Production method for amino acid-containing hydrotalcite

Abstract

The present invention provides a novel production method which is for amino acid-containing hydrotalcite and by which the amount of an alkaline solution used can be reduced, and amino acid-containing hydrotalcite having stable quality can be obtained even when a reused amino acid aqueous solution is used as a raw material.　The present disclosure is a production method for amino acid-containing hydrotalcite. The production method comprises step (A), a solution preparation step, and a generation step.　Step (A) is a step for separating a slurry containing first amino acid-containing hydrotalcite and a dissolved amino acid into first amino acid-containing hydrotalcite and a dissolved amino acid-containing solution.　The solution preparation step is a step for preparing a slurry solution by mixing a composite metal oxide with an amino acid aqueous solution derived from the dissolved amino acid-containing solution separated from the slurry after step (A).　The generation step is a step for generating second amino acid-containing hydrotalcite by heating the slurry solution.

Description

Method for producing amino acid-containing hydrotalcite

[0001] The present invention relates to a method for producing amino acid-containing hydrotalcite.

[0002] Hydrotalcite-type compounds, which represent hydrotalcite or its calcined product, have ion exchange ability and are used in various applications, such as suppressing resin deterioration by blending them with resins. A method for increasing the aspect ratio of this type of hydrotalcite-type compound by using amino acids is known (Patent Document 1 and Non-Patent Document 1).

[0003] In such a conventional method, a mixture of a hydrotalcite-type compound and an aqueous amino acid solution is heat-treated to obtain an amino acid-containing hydrotalcite, which is a complex of a hydrotalcite-type compound and an amino acid.

[0004] International Publication No. 2019 / 092453

[0005] NATURE COMMUNICATIONS (2019) 10:2398, High gas barrier coating using non-toxic nanosheet dispersions for flexible food packaging film.

[0006] Amino acid-containing hydrotalcite, which is obtained by heat-treating a mixture of a hydrotalcite compound and an aqueous amino acid solution, is obtained in the form of a slurry containing the amino acid-containing hydrotalcite and dissolved amino acids. In Non-Patent Document 1, an alkaline solution is added to this slurry to precipitate the amino acid-containing hydrotalcite, thereby obtaining purified amino acid-containing hydrotalcite. In this case, the subsequent use of the amino acid used in the production of the amino acid-containing hydrotalcite has not been considered.

[0007] In recent years, with the SDGs (Sustainable Development Goals) adopted at the United Nations Summit gaining momentum, there is a demand for more efficient and effective utilization of raw materials. However, it is not known how to utilize the aqueous amino acid solution obtained after precipitating amino acid-containing hydrotalcite.

[0008] An object of the present invention is to provide a novel method for producing amino acid-containing hydrotalcite using an aqueous amino acid solution as a raw material.

[0009] The present disclosure includes the following aspects.

[0010] (First Disclosure) This first disclosure relates to a method for producing amino acid-containing hydrotalcite. The production method is characterized by including the following steps (A): a solution preparation step and a production step. Step (A) is a step of separating a slurry containing a first amino acid-containing hydrotalcite and dissolved amino acids into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acids. The solution preparation step is a step of preparing a slurry solution after step (A) by mixing an aqueous amino acid solution derived from the solution containing the dissolved amino acids separated from the slurry with a composite metal oxide obtained by calcining a precursor hydrotalcite compound. The production step is a step of heating the slurry solution to produce a second amino acid-containing hydrotalcite.

[0011] (Second Disclosure) In this second disclosure, in the first disclosure, the step (A) is characterized in that water is added to the slurry to separate it into the first amino acid-containing hydrotalcite and the solution containing the dissolved amino acid.

[0012] (Third Disclosure) In this third disclosure, in the first disclosure, the step (A) is characterized in that, without adding water to the slurry, the slurry is separated into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and a solution containing the remainder of the dissolved amino acids. Thereafter, water is added to the slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and the slurry is separated into the first amino acid-containing hydrotalcite and the solution containing the dissolved amino acids.

[0013] (Fourth Disclosure) In this fourth disclosure, in the first disclosure, step (A) comprises the following steps (a1) and (a2), and step (a2) is performed once or multiple times. Step (a1) is a step of separating the slurry into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and a solution containing the remainder of the dissolved amino acids, without adding water to the slurry. Step (a2) is a step of adding water to the slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids, after step (a1), to separate the slurry into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids or no dissolved amino acids, and a solution containing the remainder of the dissolved amino acids.

[0014] (Fifth Disclosure) The present fifth disclosure is characterized in that, in any of the first to fourth disclosures, the method further includes the following solution preparation step and production step before step (A). The solution preparation step is a step of preparing a slurry solution by mixing an amino acid aqueous solution with a composite metal oxide obtained by calcining a precursor hydrotalcite compound. The production step is a step of heating the slurry solution to produce the first amino acid-containing hydrotalcite.

[0015] (Sixth Disclosure) The present sixth disclosure is characterized in that, in any one of the first to fifth disclosures, the method further comprises, after the step (A), a step (B) of reducing amino acids from the first amino acid-containing hydrotalcite with an alkaline solution.

[0016] (Seventh Disclosure) The seventh disclosure is the sixth disclosure, wherein the step (B) comprises adding the alkaline solution to the first amino acid-containing hydrotalcite while stirring the first amino acid-containing hydrotalcite.

[0017] (Eighth Disclosure) In the eighth disclosure, in any one of the first to seventh disclosures, the amino acid has a solubility of 10 g / 100 mL H ２ It is characterized by being an amino acid of 0 or more.

[0018] (Ninth Disclosure) The present ninth disclosure is characterized in that in any one of the first to eighth disclosures, the amino acid is a glycine-related compound.

[0019] (Tenth Disclosure) The tenth disclosure is characterized in that in any one of the first to ninth disclosures, the hydrotalcite-type compound contained in the first amino acid-containing hydrotalcite is represented by the following formula (1): (M ２＋ ) １－Ｘ (M ３＋ ) Ｘ (OH) ２ (A ｎ－ ) Ｘ／ｎ ・mH ２ O... (1) (In formula (1), M ２＋ is a divalent metal cation. ３＋ is a trivalent metal cation. ｎ－ is an n-valent anion. X is a number that satisfies 0.17<X<0.36. n is an integer from 1 to 6. m is a number that satisfies 0<m<1.80.

[0020] (Eleventh Disclosure) The eleventh disclosure is characterized in that in any one of the first to tenth disclosures, the amino acid concentration of the slurry is less than 0.6 mol / L.

[0021] The present invention can provide a novel method for producing amino acid-containing hydrotalcite using an aqueous amino acid solution as a raw material.

[0022] Fig. 1 is a flow diagram showing an example of a first embodiment of the present invention. Note that dashed lines in Fig. 1 indicate the content of claim 1. Fig. 2 is a flow diagram showing an example of a second embodiment of the present invention. Fig. 3 is a flow diagram showing an example of a third embodiment of the present invention. Fig. 4 is a flow diagram showing an example of a fourth embodiment of the present invention.

[0023] A preferred embodiment of the method for producing an amino acid-containing hydrotalcite of the present invention will be described in detail below. In this specification, the term "amino acid-containing hydrotalcite" refers to a hydrotalcite compound chemically modified with an amino acid.

[0024] [Method for Producing Amino Acid-Containing Hydrotalcite] In one embodiment of the present invention, the method for producing amino acid-containing hydrotalcite comprises the following steps. The production method first comprises step (A) of separating a slurry containing a first amino acid-containing hydrotalcite and dissolved amino acids into the first amino acid-containing hydrotalcite and a solution containing dissolved amino acids. After step (A), the production method further comprises a solution preparation step of mixing an aqueous amino acid solution derived from the solution containing dissolved amino acids separated from the slurry with a composite metal oxide obtained by calcining a precursor hydrotalcite compound to prepare a slurry solution. The production method then comprises a generation step of heating the slurry solution to produce a second amino acid-containing hydrotalcite.

