JPH08252430A - Removal of carbon dioxide contained in combustion exhaust gas - Google Patents

Abstract

PURPOSE: To make it possible to accelerate an absorption rate and enhance an absorption efficiency by using an aqueous amine mixed solution containing a secondary amine and a tertiary amine respectively falling within specific ranges of their concentrations, in a system in which the aqueous amine solution comes into contact with an exhaust gas. CONSTITUTION: A combustion exhaust gas compressed into a carbon dioxide removing tower 1 is caused to come into a counter-current contact with an absorption liquid of a specified concentration supplied from a nozzle 7, in a lower packed part 2. The CO2 contained in the combustion exhaust gas is absorbed and removed by the absorption liquid, and the CO2 -free combustion exhaust gas ascends to an upper packed part 3. Since the absorption liquid used is an aqueous amine mixed liquid of a secondary amine and a tertiary amine each falling within a range of concentration of 10 to 45wt.%, the absorption liquid supplied to the carbon dioxide removing tower 1 after absorbing the CO2 has a higher temperature than that at an absorption liquid supply aperture 6 due to a reaction heat caused by the absorption of CO2 . Further, the absorption liquid is sent to a heat exchanger 14 by a discharge pump 13 of the absorption liquid which has absorbed the CO2 , then is heated and guided to an absorption liquid regeneration tower 5. The temperature of the regenerated absorption liquid is adjusted by a cooler 27 installed on the heat exchanger 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing CO ₂ (carbon dioxide) contained in flue gas, and more specifically, it uses an aqueous solution of a secondary amine and a tertiary amine at atmospheric pressure. The present invention relates to a method for efficiently removing CO ₂ in the lower combustion exhaust gas.

[0002]

2. Description of the Related Art In recent years, the greenhouse effect of CO ₂ has been pointed out as one of the causes of the global warming phenomenon, and countermeasures against it have become urgent internationally in order to protect the global environment. CO ₂
As the source of the emission of carbon dioxide, it extends to all human activity fields that burn fossil fuels, and there is a tendency that the demand for emission control thereof becomes even stronger. Along with this, for a power generation facility such as a thermal power plant that uses a large amount of fossil fuel, a method of contacting the combustion exhaust gas of a boiler with an alkanolamine aqueous solution or the like to remove CO ₂ from the combustion exhaust gas, and collecting A method of storing recovered CO ₂ without releasing it to the atmosphere has been vigorously studied.

Examples of the alkanolamine include monoethanolamine, triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine and diglycolamine.
Usually monoethanolamine (MEA) is preferably used. In addition, the use of other secondary and tertiary hindered amine aqueous solutions is also being considered.

By the way, there are many known techniques for separating an acidic gas from various mixed gases using an amine compound. JP-A-53-100180 discloses (1) at least one secondary amino group or tertiary carbon atom which is part of a ring and is bonded to either a secondary carbon atom or a tertiary carbon atom. An amine mixture comprising at least 50 mol% sterically hindered amine containing bound primary amino groups and at least about 10 mol% tertiary amino alcohol, and (2) said amine being a physical absorbent for acid gases. A process for the removal of acid gases is described, which comprises contacting the amine-solvent liquid absorbent, which comprises a solvent for the mixture, with a normally gaseous mixture. The sterically hindered amine may be 2-piperidine ethanol [2- (2-hydroxyethyl) -piperidine] and 3-amino-3-methyl-1-butanol, and the solvent may contain up to 25% by weight of water. As an example of a processing gas, a sulfoxide compound or the like is further described in the upper left column on page 11 of the same publication, "Regular gaseous form having high concentration of carbon dioxide and hydrogen sulfide, for example, 35% CO ₂ and 10 to 12% H ₂ S." A mixture of) and CO ₂ itself is used in the examples.

JP-A-61-71819 describes a composition for acidic gas scraping containing a sterically hindered amine and a non-aqueous solvent such as sulfolane. Further, this publication describes the advantage of sterically hindered amines with respect to CO ₂ absorption by using a reaction formula.

