JP2016003156A - METHOD FOR MANUFACTURING α-SODIUM FERRITE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel material exhibiting high COabsorption rate in a low temperature range of 400°C or less without using lithium as a main raw material, a manufacturing method of the material, an absorption method of carbonic acid gas, a carbonic acid gas absorption device, and a carbonic acid gas separation device.SOLUTION: There is provided a manufacturing method of α-lithium ferrite including a process (a1) of mixing γ- FeOand NaNOto obtain a mixture powder MP1 or a process (a2) of mixing γ- FeO, NaNOand LiNOand/or KNOto obtain a mixture powder MP2, where a molar ratio of LiNOand/or KNOto NaNOis in a range of 0.85:0.15 to less than 1:over 0, and a process (b1) of heating the resulting mixture powder MP1 or MP2 at a temperature of 570°C to 700°C to produce α-NaFeOor substituted type-NaFeOor a process (b2) of heating the resulting mixture powder MP1 or MP2 at a temperature T1 of 550 to 600°C, then increasing the temperature to a temperature T2 of 570 to 750°C, where T1<T2, and then further heating the powder to produce α-NaFeOor substituted type-NaFeO, where the substituted type-NaFeOis a compound with a part of Na substituted by Li and/or K.

Description

  The present invention relates to a method for producing α-sodium ferrites.

As one of the measures against global warming, CO ₂ removal technology from exhaust gas is attracting attention. As one of representative methods, a CO ₂ absorbent using lithium ferrite (α-LiFeO ₂ ) is known.

Japanese Patent Laying-Open No. 2005-270842 (Patent Document 1) discloses a CO ₂ absorbent using lithium ferrite (α-LiFeO ₂ ) having an absorption temperature of CO ₂ gas of about 300 to 500 ° C. This CO ₂ absorber is α-LiFeO ₂ synthesized by substituting a part of iron with cobalt or manganese, and it improves the absorption rate of CO ₂ gas and the regeneration temperature to α-LiFeO ₂ after CO ₂ absorption We aim to lower the temperature.

Similarly, it is a CO ₂ absorber using lithium ferrite (α-LiFeO ₂ ), which has improved CO ₂ absorption rate, and relates to lithium ferrite obtained by mixing α-LiFeO ₂ and potassium carbonate. Technology has also been published [M.Kato et al., CO ₂ absorption property of lithium ferrite for application as a high-temperature CO ₂ absorption, Journal of the ceramic society of Japan, 113 [10], 684-686 (2005) ( Non-patent document 1)].

Furthermore, Patent Document 2 discloses a new α-LiFeO ₂ having a CO ₂ absorption ability in a temperature range of 200 to 500 ° C. and improved CO ₂ absorption in a relatively low temperature range of 450 ° C. or less, and its production method. It is described in.

JP 2005-270842 A JP 2009-234810 A (Patent No. 5279310)

M. Kato et al., Journal of the ceramic society of Japan, 113 [10], 684-686 (2005) M.C.Blesa et al., Solid State Ionic 126 (1999) 81-87 M.C.Blesa et al., Journal of Solid State Chemistry 129, 123-129 (1997)

As described above, α-LiFeO ₂ described in Patent Document 2 has a CO ₂ absorption capacity in a temperature range of 200 to 500 ° C. and a material with an improved CO ₂ absorption rate in a relatively low temperature range of 450 ° C. or less. It was a material effective in absorbing carbon dioxide gas. However, since lithium is used as a component, it is a material with high cost and anxiety about acquisition of resources. Furthermore, it is desired to provide a new material that enables CO ₂ absorption at lower temperatures.

Therefore, the present invention aims to solve the above-mentioned problems, and a new material that exhibits a high CO ₂ absorption rate in a low temperature range of 400 ° C. or less without using lithium as a main raw material and its production The main purpose is to propose a method.

  Another object of the present invention is to provide a carbon dioxide gas absorption method, a carbon dioxide gas absorption device, and a carbon dioxide gas separation device using the new material as a carbon dioxide gas absorbent.

