JP5425839B2 - Method for producing gas separation material - Google Patents

Description

  The present invention relates to a method for producing a hydrogen gas separator and other gas separators.

  Hydrogen gas separation materials used for supplying hydrogen in fuel cells, catalyst membrane reactors, and the like are known. Such a hydrogen gas separator is typically excellent in heat resistance and water vapor resistance in addition to high hydrogen permeability. As one typical method for producing such a hydrogen gas separation material, for example, a porous substrate made of a ceramic material and having pores with a pore diameter of 50 nm or more has a pore diameter of 0.6 nm or less. There is known a method including a process of forming a porous silica film and thereby reducing the opening size of the pores of the substrate. Typical examples of the method for forming such a silica film include a chemical vapor deposition (CVD) method and a sol-gel method. Patent Documents 1 and 2 are cited as prior art documents relating to the formation of a silica film using CVD.

JP 2005-254161 A JP 2009-106912 A

The method for forming a silica film by CVD described in Patent Documents 1 and 2 is tetraethoxysilane (Tetraethyl).
A silica source such as Orthosilicate: TEOS) or tetramethoxysilane (Tetramethyl Orthosilicate: TMOS) is vaporized and supplied from one surface of the porous substrate in a gas state, and from the other surface (back surface) of the substrate. By supplying a gas such as ozone (O ₃ ) or oxygen (O ₂ ), they react with each other in the pores of the base material to form a silica film (hereinafter, this type of CVD is performed). Sometimes called “opposite diffusion CVD”.)

When manufacturing the hydrogen gas separator and other gas separators by applying the counter diffusion CVD, the gas described above is supplied to the porous substrate, and the porous substrate is often called a pinhole. Coarse pores (defects) are present. It is extremely difficult to completely remove this defect from the porous base material, and when the porous base material having the defect is separated by inspection, the inspection process is very expensive. Furthermore, since the yield of the porous base material is remarkably lowered, as a result, the manufacturing cost of the gas separation material is increased.
However, when a gas separation material is manufactured by counter diffusion CVD under certain film formation conditions using a porous substrate having defects, the gas separation performance of the gas separation material is determined based on the presence or absence of defects in the porous substrate. The amount is greatly affected. That is, the reproducibility of the performance of the produced gas separation material is significantly reduced.

  Accordingly, the present invention provides a method for producing a hydrogen gas separation material or other gas separation material having a silica film formed by counter diffusion CVD, and has a good performance even when a porous substrate having defects is used. It aims at providing the manufacturing method of the gas separation material which can form a membrane stably.

In order to achieve the above object, the present invention provides a method for producing a gas separation material (typically a hydrogen gas separation material) comprising a porous substrate and a silica membrane. That is, the manufacturing method disclosed herein includes a step of preparing the porous substrate. Also, chemical vapor deposition in which a vaporized silica source supplied together with an inert gas as a silica source-containing gas on one surface side of the substrate reacts with an oxygen-containing gas supplied on the other surface side of the substrate. The method includes a step of forming a silica film on the substrate by a method. Furthermore, it includes the step of determining the end point of the formation of the silica film by monitoring the gas composition discharged in the step of forming the silica film.
When a silica film is deposited on a porous substrate by the chemical vapor deposition method, that is, counter diffusion CVD, if a porous substrate having defects is used, it is affected by the presence or amount of defects in the porous substrate. The reproducibility of the performance of the gas separation material to be produced is significantly reduced. On the other hand, if a porous substrate having no defect is used, the manufacturing cost of the gas separation material increases.
In the production method according to the present invention, the end point of the formation of the silica film is determined by monitoring the gas composition discharged in the step of forming the silica film, so that a porous substrate having defects is used. However, it is possible to stably form a silica film having good performance. Therefore, an increase in the manufacturing cost of the gas separation material (for example, hydrogen gas separation material) can be suppressed.

  In a preferred embodiment of the method for producing a gas separation material disclosed herein, the monitoring is performed by gas chromatography. Preferably, in the step of determining the end point of the formation of the silica film, the amount of the inert gas is monitored by gas chromatography. Typically, the inert gas is nitrogen gas. According to the manufacturing method of this embodiment, nitrogen gas and other inert gases are monitored in real time by gas chromatography, whereby the end point of the reaction in counter diffusion CVD can be determined.

  In a preferred embodiment of the method for producing a hydrogen gas separator or other gas separator disclosed herein, the oxygen-containing gas used in the step of forming the silica membrane is a pure oxygen gas or a mixture containing 25 vol% or more of oxygen. Gas. By using such a gas as a reactive gas, good counter diffusion CVD can be performed.

In a preferred embodiment of the method for producing a hydrogen gas separator or other gas separator disclosed herein, in the step of determining the end point of the formation of the silica membrane, the silica supplied to one surface side of the base material The concentration of the inert gas contained in the source-containing gas that has passed through the base material and has been contained in the oxygen-containing gas supplied to the other surface side of the base material To.
Monitor the concentration of inert gas (for example, nitrogen) involved in the formation of such a gas separation membrane and leak to the side opposite to the side where the gas is supplied across the porous substrate. By doing (typically employing gas chromatography), it is possible to accurately determine a suitable end point of the CVD reaction in counter diffusion CVD.

In one preferred embodiment of the method for producing a gas separation material disclosed herein, the porous substrate has an average pore diameter or a peak value of a pore diameter distribution formed on a porous support of 2 nm to A film-like porous substrate having a thickness of 100 nm is used.
By applying counter diffusion CVD to a porous substrate having a peak value of the average pore size or pore size distribution to form a silica film, the pores of the substrate are formed of a gas composed of molecular species having a fine size. It can be efficiently reduced to a size suitable for separation, typically hydrogen gas separation. Further, since the base material is supported by the porous support (typically a support made of a ceramic material), the base material is made thinner while ensuring the necessary mechanical strength. Can do. Therefore, it is possible to provide a hydrogen gas separation material having an excellent balance between hydrogen gas permeability and selectivity (separation).

In one Embodiment, it is a figure explaining the process of forming a silica film in a porous base material, and is a typical perspective view of a porous structure. It is a schematic diagram which expands and shows the part enclosed with the dotted line II in FIG. It is a schematic diagram which expands and shows the principal part of FIG. It is a schematic block diagram which shows one suitable example of the silica film formation apparatus used for a silica film formation process. It is a schematic block diagram which shows the other suitable example of the silica film formation apparatus used for a silica film formation process. It is typical sectional drawing explaining the suitable example of the multitubular module which comprises some silica film forming apparatuses. It is the VII-VII sectional view taken on the line of FIG. It is the graph which plotted the gas composition discharged | emitted from the inner tube | pipe exit of the reaction tube in the silica film formation process which concerns on one Example with film forming time.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The porous base material used in the method for producing a hydrogen gas separation material disclosed herein and the material of the porous support used as necessary can form a silica membrane by CVD and are in use (ie, Any material that can withstand the usage environment during gas separation is acceptable. For example, ceramic materials such as α-alumina, γ-alumina, silica, zirconia, silicon nitride, silicon carbide, titania, calcia, and various zeolites can be preferably used. Moreover, the porous base material (as well as the porous support body employ | adopted as needed) formed from these composites or a mixture may be sufficient.

