Method for producing hydrogen separation membrane and method for hydrogen separation

Abstract

To provide a method for producing a hydrogen separation membrane and a method for hydrogen separation that enable production of a hydrogen separation membrane exhibiting superior hydrogen separation performance under high-temperature conditions of 500°C or more and in an atmosphere with high steam content.SOLUTION: The present invention provides a method for producing a hydrogen separation membrane, comprising a step of forming an amorphous silica layer on one surface of a porous aluminum oxide support having an average pore diameter of 30 nm to 1000 nm by chemical vapor deposition using a silica source containing trimethylmethoxysilane, and an application thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a hydrogen separation membrane and a method for separating hydrogen. [Background technology]

[0002] In recent years, hydrogen has been attracting attention as a clean energy source. Because natural, high-purity hydrogen is rarely found in nature, hydrogen is produced by generating it from compounds containing hydrogen atoms. However, hydrogen production by methods such as reforming fossil fuels or electrolysis of water poses problems such as energy inefficiency and carbon dioxide emissions.

[0003] For this reason, methods for selectively extracting only hydrogen from hydrogen-containing compounds are being investigated. For example, hydrogen can be efficiently produced by extracting only the hydrogen obtained through the steam reforming reaction of methane contained in biogas from the reaction system.

[0004] As a hydrogen separation membrane used for selective permeation of hydrogen, for example, a hydrogen separation membrane with good heat resistance has been proposed in which silica is formed using oxygen and a vaporized silica source so as to partially block the pores of a porous substrate (see Patent Document 1). Patent Document 2 discloses a method for producing a hydrogen separation membrane, which includes a step of forming an amorphous silica layer having an average pore diameter of 0.2 nm to 0.3 nm on one surface of a porous aluminum oxide body having an average pore diameter of 30 nm to 1000 nm by chemical vapor deposition using a silica source containing dimethoxydimethylsilane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4728308 [Patent Document 2] Japanese Patent Publication No. 2022-54267 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a demand for membranes that can separate gases under conditions of high temperature and high water vapor partial pressure. For example, in the development of a membrane reactor for producing hydrogen from biogas, biogas and a gas containing approximately 1.8 times the amount of water vapor as biogas are supplied to the membrane at approximately 500 to 700°C, and it is necessary to achieve high hydrogen permeability under such harsh conditions. Gas separation membranes made from silica are expected to achieve this, but from a practical perspective, a membrane with even higher hydrogen permeability than the hydrogen separation membranes disclosed in Patent Documents 1 and 2 is required.

[0007] An object of one embodiment of the present invention is to provide a method for producing a hydrogen separation membrane and a hydrogen separation method that can produce a hydrogen separation membrane that exhibits high hydrogen separation properties even at high temperatures of 500°C or higher and in an atmosphere containing a large amount of water vapor. [Means for solving the problem]

[0008] Solutions to the above problems include the following embodiments. <1> A method for producing a hydrogen separation membrane, comprising the step of forming an amorphous silica layer on one surface of an aluminum oxide porous support having an average pore diameter of 30 nm to 1000 nm by chemical vapor deposition using a silica source containing trimethylmethoxysilane. <2> The chemical vapor deposition method is a counter-diffusion chemical vapor deposition method. <1> A method for producing the hydrogen separation membrane according to claim 1. <3> <1> or <2> a gas supplying step of supplying a mixed gas containing hydrogen and at least one gas other than hydrogen to the hydrogen separation membrane manufactured by the method for manufacturing a hydrogen separation membrane according to the above item; a gas separation step in which a portion of the mixed gas permeates the hydrogen separation membrane and is separated as a permeated gas having a higher hydrogen concentration than the mixed gas; A hydrogen separation method comprising: <4> The gas separation process is carried out in an environment of 500°C or higher <3> The hydrogen separation method according to claim 1. [Effects of the Invention]

[0009] According to one embodiment of the present invention, a method for producing a hydrogen separation membrane and a method for hydrogen separation can be provided, which can produce a hydrogen separation membrane that exhibits high hydrogen separation properties even at high temperatures of 500°C or higher and in an atmosphere containing a large amount of water vapor. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the relationship between the concentration of TMMOS (TriMethylMethOxySilane) used as a silica source in the formation of a hydrogen separation membrane, and the hydrogen and nitrogen permeabilities and hydrogen / nitrogen selectivity of the formed hydrogen separation membrane at 600° C. [Figure 2] 1 is a graph showing the relationship between the nitrogen flow rate when TMMOS used as a silica source in the formation of a hydrogen separation membrane is supplied with nitrogen as a carrier gas, and the hydrogen and nitrogen permeabilities and hydrogen / nitrogen selectivity of the formed hydrogen separation membrane at 600°C. [Figure 3] 1 is a graph showing the relationship between the film formation time and the hydrogen and nitrogen permeabilities and hydrogen / nitrogen selectivity of the hydrogen separation membrane formed by CVD using TMMOS as the silica source at 600°C. [Figure 4] This is an Arrhenius plot showing the temperature dependence of hydrogen permeability and nitrogen permeability at 500 to 600°C for a membrane using TMMOS as a silica source (TMMOS membrane) and a membrane using DMDMS (DiMethoxyDiMethylSilane) (DMDMS membrane) in the production of a hydrogen separation membrane. [Figure 5] 1 is a graph showing the change over time in hydrogen permeability in a water vapor atmosphere for a membrane using TMMOS as a silica source (TMMOS membrane) and a membrane using DMDMS as a silica source (DMDMS membrane) in the production of a hydrogen separation membrane. [Figure 6] 1 is a partially enlarged cross-sectional view schematically illustrating one embodiment of a hydrogen separation membrane according to the present disclosure. [Figure 7] 1 is a schematic diagram showing an example of a hydrogen production device to which the hydrogen separation membrane of the present disclosure can be applied. [Figure 8]FIG. 8 is a schematic cross-sectional view showing an example of a membrane reactor that can be used in the hydrogen production device shown in FIG. [Figure 9] FIG. 8 is a schematic cross-sectional view showing an example of a membrane reactor that can be used in the hydrogen production device shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] The hydrogen separation membrane manufacturing method and hydrogen separation method according to the present disclosure will be described in detail below with reference to specific embodiments. The present disclosure is not limited to the following embodiments and can be implemented in various variations within the spirit of the present disclosure. Variations include, for example, scaling up the apparatus, replacing components in the apparatus with components having equivalent performance, changing the position of components in the apparatus as long as the effects are not impaired, and changing the type, amount, and packing mode of the catalyst constituting the membrane reactor produced using the hydrogen separation membrane.

