Metal complex, separating agent, and method for separating target gas

Abstract

The purpose of the present invention is to provide a metal complex with which a target gas, especially carbon dioxide, can be separated and recovered from a mixed gas with higher energy efficiency than conventional materials. The metal complex is composed of: a dianion of an aromatic 1,3-dicarboxylic acid compound; a metal dication selected from magnesium, calcium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc and cadmium; and an organic bidentate ligand having a bispyridylethylene structure, and has a structure including two-dimensional sheets stacked in mutual engagement.

Description

Metal complex, separating agent, and target gas separation method

[0001] The present disclosure relates to a metal complex that can be used as a separating agent for selectively adsorbing and desorbing a target gas from a mixed gas containing the target gas, and a method for separating the target gas.

[0002] To achieve carbon neutrality as a measure against global warming, it is desirable to develop separation and capture technologies that can efficiently capture carbon dioxide contained in exhaust gases emitted from various emission sources.

[0003] The carbon dioxide concentration in exhaust gas varies greatly depending on the emission source. For example, while exhaust gas containing high concentrations of carbon dioxide exceeding 96% can be emitted from manufacturing processes in the chemical industry, the carbon dioxide concentration in exhaust gases from cement or steel manufacturing and combustion exhaust gases from fossil fuel-fired power plants is below about 30% (Non-Patent Document 1). These exhaust gases are usually released at atmospheric pressure (101 kPaA), so the partial pressure of the carbon dioxide contained therein is approximately 30 kPaA or less.

[0004] Absorption methods such as the hot potassium carbonate method and the amine method are known as separation and recovery methods that are useful when the concentration of carbon dioxide in exhaust gas is high. However, these absorption methods require a large amount of absorbent, such as an amine aqueous solution, and also require a large amount of thermal energy in the process of releasing the absorbed carbon dioxide. For this reason, when the concentration of carbon dioxide in exhaust gas is low, these absorption methods are inefficient and not suitable for industrial use.

[0005] Pressure swing adsorption (PSA) is a known separation and recovery method that replaces absorption. This method utilizes solid adsorbents (also called separating agents) with different adsorption capacities and adsorption rates for two or more gases. Specifically, a mixed gas is supplied to an adsorption tower filled with the separating agent, and a specific gas is adsorbed by the separating agent under pressure. A desorption process is then performed alternately. The adsorbed gas is desorbed by depressurizing the adsorption tower, evacuated, and recovered. Activated carbon and zeolite have been used as separating agents.

[0006] Existing separating agents such as activated carbon and zeolite have a strong interaction with carbon dioxide, and adsorb a large amount even at low carbon dioxide partial pressures. Therefore, when these separating agents are used with exhaust gases with low carbon dioxide partial pressures, i.e., low carbon dioxide concentrations, the desorption process must be carried out at extremely low pressures. This requires a process that involves large pressure fluctuations, which significantly increases the cost of capture.

[0007] The cost of separating and recovering carbon dioxide using a PSA process with zeolite (13X zeolite) as a separating agent has been estimated by Floudas et al. (Non-Patent Document 2). Floudas et al. calculated the cost required to recover at least 90% by volume of carbon dioxide from a feed gas consisting of carbon dioxide, nitrogen, oxygen, and water at 1 bar and 55°C, with the oxygen concentration fixed at 5.5% by volume and the carbon dioxide concentration varied within the range of 1 to 70% by volume. The calculation shows that the cost does not change significantly when the mole fraction of carbon dioxide in the feed gas is in the range of 0.3 to 0.7, but begins to increase significantly when the mole fraction falls below 0.3.

[0008] Meanwhile, development of porous metal complexes as porous materials with separation capabilities is progressing. Non-Patent Documents 3 and 4 report metal complexes that undergo dynamic structural changes upon adsorption and desorption of guest molecules. Patent Document 1 reports a metal complex that selectively adsorbs carbon dioxide, which has a triple-interpenetrated pseudodiamond framework structure manufactured from a metal ion, a dicarboxylic acid compound, and a bidentate organic ligand. Patent Document 2 reports a metal complex with an interpenetrated two-dimensional sheet structure that can be used as an adsorbent with carbon dioxide adsorption properties. Patent Document 3 reports an organometallic complex with an interdigitated structure as an organometallic complex for adsorbing and separating carbon dioxide. Non-Patent Document 5 reports the adsorption behavior of a metal complex with a structure in which two-dimensional sheets are interdigitated and stacked, toward ethanol, etc.

[0009] JP 2013-107826 A JP 2013-216622 A Japanese Patent No. 4994398 A

[0010] Technology Strategy Research Center Report, TSC Foresight, Vol. 118, Carbon Recycling Field (CO2 Separation and Capture Technology) (February 2024), New Energy and Industrial Technology Development Organization (NEDO) Technology Strategy Research Center (TSC) Ind. Eng. Chem. Res. 2012, 51, 15665-15682. Uemura, K., Kitagawa, S., Future Materials, Vol. 2, pp. 44-51 (2002). Matsuda, R., Kitagawa, S., Petrotech, Vol. 26, pp. 97-104 (2003). Chem. Commun. 2007, 3395-3397.

[0011] One way to reduce separation costs in PSA is to narrow the pressure fluctuation range. From this perspective, the inventors focused on metal complexes that exhibit a unique gas adsorption behavior known as the gate phenomenon. Such metal complexes are called gate-type metal complexes.

[0012] Gate-type metal complexes exhibit dynamic structural changes in response to external stimuli. For example, gate-type metal complexes that exhibit a gate phenomenon in response to carbon dioxide pressure exhibit a low amount of carbon dioxide adsorption in the low carbon dioxide partial pressure range, but exhibit a behavior in which the amount of carbon dioxide adsorption increases rapidly when a certain pressure, i.e., open gate pressure, is reached. If a porous metal complex exhibiting such a gate phenomenon is used as a carbon dioxide separating agent, the PSA process can be performed with a narrow pressure fluctuation range. Therefore, the power costs for driving the blower and pump used to achieve the pressure fluctuation can be reduced, and as a result, the cost of the separation process can be significantly reduced.

[0013] However, existing gate-type metal complexes have the problem of high open gate pressure within the industrially applicable temperature range. When using gate-type metal complexes as separation agents, it is necessary to increase the total pressure of the feed gas so that the partial pressure of the target gas is equal to or greater than the open gate pressure before supplying it to the separation agent. Therefore, when using gate-type metal complexes with high open gate pressure to recover a target gas from a feed gas with a low target gas concentration, a large amount of energy is consumed to increase the pressure of gas components other than the target gas, resulting in a poor energy consumption rate for the entire process. For this reason, it has been difficult to industrially use gate-type metal complexes with a feed gas with a low target gas concentration.

[0014] The metal complexes in Patent Document 1 do not exhibit the gating phenomenon for carbon dioxide. Such metal complexes require extremely low pressure in the desorption process for separating and recovering carbon dioxide using a PSA method, which increases the cost required for recovery. Patent Document 1 also reports a metal complex that exhibits the gating phenomenon for ethane, but the open gate pressure is high at 500 to 600 kPaA, which poses a problem of high costs due to the need to increase the pressure.

[0015] Patent Document 2 reports a metal complex that exhibits a gate phenomenon in the adsorption / desorption isotherm of carbon dioxide. However, while the closed gate pressure is below 20 kPaA, the open gate pressure is as high as about 80 kPaA, which necessitates pressure increase when using a feed gas with a low carbon dioxide concentration, and the pressure fluctuation range in the PSA method becomes wide, resulting in high costs.

[0016] Patent Document 3 describes a method for producing a cellulose acetate copolymer using zinc nitrate, an isophthalic acid derivative (X=NO ２It has been shown that metal complexes produced from tetrahydrofuran, tetrahydrofuran, and bipyridine exhibit gating in the carbon dioxide adsorption isotherm at 25°C. However, the open gate pressure is high, at 200 to 300 kPaA, which poses a problem of high costs due to the need to increase the pressure. Patent Document 3 also discloses metal complexes whose carbon dioxide adsorption isotherms rise sharply at pressures near 0 kPa and do not exhibit the gating phenomenon. Although the desorption isotherms of these metal complexes are not disclosed, the desorption isotherms generally overlap with the adsorption isotherms or are shifted to the low-pressure side. Therefore, in order to separate and recover a certain amount of carbon dioxide by desorption, it is necessary to lower the pressure to near 0 kPa. This is thought to increase energy costs.

[0017] Therefore, there has been a need for the development of a metal complex with a low open gate pressure that can be used to separate and recover a target gas from a mixed gas containing a low concentration of the target gas.

