JP2009148724A - Carbon dioxide absorbent and carbon dioxide separation method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CO<SB>2</SB>absorbent which can absorb CO<SB>2</SB>at higher temperature than in case of using lithium silicate and also discharge CO<SB>2</SB>from a lower temperature compared with the case of using Ba<SB>2</SB>TiO<SB>4</SB>. <P>SOLUTION: A material containing at least one kind of composite oxides shown by a general formula : Ba<SB>3</SB>W<SB>2</SB>O<SB>9</SB>, Ba<SB>2</SB>WO<SB>5</SB>and Ba<SB>3</SB>WO<SB>6</SB>, is used as the CO<SB>2</SB>absorbent. Then, Ba<SB>3</SB>W<SB>2</SB>O<SB>9</SB>, Ba<SB>2</SB>WO<SB>5</SB>and Ba<SB>3</SB>WO<SB>6</SB>as main components are made to contact with CO<SB>2</SB>to abosrb CO<SB>2</SB>by forming BaWO<SB>4</SB>and BaCO<SB>3</SB>. The CO<SB>2</SB>absorbent absorbing CO<SB>2</SB>is made to discharge CO<SB>2</SB>under the condition of the CO<SB>2</SB>partial pressure of 20 kPa or below and the temperature of 890°C or above to be regenerated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon dioxide absorbing material that can be repeatedly used by absorbing carbon dioxide, releasing carbon dioxide absorbed under a predetermined condition, and regenerating, and a carbon dioxide separation method using the same. About.

Examples of the material that absorbs carbon dioxide in a temperature range exceeding 500 ° C. include a carbon dioxide absorbent containing at least one selected from the group consisting of lithium silicate represented by the general formula: Li _x Si _y O _z Is known (see Patent Document 1).

  However, when lithium silicate is used, it is difficult to efficiently absorb carbon dioxide gas from a high-temperature gas exceeding 700 ° C. such as combustion exhaust gas.

Further, as a carbon dioxide absorbing material that can be repeatedly used by absorbing carbon dioxide under a high temperature condition and releasing and regenerating the carbon dioxide absorbed under a predetermined condition, CaO, Ba ₂ TiO ₄ etc. have been proposed. Of these, Ba ₂ TiO ₄ has a high carbon dioxide absorption rate per unit weight from 600 ° C. to 800 ° C., and is effective for carbon dioxide absorption at temperatures of 600 ° C. or higher (see Patent Document 2).

When this Ba ₂ TiO ₄ is used as a carbon dioxide absorbent, a reaction represented by the following formula (A) is used.
Ba ₂ TiO ₄ + CO ₂ ⇔ BaTiO ₃ + BaCO ₃ ...... (A)
The equilibrium temperature of the reaction shown in this formula (A) varies depending on the carbon dioxide partial pressure. For example, when carbon dioxide is absorbed from an air stream having a carbon dioxide partial pressure of 5 kPa (total pressure 100 kPa), the reaction of formula (A) The equilibrium temperature is about 900 ° C.
Therefore, by bringing the gas stream containing carbon dioxide into contact with a carbon dioxide absorbent (Ba ₂ TiO ₄ ) heated to about 600 ° C. to 800 ° C., the reaction of formula (A) proceeds to the right side, Reaction absorption takes place.

In addition, when the material that has absorbed carbon dioxide gas is heated at a temperature of about 1000 ° C., the reaction of formula (A) proceeds to the left side and carbon dioxide gas is released.
When Ba ₂ TiO ₄ is used as a carbon dioxide absorbing material, carbon dioxide can be separated and recovered by repeating carbon dioxide absorption / release regeneration as described above.

However, the above-mentioned conventional carbon dioxide absorbent has a high carbon dioxide release temperature. In an atmosphere having a carbon dioxide partial pressure of 20 kPa, it is necessary to raise the temperature to 1000 ° C. or higher, and the consumption of heat energy is large. There is a problem.
JP 2000-262890 A International Publication No. 2006/013695 Pamphlet

The present invention solves the above problems, can absorb carbon dioxide gas at a higher temperature than when using lithium silicate, and from a lower temperature than when using Ba ₂ TiO _4. An object of the present invention is to provide a carbon dioxide absorbent capable of releasing carbon dioxide and a carbon dioxide separation method using the same.