The present inventors have made various studies for the purpose of solving the above problems. As a result, it was found that α-NaFeO ₂ and substituted α-NaFeO _{2 in} which a part of Na was substituted with another alkali metal showed a high CO ₂ absorption rate in a low temperature range of 400 ° C. or less, and The present invention was completed by finding a new production method.

Α-NaFeO ₂ is a compound that has been known for more than 100 years. As a production method, for example, a hydrothermal synthesis method using an aqueous solution of goethite (FeOOH) and NaOH described in Non-Patent Document 2 as raw materials. In addition, a solid phase synthesis method using α-Fe ₂ O ₃ and Na ₂ O ₂ cited in Non-Patent Document 3 as raw materials is known. However, these documents do not describe the CO ₂ absorption behavior of α-NaFeO ₂ .

The present invention is as follows.
[1]
Step (a1) of obtaining γ-Fe ₂ O ₃ and NaNO ₃ to obtain mixed powder MP1, or γ-Fe ₂ O ₃ , NaNO ₃ and LiNO ₃ and / or KNO ₃ to obtain mixed powder MP2 step (a2), provided that the molar ratio of LiNO ₃ and / or KNO ₃ for NaNO ₃ 0.85: less than 0.15: 0 range greater than,
Step (b1) of heating the obtained mixed powder MP1 or MP2 to a temperature of 570 ° C. to 750 ° C. to produce α-NaFeO ₂ or substituted-NaFeO ₂ , or the obtained mixed powder MP1 or MP2 from 550 to 550 ° C. Heating to a temperature T1 of 600 ° C., then raising the temperature to a temperature T2 of 570 to 750 ° C. (where T1 <T2) and further heating to produce α-NaFeO ₂ or substituted-NaFeO ₂ (b2 ),
However, substituted-NaFeO ₂ is a compound in which a part of Na is substituted with Li and / or K.
For producing α-lithium ferrites comprising
[2]
The manufacturing method according to [1], wherein the heating time of the mixed powder MP1 or MP2 in the step (b1) is 40 hours or more.
[3]
The heating time of the mixed powder MP1 or MP2 at the temperature T1 in the step (b2) is 1 to 50 hours, and the heating time of the mixed powder MP1 or MP2 at the temperature T2 is in the range of 5 to 30 hours. Manufacturing method.
[4]
A gas containing carbon dioxide gas is brought into contact with a carbon dioxide absorbent containing α-lithium ferrites obtained by the production method according to any one of [1] to [3], and the gas containing the carbon dioxide gas A carbon dioxide absorption method for selectively reacting with the carbon dioxide.
[5]
Carbon dioxide gas absorbent containing α-lithium ferrites obtained by the production method according to any one of [1] to [3], and carbon dioxide for containing the carbon dioxide absorbent and introducing carbon dioxide A carbon dioxide absorption device comprising: comprising a gas inlet.
[6]
A product produced by reacting carbon dioxide with the carbon dioxide absorbent containing the α-lithium ferrite obtained by the production method according to any one of [1] to [3], and heating the product. A carbon dioxide gas separation device comprising: a heating device for releasing carbon dioxide gas; and a product gas outlet for containing the product and discharging the carbon dioxide gas.

According to the present invention, it is possible to propose a new material exhibiting a high CO ₂ absorption rate in a low temperature range of 400 ° C. or lower and a method for producing the same without using lithium as a main raw material.
Furthermore, according to the present invention, it is possible to provide a carbon dioxide absorption method, a carbon dioxide absorption device, and a carbon dioxide separation device that use the new material as a carbon dioxide absorbent.

The XRD pattern of the conventional CO ₂ absorber α-LiFeO ₂ is shown. _{(a) α-LiFeO 2,} (b) Na5% substituted _{α-LiFeO 2, (b)} Na15% substituted alpha-LiFeO ₂ The XRD pattern of the powder obtained by one-step heat treatment at 550 ° C, 600 ° C, or 750 ° C for 15 hours is shown. The XRD pattern of the powder which heat-treated the raw material mixed powder for 15 hours at 550 ° C. for 15 hours and then at 600 ° C. for 15 hours (two-step heat treatment) is shown. An XRD pattern of a powder obtained by heat-treating a raw material mixed powder containing 10% or 5% of KNO ₃ or LiNO ₃ at 600 ° C. for 15 hours after heat treatment at 550 ° C. for 15 hours (two-stage heat treatment) is shown. (a) K10% substituted α-NaFeO ₂ , (b) Li5% substituted α-NaFeO ₂ The XRD pattern of the powder which heat-processed 650-750 degreeC 15h (two-step heat treatment) after 550 degreeC15h heat processing for the raw material mixed powder is shown. (a) α-NaFeO _2, (b) α-NaFeO _2, (c) α-NaFeO _2,

