Method for producing metal-organic framework

Abstract

To provide a method capable of producing metal-organic frameworks using aluminum dross.SOLUTION: There is provided a method for producing a metal-organic framework in which an organic ligand coordinates to an aluminum ion, the method comprising: a preparation step of preparing a reaction system by adding aluminum dross containing an aluminum ion source, an organic compound having an organic ligand, and an acid or alkali having a counterion that forms a salt with the aluminum ion; and a generation step of obtaining the metal-organic framework composed of the aluminum ions and the organic ligands by mixing the reaction system, wherein in the generation step the molar ratio of the acid or alkali added to the reaction system to the aluminum contained in the reaction system is 0.5 times or more and 4 times or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a metal-organic framework in which organic ligands are coordinated to aluminum ions, and more particularly to a method for producing a metal-organic framework in which a metal-organic framework is obtained using aluminum dross containing aluminum ions. [Background technology]

[0002] In the manufacturing process of aluminum products, aluminum dross is generated as a by-product in the process of melting aluminum bullion or scrap. This aluminum dross accounts for approximately 5 to 10 mass% of the amount of aluminum melted by superheating, and contains not only metallic aluminum, but also aluminum oxides, aluminum nitrides, aluminum halides, and oxides of additive elements contained in the alloy.

[0003] Until now, aluminum dross has been disposed of as waste, but due to the difficulty of securing disposal sites, development of recycling technology for aluminum dross is underway.

[0004] For example, a method for producing artificial zeolite is known in which aluminum dross is reacted with sodium hydroxide to obtain a reaction mixture, and the reaction mixture is then reacted with sodium silicate and sodium hydroxide in the presence of nitrate or nitrite (see Patent Document 1).

[0005] Metal-organic frameworks (MOFs) are porous materials composed of metal ions and organic ligands. These MOFs have characteristics not found in carbon or zeolites, and exhibit a wide range of functionalities, including gas storage and separation, catalytic activity, and ionic and electronic conductivity, making them promising for many applications.

[0006] Among these, aluminum-based MOFs have been widely studied and are considered to be one of the most promising MOFs due to their excellent framework stability. Furthermore, aluminum is a relatively inexpensive and abundant metal source, making it an attractive metal source for the mass production of MOFs.

[0007] To obtain such an MOF using aluminum as the metal ion, a method is known in which a predetermined MOF is produced using, as raw materials, a metal aluminum salt such as a nitrate or sulfate and an organic ligand such as 1,4-terephthalic acid or 4,4'-biphenyldicarboxylic acid (see Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-192336 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-105275 Summary of the Invention [Problem to be solved by the invention]

[0009] With the growing interest in the Sustainable Development Goals (SDGs) in recent years, there is growing expectation for technology that can effectively utilize aluminum dross, which has previously been discarded, as a raw material. In particular, to make recycling commercially viable, it would be desirable to be able to manufacture high-value-added materials using aluminum dross as a raw material.

[0010] MIL-53(Al), a type of MOF synthesized by the coordination bond between aluminum ions and 1,4-benzenedicarboxylate (terephthalic acid), has been suggested as a potential liquid-phase adsorbent due to its high specific surface area and hydrolysis resistance. Specifically, MIL-53(Al) is known to have excellent ability to remove dimethyl phthalate (DMP), a commonly used plasticizer in the polymer materials industry that may cause endocrine disruption in humans at ppb levels, and nitrobenzene, a highly toxic and persistent pollutant used in the production of pigments, explosives, and pesticides (T. Wu, N. Prasetya, K. Li, J. Membrane. Sci., 2020, 615, 118493).

[0011] Under these circumstances, the present inventors have conducted extensive research to find a way to effectively utilize aluminum dross. As a result, they have found that, in producing a metal-organic framework (MOF) in which organic ligands are coordinated to aluminum ions, it is possible to produce a metal-organic framework (MOF) by using aluminum dross as an aluminum ion source and blending an acid or alkali having a counter ion that forms a salt with the aluminum ion in a predetermined ratio, thereby completing the present invention.

[0012] Therefore, an object of the present invention is to provide a method for producing a metal-organic framework (MOF) by using aluminum dross. [Means for solving the problem]

[0013] That is, the gist of the present invention is as follows. (1) A method for producing a metal organic framework in which organic ligands are coordinated to aluminum ions, A method for producing a metal organic framework, comprising: a preparation step of preparing a reaction system by adding aluminum dross containing an aluminum ion source, an organic compound having the organic ligand, and an acid or alkali having a counter ion that forms a salt with the aluminum ion; and a production step of mixing the reaction system to obtain the metal organic framework comprising the aluminum ion and the organic ligand, wherein in the production step, a molar ratio of the acid or alkali added to the reaction system relative to the aluminum contained in the reaction system is 0.5 to 4 times. (2) The method for producing a metal organic framework according to (1), wherein the aluminum content in the aluminum dross is 30 mass % or more and less than 100 mass %. (3) The method for producing a metal organic framework according to (1), wherein the aluminum dross has a metallic aluminum content of 10% by mass or more and less than 100% by mass. (4) The method for producing a metal organic framework according to (1), wherein in the generating step, a molar ratio of aluminum to the organic ligand contained in the reaction system is 0.5 or more and 10 or less. (5) The method for producing a metal organic framework according to (1), wherein in the generating step, a molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to the aluminum contained in the reaction system is 0.2 to 1.5 times greater than or equal to 0.2 and less than or equal to 1.5. (6) The method for producing a metal organic framework according to (1), wherein the aluminum dross contains an aluminum compound other than metallic aluminum, and the amount of aluminum contained in the aluminum compound contained in the aluminum dross is greater than 0 mass% and 100 mass% or less. (7) The method for producing a metal organic structure according to (1), wherein the organic compound is at least one selected from the group consisting of terephthalic acid, fumaric acid, 1,3,5-benzenetricarboxylic acid, 2,6-naphthalenedicarboxylic acid, mellitic acid, pyromellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,5-furandicarboxylic acid, 1,3,5-tris(4-carboxyphenyl)benzene, benzophenone-4,4'-dicarboxylic acid, 4,4'-dicarboxydiphenyl sulfone, 1,4-cyclohexanedicarboxylic acid, 2,5-thiophenedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, and derivatives thereof. (8) The aluminum dross contains a flux component derived from an aluminum alloy, The method for producing a metal organic framework according to (1), wherein the content of the flux component contained in the aluminum dross is 0 mass % or more and 50 mass % or less. (9) The method for producing a metal organic framework according to (1), wherein in the producing step, the metal organic framework is obtained by heat-treating the reaction system consisting of a reaction solution containing the aluminum dross, the organic compound, and a solvent which is an acid solvent or an alkaline solvent. (10) The method for producing a metal organic framework according to (8), wherein in the preparing step, the aluminum dross and the organic compound are mixed in the solvent, and an acid or alkali having a counter ion that forms a salt with the aluminum ion is added to the solvent. (11) The method for producing a metal organic framework according to (10), wherein in the generating step, a molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to the aluminum contained in the reaction solution is 0.2 to 1.5 times greater than or equal to 0.2 and less than or equal to 1.5. (12) The method for producing a metal organic framework according to (10), wherein the acid is at least one selected from the group consisting of hydrochloric acid, chloric acid, perchloric acid, hydrogen iodide, iodic acid, periodic acid, hydrogen bromide, bromic acid, nitric acid, sulfuric acid, and permanganic acid, and the alkali is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and calcium hydroxide. (13) In the producing step, The method for producing a metal organic framework according to (9), wherein the aluminum contained in the reaction solution is 0.1 mol / L or more and 100 mol / L or less. [Effects of the Invention]

