Separation membrane and membrane reactor

Abstract

The present invention addresses the problem of providing a separation membrane capable of selectively separating methanol with high efficiency from a gas containing carbon dioxide, hydrogen, and methanol. This separation membrane is provided with a separation layer containing MFI zeolite. In the MFI zeolite, the ratio I200 / I104 of the intensity I200 of a diffraction peak of a (200) plane to the intensity I104 of a diffraction peak of a (104) plane by X-ray diffraction measurement is 0.05-1.5, and the number-based cumulative particle diameter D50 at a cumulative number of 50% in a particle size distribution obtained by analyzing an image obtained by laser microscope observation is 2-10 µm.

Description

Separation membranes and membrane reactors

[0001] This invention relates to separation membranes and membrane reactors.

[0002] Zeolites are usually in powder form, but it has been proposed to form them into membranes and use them as separation membranes. For example, Patent Document 1 proposes using an MFI zeolite separation membrane to separate ethanol from a mixed solution of water and ethanol. In this separation membrane, the separation efficiency of water and ethanol is improved by orienting the c-axis of the MFI zeolite in a specific direction.

[0003] Patent Document 2 proposes using an MFI zeolite separation membrane to separate linear hydrocarbons from a hydrocarbon mixture containing linear hydrocarbons and branched or cyclic hydrocarbons with equal carbon numbers. In this separation membrane, the separation efficiency of hydrocarbons is increased by setting the ratio of diffraction peaks in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the MFI zeolite to a specific value.

[0004] Patent document 3 describes a technique for selectively separating methanol and water from carbon dioxide and hydrogen by supporting a separation membrane on a porous material support. The separation membrane consists of a ZSM-5 type zeolite membrane with a Si / Al ratio of 10 to 20.

[0005] US2008 / 217240A1US2018 / 200679A1JP2024-68972A

[0006] In recent years, as part of efforts to prevent global warming by reducing carbon dioxide emissions, various methods have been considered to synthesize methanol by reacting carbon dioxide and hydrogen, as described in Patent Document 3. However, the methanol produced needs to be separated from the raw materials, carbon dioxide and hydrogen, but the technology described in the same document did not have sufficient methanol separation efficiency.

[0007] Therefore, the object of the present invention is to provide a separation membrane capable of selectively separating methanol from a gas containing carbon dioxide, hydrogen, and methanol with high efficiency.

[0008] The present invention relates to a separation membrane comprising a separation layer containing an MFI zeolite, wherein the MFI zeolite has an intensity I of the diffraction peak of the (104) plane as measured by X-ray diffraction. １０４ The intensity of the diffraction peak at the (200) plane relative to ２００ Ratio I ２００ / I １０４ The particle size is between 0.05 and 1.5, and the cumulative particle size D at 50% of the cumulative number of particles in the particle size distribution obtained by analyzing images obtained by laser microscopy observation is also obtained. ５０ The present invention provides a separation membrane having a thickness of 2 μm or more and 10 μm or less.

[0009] The present invention also provides a membrane reactor comprising the separation membrane and a catalyst layer provided on the separation layer in the separation membrane.

[0010] Furthermore, the present invention relates to a method for producing a separation membrane, comprising the steps of immersing a porous support to which seed crystals of MFI zeolite are attached in an aqueous gel containing a silica source and an alumina source, and forming a separation membrane containing MFI zeolite on the porous support by hydrothermal synthesis, wherein the seed crystals of MFI zeolite have a Si / Al ratio of 10 or more and 500 or less, and the cumulative particle size D at 50% of the cumulative number in the particle size distribution obtained by laser diffraction / scattering method ５０ The present invention provides a method for manufacturing a separation membrane in which the wavelength is between 50 nm and 1000 nm.

[0011] Figure 1 is a schematic diagram showing the cross-sectional structure of the separation membrane of the present invention. Figure 2 is a schematic diagram showing the cross-sectional structure of the membrane reactor of the present invention. Figure 3 is an X-ray diffraction pattern of the MFI zeolite of Example 2 and Comparative Example 1. Figure 4 is a schematic diagram showing the methanol synthesis apparatus used in the example and comparative example.

[0012] The present invention will be described below based on its preferred embodiments. The present invention relates to a separation membrane. The separation membrane comprises a separation layer containing MFI zeolite. The separation membrane may consist only of this separation layer, or it may comprise a porous support and the separation layer provided on the porous support.

[0013] The separation layer is composed of MFI zeolite as described above. The separation layer may be composed only of MFI zeolite, or may optionally contain components that can impart additional performance to the separation layer in addition to MFI zeolite.

