JP3850843B2 - Carbon dioxide absorbing material, carbon dioxide absorbing method, carbon dioxide absorbing device, carbon dioxide separating device, and method for producing lithium composite oxide - Google Patents

Description

The present invention relates to a carbon dioxide absorbent using a lithium composite oxide, a carbon dioxide absorption method, a carbon dioxide separation method, a carbon dioxide absorber, a carbon dioxide separator, and a method for producing a lithium composite oxide.

In an apparatus such as an engine that burns fuel mainly composed of hydrocarbons, the temperature of an exhaust gas discharge portion, which is a place suitable for the recovery of carbon dioxide gas, often reaches a high temperature of 300 ° C. or higher.

By the way, as a method for recovering carbon dioxide, a conventional method using cellulose acetate, chemical absorption by an alkanolamine solvent, and the like are known. However, any of the above-described recovery methods needs to suppress the introduction temperature of carbon dioxide gas to 200 ° C. or lower. Therefore, for exhaust gas that requires recycling at a high temperature, it is necessary to cool the exhaust gas to 200 ° C. or less once by a heat exchanger or the like, resulting in a large amount of energy consumption for carbon dioxide recovery. There was a problem of becoming.

Lithium zirconate is known as a carbon dioxide absorbing material that exhibits carbon dioxide absorbing characteristics in a high temperature range exceeding 500 ° C. for such problems. This lithium zirconate utilizes a phenomenon in which it reacts with carbon dioxide at a temperature of 500 ° C. or higher and separates into zirconia and lithium carbonate.

Further, lithium composite oxides other than lithium zirconate, such as lithium composite oxides such as lithium aluminate, lithium titanate, lithium ferrite, lithium nickelate, and lithium silicate containing aluminum, titanium, iron, nickel, or silicon, are also included. Reacts with carbon dioxide at high temperature exceeding ℃, oxide (alumina, titanium oxide,
For example, Patent Document 1 discloses that carbon dioxide gas can be absorbed (absorption reaction) by decomposition into iron oxide, nickel oxide, or silica) and lithium carbonate.

Furthermore, the carbon dioxide absorption reaction of these lithium composite oxides is reversible, and carbon dioxide gas is released from the reaction product of the lithium composite oxide and carbon dioxide at a temperature higher than the temperature during the absorption reaction (release reaction). . Therefore, these carbon dioxide absorbing materials can recycle lithium composite oxide by releasing the absorbed carbon dioxide again, and can be used repeatedly.

However, for example, in the case of lithium ferrite, the carbon dioxide absorption reaction is 300-50.
As the carbon dioxide releasing reaction from lithium carbonate which has occurred at 0 ° C. and absorbed carbon dioxide occurs at 500 ° C. or higher, the carbon dioxide releasing reaction is a reaction under a higher temperature condition than the carbon dioxide absorbing reaction. For this reason, when carbon dioxide gas is released from the carbon dioxide absorbent that has absorbed carbon dioxide for regeneration, it is necessary to keep the carbon dioxide absorbent at a temperature higher than the temperature during the absorption reaction. Therefore, until now, the heat-resistant temperature of the device itself has to be high, there is a problem that the material for the device used in the carbon dioxide absorption and release reaction is limited, and the use application is also limited. There was a point.

If there is a carbon dioxide absorbing material that can perform carbon dioxide releasing reaction, that is, regeneration reaction of carbon dioxide absorbing material in a state where carbon dioxide is absorbed, at a lower temperature, the range of equipment materials used in the plant and the intended use Can be spread. From this point of view, a material having a lower regeneration reaction temperature and a high carbon dioxide absorption rate has been demanded.
Japanese Patent Application Laid-Open No. 11-90219

The present invention has been made to solve the above-described problems, and an object of the present invention is to allow a release reaction at a low temperature when carbon dioxide gas is released from a state where carbon dioxide gas is absorbed.

In order to achieve the above object, the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent that is a composite oxide containing lithium and iron partially substituted with cobalt or manganese,
An alkali carbonate selected from sodium and potassium or an alkaline earth metal selected from calcium, strontium and barium is added to the composite oxide .

