Excipient composed of metal organic structure, and method for producing said excipient

Abstract

Provided are: an excipient composed of a metal organic structure, the excipient having a stabilized form despite no binder component being contained therein, effectively suppressing collapse and powderization resulting from adsorption and desorption, being capable of efficiently expressing the exceptional adsorption performance of a metal organic structure, and being exceptional in terms of storage stability of a gas; and a method for manufacturing the excipient. An excipient according to the present invention is characterized by being molded from a metal organic structure provided with a metal and an organic ligand coordinated to the metal.

Description

Shaped body made of metal organic framework and method for producing the same

[0001] The present invention relates to a shaped body made of a metal-organic framework, and more particularly to a shaped body made of a metal-organic framework and having excellent gas storage performance, and a method for producing the same.

[0002] A substance consisting of a central metal and a multidentate organic ligand coordinated thereto, called a metal-organic framework (MOF) or porous coordination polymer (PCP), is a porous three-dimensional structure formed by the accumulation of metal complexes consisting of a central metal and organic ligands. Unlike other porous materials such as zeolite and activated carbon, the pores of metal-organic frameworks are capable of designing the pore size and the space within the pores, and many types have been reported based on the combination of metal ions and organic ligands. Metal-organic frameworks have pore sizes of about 0.3 nm to about 3 nm and specific surface areas of about 1,000 m. ２ / g ~ approx. 2000m ２ / g to a maximum of 5000m ２ / g or more have been reported, and metal organic frameworks having such regular pore diameters and high specific surface areas have the property of being able to adsorb gases in the pores, and various developments are underway for their use as adsorbents.

[0003] For example, Patent Document 1 below describes, as a solid adsorbent, a shaped body of a porous polymer metal complex containing a flexible resin consisting of a flexible porous polymer metal complex and a copolymer of a specific methacrylic acid ester, and describes that this shaped body is prevented from collapsing or powdering, has excellent gas adsorption performance, and can be used as a gas adsorption material to be stored inside a gas storage device.

[0004] The flexible porous polymer metal complex used in Patent Document 1 is prone to collapse and powdering when made into a shaped body due to changes in the material structure caused by the adsorption and desorption of gas. However, Patent Document 1 uses a specific flexible resin that can follow the structural changes of the flexible porous polymer metal complex, thereby effectively preventing the shaped body from collapsing and powdering even when adsorption and desorption are repeated.

[0005] Patent No. 7278543

[0006] However, if a shaped body made of such a metal organic framework contains a binder component, the organic compound such as a resin that is the binder component may clog the pores of the metal organic framework, and the excellent adsorption performance inherent to the metal organic framework may not be fully exhibited. Furthermore, the shaped body of Patent Document 1 is required to be used only as an adsorbent, and also to have the ability to efficiently retain and store the adsorbed gas within the metal organic framework.

[0007] Therefore, an object of the present invention is to provide a shaped body made of a metal-organic framework, which has a stable form even without containing a binder component, is effectively inhibited from collapsing or powdering due to adsorption and desorption, can efficiently exhibit the excellent adsorption performance of the metal-organic framework, and has excellent gas storage stability, and a method for producing the same. Another object of the present invention is to provide a gas storage container containing the above shaped body.

[0008] According to the present invention, there is provided a shaped body characterized by being formed from a metal-organic framework comprising a metal and an organic ligand coordinated to the metal.

[0009] In the shaped body of the present invention, it is preferable that: (1) the metal organic framework is a metal organic framework having a hydroxyl group; (2) the organic ligand is cyclodextrin; (3) the shaped body does not contain any organic compound other than the organic ligand; and (4) the shaped body is used for gas storage.

[0010] The present invention also provides a gas storage container comprising the above-described shaped body.

[0011] According to the present invention, there is further provided a method for producing the above-mentioned shaped body, which is characterized by press-molding the metal organic framework under conditions of 20 to 200°C and a surface pressure of 4 MPa or more.

[0012] In the shaped body of the present invention, by using a specific metal-organic framework as the metal-organic framework, it is possible to maintain its shape with good stability without blending a binder component, and it does not collapse even after repeated adsorption and desorption like conventional adsorbents, and can be used as an adsorbent for a long period of time. Furthermore, as is clear from the results of the examples described below, the shaped body shaped under specified pressurized conditions can exhibit better gas storage performance than the powder state before shaping, and is particularly useful as a storage material for gases such as nitrogen, carbon dioxide, or hydrogen.