[0014] According to the present invention, it becomes possible to produce a metal-organic framework (MOF) using aluminum dross.

[0015] In particular, MOFs are attracting attention as they exhibit a wide range of functionality, including as adsorbents for removing harmful pollutants. Aluminum is relatively cheap and abundant compared to other metals, and this invention can also be used to recycle aluminum dross generated during the manufacturing process of aluminum products. Therefore, this invention can be said to be extremely beneficial from the perspective of the Sustainable Development Goals (SDGs). [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows FT-IR spectra of the samples obtained in the examples (Reference Example 1, Examples 1 to 5, and Comparative Example 1). [Figure 2] FIG. 2 shows XRD patterns of the samples obtained in the examples (Reference Example 1, Examples 1 to 5, and Comparative Example 1). [Figure 3] FIG. 3 shows nitrogen adsorption isotherms of the samples obtained in the examples (Reference Example 1, Examples 1 to 5, and Comparative Example 1). [Figure 4] FIG. 4 shows TG curves of the samples obtained in the examples (Reference Example 1, Examples 1 to 5, and Comparative Example 1). [Figure 5]FIG. 5 shows FT-IR spectra of the samples obtained in the examples (Reference Example 1, Examples 4, 6 and 7). [Figure 6] FIG. 6 shows XRD patterns of the samples obtained in the examples (Reference Example 1, Examples 4, 6 and 7). [Figure 7] FIG. 7 shows nitrogen adsorption isotherms of the samples obtained in the examples (Reference Example 1, Examples 4, 6 and 7). [Figure 8] FIG. 8 shows TG curves of the samples obtained in the examples (Reference Example 1, Examples 4, 6 and 7). DETAILED DESCRIPTION OF THE INVENTION

[0017] The method for producing a metal organic framework according to the present invention will be described in detail below. The components of the present invention described below can be combined in part or in whole as appropriate.

[0018] [1. Method for manufacturing metal-organic framework] The present invention provides a method for producing a metal organic framework in which organic ligands are coordinated to aluminum ions, the method comprising: a preparation step of preparing a reaction system by adding aluminum dross containing an aluminum ion source, an organic compound having an organic ligand, and an acid or alkali having a counter ion that forms a salt with the aluminum ion; and a production step of mixing the reaction system obtained above to obtain a metal organic framework composed of aluminum ions and organic ligands, wherein the molar ratio of the acid or alkali added to the reaction system to the aluminum contained in the reaction system in the production step is 0.5 to 4 times.

[0019] As a method for producing a metal-organic framework (MOF) in the present invention, any known method can be used as long as it includes the preparation step and production step described above. For example, a hydrothermal reaction method (solvothermal method), a solution method (reflux method), a spray-drying method, a microwave method, an ultrasonic method, an electrolysis method, a solid-phase synthesis method (mechanochemical method), and the like are known, and any of these methods may be used. In this embodiment, a hydrothermal reaction method is described as an example, but other methods for producing MOFs can also be used. The reaction system may involve reacting aluminum dross and an organic compound in a reaction system (liquid phase system) consisting of a reaction solution containing a solvent. Alternatively, the aluminum dross and an organic compound may be reacted in a reaction system (solid phase system) that does not contain a solvent or contains little or no solvent. In this specification, when there is no particular distinction between a liquid phase system and a solid phase system, the term "reaction system" will be used to refer to both a liquid phase system and a solid phase system.

[0020] [1-1. Preparation process] First, in the preparation step, a reaction system is prepared by adding aluminum dross containing an aluminum ion source, an organic compound having an organic ligand, and an acid or alkali having a counter ion that forms a salt with the aluminum ion.

[0021] <Aluminum dross> Aluminum dross is generated during the process of melting aluminum bullion or scrap, and contains metallic aluminum, aluminum oxide, aluminum nitride, aluminum halides, and oxides of additive elements contained in the alloy.

[0022] In the present invention, the aluminum content of the aluminum dross is preferably 30% by mass or more. Using dross containing small amounts of impurities other than aluminum reduces the effect of impurities in the dross on the synthesis of MOFs, making it easier to increase the specific surface area of ​​the MOFs and also to increase the yield of MOFs. Therefore, the aluminum content is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, the aluminum content of the aluminum dross is preferably less than 100% by mass, preferably 90% by mass or less, and more preferably 80% by mass or less. Here, the aluminum content means the mass % of aluminum (Al) contained in both metallic aluminum and aluminum compounds contained in the aluminum dross, and can be calculated from the amount of aluminum element (mass %) contained in the aluminum dross and the mass of the aluminum dross.

