JP2019042639A - Carbon dioxide adsorbent, regeneration process of carbon dioxide adsorbent, and production process of elimination-type layered metal hydroxide - Google Patents

Abstract

To solve problems of a conventional layered metal hydroxide: that, in order to efficiently eliminate carbon dioxide from the layered metal hydroxide, a high temperature condition (for example, a high temperature condition exceeding 400°C) is necessary, resulting in destruction of a layered structure of the layered metal hydroxide when eliminating carbon dioxide; and that, when the layered structure is destroyed, the layered metal hydroxide cannot adsorb and eliminate carbon oxide repeatedly.SOLUTION: A carbon dioxide adsorbent comprises an elimination-type layered metal hydroxide having an average particle size of 150 nm or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a carbon dioxide adsorbent, a method for regenerating a carbon dioxide adsorbent, and a method for producing a desorption-type layered metal hydroxide.

  The layered metal hydroxide is a layered compound in which a host layer containing a metal hydroxide and a guest layer containing an anion and water are alternately stacked.

Expressing layered metal hydroxides by the ^formula, shown in _{^{[M 2+ 1-x M 3+}} x (OH) 2] x + [A n- x / n] x- · mH 2 O, this time, the host layers ^are indicated by _{^{+ [M 2+ 1-x M}} 3+ x (OH) 2] x, the guest layer ^is indicated by ^{_{[A n- x / n] x-}} · mH 2 O.

The host layer includes a divalent metal ion (M ²⁺ : Mg ²⁺ , Zn ²⁺ , Co ²⁺ , or Ni ²⁺ ) and a trivalent metal ion (M ³⁺ : Al ³⁺ , Fe ³⁺ , Cr ³⁺ , or and Ga ³⁺ etc.) includes, may be formed by octahedrons metal ions are six hydroxyl groups is taken in formed to share edges to each other. The host layer has a positive charge because some of the divalent metal ions are replaced by trivalent metal ions, and the host layer forms a layered structure with the hydroxide sheets overlapping. .

On the other hand, the guest layer contains anions (A ⁿ⁻ : Cl ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , PO ₄ ^3−, etc.) and water, and other molecules. May also be included. The guest layer contains anions so that the layered metal hydroxide is electrically neutral.

  By changing the composition of metal ions contained in the host layer, the charge density of the host layer can be controlled. If the charge density of the host layer is controlled to a specific value, a specific anion can be adsorbed on the host layer. That is, by changing the composition of metal ions contained in the host layer, the host layer can be given adsorption characteristics for specific anions.

  If a specific anion adsorbed on the host layer can be desorbed, the host layer can be used as a functional material that can be regenerated. Therefore, in recent years, not only a technique for adsorbing specific anions on the host layer but also a technique for desorbing specific anions adsorbed on the host layer has been actively developed.

For example, Non-Patent Document 1 and Non-Patent Document 2 use Mg ^{2+ as} a divalent metal ion, Al ³⁺ as a trivalent metal ion, and CO ₃ ²⁻ (in other words, carbon dioxide) as an anion. The layered metal hydroxide used is disclosed. Furthermore, these non-patent documents disclose the release behavior of carbon dioxide when the layered metal hydroxide is heated and the change in the layer structure of the layered metal hydroxide.

Nick D. Hutson et. Al., Chem. Mater., 2004, 16, p.4135-4143 Toshiyuki Hibino et.al., Clays and Clay minerals, Vol.43, No.4, p.427-432, 1995

  However, the conventional layered metal hydroxide requires a high temperature condition (for example, a high temperature condition exceeding 400 ° C.) in order to efficiently desorb carbon dioxide from the layered metal hydroxide. When carbon dioxide is desorbed from an object, the layer structure of the layered metal hydroxide is destroyed. When the layer structure of the layered metal hydroxide is destroyed, carbon dioxide cannot be repeatedly adsorbed and desorbed from the layered metal hydroxide unless the layer structure is reconstructed.

  One embodiment of the present invention has been made in view of the above problems, and has an object of being able to efficiently desorb carbon dioxide from a layered metal hydroxide under a low temperature condition, and to perform layered metal hydroxide. An object of the present invention is to provide a technique in which at least a part of a layer structure of a layered metal hydroxide is not destroyed when carbon dioxide is desorbed from an object.

  As a result of intensive studies, the present inventors have made it possible to efficiently desorb carbon dioxide from the layered metal hydroxide at low temperatures by forming the layered metal hydroxide into nanoparticles, and the layered metal hydroxide. It was found that at least a part of the layer structure of the layered metal hydroxide can be maintained when carbon dioxide is desorbed from the carbon dioxide, and the present invention has been completed. In addition, there is no example which used what made the layered metal hydroxide the nanoparticle as a carbon dioxide absorber until now. That is, the present invention includes the following configurations.

  [1] A carbon dioxide adsorbent characterized by containing a desorption-type layered metal hydroxide having an average particle diameter of 150 nm or less.

[2] The carbon dioxide adsorbent according to [1], wherein the desorption-type layered metal hydroxide includes a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).

  [3] The carbon dioxide adsorbent according to [2], wherein the desorbable layered metal hydroxide satisfies 0.34 ≦ x <1 in the general formula (1). .