[0014] The MFI zeolite contained in the separation layer is a zeolite characterized by having linearly arranged straight pores in one direction. The pore diameter of the pores of the MFI zeolite is generally about 0.5 nm to 0.6 nm, and in the present invention, selective separation of methanol is performed using these pores. Representative examples of MFI zeolite include, but are not limited to, ZSM-5.

[0015] In the separation membrane of the present invention, the crystals of the MFI zeolite constituting the separation layer have one of the characteristics. Specifically, one of the characteristics of the MFI zeolite is that its crystal grains are large. The fact that the crystal grains are large means that the number of grain boundaries is small. Since the MFI zeolite has linearly arranged straight pores in one direction as described above, the fact that the number of grain boundaries is small means that the passage of methanol through the pores is less likely to be inhibited. On the other hand, when the crystal grains of the MFI zeolite are small, the number of grain boundaries increases, so the passage of methanol through the pores is likely to be inhibited.

[0016] As a result of the inventors' study on MFI zeolite with large crystal grains, the ratio I １０４ of the intensity I ２００ of the diffraction peak of the (104) plane to the intensity I ２００ of the diffraction peak of the (200) plane by X-ray diffraction measurement (hereinafter also referred to as "XRD measurement") was found to show a characteristic value. Specifically, the MFI zeolite that can be used in the present invention preferably has I １０４ / I ２００ / I １０４ is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.14 or more. Also, the MFI zeolite that can be used in the present invention has I ２００ / I １０４Preferably, it is 1.5 or less, more preferably 1.0 or less, even more preferably 0.8 or less, and even more preferably 0.7 or less. ２００ / I １０４ By using an MFI zeolite having this range in the separation layer, the separation membrane of the present invention can selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with high efficiency.

[0017] The term "diffraction peak intensity" refers to the height of the diffraction peak. The same applies in the following explanation.

[0018] The MFI zeolite that can be used in this invention has an intensity I of the diffraction peak of the (200) plane in relation to XRD measurement. ２００ The intensity of the diffraction peak of the (101) plane relative to I １０１ Ratio I １０１ / I ２００ It is also preferable that it be within a specific range. In particular, the MFI zeolite that can be used in the present invention is I １０１ / I ２００ Preferably, it is 0.85 or higher, more preferably 1.00 or higher, even more preferably 1.50 or higher, and even more preferably 2.50 or higher. Furthermore, the MFI zeolite that can be used in the present invention is I １０１ / I ２００ Preferably, it is 7.5 or less, more preferably 7.4 or less, and even more preferably 7.3 or less. １０１ / I ２００ By using an MFI zeolite having this range in the separation layer, the separation membrane of the present invention can selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with even higher efficiency.

[0019] The MFI zeolite that can be used in this invention has an intensity I of the diffraction peak of the (501) plane in relation to XRD measurement. ５０１ The intensity of the diffraction peak of the (103) plane relative to I １０３ Ratio I １０３ / I ５０１ It is also preferable that it be within a specific range. In particular, the MFI zeolite that can be used in the present invention is I １０３ / I ５０１Preferably, it is 0.20 or higher, more preferably 0.24 or higher, even more preferably 0.27 or higher, and even more preferably 0.29 or higher. Furthermore, the MFI zeolite that can be used in the present invention is I １０３ / I ５０１ It is preferably 1.5 or less, more preferably 1.0 or less, and even more preferably 0.75 or less. １０３ / I ５０１ By using an MFI zeolite having this range in the separation layer, the separation membrane of the present invention can selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with even higher efficiency.

[0020] The MFI zeolite that can be used in this invention has an intensity I of the diffraction peak of the (501) plane in relation to XRD measurement. ５０１ The intensity of the diffraction peak of the (303) plane relative to I ３０３ Ratio I ３０３ / I ５０１ It is also preferable that it be within a specific range. In particular, the MFI zeolite that can be used in the present invention is I ３０３ / I ５０１ Preferably, it is 0.40 or higher, more preferably 0.65 or higher, even more preferably 0.72 or higher, and even more preferably 0.80 or higher. Furthermore, the MFI zeolite that can be used in the present invention is I ３０３ / I ５０１ Preferably, it is 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. ３０３ / I ５０１ By using an MFI zeolite having this range in the separation layer, the separation membrane of the present invention can selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with even higher efficiency.

