Zeolite membrane structure

Abstract

A zeolite membrane structure (10) includes a support (20), a zeolite membrane (30), and a protective film (40). The zeolite membrane (30) is formed on a surface (23S) of the support (20). The protective film (40) is formed on a surface (30S) of the zeolite membrane (30). The protective film (40) is composed of organic-inorganic hybrid silica or carbon.

Description

[0001] This application is a divisional application of the invention patent application with application number 201680013539.8 (international application number PCT / JP2016 / 059047), application date March 22, 2016, entitled "Zeolite Membrane Structure". Technical Field

[0002] This invention relates to a zeolite membrane structure having a zeolite membrane. Background Technology

[0003] Ceramic filters with zeolite membranes formed on a support have superior mechanical strength compared to polymer membranes, and are therefore suitable for separating or concentrating desired components from liquid mixtures or gas mixtures (see, for example, Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2013 / 054794 Summary of the Invention

[0007] However, there is still room for improvement in the durability of zeolite membranes.

[0008] The present invention was carried out in view of the above-mentioned situation, and its object is to provide a zeolite membrane structure that can improve durability.

[0009] The zeolite membrane structure of this invention includes a support, a zeolite membrane, and a protective membrane. The zeolite membrane is formed on the surface of the support. The protective membrane is formed on the surface of the zeolite membrane. The protective membrane is composed of organic-inorganic hybrid silicon dioxide or carbon.

[0010] According to the present invention, a zeolite membrane structure with improved durability can be provided. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of a zeolite membrane structure. Detailed Implementation

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following drawings, the same or similar parts are given the same or similar symbols. However, the drawings are schematic diagrams, and the ratios of various dimensions may sometimes differ from actual size ratios. Therefore, specific dimensions should be determined with reference to the following description. Furthermore, the drawings naturally include portions with different dimensional relationships and ratios.

[0013] (Composition of the separation membrane structure 10)

[0014] Figure 1 This is a cross-sectional view showing the composition of the separation membrane structure 10. The separation membrane structure 10 includes: a support 20, a zeolite membrane 30, and a protective membrane 40.

[0015] The support 20 supports the zeolite membrane 30. The support 20 has chemical stability that enables the zeolite membrane 30 to be formed (crystallized, coated, or precipitated) into a film. The support 20 only needs to be shaped to supply the mixed fluid to be separated to the zeolite membrane 30. Examples of shapes for the support 20 include: honeycomb, monolithic, flat, tubular, cylindrical, cylindrical, and prismatic.

[0016] In this embodiment, the support 20 has a base 21, an intermediate layer 22 and a surface layer 23.

[0017] The matrix 21 is composed of a porous material. Examples of porous materials include sintered ceramics, metals, organic polymers, glass, and carbon. Examples of sintered ceramics include alumina, silicon dioxide, andalusite, zirconium oxide, titanium dioxide, yttrium oxide, silicon nitride, and silicon carbide. Examples of metals include aluminum, iron, bronze, silver, and stainless steel. Examples of organic polymers include polyethylene, polypropylene, polytetrafluoroethylene, polysulfone, and polyimide.

[0018] The matrix 21 may contain an inorganic binder. As an inorganic binder, at least one of titanium dioxide, andalusite, easily sinterable alumina, silica, glass frit, clay minerals, and easily sinterable cordierite may be used.

[0019] The average pore size of the matrix 21 can be, for example, 5 μm to 25 μm. The average pore size of the matrix 21 can be measured using a mercury porosimeter. The porosity of the matrix 21 can be, for example, 25% to 50%. The average particle size of the porous material constituting the matrix 21 can be, for example, 5 μm to 100 μm. The average particle size of the matrix 21 is obtained by arithmetic averaging the maximum diameters of 30 test particles measured using SEM (scanning electron microscopy) to observe the cross-sectional microstructure.

[0020] An intermediate layer 22 is formed on the surface 21S of the substrate 21. The intermediate layer 22 can be made of the aforementioned porous material suitable for use with the substrate 21. The average pore size of the intermediate layer 22 can be smaller than the average pore size of the substrate 21, for example, it can be 0.005 μm to 2 μm. The average pore size of the intermediate layer 22 can be measured using a pore size distribution measuring device. The porosity of the intermediate layer 22 can be, for example, 20% to 60%. The average thickness of the intermediate layer 22 can be, for example, 30 μm to 300 μm.