[0023] In the present invention, the metallic aluminum content in the aluminum dross is preferably 10% by mass or more. Similarly to the above, using dross containing a small amount of impurities other than metallic aluminum reduces the effect of impurities in the dross on the synthesis of MOFs, making it easier to increase the specific surface area of ​​the MOFs and also to increase the yield of MOFs. Therefore, the metallic aluminum content is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. The metallic aluminum content in the aluminum dross is preferably less than 100% by mass, preferably 80% by mass or less, and more preferably 70% by mass or less. Here, the metallic aluminum content is based on the quantitative results obtained by "4.1 c) Hydrochloric acid dissolved gas volumetric method" specified in JIS 2404:2015 Analysis method for aluminum dross for iron and steel.

[0024] As described above, aluminum dross generally contains aluminum compounds other than metallic aluminum. Therefore, in the present invention, the aluminum element content (Al element content) contained in the aluminum compound contained in the aluminum dross is preferably greater than 0 mass% and not more than 100 mass%. The aluminum element content contained in the aluminum compound is preferably 5 mass% or more, more preferably 10 mass% or more, and even more preferably 15 mass% or more. Furthermore, the aluminum element content contained in this aluminum compound is preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less.

[0025] Examples of aluminum compounds contained in aluminum dross include aluminum chloride, aluminum oxide, aluminum nitride, aluminum sulfide, aluminum hydroxide, and aluminum fluoride, and generally contain one or more of these. More specifically, the following are examples: aluminum chlorides include AlCl3, and aluminum oxides include Al2O3 and Na2Al 22 O 34、 Examples of aluminum nitrides include AlN, aluminum sulfides include AlS, and aluminum hydroxides include Al(OH). Examples of aluminum fluorides include AlF, NaAlF, and KAlF.

[0026] The aluminum dross may also contain a flux component derived from the aluminum alloy. Generally, the content of the flux component in the aluminum dross is 0% by mass or more, and 50% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and more preferably 5% by mass or less.

[0027] Such flux components include AlF3, NaF, MgF, CaF, K2SiF6, Na2SiF6, KBF4, K2TiF6, K2ZrF6, Na3AlF6, K3AlF6, AlCl3, KCl, NaCl, CaCl2, MgCl2, K2CO3, Na2CO3, CaCO3, KNO3, NaNO3, K2SO4, Na2SO4, Na, P4, and the like, and the flux may contain one or more of these.

[0028] <Organic compounds> The organic compound has an organic ligand, and the organic ligand coordinates with the aluminum ion generated from the aluminum dross to form a metal-organic framework (MOF). There are no particular limitations on such organic compounds, and those similar to known MOFs can be used.

[0029] Examples of such organic compounds include terephthalic acid, fumaric acid, 1,3,5-benzenetricarboxylic acid, 2,6-naphthalenedicarboxylic acid, mellitic acid, pyromellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,5-furandicarboxylic acid, 1,3,5-tris(4-carboxyphenyl)benzene, benzophenone-4,4'-dicarboxylic acid, 4,4'-dicarboxydiphenyl sulfone, 1,4-cyclohexanedicarboxylic acid, 2,5-thiophenedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, and derivatives thereof. These may be used alone or in combination of two or more.

[0030] <Acid or alkali> The reaction system in the present invention contains an acid or alkali having a counter ion that forms a salt with the aluminum ion. This acid or alkali forms a salt with the aluminum metal contained in the aluminum dross or the aluminum ion in the aluminum compound, thereby facilitating the formation of an MOF by allowing the organic ligands of the organic compound in the reaction system to coordinate with the aluminum ion.

[0031] The amount of acid or alkali added must be such that the metallic aluminum or aluminum compound contained in the aluminum dross is sufficiently ionized to coordinate the organic ligands in the organic compound, and the influence of impurities contained in the dross is reduced to form an MOF. Therefore, the molar ratio of acid or alkali to aluminum contained in the reaction system is set to 0.5 or more, preferably 1 or more, more preferably 2 or more, even more preferably 2.5 or more, and particularly preferably 3 or more. Furthermore, to prevent the formation of MOFs from being adversely affected by excessive addition of acid or alkali, the molar ratio of acid or alkali to aluminum contained in the reaction system is set to 4 or less.

[0032] Examples of such acids include hydrochloric acid, chloric acid, perchloric acid, hydrogen iodide, iodic acid, periodic acid, hydrogen bromide, bromic acid, nitric acid, sulfuric acid, permanganic acid, etc., and one or more of these can be used. Examples of alkalis include sodium hydroxide, potassium hydroxide, calcium hydroxide, etc., and one or more of these can be used.

[0033] Here, in the present invention, when a method for synthesizing an MOF in a reaction solution, such as a hydrothermal reaction method (solvothermal method) or a solution method (reflux method), is employed, a reaction system containing an acid or alkali may be prepared, i.e., a reaction system consisting of a reaction solution, and then the MOF may be synthesized. In this case, for example, aluminum dross and an organic compound may be mixed in a solvent, and an acid or alkali having a counter ion that forms a salt with the aluminum ion may be added to the solvent. A reaction system consisting of a reaction solution may be formed by adding an acidic or alkaline solvent to the aluminum dross and organic compound. Adding an acid or alkali to a solvent containing aluminum dross and an organic compound in this manner ionizes the aluminum contained in the reaction solution and promotes the production of a metal-organic framework. However, it is preferable to add an acid or alkali to the solvent in advance in the preparation step, then add the aluminum dross and then add the organic compound to the reaction solution. When forming the reaction solution, it is preferable to add an acid or alkali to the solvent before adding the aluminum dross to ionize the aluminum contained in the aluminum dross. If the organic compound is added to the solvent first, it may be decomposed, so it is better to add the organic compound later to ensure a proper reaction with the aluminum dross.

