JP4871312B2 - Method for producing hydrogen gas separator - Google Patents

Description

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

  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 and Non-Patent Documents 1 to 3 are cited as prior art documents regarding silica film formation using CVD. On the other hand, Non-Patent Documents 4 and 5 are cited as prior art documents relating to the formation of a silica film using a sol-gel method.

JP 2005-254161 A JP 2006-239663 A M. Nomura et al. Ind. Eng. Chem. Res. Vol. 36 No. 10, 1997, p.4217-4223 M. Nomura et al. Journal of Membrane Science 187, 2001, p.203-212 S. Nakao et al. Microporous and Mesoporous Materials 37, 2000, p.145-152 B. N. Nair et al. Journal of Membrane Science 135, 1997, p.237-243 B. N. Nair et al. Adv. Mater. Vol.10, No.3, 1998, p249-252

The method of forming a silica film by CVD described in Patent Documents 1 and 2 and Non-Patent Documents 1 to 3 uses a silica source such as tetraethoxysilane (Tetraethyl Orthosilicate: TEOS) or tetramethoxysilane (Tetramethyl Orthosilicate: TMOS). By vaporizing and supplying from one surface of the porous substrate in a gas state, and supplying gas such as ozone (O ₃ ) and oxygen (O ₂ ) from the other surface (back surface) of the substrate These are reacted in the pores of the substrate to form a silica film (hereinafter, this type of CVD is sometimes referred to as “opposite diffusion CVD”).

When manufacturing the hydrogen gas separation material by applying the above-described counter diffusion CVD, the film thickness of the silica film is a predetermined thickness depending on the film forming time (the reaction time between the silica source and O ₃ or O ₂ gas). Can be controlled. For this reason, it is typically preferable to produce a hydrogen gas separation material having high hydrogen permeation performance by shortening the reaction time and reducing the film thickness. The shortening of the film forming time is also effective in terms of improving the efficiency of the manufacturing process of the hydrogen gas separation material. For example, in Patent Document 2, TEOS is used as a silica source, both vaporized TEOS gas and O ₂ gas are supplied at a rate of 200 mL / min, and both are reacted. A silica film is formed on the porous substrate. When the film formation time is shortened to 120 minutes, 30 minutes, and 5 minutes, the hydrogen permeability [mol · m ⁻² · s ⁻¹ · Pa ⁻¹ ] of the hydrogen gas separation material provided with this silica membrane is 3 respectively. 0.0 × 10 ⁻⁷ , 3.5 × 10 ⁻⁷ , and 7 × 10 ⁻⁷ .

However, when the time for forming the silica membrane is shortened, the heat resistance and water vapor resistance (high temperature water vapor resistance) of the hydrogen gas separation material (silica membrane) are lowered in contrast to the improvement in hydrogen permeability. This phenomenon becomes particularly prominent when the area of the silica film is enlarged. For example, TMOS is used as a silica source, vaporized TMOS gas and O ₂ gas are supplied at 200 mL / min, and a porous material made of γ-alumina at a temperature of 600 ° C. and a film forming time of 120 minutes. A silica film was formed on the substrate. At this time, the hydrogen gas separation material having a silica membrane formed with a film formation area of 1 × 10 ⁻³ m ² had stable performance that could withstand actual use. On the other hand, when the silica film was formed by expanding to an area range of 40 × 10 ⁻³ m ² , the film formability of the silica film was lowered. For example, when hydrogen is passed through a hydrogen gas separation material provided with the silica membrane, cracks are generated, and performance degradation such as hydrogen permeation performance and hydrogen selection (separation) performance is observed in a high-temperature (eg, 600 ° C.) steam atmosphere. It was.

In order for the hydrogen gas separation material provided with the silica membrane as described above to reach a practical level as a hydrogen gas separation material suitable for a fuel cell, a catalyst membrane reactor or the like, the time required for forming the silica membrane can be shortened (for example, 30 minutes or less) and enlargement of the film forming area (for example, 10 × 10 ⁻³ m ² or more) is important. However, none of the above-mentioned patent documents and non-patent documents have left an experimental level in terms of the above points.

  Therefore, the present invention is a method for producing a hydrogen gas separation material provided with a silica membrane formed by counter diffusion CVD, which is good even if the film-forming time is shortened, preferably the film-forming area is enlarged. It is an object of the present invention to provide a method for producing a hydrogen gas separator that can stably form a silica membrane having performance.

