Adsorbent and its manufacturing method

Abstract

Provided is an adsorbent having a core-shell structure, wherein: the core is configured from a zeolite; the shell meets the following requirements (A)-(C), i.e., (A) the shell is a silicate or is a silicate-based oxide configured from an aluminosilicate in which the molar ratio SiO2 / Al2O3 is 750 or higher, (B) the shell has a zeolite structure, and (C) all ratios (ISi-OH / ISi-O) of the peak intensity ISi-OH of Si-OH peaks ((3,788±50) cm–1) to the peak intensity ISi-O of Si-O peaks ((1,868±70) cm–1) are equal to or less than 3.0; and the structure of the zeolite constituting the core and the structure of the zeolite constituting the shell do not have a shared composite structural unit.

Description

[Technical Field]

[0001] The present invention relates to an adsorbent and a method for producing the same, and more particularly to an adsorbent suitable for adsorbing CO2, and a method for producing the adsorbent. [Background technology]

[0002] In the fields of exhaust gas purification and carbon neutrality, adsorbents that adsorb specific target substances are used.

[0003] For example, FAU-type zeolite is known as a CO2 adsorption material. However, when water coexists in the atmosphere, FAU-type zeolite suffers from competitive adsorption between CO2 and water, resulting in a decrease in the amount of CO2 adsorbed.

[0004] In order to solve this problem, attempts have been made to prepare composite particles by using a zeolite core having gas adsorption ability and coating the core with a shell having hydrophobic and gas diffusing properties.

[0005] For example, Non-Patent Document 1 describes composite particles in which a zeolite 13X core is coated with a silicalite shell, and Non-Patent Document 2 describes composite particles in which a Na-Y zeolite core is coated with a silicalite shell. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Mater.Chem.Phys.,2012(133),pp1144-1151 [Non-patent document 2] Ind.Eng.Chem.Res.,2018(57),pp16358-16366 Summary of the Invention [Problem to be solved by the invention]

[0007] Core-shell zeolite materials are expected to be adsorbents that do not reduce the amount of adsorbed substances even when water is present in the atmosphere. However, core-shell zeolite materials obtained by conventional methods have insufficient shell coverage and many Si-OH bonds on the shell surface, resulting in insufficient hydrophobicity.

[0008] In this regard, Non-Patent Document 1 describes improving the hydrophobicity of composite particles by silylating the surfaces thereof. However, surface-silylated composite particles have low heat resistance, and their application is limited.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an adsorbent that is highly heat-resistant and that suppresses a decrease in the amount of an adsorbed substance in the presence of water, and a method for producing the same. [Means for solving the problem]

[0010] The present invention is as follows.

[0011] <Embodiment 1> An adsorbent having a core-shell structure, the core is made of zeolite; The shell meets the following requirements (A) to (C): (A) A silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more; (B) having a zeolite structure, and (C) The Si-O peak ((1,868±70) cm) in the FT-IR of the adsorbent -1 ) peak intensity I Si-O The Si-OH peak ((3,788±50) cm -1 ) peak intensity I Si-OH The ratio (I Si-OH / I Si-O ) is 3.0 or less All of the above are satisfied, and the structure of the zeolite constituting the core and the structure of the zeolite constituting the shell do not have a common composite structural unit; Adsorbent material. Aspect 2: The adsorbent according to aspect 1, wherein the zeolite constituting the core has an SiO2 / Al2O3 molar ratio of 20 or less. Aspect 3: The adsorbent according to aspect 1 or 2, wherein the zeolite constituting the core has a framework structure selected from FAU, AEI, and CHA. Aspect 4: The adsorbent according to any one of Aspects 1 to 3, wherein the substance to be adsorbed by the adsorbent is CO2. Aspect 5: The adsorbent according to any one of Aspects 1 to 4, wherein an alkali metal or alkaline earth metal is supported on the zeolite that constitutes the core. Aspect 6: The adsorbent according to any one of Aspects 1 to 5, wherein the silicate-based oxide constituting the shell has a skeletal structure of MFI. Aspect 7: The adsorbent according to any one of Aspects 1 to 6, wherein the shell has a coverage of 75% or more. Aspect 8: A method for producing the adsorbent according to any one of aspects 1 to 7, comprising: a core composed of zeolite; silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more; to contact; depositing a seed shell composed of the silicate-based oxide on the surface of the core to synthesize an adsorbent precursor; and heating the adsorbent precursor in the presence of a silicate-based oxide source and an organic structure-directing agent to grow a shell crystal; Including, Method for manufacturing adsorbent. Aspect 9: Synthesizing the adsorbent precursor comprises: by spray drying a mixture of the core and the silicate-based oxide; A method for producing the adsorbent according to aspect 8. Aspect 10: Synthesizing the adsorbent precursor comprises: by heating a mixture of the core and the silicate-based oxide; A method for producing the adsorbent according to aspect 8. [Effects of the Invention]

[0012] According to the present invention, there are provided an adsorbent that is highly heat-resistant and in which the decrease in the amount of adsorbed substances in the presence of water is suppressed, and a method for producing the same. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1(a) is an FE-SEM image of Na-FAU (FAU core) used as a raw material in Example 1, and FIG. 1(b) is an FE-SEM image of the core-shell type FAU-MFI composite obtained in Example 1. [Figure 2] FIG. 2 is an SEM image of the core-shell type FAU-MFI complex obtained in Example 1. [Figure 3] FIG. 3 is an FE-SEM image of the core-shell type FAU-MFI composite precursor obtained in Comparative Example 1. [Figure 4] FIG. 4 is an FT-IR chart measured for the FAU core and the sample of Example 1 60 seconds after the start of the flow of the hydrated nitrogen gas. [Figure 5] FIG. 5 is a graph showing the change over time in the water adsorption rate measured for each of the FAU-MFI complexes obtained in Examples 1 and 3 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] Absorbent Material The adsorbent of the present invention comprises: An adsorbent having a core-shell structure, the core is made of zeolite; The shell meets the following requirements (A) to (C): (A) A silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more; (B) having a zeolite structure, and (C) The Si-O peak ((1,868±70) cm) in the FT-IR of the adsorbent -1 ) peak intensity I Si-O The Si-OH peak ((3,788±50) cm -1 ) peak intensity I Si-OH The ratio (I Si-OH / I Si-O ) is 3.0 or less All of the above are satisfied, and the structure of the zeolite constituting the core and the structure of the zeolite constituting the shell do not have a common composite structural unit; It is an adsorbent.

[0015] The core of the adsorbent of the present invention is composed of zeolite. Zeolite is advantageous as an adsorbent core in that the aluminosilicate that constitutes it is generally suitable for gas adsorption and that the pore size optimal for adsorption of the target substance can be selected by selecting the framework structure.

[0016] The shell of the adsorbent of the present invention is made of a silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more. That is, the shell of the adsorbent has an extremely low content of aluminum element or does not contain aluminum element at all. Such a shell is highly hydrophobic. The adsorbent of the present invention, which includes a highly hydrophobic shell, can adsorb a target substance at a desired adsorption amount even in the coexistence of water. Here, "SiO2 / Al2O3 molar ratio" refers to the molar ratio (SiO2 / Al2O3) of silica (SiO2) to alumina (Al2O3).

