JP2005021781A - Carbon dioxide absorption material, production method for carbon dioxide absorption material, absorption method for carbon dioxide, carbon dioxide separation method, and carbon dioxide separation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon dioxide absorption material having a carbon dioxide releasing reaction temperature suppressed to low and a high carbon dioxide absorption speed. <P>SOLUTION: As the carbon dioxide absorption material 1 capable of both absorbing and desorbing carbon dioxide and repeatedly usable, an α-lithium ferrite is used. The carbon dioxide releasing temperature can be suppressed to low and the carbon dioxide absorption speed of the carbon dioxide absorption material 1 is high. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon dioxide absorbing material, and in particular, a carbon dioxide absorbing material using a lithiated composite oxide, a production method thereof, a carbon dioxide absorbing method using the same, a carbon dioxide separating method using the same, and a method using the same. The present invention relates to a carbon dioxide absorber.
[0002]
[Prior art]
In an apparatus such as an engine that burns fuel mainly composed of hydrocarbons, a technique for collecting carbon dioxide in exhaust gas and suppressing release of carbon dioxide into the atmosphere has been studied. However, in such an apparatus, the temperature of the exhaust gas discharge portion, which is a place suitable for the recovery of carbon dioxide gas, often becomes a high temperature of 300 ° C. or higher.
[0003]
By the way, as a method for separating carbon dioxide, a method using cellulose acetate, a chemical absorption method using an alkanolamine solvent, and the like are known. However, any of the above-described separation methods needs to suppress the introduced gas temperature to 200 ° C. or lower. Therefore, for exhaust gas that requires recycling at high temperature, it is necessary to cool the exhaust gas to 200 ° C. or less once with a heat exchanger or the like, resulting in an increase in energy consumption for carbon dioxide separation. There was a problem.
[0004]
For such a problem, for example, Patent Document 1 discloses a carbon dioxide absorbing material that exhibits carbon dioxide absorbing ability in a high temperature range exceeding 500 ° C. This carbon dioxide absorbing material is made of lithium zirconate, and utilizes the phenomenon that this lithium zirconate reacts with carbon dioxide at a temperature of 500 ° C. or higher and decomposes into zirconia and lithium carbonate.
[0005]
Lithium complex oxides other than lithium zirconate, for example, lithium aluminate, lithium titanate, lithium ferrite, lithium nickelate, lithium silicate, etc. containing aluminum, titanium, iron, nickel, or silicon For example, Patent Document 2 shows that carbon dioxide gas can be absorbed by reacting with carbon dioxide at a high temperature exceeding 200 ° C. and decomposing it into an oxide (alumina, titanium oxide, iron oxide, nickel oxide or silica) and lithium carbonate. And Patent Document 3 and the like.
[0006]
Since the oxide and lithium carbonate produced by the reaction between these lithiated composite oxides and carbon dioxide gas undergo a reverse reaction (carbon dioxide gas release reaction), the absorbed carbon dioxide gas is released and the lithiated composite oxides are released. Can be played back and used repeatedly.
[0007]
However, the reverse reaction described above is a reaction under a higher temperature condition than the carbon dioxide absorption reaction. For example, in the case of lithium silicate, the carbon dioxide absorption reaction is 450 to 700 ° C., and the reverse reaction is 700 to 900 ° C. For this reason, in order to reversely react the carbon dioxide absorbing material that has absorbed carbon dioxide, it is necessary to increase the heat resistance temperature of the device itself, and there is a problem that the range of selection of the material for the device is narrowed and the usage is limited. there were.
[0008]
Therefore, if there is a material having a lower temperature of the reverse reaction, the range of selection of the device material and the usage application in the system can be expanded. From this viewpoint, a material having a lower reverse reaction temperature and a high carbon dioxide absorption rate has been demanded.
[0009]
[Patent Document 1] JP-A-9-99214 [Patent Document 2] JP-A-11-90219 [Patent Document 3] JP-A 2000-262890 [0010]
[Problems to be solved by the invention]
The present invention has been made in view of such problems, and in a carbon dioxide absorbent that can be used repeatedly by absorbing and releasing carbon dioxide, the carbon dioxide gas release reaction temperature can be kept low, and carbon dioxide absorption. An object of the present invention is to provide a carbon dioxide absorbing material having a high speed, a method for producing the same, a carbon dioxide absorbing method using the carbon dioxide absorbing material, a carbon dioxide separating method using the carbon dioxide absorbing material, and a carbon dioxide absorbing device using the carbon dioxide absorbing method.