[0021] Surface layer 23 is formed on the surface 22S of intermediate layer 22. Surface layer 23 can be made of the aforementioned porous material suitable for use in substrate 21. The average pore size of surface layer 23 can be smaller than that of intermediate layer 22, for example, it can be 0.001 μm to 0.5 μm. The average pore size of surface layer 23 can be measured using a pore size distribution measuring instrument. The porosity of surface layer 23 can be, for example, 20% to 60%. The average thickness of surface layer 23 can be, for example, 1 μm to 50 μm.

[0022] Surface 23 has a surface 23S in contact with the zeolite film 30. Surface 23S is the outermost surface of the support 20. The surface roughness Ra of surface 23S is preferably 2.13 μm or less. The surface roughness Ra of surface 23S is preferably 0.29 μm or more. The surface roughness Ra of surface 23S can be determined by using a 25 μm long cross-sectional curve obtained by SEM according to the method in JIS B 0601.

[0023] Zeolite film 30 is formed on surface 23S of surface layer 23. The framework structure (type) of zeolite contained in zeolite film 30 and used as the main component is not particularly limited, and examples include: MFI, LTA, CHA, DDR, MOR, DOH, FAU, OFF / ERI, LTL, FER, BEA, BEC, CON, MSE, MEL, MTW, MEI, MWW, RHO, BOG, SZR, EMT, SOD, AEI, AEL, AEN, AET, AFN, AFO, AFR, AFS, AFT, AFI, AFX, ANA, CAN, GIS, GME, HEU, JBW, KFI, LAU, LEV, MAZ, MER, MFS, MTT, PHI, SFG, TUN, TON, UFI, VET, VFI, VNI, and VSV, etc. In particular, MFI, DDR, MEL, BEA, CHA, MOR, FAU, LTA, FER, and SOD, which are zeolites that are easy to crystallize, are preferred, and MFI, DDR, MEL, BEA, and CHA, which have high chemical stability, are especially preferred.

[0024] In this embodiment, the inclusion of substance Y as a "main component" in composition X means that substance Y preferably accounts for 60% or more by weight, more preferably 70% or more by weight, and even more preferably 90% or more by weight in the whole composition X.

[0025] Zeolite membrane 30 may contain inorganic binders (silica, alumina, etc.), organic binders (polymers, etc.) and silanizing agents, etc.

[0026] There are no particular restrictions on the Si / Al atomic ratio in the zeolite film 30; for example, it can be 1.5 or higher. The zeolite film 30 can be composed of high-silica zeolite with a Si / Al atomic ratio of 200 or higher. This high-silica zeolite contains almost no or no aluminum and has high corrosion resistance and few film defects. The Si / Al atomic ratio in the zeolite film 30 can be adjusted by controlling the reaction solution and reaction conditions used for hydrothermal synthesis. The Si / Al atomic ratio in the zeolite film 30 can be determined by SEM-EDX (scanning electron microscopy-energy dispersive X-ray spectrometry).

[0027] The average thickness of the zeolite membrane 30 is not particularly limited, and can be, for example, from 0.1 μm to 10 μm. If the zeolite membrane 30 is made thinner, there is a tendency for increased permeation. If the zeolite membrane 30 is made thicker, there is a tendency for increased selectivity and membrane strength. The thickness of the zeolite membrane 30 can be adjusted by controlling the hydrothermal synthesis time.

[0028] The zeolite membrane 30 has fine pores. The average pore size of the zeolite membrane 30 is not particularly limited, and can be determined based on the liquid mixture or gas mixture to be separated. The average pore size of the zeolite membrane 30 can be adjusted by changing, for example, the type and size of the structure-directing agent or template, to determine the zeolite's framework structure. The average pore size of the zeolite membrane 30 can, for example, be 0.2 nm to 2.0 nm. The average pore size of the zeolite membrane 30 can have both a major and minor axis. For example, the minor axis of the pores in a DDR-type zeolite membrane is 0.36 nm, and the major axis is 0.44 nm.