Chemical Engineering Science (C
chemical engineering science
ce), Vol. 41, No. 2, pp. 997-1003, the carbon dioxide absorption behavior of an aqueous solution of 2-amino-2-methyl-1-propanol (AMP) which is a hindered amine is disclosed. As the gas to be absorbed, CO _{2 at} atmospheric pressure and a mixture of CO ₂ and N ₂ are used.

Chemical Engineering Science (C
chemical engineering sien
ce), Vol. 41, No. 4, pp. 997-1003, the carbon dioxide absorption behavior of an aqueous solution of 2-amino-2-methyl-1-propanol (AMP) which is a hindered amine is disclosed. As the gas to be absorbed, CO _{2 at} atmospheric pressure and a mixture of CO ₂ and nitrogen are used.

Chemical Engineering Science (C
chemical engineering sien
ce), Vol. 41, No. 2, p. 405-408, hindered amines such as AMP and MEA at around room temperature.
Absorption rates of CO ₂ and H ₂ S from various aqueous solutions of such linear amines have been reported.

US Pat. No. 3,622,267 uses an aqueous mixture containing methyldiethanolamine and monoethylmonoethanolamine to produce a high partial pressure of CO ₂ contained in a synthesis gas such as a partial oxidizing gas such as crude oil. , For example, a technique for purifying a syngas containing 30% CO _{2 at} 40 atm is disclosed.

German Laid-Open Patent 1,542,415 discloses a technique for adding a monoalkylalkanolamine or the like to a physical or chemical absorbent in order to improve the absorption rate of CO ₂ , H ₂ S and COS. . Similarly, German Published Patent 1,904,428 discloses a technique in which monomethylethanolamine is added for the purpose of improving the absorption rate of methyldiethanolamine.

In US Pat. No. 4,336,233, 0.81 to 1.3 mol / liter aqueous solution of piperazine is used as a cleaning liquid for the purification of natural gas, synthetic gas and gasified coal gas, and piperazine is methyl. A technique is disclosed in which an aqueous solution is used as a cleaning liquid together with a solvent such as diethanolamine, triethanolamine, diethanolamine, and monomethylethanolamine.

Similarly, Japanese Unexamined Patent Publication (Kokai) No. 52-63171 discloses a CO ₂ absorbent obtained by adding a piperazine or a piperazine derivative such as hydroxyethylpiperazine to a tertiary alkanolamine or monoalkylalkanolamine as an accelerator. ing.

[0013]

The above-mentioned alkanolamine aqueous solution represented by MEA, or the aqueous solution of the hindered amines or the mixture of amines described in the above-mentioned publicly known documents is used as a liquid absorbing CO _{2 in} combustion exhaust gas. even, CO ₂ absorption quantity per unit amine molar in the amine aqueous solution, the absorption rate of CO ₂ at a given concentration, more in light like the heat energy required for the regeneration of the alkanolamine solution after the absorption, not necessarily be satisfactory Absent. In general, secondary hindered amines and tertiary hindered amines are superior to MEA in terms of CO ₂ absorption amount and thermal energy of regeneration, but it is necessary to further improve the absorption rate, and absorption for improving absorption efficiency is required. There are major problems to be solved, such as an increase in CO ₂ absorption amount per unit mole of the agent and an increase in CO ₂ absorption amount per unit volume of the aqueous solution due to high concentration of the amine aqueous solution. Furthermore, after absorbing CO _2, an absorbent having less heat energy required for separating CO ₂ and regenerating the absorbing liquid is desired.