[0011]
[Means for Solving the Problems]
The present invention is a carbon dioxide gas absorbent characterized by using alpha-lithium ferrite.
[0012]
The present invention relates to a carbon dioxide gas absorbent characterized by mixing lithium carbonate and alpha-ferric oxide, and firing the mixture at 700 ° C. or higher to obtain alpha-lithium ferrite to obtain a carbon dioxide absorbent. It is a manufacturing method.
[0013]
The present invention is characterized in that alpha-lithium ferrite is used for the carbon dioxide absorbent when the carbon dioxide absorbent is brought into contact with a gas containing carbon dioxide to separate the carbon dioxide from the gas containing carbon dioxide. This is a carbon dioxide absorption method.
[0014]
The present invention is a carbon dioxide separation method in which a product obtained by absorbing carbon dioxide in a carbon dioxide absorbent using alpha-lithium ferrite is heated to separate the carbon dioxide from the product.
[0015]
The present invention comprises a reaction vessel having a carbon dioxide gas inlet and a product gas outlet;
This is a carbon dioxide absorbing device provided with a carbon dioxide absorbing material using alpha-lithium ferrite accommodated in the reaction vessel.
[0016]
As a result of intensive studies on the carbon dioxide absorption / release characteristics of various materials, the present inventors, among the lithiated composite oxides, lithium ferrite performs a carbon dioxide absorption reaction at about 300 ° C. to 500 ° C. The temperature at which the reverse reaction (release reaction) is turned on is also in the range of about 500 ° C., which is slightly higher than the absorption reaction, and this temperature is focused on the fact that the reverse reaction temperature is lower than that of lithium silicate and the like. Furthermore, as a result of further examination on the relationship between the crystal structure of lithium ferrite and the carbon dioxide absorption / release characteristics, carbon dioxide absorbers composed mainly of alpha-lithium ferrite release carbon dioxide compared to lithium ferrites with other crystal structures. It was found that the reaction temperature can be kept low and the carbon dioxide absorption rate is faster than other structures.
[0017]
The reason why the absorption rate of carbon dioxide gas is faster than that of beta-lithium ferrite, in which alpha-lithium ferrite has another crystal structure, and gamma-lithium ferrite, can be considered as follows.
[0018]
Beta-lithium ferrite and gamma-lithium ferrite have a tetragonal crystal structure, whereas alpha-lithium ferrite has a cubic crystal system and is more symmetric and has a shorter lattice length. Since a short lattice means fewer iron ions, it has a crystal structure in which lithium ions are excessively contained compared to iron ions (JC Anderson et al., J. Phys. Chem. Solids, 25 , 961-968, 1964). Therefore, since alpha-lithium ferrite has more sites that react with carbon dioxide molecules than other structures, the absorption rate of carbon dioxide is considered to increase. From a three-dimensional comparison of crystal structures, alpha-lithium ferrite is more likely to be in contact with carbon dioxide molecules than the gamma-lithium ferrite because the arrangement of lithium ions is more at the lattice corners. This is also considered to be the reason why the absorption rate of carbon dioxide is fast.
[0019]
Therefore, according to the present invention, a carbon dioxide absorbent that can absorb and release carbon dioxide and can be used repeatedly is provided. This carbon dioxide absorbent has a low carbon dioxide release reaction temperature and a high carbon dioxide absorption rate. It is. As a result, carbon dioxide gas can be absorbed / released without any practical problems, and the range of selection and use of the device material that can relatively reduce the heat-resistant temperature of the device can be widened, and the industrial value is great.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the carbon dioxide absorbing material according to the present invention will be described in detail.
It is preferable to use the lithium ferrite of the present invention represented by the molecular formula of LiFeO ₂ . The carbon dioxide absorption reaction of lithium ferrite is shown in equation (1) and regeneration reaction equation (2).
[0021]
Absorption: 2LiFeO ₂ + CO ₂ → Fe ₂ O ₃ + Li ₂ CO ₃ (1)
Regeneration: Fe ₂ O ₃ + Li ₂ CO ₃ → 2LiFeO ₂ + CO ₂ (2)
[0022]
The carbon dioxide absorbent comprising lithium ferrite as a main component absorbs carbon dioxide in an absorption temperature range of about 500 ° C. (for example, 300 ° C. or more and 530 ° C. or less when the carbon dioxide concentration is 100%). As shown in Fig. 2, it chemically changes to ferric oxide and lithium carbonate.