<Method for producing α-lithium ferrites>
Step (a1)
In step (a1), γ-Fe ₂ O ₃ and NaNO ₃ are mixed to obtain a mixed powder MP1. The mixing ratio of γ-Fe ₂ O ₃ and NaNO ₃ is suitably 1: 1 as a molar ratio. The target α-lithium ferrites can be obtained even when the molar ratio deviates from 1: 1. Practically, for example, it is preferably in the range of 1: 0.9 to 1.2, and 1: 0.95 to 1.15. It is more preferable to set the range. The .gamma. Fe ₂ O ₃ and NaNO ₃ is used as a raw material is not particularly limited, can be used as a commercial product. However, depending on the purity of the commercially available product, it can be made into a mixed powder after being appropriately purified by a known method. In addition, considering the reactivity with NaNO ₃ , γ-Fe ₂ O ₃ may be preferably a powder having a relatively small particle size.

Step (a2)
In the step (a2), γ-Fe ₂ O ₃ , NaNO ₃ and LiNO ₃ and / or KNO ₃ are mixed to obtain a mixed powder MP2. The mixing ratio of γ-Fe ₂ O ₃ and NaNO ₃ , LiNO ₃ and / or KNO ₃ (γ-Fe ₂ O ₃ : (NaNO ₃ + LiNO ₃ and / or KNO ₃ )) is 1: 1 at a molar ratio. is there. The target α-lithium ferrites can be obtained even when the molar ratio deviates from 1: 1. Practically, for example, it is preferably in the range of 1: 0.9 to 1.2, and 1: 0.95 to 1.15. It is more preferable to set the range. The molar ratio of LiNO ₃ and / or KNO ₃ for NaNO ₃ 0.85: less than 0.15: 0, such as more than, 0.999: in the range of 0.001. The molar ratio of LiNO ₃ and / or KNO ₃ for NaNO ₃ is determined in consideration of the CO ₂ absorption properties that change depending on the substitution of Na by Li and / or K, of Na by Li and / or K This can be determined as appropriate based on the desired substitution amount. However, when the molar ratio is out of 0.85: 0.15, it tends to be difficult to produce substituted-NaFeO ₂ under the following heating conditions. From the viewpoint of ease of synthesis of substituted-NaFeO ₂ and the effect of the CO ₂ absorption characteristics and substitution become more apparent, the molar ratio of LiNO ₃ and / or KNO ₃ to NaNO ₃ is 0.9: 0.1 to 0.99: 0.01. Range. In addition, in consideration of reactivity with NaNO ₃ , LiNO ₃ and / or KNO ₃ , γ-Fe ₂ O ₃ may be preferably a powder having a relatively small particle size.

Step (b1)
In the step (b1), the obtained mixed powder MP1 or MP2 is heated to a temperature of 570 ° C. to 750 ° C. to produce α-NaFeO ₂ or substituted-NaFeO ₂ .
When the mixed powder MP1 is heated to a temperature of 570 ° C. to 750 ° C., α-NaFeO ₂ is generated. The heating time can be appropriately determined based on the production state of α-NaFeO _2. For example, in the range of 570 ° C. to 625 ° C., which is a relatively low temperature, for example, 40 hours or more is appropriate. There is no upper limit on the heating time, but it can be, for example, 100 hours or less. For example, in the range of 570 ° C. to less than 600 ° C., preferably 45 hours or more, and in the range of 600 ° C. to 625 ° C., preferably 40 hours or more. Further, in the range of 625 ° C. which is a relatively high temperature, for example, α-NaFeO ₂ can be generated by heating for less than 40 hours. However, the heating time is a guide and is not intended to be limited. In the step (b1), the heating temperature can be raised or lowered once or twice or more during the heating.

