JP2871422B2 - Method for removing carbon dioxide in flue gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion relates to a method of removing CO ₂ and (CO) contained in exhaust gas, more particularly CO ₂ in the combustion exhaust gas under atmospheric pressure by using a mixed aqueous solution of specific amines And a method for efficiently removing the same.

[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 have been urgently required internationally to protect the global environment. CO ₂
As a source of the occurrence, all human activities that burn fossil fuels are in demand, and there is a tendency that demands for emission control are further intensified. Along with this, a method and recovery method for contacting boiler flue gas with an alkanolamine aqueous solution to remove and recover CO ₂ in flue gas for power generation facilities such as thermal power plants that use large amounts of fossil fuels Methods for storing the released CO ₂ without releasing it to the atmosphere are being vigorously studied.

Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine and the like, and monoethanolamine (MEA) is usually preferably used. However, the above alkanolamine aqueous solution represented by MEA absorbs CO ₂ in the combustion exhaust gas.
Even when used as an absorbent to be removed, the absorption amount of CO ₂ per a predetermined amount of an aqueous amine solution of a predetermined concentration, the CO ₂ absorption amount per unit amine mole of the aqueous amine solution of a predetermined concentration, the absorption rate of CO _{2 at} a predetermined concentration, Is not always satisfactory in light of the thermal energy required for regeneration of the aqueous alkanolamine solution after absorption.

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 which is part of a ring and is bonded to either a secondary carbon atom or a tertiary carbon atom. An amine mixture consisting of at least 50 mol% of a sterically hindered amine containing a primary amino group bonded to an atom and at least about 10 mol% of a tertiary amino alcohol, and (2) the amine which is a physical absorbent for acidic gases A method for removing acidic gases comprising contacting a gaseous mixture with an amine-solvent liquid absorbent comprising a solvent for the mixture is described. The sterically hindered amine is 2
-Piperidineethanol [2- (2-hydroxyethyl) -piperidine] and 3-amino-3-methyl-1-
Butanol, as a solvent, a sulfoxide compound that may contain up to 25% by weight of water, and the like. Further, examples of the processing gas include high-concentration carbon dioxide and hydrogen sulfide,
For example normally gaseous mixture with a 35% CO ₂ and 10-12% of H ₂ S is illustrated, also in Example CO
₂ itself is used.

JP-A-61-71819 discloses a composition for scraping acidic gas containing a non-aqueous solvent such as a sterically hindered amine and sulfolane. As the sterically hindered primary monoamino alcohol, 2-amino-2-methyl-1-propanol (AMP) and the like are exemplified and used. In the embodiment, the gas to be treated is C
O ₂ and nitrogen, CO ₂ and helium are used. Also, an aqueous solution of an amine and potassium carbonate is used as the absorbent. It also describes the use of water. Further, this publication describes the advantage of the sterically hindered amine with respect to the absorption of CO ₂ using a reaction formula.

[0006] Chemical Engineering Science (C
chemical Engineering Science), Vol. 41, No. 4, 99
Pages 7 to 1003 disclose the carbon dioxide absorption behavior of an aqueous AMP solution that is a hindered amine. As a gas to be absorbed, atmospheric pressure CO ₂ and a mixture of CO ₂ and nitrogen are used.

Chemical Engineering Science (C)
chemical Engineering Science), Vol. 41, No. 2, 40
On pages 5 to 408, the absorption rates of hindered amines such as AMP and linear amines such as MEA for CO ₂ and H ₂ S are reported at around normal temperature. According to this, when the partial pressure of CO ₂ is 1 atm, there is no great difference between the two at an aqueous solution concentration of 0.1 to 0.3M. However, using an aqueous solution having a concentration of 0.1 M, the partial pressure of CO ₂ was set to 1,
When it is reduced to 0.5 and 0.05 atm, 0.05 atm
At m, AMP has a much lower absorption rate than MEA.

[0008] US Patent 3,622,267 describes
Is methyldiethanolamine and monoethylmonoethanol
Using an aqueous mixture containing nolamine, such as crude oil
High partial pressure C contained in synthesis gas such as partial oxidation gas
O_TwoFor example, 40 atm of 30% CO _TwoElaborate the synthesis gas
The technology for manufacturing is disclosed.

[0009] German Patent Publication No. 1,542,415 discloses a technique in which a monoalkylalkanolamine or the like is added to a physical or chemical absorbent to improve the absorption rate of CO ₂ , H ₂ S, and COS. I have. Similarly, German Offenlegungsschrift 1,904,428 discloses a technique in which monomethylethanolamine is added for the purpose of improving the absorption rate of methyldiethanolamine.