[0017] The shell has a zeolite structure. The zeolite structure has pores. In the adsorbent of the present invention, which includes a shell having pores, the gas containing the substance to be adsorbed can easily permeate the shell, so the presence of the shell does not interfere with the adsorption of the substance to be adsorbed to a great extent.

[0018] Furthermore, the adsorbent of the present invention has a Si-O peak ((1,868±70) cm) in FT-IR. -1 ) peak intensity I Si-O The Si-OH peak ((3,788±50) cm -1 ) peak intensity I Si-OH The ratio (I Si-OH / I Si-O ) shows a small value of 3.0 or less. Si-OH / I Si-O A small value of the ratio (I) means that the concentration of Si-OH groups in the shell is low and the shell is highly hydrophobic. Si-OH / I Si-O ) is small, at 3.0 or less, so the shell is highly hydrophobic. Therefore, the adsorbent of the present invention has the advantage that, even in the coexistence of water, competitive adsorption between the substance to be adsorbed and water is suppressed, and the degree of loss of the amount of the substance to be adsorbed is small.

[0019] The elements constituting the adsorbent of the present invention will be explained below in order.

[0020] <core> The core of the adsorbent of the present invention has the function of adsorbing a target substance. The core is made of zeolite. Zeolite has excellent adsorption capacity and is therefore ideal as the core of the adsorbent of the present invention.

[0021] The SiO2 / Al2O3 molar ratio of the zeolite constituting the core may be 0.5 or more, 1.0 or more, 1.5 or more, or 2.0 or more to increase durability, and may be 500 or less, 300 or less, 100 or less, 80 or less, 40 or less, 20 or less, 10 or less, or 5.0 or less to increase the amount of the substance to be adsorbed.

[0022] The International Zeolite Association assigns a skeleton code consisting of three capital letters to the skeletal structure of a zeolite. In this specification, a zeolite having a certain skeleton structure may be referred to by the skeleton code indicating the skeleton structure. Furthermore, an ion-exchanged zeolite may be referred to by a notation in which the ion species and the skeleton code are combined with a hyphen. For example, a zeolite having a skeleton structure represented by the skeleton code FAU may be written as "FAU," and FAU ion-exchanged with Na may be written as "Na-FAU."

[0023] The present specification may also refer to the pore diameter of a zeolite. This pore diameter is the value listed as the "Maximum diameter of a sphere that can diffuse along" in the Database of Zeolite Structures (URL: https: / / asia.iza-structure.org / IZA-SC / ftc_table.php) published by the International Zeolite Society. If this value differs among the a-axis, b-axis, and c-axis directions, the largest of these pore diameters is used. In this database, for example, the pore diameters of AFI are listed as 2.22 Å along the a-axis, 2.22 Å along the b-axis, and 7.42 Å along the c-axis. In the present specification, the largest of these values, "7.42 Å," is considered to be the pore diameter of AFI.

[0024] The skeletal structure of the zeolite constituting the core of the adsorbent of the present invention may be appropriately selected depending on the substance to be adsorbed. The substance to be adsorbed may be, for example, CO2. In this case, the zeolite of the core may be one or more selected from, for example, AFI, ATO, BEA, CHA, CON, FAU, GME, LTA, LTL, MOR, MTW, AFX, AEI, MFI, OFF, etc.

[0025] When the substance to be adsorbed is CO2, the pore size of the core zeolite may be 3.5 Å or more, 4.0 Å or more, 5.0 Å or more, 6.0 Å or more, 7.0 Å or more, or 7.2 Å or more, and may be 10.0 Å or less, 9.0 Å or less, or 8.0 Å or less. When the substance to be adsorbed is CO2, the core zeolite may be one or more types selected from AFI, CHA, FAU, AEI, GME, LTA, LTL, MFI, MOR, OFF, etc., and particularly one or more types selected from FAU, AEI, and CHA.

[0026] When the substance to be adsorbed is CO2, the core zeolite may be supported with an alkali metal or alkaline earth metal. Zeolites supported with alkali metals or alkaline earth metals have a high basicity, which has the advantage of increasing the amount of CO2 adsorbed.

[0027] The particle size of the zeolite constituting the core of the adsorbent of the present invention may be 1.0 μm or more, 1.2 μm or more, 1.5 μm or more, or 2.0 μm or more, and may be 5.0 μm or less, 4.0 μm or less, 3.5 μm or less, or 3.0 μm or less. This particle size is the number average particle size obtained by microscopic observation.

[0028] <shell> The shell in the adsorbent of the present invention has the function of imparting hydrophobicity to the adsorbent and protecting the zeolite core from moisture while allowing the substance to be adsorbed to pass through to the core.

[0029] The shell meets all of the following requirements (A) to (C). (A) A silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more; (B) having a zeolite structure, and (C) The Si-O peak ((1,868±70) cm) in the FT-IR of the adsorbent -1 ) peak intensity I Si-O The Si-OH peak ((3,788±50) cm -1 ) peak intensity ISi-OH The ratio (I Si-OH / I Si-O ) is 3.0 or less.

[0030] The requirements (A) to (C) that the adsorbent shell must satisfy will be explained below in order.

[0031] (A) A silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more. The shell of the adsorbent is a silicate-based oxide composed of silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or greater.

[0032] The shell of the adsorbent is composed of such a silicate-based oxide, which ensures high hydrophobicity and pores, as described above. The adsorbent of the present invention, which includes such a shell, has the advantage of being able to adsorb a desired amount of a target substance even in the presence of water.

[0033] To achieve the above, when the silicate-based oxide is an aluminosilicate, its SiO2 / Al2O3 molar ratio is 750 or more, and may be 1,000 or more, 1,500 or more, 2,000 or more, 2,500 or more, 3,000 or more, 4,000 or more, or 5,000 or more.

[0034] (B) Having a zeolite structure The shell of the adsorbent has a zeolite structure.

[0035] Zeolite has a porous structure that allows the target substance to pass through efficiently to the core. Furthermore, by selecting the pore size, it may be possible to deliver only a specific target substance to the core.

[0036] The pore diameter of the silicate-based oxide constituting the shell may be 3.0 Å or more, 3.5 Å or more, or 4.0 Å or more, and may be 8.0 Å or less, 7.0 Å or less, 6.0 Å or less, or 5.0 Å or less.

[0037] The zeolite structure of the silicate-based oxide constituting the shell may be, for example, AEL, EUO, FER, HEU, MEL, MFI, NES, TON, WEI, etc., and may have one or more framework structures selected from these.

[0038] The shell in the adsorbent of the present invention may in particular be a silicate-based oxide having an MFI-type framework structure.

[0039] (C) Si-O peak ((1,868±70) cm) in FT-IR of the adsorbent -1 ) peak intensity I Si-O The Si-OH peak ((3,788±50) cm -1 ) peak intensity I Si-OH The ratio (I Si-OH / I Si-O ) is 3.0 or less The ratio of adsorbent (I Si-OH / I Si-O ) of 3.0 or less means that the amount of Si-OH groups in the shell is small. This indicates that the shell is highly hydrophobic, which allows the adsorbent of the present invention to exhibit high adsorption capacity even in the presence of water.

[0040] Ratio (I Si-OH / I Si-O ) may be 2.8 or less, 2.6 or less, 2.4 or less, 2.2 or less, 2.0 or less, or 1.8 or less. Si-OH / I Si-O ) may be zero (0), but in relation to the effects of the present invention, the ratio (I Si-OH / I Si-O ) is sufficient if it is 0.5 or more, 1.0 or more, or even 1.5 or more.