  [4] A carbon dioxide adsorbent comprising a step of heating the carbon dioxide adsorbent according to any one of [1] to [3] adsorbing carbon dioxide to 200 ° C. or higher and 400 ° C. or lower. How to play.

  [5] A desorption-type layered metal hydroxide comprising a step of heating a non-desorption type layered metal hydroxide having an average particle size of 150 nm or less to 200 ° C. or more and 400 ° C. or less. Production method.

[6] The production method according to [5], wherein the non-detachable layered metal hydroxide includes a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).

  [7] The production method according to [6], wherein the non-detachable layered metal hydroxide satisfies 0.34 ≦ x <1 in the general formula (1).

  According to one aspect of the present invention, carbon dioxide can be desorbed from a layered metal hydroxide under low temperature conditions, and the layer structure of the layered metal hydroxide can be desorbed when desorbing carbon dioxide from the layered metal hydroxide. At least some can be maintained. Therefore, according to one embodiment of the present invention, there is an effect that adsorption and desorption of carbon dioxide with respect to the layered metal hydroxide can be repeatedly performed.

Layered metal hydroxide nanoparticles obtained by a hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours, and commercially available hydrotalcite (manufactured by Wako Pure Chemical, XRD peak by powder X-ray diffraction measurement (XRD) is shown below. Layered metal hydroxide nanoparticles obtained by a hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours, and commercially available hydrotalcite (manufactured by Wako Pure Chemical, (Hereinafter also referred to as HT), and the average particle diameter obtained by observation with a scanning electron microscope (SEM) and dynamic light scattering measurement (DLS). Layered metal hydroxide nanoparticles obtained by a hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours, and commercially available hydrotalcite (manufactured by Wako Pure Chemical, The composition formula of the layered metal hydroxide calculated from the content of Al ions and Mg ions and the content ratio of Al ions and Mg ions by coupled plasma emission spectroscopy (ICP) is shown below. Layered metal hydroxide nanoparticles obtained by a hydrothermal synthesis method for 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours, and commercially available hydrotalcite (manufactured by Wako Pure Chemical, (Hereinafter also referred to as HT) shows the result of measuring the amount of water and carbon dioxide desorption by heating from room temperature to 600 ° C. with a gas chromatograph mass spectrometer. A layered metal hydroxide nanoparticle obtained by a hydrothermal synthesis method having a reaction time of 4 hours and a commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) at room temperature, 350 ° C., And the structure of the layered metal hydroxide after heating to 600 ° C. shows an XRD peak by powder X-ray diffraction measurement (XRD). Adsorption and desorption of carbon dioxide between layered metal hydroxide nanoparticles obtained by a hydrothermal synthesis method with a reaction time of 4 hours and commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) It shows the result of measuring the desorption amount of carbon dioxide when repeating the above with a gas chromatograph mass spectrometer.

  An embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to each configuration described below, and various modifications can be made within the scope shown in the claims, and technical means disclosed in different embodiments and examples respectively. Embodiments and examples obtained by appropriately combining them are also included in the technical scope of the present invention. Moreover, all the academic literatures and patent literatures described in this specification are used as references in this specification. Unless otherwise specified in this specification, “A to B” representing a numerical range is intended to be “A or more and B or less”. In addition, in this specification, the “layered metal hydroxide” intends a layered metal hydroxide having the same crystal structure as a layered double hydroxide (LDH).

[1. Carbon dioxide adsorbent
The carbon dioxide adsorbent of the present embodiment includes a desorption type layered metal hydroxide having an average particle size of 150 nm or less.

  In the present specification, the “detachable layered metal hydroxide” means a layered metal hydroxide including a host layer from which a guest layer is detached. At this time, in the “leaving-type layered metal hydroxide”, it is sufficient that at least a part of the guest layer is detached from the host layer, and it is not necessary that all the guest layers are detached from the host layer. For example, when the weight of the guest layer when the guest layer is adsorbed to the host layer in a saturated state is “1”, the “desorption-type layered metal hydroxide” is 0.9 or less, more preferably 0.8 or less, more preferably 0.7 or less, more preferably 0.6 or less, more preferably 0.5 or less, more preferably 0.4 or less, more preferably 0. .3 or less, more preferably 0.2 or less, and most preferably 0.1 or less guest layer may be adsorbed.

  On the other hand, the term “non-detached layered metal hydroxide” in this specification means a layered metal hydroxide provided with a host layer to which a guest layer is adsorbed. At this time, in the “non-detached layered layer metal hydroxide”, the guest layer only needs to be adsorbed to at least a part of the host layer, and the guest layer is adsorbed to the host layer in a saturated state. You don't have to. For example, when the weight of the guest layer when the guest layer is adsorbed to the host layer in a saturated state is “1”, the “non-detached layered metal hydroxide” is More than 0.1, more than 0.2, more than 0.3, more than 0.4, more than 0.5, more preferably more than 0.6, more preferably More than 0.7, more preferably more than 0.8, most preferably more than 0.9 guest layers may be adsorbed.