[0013] (Metal-organic framework) The shaped body of the present invention comprises a metal-organic framework comprising a metal and an organic ligand coordinated to the metal. While known metal-organic frameworks conventionally used in adsorbents can be used, metal-organic frameworks having hydroxyl groups are particularly preferred. As described in Patent Document 1, flexible porous polymer metal complexes undergo a change in skeletal structure and an increase in volume as they adsorb and desorb adsorbed gases. Therefore, when shaped into a molded body, stress is applied, cracks occur, and the body collapses (pulverizes). In the present invention, by using a specific metal-organic framework having hydroxyl groups, even with such a metal-organic framework, it is possible to obtain a shaped body that does not collapse even when gas is adsorbed and desorbed, without containing a binder component. In other words, the hydroxyl groups of the metal-organic framework used in the present invention form bonds and themselves function as a binder, thereby promoting the formation of a shaped body. Furthermore, the hydroxyl groups act as a cushion, allowing the body to adapt to volume changes and effectively suppressing the collapse of the shaped body. Furthermore, a shaped body made of a metal-organic framework having hydroxyl groups generates new grain boundaries, and the hydroxyl groups present at the grain boundary interfaces make it possible to capture polar gases such as carbon dioxide gas and gas molecules with molecular diameters equal to or smaller than the pore diameter of the grain boundary interfaces, resulting in superior gas storage performance compared to unshaped bodies.

[0014] The organic ligand constituting such a metal organic framework having a hydroxyl group may be any organic ligand that forms a coordinate bond with the metal. A compound having a functional group that forms a coordinate bond with the metal can be used as the organic ligand. In one embodiment, a compound having a structure that can encapsulate a guest molecule can be used as the organic ligand. For example, a cyclodextrin-based compound can be used. Examples of cyclodextrin-based compounds include α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0015] On the other hand, the organic ligand itself does not necessarily have to have the function of being able to encapsulate guest molecules. Any substance may be used as long as the metal organic framework as a whole has the function of being able to encapsulate guest molecules. Examples of such organic ligands include compounds having a monocyclic or polycyclic skeleton (e.g., hydroxytrimesic acid, etc.). In the present invention, the organic ligand is preferably a compound having a structure that can encapsulate guest molecules, and cyclodextrin-based compounds can be particularly preferably used.

[0016] Furthermore, the metal constituting the metal organic framework may be any metal capable of forming a coordinate bond with an organic ligand, and is not limited thereto, but examples thereof include metal ions such as Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Ar, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, and Bi, and at least one can be selected from these. Among these, alkali metal ions are preferred, and potassium ions can be particularly preferred.

[0017] In a metal organic framework (CD-MOF) in which the organic ligand is a cyclodextrin-based compound and the metal is potassium, a metal organic framework in which the cyclodextrin-based compound is bonded to 1 mole of potassium ions in an amount in the range of 0.05 to 0.80 moles, more preferably in the range of 0.10 to 0.20 moles, is suitable for exhibiting excellent storage performance when made into a shaped body.

[0018] As shown in Table 1 below, the metal organic framework having a hydroxyl group used in the shaped body of the present invention has a mass transfer coefficient of 0.010 to 0.300 sec in nitrogen gas. －１ The surface diffusion coefficient is in the range of 0.010 to 0.200 sec －１ Therefore, the material has gas storage performance and higher gas release performance than zeolite and metal organic frameworks that do not have hydroxyl groups. In addition, for carbon dioxide gas, the material has a mass transfer coefficient of 0.001 to 0.160 sec compared to zeolite and metal organic frameworks that do not have hydroxyl groups. －１ The surface diffusion coefficient is in the range of 0.001 to 0.015 sec －１ In addition, the formed shaped body has excellent gas storage performance because new grain boundaries are generated compared to the powder state, and it is thought that the mass transfer coefficient and surface diffusion coefficient are superior.