[0041] The FT-IR of the adsorbent may be measured by a transmission method in accordance with JIS K0117:2017 (General rules for infrared spectroscopic analysis).

[0042] In the adsorbent of the present invention, the shell coverage may be 75% or more. By having the shell coverage of 75% or more, the adsorbent has extremely high heat resistance while highly suppressing the decrease in the amount of the adsorbed substance in the presence of water. From this perspective, the shell coverage may be 78% or more, 80% or more, 82% or more, 85% or more, 90% or more, or 95% or more, or may be 100%.

[0043] The shell coverage of the adsorbent of the present invention is defined as the proportion of the surface area of ​​the adsorbent that is covered with the shell and has no exposed core. The shell coverage may be measured by a method known to those skilled in the art, such as XPS, FIB-SEM, or FT-IR. The method for measuring the shell coverage may be appropriately selected depending on the SiO / AlO molar ratio of the core.

[0044] For example, when the SiO2 / Al2O3 molar ratio of the core is 5 or less, the shell coverage may be calculated from the results of XPS analysis measured on the adsorbent, taking into account the SiO2 / Al2O3 molar ratios of the core and shell. When the SiO2 / Al2O3 molar ratio of the core exceeds 5, the shell coverage may be measured by FIB-SEM, FT-IR, or the like.

[0045] The shell coverage rate may be measured by FIB-SEM, for example, by image analysis of an SEM image of a cross section of the adsorbent processed by FIB.

[0046] The shell coverage may be measured by FT-IR, for example, by FT-IR measurement of an adsorbent to which quinoline has been adsorbed. In this case, quinoline has a large molecular size and cannot be adsorbed into the pores of the core, but is adsorbed only to the shell. Therefore, the shell coverage can be calculated from the peak intensity of quinoline in FT-IR.

[0047] The shell proportion in the adsorbent of the present invention may be 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, and may be 50% by mass or less, 45% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total mass of the adsorbent. If the shell proportion is within this range, the adsorbent will have very high heat resistance while being highly inhibited from reducing the amount of adsorption of the substance to be adsorbed in the presence of water.

[0048] The shell ratio in the adsorbent of the present invention is defined as the ratio of the mass of the shell to the total mass of the adsorbent.

[0049] The shell thickness of the adsorbent of the present invention may be 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, or 220 nm or more, and may be 1,000 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, or 250 nm or less. When the shell thickness is within this range, the adsorbent has very high heat resistance while highly suppressing the decrease in the amount of the adsorbed substance in the presence of water. If the shell thickness is too thick, it may be difficult for the adsorbed substance to pass through, which is undesirable.

[0050] The shell thickness of the adsorbent of the present invention may be measured as a number average value by observation under an electron microscope.

[0051] <The structure of the zeolite constituting the core and the structure of the zeolite constituting the shell do not have a common composite structural unit> Furthermore, in the adsorbent of the present invention, the structure of the zeolite constituting the core and the structure of the zeolite constituting the shell must not have a common composite structural unit.

[0052] Zeolites are composed of a combination of basic structures called "Composite Building Units (CBUs)," which are made up of multiple TO4 units (several to several tens of units) linked together, each of which is a TO4 unit consisting of a tetrahedral Si or Al atom and an O atom. A single type of zeolite may contain one or more types of CBUs.

[0053] For example, zeolites with framework structures of FAU, AEI, CHA, BEA, and MFI are each composed of the following CBUs: FAU: d6r, sod (2 types) AEI:d6r(1 type) CHA: d6r, cha (2 types) BEA:mor, bea, mtw (3 types) MFI: mor, cas, mfi, mel (4 types)

[0054] For example, BEA and MFI share a common composite structural unit called "mor." Therefore, for example, a core-shell adsorbent having a BEA-type core and an MFI-type shell does not fall under the category of the adsorbent of the present invention.

[0055] On the other hand, for example, FAU and MFI do not share a common composite structural unit, and therefore, for example, a core-shell adsorbent having an FAU-type core and an MFI-type shell falls within the scope of the adsorbent of the present invention if it satisfies other requirements.

[0056] As will be demonstrated in the examples below, a core-shell adsorbent with a high CO2 adsorption capacity can be obtained by using zeolites that do not have a common composite structural unit as the core and shell.

[0057] It is also desirable that the core has a high CO2 adsorption capacity and that the shell has a high SiO2 / Al2O3 molar ratio, making it possible to increase the hydrophobicity of the shell.

[0058] From the above viewpoints, in the adsorbent of the present invention, the zeolite constituting the core may have a skeletal structure selected from FAU, AEI, and CHA, and the silicate-based oxide constituting the shell may have a skeletal structure of MFI.

[0059] <Method for measuring the SiO2 / Al2O3 molar ratio of the core and shell> The SiO2 / Al2O3 molar ratio of the core and shell in the adsorbent of the present invention may be measured, for example, by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) of a cross section of the adsorbent.

[0060] In SEM-EDX, first, SEM analysis of the cross section of the adsorbent is performed, and in the obtained SEM image, the core portion and shell portion of the adsorbent are defined based on the image contrast. Next, in this SEM image, a single imaginary line is set so as to pass through both the core portion and the shell portion. Subsequently, EDX line analysis is performed along the set imaginary line to measure the Si element concentration and Al element concentration (mass%) in each of the core portion and the shell portion. Then, from the obtained measured values, the SiO2 / Al2O3 molar ratio in each of the core portion and the shell portion can be calculated.

[0061] <<Method for manufacturing adsorbent>> The adsorbent of the present invention described above may be produced by any method as long as it satisfies the above-mentioned characteristics.

[0062] The adsorbent of the present invention may be produced, for example, by the following production method.

[0063] a core composed of zeolite; silicate or aluminosilicate with a SiO2 / Al2O3 molar ratio of 750 or more; (contacting the core with a silicate-based oxide); depositing a seed shell composed of the silicate-based oxide on the surface of the core to synthesize an adsorbent precursor (synthesis of an adsorbent precursor); and Heating the adsorbent precursor in the presence of a silicate-based oxide source and an organic structure-directing agent to grow shell crystals (shell crystal growth). Including, Method for manufacturing adsorbent.

[0064] The resulting adsorbent may be calcined as necessary before use.

[0065] The method for producing an adsorbent of the present invention has the advantage that a core-shell structure can be formed without considering the commonality of structure between the zeolite constituting the shell and the zeolite constituting the core.

[0066] The elements constituting the above-mentioned method for producing an adsorbent will be explained below in order.

[0067] <Contact between core and silicate-based oxide> First, the core is brought into contact with a silicate-based oxide. (core) The core may be appropriately selected depending on the desired core in the adsorbent of the present invention. When the substance to be adsorbed is CO2, a zeolite substituted with an alkali cation may be used. The alkali cation may be, for example, an alkali metal cation, an alkaline earth metal cation, an ammonium cation, or the like. In such a zeolite, the alkali cation serves as a chemical adsorption site for CO2, and therefore has the advantage of being able to adsorb a higher amount of CO2 than other cation-substituted zeolites (e.g., H-zeolite) that only have physical adsorption sites. The alkali cation is particularly Na + It may be.