[0021] The MFI zeolite that can be used in this invention has an intensity I of the diffraction peak of the (501) plane in relation to XRD measurement. ５０１ The intensity of the diffraction peak of the (104) plane relative to I １０４ Ratio I １０４ / I ５０１ It is also preferable that it be within a specific range. In particular, the MFI zeolite that can be used in the present invention is I １０４ / I５０１ Preferably, it is 0.15 or higher, more preferably 0.19 or higher, even more preferably 0.23 or higher, and even more preferably 0.28 or higher. Furthermore, the MFI zeolite that can be used in the present invention is I １０４ / I ５０１ Preferably, it is 0.50 or less, more preferably 0.47 or less, and even more preferably 0.44 or less. １０４ / I ５０１ By using an MFI zeolite having this range in the separation layer, the separation membrane of the present invention can selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with even higher efficiency.

[0022] As described above, one of the characteristics of the MFI zeolite that can be used in the present invention is that its crystal grains are large, and it is preferable from the viewpoint of improving methanol separation efficiency that the particle size is also controlled in relation to the size of the crystal grains. Specifically, the MFI zeolite has a cumulative particle size D at 50% of the cumulative number of particles in the particle size distribution determined by analyzing images obtained by laser microscopy observation. ５０ (Hereafter simply referred to as "Particle Size D") ５０ It is also called ". The particle size is preferably 2 μm or larger, more preferably 2.05 μm or larger, and even more preferably 2.10 μm or larger. In addition, the MFI zeolite has a particle size D ５０ The particle size D of the MFI zeolite is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 4 μm or less, and even more preferably 3.5 μm or less. ５０ Being within this range makes it less likely for methanol to pass through the pores to be inhibited, enabling highly efficient and selective separation of methanol from a gas containing carbon dioxide, hydrogen, and methanol. Particle size D ５０ The measurement method will be explained in the examples described later.

[0023] The MFI zeolite that can be used in this invention is one in which sodium ions or protons occupy its ion exchange sites. ＋ Type or H ＋ It is preferable that it be of the Na type. ＋ Type or H＋ In type MFI zeolites, Na ＋ or H ＋ Since methanol is readily adsorbed onto this material, while carbon dioxide and hydrogen are not, the equilibrium of the methanol synthesis reaction tends to shift to the product system when performing a reaction to synthesize methanol from carbon dioxide and hydrogen. As a result, methanol can be separated selectively with high efficiency.

[0024] The MFI zeolite that can be used in the present invention also has a distinctive Si / Al ratio. Specifically, the Si / Al ratio of the MFI zeolite is controlled to a low value. This makes it easier for the MFI zeolite to be C-axis oriented and for linear pores aligned in one direction to be formed. As a result, the above-mentioned intensity ratio measured by XRD can be easily satisfied, and methanol can be selectively separated with high efficiency. From this viewpoint, the Si / Al ratio of the MFI zeolite is preferably 500 or less, more preferably 50 or less, and even more preferably 15 or less. From a similar viewpoint and from the viewpoint of zeolite stability, the Si / Al ratio of the MFI zeolite is preferably 5 or more, more preferably 7 or more, and even more preferably 9 or more. MFI zeolite having a Si / Al ratio within the above range can be suitably produced by the method described later.

[0025] In the present invention, as shown in Figure 1, the separation membrane 10 may have a porous support 12 and a separation layer 11 containing MFI zeolite. The separation layer 11 is formed on one surface of the porous support 12. There are no particular restrictions on the shape of the porous support 12. The porous support 12 may be, for example, plate-shaped. Alternatively, the porous support 12 may be, for example, tubular or honeycomb-shaped. If the porous support 12 is plate-shaped, the separation layer 11 may be formed on one of the two surfaces of the plate-shaped porous support 12. If necessary, the separation layer 11 may be formed on both surfaces of the plate-shaped porous support 12. If the porous support 12 is tubular, the separation layer 11 may be formed on the outer or inner surface of the tubular porous support 12. If the porous support 12 is tubular, it is preferable to have an inner diameter of about 1 cm to 2 cm and a length of about 40 cm to 120 cm. Regardless of the shape of the porous support 12, from the viewpoint of improving methanol permeability, the thickness of the porous support 12 is preferably about 1 mm to 3 mm.

[0026] As the porous support 12, a porous body made of a material that has good separation efficiency for carbon dioxide, hydrogen, and methanol and is inert to water can be used. Examples of such materials include porous ceramic materials made of alumina, mullite, zirconia, and cordierite, as well as porous sintered metals such as stainless steel. The porous support 12 preferably has a porosity of 25% or more in order to improve its permeability. The porous support 12 preferably has a porosity of 55% or less in order to improve its pressure resistance. In relation to porosity, the porous support 12 preferably has an average pore diameter of 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.7 μm or more, and even more preferably 1.0 μm or more. Furthermore, the porous support 12 preferably has an average pore diameter of 10 μm or less, more preferably 9.0 μm or less, even more preferably 8.0 μm or less, and even more preferably 7.0 μm or less. The average pore size of the porous support 12 is measured by the mercury intrusion method.