[0012] In the present disclosure, a numerical range described using "to" indicates a numerical range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in the present disclosure, the upper limit value described in a certain numerical range may be replaced with the upper limit value of another numerical range described in stages, and the lower limit value described in a certain numerical range may be replaced with the lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. Also, in the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the drawings, components designated by the same reference numerals are the same components. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0013] The inventors of the present disclosure have conducted extensive research into methods for producing hydrogen separation membranes by CVD using silicon compounds as silica sources, and have found that a membrane produced using trimethylmethoxysilane (sometimes abbreviated as "TMMOS" in this disclosure) (sometimes referred to as a "TMMOS membrane" in this disclosure) exhibits higher hydrogen separation properties even at high temperatures and high water vapor partial pressures than a membrane produced using dimethoxydimethylsilane (sometimes referred to as "DMDMS" in this disclosure) (sometimes referred to as a "DMDMS membrane" in this disclosure). The reason for this is unclear, but the TMMOS membrane is presumed to have the following properties. The pore sizes of the DMDMS and TMMOS films are almost the same, or slightly larger, and the separation active layer thickness of the TMMOS film is thinner. Furthermore, the TMMOS film may contain residual methyl groups.

[0014] <Method of manufacturing hydrogen separation membrane> The method for producing a hydrogen separation membrane according to the present disclosure includes a step of forming an amorphous silica layer on one surface of an aluminum oxide porous support having an average pore size of 30 nm to 1000 nm by chemical vapor deposition (CVD) using a silica source containing trimethylmethoxysilane. The structural formula of TMMOS is as follows:

[0015] [ka]

[0016] (Porous support) The porous support that supports the amorphous silica layer can be any support that has gas-permeable pores and has heat resistance and water vapor resistance appropriate for the environment in which the hydrogen separation membrane according to the present disclosure will be used, without any particular restrictions. The porous support may be porous ceramics, which have an appropriate pore size and are readily available. Metal oxides, metal nitrides, and metal nitrides are preferred from the viewpoint of good heat resistance. More specifically, supports such as alumina, silica, titania, zirconia, and magnesia are preferred, with α-alumina supports being more preferred. In the case of a tubular porous support, for example, a porous tubular support having an outer diameter of about 3 mm to 20 mm, an inner diameter of about 1 mm to 15 mm, and a tube thickness of about 1 mm to 3 mm is suitable. The average pore diameter of the porous support is preferably in the range of 30 nm to 1000 nm, more preferably in the range of 50 nm to 500 nm, and even more preferably in the range of 80 nm to 180 nm.

[0017] A preferred double-layer porous support is one in which the support layer is made of tubular α-alumina with an average pore size of 30 nm to 1000 nm, preferably 80 nm to 180 nm, and the outer surface of the tubular support layer is provided with an intermediate γ-alumina layer with an average pore size of 1 nm to 20 nm, preferably 3 nm to 5 nm. The thickness of the support layer can be selected arbitrarily depending on the purpose. Considering the size of the hydrogen production device, the thickness of the support layer can be set to 0.5 mm to 3 mm, and a range of 1 mm to 2 mm is preferable from the viewpoint of the balance between strength and gas permeability. The thickness of the intermediate layer can usually be set to 0.5 μm to 10 μm, and is preferably in the range of 1 μm to 5 μm.

[0018] There are no particular limitations on the method for providing an intermediate layer on a support layer serving as a porous support, and known methods for producing porous layers can be applied as appropriate. When the support layer is made of a material with good heat resistance, such as alumina, a method of coating the support layer with an intermediate layer-forming material containing boehmite sol, which will be described in detail below, and firing the coating is preferred. According to the method of forming an intermediate layer using an intermediate layer-forming material containing boehmite sol, an intermediate layer of any desired thickness can be formed by adjusting the coating amount of the intermediate layer-forming material, the firing temperature, and by performing coating and firing multiple times.

[0019] One example of a method for producing a porous support having a two-layer structure is to dip-coat the outer surface of a ring of a tubular porous support layer made of α-alumina with boehmite sol, which is an intermediate layer-forming material, two to three times, and then bake the resulting layer to form a γ-alumina intermediate layer having an average pore size of 3 nm to 5 nm. When coating the tubular support layer with the intermediate layer-forming material, it is preferable to seal the ends of the ring to prevent the intermediate layer-forming material from penetrating into the ring, which is the support layer. The boehmite sol can be produced by a conventional method using aluminum s-butoxide (ALSB), 2-propanol, and gallium (III) nitrate-8-hydrate, or using aluminum s-butoxide (ALSB), 2-propanol, and 1 mol / L (liter) nitric acid.

[0020] The average pore size of the porous support can be measured by measuring the pore size distribution using a through-pore size evaluation device based on the bubble point method of ASTM F316-86 (JIS K 3832). Examples of devices used for the measurement include a Perm Porometer manufactured by Seika Digital Image Co., Ltd.

[0021] The thicknesses of the support layer and intermediate layer in the porous support can be measured by cutting the hydrogen separation membrane to obtain a cross section, platinum sputtering the cross section, and observing it with a field emission-scanning electron microscope (FE-SEM). An example of an FE-SEM device is the JSM-6701F (manufactured by JEOL Ltd.). The accelerating voltage of the FE-SEM can be, for example, 10.0 kV.

