JP2005255441A - Method for producing layered double hydroxide having ion-exchangeable anion by removing carbonate ion from hydrotalcite and use of the hydroxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical and extremely-easy chemical method for synthesizing a layered double hydroxide containing an easily-exchangeable anion (for example, a nitrate ion and a chlorine ion) from hydrotalcite or its analogues containing a hard-to-exchange carbonate ion in an interlayer without varying the particle size and uniformity of hydrotalcite. <P>SOLUTION: This method for producing the layered double hydroxide comprises the steps of: using dilute hydrochloric acid whose function of removing the carbonate ion is low but which does not vary the particle size, external form and uniformity of hydrotalcite; and adding neutral hydrochloride (for example, sodium chloride) to the dilute hydrochloric acid system so that the neutral hydrochloride-added dilute hydrochloric acid acts on hydrotalcite at room temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a layered double hydroxide having an easily ion-exchangeable anion by treating a hydrotalcite having a difficult ion-exchangeable carbonate ion between layers or a layered double hydroxide having a similar structure. The present invention relates to manufacturing methods and inventions of their use.

  Conventionally, many layered compounds have been developed by using a layered compound such as a clay mineral and including various cations and cationic functional organic substances (Non-patent Document 1). Unlike clay minerals, hydrotalcite is an inorganic compound having a positive charge in the layer itself, having an anion between layers, and having anion exchange properties. There are extremely few types of anionic exchangeable substances compared to cation exchangeable compounds, and hydrotalcite or layered double hydroxides are typical examples.

  In recent years, it has been used to capture carbon dioxide by utilizing the anion exchange properties of layered double hydroxides, and by introducing other anions between layers, functional molecules and organic substances can be introduced between layers. Nano-layered compounds that have been included at the nano level have been synthesized, and many studies have been conducted on catalysts or catalyst carriers based on their surface area and their catalytic action (Non-patent Document 2).

  The hydrotalcite that is usually synthesized and produced is a layered double hydroxide that has carbonate ions between the layers. Recently, using “urea” in particular, nucleation is performed uniformly, and the particle size is reduced. A uniform and controlled hydrotalcite is synthesized (Non-patent Document 3). Usually, in layered double hydroxides containing anions other than carbonate ions, the layered double hydroxides containing the anions are exchanged in a solution containing a large amount of anions to be included, without changing the structure. Can be converted to hydroxide.

  However, in the case of layered double hydroxides such as hydrotalcite containing carbonate ions, carbonate ions are stably present between the layers, so the ion exchange property is extremely low and almost no ion exchange occurs. The use as an agent has been extremely limited (Non-Patent Document 4).

  Therefore, in order to synthesize an anion-exchange layered double hydroxide, for example, magnesium / aluminum layered double water is used in a carbon dioxide-free atmosphere such as a nitrogen stream using decarboxylated distilled water that does not dissolve carbon dioxide In the case of oxides, a layer containing an anion other than carbonic acid (for example, nitrate ion, chlorine ion, etc.) and easily exchangeable by coprecipitation reaction of magnesium salt, aluminum salt and sodium hydroxide aqueous solution. A double hydroxide was synthesized (Non-patent Document 5).

  Another method uses structural changes caused by heating. That is, the hydrotalcite undergoes a structural change and decarboxylates by heating at about 500 ° C., but the obtained product is converted into an aqueous solution containing anions other than carbonate ions (for example, nitrate ions, chlorine ions, etc.). It is known that the layered double hydroxide containing the anion is reconstructed by introducing (Non-patent Document 6). Using this method, this reaction can be used for the purpose of capturing carbon dioxide, and any anion can enter the interlayer by this reconstruction, so that functional molecules and organic substances can be encapsulated between the layers at the nano level. Nanolayered compounds in contact have been synthesized.

However, in the former method, the conditions of particle size and uniformity differ depending on the combination, so it is difficult to optimize the synthesis conditions. Also, the reaction itself is complicated due to atmosphere control and construction of a reaction system from which carbon dioxide is removed. In the latter method, since the structure is changed by heating, the direction after the reconstruction is not the same as that of the starting material, and the particle size and uniformity are changed. In order to use it, it uses rather severe conditions in terms of decarboxylation, which is not practical in terms of energy and time and is disadvantageous.