  In the carbon dioxide adsorbent of the present embodiment, the desorbable layered metal hydroxide has an average particle size of 150 nm or less, preferably 140 nm or less, more preferably 130 nm or less, more preferably 120 nm or less, more preferably 110 nm or less, more preferably 100 nm or less, more preferably 90 nm or less, more preferably 80 nm or less, more preferably 70 nm or less, more preferably 60 nm or less, more preferably 50 nm or less, more preferably 40 nm or less, more preferably 30 nm or less. More preferably, it is 20 nm or less, and most preferably 10 nm or less. The lower limit value of the average particle diameter is not limited, but may be, for example, 0.01 nm, 0.1 nm, 1 nm, or 5 nm. According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed under low temperature conditions, and at least part of the carbon dioxide adsorbent is desorbed when desorbing carbon dioxide from the carbon dioxide adsorbent. The layer structure can be maintained. Therefore, according to this configuration, a carbon dioxide adsorbent capable of repeatedly adsorbing and desorbing carbon dioxide can be realized.

  The average particle diameter can be determined by dynamic light scattering measurement (DLS). The dynamic light scattering measurement may be performed using a commercially available device (for example, ELSZ-1000ZS manufactured by Otsuka Electronics Co., Ltd.) according to the protocol attached to the commercially available device.

The detachable layered metal hydroxide may include a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).

“M ²⁺ ” is not particularly limited, and examples thereof include Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Mn ²⁺ , Ni ²⁺ , Co ²⁺ , Cu ²⁺ , and Sr ²⁺ . On the other hand, “M ³⁺ ” is not particularly limited, and examples thereof include Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Mn ³⁺ , Ga ³⁺ , and Co ³⁺ . The combination of “M ²⁺ ” and “M ³⁺ ” in the general formula (1) is not particularly limited, and Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Mn ²⁺ , Ni ²⁺ , Co ²⁺ , Cu ²⁺ , and , Any “M ²⁺ ” selected from the group consisting of Sr ²⁺ , and any “M ³⁺ ” selected from the group consisting of Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Mn ³⁺ , Ga ³⁺ , and Co ³⁺ And a combination. Each of “M ²⁺ ” and “M ³⁺ ” may be configured by a single type of ion, but may be configured by a plurality of types of ions. That is, each of “M ²⁺ ” and “M ³⁺ ” may be configured by mixing a plurality of types of ions selected from the respective groups. In addition, when comprised by multiple types of ion, it can be comprised by 2 types of ions, 3 types of ions, 4 types of ions, or 5 or more types of ions.

From the viewpoint that carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at lower temperature conditions, and when the carbon dioxide is desorbed from the carbon dioxide adsorbent, the layer structure of the carbon dioxide adsorbent can be maintained more stably. Is more preferably Mg ²⁺ , Zn ²⁺ , or Ni ²⁺ in the above-mentioned “M ²⁺ ”, and more preferably Al ³⁺ or Ga ^{3+ in} the above-mentioned “M ³⁺ ”. Among the combinations of “M ²⁺ ” and “M ³⁺ ”, it can be said that a combination of Mg ²⁺ and Al ³⁺ , a combination of Zn ²⁺ and Al ³⁺ , or a combination of Ni ²⁺ and Al ³⁺ is more preferable.

  x may be a number such that 0 <x <1, but is preferably a number such that 0.34 ≦ x <1 and more preferably a number such that 0.35 ≦ x <1. In the range of these x values, the upper limit value of x is “less than 1”, but is not limited to the upper limit value, and the upper limit values are “0.90 or less”, “0.80 or less”, “0” .70 or less "," 0.60 or less "," 0.50 or less ", or" 0.40 or less ". According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at a low temperature, and at least the layer structure of the carbon dioxide adsorbent when desorbing carbon dioxide from the carbon dioxide adsorbent. Some can be maintained. Therefore, according to this configuration, a carbon dioxide adsorbent capable of repeatedly adsorbing and desorbing carbon dioxide can be realized.

  The amount of the desorption-type layered metal hydroxide contained in the carbon dioxide adsorbent of the present embodiment is not particularly limited. For example, when the carbon dioxide adsorbent is 100% by weight, 0.001 % By weight to 100% by weight, 0.01% to 100% by weight, 0.1% to 100% by weight, 0.1% to 95% by weight %, 0.1 wt% to 90 wt%, 0.1 wt% to 80 wt%, or 0.1 wt% to 70 wt% It may be 0.1 wt% to 60 wt%, 0.1 wt% to 50 wt%, 0.1 wt% to 40 wt%, % To 30% by weight, 0.1% to 20% by weight, or 0.1% to 10% by weight. It may be.

  The carbon dioxide adsorbent of the present embodiment can contain components other than the desorbable layered metal hydroxide. These components include, for example, a non-desorbable layered metal hydroxide, and a carrier supporting the desorbed and / or non-desorbed layered metal hydroxide (for example, a porous carrier), Can be mentioned.

  The amount of components other than the desorption-type layered metal hydroxide contained in the carbon dioxide adsorbent of the present embodiment is not particularly limited. For example, when the carbon dioxide adsorbent is 100% by weight, It may be 0% to 99.999% by weight, 0% to 99.99% by weight, 0% to 99.9% by weight, or 5% to 99%. 9.9 wt%, 10 wt% to 99.9 wt%, 20 wt% to 99.9 wt%, 30 wt% to 99.9 wt% May be 40 wt% to 99.9 wt%, 50 wt% to 99.9 wt%, 60 wt% to 99.9 wt%, 70% to 99.9% by weight, 80% to 99.9% by weight, 90% by weight It may be 99.9 wt%.