[0018] The present disclosure provides a metal complex that can separate and recover a target gas, particularly carbon dioxide, from a mixed gas with higher energy efficiency than conventional materials.

[0019] The present disclosure relates to the following items [1] to

[21] . [1] A compound represented by the following general formula (1): (In the formula, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ and R ８and an organic bidentate ligand (II) capable of coordinating to the metal dication, represented by the following formula: (wherein each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a formyl group, an acyloxy group, an alkoxycarbonyl group having 2 to 4 carbon atoms, a nitro group, a cyano group, an amino group, a monoalkylamino group having 1 to 4 carbon atoms, a dialkylamino group having 2 to 4 carbon atoms, an acylamino group having 2 to 4 carbon atoms, or a halogen atom.) [2] The metal complex according to [1], wherein the open gate pressure and the closed gate pressure are both 1 to 60 kPaA in a carbon dioxide adsorption / desorption isotherm measured at any temperature from 150 to 350 K. [3] The metal complex according to [1] or [2], wherein the aromatic 1,3-dicarboxylic acid compound (I) is a monocyclic six-membered aromatic 1,3-dicarboxylic acid compound or a monocyclic five-membered aromatic 1,3-dicarboxylic acid compound. [4] The metal complex according to any one of [1] to [3], wherein the aromatic 1,3-dicarboxylic acid compound (I) is a monocyclic six-membered aromatic 1,3-dicarboxylic acid compound, and the aromatic ring of the monocyclic six-membered aromatic 1,3-dicarboxylic acid compound has, in addition to two carboxy groups, at least one substituent selected from a halogen atom, a hydroxyl group, and a nitro group. [5] The metal complex according to any one of [1] to [3], wherein the aromatic 1,3-dicarboxylic acid compound (I) is a compound represented by the following general formula (2): (Wherein, X is CH or N, and R ９ is a halogen atom, a hydroxyl group, or a nitro group. [6] The metal complex according to [4], wherein the aromatic 1,3-dicarboxylic acid compound (I) is represented by the following general formula (3): wherein Y is NH, S, or O; １０ and R １１ are each independently a hydrogen atom or an alkoxy group having 1 to 3 carbon atoms, and R １０ and R １１ may be bonded to each other to form a ring structure. [7] The metal complex according to [1] or [2], wherein R １０ and R １１are both hydrogen atoms. [8] The metal complex according to any one of [1] to [7], wherein the composition ratio (molar ratio) of the metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II) in the metal complex is 1:0.9-1.1:0.9-1.1. [9] A separating agent comprising the metal complex according to any one of [1] to [8].

[10] A method for separating a target gas, comprising: contacting a mixed gas containing a target gas to be separated and other gases with the separating agent according to [9] to adsorb the target gas onto the separating agent; and desorbing the target gas.

[11] The separation method according to

[10] , wherein the mixed gas is a gas containing at least two species selected from oxygen gas, nitrogen gas, water vapor, nitrogen oxide gas, sulfur oxide gas, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrogen sulfide gas, ammonia, a hydrocarbon gas having 1 to 4 carbon atoms, a rare gas, and a siloxane.

[12] The separation method according to

[10] or

[11] , wherein the target gas is carbon dioxide gas.

[13] The separation method according to any of

[10] to

[12] , wherein the mixed gas is combustion exhaust gas discharged from a plant, and the target gas is carbon dioxide gas.

[14] A method for separating a target gas, comprising: bringing a mixed gas containing the target gas to be separated and another gas into contact with a separating agent to adsorb the target gas onto the separating agent; and desorbing the target gas, wherein the separating agent contains a metal complex having a structure in which two-dimensional sheets are interdigitated and stacked, and in which the open gate pressure and closed gate pressure are both 1 to 60 kPaA in a carbon dioxide adsorption isotherm at an operating temperature.

[15] The separation method according to

[14] , wherein the mixed gas contains at least two gases selected from oxygen gas, nitrogen gas, water vapor, nitrogen oxide gas, sulfur oxide gas, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrogen sulfide gas, ammonia, hydrocarbon gases having 1 to 4 carbon atoms, rare gases, and siloxane.

[16] The separation method according to

[14] or

[15] , wherein the target gas is carbon dioxide gas.

[17] The separation method according to any one of

[14] to

[16] , wherein the metal complex is the metal complex according to any one of [1] to [8].

[18] The separation method according to

[16] , wherein the partial pressure of carbon dioxide in the mixed gas is 1 to 30 kPaA.

[19] The separation method according to any one of

[14] to

[18] , wherein the operating temperature is 150 to 350 K.

[20] A carbon dioxide separator equipped with a separating agent containing the metal complex according to any one of [1] to [8].

[21] A metal complex having a structure in which two-dimensional sheets are interdigitated and stacked, wherein the open gate pressure and the closed gate pressure are both 1 to 60 kPaA in a carbon dioxide adsorption / desorption isotherm measured at any one of temperatures from 150 to 350 K.

[0020] According to the present disclosure, it is possible to provide a metal complex that can separate and recover a target gas, particularly carbon dioxide, from a mixed gas with higher energy efficiency than conventional materials.

[0021] 1 is a schematic diagram of a structure (CID structure) in which two-dimensional sheets are stacked while interdigitating. FIG. 2 is a diagram schematically showing the adsorption and desorption isotherms of a gate-type metal complex. FIG. 3 is an Oak Ridge Thermal Ellipsoid Plot (ORTEP) diagram of the crystal of metal complex A obtained in Synthesis Example 1, based on single crystal X-ray crystal structure analysis. FIG. 4 is a crystal structure model of metal complex A obtained in Synthesis Example 1. FIG. 5 is a powder X-ray diffraction pattern of metal complex A in Synthesis Example 1 before vacuum drying. FIG. 6 is a powder X-ray diffraction pattern of metal complex A in Synthesis Example 1 after vacuum drying. FIG. 7 is an ORTEP diagram of the crystal of metal complex B obtained in Synthesis Example 2, based on single crystal X-ray crystal structure analysis. FIG. 8 is a crystal structure model of metal complex B obtained in Synthesis Example 2. FIG. 9 is a powder X-ray diffraction pattern of metal complex B in Synthesis Example 2. FIG. 10 is an ORTEP diagram of the crystal of metal complex C obtained in Synthesis Example 3, based on single crystal X-ray crystal structure analysis. 1 is a crystal structure model of metal complex C obtained in synthesis example 3. FIG. 2 is a powder X-ray diffraction pattern of metal complex D in synthesis example 4. FIG. 3 is a powder X-ray diffraction pattern of metal complex E in synthesis example 5. FIG. 4 is a powder X-ray diffraction pattern of metal complex F in synthesis example 6. FIG. 5 is a powder X-ray diffraction pattern of comparative metal complex P in comparative synthesis example 1. FIG. 6 is a powder X-ray diffraction pattern of comparative metal complex Q in comparative synthesis example 2. FIG. 7 is an ORTEP diagram of the crystal of comparative metal complex R obtained in comparative synthesis example 3 based on single crystal X-ray crystal structure analysis. FIG. 8 is a crystal structure model of comparative metal complex R obtained in comparative synthesis example 3. FIG. 9 is a carbon dioxide adsorption / desorption isotherm at 298 K for metal complex A in synthesis example 1. FIG. 10 is a carbon dioxide adsorption / desorption isotherm at 195 K for metal complex B in synthesis example 2. FIG. 11 is a carbon dioxide adsorption / desorption isotherm at 195 K for metal complex C in synthesis example 3. 1 shows the carbon dioxide adsorption / desorption isotherm at 298K for metal complex D of Synthesis Example 4. FIG. 2 shows the carbon dioxide adsorption / desorption isotherm at 298K for metal complex E of Synthesis Example 5. FIG. 3 shows the carbon dioxide adsorption / desorption isotherm at 298K for metal complex F of Synthesis Example 6. FIG. 4 shows the carbon dioxide adsorption / desorption isotherm at 298K for comparative metal complex Q of Comparative Synthesis Example 2. FIG. 5 shows the carbon dioxide adsorption / desorption isotherm at 298K for comparative metal complex R of Comparative Synthesis Example 3. FIG. 6 shows the carbon dioxide adsorption / desorption isotherm at 195K for comparative metal complex S of Comparative Synthesis Example 4.

[0022] Hereinafter, embodiments of the present invention will be described, but it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention. In this disclosure, when "to" is used to describe a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0023] [Metal Complex] In one embodiment, the metal complex comprises a dianion of an aromatic 1,3-dicarboxylic acid compound (I), a specific metal dication, and an organic bidentate ligand (II) capable of coordinating to the metal dication, and has a structure in which two-dimensional sheets are interdigitated and laminated. The two-dimensional sheets may contain solvent molecules used in producing the metal complex.