[0027] The separation layer 11 formed on the porous support 12 is preferably 0.5 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more, from the viewpoint of suppressing the occurrence of pinholes and improving the methanol separation efficiency. Furthermore, from the viewpoint of suppressing a decrease in the permeate flux of the separation layer 11, the separation layer 11 is preferably 10 μm or less, more preferably 5.0 μm or less, and even more preferably 3.5 μm or less. The thickness of the separation layer 11 can be controlled, for example, by adjusting the average particle size of the MFI zeolite seed crystals used to form the separation layer 11, or the synthesis conditions of the MFI zeolite (e.g., the composition of the aqueous gel, the synthesis temperature and time). The thickness of the separation layer 11 can be measured, for example, using a scanning electron microscope (SEM).

[0028] Another embodiment of the present invention is the membrane reactor 20 shown in Figure 3. The membrane reactor 20 shown in the figure comprises a porous support 12, a separation layer 11 disposed thereon, and a catalyst layer 13 disposed thereon. The porous support 12 and the separation layer 11 are the same as those used in the embodiment shown in Figure 1. The catalyst layer 13 contains a catalyst for the reaction that produces methanol from carbon dioxide and hydrogen. As the catalyst, known catalysts such as copper-zinc catalysts can be used. According to the membrane reactor 20 of this embodiment, the raw material gases, carbon dioxide and hydrogen, react on the catalyst layer 13 to produce methanol and water. The produced methanol and water selectively permeate through the separation layer 11 and the porous support 12, separating them from carbon dioxide and hydrogen.

[0029] Next, a preferred method for manufacturing the separation membrane of the present invention will be described using the embodiment shown in Figure 1 as an example. This manufacturing method includes the following steps (a) and (b) in this order: (a) A step of attaching seed crystals to a porous support. (b) A hydrothermal synthesis step. Each of these steps will be described in detail below.

[0030] (a) Step of attaching seed crystals to the porous support In this step, first, MFI zeolite seed crystals are attached to the porous support. There are no particular restrictions on the method of attaching the seed crystals. For example, the porous support is immersed in an aqueous solution containing MFI zeolite seed crystals. If the porous support is, for example, tubular, both ends of the porous support are sealed to prevent liquid from entering the interior, and then the porous support is immersed in an aqueous solution containing seed crystals. This makes it possible to attach seed crystals only to the outer surface of the tubular porous support.

[0031] The concentration of seed crystals in the aqueous solution is preferably 0.01% by mass or more and 3% by mass or less, more preferably 0.05% by mass or more and 1.0% by mass or less, and even more preferably 0.1% by mass or more and 0.7% by mass or less, from the viewpoint of attaching an appropriate amount of seed crystals to the surface of the porous support.

[0032] After removing the porous support from the aqueous solution containing the seed crystal and removing excess moisture by drying, the surface of the porous support, i.e., the surface to which the MFI zeolite seed crystal is attached, may be rubbed. Rubbing refers to the operation of rubbing the surface of the layer of MFI zeolite seed crystal in one direction with a cloth or the like after forming a layer of MFI zeolite seed crystal on the surface of the porous support. Specific methods of rubbing include, for example, using a nonwoven fabric wiper with low dust generation performance to rub the surface of the MFI zeolite seed crystal layer. The purpose of rubbing is to adjust the dispersibility and amount of seed crystal attached, and to strengthen the attachment of the seed crystal to the porous support.

[0033] The attachment of seed crystals to a porous support, drying, and rubbing of the attachment surface may be performed as a set of operations, and this operation may be repeated multiple times to complete the seed crystal attachment process. Alternatively, after performing the above operations multiple times, the seed crystals may be attached to the porous support last, followed by the removal of moisture by drying to complete the seed crystal attachment process.

[0034] The MFI zeolite seed crystals used to adhere to the porous support have a Si / Al ratio within a specific range. This allows for the formation of a separation layer with the desired methanol permeability. Specifically, the Si / Al ratio of the MFI zeolite seed crystal is preferably 10 or more, more preferably 20 or more, even more preferably 30 or more, even more preferably 40 or more, and particularly preferably 50 or more. Furthermore, the Si / Al ratio of the MFI zeolite seed crystal is preferably 500 or less, more preferably 250 or less, and even more preferably 100 or less. The MFI zeolite seed crystals are, for example, NH ４ ＋ It could be a type. Alternatively, the MFI zeolite seed crystal could be, for example, Na ＋ Type or H ＋ It can be of a certain type. Seed crystals of MFI zeolite having the Si / Al ratio described above can be obtained by using a gel containing, for example, a silica source, an alumina source, an alkali source, and water, and further containing a structure-controlling agent (hereinafter also referred to as "SDA"), and subjecting the gel to hydrothermal synthesis. As the SDA, for example, quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide can be used.