The size of the pores of the porous substrate may be any size as long as pores having a size suitable for separation of a predetermined gas species (for example, hydrogen gas) can be formed by a silica film formed in the vapor deposition step described later. . For example, when used for separation of hydrogen gas (that is, hydrogen molecules), the average pore size (or the peak value of the pore size distribution; typically, the peak value of the pore size distribution can be approximated to the average pore size) is about 100 nm. The following porous substrates can be preferably used, and the pore diameter is more preferably about 50 nm or less (for example, about 20 nm or less, and further about 10 nm or less).
When the pore size of the porous substrate exceeds the above range, it takes a long time to form a silica membrane and reduce the pore size to a size suitable for separation of a desired gas (for example, hydrogen gas). . That is, the production efficiency of the gas separation material is lowered. On the other hand, if the pore size of the porous substrate is too small, the thickness of the silica membrane required to reduce the pore size to a size suitable for the desired gas separation is too small. Variation can easily occur.
Therefore, considering the ease of production of the porous substrate and the formation efficiency of the silica membrane (production efficiency of the hydrogen gas separator), it is appropriate that the average pore diameter or the peak value of the pore diameter distribution is 2 nm or more. It is preferable that it is 4 nm or more. For example, a porous substrate having an average pore diameter or a peak value of pore diameter distribution of 2 nm to 100 nm (for example, 4 nm to 100 nm), further a porous substrate of 2 nm to 50 nm (for example, 4 nm to 50 nm), and further 2 nm to 20 nm A porous substrate (for example, 4 nm to 20 nm), particularly a porous substrate of 2 nm to 10 nm (for example, 4 nm to 10 nm) can be preferably used. A porous substrate having a narrow pore size distribution (high uniformity in pore size) is preferable.
In this specification, the average pore diameter (or peak value of pore diameter distribution) is, for example, a general bubble point test method (JIS K3832; for example, when the pore diameter is in the range of 2 nm to 50 nm) or a mercury intrusion method. The average pore diameter (or the peak value of the pore diameter distribution) calculated based on (JIS R1655; for example, when the pore diameter is 20 nm to 100 nm or more).

  The shape of the porous substrate is not particularly limited, and can take various shapes depending on the application. As one preferred example of an advantageous shape for improving a higher hydrogen gas permeability, a membrane-like (thin plate-like) porous substrate can be preferably employed. For example, it is preferable to use a membrane-like porous substrate (porous membrane) having a thickness of about 0.1 μm to 100 μm (more preferably 0.1 μm to 10 μm, for example, 0.5 μm to 5 μm). The porosity (porosity) of this porous substrate is usually suitably about 20 vol% to 60 vol%. For example, a porous substrate having a porosity of about 30 vol% to 50 vol% is preferably used. Can do.

In a preferred embodiment, such a membrane-like (thin plate-like) porous substrate is formed (provided) on a porous support. Thus, by using a porous substrate supported by a porous support (hereinafter sometimes simply referred to as “support”), the substrate can be further maintained while maintaining necessary mechanical strength. It can be thinned.
By such thinning, in the hydrogen gas separation material formed by forming a silica membrane on the porous base material, higher hydrogen gas separation performance (for example, higher hydrogen gas permeability and / or selectivity is exhibited, or It is possible to realize a high balance between hydrogen gas permeability and selectivity at a higher level.

The shape of the support is not particularly limited, and may be a tube shape, a membrane (thin plate) shape, a sheet shape, a monolith shape, a honeycomb shape, a polygonal flat plate shape, or other three-dimensional shapes depending on applications. Among these shapes, the tube shape is suitable as a hydrogen gas separation module because it can be easily applied to a reactor such as a reformer. For example, a porous structure having a configuration in which a membrane-like porous substrate (porous membrane) is provided on the outer peripheral surface and / or inner peripheral surface (typically only the outer peripheral surface) of a tubular porous support. And the structure is preferably subjected to a silica film forming step (opposite diffusion CVD) described later.
The support may have a laminated structure. For example, two or more porous layers are laminated so that the relative average pore diameter gradually decreases toward the side on which the porous substrate is formed. It may be a support having a structured structure. Moreover, the material of each layer of the porous layer may be the same or different. In addition, the support body of a desired shape can be manufactured by implementing the well-known shaping | molding technique (extrusion molding, press molding, casting molding, etc.) and the ceramic baking technique currently performed conventionally. Such a technique itself does not characterize the present invention and will not be described in detail.

The pore diameter of the pores of the support is not particularly limited as long as it does not significantly impede the permeation of gas such as hydrogen gas and oxygen gas. Those having an average pore size larger than the average pore size of the porous substrate (typically about 2 to 200 times larger) are suitable.
For example, a support having a peak value of pore size distribution and / or an average pore size of preferably about 10 nm to 10000 nm, more preferably 50 nm to 1000 nm is used. A support having a narrow pore size distribution is preferred.
Moreover, the porosity of this support body can be made into about 20 vol%-60 vol%, for example, Usually, it is preferable to make this porosity into about 30 vol%-50 vol%.
The thickness of the support can be appropriately set so as to appropriately support the porous substrate while maintaining the desired mechanical strength depending on the application. Although it does not specifically limit, For example, when the thickness of a porous base material is about 0.1 micrometer-10 micrometers, the thickness of a support body can be about 100 micrometers-about 10 mm.

The material of the porous support may be the same as or different from the material constituting the porous substrate, but from the viewpoint of maintaining the bonding strength with the porous substrate, the same material as the porous substrate described above Are preferably used. For example, it is preferable that the porous support and the porous substrate are both made of a ceramic material (alumina, silica, etc.). It is particularly preferable that the porous support and the porous substrate are made of the same kind of ceramic material. . For example, a support made of α-alumina (typically a support having an average pore diameter of 50 nm or more, for example, an average pore diameter of about 50 nm to 1000 nm), and a porous substrate composed of γ-alumina or silica (typically For example, a combination with a porous substrate having an average pore diameter of 2 nm or more, for example, an average pore diameter of about 2 nm to 20 nm, can be preferably used.
By subjecting the porous structure having such a structure to a silica film formation step (opposite diffusion CVD) described later, a silica film is formed on the porous structure (typically, the porous substrate constituting the structure). Thus, a hydrogen gas separation material can be preferably produced.

The method for forming the porous substrate in the form of a film on the surface of the support is not particularly limited, and various conventionally known methods can be appropriately employed. For example, a general sol-gel method can be preferably employed as an example of a method suitable for forming the porous ceramic film having the above-mentioned preferable pore diameter.
In a typical embodiment of such a sol-gel method, a sol containing a ceramic precursor (corresponding metal alkoxide or the like) according to the composition of the target ceramic film is prepared, and the sol is porous supported by dip coating or the like. A gel-like film containing the ceramic precursor is formed by applying to a body and drying. By baking the gel-like film, a porous ceramic film can be formed on the porous support. This also provides a porous structure having a structure in which a porous ceramic membrane (porous substrate) is provided on the porous support.