The ratio of cobalt or manganese to iron is preferably in the range of 5 to 40%.

The amount of the carbonate or alkaline earth metal added is preferably 0.01 to 40 mol% with respect to the composite oxide containing lithium and iron partially substituted with cobalt or manganese. .

Further, the carbon dioxide absorption method of the present invention is the carbon dioxide absorption method in which a carbon dioxide absorbent is brought into contact with a gas containing carbon dioxide and selectively reacted with the carbon dioxide in the gas containing carbon dioxide. The carbon dioxide absorber includes a composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese , sodium carbonate, potassium carbonate, calcium, strontium, and And at least one additive selected from barium .

Further, the carbon dioxide absorption device of the present invention includes a composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese , and sodium carbonate and potassium carbonate. A carbon dioxide absorbent containing at least one additive selected from calcium, strontium, and barium, and a carbon dioxide inlet for containing the carbon dioxide absorbent and introducing carbon dioxide. Features.

Further, the carbon dioxide separation device of the present invention comprises a product produced by reacting carbon dioxide with a composite oxide containing lithium and iron partially substituted with cobalt or manganese , and heating the product. It comprises a heating device for releasing carbon dioxide, and a product gas outlet for containing the product and discharging the carbon dioxide.

According to the present invention, when carbon dioxide is released from a state in which carbon dioxide has been absorbed, a release reaction at a low temperature is possible.

  The present invention will be described in detail below.

The carbon dioxide absorbing material made of lithium composite oxide absorbs carbon dioxide at a predetermined temperature or lower. This reaction is reversible, and carbon dioxide gas is released from the reaction product of the lithium composite oxide and carbon dioxide at a temperature higher than the predetermined temperature described above to regenerate the lithium composite oxide. This reverse reaction is hereinafter referred to as a release reaction or a regeneration reaction.

For example, among lithium composite oxides, lithium ferrite containing only iron (Fe) is about 3
The carbon dioxide absorption reaction is performed at about 00 ° C. to 500 ° C., and the temperature of the release reaction is slightly higher than the absorption reaction and is in the range of 500 ° C. This is better than other lithium composite oxides such as lithium silicate.
It is characterized by a low release reaction rate. Furthermore, as a result of further examination on the relationship between the absorption and release characteristics of lithium and iron-containing composite oxides to carbon dioxide, lithium composite oxides in which part of iron was replaced with transition metal elements were compared with lithium ferrite. The carbon dioxide gas release reaction temperature can be kept low, and the carbon dioxide absorption rate is high, and the carbon dioxide absorption material of the present invention, the carbon dioxide absorption method, the carbon dioxide separation method, and the carbon dioxide absorption device using the same. And a carbon dioxide separator.

Lithium composite oxide in which a part of iron is substituted with cobalt and manganese, in particular, has a lower reaction temperature when releasing carbon dioxide (CO ₂ ) than lithium ferrite, and has a high carbon dioxide absorption rate. . The reason why the absorption rate is increased is considered to be that substitution of an atom having an atomic diameter close to that of an iron atom causes distortion in the crystal lattice of the lithium ferrite and facilitates contact between the lithium ion and the CO ₂ molecule.

The composite oxide containing lithium and iron is allowed to be further added with an alkali carbonate selected from sodium and potassium, and an alkaline earth metal selected from calcium, strontium and barium. By adding such a carbonate, the carbon dioxide absorption and release reactions of the obtained carbon dioxide absorbent are promoted. The amount of carbonate added is preferably 0.01 to 40 mol% with respect to the composite oxide containing lithium and iron partially substituted with cobalt or manganese . When the amount of carbonate added is less than 0.01 mol%, it is difficult to sufficiently exhibit the effect of promoting the carbon dioxide gas absorption reaction. On the other hand, if the amount of carbonate added exceeds 40 mol%, the effect of promoting the carbon dioxide absorption reaction cannot be obtained, or the amount of carbon dioxide absorbed per volume of the carbon dioxide absorbent may be reduced.