[0022] (amorphous silica layer) An amorphous silica layer is formed on one surface of the porous support by a CVD method using a silica source containing TMMOS. CVD methods used to form an amorphous silica layer include a one-way diffusion CVD method in which a silica precursor derived from a silica source and an oxidizing agent, preferably oxygen, are supplied to one side of a porous support to form an amorphous silica layer, and a counter-diffusion CVD method in which a silica precursor derived from a silica source is supplied to one side of a porous support and an oxidizing agent is supplied to the other side of the porous support. In particular, in the counter-diffusion CVD method, by maintaining equal pressure on both sides of the porous support, the silica precursor diffused in the pores of the porous support comes into contact with the oxidizing agent within the pores to produce silica, and an amorphous silica layer is formed on the pore walls within the porous pores. The reaction automatically terminates when the pores are filled with the silica layer. Meanwhile, the reaction between the silica precursor and oxygen continues within pores in the porous support that are not filled with the silica layer. Therefore, the reaction continues until all pores are filled with the amorphous silica layer, making it easy to obtain a high-performance amorphous silica layer with good reproducibility. In other words, by using the counter-diffusion CVD method, it is possible to easily produce a hydrogen separation membrane having an amorphous silica layer not only on the surface of the intermediate layer of the double-structure porous support, which is the preferred embodiment described above, but also inside the pores of the intermediate layer.

[0023] For example, the amorphous silica layer can be formed by counter-diffusion CVD. TMMOS, the silica source, is placed in a bubbler and heated while nitrogen gas is supplied, causing TMMOS vapor to be supplied into the enclosure. The temperature inside the enclosure can be set to 300°C to 700°C. TMMOS vapor, the silica source inside the enclosure, is supplied to one side of a porous support, and oxygen is circulated to the other side, causing the two to react within the porous support. The reaction was carried out with a tubular porous support with a membrane length of 10 mm to 100 mm, with a TMMOS vapor concentration of 0.80 to 0.95 mol / m 3 A suitable amorphous silica layer can be formed by setting the oxygen flow rate to 100 to 300 mL / min and the film formation time to 30 to 120 minutes. Thereafter, the TMMOS vapor is stopped, the inside of the enclosure is purged with oxygen, the supply of oxygen is stopped, and nitrogen is supplied into the inside of the porous support and purged to obtain an amorphous silica layer.

[0024] The method for producing a hydrogen separation membrane according to the present disclosure preferably includes a step of forming an amorphous silica layer having an average pore diameter of 0.2 nm to 0.3 nm on a porous aluminum oxide body having an average pore diameter of 30 nm to 1000 nm by a CVD method using a silica source containing TMMOS. As described above, the porous support has a two-layer structure comprising at least a support layer and an intermediate layer, and the support layer is preferably a porous body having an average pore diameter of 50 nm to 200 nm, and the intermediate layer is preferably a porous body having an average pore diameter of 3 nm to 5 nm. It is more preferable to form an amorphous silica layer on the intermediate layer of the two-layer support by a counter-diffusion CVD method not only on the surface of the intermediate layer but also within the pores. An example of the method for producing the porous support having a two-layer structure is as described above.

[0025] There is no particular limitation on the thickness of the amorphous silica layer. Generally, the thicker the silica layer in a hydrogen separation membrane, the better the hydrogen separation efficiency, but the lower the gas permeability. From this perspective, the thickness of the separation active region in the amorphous silica layer can be 5 nm to 100 nm, and preferably in the range of 5 nm to 15 nm. Here, the separation active region in the amorphous silica layer refers to a dense region in the amorphous silica layer that contributes to hydrogen separation. The inventors presume that a region of the amorphous silica layer formed inside the pores of the intermediate layer, which has a denser structure, functions as a separation active region with higher hydrogen separation activity than a silica film formed in a free state on the surface of the intermediate layer, which has no pores. This region is referred to as the separation active region in the amorphous silica layer. The separation active region in the amorphous silica layer can be identified as a region where Al2p increases and Si2p decreases based on the elemental composition in the depth direction of the formed amorphous silica layer, as a result of analysis by X-ray photoelectron spectroscopy (XPS) described below.

[0026] The thickness of the amorphous silica layer and the thickness of the separation active region in the amorphous silica layer can be measured by performing elemental composition analysis of the amorphous silica layer in the formed hydrogen separation membrane from the surface opposite to the porous support side, in the depth direction of the membrane, using X-ray photoelectron spectroscopy (hereinafter referred to as XPS). In this disclosure, an XPS VG ESCALAB 250 spectrometer (manufactured by Thermo Fisher Scientific) equipped with an Al K radiation source was used, and the chamber pressure was set at 10 -8 The values ​​used were measured at less than Pa and an etching rate of 0.05 nm / s. The elements and electron orbitals analyzed by XPS were Si: 2p, Al: 2p, O: 1s, and C: 1s.

[0027] The hydrogen separation membrane produced by the hydrogen separation membrane manufacturing method according to the present disclosure (sometimes referred to as the "hydrogen separation membrane of the present disclosure") is preferably a hydrogen separation membrane having an aluminum oxide porous support having an average pore diameter of 30 nm to 1000 nm, and an amorphous silica layer on one side of the porous support, the amorphous silica layer including a separation active region having an average pore diameter of 0.2 nm to 0.3 nm, derived from a silica source containing TMMOS, and more preferably a hydrogen separation membrane in which the amorphous silica layer is formed all the way to the inside of the pores of the porous support.

[0028] The hydrogen separation membrane of the present disclosure exhibits good hydrogen separation properties and gas permeability, particularly in high-temperature and high-humidity environments of 500°C or higher. The gas permeability (also referred to as gas transmission rate) of a hydrogen separation membrane can be measured by the following method. When the flow rate of the permeating gas is relatively high, for example, about 1 mL / min or more, the gas permeability can be measured using a bubble flow meter (hereinafter also referred to as BFM). On the supply side, for example, in the case of a membrane reactor having a cross-sectional view shown in FIG. 7 described later, gas is supplied to the outside of the tubular porous support (the outside of the tubular porous support, i.e., the side having the hydrogen separation membrane) to set the supply side pressure to 0.2 MPaG, and the gas is allowed to permeate using a dead-end method with a transmembrane pressure difference of 0.2 MPa. The flow rate of the permeated gas obtained from the permeation side (the inside of the tubular porous support, i.e., the support layer side of the porous support) can be measured using a soap film flow meter (BFM) (manufactured by HORIBA, Ltd.).

[0029] When the permeate gas flow rate is too low to measure using BFM, the permeate gas flow rate is measured using the pressure change method. For this method, the supply pressure is set to 0.25 MPaG, and the permeate side is evacuated for at least one hour using an oil rotary vacuum pump (manufactured by ULVAC, Inc.), creating a transmembrane pressure difference of approximately 0.35 MPa. By shutting off the line leading to the vacuum pump on the permeate side, the permeate gas accumulates on the permeate side, causing the pressure to rise. The rate of this pressure rise can be measured, and the amount of permeate gas can be calculated from the permeate side volume.

