JPH07100334A - Method for removing carbon dioxide in waste combustion gas - Google Patents

Abstract

PURPOSE:To improve the absorption speed of a specific amino compd. and to efficiently remove CO2 from waste combustion gases by mixing a relatively small amount of a specific amino compd. into the former specific amino compd. and using the mixture. CONSTITUTION:An amino compd. (X) which has one alcoholic hydroxyl group and tertiary amino groups in the molecule and in which >=1 groups bonded to the tertiary amino groups have >=2C chains including their bond carbon atoms and further, two among the groups bonded to the tertiary amino groups are non-substd. lower alkyl groups is used at 100 pts.wt. An amino compd. (Y) selected from ethyleneamines (excluding ethylenediamine), general formula R<1>(CH2NH2)2 (where R<1> is 1 to 5C methylene chain substd. with a lower alkyl group), etc., is mixed at 1 to 25 pts.wt. into the former amino compd. The CO2 in the waste combustion gases under an atm. pressure is then efficiently removed.

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 to CO _{2 in} flue gas under atmospheric pressure using a mixed aqueous solution of a specific amine. The present invention relates to a method for efficiently removing the.

[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 fields of human activity that burn fossil fuels, and the demand for emission control tends to become stronger. Along with this, for power generation equipment such as a thermal power plant that uses a large amount of fossil fuel, a method and a method of recovering CO ₂ in the combustion exhaust gas by contacting the combustion exhaust gas of the boiler with an alkanolamine aqueous solution and the like. The method of storing the stored CO ₂ without releasing it to the atmosphere has been vigorously studied.

Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine and the like, but monoethanolamine (MEA) is usually preferred. However, the above alkanolamine aqueous solution represented by MEA absorbs CO _{2 in} combustion exhaust gas.
Be used as an absorbent to remove, absorption of CO ₂ per predetermined amount of the aqueous amine solution having a predetermined concentration, CO ₂ absorption quantity per unit amine molar amine aqueous solution having a predetermined concentration, the absorption rate of CO ₂ at a given concentration, further Is not always satisfactory in light of the heat energy required to regenerate the alkanolamine aqueous solution after absorption.

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 which is part of the ring and is bonded to either the secondary carbon atom or the tertiary carbon atom. Amine mixtures consisting of at least 50 mol% of sterically hindered amines containing atom-bonded primary amino groups and at least about 10 mol% of tertiary amino alcohols, and (2) said amines being physical absorbers for acid gases. A process for the removal of acid gases is described which consists in contacting an amine-solvent liquid absorbent consisting of a solvent for the mixture with a normally gaseous mixture. 2 as a sterically hindered amine
-Piperidine ethanol [2- (2-hydroxyethyl) -piperidine] and 3-amino-3-methyl-1-
Butanol and the like, solvents such as sulfoxide compounds which may contain up to 25% by weight of water, further examples of process gases are high concentrations of carbon dioxide and hydrogen sulfide,
A normally gaseous mixture having, for example, 35% CO ₂ and 10-12% H ₂ S is illustrated, and the examples also show CO.
₂ itself is used.

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

Chemical Engineering Science (C
hemical Engineering Science), 41, No. 4, 99
Pages 7 to 1003 disclose the carbon dioxide gas absorption behavior of an AMP aqueous solution which is a hindered amine. 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
hemical Engineering Science), 41, No. 2, 40
On pages 5 to 408, absorption rates of CO ₂ and H ₂ S of aqueous solutions of hindered amines such as AMP and linear amines such as MEA are reported near room temperature. According to this, when the partial pressure of CO ₂ is 1 atm, the aqueous solution concentration is 0.1 to 0.3 M, and there is no great difference between the two. However, using a 0.1 M aqueous solution, CO ₂ partial pressure of 1,
When reduced to 0.5 and 0.05 atm, 0.05 at
At m, AMP has a much lower absorption rate than MEA.