In order to solve the above problems, the carbon dioxide absorbent of the present invention (Claim 1)
It is characterized by containing at least one of the complex oxides represented by the general formula: Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ .

Further, the carbon dioxide absorbent of claim 2 is mainly composed of the Ba ₃ W ₂ O ₉ and mainly absorbs carbon dioxide,
(a) It is characterized in that it is carried out based on a reaction in which Ba ₃ W ₂ O ₉ and carbon dioxide gas contact to form BaWO ₄ .

Further, the carbon dioxide gas absorbent is mainly composed of the Ba ₂ WO ₅ and mainly absorbs carbon dioxide gas.
(a) a reaction in which Ba ₂ WO ₅ and carbon dioxide contact with each other to form Ba ₃ W ₂ O ₉ , and
(b) It is characterized in that it is carried out based on a reaction in which the Ba ₃ W ₂ O ₉ produced in the reaction of (a) is contacted with carbon dioxide to produce BaWO ₄ .

Further, the carbon dioxide absorbent of claim 4 is mainly composed of the Ba ₃ WO ₆ and mainly absorbs carbon dioxide,
(a) a reaction in which Ba ₃ WO ₆ and carbon dioxide contact with each other to form Ba ₂ WO ₅ ;
(b) a reaction in which the Ba ₂ WO ₅ produced in the reaction of (a) is contacted with carbon dioxide to produce Ba ₃ W ₂ O ₉ , and
(c) It is characterized in that it is carried out based on a reaction in which the Ba ₃ W ₂ O ₉ produced by the reaction of (b) is contacted with carbon dioxide to produce BaWO ₄ .

Further, the carbon dioxide gas separation method according to claim 5 is:
A step of absorbing carbon dioxide in the carbon dioxide absorbent according to claim 1;
And a step of releasing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 890 ° C. or more.

Further, the carbon dioxide separation method of claim 6
A step of causing carbon dioxide gas to be absorbed by the carbon dioxide absorbent according to claim 2 to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide gas absorbed by the carbon dioxide absorbent in the above step under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 950 ° C. or less.

In addition, the carbon dioxide separation method of claim 7
A step of causing the carbon dioxide gas absorbent of claim 3 to absorb carbon dioxide to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide absorbed in the carbon dioxide absorbent in the above step under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1100 ° C. or less.

The carbon dioxide gas separation method according to claim 8
A step of causing carbon dioxide gas to be absorbed by the carbon dioxide absorbent according to claim 4 to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide absorbed in the carbon dioxide absorbent in the above step under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1150 ° C. or less.

The carbon dioxide absorbent of the present invention (Claim 1) contains at least one of the complex oxides represented by the general formulas: Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO _6. In addition, by using the carbon dioxide absorbent of the present invention, it is possible to absorb carbon dioxide at a higher temperature than when using lithium silicate, and from a lower temperature than when using Ba ₂ TiO _4. Carbon dioxide can be released.

That is, Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ absorb carbon dioxide gas by reactions of the following formulas (1), (2), and (3), respectively.
Ba ₃ W ₂ O ₉ + CO ₂ ⇔2BaWO ₄ + BaCO ₃ (1)
2Ba ₂ WO ₅ + CO ₂ ⇔Ba ₃ W ₂ O ₉ + BaCO ₃ (2)
Ba ₃ WO ₆ + CO ₂ Ｂ Ba ₂ WO ₅ + BaCO ₃ ...... (3)
When the reaction (1) is used, for example, when carbon dioxide is absorbed from an air current having a carbon dioxide partial pressure of 20 kPa (total pressure of 100 kPa), the equilibrium temperature is varied. Is about 790 ° C., and when the carbon dioxide-containing air stream is brought into contact with a carbon dioxide absorbent heated to about 600 to 720 ° C., the reaction of formula (1) proceeds to the right side, and the reaction absorption of carbon dioxide is Done.
The material that has absorbed the carbon dioxide gas is heated at a relatively low temperature of about 890 ° C. in an atmosphere of carbon dioxide partial pressure of 20 kPa, for example. discharge.
Therefore, by using the carbon dioxide absorbing material of the present invention, it is possible to release carbon dioxide from a lower temperature than when using the conventional Ba ₂ TiO ₄ .