[0030] <Hydrogen separation membrane> Fig. 6 is a partially enlarged cross-sectional view schematically illustrating one embodiment of a hydrogen separation membrane 16 according to the present disclosure. The hydrogen separation membrane 16 shown in Fig. 6 has an amorphous silica layer 30, which has a hydrogen separation function, on one surface of a porous support 25. As described above, the amorphous silica layer may be formed not only on the surface of the porous support 25 but also within the pores of the porous support 25. In the embodiment shown in FIG. 6, the porous support 25 has a two-layer structure consisting of a support layer 26 and an intermediate layer 28, and it is preferable that the support layer 26 is a porous body having an average pore diameter of 50 nm to 200 nm, and the intermediate layer 28 is a porous body having an average pore diameter of 3 nm to 5 nm. The porous support 25 has a two-layer structure including a support layer 26 that has good strength, gas permeability, and is cost-effective, and an intermediate layer 28 that better retains the amorphous silica layer 30 and has smaller pores than the support layer 26, which is preferable from the viewpoint of being able to more stably fix the amorphous silica layer and ensure that the amorphous silica layer remains stable for a longer period of time. In the present disclosure, the surface of the intermediate layer opposite to the surface that contacts the support layer is referred to as the "surface of the intermediate layer."

[0031] The porous support having a two-layer structure has an amorphous silica layer on at least the side of the intermediate layer opposite the support layer side. The amorphous silica layer may be formed only on the surface of the intermediate layer, or may be formed not only on the surface of the intermediate layer but also extending into the pores of the intermediate layer. In the porous support having a two-layer structure, it is preferable that an amorphous silica layer is present inside the pores of the intermediate layer and on the surface of the intermediate layer. It is believed that the presence of an amorphous silica layer inside the pores allows the amorphous silica layer to be packed more densely and more stably in the pores, thereby improving the function of the amorphous silica layer as a molecular sieve and allowing the amorphous silica layer to function as a separation active region with good hydrogen separation function. The separation active region will be described later.

[0032] Here, "having an amorphous silica layer inside the pores" refers to both a state in which the amorphous silica layer is formed on the inner wall surface of the pores and a state in which the pores are filled with an amorphous silica layer. For example, when forming an amorphous silica layer by the chemical vapor deposition method described below, a silica precursor in a gaseous state penetrates the inside of the pores and is converted into an amorphous silica layer on the inner wall surface of the pores. If the chemical vapor deposition is continued, the thickness of the amorphous silica layer formed on the inner wall surface of the pores increases, and the pore diameter may be filled with an amorphous silica layer. Both of these are referred to as having an amorphous silica layer inside the pores. A preferred embodiment of the hydrogen separation membrane of the present disclosure has an amorphous silica layer inside the pores of the intermediate layer and on the surface of the intermediate layer, the thickness of the hydrogen separation active region in the amorphous silica layer is 5 nm to 15 nm, and the membrane length of the amorphous silica layer is 6 cm or more.

[0033] <Hydrogen separation method> The hydrogen separation membrane of the present disclosure has excellent hydrogen permeation selectivity and can be suitably used in hydrogen separation methods. That is, the hydrogen separation method according to the present disclosure includes a gas supply step of supplying a mixed gas containing hydrogen and at least one gas other than hydrogen to a hydrogen separation membrane manufactured by the method for manufacturing a hydrogen separation membrane according to the present disclosure described above; and a gas separation step of separating a portion of the mixed gas through the hydrogen separation membrane to produce a permeated gas having a higher hydrogen concentration than the mixed gas.

[0034] The gases other than hydrogen contained in the mixed gas are not particularly limited, and examples thereof include methane, nitrogen, oxygen, carbon monoxide, and carbon dioxide.

[0035] The hydrogen separation membrane disclosed herein has excellent heat resistance and exhibits high hydrogen selectivity even in high-temperature, high-steam environments. For example, by supplying a mixed gas (feed gas) containing hydrogen produced by steam reforming of methane, water vapor, and carbon dioxide to the hydrogen separation membrane disclosed herein in an environment of 500°C or higher and allowing hydrogen to selectively permeate, a permeated gas with a higher hydrogen concentration than the feed gas can be obtained.

[0036] <Hydrogen production equipment> The hydrogen separation membrane of the present disclosure can be suitably used, for example, in a hydrogen production device that supplies a mixed gas containing hydrogen and separates it into a permeable gas containing hydrogen at a high concentration. One embodiment of a hydrogen production device equipped with the hydrogen separation membrane of the present disclosure (sometimes referred to as the hydrogen production device of the present disclosure) comprises a biogas supplier that supplies biogas, a membrane reactor inside a cylindrical body that contains a catalyst for producing hydrogen gas from the biogas supplied from the biogas supplier and a hydrogen separation membrane that selectively allows hydrogen gas to permeate, and a recovery device that recovers hydrogen gas with a purity of 99% or more separated by the membrane reactor, wherein the hydrogen separation membrane is the hydrogen separation membrane of the present disclosure.

[0037] Another embodiment of the hydrogen production device of the present disclosure is a hydrogen production device comprising: a biogas supplier that supplies biogas; a membrane reactor that has a cylindrical body and is equipped inside with a catalyst that produces hydrogen gas from the biogas supplied from the biogas supplier and a hydrogen separation membrane that selectively allows hydrogen gas to permeate; and a recovery device that recovers hydrogen gas with a purity of 99% or more separated by the membrane reactor, wherein the hydrogen separation membrane is the hydrogen separation membrane of the present disclosure.