  If it is relatively easy to synthesize, particle size is controlled, and uniform hydrotalcite contains anions (eg, nitrate ions, chloride ions, etc.) that can be easily exchanged by simple chemical methods. If double hydroxides can be synthesized without changing the particle size and uniformity, a wide range of applications can be expected industrially as well as at research and test levels. In this regard, a method using 0.01 N hydrochloric acid has been reported to date (Non-Patent Document 7). There is also a report of treatment with hydrogen chloride gas at 150 ° C. (Non-patent Document 8). However, the latter method cannot be said to be a simple method due to the extreme risk and reaction conditions. Also, when the reaction is actually performed in the former method, it is also shown in [Example 2]. As described above, there is always a balance between decarboxylation ions and weight loss due to dissolution, and it is virtually impossible to perform decarboxylation ions without weight reduction, and this is not a complete method.

  In this way, the layered double hydroxide containing anions (for example, nitrate ions, chlorine ions, etc.) that can be easily exchanged from hydrotalcite by a simple chemical method changes the particle size and uniformity. There has been no conventional method for synthesis. As a result, different inorganic anions are introduced between layers, or functional organic substances having ionicity are introduced by ion exchange, which is a technique for synthesizing new functional materials, to form functional layered composites. Attempts to synthesize and provide new materials by soft chemical techniques such as those described above have not been made using layered double hydroxides derived from hydrotalcite.

  Carbon dioxide is a major factor in causing global warming and needs to be captured when discharged. Layered double hydroxides are used for that purpose and are representative of inorganic decarboxylation materials. The decarboxylation uses the phenomenon of “reconstruction” as described above, and the hydrotalcite undergoes a structural change by heating at about 500 ° C. and decarboxylates. It was used for capture and was disadvantageous in terms of energy and time. However, this decarboxylation is achieved by a simple chemical method under mild conditions such as room temperature, and further, a layered complex containing anions (for example, nitrate ions, chloride ions, etc.) that can be easily anion-exchanged. If it can be converted to hydroxide and used repeatedly, it is also promising as a carbon dioxide capture cycle.

  Two-dimensional layered materials are also attracting attention as fillers for improving the mechanical strength of other general-purpose polymers. For example, compounds containing two-dimensional layers such as clay minerals are used. However, there is a problem in that the process is not completely performed and the affinity with the matrix is not sufficient, and many problems to be solved remain in dispersibility. Unlike clay minerals, the layered double hydroxide layer is cationic and can include anionic monomers that cannot be handled by clay. If a polymer monomer can be included between layers to cause a reaction, a polymer that cannot be used with clay minerals can be used, and peeling to the layer can be expected. The improvement of mechanical strength and gas barrier property can be greatly expected.

In this way, layered double hydroxides containing easily exchangeable anions (eg, nitrate ions, chlorine ions, etc.) can be changed from hydrotalcite to the particle size and uniformity by a simple chemical method. If synthesis is possible, breakthroughs can be expected in a wide range of fields from laboratory level to industrial level and from environmental problems to nanotechnology. However, such a method has not been developed so far.
Yoshihiko Komori and Kazuyuki Kuroda “Interaction between Inorganic Layered Substances and Organic Substances” Chemistry Review (The Chemical Society of Japan, Society Publishing Center) 42, p33-44, (1994). Cavani, F .; Trifiro, F .; Vaccari, A. Catal. Today 1991, 11,173. Ogawa, M .; Kaiho, H. Langmuir 2002, 18, 4240. Miyata, S. Clays Clay Miner. 1983, 31, 305. Reichle, WT Solid States Ionics 1986, 22,135. Junichi Suzuki, Yoshio Ono “Intercalation Chemistry of Hydrotalcite”, Review of Chemistry (Edited by The Chemical Society of Japan, Society Publishing Center) 21, p49-55, (1994). Bish, DL, Bull.Mineral. 1980, 103,170. Adachi-Pagano, M .; Forano, C .; Besse, JP. J. Mat. Chem. 1988, 13, 1988.

  The present invention relates to a layered double water containing anions (for example, nitrate ions, chloride ions, etc.) that can be easily exchanged from a hydrotalcite containing hardly ion-exchangeable carbonate ions between layers by a simple and mild chemical method. The purpose of the present invention is to provide a practical and extremely simple chemical synthesis method for obtaining an oxide without changing the particle size and uniformity. In addition, it provides a new hydrotalcite decarboxylation method that is highly practical and contributes to the construction of a system that can repeatedly desorb carbon dioxide. The thus obtained layered double hydroxide exhibiting easy anion exchangeability has anion exchangeability, so it can be easily exchanged with other anions including carbonate ions and cationic anions. It can be exchanged for anions such as functional organic substances.