[0024] <Aromatic 1,3-dicarboxylic acid compound (I)> In the present disclosure, the aromatic 1,3-dicarboxylic acid compound (I) is a compound in which carboxy groups are bonded to atoms at the 1- and 3-positions of an aromatic ring. The aromatic ring is preferably a 5- or 6-membered ring. Here, the 1- and 3-positions refer to the substitution types shown in general formulas (4) and (5) for the 5-membered ring and the 6-membered ring, respectively. The same applies to other ring structures. (In the formula, A １ ~A ５ represents atoms forming an aromatic 5-membered ring which may have a substituent. (In the formula, A １ ~A ６ represents an atom forming a 6-membered ring having aromaticity, which may have a substituent. １ and A ３ is any one of a carbon atom, a nitrogen atom, and a sulfur atom. ２ and A ４ ~A ６ is any one of a carbon atom, a nitrogen atom, an oxygen atom, and a sulfur atom.２ and A ４ ~A ６ The carbon atom or nitrogen atom represented by may be bonded to a hydrogen atom or a substituent. Examples of the substituent include an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a halogen atom, a hydroxyl group, and a nitro group.

[0025] When naming is performed in accordance with the nomenclature recommended by the International Union of Pure and Applied Chemistry (IUPAC) (2013), if a functional group having a higher priority than a carboxy group is bonded to an aromatic ring, a position number other than 1,3 positions (for example, 2,4 positions, 2,5 positions, 3,5 positions, or 2,6 positions) may be assigned; however, in the present disclosure, these are also considered to be aromatic 1,3-dicarboxylic acid compounds.

[0026] Examples of atoms constituting the aromatic ring include a carbon atom, a nitrogen atom, an oxygen atom, and a sulfur atom. The aromatic 1,3-dicarboxylic acid compound (I) is preferably a monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound or a monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound, and more preferably isophthalic acid having a substituent or 2,5-pyrroledicarboxylic acid which may have a substituent.

[0027] (Monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound) A monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound refers to an aromatic 1,3-dicarboxylic acid compound having one aromatic ring, the aromatic ring being composed of six atoms. The aromatic ring may form a fused ring with a non-aromatic ring. The monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound may have a substituent other than a carboxy group. The aromatic ring of the monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound preferably has, in addition to two carboxy groups, at least one substituent selected from a halogen atom, a hydroxyl group, and a nitro group. Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound is preferably a compound represented by the following general formula (2): (Wherein, X is CH or N, and R ９is a halogen atom, a hydroxyl group, or a nitro group.

[0028] R ９ Examples of the halogen atom represented by include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. From the viewpoint of setting the adsorption pressure and desorption pressure in an appropriate range when separating a target gas such as carbon dioxide by the PSA method, a chlorine atom, a bromine atom, and an iodine atom are preferred as the halogen atom, and a bromine atom is more preferred.

[0029] In terms of adsorption and desorption properties as a separation agent, R ９ is preferably a bromine atom, a hydroxyl group or a nitro group, more preferably a hydroxyl group.

[0030] Specific examples of the monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound include 4-fluoroisophthalic acid, 4-chloroisophthalic acid, 4-bromoisophthalic acid, 4-iodoisophthalic acid, 5-fluoroisophthalic acid, 5-chloroisophthalic acid, 5-bromoisophthalic acid, 5-iodoisophthalic acid, 4-hydroxyisophthalic acid, 5-hydroxyisophthalic acid, 4-nitroisophthalic acid, 5-nitroisophthalic acid, 4-chloro-2,6-pyridinedicarboxylic acid, 4-hydroxy-2,6-pyridinedicarboxylic acid, 4-nitro-2,6-pyridinedicarboxylic acid, etc. From the viewpoint of reducing the open gate pressure and the closed gate pressure, 4-hydroxyisophthalic acid, 5-bromoisophthalic acid, and 4-nitroisophthalic acid are preferred, and 4-hydroxyisophthalic acid is more preferred.

[0031] (Monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound) A monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound refers to an aromatic 1,3-dicarboxylic acid compound having one aromatic ring, which is composed of five atoms. The aromatic ring may form a fused ring with a non-aromatic ring. The monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound is preferably 2,5-pyrrole dicarboxylic acid which may have a substituent. The monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound is more preferably a compound represented by the following general formula (3): wherein Y is NH, S, or O;１０ and R １１ are each independently a hydrogen atom or an alkoxy group having 1 to 3 carbon atoms, and R １０ and R １１ may be bonded to each other to form a ring structure.

[0032] From the viewpoint of adsorption and desorption properties as a separation agent, Y is preferably NH or S. In particular, when Y is NH, the open gate pressure of the metal complex can be reduced.

[0033] R １０ and R １１ Examples of the alkoxy group having 1 to 3 carbon atoms represented by include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, and the like.

[0034] R １０ and R １１ is preferably a hydrogen atom.

[0035] Specific examples of the monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound include 1H-2,5-pyrroledicarboxylic acid, 2,5-thiophenedicarboxylic acid, 3,4-ethylenedioxythiophene-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, etc. From the viewpoint of reducing the open gate pressure and the closed gate pressure, 1H-2,5-pyrroledicarboxylic acid and 3,4-ethylenedioxythiophene-2,5-dicarboxylic acid are preferred, and 1H-2,5-pyrroledicarboxylic acid is more preferred.

[0036] The monocyclic 6-membered aromatic 1,3-dicarboxylic acid compound or the monocyclic 5-membered aromatic 1,3-dicarboxylic acid compound and the other aromatic 1,3-dicarboxylic acid compound (I) may be used in combination of two or more kinds.

[0037] <Metal Dication> The metal dication constituting the metal complex is a dication of a metal (also referred to as "metal dication") selected from magnesium, calcium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc, and cadmium. Among these, zinc dication (Zn) is preferred from the viewpoints of reactivity in producing the metal complex and ease of availability. ２＋), cobalt dication (Co ２＋ ), and copper dication (Cu ２＋ ) is preferred, and zinc dication and cobalt dication are more preferred. These metal dications may be used in combination of two or more.

[0038] When preparing a metal complex, a salt of the metal can be used as the source of the metal dication.

[0039] <Organic bidentate ligand (II)> The organic bidentate ligand (II) is a neutral ligand having two sites where an unshared electron pair coordinates to a metal dication, and is represented by the following general formula (1): (In the formula, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ and R ８ are each independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a formyl group, an acyloxy group, an alkoxycarbonyl group having 2 to 4 carbon atoms, a nitro group, a cyano group, an amino group, a monoalkylamino group having 1 to 4 carbon atoms, a dialkylamino group having 2 to 4 carbon atoms, an acylamino group having 2 to 4 carbon atoms, or a halogen atom.

[0040] R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ and R ８ From the viewpoint of availability, R is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and particularly preferably all hydrogen atoms. １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ and R ８When all of are hydrogen atoms, the organic bidentate ligand (II) is trans-1,2-bis(4-pyridyl)ethylene.

[0041] The organic bidentate ligand (II) may be used in combination of two or more kinds.

[0042] <Structure of Metal Complexes> Metal complexes have a structure in which two-dimensional sheets constructed by covalent and coordinate bonds are interdigitated and stacked. Interdigitation refers to a structure in which the two-dimensional sheets interpenetrate each other, and there are no covalent or coordinate bonds between the sheets. Because there are no covalent or coordinate bonds between the two-dimensional sheets, when they come into contact with gas at a certain pressure or above (partial pressure in the case of a mixed gas), the sheets shift, expanding the space between the sheets, allowing gas molecules to be trapped and adsorbed between the sheets. Figure 1 is a schematic diagram showing how gas molecules, represented by spheres, are adsorbed and desorbed to a structure in which two-dimensional sheets are interdigitated and stacked.

[0043] In the metal complex, a dianion of an aromatic 1,3-dicarboxylic acid compound (I) and an organic bidentate ligand (II) are coordinately bonded to a metal dication to form a two-dimensional sheet. This two-dimensional sheet has a framework structure with fin-like protrusions, and the fins interdigitate to form a stacked structure through interdigitation. This structure is also called a CID structure (Coordination Polymer with Interdigitated Structure) (Non-Patent Document 5: Chem. Commun., 2007, 3395-3397). More specifically, the metal complex has a structure in which the organic bidentate ligand (II) is coordinated to the metal dication in a plane, i.e., to form a plane, i.e., a two-dimensional sheet, the dianion of the aromatic 1,3-dicarboxylic acid compound (I) is coordinated to the metal dication in an axial direction, to form a fin portion, and a plurality of two-dimensional sheets each composed of the organic bidentate ligand (II) and the metal dication are stacked, and these two-dimensional sheets are interdigitated with each other via the dianion portion of the aromatic 1,3-dicarboxylic acid compound (I).