  The carbon dioxide adsorbent of the present embodiment will be described later [2. Regeneration method of carbon dioxide adsorbent] and / or [3. Production method of detachable layered metal hydroxide]. When a layered metal hydroxide is produced in accordance with the hydrothermal synthesis method, carbon dioxide existing in the atmosphere is adsorbed on the host layer, and the “non-desorption type layered metal water represented by the following general formula (2) is shown. An “oxide” may be formed. For example, the “non-detachable layered metal hydroxide” is 200 ° C. or higher and 400 ° C. or lower, preferably 200 ° C. or higher and 390 ° C. or lower, more preferably 200 ° C. or higher and 380 ° C. or lower, more preferably 200 ° C. or higher and 370 ° C. Or less, more preferably 200 ° C. or higher and 360 ° C. or lower, more preferably 200 ° C. or higher and 350 ° C. or lower, more preferably 200 ° C. or higher and 320 ° C. or lower, more preferably 200 ° C. or higher and 300 ° C. or lower, more preferably 200 ° C. or higher and 270 ° C. Hereinafter, the carbon dioxide adsorbent of the present embodiment can be produced by heating to 200 ° C. or higher and 250 ° C. or lower, most preferably 200 ° C. or higher and 220 ° C. or lower.

[2. (Regeneration method of carbon dioxide adsorbent)
In the carbon dioxide adsorbent regeneration method of this embodiment, the carbon dioxide adsorbent adsorbing carbon dioxide is 200 ° C. or higher and 400 ° C. or lower, preferably 200 ° C. or higher and 390 ° C. or lower, more preferably 200 ° C. or higher and 380 ° C. Or less, more preferably 200 ° C. or more and 370 ° C. or less, more preferably 200 ° C. or more and 360 ° C. or less, more preferably 200 ° C. or more and 350 ° C. or less, more preferably 200 ° C. or more and 320 ° C. or less, more preferably 200 ° C. or more and 300 ° C. or less. In the following, a step of heating to 200 ° C. or higher and 270 ° C. or lower, more preferably 200 ° C. or higher and 250 ° C. or lower, most preferably 200 ° C. or higher and 220 ° C. or lower is included.

  In other words, the method for regenerating a carbon dioxide adsorbent according to the present embodiment is such that carbon dioxide is adsorbed onto a carbon dioxide adsorbent containing a desorption-type layered metal hydroxide, so that a non-desorption type layered metal water is obtained. The carbon dioxide adsorbent that has become an oxide-containing carbon dioxide adsorbent is 200 ° C to 400 ° C, preferably 200 ° C to 390 ° C, more preferably 200 ° C to 380 ° C, more preferably 200 ° C to 370 ° C. Or less, more preferably 200 ° C. or higher and 360 ° C. or lower, more preferably 200 ° C. or higher and 350 ° C. or lower, more preferably 200 ° C. or higher and 320 ° C. or lower, more preferably 200 ° C. or higher and 300 ° C. or lower, more preferably 200 ° C. or higher and 270 ° C. The step of heating to 200 ° C. or higher and 250 ° C. or lower, most preferably 200 ° C. or higher and 220 ° C. or lower is more preferable.

  Here, the carbon dioxide adsorbent before adsorbing carbon dioxide has been described above [1. Since it has already been described in the column of “carbon dioxide adsorbent”, the description thereof is omitted here.

  The carbon dioxide adsorbent adsorbing carbon dioxide can contain a non-desorbed layered metal hydroxide having an average particle size of 150 nm or less.

  The non-detached layered metal hydroxide has an average particle size of 150 nm or less, preferably 140 nm or less, more preferably 130 nm or less, more preferably 120 nm or less, more preferably 110 nm or less, more preferably 100 nm or less, More preferably 90 nm or less, more preferably 80 nm or less, more preferably 70 nm or less, more preferably 60 nm or less, more preferably 50 nm or less, more preferably 40 nm or less, more preferably 30 nm or less, more preferably 20 nm or less, most preferably Is 10 nm or less. The lower limit value of the average particle diameter is not limited, but may be, for example, 0.01 nm, 0.1 nm, 1 nm, or 5 nm. According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at a low temperature, and at least the layer structure of the carbon dioxide adsorbent when desorbing carbon dioxide from the carbon dioxide adsorbent. Some can be maintained. Therefore, according to this configuration, it is possible to regenerate the carbon dioxide adsorbent that maintains the ability to repeatedly adsorb and desorb carbon dioxide.

  The average particle diameter can be determined by dynamic light scattering measurement (DLS). The dynamic light scattering measurement may be performed using a commercially available device (for example, ELSZ-1000ZS manufactured by Otsuka Electronics Co., Ltd.) according to the protocol attached to the commercially available device.

The non-detachable layered metal hydroxide may include a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1),
More specifically, the non-detachable layered metal hydroxide may include a composite of a host layer and a guest layer represented by the following general formula (2):
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ (CO ₃ ) _{x / 2} · mH ₂ O] General formula (2)
(In General Formula (1) and General Formula (2), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, x represents a number of 0 <x <1, and m represents Indicates a number greater than or equal to zero.