  Of course, the above-mentioned process can be used as a simple and practical decarboxylation process, and by making use of the ion exchange property of the layered double hydroxide showing the easy anion exchange property produced thereby, the layered compound can be easily obtained. Functional molecules can be introduced, and it is also possible to provide a novel functional layered compound that has not existed before, and its availability is also in the sense of providing a new compound, In the field of environmental problems, it is extremely excellent and practical, and can be said to have great significance.

  As already mentioned, there are examples of hydrotalcite treatment with hydrochloric acid so far. At this time, protons in hydrochloric acid are easily combined with carbonate ions between the layers to become hydrogen carbonate ions and have a minus monovalent charge, so that the ion exchange property changes, that is, the ion exchange is easier. It is thought that it becomes. In the two phases of water and the layered double hydroxide, it can be said that the hydrogen carbonate ions and the chlorine ions are in an equilibrium state and are distributed in both phases according to the equilibrium coefficient. At this time, if there is a large amount of chlorine ions, it is considered that the equilibrium between hydrogen carbonate ions and chlorine ions will shift in the direction in which chlorine ions enter between the layers from Le Chatelier's principle. It is done.

  From these, it came to the idea that decarboxylation can be performed from hydrotalcite by adding a large amount of anions to be introduced during acid treatment. The inventors based on the above idea, specifically, if hydrotalcite is put into an aqueous solvent containing hydrochloric acid and chlorine anion, hydrogen chloride gas that is highly heated and corrosive is used. Even without using a reaction system such as the above, the inventors have come up with the idea that decarboxylation ions and conversion to layered double hydroxides that exhibit easy anion exchange can be synthesized.

As a result of diligent research based on the basic policy described above, dehydrocarbonate ion has a low action, but dilute hydrochloric acid that does not change the particle size, shape, and uniformity of hydrotalcite, and neutral hydrochloric acid in the system. By adding (for example, sodium chloride) and allowing it to act at room temperature, decarboxylation ions are remarkably accelerated, and decarboxylation ions are added and added in an extremely short time while maintaining the external shape, particle size, and weight. It came to find out that it converted into the layered double hydroxide containing an anion.

  In addition to hydrochloric acid, nitric acid and sulfuric acid, which are other protic strong acids with the same specified concentration, also have the same effect as acid, and by using nitrate or sulfate other than hydrochloride as neutral salt, It has been found that the type of anion incorporated into the product can be changed.

  From the above, the present inventors do not change the particle size or uniformity with a mixed solution containing anions such as acid and a large amount of chlorine ions under a mild condition of room temperature and in a very short time. The present invention succeeds in converting a hardly ion-exchangeable hydrotalcite into a layered double hydroxide containing an easily exchangeable anion (for example, nitrate ion, chlorine ion, etc.) by decarboxylation.

That is, the present invention has been achieved by taking the solutions described in (1) to (10) below.
(1) General formula; M _x N (OH) _z (CO ₃ ^2- ) _0.5 · nH ₂ O (wherein x represents a numerical range of 1.8 ≦ x ≦ 4.2. Z is 2 (x + 1 M is a divalent metal ion, N is a trivalent metal ion, and n varies depending on the humidity of the environment, but has a composition represented by 2) and is similar to hydrotalcite Carbonate ions in the layered double hydroxide are obtained by contacting the mixed double hydroxide containing carbonate ions having the above structure with a mixed aqueous solution containing a salt of a protic acid and an anion (X) to exchange anions. Is eluted into an aqueous solution, and an anion (X) is introduced into the carbonate ion site in the eluted layered double hydroxide. The general formula: M _x N (OH) _z (X) · nH ₂ O (where, x Represents a numerical range of 1.8 ≦ x ≦ 4.2, z represents 2 (x + 1), M represents a divalent metal ion, N represents a trivalent metal ion, and n represents an environmental humidity. Although it changes, it has a composition represented by 2) Characterized in that to produce the layered double hydroxide-rich-exchange properties, method for producing the anion-exchange layered double hydroxides.

(2) The method for producing an anion-exchange layered double hydroxide as described in (1) above, wherein the anion exchange operation is performed in a low temperature region from room temperature to less than 100 ° C.
(3) The protic acid is hydrochloric acid, and the salt of the anion (X) is sodium chloride (salt)
The method for producing an anion-exchanging layered double hydroxide as described in (1) above.
(4) The above item (1) or (3), wherein the concentration of the protic acid in the aqueous solution is 0.00005 to 0.025 N and the salt concentration of the anion (X) is 2% by weight or more. A process for producing an anion-exchange layered double hydroxide as described in 1.
(5) The starting layered double hydroxide represented by the general formula is a hydrotalcite in which the metal ion M is magnesium ion Mg and the trivalent metal ion N is aluminum ion Al in the formula (1) The manufacturing method of the anion exchange layered double hydroxide as described in the item.
(6) The method for producing an anion-exchange layered double hydroxide according to any one of (1) to (5), wherein the anion in the anion-exchange layered double hydroxide is a chlorine ion. .