[0044] The fact that the metal complex has a structure in which two-dimensional sheets are interdigitated and stacked can be confirmed, for example, by single crystal X-ray structural analysis or powder X-ray analysis. Specifically, this can be confirmed by the method described in the Examples. Even if the constituent substances are the same metal complex, if the manufacturing method is different, the structure in which two-dimensional sheets are interdigitated and stacked may not be constructed, and it can be distinguished from the metal complex of the present disclosure by analytical methods such as single crystal X-ray structural analysis and powder X-ray analysis.

[0045] By performing single crystal X-ray structural analysis, the crystal system, space group, lattice constant, and the like of the metal complex crystal can be determined, for example, as shown in Table 1. Furthermore, because atomic coordinates can also be determined, the structure of the metal complex can be three-dimensionally drawn using a specific drawing program, for example, as shown in Figure 3, as an ORTEP (Oak Ridge Thermal Ellipsoid Plot) diagram, as well as a wireframe diagram or a capped sticks diagram. The fact that the metal complex has a structure in which two-dimensional sheets are interdigitated and stacked can be confirmed by drawing a crystal structure model in which unit cells are arranged three-dimensionally, as shown in Figure 4. Figure 4 shows a structure in which two-dimensional sheets composed of an organic bidentate ligand (II) and a metal dication are interdigitated with the dianion of the aromatic 1,3-dicarboxylic acid compound (I) standing perpendicular to the sheet.

[0046] The diffraction pattern obtained by powder X-ray analysis depends on the arrangement of atoms constituting the crystal, and is therefore specific to the crystal structure. For a metal complex known from single crystal X-ray structural analysis to have a structure in which two-dimensional sheets are interdigitated and stacked, powder X-ray analysis can obtain a powder X-ray diffraction pattern specific to this structure. By comparing this specific powder X-ray diffraction pattern with the powder X-ray diffraction pattern of a certain metal complex, it is possible to determine whether the certain metal complex has a structure in which two-dimensional sheets are interdigitated and stacked.

[0047] In the metal complex, the composition ratio (molar ratio) of the metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II) is preferably 1:0.9-1.1:0.9-1.1. From the viewpoint of high purity of the structure in which the two-dimensional sheets are interdigitated and stacked, and high adsorption performance, the composition ratio (molar ratio) is more preferably 1:0.95-1.05:0.95-1.05, and particularly preferably 1:0.98-1.02:0.98-1.02.

[0048] <Method for Producing Metal Complex> The metal complex can be produced, for example, by reacting an aromatic 1,3-dicarboxylic acid compound (I), a salt of a metal selected from magnesium, calcium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc, and cadmium, and an organic bidentate ligand (II) capable of coordinating to a dication of the metal, in a solvent under normal pressure for several hours to several days, and then precipitating the complex.

[0049] Examples of the metal salts include organic acid salts such as acetates and formates, and inorganic acid salts such as chlorides, bromides, sulfates, nitrates, carbonates, etc. It is preferable to use a single metal salt as the metal salt, but two or more metal salts may be used in combination.

[0050] When producing a metal complex, the mixing ratio (molar ratio) of the organic bidentate ligand (II) to the aromatic 1,3-dicarboxylic acid compound (I) is preferably in the range of organic bidentate ligand (II):aromatic 1,3-dicarboxylic acid compound (I) = 1:8 to 1:0.2, more preferably in the range of 1:6 to 1:0.33. Even if the reaction is carried out outside this range, the target metal complex can be obtained, but side reactions may increase and the yield may decrease.

[0051] When producing a metal complex, the mixing ratio (molar ratio) of the organic bidentate ligand (II) to the metal salt is preferably in the range of 1:3 to 1:0.33, more preferably 1:2 to 1:0.5, of organic bidentate ligand (II):metal salt. If the ratio is outside this range, the yield of the target metal complex may decrease, or unreacted raw materials may remain, making it difficult to purify the obtained metal complex.

[0052] The molar concentration of the aromatic 1,3-dicarboxylic acid compound (I) in the solution for producing the metal complex is preferably 0.005 to 5.0 mol / L, more preferably 0.01 to 2.0 mol / L. Although the target metal complex can be obtained by carrying out the reaction at a concentration lower than this range, this is not preferred because the yield decreases. At a concentration higher than this range, the solubility decreases and the reaction may not proceed smoothly.

[0053] The molar concentration of the metal salt in the solution for producing a metal complex is preferably 0.005 to 5.0 mol / L, more preferably 0.01 to 2.0 mol / L. Although the target metal complex can be obtained by carrying out the reaction at a lower concentration than this, this is not preferred because the yield decreases. At a higher concentration than this, unreacted metal salt remains, which may make purification of the resulting metal complex difficult.

[0054] The molar concentration of the organic bidentate ligand (II) in the solution for producing the metal complex is preferably 0.005 to 5.0 mol / L, more preferably 0.01 to 2.0 mol / L. Although the target metal complex can be obtained by carrying out the reaction at a concentration lower than this range, this is not preferred because the yield decreases. At a concentration higher than this range, the solubility decreases and the reaction may not proceed smoothly.

[0055] The production of the metal complex is believed to proceed by forming a layered structure in which two-dimensional sheets interdigitate with each other through reversible coordinate bonds between the solvated metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II) in solution, and then precipitating as crystals from the solution. When the layered structure in which two-dimensional sheets interdigitate with each other is formed, the reaction to form the metal complex is believed to proceed by incorporating solvent molecules, particularly N,N-dimethylformamide, N,N-dimethylacetamide, etc., as a template. In other words, the structure of the metal complex is believed to be one in which the sum of the energies acting between the template solvent molecules and each of the components constituting the metal complex, i.e., the metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II), in the solvent used is minimized. Therefore, the structure of the metal complex can be adjusted by selecting an appropriate solvent type and volumetric mixing ratio depending on the combination of raw materials.

[0056] Examples of solvents used in producing metal complexes include organic solvents, water, and mixed solvents thereof. Specific examples include methanol, ethanol, n-propanol, isopropanol, diethyl ether, dimethoxyethane, tetrahydrofuran, hexane, cyclohexane, heptane, benzene, toluene, methylene chloride, chloroform, acetone, ethyl acetate, acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), water, and mixed solvents thereof. Among these, from the viewpoint of efficiently obtaining a metal complex having a structure in which two-dimensional sheets are interdigitated and stacked, solvents containing at least one of N,N-dimethylformamide and N,N-dimethylacetamide are preferred, such as N,N-dimethylformamide or N,N-dimethylacetamide alone, or a mixed solvent of N,N-dimethylformamide or N,N-dimethylacetamide with water. Particularly preferred solvents are N,N-dimethylformamide alone and a mixed solvent of N,N-dimethylformamide and water. The volumetric mixing ratio of N,N-dimethylformamide to water is preferably water / N,N-dimethylformamide (volume ratio before mixing)=0 to 1.5, particularly preferably 0 to 1.0.

[0057] In addition, the solvent molecules that act as a template during synthesis and contribute to the formation of the structure of the metal complex can be removed from the metal complex by subsequent operations such as atmospheric drying or vacuum drying. When used as a gas separating agent, it is preferable to remove the solvent molecules from the viewpoint of forming a space for adsorbing the target gas molecules to be separated. However, the solvent may remain within a range that does not impair the function as a separating agent. The amount of residual solvent is preferably 1% by mass or less in the metal complex. The amount of residual solvent is, for example, 0.001% by mass or more in the metal complex.

[0058] The reaction temperature is not particularly limited, but is preferably −20 to 200° C., more preferably 10 to 150° C., and particularly preferably 50 to 120° C. If the reaction temperature is too low, the reaction time becomes long, which is disadvantageous from the viewpoint of production costs. If the reaction temperature is too high, the cost required for heating becomes high, which is disadvantageous from the viewpoint of production costs.

[0059] The reaction time is not particularly limited, but is preferably 72 hours or less, more preferably 48 hours or less, since a reaction time longer than this is disadvantageous from the viewpoint of production costs.

[0060] The atmosphere during synthesis is not particularly limited, but from the viewpoint of increasing the yield, an inert gas atmosphere is preferred. Examples of inert gases include nitrogen gas and argon gas. In an air atmosphere, the aromatic 1,3-dicarboxylic acid compound (I) and the organic bidentate ligand (II) may be altered, for example, by oxidation, resulting in a decrease in yield.

[0061] The reaction pressure is not particularly limited, but is preferably 0.01 to 5 MPaA, more preferably 0.05 to 3 MPaA, and particularly preferably 0.1 to 0.5 MPaA.