[0019] Furthermore, the CD-MOF preferably used for the shaped object of the present invention has a viscosity of 0.300 to 0.600 cm ３ / g, preferably 0.350 to 0.550 cm ３ / g and an average pore diameter of 1.300 to 1.600 nm, preferably 1.400 to 1.550 nm. The pore volume, pore diameter, and average pore diameter are measured by the methods described in the Examples below.

[0020] (Method for Producing Metal-Organic Framework) The metal-organic framework capable of forming the shaped body of the present invention can be produced by, but is not limited to, the following method. That is, a first aqueous solution containing metal ions and a cyclic organic compound that is an organic ligand capable of coordinating with the metal ions is prepared, and then a second solution containing an organic solvent is added to this first aqueous solution to produce a metal-organic framework in which the organic ligand is coordinated with the metal ions. In the first aqueous solution, examples of metal compounds that provide the metal ions include, but are not limited to, metal hydroxides, inorganic halide salts such as chloride salts, and inorganic acid salts such as nitrates and acetates. Specifically, when the metal ions are alkali metal ions such as potassium ions, it is preferable to use an alkali metal hydroxide, and when the metal ions are Zn ions or Fe ions, it is preferable to use an inorganic acid salt.

[0021] In the first aqueous solution, the amount of organic ligand per mole of metal ion is preferably in the range of 0.05 to 50 moles, more preferably 0.1 to 40 moles, and more preferably 0.125 to 30 moles. When the metal ion is an alkali metal ion, the amount of organic ligand per mole of metal ion is preferably in the range of 0.05 to 5 moles, and particularly preferably 0.125 to 0.80 moles. When the metal ion is a potassium ion and the organic ligand is a cyclodextrin-based compound, as mentioned above, the amount is preferably in the range of 0.05 to 0.80 moles, and particularly preferably in the range of 0.125 to 0.375 moles when the organic ligand is α-cyclodextrin and 0.125 to 0.750 moles when the organic ligand is γ-cyclodextrin.

[0022] The amount of water in the first aqueous solution is preferably in the range of 50 to 5,000 moles per mole of metal ion, and when the metal ion is an alkali metal ion, the amount of water is preferably in the range of 80 to 200 moles per mole of metal ion, and particularly preferably in the range of 100 to 150 moles. The molar ratio of organic ligand to water (organic ligand:water) is preferably in the range of 1:50 to 1:2,000, and particularly when the organic ligand is a cyclodextrin-based compound, it is desirable that it be in the range of 1:100 to 1:1,300.

[0023] The second solution to be added to the first aqueous solution prepared as described above is preferably a solution capable of lowering the pH of the first aqueous solution, and preferably an organic solvent capable of deprotonating the coordinate bond site of the organic ligand is used. The organic ligand is deprotonated and a coordinate bond is formed between the organic ligand and the metal ion, thereby producing a metal-organic framework. Examples of such organic solvents include at least one solvent selected from alcoholic solvents such as methanol, ethanol, 1-propanol, and 1-butanol; ketone solvents such as acetone; and aprotic solvents such as N,N-dimethylformamide. Among these, alcoholic solvents are preferred, and methanol is particularly suitable. The organic solvent is preferably added in an amount of 3 to 1,000 moles, particularly 5 to 500 moles, per mole of metal ion. In particular, when the metal ion is a potassium ion and the organic ligand is α-cyclodextrin, the organic solvent is suitably added in an amount of 10 to 400 mol, preferably 50 to 300 mol, more preferably 100 to 200 mol, per mol of potassium ion. When the organic ligand is γ-cyclodextrin, the organic solvent is suitably added in an amount of 3 to 100 mol, preferably 5 to 50 mol, more preferably 10 to 30 mol, per mol of potassium ion.

[0024] The second solution is preferably added to the first aqueous solution over a period of 1 to 20 minutes, preferably 10 to 15 minutes, while stirring the first aqueous solution. Adding the second solution all at once may result in cloudiness and prevent the desired metal-organic framework from being obtained. However, adding the second solution over the above-mentioned period of time allows nuclei to form and allows the growth of a crystal structure, making it easier to obtain the desired metal-organic framework. The addition method is not limited to this, but examples include a method of adding the solution at a constant rate using a dropping funnel, a method of adding a fixed amount at regular intervals, and a method of adding the solution in a gradually changing amount. After the addition of the second solution is complete, the mixed solution is preferably stirred at room temperature for 5 to 50 hours, preferably 10 to 30 hours. The produced metal-organic framework is isolated by filtration or the like, washed with an organic solvent such as methanol if necessary, and then dried to remove the organic solvent and water, thereby obtaining a powder of the metal-organic framework.