(7) The anion exchange layered double hydroxide produced by the process according to any one of (1) to (6) is used as a carbon dioxide scavenger in the carbon dioxide removal process in the exhaust gas. And using the anion-exchange layered double hydroxide in contact with a liquid phase containing carbon dioxide or carbon dioxide to fix carbon dioxide as a carbonate of the layered double hydroxide, Carbon dioxide removal method.
(8) Following the process of immobilizing carbon dioxide, a layered double hydroxide in which carbon dioxide is immobilized as carbonate ions is recovered, and this is dissolved in an aqueous solution containing a salt of a protic acid and an anion (X). The carbonated ion and anion (X) are anion-exchanged, and the recovered layered double hydroxide is converted to an anion-exchangeable layered hydroxide, recovered, and recycled to the carbon dioxide removal process. The method for removing carbon dioxide according to (7) above, wherein the method is used.

(9) The anion exchange layered double hydroxide produced by the process according to the above (1) to (6) or a material containing the anion exchange material is brought into contact with a monomer of a functional organic compound having an anion. An inorganic organic composite modified and modified with a functional organic compound, wherein a monomer is introduced into a layered double hydroxide and then the monomer is polymerized.
(10) The inorganic-organic composite according to (9), wherein the inorganic-organic composite is modified and modified with an organic compound having a function of improving dispersibility.
(11) The inorganic-organic composite according to (10), wherein the inorganic-organic composite is used as a filler.

In the above, regarding the chemical formula of the layered double hydroxide, which is the starting material represented by the general formula, the carbonate ion (CO ₃ ^2- ) is set to be ~ 0.5. The most difficult composition is defined, and the present invention defines a feasible region including this region.

Further, the anion-exchange layered double hydroxide produced in (1) and its embodiment items (2) to (5) and (7) has a general formula: M _x N (OH) _z (CO _{Since the} starting material (CO ₃ ^2- ) carbonate ion represented by ₃ ^2- ) to _0.5 · nH ₂ O is anion-exchanged with an anion (X), it depends on the degree of exchange. A wide range from the state substituted by (X) to the one in which (CO ₃ ^2- ) remains is obtained, and the anion-exchange layered double hydroxide of the present invention has an anion (X Even if the carbonate ions remain due to the introduction of), the product is included as an embodiment of the invention because the anion exchange is easy. The product completely treated with decarbonated ions has a general formula: M _x N (OH) _z (X) · nH ₂ O (wherein x represents a numerical range of 1.8 ≦ x ≦ 4.2. Z is , 2 (x + 1), M is a divalent metal ion, N is a trivalent metal ion, and n varies depending on the humidity of the environment, but is expressed by 2). It is not meant to be limited to only.

  By adopting the above configuration, the present invention generates decarbonated ions in a very short time while maintaining the external shape, particle size, and weight of the hydrotalcite, and converts it into a layered double hydroxide containing the added anion. Has been successful. And with this success, we have also succeeded in providing a carbon dioxide removal process or inorganic-organic composite.

  The present invention has succeeded in simple decarboxylation of a layered double hydroxide represented by a hydrotalcite having carbonate ions between layers, which has not been conventionally known, and the process itself can be used industrially. It is significant. In addition, since the layered double hydroxide containing anions can be anion exchanged, it can be converted to other anions, and new compounds containing organic-inorganic nanocomposites can be synthesized. Expected to be widely used in various fields. For example, when combined with carbonate ions again, use as a carbon dioxide capture and separation agent can be considered. In addition to its use as a carbon dioxide scavenger, the particle size and shape are controlled by so-called soft chemical reactions by an extremely simple operation such as an ion exchange process for anionic functional organic molecules. Therefore, it is expected to lead to the development and promotion of new substances having new functions.

Furthermore, the present invention provides a simple reaction from a layered double hydroxide containing carbonate ions, which can be produced with an arbitrary uniform particle size, without any change in particle size, external shape, and weight. It has been shown that layered double hydroxides containing ions can be provided, and it is possible to form an alignment film on a substrate, and new applications such as the construction of highly oriented nanodevices that have attracted attention in recent years It is conceivable to develop and extend to the field, and the effects brought about by it are extremely technically significant.