When the mixed powder MP2 is heated to a temperature of 570 ° C. to 700 ° C., substitution-type α-NaFeO ₂ is produced. The heating time can be appropriately determined based on the production state of the substitutional type-α-NaFeO _2. For example, in the range of 570 ° C. to 625 ° C. which is a relatively low temperature, it is appropriate that the heating time is 40 hours or more. . There is no upper limit on the heating time, but it can be, for example, 100 hours or less. For example, in the range of 570 ° C. to less than 600 ° C., preferably 45 hours or more, and in the range of 600 ° C. to 625 ° C., preferably 40 hours or more. Further, in the range of 625 ° C. which is a relatively high temperature, for example, α-NaFeO ₂ can be generated by heating for less than 40 hours.

Process (b2)
In step (b2), the obtained mixed powder MP1 or MP2 is heated to a temperature T1 of 550 to 600 ° C., and then heated to a temperature T2 of 570 to 750 ° C. (where T1 <T2). Thus, α-NaFeO ₂ or substituted-NaFeO ₂ is produced.
Even when the mixed powder MP1 is heated to a temperature T1 of 550 ° C. to 600 ° C., α-NaFeO ₂ is hardly generated or not generated when the heating time is relatively short. However, if the sample heated to the temperature T1 is heated to a temperature T2 (where T1 <T2) of 570 to 750 ° C. and further heated, α-NaFeO ₂ can be generated relatively easily. The heating time of the powder can be appropriately determined based on the production status of α-NaFeO ₂ , the heating at the temperature T1 is, for example, in the range of 1 to 50 hours, and the heating at the temperature T2 is, for example, Α-NaFeO ₂ can be generated by setting the time in the range of 5 to 30 hours. More specifically, the heating time in the range where the temperature T1 is 550 ° C. to less than 570 ° C. is preferably in the range of 10 to 50 hours, and the heating time in the range where the temperature T1 is 570 ° C. or more and less than 600 ° C. is Preferably it is 1 to less than 40 hours. In the heating at the temperature T2 in the step (b2), the heating temperature can be raised or lowered once or twice or more during the heating.

Even when the mixed powder MP2 is heated to a temperature T1 of 550 ° C. to 600 ° C., if the heating time is relatively short, the substitutional α-NaFeO ₂ is not easily generated or generated. However, when the sample heated to the temperature T1 is heated to a temperature T2 of 570 to 750 ° C. (where T1 <T2) and further heated, the substitutional α-NaFeO ₂ can be generated relatively easily. The heating time of the mixed powder MP2 can be appropriately determined based on the production status of α-NaFeO ₂ , the heating at the temperature T1 is, for example, in the range of 1 to 50 hours, the heating at the temperature T2 is For example, substitution type α-NaFeO ₂ can be produced by setting the time in the range of 5 to 30 hours. More specifically, the heating time in the range where the temperature T1 is 550 ° C. to less than 570 ° C. is preferably in the range of 10 to 50 hours, and the heating time in the range where the temperature T1 is 570 ° C. or more and less than 600 ° C. is Preferably it is 1 to less than 40 hours. In the heating at the temperature T2 in the step (b2), the heating temperature can be raised or lowered once or twice or more during the heating.

Substituted α-NaFeO ₂ is a compound in which a part of Na is substituted with Li and / or K, and the molar ratio of Li and / or K to Na is from 0.85: 0.15 to less than 0: 0, for example, 0.999 : The range is 0.001. The substitutional α-NaFeO ₂ changes in CO ₂ absorption characteristics according to the amount of substitution of Na by Li and / or K. The molar ratio of Li and / or K to Na can range, for example, from 0.9: 0.1 to 0.99: 0.01. Substitution type α-NaFeO ₂ is a part of Na substituted with Li, Li substitution type α-NaFeO ₂ , part of Na substituted with K, K substitution type α-NaFeO ₂ and part of Na And K, Li substituted α-NaFeO ₂ substituted with and K.