[0025] (Shaped body and manufacturing method thereof) The shaped body of the present invention is composed of the above-mentioned metal-organic framework, preferably a metal-organic framework having a hydroxyl group, more preferably CD-MOF, and has an important feature of not containing any organic compounds other than the organic ligands constituting the metal-organic framework. The absence of any organic compounds other than the organic ligands eliminates the risk of the pores of the shaped body and the metal-organic framework being blocked. The shaped body of the present invention may be composed of a mixture of a metal-organic framework and an inorganic binder component. Examples of the inorganic binder component include known components such as alumina. When a metal-organic framework and an inorganic binder component are used to manufacture the shaped body of the present invention, the blending amount of the inorganic binder component is typically 40% by mass or less, preferably 4% by mass or less, and more preferably 2% by mass or less, relative to the total amount of the metal-organic framework and the inorganic binder component. When the blending amount of the inorganic binder component is within the above range, it is possible to achieve both shape retention and gas storage performance of the shaped body. Furthermore, when the shaped body is made of a metal organic framework having a hydroxyl group, the shaped body can retain its shape and exhibit better gas storage performance even without containing an inorganic binder component.

[0026] The form of the shaped body may be tablet-like, pellet-like, granular, or the like, but in the present invention, it is important that the metal-organic framework made of powder is solidified by press molding at 20 to 200 ° C and a surface pressure of 4 MPa or more. In particular, in the case of CD-MOF, it is preferable that it is press molded at 10 to 180 ° C and a surface pressure of 4 to 100 MPa, and more preferably at a surface pressure of 4 to 60 MPa. A shaped body solidified under such conditions can have gas storage properties that could not be obtained in powder form.

[0027] The shaped object of the present invention has excellent adsorption and storage properties for carbon dioxide gas, nitrogen gas, hydrogen gas, etc., and can be suitably used as an adsorption and storage material for these gases. In particular, it has excellent adsorption and storage properties for carbon dioxide gas. The shaped object of the present invention can also release gas in a short period of time. The shaped object of the present invention can be molded into a predetermined shape and filled into a column or the like to be used as an adsorbent, but it is more suitable to fill it into a pressure vessel or the like and use it as part of a gas storage container.

[0028] As a method for storing these gases, the shaped body of the present invention can be brought into contact with a gas under pressure to adsorb the gas and store the gas within the shaped body. The pressure conditions are preferably in the range of 0.01 to 8.00 MPa and for 0.01 to 24 hours. The stored gas can be released (desorbed) by heating to a temperature equal to or higher than the adsorption temperature. The shaped body after release can be reused, and the gas can be stored by contacting it again with the gas.

[0029] In order to explain the present invention in more detail, examples carried out by the present inventors will be described below.

[0030] (Measurement Method) [Pore Volume and Pore Diameter] The pore diameter and pore volume of the metal organic framework were calculated by measuring the adsorption isotherm of nitrogen gas at liquid nitrogen temperature by a multipoint method using a BELSORP MAX II type manufactured by Microtrackbell, and then calculating the values ​​by MP calculation.

[0031] [Evaluation of Gas Mass Transfer Coefficient and Surface Diffusion Coefficient] The mass transfer coefficient and surface diffusion coefficient of nitrogen gas of the metal organic framework were calculated by measuring the gas adsorption rate at liquid nitrogen temperature by a multipoint method using a BELSORP MAX II type manufactured by Microtrackbell. The results are shown in Table 1. In addition, the CO ２ The mass transfer coefficient and surface diffusion coefficient of the gas were calculated by measuring the gas adsorption rate at 298 K and a measurement pressure range of 0 to 100 kPa using a BELSORP MAX II model manufactured by Microtrackbell Corporation using a multipoint method. The results are shown in Table 1. The mass transfer coefficient is a value related to the amount of substance gas passing through a unit area per unit time, and is a value that varies depending on the measurement conditions. The surface diffusion coefficient is a value related to the amount of substance gas passing through a unit area per unit time, and is not a value that varies depending on the measurement conditions, but is a value specific to the object being measured. For reference, Table 1 also shows the mass transfer coefficients and surface diffusion coefficients of zeolite (Shilton MT-8000 manufactured by Mizusawa Industrial Chemicals, Ltd.) and ZIF-8 (manufactured by Sigma-Aldrich), a metal organic framework having no hydroxyl groups.