[0068] The core for producing the adsorbent of the present invention may be one or more types selected from AFI, ATO, BEA, CHA, CON, FAU, GME, LTA, LTL, MOR, MTW, AFX, AEI, MFI, OFF, etc., having an SiO2 / Al2O3 molar ratio of 0.5 to 10 and a particle size of 1.0 μm to 5.0 μm.

[0069] The core may be surface-modified with a polycation upon contact with the silicate-based compound, such as an ammonium polycation, a quaternary ammonium cation, or the like.

[0070] The polycationic surface modification of the core may be carried out, for example, by contacting the core with a polycationizing agent, which may be selected from, for example, poly(diallyldimethylammonium chloride), alkylmethylamine, etc.

[0071] The amount of polycationizing agent used may be 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the core. The core and the polycationizing agent may be contacted, for example, in water. The contact temperature may be appropriately selected from the range of 0°C or more and 100°C or less, but room temperature is sufficient.

[0072] (Silicate oxides) The silicate-based oxide is a component that deposits on the surface of the core upon contact with the core, forming a "seed shell." Therefore, this silicate-based oxide may have the same skeletal structure as the desired shell of the adsorbent of the present invention. This silicate-based oxide may be, for example, an MFI-type silicate. The SiO2 / Al2O3 molar ratio of this silicate is arbitrary. That is, even if the SiO2 / Al2O3 molar ratio of the "seed shell" differs from the desired SiO2 / Al2O3 molar ratio of the adsorbent shell, the SiO2 / Al2O3 molar ratio of the adsorbent shell can be controlled to the desired value by changing the SiO2 / Al2O3 molar ratio of the silicate-based oxide source used for crystal growth of the shell.

[0073] The particle size of the silicate-based oxide may be, for example, 30 nm or more and 120 nm or less.

[0074] The silicate-based oxide may be synthesized by heating a suitable silicate-based oxide source in the presence of water. The silicate-based oxide may be synthesized in the presence of an organic structure directing agent (OSDA).

[0075] The silicate-based oxide source used here may be selected from any silicon source, such as orthosilicic acid, alkoxide of silicic acid, alkali metal salt of silicic acid, fumed silica, colloidal silica, etc., and one or more selected from these may be used. Specifically, the alkoxide of silicic acid may be, for example, tetraethyl orthosilicate, and the alkali metal salt of silicic acid may be, for example, sodium silicate.

[0076] When the shell of the desired adsorbent contains Al, the silicate oxide source may contain Al, or a mixture of the silicate oxide source and the Al source may be used. Examples of silicate oxide sources containing Al include aluminosilicate, aluminosilicate alkoxides, and alkali metal salts of aluminosilicate. Examples of Al sources include aluminates, Al(OiPr)3, and the like. Examples of aluminates include sodium aluminate, and the like.

[0077] During the synthesis of silicate-based oxides, an organic structure-directing agent (OSDA) may optionally be present. The OSDA may be selected from, for example, those capable of forming an MFI structure. Specifically, the OSDA may be selected from, for example, alkylammonium hydroxides, 1,2,3-triethylimidazolium, etc. The alkylammonium hydroxide may be selected from, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, benzyltrimethylammonium hydroxide, N,N,N-trimethyladamantanammonium hydroxide, N,N-diethyl-2,6-dimethylpiperidinium hydroxide, 1,4-bis(1-azabicyclo[2.2.2]octane)butyl hydroxide, etc.

[0078] The amount of OSDA used may be 0.3 parts by mass or more, 15 parts by mass or more, or 30 parts by mass or more per 100 parts by mass of the silica-based oxide source in terms of silica; It may be 680 parts by weight or less, 340 parts by weight or less, or 240 parts by weight or less.

[0079] When the amount of OSDA used is expressed as a molar ratio, the ratio of the number of moles of OSDA to 1 mole of silicon atoms in the silicate-based oxide source (OSDA / Si) can be, for example, in the range of 0.1 to 0.7.

[0080] The silicate-based oxide may be synthesized by heating the silicate-based oxide source as described above in the presence of water, optionally in the presence of an OSDA. The silicate-based oxide may typically be synthesized in water.

[0081] The heating temperature when synthesizing the silicate-based oxide may be, for example, 50° C. or more and 175° C. or less, and the heating time may be, for example, 10 hours or more and 300 hours or less.

[0082] (Contact conditions between core and silicate-based oxide) The contact between the core and the silicate-based oxide is carried out in the presence of water. The contact between the core and the silicate-based oxide may typically be carried out in water. In this case, the contact between the core and the silicate-based oxide is carried out in the form of a mixture containing the core and the silicate-based oxide in water. When the contact between the two is carried out in this manner, the resulting mixture can be conveniently used as is in the next step, "synthesis of an adsorbent precursor (deposition of a seed shell)."

[0083] The amount of silicate-based oxide used may be, for example, 70 parts by mass or more, 100 parts by mass or more, or 200 parts by mass or more, expressed as the silica-equivalent mass of silicate-based oxide per 100 parts by mass of the core, and may be, for example, 10,000 parts by mass or less, 3,400 parts by mass or less, or 2,000 parts by mass or less.

[0084] <Synthesis of Adsorbent Precursor (Seed Shell Deposition)> The adsorbent precursor is then synthesized by depositing a seed shell composed of a silicate-based oxide onto the core.

[0085] Deposition of the seed shell onto the core may be carried out, for example, by spray drying a mixture of the core and the silicate-based oxide, by heating a mixture of the core and the silicate-based oxide, or the like.

[0086] The mixture of the core and the silicate-based oxide may contain water. The mixture of the core and the silicate-based oxide containing water may be prepared by adding the core and the silicate-based oxide to water, or the mixture obtained when the core and the silicate-based oxide are contacted in water may be used as is.

[0087] The mixture of the core and silicate-based oxide may be spray-dried at a predetermined flow rate at a temperature of, for example, 100 to 300°C using a commercially available spray-drying device.

[0088] The mixture of the core and silicate-based oxide may be heated, for example, at a temperature of 50° C. or more and 120° C. or less for a time of 12 hours or more and 150 hours or less.

[0089] Shell crystal growth The adsorbent precursor obtained above is then heated in the presence of a silicate-based oxide source and an organic structure-directing agent to grow shell crystals.

[0090] (silicate oxide source) The silicate-based oxide source used for growing the shell crystals may be appropriately selected from the silicate-based oxide sources exemplified above as silicate-based oxide sources for synthesizing the silicate-based oxide that will become the "seed shell."

[0091] The amount of the silicate-based oxide source used, expressed as the silica-equivalent mass of the silicate-based oxide source relative to 100 parts by mass of the adsorbent precursor, may be more than 0 parts by mass, 0.1 parts by mass or more, 1 part by mass or more, or 5 parts by mass or more, or may be 100 parts by mass or less, 50 parts by mass or less, or 25 parts by mass or less, and may be selected appropriately depending on the desired shell ratio.

[0092] <Organic structure directing agent> The organic structure-directing agent (OSDA) used for the crystal growth of the shell may be appropriately selected from the OSDAs exemplified above as OSDAs for synthesizing the silicate-based oxide that becomes the "seed shell."

[0093] The amount of OSDA used may be 3 parts by mass or more, 20 parts by mass or more, or 30 parts by mass or more, and may be 240 parts by mass or less, 120 parts by mass or less, 100 parts by mass or less, or 85 parts by mass or less, per 100 parts by mass of the adsorbent precursor.