[0025] In the production method of this embodiment, step (A) is a step of separating a slurry containing a first amino acid-containing hydrotalcite and a dissolved amino acid into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acid. In this step (A), the slurry is a slurry after the step of producing the first amino acid-containing hydrotalcite, and is a slurry containing the first amino acid-containing hydrotalcite and a dissolved amino acid. This slurry has not been subjected to a washing treatment with an alkaline solution after the step of producing the first amino acid-containing hydrotalcite, and therefore is a slurry to which no additional alkaline solution has been added. Here, the additional alkaline solution is an alkaline solution intended to remove the amino acid contained in the slurry. In step (A), such a slurry is separated into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acid.

[0026] The first amino acid-containing hydrotalcite production step is a step of heating a slurry solution obtained by mixing an amino acid aqueous solution with a composite metal oxide obtained by calcining a precursor hydrotalcite compound to produce the first amino acid-containing hydrotalcite. In this specification, this production step may be referred to as a heating step. This production step will be described in detail in the explanation of each step below.

[0027] In order to sufficiently reduce the amino acids contained in the amino acid-containing hydrotalcite under the condition that a large amount of dissolved amino acids is present in the slurry, it is necessary to use an alkaline solution of a certain amount or more, and there is room for improvement in terms of resource saving and production cost. Furthermore, the present inventors have found that even if the dissolved amino acids separated from the solid liquid after using the alkaline solution for the purpose of removing amino acids are reused as the raw amino acid aqueous solution, the amount of metal ions in the aqueous solution is likely to vary, and the amount of amino acids in the slurry is likely to be OH. － However, the amount of amino acid in the hydrotalcite is relatively less than that in the case of the amino acid-containing hydrotalcite of the present invention, and therefore, it is difficult to obtain amino acid-containing hydrotalcite of stable quality.

[0028] The present inventors have found that the amount of alkaline solution used can be reduced by a method of separating the slurry after the heating step into amino acid-containing hydrotalcite and a solution containing dissolved amino acids without treating the slurry with an alkaline solution. In this method, the slurry is separated into the amino acid-containing hydrotalcite and the solution containing dissolved amino acids, and then the amino acid-containing hydrotalcite is treated with an alkaline solution. Furthermore, the present inventors have found that this method allows amino acid-containing hydrotalcite of stable quality to be obtained even when recycled amino acid solution is used as a raw material.

[0029] The present invention was completed based on these findings, and as described above, in a production method according to one embodiment of the present invention, the slurry after the production step is not treated with an alkaline solution, but is separated into a first amino acid-containing hydrotalcite and a solution containing dissolved amino acids in step (A). Therefore, in the production method of this embodiment, the separated first amino acid-containing hydrotalcite may be treated with an alkaline solution at any time after step (A). In this case, the separated first amino acid-containing hydrotalcite contains almost no dissolved amino acids, so the amount of alkaline solution required during the alkaline treatment can be minimized. In other words, the production method of this embodiment can reduce the amount of alkaline solution used.

[0030] Furthermore, as described above, the production method of this embodiment includes, after step (A), a step of reusing the solution containing the dissolved amino acids separated from the slurry and using it as a raw material aqueous solution in the production of the next amino acid-containing hydrotalcite. That is, this production method includes a solution preparation step of mixing the amino acid aqueous solution derived from the separated dissolved amino acid-containing solution with a composite metal oxide to prepare a slurry solution, and a production step of heating the slurry solution to produce the next second amino acid-containing hydrotalcite.

[0031] In the production method of this embodiment, the solution containing the dissolved amino acids separated in step (A) is not treated with an alkaline solution. Therefore, even if such a solution is reused as a raw material aqueous solution in the next production, the amount of metal ions in the aqueous solution is unlikely to vary, and the amount of amino acid ions in the slurry is unlikely to be OH. － Therefore, the production method of this embodiment makes it easy to obtain amino acid-containing hydrotalcite of stable quality even when a recycled amino acid aqueous solution is used as a production raw material. Note that, because the production method of this embodiment has excellent recyclability, it also has the advantage of being able to contribute to the achievement of the SDGs (Sustainable Development Goals) adopted at the United Nations Summit.

[0032] Here, the term "amino acid aqueous solution derived from a solution containing dissolved amino acids" includes not only the solution containing dissolved amino acids itself, but also an amino acid aqueous solution in which the amino acid concentration has been adjusted by subjecting the solution containing dissolved amino acids to various treatments such as concentration, dilution, and adsorption.

[0033] In the production method of this embodiment, the slurry before separation in step (A) may be obtained by steps similar to the solution preparation step and production step described above. That is, the production method of this embodiment may further include a solution preparation step and a production step before step (A). Here, the solution preparation step is a step of preparing a slurry solution by mixing an amino acid aqueous solution with a composite metal oxide obtained by calcining a precursor hydrotalcite compound. The production step is a step of heating the slurry solution to produce a first amino acid-containing hydrotalcite.

[0034] By including such a solution preparation step and a production step before step (A), various production conditions can be adjusted in these steps, and therefore a slurry containing the desired first amino acid-containing hydrotalcite and dissolved amino acids can be obtained with greater precision, thereby more reliably achieving the effects of the above-described embodiment.

[0035] The production method of this embodiment may further include a cooling step of cooling the slurry after the above-mentioned generating step and before step (A). This cooling step will be described in detail in the description of each step below.

[0036] Hereinafter, each step that may be included in the method for producing amino acid-containing hydrotalcite of this embodiment will be described in more detail using exemplary first to fourth embodiments. In the following description of each step, hydrotalcite may be abbreviated as "HT."

[0037] [First embodiment] Fig. 1 is a flow diagram showing an example of a first embodiment of the present invention. As shown in Fig. 1, the first embodiment of the present invention includes a solution preparation step, a production step, a cooling step, step (A) which is a separation step, and step (B) which is an alkali treatment step. In this first embodiment, a purified product of the first amino acid-containing hydrotalcite (purified amino acid-containing HT) is obtained through these steps.

[0038] Furthermore, the first embodiment further includes, after step (A), step (C) of treating and reusing the solution containing dissolved amino acids, which is the liquid fraction separated by step (A), so that it can be used as part of the raw material for producing the next amino acid-containing hydrotalcite.

[0039] Step (C) of this first embodiment includes a step of treating the solution containing dissolved amino acids separated from the slurry in step (A) in a concentration step to obtain a concentrated amino acid aqueous solution. The concentrated amino acid aqueous solution is an example of an "amino acid aqueous solution derived from a solution containing dissolved amino acids." The concentrated amino acid aqueous solution obtained here is reused as part of the raw material for producing the next amino acid-containing hydrotalcite (second amino acid-containing hydrotalcite). In other words, the concentrated amino acid aqueous solution is subjected to a solution preparation step when producing the second amino acid-containing hydrotalcite, and is mixed with a composite metal oxide obtained by calcining a precursor hydrotalcite compound.

[0040] Furthermore, in the first embodiment, the purified amino acid-containing HT obtained after step (B) may be subjected to any additional step, such as a drying step or a surface treatment step.

[0041] Each step of the manufacturing method according to the first embodiment will be described in detail below.