[0062] A metal complex with good crystallinity has high purity and good adsorption performance. In order to enhance the crystallinity, it is preferable to add an appropriate acid or base in an amount of 0.1 to 100 equivalents relative to the organic bidentate ligand (II) in addition to the metal salt, aromatic 1,3-dicarboxylic acid compound (I), and organic bidentate ligand (II) at the start of the reaction, thereby adjusting the rate at which the metal complex precipitates from the reaction solvent.

[0063] As the reaction proceeds and a metal complex is formed, the metal complex precipitates as a solid from the reaction solvent. The completion of the reaction can be confirmed by quantifying the remaining amount of the raw material using a known analytical method such as gas chromatography or high-performance liquid chromatography. After the reaction is completed, the resulting mixture can be subjected to suction filtration to separate the precipitated metal complex, and the separated metal complex can be obtained by washing with an organic solvent.

[0064] The obtained crystals of the metal complex may be further dried. Examples of drying procedures include vacuum drying and atmospheric drying. When the crystals of the metal complex contain adsorbed water, solvent molecules, etc., these can be removed by this procedure. The drying temperature is preferably 40 to 250°C, more preferably 45 to 230°C, and even more preferably 50 to 220°C. If the temperature is too low, drying takes a long time, which is disadvantageous from the perspective of production costs. If the temperature is too high, the metal complex is likely to decompose. In the case of vacuum drying, the pressure for vacuum drying is preferably 100 Pa or less, more preferably 50 Pa or less. If the pressure is too high, drying takes a long time, which is disadvantageous from the perspective of production costs. The drying time is preferably 72 hours or less, and more preferably 24 hours or less.

[0065] [Separating Agent] The metal complex of one embodiment can be used as a separating agent for separating a target gas from a mixed gas containing the target gas to be separated and other gases. <Gate-type Metal Complex> The metal complex of one embodiment can be used as a separating agent for separating carbon dioxide (CO ２ The metal complex is a metal complex that exhibits a gate-type adsorption / desorption isotherm for a target gas such as a carbon dioxide gas, i.e., a gate-type metal complex. In one embodiment, the metal complex has an open gate pressure and a closed gate pressure of 1 to 60 kPaA in the adsorption / desorption isotherm for carbon dioxide at a measurement temperature of 150 to 350 K, and has a structure in which two-dimensional sheets are interdigitated and stacked. Figure 2 shows a gate-type CO ２ This is a diagram for explaining adsorption / desorption isotherms, with the solid line representing the adsorption isotherm and the dashed line representing the desorption isotherm. The "gate phenomenon" refers to the phenomenon where the adsorption isotherm does not show any adsorption or only rises slowly in the region where the pressure (partial pressure in the case of a mixed gas) of the gas to be adsorbed / desorbed is low. ｇｏThis is a phenomenon in which the adsorption isotherm rises sharply as the pressure approaches 0 kPa, and then the slope disappears or becomes gentler once the open gate pressure is exceeded. In the case of a desorption isotherm, the route is reversed. When the pressure of the target gas is low, that is, when the adsorption isotherm rises sharply from a region near 0 kPa and then only transitions to a roughly horizontal section, this is not called a gating phenomenon in the present disclosure. In such cases, the pressure must be significantly lowered when desorbing and recovering a certain amount or more of the target gas, which may increase energy costs. When a metal complex exhibits the gating phenomenon, the desorption process is carried out at a closed gate pressure P ｇｃ Since the pressure can be reduced to a slightly lower level, energy costs and operating time of the equipment can be reduced.

[0066] In a gate-type adsorption isotherm, the adsorption ｇｏ The amount of gas adsorbed is small until the pressure P ｇｏ When the temperature reaches 1000 K, the structure of the metal complex changes due to factors such as an increase in the spacing between the stacked two-dimensional sheets, and the metal complex begins to rapidly adsorb gas. ｇｏ is called "open gate pressure". Conversely, when the pressure is lowered, the pressure is ｇｃ When the temperature is lower than this, the structure of the metal complex changes, for example, the spacing between the stacked two-dimensional sheets narrows, and the gas is rapidly desorbed. ｇｃ This is called the "closed gate pressure." This behavior is thought to be due to the fact that at low pressures, it is energetically more stable for the metal complex and gas molecules to exist separately, but at the open gate pressure boundary, gas molecules are incorporated into the metal complex, forming a more stable inclusion complex, which is energetically more stable. When moving from high pressure to low pressure, the opposite phenomenon occurs at the closed gate pressure boundary.

[0067] In the present disclosure, the open gate pressure P ｇｏ is the intersection of the tangent line at the inflection point in the region where the adsorption amount increases rapidly on the adsorption isotherm and the extension line of the constant slope portion on the low pressure side of the inflection point. In Figure 2, the pressure at the intersection point Q is the open gate pressure P ｇｏIf there are two or more parts with a constant slope, the extension line of the part with the highest pressure and constant slope is used. ｇｃ is the intersection of the tangent line at the inflection point in the region where the adsorption amount drops sharply on the desorption isotherm and the extension line of the constant slope part on the high-pressure side of the inflection point. In Figure 2, the pressure at the intersection point R is the close gate pressure P ｇｃ In addition, when two or more parts with a constant slope are observed, the extension line of the part with the constant slope on the lowest pressure side is used. In the present disclosure, the adsorption / desorption isotherm is measured by the method described in the Examples.

[0068] The open gate pressure and closed gate pressure vary with temperature. Generally, the open gate pressure and closed gate pressure decrease at low temperatures, and increase at high temperatures. In one embodiment, the gate-type metal complex has an open gate pressure and closed gate pressure of 1 to 60 kPaA in the carbon dioxide adsorption / desorption isotherm at any measurement temperature between 150 and 350 K. The open gate pressure and closed gate pressure may be 1 kPaA or more, 2 kPaA or more, or 3 kPaA or more, and may be 60 kPaA or less, 50 kPaA or less, or 30 kPaA or less. From the viewpoint of improving energy efficiency, the open gate pressure and closed gate pressure are more preferably 2 to 50 kPaA, and particularly preferably 3 to 30 kPaA. "Any measurement temperature" means at least one measurement temperature within the range of 150 to 350 K. That is, the gate-type metal complex of one embodiment exhibits an open gate pressure and a closed gate pressure of 1 to 60 kPaA, 2 to 50 kPaA, or 3 to 30 kPaA over the entire, a part, or one point in the temperature range of 150 to 350 K. The adsorption isotherm and desorption isotherm for determining the open gate pressure and the closed gate pressure are measured at the same temperature. From the viewpoint of cost reduction, the gate-type metal complex preferably has an open gate pressure and a closed gate pressure of 1 to 60 kPaA, more preferably 2 to 50 kPaA, and even more preferably 3 to 30 kPaA, in the carbon dioxide adsorption / desorption isotherm at 298 K.

[0069] <Forming into a separating agent> The separating agent of one embodiment contains a metal complex. The separating agent of one embodiment is a molded product of the metal complex. The separating agent may contain additives such as a lubricant or a binder. The separating agent can be used, for example, as a random packing formed into beads, rings, strands, or tablets, or as a regular structure such as a regular packing, a honeycomb body, or a monolith. Known methods such as tableting can be used to mold the metal complex. The separating agent is usually used by filling it into a container such as an adsorption tower or a tank.

[0070] [Method for Separating Target Gas] The separating agent can selectively adsorb and separate the target gas in a mixed gas containing the target gas to be separated and other gases. That is, the mixed gas is contacted with the separating agent, the target gas is adsorbed onto the separating agent, and then the target gas is desorbed, thereby separating the target gas. The adsorption / desorption operation is preferably performed by pressure swing adsorption (PSA). In one embodiment, the separating agent can selectively adsorb and separate only the target gas in a mixed gas containing the target gas to be separated and other gases.

[0071] <Mixed Gas and Target Gas> The mixed gas is, for example, a gas containing at least two selected from oxygen gas, nitrogen gas, water vapor, nitrogen oxide gas, sulfur oxide gas, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrogen sulfide gas, ammonia, hydrocarbon gas having 1 to 4 carbon atoms, rare gas, and siloxane. Examples of hydrocarbon gas having 1 to 4 carbon atoms include methane, ethane, ethylene, and acetylene. Examples of rare gases include helium, neon, argon, krypton, and xenon. Examples of siloxanes include hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane. The mixed gas may also contain other organic vapors.