[0035] From the viewpoint of successfully forming a separation layer containing the target MFI zeolite, the seed crystal of the MFI zeolite preferably has a particle size of 50 nm or more, more preferably 100 nm or more, and even more preferably 300 nm or more. From a similar viewpoint, the particle size of the seed crystal of the MFI zeolite preferably has a particle size of 1000 nm or less, more preferably 800 nm or less, and even more preferably 600 nm or less. In this specification, the particle size of the seed crystal of the MFI zeolite refers to the cumulative particle size D at 50% of the cumulative number of particles in the particle size distribution obtained by laser diffraction and scattering. ５０ It means that.

[0036] The seed crystal of MFI zeolite is H ＋ It can be of a certain type, Na ＋It may be of a specific type. Alternatively, an MFI zeolite ion-exchanged with other cations can be used as a seed crystal. For example, NH ４ ＋ A seed crystal of a specific type may also be used.

[0037] After attaching seed crystals of MFI zeolite to the surface of a porous support, the porous support is immersed in an aqueous gel containing a silica source and an alumina source. The aqueous gel is preferably obtained by mixing the silica source, alumina source, alkali source, and water to have a composition represented by the following molar ratios: • SiO ２ / Al ２ O ３ = 100-1500, especially 150-500 ・Na ２ O / SiO ２ = 0.1 to 0.5, especially 0.2 to 0.4 ・H ２ O / SiO ２ = 25-60, especially 30-55

[0038] Examples of silica sources include silica itself and silicon-containing compounds capable of generating silicate ions in water. Specifically, these include wet-process silica, dry-process silica, colloidal silica, sodium silicate, and aluminosilicate gel. These silica sources can be used individually or in combination of two or more.

[0039] As an alumina source, for example, water-soluble aluminum-containing compounds can be used. Specifically, these include sodium aluminate, aluminum nitrate, and aluminum sulfate. Aluminum hydroxide is also a suitable alumina source. These alumina sources can be used individually or in combination of two or more.

[0040] For example, sodium hydroxide can be used as an alkali source. Furthermore, when sodium silicate is used as a silica source or sodium aluminate as an alumina source, the sodium contained therein, which is an alkali metal component, is simultaneously considered as NaOH and is also an alkali component. Therefore, the aforementioned Na ２ O is calculated as the sum of all alkaline components in the reaction mixture.

[0041] The order in which the raw materials are added when preparing the aqueous gel should be such that a method is adopted that easily yields a uniform gel. For example, a uniform aqueous gel can be obtained by adding and dissolving an alumina source and an alkali source in water at room temperature, and then adding a silica source and stirring. There are no particular restrictions on the temperature when preparing the aqueous gel.

[0042] The aqueous gel may or may not contain SDA. In particular, not using SDA when forming a separation membrane containing MFI zeolite by hydrothermal synthesis is preferable from the viewpoint of successfully forming a separation membrane containing MFI zeolite having the desired physical properties. From this viewpoint, it is advantageous that the aqueous gel does not contain SDA and that the Si / Al ratio of the seed crystal attached to the porous support is high. A high Si / Al ratio of the seed crystal means, for example, that the Si / Al ratio is preferably 30 to 500, more preferably 40 to 250, and even more preferably 50 to 100.

[0043] If the aqueous gel does not contain SDA, the aqueous gel may have, for example, the composition described in US2013 / 156690A1. This publication is incorporated herein by reference as part of the present invention.

[0044] (b) Hydrothermal synthesis step In this step, a porous support to which seed crystals of MFI zeolite are attached is immersed in an aqueous gel and heated in a sealed state to perform hydrothermal synthesis under self-stimulating pressure, thereby forming a separation membrane containing MFI zeolite on the porous support. For hydrothermal synthesis, a reaction vessel such as an autoclave can be used. The temperature of the hydrothermal synthesis is preferably 150°C to 200°C, more preferably 160°C to 190°C, and even more preferably 170°C to 180°C, from the viewpoint of successfully forming a separation membrane containing MFI zeolite having the desired physical properties.

[0045] While the MFI zeolite is being crystallized by hydrothermal synthesis, the aqueous gel may be stirred to ensure uniform temperature. Stirring can be done by mixing with a stirring blade or by rotating the container. The stirring intensity and rotation speed should be adjusted according to the uniformity of temperature and the amount of impurities produced as by-products. Intermittent stirring is also acceptable instead of continuous stirring. Instead of stirring the aqueous gel, hydrothermal synthesis may be performed under static conditions.