[0029] The zeolite film 30 has a surface 30S that contacts the protective film 40. The surface roughness Ra of surface 30S is not particularly limited, but is preferably 1.74 μm or less. This improves the peel strength of the protective film 40, which will be described later. The surface roughness Ra of surface 30S is preferably 0.28 μm or more. This improves the tightness of contact between the zeolite film 30 and the protective film 40. The surface roughness Ra of surface 30S can be determined using a 25 μm cross-sectional curve obtained by SEM according to the method in JIS B 0601.

[0030] A protective film 40 is formed on the surface 30S of the zeolite membrane 30. The protective film 40 covers the surface 30S of the zeolite membrane 30. This prevents water and water vapor contained in the liquid mixture or gas mixture to be separated from directly contacting the zeolite membrane 30. Therefore, it is possible to suppress defects caused by a portion of the zeolite membrane 30 dissolving into water or water vapor.

[0031] The protective film 40 is composed of organic-inorganic hybrid silicon dioxide material or carbon material.

[0032] Organic-inorganic hybrid silica materials are materials obtained by the chemical combination of organic and inorganic components, or materials in a mixed state of organic and inorganic components. As organic-inorganic hybrid silica materials, substances obtained by hydrolysis and dehydration condensation of silane coupling agents or alkoxysilanes can be used. More specifically, substances with the structural formula (C2H5O)3SiC can be used. n H 2n The substance is obtained by hydrolysis and condensation of bis(triethoxysilyl) compounds of Si(C2H5O)3 (n≥1). This substance is in a state of chemical bonding between organic components and inorganic components containing silicon.

[0033] As a carbon material, materials known for use in separation membranes can be used. Details regarding the materials used in separation membranes are described in Japanese Patent Application Publication No. 2003-286018.

[0034] The organic-inorganic hybrid silica and carbon material is a porous, water-resistant material. Therefore, it can also suppress defects in the protective film 40 caused by water and water vapor contained in the liquid mixture or gas mixture being separated.

[0035] The average thickness of the protective film 40 can be from 30 nm to 300 nm. Preferably, the average thickness of the protective film 40 is 172 nm or less. This helps to suppress cracking of the protective film 40 and the zeolite film 30 during the drying and firing processes described later. Preferably, the average thickness of the protective film 40 is 44 nm or more. This further improves the durability of the protective film 40.

[0036] In this embodiment, the “average thickness” of each membrane is the arithmetic mean of the thickness at any 10 locations, obtained by observing the cross-sectional microstructure using a TEM (Transmission Electron Microscope).

[0037] (Manufacturing method of separation membrane structure)

[0038] The manufacturing method of the separation membrane structure 10 will be described below.

[0039] First, a molded body of the substrate 21 with the desired shape is formed by extrusion molding, compression molding, casting molding, or other methods. Next, the molded body of the substrate 21 is fired (for example, at 900°C to 1450°C) to form the substrate 21.

[0040] Next, an intermediate layer slurry prepared using ceramic raw materials of the desired particle size is deposited on the surface 21S of the substrate 21, thereby forming a molded body of the intermediate layer 22. Next, the molded body of the intermediate layer 22 is fired (e.g., 900°C to 1450°C) to form the intermediate layer 22.

[0041] Next, a surface slurry prepared using ceramic raw materials of the desired particle size is formed on the surface 22S of the intermediate layer 22, thereby forming a molded body of the surface layer 23. Next, the molded body of the surface layer 23 is fired (e.g., 900°C to 1450°C) to form the surface layer 23.

[0042] Next, the seed crystals obtained by dispersing zeolite seed crystals in alcohol are introduced into the surface 23S of the surface layer 23 by means of flow-down method, impregnation method, etc.

[0043] Next, a support 20 with zeolite seed crystals is impregnated in a pressure-resistant container containing a raw material solution including a silica source, an alumina source, an alkali source, and water. The raw material solution may contain an organic template.

[0044] Next, the pressure-resistant container is placed in a desiccator and heated at 100-200°C (hydrothermal synthesis) for about 1-240 hours, thereby causing the zeolite seed crystals to crystallize and grow into a film.