For example, when a γ-alumina film as a porous substrate is formed on a porous support using a sol-gel method, the following method may be used as an example. That is, an aluminum alkoxide (preferably an alkoxide having about 1 to 3 carbon atoms, for example, isopropoxide) is hydrolyzed and dissolved with an acid to prepare a boehmite sol.
This boehmite sol is applied to a desired portion of the porous support (for example, the outer peripheral surface of a tubular porous support) by, for example, a dip coating method. In this case, the dip time can be set to about 5 to 30 seconds, for example. Further, the support may be taken out from the sol at a pulling rate of about 0.5 mm / second to 2.0 mm / second, for example. This is dried at a temperature of room temperature to about 60 ° C. for about 6 hours to 18 hours, and then baked at a temperature of about 400 ° C. to 900 ° C. for about 5 hours to 10 hours to form a γ-alumina film.
The sol application, drying, and baking operations can be performed by repeating a part or a series of operations a plurality of times as necessary. Usually, it is preferable to form a γ-alumina film by the repetition.

  Further, as another example of a technique suitable for forming the porous ceramic film (porous substrate) having the above-mentioned preferable pore diameter on the surface of the support, fine particles (preferably made of ceramic constituting the ceramic film) May employ a technique in which a dispersion in which ceramic fine particles having an average particle diameter of about 20 nm to 200 nm are dispersed in an appropriate liquid medium is applied to a support and dried, followed by firing.

Next, the silica film forming process will be described.
In the silica membrane forming step in the method for producing a gas separation material disclosed herein, the silica source-containing gas supplied to one surface side of the porous substrate and the other surface side of the substrate are supplied. A silica film is formed on the porous substrate by a chemical vapor deposition method in which an oxygen-containing gas is reacted, that is, counter diffusion CVD.
Here, the silica source-containing gas refers to a mixed gas composed of a vaporized silica source and a carrier gas (inert gas). The silica source-containing gas is supplied to one surface side of the porous substrate. On the other hand, the oxygen-containing gas is supplied from the other surface side of the porous substrate and diffuses to the one surface side through the pores of the porous substrate.
The oxygen-containing gas and the silica-source-containing gas are brought into contact with each other under a high-temperature condition to react them (typically, the silica source is thermally decomposed or oxidized), and silica is formed on the porous substrate. A film is formed.
The location where the silica film is formed may vary depending on the position where the silica source-containing gas and the oxygen-containing gas are in contact. For this reason, the silica source-containing gas and the oxygen-containing gas are mainly in the pores of the porous substrate and / or in the vicinity of the pore openings on the one surface side of the substrate (near the pore entrance or its periphery). It is preferable to perform counter diffusion CVD so as to contact with each other. As a result, the pore size of the porous substrate is reduced to a size suitable for separation of a gas species having a molecular size smaller than oxygen or nitrogen, typically hydrogen gas.

Here, how a silica film is formed on a porous substrate by counter diffusion CVD will be described with reference to FIGS.
FIG. 1 is a diagram for explaining a process of forming a silica film 21 (see FIG. 3) on the porous substrate 12, and is a schematic perspective view of the porous structure 10. FIG. 2 is an enlarged schematic view showing a portion surrounded by a dotted line II in FIG. FIG. 3 is a schematic diagram showing the main part of FIG. 2 further enlarged.
Here, as a preferred embodiment of the porous substrate, a porous film formed on a porous support will be described as an example. However, the porous substrate in the method according to the present invention is not intended to be limited. .
In such an embodiment, as shown in FIG. 1, counter diffusion CVD is applied to the porous structure 10 including the porous substrate 12 on the porous support 14 to form the silica film 21 (see FIG. 3). be able to. Although not particularly limited, typically, the oxygen-containing gas 3 is supplied from the support 14 side of the porous structure 10, and the silica source-containing gas 2 is supplied to the porous substrate (porous membrane) 12 side. It is preferable to supply and perform counter diffusion CVD.
As shown in FIG. 1, the porous substrate 12 is formed on the outer peripheral surface of a tubular support 14, and counter diffusion CVD is applied to the tubular porous structure 10 as a whole. When carrying out, while circulating the silica source containing gas 2 containing the silica source 2a on the outer peripheral surface side 10a (that is, along the outer wall of the porous structure 10) of the porous structure 10, the porous structure 10 The oxygen-containing gas 3 may be circulated inside (hollow part 10b). A reactive gas containing molecules 3a made of oxygen atoms (or O ₃ in addition to O ₂ ) is referred to as “oxygen-containing gas 3”.

When oxygen-containing gas (for example, high-purity O ₂ gas) 3 is circulated (supplied) through the hollow portion 10b of the porous structure 10, as shown in FIG. 2, which is a partially enlarged view of a dotted line portion II in FIG. In addition, at least a part of the oxygen-containing gas 3 diffuses from the inner peripheral side of the support 14 (hollow portion 10b of the porous structure 10) to the outer peripheral side through the pores of the support 14, so that the porous group It reaches the inner peripheral surface 12 b of the material 12 and further diffuses toward the outer peripheral surface 12 a of the porous substrate 12 through the pores of the porous substrate 12.
On the other hand, at least a part of the silica source-containing gas 2 flowing (supplied) on the outer peripheral surface side 10 a of the porous structure 10 passes through the pores of the base material 12 from the outer peripheral surface 12 a of the porous base material 12. It tries to diffuse toward the peripheral side (inner peripheral surface 12b). As a result, the silica film 21 (see FIG. 3) is formed by the reaction between the silica source-containing gas 2 and the oxygen-containing gas 3 which are diffused facing from both surfaces 12a and 12b of the porous substrate 12 and contact each other. The

As shown in FIG. 3, such counter diffusion CVD is preferably performed by the silica source-containing gas 2 and the oxygen-containing gas 3 to be counter-diffused mainly inside the pores 20 of the porous substrate 12 and / or. The contact is made in the vicinity of the opening on one surface side 12a of the pore 20, so that the silica film 21 is formed inside the pore 20 or in the vicinity of the opening.
Usually, the silica source 2a has a larger molecular size than the gas molecules 3 composed of oxygen atoms typified by O ₂ gas. Therefore, by appropriately setting the size (pore diameter) of the pores 20, the silica source 2 and By utilizing the difference in molecular size of the gas molecules 3 composed of oxygen atoms, it is possible to control the silica film 21 to be efficiently formed at the above-mentioned location.
The target gas separation material 1 is obtained by reducing the size of the pores 20 to a size suitable for separation of a predetermined gas (for example, hydrogen gas) by the silica membrane 21.
In contrast to the example shown in FIGS. 1 to 3, the oxygen-containing gas 3 is circulated through the outer peripheral surface side 10 a of the porous structure 10 (that is, along the outer peripheral surface 12 a of the porous substrate 12), and the porous structure 10 is porous. The silica film 21 may be formed by a mode in which the silica source-containing gas 2 is circulated through the hollow portion 10b of the porous structure 10.