[0014]

In view of the above-mentioned problems, the inventors of the present invention have made earnest studies on an absorbing liquid used for removing CO _{2 in} combustion exhaust gas, and as a result, secondary amine and tertiary amine have been obtained.
The present invention has been completed by finding that it is particularly effective to use a mixed aqueous solution of a primary amine having a predetermined concentration or more. That is, according to the present invention, the flue gas under atmospheric pressure and the amine aqueous solution are brought into contact with each other to reduce CO in the flue gas.
_In the method of removing ₂ , as the amine aqueous solution,
The concentration of each of the secondary amine and the tertiary amine is 10
A method for removing CO ₂ in flue gas is provided, which comprises using an amine mixed aqueous solution in the range of ˜45 wt%. According to the present invention, the concentration of the tertiary amine in the amine-mixed aqueous solution is the maximum CO ₂ absorption amount per unit volume of the aqueous solution when a single aqueous solution of the tertiary amine is used under the same absorption conditions. comprising tertiary CO ₂ of the combustion exhaust gas is in the range of about 10 wt% of the concentration of the amine
There is provided a method of removing. Further, according to the present invention, there is provided a method for removing CO _{2 in} combustion exhaust gas in which the total concentration of amines in the amine mixed aqueous solution is 70% by weight or less. Further, according to the present invention, as the amine aqueous solution,
Selected from the group of 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, 2-n-butylaminoethanol, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine and 2-piperidinoethanol. Secondary amine, and 2-dimethylaminoethanol, 2-diethylaminoethanol, 3-dimethylamino-1-propanol, 4-dimethylamino-1-butanol, 2-dimethylamino-
A method for removing CO _{2 in} combustion exhaust gas using a mixed aqueous solution of a tertiary amine selected from the group of 2-methyl-1-propanol and N-ethyl-N-methylethanolamine is provided. Further, according to the present invention, there is provided a method for removing CO _{2 in} combustion exhaust gas in which both the secondary amine and the tertiary amine have one alcoholic hydroxyl group. Further, according to the present invention, as the amine aqueous solution, 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, 2
A secondary amine selected from the group of -n-butylaminoethanol, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine and 2-piperidinoethanol, and N-methyldiethanolamine, N-ethyldiethanolamine, N- t-Butyldiethanolamine and N
CO _{2 in} flue gas using a mixed aqueous solution of a tertiary amine selected from the group of methyldiisopropanolamine
There is provided a method of removing. Furthermore, according to the present invention, 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, 2-n
- a method for removing CO ₂ in the combustion exhaust gas using the secondary amine selected from butyl aminoethanol is provided.

[0015]

In the present invention, an aqueous solution obtained by mixing the secondary amine and the tertiary amine in the range of 10 to 45% by weight is used as the absorbing liquid. The tertiary amine has a large CO ₂ absorption amount per unit mole but a low absorption rate, but the absorption rate is promoted by using the secondary amine together, and there is a great advantage in terms of the absorption rate as compared with the case where each of them is used alone. There is.

The absorption of CO ₂ is usually carried out by gas-liquid countercurrent contact in the absorption tower, and CO ₂ is separated and the absorption liquid is regenerated by steam stripping in the regeneration tower.
At that time, the saturated absorption amount (X axis) of CO ₂ per unit mole of amine in the absorbing liquid at a constant temperature and CO _{2 in} gas
The relationship with the partial pressure (Y axis), that is, the equilibrium curve is obtained for each amine under both the absorption tower and regeneration tower temperature / CO ₂ partial pressure conditions. If the line can be set parallel to the equilibrium curve,
This is advantageous because it is easy to set the theoretical number of absorption stages. The equilibrium curve of the tertiary amine has a smaller slope than that of the secondary amine, and therefore has a larger absorption capacity, but is more disadvantageous than the secondary amine in relation to the operating line. However, by mixing both amines, the equilibrium curve of the mixed amine aqueous solution moves between the secondary amine and the tertiary amine, which is advantageous in that the absorption operation condition can be easily set.