US Pat. No. 3,622,267
Is methyldiethanolamine and monoethylmonoethane
Using an aqueous mixture containing a nolamine, such as crude oil
High partial pressure C contained in synthesis gas such as partial oxidation gas
O₂, 30% CO at 40 bar, for example ₂Contained syngas
A manufacturing technique 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. There is. Similarly, DE-A-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, JP-A-52-63171 discloses a CO ₂ absorbent obtained by adding a piperazine or a derivative of piperazine such as hydroxyethylpiperazine to tertiary alkanolamine, monoalkylalkanolamine and the like. ing.

[0012]

As described above, a method for efficiently removing CO ₂ from combustion exhaust gas is desired.
In particular, when the combustion exhaust gas is treated with an aqueous solution containing a constant concentration of CO ₂ absorbent (amine compound), the amount of CO ₂ absorbed per unit mole of the absorbent and the amount of CO ₂ per unit volume of the aqueous solution.
The major problem for the time being is to select an absorbent having a large absorption amount and absorption rate. Furthermore, after absorbing CO ₂ , C
Absorbents that require less heat energy to separate O ₂ and regenerate the absorbent are desired. In particular, it is desired to improve the absorption rate of an absorbent having a low absorption rate despite its large CO ₂ absorption capacity.

[0013]

In view of the above-mentioned problems, the inventors of the present invention have made earnest studies on an absorbent used for removing CO _{2 in} combustion exhaust gas, and as a result, have found that the specific amine compound (X) is relatively It was found that the use of a small amount of the specific amine compound (Y) mixed is particularly effective in improving the absorption rate of the specific amine compound (X), and the present invention can be completed. It was

That is, the present invention has an alcoholic property in the molecule.
Having one hydroxyl group and a tertiary amino group, the tertiary amino group
At least one group attached to contains a carbon atom to which it is attached.
Having a chain of 2 or more carbon atoms and further having a tertiary amino group
Two of the groups attached to are unsubstituted lower alkyl groups
100 parts by weight of amine compound (X) and (A) ethylene
Mines (excluding ethylenediamine), (B)
General formula R¹(CH₂NH ₂)₂(R¹Is a lower alkyl group
Shows an optionally substituted methylene chain having 1 to 5 carbon atoms.
You ) Amines represented by (C) NH_m{(CH₂)
_nNH₂}_3-m(M is 1 or zero, n is 2 or 3
Show. ), Amines represented by (D) Pip-R²-N
H₂(Pip represents a piperazinyl group, R²Is lower al
Methylene chain having 1 to 4 carbon atoms which may be substituted with a kill group
Indicates. ) Piperazine compound represented by
Has one alcoholic hydroxyl group and has a carbon number of 4 or less
C2 or more, including the substituted alkyl group and the bonded carbon atom
Secondary amino having N atom bound to a group having a chain
Selected from the group of compounds having a group and (F) homopiperazine
Aqueous amine compound (Y) 1 to 25 parts by weight mixed aqueous solution
And the combustion exhaust gas under atmospheric pressure are contacted, and the combustion exhaust gas
CO in₂Is a method of removing.

[0015]

The combination of the specific amine compounds (X) and (Y) used in the present invention is as described above.
Each amine compound of (Y) can be used alone in combination with the amine compound (X), or can be used in combination with two or more amine compounds (Y) in combination with the amine compound (X).

The molecule used in the present invention has one alcoholic hydroxyl group and a tertiary amino group, and at least one group bonded to the tertiary amino group has 2 carbon atoms including the bonding carbon atom. In the amine compound (X) having the above-mentioned chain and two of the groups bonded to the tertiary amino group are unsubstituted lower alkyl groups, the two unsubstituted lower alkyl groups are the same or different from each other. And may represent a methyl group, an ethyl group, a propyl group, an isopropyl group or the like. Preferred examples of such compounds include 2-
(Dimethylamino) -ethanol, 2- (diethylamino) -ethanol (DEAE), 2- (ethylmethylamino) -ethanol, 1- (dimethylamino) -ethanol, 1- (diethylamino) -ethanol, 1- (ethylmethyl) Amino) -ethanol, 3-dimethylamino-1-propanol, 4-dimethylamino-1-butanol and 2-dimethylamino-2-methyl-1-propanol can be exemplified, and DEAE is particularly preferable.