[0072] Organic vapor refers to the vaporized gas of an organic substance that is liquid at room temperature and pressure. Examples of such organic substances include alcohols such as methanol and ethanol, amines such as trimethylamine, aldehydes such as acetaldehyde, aliphatic hydrocarbons having 5 to 16 carbon atoms, aromatic hydrocarbons such as benzene and toluene, ketones such as acetone and methyl ethyl ketone, and halogenated hydrocarbons such as methyl chloride and chloroform.

[0073] Preferred gases contained in the mixed gas include oxygen gas, nitrogen gas, carbon dioxide gas, water vapor, nitrogen oxide gas, and sulfur oxide gas, more preferred gases include oxygen gas, nitrogen gas, carbon dioxide gas, and water vapor, and even more preferred gases include oxygen gas, nitrogen gas, and carbon dioxide gas.

[0074] The target gas is not particularly limited as long as it is a gas contained in the mixed gas, and the target gas may be one type or two or more types. The target gas is preferably carbon dioxide gas.

[0075] The metal complex of one embodiment exhibits a low open gate pressure against carbon dioxide, and therefore, carbon dioxide can be efficiently separated and recovered from a mixed gas containing a low concentration of carbon dioxide. The carbon dioxide separation device of one embodiment includes a separating agent containing a metal complex.

[0076] In one preferred embodiment of the present disclosure, the mixed gas containing carbon dioxide gas is combustion exhaust gas discharged from various plants, such as exhaust gas from a naphtha cracker, exhaust gas from a natural gas-fired power plant, exhaust gas from a coal-fired power plant, exhaust gas from a steel plant, and exhaust gas from a cement plant.

[0077] The partial pressure of carbon dioxide in a mixed gas containing carbon dioxide gas may be 1 kPaA or more, 2 kPaA or more, or 3 kPaA or more, and may be 30 kPaA or less, 25 kPaA or less, or 20 kPaA or less. The partial pressure of carbon dioxide in the mixed gas is preferably 1 to 30 kPaA, more preferably 2 to 25 kPaA, and particularly preferably 3 to 20 kPaA. In order to efficiently adsorb carbon dioxide to the separating agent, it is preferable that the partial pressure of carbon dioxide is equal to or higher than the open gate pressure. Therefore, if the partial pressure of carbon dioxide is 1 kPaA or more, the amount of pressure increase of the mixed gas can be reduced, and the energy efficiency of the separation process is improved. On the other hand, in order to efficiently desorb carbon dioxide, it is preferable that the partial pressure of carbon dioxide is equal to or lower than the closed gate pressure. Therefore, if the partial pressure of carbon dioxide is 30 kPaA or less, the amount of pressure reduction can be reduced, and the energy efficiency of the separation process is improved.

[0078] <Pressure Swing Adsorption (PSA) Method> The separating agent can be used as a separating agent to be filled in an adsorption tower in a pressure swing adsorption (PSA) method. The size of the adsorption tower and the amount of separating agent to be filled can be adjusted depending on the amount of mixed gas to be treated and the partial pressure of the target gas in the mixed gas.

[0079] The apparatus used for the PSA method is not particularly limited, and the method described in known literature (for example, "Latest Adsorption Technology Handbook, Revised Third Edition, NTS Publishing (2020) pp. 141-145") can be used.

[0080] The adsorption tower may be provided with equipment for increasing or decreasing the temperature of the separating agent packed therein. The equipment is not particularly limited, and examples thereof include equipment with an external heating device or cooling device, and equipment with an internal heating device or cooling device.

[0081] The operating temperature may be 150 K or higher, 190 K or higher, or 280 K or higher, and may be 350 K or lower, 340 K or lower, or 320 K or lower. The operating temperature is preferably 150 to 350 K, more preferably 190 to 340 K, and particularly preferably 280 to 320 K. If the operating temperature is 150 K or higher, the cost required for cooling can be reduced. If the operating temperature is 320 K or lower, a decrease in the adsorption amount can be suppressed. In the present disclosure, the operating temperature means the temperature of the separating agent during adsorption and desorption.

[0082] In the PSA method, a plurality of adsorption towers are usually used. The number of adsorption towers is not particularly limited, but when a plurality of adsorption towers are used, at least one, preferably all, of the adsorption towers can be filled with the separating agent of one embodiment.

[0083] EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Analysis and evaluation in the examples and comparative examples were carried out as follows.

[0084] (1) Single-crystal X-ray structure analysis: Measurements were performed using a single-crystal X-ray diffractometer, XtaLAB P200 (Rigaku Corporation), at 195 K under nitrogen flow cooling. Mo Kα radiation (λ = 0.71075 Å) was used as the X-ray source. The structure was solved using a direct method (SHELXT) and refined using full-matrix least-squares (SHELXL). Atoms other than hydrogen were anisotropically optimized, and hydrogen atoms were positioned using AFIX instructions.

[0085] (2) Measurement of Powder X-ray Diffraction Pattern An X-ray diffractometer: Miniflex 600-C, SmartLab, or Multiflex (all manufactured by Rigaku Corporation) was used, and measurements were made by the symmetric reflection method, scanning the range of diffraction angle (2θ) = 3 to 40° at a scanning speed of 5° / min.

[0086] (3) Measurement of adsorption / desorption isotherms Measurements were performed using a gas adsorption amount measuring device (Microtrac-Bell, BELSORP MAX or BELSORP MAX II) by the volumetric method (equilibration waiting time: 300 seconds or more). The measurement temperature was 195 K or 298 K, and the measurement pressure range was 0 kPaA (lower limit) and 100 kPaA (upper limit). Prior to the measurement, the sample was dried using a pretreatment device (Microtrac-Bell, BELPREP VAC II) at 130°C or higher and 50 Pa or lower for 2 hours or more to remove solvent molecules and adsorbed water.

[0087] Synthesis Example 1 Synthesis of Metal Complex A 1.19 g (4.0 mmol) of zinc nitrate hexahydrate, 0.729 g (4.0 mmol) of 4-hydroxyisophthalic acid, and 0.729 g (4.0 mmol) of trans-1,2-bis(4-pyridyl)ethylene were dissolved in 120 mL of N,N-dimethylformamide and 100 mL of water, and the mixture was stirred at atmospheric pressure and 95°C for 16 hours. A portion of the precipitated crystals was removed and subjected to single-crystal X-ray structural analysis. Figure 3 shows the ORTEP diagram of the results of single-crystal X-ray structural analysis. N,N-dimethylformamide solvent molecules were present in the crystals, but these have been omitted. Structural analysis revealed that the resulting metal complex had a composition of zinc dication: 4-hydroxyisophthalic acid dianion: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1. Table 1 shows the lattice constants and other information.

[0088] Single-crystal X-ray structural analysis determines the arrangement of the metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II) in the crystal, i.e., the crystal structure. Figure 4 shows a crystal structure model of metal complex A. The area surrounded by a dashed line represents one of the two-dimensional sheets with fin-like protrusions. Figure 4 shows that the organic bidentate ligand (II) is coordinated in the planar direction of the metal dication to form a two-dimensional sheet, and furthermore, the dianion of the aromatic 1,3-dicarboxylic acid compound (I) coordinated to the metal dication protrudes in a direction approximately perpendicular to the two-dimensional sheet, forming a fin-like structure. Furthermore, these fin-like structures are interdigitated to form stacked two-dimensional sheets, which indicates that the crystal of metal complex A has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0089]

[0090] After the crystals for single-crystal X-ray structural analysis were removed, the precipitated metal complex was recovered by suction filtration from the reaction solution and then washed three times with methanol. Subsequently, the precipitate was vacuum dried (10-20 Pa) at 200°C for 2 hours using a vacuum dryer DRV320DA (Advantec Toyo Co., Ltd.), yielding 1.49 g of the target metal complex A (yield 87%). The powder X-ray diffraction patterns of the obtained metal complex A before and after vacuum drying are shown in Figures 5-1 and 5-2, respectively.

[0091] As shown in Figures 3 and 4, Metal Complex A has a CID structure before vacuum drying, and Figure 5-1 is a powder X-ray diffraction pattern specific to the CID structure. Furthermore, Figures 5-1 and 5-2 show nearly identical diffraction patterns, indicating that the CID structure is maintained even after the solvent is removed. The change in the diffraction pattern before and after vacuum drying occurs because the removal of the solvent narrows the distance between the sheets while maintaining the CID structure. In the CID structure before vacuum drying, for example, relatively strong peaks are observed at diffraction angles (2θ) of 8.5°, 9.5°, 12.9°, 15.8°, 19.3°, 22.4°, and 26.0°. In the CID structure after vacuum drying, for example, relatively strong peaks are observed at diffraction angles (2θ) of 9.2°, 9.7°, 12.1°, 13.1°, 16.9°, 20.4°, 23.7°, and 26.7°.