Carbon dioxide absorbent according to the present embodiment described _{above, Li (Fe x M 1-} x) O2 ( although, M is considered to contact with 0 ₂ molecule with a cobalt or manganese is promoted. Therefore, When the molecular ratio of iron with respect to cobalt or manganese to be substituted is 0.95 or more, the crystal lattice does not change so that the contact with the CO ₂ molecule is promoted, and the carbon dioxide absorption characteristic decreases, and 0.6 Since the amount of cobalt or manganese to be substituted is too large, the carbon dioxide absorption characteristics as lithium ferrite may be impaired.

For molding, a binder material (binding material) for binding particles can be used. For the binder, either an inorganic material or an organic material can be used. For example, examples of the inorganic material include clay, mineral, and lime milk. Examples of the organic material include starch, methylcellulose, polyvinyl alcohol, and paraffin. The added amount of the binder is preferably 0.1 to 20 wt% with respect to the carbon dioxide absorbent component. The binder is held in a porous body of a solution dissolved in a solvent, and the alkali carbonate selected from lithium, sodium and potassium added is held in the pores.

The carbon dioxide absorbing material related to the present embodiment described above is Li (FexM1-x) O2 (however,
M is a composite oxide containing at least one selected from transition metals other than Fe and represented by a molecular formula of 0 <x <1) and lithium partially substituted with a transition metal element. The range of x indicating the exchange rate with other transition metal elements for exhibiting the temperature characteristics of the composite oxide containing iron partially substituted with lithium and transition metal is 0.6 ≦ x It is desirable that ≦ 0.95. When replacing a part of iron of the lithium composite oxide containing iron with another transition metal,
As described above, it is considered that the change of the crystal lattice promotes the contact with the CO ₂ molecule.
Therefore, when the molecular ratio of iron to the transition metal to be substituted is 0.95 or more, the crystal lattice does not change so that the contact with the CO ₂ molecule is promoted, so that the carbon dioxide absorption characteristic is reduced. If the amount is 6 or less, the amount of transition metal to be substituted is too large, and the carbon dioxide absorption characteristics as lithium ferrite may be impaired.

This carbon dioxide absorbent absorbs and reacts with carbon dioxide as shown in the following formula (1) to generate lithium carbonate.
_{Absorption: 2LiFe x M y O 2 +} CO 2 → (Fe x M y) 2O 3 + Li 2 CO 3 ··· (1)
Further, when heated to a specific temperature or higher, formula (2) of the reverse reaction (regeneration reaction) of formula (1) occurs, and carbon dioxide gas is released.
_{Play: (Fe x M y) 2O} 3 + Li 2 CO 3 → 2LiFe x M y O 2 + CO 2 ··· (2)

Although these reaction temperatures differ somewhat depending on the carbon dioxide concentration, the reaction shown in the formula (1) is performed at an absorption temperature range of about 500 ° C. (for example, 300 ° C. or more and 510 ° C. or less when the carbon dioxide concentration is 100%). As a result, the carbon dioxide absorbent comprising a composite oxide containing lithium and iron as a main component absorbs carbon dioxide.

The reaction shown in the formula (2) occurs at 500 ° C. or more exceeding the absorption temperature range (depending on the carbon dioxide concentration, for example, 510 ° C. or more when a gas with a carbon dioxide concentration of 100% is flowed), and releases carbon dioxide. Regenerated to the original composite oxide containing lithium and iron. Such carbon dioxide absorption by the carbon dioxide absorbent and the reaction of releasing the carbon dioxide and returning (regenerating) it to the original carbon dioxide absorbent can be repeated.

Note that the temperature range where carbon dioxide absorption and release reactions occur varies depending on the carbon dioxide concentration in the reaction atmosphere, and the upper limit temperature related to the absorption and release reactions increases as the carbon dioxide concentration increases. For example, in the case of lithium ferrite, the CO ₂ concentration is 20%
In this case, the release reaction starts to occur at around 476 ° C., but when the CO ₂ concentration reaches 100%, 51
A release reaction occurs around 0 ° C.

A lithium composite oxide in which a part of lithium and iron is substituted with cobalt or manganese can be prepared by a precipitation method (citric acid method) using a metal organic acid salt. A specific manufacturing method is shown below.