[0034] [1-2. Generation process] Next, in the production step, the reaction system obtained in the preparation step is mixed to obtain an MOF consisting of aluminum ions and organic ligands.

[0035] In the production step, with respect to the acid or alkali having a counter ion that forms a salt with the aluminum ion added to the reaction system in the preparation step, it is preferable that the ratio (B / A) of the molar ratio B to the molar ratio A be 0.2 or more and 1.5 or less in relation to the aluminum ion contained in the reaction system. Molar ratio A: The molar ratio of counter ions to aluminum ions contained in the salt formed by aluminum ions and counter ions Molar ratio B: The ratio of the amount of substance B2 to the amount of substance B1 (B2 / B1) ·Substance amount B1: Amount of aluminum contained in the reaction system ·Substance amount B2: The amount of counter ions that form salts with aluminum ions contained in the acid or alkali added to the reaction system In other words, the molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to the aluminum contained in the acid or alkali added to the reaction system should be 0.2 to 1.5 times the molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions.

[0036] Here, when a method for synthesizing an MOF in a reaction solution, such as a hydrothermal reaction method (solvothermal method) or a solution method (reflux method), is employed, in the present invention, the molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to the aluminum contained in the reaction solution, in relation to the molar ratio of the counter ions to the aluminum contained in the acid or alkali added to the reaction solution, is preferably 0.2 to 1.5 times.

[0037] For example, when hydrochloric acid (HCl) is added as an acid having a counter ion that forms a salt with aluminum ions, AlCl3 is assumed to be the salt formed by the aluminum ions and the counter ions. In this case, the aluminum ions (Al 3+ ) to the counter ion (Cl - ) (3 / 1=3), the molar ratio of the amount of chloride ions, which are counter ions contained in the added hydrochloric acid and form salts with the aluminum ions, to the amount of aluminum in the reaction solution should be 0.2 to 1.5 times.

[0038] In the above example, aluminum ions (Al 3+ ) to the counter ion (Cl - ) (=3) as a standard, if the molar ratio of chloride ions contained in hydrochloric acid to aluminum in the reaction solution is 3, the amount of hydrochloric acid to be added at this time is 1. If the molar ratio of chloride ions contained in hydrochloric acid to aluminum in the reaction solution is 4.5, the amount of hydrochloric acid to be added at this time is 1.5. In addition to this example, if aluminum sulfate (Al2(SO4)3) is assumed as the salt formed by aluminum ions and counter ions, 3+ ) to the counter ion (SO4 2- ) is used as a reference, and if the molar ratio of sulfate ions contained in sulfuric acid to the amount of aluminum in the reaction solution is 1.5, the amount of sulfuric acid added at this time is 1.

[0039] From the viewpoint of forming an MOF by sufficiently ionizing the aluminum metal or aluminum compound contained in the aluminum dross and forming coordinate bonds with the organic ligands in the organic compound and reducing the influence of impurities contained in the dross, the ratio of molar ratio B to molar ratio A (B / A) is preferably 0.2 or more, more preferably 0.7 or more, more preferably 0.9 or more, and even more preferably 1 or more. Furthermore, from the viewpoint of preventing the formation of an MOF from being adversely affected by the addition of an excessive amount of acid or alkali, the ratio of molar ratio B to molar ratio A (B / A) is preferably 1.5 or less.

[0040] As described above, in the production step, the molar ratio of the acid or alkali added to the reaction system to the aluminum contained in the reaction system is set to 0.5 to 4. Here, aluminum refers to the amount of aluminum (Al) contained in both metallic aluminum and the aluminum compound.

[0041] Here, in the production step, it is preferable that the molar ratio of aluminum to the organic ligands contained in the reaction system is 0.5 or more and 10 or less. In particular, from the viewpoint of reliably forming an MOF, it is preferable that there is an excess of aluminum relative to the organic ligands, and the molar ratio of aluminum to the organic ligands is preferably 1 or more, and more preferably 2 or more. Here, aluminum refers to the amount of aluminum (Al) contained in both metallic aluminum and the aluminum compound.

[0042] In this case, when a reaction solution is used as the reaction system as described above, it is preferable to obtain MOFs by heat-treating the reaction system consisting of a reaction solution containing aluminum dross, an organic compound, and an acidic or alkaline solvent in the production step. By adding an acid or alkaline to the solvent and heat-treating the reaction system consisting of the reaction solution in this way, the aluminum contained in the reaction solution can be ionized, further promoting the production of MOFs.

[0043] Furthermore, when a reaction solution is used as the reaction system, it is preferable that the aluminum content of the reaction solution is 0.1 mol / L or more and 100 mol / L or less. The aluminum content here refers to the molar concentration of aluminum (Al) contained in both the amount of metallic aluminum and the amount of an aluminum compound.

[0044] When a reaction solution is used as the reaction system, the solvent is not particularly limited and known solvents can be used, such as water, methanol, ethanol, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-diethylformamide, and one or more of these may be used.

[0045] Furthermore, when a reaction solution is used as the reaction system, if the solvent is an acid solvent, the pH is preferably -1 or more and 7 or less, and if the solvent is an alkaline solvent, the pH is preferably 7 or more and 15 or less. Among these, a low pH range (strong acid) achieved by adding an acid, or a high pH range (strong alkali) achieved by adding an alkali, is preferred. In the case of an acid solvent, the pH of the solvent is preferably -1 or more, more preferably 0 or more, and preferably 4 or less, more preferably 3 or less, even more preferably 2 or less, and particularly preferably 1 or less. In the case of an alkaline solvent, the pH of the solvent is preferably 10 or more, more preferably 11 or more, even more preferably 12 or more, and particularly preferably 13 or more, and preferably 15 or less, more preferably 14 or less.