In order to achieve the above object, the present invention provides a method for producing a hydrogen gas separator comprising a porous substrate and a silica membrane. That is, the manufacturing method disclosed herein includes a step of preparing the porous substrate. In addition, a vaporized silica source (that is, a silica film forming material) supplied together with a carrier gas as a silica source-containing gas on one surface side of the substrate, and an oxygen-containing material supplied on the other surface side of the substrate It includes a step of forming a silica film on the substrate by a chemical vapor deposition method in which a gas is reacted. Furthermore, the film | membrane stabilization process which supplies oxygen-containing gas to each one side of the said base material and / or the other surface, and stabilizes the said silica membrane is included. Preferably, in the film stabilization step, the silica source-containing gas is replaced on one side of the substrate on which the silica film is formed and on the side where the silica source vaporized in the silica film formation step is supplied. Supply oxygen-containing gas.
When the silica film is formed on the porous substrate, the deposition takes a long time of several hours (for example, 2 hours to 5 hours) only by depositing the silica film on the porous substrate by counter diffusion CVD. In addition, the formed silica film is unstable and lacks accuracy, and in many silica films, cracks occurred when hydrogen was passed, and performance was deteriorated in a high-temperature steam atmosphere.
However, in such a production method, in the membrane stabilization step, oxygen-containing gas is supplied to both sides or one side of the porous substrate after the formation of the silica film, so that the pores of the porous substrate are not yet filled. The silica source remaining in the reaction or incomplete reaction stage is oxidized to silica. As a result, the silica film can reach a state of being completely and completely oxidized throughout, so that the silica film can be stably formed on the porous substrate (that is, maintain a certain accuracy or performance). Moreover, even if the production time of the silica film (silica source supply time) in the silica film formation process is shortened to 30 to 5 minutes by including such a film stabilization process, the manufacturing method includes hydrogen permeation. A silica membrane capable of satisfactorily exhibiting membrane performance such as performance and hydrogen separation performance can be formed on the porous substrate. Typically, the vaporized silica source is mixed with an inert gas such as nitrogen and supplied to one surface side of the porous substrate as a silica source-containing gas.

Further, in the conventional method for producing a hydrogen gas separation material that does not include the membrane stabilization step, for example, even if a film forming time of 2 hours is spent, a stable silica membrane is porous with a film forming area of 40 × 10 ⁻³ m ^2. It could not be formed on a porous substrate. However, in such a manufacturing method, a stable silica film can be formed by passing through the film stabilization step, for example, even if the film forming area is expanded to the above area.

In a preferred embodiment of the method for producing a hydrogen gas separator disclosed herein, the membrane stabilization step is performed under a temperature condition of 300 ° C to 1000 ° C. More preferably, the temperature is 500 ° C. or higher, and the temperature is typically about the vapor deposition temperature (film forming temperature) of the silica source in the silica film forming step. Further, the upper limit of the temperature condition is preferably less than the limit temperature (for example, decomposition temperature) at which the silica source does not cause decomposition or chemical reaction.
In such an embodiment, the oxidation reaction of the silica source that is supplied to the porous substrate and remains in the pores of the substrate is promoted, which is effective in forming a more stable silica film. Further, when the hydrogen gas separation material produced by such a production method is applied to, for example, a methane steam reforming membrane reactor or a steam reforming fuel cell, the hydrogen gas separation material is heated to a high temperature (eg, 500 ° C.). Exposure to water vapor atmosphere. In the film stabilization step, a silica film having excellent heat resistance can be formed by exposing the silica film to an atmosphere under the high temperature conditions as described above. As a result, the hydrogen gas separation material obtained by the manufacturing method of this aspect can be used suitably.

In another preferable aspect of the method for producing a hydrogen gas separator disclosed herein, the oxygen-containing gas used in the membrane stabilization step is pure oxygen gas or a mixed gas containing 20 vol% or more of oxygen. Pure oxygen gas is preferred.
According to this aspect, the silica source remaining in the pores of the porous substrate can be efficiently oxidized by the oxygen-containing gas, and a stable silica film can be formed. Further, the higher the oxygen concentration, the smaller the supply amount of the oxygen-containing gas and the shorter the supply time. The oxygen-containing gas may be air (a mixed gas containing approximately 20 vol% oxygen and approximately 80 vol% nitrogen).