[0094] (Conditions for shell crystal growth) The crystal growth of the shell may be carried out in the presence of water, or an alcohol may be co-present. Typically, a mixture containing the adsorbent precursor, the silicate-based oxide source, the organic structure directing agent, and the alcohol is heated in water.

[0095] The alcohol functions to make the silicate-based oxide source more soluble in the solvent. Examples of alcohol that can be used include ethanol and methanol, with ethanol being preferred. The amount of alcohol used may be greater than 0 parts by mass, at least 10 parts by mass, at least 75 parts by mass, or at least 150 parts by mass, and may be at most 15,000 parts by mass, at most 7,500 parts by mass, at most 4,000 parts by mass, or at most 3,000 parts by mass, per 100 parts by mass of the adsorbent precursor.

[0096] The heating temperature for growing the shell crystals may be, for example, 80° C. or more, 100° C. or more, 120° C. or more, 150° C. or more, or 180° C. or more, and 300° C. or less, 250° C. or less, 200° C. or less, 180° C. or less, or 150° C. or less. The heating time for growing the shell crystals may be, for example, 10 minutes or more, 20 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 4 hours or more, 6 hours or more, 8 hours or more, 12 hours or more, or 24 hours or more, and 72 hours or less, 48 ​​hours or less, 36 hours or less, 24 hours or less, 12 hours or less, 8 hours or less, 6 hours or less, 4 hours or less, or 2 hours or less.

[0097] Here, when the heating temperature is relatively high, the heating time may be relatively short, and when the heating time is relatively long, the heating temperature may be relatively low. For example, when the heating temperature is 80°C or higher and 150°C or lower, the heating time may be 6 hours or higher and 72 hours or lower. For example, when the heating temperature is 180°C or higher and 300°C or lower, the heating time may be 10 minutes or higher and 2 hours or lower.

[0098] <Cleaning and baking> The adsorbent of the present invention can be obtained in the manner described above. The obtained adsorbent may be washed and calcined, if necessary, before use.

[0099] The washing may be carried out with one or more solvents selected from, for example, water and organic solvents. Washing with a water-soluble organic solvent or a mixed solvent containing water and a water-soluble organic solvent is particularly preferred. The water-soluble organic solvent may be selected from, for example, methanol, ethanol, acetone, n-propanol, i-propanol, etc. This washing removes residual organic matter derived from the silicate-based oxide source, OSDA, etc.

[0100] The firing may be carried out, for example, at a temperature of 400°C to 800°C for a time of 1 hour to 12 hours. Air is sufficient as the ambient atmosphere during firing. This firing not only burns off any remaining organic matter that could not be removed by washing, but also has the advantage of fixing the shell to the surface of the core. [Example]

[0101] I. Influence of manufacturing method of core-shell composite The CO2 adsorption capacity of core-shell FAU-MFI composites (adsorbents) produced by various methods was investigated in Examples 1 to 6 and Comparative Examples 1 to 4. FAU has two types of composite structural units (CBUs): d6r and sod, and MFI has four types: mor, cas, mfi, and mel. Example 1 In Example 1, the MFI was deposited on the surface of the FAU by spray drying.

[0102] 1. Synthesis of core-shell FAU-MFI complex (1) Pretreatment of the FAU core surface (synthesis of PDADMAC-modified Na-FAU) 100 g of Na-FAU (SiO2 / Al2O3 molar ratio = 2.2, Na / Al = 0.65 (molar ratio), particle size 2-3 μm) was added to 1,330 g of water, and ultrasonic waves were applied for 2 hours. 5.6 g of PDADMAC (poly(diallyldimethylammonium chloride)) aqueous solution (35 mass%, Sigma-Aldrich) was added and stirred to modify the FAU surface with PDADMAC. The solid content was then collected by centrifugation to obtain PDADMAC-modified Na-FAU.

[0103] (2) Synthesis of nano-MFI shell 180 g of TEOS (tetraethyl orthosilicate) aqueous solution (SiO2 equivalent concentration 28 mass%, manufactured by Tokyo Chemical Industry Co., Ltd.) and 100 g of TPAOH (tetrapropylammonium hydroxide) aqueous solution (40 mass%, manufactured by Seichem Japan Co., Ltd.) as an organic structure directing agent (OSDA) were added to 100 g of water and mixed, and the mixture was maintained at 80°C with stirring for 96 hours to perform hydrothermal synthesis, thereby obtaining a dispersion containing a seed shell (MFI type silicate).

[0104] (3) Deposition of MFI on the FAU surface (synthesis of core-shell type FAU-MFI complex precursor) The PDADMAC-modified Na-FAU obtained in "(1) Pretreatment of the FAU Core Surface" was added to the dispersion containing the nano-MFI shell obtained in "(2) Synthesis of the Nano-MFI Shell" to obtain a mixture. While stirring, this mixture was spray-dried using a laboratory spray dryer (Okawahara Manufacturing Co., Ltd.) at a flow rate of 18 mL / min and a temperature of 200 °C to deposit a seed shell on the core surface. The resulting powder was collected to obtain a core-shell FAU-MFI composite precursor. The ratio of the mass of FAU in the mixture to the mass of TEOS in terms of SiO was 2.08.

[0105] (4) Crystal growth of the MFI shell (synthesis of core-shell type FAU-MFI composite) 8 g of TEOS aqueous solution, 1.3 g of TPAOH aqueous solution, and 33 g of ethanol were added to 143 g of water and stirred thoroughly to obtain an MFI shell precursor solution. 10 g of the core-shell FAU-MFI composite precursor obtained in "(3) Deposition of MFI on the FAU Surface" was added to the solution and sealed in a container. This container was then placed in an autoclave and rotated at 20 rpm while maintaining the temperature at 135°C for 24 hours to perform hydrothermal synthesis and grow shell crystals.

[0106] The solids in the reaction mixture were then recovered by centrifugation at 300 rpm and washed with water and acetone, in that order. These washes were carried out by adding water or acetone in an amount twice the mass of the solids, stirring for 15 minutes, and then centrifuging for 30 minutes. The washed solids were then recovered, dried at 100°C for 10 hours, and calcined at 550°C for 5 hours to obtain a core-shell FAU-MFI composite (adsorbent). The shell of the resulting core-shell FAU-MFI composite does not contain Al atoms, and therefore the SiO2 / Al2O3 molar ratio of the shell is ∞ (infinity).

[0107] (5)Analysis (5-1) Measurement of shell ratio The raw material Na-FAU and the core-shell FAU-MFI composite obtained above were observed using a field emission scanning electron microscope (FE-SEM). An FE-SEM image of Na-FAU is shown in Figure 1(a), and an FE-SEM image of the core-shell FAU-MFI composite is shown in Figure 1(b). A cross-sectional SEM image of the core-shell FAU-MFI composite obtained above is shown in Figure 2. This SEM image was taken after a cross section of the core-shell FAU-MFI composite powder was extracted using focused ion beam (FIB) processing. The FIB processing conditions were as follows: Pretreatment: After applying carbon paste to an aluminum sample stage, powder of the core-shell type FAU-MFI composite was sprinkled on the carbon paste, and then osmium (Os) was evaporated for 5 seconds. Protective film: C deposition Rough processing conditions: accelerating voltage 30 kV, probe current 1.2 nA Cleaning processing conditions: Accelerating voltage 30 kV (constant), probe current 0.75 nA → 0.26 nA → 41 pA (stepwise decrease)

[0108] Furthermore, the raw material FAU and the core-shell FAU-MFI composite were analyzed by X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS), respectively, to measure the shell ratio and shell coverage in the composite, taking advantage of the fact that the shell does not contain Al atoms. FT-IR analysis of the core-shell FAU-MFI composite was also performed.