Further, when the reactions of the above formulas (2) and (3) are used, the equilibrium temperature and the carbon dioxide gas releasing temperature when absorbing carbon dioxide are higher than when the reaction of (1) is used. .
That is, the release temperature of carbon dioxide when using the reaction of the above formula (2) is about 950 ° C. in an atmosphere having a partial pressure of carbon dioxide of 20 kPa. However, even in that case, the carbon dioxide gas can be released at a temperature lower than the release temperature in the case of using the conventional Ba ₂ TiO ₄ .
In addition, when the reaction of the above formula (3) is used, the carbon dioxide gas release start temperature is as high as about 1100 ° C., but from the viewpoint that carbon dioxide gas can be absorbed at a high temperature, Ba ₂ TiO ₄ and Similarly, it can be said that it is a significant carbon dioxide absorbent.
In addition, BaWO ₄ is produced when Ba ₃ W ₂ O ₉ absorbs CO ₂ based on the reaction of the above formula (1). However, this BaWO ₄ does not have carbon dioxide absorption ability as will be described later. It has been confirmed that it is a substance.

Further, when a composite oxide containing Ba (barium) and W (tungsten) is represented by the general formula Ba _X WO _{(3 + X)} , X can take various values. In this case, the crystal phase is In the range of X = 1 to 3, as will be described later, any one of four kinds of complex oxides of BaWO ₄ , Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ , or those Of these, it has been confirmed that it is a mixture of two or more complex oxides.

The carbon dioxide absorbent of claim 2 is a reaction in which Ba ₃ W ₂ O ₉ is a main component and Ba ₃ W ₂ O ₉ and carbon dioxide come into contact with each other to produce BaWO ₄ , that is, the above formula ( Since carbon dioxide is absorbed based on the reaction of 1), it is possible to efficiently absorb and release carbon dioxide at a low temperature.

Further, the carbon dioxide gas absorbent is mainly composed of Ba ₂ WO ₅ , and the carbon dioxide gas is absorbed mainly based on the reactions of the above formulas (1) and (2). The release temperature in an atmosphere of 20 kPa is 950 ° C., which is higher than in the case of claim 2, but is higher because both reactions of formulas (1) and (2) can be used ( 8% by weight or more) It is possible to realize the absorption / release amount of carbon dioxide.

The carbon dioxide absorbent of claim 4 is mainly composed of the Ba ₃ WO ₆ , and the absorption of carbon dioxide is mainly performed based on the reactions of the above formulas (1), (2) and (3). Therefore, when carbon dioxide gas is released using the reaction of (3), the carbon dioxide gas releasing temperature is high (about 1100 ° C. at the maximum), but the equations (1), (2) and (3 ) Can be utilized, and therefore, a higher carbon dioxide absorption / release amount can be realized.

  The carbon dioxide gas separation method according to claim 5 is a carbon dioxide gas absorbing material according to claim 1, wherein the carbon dioxide gas absorbing material absorbs carbon dioxide gas, and the carbon dioxide gas absorbing material absorbed carbon dioxide gas has a carbon dioxide partial pressure of 20 kPa or less. And a step of releasing carbon dioxide under the condition of a temperature of 890 ° C. or higher, so that the absorption of carbon dioxide at a high temperature and the release of the absorbed carbon dioxide (regeneration of carbon dioxide absorbent) are efficiently performed. By using this method, it is possible to economically and efficiently separate carbon dioxide from the air stream.