The α-NaFeO ₂ obtained by the production method of the present invention and the substituted α-NaFeO ₂ can have a specific surface area in the range of 3 to 5 m ² / g, and in the range of 3.5 to 4.6 m ² / g. Can be. Alpha-NaFeO ₂ class of the present invention has a reactivity with CO ₂ at a temperature ranging from 100 to 600 ° C. As shown in Table 1 of Example, in particular, beta-NaFeO _2, and alpha-LiFeO ₂ Compared to the above, it showed excellent CO ₂ absorption capacity at a relatively low temperature of 200 to 500 ° C.

[CO2 absorption method]
The present invention includes a carbon dioxide absorption method. In this carbon dioxide absorption method, a carbon dioxide gas containing sodium ferrite obtained by the production method of the present invention is brought into contact with a gas containing carbon dioxide, and the carbon dioxide gas in the gas containing carbon dioxide is selected. It reacts automatically. The reaction formula is as follows when the sodium ferrite is α-NaFeO ₂ .
Reaction formula: 2α-NaFeO ₂ + CO ₂ → Na ₂ CO ₃ + Fe ₂ O ₃

  The carbon dioxide absorbing material contains sodium ferrites, but the carbon dioxide absorbing material is difficult to handle in the work as it is in powder form, especially when the reaction vessel is filled with the carbon dioxide absorbing material and used. The powder is concentrated and pressure loss is likely to occur. Therefore, the carbon dioxide absorbing material can be used by forming into a porous body made of particles having an average particle diameter of 0.1 to 5.0 mm, for example. 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. The molding can be made into a granule, a columnar shape, a disc shape, a honeycomb shape or the like by granulation or extrusion. This porous porosity is preferably 30 to 50%. If the porosity exceeds 50%, the volume ratio of the components of the carbon dioxide absorbent (sodium ferrites) decreases, the carbon dioxide absorption characteristics deteriorate, and if the porosity is less than 30%, the ratio of the carbon dioxide absorbent There is a possibility that the surface area, that is, the contact area with carbon dioxide gas becomes small, and the carbon dioxide absorption rate is lowered.

  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 (rock salt type lithium ferrite).

The temperature of the carbon dioxide absorption reaction varies somewhat depending on the carbon dioxide concentration, but can be carried out in a temperature range of 200 to 500 ° C., for example. The reaction product mixture of Na ₂ CO ₃ and Fe ₂ O ₃ is regenerated to the original sodium ferrite even when carbon dioxide is released, for example, by heating in an atmosphere not containing carbon dioxide. The Such carbon dioxide absorption of 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.

[CO2 absorber]
The present invention also includes a carbon dioxide absorber. The carbon dioxide absorbing device includes a carbon dioxide absorbing material containing the sodium ferrite and a carbon dioxide introducing port for storing the carbon dioxide absorbing material and introducing carbon dioxide.

  Specifically, the carbon dioxide absorbing device of the present invention includes a reaction vessel, and the carbon dioxide absorbing material is filled in the reaction vessel. Furthermore, it can be composed of an introduction pipe for introducing the carbon dioxide-containing gas into the reaction vessel, and an inner pipe connected to one end of the introduction tube and in the reaction vessel. The wall surface of the inner tube is provided with a vent hole so that the gas introduced from the introduction tube into the inner tube can be vented into the reaction vessel. For example, a material made of a porous ceramic such as porous alumina and having gas permeability may be used.

When the CO ₂ -containing gas is supplied from the introduction tube, the carbon dioxide absorbent absorbs the CO ₂ -containing gas supplied from the inner tube and generates a reaction product (absorption reaction).

[Carbon dioxide separator]
The present invention includes a product produced by reacting carbon dioxide with a carbon dioxide absorbent containing the sodium ferrite, a heating device for heating the product to release carbon dioxide, and the product. And a product gas discharge port for discharging the carbon dioxide gas.