[0042] <Solution Preparation Step> The solution preparation step is a step of preparing a slurry solution by mixing an aqueous amino acid solution with a composite metal oxide obtained by calcining a precursor hydrotalcite compound. This solution preparation step is a step that is commonly performed not only when producing a first amino acid-containing hydrotalcite, but also when producing a subsequent second amino acid-containing hydrotalcite and any subsequent amino acid-containing hydrotalcites. However, at least a portion of the aqueous amino acid solution used as the raw material is derived from a solution containing dissolved amino acids separated and recovered during the previous production of amino acid-containing hydrotalcite. For example, at least a portion of the aqueous amino acid solution used when producing the second amino acid-containing hydrotalcite is derived from a solution containing dissolved amino acids separated and recovered during the production of the first amino acid-containing hydrotalcite.

[0043] In the solution preparation step, first, the precursor hydrotalcite compound is calcined to obtain a composite metal oxide. The calcination conditions for calcining the precursor hydrotalcite compound are not particularly limited, and any calcination conditions can be adopted depending on the calcination means, etc. For example, when calcining using a calcination furnace, the calcination temperature can be 300°C or higher and 800°C or lower. Furthermore, in this case, the calcination time can be 0.1 hours or higher and 24 hours or lower. Similarly, when calcining using microwaves, for example, the calcination temperature can be 300°C or higher and 800°C or lower. Furthermore, in this case, the calcination time can be 1 minute or higher and 12 hours or lower.

[0044] Next, a slurry solution is obtained by adding a predetermined concentration of an aqueous amino acid solution to the powder of composite metal oxide obtained by calcining the precursor hydrotalcite compound and mixing it. At this time, as described above, at least a part of the aqueous amino acid solution is derived from the solution containing dissolved amino acids separated and recovered during the previous production of amino acid-containing hydrotalcite.

[0045] In the solution preparation step, the slurry concentration of the slurry solution obtained by mixing the composite metal oxide and the amino acid aqueous solution is preferably less than 30 g / L. If the slurry concentration is less than 30 g / L, the interparticle interaction of the hydrotalcite-based compound is reduced, making it less likely for gelation to occur during the exfoliation process of the hydrotalcite-based compound. This makes it easier to maintain the slurry state of the slurry solution, allowing for more stable production of the desired amino acid-containing hydrotalcite.

[0046] In terms of productivity, the slurry concentration in the solution preparation step is more preferably in the range of 1 g / L to 28 g / L. The slurry concentration can be calculated using the following formula: Slurry concentration (g / L) = Weight of composite metal oxide (g) / Volume of slurry (L)

[0047] In the solution preparation step, the composite metal oxide is hydrated using an aqueous solution of an amino acid that functions as a release agent. During this hydration, amino acid molecules in the solution are incorporated as anions between the layers of the hydrotalcite compound. Furthermore, by heating in the subsequent production step, the hydrotalcite layers are peeled off, forming thin amino acid-containing hydrotalcite. Furthermore, at this time, particle growth in the width direction of the amino acid-containing hydrotalcite is promoted. In other words, amino acid-containing hydrotalcite particles with a high aspect ratio are formed.

[0048] (Hydrotalcite-based Compound) The precursor hydrotalcite-based compound that can be used in this embodiment is not particularly limited, and examples thereof include hydrotalcite-based compounds represented by the following formula (1): (M ２＋ ) １－Ｘ (M ３＋ ) Ｘ (OH) ２ (A ｎ－ ) Ｘ／ｎ ・mH ２ O (1) In formula (1), M ２＋ is a divalent metal cation. ３＋ is a trivalent metal cation. ｎ－ is an n-valent anion. X is a number that satisfies 0.17<X<0.36. n is an integer from 1 to 6. m is a number that satisfies 0<m<1.80.

[0049] In the above formula (1), preferred M ２＋ is Mg ２＋ In the above formula (1), preferred M ３＋ is Al ３＋ These hydrotalcite compounds have the advantage of being highly safe for living organisms. In addition, these hydrotalcite compounds have a refractive index close to that of resins such as polypropylene and polyethylene, and have the advantage of easily maintaining the transparency of compositions with such resins. Furthermore, Mg / Al ２ The molar ratio is preferably in the range of 4 to 8, since a hydrotalcite structure can be more reliably obtained.

[0050] In the above formula (1), Aｎ－ The type of anion is not particularly limited, and examples thereof include carbonate ions (CO ３ ２－ ), hydroxide ions (OH － For example, carbonate ions are preferred in that they are less likely to generate corrosive gases such as chlorine gas and nitrogen dioxide gas when the precursor hydrotalcite compound is calcined.

[0051] The above-mentioned hydrotalcite-type compounds are precursor hydrotalcite-type compounds that are raw materials for producing amino acid-containing hydrotalcites, but the same applies to the hydrotalcite-type compounds contained in the finally obtained amino acid-containing hydrotalcite. That is, the hydrotalcite-type compound contained in the finally obtained amino acid-containing hydrotalcite may be the hydrotalcite-type compound represented by the above formula (1). Here, the finally obtained amino acid-containing hydrotalcite may be not only the first amino acid-containing hydrotalcite, but also the second amino acid-containing hydrotalcite produced subsequently, or any amino acid-containing hydrotalcite produced thereafter.

[0052] (Amino Acids) The amino acids that can be used in this embodiment are not particularly limited, and examples include various amino acids such as α-amino acids, β-amino acids, and γ-amino acids. More specific examples include aspartic acid, glutamic acid, asparagine, serine, glycine, β-alanine, β-aminobutyric acid, γ-aminobutyric acid, and β-leucine. One type of these amino acids may be used alone, or two or more types of amino acids may be used in combination.

[0053] Among the above amino acids, the solubility of 10g / 100mLH ２ Amino acids of 0 or higher are preferred, and glycine compounds are more preferred. Such amino acids, particularly glycine compounds, have a high dielectric constant, making it easy to obtain amino acid-containing hydrotalcites with thin primary particles. Furthermore, glycine has a bacteriostatic effect and is used in supplements, coloring agents, fragrances, etc., and is also advantageous in terms of biological safety.

[0054] In this specification, "solubility 10 g / 100 mL H ２ The term "solubility of 10 g or more" means that the mass of the target substance that dissolves in 100 g of water at 25° C. is 10 g or more. In this example, the target substance is an amino acid.

[0055] The above-mentioned amino acids are amino acids used as raw materials for producing amino acid-containing hydrotalcite, but the same applies to the amino acids contained in the finally obtained amino acid-containing hydrotalcite. That is, the amino acids contained in the finally obtained amino acid-containing hydrotalcite may be the various amino acids described above. However, the amino acids contained in the amino acid-containing hydrotalcite may also contain multimers formed by the bonding of multiple amino acids, which may be produced during the production process. Here, the multimers are peptides. In this specification, substances containing such amino acids and amino acid multimers may be referred to as "amino acid compounds." For example, a substance containing glycine and polyglycine is referred to as a "glycine compound."

[0056] In the solution preparation step, the amino acid concentration of the slurry solution is not particularly limited, but is preferably less than 0.6 mol / L. When the amino acid concentration of the slurry solution is within this range, it is easy to obtain an amino acid-containing hydrotalcite that has an aspect ratio of 85 or more and is less likely to become discolored when formed into a resin composition. Resin compositions containing such amino acid-containing hydrotalcite have advantages such as high gas barrier properties and the ability to form highly transparent coating layers with little discoloration. It is more preferable that the amino acid concentration of the slurry solution be within the range of 0.02 mol / L to 0.5 mol / L.