The carbon dioxide gas separation method according to claim 6 is characterized in that carbon dioxide gas is absorbed by the carbon dioxide gas absorbent according to claim 2 containing Ba ₃ W ₂ O ₉ as a main component to produce a mixture of BaWO ₄ and BaCO _3. And the step of releasing the carbon dioxide gas absorbed by the carbon dioxide absorbent under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 950 ° C. or less, the reaction of the above formula (1) It is possible to efficiently separate carbon dioxide gas at a low temperature by using.

Further, the carbon dioxide gas separation method of claim 7 is a step of producing a mixture of BaWO ₄ and BaCO ₃ by absorbing carbon dioxide gas to the carbon dioxide gas absorbent material according to claim 3 containing Ba ₂ WO ₅ as a main component. And the step of releasing the carbon dioxide absorbed by the carbon dioxide absorbent under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1100 ° C. or less, the above formulas (1) and (2) By using this reaction, it becomes possible to efficiently separate carbon dioxide.
In the case where carbon dioxide gas is released under conditions that use both of the reactions of formulas (1) and (2) (for example, carbon dioxide partial pressure of 20 kPa and temperature is raised to 1100 ° C.), This makes it possible to perform efficient carbon dioxide gas separation with a large amount of carbon dioxide absorption / release in the single absorption / release process.

Further, the carbon dioxide gas separation method of claim 8 is a step of producing a mixture of BaWO ₄ and BaCO ₃ by absorbing carbon dioxide gas to the carbon dioxide absorbent material according to claim 4 containing Ba ₃ WO ₆ as a main component. And the step of releasing the carbon dioxide absorbed by the carbon dioxide absorbent under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1150 ° C. or less, the above formulas (1) and (2) , (3) can be used to efficiently separate carbon dioxide.
Carbon dioxide gas is released under conditions that use all the reactions of formulas (1), (2), and (3) (for example, carbon dioxide partial pressure is 20 kPa and temperature is raised to 1150 ° C.). In this case, it is possible to perform an extremely efficient separation of carbon dioxide gas, which has a larger amount of carbon dioxide absorption / release in one absorption / release process.

  Examples of the present invention will be described below to describe the features of the present invention in more detail.

[Production of carbon dioxide absorber]
As a composite oxide represented by the general formula: Ba _X WO _{(3 + X)} , the value of X is changed in the range of X = 1 to 3, and the carbon dioxide absorbent of the present invention is also included in the range. A composite oxide represented by the general formula: Ba _X WO _{(3 + X)} was prepared.
Specifically, a carbon dioxide absorbing material, which is a composite oxide powder represented by the general formula: Ba _X WO _{(3 + X)} , was prepared by the following procedure.

First, BaCO ₃ and WO ₃ were charged into a container so as to have a desired composition ratio X (X = 1 to 3), and mixed in a ball mill for 2 hours.
Then, the obtained powder was fired under conditions of 1100 ° C./2 hours to obtain a composite oxide powder.

  And about the obtained complex oxide powder, the crystal phase was identified by XRD (X-ray diffractometer). The results are shown in Table 1.

As shown in Table 1, composite oxides having respective X values are composite oxides represented by BaWO ₄ , Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ or mixtures thereof. It was confirmed that there was.

[Characteristic evaluation]
Next, in order to confirm the presence or absence of CO ₂ absorption ability of each composite oxide (carbon dioxide absorbent), carbon dioxide partial pressure of 20 kPa is used using a TG-DTA device (thermogravimetric analysis-differential thermal analyzer). The presence or absence of CO ₂ absorption at 700 ° C. was confirmed.
The results are also shown in Table 1.

From Table 1, it was confirmed that X = 1.0 complex oxide BaWO ₄ of sample number 1 did not have CO ₂ absorption ability.
Further, after the CO ₂ was absorbed by the composite oxides (carbon dioxide absorbers) of sample numbers 2 to 7, the crystal phase was identified by XRD for each sample. As a result, it was confirmed that all were in the state of “a mixture of BaWO ₄ phase and BaCO ₃ phase”.

From the above results, it was confirmed that the composite oxide represented by the general formula: Ba _X WO _{(3 + X)} functions as a carbon dioxide absorbent in a composition in the range of 1.0 <X ≦ 3.0. It was.