“M ²⁺ ” is not particularly limited, and examples thereof include Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Mn ²⁺ , Ni ²⁺ , Co ²⁺ , Cu ²⁺ , and Sr ²⁺ . On the other hand, “M ³⁺ ” is not particularly limited, and examples thereof include Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Mn ³⁺ , Ga ³⁺ , and Co ³⁺ . The combination of “M ²⁺ ” and “M ³⁺ ” in general formula (1) and general formula (2) is not particularly limited, and Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Mn ²⁺ , Ni ²⁺ , Co ^{2+, Cu 2+,} and any ^{"M 2+"} is selected from the group consisting of ^{Sr 2+, Al 3+, Fe 3+} , Cr 3+, Mn 3+, Ga 3+, and is selected from the group consisting of ^{Co 3+} It can be a combination with any “M ³⁺ ”. Each of “M ²⁺ ” and “M ³⁺ ” may be configured by a single type of ion, but may be configured by a plurality of types of ions. That is, each of “M ²⁺ ” and “M ³⁺ ” may be configured by mixing a plurality of types of ions selected from the respective groups. In addition, when comprised by multiple types of ion, it can be comprised by 2 types of ions, 3 types of ions, 4 types of ions, or 5 or more types of ions.

From the viewpoint that carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at lower temperature conditions, and when the carbon dioxide is desorbed from the carbon dioxide adsorbent, the layer structure of the carbon dioxide adsorbent can be maintained more stably. Is more preferably Mg ²⁺ , Zn ²⁺ , or Ni ²⁺ in the above-mentioned “M ²⁺ ”, and more preferably Al ³⁺ or Ga ^{3+ in} the above-mentioned “M ³⁺ ”. Among the combinations of “M ²⁺ ” and “M ³⁺ ”, it can be said that a combination of Mg ²⁺ and Al ³⁺ , a combination of Zn ²⁺ and Al ³⁺ , or a combination of Ni ²⁺ and Al ³⁺ is more preferable.

  x may be a number such that 0 <x <1, but is preferably a number such that 0.34 ≦ x <1 and more preferably a number such that 0.35 ≦ x <1. In the range of these x values, the upper limit value of x is “less than 1”, but is not limited to the upper limit value, and the upper limit values are “0.90 or less”, “0.80 or less”, “0” .70 or less "," 0.60 or less "," 0.50 or less ", or" 0.40 or less ". According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at a low temperature, and at least the layer structure of the carbon dioxide adsorbent when desorbing carbon dioxide from the carbon dioxide adsorbent. Some can be maintained. Therefore, according to this configuration, it is possible to regenerate the carbon dioxide adsorbent that maintains the ability to repeatedly adsorb and desorb carbon dioxide.

  m may be a number of 0 or more, preferably 0.1 ≦ m ≦ 10, and more preferably 0.3 ≦ m ≦ 5. According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at a low temperature, and at least the layer structure of the carbon dioxide adsorbent when desorbing carbon dioxide from the carbon dioxide adsorbent. Some can be maintained. Therefore, according to this configuration, it is possible to regenerate the carbon dioxide adsorbent that maintains the ability to repeatedly adsorb and desorb carbon dioxide.

  The regeneration method of the carbon dioxide adsorbent of the present embodiment includes a step of heating the carbon dioxide adsorbent adsorbing carbon dioxide to 200 ° C. or higher and 400 ° C. or lower. In this process, the carbon dioxide adsorbent adsorbing carbon dioxide is 200 ° C. or higher and 390 ° C. or lower, 200 ° C. or higher and 380 ° C. or lower, 200 ° C. or higher and 370 ° C. or lower, 200 ° C. or higher and 360 ° C. or lower, 200 ° C. or higher and 350 ° C. or lower. Hereinafter, it may be heated to 200 ° C. or higher and 320 ° C. or lower, 200 ° C. or higher and 300 ° C. or lower, 200 ° C. or higher and 270 ° C. or lower, 200 ° C. or higher and 250 ° C. or lower, or 200 ° C. or higher and 220 ° C. or lower. With the carbon dioxide adsorbent used in the present embodiment, carbon dioxide can be efficiently desorbed even at low temperatures, and the structure of the carbon dioxide adsorbent can be stably maintained. If carbon dioxide can be efficiently desorbed at a low temperature, (i) the carbon dioxide adsorbent can be heated to a desired temperature by an inexpensive and simple heating device, and (ii) energy required for heating There is an advantage that (fuel and / or electric power) can be saved. On the other hand, if the structure of the carbon dioxide adsorbent can be stably maintained, (iii) the cost for recovering carbon dioxide can be reduced by repeatedly using the carbon dioxide adsorbent, and (iv) By repeatedly using the carbon dioxide adsorbent, there is an advantage that a troublesome work required for replacing the carbon dioxide adsorbent can be omitted.

  The non-desorbable layered metal hydroxide is not particularly limited in crystallite size, but is 0 to 150 nm, more preferably 5 to 150 nm, more preferably 10 to 150 nm, more preferably 13 to 150 nm, and more preferably. Is 14 to 150 nm, more preferably 15 to 150 nm, more preferably 16 to 150 nm, more preferably 17 to 150 nm, more preferably 18 to 150 nm, more preferably 19 to 150 nm, most preferably 20 to 150 nm. It is. Note that the above-described upper limit value of the crystallite size is not limited to 150 nm, and may be 50 nm, 100 nm, or 150 nm. According to this configuration, carbon dioxide adsorbed on the carbon dioxide adsorbent can be desorbed at a low temperature, and at least the layer structure of the carbon dioxide adsorbent when desorbing carbon dioxide from the carbon dioxide adsorbent. Some can be maintained. Therefore, according to this configuration, it is possible to regenerate the carbon dioxide adsorbent that maintains the ability to repeatedly adsorb and desorb carbon dioxide.