In another preferred embodiment of the method for producing a hydrogen gas separator disclosed herein, the flow rate of the oxygen-containing gas supplied in place of the silica source-containing gas in the membrane stabilization step is at least 0.01 MPa. The gas pressure difference is adjusted to be higher than the flow rate of the oxygen-containing gas on the other surface side.
In still another preferred embodiment, in the film stabilization step, the silica source-containing gas is provided on one side of the porous substrate and on the side supplied with the silica source vaporized in the silica film formation step. Instead of supplying an oxygen-containing gas, and on the other surface side of the porous substrate, the supply of the oxygen-containing gas is stopped on the side where the oxygen-containing gas is supplied in the silica film forming step, The other side is depressurized so as to produce a gas pressure difference of at least 0.01 MPa on both sides of the porous substrate.
In such an embodiment, on the one surface side of the porous base material and on the side where the silica source is supplied in the silica film forming step, the supplied gas is replaced with an oxygen-containing gas from the silica source-containing gas, An oxygen-containing gas flows on both sides of the porous substrate. At this time, the gas pressure of the oxygen-containing gas on the substituted side is higher than that on the other surface side by a gas pressure difference of at least 0.01 MPa (preferably 0.01 MPa to 1 MPa, typically 0.1 MPa to 1 MPa). It has been adjusted. Alternatively, the silica source-containing gas is replaced with an oxygen-containing gas on the one side, and the supply of the oxygen-containing gas is stopped on the other surface side, resulting in a gas pressure difference of at least 0.01 MPa on both sides of the substrate. Thus, the pressure on the other surface side is reduced. As a result, since the silica source remaining in the pores of the base material is pushed deeply into the base material, the silica source-containing gas and the other side (opposite to the side where the silica source-containing gas is supplied) The contact frequency with the oxygen-containing gas supplied from the side) is improved. As a result, the oxygen-containing gas can efficiently contact and oxidize the silica source, so that the film stabilization step can be performed efficiently.
In this aspect, the side to which the oxygen-containing gas is supplied in the silica film forming step is opened to the atmospheric pressure and exposed to air, and the other side, that is, the side to which the silica source is supplied in the silica film forming step. Alternatively, the oxygen-containing gas may be supplied at a pressure of at least 0.01 MPa from atmospheric pressure.

In another preferable aspect of the method for producing a hydrogen gas separator disclosed herein, a gas supplied to one surface side of the porous substrate between the silica film forming step and the membrane stabilizing step. Is replaced with an inert gas from the silica source-containing gas, and then (after being replaced with the inert gas), is supplied to one surface side of the porous substrate in the film stabilization step. The gas is replaced from an inert gas to an oxygen-containing gas.
In such an embodiment, before replacing the silica source-containing gas supplied to one surface side of the porous substrate with the oxygen-containing gas, the inert gas is once replaced with one of the substrates. The silica source that remains unreacted as a gas on the surface side is completely exhausted, and contamination in a predetermined silica film forming apparatus (that is, in the film forming chamber) due to the reaction between the silica source and the oxygen-containing gas. Can be prevented.

Moreover, in one preferable aspect of the method for producing a hydrogen gas separator disclosed herein, the porous base material has an average pore diameter as a porous membrane having an average pore diameter or a peak value of pore diameter distribution of 2 nm to 20 nm. Or it forms on the porous support body whose peak value of pore diameter distribution is 4 nm-1000 nm.
By applying counter diffusion CVD to a porous substrate having a peak value of the average pore diameter or pore diameter distribution to form a silica film, the pores of the substrate are efficiently reduced to a size suitable for hydrogen gas separation. Can be reduced well. Further, since the substrate is supported by a porous support (typically a support formed of a ceramic material), the substrate can be made thinner while ensuring the necessary mechanical strength. it can. Therefore, a hydrogen gas separation material having an excellent balance between hydrogen gas permeability and selectivity (separation) can be provided.