[0045] Next, the support 20 on which the zeolite film 30 is formed is cleaned and dried at 80–100°C. Then, with the organic template contained in the raw material solution, the support 20 is placed in an electric furnace and heated in the atmosphere (400–800°C, 1–200 hours), thereby burning off the organic template.

[0046] Next, a protective film 40 is formed on the surface 30 of the zeolite film 30. The method for forming an organic-inorganic hybrid silica film as the protective film 40 will be described below.

[0047] First, organic-inorganic hybrid silica obtained by hydrolysis, dehydration and condensation of silane coupling agents or alkoxysilanes is dispersed in solvents such as alcohols to prepare a sol.

[0048] Next, the sol is coated onto the surface of the zeolite film 30 for 30 seconds, and then dried by ventilation. The preferred air velocity at this time is 5.0 m / s to 10 m / s, more preferably 6.0 m / s to 9.0 m / s. This allows for appropriate drying at room temperature. Furthermore, the preferred air temperature is 10°C to 80°C. This helps to suppress cracking of the film surface and allows for rapid drying. Additionally, the dew point is preferably lower than the supply air temperature, for example, -70°C to 70°C. To lower the dew point temperature, a dehumidifying rotor with a honeycomb structure firmly bonded to the adsorbent can be used to adsorb the remaining moisture. By drying the sol with supplied air in this way, a uniform sol coating film can be formed. Furthermore, compared to the case of natural drying of the sol, it is possible to achieve uniform coating thickness, rapid drying of the coating film, and suppression of condensation.

[0049] Next, the dried sol is heated at 300℃~350℃ in a reducing atmosphere to form an organic-inorganic hybrid silica film.

[0050] (Other implementation methods)

[0051] In the above embodiments, the support 20 has a base 21, an intermediate layer 22 and a surface layer 23. However, it may not have one or both of the intermediate layer 22 and the surface layer 23.

[0052] When the support 20 does not have a surface layer 23, the zeolite film 30 is formed on the surface 22S of the intermediate layer 22. In this case, the surface roughness Ra of the surface 22S is preferably 2.13 μm or less, and preferably 0.29 μm or more.

[0053] When the support 20 does not have either the intermediate layer 22 or the surface layer 23, the zeolite film 30 is formed on the surface 21S of the substrate 21. In this case, the surface roughness Ra of the surface 21S is preferably 2.13 μm or less, and preferably 0.29 μm or more.

[0054] In the above embodiments, zeolite seed crystals are used to form the zeolite film 30. However, the zeolite film 30 can also be formed without using zeolite seed crystals.

[0055] Example

[0056] The following describes embodiments of zeolite membrane structures. However, the present invention is not limited to the embodiments described below.

[0057] (Production of samples No. 1 to 8, 13)

[0058] The following describes the zeolite membrane structure involved in the fabrication of sample No.1.

[0059] First, 20 parts by mass of inorganic binder are added to 100 parts by mass of alumina particles with an average particle size of 50 μm. Then, water, dispersant and thickener are added and the mixture is kneaded to produce a green body.

[0060] Next, the green body is extruded and molded to obtain a molded body with a monolithic matrix having multiple through holes. Then, the molded body is fired (1250°C, 1 hour).

[0061] Next, PVA (organic binder) was added to alumina and titanium dioxide with an average particle size of 50 μm to prepare a slurry for the intermediate layer. The intermediate layer was then formed on the inner surface of each through-hole by filtration. The intermediate layer was then fired (1250 °C, 2 hours) to form the intermediate layer.

[0062] Next, a surface layer slurry was prepared using alumina with an average particle size of 0.3 μm to 0.6 μm (refer to Table 1). The surface layer was then formed on the inner surface of each intermediate layer using either a filtration or flow-through method (refer to Table 1). For samples using the filtration method, PVA (organic binder) was added to the alumina to prepare the surface layer slurry. The amount of PVA added was adjusted for each sample to adjust the surface roughness Ra of the surface layer as shown in Table 1. For samples using the flow-through method, the surface layer slurry was prepared without adding PVA. This flow-through method resulted in a smoother surface layer than the filtration method. The time for plasticizing the surface layer slurry in a ball mill was varied for each sample to adjust the surface roughness Ra of the surface layer as shown in Table 1. The surface layer was then fired to form the surface layer. The support was thus completed through these operations.