Lithium carbonate, iron carbonate, and basic cobalt carbonate are mixed in a mortar at a predetermined molar ratio, dispersed in pure water, and heated to 60 ° C. Thereafter, citric acid is added and stirred, and the resulting citrate slurry is filtered off and dried at 120 ° C. The obtained powder was calcined at 350 ° C., and the calcined powder was calcined at 400 ° C. to 1000 ° C. for 6 hours to obtain a carbon dioxide absorbent powder.

Subsequently, the carbon dioxide gas absorbent powder was filled in a metal mold having a diameter of 12 mm and pressure-molded to produce a molded body having a porosity of 40%.

1-3 shows a schematic cross-sectional view of a carbon dioxide absorbing device according to the present invention. 1 to 3
The carbon dioxide absorbing device shown in FIG. 1 is an example, and the carbon dioxide absorbing device according to the present invention is not limited to this.

In FIG. 1, a reaction vessel 1 includes an introduction tube 2 for introducing a carbon dioxide-containing gas into the reaction vessel, and an inner tube 3 connected to one end of the introduction tube 2 and located in the reaction vessel. . The wall surface of the inner tube 3 is provided with a ventilation hole so that the gas introduced from the introduction tube 2 into the inner tube 3 can be vented into the reaction vessel 1. For example, a material made of a porous ceramic such as porous alumina and having gas permeability may be used. A carbon dioxide absorbent 4 that reacts with carbon dioxide (CO ₂ ) to produce carbonate is filled in the reaction vessel 1.

First, in the absorption reaction, a CO ₂ -containing gas in a temperature region where the carbon dioxide absorption reaction represented by the formula (1) occurs is supplied from the introduction pipe 2. The carbon dioxide absorbing material 4 undergoes a reaction that absorbs the CO ₂ -containing gas supplied from the inner tube 3 to generate a reaction product.

On the other hand, in the regeneration reaction, the heating means 6 such as a heater is used so that the reaction product (carbonate) generated by the absorption reaction of carbon dioxide is in a temperature region where the release of carbon dioxide represented by the formula (2) occurs.
To heat reaction vessel 1. When the predetermined temperature is reached, CO ₂ from the reaction product (carbonate)
Is released, and CO ₂ is released from the introduction pipe 4 through the inner pipe 3. The heating means 6 may be a method in which any heated gas is brought into contact with the outer periphery of the reaction vessel 1 and the reaction vessel 1 is heated to a predetermined temperature.

In addition, as shown in FIG. 2, if the reaction vessel 21 equipped with inlet pipe 2 and the discharge pipe 25 for introducing a CO ₂ containing gas, while the CO ₂ absorbing reaction is supplied from inlet pipe 2 a CO ₂ containing gas The gas from which CO ₂ has been continuously removed after the absorption reaction can be taken out from the discharge pipe 25.
In this case, the regeneration reaction may be performed by supplying any gas as a carrier gas from the introduction pipe 2 in a temperature region where the carbon dioxide gas releasing reaction represented by the formula (2) occurs. It is also possible to discharge from the continuous discharge pipe 25 of CO ₂ emitted as CO ₂ containing gas CO ₂ from the carbon dioxide gas absorbent of the absorbed state.

Furthermore, in both cases of the absorption reaction and the release reaction, the container 31 can be a fluidized bed type reaction container. In this case, as shown in FIG. 3, the reaction product (carbonate) generated by reacting with the carbon dioxide absorbent 4 or CO ₂ flows by the CO ₂ -containing gas or carrier gas introduced from the introduction pipe 32. Contact efficiency is improved. As in the case of FIG. 2, if the reaction vessel 31 includes the introduction pipe 32 for introducing the CO ₂ -containing gas and the discharge pipe 35, the CO ₂ absorption reaction is performed by supplying the CO ₂ -containing gas from the introduction pipe 32. However, the gas from which the CO ₂ has been continuously removed after the absorption reaction can be taken out from the discharge pipe 35.

(Experiment 1)
The carbon dioxide absorbent used in the experiment is a lithium composite oxide in which a part of lithium and iron is replaced with cobalt . This lithium composite oxide was synthesized as follows.