US Pat. No. 4,336,233 discloses that a 0.81-1.3 mol / l aqueous solution of piperazine is used as a washing liquid for purification of natural gas, synthesis gas and gasified coal gas, and that piperazine is methyl. A technique is disclosed which is used as a washing solution in an aqueous solution together with a solvent such as diethanolamine, triethanolamine, diethanolamine, and monomethylethanolamine.

Similarly, Japanese Patent Application Laid-Open No. 52-63171 discloses a CO ₂ absorbent in which a piperazine derivative such as piperazine or hydroxyethylpiperazine is added as an accelerator to a tertiary alkanolamine, a monoalkylalkanolamine or the like. ing.

[0012]

As described above, there is a need for a method for efficiently removing CO ₂ from combustion exhaust gas.
In particular, when treating flue gas with an aqueous solution containing a certain concentration of a CO ₂ absorbent (amine compound), the amount of CO ₂ absorbed per unit mole of the absorbent and the CO ₂ per unit volume of the aqueous solution
It is a major problem for the time being to select an absorbent having a large absorption amount and absorption rate. Furthermore, after absorbing CO ₂ , C
It is desired to use an absorbent that requires less heat energy when separating the O ₂ to regenerate the absorbent. In particular, it is desired to improve the absorption rate of an absorbent having a small absorption rate despite the large CO ₂ absorption capacity.

[0013]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies on an absorbent used for removing CO ₂ in a combustion exhaust gas, and as a result, a specific amine compound (X1) or The use of (X2) mixed with a relatively small amount of the specific amine compound (Y1) or (Y2) is particularly effective for improving the absorption rate of the specific amine compound (X1) or (X2). With the knowledge of
The present invention has been completed.

[0014]That is, the present invention relates to (1) 1- (di-unsubstituted
Amine compounds that are lower alkylamino) -ethanol
(X1) 100 parts by weight and (A) ethyleneamines (provided that
And excluding ethylenediamine. ), (B) general formula R
¹ (CH _Two NH _Two ) _Two (R ¹ Is substituted with a lower alkyl group.
And represents a methylene chain having 1 to 5 carbon atoms which may be substituted. )so
Amines represented by (C) NH _m ｛(CH _Two ) _n N
H _Two ｝ _3-m (M is 1 or zero, n is 2 or 3
You. (D) Pip-R ^Two -NH
_Two (Pip represents a piperazinyl group; ^Two Is lower alk
A methylene chain having 1 to 4 carbon atoms which may be substituted with
Show. A) a piperazine compound represented by the formula (E):
Having one alcoholic hydroxyl group and not having 4 or less carbon atoms
Having two or more carbon atoms including a substituted alkyl group and a bonding carbon atom
Secondary amino group having an N atom attached to a group having a chain
Selected from the group consisting of compounds having the formula (I) and (F) homopiperazine
Aqueous solution of 1 to 25 parts by weight of amine compound (Y1)
And the flue gas under atmospheric pressure are brought into contact with each other,
CO _Two And (2) Al in the molecule.
Having one cholic hydroxyl group and a tertiary amino group;
At least one group attached to the amino group is a carbon atom
Having a chain of 2 or more carbon atoms, including atoms,
Two of the groups bonded to the amino group are unsubstituted lower alkyl
Amine compound (provided that 1- (di-unsubstituted lower alkyl)
(Kilamino) -ethanol is excluded. ) (X2) 100 weight
And (C) NH _m ｛(CH _Two ) _n NH _Two ｝ _3-m (M
Represents 1 or zero, and n represents 2 or 3. )
Selected from the group of amines and (F) homopiperazine
Aqueous solution containing 1 to 25 parts by weight of amine compound (Y2)
Contact with the flue gas under atmospheric pressure,
CO _Two It is a method of removing.

[0015]

The specific amine compound (X ) used in the present invention
The combination of (1) or (X2) with (Y1) or (Y2) is as described above, but (Y1) or (Y
Each amine compound of 2) is a single compound
In addition to being used in combination with (X1) or (X2) , it is also possible to use two or more amine compounds (Y1) or (Y2) in combination with amine compound (X1) or (X2) .