[0046] Here, taking the solvothermal synthesis of MOFs as an example, the preferred synthesis conditions are as follows. Specifically, the heating temperature of the reaction solution is preferably 80°C or higher and 400°C or lower. Furthermore, the pressure conditions are preferably 0 MPa or higher and 600 MPa or lower, and the reaction time is preferably 1 hour or higher and 100 hours or lower. Furthermore, the reaction solution may be stirred to promote crystal growth, and the stirring rate is preferably greater than 0 ppm and less than 3000 ppm. When the solvothermal method is employed, a sample containing crystals can be obtained by this production process.

[0047] [1-3. Post-process] A metal-organic framework (MOF) can be produced by the preparation and production steps described above. Subsequent processing varies depending on the synthesis method employed and is not particularly limited. However, when a reaction solution is used as the reaction system, it is preferable to perform the following post-processing, for example. Specifically, a sample containing the MOF is recovered by vacuum filtration from the reaction solution synthesized in the production step (recovery step). The recovered sample is then washed (washing step), and the washed sample is dried (drying step). The dried sample is then calcined (calcination step), and unreacted materials in the pores are removed, resulting in a porous MOF.

[0048] The conditions for the calcination step are not particularly limited as long as a porous MOF can be obtained, but the calcination temperature is usually 100°C or higher and 550°C or lower.

[0049] [2. Action and Effects] When producing a metal-organic framework using aluminum dross as a raw material, a possible method involves mixing a reaction system containing aluminum dross containing an aluminum ion source with an organic compound having an organic ligand. Here, to obtain a metal-organic framework, it is necessary to form a coordinate bond between the aluminum ions contained in the reaction system and the organic ligand. Usually, simply mixing aluminum dross with an organic compound may not sufficiently promote the reaction between the aluminum ions derived from the aluminum metal contained in the aluminum dross and the organic ligand. Also, usually, simply mixing aluminum dross with an organic compound may not sufficiently promote the reaction between the aluminum ions contained in aluminum compounds, such as alumina, contained in the aluminum dross and the organic ligand. Therefore, simply mixing aluminum dross with an organic compound leaves unreacted aluminum metal or aluminum compounds in the reaction system, making it difficult to synthesize MOFs using aluminum dross as a raw material.

[0050] The present invention includes a production step of obtaining a metal-organic framework composed of aluminum ions and organic ligands by mixing a reaction system containing aluminum dross containing an aluminum ion source, an organic compound having an organic ligand, and an acid or alkali having a counter ion that forms a salt with the aluminum ion. Furthermore, in the production step, the molar ratio of the acid or alkali to the aluminum contained in the reaction system is set to 0.5 to 4. By adding an appropriate amount of acid or alkali to the aluminum contained in the reaction system, the counter ions of the acid or alkali added to the reaction system form salts with the aluminum ions in the aluminum metal or aluminum compound contained in the aluminum dross, promoting coordination of the organic ligand to the aluminum ions and facilitating the formation of an MOF. This reduces the amount of aluminum metal or aluminum compound remaining unreacted in the reaction system. Furthermore, adding an appropriate amount of acid or alkali to the reaction system can dissolve substances (impurities) other than the aluminum metal or aluminum compound contained in the aluminum dross that can be dissolved (liberated) by the acid or alkali. This makes it easier to reduce the amount of such impurities remaining as solids in the reaction system. Examples of such impurities include aluminum-free flux components contained in aluminum dross, MgO, and the like. Furthermore, in the present invention, by reducing metallic aluminum, aluminum compounds, impurities, and the like present in the reaction system after the production step, it is easier to prevent these components other than the MOF product from remaining as solids in the reaction system and being captured and recovered together with the MOF in the filtration step following the production step. Furthermore, in the calcination step following the filtration step, it is easier to prevent substances that were not completely removed in the filtration step from remaining in the MOF, the final product after calcination. For the reasons described above, the present invention makes it easier to reduce the amount of impurities contained in MOFs and to increase the specific surface area of ​​MOFs.

[0051] MOFs are porous materials composed of metal ions and organic ligands. They possess a wide range of functionalities, including gas storage and separation, catalysis, and ionic and electronic conductivity. MOFs using aluminum ions as the metal ion exhibit particularly excellent chemical stability. Among these, MIL-53(Al), synthesized by the coordination bond between aluminum ions and terephthalic acid, has a high specific surface area and hydrolysis resistance, making it suitable for use as a liquid-phase adsorbent. This invention makes it possible to produce such high-value-added MOFs using aluminum dross, which has previously been disposed of as waste. This not only promotes the development of MOFs, but also contributes to the recycling of aluminum dross, making it extremely beneficial from the perspectives of the environment and sustainable development goals. [Example]

[0052] Preferred embodiments of the present invention will be specifically described below based on examples and comparative examples, but the present invention should not be construed as being limited thereto.

[0053] [Reference example 1] To obtain reagent-derived MIL-53(Al), synthesis was carried out according to the following procedure. First, ion-exchanged water, terephthalic acid (Tokyo Chemical Industry Co., Ltd., purity >99.0%), and aluminum chloride hexahydrate (Fujifilm Wako Pure Chemical Industries, Ltd., purity >98.0%) were prepared. A reaction solution was prepared using 50 mL of ion-exchanged water in a ratio of terephthalic acid:aluminum chloride hexahydrate:ion-exchanged water = 1:2:172. This reaction solution (suspension) was placed in a pressure-resistant synthesis vessel (Chanshu Deschem Science Supply, capacity: 100 mL, inner tube: PTFE, outer tube: stainless steel) and heated at 493 K for 72 hours to produce crystals. The resulting crystals were collected by vacuum filtration (filter holder: Shibata Scientific, SPC filter holder; filtration filter: Merck, Omnipore JVWP04700; vacuum pump: Shibata Scientific, Rocker 300C). The recovered crystals were then washed by placing them in ion-exchanged water, stirring with a magnetic stirrer for about 24 hours, and then filtering. This procedure was repeated three times. The resulting crystals were dried at 100°C for 24 hours. They were then activated by firing at 673K ​​for 72 hours in a muffle furnace (AS ONE, ROP-001P) to develop micropores. In this way, MIL-53(Al) according to Reference Example 1 was obtained.