[0038] An example of a hydrogen production device according to the present disclosure will be described with reference to the drawings. Fig. 7 is a schematic diagram showing one embodiment of a hydrogen production apparatus according to the present disclosure. The hydrogen production apparatus 10 shown in Fig. 7 includes a biogas supplier 12, a pipe 24A connected to the biogas supplier 12 and transporting the biogas supplied from the biogas supplier 12 to a membrane reactor 14A, and the membrane reactor 14A for treating the biogas. In the embodiment shown in FIG. 7, the membrane reactor 14A is provided with, inside a hollow cylinder, a catalyst 18 that produces hydrogen gas from biogas, and a hydrogen separation membrane 16 that selectively allows permeation of high-purity hydrogen gas produced by the catalyst, specifically, hydrogen gas with a purity of 99% or more. The biogas transported from pipe 24A is supplied to the center of the inner cylinder (hydrogen separation membrane) of the double cylinders, which is filled with catalyst 18, and is separated into hydrogen gas and carbon dioxide by the function of catalyst 18, producing hydrogen gas. The produced hydrogen gas passes through hydrogen separation membrane 16 and is guided between hydrogen separation membrane 16, which is the outermost layer of membrane reactor 14A made up of double cylinders, and the outer cylinder, and is discharged to the outside of membrane reactor 14A. The extracted hydrogen gas is supplied to a gas-liquid separator 20A equipped with a cooler via a pipe 24A equipped with a temperature control device 24B for the pipe, where the remaining water vapor is separated into water, and the high-purity hydrogen gas is recovered via the pipe 24A in a hydrogen gas recovery device (not shown).

[0039] The temperature control device for the pipe is appropriately selected from known temperature control devices depending on the size, material, etc. of the pipe in the hydrogen production device. A typical example is a heater with a temperature control function. For small-scale hydrogen production devices, a ribbon heater can be used. A temperature control device 22 for controlling the temperature inside the membrane reactor 14A is attached to the outside of the membrane reactor 14A, and controls the temperature inside the membrane reactor 14A to a temperature suitable for reaction efficiency. A pipe temperature control device 24B is attached to the outside of the pipe 24A connecting the biogas supplier 12 and the membrane reactor 14A and the pipe 24A that discharges the obtained hydrogen gas, and the temperature is controlled within a range that does not cause liquefaction of the gas transported through the pipe. The mixed gas containing carbon dioxide from which hydrogen gas has been separated in the membrane reactor 14A passes through the center of the cylindrical membrane reactor 14A and is discharged to the outside of the membrane reactor 14A. The discharged mixed gas is supplied to a gas-liquid separator 20B equipped with a cooler via a pipe 24A equipped with a temperature control device 24B for the pipe, and the remaining water vapor is separated into water in the gas-liquid separator 20B and recovered in a recovery device not shown.

[0040] Fig. 8 is a schematic cross-sectional view of the membrane reactor 14A of the hydrogen production device 10 shown in Fig. 7. As shown in Fig. 8, the membrane reactor 14A has a double-tube structure consisting of a cylindrical outer tube 17 and an inner tube made of a hydrogen separation membrane 16. Biogas is introduced into a flow path inside a cylindrical inner tube, a hydrogen separation membrane 16 filled with a catalyst 18, and hydrogen generated by the catalyst 18 passes through the hydrogen separation membrane 16 in the direction of the arrow shown in Figure 8 and is discharged into the space between the double cylindrical hydrogen separation membrane 16 and the outer tube 17. In the cylindrical membrane reactor 14A shown in FIG. 8, the catalyst 18 is filled in the center of the cylindrical membrane reactor 14A, i.e., inside the inner tube which is the hydrogen separation membrane 16, but the embodiment of the membrane reactor is not limited to this.

[0041] Figure 9 is a schematic cross-sectional view showing another embodiment of a cylindrical membrane reactor. In the membrane reactor 14B shown in Figure 9, a catalyst 18 is filled in the space between the hydrogen separation membrane 16 and the outer tube 17 of the cylindrical membrane reactor 14B. In the membrane reactor 14B shown in Figure 9, biogas supplied from the biogas supplier 12 is introduced into the space between the outer tube 17 and the hydrogen separation membrane 16 of the cylindrical membrane reactor 14B, and the hydrogen gas produced by the catalyst 18 passes through the hydrogen separation membrane 16, which is the cylindrical inner tube of a double structure, in the direction of the arrow shown in the figure, and is led to the inside of the hydrogen separation membrane 16 in the cylindrical membrane reactor 14B. Although Figure 9 shows an embodiment in which only one hydrogen separation membrane 16 is present in the outer tube 17, this is not limited to this, and the outer tube may have a structure in which multiple hydrogen separation membranes are present.

[0042] The membrane reactor may have any shape as long as it contains a catalyst and generates hydrogen from biogas, and separates the generated hydrogen from the biogas through a hydrogen separation membrane. Among these, the double-structured cylindrical reactor shown in Figures 8 and 9, in which the inner cylinder is a hydrogen separation membrane 16, is preferred because it can separate hydrogen efficiently with a simple structure. The size of the cylindrical membrane reactor shown in FIGS. 8 and 9 can be selected arbitrarily depending on the purpose. From the viewpoint of being able to set the size of the hydrogen production device in an appropriate range, the outer diameter is preferably in the range of 30 mm to 150 mm, more preferably in the range of 40 mm to 80 mm. The outer diameter of the inner cylinder equipped with the hydrogen separation membrane is preferably in the range of 5 mm to 20 mm, more preferably in the range of 5 mm to 10 mm. If the length of the membrane reactor, that is, the length of the cylinder of a cylindrical membrane reactor, is long, a hydrogen separation membrane of a larger size can be accommodated. From the viewpoint of being able to produce a sufficient amount of hydrogen, the membrane length of the hydrogen separation membrane housed in the membrane reactor is preferably 6 cm or more, and more preferably 8 cm or more. Note that the membrane length of the hydrogen separation membrane means the length from the end of the hydrogen separation membrane housed in the membrane reactor on the biogas inlet side to the end on the opposite side.

[0043] When the membrane reactor size is within the above range, more efficient hydrogen production becomes possible. One hydrogen production device may include only one membrane reactor, or may include two or more membrane reactors. The membrane reactors may be provided in parallel or in series, but from the viewpoint of hydrogen production efficiency, it is preferable to arrange multiple membrane reactors in parallel. In order to further increase the amount of hydrogen produced, it is possible to arrange two or more membrane reactors in parallel for one hydrogen production device. The number of membrane reactors for one hydrogen production device can be selected appropriately depending on the purpose of the hydrogen production device. For example, when installing a hydrogen production device in a sewage treatment facility, it is possible to install more than 1,000 membrane reactors to process a large amount of biogas.