Next, after absorbing CO ₂ at 700 ° C. with respect to three types of composite oxides (carbon dioxide absorbents) of Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ having a stoichiometric composition, The release behavior of CO _{2 in} an atmosphere of carbon dioxide partial pressure of 20 kPa was examined.
Specifically, using a TG-DTA apparatus, “CO ₂ release behavior between 700 and 1200 ° C.” was measured while gradually heating in an atmosphere of carbon dioxide partial pressure of 20 kPa. The result is shown in FIG.

Further, the crystal phases before and after the CO ₂ releasing reaction at 700 to 1200 ° C. were identified by XRD.
As a result, it was confirmed that reactions in the left direction of the following formulas (1), (2), and (3) occurred in each release step. In the CO ₂ absorption step, it goes without saying that each reaction occurs in the opposite direction.
Ba ₃ W ₂ O ₉ + CO ₂ ⇔2BaWO ₄ + BaCO ₃ (1)
2Ba ₂ WO ₅ + CO ₂ ⇔Ba ₃ W ₂ O ₉ + BaCO ₃ (2)
Ba ₃ WO ₆ + CO ₂ Ｂ Ba ₂ WO ₅ + BaCO ₃ ...... (3)

From the above results, the following was confirmed.
First, (see equation _{(1)) Ba 3 W 2} O 9 is next 2BaWO ₄ + BaCO ₃ absorbs CO _2, the CO ₂ in the carbon dioxide gas releasing reaction in one step (reaction to the left side of equation (1)) Release and return to the original Ba ₃ W ₂ O ₉ . It can be seen from FIG. 1 that the CO ₂ release reaction in the first stage occurs from about 890 ° C.

Ba ₂ WO ₅ absorbs CO ₂ and becomes Ba ₃ W ₂ O ₉ + BaCO ₃ (see formula (2)), and the generated Ba ₃ W ₂ O ₉ further absorbs CO ₂ to absorb 2BaWO ₄ + BaCO _3. (See formula (1)), CO ₂ is released in a two-stage reaction (reaction to the left side of the reaction formulas (1) and (2)), and the original Ba ₂ WO ₅ is restored. From FIG. 1, the first stage CO ₂ release reaction (reaction of formula (1)) starts from about 875 ° C., and the second stage CO ₂ release reaction (reaction of formula (2)) is about 955 ° C. It can be seen that

Ba ₃ WO ₆ absorbs CO ₂ to become Ba ₂ WO ₅ + BaCO ₃ (see formula (3)), and the generated Ba ₂ WO ₅ further absorbs CO ₂ to absorb Ba ₃ W ₂ O ₉ + BaCO _3. Then (see formula (2)), the generated Ba ₃ W ₂ O ₉ further absorbs CO ₂ and becomes 2BaWO ₄ + BaCO ₃ (see formula (1)). Then, CO ₂ is released in a three-stage reaction (reaction to the left side of the formulas (1), (2), and (3)), and the original Ba ₃ WO ₆ is restored. From FIG. 1, the first stage CO ₂ releasing reaction (reaction of formula (1)) starts from about 880 ° C., and the second stage CO ₂ releasing reaction (reaction of formula (2)) is about 955 ° C. It can be seen that the third stage CO ₂ release reaction (reaction of formula (3)) occurs from about 1105 ° C.
Table 2 summarizes the relationship between the X value of the carbon dioxide absorbent represented by the general formula: Ba _X WO _{(3 + X)} and the CO ₂ release reaction that occurs.

From the above results, by selecting a material composition in which X exceeds 1.0 among the composite oxides represented by the general formula: Ba _X WO _{(3 + X)} , CO ₂ of the above formula (1) is selected. Since absorption / release reactions can be used, for example, after absorbing CO ₂ at a temperature of about 700 ° C., in an atmosphere of carbon dioxide partial pressure of 20 kPa, CO ₂ is reduced from 890 ° C. in the lowest case. It can be seen that the carbon dioxide absorbent can be regenerated and regenerated.