73.9 g of lithium carbonate (39.85 wt% as lithium oxide) and iron hydroxide 419.
4 g (68.25 wt% as Fe ₂ O ₃ ) and basic cobalt 24.8 g (61.04 wt)
%) Was dispersed in 1000 g of pure water and heated to 50 to 60 ° C., and then 433 g of citric acid was added and stirred.

The obtained citric acid slurry was filtered off, dried at 120 ° C. and calcined at 350 ° C.
Firing was performed at 0 ° C. to 1000 ° C. for 12 hours to obtain a carbon dioxide absorbent LiFe _0.9 Co _0.1 O ₂ .

The carbon dioxide absorption and release characteristics of the obtained carbon dioxide absorbent were evaluated as follows.

First, the carbon dioxide absorption characteristic of the carbon dioxide absorbent is such that the carbon dioxide absorbent is installed in an electric furnace and is held at a temperature of 500 ° C. for 3 hours while carbon dioxide is circulated in the electric furnace to absorb the carbon dioxide. It was. The change in weight of the carbon dioxide absorbent before and after absorption of carbon dioxide was measured, and this change in weight was evaluated as the amount of carbon dioxide absorbed.

The carbon dioxide gas-absorbing property of the carbon dioxide absorbent that has absorbed carbon dioxide gas is first maintained at 500 ° C. for 3 hours while circulating the carbon dioxide gas through the carbon dioxide absorbent, and once returned to room temperature, the weight is measured ( This is defined as the weight of the carbon dioxide absorbent before releasing carbon dioxide), and then the gas conditions were the same as those for the carbon dioxide absorption reaction, and the carbon dioxide was released by holding at 700 ° C. for 1 hour. The change in weight before and after the release of carbon dioxide was measured, and this change in weight was evaluated as the amount of released carbon dioxide.
The results at this time are shown in Table 1.

(Experiment 2)
To change the amount of cobalt substitution for iron to the amount shown in Table 1, 73.9 lithium carbonate
g (39.85 wt% as lithium oxide) and iron hydroxide 372.8 g (Fe ₂ O ₃ as 6
8.25 wt%) and 49.6 g (61.04 wt%) of basic cobalt were dispersed in 1000 g of pure water and heated to 50-60 ° C., after which 433 g of citric acid was added and stirred.

Firing and carbon dioxide absorbing materials were prepared in the same manner as in Experiment 1, and further, carbon dioxide absorbing characteristics and releasing characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

(Experiment 3)
To change the amount of cobalt substitution for iron to the amount shown in Table 1, 73.9 lithium carbonate
g (39.85 wt% as lithium oxide) and 326.2 g of iron hydroxide (6 as Fe ₂ O ₃
8.25 wt%) and 99.2 g (61.04 wt%) of basic cobalt were dispersed in 1000 g of pure water and heated to 50 to 60 ° C., after which 433 g of citric acid was added and stirred.

Firing and carbon dioxide absorbing materials were prepared in the same manner as in Experiment 1, and further, carbon dioxide absorbing characteristics and releasing characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

(Experiment 4)
Instead of cobalt, a carbon dioxide absorbent in which iron was replaced with manganese was used.

73.9 g of lithium carbonate (39.85 wt% as lithium oxide) and iron hydroxide 419.
4 g (68.25 wt% as Fe ₂ O ₃ ) and manganese carbonate 21.9 g (61.04 wt%)
) Was dispersed in 1000 g of pure water and heated to 50-60 ° C., and then 433 g of citric acid was added and stirred.

The obtained citric acid slurry was filtered off, dried at 120 ° C. and calcined at 350 ° C.
The carbon dioxide absorbent LiFe _0.9 Mn _0.1 O ₂ was obtained by firing at 0 ° C. to 1000 ° C. for 12 hours.

