JP3197173B2 - Method of removing carbon dioxide from flue gas - Google Patents

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 particularly, to a method for removing CO ₂ (carbon dioxide) contained in flue gas at atmospheric pressure using an aqueous solution of a specific piperazine derivative. 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 have been urgently required internationally to protect the global environment. CO ₂
As a source of the occurrence, all human activity fields burning fossil fuels tend to be increasingly demanded for emission control. Aiming at power generation facilities such as thermal power plants that use a large amount of fossil fuels, the boiler's flue gas is brought into contact with an alkanolamine aqueous solution to remove and recover CO ₂ in the flue gas. Done C
Methods for storing O ₂ without releasing it to the atmosphere are being vigorously studied.

Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, and diglycolamine. 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 absorption amount of CO ₂ per unit amine mole of the aqueous amine solution of a predetermined concentration, the absorption rate of CO _{2 at} a predetermined concentration, Furthermore, it is not always satisfactory in light of heat energy required for regeneration of the aqueous alkanolamine solution after absorption.

By the way, amine compounds are prepared from various mixed gases.
There are many known technologies for separating acid gas using
You. JP-A-53-100180 discloses that (1)
A partial carbon atom or a tertiary carbon atom
At least one secondary amino attached to either of the offspring
Group or a primary amino group attached to a tertiary carbon atom.
A tertiary amine having at least 50 mol% of a sterically hindered amine
Amine comprising at least about 10 mol% of alcohol
Physical absorber for mixtures and (2) acidic gases
Amine-solvent liquid absorption comprising a solvent for the amine mixture
Acids, usually consisting of contacting a gaseous mixture with a sorbent
A method for removing volatile gases is described. As a sterically hindered amine
Is 2-piperidineethanol [2- (2-hydroxy
Ethyl) -piperidine] and 3-amino-3-methyl-
1-butanol, etc., and up to 25% by weight as a solvent.
Sulphoxide compounds that may contain water
As an example of the processing gas, "High concentration
Carbon dioxide and hydrogen sulfide, for example 35% CO _Twoas well as
10-12% H_TwoA normally gaseous mixture containing S "
Illustrated, and in the examples, CO 2_TwoUsed itself
I have.

JP-A-61-71819 describes a composition for scraping an acidic gas containing a non-aqueous solvent such as a sterically hindered amine and sulfolane. In addition, this publication describes the advantage of sterically hindered amines with respect to CO ₂ absorption 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 solution of hindered amine 2-amino-2-methyl-1-propanol (AMP). 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.

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

[0009] German Patent Publication No. 1,542,415 discloses a technique of 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 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 has a small thermal energy required for separating O ₂ and regenerating the absorbent.

[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 flue gas, and as a result, it is particularly effective to use a specific piperazine derivative. Thus, the present invention was completed. That is, the present invention provides a piperazine derivative represented by the following general formula [1] having a concentration of 15 %.
The present invention relates to a method for removing CO ₂ from the flue gas by bringing an aqueous solution of up to 65% by weight into contact with flue gas at atmospheric pressure.

Embedded image (In the formula, R ¹ is a lower alkyl group, and R ² is a hydrogen atom or a lower alkyl group.)

[0014] The present invention also relates to a method for removing CO ₂ in the combustion exhaust gas wherein the piperazine derivative is 2-methylpiperazine . Below, the present invention is described in detail.

[0015]

In the piperazine derivative represented by the general formula [1] used in the present invention, each lower alkyl group represented by R ¹ and R ² is preferably a methyl group having 1 to 3 carbon atoms, an ethyl group, a propyl group. Groups and the like,
Particularly preferred is a methyl group. Specific compounds include 2-methylpiperazine, 2-ethylpiperazine,
-Propylpiperazine, 2,5-dimethylpiperazine,
Examples thereof include 2-methyl-5-ethylpiperazine and 2,5-diethylpiperazine. Among them, 2-methylpiperazine and 2,5-dimethylpiperazine are preferred. The piperazine derivatives represented by the general formula [1] can be used alone or in combination of two or more.

The concentration of the aqueous solution of the piperazine derivative (hereinafter also referred to as absorption liquid) used for contact with the combustion exhaust gas of the present invention is usually 15 to 65% by weight, preferably 30 to 50% by weight. The temperature of the absorbent at the time of contact with the combustion exhaust gas is usually in the range of 30 to 70 ° C. Further, a corrosion inhibitor, a deterioration inhibitor, and the like are added to the absorbing 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 that can be employed in the method of the present invention for removing CO ₂ from flue gas is not particularly limited, but 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 inlet, and 5 is a CO ₂ removal section.
Combustion exhaust gas outlet, 6 is an absorbent supply port, 7 is a nozzle, 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 make-up water supply line, 13 is an absorption liquid discharge pump that has absorbed CO ₂ , 14 is a heat exchanger, 15 is an absorption liquid regeneration (hereinafter, referred to as
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, and 22 is recovered CO. ₂ discharge line, 23 is a regeneration tower reflux condenser, 24
Is a nozzle, 25 is a regeneration tower reflux water supply line, 26 is a combustion exhaust gas supply blower, and 27 is a cooler.

In FIG. 1, the flue gas is pushed into the flue gas cooler 8 by the flue gas supply blower 26,
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 in contact with the combustion exhaust gas accumulates 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 through the makeup water supply line 12.

The combustion exhaust gas trapped in the CO ₂ removal tower 1 is brought into countercurrent contact with the absorbent having a constant concentration supplied from the nozzle 7 in the lower filling section 2, and CO ₂ in the combustion exhaust gas is supplied to the absorbent supply port. The CO ₂ -exhaust gas is absorbed and removed by the absorbing solution from 6, and goes to the upper filling section 3. Absorbing liquid supplied to de-CO ₂ tower 1 absorbs CO _2, because of the heat of reaction due to the absorption becomes a temperature higher than the temperature in conventional absorbent liquid supply port 6, absorbent that has absorbed CO ₂ absorption liquid discharge Pump 13
Is sent to the heat exchanger 14, heated, and guided to the absorbent regeneration tower 15.