[0092] Synthesis Example 2 Synthesis of Metal Complex B 1.72 g (87% yield) of Metal Complex B was obtained in the same manner as in Synthesis Example 1, except that 4-hydroxyisophthalic acid was replaced with 0.980 g (4.0 mmol) of 5-bromoisophthalic acid. Single crystal X-ray structural analysis was performed on a portion of the crystals precipitated from the reaction solution. An ORTEP diagram of the results of the single crystal X-ray structural analysis is shown in Figure 6. As a result of the structural analysis, it was found that Metal Complex B had a composition of zinc dication: dianion of 5-bromoisophthalic acid: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1. Table 1 shows the lattice constants and other information.

[0093] Figure 7 shows a crystal structure model of metal complex B. From Figure 7, it can be seen that the crystal of metal complex B has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0094] The powder X-ray diffraction pattern of the obtained metal complex B after vacuum drying is shown in Figure 8. Relatively strong peaks were observed at diffraction angles (2θ) of 9.1°, 9.9°, 11.7°, 13.0°, 16.7°, 23.6°, and 25.7°, which is in good agreement with the diffraction pattern specific to the CID structure shown in Figure 5-2.

[0095] Synthesis Example 3 Synthesis of Metal Complex C A solution of 0.149 g (0.5 mmol) of zinc nitrate hexahydrate in 10 mL of N,N-dimethylformamide was added to a solution of 0.106 g (0.5 mmol) of 4-nitroisophthalic acid and 0.091 g (0.5 mmol) of trans-1,2-bis(4-pyridyl)ethylene in 10 mL of N,N-dimethylformamide, and the mixture was then allowed to stand at atmospheric pressure and 120°C for 48 hours. A portion of the precipitated crystals was removed and subjected to single-crystal X-ray structural analysis. The ORTEP diagram of the results of single-crystal X-ray structural analysis is shown in Figure 9. The crystals contained solvent molecules, N,N-dimethylformamide, and these were also included in the analysis. As a result of the structural analysis, it was determined that Metal Complex C had a composition of zinc dication: 4-nitroisophthalic acid dianion: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1. Table 1 shows the lattice constants and other information.

[0096] Figure 10 shows a crystal structure model of metal complex C. From Figure 10, it can be seen that the crystal of metal complex C has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0097] Synthesis Example 4 Synthesis of Metal Complex D 0.097 g (0.4 mmol) of copper nitrate trihydrate, 0.073 g (0.4 mmol) of 4-hydroxyisophthalic acid, and 0.073 g (0.4 mmol) of trans-1,2-bis(4-pyridyl)ethylene were dissolved in 12 mL of N,N-dimethylformamide and 10 mL of water, and the solution was allowed to stand at atmospheric pressure and 95°C for 16 hours. A portion of the precipitated crystals was taken and subjected to powder X-ray structural analysis, the results of which are shown in Figure 11. Relatively strong peaks were observed at diffraction angles (2θ) of 8.4°, 8.9°, 13.3°, 15.7°, 19.3°, and 22.6°, which closely matched the diffraction pattern specific to the CID structure shown in Figure 5-1. Therefore, it is clear that Metal Complex D obtained in Synthesis Example 4 has a composition of copper dication: dianion of 4-hydroxyisophthalic acid: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1, and has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0098] Synthesis Example 5 Synthesis of Metal Complex E 0.595 g (2.0 mmol) of zinc nitrate hexahydrate, 0.310 g (2.0 mmol) of 1H-2,5-pyrroledicarboxylic acid, and 0.369 g (2.0 mmol) of trans-1,2-bis(4-pyridyl)ethylene were dissolved in 60 mL of N,N-dimethylformamide and 50 mL of water, and the mixture was stirred at atmospheric pressure and 80°C for 16 hours. The precipitated metal complex was recovered by suction filtration and then washed three times with methanol. Subsequently, the mixture was vacuum dried at 200°C (10 to 20 Pa) for 2 hours using a vacuum dryer DRV320DA (Advantec Toyo Co., Ltd.), yielding 0.396 g (50% yield) of the target metal complex E. The powder X-ray diffraction pattern of the obtained metal complex E is shown in FIG. 12. Relatively strong peaks were observed at diffraction angles (2θ) of 8.8°, 9.4°, 13.1°, 14.0°, 19.0°, 21.4°, 24.9°, and 26.7°, which closely matched the diffraction pattern specific to the CID structure shown in Figure 5-2. Therefore, it was found that Metal Complex E obtained in Synthesis Example 5 has a composition of zinc dication: dianion of 1H-2,5-pyrroledicarboxylic acid: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1, and has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0099] Synthesis Example 6 Synthesis of Metal Complex F The target metal complex F (0.5037 g, 63% yield) was obtained in the same manner as in Synthesis Example 5, except that zinc nitrate hexahydrate was replaced with 0.5877 g (2.0 mmol) of cobalt nitrate hexahydrate and the reaction temperature was 95°C. The powder X-ray diffraction pattern of the obtained metal complex F is shown in Figure 13. Relatively strong peaks were observed at diffraction angles (2θ) of 9.0°, 9.6°, 13.2°, 18.6°, 21.2°, 24.7°, and 26.2°, which is in good agreement with the diffraction pattern specific to the CID structure shown in Figure 5-2. Therefore, it is clear that Metal Complex F obtained in Synthesis Example 6 has a composition of cobalt dication: dianion of 1H-2,5-pyrroledicarboxylic acid: trans-1,2-bis(4-pyridyl)ethylene = 1:1:1, and has a structure in which two-dimensional sheets are interdigitated and stacked (CID structure).

[0100] Comparative Synthesis Example 1 Synthesis of Comparative Metal Complex P According to the method described in Example 1 of JP 2013-107826 A, zinc nitrate hexahydrate, isophthalic acid, and trans-1,2-bis(4-pyridyl)ethylene were stirred in a mixed solution of N,N-dimethylformamide and water at atmospheric pressure and 80°C for 72 hours to synthesize comparative metal complex P. The results of single-crystal X-ray structural analysis of comparative metal complex P are described in JP 2013-107826 A, and it has a structure in which pseudo-diamond frameworks are interpenetrated threefold.

[0101] The powder X-ray diffraction pattern of comparative metal complex P is shown in Figure 14. Relatively strong peaks are observed at diffraction angles (2θ) of 13.6°, 16.9°, 17.9°, 20.0°, 26.6°, and 27.5°.

[0102] Comparative Synthesis Example 2: The same reaction as in Synthesis Example 1 was carried out, except that the synthesis solvent for comparative metal complex Q was changed to 200 mL of water alone and the reaction time was changed to 18 hours, to obtain 0.394 g of comparative metal complex Q. The powder X-ray diffraction pattern of the obtained comparative metal complex Q is shown in Figure 15. Relatively strong peaks are observed at diffraction angles (2θ) of 13.5°, 16.8°, 17.8°, 19.9°, 26.4°, and 27.5°, which closely matches the diffraction pattern characteristic of the triple-interpenetrated pseudo-diamond framework structure shown in Figure 14. This indicates that comparative metal complex Q obtained in Comparative Synthesis Example 2 has a triple-interpenetrated pseudo-diamond framework structure.

[0103] Comparative Synthesis Example 3 Synthesis of Comparative Metal Complex R 0.119 g (0.4 mmol) of zinc nitrate hexahydrate, 0.084 g (0.4 mmol) of 4-nitroisophthalic acid, and 0.073 g (0.4 mmol) of trans-1,2-bis(4-pyridyl)ethylene were dissolved in 12 mL of N,N-dimethylformamide and 10 mL of water, and the solution was allowed to stand at 95°C for 16 hours. A portion of the precipitated crystals was removed and subjected to single crystal X-ray structural analysis. An ORTEP diagram of the results of the single crystal X-ray structural analysis is shown in Figure 16. Figure 17 shows a crystal structure model of Comparative Metal Complex R. From Figure 17, it can be seen that Comparative Metal Complex R has a structure in which pseudo-diamond frameworks are triple-interpenetrated. Table 1 shows the lattice constants and other information.

[0104] Comparative Synthesis Example 4 Synthesis of Comparative Metal Complex S 0.119 g (0.4 mmol) of zinc nitrate hexahydrate, 0.073 g (0.4 mmol) of 4-hydroxyisophthalic acid, and 0.074 g (0.4 mmol) of 1,2-bis(4-pyridyl)ethane were dissolved in 12 mL of N,N-dimethylformamide and 10 mL of water, and the solution was allowed to stand at 95° C. for 16 hours, yielding Comparative Metal Complex S as a precipitate.

[0105] The reaction conditions and results of the above synthesis examples are shown in Table 2.