At that time, under the condition of 1.0 <X ≦ 1.5, all of the CO ₂ absorbed by the carbon dioxide absorbent can be released. On the other hand, when 1.5 <X, the release temperature due to the reaction of the above formulas (2) and (3) occurs only at a higher temperature, so at 890 ° C., the CO ₂ absorbed by the carbon dioxide absorbent Only some of them will be released. Of course, when the temperature is further raised, the reactions of the formulas (2) and (3) can be caused to release all the CO ₂ .

<Carbon dioxide absorption / release test 1>
In accordance with the method for producing the carbon dioxide absorbent in Example 1 above, Ba ₃ W ₂ O ₉ (carbon dioxide gas), which is a composite oxide having a value of X of 1.5 in the general formula: Ba _x WO _{(3 + X)} Absorbent) was prepared.
Then, using this carbon dioxide absorbent, CO ₂ was absorbed under the conditions of a carbon dioxide partial pressure of 20 kPa and a temperature of 700 ° C. of the gas to be treated.

As a result, 4.8% by weight of CO _{2 was} absorbed by the progress of the reaction of the above formula (1).

Next, the temperature was raised, and the CO ₂ release behavior in an atmosphere with a carbon dioxide partial pressure of 20 kPa was examined. As a result, it was confirmed that the release of CO ₂ started from 890 ° C. This can be understood from FIG.

<Carbon dioxide absorption / release test 2>
In accordance with the method for producing the carbon dioxide absorbent in Example 1 above, Ba ₂ WO ₅ (carbon dioxide absorbent) which is a composite oxide having a value of X of 2.0 in the general formula: Ba _x WO _{(3 + X)} ) Was produced.
Then, using this carbon dioxide absorbent, CO ₂ was absorbed under the conditions of a carbon dioxide partial pressure of 20 kPa and a temperature of 700 ° C. of the gas to be treated.

As a result, as the reactions of the above formulas (1) and (2) proceeded, it was possible to absorb 8.2% by weight of CO ₂ .
Next, the temperature was raised, and the CO ₂ release behavior in an atmosphere with a carbon dioxide partial pressure of 20 kPa was examined. As a result, the approximately 890 ° C. for CO ₂ of the first-stage release is initiated, it was confirmed that the release of CO ₂ is started from about 950 ° C.. This can be understood from FIG.

<CO2 absorption / release test 3>
In addition, using the same carbon dioxide absorbent as the carbon dioxide absorbent of above carbon dioxide absorption / release test 2, CO ₂ absorption / release was repeated 15 times continuously under the following absorption / release conditions. It was.
In the the CO ₂ release steps were performed the release of CO ₂ while supplying N ₂ gas as a carrier gas.
(Absorption conditions)
Temperature: 700 ° C
Gas to be treated: CO ₂ : 20 vol% / N ₂ : 80 vol%
Absorption time: 30 minutes Operating pressure: Normal pressure (release conditions)
Temperature: 800 ° C
Carrier gas: N ₂
Release time: 30 minutes Operating pressure: Normal pressure

As a result of the above test, as shown in FIG. 2, it was confirmed that the CO ₂ absorption amount was not decreased by repetition, and stable absorption / release behavior of CO ₂ was exhibited.
Further, in the N ₂ gas stream, it was confirmed that the release of CO ₂ was completed within 30 minutes at 800 ° C., and the carbon dioxide absorbent was regenerated.

<Comparative Example 1>
In accordance with the method for producing the carbon dioxide absorbent in Example 1, BaWO ₄ , which is a composite oxide having a value of X of 1.0 in the general formula: Ba _x WO _{(3 + X),} was produced.
Then, using this BaWO _4, in an atmosphere of carbon dioxide gas partial pressure 20 kPa, was subjected to absorption test of CO ₂ under the conditions of 700 ° C., the absorption of CO ₂ is not observed, BaWO ₄ is a carbon dioxide gas absorption ability It was confirmed that they do not have.