[0057] In the solution preparation step, the molar ratio of the amino acid in the slurry solution to the trivalent metal cation of the hydrotalcite-based compound, i.e., amino acid / (M ３＋ ) ２ The molar ratio of is preferably in the range of 2 to 6. For example, when the amino acid is glycine and the trivalent metal cation of the hydrotalcite compound is Al ３＋ If glycine / Al ２The molar ratio is preferably within the range of 2 to 6. When the molar ratio is within this range, it is easy to obtain an amino acid-containing hydrotalcite that has an aspect ratio of 85 or more and is resistant to coloration when formed into a resin composition. Furthermore, when the molar ratio is within this range, the primary particle thickness of the obtained amino acid-containing hydrotalcite can be, for example, 20 nm or less. In this case, by blending it with a polymer or the like in a coating liquid and forming a coating layer on a resin substrate, high gas barrier properties can be achieved due to the labyrinth effect. Resin compositions containing such amino acid-containing hydrotalcite have advantages such as being able to form coating layers that have high gas barrier properties and are highly transparent and have little coloration.

[0058] <Production Step> The slurry solution obtained in the solution preparation step is subjected to the next production step. In the production step, the slurry solution is heated to produce amino acid-containing hydrotalcite. In the production step, the slurry solution obtained in the above-mentioned solution preparation step is heated to promote particle growth of the hydrotalcite-based compound. At this time, amino acid molecules in the solution are incorporated as anions between the layers of the hydrotalcite-based compound. This causes peeling between the layers of the hydrotalcite-based compound, forming thin particles. At this time, the growth of the particles in the width direction is also promoted. As a result, amino acid-containing hydrotalcite, which is a complex of the hydrotalcite-based compound and the amino acid, is produced as particles with a high aspect ratio.

[0059] In the production step, the slurry solution is preferably heated while being stirred. The stirring means is not particularly limited, but it is preferable to use a means that can stir the slurry solution uniformly while maintaining its fluidity.

[0060] In the production step, the heating temperature is not particularly limited, but is preferably within the range of 20°C to 250°C. From the viewpoint of easily suppressing denaturation of amino acids, a more preferable upper limit of the heating temperature is 170°C. In the production step, the heating time is not particularly limited, but is preferably within the range of 1 minute to 100 hours. In addition, the production step is preferably carried out so as not to fluctuate the concentration of the slurry solution. For example, the production step may be carried out in a closed system, or in an open system where evaporated water is appropriately added.

[0061] <Cooling Step> In this embodiment, the slurry after the production step is subjected to a cooling step, as shown in Fig. 1. The cooling step is a step of cooling the slurry containing the amino acid-containing hydrotalcite and dissolved amino acids obtained in the production step so that it can be subjected to the subsequent solid-liquid separation step, i.e., step (A). Therefore, the cooling step is carried out after the production step and before step (A).

[0062] In the cooling step, the slurry containing the amino acid-containing hydrotalcite and the dissolved amino acids may be cooled during the process of transferring it from the production step to step (A). In the cooling step, the slurry may be cooled using any cooling device. Alternatively, in the cooling step, the slurry may be allowed to cool without using a cooling device.

[0063] In the cooling step, the cooling temperature is not particularly limited, but is preferably within a range of 10° C. to 80° C. From the viewpoint of ease of handling, etc., a more preferred cooling temperature is about room temperature. In the cooling step, the cooling time is not particularly limited, but is preferably within a range of 1 minute to 48 hours from the viewpoint of productivity, etc.

[0064] In addition, if the slurry after the production step can be directly subjected to the next step (A), such a cooling step does not need to be performed. For example, even if the slurry is at a high temperature, the tools and devices used in the subsequent separation step can operate normally. On the other hand, if the tools and devices used in the subsequent separation step do not operate normally due to the high temperature of the slurry, it is preferable to perform the cooling step. Examples of when it is preferable to perform the cooling step include when the separation membrane has poor heat resistance or when the separation device malfunctions due to heat.

[0065] <Step (A) / Separation Step> The slurry containing amino acid-containing hydrotalcite and dissolved amino acids after the cooling step is subjected to step (A), which is a solid-liquid separation step. Step (A) is a step of solid-liquid separation of the slurry containing amino acid-containing hydrotalcite and dissolved amino acids into amino acid-containing hydrotalcite and a solution containing dissolved amino acids. In this specification, "separation" includes not only the case where the solid content and liquid content are completely separated, but also the case where a small amount of water is unavoidably contained in the solid content.

[0066] The separation means that can be used in step (A) is not particularly limited, and examples thereof include membrane separation means, centrifugal separation means, solid-liquid separation means, and natural settling means.

[0067] In this embodiment, step (A) may be performed by using a slurry containing amino acid-containing hydrotalcite and dissolved amino acids as is to separate the amino acid-containing hydrotalcite and a solution containing dissolved amino acids, but is not limited to such a form. For example, step (A) may involve adding water to a slurry containing amino acid-containing hydrotalcite and dissolved amino acids to separate the amino acid-containing hydrotalcite and a solution containing dissolved amino acids. In this case, step (A) may involve adding water to the slurry and then separating the amino acid-containing hydrotalcite and a solution containing dissolved amino acids. Alternatively, step (A) may involve adding water to the slurry to separate the amino acid-containing hydrotalcite and a solution containing dissolved amino acids. In this way, by adjusting the water content of the slurry before or during separation, the slurry can be more accurately separated into the amino acid-containing hydrotalcite and a solution containing dissolved amino acids.

[0068] When adding water to the slurry, the entire amount of water may be added to the slurry at once, or a predetermined amount of water may be added to the slurry in multiple portions. When adding water to the slurry to separate it into amino acid-containing hydrotalcite and a solution containing dissolved amino acids, the amount of water supplied may be fixed at a constant amount or may be adjusted to vary arbitrarily. The water added to the slurry is not particularly limited, and examples thereof include ion-exchanged water.

[0069] In step (A), the step of separating the slurry containing the amino acid-containing hydrotalcite and the dissolved amino acids into the amino acid-containing hydrotalcite and the solution containing the dissolved amino acids may be carried out only once, or may be carried out multiple times, such as two or more times. Step (A) in which such a separation step is carried out multiple times will be described in another embodiment below.

[0070] <Step (B) / Alkali Treatment Step> In this embodiment, the amino acid-containing hydrotalcite in the solid content separated in the above-mentioned step (A) is subjected to step (B), which is an alkali treatment step, as shown in Figure 1. Step (B) is a washing step that follows step (A) and reduces amino acids from the amino acid-containing hydrotalcite using an alkaline solution. This step (B) removes amino acids as impurities from the amino acid-containing hydrotalcite, and a purified amino acid-containing hydrotalcite (purified amino acid-containing HT) is obtained. Note that the majority of the amino acids contained in the solid content separated in step (A) are amino acids that have been incorporated between the layers of the hydrotalcite, and there is a possibility that some amino acids that have adhered to the surface of the hydrotalcite are also included.

[0071] If such an alkaline treatment step is carried out before the slurry after the production step is separated into the amino acid-containing hydrotalcite and the solution containing dissolved amino acids, a large amount of alkaline solution will be required because the slurry contains a large amount of amino acids.

[0072] On the other hand, in this embodiment, the slurry after the production step is separated into amino acid-containing hydrotalcite and a solution containing dissolved amino acids, and then the amino acid-containing hydrotalcite is treated with an alkaline solution. Since the amino acid-containing hydrotalcite after separation has a low amino acid content, in this embodiment, the amino acids contained in the amino acid-containing hydrotalcite can be reduced with a small amount of alkaline solution. In other words, in this embodiment, the amount of alkaline solution used in the alkaline treatment step can be reduced.