[0106] Example 1 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) at 298 K were measured for Metal Complex A obtained in Synthesis Example 1. The results are shown in Figure 18. From the adsorption / desorption isotherm, the open gate pressure was 16 kPaA and the closed gate pressure was 14 kPaA.

[0107] Example 2 The adsorption isotherm (ADS) and desorption isotherm (DES) of carbon dioxide at 195 K were measured for Metal Complex B obtained in Synthesis Example 2. The results are shown in Figure 19. From the adsorption / desorption isotherm, the open gate pressure was 20 kPaA and the closed gate pressure was 17 kPaA.

[0108] Example 3 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) at 195 K were measured for Metal Complex C obtained in Synthesis Example 3. The results are shown in Figure 20. From the adsorption / desorption isotherm, the open gate pressure was 25 kPaA and the closed gate pressure was 12 kPaA.

[0109] Example 4 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) at 298 K were measured for Metal Complex D obtained in Synthesis Example 4. The results are shown in Figure 21. From the adsorption / desorption isotherm, the open gate pressure was 18 kPaA and the closed gate pressure was 16 kPaA.

[0110] Example 5 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) at 298 K were measured for Metal Complex E obtained in Synthesis Example 5. The results are shown in Figure 22. From the adsorption / desorption isotherm, the open gate pressure was 9 kPaA and the closed gate pressure was 9 kPaA.

[0111] Example 6 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) at 298 K were measured for Metal Complex F obtained in Synthesis Example 6. The results are shown in Figure 23. From the adsorption / desorption isotherm, the open gate pressure was 6 kPaA and the closed gate pressure was 6 kPaA.

[0112] Comparative Example 1 The adsorption isotherm (ADS) and desorption isotherm (DES) of carbon dioxide at 298 K were measured for comparative metal complex Q obtained in Comparative Synthesis Example 2. The results are shown in Figure 24. Unlike Example 1, comparative metal complex Q did not exhibit the gating phenomenon. Such a metal complex is not preferred because it requires the desorption step to be carried out at an extremely low pressure in the separation and recovery of carbon dioxide by the PSA method, which increases the cost required for recovery.

[0113] Comparative Example 2 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) of comparative metal complex R obtained in Comparative Synthesis Example 3 at 298 K were measured, but no carbon dioxide adsorption was observed. The results are shown in Figure 25.

[0114] Comparative Example 3 The carbon dioxide adsorption isotherm (ADS) and desorption isotherm (DES) of comparative metal complex S obtained in Comparative Synthesis Example 4 at 195 K were measured, but no carbon dioxide adsorption was observed. The results are shown in Figure 26.

[0115] The open gate pressures and closed gate pressures of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 3. As can be seen from Examples 1 to 6, metal complexes A to F have low open gate pressures and closed gate pressures, and are therefore useful as separation agents capable of separating and recovering carbon dioxide from mixed gases containing low concentrations of carbon dioxide with high energy efficiency.

[0116]

[0117] Example 7 Separation of a mixed gas (carbon dioxide, nitrogen) Metal complex A (10.6 g) obtained in Synthesis Example 1 as a separating agent was packed into a jacketed stainless steel tube with a volume of 32 mL (inner diameter 1 cm, length 40 cm). Carbon dioxide (CO ２ ): Nitrogen (N ２The adsorption and desorption operation of a mixed gas with a volume ratio of 1:9 was repeated. ２ The mixed gas was supplied to the stainless steel tube at a partial pressure of 30 kPaA. In the desorption operation, the stainless steel tube was evacuated using a diaphragm pump, and the desorbed gas was recovered. The above adsorption and desorption operations were repeated, and the desorbed gas was analyzed when the carbon dioxide concentration of the desorbed gas reached a constant value (steady state). ２ The concentration was 58.9% by volume. ２ The concentration was increased by approximately six times from 10% by volume.

[0118] The results of Example 7 reveal that Metal Complex A is an excellent agent for separating carbon dioxide from a mixed gas containing a low concentration of carbon dioxide.

Claims

1. A dianion of an aromatic 1,3-dicarboxylic acid compound (I), a metal dication selected from magnesium, calcium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper, zinc, and cadmium, and a compound represented by the following general formula (1): (In the formula, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ and R ８ and an organic bidentate ligand (II) capable of coordinating to the metal dication, represented by the following formula (1): wherein each of the groups independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a formyl group, an acyloxy group, an alkoxycarbonyl group having 2 to 4 carbon atoms, a nitro group, a cyano group, an amino group, a monoalkylamino group having 1 to 4 carbon atoms, a dialkylamino group having 2 to 4 carbon atoms, an acylamino group having 2 to 4 carbon atoms, or a halogen atom, and wherein the metal complex has a structure in which two-dimensional sheets are interdigitated and stacked.

2. The metal complex according to claim 1, wherein the open gate pressure and the closed gate pressure in the carbon dioxide adsorption / desorption isotherm measured at any temperature between 150 and 350 K are both between 1 and 60 kPaA.

3. The metal complex according to claim 1 or 2, wherein the aromatic 1,3-dicarboxylic acid compound (I) is a monocyclic six-membered aromatic 1,3-dicarboxylic acid compound or a monocyclic five-membered aromatic 1,3-dicarboxylic acid compound.

4. The metal complex according to claim 1 or 2, wherein the aromatic 1,3-dicarboxylic acid compound (I) is a monocyclic six-membered aromatic 1,3-dicarboxylic acid compound, and the aromatic ring of the monocyclic six-membered aromatic 1,3-dicarboxylic acid compound has, in addition to two carboxy groups, at least one substituent selected from a halogen atom, a hydroxyl group, and a nitro group.

5. The aromatic 1,3-dicarboxylic acid compound (I) is represented by the following general formula (2): (Wherein, X is CH or N, and R ９ The metal complex according to claim 4 , wherein:

6. The aromatic 1,3-dicarboxylic acid compound (I) is represented by the following general formula (3): wherein Y is NH, S, or O; １０ and R １１ are each independently a hydrogen atom or an alkoxy group having 1 to 3 carbon atoms, and R １０ and R １１ The metal complex according to claim 1 or 2, wherein:

7. R １０ and R １１ and each represent a hydrogen atom.

8. The metal complex according to claim 1 or 2, wherein the compositional ratio (molar ratio) of the metal dication, the dianion of the aromatic 1,3-dicarboxylic acid compound (I), and the organic bidentate ligand (II) in the metal complex is 1:0.9-1.1:0.9-1.

1.

9. A separating agent comprising the metal complex according to claim 1 or 2.

10. A method for separating a target gas, comprising: bringing a mixed gas containing a target gas to be separated and other gases into contact with the separating agent described in claim 9, thereby adsorbing the target gas onto the separating agent; and desorbing the target gas.

11. The separation method according to claim 10, wherein the mixed gas contains at least two gases selected from oxygen gas, nitrogen gas, water vapor, nitrogen oxide gas, sulfur oxide gas, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrogen sulfide gas, ammonia, hydrocarbon gas having 1 to 4 carbon atoms, rare gas, and siloxane.

12. The separation method according to claim 10, wherein the target gas is carbon dioxide gas.

13. The separation method according to claim 10, wherein the mixed gas is a combustion exhaust gas discharged from a plant, and the target gas is carbon dioxide gas.

14. A method for separating a target gas, comprising: bringing a mixed gas containing a target gas to be separated and other gases into contact with a separating agent to adsorb the target gas onto the separating agent; and desorbing the target gas, wherein the separating agent contains a metal complex having a structure in which two-dimensional sheets are interdigitated and stacked, and in which the open gate pressure and closed gate pressure are both 1 to 60 kPaA in the carbon dioxide adsorption isotherm at the operating temperature.

15. The separation method according to claim 14, wherein the mixed gas contains at least two gases selected from oxygen gas, nitrogen gas, water vapor, nitrogen oxide gas, sulfur oxide gas, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrogen sulfide gas, ammonia, hydrocarbon gas having 1 to 4 carbon atoms, rare gas, and siloxane.

16. The separation method according to claim 14 or 15, wherein the target gas is carbon dioxide gas.

17. The separation method according to claim 14, wherein the metal complex is a metal complex according to claim 1 or 2.

18. The separation method according to claim 16, wherein the partial pressure of carbon dioxide in the mixed gas is 1 to 30 kPaA.

19. The separation method according to claim 14 or 15, wherein the operating temperature is 150 to 350K.

20. A carbon dioxide separation device equipped with a separating agent containing the metal complex according to claim 1 or 2.

21. A metal complex having a structure in which two-dimensional sheets are interdigitated and stacked, and in which the open gate pressure and closed gate pressure are both 1 to 60 kPaA in the carbon dioxide adsorption / desorption isotherm measured at any temperature between 150 and 350 K.

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