[0023]
When ferric oxide and lithium carbonate in a state of absorbing the carbon dioxide gas are heated to a high temperature of 500 ° C. or more exceeding the absorption temperature range (for example, about 530 ° C. or more when flowing a gas having a carbon dioxide concentration of 100%), As shown in the formula (2), even if carbon dioxide gas is released, it is regenerated into the original lithium ferrite.
[0024]
Such a carbon dioxide absorption of the carbon dioxide absorbent and the regeneration reaction to the carbon dioxide absorbent can be repeated.
[0025]
The absorption / release temperature range of carbon dioxide varies depending on the carbon dioxide concentration in the reaction atmosphere, and the upper limit temperature of the absorption / release temperature range increases as the carbon dioxide concentration increases.
[0026]
The carbon dioxide absorbing material of the present invention uses alpha-lithium ferrite, and it is assumed that the lithium ferrite component in the carbon dioxide absorbing material contains 90 wt% or more of alpha-lithium ferrite. It may contain 10 wt% or less of beta-lithium ferrite and gamma-lithium ferrite. Further, as will be described later, the carbon dioxide absorbing material may contain an alkali carbonate, a binder component, impurities and the like in addition to the lithium ferrite component.
[0027]
Next, a method for producing the carbon dioxide absorbent of the present invention will be described.
A method for producing a carbon dioxide absorbent comprising lithium ferrite as a main component is obtained by mixing and firing, for example, a raw material powder containing lithium carbonate and ferric alpha oxide as a main component, and a lithium ferrite fired powder is obtained. It becomes an absorbent material.
[0028]
The firing temperature of the raw material powder is 700 ° C. or higher and 1200 ° C. or lower. When calcined at 700 ° C. or lower, not alpha-lithium ferrite but beta-lithium ferrite and gamma-lithium ferrite having different crystal structures are formed. By firing at 700 ° C. or higher, it is possible to obtain alpha-lithium ferrite having a structure in which lithium ions are more likely to be contained excessively and easily contact with other molecules.
[0029]
Here, it is a starting material lithium carbonate and alpha lithium ferrite - mixing ratio of the ferric oxide _{(Li 2 CO 3: Fe 2} O 3) molar ratio can be set to 1: 1. Lithium carbonate may be used in an excessive amount in order to prevent uneven distribution and evaporation.
[0030]
Furthermore, in order to improve the absorption rate of carbon dioxide, an alkali carbonate can be added to the alpha lithium ferrite obtained as described above. The alkali carbonate may be added to the raw material powder before firing and then fired, or may be added after firing. By adding alkali carbonate, lithium ferrite formed by absorption of carbon dioxide and lithium carbonate form eutectic salt with lithium carbonate, the melting point of the material is lowered, and a liquid phase is formed and lithium is easy to move This is considered to promote the carbon dioxide absorption rate.
[0031]
The alkali carbonate is potassium carbonate, sodium carbonate, lithium carbonate or the like, and a mixture thereof can also be added. In the present invention, the addition concentration of the alkali carbonate is desirably 0.01 to 40 mol% with respect to the lithium ferrite component. When the amount is less than 0.01 mol%, the effect of adding potassium carbonate is not observed, and when the amount is more than 40 mol%, the net amount of lithium ferrite is reduced and the carbon dioxide absorption performance is lowered.
[0032]
The carbon dioxide absorbing material is difficult to handle in the powder state, and particularly when the reaction vessel is filled with the absorbing material, the powder is too fine and tends to be dense and cause pressure loss. Therefore, the carbon dioxide absorbing material can be molded into a porous body and used. If it is processed into a molded body, it is easy to handle in terms of work, and if a carbon dioxide gas passage is secured, pressure loss is less likely to occur.
[0033]
The molding can be made into a granule, a columnar shape, a disc shape, a honeycomb shape or the like by granulation or extrusion. Alternatively, the raw material powder before firing may be molded and then fired, or the raw material powder may be fired and then molded.
[0034]
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, methyl cellulose, polyvinyl alcohol, and paraffin. The added amount of the binder is preferably 0.1 to 20 wt% with respect to the lithium ferrite component. The binder can be added in the form of a solution dissolved in an appropriate solvent. As the solvent, water or an organic solvent can also be used.
[0035]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a carbon dioxide absorbing device according to the present invention. 1 is an example, and the carbon dioxide absorber according to the present invention is not limited to this.