[0073] The extent to which the amount of alkaline solution used can be reduced depends on the treatment conditions, such as the type and means of the alkaline solution used, but depending on these conditions, it is expected that the amount of alkaline solution used can be reduced by about 60% compared to when the alkaline treatment step is performed before the separation step. For example, when glycine is used as the amino acid and sodium hydroxide is used as the alkali, if the total amount of amino acids used is glycine / Al ２ = 5.26, the interlayer amino acid of the peeled HT is glycine / Al ２= 2, and the possible alkali reduction amount is [1 - (2 / 5.26)] x 100 = 62%. Note that this calculation is based on the assumption that all interlayer spaces of the hydrotalcite are filled with glycine and that no glycine is attached to the surface of the hydrotalcite.

[0074] In this embodiment, the type of alkaline component of the alkaline solution that can be used in step (B) is not particularly limited, as long as it can reduce amino acids from the amino acid-containing hydrotalcite described above. Examples of such alkaline components include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, ammonia, and sodium carbonate. Among these alkaline components, sodium hydroxide, potassium hydroxide, and ammonia are preferred, sodium hydroxide and potassium hydroxide are more preferred, and sodium hydroxide is even more preferred. Note that these alkaline components may be used alone or in combination of two or more types.

[0075] In step (B), the treatment concentration when treating the amino acid-containing hydrotalcite with the alkaline solution is not particularly limited as long as it is a concentration that can reduce amino acids from the amino acid-containing hydrotalcite, but from the viewpoint of suppressing aggregation, a condition in which the concentration is not too high is preferable. Note that the treatment concentration means the alkali content ratio to the total volume of the mixture obtained by adding the alkaline solution to the amino acid-containing hydrotalcite, i.e., the slurry.

[0076] The concentration of the alkaline solution used in the alkaline treatment is not particularly limited, as long as it is within a range in which the slurry obtained by adding the alkaline solution to the amino acid-containing hydrotalcite does not thicken. For example, the upper limit of the alkaline solution concentration can be 4.0 mol / L or less, preferably 3.0 mol / L or less, and more preferably 2.0 mol / L or less. The lower limit of the alkaline solution concentration is higher than 0 mol / L, preferably 0.1 mol / L or more, and more preferably 0.2 mol / L or more.

[0077] In this embodiment, step (B) can be performed by stirring a slurry obtained by adding an alkaline solution to the amino acid-containing hydrotalcite. In this case, in step (B), stirring may be started after the alkaline solution has been added to the amino acid-containing hydrotalcite, or stirring may be performed while the alkaline solution is being added to the amino acid-containing hydrotalcite.

[0078] The stirring conditions in step (B) are not particularly limited, but are preferably a stirring speed and stirring force that can at least stir the slurry. For example, the stirring speed is preferably adjusted so that foaming, scattering, and gelation can be suppressed and the slurry solution becomes uniform. In particular, when adding the alkaline solution, it is preferably adjusted to prevent local pH bias. The stirring speed can be any speed depending on the stirring blade, type of stirrer, size and shape of the container, slurry viscosity, slurry concentration, alkaline solution concentration, alkaline solution addition rate, etc., but is, for example, 50 to 2000 rpm, preferably 100 to 1500 rpm. The temperature during stirring is not particularly limited, but is, for example, room temperature.

[0079] In step (B) of this embodiment, when adding the alkaline solution to the amino acid-containing hydrotalcite, it is preferable to add the alkaline solution while stirring the amino acid-containing hydrotalcite. At this time, it is preferable to gradually add the alkaline solution to the amino acid-containing hydrotalcite while stirring so as to maintain a slurry state, i.e., while stirring so as to maintain a stirrable state. By adding the alkaline solution while stirring in this manner, local aggregation of the slurry can be suppressed.

[0080] When adding the alkaline solution to the amino acid-containing hydrotalcite, the conditions such as timing, supply amount, temperature, and stirring speed are preferably adjusted appropriately according to the viscosity of the slurry so as not to thicken the slurry.

[0081] <Step (C) / Recycling Step> In this embodiment, the solution containing dissolved amino acids, which is the liquid fraction separated in the above-mentioned step (A), is subjected to step (C), which is a recycling step, as shown in Fig. 1. Step (C) is a step of treating and reusing the solution containing dissolved amino acids separated in step (A) so that it can be used as part of the raw material for the subsequent production of amino acid-containing hydrotalcite.

[0082] In step (C), when the solution containing dissolved amino acids can be used as a raw material for producing amino acid-containing hydrotalcite as it is, the solution can be reused as it is without any special treatment, but it is usually necessary to adjust the amino acid concentration in the solution.

[0083] In this embodiment, as shown in Figure 1, step (C) includes a concentration step in order to adjust the amino acid concentration of the solution containing the dissolved amino acids separated in step (A). In this embodiment, the concentration step is a step in which the solution containing the dissolved amino acids is heated and concentrated to increase the amino acid concentration in the aqueous solution. The concentrated amino acid aqueous solution obtained through this concentration step is reused as part of the raw material for producing the next amino acid-containing hydrotalcite. For example, the solution containing dissolved amino acids separated and recovered during the production of the first amino acid-containing hydrotalcite is converted into a concentrated amino acid aqueous solution through the concentration step of step (C) and is then subjected to the solution preparation step during the production of the second amino acid-containing hydrotalcite.

[0084] The process for adjusting the amino acid concentration of a solution containing dissolved amino acids is not limited to the concentration process by heating and concentration described above. Other examples of the process for adjusting the amino acid concentration include an amino acid addition process for adding amino acids, a dilution process for adding ion-exchanged water, and an adsorption process for adding a composite metal oxide (calcined HT) to adsorb amino acids. Note that these processes may be used alone or in combination.

[0085] In addition to the step of adjusting the amino acid concentration, step (C) may also include a pH adjustment step and a step of adjusting the amount of metal ions, such as magnesium and aluminum, eluted from the hydrotalcite. In particular, when the production of amino acid-containing hydrotalcite is repeatedly carried out, the amount of metal ions, such as magnesium and aluminum, may accumulate in the solution, which may have a significant impact on the molar ratio of the production raw materials. By performing a step of adjusting the amount of metal ions in step (C) and reducing the amount of metal ions in the solution, amino acid-containing hydrotalcite can be repeatedly produced with greater accuracy. The step of adjusting the amount of metal ions is not particularly limited, and examples thereof include a step of precipitating and removing the target metal ions as hydroxides, and a step of adsorbing and removing them by adding negatively charged particles.

[0086] <Other Treatment Steps> In this embodiment, the purified amino acid-containing HT obtained after the above-described step (B) may be subjected to any treatment step. Examples of such treatment steps include a drying step in which the solid content obtained in step (B) is dried to obtain a powder of purified amino acid-containing HT, a surface treatment step in which the surfaces of the particles of the purified amino acid-containing HT are treated with various surface treatment agents, and a coating liquid preparation step in which the solid content obtained in step (B) is mixed with a polymer solution or the like without being dried to prepare a coating liquid.

[0087] According to the production method of this embodiment as described above, it is possible to obtain an amino acid-containing hydrotalcite having a high aspect ratio. Such an amino acid-containing hydrotalcite having a high aspect ratio will be described later.

[0088] Hereinafter, second to fourth embodiments of the present invention, which differ from the first embodiment described above only in the aspects of steps (A) to (C), will be described with reference to the drawings. In the following description, steps other than those different from the first embodiment are basically the same as those in the first embodiment described above, and therefore will not be described again.

[0089] [Second embodiment] Fig. 2 is a flow diagram showing an example of a second embodiment of the present invention. As shown in Fig. 2, the second embodiment of the present invention has, similarly to the first embodiment described above, a solution preparation step, a generation step, a cooling step, a separation step (A), an alkali treatment step (B), and a reuse step (C).