  According to another aspect of the method for producing a hydrogen gas separator disclosed herein, a porous support having an average pore diameter of about 4 nm to 1000 nm and an average pore diameter of about 2 nm to 20 nm formed in a film shape on the support are disclosed. A hydrogen gas separation membrane having an average pore diameter of 1.0 nm or less (typically about 0.3 nm to 0.6 nm) formed by forming a silica membrane on the porous substrate (porous membrane) of A hydrogen gas separator is provided. The silica film is preferably a chemical vapor deposition method in which a silica source-containing gas supplied to one surface side of the porous substrate and an oxygen-containing gas supplied to the other surface side of the substrate are reacted. The silica film formed by

  Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, mixing method of raw material powders) are design matters of those skilled in the art based on the prior art in the relevant field. Can be grasped as. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The material of the porous base material used in the method for producing a hydrogen gas separation material disclosed herein can form a silica film by CVD and can withstand the use environment during use (ie, during hydrogen gas separation). If it is. 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 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 hydrogen gas separation can be formed by the silica film formed in the vapor deposition step described later. For example, a porous substrate having an average pore diameter (or peak value of pore diameter distribution; typically, the peak value of pore diameter distribution can be approximated to the average pore diameter) of about 100 nm or less can be preferably used. 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 size of the pore diameter of the porous substrate exceeds the above range, it takes a long time to form a silica membrane and reduce the pore diameter to a size suitable for hydrogen gas separation. That is, the production efficiency of the hydrogen gas separator 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 hydrogen 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), a porous substrate having an average pore diameter of 2 nm to 20 nm can be particularly 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 the peak value of the pore diameter distribution) is, for example, a general bubble point test method (JIS K3832; when the pore diameter is in the range of 2 nm to 50 nm) or a mercury intrusion method ( JIS R1655: Mean pore diameter (or peak value of pore diameter distribution) calculated based on pore diameter of 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 a suitable 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 10 μm (more preferably 0.1 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 40 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 50 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 4 nm to 1000 nm, more preferably about 4 nm to 100 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%-40%. 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 0.1 micrometer-5 micrometers, the thickness of a support body can be about 100 micrometers-10 mm.

  As the material of the support, the same material as that of the porous substrate described above can be appropriately employed. The material constituting the porous substrate may be the same or different. For example, a support composed 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 (typically A combination with an average pore diameter of 2 nm or more, for example, a porous substrate having 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 firing the gel 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, such as 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 completed at a temperature of room temperature to about 60 ° C. for about 6 hours to 18 hours, and then fired 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 hydrogen gas separator 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. Thereby, the pore size of the porous substrate is reduced to a size suitable for hydrogen gas separation.

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 of this porous structure 10 (that is, along the outer wall of the porous structure 10), The oxygen-containing gas 3 may be circulated inside (hollow part 10b). An oxygen-containing 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. Such a silica membrane 21 reduces the size of the pores 20 to a size suitable for hydrogen gas separation, whereby the hydrogen gas separation material 1 is obtained. 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 base material 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 two or more oxygen sources (gas species) selected from oxygen allotrope gas (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%, a high-purity oxygen gas of 90% or more, or a mixed gas with the above-described inert gas. In the case of the mixed gas, O ₂ gas and / or O ₃ gas is preferably used at a concentration of 20 vol% (preferably 40 vol% or more, more preferably 60 vol% or more), and the inert gas used is silica. It is preferable that it is the same kind of gas (for example, N ₂ gas) as the inert gas used for the source-containing gas.

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 formation temperature (film formation 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.

In one preferred embodiment of the method disclosed herein, a porous group is formed before the film stabilization process performed after the silica film formation process, that is, between the silica film formation process and the film stabilization process. A gas replacement step is included in which the gas supplied to one side of the material is replaced with an inert gas from the silica source-containing gas. For example, in a tubular porous structure 10 as shown in FIG. 1, the silica source-containing gas 2 is supplied to the outer peripheral surface side 10 a and the oxygen-containing gas 3 is supplied to the hollow portion 10 b of the structure 10. Thus, when a silica film is formed on the outer peripheral surface 12a of the porous substrate 12, an inert gas is formed on the outer peripheral surface 10a side of the porous structure 10 on which the silica film 21 is formed in the gas replacement step. Is supplied. As the inert gas supplied here, the same type of gas (for example, N ₂ gas) as the inert gas used for the silica source-containing gas 2 can be preferably used.
In such an embodiment, the one side of the porous substrate that is supplied with the silica source-containing gas in the silica film forming step (for example, the outer peripheral surface 10a of the porous structure 10 shown in FIG. 1). Before replacing the silica source-containing gas atmosphere with the oxygen-containing gas atmosphere, once the inert gas is circulated and replaced with the inert gas atmosphere on the porous substrate (for example, the porous structure The silica source that does not contribute to the silica film formed on the outer peripheral surface 12a) of the porous substrate 12 in FIG. 10 (silica source remaining unreacted in the atmosphere on the one surface side) is completely exhausted. Is done. For this reason, generation | occurrence | production of the silica powder by reaction of this silica source and oxygen supply gas newly supplied can be prevented, and the contamination in the apparatus by this silica powder can be prevented.
The supply time (replacement time) of the inert gas replaced in the gas replacement step is not particularly limited as long as the silica source can be completely exhausted, and the flow rate of the gas and the side on which the gas is supplied are not limited. It may vary depending on the volume. For example, the supply time (replacement time) can be about 1 to 10 minutes at a flow rate of 100 mL / min to 1000 mL / min, and typically about 2 to 5 minutes.
Further, the other surface side of the porous substrate and the side to which the oxygen-containing gas is supplied in the silica film forming step (for example, in the porous structure 10, the hollow portion 10b of the structure 10 or the porous In the inner peripheral surface 12b) of the substrate 12, the oxygen-containing gas may be continuously supplied in the gas replacement step, but the supply of the oxygen-containing gas may be stopped.

