JPH07246314A - Method for removing carbon dioxide in exhaust combustion gas - Google Patents

Abstract

PURPOSE:To efficiently remove CO2 from a waste combustion gas by using a combination of an amine compd. X and a relatively small amt. of an amine compd. Y. CONSTITUTION:An amine compd. X has an alcoholic hydroxyl in the molecule and a primary amine joined to a tertiary carbon atom having two unsubstituted alkyls. An amine compd. Y is selected from a group consisting of ethyleneamines other than ethylenediamine, iminobispropylamine, diaminotoluenes, amines expressed by R<1> (CH2NH2)2 (R<1> is a 1-5C methylene chains substitutable by lower alkyls), piperazine compds. expressed by Pip-R<2>-NH2 (R<2> is a 1-4C methylene chains substitutable by lower alkyls) and homopiperazines. The waste combustion gas under atmospheric pressure is brought into contact with an aq. mixed soln. of 100 pts.wt. of the amine compd. X and 1-25 pts.wt. of the amine compd. Y to remove CO2.

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

[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
The sources of methane are all human activity fields that burn fossil fuels, and the demand for emission control tends to become 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 and a method for recovering by removing CO ₂ in the combustion exhaust gas by bringing the combustion exhaust gas of the boiler into contact with an alkanolamine aqueous solution, etc. 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, even if the above-mentioned alkanolamine aqueous solution typified by MEA is used as an absorbent for absorbing and removing CO _{2 in} combustion exhaust gas, it absorbs CO ₂ per a predetermined amount of an amine aqueous solution of a predetermined concentration. the amount, 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, more in light like the heat energy required for the regeneration of the alkanolamine solution after the absorption, not necessarily be satisfactory is not.

By the way, there are many known techniques for separating an acidic gas from various mixed gases using an amine compound.

Japanese Patent Laid-Open No. 53-100180 discloses that
(1) Containing at least one secondary amino group bound to either a secondary or tertiary carbon atom or a primary amino group bound to a tertiary carbon atom which is part of a ring An amine-solvent liquid absorbent comprising an amine mixture comprising at least 50 mol% sterically hindered amine and at least about 10 mol% tertiary amino alcohol and (2) a solvent for said amine mixture which is a physical absorbent for acid gases. A method for the removal of acid gases, which consists in contacting a normally gaseous mixture, is described. 2-Piperidine ethanol {alias 2- (2
-Hydroxyethyl) -piperidine} and 3-amino-3-methyl-1-butanol, and sulfoxide compounds which may contain up to 25% by weight of water as a solvent. In the upper left column of page 11, "high concentration carbon dioxide and hydrogen sulfide, for example 35
% CO ₂ and 10-12% H ₂ S in a normally gaseous mixture ”, 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. 2-Amino-2-methyl-1-propanol (AMP) and the like are exemplified and used as the sterically hindered primary monoamino alcohol. In the embodiment, CO ₂ and nitrogen, and CO ₂ and helium are used as the gas to be treated.
Also, as the absorbent, an aqueous solution of amine and potassium carbonate is used. It also describes the use of water. Further, the publication describes the advantage of a sterically hindered amine for absorption of CO ₂ by using a reaction formula.

Chemical Engineering Science (Ch
emical Engineering Science), 41, No. 4, 997
On pages 1003, 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 (Ch
emical Engineering Science), Volume 41, Issue 2, 405
On pages 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, a CO ₂ partial pressure of 1, 0.5,
If it is reduced to 0.05 atm, AMP will be
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, syngas 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 piperazine derivative such as hydroxyethylpiperazine as a promoter to a tertiary alkanolamine, monoalkylalkanolamine, or the like. ing.

[0014]

As described above, there is a demand for a method of efficiently removing CO ₂ from combustion exhaust gas. In particular, when treating a combustion exhaust gas 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, the C per unit volume of the aqueous solution
A major problem for the time being is to select an absorbent having a large absorption amount and absorption rate of O ₂ . Further, after absorbing CO _2, an absorbent that separates CO ₂ and regenerates the absorbing liquid requires less heat energy is desired. Above all, it is desired to improve the absorption rate of an absorbent having a low absorption rate, although the absorption capacity of CO ₂ is large.

[0015]

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 The present invention has been completed by finding that it is effective to mix a small amount of a specific amine compound (Y) to improve the absorption rate of the specific amine compound (X). .