In the carbon dioxide absorption device of the present invention, when the absorption reaction is completed, a heating means such as a heater is used so that the reaction product (carbonate) generated by the carbon dioxide absorption reaction is in a temperature region in which carbon dioxide is released. To heat the reaction vessel. The reaction product reaches a predetermined temperature to release the introduction pipe of CO ₂ through the resulting release of CO ₂ from (carbonate) is tube. The heating means may be a method in which an arbitrary heated gas is brought into contact with the outer periphery of the reaction vessel and the reaction vessel is heated to a predetermined temperature (regeneration reaction).

  In both the absorption reaction and the release reaction, the reaction vessel can be a fluidized bed type reaction vessel in consideration of contact efficiency.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the examples are illustrative of the present invention, and the present invention is not intended to be limited to the examples.

[Preparation of the sodium ferrites]
・ One-step method (synthesis of α-NaFeO ₂ )
Commercial reagents γ-Fe ₂ O ₃ and NaNO ₃ were weighed so that Fe: Na = 1: 1 (molar ratio), and added to ion-exchanged water, followed by ultrasonic stirring for 1 h. Thereafter, ion-exchanged water was removed using an evaporator and dried at 120 ° C. for 2 hours. The raw material mixed powder obtained by drying was mixed in an agate mortar for 30 min on a 120 ° C. hot plate so that NaNO ₃ was not deliquescent. Α-NaFeO ₂ powder by heat treatment of the prepared raw material mixed powder at 550 ° C for 5 to 50 h, then 575 ° C for 5 to 50 h, or 600 to 650 ° C for 15 h to promote thermal decomposition of NaNO ₃ Was synthesized. Conditions and results are shown in Tables 1 and 2.

・_Two -step method (synthesis of α-NaFeO ₂ )
Commercially available γ-Fe ₂ O ₃ and NaNO ₃ were weighed so that Fe: Na = 1: 1 to 1.15 (molar ratio), and added to ion-exchanged water, followed by ultrasonic stirring for 1 h. Thereafter, ion-exchanged water was removed using an evaporator and dried at 120 ° C. for 2 hours. The dried raw material mixed powder was mixed in an agate mortar for 30 min on a hot plate at 120 ° C. so that NaNO ₃ was not deliquescent. The raw material mixed powder thus prepared was heat-treated in the atmosphere at 550 ° C. for 5 to 50 h or at 575 ° C. for 5 to 50 h in order to promote thermal decomposition of NaNO ₃ . The heat-treated powder was pulverized for 10 minutes in an agate mortar on a 120 ° C. hot plate, and then heat-treated in the atmosphere at 600 to 650 ° C. for 15 hours to synthesize α-NaFeO ₂ powder. Conditions and results are shown in Tables 1-3.

-Two-step method (synthesis of K- and Li-substituted α-NaFeO ₂ )
Commercially available γ-Fe ₂ O ₃ , NaNO ₃ and KNO ₃ or LiNO ₃ are weighed so that Fe: Na + K or Na + Li = 1: 1 to 1.15 (molar ratio) and added to ion-exchanged water. Ultrasonic stirring was performed for 1 h. Thereafter, ion-exchanged water was removed using an evaporator and dried at 120 ° C. for 2 hours. The dried raw material mixed powder was mixed in an agate mortar for 30 min on a 120 ° C. hot plate so that NaNO ₃ and KNO ₃ were not deliquescent. The raw material mixed powder thus prepared was heat-treated at 550 ° C. for 15 h in the atmosphere to promote thermal decomposition of NaNO ₃ , KNO ₃ and LiNO ₃ . This heat-treated powder was pulverized in an agate mortar on a 120 ° C hot plate for 10 minutes, and then heat-treated at 600 ° C for 15 hours in the atmosphere to obtain K- and Li-substituted α-NaFeO ₂ powder (shown as α phase in Table 4) Was synthesized. Table 4 shows the conditions and results. When the K or Li substitution amount shown in Table 4 was 0.15, in addition to K or Li substitution type α-NaFeO ₂ , raw material γ-Fe ₂ O ₃ was detected. This suggests that the reactivity of KNO ₃ and LiNO ₃ with γ-Fe ₂ O ₃ is lower than NaNO ₃ , and by increasing the reaction (heating) temperature or increasing the heating time, α A phase can be obtained.