[0036]
In FIG. 1, a reaction vessel 4 is provided with a vessel containing a carbon dioxide absorbent 1 in the center, and a carbon dioxide containing gas flow channel 2 to be recovered and a recovered carbon dioxide gas flow channel 3 are provided on both sides thereof. Is provided. A plurality of holes are provided in the wall surface of the container in which the carbon dioxide absorbent 1 is accommodated, and the gas flowing through the flow path 2 and the flow path 3 can flow. A carbon dioxide gas inlet 5 and a product gas outlet 6 are connected to the flow path 2.
[0037]
First, a carbon dioxide-containing gas in a temperature region in which the carbon dioxide absorption reaction shown in (1) above occurs is supplied from the carbon dioxide inlet 5 of the flow path 2. Then, in the surface with respect to the flow path 2 of the absorber 1, a carbon dioxide absorption reaction arises with a carbon dioxide absorber and carbon dioxide, and a reaction product produces | generates. A gas from which carbon dioxide gas has been selectively removed is recovered from the product gas outlet 6.
[0038]
On the other hand, a gas introduction port 7 and a product gas discharge port 8 are connected to the flow path 3, and an arbitrary gas in a temperature region where the carbon dioxide gas release reaction shown in (2) occurs is supplied. However, the reaction product moves to the side of the absorbent material 1 facing the flow path 3, and on the surface of the absorbent material 1 with respect to the flow path 3, carbon dioxide gas is released from the reaction product, and only the carbon dioxide gas is flowed. 3 is released. In order to promote the movement of the reaction product to the side of the absorbent material 1 facing the flow path 3, it is preferable to use a means such as a fluidized bed.
[0039]
Hereinafter, examples showing the characteristics of the carbon dioxide absorbent according to the present invention will be described.
[0040]
(Example 1)
An alpha-ferric oxide powder having an average particle diameter of 10 μm and a lithium carbonate powder having an average particle diameter of 1 μm were prepared in an amount such that the molar ratio of ferric oxide: lithium carbonate was 1: 1. These powders were combined and mixed while being pulverized by a ball mill to obtain a raw material mixed powder having an average particle diameter of 5 μm.
[0041]
The raw material mixed powder was heat-treated at 900 ° C. for 8 hours in the air in a box-type electric furnace to synthesize lithium ferrite powder. When this lithium ferrite powder was examined with an X-ray diffractometer, it was found that 95% or more of alpha-lithium ferrite was contained.
[0042]
Further, potassium carbonate powder having an average particle diameter of 1 μm was prepared in an amount such that the molar ratio of lithium ferrite: potassium carbonate was 1: 0.02, and mixed with the synthesized lithium ferrite to obtain a carbon dioxide absorbent.
[0043]
The carbon dioxide absorption and release performance of this carbon dioxide absorbent was evaluated. 50 g of carbon dioxide gas absorbent powder was placed in an alumina mortar, and the mortar was placed in an electric furnace. While flowing carbon dioxide, it was held at 450 ° C. for 1 hour to absorb carbon dioxide, and then held at 650 ° C. for 1 hour to release carbon dioxide.
[0044]
The weight of the carbon dioxide absorbent increased by 10 wt% in one hour after carbon dioxide absorption, and the weight of the carbon dioxide absorbent decreased by 9.5 wt% in one hour after carbon dioxide release. That is, 10 wt% of carbon dioxide gas is absorbed with respect to the weight of lithium ferrite before absorption, and 9.5 wt% of carbon dioxide gas is released with respect to the weight of the absorbed carbon dioxide gas absorber composed of iron oxide and lithium carbonate. did.
[0045]
(Example 2)
The same method as in Example 1 and a carbon dioxide absorbent containing lithium ferrite powder as a main component were synthesized. This lithium ferrite powder was filled in a mold having an inner diameter of 5 mm and subjected to pressure molding to produce a molded body having a porosity of 40%.
[0046]
50 g of the lithium ferrite molded body was placed in an alumina mortar, and the carbon dioxide absorption and release performance was evaluated in the same manner as in Example 1. At this time, the absorption amount of carbon dioxide gas in 1 hour at the time of carbon dioxide absorption is 9.0 wt% of lithium ferrite before absorption, and the release amount in 1 hour at the time of carbon dioxide release is 8% of lithium ferrite before absorption. It was 0.5 wt%.