[0109] The shell ratio of the core-shell type FAU-MFI complex was calculated using the following formula. Shell fraction (mass%) = SiO2(FAU-MFI) - [{Al2O3(FAU-MFI) / 101.96} × SAR(FAU) × 60.08]

[0110] The abbreviations in the above formulas have the following meanings: SiO2 (FAU-MFI): Silica content (mass%) in the core-shell FAU-MFI composite determined by XRF quantitative analysis Al2O3 (FAU-MFI): Alumina content (mass%) in the core-shell type FAU-MFI composite determined by XRF quantitative analysis SAR(FAU): SiO2 / Al2O3 molar ratio of raw FAU core Note that 101.96 and 60.08 are the formula weights of Al2O3 and SiO2, respectively.

[0111] (5-2) Measurement of shell coverage The shell coverage was determined by XPS analysis as follows. First, XPS analysis was performed on the raw material FAU and the obtained core-shell FAU-MFI composite, and the amount of Al exposed on the surface of each sample was measured as the area of ​​the Al2p peak (Al peak area) (λ = 74 eV). Next, the shell coverage was calculated from each obtained Al peak area using the following formula. Coverage (%) = {(Al peak area of ​​raw FAU - Al peak area of ​​FAU-MFI composite) / Al peak area of ​​raw FAU} × 100

[0112] In the FT-IR of the core-shell type FAU-MFI composite, the Si-O peak of the MFI skeleton (1,868 ± 70 cm) -1 ) peak intensity I Si-O The Si-OH peak (3,788 ± 50 cm -1 ) peak intensity I Si-OH / ratio(I Si-OH / I Si-O ) was calculated. Si-OH / I Si-O ) is thought to be smaller, the proportion of Si-OH is smaller, and therefore the number of defects in the shell is smaller.

[0113] The FT-IR measurement was performed in accordance with JIS K0117:2017 (General rules for infrared spectroscopic analysis) by the following procedure. The zeolite samples obtained in each Example or Comparative Example were pulverized in a mortar. 10 mg of the pulverized material was compression molded under a pressure of 10 MPa to prepare a disk sample with a diameter of 10 mm. FT-IR measurement of the obtained disk sample was performed under the following conditions. Measurement equipment: Fourier transform infrared spectrophotometer, "FT / IR-6600" manufactured by JASCO Corporation Measurement method: Transmission method Measurement wavelength range: 4,000 to 1,000 cm -1 Resolution: 4cm -1 Detector: Mid-band cadmium mercury telluride (MCT) detector Accumulation count: 64 times Measurement temperature: 500℃ Measurement atmosphere: 20% by volume O2 / N2 flow

[0114] The zeolite spectrum was measured using the following method: A disk sample similar to that described above was loaded into the sample chamber of the measurement device, and the temperature was raised from room temperature to 500°C at a rate of 20°C / min in a 20% by volume O2 / N2 flow, and the temperature was maintained at 500°C for 30 minutes before measurement.

[0115] (5-3) Measurement of the SiO2 / Al2O3 molar ratio of the core and shell The SiO2 / Al2O3 molar ratios of the core and shell of the core-shell FAU-MFI composites were measured by SEM-EDX. The following measuring equipment was used for the SEM-EDX measurement. Measurement equipment: Thermo Fisher, dual beam scanning electron microscope, model name "Helios G4UX (FIB-SEM)" SEM: 5kV / 0.1nA, WD4mm, Dwell time200ns, Resolution 1536×1024pixel EDS: 10kV, 0.8nA, Dwell time 150μs, 40 integrations, resolution 512 pixels (Map analysis)

[0116] Specifically, the measurement was carried out as follows. First, a cross-section of the core-shell FAU-MFI composite powder was analyzed by SEM in the same manner as in "(5-1) Measurement of the shell ratio" to obtain an SEM image. In the obtained SEM image, the core and shell portions of the adsorbent were defined based on the contrast of the image, and a virtual line passing through both the core and shell portions was set. Subsequently, EDX line analysis was carried out along the set imaginary line to measure the Si element concentration and Al element concentration (mass %) in each of the core portion and the shell portion. Then, the SiO2 / Al2O3 molar ratios of the core and shell were calculated from the obtained measurements.

[0117] (6) Evaluation of CO2 adsorption amount Approximately 0.1 g of the core-shell FAU-MFI composite was weighed out and placed in a sample tube of a catalyst analyzer "BELCAT II" (atmospheric pressure flow type) manufactured by Microtrac-Bell, Inc. The amount of CO2 adsorption was calculated from the difference in area of ​​the CO2 adsorption breakthrough curve between the presence of the sample and the blank. The measurement was carried out according to the following procedure. Heating: Helium gas flow rate 30 mL / min, temperature increase rate 10 °C / min from room temperature to 400 °C Isothermal treatment: Maintain a temperature of 400°C for 30 minutes in a He gas flow at a flow rate of 30 mL / min Cooling: In a He gas flow of 30 mL / min, the temperature was decreased from 400°C to 50°C at a rate of 20°C / min. Measurement of adsorption breakthrough curve: While maintaining the temperature at 50°C, a CO2-containing model gas was flowed at a flow rate of 5 mL / min to measure the CO2 adsorption breakthrough curve.

[0118] The composition of the CO2-containing model gas is as follows: CO2: 16% by volume H2O: 3% by volume He: Balance

[0119] The amount of CO2 adsorption was calculated by taking the difference between the cumulative area of ​​the CO2 adsorption breakthrough curve when the CO2-containing model gas was flowed and the blank area for 15 minutes, and assigning this difference to the mass of the FAU core in the sample, which was calculated by multiplying the mass of the sample (g) by (100 - shell ratio (%)).

[0120] The results are shown in Table 1. In Table 1, the SiO2 / Al2O3 molar ratio of the shell is shown as both the theoretical value based on the charge and the value actually measured by the above-mentioned method. The theoretical value of the SiO2 / Al2O3 molar ratio of the shell in Example 1 was ∞ (infinity).

[0121] Example 2 In Example 2, a core-shell type FAU-MFI complex was synthesized in the same manner as in Example 1, except that in "(4) Crystal growth of MFI shell," the conditions for growing the shell crystal were changed to 200°C and 30 minutes, and various evaluations were performed.

[0122] Example 3 In Example 3, MFI was deposited on the surface of FAU by hydrothermal synthesis.

[0123] In "(3) Deposition of MFI on the surface of FAU," MFI was deposited on the surface of FAU by hydrothermal synthesis according to the following procedure instead of spray drying. A core-shell type FAU-MFI composite was synthesized in the same manner as in Example 1, and various evaluations were performed.

[0124] Deposition of MFI on the surface of FAU by hydrothermal synthesis was carried out by the following procedure.