The amine compound (X1) used in the present invention is 1
-(Di-unsubstituted lower alkylamino) -ethanol
In the amine compound (X1), two unsubstituted lower
Alkyl is methyl which may be the same or different from each other
Group, ethyl group, propyl group, isopropyl group, etc.
You. Preferred examples of such compounds include 1-di
Methylaminoethanol, 1-diethylaminoethanol
Exemplify 1-methylethylaminoethanol
Can be. The amine compound (X2) used in the present invention has one alcoholic hydroxyl group and a tertiary amino group in the molecule, and at least one group bonded to the tertiary amino group includes its bonding carbon atom. An amine compound having two or more carbon atoms and two of the groups bonded to the tertiary amino group are unsubstituted lower alkyl groups (provided that 1- (di
Excluding lower alkylamino) -ethanol),
In the amine compound (X2) , the two unsubstituted lower alkyl groups may be the same or different from each other;
It represents a methyl group, an ethyl group, a propyl group, an isopropyl group, and the like. Preferred of such compounds are 2
- di Mechiruami Noe pentanol, 2 - di ethylamine Noe data <br/> Nord (DEAE), 2 - d Chirumechiruami Noe Tano <br/> Le, 3 - dimethylamino-1-propanol, 4-dimethylamino-1-butanol , 2-dimethylamino-2
-Methyl-1-propanol, among which DEA
E is particularly preferred.

In the present invention, a combination with the amine compound (X1)
Among the amine compounds (Y 1 ) to be used, examples of (A) ethyleneamines include diethylenetriamine, triethylenetetramine (TETA), and tetraethylenepentamine (TEPA).

Among the amine compounds (Y 1 ), (B) In the amines represented by the general formula R ¹ (CH ₂ NH ₂ ) ₂ , R ¹ has 1 carbon atom which may be substituted by a lower alkyl group. The lower alkyl group is preferably a methyl group having 1 to 3 carbon atoms, an ethyl group, a propyl group, or the like. Preferred compounds are 2,2-dimethyl-1,3-diaminopropane (DMDAP) and hexamethylenediamine (HM
DA) and 1,4-diaminobutane (DAB).

Among the amine compounds (Y 1 ), (C) NH
_{In the} amines represented by _m ｛(CH ₂ ) _n NH ₂ ｝ _3-m , _m represents 1 or 0, n represents 2 or 3, and a preferred compound is 3,3-iminobispropyl. Amine (IBPA) and tris (2-aminoethyl)
An amine (TAEA) can be exemplified.

Among the amine compounds (Y 1 ), (D) Pi
In a piperazine compound represented by pR ² —NH ₂ ,
The methylene chain having 1 to 4 carbon atoms represented by R ² is preferably a methylene chain having 1 to 2 carbon atoms, and the lower alkyl group as a substituent of the methylene chain is preferably R 1
^The example illustrated in ¹ can be exemplified. Preferred piperazine compounds include N- (2-aminoethyl) piperazine (A
EP) can be exemplified.

Among the amine compounds (Y 1 ), (E) a chain having one or more alcoholic hydroxyl groups in the molecule and having two or more carbon atoms including an unsubstituted alkyl group having four or less carbon atoms and a bonding carbon atom. In a compound having a secondary amino group having an N atom bonded to a group having the formula, an unsubstituted alkyl group having 4 or less carbon atoms represents a methyl group, an ethyl group, a propyl group, a butyl group, and a propyl group and a butyl group are It may be branched.
In addition, a chain having 2 or more carbon atoms is preferably a chain having 2 to 2 carbon atoms.
There are three. Such compounds include 2
- et Chiruami Noe pentanol, 2 - main Chiruami Noe Tano <br/> le, 2 - flop Ropiruami Noe pentanol, 2 - b an isopropyl <br/> Ami Noe pentanol, 2- (n-butylamino) - ethanol, 2- (Sec-butylamino) -ethanol, 2
- (i-butylamino) - ethanol, 2-(t-butylamino) - ethanol, 1 - d Chiruami Noe Tano <br/> le, 1 - main Chiruami Noe pentanol, 1 - flop Ropiruami Bruno
Ethanol, 1 - Lee Sopuropiruami Noe like can be exemplified methanol, among others 2 - d Chiruami Noe Tano <br/> Le (EAE), 2 - main Chiruami Noe pentanol, 2-(n
It is preferred to use -butylamino) -ethanol.

Other amine compound (Y 1 ) used in the present invention
Examples include (F) homopiperazine (HP). Departure
Amine used in combination with amine compound (X2)
Compound (Y2) is a compound of the amine compound (Y1)
They are the same as (C) and (F).