[0046] When performing hydrothermal synthesis at the temperatures mentioned above, it is preferable to perform the synthesis for 5 to 50 hours from the viewpoint of sufficiently crystallizing the MFI zeolite.

[0047] Once the hydrothermal synthesis is complete, the porous support is removed from the reaction vessel. A separation layer containing MFI zeolite is formed on the surface of the porous support. In this way, the desired separation membrane is obtained. The obtained separation membrane is subjected to a subsequent washing process to remove any unreacted aqueous gel or amorphous MFI zeolite. For this purpose, for example, washing with hot water, steam spraying, or a combination thereof is used.

[0048] The separation membrane obtained in this manner is suitably used to selectively separate methanol and water from a mixed gas containing carbon dioxide, hydrogen, methanol, and water when methanol is synthesized using carbon dioxide and hydrogen as raw materials.

[0049] Furthermore, a membrane reactor having the structure shown in Figure 2 can also be manufactured by arranging catalyst pellets on the separation layer of the separation membrane obtained in this manner. For example, a membrane reactor can be manufactured by arranging catalyst pellets in a cylindrical shape on the separation layer of a separation membrane, which is formed by forming a separation layer on the outer surface of a cylindrical porous support.

[0050] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0051] [Example 1] (1) Preparation of porous support A porous tube made of α-alumina (inner diameter: 9 mm, outer diameter: 12 mm) was prepared as a porous support. The porosity was 30%, and the average pore size was 3 to 5 μm. (2) Preparation of aqueous solution containing seed crystal The Si / Al ratio was 80, and the cumulative particle size D was determined by laser diffraction and scattering. ５０ NH is 400 nm ４ ＋ Seed crystals of type MFI zeolite were prepared. These seed crystals were dispersed in deionized water to prepare a 0.6% aqueous solution. (3) Seed crystal attachment The porous support prepared in (1) was immersed in the aqueous solution prepared in (2). Both ends of the porous support were closed to prevent liquid from entering the tubes. Forty seconds after immersion, the porous support was removed from the aqueous solution, dried at 200°C, cooled to room temperature, and then rubbed. For rubbing, Bencot (manufactured by Asahi Kasei), a continuous long-fiber nonwoven fabric wiper made of 100% cellulose, was used. Specifically, the entire outer surface of the porous support on which the seed crystal layer was formed was lightly rubbed with the wiper in a back-and-forth motion two to three times. After repeating immersion, drying, and rubbing twice, the support was immersed again, and forty seconds after immersion, the porous support was removed from the aqueous solution, and excess moisture was removed by drying to complete the seed crystal attachment operation. (4) Preparation of aqueous gel An aqueous solution was obtained by dissolving sodium aluminate and sodium hydroxide aqueous solution in deionized water. Silica sol (Snowtex® ST-S manufactured by Nissan Chemical Corporation) was added to this aqueous solution and mixed uniformly to obtain an aqueous gel having the composition shown in Table 1 below. (5) Hydrothermal synthesis The aqueous gel obtained in (4) above was packed into an autoclave with an inner diameter of 14 mm. The packing amount was 49 g. Furthermore, the porous support with seed crystals attached obtained in (3) above was placed inside the autoclave. After sealing the autoclave, it was heated to the temperature shown in Table 1 and maintained at that temperature for the time shown in the same table. After that, heating was stopped and the autoclave was allowed to cool naturally to room temperature. (6) Washing The separation membrane to be used was removed from the autoclave which had cooled to room temperature, and steam was blown on it for 5 minutes, followed by washing with hot water for 5 hours, and Na was applied to the outer surface of the porous support. ＋A separation layer containing type MFI zeolite was formed. (7) Formation of the catalyst layer Catalyst pellets were cylindrically arranged on the separation layer in the obtained separation membrane, and a membrane reactor in which a porous support, a separation layer containing type Na ＋ MFI zeolite, and a catalyst layer were laminated in this order was obtained. The catalyst pellets were Copper based methanol synthesis Catalyst Pellets (dimensions: 5.4 mm × 3.6 mm) manufactured by Alfa Aesar.

[0052] [Example 2] In (3) of Example 1, after repeating immersion, drying, and rubbing three times, excess moisture was removed by drying to complete the attachment operation of the seed crystals. Also, the composition of the aqueous gel in (4) was as shown in Table 1. A membrane reactor was obtained in the same manner as in Example 1 except for these.