[0032] [Gas storage container evaluation] The gas storage container evaluation was carried out with an internal volume of 154 cm ３ A shaped or unshaped form of the metal-organic framework described below was introduced into a pressure holding vessel equipped with a pressure gauge made of a stainless steel vessel, and the vessel was pressurized to an internal pressure of 0.8 MPa, and nitrogen gas or carbon dioxide gas was filled until the introduced pressure and the internal pressure of the vessel became the same value, and the change in internal pressure after the valve was opened was measured.

[0033] Preparation and Evaluation of Gas Adsorbent Example 1 Pure water was added to a 150 ml container, and potassium hydroxide was then added to the container and dissolved at room temperature. γ-Cyclodextrin was then added and dissolved at room temperature. The pH of the resulting solution was 13.98. Next, while stirring this solution with a stirrer, methanol was added dropwise over approximately 15 minutes. After the addition, the solution was stirred for 24 hours to obtain a suspension containing a solid product. The pH of the solution after the addition of methanol was 13.85. The solid product was filtered from the resulting suspension, and the isolated solid product was washed with methanol. After washing, the solid product was dried overnight at 50°C to obtain a metal organic framework A according to Example 1. The molar ratio of each component was potassium ion:γ-cyclodextrin:water:methanol = 1.00:0.12:20.37:2.86. The pore diameter of the obtained metal organic framework A was 0.5 to 2.0 nm, and the pore volume at an average pore diameter of 1.508 nm was 0.538 cm ３ / g. Metal organic framework A (0.5 g) was added to a Φ10 hot press metal, and pressurization was carried out for 5 minutes at 25.0 ° C. and 0.5 MPa using a press machine to produce shaped body B. Furthermore, shaped body B (10 g) was filled into a pressure holding container, which was then filled with a fill gas to produce a gas storage container.

[0034] Comparative Example 1 The metal-organic framework A (unshaped body C) was filled into a pressure holding vessel, and then a fill gas was filled therein to produce a gas storage vessel.

[0035]

[0036] (Gas storage container evaluation results) Nitrogen gas storage results: The amount of internal pressure change after a certain period of time was the same, but by filling with shaped body B, gas could be released in a shorter time than when filled with unshaped body C, and the decrease in internal pressure was improved. In addition, the shaped body did not undergo any change in shape before or after gas filling. Carbon dioxide gas storage results: By filling with shaped body B, gas could be released in a shorter time than when filled with unshaped body C, and the decrease in internal pressure was improved. In addition, as the amount of carbon dioxide gas adsorbed increased by molding into a shaped body, the amount of gas released also increased, and the amount of internal pressure change was also greater than when filled with unshaped body C. In addition, the shaped body did not undergo any change in shape before or after gas filling. From the above, it was revealed that even with the same CD-MOF, the shaped body has better gas storage and gas release performance than the powder form, and therefore it is possible to release the stored filler gas after opening the valve of the pressure vessel, thereby suppressing the decrease in pressure inside the can.

[0037] The shaped object of the present invention has excellent gas storage properties, and is particularly excellent in adsorption and storage properties for gases such as carbon dioxide, nitrogen, and hydrogen, and therefore can be suitably used as a gas storage container.

Claims

1. A shaped object characterized by being formed from a metal-organic framework comprising a metal and an organic ligand coordinated to the metal.

2. The shaped body according to claim 1, wherein the metal organic framework is a metal organic framework having a hydroxyl group.

3. The shaped body according to claim 1, wherein the organic ligand is cyclodextrin.

4. The shaped body according to claim 1, which does not contain any organic compounds other than the organic ligand.

5. The shaped object according to any one of claims 1 to 4, which is used for gas storage.

6. A gas storage container comprising the shaped body according to claim 5.

7. A method for producing a shaped body according to claim 1, characterized in that the metal-organic framework is pressure-molded under conditions of 20 to 200°C and a surface pressure of 4 MPa or more.

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