[0125] The PDADMAC-modified Na-FAU obtained in "(1) Pretreatment of the FAU core surface" was added to the dispersion containing the nano-MFI shell obtained in "(2) Synthesis of the nano-MFI shell" to obtain a mixture. This mixture was sealed in a container, placed in an autoclave, and left to stand at 80°C for 24 hours to perform hydrothermal synthesis. Here, the ratio of the mass of FAU in the mixture to the mass of TEOS in terms of SiO2 was 2.08.

[0126] The solids in the reaction mixture were collected by centrifugation at 300 rpm and washed with water and then with acetone. These washes were carried out by adding water or acetone in an amount twice the mass of the solids, stirring for 15 minutes, and then centrifuging for 30 minutes. The washed solids were then dried at 100°C for 12 hours to obtain a core-shell FAU-MFI composite precursor.

[0127] Example 4 In Example 4, a core-shell type FAU-MFI complex was synthesized in the same manner as in Example 3, except that in "(4) Crystal growth of MFI shell," the conditions for growing the shell crystal were changed to 200°C and 30 minutes, and various evaluations were performed.

[0128] Example 5 In Example 5, MFI was deposited on the surface of FAU by repeating the spray drying twice.

[0129] An intermediate of a core-shell FAU-MFI complex precursor was obtained by carrying out "(1) pretreatment of the FAU core surface," "(2) synthesis of a nano-MFI shell," and "(3) deposition of MFI on the FAU surface" in the same manner as in Example 1. Next, a core-shell FAU-MFI complex precursor was obtained by carrying out "(1) pretreatment of the FAU core surface," "(2) synthesis of a nano-MFI shell," and "(3) deposition of MFI on the FAU surface" again by the same procedure, except that the obtained intermediate of the core-shell FAU-MFI complex precursor was used instead of Na-FAU.

[0130] Using the above-obtained precursor of the core-shell FAU-MFI complex, the core-shell FAU-MFI complex was synthesized by carrying out "(4) Crystal growth of MFI shell" in the same manner as in Example 1, and various evaluations were carried out.

[0131] Example 6 In Example 4, MFI was deposited on the surface of FAU by repeating the hydrothermal synthesis twice.

[0132] An intermediate core-shell FAU-MFI complex precursor was obtained by carrying out "(1) Pretreatment of the FAU core surface," "(2) Synthesis of nano-MFI shell," and "(3) Deposition of MFI on the FAU surface" in the same manner as in Example 3. The supernatant obtained by centrifugation, which was performed to recover the solid content from the reaction mixture obtained in "(3) Deposition of MFI on the FAU surface," was stored.

[0133] The obtained core-shell type FAU-MFI composite precursor intermediate was dried at 100° C. for 12 hours.

[0134] Next, "(1) Pretreatment of the FAU core surface" was performed again using the same procedure, except that the dried intermediate of the core-shell type FAU-MFI complex precursor obtained above was used instead of Na-FAU.

[0135] A core-shell FAU-MFI complex precursor was obtained by performing "(3) Deposition of MFI on the FAU surface" again in the same manner as in Example 1, except that the pretreated intermediate obtained above was used instead of the PDADMAC-modified Na-FAU and the centrifuged supernatant stored above was used instead of the MFI shell precursor solution. A core-shell FAU-MFI complex was synthesized by performing "(4) Crystal growth of the MFI shell" in the same manner as in Example 1, except that the obtained core-shell FAU-MFI complex precursor was used, and various evaluations were performed.

[0136] Comparative Example 1 In Comparative Example 1, the core-shell type FAU-MFI composite precursor obtained by spray drying in the same manner as in Example 1 was subjected to various evaluations without carrying out "(4) Crystal growth of the MFI shell."

[0137] An FE-SEM image of the core-shell type FAU-MFI composite precursor obtained in Comparative Example 1 is shown in FIG.

[0138] Comparative Example 2 In Comparative Example 2, similarly to Example 2, the core-shell type FAU-MFI composite precursor obtained by hydrothermal synthesis was subjected to various evaluations without carrying out "(4) Crystal growth of MFI shell".

[0139] Comparative Example 3 Comparative Example 3 was carried out in the same manner as Comparative Example 2, except that the hydrothermal synthesis temperature was changed. That is, the autoclave temperature in the hydrothermal synthesis in "(3) Deposition of MFI on the surface of FAU" was set to 135°C, and the synthesis of a core-shell type FAU-MFI composite precursor was attempted in the same manner as Example 2. The obtained product was not subjected to "(4) Crystal growth of MFI shell," and the precursor was subjected to various evaluations as it was.

[0140] The product obtained in Comparative Example 3 did not have a core-shell structure, so "(6) Evaluation of CO2 adsorption amount" was not performed. It is presumed that the product obtained in Comparative Example 3 did not have a core-shell structure because there were areas where the shell silicate particles aggregated and the shell silicate grew into crystals of several μm in size.

[0141] Also, "ratio (I Si-OH / I Si-O ) column, the value "7.3" is listed, which is presumably due to the detection of Si-OH in the core in the FT-IR analysis.

[0142] Comparative Example 4 In Comparative Example 4, the core-shell FAU-MFI composite precursor obtained by repeating spray drying four times was subjected to various evaluations without undergoing "(4) Crystal growth of the MFI shell." Specifically, samples were prepared by the following procedure.

[0143] Similar to Example 1, "(1) Pretreatment of the FAU core surface," "(2) Synthesis of a nano-MFI shell," and "(3) Deposition of MFI on the FAU surface" were performed to obtain intermediate (1) of the core-shell FAU-MFI complex precursor. Next, the same procedures were repeated except that intermediate (1) of the core-shell FAU-MFI complex precursor was used instead of Na-FAU, and "(1) Pretreatment of the FAU core surface," "(2) Synthesis of a nano-MFI shell," and "(3) Deposition of MFI on the FAU surface" were performed again to obtain intermediate (2) of the core-shell FAU-MFI complex precursor. Furthermore, the same cycle was repeated four times, and a core-shell FAU-MFI complex precursor was obtained.

[0144] The obtained core-shell type FAU-MFI composite precursor was subjected to various evaluations as it was, without carrying out "(4) Crystal growth of MFI shell."

[0145] All the above results are shown in Table 1.

[0146] [Table 1]

[0147] As can be seen from Table 1, the adsorbent of the comparative example, in which no shell crystal growth was performed, had an insufficient CO2 adsorption capacity. In contrast, the adsorbent of the example, in which the shell crystal growth was appropriately performed to form a predetermined core-shell structure, exhibited a sufficiently large CO2 adsorption capacity.

[0148] <Evaluation of Hydrophobicity> The change in water adsorption rate over time was examined for each of the Na-FAU (FAU core) used as the core in the above examples and comparative examples, and the FAU-MFI composites obtained in examples 1 and 3 and comparative examples 1 and 2 under the following conditions. Pretreatment: Under a nitrogen stream, the temperature was raised to 400°C at a rate of 20°C / min. After reaching 400°C, the temperature was maintained for 60 minutes, and then the temperature was allowed to cool to 200°C. Measurement: FT-IR measurements were taken every 5 seconds while passing a stream of hydrated nitrogen at 200°C. Composition of hydrated nitrogen gas stream: 1.5% water (water vapor) by volume, nitrogen balance Flow rate of hydrated nitrogen gas: 200 mL / min

[0149] 1,655 cm originating from the OH plagioclase vibration -1 The peak area around the peak was used as an index of the amount of water adsorption, and the ratio of the peak area at each measurement time to the peak area at saturated adsorption was calculated, and this was taken as the water adsorption rate. The peak area at saturated adsorption was the value at which the peak area no longer changed even after continued measurement under a stream of hydrated nitrogen.