[0047]
(Comparative Example 1)
In the same manner as in the example, a raw material mixed powder composed of lithium carbonate and ferric oxide was produced. This mixed powder was pulverized and mixed to obtain a raw material mixed powder.
[0048]
This raw material mixed powder was heat-treated in a box-type electric furnace at 600 ° C. for 8 hours in the atmosphere to synthesize lithium ferrite fired powder. When this lithium ferrite powder was examined with an X-ray diffractometer, it was found that it contained 95% or more of gamma-ferrite.
[0049]
Further, potassium carbonate powder having an average particle diameter of 1 μm was prepared in an amount such that the molar ratio of lithium ferrite: potassium carbonate was 1: 0.02, and mixed with the synthesized lithium ferrite to obtain a carbon dioxide absorbent.
[0050]
The carbon dioxide absorption and release performance of this carbon dioxide absorbent was evaluated. 50 g of lithium ferrite powder was placed in an alumina pot, this pot was placed in an electric furnace, kept at 450 ° C. for 1 hour while flowing carbon dioxide gas, and then held at 650 ° C. for 1 hour. At this time, the amount of carbon dioxide absorbed in one hour at the time of carbon dioxide absorption is 0.8 wt% of lithium ferrite before absorption, and the amount of carbon dioxide released in one hour at the time of carbon dioxide release is lithium before absorption. It was 0.5 wt% of ferrite.
[0051]
(Comparative Example 2)
In the same manner as in the example, a raw material mixed powder composed of lithium carbonate and ferric oxide was produced. This mixed powder was pulverized and mixed to obtain a raw material mixed powder.
This raw material mixed powder was heat-treated at 450 ° C. for 8 hours in a box-type electric furnace to synthesize beta-lithium ferrite calcined powder. When this lithium ferrite powder was examined with an X-ray diffractometer, it was found that it contained 95% or more of beta ferrite.
[0052]
Further, potassium carbonate powder having an average particle diameter of 1 μm was prepared in an amount such that the molar ratio of lithium ferrite: potassium carbonate was 1: 0.02, and mixed with the synthesized lithium ferrite to obtain a carbon dioxide absorbent.
[0053]
The carbon dioxide absorption and release performance of this carbon dioxide absorbent was evaluated. 50 g of lithium ferrite powder was placed in an alumina pot, this pot was placed in an electric furnace, held at 450 ° C. for 1 hour while flowing carbon dioxide gas, and then held at 650 ° C. for 1 hour. At this time, the amount of carbon dioxide absorbed in one hour at the time of carbon dioxide absorption is 0.8 wt% of lithium ferrite before absorption, and the amount of carbon dioxide released in one hour at the time of carbon dioxide release is lithium before absorption. It was 0.5 wt% of ferrite.
【The invention's effect】
As described above, according to the present invention, in a carbon dioxide absorbent that can be used repeatedly by absorbing and releasing carbon dioxide, the carbon dioxide absorption is performed with a low carbon dioxide release reaction temperature and a high carbon dioxide absorption rate. Material can be provided. As a result, carbon dioxide can be absorbed / released without any practical problem, and the heat-resistant temperature of the apparatus can be kept relatively low, so that the range of selection and use of the apparatus material can be expanded, and the industrial value is great.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a carbon dioxide absorber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Carbon dioxide gas absorbing material 2 ... Channel 3 ... Channel 4 ... Reaction vessel 5 ... Carbon dioxide gas inlet 6 ... Product gas outlet 7 ... Gas inlet 8 ... Production gas outlet

Claims (5)

A carbon dioxide absorbent characterized by using alpha-lithium ferrite. A method for producing a carbon dioxide absorbing material, comprising mixing lithium carbonate and alpha-ferric oxide, and firing the mixture at 700 ° C. or higher to obtain alpha-lithium ferrite to obtain a carbon dioxide absorbing material. Carbon dioxide absorption, characterized in that alpha-lithium ferrite is used as the carbon dioxide absorbent when the carbon dioxide absorbent is brought into contact with a gas containing carbon dioxide to separate the carbon dioxide from the gas containing carbon dioxide. Method. A carbon dioxide separation method for separating carbon dioxide from the product by heating a product obtained by absorbing carbon dioxide in a carbon dioxide absorbent using alpha-lithium ferrite. A reaction vessel having a carbon dioxide gas inlet and a product gas outlet;
A carbon dioxide absorber comprising a carbon dioxide absorbent using alpha-lithium ferrite accommodated in the reaction vessel.

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