An amine compound (X1) or (X2)
The mixing ratio of (Y1) or (Y2) depends on the amine compound (X
1) or (X2) 100 parts by weight of amine compound
(Y1) or (Y2) is in the range of 1 to 25 parts by weight, more preferably 1 to 10 parts by weight. The amine compound (X1) in the mixed aqueous solution (hereinafter also referred to as absorption liquid )
The concentration of (X2) is usually 15 to 65% by weight. The temperature of the mixed aqueous solution at the time of contact with the combustion exhaust gas is usually 30 to 7
It is in the range of 0 ° C. Further, a corrosion inhibitor, a deterioration inhibitor and the like are added to the mixed aqueous solution used in the present invention as needed.

Further, the term “under atmospheric pressure” in the present invention includes a pressure range near atmospheric pressure at which a blower or the like acts to supply combustion exhaust gas.

The process which can be employed in the method of the present invention for removing CO ₂ from flue gas is not particularly limited, and one 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 filling section, 3 is an upper filling section or tray, 4 is a CO ₂ removal tower exhaust gas supply port, 5 is a CO ₂ removal exhaust gas outlet, 6
Is an absorption liquid supply port, 7, 7 'are nozzles, 8 is a flue gas cooler provided as required, 9 is a nozzle, 10 is a filling section, 11 is a humidification cooling water circulation pump, 12 is a makeup water supply line, 13 Is an absorption liquid discharge pump absorbing CO ₂ , 14
Is a heat exchanger, 15 is an absorption liquid regeneration (hereinafter abbreviated as "regeneration") tower, 16 and 16 'are nozzles, 17 is a lower filling section, 1
8 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 recovered CO
₂ discharge line, 23 is a regeneration tower reflux condenser, 24 is a regeneration tower reflux water supply line, 25 is a combustion exhaust gas supply blower, 26
Is a cooler, and 27 is a pressure control valve.

In FIG. 1, the flue gas is pushed into the flue gas cooler 8 by the flue gas supply blower 25,
Contact with humidifying cooling water and the filling section 10 from the nozzle 9, is fogging, de-C through the de-CO ₂ tower combustion exhaust gas feed 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 accumulates in a lower portion of the combustion exhaust gas cooler 8 and is circulated to the nozzle 9 by the humidified cooling water circulation pump 11. Since the humidified cooling water is gradually lost by humidifying and cooling the combustion exhaust gas, it is replenished through the makeup water supply line 12.

The combustion exhaust gas pushed into the CO ₂ removal tower 1 is brought into countercurrent contact with the absorption liquid of 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 absorption liquid. Then, the CO ₂ -free flue gas is directed to the upper filling section 3. The absorbing solution supplied to the CO ₂ removal tower 1 is CO
₂ is absorbed, and due to the heat of reaction caused by the absorption, the temperature becomes higher than the temperature of the absorbent at the normal supply port 6, and is sent to the heat exchanger 14 by the absorbent discharge pump 13 that has absorbed CO ₂ , heated, and regenerated. Guided to tower 15. The temperature control of the absorbent can be performed by the heat exchanger 14 or, if necessary, the cooler 26 provided between the heat exchanger 14 and the absorbent supply port 6.

In the regeneration tower 15, the absorbent is regenerated by heating by the regeneration heater 8, cooled by the heat exchanger 14 and decarbonized.
It is returned to the O ₂ tower 1. In the upper part of the regeneration tower 15, the CO ₂ separated from the absorbing solution comes into contact with the reflux water supplied from the nozzle 16 ′, is cooled by the regeneration tower reflux cooler 23, and is entrained with the CO ₂ in the CO ₂ separator 21. The collected steam is separated from the condensed reflux water, and guided to the CO ₂ recovery step through the recovered CO ₂ discharge line 22. A part of the reflux water is returned to the regeneration tower 15 by the reflux water pump 20.

[0030]

The present invention will be described below in detail with reference to examples. (Examples 1 to 9, Comparative Example 1) 50 ml of a 30% by weight aqueous solution of DEAE (X2) was placed in a glass reaction vessel installed in a thermostat, and an amine compound (Y 2 ) shown in Table 1 was further added. The aqueous DEAE solution was mixed at a ratio of 1.5% by weight. While stirring at a temperature of 40 ° C., the test gas was passed at a flow rate of 1 liter / min under atmospheric pressure through a filter through a filter so as to easily generate bubbles. As a test gas, a model combustion exhaust gas of 40 ° C. having a composition of 10 mol% of CO _2, 3 mol% of O ₂ , and 87 mol% of N ₂ was used.