  The crystallite size can be determined from the (003) diffraction line observed by the well-known powder X-ray diffraction measurement (XRD).

[3. Method for producing detachable layered metal hydroxide]
The method for producing a detachable layered metal hydroxide according to the present embodiment includes a step of heating a non-detached layered metal hydroxide having an average particle diameter of 150 nm or less to 200 ° C. or more and 400 ° C. or less. doing.

  Examples of the “non-detachable layered metal hydroxide”, “average particle diameter of the non-detached layered metal hydroxide” and “temperature of the heating step” have been described above [1. Carbon dioxide adsorbent] and / or [2. The same configuration as described in the method for regenerating carbon dioxide adsorbent] can be used.

For example, in the method for producing a detachable layered metal hydroxide of the present embodiment, the non-detached layered metal hydroxide includes a host layer represented by the following general formula (1). May be:
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).

  For example, in the method for producing a detachable layered metal hydroxide according to the present embodiment, the non-detached layered metal hydroxide satisfies 0.34 ≦ x <1 in the general formula (1). It may be a thing.

<1. Production of layered metal hydroxide nanoparticles>
Below, the manufacturing method of the nanoparticle of the layered metal hydroxide in a present Example is demonstrated. In this example, layered metal hydroxide nanoparticles with various particle sizes were produced according to a hydrothermal synthesis method.

First, a 0.6 M MgCl ₂ aqueous solution (5 mL) and a 0.2 M AlCl ₃ aqueous solution (5 mL) are mixed, so that the final concentration of MgCl ₂ is 0.3 M and the final concentration of AlCl ₃ is 0.00. Solution A (10 mL) was prepared, which was 1M.

Separately, a 0.3 M NaOH aqueous solution (20 mL) and a 0.026 M Na ₂ CO ₃ aqueous solution (20 mL) are mixed, so that the final concentration of NaOH is 0.15 M, and the final concentration of Na ₂ CO ₃ is Solution B (40 mL) was prepared, which was 0.013M.

  Solution B was added to a 200 mL Erlenmeyer flask, and Solution A was added to Solution B while stirring Solution B in the Erlenmeyer flask. The mixture of solution A and solution B was then stirred at room temperature for 10 minutes to form a white product.

  The mixture of Solution A and Solution B was centrifuged to collect a white precipitate. The precipitate was washed twice with ion exchange water.

  The washed precipitate was suspended in 40 mL of ion-exchanged water, and layered metal hydroxide nanoparticles were produced according to a hydrothermal synthesis method. The reaction conditions were 100 ° C., and the reaction time was 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours. In addition, about the detail of the hydrothermal synthesis method, it followed the method as described in AU2005318862A1.

  It was confirmed that the white turbidity of ion-exchanged water containing precipitates increased as the hydrothermal synthesis time elapsed (not shown).

<2. Powder X-ray diffraction measurement (XRD)>
Below, the test method of a powder X-ray-diffraction measurement and a test result are demonstrated. In this test, <1. Production of layered metal hydroxide nanoparticles> The layered metal hydroxide nanoparticles obtained by the hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours described in the column> Particles were used, and a commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) was used for the comparative test.

Below, the test method of powder X-ray diffraction measurement is demonstrated.
(Equipment used)
X-ray diffractometer: D8-ADVANCE (Burker AXS Co., Ltd.)
Detector: D8-ADVANCE VANTEC (manufactured by Burker AXS)
Measurement source: Cu Kα with a wavelength of 1.5418 mm
Filter: Ni
(Measurement condition)
X-ray tube load: 40 mA, 35 kV
Measurement angle: 5.0-70.0deg
Sampling interval: 0.007 deg
Divergence slit (incident): 0.6 mm
Receiving slit Detector slit: 12.09mm
Antisitting slit: 7.87mm
Detector acceptance angle: 3.00 °
Next, test results of powder X-ray diffraction measurement will be described.

  FIG. 1 shows the XRD peak. (A) 4 hours reaction time, (b) 8 hours reaction time, (c) 16 hours reaction time, (d) 48 hours reaction time, (e) 72 hours reaction time, Shows the XRD peak of the layered metal hydroxide nanoparticles prepared as (f), and (f) shows the XRD peak of the commercially available hydrotalcite.

  Hereinafter, the symbols (a) to (e) indicate the layered metal hydroxide nanoparticles produced with the reaction time of the hydrothermal synthesis method being 4 hours, 8 hours, 16 hours, 48 hours, and 72 hours, respectively. (F) shows the test result of hydrotalcite which is a commercial product.

  (003) and (006) shown in FIG. 1 show peaks peculiar to the layered metal hydroxide. The above peaks were observed in all of (a) to (e) and (f). Therefore, it became clear that the layered metal hydroxide nanoparticles produced by the production method of the present invention have the same layer structure as the commercially available hydrotalcite even when the reaction time is changed.

  Further, the crystallite size calculated by a well-known method using (003) diffraction lines is 13.4 nm, 13.1 nm, 14.5 nm, 17.1 nm, 17.1 nm for each of (a) to (f). 0 nm and 20.3 nm.