[0044] There are no particular limitations on the catalyst that is packed in the membrane reactor and that produces hydrogen from biogas, and any known reforming catalyst can be used. As the reforming catalyst, a catalyst containing nickel (Ni), rhodium (Rh), ruthenium (Ru), or the like as an active species can be used. The catalyst may be commercially available or may be prepared from a metal precursor. An example of a commercially available product is reforming catalyst TRC10-2A (trade name, diameter approximately 2 mm) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. As a method for preparing the catalyst, for example, Ni catalyst is prepared by adding Ce to the precursor, Nickel (II) Nitrate Hexahydrate aqueous solution, with Ni as the active species. 0.15 Zr 0.85Add O₂ and react, dry to form a powder and take it out, bake at a temperature of about 500 °C to 600 °C in an electric furnace, then heat at about 500 °C to 600 °C, and it can be obtained by hydrogen reduction. Usually, a catalyst obtained by supporting a metal precursor for the catalyst on a spherical carrier is used. The size of the catalyst depends on the size of the carrier. For a Ni catalyst, it can be 400 μm to 2000 μm, and 500 μm to 750 μm is preferred. As the Rh catalyst, a Rh / ALO-6 catalyst obtained by an impregnation method using γ-alumina as a carrier is preferably used. The average particle diameter of the spherical ALO-6 serving as the carrier is about 1.6 mm. The amount of the catalyst filled in the membrane reactor may be appropriately selected according to the purpose.

Examples

[0045] Hereinafter, examples will be given to specifically explain the method for manufacturing a hydrogen separation membrane and the hydrogen separation method according to the present disclosure. However, the present disclosure is not limited to the following examples and can be implemented in various modified examples as long as the gist thereof is not exceeded. Note that “%” indicating the mixing ratio of gases represents “volume %” unless otherwise specified.

[0046] [Manufacturing of a TMMOS membrane with changed film-forming conditions] Using TMMOS as the silica source, film formation and evaluation were performed in the same manner as in Example 1 described later, except that the TMMOS concentration during CVD, the nitrogen flow rate as the carrier gas, and the CVD time were changed, and the permeation rates and ideal separation factors of hydrogen and nitrogen at 600 °C were calculated.

[0047] [Effect of TMMOS concentration during CVD film formation on film performance] As in the following film-forming conditions, the carrier (N₂) gas flow rate was 200 mL / min -1 , and film formation was carried out with the CVD time fixed at 60 min. (Film-forming conditions) Film-forming temperature: 600 [°C] O₂ flow rate: 200 [cm 3 / min] N₂ flow rate: 200 [cm3 / min] Film formation time: 60 [min] Figure 1 is a graph showing the relationship between the concentration of TMMOS used as a silica source in the formation of a hydrogen separation membrane, the hydrogen and nitrogen permeation rates of the formed hydrogen separation membrane at 600 °C, and the hydrogen / nitrogen selectivity (theoretical value), indicating the influence of the concentration of TMMOS, which is the silica source, on the membrane performance.

[0048] <Influence of the carrier (N2) gas flow rate during CVD film formation on the membrane performance> Under the following film formation conditions, the film was formed with the TMMOS concentration fixed at 0.916 molm -3 , and the CVD time fixed at 60 min. (Film formation conditions) Vapor concentration: 0.916 [mol / m 3 Film formation temperature: 600 [°C] O2 flow rate: 200 [cm 3 / min] Film formation time: 60 [min] Figure 2 is a graph showing the relationship between the nitrogen flow rate when TMMOS used as a silica source in the formation of a hydrogen separation membrane is supplied with nitrogen as a carrier gas, the hydrogen and nitrogen permeation rates of the formed hydrogen separation membrane at 600 °C, and the hydrogen / nitrogen selectivity.

[0049] <Influence of CVD time on the membrane performance> Under the following film formation conditions, the film was formed with the TMMOS concentration fixed at 0.833 molm -3 , and the carrier (N2) gas flow rate fixed at 200 mLmin -1 . (Film formation conditions) Vapor concentration: 0.​​Figure 3 is a graph showing the relationship between the deposition time and the hydrogen and nitrogen permeabilities and hydrogen / nitrogen selectivity of the hydrogen separation membrane at 600°C when a hydrogen separation membrane is deposited by CVD using TMMOS as the silica source, and shows the effect of CVD time on membrane performance.

[0050] As a result of the above experiments, the TMMOS concentration was 0.8 to 0.95 mol / m 3 The optimum conditions for the carrier gas flow rate and CVD time were 200 mL / min and 60 minutes, respectively (Figs. 1 to 3). The hydrogen permeability of the hydrogen separation membrane at 600°C was 4.6 × 10 -7 mol m -2 s -1 Pa -1 It was confirmed that the hydrogen permeability was good.

[0051] Example 1 (Manufacturing hydrogen separation membranes) 1. Fabrication of Porous Support (1-1. Preparation of porous substrate) A tubular α-alumina substrate (manufactured by Noritake Co., Ltd.) was used as the support layer of the porous support. The tubular substrate had an outer diameter of 6 mm, an inner diameter of 4 mm, and a catalog value of 150 nm pore diameter. The tubular substrate was cut to a length of 120 mm using a diamond cutter, and both ends of 20 mm were glass sealed. Therefore, the length of the portion of the 120 mm long tubular substrate that functions as a porous substrate, i.e., the portion where the silica membrane described below is formed and functions as a hydrogen separation membrane, is 80 mm (8 cm).

[0052] (1-2. Preparation of Coating Solution for Forming Intermediate Layer) The prepared substrate was coated with γ-alumina to form an intermediate layer. 500 g of aluminum s-butoxide (ALSB: Fujifilm Wako Pure Chemical Industries, Ltd.), 500 mL of 2-propanol (Fujifilm Wako Pure Chemical Industries, Ltd.), and 25 g of gallium(III) nitrate 8-hydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) were prepared. The boehmite sol was prepared in a nitrogen-substituted glove box (manufactured by AS ONE Corporation).