That is, the present invention has 100 parts by weight of an amine compound (X) having an alcoholic hydroxyl group in the molecule and a primary amino group bonded to a tertiary carbon atom having two unsubstituted alkyl groups. And (A) ethyleneamines (excluding ethylenediamine), (B) iminobispropylamine (IBPA), (C) diaminotoluenes, (D) general formula R 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.), (E) Pip-
A piperazine compound represented by 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 (F) homopiperazine ( amine compound selected from the group consisting of HP) (Y) by contacting the mixed aqueous solution of 1 to 25 parts by weight and the combustion exhaust gas under atmospheric pressure, CO ₂ of the combustion exhaust gas
Is a method of removing.

[0017]

According to the present invention, the use of the amine compound (X) in combination with a relatively small amount of the amine compound (Y) has the effect of accelerating the CO ₂ absorption rate of the amine compound (X). The amine compound (Y) may be used alone, or two or more kinds may be combined and used by mixing with the amine compound (X).

In the compound (X) having an alcoholic hydroxyl group in the molecule and a primary amino group bonded to a tertiary carbon atom having two unsubstituted alkyl groups, which is used in the present invention, The alkyl groups may be the same as or different from each other, and examples thereof include a methyl group, an ethyl group, a propyl group and the like, but both are preferably a methyl group. Examples of the compound belonging to (X) include 2-amino-2-methyl-1-propanol (A
MP), 3-amino-3-methyl-2-pentanol,
2,3-dimethyl-3-amino-1-butanol, 2-
Amino-2-ethyl-1-butanol, 2-amino-2
-Methyl-3-pentanol, 2-amino-2-methyl-1-butanol, 3-amino-3-methyl-1-butanol, 3-amino-3-methyl-2-butanol, 2
-Amino-2,3-dimethyl-3-butanol, 2-amino-2,3-dimethyl-1-butanol, 2-amino-2-methyl-1-pentanol and the like are exemplified, and AMP is preferable.

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

The (C) diaminotoluene (DAT) used in the present invention includes 2,3-DAT and 2,4-DA.
T, 2,5-DAT, 2,6-DAT, 3,4-DA
T, 3,5-DAT can be illustrated.

The general formula (D) used in the present invention is R ¹ (CH ₂
In the amines represented by NH ₂ ) ₂ , R ¹ represents a methylene chain having 1 to 5 carbon atoms which may be substituted with a lower alkyl group. Preferred examples of the lower alkyl group include a methyl group having 1 to 3 carbon atoms, an ethyl group and a propyl group. 2,2 as a preferred compound
-Dimethyl-1,3-diaminopropane (DMDA
P) and hexamethylenediamine (HMDA) can be mentioned.

(E) Pip-R ² -NH used in the present invention
1 to 4 carbon atoms in the piperazine compound represented by ₂
The methylene chain is preferably a methylene chain having 1 to 2 carbon atoms, and examples of the optionally substituted lower alkyl group include those exemplified for R ² . Preferred examples of the piperazine compound include N- (2-aminoethyl) piperazine (AEP).

The mixing ratio of the amine compounds (X) and (Y) is in the range of 1 to 25 parts by weight, preferably 1 to 1 part by weight, with respect to 100 parts by weight of the amine compound (X).
It is in the range of 0 parts by weight, and more preferably in the range of 1 to 6 parts by weight.