Further, according to the findings of the present inventors, C in a gas having a small partial pressure of CO ₂ such as combustion exhaust gas.
At the time of absorbing O ₂ , in the tertiary amine aqueous solution, when the concentration of the tertiary amine in the aqueous solution is increased, there is a concentration at which the CO ₂ absorption amount becomes maximum (maximum CO ₂ absorption concentration),
If it exceeds that, the amount of absorption decreases. The amine concentration at that time is about 30% by weight, though it depends on the kind of amine.
It is a degree. In contrast, with secondary amines, the CO ₂ absorption increases as the concentration increases. Regarding the concentration of the absorption liquid, there is an upper limit naturally in terms of viscosity increase, gas-liquid contact property, fluidity, etc. Therefore, the concentration of the tertiary amine should be the maximum CO
₂ Set the absorption concentration to around, add secondary amine within the range up to the above upper limit, and increase the concentration by mixing both amines to maximize the absorption capacity of both There is an advantage that you can.

The secondary amine and tertiary amine used as the CO ₂ absorbent in the present invention may or may not have an alcoholic hydroxyl group in the molecule. . Both of them may be acyclic or cyclic, but the tertiary amine is preferably acyclic.

Preferred secondary amines in the present invention are 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol and 2-methylaminoethanol.
Acyclic amines such as n-butylaminoethanol, also piperazine, 2-methylpiperazine (MP), 2,5-
Illustrative are cyclic amines such as dimethylpiperazine and 2-piperidinoethanol. The secondary amines may be used alone or in combination of two or more.

Further, as a preferred tertiary amine, 2-
Dimethylaminoethanol, 2-diethylaminoethanol, 3-dimethylamino-1-propanol, 4-
Examples thereof include one having one alcoholic hydroxyl group such as dimethylamino-1-butanol, 2-dimethylamino-2-methyl-1-propanol and N-ethyl-N-methylethanolamine. Further, examples having two alcoholic hydroxyl groups include N-methyldiethanolamine, N-ethyldiethanolamine, Nt-butyldiethanolamine and N-methyldiisopropanolamine. When using those having two alcoholic hydroxyl groups, it is preferable to increase the concentration of the secondary amine of the partner to, for example, 15% by weight or more, and further to use it by increasing it to 30% by weight or more. preferable. The tertiary amines may be used alone or in combination of two or more.

The concentration of the mixed aqueous solution of the secondary amine and the tertiary amine (hereinafter, also referred to as absorbing solution) used for contacting with the combustion exhaust gas of the present invention is 10 to 45 for each amine.
It is in the range of% by weight. Particularly, the concentration of the tertiary amine is preferably in the range of 10% by weight before and after the maximum CO ₂ absorption concentration of the tertiary amine, and more preferably in the range of 5% by weight before and after the maximum CO ₂ absorption concentration. Therefore, the preferable concentration range of the tertiary amine is about 20 to 40% by weight.
On the other hand, as described above, since the secondary amine usually has a higher saturated absorption amount as the concentration increases, the higher concentration is preferable, but the total concentration with the tertiary amine is 70% by weight.
The following is preferable from the viewpoint of gas-liquid contactability and fluidity. Particularly, as a preferable concentration range of the secondary amine,
It is about 15 to 20% by weight. In the present invention, the temperature of the absorbing liquid at the time of contact with the combustion exhaust gas is usually in the range of 30 to 70 ° C. In addition, a corrosion inhibitor, a deterioration inhibitor, etc. may be added to the absorbent used in the present invention, if necessary.

Further, the term "atmospheric pressure" in the present invention includes a pressure range in the vicinity of atmospheric pressure to the extent that a blower or the like acts to supply combustion exhaust gas.