[0090] In the second embodiment, only the steps (A) and (C) are different from those in the first embodiment, and the other steps are the same as those in the first embodiment.

[0091] <Step (A) of Second Embodiment> In the second embodiment, step (A) is a step of performing solid-liquid separation of a slurry containing amino acid-containing hydrotalcite and dissolved amino acids into an amino acid-containing hydrotalcite and a solution containing dissolved amino acids, the solid-liquid separation being carried out multiple times. In the example shown in Figure 2, the separation step is carried out twice.

[0092] Specifically, in step (A) of the second embodiment, first, without adding water to a slurry containing amino acid-containing hydrotalcite and dissolved amino acids, the slurry is separated into a slurry containing the amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and a solution containing the remainder of the dissolved amino acids. Then, water is added to the slurry containing the amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and the slurry is separated into the amino acid-containing hydrotalcite and the solution containing the dissolved amino acids.

[0093] When adding water to the slurry, the entire amount of water may be added to the slurry at once, or a predetermined amount of water may be added to the slurry in multiple batches. Alternatively, water may be added to the slurry, followed by separation into the amino acid-containing hydrotalcite and a solution containing dissolved amino acids, or the amino acid-containing hydrotalcite and a solution containing dissolved amino acids may be separated while adding water to the slurry. When separating the amino acid-containing hydrotalcite and a solution containing dissolved amino acids while adding water to the slurry, the amount of water supplied may be fixed at a constant amount, or may be adjusted to vary arbitrarily. The water added to the slurry is not particularly limited, and examples thereof include ion-exchanged water.

[0094] As in step (A) of the second embodiment, by dividing the separation step into multiple steps, it is possible to reduce the amount of amino acids contained in the obtained amino acid-containing hydrotalcite. Furthermore, by dividing the separation step into multiple steps, it is possible to improve the reuse rate of the amino acids to be reused. Furthermore, by reducing the amount of amino acids contained in the obtained amino acid-containing hydrotalcite, it is possible to reduce the amount of alkaline solution used in the subsequent step (B).

[0095] Step (A) of the second embodiment is the same as step (A) of the first embodiment except for the points described above.

[0096] <Step (C) of Second Embodiment> In this second embodiment, step (C) is a step of treating and reusing the solution containing multiple types of dissolved amino acids separated and recovered by the multiple separation steps of step (A) described above so that it can be used as part of the raw material for producing the next amino acid-containing hydrotalcite.

[0097] Specifically, in step (C) of this second embodiment, first, a solution containing the remaining dissolved amino acids separated in the first separation step of step (A) is recovered. Next, the solution containing the dissolved amino acids separated in the second separation step of step (A) is recovered and heated and concentrated in a concentration step to obtain a concentrated amino acid aqueous solution with an adjusted amino acid concentration. Then, the solution containing the remaining dissolved amino acids and the concentrated amino acid aqueous solution are mixed to obtain a mixed amino acid aqueous solution. Thereafter, the obtained mixed amino acid aqueous solution is reused as part of the raw material for producing the next amino acid-containing hydrotalcite.

[0098] As in step (C) of the second embodiment, by using a solution containing multiple types of dissolved amino acids separated and recovered by multiple separation steps as part of the raw materials for producing the next amino acid-containing hydrotalcite, the reuse rate of the amino acids to be reused can be improved. Furthermore, as in step (C) of the second embodiment, by treating each solution containing multiple types of dissolved amino acids separated and recovered by multiple separation steps individually according to the amino acid concentration of the solution, etc., the next amino acid-containing hydrotalcite can be produced with greater accuracy.

[0099] In step (C), a concentration step is not necessarily required. However, if the amino acid concentration of the solution containing dissolved amino acids decreases with an increase in the number of separation steps, it is preferable to perform a concentration step on the solution containing dissolved amino acids after the second or subsequent separation steps.

[0100] Step (C) of the second embodiment is the same as step (C) of the first embodiment except for the points described above.

[0101] [Third Embodiment] Fig. 3 is a flow diagram showing an example of a third embodiment of the present invention. As shown in Fig. 3, the third embodiment of the present invention also includes a solution preparation step, a generation step, a cooling step, a separation step (A), an alkali treatment step (B), and a reuse step (C), similar to the first and second embodiments described above.

[0102] In the third embodiment, only step (C) is different from the second embodiment, and the other steps are the same as those in the second embodiment. That is, the steps other than steps (A) and (C) are the same as those in the first embodiment.

[0103] <Step (C) of the Third Embodiment> In this third embodiment, step (C) is also a step of treating and reusing a solution containing multiple types of dissolved amino acids separated and recovered by the multiple separation steps of step (A) described above so that it can be used as part of the raw material for the subsequent production of amino acid-containing hydrotalcite. However, step (C) of this third embodiment differs from step (C) of the second embodiment in that, after the solution containing dissolved amino acids separated in the second separation step of step (A) described above is recovered, the amino acid concentration is adjusted by an adsorption step and a separation step to form a slurry.

[0104] Specifically, in step (C) of this third embodiment, first, a solution containing the remaining dissolved amino acids separated in the first separation step of step (A) is recovered. Next, the solution containing the dissolved amino acids separated in the second separation step of step (A) is recovered, and a composite metal oxide, which is a calcined product of a hydrotalcite-type compound, is added to it, and an adsorption step is carried out to adsorb the amino acids in the solution. Furthermore, a separation step is carried out in which the slurry after the adsorption step is solid-liquid separated into a solid content containing hydrotalcite and amino acids and water. Then, the solution containing the remaining dissolved amino acids is mixed with the solid content after the separation step to obtain a slurry containing hydrotalcite and amino acids (HT / amino acid slurry). Thereafter, a new amino acid aqueous solution is added to the obtained HT / amino acid slurry, and the slurry is reused as an amino acid raw material in the solution preparation step when producing the next amino acid-containing hydrotalcite.

[0105] In step (C) of the third embodiment, the solution containing multiple types of dissolved amino acids separated and recovered by multiple separation steps is used as part of the raw materials for producing the next amino acid-containing hydrotalcite, thereby improving the reuse rate of the amino acids to be reused.Furthermore, in step (C) of the third embodiment, the solution containing multiple types of dissolved amino acids separated and recovered by multiple separation steps is treated individually according to the amino acid concentration of each solution, thereby enabling the next amino acid-containing hydrotalcite to be produced with greater accuracy.

[0106] Furthermore, in the third embodiment, as described above, in step (C), the solution containing the multiple dissolved amino acids separated and recovered by the multiple separation steps in step (A) is reused as the amino acid raw material in the solution preparation step in the next production of amino acid-containing hydrotalcite. Therefore, the third embodiment has the advantage of excellent production efficiency when amino acid-containing hydrotalcite is repeatedly produced.

[0107] In addition, in the step (C) of the third embodiment, the points other than those described above are the same as the step (C) of the first and second embodiments described above.

[0108] [Fourth embodiment] Fig. 4 is a flow diagram showing an example of a fourth embodiment of the present invention. As shown in Fig. 4, the fourth embodiment of the present invention also includes a solution preparation step, a generation step, a cooling step, a separation step (A), an alkali treatment step (B), and a reuse step (C), similar to the first embodiment described above.

[0109] In this embodiment, only the steps (A) and (C) are different from the first embodiment, and the other steps are the same as those in the first embodiment.

[0110] <Step (A) of Fourth Embodiment> In the fourth embodiment, step (A) is a step of performing solid-liquid separation of a slurry containing amino acid-containing hydrotalcite and dissolved amino acids into an amino acid-containing hydrotalcite and a solution containing dissolved amino acids, the step being carried out in two or more separate steps.