[0053] [Example 3] In (3) of Example 1, after repeating immersion, drying, and rubbing three times, excess moisture was removed by drying to complete the attachment operation of the seed crystals. Also, the composition of the aqueous gel in (4) was as shown in Table 1. Further, in (5), an autoclave with an inner diameter of 29 mm was used. The filling amount of the aqueous gel was 220 g. A membrane reactor was obtained in the same manner as in Example 1 except for these.

[0054] [Example 4] In (3) of Example 1, after repeating immersion, drying, and rubbing twice, excess moisture was removed by drying to complete the attachment operation of the seed crystals. Also, in (5), an autoclave with an inner diameter of 29 mm was used. The filling amount of the aqueous gel was 49 g. A membrane reactor was obtained in the same manner as in Example 1 except for these.

[0055] [Comparative Example 1] In (2) of Example 1, ZMS-5 (product number HSZ-822HOA), which is an MFI zeolite manufactured by Tosoh Corporation, was used as the seed crystal. This zeolite has a Si / Al ratio of 12 and H ＋It was of the type. 16.5 g of this zeolite was pulverized by an automatic mortar for 6 hours, and the pulverized zeolite was dispersed in 1 liter of ion-exchanged water. After allowing this dispersion to stand for 3 days, the supernatant was collected and used as a slurry of seed crystals. The concentration of this slurry was 0.3%, and the cumulative particle size D ５０ of the seed crystals was 400 nm. Also, in (3) of Example 1, dipping and drying were repeated twice to complete the operation of attaching the seed crystals. Rubbing was not performed. Also, the composition of the aqueous gel in (4) was as shown in Table 1. Also, in (5), an autoclave with an inner diameter of 29 mm was used. The filling amount of the aqueous gel was 330 g. The hydrothermal synthesis time was as shown in Table 1. Further, in the washing in (6), steam was blown for 5 minutes, followed by washing with warm water for 14 hours, and then steam was blown for 5 minutes. A membrane reactor was obtained in the same manner as in Example 1 except for these.

[0056]

[0057] [Evaluation 1] The thickness of the separation layer of the membrane reactors obtained in the examples and comparative examples was measured by SEM. Also, XRD measurement was performed on the MFI zeolite contained in the separation layer, and I ２００ / I １０４ 、I １０１ / I ２００ 、I １０３ / I ５０１ 、I ３０３ / I ５０１ and I １０４ / I ５０１The following was determined. The results are shown in Table 2. The X-ray diffraction patterns measured for Example 2 and Comparative Example 1 are shown in Figure 3. The conditions for XRD measurement targeting MFI zeolite were as follows. The cylindrical separation membrane obtained in the process of manufacturing the membrane reactors obtained in the Examples and Comparative Examples was used as the measurement target. In order to irradiate the surface of the cylindrical separation membrane with X-rays, a jig for fixing the separation membrane was attached to the X-ray sample holder. A SmartLab (manufactured by Rigaku Corporation, Kα1 unit) was used as the X-ray measuring device. Cu Kα was used as the X-ray source. A D / teX Ultra 250 HE (manufactured by Rigaku Corporation) was used as the detector. The measurement conditions were a tube voltage of 45 kV and a tube current of 200 mA. The X-ray scanning conditions were a concentrated method, 2θ / θ: 3-40 deg, 0.005 deg step, and 1 deg / min. Since the outer surface of the separation membrane is curved, the flat portion was used as the measurement target whenever possible.

[0058] Furthermore, the particle size D of MFI zeolite ５０ The following method was used to measure the particle size. The results are shown in Table 2. The cylindrical separation membrane obtained during the manufacturing process of the membrane reactors obtained in the examples and comparative examples was used as the measurement target. The surface of the separation membrane (i.e., the surface of the separation layer) was observed at 3600x magnification using a white light interferometer-equipped laser microscope (VK-X3000, manufactured by Keyence). Three locations were observed on the cylindrical separation membrane: both ends and the center, and image data was acquired from these three locations. Fifty locations were randomly selected for each image data location, and the particle size of the zeolite particles at those locations was measured. Particle size is defined as the diameter of a circle with the same area as the projected area of ​​the particle. A particle size distribution based on the number of particles was created from the measured data, and its median diameter was defined as D ５０ It was calculated as follows.

[0059] Furthermore, the separation membrane was cut into approximately 1 cm wide sections using a wire saw, and the resulting cross-sections were prepared as clean observation samples that were smooth, free from distortion and scratches (grinding marks), using a cross-section polisher (CP, manufactured by JEOL Ltd.) with an argon broad ion beam. Elemental analysis of these cross-sections was performed using FE-SEM EDX to determine the Si / Al ratio. The results are shown in Table 2.