  The solution of the present invention is as described above, and will be specifically described below based on examples. However, these examples are shown as an aid for easily understanding the present invention, and are not intended to limit the present invention. Further, in order to show the superiority of the production method, in Example 2, a comparative experiment using hydrochloric acid alone is shown.

A commercially available hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd., average particle diameter of about 0.5 to 1 μm) represented by the general formula: Mg ₃ Al (OH) ₈ (CO ₃ ^2- ) _0.5 · 2H ₂ O 20 mg was taken, and 10 ml of an aqueous solution having a hydrochloric acid concentration of 0.005 N and a sodium chloride concentration adjusted to 13.3% by weight was added, and the mixture was allowed to stand at 25 ° C. for 15 seconds to 24 hours. Thereafter, the precipitate was sufficiently washed with distilled water that was filtered through a 0.2 micron membrane filter in a nitrogen stream and decarboxylated by boiling. The precipitate collected by filtration was collected, immediately depressurized, and dried under vacuum for 1 hour or longer to obtain a white powder.

This was analyzed by methods such as infrared spectroscopic analysis, powder X-ray analysis, elemental analysis (CHN analysis, etc.), thermal analysis and the like. As a result, the infrared spectrum is 1368 cm ⁻¹ carbonate C—O
Absorption due to stretching vibration left only a slight residue. Further, disappearance in the vicinity of 668 cm ⁻¹ due to carbon dioxide O—O bending vibration and absorption near 627 cm ⁻¹ appeared. In addition, a broad peak near 3000 cm ^−1, which was attributed to the interaction between water and carbonate ions, was also lost (FIG. 1). Almost no decarboxylation occurred with sodium chloride and hydrochloric acid alone (FIG. 1).

Further, in powder X-ray diffraction (PXRD), a sharp peak of 001 reflection was observed, and it was found that the layer spacing was changed from 0.780 nm to 0.797 nm. This value of the bottom surface spacing is in good agreement with the value of the change in the bottom surface spacing of the magnesium / aluminum layered double hydroxide by the inclusion of Cl ions already reported. It was found that the weight of the obtained compound could be recovered quantitatively in consideration of weight loss due to operations such as filtration and changes in molecular weight due to ion exchange. In the CHN analysis, the weight% of C contained was 0.3% or less, and in the starting material DHT-6, it was 2.3%, so that considerable decarboxylation ions were generated. The analysis value of chlorine ions in the product is 11% by weight, which is almost coincident with the theoretical value of 11.5% by weight, indicating that the chloride ions are surely included between the layers. Also, in the image obtained with a scanning electron microscope, it was confirmed that the product had no change in its particle size and outer shape (Fig. 2-1,
Fig. 2-2).

Next, in order to investigate the reaction time, the time from the addition of the hydrochloric acid-salt mixed solution to the filtration was changed, and when the progress of decarboxylation ion was examined by infrared spectroscopy, the reaction time was extremely fast. Until filtration, it was found that even the shortest 15-second reaction achieved the same degree of decarboxylation ion as the 20-hour reaction (FIG. 3).
In addition, since the particle size of the starting material belongs to a relatively large class as the particle size of this compound, it can be sufficiently applied to those having a small particle size.

In order to investigate the effect of hydrochloric acid alone, a commercially available hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) represented by the general formula; Mg ₃ Al (OH) ₈ (CO ₃ ^2- ) _0.5 · 2H ₂ O 10 mg of an aqueous solution adjusted to various hydrochloric acid concentrations of 0.1 to 0.001 N was added thereto, and the mixture was allowed to stand at 25 ° C. for 20 hours. Thereafter, the precipitate was sufficiently washed with distilled water filtered through a 0.2 micron membrane filter in a nitrogen stream and decarboxylated by boiling. The precipitate collected by filtration was collected, immediately depressurized, and dried under vacuum for 1 hour or longer to obtain a white powder.

The extent of decarboxylation, weight change, and recovery rate were examined by infrared spectroscopic analysis and weight measurement (FIGS. 4-1, 4-2). As a result, at a hydrochloric acid concentration of 0.008 N or more, carbonate ions of 50% or more were reduced, but at a hydrochloric acid concentration of 0.005 N or less, carbonate ions were reduced only to a degree of less than 40%. (Figure 4-1).
On the other hand, at a hydrochloric acid concentration of 0.005 N or less, it was quantitatively recovered without weight reduction, but at a hydrochloric acid concentration of 0.008 N or more, a weight reduction of 10% or more occurred, and a concentration of more than 0.05 N Then, it was hardly dissolved and could not be recovered (Fig. 4-2).