In the method disclosed herein, it is preferable to use a silicon compound capable of forming silica (SiO ₂ ) by reaction with an oxygen-containing gas as a silica source used for forming the silica film in the silica film forming step. it can.
Examples of such silicon compounds include tetraalkoxysilanes such as TEOS and TMOS (typically tetralower alkoxysilanes having an alkoxy group containing a lower alkyl group having about 1 to 4 carbon atoms); methyltrimethoxysilane, n- Trialkoxysilanes such as octyltriethoxysilane, n-decyltrimethoxysilane, m, p-ethylphenethyltrimethoxysilane; dialkoxysilanes such as diphenyldiethoxysilane; monoalkoxysilanes such as octyldimethylmethoxysilane; SiCl _{4 and the} like And silane (SiH ₄ ); disiloxanes such as hexamethyldisiloxane (HMDS) and 1,3-divinyltetramethyldisiloxane; and the like.
Moreover, the suitable silica source containing gas used in the said silica film formation process is a mixed gas of this silica source and an inert gas. Inert gas is not particularly limited, for example, nitrogen (N ₂₎ gas, argon (Ar) gas, preferably used helium (He) gas, neon (Ne) one or more kinds selected from a gas, such as be able to. Of these, the use of N ₂ gas is particularly preferable.

The oxygen-containing gas used in the silica film forming step includes a gas species containing at least one oxygen atom in the molecule and capable of generating SiO ₂ by reacting with a silica source during the formation of the silica film. A pure gas consisting of only species or a mixed gas containing the gas species) can be used.
For example, it is preferable to use a gas containing one or more oxygen sources (gas species) selected from allotrope gases of oxygen (that is, O ₂ gas and O ₃ gas) and H ₂ O gas (water vapor). it can. Of these, use of those containing O ₂ gas molecules is particularly preferable. This type of oxygen-containing gas may be a pure oxygen gas having an oxygen content of 100 mol%, a high-purity oxygen gas of 90 mol% or more, or a mixed gas with the above-described inert gas.
In the case of the mixed gas, it is preferable to use O ₂ gas and / or O ₃ gas at a concentration of 20 vol% or more (for example, 25 vol% or more, preferably 40 vol% or more, more preferably 60 vol% or more).

In the silica film forming step, the formation of the silica film is typically performed under the condition where the porous substrate is heated to a temperature of about 200 ° C. to 700 ° C., preferably 400 ° C. to 700 ° C. However, a more preferable film forming temperature (film forming temperature or reaction temperature) may vary depending on the type of silica source used, the type of oxygen-containing gas, the supply amount of the silica source and oxygen-containing gas, and the like.
The time for forming the silica film (depositing the silica source) may be set so that the pore size of the porous substrate can be appropriately reduced by the silica film, and is not particularly limited. For example, the formation time (film formation time or reaction time) can be about 3 minutes to 180 minutes, and typically about 3 minutes to 60 minutes.

  The silica film formation process in the method disclosed here can be preferably implemented using the silica film formation apparatus 100 provided with the schematic structure shown by FIG. 4, for example. Here, as shown in FIG. 1, as an example, the silica film forming step is performed on the porous structure 10 having the structure in which the porous film 12 is formed on the outer peripheral surface of the tubular porous support 14. explain.

As shown in FIG. 4, the silica film forming apparatus 100 includes a reaction tube 30 in which the porous structure 10 having the above-described configuration is disposed. The reaction tube 30 has a substantially double tube structure including a coaxial inner tube and an outer tube. The porous structure 10 is arranged substantially coaxially with the reaction tube 30 so as to bear a part of the inner tube constituting the double tube structure.
Here, the inner tube of the reaction tube 30 and the outer peripheral surface of the porous structure 10 that bears a part of the inner tube (the outer peripheral surface 12a of the porous substrate 12) and the inner peripheral surface of the outer tube are partitioned. This space is defined as an external gas passage 30a. Further, a space including the inside of the inner tube of the reaction tube 30 and the hollow portion 10b of the porous structure 10 that bears a part of the inner tube is defined as an inner gas passage 30b. Then, the outer peripheral surface of the porous structure 10 (the outer peripheral surface 12a of the porous substrate 12) faces the external gas passage 30a, and the inner peripheral surface of the structure 10 (the inner peripheral surface of the porous support 14). The structure 10 is arranged so as to face the internal gas passage 30b. In addition, the both ends of the reaction tube 30 are sealed between the inner tube and the outer tube, whereby both ends in the longitudinal direction of the external gas passage 30a are closed.
A tubular heater (for example, an electric furnace) 36 is disposed on the outer periphery of the reaction tube 30. The heater 36 adjusts the output based on, for example, an input from a temperature detector 37 that detects the temperature in the reaction tube 30 to adjust the temperature of the reaction tube 30 to a predetermined temperature profile (for example, a constant temperature). To be controllable).

Connected to the reaction tube 30 are an oxygen-containing gas supply unit 40 and a silica source supply unit 50 for supplying the oxygen-containing gas 3 during the silica film formation step.
The oxygen-containing gas supply unit 40 supplies an oxygen-containing gas (O ₂ gas) 3 supplied from an oxygen-containing gas (O ₂ gas here) supply source 42 and controlled in flow rate by a mass flow controller (MFC) 43 to the length of the inner pipe. It is configured so that it can be introduced into the internal gas passage 30b from an inner pipe inlet 32 provided at one end in the direction. From the inner tube outlet 33 provided at the other end in the longitudinal direction of the inner tube, an unreacted oxygen-containing gas (O ₂ gas) 3, a double product (for example, carbon dioxide or water) by thermal decomposition of the silica source 2a, etc. Is discharged.
Further, the silica source supply unit 50, a silica source 2a includes a vaporizer 52 capable of storing the (typically liquid in), N ₂ gas, which is a flow rate controlled by MFC55 supplied from N ₂ gas supply source 54 to the interior The silica source 2a is vaporized by introducing it into the vaporizer 52 and bubbling the N ₂ gas, and the vaporized silica source 2a together with the N ₂ gas is provided on the side of one end side of the outer tube. It is configured such that it can be introduced from the pipe inlet 34 into the external gas passage 30a.
Unreacted silica source 2a, N ₂ gas, and the like are discharged from an outer tube outlet 35 provided on the side of the other end of the outer tube. The unreacted silica source 2 a discharged from the outer tube outlet 35 is collected by a trap (for example, a cold trap) 38.

  Furthermore, a gas chromatograph 60 for monitoring the gas composition discharged during the silica film forming process is connected to the inner tube outlet 33 of the reaction tube 30. The gas chromatograph 60 is a device that performs chromatography using a gas as a mobile phase, and a sample measured by the gas chromatograph is separated by a column, and the separated sample is detected by a detector.

The gas chromatograph 60 of the present embodiment includes an inert gas (N ₂ gas here) and / or an oxygen-containing gas (here O ₂ gas) discharged from the inner tube outlet 33 of the reaction tube 30 during the silica film forming step. To monitor. When the amount of the inert gas (N ₂ gas) and / or oxygen-containing gas (here O ₂ gas) diffusing through the porous substrate 10 becomes a constant value by the monitoring (for example, the minimum time). It can be the end point of the silica film forming step. Specifically, when the concentration of N ₂ gas in the O ₂ gas discharged from the inner tube outlet 33 of the reaction tube 30 becomes a constant value (for example, 1 mol%, 2 mol%, 3 mol%, or 5 mol%). Can be the end point of the silica film forming step.
Here, “at the time when the value has reached a certain value” means a state in which the fluctuation of the value measured by the gas chromatograph converges to a predetermined value (for example, 2 mol%). For example, when the fluctuation range of the measured value is within a predetermined range (for example, within ± 10% of the predetermined value) with the predetermined value as the center, it can be determined that the “time when the predetermined value is reached”.

