recirculated in the absorption tower as a carbon dioxide-poor solution by heating and releasing carbon, in order to reduce oxidative deterioration of the absorbent. Carbon dioxide absorption in a gas to be treated, characterized in that, as the oxidation inhibitor, the one or more organic sulfur compounds selected from the mercaptoimidazoles and mercaptobenzimidazoles according to claim 1 are used. Method. 5. An absorption liquid containing an organic sulfur compound in an amount of 100 to 10,000 ppm, preferably 1,000 to 5,000 ppm, based on the total weight of the absorption liquid is used. A method for absorbing carbon dioxide in the treated gas.