In the absorbent regeneration tower 15, the absorbent is regenerated by heating by the regeneration heater 8, cooled by the heat exchanger 14 and a cooler 27 provided as necessary, and absorbed by the CO ₂ removal tower 1. It is returned to the supply port 6. In the upper part of the absorption liquid regeneration tower 15, CO ₂ separated from the absorption liquid
Contact with the reflux water supplied from the
And the steam accompanying the CO ₂ is condensed in the CO ₂ separator 21 and separated as reflux water, and the recovered CO ₂
It is led to the CO ₂ recovery step from the discharge line 22. A part of the reflux water is refluxed by the reflux water pump 20 to the absorbent regeneration tower 15 via the nozzle 24, and another part is supplied to the upper part of the CO ₂ removal tower 1 from the regeneration tower reflux water supply line 25.

[0021]

The present invention will be described below in detail with reference to examples.

(Example 1, Comparative Example 1) Installed in a thermostat
30 weight of 2-methylpiperazine in a glass reaction vessel
50 ml of a 1% aqueous solution was charged. While stirring at a temperature of 40 ° C
Bubble the test gas at 1 liter / min.
Through the filter to make it easier to generate
Was. The test gas is CO_Two: 10 mol%, O_Two: 3 mo
%, N_Two: Model at 40 ° C. having a composition of 87 mol%
Combustion exhaust gas was used. Continue to pass test gas,
CO_TwoWhen the concentration becomes equal, it is contained in the absorbing solution
CO_TwoTo CO_TwoMeasured using an analyzer (total organic carbon meter)
And the absorption liquid CO_TwoSaturated absorption (Nm^ThreeCO_Two/ M^ThreeDissolution
Liquid, molar CO_Two/ Molar absorption solution)
90% saturated absorption as a measure of average absorption speed up to sum
The required time and the average absorption rate during that time were determined. Also the absorption test
In the gas at the outlet of the reaction vessel at the beginning of the experiment_Twoconcentration
(Initial outlet gas CO_TwoConcentration). This exit CO_Two
The smaller the initial concentration, the more CO _TwoHigh absorption speed
I can say that. Further early exit CO_TwoTrack concentration
The initial absorption rate obtained by the
Comparison with the case (initial absorption rate ratio). As Comparative Example 1,
An absorption test using an MEA aqueous solution was performed. Table-
1 is shown. Heat the mixed solution after absorption.
And confirm that the absorbent can be regenerated without any problems.
Was.

[0023]

[Table 1]

As is evident from the results in Table 1, the use of an aqueous solution of a piperazine derivative according to the present invention as an absorbent for combustion exhaust gas results in superior saturation absorption per mole as compared with the case of using an aqueous MEA solution. I understand.

Example 2 and Comparative Example 2 In order to examine the heat energy required for regenerating the absorbing solution, the absorption solution (concentration 30% by weight) used in Example 1 and Comparative Example 1 was mixed with CO ₂ . The heat of reaction (absorption calorific value) was measured. 200 g of the absorbing solution was placed in an adiabatic tester, stirred with a magnetic stirrer, and allowed to stand until the temperature of the absorbing solution was stabilized. Then the net CO ₂ about 2
00CC / min in blown within the tester, CO ₂ flow rate of the inlet and outlet of the tester and the temperature of the absorbing solution continuously recorded. The test was terminated when the CO ₂ flow rate at the outlet of the tester sharply increased. Absorbing liquid moles of absorbed CO ₂ to (moles load), reaction heat when absorbing liquid from a raised temperature from blowing initiation of CO ₂ is 1 mol absorb CO ₂ (Kcal
/ Mol) was determined for each molar interval of absorbed CO ₂ . The heat capacity of the tester was as follows.
The heater was energized at 0.3 A for a predetermined time, and the temperature was determined from the temperature rise. The temperature range of the test was 20 to 80 ° C, and the room temperature at the time of measurement was 20 to 25 ° C. Table 2 shows the results.

[0026]

[Table 2]

As can be seen from Table 2, 2 according to the present invention
- heat of reaction with methylpiperazine absorbing solution and CO ₂ is MEA
The section where the number of moles of absorbed CO ₂ is larger than that in the case of the absorbing solution is small, and it can be seen that the energy required for regeneration is smaller than that in the case of the MEA and is advantageous.

[0028]

As described in detail above, the method of the present invention uses an aqueous solution of a piperazine derivative as an absorbing solution in flue gas at atmospheric pressure, thereby making it possible to achieve a better result than using a conventional MEA aqueous solution. Thus, the improvement of the CO ₂ absorption capacity is achieved.

[Brief description of the drawings]

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

Continued on the front page (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Kaoru Mitsuoka 4-2-2 Kanon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory (56) References JP-A-6-198120 (JP, A) JP-A-53-81490 (JP, A) JP-A-52-63171 (JP, A) JP-A-3-154611 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/62

Claims (2)

(57) [Claims] 1. A following general formula (1) of the piperazine derivative represented by the concentration in the CO ₂ of the combustion exhaust gas which comprises bringing into contact with the combustion exhaust gas under atmospheric pressure and an aqueous solution of 15 to 65 wt% Removal method. Embedded image (In the formula, R ¹ is a lower alkyl group, and R ² is a hydrogen atom or a lower alkyl group.) _2. The method for removing CO _{2 from} combustion exhaust gas according to claim 1, wherein the piperazine derivative is 2-methylpiperazine.