[0054] [Examples 1 to 7, Comparative Example 1] In order to obtain a test MOF using aluminum dross as an aluminum source, synthesis was carried out as follows based on the synthesis method of Reference Example 1 above. First, three types of aluminum dross a to c with different metallic aluminum contents generated at the Mie Plant of Nikkei MC Aluminum Co., Ltd. were prepared as aluminum sources (aluminum ion sources). XRD measurements were performed on these aluminum dross a to c (hereinafter simply referred to as "dross a," "dross b," and "dross c"). Dross a contained Al, AlN, Al2O3, MgAl2O4, KCl, MgF2, Si, NaCl, and Na2Al. 22 O 34Dross b contained Al, AlN, Al2O3, MgAl2O4, KCl, MgF2, Si, NaCl, and SiO2. Dross c contained Al, AlN, Al2O3, MgAl2O4, KCl, MgF2, Si, NaCl, Na2Al 22 O 34 , and MgO.

[0055] Elemental analysis was performed on these drosses a to c. The results are shown in Table 1. Elements Na and K were analyzed by boiling extraction ICP atomic emission spectroscopy, elements Mg, Al, and Si by ICP atomic emission spectroscopy, and element Cl by boiling extraction ion chromatography. The metallic aluminum (Al) concentration was also measured for drosses a to c. The results are also shown in Table 1. This metallic aluminum concentration was determined based on "4.1c) Hydrochloric acid dissolved gas volumetric method" specified in JIS 2404:2015, Analysis Method for Aluminum Drosses for Iron and Steel. Based on these results, Table 1 also shows the aluminum concentration of aluminum compounds other than metallic aluminum contained in the aluminum drosses, calculated by subtracting the metallic aluminum concentration value from the aluminum element concentration value. Furthermore, Table 1 also shows the content of flux components contained in drosses a to c.

[0056] [Table 1]

[0057] In the previous Reference Example 1, aluminum chloride (AlCl3) was used as the aluminum source (aluminum ion source). Therefore, in Examples 1 to 7 and Comparative Example 1, in order to make the components of the reaction solution uniform, hydrochloric acid (35%) was added to ion-exchanged water in varying amounts to prepare an acid solvent. Then, drosses a to c were added to this acid solvent, and terephthalic acid (Tokyo Chemical Industry Co., Ltd., purity >99.0%) was then added to prepare the reaction solutions shown in Table 2. Note that the amount of substance ratios of the reaction solutions (synthetic solutions) in Examples 1 to 7 and Comparative Example 1 were calculated without taking into consideration the Cl contained in the drosses a to c.

[0058] That is, with regard to the amount of hydrochloric acid added, because the aluminum source in Reference Example 1 involving reagent-derived synthesis was aluminum chloride (AlCl), the molar ratio of counter ions to aluminum ions contained in the salt formed by aluminum ions and counter ions was set to a molar ratio of Al source:hydrochloric acid = 1:3 (defined as 1), and the molar ratio (multiplication factor) of acid to metallic aluminum contained in the reaction solution was set as follows: The amounts of hydrochloric acid added were compared at 0.5 times (Example 1), 0.75 times (Example 2), 1 time (Example 3), 1.25 times (Examples 4, 6, and 7), 1.5 times (Example 5), and 2 times (Comparative Example 1). Specifically, 4.6 ml (52 mmol: Example 1), 6.9 ml (78 mmol: Example 2), 9.2 ml (104 mmol: Example 3), 11.5 ml (130 mmol: Examples 4, 6, and 7), 13.8 ml (156 mmol: Example 5), and 18.4 ml (208 mmol: Comparative Example 1) of hydrochloric acid were added to 50 ml (2.7 mol) of ion-exchanged water. Then, 1.46 g of dross a (metallic Al, 34.6 mmol: Examples 1 to 5, Comparative Example 1), 2.09 g of dross b (metallic Al, 34.6 mmol: Example 6), or 5.27 g of dross c (metallic Al, 34.6 mmol: Example 7) was added to the solution, and terephthalic acid (Benzene-1,4-dicarboxylic acid Acid: BDC) was added in an amount of 2.88 g (17.3 mmol: Examples 1 to 7, Comparative Example 1) to obtain a reaction solution (suspension).

[0059] The resulting reaction solution was then placed in the same pressure-resistant synthesis vessel as in Reference Example 1 and heated at 493 K for 72 hours, as in Reference Example 1, to carry out synthesis. After synthesis, the resulting sample was collected by vacuum filtration, as in Reference Example 1, placed in ion-exchanged water, stirred with a magnetic stirrer for approximately 24 hours, and filtered. This procedure was repeated three times, and the resulting sample was dried at 100°C for 24 hours. It was then activated by calcining at 673 K for 72 hours in a muffle furnace, as in Reference Example 1, to develop micropores. In this way, test MOFs according to Examples 1 to 7 and Comparative Example 1 were obtained. The properties of the resulting test MOFs were evaluated using a Fourier transform infrared spectrophotometer (JASCO Corporation, FT / IR-4600ST), an X-ray diffractometer (Rigaku Corporation, MiniFlex600), a nitrogen gas adsorption measurement device (Microtrack-Bell Corporation, BELSORP-miniX), and a thermogravimetric analyzer (Shimadzu Corporation, DTG-60H).

[0060] In Table 2, the "multiple of the amount of hydrochloric acid added" represents the multiple of the amount of hydrochloric acid added when the molar ratio of the amount of hydrochloric acid added to the amount of metallic aluminum in the reaction solution = 3 is taken as 1. Similarly, the "molar ratio of the amount of hydrochloric acid added" represents the molar ratio of the amount of hydrochloric acid added to the amount of aluminum in the reaction solution. Similarly, the "ratio of molar ratio B to molar ratio A (B / A)" represents the ratio of the molar ratio of counter ions (=3) to aluminum ions contained in the salt formed by aluminum ions and counter ions to the molar ratio of counter ions (=3) to aluminum ions contained in the acid added to the reaction solution that form a salt with aluminum ions. Specifically, molar ratio A is the molar ratio of counter ions to aluminum ions contained in the salt formed by aluminum ions and counter ions, and molar ratio B is the ratio of the amount of substance B2 (B2 / B1) to the amount of substance B1 below. That is, the amount of substance B1 is the amount of aluminum contained in the reaction system, and the amount of substance B2 is the amount of counter ions (=3) that form a salt with aluminum ions contained in the acid added to the reaction system. Similarly, the "molar ratio of aluminum to organic ligand" refers to the molar ratio of aluminum to organic ligand in the reaction solution.