The concentration of the amine compound (X) in the mixed aqueous solution (hereinafter, also referred to as "absorption liquid") 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 in the range of 30 to 70 ° C. In addition, a corrosion inhibitor, a deterioration inhibitor, etc. may be added to the mixed aqueous solution used in the present invention, if necessary. Furthermore, the term "under 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 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 CO-free₂Tower 2 is lower
Filling unit, 3 is an upper filling unit or tray, and 4 is CO-free₂Tower
Combustion exhaust gas supply port, 5 de-CO₂Combustion exhaust gas outlet, 6
Is an absorption liquid supply port, 7 is a nozzle, and 8 is provided as needed.
Combustion exhaust gas cooler, 9 is a nozzle, 10 is a filling part, 1
1 is a humidification cooling water circulation pump, 12 is a makeup water supply line,
13 is CO₂Absorbing liquid discharge pump that absorbed
Exchanger, 15 is absorption liquid regeneration (hereinafter also referred to as "regeneration")
Tower, 16 nozzle, 17 lower filling part, 18 regenerative heating
Vessel (reboiler), 19 is the upper filling part, 20 is the reflux water port
Pump, 21 is CO ₂Separator, 22 is recovery CO₂Emission lie
, 23 is a regenerator reflux condenser, 24 is a nozzle, and 25 is a re-cooler.
Raw tower reflux water supply line, 26 is a combustion exhaust gas supply blower,
Reference numeral 27 is a cooler, and 28 is a regeneration tower reflux 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 portion of the combustion exhaust gas cooler 8 and is circulated to the nozzle 9 by the pump 1. 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 absorbing liquid having a constant concentration supplied from the nozzle 7 in the lower filling section 2, so that CO ₂ in the combustion exhaust gas is absorbed by the absorbing liquid. The removed CO ₂ -exhausted exhaust gas flows to the upper filling section 3. The absorption liquid supplied to the CO ₂ removal tower 1 is CO ₂
Is normally absorbed by the reaction heat due to the absorption of
The temperature becomes higher than the temperature in the above, and is sent to the heat exchanger 14 by the absorption liquid discharge pump 13 that has absorbed CO ₂ , is heated, and is guided to the regeneration tower 5. The temperature of the regenerated absorption liquid can be adjusted by the heat exchanger 14 or, if necessary, the cooler 27 provided between the heat exchanger 14 and the absorption liquid supply port 6.

In the absorption liquid regenerator 15, the absorption liquid is regenerated in the lower filling section 17 by heating by the regeneration heater 18, cooled by the heat exchanger 14 and returned to the CO ₂ removal column 1. In the upper part of the absorption liquid regenerator 15, the CO ₂ separated from the absorption liquid comes into contact with the reflux water supplied from the nozzle 24 in the upper filling part 19, and is cooled by the regenerator reflux condenser 23.
In the CO ₂ separator 21, the water vapor entrained in CO ₂ is separated from the condensed reflux water, and is guided to the CO ₂ recovery process from 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, and a part of the reflux water is supplied to the regeneration tower reflux water supply port 28 of the CO ₂ removal tower 1 through the regeneration tower reflux water supply line 25. It Since the recirculation tower reflux water contains a small amount of the absorbing liquid, it comes into contact with the exhaust gas in the upper filling portion 3 of the CO ₂ removal tower 1 and a small amount of the CO contained in the exhaust gas.
Contribute to the removal of ₂ .

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples.
It (Examples 1 to 9 and Comparative Example 1) Glass installed in a constant temperature bath
Put 50 ml of 30% by weight aqueous solution of AMP into the reaction vessel,
Furthermore, the amine compound (Y) shown in Table 1 was added to the AMP water.
The solution was mixed at a ratio of 1.5% by weight. Temperature 40
Test gas at 1 liter / min under atmospheric pressure while stirring at ℃
Through the absorbent at a flow rate of. CO as test gas₂10
Mol%, O₂3 mol%, N₂It has a composition of 87 mol%.
A model combustion exhaust gas at 40 ° C. was used. Pass test gas
Ke, CO in and out gas₂Only when the concentrations are equal
CO contained in the absorption liquid₂CO₂Analyzer (total organic carbon
CO) to measure CO₂The saturated absorption amount was calculated. Also
CO in the gas at the outlet of the reaction vessel at the initial stage of the absorption test ₂
Concentration (exit CO₂The initial concentration) was determined. This exit CO₂
The smaller the initial concentration, the more CO₂Absorption rate is high
Can be said.

As Comparative Example 1, an absorption liquid containing only AMP was used.
Absorption test. CO obtained ₂Saturated absorption and
Exit CO₂The results of the initial concentration are 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.

[0033]

[Table 1]

[0034]

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 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.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location C01B 31/20 B (72) Inventor Masaki Iijima 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. In-house (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. Having an alcoholic hydroxyl group in the molecule,
100 parts by weight of an amine compound (X) having a primary amino group bonded to a tertiary carbon atom having two unsubstituted alkyl groups, (A) ethylene amines (excluding ethylene diamine), (B). ) Iminobispropylamine,
(C) diaminotoluenes, (D) general formula R 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), (E) Pip-R ² —NH ₂ (Pip is An amine compound selected from the group consisting of a piperazinyl group, R ² is a methylene chain having 1 to 4 carbon atoms which may be substituted with a lower alkyl group, and (F) a homopiperazine (Y ) A method of removing 1 to 25 parts by weight of the mixed aqueous solution and the combustion exhaust gas under atmospheric pressure to remove CO ₂ from the combustion exhaust gas.