<Comparative example 2>
Ba ₂ TiO ₄ was synthesized as a carbon dioxide absorbent for comparison. Then, using the carbon dioxide gas absorbent for the comparison, in an atmosphere of carbon dioxide gas partial pressure 20 kPa, was CO ₂ absorption under the condition of 700 ° C.. At this time, CO ₂ was absorbed by the reaction of the following formula (A), and BaTiO ₃ and BaCO ₃ were produced.
Ba ₂ TiO ₄ + CO _{2 Ｂ} BaTiO ₃ + BaCO ₃ ...... (A)
Next, the temperature was raised, and the CO ₂ release behavior in an atmosphere with a carbon dioxide partial pressure of 20 kPa was examined. The result is shown in FIG.
FIG. 3 also shows the CO ₂ release behavior after Ba ₂ WO ₅ which is the carbon dioxide absorbent of the present invention absorbs the carbon dioxide absorbent.

As shown in FIG. 3, when Ba ₂ TiO ₄ was used as the carbon dioxide gas absorbent, it was confirmed that CO ₂ emission started from around 1030 ° C.
On the other hand, when CO ₂ is absorbed using Ba ₂ WO ₅ which is the carbon dioxide absorbent of the present invention, the first stage of CO ₂ release starts at about 890 ° C., and the second stage. Form release begins at about 950 ° C.
From this result, it can be seen that CO ₂ is released at a lower temperature when Ba ₂ WO ₅ is used than when Ba ₂ TiO ₄ is used as the carbon dioxide absorbent.

[Carbon dioxide separation device used for carrying out the carbon dioxide separation method of the present invention]
FIG. 4 is a schematic configuration diagram showing an example of a carbon dioxide separator using the carbon dioxide absorbent of the present invention, which is used when the carbon dioxide separation method of the present invention is carried out.

The carbon dioxide separation apparatus, the absorption of CO ₂ in the (feed gas containing CO ₂₎ flue gas by carbon dioxide gas absorbent, after separation, by releasing CO ₂ from the carbon dioxide-absorbing material that has absorbed CO ₂ This is a carbon dioxide separation device for recovery, and includes a switching valve 10 that switches the flow of combustion exhaust gas, and two mechanism parts A and B that function as a carbon dioxide absorption mechanism part and a carbon dioxide release mechanism part. FIG. 4 shows a state in which the switching valve 10 is set so that carbon dioxide-containing gas (raw material gas) is supplied to the left mechanism A, and the left mechanism A is the carbon dioxide absorption mechanism. It shows a state in which the right mechanism part B functions as a carbon dioxide gas release mechanism part that releases CO ₂ .

Each mechanism A and B includes a container 11, a heater 12, and a carbon dioxide absorbent 3 filled in the container 11, and the carbon dioxide absorbent 3 in the container 11 is removed by the heater 12. It is comprised so that it can heat. Then, by switching the switching valve 10 so that the combustion exhaust gas is supplied to the mechanism part A and supplying the combustion exhaust gas, the mechanism part A absorbs CO ₂ .

On the other hand, in the mechanism part (carbon dioxide release mechanism part) B, the carbon dioxide absorbing material 3 in the carbon dioxide absorbing state in the container 11 is heated by the heater 12, and vacuum suction is performed from the outlet side of the container 11, for example, and the pressure is 1000 Pa. By setting the following reduced pressure state (for example, 100 Pa), CO ₂ is released from the carbon dioxide absorbent 3, and the released CO ₂ is recovered at a high concentration, and the carbon dioxide absorbent 3 that has absorbed CO ₂ is regenerated. And will be used again. As a method other than vacuum suction, it is also possible to use a method of recycling a material by circulating a gas having a low CO ₂ partial pressure.

  By using this carbon dioxide separation device, it becomes possible to reliably carry out the carbon dioxide separation method of the present invention using the carbon dioxide absorbent of the present invention, and the carbon dioxide can be separated efficiently. .

The present invention is not limited to the above examples, the general formula carbon dioxide gas absorbent of the present invention: Ba _X WO value of X in the case where expressed by (3 _{+ X),} the absorption conditions of the CO ₂ Various applications and modifications can be made within the scope of the invention with respect to the release conditions and the like.