  In the film stabilization process in the method disclosed herein, by supplying an oxygen-containing gas to one and / or the other surface side of the porous substrate on which the silica film is formed by counter diffusion CVD in the film formation process, The silica film is stabilized. Here, stabilization is a silica source remaining in the pores of the porous substrate, which is unreacted, or a silica film is formed on the porous substrate, but incomplete. It means that the compound in the reaction stage is oxidized to promote the formation of a Si—O—Si bond having a high bond strength and high chemical stability, preferably to a fully oxidized state. In a preferred embodiment of such a membrane stabilization step, an inert gas is passed through one side of the porous substrate in the gas replacement step for a predetermined time to replace the inert gas, and oxygen is further contained from the inert gas. Replace with gas. The porous substrate used for membrane stabilization is, for example, a membrane-like porous substrate (porous membrane) 12 formed on the porous support 14 in the porous structure 10 shown in FIG. In some cases, the outer peripheral surface side 10a of the porous structure 10 (that is, the outer peripheral surface 12a side of the porous substrate 12) and / or the hollow portion 10b of the porous structure 10 (inside the porous support member 14) An oxygen-containing gas (hereinafter referred to as “oxygen-containing gas 4”) is passed through the peripheral surface). Thereby, the silica film 21 formed in the vicinity of the opening of the outer peripheral surface 12a can be stabilized.

  This film stabilization step is preferably performed under a temperature condition of 300 ° C to 1000 ° C. More preferably, the temperature is 500 ° C. or higher, and the temperature is typically about the vapor deposition temperature (film forming temperature) of the silica source in the silica film forming step. The silica source is preferably performed at a temperature lower than the temperature at which no thermal decomposition or chemical reaction occurs. For example, when the silica source is TMOS, the film stabilization step is suitably performed under a temperature condition of about 600 ° C.

As an oxygen-containing gas suitably used in the film stabilization step, pure oxygen gas (that is, an oxygen-containing gas having an oxygen content of 100 vol%), high purity oxygen gas of 90% or more, or 20 vol% or more (preferably 40 vol) % Or more, and more preferably 60 vol% or more). As this oxygen-containing gas, the same gas as the oxygen-containing gas used in the silica film forming step can be preferably used. That is, a gas that contains a gas species having at least one oxygen atom in the molecule and can generate SiO ₂ by reacting with a silica source at the time of forming a silica film (a pure gas consisting only of the gas species or a mixture containing the gas species) Gas). For example, it is preferable to use a gas containing one or two or more oxygen sources (gas species) selected from oxygen allotrope gas (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. The inert gas contained in the oxygen-containing gas (mixed gas) is not particularly limited, and examples thereof include nitrogen (N ₂ ) gas, argon (Ar) gas, helium (He) gas, and neon (Ne) gas. One or two or more selected can be suitably used. Of these, the use of N ₂ gas is particularly preferable.