The test gas continues to pass through, and the CO ₂
CO contained in the absorbing solution at the time when the concentration became equal
₂ was measured using a CO ₂ analyzer (total organic carbon meter)
The O ₂ saturated absorption was determined. Further, to determine the CO ₂ concentration in the gas in the reaction vessel outlet in the initial absorption test (outlet CO ₂ initial concentration). It can be said that the smaller the initial CO ₂ concentration at the outlet, the higher the CO ₂ absorption rate of the absorbing solution.

As Comparative Example 1, an absorption test was carried out using an absorbent containing DEAE alone. The results of the obtained CO ₂ saturated absorption amount and the initial concentration of CO _{2 at the} outlet are also shown in Table 1.

From Table 1, it can be seen that the initial concentration of CO _{2 at} the outlet was improved as compared with Comparative Example 1 when the absorbing solution of the present invention was used. In addition, it was confirmed that the absorption solution can be regenerated without any trouble by heating the mixed solution after the absorption.

[0034]

[Table 1]

[0035]

As described above in detail, a specific amine compound (X) is added to flue gas at atmospheric pressure by the method of the present invention.
1) or (X2) and a specific amine compound (Y1) or
By using the mixed aqueous solution of (Y2) as the absorbing solution, an improvement in the absorption rate of CO ₂ can be achieved as compared with the case where the amine compound (X1) or (X2) is used alone.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Zenji Hotta 3-2-2, Nakanoshima, Kita-ku, Osaka-shi, Osaka Inside Kansai Electric Power Co., Inc. (72) Koichi Kitamura 3-3-1 Nakanoshima, Kita-ku, Osaka, Osaka No. 22 Kansai Electric Power Co., Inc. (72) Inventor Yukihiro Jinno 3-2-2 Nakanoshima, Kita-ku, Osaka-shi, Osaka Prefecture In-house Kansai Electric Power Co., Ltd. (72) Tomio Mimura 3-chome, Nakanoshima, Kita-ku, Osaka, Osaka No.22 Kansai Electric Power Co., Inc. No. Mitsubishi Heavy Industries, Ltd. (72) Inventor Kaoru Mitsuoka 4-2-2 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Research Institute (56) References Table flat 2-504367 (JP, A) (58 ) investigated the field (Int.Cl. ^6, DB name) B01D 53/62

Claims (2)

(57) [Claims] 1. 1- (Di-unsubstituted lower alkylamino)-
100 parts by weight of an amine compound (X 1 ) which is ethanol , (A) ethyleneamines (excluding ethylenediamine), (B) a general formula R ¹ (CH ₂ NH ₂ ) ₂ (R
¹ has 1 to 1 carbon atoms which may be substituted with a lower alkyl group.
5 shows the methylene chain of 5. Amines represented by), (C)
Amines represented by NH _m ｛(CH ₂ ) _n NH ₂ ｝ _3-m (m represents 1 or 0, n represents 2 or 3);
(D) a piperazine compound represented by Pip-R ² —NH ₂ (Pip represents a piperazinyl group, and R ² represents a methylene chain having 1 to 4 carbon atoms which may be substituted with a lower alkyl group); E) N bonded to an unsubstituted alkyl group having 4 or less carbon atoms and a chain having 2 or more carbon atoms including a bonding carbon atom, having one alcoholic hydroxyl group in the molecule.
A compound having a secondary amino group having an atom and an amine compound (Y 1 ) 1 selected from the group of (F) homopiperazine
25 contacting the flue gases under a mixed aqueous solution and the atmospheric pressure of the parts, a method for removing CO ₂ in the combustion exhaust gas. (2)One alcoholic hydroxyl group in the molecule
A tertiary amino group having at least three amino groups;
Each of the groups has at least 2 carbon atoms, including the bonding carbon atom
And a group bonded to the tertiary amino group.
Two are amine compounds which are unsubstituted lower alkyl groups (however,
And 1- (di-unsubstituted lower alkylamino) -ethanol
except for. ) (X2) 100 parts by weight and (C) NH
_m ｛(CH _Two ) _n NH _Two ｝ _3-m (M is 1 or zero, n
Represents 2 or 3. Amines represented by), and
(F) an amine compound selected from the group of homopiperazines
(Y2) 1 to 25 parts by weight of a mixed aqueous solution and combustion under atmospheric pressure
By contacting with exhaust gas, CO _Two Excluding
How to leave.