Among the amine compounds (Y) used in the present invention, examples of (A) ethyleneamines include diethylenetriamine, triethylenetetramine (TETA) and tetraethylenepentamine (TEPA).

Among the amine compounds (Y), in (B) amines represented by the general formula R ¹ (CH ₂ NH ₂ ) ₂ ,
R ¹ has 1 carbon atom which may be substituted with a lower alkyl group.
The above 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), hexamethylenediamine (HMD
A) and 1,4-diaminobutane (DAB) can be mentioned.

Of the amine compounds (Y), (C) NH _m
In the amines represented by {(CH ₂ ) _n NH ₂ } _3-m , _m in the formula is 1 or zero, and n is 2 or 3, and 3,3-iminobispropylamine is preferable. (IBPA) and tris (2-aminoethyl)
An example is amine (TAEA).

Of the amine compounds (Y), (D) Pip
In the piperazine compound represented by —R ² —NH ₂ , R
The methylene chain of 1 to 4 ^carbon atoms ² represents preferably a methylene chain having 1 to 2 carbon atoms, and preferably a lower alkyl group as the substituent for the methylene chain R ¹
The examples shown in can be exemplified. A preferable piperazine compound is N- (2-aminoethyl) piperazine (AE
P) can be illustrated.

In the amine compound (Y), (E) has a chain of 2 or more carbon atoms including one alcoholic hydroxyl group in the molecule, an unsubstituted alkyl group of 4 or less carbon atoms and a bonding carbon atom. In the compound having a secondary amino group having an N atom bonded to the group having, the unsubstituted alkyl group having 4 or less carbon atoms represents a methyl group, an ethyl group, a propyl group or a butyl group, and the propyl group and the butyl group are separated from each other. It may be branched. Further, the chain having 2 or more carbon atoms preferably has 2 to 3 carbon atoms.
I can give you one. Such compounds include 2-
(Ethylamino) -ethanol, 2- (methylamino)
-Ethanol, 2- (propylamino) -ethanol,
2- (isopropylamino) -ethanol, 2- (n-
Butylamino) -ethanol, 2- (sec-butylamino) -ethanol, 2- (i-butylamino) -ethanol, 2- (t-butylamino) -ethanol, 1-
(Ethylamino) -ethanol, 1- (methylamino)
-Ethanol, 1- (propylamino) -ethanol,
1- (Isopropylamino) -ethanol and the like can be exemplified, and among them, 2- (ethylamino) -ethanol (EAE), 2- (methylamino) -ethanol, 2
It is preferred to use-(n-butylamino) -ethanol.

Another amine compound (Y) used in the present invention is (F) homopiperazine (HP).

The mixing ratio of the amine compounds (X) and (Y) is in the range of 1 to 25 parts by weight, more preferably 1 to 25 parts by weight with respect to 100 parts by weight of the amine compound (X).
It is in the range of 10 parts by weight. The concentration of the amine compound (X) in the mixed aqueous solution (hereinafter, also referred to as absorbing solution) is usually 15 to 6
It is 5% by weight. The temperature of the mixed aqueous solution 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. are added to the mixed aqueous solution 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 at which a blower or the like acts to supply combustion exhaust gas.

The process that can be used in the method for 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 a tray, 4 is a CO ₂ removal tower combustion exhaust gas supply port, 5 is a CO ₂ removal exhaust gas exhaust port, and 6
Is an absorption liquid supply port, 7, 7'is a 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 pump for absorbing CO ₂ , 14
Is a heat exchanger, 15 is an absorption liquid regeneration (hereinafter also referred to 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 lines, 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 combustion exhaust gas is pushed into the combustion exhaust gas cooler 8 by the combustion exhaust gas supply blower 25,
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 humidification cooling water circulation 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.

The combustion exhaust gas pushed into the CO ₂ removal tower 1 is brought into countercurrent contact with the absorption 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 absorption 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 becomes higher than the temperature of the absorption liquid at the supply port 6, and is sent to the heat exchanger 14 by the absorption liquid discharge pump 13 that has absorbed CO ₂ , heated and regenerated. You are led to the tower 15. The temperature of the absorbing liquid can be adjusted by the heat exchanger 14 or, if necessary, by the cooler 26 provided between the heat exchanger 14 and the absorbing liquid supply port 6.