  In the configuration example shown in FIG. 4, a flow meter 62 is connected to a pipe connecting the reaction tube 30 and the gas chromatograph 60, and the gas flow rate discharged from the inner tube outlet 33 of the reaction tube 30 can be measured. . A vacuum pump 64 and a pressure gauge 66 are connected to the pipe to which the gas chromatograph 60 is connected.

Formation of the silica film using the silica film forming apparatus 100 configured as described above can be performed, for example, as follows.
That is, the heater 36 is operated to heat the inside of the reaction tube 30 to a predetermined temperature (preferably 200 ° C. to 700 ° C., for example, 550 ° C. to 600 ° C.). While maintaining the temperature, the O ₂ gas 3 from the O ₂ gas supply source 42 is circulated through the internal gas passage 30b (hollow portion 10b of the porous structure 10) at a predetermined supply rate (gas flow rate), and thus porous. It supplies to the other surface 12b of the quality base material 12. FIG.
On the other hand, is introduced into the vaporizer 52 from the N ₂ gas supply source 54 and N ₂ gas at a predetermined feed rate is vaporized silica source 2a, the vaporized silica source 2a and N ₂ gas (a silica source containing gas 2) The gas is passed through the external gas passage 30 a (the outer peripheral surface side 10 a of the porous structure 10) and supplied to the one surface 12 a of the porous substrate 12. As a result, the O ₂ gas 3 and the silica source 2a in the silica source-containing gas are diffused in the reaction tube 30 in the thickness direction of the porous substrate 12, and the silica source 2a in contact with the O ₂ gas 3 is oxidized. By performing (thermal decomposition), the silica film 21 can be formed inside the pores 20 of the porous substrate 12 and / or in the vicinity of the opening on one surface side 12a of the pores 20.
For example, in the case of a porous structure having a structure in which a membrane-like porous substrate is formed on the outer peripheral surface of a tubular porous support having a size as used in Examples described later, supply of O ₂ gas The amount of N ₂ gas and the supply amount of N ₂ gas can be about 100 mL / min to about 1000 mL / min, respectively. Moreover, the silica source 2a stored in the vaporizer 52 can be heated as necessary. For example, the silica source 2 a may be heated to a temperature of about 30 ° C. to 80 ° C. in the vaporizer 52.

Here, in the initial stage in the silica film forming process, the vicinity of the opening of the pores 20 of the porous substrate 12 is not blocked by the silica film 21, so that nitrogen (N ₂ ) and oxygen (O ₂ ) are porous. The inside of the pores 20 of the porous substrate 12 is diffused and transmitted. However, when the formation reaction of the silica film 21 proceeds and the vicinity of the opening of the pore 20 starts to be blocked by the silica film 21, nitrogen (molecular diameter larger than the size of the opening narrowed by the silica film 21 ( N ₂ ) and oxygen (O ₂ ) diffuse permeation (amount of leakage (outflow) to the side opposite to the supply side across the substrate) starts to decrease.
In the method for producing a hydrogen gas separator according to this embodiment, the amount of nitrogen (N ₂ ) and / or oxygen (O ₂ ) diffused and permeated is measured by the gas chromatograph 60, thereby executing the process of forming the silica film 21. Meanwhile, the film forming state of the silica film 21 can be confirmed. Therefore, when the porous substrate 12 having defects is used, when the silica film 21 is vapor-deposited on the porous substrate 12, the counter diffusion is performed while confirming the film formation state of the silica film 21 by the gas chromatograph 60. The end point of the CVD reaction can be determined.
That is, when a hydrogen gas separation material is produced by depositing a silica film 21 on a porous substrate 12 having defects, if the reaction end point is determined in a certain film formation time, the porous substrate 12 The performance of the hydrogen gas separating material produced varies greatly depending on the presence or absence or amount of defects of On the other hand, in the production method of the present embodiment, the reaction end point is not determined by the film formation time, but the gas composition exhausted in the silica film formation step is monitored in real time by gas chromatography. The reaction end point can be determined for each material. Therefore, even when the porous substrate 12 having defects is used, the silica film 21 having good performance can be stably formed.

In addition, the method for producing the hydrogen gas separation material according to the present embodiment is not limited to the method using the silica film forming apparatus 100 shown in FIG. 4, and can be executed using another silica film forming apparatus. is there. For example, a tubular porous structure 10 whose one end in the axial direction (longitudinal direction) is sealed, or a multi-tubular module 70 including a plurality of porous structures (elements) 10 (see FIG. 6). On the other hand, when the silica film is formed, the silica film forming apparatus 110 having a schematic configuration as shown in FIG. 5 can be used. The silica film forming apparatus 110 is different from the silica film forming apparatus 100 in an oxygen-containing gas supply unit 40.
As shown in FIG. 5, the oxygen-containing gas supply unit 40 is attached to one end portion in the axial direction of the porous structure 10 in addition to the O ₂ gas supply source 42 and the MFC 43 to fix the structure 10. A hollow (tubular) structure fixing member 44, an O ₂ gas supply pipe 45 inserted into the hollow portion of the structure fixing member 44, and the hollow portion 10b of the fixed porous structure 10; Consists of
The porous structure 10 is sealed with a sealing plug 11 at one end in the axial direction. When the porous structure 10 is fixed to the structure fixing member 44 through the end opposite to the sealed side, the fixing member 44 fixes the reaction tube 30 with the structure 10 fixed. Inserted into. The reaction tube 30 is configured to be closed so that the hermeticity is maintained even when the fixing member 44 is inserted.

When supplying the oxygen-containing gas 3 to the other surface 12b side of the porous substrate 12 (the hollow portion 10b of the porous structure 10), the O ₂ gas (oxygen-containing gas) 3 flows through the following path. That is, the gas 3 flows out of the O ₂ gas supply source 42 at a flow rate controlled by the MFC 43, passes through the O ₂ gas supply pipe 45, and is supplied (released) into the hollow portion 10 b of the porous structure 10. .
Thereafter, the O ₂ gas 3 is porous while flowing through a space constituted by the inner peripheral surface of the porous structure 10 (the inner peripheral surface of the porous support 14) and the outer peripheral surface of the O ₂ gas supply pipe 45. After exiting the hollow portion 10 b of the structure 10, it flows into a space formed by the inner peripheral surface of the structure fixing member 44 and the outer peripheral surface of the O ₂ gas supply pipe 45 and flows out from the discharge port 44 a.