Further, the carbon dioxide absorption and release characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

(Comparative Experiment 1)
Except for using lithium ferrite, the carbon dioxide absorption and release characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

(Comparative experiment 2)
To change the amount of cobalt substitution for iron to the amount shown in Table 1, 73.9 lithium carbonate
g (39.85 wt% as lithium oxide) and 186.4 g of iron hydroxide (6 as Fe ₂ O ₃
8.25 wt%) and 148.8 g (61.04 wt%) of basic cobalt in 1000 g of pure water
The mixture was dispersed therein and heated to 50-60 ° C., and then 433 g of citric acid was added and stirred. Experiment 1
In the same manner as above, firing and carbon dioxide absorbing materials were prepared, and the carbon dioxide absorbing characteristics and releasing characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

(Comparative Experiment 3)
Lithium ferrite and a lithium composite oxide containing cobalt were mixed at a ratio of 9: 1, and the carbon dioxide absorption and release characteristics were evaluated in the same manner as in Experiment 1. The results are also shown in Table 1.

From Table 1, the carbon dioxide absorbents in Experiments 1 to 4 are lithium ferrite (Comparative Experiment 1).
Compared with the carbon dioxide gas absorbent material, the carbon dioxide gas absorption amount was large, and it was revealed that it has excellent carbon dioxide gas absorption characteristics. Further, in terms of the amount of carbon dioxide released, the carbon dioxide absorbents of Examples 1 to 4 were superior to Comparative Experiment 1 and were confirmed to be materials that can be absorbed and released.

Further, the carbon dioxide absorbing material of Experiments 1 to 4 has a larger carbon dioxide absorption than the carbon dioxide absorbing material of Comparative Experiment 2, and the amount of carbon dioxide released is also released in the case of Examples 1 to 4 compared to Comparative Experiment 2. The amount is large. In particular, it was confirmed that the most excellent carbon dioxide absorption characteristic or emission characteristic was exhibited when the substitution amount of cobalt with respect to iron was 9: 1 by molar ratio.

Further, the carbon dioxide absorption material of Experiment 1 has a larger carbon dioxide absorption and release amount than the absorption material of Comparative Experiment 3, and the lithium composite oxide in which a part of iron is substituted with cobalt or manganese has excellent absorption characteristics. And the release characteristics were revealed.

1 is a schematic cross-sectional view of a carbon dioxide absorbing device according to the present invention. 1 is a schematic cross-sectional view of a carbon dioxide absorbing device according to the present invention. 1 is a schematic cross-sectional view of a carbon dioxide absorbing device according to the present invention.

Explanation of symbols

1, 21, 31 ... reaction vessel,
2, 32 ... introduction pipe,
3 ... Inner pipe,
4 ... Carbon dioxide absorber,
25, 35 ... exhaust pipe,
6 ... Heating device

Claims (6)

A composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese;
  At least one additive selected from sodium carbonate, potassium carbonate, calcium, strontium and barium;
  A carbon dioxide absorbent comprising: The carbon dioxide gas absorbent according to claim 1, wherein the ratio of at least one element selected from cobalt and manganese to iron is in the range of 5 to 40%. The additive is 0.01 to 40 mol% with respect to the composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese. The carbon dioxide absorbing material according to claim 1. In the carbon dioxide absorption method of bringing a carbon dioxide absorbent into contact with a gas containing carbon dioxide and selectively reacting with the carbon dioxide in the gas containing carbon dioxide,
The carbon dioxide absorbent is a composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese ,
At least one additive selected from sodium carbonate, potassium carbonate, calcium, strontium and barium;
Carbon dioxide absorption method characterized by including . A composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese, and at least one selected from sodium carbonate, potassium carbonate, calcium, strontium and barium A carbon dioxide absorber containing seed additives ,
A carbon dioxide absorbing device comprising: the carbon dioxide absorbing material; and a carbon dioxide inlet for introducing carbon dioxide. A composite oxide containing lithium and iron partially substituted with at least one element selected from cobalt and manganese ;
A product produced by reacting carbon dioxide with a carbon dioxide absorbent containing at least one additive selected from sodium carbonate, potassium carbonate, calcium, strontium and barium ;
A heating device for heating the product and releasing carbon dioxide;
A carbon dioxide separator, comprising a product gas outlet for storing the product and discharging the carbon dioxide.

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