<3. Scanning Electron Microscope Observation (SEM) and Dynamic Light Scattering Measurement (DLS)>
Below, the test method of scanning electron microscope observation and a test result are demonstrated. Moreover, the test method and test result of dynamic light scattering measurement will be described below. In this test, <1. Layered metal hydroxides obtained by a hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours described in the column “Production of nanoparticles of layered metal hydroxides> In the comparative control test, commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) was used.

Below, the test method of scanning electron microscope observation is demonstrated.
(Used equipment)
Scanning electron microscope: S4800 (manufactured by Hitachi)
(Measurement condition)
Accelerating voltage: 15kV (normal)
20kV (when using EDX)
Next, test results of observation with a scanning electron microscope will be described.

  FIG. 2 shows images observed by SEM from (a) to (f). In all of (a) to (e), hexagonal plate-like crystals were observed, and an increasing tendency of the particle diameter with increasing reaction time was observed. On the other hand, since the crystal in (f) is agglomerated, the shape of the crystal could not be confirmed.

The dynamic light scattering measurement test method will be described below.
(Used equipment)
Dynamic light scattering measuring device: ELSZ-1000ZS (manufactured by Otsuka Electronics Co., Ltd.)
Next, test results of dynamic light scattering measurement will be described.

  The average particle sizes of (a) to (f) are (a) about 61 nm, (b) about 70 nm, (c) about 82 nm, (d) about 98 nm, and (e) about 116 nm, respectively. there were.

<4. Coupled Plasma Emission Spectroscopy (ICP)>
Below, the test method of a coupled plasma emission spectroscopic analysis and a test result are demonstrated. In this test, <1. Production of layered metal hydroxide nanoparticles> The layered metal hydroxide nanoparticles obtained by the hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours described in the column> Particles were used, and a commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) was used for the comparative test.

A test method for coupled plasma emission spectroscopic analysis will be described below.
(Used equipment)
ICP measuring device: iCAP6500 (manufactured by Thermo Fisher Scientific Co., Ltd.)
(Measurement condition)
Measuring elements: Al and Mg
Measurement direction: Axial Sample form: Liquid Calibration curve condition: Absolute calibration curve method (sample preparation method)
A sample of 10 mg was dissolved in 1 ml of NHO ₃ and the volume was adjusted to 50 ml with ultrapure water. A fixed volume sample was diluted 5 times to obtain a measurement sample.

As the standard solution for Al, to prepare a solution containing 2.0,4.0,6.0 and 8.0ppm of _{Al (NO 3) 3 · 9H} 2 O, a calibration curve was prepared by using the solution.

As a standard solution for Mg, a solution containing 2.5, 5.0, 7.5, and 10 ppm of Mg (NO ₃ ) ₂ .6H ₂ O was prepared, and a calibration curve was prepared using the solution. .

  Next, the test result of the coupled plasma emission spectroscopic analysis will be described.

  FIG. 3 shows the contents and composition of Al and Mg contained in (a) to (f).

  As shown in (a) to (e) of FIG. 3, the content of Al ions relative to the metal ions (added with the content of Al ions and the content of Mg ions) contained in the layered metal hydroxide nanoparticles No difference was observed in the ratio, and x in the general formula (1) became constant. Therefore, it became clear that the reaction time had no effect on the composition. In addition, sodium carbonate is used as a raw material for the layered metal hydroxide nanoparticles, and since the layered metal hydroxide nanoparticles have the property of easily inserting carbonate ions into the guest layer, carbonate ions are selected as anions. Has been inserted.

  As shown in FIG. 3 (f), the commercially available hydrotalcite had a composition different from the layered metal hydroxide nanoparticles prepared by the hydrothermal synthesis method.

<5. Carbon dioxide and water desorption behavior observation test>
Below, the test method of the desorption behavior observation test of carbon dioxide and water and the test results will be described. In this test, <1. Production of layered metal hydroxide nanoparticles> The layered metal hydroxide nanoparticles obtained by the hydrothermal synthesis method with a reaction time of 4 hours, 8 hours, 16 hours, 48 hours, or 72 hours described in the column> Particles were used, and a commercially available hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) was used for the comparative test.

Below, the test method of the desorption behavior observation test of carbon dioxide and water will be described.
(Used equipment)
Mass spectrometer: JMS-Q1050GC (manufactured by JEOL Ltd.)
Carrier gas: Ar (100 cc / min.)
(Measurement condition)
Quartz wool and about 30 mg of layered metal hydroxide sample are placed in a quartz tube cell, heated to 600 ° C. at 10 ° C./min in an electric furnace, and desorbed carbon dioxide and water are analyzed with a gas chromatograph mass spectrometer. Went.

  Next, the test results of the carbon dioxide and water desorption behavior observation test will be described.

  FIG. 4 shows the desorption behavior of water and carbon dioxide in the layered metal hydroxide nanoparticles (a) to (e) and the hydrotalcite (f).