A gas chromatograph 60 for monitoring the gas composition discharged during the silica film forming process is connected to the piping extending from the discharge port 44a. As described above, the end point of the silica film forming step can be determined by monitoring the measured value by the gas chromatograph 60. Although not explicitly shown in FIG. 5, a flow meter 62, a vacuum pump 64, and a pressure gauge 66 can be provided in the same manner as the configuration shown in FIG.
Further, in the silica film forming apparatus 110, the path for supplying the silica source-containing gas 2 to the external gas passage 30a of the reaction tube 30 is the same as that of the silica film forming apparatus 100, and the silica source-containing gas 2 and the oxygen-containing gas 3 Each is supplied from an outer tube inlet (reaction tube inlet) 34 of the reaction tube 30 to the external gas passage 30 a and discharged from an outer tube outlet (reaction tube outlet) 35.

As a multi-tube module to which the silica film forming apparatus 110 shown in FIG. 5 can be suitably applied, for example, a cylindrical multi-tube module 70 as shown in FIGS. FIG. 6 is a longitudinal sectional view of the multi-tube module 70. 7 is a cross-sectional view taken along line VII-VII in FIG.
The multi-tubular module 70 includes, for example, a glass cylindrical reaction vessel 71, a plurality (six in FIGS. 6 and 7) of porous structures (elements) 10, a dense O _{2 made of} alumina or the like. The gas supply pipe 72 includes a pair of opposed support members 73a and 73b that support the porous structure 10 so as to sandwich both ends in the axial direction.
The reaction vessel 71 is provided with an inlet 74 for the silica source supply gas 2 at one end in the axial direction thereof, and an outlet 75 is provided near the other end. The support members 73a and 73b are both hollow and substantially disc bodies made of dense alumina or the like.

At both ends of the porous structure 10 and the O ₂ gas supply pipe 72, one end is flown to the support member 73 b disposed at the end on the inflow port 74 side in the reaction vessel 71 and the other end is allowed to flow. It is inserted into a support member 73a disposed at the end on the outlet 75 side, and inserted into the hollow interior of each support member 73a, 73b. In this manner, the support members 73a and 73b are configured to face each other with the porous structure 10 and the O ₂ gas supply pipe 72 interposed therebetween.
In the support member 73a, an O ₂ gas supply pipe 72 penetrates the hollow interior from the surface facing the support member 73b to the opposite side, and an exhaust pipe 76 is provided in the opposite disk portion. Is formed.

As shown in FIG. 7, with respect to the arrangement of the porous structure 10 and the O ₂ gas supply pipe 72 in the disk portion of the support member 73a, the O ₂ gas supply pipe 72 is arranged at the center thereof, The porous structure 10 is disposed so as to surround at equal intervals. Since the dense O ₂ gas supply pipe 72 is arranged at the center, the mechanical strength of the assembly composed of the plurality of porous supports 10 and the support members 73a and 73b is increased, and the assembly It is effective for shape retention.

The flow path of the silica source-containing gas 2 in the multi-tube module 70 is as follows. That is, the silica source-containing gas 2 supplied from the inlet 74 of the reaction vessel 71 flows along the outer peripheral surface of each porous structure 10 and flows out from the outlet 75.
On the other hand, the flow path of the oxygen-containing gas 3 supplied when forming the silica film is as follows. That is, the oxygen-containing gas (O ₂ gas) 3 flows into the reaction vessel 71 through the O ₂ gas supply pipe 72 and is supplied (released) into the hollow interior of the support member 73b. The gas 3 flows through the hollow portion 10b of each porous structure 10 to the hollow inside of the support member 73a, and flows out of the reaction vessel 71 through the exhaust pipe 76.
Regarding the silica film forming apparatus 110 into which the multi-tube module 70 has been introduced, in FIG. 5, the reaction vessel 30 is the multi-tube module 70, the outer tube inlet 34 is the inlet 74, and the outer tube outlet 35 is the outlet 75. Instead, the O ₂ gas supply pipe 45 may be regarded as the O ₂ gas supply pipe 72.

Also in the silica film forming apparatus 110 shown in FIG. 5, the gas composition (for example, nitrogen (N ₂ ) and / or oxygen (O ₂ )) discharged from the discharge port 44 a of the structure fixing member 44 is measured by the gas chromatograph 60. Accordingly, the formation state of the silica film 21 can be confirmed while executing the process of forming the silica film 21. Therefore, also in the silica film forming apparatus 110 shown in FIG. 5, when the silica film 21 is deposited on the porous substrate 12 having defects, the film formation state of the silica film 21 is confirmed by the gas chromatograph 60 in real time. However, it is possible to determine the end point of the counter diffusion CVD reaction.

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
A gas separation material (hydrogen gas separation material) 1 having the configuration schematically shown in FIG. 1 was manufactured by the procedure described below.
First, the porous structure 10 set to the silica film forming apparatus 100 shown in FIG. 4 was prepared. The prepared porous structure 10 has a circular tube shape (outer diameter 6 mm, inner diameter 4 mm, length 140 mm), and the both ends of the porous structure 10 are densely sealed with glass. Such a porous structure 10 may be referred to as a “single tube”.

The porous structure 10 includes a porous support 14 (α-alumina support) made of α-alumina and a porous film 12. The porous membrane 12 in this embodiment has a two-layer structure, and includes a first porous layer made of α-alumina formed on the outer peripheral surface of the porous support 14, and the first porous layer. It is comprised from the 2nd porous layer which consists of (gamma) -alumina formed in the outer peripheral surface.
The average pore diameter of the porous support 14 was 700 nm, and the porosity (porosity) was 35 vol%. The thickness of the first porous layer made of α-alumina was 50 μm, the average pore diameter was 70 nm, and the porosity (porosity) was 35 vol%. Moreover, the thickness of the 2nd porous layer (namely, porous base material) which consists of (gamma) -alumina was 1 micrometer, the average pore diameter was 4 nm, and the porosity (porosity) was 50 vol%.

Next, the obtained single tube (porous structure 10) is set in a silica film forming apparatus 100 having a schematic configuration shown in FIG. 4, and counter diffusion CVD is performed using hexamethyldisiloxane (HMDS) as a silica source. It was. O ₂ gas was used as the oxygen-containing gas used in the silica film forming step. By this counter diffusion CVD, as shown in FIG. 3, a silica film 21 was formed on the porous film 12 (γ-alumina film) constituting the single tube.

The counter diffusion CVD was performed under the conditions of a reaction temperature (silica film formation temperature) of 600 ° C., an N ₂ gas supply rate of 200 mL / min, and an O ₂ gas supply rate of 200 mL / min. In the vaporizer 52, HMDS heated to 45 ° C. was bubbled with N ₂ gas and vaporized. The reaction time (silica film formation time or film formation time) was determined by monitoring the concentration of N ₂ gas by gas chromatograph 60. The gas chromatograph 60 is Micro-GC, CP-2002 manufactured by VARIAN, and MOLSIEV SA was used for the column. In Example 1, oxygen and nitrogen peaks were detected by the gas chromatograph 60.

Through the above steps, a single-pipe hydrogen gas separator 1 was obtained. The H ₂ gas supply source 58 in FIG. 4 is used for evaluating the gas separation membrane (hydrogen gas separation membrane) 1 after film formation.
FIG. 8 is a graph in which the gas composition discharged from the inner tube outlet 33 of the reaction tube 30 in the silica film forming step is plotted along with the film forming time. In the graph shown in FIG. 8, the nitrogen concentration (mol%) in oxygen is plotted. As shown in FIG. 8, at 75 minutes after the start of film formation, the nitrogen concentration in the discharged oxygen was 2 mol% (or less), and the change thereafter was slight. Based on the result, in this example, the end point of film formation was determined to be a nitrogen concentration of 2 mol%.