・ One-step method (synthesis of β-NaFeO ₂ )
Commercially available γ-Fe ₂ O ₃ and NaNO ₃ were weighed so that Fe: Na = 1: 1.15 (molar ratio), added to ion-exchanged water, and subjected to ultrasonic stirring for 1 h. Thereafter, ion-exchanged water was removed using an evaporator and dried at 120 ° C. for 2 hours. The dried raw material mixed powder was mixed in an agate mortar for 30 min on a hot plate at 120 ° C. so that NaNO ₃ was not deliquescent. The prepared raw material mixed powder was heat-treated at 750 ° C. for 15 hours. The product was β-NaFeO ₂ powder.

・ Evaluation of CO ₂ absorption capacity
Using a TG-DTA apparatus, the weight increase rate of the sample under a CO ₂ gas flow of 0.01 MP and 100 ml / min was evaluated. The results are shown in Table 5.

(* 1) The reaction rate is calculated with the rate of weight increase due to the following reactions as 100% (M: alkali metal)
2MFeO ₂ + CO ₂ → M ₂ CO ₃ + Fe ₂ O ₃
(* 2) N ₂ adsorption BET method (* 3) Replace 10% of Na with K (* 4) Replace 5% of Na with Li The synthesis conditions for each sample are as follows.
α-NaFeO ₂ ; two-stage heat treatment (550 ° C 15h, 600 ° C 15h)
K-substituted α-NaFeO ₂ ; two-step heat treatment (550 ° C 15h, 600 ° C 15h)
Li-substituted α-NaFeO ₂ ; two-stage heat treatment (550 ° C 15h, 600 ° C 15h)
β-NaFeO ₂ ; one-step heat treatment (750 ° C for 15 hours)
α-LiFeO ₂ ； Two-step heat treatment (600 ℃ 4h)

The present invention is useful in the field related to materials having CO ₂ absorption ability.

Claims (6)

Step (a1) of obtaining γ-Fe ₂ O ₃ and NaNO ₃ to obtain mixed powder MP1, or γ-Fe ₂ O ₃ , NaNO ₃ and LiNO ₃ and / or KNO ₃ to obtain mixed powder MP2 step (a2), provided that the molar ratio of LiNO ₃ and / or KNO ₃ for NaNO ₃ 0.85: less than 0.15: 0 range greater than,
Step (b1) of heating the obtained mixed powder MP1 or MP2 to a temperature of 570 ° C. to 700 ° C. to produce α-NaFeO ₂ or substituted-NaFeO ₂ , or the obtained mixed powder MP1 or MP2 from 550 to Heating to a temperature T1 of 600 ° C., then raising the temperature to a temperature T2 of 570 to 750 ° C. (where T1 <T2) and further heating to produce α-NaFeO ₂ or substituted-NaFeO ₂ (b2 ),
However, substituted-NaFeO ₂ is a compound in which a part of Na is substituted with Li and / or K.
For producing α-lithium ferrites comprising The manufacturing method of Claim 1 whose heating time of mixed powder MP1 or MP2 in a process (b1) is 40 hours or more. The heating time of the mixed powder MP1 or MP2 at the temperature T1 in the step (b2) is 1 to 50 hours, and the heating time of the mixed powder MP1 or MP2 at the temperature T2 is in the range of 5 to 30 hours. Manufacturing method. The carbon dioxide in the gas containing the carbon dioxide gas is brought into contact with a carbon dioxide gas-containing material containing α-lithium ferrites obtained by the production method according to claim 1 to a gas containing carbon dioxide gas. Carbon dioxide absorption method that selectively reacts with gas. A carbon dioxide absorber containing the α-lithium ferrites obtained by the production method according to any one of claims 1 to 3, and a carbon dioxide introduction for containing the carbon dioxide absorber and introducing carbon dioxide. A carbon dioxide absorbing device, comprising: comprising a mouth. A product produced by reacting carbon dioxide with a carbon dioxide absorbent containing the α-lithium ferrites obtained by the production method according to any one of claims 1 to 3, and the product heated to produce carbon dioxide A carbon dioxide gas separation device comprising: a heating device for releasing gas; and a product gas outlet for containing the product and discharging the carbon dioxide gas.