According to the present invention, CO ₂ can be absorbed at a higher temperature than when lithium silicate is used, and CO ₂ can be absorbed and released at a lower temperature than when Ba ₂ TiO ₄ is used. In addition, it is possible to provide a carbon dioxide gas absorbent, and it is possible to efficiently separate carbon dioxide using the carbon dioxide absorbent.
Accordingly, the present invention is the removal or CO ₂ in the combustion exhaust gas generated at the factory, including removal of CO ₂ in the exhaust gas discharged from the engine, CO ₂ from a gas containing CO ₂ that occurs in a variety of fields It can be widely applied to the separation of

It is a diagram showing a CO ₂ release behavior of carbon dioxide gas absorbent according to an embodiment of the present invention. It is a diagram showing the behavior when were repeated absorption and release of embodiments using such carbon dioxide absorbent in Example CO ₂ of the present invention. Shows the CO ₂ release behavior in the case of using the carbon dioxide absorbent according _{(Ba 2 WO 5 (X =} 2.0)) and carbon dioxide gas absorbent for comparison (Ba ₂ TiO ₄₎ to an embodiment of the present invention It is. It is a schematic block diagram which shows an example of the carbon dioxide separator using the carbon dioxide absorber of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas absorption pipe 2 Heater 3 Carbon dioxide gas absorption material 10 Switching valve 11 Container 12 Heater A, B Mechanism part

Claims (8)

A carbon dioxide gas absorbent comprising at least one of complex oxides represented by the general formula: Ba ₃ W ₂ O ₉ , Ba ₂ WO ₅ , and Ba ₃ WO ₆ . The main component is Ba ₃ W ₂ O ₉ , and absorption of carbon dioxide gas is mainly,
_2. The carbon dioxide absorbent according to claim 1, wherein the carbon dioxide absorbent is performed on the basis of (a) a reaction in which Ba ₃ W ₂ O ₉ and carbon dioxide come into contact to produce BaWO ₄ . The main component is Ba ₂ WO ₅ , mainly absorbing carbon dioxide gas,
(a) a reaction in which Ba ₂ WO ₅ and carbon dioxide contact with each other to form Ba ₃ W ₂ O ₉ , and
The carbon dioxide gas according to claim 1, wherein the carbon dioxide gas is formed based on (b) a reaction in which the Ba ₃ W ₂ O ₉ produced in the reaction of (a) is contacted with carbon dioxide gas to produce BaWO _4. Absorber. The main component of the Ba ₃ WO ₆ is absorption of carbon dioxide gas,
(a) a reaction in which Ba ₃ WO ₆ and carbon dioxide contact with each other to form Ba ₂ WO ₅ ;
(b) a reaction in which the Ba ₂ WO ₅ produced in the reaction of (a) is contacted with carbon dioxide to produce Ba ₃ W ₂ O ₉ , and
The carbon dioxide gas according to claim 1, which is carried out based on a reaction in which (c) the Ba ₃ W ₂ O ₉ produced in the reaction of (b) and carbon dioxide gas come into contact to produce BaWO _4. Absorber. A step of absorbing carbon dioxide in the carbon dioxide absorbent according to claim 1;
And a step of releasing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 890 ° C. or more. A step of causing carbon dioxide gas to be absorbed by the carbon dioxide absorbent according to claim 2 to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide gas absorbed in the carbon dioxide absorbent in the above step under conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 950 ° C. or less. A step of causing the carbon dioxide gas absorbent of claim 3 to absorb carbon dioxide to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide gas absorbed by the carbon dioxide absorbent in the above step under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1100 ° C. or less. A step of causing carbon dioxide gas to be absorbed by the carbon dioxide absorbent according to claim 4 to produce a mixture of BaWO ₄ and BaCO ₃ ;
And a step of releasing the carbon dioxide gas absorbed in the carbon dioxide absorbent in the above step under the conditions of a carbon dioxide partial pressure of 20 kPa or less and a temperature of 1150 ° C. or less.

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