[0111] Specifically, the step (A) of the fourth embodiment includes the following steps (a1) and (a2), as shown in FIG.

[0112] Step (a1) is a step of separating a slurry containing amino acid-containing hydrotalcite and dissolved amino acids into a slurry containing amino acid-containing hydrotalcite and a portion of the dissolved amino acids and a solution containing the remainder of the dissolved amino acids without adding water to the slurry.

[0113] Step (a2) is a step of adding water to the slurry containing the amino acid-containing hydrotalcite and a portion of the dissolved amino acids after the above step (a1), and separating the slurry into a slurry containing the amino acid-containing hydrotalcite and a portion of the dissolved amino acids or no dissolved amino acids, and a solution containing the remainder of the dissolved amino acids. This step (a2) is carried out once or multiple times.

[0114] When adding water to the slurry, the entire amount of water may be added to the slurry at once, or a predetermined amount of water may be added to the slurry in multiple batches. Alternatively, water may be added to the slurry, followed by separation into the amino acid-containing hydrotalcite and a solution containing dissolved amino acids, or the amino acid-containing hydrotalcite and a solution containing dissolved amino acids may be separated while adding water to the slurry. When separating the amino acid-containing hydrotalcite and a solution containing dissolved amino acids while adding water to the slurry, the amount of water supplied may be fixed at a constant amount, or may be adjusted to vary arbitrarily. The water added to the slurry is not particularly limited, and examples thereof include ion-exchanged water.

[0115] In step (A) of the fourth embodiment, the separation step can also be divided into multiple steps to reduce the amount of amino acids contained in the resulting amino acid-containing hydrotalcite. Furthermore, by dividing the separation step into multiple steps, the reuse rate of the amino acids to be reused can also be improved. Furthermore, by reducing the amount of amino acids contained in the resulting amino acid-containing hydrotalcite, the amount of alkaline solution used in the subsequent step (B) can be reduced.

[0116] In addition, in the step (A) of the fourth embodiment, the points other than those described above are the same as the step (A) of the first and second embodiments.

[0117] <Step (C) of Fourth Embodiment> In this fourth embodiment, step (C) is also a step of treating and reusing a solution containing multiple types of dissolved amino acids separated and recovered by the multiple separation steps of step (A) described above so that it can be used as part of the raw material for the subsequent production of amino acid-containing hydrotalcite. However, step (C) of this fourth embodiment differs from step (C) of the first to third embodiments in that the solutions containing dissolved amino acids separated by the multiple separation steps of step (A) described above are mixed, and a composite metal oxide is added to the obtained mixed amino acid aqueous solution to form a slurry.

[0118] Specifically, in step (C) of the fourth embodiment, solutions containing multiple dissolved amino acids separated in the multiple separation steps of step (A) described above, i.e., step (a1) and one or more steps (a2), are recovered and mixed to obtain a mixed amino acid aqueous solution. Next, a composite metal oxide, which is a calcined product of a hydrotalcite-type compound, is added to this mixed amino acid aqueous solution to obtain a slurry containing hydrotalcite and amino acids (HT / amino acid slurry). This HT / amino acid slurry is then reused as the amino acid raw material in the solution preparation step during the subsequent production of amino acid-containing hydrotalcite.

[0119] In step (C) of this fourth embodiment, the solution containing multiple types of dissolved amino acids separated and recovered by the multiple separation steps is used as part of the raw material for producing the next amino acid-containing hydrotalcite, thereby improving the reuse rate of the amino acids to be reused. Furthermore, as described above, in step (C) of this fourth embodiment, the solution containing multiple types of dissolved amino acids separated and recovered by the multiple separation steps of step (A) is reused as the amino acid raw material in the solution preparation step when producing the next amino acid-containing hydrotalcite. Therefore, this fourth embodiment also has the advantage of excellent production efficiency when repeatedly producing amino acid-containing hydrotalcite.

[0120] In addition, in the step (C) of the fourth embodiment, the points other than those described above are the same as the step (C) of the first to third embodiments.

[0121] According to the manufacturing method of each embodiment of the present invention as described above, the use of an amino acid as a release agent causes delamination of the hydrotalcite compound, making it possible to obtain amino acid-containing hydrotalcite having thin primary particles, i.e., a high aspect ratio. Next, the amino acid-containing hydrotalcite obtained by the manufacturing method of each embodiment described above will be described.

[0122] [Amino Acid-Containing Hydrotalcite] The amino acid-containing hydrotalcite obtained by the production method of each of the above-described embodiments is an amino acid-containing hydrotalcite having a high aspect ratio of 85 or more.

[0123] Such amino acid-containing hydrotalcites with a high aspect ratio can be mixed with a polymer such as polyvinyl alcohol to form a coating liquid. When the coating liquid is applied to a substrate to form a coating layer, multiple amino acid-containing hydrotalcites are aligned parallel to the surface of the coating layer, thereby exhibiting excellent gas barrier properties. Therefore, the amino acid-containing hydrotalcites obtained by the manufacturing methods of the above-described embodiments can be used in a wide variety of applications requiring gas barrier properties. For example, when a coating liquid containing such amino acid-containing hydrotalcite is applied to a film, high gas barrier properties can be imparted to the film.

[0124] In this specification, the aspect ratio of the amino acid-containing hydrotalcite is the ratio of the width (diameter) to the thickness of a primary particle of the amino acid-containing hydrotalcite having a layered structure. The aspect ratio can be determined by dividing the width by the thickness of the primary particle of the amino acid-containing hydrotalcite.

[0125] The coating liquid containing the amino acid-containing hydrotalcite and the polymer may contain other additive components. Examples of such additive components include, but are not limited to, antioxidants, reinforcing agents, ultraviolet absorbers, pigments, crosslinking agents, and flame retardants. These additive components may be used alone or in combination of two or more.

[0126] Films using the amino acid-containing hydrotalcite described above can be applied in a wide range of fields, such as food packaging films, beverage packaging films, beverage bottles, pharmaceutical packaging films, industrial gas barrier films, gas separation films, and paper barrier materials.

[0127] The manufacturing method of the present invention is not limited to the above-described embodiments or the examples described below, and can be appropriately combined, substituted, modified, etc. within the scope that does not deviate from the purpose and intent of the present invention.

[0128] EXAMPLES The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples.

[0129] Example 1 (Production of Precursor Hydrotalcite Compound) Ion-exchanged water was placed in a 1 L reaction vessel. While stirring, 160 mL of a 1.5 mol / L magnesium chloride aqueous solution, 120 mL of a 1 mol / L aluminum chloride aqueous solution, and a mixed solution of 90 mL of an 8 mol / L sodium hydroxide aqueous solution and 60 mL of a 1 mol / L sodium carbonate aqueous solution were simultaneously added dropwise to the reaction vessel to obtain a reaction product. The pH during the reaction was 9.5. The resulting reaction product was washed with water. Ion-exchanged water was then added to the reaction product to obtain 700 mL of a re-emulsified slurry. The resulting re-emulsified slurry was subjected to hydrothermal treatment at 170°C for 13 hours. The resulting solid was washed with water. The washed solid was dried at 105°C for 16 hours. The dried solid was then pulverized. The chemical formula of the resulting powder was Mg ０．６７ Al ０．３３ (OH) ２ (CO ３ ) ０．１７ ・0.50H ２ The hydrotalcite-based compound was a hydrotalcite-based compound represented by the formula: O. This hydrotalcite-based compound was used as a precursor hydrotalcite-based compound for producing an amino acid-containing hydrotalcite.