In order to investigate the effect of salt addition, a commercial hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) represented by the general formula: Mg ₃ Al (OH) ₈ (CO ₃ ^2- ) _0.5 · 2H ₂ O Take 20 mg of the average diameter (approx. 0.5-1 μm), add 10 ml of two hydrochloric acid concentrations of 0.005 and 0.0025 N and various sodium chloride concentrations, and let stand at 25 ° C. for 20 hours. did. Each sample was then filtered through a 0.2 micron membrane filter in a nitrogen stream, and the precipitate was thoroughly washed with distilled water subjected to decarbonation by boiling. The precipitate collected by filtration was collected, immediately depressurized, and dried under vacuum for 1 hour or longer to obtain a white powder.

  This was examined by infrared spectroscopic analysis and gravimetric measurement for the degree of decarbonated ions, weight change and recovery (FIG. 5). As a result, at two hydrochloric acid concentrations of 0.005 and 0.0025N, a remarkable effect is observed by adding salt, that is, adding chlorine ions. For example, in the case of hydrochloric acid having a concentration of 0.0025N, carbonate ions are reduced by about 20%. However, when the salt concentration was adjusted to about 25% by weight, a remarkable decrease of about 90% was observed. In any of these samples, the recovery rate was almost 100%.

In order to investigate the ion exchange ability of layered double hydroxides containing chlorine ions obtained by treatment with a mixed solution of hydrochloric acid and sodium chloride, a general formula; Mg ₃ Al (OH) ₈ (CO ₃ ^2- ) _0.5 · 2H ₂ O 20 mg of a commercially available hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd., average particle size is about 0.5 to 1 μm) is taken, and hydrochloric acid concentration of 0.005N and 13% by weight of chloride are taken. 10 ml of a saline solution adjusted to a sodium concentration was added, and the mixture was allowed to stand at 25 ° C. for 20 hours. Each sample was then filtered through a 0.2 micron membrane filter in a nitrogen stream, and the precipitate was thoroughly washed with distilled water subjected to decarbonation by boiling. The precipitate collected by filtration was collected, immediately depressurized, and dried under vacuum for 1 hour or longer to obtain a white powder. This was again charged with sodium sulfate and sodium carbonate in 10 ml of two aqueous solutions and left at 25 ° C. for 20 hours. Each sample was then filtered through a 0.2 micron membrane filter in a nitrogen stream, and the precipitate was thoroughly washed with distilled water subjected to decarbonation by boiling. The precipitate collected by filtration was collected, immediately depressurized, and dried under vacuum for 1 hour or longer to obtain a white powder.

  This was examined by infrared spectroscopic analysis and gravimetric measurement for the degree of decarboxylated ions, weight change and recovery rate. As a result, each was converted into a layered double hydroxide containing sulfate ions and carbonate ions. Its infrared absorption spectrum is shown in FIG.

As a result, the action of decarboxylation ions is low, but dilute hydrochloric acid that does not change the particle size, shape, and uniformity of hydrotalcite is used, and neutral hydrochloride (for example, sodium chloride) is used in the system. Is added and allowed to act at room temperature, decarboxylation ions are remarkably accelerated, and decarboxylation ions are carried out in a very short time while maintaining the external shape, particle size and weight, and the layered double water containing the added anions It became clear to convert to oxide. The layered double hydroxide containing anions obtained by the method is further subjected to simple ordinary ion exchange while maintaining the outer shape, particle size and weight of the layered double hydroxide containing other anions. It became clear that further conversion was necessary.

Hereinafter, the mechanism presumed from an Example is described and supplementarily demonstrated about the decarboxylation ion reaction by the effect | action of the aqueous solution of hydrochloric acid-salt.
When a layered double hydroxide such as hydrotalcite containing carbonate ions between layers is put into an acidic aqueous solution, the carbonate ions (CO ₃ ^2- ) between the layers combine with protons, and −1 valent hydrogen carbonate changes to, at the same time, chlorine ions for charge balance ^- ions (HCO ₃₎ ^- clathrating equal amounts, the interlayer (Cl). Since this hydrogen carbonate ion is −1 valent unlike carbonate ion, it is considered that the bond between the layered double hydroxide and the cationic layer becomes weak, and ion exchange is facilitated. Therefore, if there is a large amount of anionic species in the aqueous solution, ion exchange occurs with the ionic species.