[0061] [Table 2]

[0062] <Comparative study of the amount of hydrochloric acid added> FIG. 1 shows the FT-IR spectra of the test MOFs obtained in Examples 1 to 5 and Comparative Example 1, along with MIL-53(Al) obtained in Reference Example 1. Similarly, FIG. 2 shows the XRD patterns for Reference Example 1 and Examples 1 to 5, FIG. 3 shows the nitrogen adsorption isotherms for Reference Example 1 and Examples 1 to 5, and FIG. 4 shows the TG curves for Reference Example 1 and Examples 1 to 5. The BET specific surface area of ​​each sample was calculated using the BET method from the obtained nitrogen adsorption isotherms (FIG. 3), and the results are shown in Table 3. The yield based on aluminum and the yield based on terephthalic acid (BDC) were calculated from the TG curves (FIG. 4), and are also shown in Table 3. Note that for Comparative Example 1, the yield was very low, so only the FT-IR spectrum was analyzed.

[0063] [Table 3]

[0064] According to the FT-IR spectrum shown in FIG. 1, the test MOFs of Examples 1 to 5 have a peak intensity of 460 to 570 cm -1 A peak due to Al-O bonds can be confirmed in the 1400-1700 cm -1In the XRD patterns shown in Figure 2, peaks attributable to -COOH bonds in terephthalic acid (BDC) were observed. These peaks are the same as those of MIL-53(Al) synthesized in Reference Example 1, suggesting that MIL-53(Al) was produced in Examples 1 to 5. In contrast, these peaks could not be confirmed in Comparative Example 1. Furthermore, the XRD patterns of the test MOFs in Examples 1 to 5 are consistent with the XRD patterns of MIL-53(Al) synthesized in Reference Example 1.

[0065] Furthermore, according to the nitrogen adsorption isotherms in FIG. 3, the test MOFs of Reference Example 1 and Examples 3 to 5 exhibited type I adsorption isotherms as defined by IUPAC. Furthermore, Examples 1 and 2 exhibited adsorption isotherms that were primarily type I but also mixed with type II. These results suggest that micropores were present in Examples 1 to 5. In particular, the BET specific surface areas calculated from the nitrogen adsorption isotherms in Examples 3 to 5 were equivalent to those of MIL-53(Al) in Reference Example 1. Furthermore, according to the TG curves in FIG. 4, mass loss associated with decomposition of products containing organic ligands was confirmed in Examples 1 to 5, including Reference Example 1, at temperatures between 450 and 600°C. In particular, as shown in Table 3, the test MOFs of Examples 3 to 5 exhibited mass loss approximately equivalent to that of MIL-53(Al) in Reference Example 1. However, a correlation could not be immediately confirmed from the yield of each sample calculated from the rate of mass loss associated with loss of organic ligands at temperatures between 450 and 600°C.

[0066] These results indicate that MIL-53(Al) was produced in Examples 1 to 5. In particular, the test MOFs in Examples 3 to 5 were similar to the MIL-53(Al) derived from the reagent in Reference Example 1. It is believed that the test MOF in Example 4, in particular, was equivalent to the MIL-53(Al) derived from this reagent. In Examples 1 to 5, the molar ratio of the amount of hydrochloric acid added to the aluminum contained in the reaction solution was 1.25 (Example 1), 1.87 (Example 2), 2.50 (Example 3), 3.12 (Example 4), and 3.74 (Example 5). In contrast, in Comparative Example 1, the molar ratio of the amount of hydrochloric acid added to the aluminum contained in the reaction solution was 4.99. Consequently, it is presumed that the excessive amount of hydrochloric acid contained adversely affected the production of MIL-53(Al).

[0067] <Comparative study based on aluminum content in dross> Figure 5 shows the FT-IR spectra of the test MOFs obtained in Examples 4, 6 to 7, as well as MIL-53(Al) obtained in Reference Example 1. Similarly, Figure 6 shows the XRD patterns for Reference Example 1, Examples 4, 6 to 7, Figure 7 shows the nitrogen adsorption isotherms for Reference Example 1, Examples 4, 6 to 7, and Figure 8 shows the TG curves for Reference Example 1, Examples 4, 6 to 7. The BET specific surface area of ​​each sample was calculated using the BET method from the obtained nitrogen adsorption isotherm (Figure 7), and the results are shown in Table 3 above. The yield based on aluminum and the yield based on terephthalic acid (BDC) were also calculated from the TG curve (Figure 8), and are also shown in Table 4.

[0068] According to the FT-IR spectrum shown in FIG. 5, the test MOFs of Examples 4, 6, and 7 have a peak intensity of 460 to 570 cm -1 A peak due to Al-O bonds can be confirmed in the 1400-1700 cm -1In the XRD pattern of the test MOFs in Examples 4, 6, and 7, peaks due to the -COOH bond in terephthalic acid (BDC) were confirmed. As mentioned above, these peaks are the same as those of MIL-53(Al) synthesized in Reference Example 1, and therefore it is believed that MIL-53(Al) was produced in Examples 4, 6, and 7. Furthermore, the XRD patterns in Figure 6 also show that the XRD patterns of the test MOFs in Examples 4, 6, and 7 match those of MIL-53(Al) synthesized in Reference Example 1.