[0063] Next, the DDR-type zeolite powder prepared according to the method described in International Publication No. 2010 / 090049A1 will be pulverized, and the pulverized material will be used as a nucleus to prepare DDR-type zeolite seed crystals (hereinafter referred to as seed crystals).

[0064] Next, while stirring, the dispersion obtained by dispersing the seed crystals in water is added dropwise to ethanol to prepare a slurry for introducing the seed crystals.

[0065] Next, seed slurry is injected into a wide-mouthed funnel positioned above the vertically placed support. The seed slurry flowing from the outlet of the funnel flows into the through holes of the support. Then, room temperature air is introduced into each through hole to dry the seed slurry.

[0066] Next, an ethylenediamine solution containing 1-adamantaneamine was added to the silica dispersion and stirred. Ion-exchanged water was then added to the stirred solution to dilute it and prepare the raw material solution for membrane formation.

[0067] Next, a support with seed crystals is placed in a stainless steel pressure vessel with an inner fluororesin cylinder, and a prepared film-forming raw material solution is placed inside and heated (hydrothermal synthesis). This forms a DDR-type zeolite film containing 1-adamantaneamine on the inner surface of the through-holes of the support.

[0068] Next, the support on which the DDR-type zeolite film containing 1-adamantaneamine is formed is heated and the 1-adamantaneamine is removed by combustion.

[0069] Next, while maintaining the water temperature at 3°C, 11.34g of BTESE (bis(triethoxysilyl) compound: structural formula (C2H5O)3SiC) was added. n H 2nSi(C2H5O)3 (n≥1: manufactured by Gelest) and 29.53 g of ethanol were mixed and stirred (A). 0.56 g of nitric acid was added to 3.02 g of water (B). B was added dropwise to A and stirred at 60 °C for 3 hours (C). Ethanol was added to C to adjust the solid content to 0.12% to 0.36% by mass (refer to Table 1), thus obtaining the protective film raw material sol.

[0070] Next, similar to the coating process for the seed crystal introduction slurry, the protective film raw material sol is flowed into the inner side of the DDR type zeolite film. Then, air at 23°C (dew point: -21°C) is introduced into each through hole at a wind speed of 7.5 m / s for 30 minutes to dry the protective film raw material sol.

[0071] Next, the dried protective film raw material sol is calcined at 350°C for 1 hour in a N2 atmosphere, thereby forming an organic-inorganic hybrid silica film.

[0072] (Preparation of samples No. 9-12)

[0073] First, the support and DDR-type zeolite membrane were manufactured using the same process as samples No.1 to No.8.

[0074] Next, 4.00 g of phenolic resin (Bellpearl S899: manufactured by Air Water) and 196.00 g of ethanol were mixed and stirred. Then, ethanol was added to adjust the solid content to 0.12% to 0.36% by mass (refer to Table 1) to obtain the protective film raw material sol.

[0075] Next, similar to the coating process for the seed crystal introduction slurry, the protective film raw material sol is flowed into the inner side of the DDR type zeolite film. Then, air at 23°C (dew point: -21°C) is introduced into each through hole at a wind speed of 7.5 m / s for 30 minutes to dry the protective film raw material sol.

[0076] Next, the dried protective film raw material sol is calcined at 500°C for 1 hour in a N2 atmosphere to form a carbon film.

[0077] (Production of Sample No. 14)

[0078] The support and DDR-type zeolite membrane were manufactured using the same process as samples No.1 to No.8, but no protective film was formed covering the DDR-type zeolite membrane.

[0079] (Determination of surface roughness Ra of the surface layer)

[0080] For each sample, the surface cross-section of the surface layer was observed by SEM, and the surface roughness Ra of the surface in contact with the DDR type zeolite film was determined according to the method of JIS B0601 using a 25 μm long cross-sectional curve. The measurement results are shown in Table 1.

[0081] (Determination of surface roughness Ra of DDR type zeolite separation membrane)

[0082] For each sample, the cross-section of the DDR-type zeolite film surface was observed by SEM, and the surface roughness Ra of the surface in contact with the protective film was determined according to JIS B 0601 using a 25 μm long cross-sectional curve. The measurement results are shown in Table 1.