Such a membrane stabilization step is preferably performed by supplying an oxygen-containing gas to one side of the porous substrate and both sides of the other side. At this time, the oxygen-containing gas on each side may be circulated (supplied) in an equal amount (for example, 200 mL / min). In addition, the supply flow rate to the one surface side to which the silica source vaporized in the silica film forming step is supplied is set to be higher than the flow rate on the other surface side, or on the other surface side. By making the flow rate lower than the flow rate on the one surface side, the gas pressure on the one surface side is at least 0.01 MPa (preferably 0.01 MPa to 1 MPa, typically on the other surface side) You may adjust so that it may become high with the gas pressure difference of about 0.1 MPa-1 MPa.
In addition, an oxygen-containing gas is supplied to one side of the porous base material to which the silica source is supplied in the silica film forming step, and an oxygen-containing gas is supplied to the other side of the base material. The other side (the side where the supply of the oxygen-containing gas is stopped) may be depressurized so that the gas pressure difference is generated on both sides of the substrate.
Further, the other surface side where the oxygen-containing gas is supplied in the silica film forming step (the side where the supply of the oxygen-containing gas is stopped) is opened to atmospheric pressure and exposed to air, and the one surface is By supplying (circulating) an oxygen-containing gas to the side to which the silica source is supplied in the silica film forming step, the one side is at least 0.01 MPa (preferably 0.01 MPa) than atmospheric pressure. ˜1 MPa, typically 0.1 MPa to 1 MPa).
In an embodiment in which a gas pressure gradient is generated from the one side of the porous base material to the other side due to such a gas pressure difference, a large amount of residual gas may remain in the pores near the one side along the gradient. A silica source in reaction or incomplete reaction is pushed deeper toward the other side of the porous substrate. For this reason, the contact frequency with the oxygen containing gas which is supplied from the said other side and exists in the pore of the said porous base material improves. As a result, complete oxidation of the silica film can be more efficiently promoted and the silica film can be stabilized.
The preferable supply time of the oxygen-containing gas varies depending on the oxygen concentration of the oxygen-containing gas, the size of the porous substrate (silica film area), etc., but it is 2 minutes to 60 minutes, preferably 5 minutes to 30 minutes. is there. For example, when air is supplied at 200 mL / min to a porous substrate on which a silica film is formed with an area of 1.0 × 10 ⁻³ m ² , a supply time of at least about 30 minutes is preferable. On the other hand, when supplying pure oxygen gas having a concentration of 100% at the above flow rate, it may be about 5 minutes (for example, about 5 to 30 minutes).

The silica film formation process, the gas replacement process, and the film stabilization process in the method disclosed herein can be preferably performed using a silica film formation apparatus 100 having a schematic configuration shown in FIG. 4, for example. Here, as shown in FIG. 1, a silica film forming step, a gas replacement step, and a membrane for a porous structure 10 having a structure in which a porous membrane 12 is formed on the outer peripheral surface of a tubular porous support 14. The case where a stabilization process is implemented is demonstrated as an example.
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. If the space consisting of the hollow portion 10b of the porous structure 10 that bears the inside of the inner tube of the reaction tube 30 and a part of the inner tube is the inner gas passage 30b, the outer gas passage 30a is the porous gas. The outer peripheral surface of the 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) is the internal gas passage 30b. The structure 10 is arranged so as to face. 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.

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, and the vaporized silica source 2a and N ₂ gas (a silica source containing gas 2) Is circulated 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 2 a in the silica source-containing gas 2 are diffused in the reaction tube 30 in the thickness direction of the porous substrate 12, and the silica source 2 a in contact with the O ₂ gas 3 is Oxidation (thermal decomposition) can form a silica film 21 in the inside of 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.

Next, the gas replacement process performed with respect to the hydrogen gas separation material 1 formed by forming the silica membrane 21 on the porous structure 10 can be performed as follows, for example. That is, by operating the heater 36 (continuously operating from the time of forming the silica film), the inside of the reaction tube 30 is adjusted to a predetermined temperature (preferably a temperature at the time of forming the silica film, for example, 550 ° C. to 600 ° C.). N ₂ N ₂ gas supplied from the gas supply source 54 stops supplying the external gas passage 30a through the vaporizer 52 to directly flow into the said external gas passages 30a of the N ₂ gas. For the internal gas passage 30b, the oxygen-containing gas 3 may be continuously supplied at a flow rate similar to that of the N ₂ gas, for example. In this manner, the atmosphere in the external gas passage 30a is replaced with the pure N ₂ gas from the silica source-containing gas 2 to prevent contamination in the passage 30a. In addition, after the porous structure 10 is once mounted on the silica film forming apparatus 100, it is possible to continue from the silica film forming process to the film stabilizing process only by replacing the supplied gas without removing or remounting. Can proceed. That is, the silica film forming apparatus 100 having the above-described configuration is effective for producing a simple and efficient hydrogen gas separation material.