[0060] [Evaluation 2] Methanol was synthesized from carbon dioxide and hydrogen using the apparatus shown in Figure 4. The gases from the permeate and non-permeate sides of the membrane reactor in the apparatus shown in the same figure were recovered and quantitatively analyzed by gas chromatography. Based on the results, the methanol yield and methanol permeate rate were calculated. The results are shown in Table 2. The synthesis conditions were a temperature of 250°C, a pressure of 5 MPa, a flow rate of 1.67 NL / min (carbon dioxide: 0.42 NL / min, hydrogen: 1.25 NL / min), and a catalyst packing amount of 94 g in the pre-column. The catalyst packed in the pre-column was the same catalyst as that in the membrane reactor. The methanol permeate rate was measured by the method described below. The pre-column and catalyst were removed from the apparatus shown in Figure 4, nitrogen gas and methanol vapor were introduced into the membrane reactor, and the amount of methanol that permeated through the separation membrane was measured to calculate the methanol permeate rate per hour. The methanol permeation conditions were set to a temperature of 200°C, a pressure of 0.6 MPa, and a flow rate of 1.67 NL / min (1 NL / min nitrogen, 0.67 NL / min methanol).

[0061]

[0062] As is clear from the results shown in Table 2, each example showed higher methanol yield and methanol permeation compared to the comparative example.

[0063] As described in detail above, the separation membrane of the present invention makes it possible to selectively separate methanol from a gas containing carbon dioxide, hydrogen, and methanol with high efficiency.

Claims

1. A separation membrane comprising a separation layer containing MFI zeolite, wherein the MFI zeolite has an intensity I of the diffraction peak of the (104) plane as measured by X-ray diffraction. １０４ The intensity of the diffraction peak at the (200) plane relative to ２００ Ratio I ２００ / I １０４ The particle size is between 0.05 and 1.5, and the cumulative particle size D at 50% of the cumulative number of particles in the particle size distribution obtained by analyzing images obtained by laser microscopy observation is also obtained. ５０ A separation membrane having a diameter of 2 μm or more and 10 μm or less.

2. The MFI zeolite has an intensity I of the diffraction peak of the (200) plane by X-ray diffraction measurement ２００ relative to the intensity I of the diffraction peak of the (101) plane １０１ with a ratio I １０１ / I ２００ of 0.85 or more and 7.5 or less. The separation membrane according to claim 1 3. The MFI zeolite has an intensity I of the diffraction peak of the (501) plane measured by X-ray diffraction. ５０１ The intensity of the diffraction peak of the (103) plane relative to I １０３ Ratio I １０３ / I ５０１ The separation membrane according to claim 1, wherein the ratio is 0.20 or more and 1.5 or less.

4. The MFI zeolite has an intensity I of the diffraction peak of the (501) plane measured by X-ray diffraction. ５０１ The intensity of the diffraction peak of the (303) plane relative to I ３０３ Ratio I ３０３ / I ５０１ The separation membrane according to claim 1, wherein the ratio is 0.40 or more and 1.5 or less.

5. The MFI zeolite has an intensity I of the diffraction peak of the (501) plane measured by X-ray diffraction. ５０１ The intensity of the diffraction peak of the (104) plane relative to I １０４ Ratio I １０４ / I ５０１ The separation membrane according to claim 1, wherein the ratio is 0.15 or more and 0.50 or less.

6. The MFI zeolite is Na ＋ Type or H ＋ A separation membrane according to claim 1, which is a type.

7. The separation membrane according to claim 1, wherein the Si / Al ratio of the MFI zeolite is 5 or more and 500 or less.

8. The separation membrane according to claim 1, used for selectively separating methanol from a gas containing carbon dioxide, hydrogen, and methanol.

9. The separation membrane according to claim 1, comprising a porous support and the separation layer provided on the porous support.

10. A membrane reactor comprising a separation membrane according to claim 9 and a catalyst layer provided on the separation layer in the separation membrane.

11. A method for producing a separation membrane, comprising the steps of immersing a porous support to which seed crystals of MFI zeolite are attached in an aqueous gel containing a silica source and an alumina source, and forming a separation membrane containing MFI zeolite on the porous support by hydrothermal synthesis, wherein the seed crystals of MFI zeolite have a Si / Al ratio of 10 or more and 500 or less, and the cumulative particle size D at 50% of the cumulative number in the particle size distribution obtained by laser diffraction / scattering method ５０ A method for producing a separation membrane, wherein the wavelength is between 50 nm and 1000 nm.

12. The method for producing a separation membrane according to claim 11, wherein no structural modifier is used when forming the separation membrane containing MFI zeolite by the hydrothermal synthesis.

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