The process that can be used in the method of removing CO ₂ in the combustion exhaust gas of the present invention is not particularly limited, but an example thereof will be described with reference to FIG. In FIG. 1, only the main equipment is shown and the auxiliary equipment is omitted. In FIG. 1, 1 is a CO ₂ removal tower, 2 is a lower packing part, 3 is an upper packing part or tray, 4 is a CO ₂ removal tower combustion exhaust gas supply port, 5 is CO ₂ removal
Combustion exhaust gas discharge port, 6 absorption liquid supply port, 7 nozzle, 8
Is a combustion exhaust gas cooler provided as necessary, 9 is a nozzle, 10 is a filling part, 11 is a humidification cooling water circulation pump, 12
Is a makeup water supply line, 13 is an absorption liquid discharge pump that has absorbed CO ₂ , 14 is a heat exchanger, and 15 is absorption liquid regeneration (hereinafter,
"Regeneration" is also abbreviated) tower, 16 is a nozzle, 17 is a lower filling section, 18 is a regenerative heater (reboiler), 19 is an upper filling section, 20 is a reflux water pump, 21 is a CO ₂ separator, 22 is CO recovery. ₂ discharge lines, 23 is a regenerator reflux condenser, 24
Is a nozzle, 25 is a regeneration tower recirculation water supply line, 26 is a combustion exhaust gas supply blower, 27 is a cooler, and 28 is a regeneration tower recirculation water supply port.

In FIG. 1, the combustion exhaust gas is pushed into the combustion exhaust gas cooler 8 by the combustion exhaust gas supply blower 26,
The humidified cooling water from the nozzle 9 comes into contact with the filling section 10, is humidified and cooled, and is decarbonized through the CO ₂ tower combustion exhaust gas supply port 4.
It is led to the O ₂ tower 1. The humidified cooling water that has come into contact with the combustion exhaust gas collects in the lower part of the combustion exhaust gas cooler 8 and is circulated to the nozzle 9 by the pump 11. Since the humidified cooling water is gradually lost by humidifying and cooling the combustion exhaust gas, it is replenished by the makeup water supply line 12. When the combustion exhaust gas is further cooled from the humidified cooling state, a heat exchanger is placed between the humidification cooling circulation pump 11 and the nozzle 9 to cool the humidified cooling water and supply it to the combustion exhaust gas cooler 8. It will be possible.

The combustion exhaust gas pushed into the CO ₂ removal tower 1 is brought into countercurrent contact with the absorbing liquid having a constant concentration supplied from the nozzle 7 in the lower filling section 2, and CO ₂ in the combustion exhaust gas is absorbed and removed by the absorbing liquid. Then, the de-CO ₂ combustion exhaust gas goes to the upper filling section 3. The absorption liquid supplied to the CO ₂ removal tower 1 is CO
₂ is absorbed, and due to the heat of reaction due to the absorption, the temperature is usually higher than the temperature at the absorption liquid supply port 6, and is sent to the heat exchanger 14 by the absorption liquid discharge pump 13 that has absorbed CO ₂ and is heated. Guided to the regeneration tower 5. The temperature of the regenerated absorption liquid is adjusted by the heat exchanger 14 or, if necessary, the cooler 2 provided between the heat exchanger 14 and the absorption liquid supply port 6.
7 can be performed.

In the regeneration tower 15, heating by the regeneration heater 18 is applied.
The absorption liquid is regenerated in the lower filling part 17 by heat,
14 and optionally C by being cooled by the cooler 27.
O₂Returned to Tower 1. Smell above the absorption liquid regeneration tower 15
CO separated from the absorption liquid ₂Is supplied from the nozzle 24
It comes into contact with the reflux water that is generated and is cooled by the regeneration tower reflux condenser 23.
Rejected, CO₂CO in the separator 21₂Water vapor
Is separated from the condensed reflux water, and the recovered CO₂Discharge line 2
CO from 2₂Guided to the recovery process. Part of reflux water is reflux
The water pump 20 recirculates to the regeneration tower 15, part of which is the regeneration tower.
CO removal via the reflux water supply line 25₂Recycle tower recycle tower 1
It is supplied to the water supply port 28. This regeneration tower reflux water has a trace amount
Since it contains the absorption liquid of₂Top filling of tower 1
Trace amount of CO contained in the exhaust gas coming into contact with the exhaust gas in Part 3
₂Contribute to the removal of.