[0083] (Average thickness of the protective film)

[0084] For samples No. 1 to No. 13, the cross-section of the protective film was observed by TEM, and the arithmetic mean of the thickness at any 10 points was calculated. The calculation results are shown in Table 1.

[0085] (Determination of water permeability and separation coefficient)

[0086] For each sample, a mixture of water and acetic acid at 90°C (weight ratio of 95:5) was supplied to the compartment, and vapor permeating through the membrane at a pressure of 50 torr on the permeate side of the compartment was recovered using a liquid N2 trap.

[0087] The composition of the permeate recovered after 5 hours was analyzed by neutralization titration, thereby calculating the water permeate volume and acetic acid concentration. The separation coefficient (α5) was calculated based on the formula (permeate water concentration / permeate acetic acid concentration) / (feed water concentration / feed acetic acid concentration). The water permeate volume and separation coefficient after 5 hours are shown in Table 1.

[0088] Furthermore, the composition of the permeate recovered after 500 hours was analyzed by neutralization titration, thereby calculating the water permeate volume and acetic acid concentration. The separation coefficient (α500) was calculated based on the formula (permeate water concentration / permeate acetic acid concentration) / (feed water concentration / feed acetic acid concentration). Then, the retention rate (α500 / α5) of the separation coefficient (α500) after 500 hours relative to the separation coefficient (α5) after 5 hours was calculated. The retention rates of the separation coefficient after 500 hours are shown in Table 1.

[0089] (Peel strength of the protective film)

[0090] For samples No. 1 to 13, a peel strength test of the protective film was conducted to determine the tight contact force between the protective film and the zeolite film. Specifically, the evaluation was performed using a bolt-pulse peel strength tester for film tight contact strength (manufactured by Phototechnica, trade name Romulus).

[0091] Table 1

[0092]

[0093] As shown in Table 1, for samples No. 1 to 13, which had zeolite membranes covered with protective films, the retention rate of the separation coefficient (α500 / α5) was improved compared to sample No. 14, which did not have a protective film formed. Therefore, it is confirmed that forming a protective film on the zeolite membrane improves the durability of the zeolite membrane structure.

[0094] Furthermore, for samples No. 1–7, 9–11, and 13 with an average protective film thickness of less than 172 nm, the separation coefficient (α5) was improved after 5 hours compared to samples No. 8 and 12 with an average protective film thickness greater than 172 nm. This is because suppressing the thickness of the protective film can inhibit cracking of the protective film during the drying and firing processes.

[0095] Furthermore, for samples No. 1–6 and 8–13 with an average protective film thickness of 44 nm or more, the separation coefficient retention rate (α500 / α5) was improved compared to sample No. 7 with an average protective film thickness of less than 44 nm. This is because ensuring sufficient protective film thickness helps to prevent peeling of the protective film during prolonged use.

[0096] Furthermore, for samples No. 1 to 12, which achieved a surface roughness Ra of 1.74 μm or less by reducing the surface roughness Ra of the zeolite film to 2.13 μm or less, the peel strength was improved compared to sample No. 13, which had a surface roughness Ra of 1.96 μm. This is because reducing the surface roughness Ra makes the thickness of the protective layer more uniform, thereby reducing the residual stress in the protective layer.

[0097] Industrial availability

[0098] According to the present invention, the durability of the zeolite membrane structure can be improved, making it useful in the field of separation membranes.

[0099] Symbol Explanation

[0100] 10 Zeolite Membrane Structure

[0101] 20 supports

[0102] 21 matrix

[0103] 22 intermediate layers

[0104] 23 Surface

[0105] 30 zeolite membrane

[0106] 40 protective film

Claims

1. A zeolite membrane structure, comprising: Support structure; A zeolite membrane is formed on the surface of the support. as well as A protective film is formed on the surface of the zeolite film and is composed of organic-inorganic hybrid silicon dioxide or carbon. The protective film, composed of organic-inorganic hybrid silicon dioxide, has an average thickness of 59 nm to 91 nm. The average thickness of the protective film made of carbon is 69 nm to 98 nm. The surface roughness Ra of the zeolite film is 0.33 μm to 1.36 μm. The surface roughness Ra of the surface of the support is 0.35 μm to 1.63 μm.

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