[0130] (Caking of Precursor Hydrotalcite Compound) The obtained precursor hydrotalcite compound was calcined in an electric furnace at 450° C. for 12 hours to obtain a calcined product (composite metal oxide).

[0131] (Solution preparation step 1) 14.0 g of the obtained fired product was placed in a glass beaker. 140 mL of a 2 mol / L glycine aqueous solution (equivalent to 21.0 g of glycine powder) was added to the glass beaker. The slurry solution in the glass beaker was stirred until it became uniform. At this time, the glycine / Al ratio of the obtained slurry solution was ２The molar ratio of glycine to glycine was 5.26. Then, ion-exchanged water was added to the slurry solution to make the total volume 700 mL. The slurry solution was further stirred again until it became homogeneous. The slurry concentration at this time was 20 g / L. The glycine concentration at this time was 0.4 mol / L.

[0132] (Production Step 1) Subsequently, the slurry solution was subjected to hydrothermal treatment at 100°C for 48 hours while being stirred at 700 rpm. The obtained slurry solution was in a slurry state. The obtained slurry solution was white. The obtained slurry solution had no particular odor.

[0133] (Step (A) / Separation Step) Next, ion-exchanged water was added to 650 mL of the obtained slurry solution to make the total volume 1300 mL. The slurry concentration at this time was 10 g / L. Furthermore, using a stirrer, the slurry solution was stirred at 400 rpm at room temperature for 16 hours. The obtained slurry after stirring was subjected to solid-liquid separation. The solution obtained after solid-liquid separation was used as a solution containing dissolved glycine compounds. The concentration of glycine compounds in the solution at this time was 0.143 mol / L. The pH of this solution was 8.9.

[0134] (Solution Preparation Step 2) 0.143 g of the calcined product obtained in the above "calcination of precursor hydrotalcite-based compound" was placed in a fluororesin container. 20 mL of the above solution containing 0.143 mol / L of dissolved glycine-based compounds was added to this fluororesin container. The slurry solution in the fluororesin container was stirred until it became uniform. At this time, the glycine-based compound / Al ratio of the obtained slurry solution was ２ The molar ratio of 1 to 10 was 5.26, and the slurry concentration was 7.15 g / L.

[0135] (Production Step 2) Subsequently, the fluororesin container was sealed. The slurry solution in the sealed fluororesin container was heat-treated at 100°C for 48 hours without stirring. The obtained slurry solution was in a slurry state. The obtained slurry solution was white.

[0136] (Step (B) / Alkali Treatment Step) Next, the obtained slurry solution was stirred at room temperature for 16 hours. While continuing to stir the slurry solution, a 4.00 mol / L aqueous sodium hydroxide solution in an amount equivalent to the amount of the glycine compound was gradually added dropwise to the slurry solution. The obtained slurry solution was subjected to solid-liquid separation to obtain the amino acid-containing hydrotalcite of Example 1.

[0137] The aspect ratio of the primary particles of the obtained amino acid-containing hydrotalcite of Example 1 was 93. The thickness of the primary particles of the obtained amino acid-containing hydrotalcite of Example 1 was 3.0 nm.

[0138] Comparative Example 1 The amino acid-containing hydrotalcite of Comparative Example 1 was obtained in the same manner as in Example 1, except that in the above-mentioned "solution preparation step 1", 17.5 g of the fired product was used, 175 ml of a 2 mol / L glycine aqueous solution (equivalent to 26.3 g of glycine powder) was used, a 4.00 mol / L aqueous sodium hydroxide solution in an amount equivalent to the glycine derivative compound was added dropwise to the slurry solution before "step (A) / separation step", the concentration of the glycine derivative compound was 0.158 mol / L, and the pH was 12.4, and that in "solution preparation step 2", 0.158 g of the fired product was used, and the slurry concentration was 7.90 g / L.

[0139] The aspect ratio of the primary particles of the obtained amino acid-containing hydrotalcite of Comparative Example 1 was 14. The thickness of the primary particles of the obtained amino acid-containing hydrotalcite of Comparative Example 1 was 18 nm.

[0140] As described above, it was found that the production method of Example 1, in which the slurry solution is treated with an alkaline solution after step (A) / separation step, can produce amino acid-containing hydrotalcite of stable quality even when using recycled amino acid aqueous solution as a raw material, compared to Comparative Example 1, in which the slurry solution is treated with an alkaline solution before step (A) / separation step.

[0141] The method for producing amino acid-containing hydrotalcite of the present invention can be suitably used for producing amino acid-containing hydrotalcite that can be applied to a wide range of fields, such as food packaging films, beverage packaging films, beverage bottles, pharmaceutical packaging films, industrial gas barrier films, gas separation films, paper barrier materials, paints, scratch-resistant materials, cosmetics, and additives.

Claims

1. A step (A) of separating a slurry containing a first amino acid-containing hydrotalcite and a dissolved amino acid into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acid; a solution preparation step of preparing a slurry solution by mixing an amino acid aqueous solution derived from the solution containing the dissolved amino acids separated from the slurry after the step (A) with a composite metal oxide obtained by calcining a precursor hydrotalcite compound; A generating step of generating a second amino acid-containing hydrotalcite by heating the slurry solution; A method for producing amino acid-containing hydrotalcite, comprising:

2. 2. The method according to claim 1, wherein the step (A) comprises adding water to the slurry to separate the slurry into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acid.

3. The step (A) includes separating the slurry into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids and a solution containing the remainder of the dissolved amino acids without adding water to the slurry, and then: The manufacturing method according to claim 1, characterized in that water is added to a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids, and the slurry is separated into the first amino acid-containing hydrotalcite and a solution containing the dissolved amino acids.

4. The step (A) includes a step (a1) of separating the slurry into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids and a solution containing the remainder of the dissolved amino acids without adding water to the slurry; and (a2) a step of adding water to the slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids after the step (a1), and separating the slurry into a slurry containing the first amino acid-containing hydrotalcite and a portion of the dissolved amino acids or no dissolved amino acids, and a solution containing the remainder of the dissolved amino acids, The method according to claim 1 , wherein the step (a2) is carried out once or a plurality of times.

5. Prior to the step (A), A solution preparation step of preparing a slurry solution by mixing an aqueous amino acid solution with a composite metal oxide obtained by calcining a precursor hydrotalcite compound; A generating step of heating the slurry solution to generate the first amino acid-containing hydrotalcite; The method of claim 1 further comprising:

6. The method according to claim 1 , further comprising, after the step (A), a step (B) of reducing amino acids from the first amino acid-containing hydrotalcite with an alkaline solution.

7. The method according to claim 6, wherein the step (B) comprises adding the alkaline solution while stirring the first amino acid-containing hydrotalcite.

8. The amino acid has a solubility of 10 g / 100 mLH ２ The method according to claim 1, characterized in that the amino acid is O or more.

9. The method according to claim 1, wherein the amino acid is a glycine compound.

10. The method according to claim 1 , wherein the hydrotalcite-based compound contained in the first amino acid-containing hydrotalcite is represented by the following formula (1): (M ２＋ ) １－Ｘ (M ３＋ ) Ｘ (OH) ２ (A ｎ－ ) Ｘ／ｎ ・mH ２ O・・・(1) (In formula (1), M ２＋ is a divalent metal cation, M ３＋ is a trivalent metal cation, A ｎ－ is an n-valent anion, X is a number satisfying 0.17<X<0.36, n is an integer from 1 to 6, and m is a number satisfying 0<m<1.

80.

11. The method according to claim 1 , wherein the slurry has an amino acid concentration of less than 0.6 mol / L.