[0150] Figure 4 shows FT-IR charts measured for the FAU core and the sample of Example 1 60 seconds after the start of the flow of the hydrated nitrogen gas. Figure 5 also shows the change in water adsorption rate over time for each sample. In Figure 5, the samples with lines to the right have slower water adsorption rates and therefore higher hydrophobicity.

[0151] Referring to Table 1, the following can be seen:

[0152] The shell ratio and the covering rate are in a nearly proportional relationship except for Comparative Example 3.

[0153] The coverage is 75% or more, and the ratio (I Si-OH / I Si-O It was confirmed that when the value of ) is 3.0 or less, the amount of CO2 adsorption is large.

[0154] On the other hand, in the sample of Comparative Example 4, the amount of CO2 adsorption was insufficient despite the coverage rate of 97%. Si-OH / I Si-O ) is higher than 3.0. Si-OH / I Si-O ) values ​​are high, suggesting that there are many defects in the shell. This may be due to the fact that the shell is prone to agglomeration, preventing CO2 from passing through the shell and reaching the FAU core.

[0155] 5, the lines showing the change in water adsorption rate over time for the samples of Examples 1 and 3 are to the right of the lines for the samples of Comparative Examples 1 and 2. This shows that the samples of Examples 1 and 3 are more hydrophobic than the samples of Comparative Examples 1 and 2.

[0156] Comparing the results in Figure 5 with those in Table 1, it is understood that the CO2 adsorption capacity of the FAU-MFI composite is correlated with its hydrophobicity. That is, the FAU-MFI composites of Comparative Examples 1 and 2 have low hydrophobicity, and the CO2 adsorption sites are presumably poisoned with water, preventing CO2 adsorption. In contrast, the FAU-MFI composites of Examples 1 and 3 have high hydrophobicity, and the CO2 adsorption sites are free and not poisoned with water, presumably resulting in high CO2 adsorption capacity.

[0157] However, the present invention is not bound by any particular theory.

[0158] II. The influence of common composite structural units The CO adsorption amounts of the core-shell composite (adsorbent) obtained in Example 1 and the adsorbents of Comparative Examples 5 and 6 below were compared to investigate the influence of the common composite structural unit (CBU) between the zeolites constituting the core and shell, respectively.

[0159] Comparative Example 5 Commercially available Na-BEA (SiO2 / Al2O3 molar ratio=50, Na / Al=0.65 (molar ratio), particle size 2-3 μm) was used as it was as the adsorbent of Comparative Example 5, and the CO2 adsorption amount was measured in the same manner as in Example 1.

[0160] BEA has three complex structural units (CBUs): mor, d4r, and mtw.

[0161] Comparative Example 6 In "1. Synthesis of core-shell type FAU-MFI composite," a core-shell type BEA-MFI composite (adsorbent) was obtained in the same manner as in Example 1, except that the same Na-BEA used in Comparative Example 5 was used instead of the FAU core. The shell ratio of the obtained BEA-MFI composite was measured using the same method as in Example 1 and was found to be 30 mass%.

[0162] There are four types of MFI CBUs: mor, cas, mfi, and mel.

[0163] The CO2 adsorption amounts of the above adsorbents are shown in Table 2.

[0164] [Table 2]

[0165] In the core-shell BEA-MFI composite of Comparative Example 6, the BEA constituting the core and the MFI constituting the shell share a common CBU, "mor." The adsorbent of Comparative Example 6 exhibited only a slight improvement in CO2 adsorption capacity compared to the adsorbent of Comparative Example 5, which did not have a shell.

[0166] In contrast, in the core-shell type FAU-MFI composite of Example 1, the FAU constituting the core and the MFI constituting the shell do not have a common CBU. The adsorbent of Example 1 has an extremely large CO2 adsorption capacity.

[0167] From the above, it has been verified that the CO2 adsorption capacity of the adsorbent of the present invention is significantly improved because the structure of the zeolite constituting the core and the structure of the zeolite constituting the shell do not have common composite structural units.

Claims

1. An adsorbent having a core-shell structure, the core is made of zeolite; The shell satisfies the following requirements (A) to (C): (A) Silicate or SiO ２ / Al ２ O ３ a silicate-based oxide composed of an aluminosilicate having a molar ratio of 750 or more; (B) having a zeolite structure, and (C) The Si—O peak ((1,868±70) cm ) in the FT-IR of the adsorbent. －１ ) peak intensity I Ｓｉ－Ｏ The Si-OH peak ((3,788±50) cm －１ ) peak intensity I Ｓｉ－ＯＨ The ratio (I Ｓｉ－ＯＨ / I Ｓｉ－Ｏ ) is 3.0 or less All of the above are satisfied, and The zeolite constituting the core has a skeletal structure selected from FAU, AEI, and CHA, and the zeolite constituting the shell has a skeletal structure selected from BEA and MFI. Adsorbent material.

2. SiO of the zeolite that constitutes the core ２ / Al ２ O ３ 2. The adsorbent of claim 1, wherein the molar ratio is 20 or less.

3. 2. The adsorbent according to claim 1, wherein the zeolite constituting the core has a framework structure of FAU.

4. The substance to be adsorbed by the adsorbent is CO ２ The adsorbent according to claim 1, wherein

5. 2. The adsorbent according to claim 1, wherein an alkali metal or alkaline earth metal is supported on the zeolite constituting the core.

6. 2. The adsorbent according to claim 1, wherein the particle size of the zeolite constituting the core is 1.0 μm or more and 5.0 μm or less.

7. 2. The adsorbent according to claim 1, wherein the silicate-based oxide constituting the shell has a framework structure of MFI.

8. 2. The adsorbent according to claim 1, wherein the thickness of the shell measured by electron microscopy is 100 nm or more and 1,000 nm or less.

9. The structure of the zeolite constituting the core has a framework structure of FAU, and The structure of the zeolite constituting the shell has a framework structure of MFI. The adsorbent of claim 1.

10. The adsorbent according to any one of claims 1 to 9, wherein the shell has a coverage of 75% or more.

11. A method for producing the adsorbent according to any one of claims 1 to 9, a core composed of zeolite; Silicate or SiO ２ / Al ２ O ３ a silicate-based oxide composed of an aluminosilicate having a molar ratio of 750 or more; contacting the depositing a seed shell composed of the silicate-based oxide on the surface of the core to synthesize an adsorbent precursor; and heating the adsorbent precursor in the presence of a silicate-based oxide source and an organic structure-directing agent to grow a shell crystal; Including, The structure of the zeolite constituting the core has a framework structure selected from FAU, AEI, and CHA, The shell has a zeolite structure, and the zeolite structure has a framework structure selected from BEA and MFI. Method for manufacturing adsorbent.

12. synthesizing the adsorbent precursor, by spray drying a mixture of the core and the silicate-based oxide; A method for producing the adsorbent according to claim 11.

13. synthesizing the adsorbent precursor, by heating a mixture of the core and the silicate-based oxide; A method for producing the adsorbent according to claim 11.

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