[0069] Furthermore, according to the nitrogen adsorption isotherms in FIG. 7, the test MOFs of Reference Example 1 and Examples 4 and 6 exhibited type I adsorption isotherms as defined by IUPAC. Furthermore, Example 7 exhibited an adsorption isotherm that was primarily type I but also mixed with type II. These results suggest that micropores were present in Examples 4, 6, and 7. In particular, the BET specific surface areas calculated from the nitrogen adsorption isotherms in Examples 4 and 6 were equivalent to those of MIL-53(Al) in Reference Example 1. Furthermore, according to the TG curves in FIG. 8, mass loss associated with decomposition of products containing organic ligands at 450°C to 600°C was confirmed in Examples 4, 6, and 7, including Reference Example 1. In particular, as shown in Table 3, the test MOFs of Examples 4 and 6 exhibited mass loss approximately equal to that of MIL-53(Al) in Reference Example 1. On the other hand, the mass loss in Example 7 was small, suggesting the presence of more impurities than the MIL-53(Al) in the other Examples.

[0070] These results indicate that MIL-53(Al) was successfully produced in Examples 4, 6, and 7. In particular, the test MOFs of Example 6, along with the test MOF of Example 4, were confirmed to have properties very similar to those of the reagent-derived MIL-53(Al) in Reference Example 1. On the other hand, in Example 7, which used dross c, which contained relatively high amounts of impurities, the specific surface area of ​​the resulting MIL-53(Al) was lower than that of the other Examples, and it exhibited properties similar to those of the test MOFs to which a relatively small amount of hydrochloric acid was added, as in Examples 1 and 2 described above. Therefore, it is believed that conditions more favorable for the production of MIL-53(Al) are achieved when aluminum dross containing relatively few impurities is used, or when a sufficient amount of acid or alkali having a counter ion that forms a salt with aluminum ions is added to the reaction system.

[0071] According to the above examples, a MOF composed of aluminum ions and organic ligands can be obtained by mixing a reaction system containing aluminum dross containing an aluminum ion source, an organic compound containing organic ligands, and an acid or alkali containing counter ions that form salts with the aluminum ions. In the present invention, the counter ions of the acid or alkali added to the reaction system form salts with the aluminum metal contained in the aluminum dross or the aluminum ions in the aluminum compound, which is thought to promote coordination of the organic ligands to the aluminum ions, resulting in the formation of an MOF. In this process, by maintaining a molar ratio of acid or alkali to aluminum in the reaction system between 0.5 and 4 times during the production process, it is believed that the amount of impurities contained in the MOF can be reduced and the specific surface area of ​​the MOF can be increased.

Claims

1. A method for producing a metal organic framework in which organic ligands are coordinated to aluminum ions, comprising: a preparation step of preparing a reaction system by adding aluminum dross containing an aluminum ion source, an organic compound having the organic ligand, and an acid or alkali having a counter ion that forms a salt with the aluminum ion; a generating step of mixing the reaction system to obtain the metal organic framework comprising the aluminum ions and the organic ligands, a molar ratio of the acid or the alkali added to the reaction system to the aluminum contained in the reaction system in the producing step being 0.5 to 4 times.

2. The aluminum content of the aluminum dross is 30% by mass or more and less than 100% by mass. The method for producing the metal-organic framework according to claim 1 .

3. The content of metallic aluminum contained in the aluminum dross is 10% by mass or more and less than 100% by mass. The method for producing the metal-organic framework according to claim 1 .

4. In the producing step, a molar ratio of aluminum to the organic ligand contained in the reaction system is 0.5 or more and 10 or less. The method for producing the metal-organic framework according to claim 1 .

5. In the generating step, a molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to a molar ratio of the counter ions to the aluminum ions contained in the acid or alkali added to the reaction system to the aluminum contained in the reaction system is 0.2 times or more and 1.5 times or less. The method for producing the metal-organic framework according to claim 1 .

6. The aluminum dross contains aluminum compounds other than metallic aluminum, the amount of aluminum contained in the aluminum compound contained in the aluminum dross is greater than 0 mass% and less than 100 mass%; The method for producing the metal-organic framework according to claim 1 .

7. the organic compound is at least one selected from the group consisting of terephthalic acid, fumaric acid, 1,3,5-benzenetricarboxylic acid, 2,6-naphthalenedicarboxylic acid, mellitic acid, pyromellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,5-furandicarboxylic acid, 1,3,5-tris(4-carboxyphenyl)benzene, benzophenone-4,4'-dicarboxylic acid, 4,4'-dicarboxydiphenyl sulfone, 1,4-cyclohexanedicarboxylic acid, 2,5-thiophenedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, and derivatives thereof; The method for producing the metal-organic framework according to claim 1 .

8. The aluminum dross contains a flux component derived from an aluminum alloy, The content of the flux component contained in the aluminum dross is 0 mass% or more and 50 mass% or less. The method for producing the metal-organic framework according to claim 1 .

9. In the producing step, the reaction system including a reaction solution containing the aluminum dross, the organic compound, and a solvent which is an acid solvent or an alkaline solvent is heat-treated to obtain the metal organic framework. The method for producing the metal-organic framework according to claim 1 .

10. In the preparation step, the aluminum dross and the organic compound are mixed in the solvent, and an acid or alkali having a counter ion that forms a salt with the aluminum ion is added to the solvent. The method for producing the metal organic framework according to claim 8 .

11. In the generating step, a molar ratio of the counter ions to the aluminum ions contained in the salt formed by the aluminum ions and the counter ions to a molar ratio of the counter ions to the aluminum ions contained in the acid or alkali added to the reaction solution to a molar ratio of the counter ions to the aluminum contained in the reaction solution is 0.2 times or more and 1.5 times or less. The method for producing the metal organic framework according to claim 10.

12. the acid is at least one selected from the group consisting of hydrochloric acid, chloric acid, perchloric acid, hydrogen iodide, iodic acid, periodic acid, hydrogen bromide, bromic acid, nitric acid, sulfuric acid, and permanganic acid; The alkali is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and calcium hydroxide. The method for producing the metal organic framework according to claim 10.

13. In the producing step, the aluminum contained in the reaction solution is 0.1 mol / L or more and 100 mol / L or less; The method for producing the metal organic framework according to claim 9 .

Images