Furthermore, as the acid concentration increases, monovalent hydrogen carbonate ions (HCO ₃ ⁻ ) change to neutral H ₂ CO ₃ and are desorbed from the interlayer into the liquid phase. At this time, if there is a large amount of anionic species in the aqueous solution, the ionic species are taken up. In this way, decarboxylation ions and anions in the liquid phase are taken up. The metal hydroxide layer of a layered double hydroxide is originally attacked by an acid, but since the carbonate ions between the layers are more likely to react with the protons of the acid, the reaction takes place predominantly, and the particle size / The outer shape and weight will not decrease. However, as the acid concentration increases, the acid begins to attack the metal hydroxide layer of the layered double hydroxide, causing gradual dissolution, eventually changing the structure and dissolving. It is done. As described above, the production method utilizes the fact that the reaction of the acid to the carbonate ion is prioritized over the reaction of the layered double hydroxide to the metal hydroxide layer.

This mechanism shows that not only the concentration of hydrochloric acid is important, but also the capacity used. In other words, using carbonate ions in the starting layered double oxide, hydrogen carbonate ions, and protons more than desorbing, ie, hydrochloric acid solution, have the same effect as increasing the acid concentration, and excess protons. It is considered that the metal hydroxide layer of the layered double hydroxide causes the dissolution. Actually, hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd., particle size average is about 0.5-1 μm) is changed to 20 mg, and the amount of 0.005N hydrochloric acid solution is changed, and the weight change is examined. As a result, a significant weight reduction was observed when the amount was 15 ml or more. In addition, the decrease of carbonate ion was also remarkable at the amount of hydrochloric acid exceeding 15 ml. At this time, the amount of protons is about 2.2 times the molar amount of carbonate (molar ratio), but this is the amount of carbonate ions that become neutral carbon dioxide, which is generally consistent with the mechanism described above. Yes.
This means that the amount of carbonate ions of the layered double hydroxide and the amount of protons in the aqueous solution is 1: 1 to 2 in terms of moles, and further, by adding chlorine ions, ion exchange of bicarbonate ions It can be said that it is a condition that decarboxylation occurs without weight reduction.
As described above, the production method is most efficient while controlling the ratio of carbonate ions and protons and ion exchange of hydrogen carbonate ions while minimizing the reaction to the metal hydroxide layer. This is a method for decarboxylation, and in terms of actual adaptation, it is necessary to set the optimum conditions in consideration of the amount of ionic species as described above.

  As described in the column of the effect of the invention, the significance of the present invention is exceptional. That is, according to the present invention, an anion-exchangeable layered double hydroxide that has not been easily obtained can be easily obtained in a short time. The resulting easily anion-exchangeable layered double hydroxide can be used industrially and has great significance. In addition, the product is expected to be used in various fields in the future due to the anion exchange property of the product. For example, anionic functional organic molecules can be synthesized and provided by a so-called soft chemical reaction by an extremely simple operation such as an ion exchange process, so that new substances having new functions can be developed and promoted. Expected to be connected.

  A layered double hydroxide such as hydrotalcite containing carbonate ions as a starting material precipitates as a flat crystal having a high aspect ratio, and the c-axis direction of the crystal is perpendicular to the flat plate. Since the outer shape and particle size do not change due to ion exchange, it is easy to control the particle size as a starting material, and a carbonate ion-containing layered double hydroxide with a high crystal aspect ratio can be used. It becomes possible to synthesize inorganic composites, opening the way to the formation of alignment films arranged in a specific direction. As a result, it can be considered that it will develop and extend to new application fields such as the construction of nanodevices by accumulation with regular orientation on the substrate.

The figure which shows the infrared spectrum of a starting material and a product. In the examples of the present invention, magnesium / aluminum layered double hydroxide containing carbonate ions (a), 0.005N hydrochloric acid treated (b), treated with only 13 wt% sodium chloride (c) The figure which shows the infrared spectrum of the process produced product (d). (In the figure, νc-o and δc-o respectively represent stretching vibration due to carbonate ions and absorption due to bending vibration.) Scanning electron micrograph of magnesium-aluminum layered double hydroxide (DHT-6) containing carbonate ions as a starting material. The scanning electron micrograph of the layered double hydroxide produced by treating the starting material (DHT-6) with an aqueous solution containing 0.005N hydrochloric acid and containing 13% by weight of sodium chloride. Infrared spectrum of layered double hydroxide (b) produced by treatment with starting material (DHT-6: (a)) and an aqueous solution containing 0.005N hydrochloric acid and 13 wt% sodium chloride for 15 seconds FIG. The figure which shows the content rate of the residual carbonate ion estimated from the infrared spectrum of the layered double hydroxide produced | generated by processing a starting material (DHT-6) with various hydrochloric acid concentration. The figure which shows the collection | recovery rate (by weight) at the time of processing a starting material (DHT-6) with various hydrochloric acid concentrations. The figure which shows the change of residual carbonate ion content when fixing hydrochloric acid concentration to 0.005N (a) thru | or 0.0025N (b) with respect to a starting material (DHT-6), and changing only salt concentration. Layered double hydroxide produced by treating the starting material (DHT-6: (a)) with the anion exchange accelerator developed in the present invention (an aqueous solution containing 0.005N hydrochloric acid concentration and 13% by weight of sodium chloride) (B), a layered double hydroxide (c) in which carbonate ions (CO ₃ ²⁻ ) have been reintroduced into the product by ion exchange, and sulfate ions (SO ₄ ² ) by ion exchange in the product (b). ^The figure which shows each infrared spectrum of the layered double hydroxide (d) which introduce | transduced-).