[0053] 3.60 g (0.06 mol) of 2-propanol was placed in a beaker, and the inner wall of the beaker was wetted. 24.6 g (0.10 mol) of ALSB was added directly from the reagent bottle to the wetted beaker, and the mixture was stirred for 1 hour. 360 mL of pure water was placed in a 500 mL beaker and heated to 90°C on a hot stirrer. The 500 mL beaker was replenished with pure water as needed to adjust the liquid level. In a glove box, a 100 mL mixture of ALSB and 2-propanol was placed in a dropping bottle, and a nitrogen balloon was attached to the top of the dropping bottle. The dropping bottle with the nitrogen balloon attached was removed from the glove box, and pure water at 90°C that had been prepared on a hot stirrer was vigorously stirred, and the mixture of ALSB and 2-propanol was added dropwise to it. Stirring was continued at 90°C until 2-propanol was evaporated, which was confirmed by the disappearance of the alcohol smell. Gallium(III) nitrate 8-hydrate (17.14 g, 0.04 mol) was added to 108 g of pure water (6 mol), and the beaker was covered with Parafilm (product name, plastic paraffin film, LMS Co., Ltd.) and stirred for at least 1 hour to prepare an aqueous gallium nitrate solution. After evaporating 2-propanol, the mixture was transferred to a 500 mL Erlenmeyer flask, and the flask was left to cool with its neck covered with aluminum foil. After cooling, the gallium nitrate solution was slowly added dropwise with vigorous stirring, and the mixture was stirred for 12 hours or more to obtain a boehmite sol.

[0054] The obtained boehmite sol was used to prepare a coating liquid. 47.5 mL of purified water was placed in a 50 mL graduated cylinder, followed by 2.5 mL of 1 M HNO3 (Fujifilm Wako Pure Chemical Corporation). This solution was transferred to a 100 mL Erlenmeyer flask equipped with a stirrer. 1.75 g of Poly(vinyl alcohol) 500 [Completely Hydrolyzed (PVA) (Fujifilm Wako Pure Chemical Corporation)] was added to the 100 L Erlenmeyer flask while gently stirring with a stirrer to avoid foaming. The 100 mL Erlenmeyer flask was then transferred to a hotplate stirrer, and the sparingly soluble PVA was heated to dissolve. The nozzle of the Erlenmeyer flask was sealed with aluminum foil, and stirring was continued while heating to 90°C. After 40 minutes, the mixture was allowed to cool while still stirring, yielding a PVA solution. 20 mL of the obtained PVA solution and 30 mL of the boehmite sol obtained above were placed in a 50 mL beaker, a stirring bar was placed inside, the opening of the beaker was covered with parafilm, and the mixture was stirred for 15 minutes to obtain a coating solution.

[0055] (1-3. Formation of the intermediate layer) In order to form an intermediate layer on the outer surface of the tubular support layer (substrate) prepared in 1-1, one side of the substrate, i.e., the lower side during dipping, was sealed with sealing tape to prevent the coating solution from penetrating inside the tubular substrate. The coating solution obtained in 1-2 was poured into a test tube, taking care not to trap air bubbles, and a substrate with a total length of 120 mm was dipped into the coating solution for 5 seconds. Care was taken not to touch the wall of the test tube when putting the substrate in or out. The dipped substrate was placed in an electric muffle furnace KM-600 (manufactured by Advantec Corporation), first heated to 60°C and held there for 3 hours, then the temperature inside the furnace was increased from 60°C to 600°C over 6 hours, held at 600°C for 3 hours, and then cooled to room temperature (25°C) over 3 hours. This dip coating and firing process was repeated three times to produce a porous support with a two-layer structure consisting of an α-alumina support layer and a γ-alumina intermediate layer laminated thereon. For the purpose of measuring the pore diameter, a substrate having a length of 20 mm was prepared and an intermediate layer was formed in the same manner to obtain a sample for evaluation of the porous support.

[0056] 2. Hydrogen separation membrane production For the production of the hydrogen separation membrane, oxygen gas was supplied from a cylinder equipped with a mass flow controller (MFC: manufactured by Kofloc Corporation), and the silica source was placed in a bubbler and supplied by bubbling with a carrier gas. In addition, to control the flow rate of the gas containing TMMOS, the silica source, nitrogen was supplied as a carrier gas from a cylinder equipped with an MFC as needed. The silica source, TMMOS, was placed in a bubbler, and nitrogen was supplied to the bubbler at a flow rate of 200 mL / min. By bubbling, vaporized TMMOS was supplied to the enclosure. To prevent TMMOS condensation in the piping, a ribbon heater was wrapped around the piping as a temperature control device, and the piping temperature was maintained at 180°C. In addition, unreacted TMMOS was collected using an ice-water cold trap (gas-liquid separator). The bubbler temperature was controlled by immersing the bubbler in a constant-temperature water bath made using a COOLNIT CL-150R (manufactured by Taitec Co., Ltd.).

[0057] The silica source for the hydrogen separation membrane was TMMOS manufactured by Tokyo Chemical Industry Co., Ltd. (product code: M0688). TMMOS has the molecular formula: CH 12 OSi, molecular weight: 104.22, specific gravity: 0.76, boiling point: 57°C.

[0058] First, the temperature control of the furnace, ribbon heater, and bubbler in the film-forming device was turned on. The furnace was heated from room temperature (25°C) to 600°C over 1.5 hours, and the ribbon heater outside the pipe was set to 180°C. Once all temperatures have stabilized, prepare an ice-water cold trap and measure the TMMOS vapor concentration using a gas line that does not pass through the enclosure. The TMMOS vapor concentration is approximately 0.93 mol / m -3 The bubbler temperature was adjusted so that After adjusting the bubbler temperature, TMMOS vapor was supplied to the outside of the tubular porous support in the housing. After 2 minutes, oxygen was circulated inside the tubular porous support at 200 mL / min to start the deposition of the hydrogen separation membrane using the counter-diffusion CVD method. After 60 minutes, the supply of TMMOS vapor was stopped, and nitrogen was circulated at full flow rate outside the porous support, while oxygen was circulated at 200 mL / min inside the case to purge the inside of the case. After 1 hour, the oxygen supply was stopped and nitrogen was purged into the substrate at full flow rate for several minutes to complete the deposition of the hydrogen separation membrane. The amorphous silica layer formed on the porous substrate had a membrane length of 8 cm.