Further, the hydrogen gas separator material 1 obtained, hydrogen (H ₂₎ measuring the gas permeability and nitrogen (N ₂₎ gas permeability, permeability coefficient between these H ₂ gas and N ₂ gas from the gas permeability and calculating the ratio _{(H 2} / _N 2).
Here, the permeation coefficient ratio (H ₂ / N ₂ ) is the ratio between the H ₂ gas permeability and the N ₂ gas permeability under the same condition, that is, the N ₂ gas with the H ₂ gas permeability under the same condition. The molar ratio to the amount of permeation. Here, the H ₂ gas permeability [mol / m ² · s · Pa] and the N ₂ gas permeability [mol / m ² · s · Pa] are respectively expressed as differential pressures (on the gas supply side with the hydrogen gas separator 1 interposed therebetween). H ₂ gas permeation amount [mol] and N ₂ gas permeation amount [mol] per unit time (1 second) and unit membrane surface area (1 m ² ) when the pressure and the gas permeation side pressure are 1 Pa. Represented.

The measurement of the H ₂ gas permeability and the N ₂ gas permeability was performed as follows using the silica film forming apparatus 100 shown in FIG. In other words, the reaction tube 30 is adjusted to a measured temperature of 600 ° C. by operating the heater 36 as required, and is controlled by the MFCs 55 and 59 from the N ₂ gas supply source 54 and the H ₂ gas supply source 58, respectively. N ₂ gas and H ₂ gas were supplied to the external gas passage 30a at the flow rates of
At this time, the differential pressure between the outer peripheral side (namely, the external gas passage 30a) and the inner peripheral side (namely, the internal gas passage 30b) of the hydrogen gas separation material was set to 2.0 × 10 ⁴ Pa. The target gas composition was analyzed by a gas chromatograph equipped with a TCD detector while measuring the gas flow rate on the permeation side (that is, the internal gas passage 30b) with a soap film flow meter (not shown).

The gas permeability of each of H ₂ gas and N ₂ gas was calculated from the following formula: Q = A / {(Pr−Pp) · S · t}; Here, Q is the gas permeability [mol / m ² · s · Pa], A is the permeation amount (mol), Pr is the pressure [Pa] on the supply side, that is, the external gas passage 30a side, and Pp is the internal gas. The pressure [Pa] on the passage 30b side, S represents the cross-sectional area [m ² ], and t represents time [second: s]. Further, the permeability coefficient ratio (H ₂ / N ₂ ) can be calculated from the ratio of the H ₂ gas permeability and the N ₂ gas permeability, that is, the following formula: α = Q _H2 / Q _N2 ; Here, α represents a permeability coefficient ratio (transmittance ratio), Q _H2 represents an H ₂ gas permeability, and Q _N2 represents an N ₂ gas permeability.

  Table 1 below shows the results of the performance of ten hydrogen gas separators 1 when film formation was performed under the conditions of Example 1. Specifically, Table 1 shows the measurement results of film formation time, hydrogen permeability at 500 ° C., nitrogen permeability, and permeability coefficient ratio (hydrogen permeability / nitrogen permeability). Here, the time when the nitrogen concentration in the discharged oxygen reaches 2 mol% is defined as the film formation end point.

  As shown in Table 1, in the hydrogen gas separation material according to Example 1, the film formation was completed when the nitrogen concentration in the discharged oxygen reached 2 mol% without using a certain film formation time as a reference for completion. It was found that the hydrogen gas separator having good performance can be stably formed by setting the point. Specifically, it was possible to stably obtain a product having good characteristics in which the permeability coefficient ratio (hydrogen permeability / nitrogen permeability) exceeded 300. In addition, there was little variation in the characteristics of the hydrogen permeability, and it was possible to obtain a uniform uniform overall. That is, in Example 1, it was confirmed that a silica film having good performance can be stably formed even when a porous substrate having defects is used.

<Comparative example>
Next, in this comparative example, 10 hydrogen gas separation membranes were manufactured under the same porous structure 10 and film forming conditions as in Example 1. The difference from the conditions of Example 1 is that in this comparative example, the end of film formation was made constant at 75 minutes. The obtained results are shown in Table 2 below.

  As shown in Table 2, in the hydrogen gas separation material according to the comparative example, although the film forming time was kept constant, performance variation occurred. Specifically, in the hydrogen gas separator according to the comparative example, a hydrogen gas separator having a high permeability coefficient ratio exceeding 1000 was obtained, while a hydrogen gas separator having a permeability coefficient ratio lower than 100 was also obtained. It was. This means that when a porous substrate having defects is used, the performance of the produced hydrogen gas separation material varies depending on the presence or absence or amount of the defects.

<Example 2>
In the present Example 2, the silica film formation process was performed on the same porous substrate 12 and film forming conditions as in Example 1. That is, also in Example 2, the silica film forming step was executed while monitoring the gas composition discharged during the silica film forming step by gas chromatography based on the measured value of the gas chromatograph 60. In Example 2, the silica film forming step was performed so that the film formation was completed when the nitrogen concentration in the discharged oxygen reached 5 mol%, 2 mol%, and 1 mol%. The results of Example 2 are shown in Table 3 below. An example in which film formation was terminated at a nitrogen concentration of 2 mol% in oxygen was sample No. 1 in Example 1. Same as 1.

As shown in Table 3, when the film formation was completed at a nitrogen concentration of 1 mol% in the exhausted oxygen, the film formation time was 120 minutes, and the film formation was performed at a nitrogen concentration of 2 mol% and 5 mol% in the exhausted oxygen. When the process was terminated, the film formation times were 70 minutes and 20 minutes, respectively.
In the example in which film formation was terminated at a nitrogen concentration of 5 mol% in the exhausted oxygen, the permeability coefficient ratio (hydrogen permeability / nitrogen permeability) was lower than that in the example in which film formation was terminated at a nitrogen concentration of 2 mol% (38 .1), on the other hand, it showed a very high hydrogen permeability (8.50 × 10 ⁻⁷ ). On the other hand, in the example in which film formation was completed at a nitrogen concentration of 1 mol% in the exhausted oxygen, the hydrogen permeability value (9.08 × 10 ⁻⁸ ) was compared to the example in which film formation was completed at a nitrogen concentration of 2 mol%. Although reduced, it showed a very high transmission coefficient ratio (2820).
Therefore, as shown in the result of Example 2, by performing film formation while monitoring the discharged gas composition, for example, a hydrogen gas separator having high selectivity or a high hydrogen permeability is obtained. It was found that a hydrogen gas separator can be produced, that is, the separation characteristics of the hydrogen gas separator can be controlled.