In the regeneration tower 15, the absorption liquid is regenerated by heating by the regeneration heater 8 and cooled by the heat exchanger 14 to remove C.
Returned to O ₂ tower 1. In the upper part of the regeneration tower 15, the CO ₂ separated from the absorption liquid comes into contact with the reflux water supplied from the nozzle 16 ′, is cooled by the regeneration tower reflux condenser 23, and is entrained in CO ₂ by the CO ₂ separator 21. The generated steam is separated from the condensed reflux water, and is guided to the CO ₂ recovery process through the recovered CO ₂ discharge line 22. A part of the reflux water is recycled to the regeneration tower 15 by the reflux water pump 20.

[0030]

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

Continuing to pass the test gas, CO ₂
CO contained in the absorption liquid when the concentrations become equal
₂ was measured using a CO ₂ analyzer (total organic carbon meter), and C
The saturated absorption amount of O ₂ was determined. Further, the CO ₂ concentration in the gas at the outlet of the reaction vessel at the initial stage of the absorption test (outlet CO ₂ initial concentration) was determined. It can be said that the smaller the initial concentration of CO _{2 at the} outlet, the higher the CO ₂ absorption rate of the absorbing liquid.

As Comparative Example 1, an absorption test was conducted using an absorption liquid containing DEAE alone. The results of the obtained CO ₂ saturated absorption amount and the outlet CO ₂ initial concentration are also shown in Table 1.

It can be seen from Table 1 that the use of the absorbing solution of the present invention improves the initial concentration of CO _{2 at} the outlet as compared with the case of Comparative Example 1. It was confirmed that the absorbing solution can be regenerated without any trouble by heating the mixed solution after absorption.

[0034]

[Table 1]

[0035]

As described above in detail, by using the mixed aqueous solution of the specific amine compound (X) and the specific amine compound (Y) as the absorbing liquid in the combustion exhaust gas under the atmospheric pressure by the method of the present invention, The CO ₂ absorption rate is improved as compared with the case where the amine compound (X) is used alone.

[Brief description of drawings]

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

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Zenji Hotta 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture Kansai Electric Power Co., Inc. (72) Koichi Kitamura 3-3, Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture No.22 in Kansai Electric Power Co., Inc. (72) Inventor Yukihiro Jinno 3-chome, Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture No. 22 Inside Kansai Electric Power Co., Inc. (72) Tomio Mimura 3-chome, Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture No.22 In Kansai Electric Power Co., Inc. (72) Inventor Shigeru Shimojo 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo No. Sanryo Heavy Industry Co., Ltd. (72) Inventor Kaoru Mitsuoka 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory

Claims (1)

[Claims] 1. A molecule having one alcoholic hydroxyl group and a tertiary amino group, and at least one group bonded to the tertiary amino group has a carbon number of 2 or more including the bonding carbon atom. Two of the groups having a chain and bonded to the tertiary amino group are unsubstituted lower alkyl groups, and 100 parts by weight of the amine compound (X) and (A) ethyleneamines (excluding ethylenediamine). ), (B) General formula R
Amine represented by ¹ (CH ₂ NH ₂ ) ₂ (R ¹ represents a methylene chain having 1 to 5 carbon atoms which may be substituted with a lower alkyl group), (C) NH _m {(CH ₂ ) _n N
H ₂ } _3-m (m represents 1 or zero, n represents 2 or 3), (D) 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), and (E) an alcoholic hydroxyl group in the molecule. A compound having 1 and having a secondary amino group having an N atom bonded to an unsubstituted alkyl group having 4 or less carbon atoms and a group having a chain having 2 or more carbon atoms including a bonded carbon atom, and (F) A method of removing CO ₂ in the combustion exhaust gas by bringing a mixed aqueous solution of 1 to 25 parts by weight of an amine compound (Y) selected from the group of homopiperazine into contact with the combustion exhaust gas under atmospheric pressure.