Claims (11)

General formula: M _x N (OH) _z (CO ₃ ²⁻ ) _0.5 · nH ₂ O (wherein x represents a numerical range of 1.8 ≦ x ≦ 4.2. Z represents 2 (x + 1)) M is a divalent metal ion, N is a trivalent metal ion, and n varies depending on the humidity of the environment, but has a composition represented by 2) and has a structure similar to hydrotalcite. A mixed aqueous solution containing a protonic acid and an anion (X) salt is brought into contact with the layered double hydroxide containing carbonate ions, and anion exchange is performed to convert the carbonate ions in the layered double hydroxide into an aqueous solution. An anion (X) is introduced into the carbonate ion site in the eluted layered double hydroxide, and the general formula; M _x N (OH) _z (X) · nH ₂ O (where x is 1.8) ≤ x ≤ 4.2 Indicates a numerical range, z indicates 2 (x + 1), M is a divalent metal ion, N is a trivalent metal ion, and n varies depending on environmental humidity. , Anion exchange having a composition represented by 2) A method for producing an anion-exchanging layered double hydroxide characterized by producing a layered double hydroxide rich in properties. The method for producing an anion-exchangeable layered double hydroxide according to claim 1, wherein the anion exchange operation is performed in a low temperature region from room temperature to less than 100 ° C. The protic acid is hydrochloric acid and the salt of the anion (X) is sodium chloride (salt);
The manufacturing method of the anion exchange layered double hydroxide of Claim 1. 4. The anion exchangeability according to claim 1, wherein the concentration of the protic acid in the aqueous solution is 0.00005 to 0.025 N, and the salt concentration of the anion (X) is 2% by weight or more. A method for producing a layered double hydroxide. The starting layered double hydroxide represented by the general formula is a hydrotalcite in which the metal ion M is a magnesium ion Mg and the trivalent metal ion N is an aluminum ion Al in the formula. The manufacturing method of the anion exchange layered double hydroxide of description. The method for producing an anion-exchange layered double hydroxide according to any one of claims 1 to 5, wherein the anion in the anion-exchange layered double hydroxide is a chlorine ion. The anion-exchange layered double hydroxide produced by the process according to any one of claims 1 to 6 is used as a carbon dioxide scavenger in a carbon dioxide removal process in exhaust gas, A method for removing carbon dioxide, comprising immobilizing carbon dioxide as a carbonate of the layered double hydroxide by bringing the ion-exchangeable layered double hydroxide into contact with a liquid phase containing carbon dioxide or carbon dioxide. Following the process of fixing carbon dioxide, the layered double hydroxide in which carbon dioxide is fixed as carbonate ions is recovered, and this is put into an aqueous solution containing a salt of a protic acid and an anion (X). Then, anion exchange between carbonate ion and anion (X) is performed, and the recovered layered double hydroxide is converted into an anion exchangeable layered double hydroxide, which is recovered and recycled for use in the carbon dioxide removal process. The carbon dioxide removing method according to claim 7, wherein: An anion-exchange layered double hydroxide produced by the process according to claim 1 or 6 or a material containing the anion-exchange layered double hydroxide is brought into contact with a monomer of a functional organic compound having an anion to form the layered double hydroxide. An inorganic-organic composite modified and modified with a functional organic compound, which is introduced into a product and then polymerized with a monomer. The inorganic-organic composite according to claim 9, wherein the inorganic-organic composite is modified with an organic compound having a function of enhancing dispersibility. The inorganic-organic composite according to claim 10, wherein the inorganic-organic composite is used as a filler.

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