<Example 3>
In the present Example 3, the silica film formation process was performed on the base material 1, the base material 2, and the base material 3 shown in Table 4 under the same film forming conditions as in Example 1. In Example 3, the silica film forming step was executed with the point in time when the nitrogen concentration in the exhausted oxygen reached 2 mol% as the film formation end point. The base material 1, the base material 2, and the base material 3 are configured such that the average pore diameters of the porous base material 12 are different from each other.
The base material 1 of Example 3 is the sample No. 1 of Example 1. Same as 1. Specifically, the average pore diameter of the porous support 14 in the substrate 1 is 700 nm, the average pore diameter of the first porous layer (α-alumina) is 70 nm (thickness 50 μm), and the first The average pore diameter of the two porous layers (γ-alumina) was 4 nm (thickness 1 μm).
The average pore diameter of the porous support 14 in the substrate 2 is 700 nm, the average pore diameter of the first porous layer (α-alumina) is 70 nm (thickness 50 μm), and the first porous layer 14 made of silica is used. The average pore diameter of the two porous layers was 20 nm (thickness 1 μm).
Furthermore, the average pore diameter of the porous support 14 in the substrate 3 was 700 nm, and the average pore diameter of the first porous layer (α-alumina) was 70 nm (thickness 50 μm). In addition, in the base material 3, the 2nd porous layer is not provided. The results of Example 3 are shown in Table 4 below.

  As shown in Table 4, the film formation time of the substrate 1 was 70 minutes, and the film formation times of the substrate 2 and the substrate 3 were 110 minutes and 210 minutes, respectively. And in the base material 1, the base material 2, and the base material 3 with different average pore diameters, the permeation coefficient ratio (hydrogen permeation rate / nitrogen permeation rate) could be obtained with good characteristics of about 300. . In addition, although the value of the hydrogen permeability has changed in the base material 1, the base material 2, and the base material 3, this is the hydrogen separation membrane formed into a film between the base material 1, the base material 2, and the base material 3. This is based on the change in the thickness of the (silica film). Specifically, as described above, since the average pore diameter of the second porous layer is relatively small as 4 nm in the substrate 1, the silica film necessary for appropriately closing the pores of the second porous layer is used. The thickness may be relatively small, and therefore the film forming time may be relatively short. On the other hand, in the base material 2, since the average pore diameter of the second porous layer is relatively large as 20 nm, the thickness of the silica film necessary for properly closing the pores of the second porous layer is relatively large. Therefore, the film forming time becomes relatively long. Further, since the second porous layer does not exist in the base material 3, the thickness of the silica film necessary for properly closing the pores of the first porous layer is the base material 1 and the base material in which the second porous layer is present. It becomes larger than 2, and the film forming time becomes longer.

  As described above, according to the method for producing a hydrogen gas separation material of the present embodiment, even when coarse pores (defects) called pinholes exist in the porous base material, the production is performed while monitoring the discharged gas composition. By executing the film, it is possible to stably form a silica film having good performance. Moreover, according to the manufacturing method of this embodiment, it is also possible to control the separation characteristics of the hydrogen gas separation material by performing film formation while monitoring the discharged gas composition. Furthermore, even when the porous substrate (porous layer) 12 having different average pore diameters is used for film formation, a good permeability coefficient ratio (hydrogen permeability / nitrogen permeability) having substantially the same value. It is also possible to produce a hydrogen gas separator having

In the above embodiment, the nitrogen gas (inert gas species) contained in the silica source-containing gas supplied to one surface side of the porous base material passes through the base material, and the base material The end point of the reaction in the counter diffusion CVD is determined based on the concentration of nitrogen gas that has been contained in the oxygen-containing gas (here pure oxygen gas) supplied to the other surface of the substrate. It is not something. Even if the inert gas as the carrier gas in the silica source-containing gas is argon, it is included in the oxygen-containing gas supplied to the other surface side of the base material through the base material as in the case of nitrogen. The end point of the reaction in the counter diffusion CVD can be determined based on the concentration of the argon gas that has been reached.
Or, conversely, the oxygen gas contained in the oxygen-containing gas supplied to one side of the porous base material, which passes through the base material and is supplied to the other side of the base material. The end point of the reaction in the counter diffusion CVD may be determined based on the concentration of the oxygen gas that has been contained in the source gas.

  Although the present invention has been described in detail above, these are merely examples, and the present invention can be implemented in other modes, and various modifications can be made without departing from the spirit of the present invention. For example, contrary to the examples shown in FIGS. 1 to 3, the oxygen-containing gas 3 is circulated on the outer peripheral surface side 10 a of the porous structure 10, and the silica portion contains the hollow portion 10 b of the porous structure 10. When the silica film 21 is formed by the mode in which the gas 2 is circulated, the configuration of the silica film forming apparatus is modified so that the piping of the gas chromatograph 60 can be changed appropriately and suitably so that appropriate exhaust gas can be monitored by gas chromatography. can do.

DESCRIPTION OF SYMBOLS 1 Gas separation material 2 Silica source containing gas 2a Silica source 3 Oxygen containing gas supplied at the silica membrane formation process 3a Gas molecule which consists of oxygen atoms 10 Porous structure 10a Outer peripheral surface side 10b Hollow part 12 Porous base material (porous Membrane)
12a One surface 12b The other surface 14 Porous support 20 Pore 21 Silica membrane 30 Reaction tube 30a External gas passage 30b Internal gas passage 45 O ₂ gas supply pipe 52 Vaporizer 70 Multi-tube module 72 O ₂ gas supply pipe 100 , 110 Silica film forming equipment

Claims (6)

A method for producing a gas separation material comprising a porous substrate and a silica membrane, comprising:
Preparing the porous substrate;
By a chemical vapor deposition method in which a vaporized silica source supplied together with an inert gas as a silica source-containing gas on one surface side of the base material and an oxygen-containing gas supplied to the other surface side of the base material are reacted. Forming a silica film on the substrate; and
Determining the end point of formation of the silica film by monitoring the composition of the gas discharged after being supplied to the substrate in the step of forming the silica film;
It encompasses,
Here, in the step of determining the end point of the formation of the silica film, it is contained in the inert gas or the oxygen-containing gas contained in the silica source-containing gas supplied to any one side of the substrate. Of the silica film based on the concentration of the inert gas or oxygen gas that has passed through the substrate and has been contained in the gas supplied to the other surface of the substrate. A manufacturing method for determining an end point of formation .   The manufacturing method according to claim 1, wherein in the step of determining the end point of formation of the silica film, the amount of the inert gas is monitored by gas chromatography.   The manufacturing method according to claim 2, wherein the inert gas is nitrogen gas.   The production method according to any one of claims 1 to 3, wherein the oxygen-containing gas used in the step of forming the silica film is a pure oxygen gas or a mixed gas containing 25 vol% or more of oxygen.   In the step of determining the end point of the formation of the silica film, the inert gas contained in the silica source-containing gas supplied to one surface side of the base material, which passes through the base material, The manufacturing method as described in any one of Claims 1-4 based on the density | concentration of the inert gas which came to be contained in the oxygen containing gas supplied to the other surface side of material. 6. The porous substrate according to any one of claims 1 to 5, wherein a membrane-like porous substrate having an average pore diameter or a peak value of pore diameter distribution formed on a porous support is 2 nm to 100 nm. The manufacturing method according to one item.

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