[0027]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Reference Examples 1 to 3] 50 ml of a tertiary amine aqueous solution having different concentrations as shown in Table 1 was put into a glass reaction container installed in a constant temperature bath as an absorbing liquid. While stirring at a temperature of 40 ° C., the test gas was stirred at atmospheric pressure at a flow rate of 1 liter / min.
The absorbent was passed through a filter to facilitate the formation of bubbles. As a test gas, a model combustion exhaust gas at 40 ° C. having a composition of CO ₂ 10 mol%, O ₂ 3 mol%, and N ₂ 87 mol% was used. Continue to pass the test gas, and when the CO ₂ concentrations of the inflow and outflow gases become equal, C contained in the absorbing liquid
O ₂ was measured using a CO ₂ analyzer (total organic carbon meter),
Saturation absorption of ^{_{CO 2 (Nm 3 CO 2 /}} m 3 absorbent solution, mol CO ₂ / amine molar absorbent) was determined. The results are shown in Table 1.
Shown in

[0028]

[Table 1]

As it is apparent from the results in Table 1, the CO ₂ absorbing ability of the tertiary amine per se for use in the present invention are all seen that there is a maximum CO ₂ absorption density before and after concentration of 30 wt%.

Reference Examples 4 to 18 By the same operation as in Reference Example 1, the secondary amine and the tertiary amine shown in Table 2 were subjected to a CO ₂ absorption test at a concentration of 30% by weight. The results are shown in Table 2.

[0031]

[Table 2]

[Examples 1 to 5 and Comparative Examples 1 to 4] In order to confirm the effect of the method for removing CO ₂ in the combustion exhaust gas according to the present invention, a small test apparatus schematically shown in FIG. 2 was used. Figure 2
In the test gas 201, the height is 1500 mm and the inner diameter is 5
Absorption tower 2 made of stainless steel with 0 mm and a filling height of 1000 mm
It is introduced into the lower part of 02 at a flow rate of 0.98 Nm ³ / h.
The composition of the test gas is 10% CO ₂ , 87% N ₂ , 3% O ₂ .
It has been adjusted to. A nozzle 203 is provided above the absorption tower 202 to spray the regenerated and circulated absorption liquid. A Dickson packing having a length of 6 mm is filled in the filling unit 204 provided in the central portion of the absorption tower, and a hot water jacket 205 is provided around the Dickson packing, so that the absorption temperature is 60 ° C.
Hot water circulation pump 206 and hot water tank 207
It has. Further, an absorption tower condenser 208 is installed above the absorption tower 202, and after the absorption processing gas is cooled here, it is analyzed by the absorption processing gas analyzer 209 and discharged. An absorption liquid extraction pump 210 is provided below the absorption tower, and the absorption liquid is preheated by a preheater 211 to a temperature of 11
After being controlled at 0 ° C., it is introduced to the upper part of the regeneration tower 212.
The regeneration tower 212 is made of stainless steel and has a height of 1500 mm, an inner diameter of 25 mm, and a filling height of 160 mm at the central portion, and is filled with the same packing as that of the absorption tower. In addition, a warm water jacket 213 for keeping the temperature constant is provided in the filling section as in the absorption tower.
It has. The CO ₂ rich absorption liquid that has flowed down from the upper part of the refilling tower 212 is the reboiler heater (electric heat) in the lower part.
It is heated by 214 (the reboiler temperature is controlled at 110 ° C.) and stripped by the steam to become a lean absorbent, which is a regenerated absorbent cooler 215, a regenerated absorbent extraction pump 216, a regenerated absorbent tank 217, and a regenerated absorbent. It is circulated and used at a flow rate of 2.8 l / h above the absorption tower via the liquid circulation pump 218 and the regenerated absorption liquid preheater 219. A part of the lean absorbent is recirculated to the inlet of the regeneration tower by the regeneration absorbent circulating pump 220. A regeneration tower condenser 221 is provided above the regeneration tower, and CO ₂ liberated from the absorbing liquid is condensed and separated by the condenser 221 and then an infrared CO ₂ gas meter (not shown) (Horiba Seisakusho V
Regeneration tower gas scrubber 22 analyzed by IA 510)
It is discharged via 2.