The upper part of FIG. 4 shows the water desorption behavior, and no difference was observed in the water desorption behavior from (a) to (f). Further, in the water desorption behavior observation test, peaks were observed at around 220 ° C., 330 ° C., and 400 ° C. These are the separation of water during thermal decomposition of typical MgAl-LDH-CO ₃ particles (layered metal hydroxide particles in which Mg ions and Al ions are used as metal ions and carbon dioxide is inserted into the guest layer). It is considered to be behavior. Specifically, desorption of water at about 220 ° C. is considered to be desorption of water contained in the interlayer (guest layer). The desorption of water at about 330 ° C. is considered to be the desorption of water due to the condensation dehydration of Al—OH. The desorption of water at about 400 ° C. is considered to be the desorption of water due to condensation dehydration of Mg—OH and decomposition of carbonate ions.

  The lower part of FIG. 4 shows the desorption behavior of carbon dioxide, and in the commercially available hydrotalcite shown in (f), almost no desorption of carbon dioxide was observed below 400 ° C. On the other hand, in the layered metal hydroxide nanoparticles shown in (a) to (e), the shorter the reaction time (in other words, the smaller the average particle diameter), the lowering of carbon dioxide at a low temperature (around 350 ° C.). It became clear that there were many.

  In order to investigate the cause of carbon dioxide desorption at low temperatures, the layer structure of the layered metal hydroxide nanoparticles shown in (a) and the layer structure of hydrotalcite shown in (f) were evaluated using XRD. .

  FIG. 5 shows XRD peaks at normal temperature, 350 ° C., and 600 ° C. in (a) and (f). Both (a) and (f) maintain the layer structure at room temperature and 350 ° C. However, in both (a) and (f), it was recognized that the layer structure was destroyed at 600 ° C. This indicates that the detachment of carbon dioxide at less than 350 ° C. of the layered metal hydroxide nanoparticles does not result from a change in the layer structure, and was manifested by making the layered metal hydroxide particles into nanoparticles. It is considered a property.

<6. Carbon dioxide adsorption / desorption test>
Hereinafter, the test method and test result of the carbon dioxide adsorption / desorption test will be described. In this test, <1. Production of layered metal hydroxide nanoparticles> The layered metal hydroxide nanoparticles obtained by the hydrothermal synthesis method with a reaction time of 4 hours described in the column> A certain hydrotalcite (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as HT) was used.

Hereinafter, a test method for the carbon dioxide adsorption / desorption test will be described.
(Used equipment)
Mass spectrometer: JMS-Q1050GC (manufactured by JEOL Ltd.)
(Measuring method)
(1) Quartz wool and about 30 mg of layered metal hydroxide sample ((a) or (f)) were placed in a quartz tube cell.
(2) Argon 100 cc / min. Under the circulation environment, the layered metal hydroxide sample was heated to 200 ° C. using an electric furnace and maintained at a constant temperature for about 1 hour.
(3) The layered metal hydroxide sample was heated to 350 ° C. to release carbon dioxide from the layered metal hydroxide sample.
(4) After the carbon dioxide is released, the layered metal hydroxide sample is cooled to 200 ° C., and a mixed gas of 1% carbon dioxide and argon is added to the layered metal hydroxide sample at 100 cc / min. And carbon dioxide was re-adsorbed to the layered metal hydroxide sample by contacting with water 1.2 cc / h for 1 hour.
(5) Carbon dioxide remaining in the system was replaced with argon.

  The process which made said process (3) to (5) 1 cycle was performed in multiple times, and the carbon dioxide detachment amount in each process was measured with the gas chromatograph mass spectrometer.

  Next, test results of the carbon dioxide adsorption / desorption test will be described.

  In FIG. 6, “0 cycle” indicates the amount of carbon dioxide released when the above (1) to (3) are performed, and “1 cycle” indicates the above (4), (5) and (3). The amount of carbon dioxide desorbed at the first time is shown, and “2 cycles” represents the amount of carbon dioxide desorbed at the second time (4), (5) and (3).

  In (f), carbon dioxide was not removed again even when carbon dioxide was released under conditions that could maintain the layer structure. On the other hand, in (a), the amount of carbon dioxide released in the 0th cycle was larger than that in (f), and carbon dioxide resorption and resorption were observed.

  The carbon dioxide adsorbent according to the present invention can be used in a power generation facility where carbon dioxide is continuously discharged.

Claims (7)

  A carbon dioxide adsorbent comprising a desorbable layered metal hydroxide having an average particle size of 150 nm or less. The carbon dioxide adsorbent according to claim 1, wherein the desorbable layered metal hydroxide includes a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).   3. The carbon dioxide adsorbent according to claim 2, wherein the desorption-type layered metal hydroxide satisfies 0.34 ≦ x <1 in the general formula (1).   It has the process of heating the carbon dioxide adsorbent of any one of Claims 1-3 which adsorb | sucks carbon dioxide to 200 to 400 degreeC, The regeneration method of a carbon dioxide adsorbent characterized by the above-mentioned .   A method for producing a desorption-type layered metal hydroxide, comprising a step of heating a non-desorption type layered metal hydroxide having an average particle diameter of 150 nm or less to 200 ° C. or more and 400 ° C. or less. The production method according to claim 5, wherein the non-detachable layered metal hydroxide includes a host layer represented by the following general formula (1):
[M2 ⁺ _1-x M3 ⁺ _x (OH) ₂ ] ... General formula (1)
(In the general formula (1), M ²⁺ represents a divalent metal ion, M ³⁺ represents a trivalent metal ion, and x represents a number of 0 <x <1).   The production method according to claim 6, wherein the non-desorbable layered metal hydroxide satisfies 0.34 ≦ x <1 in the general formula (1).