[0059] Comparative Example 1 (Manufacturing hydrogen separation membranes) A hydrogen separation membrane was produced in the same manner as in Example 1, except that the silica source and membrane production conditions in the production of the hydrogen separation membrane were changed as follows.

[0060] DMDMS (product code: D1052) manufactured by Tokyo Chemical Industry Co., Ltd. was used as the silica source for the hydrogen separation membrane. DMDMS has the molecular formula: CH 12 O2Si, molecular weight: 120.22, specific gravity: 0.87, boiling point: 81°C.

[0061] First, the temperature control of the furnace, ribbon heater, and bubbler in the film-forming device was turned on. The furnace was heated from room temperature (25°C) to 600°C over 1.5 hours, and the ribbon heater outside the pipe was set to 180°C. Once all temperatures have stabilized, prepare an ice-water cold trap and measure the DMDMS vapor concentration using a gas line that does not pass through the enclosure. The DMDMS vapor concentration is approximately 0.93 mol / m -3 The bubbler temperature was adjusted so that After adjusting the bubbler temperature, DMDMS vapor was supplied to the outside of the tubular porous support in the housing, and after 2 minutes, oxygen was circulated inside the tubular porous support at 200 mL / min to start the deposition of the hydrogen separation membrane by the counter-diffusion CVD method. After 60 minutes, the supply of DMDMS vapor was stopped, and nitrogen was circulated at full flow rate outside the porous support, while oxygen was circulated at 200 mL / min inside the case to purge the inside of the case. After 1 hour, the supply of oxygen was stopped, and nitrogen was purged inside the substrate at a full-open flow rate for several minutes to complete the formation of the hydrogen separation membrane. The film length of the amorphous silica layer formed on the porous substrate is 8 cm.

[0062] (Evaluation of Hydrogen Separation Membrane) 1. Pore Size of Porous Support The pore size of the porous support was measured using a Nano-Perm Porometer (manufactured by Seika Digital Image Co., Ltd.). When measuring the pore size, one end of the tubular porous support was fixed to a metal base using an epoxy-based adhesive (DEV-TUBE S-208 manufactured by ITW Performance Polymers & Fluids Japan Co., Ltd.) or the like, and the other end was sealed. Analysis using the relationship between the dimensionless permeability coefficient and the Kelvin diameter of the γ-alumina intermediate layer showed that the dimensionless permeability coefficient decreased most significantly between a Kelvin diameter of 3.2 nm and 4.2 nm. Therefore, the peak of the pore size distribution was estimated to be between 3.2 nm and 4.2 nm.

[0063] 2. Gas Permeability A gas permeation test was conducted using the film-forming apparatus used for forming the hydrogen separation membrane. Hydrogen gas was supplied to the supply side (outside of the tubular porous support) to set the supply side pressure to 0.2 MPaG, and hydrogen gas was permeated in a dead-end mode with a membrane differential pressure of 0.2 MPa. The flow rate of the permeated gas obtained from the permeation side (inside of the annular porous support) was measured using a soap film flow meter (Bubble Flow Meter: BFM) (manufactured by Horiba, Ltd.). The gas permeability of the hydrogen separation membrane was calculated from the permeated gas flow rate measured using the BFM. The measurement was performed at 600°C.

[0064] <Comparison of Performance between TMMOS Membrane and DMDMS Membrane> Figure 4 is an Arrhenius plot showing the temperature dependence of the hydrogen permeability and nitrogen permeability at 600°C of a membrane (TMMOS membrane: Example 1) using TMMOS as the silica source and a membrane (DMDMS membrane: Comparative Example 1) using DMDMS in the formation of the hydrogen separation membrane. The difference in performance between the TMMOS membrane and the DMDMS membrane can be seen.

[0065] <Changes in hydrogen permeability over time in a water vapor atmosphere> 5 is a graph showing the change over time in hydrogen permeability in a water vapor atmosphere (0.3 MPa, water vapor:hydrogen gas supply ratio 3:1) for a hydrogen separation membrane formed using TMMOS as the silica source (TMMOS membrane: Example 1) and a membrane formed using DMDMS (DMDMS membrane: Comparative Example 1). The TMMOS membrane has a higher hydrogen permeability than the DMDMS membrane.

[0066] When the TMMOS film (Example 1) fabricated under the optimum conditions as described above was compared with the DMDMS film (Comparative Example 1), it was found that the TMMOS film had a higher hydrogen permeability (FIG. 4). Furthermore, when the change in hydrogen permeability over time was measured in a water vapor atmosphere, the TMMOS film showed a higher hydrogen permeability (Figure 5). [Industrial Applicability]

[0067] The manufacturing method for hydrogen separation membranes disclosed herein has high hydrogen separation performance even under high temperatures and high water vapor partial pressures, and has the potential to greatly contribute to the creation of an energy-saving, decarbonized society through the use of hydrogen separated from biogas and other sources. [Explanation of symbols]

[0068] 10 Hydrogen production equipment 12 Biogas supplier 14A Membrane Reactor 14B Membrane reactor 16 Hydrogen separation membrane 18 Catalyst 20A gas-liquid separator 20B Gas-liquid separator 22 Temperature control device 24A Pipe (Plumbing) 24B Pipe Temperature Control Device 26 Support layer 28 Middle Class 30 amorphous silica layer

Claims

1. A method for producing a hydrogen separation membrane, comprising the step of forming an amorphous silica layer on one surface of an aluminum oxide porous support having an average pore size of 30 nm to 1000 nm by chemical vapor deposition using a silica source containing trimethylmethoxysilane.

2. 2. The method for producing a hydrogen separation membrane according to claim 1, wherein the chemical vapor deposition method is a counter-diffusion chemical vapor deposition method.

3. a gas supply step of supplying a mixed gas containing hydrogen and at least one gas other than hydrogen to the hydrogen separation membrane manufactured by the method for manufacturing a hydrogen separation membrane according to claim 1 or 2; a gas separation step in which a portion of the mixed gas permeates the hydrogen separation membrane and is separated as a permeated gas having a higher hydrogen concentration than the mixed gas; A hydrogen separation method comprising:

4. 4. The hydrogen separation method according to claim 3, wherein the gas separation step is carried out in an environment of 500°C or higher.

Images