An absorption / regeneration test was conducted by using the above-mentioned small-sized test apparatus and the absorption / regeneration conditions under the absorption / regeneration conditions, and the inlet gas (test gas) and the outlet gas (absorption) of the absorption tower shown in Table 3 were measured. CO ₂ concentration in treated gas), heat input of reboiler (shown in kW), CO ₂ concentration in rich absorbent and lean absorbent (“Total Organic Carbon Meter” TOC-manufactured by Shimadzu Corporation)
(According to 5000), the amount of heat for regeneration was determined. The results are shown in Table 3.

[0034]

[Table 3]

As can be seen from Table 3, the second according to the invention
It can be seen that the use of a mixed absorbing solution of a primary amine and a tertiary amine is significantly advantageous in terms of absorption capacity and regeneration energy.

[0036]

As described in detail above, by treating the combustion exhaust gas under atmospheric pressure by the method of the present invention, it is possible to comprehensively absorb CO ₂ as compared with the case of using the amine absorbing liquid which has been conventionally used. Ability improvement is achieved.

[Brief description of drawings]

FIG. 1 is an explanatory view of an example of a process for removing CO _{2 in} combustion exhaust gas that can be adopted in the present invention.

FIG. 2 is a schematic explanatory diagram of a small-sized test apparatus used in an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaki Iijima 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Kaoru Mitsuoka 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima No.22 inside Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (7)

[Claims] 1. A method for removing CO _{2 in} combustion exhaust gas by bringing the combustion exhaust gas under atmospheric pressure into contact with the amine aqueous solution, wherein the amine aqueous solution is a secondary amine or a tertiary amine.
A method for removing CO _{2 in} combustion exhaust gas, which comprises using an amine mixed aqueous solution in which the concentration of each of the primary amines is in the range of 10 to 45% by weight. 2. The concentration of the tertiary amine in the amine mixed aqueous solution is the maximum CO per unit volume of the aqueous solution when a single aqueous solution of the tertiary amine is used under the same absorption conditions.
_{2. The} method for removing CO ₂ from combustion exhaust gas according to claim 1, wherein the concentration is within a range of 10% by weight before and after the concentration of the tertiary amine that becomes ₂ absorption amount. 3. The total amount of amines in the amine mixed aqueous solution
The concentration is 70% by weight or less.
CO in the combustion exhaust gas according to claim 1 or claim 2. ₂Remove
How to do. 4. As the amine aqueous solution, 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, 2-n-butylaminoethanol, piperazine, 2-methylpiperazine, 2,5
-A secondary amine selected from the group of dimethylpiperazine and 2-piperidinoethanol, and 2-dimethylaminoethanol, 2-diethylaminoethanol, 3-dimethylamino-1-propanol, 4-dimethylamino-1-butanol. , 2-dimethylamino-2-methyl-
CO in the combustion exhaust gas according to any one of claims 1 to 3, wherein a mixed aqueous solution of a tertiary amine selected from the group of 1-propanol and N-ethyl-N-methylethanolamine is used. How to remove ₂ . 5. The CO in the combustion exhaust gas according to any one of claims 1 to 5, wherein both the secondary amine and the tertiary amine have one alcoholic hydroxyl group. How to remove ₂ . 6. The aqueous solution of amine, 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol, 2-n-butylaminoethanol, piperazine, 2-methylpiperazine, 2,5.
-A secondary amine selected from the group of dimethylpiperazine and 2-piperidinoethanol, and N-methyldiethanolamine, N-ethyldiethanolamine, Nt-
CO ₂ in the combustion exhaust gas according to any one of claims 1 to 3, wherein a mixed aqueous solution of a tertiary amine selected from the group of butyldiethanolamine and N-methyldiisopropanolamine is used. Method. 7. A second selected from 2-methylaminoethanol, 2-ethylaminoethanol, 2-isopropylaminoethanol and 2-n-butylaminoethanol.
The method for removing CO ₂ in the combustion exhaust gas according to claim 1, wherein a primary amine is used.