The film stabilization process performed after the said gas replacement process can be implemented as follows, for example. That is, a O ₂ gas to the outside gas passage 30a at a predetermined flow rate controlled by the O ₂ gas supply source 56 MFC57 for supplying an oxygen-containing gas 4 for membrane stabilization. Thereby, the atmosphere in the passage 30a is replaced with O ₂ gas. At this time, supply of N ₂ gas from the N ₂ gas supply source 54 may be continued, and the oxygen-containing gas 4 may be supplied to the external gas passage 30a as a mixed gas of O ₂ gas and N ₂ gas, The supply of the N ₂ gas may be stopped and pure O ₂ gas may be supplied to the passage 30a as the oxygen-containing gas 4. On the other hand, for the internal gas passage 30b, the oxygen-containing gas 3 is supplied from the O ₂ gas supply source 42 at a flow rate controlled by the MFC 43. Further, the supply of the oxygen-containing gas 3 may be stopped and released to atmospheric pressure, or the pressure may be reduced. In this way, the gas pressure in the external gas passage 30a is made 0.01 MPa or more (preferably 0.01 MPa to 1 MPa, for example, 0.1 MPa) higher than the gas pressure in the internal gas passage 30b. As a result, the silica source 2a that can remain in the pores 20 of the hydrogen gas separation material 1 (porous structure 10) is pushed inward (to the other surface 12b side of the porous substrate 12) and O ₂ gas. 3, the oxidation of the silica film 21 is promoted, and a chemically more stable silica film 21 is formed.

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 at one end in the axial direction with a sealing plug 11. 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 from 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 exhaust port 44 a.
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 and the path for supplying the oxygen-containing gas 4 in the film stabilization step are the same as those of the silica film forming apparatus 100. Each of the silica source-containing gas 2 and the oxygen-containing gas 4 is supplied from the outer tube inlet (reaction tube inlet) 34 of the reaction tube 30 to the external gas passage 30a and discharged from the outer tube outlet (reaction tube outlet) 35. The

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-containing gas 2 at one end in the axial direction, and an outlet 75 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.

  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 hydrogen gas separation material 1 having a configuration schematically shown in FIG. 1 was manufactured by the procedure shown in FIG.
That is, α-alumina powder having an average particle size of about 1 μm was kneaded with an organic binder and water to prepare a clay for extrusion molding. This clay is extruded and dried by a commercially available extruder, and then fired in an air atmosphere to obtain a porous support (α-) having a tubular shape (outer diameter 10 mm, inner diameter 7 mm, length 50 mm). (Alumina support) 14 was obtained (step S10).
The average pore diameter of the support 14 measured by a general mercury intrusion method was about 150 nm.

Next, a porous substrate (porous membrane) 12 was formed on the surface of the obtained α-alumina support 14 (step S20).
That is, aluminum isopropoxide was hydrolyzed and dissolved with an acid to prepare a boehmite sol. By lifting the boehmite sol with the α-alumina support 14 (both ends of the tube shape are temporarily blocked so that the sol does not enter the hollow portion) at a speed of about 1.0 mm / second, the support 14 Boehmite sol was dip-coated on the outer peripheral surface of the film. This was dried at 60 ° C. overnight (about 12 hours) and then fired in the air at 600 ° C. for 3 hours to form a γ-alumina porous film (γ-alumina film) 12. Thus, the porous structure 10 in which the γ-alumina film 12 was formed on the outer peripheral surface of the α-alumina support 14 was obtained. The thickness of the γ-alumina film 12 was about 2 μm, and the peak value of the pore diameter measured by a general nitrogen adsorption method was 4 nm to 6 nm. Hereinafter, the porous structure 10 may be referred to as a “single tube”.

The obtained single tube (porous structure 10) is set in a silica film forming apparatus having a schematic configuration shown in FIG. 4, and counter diffusion CVD is performed using tetramethoxysilane (TMOS) as a silica source. As shown in FIG. 4, a silica film 21 was formed on the γ-alumina film 12 constituting this single tube (step S30).
In the counter diffusion CVD, the reaction temperature (silica film formation temperature) is 600 ° C., the reaction time (silica film formation time or film formation time) is 5 minutes, the N ₂ gas supply rate is 200 mL / min, and the O ₂ gas supply rate is 200 mL / minute. Performed under the condition of minutes. In this way, the hydrogen gas separation material according to Example 1 was manufactured. In the vaporizer 52, the TMOS heated to 45 ° C. was bubbled with N ₂ gas and vaporized.

Next, the flow of N ₂ gas was stopped from flowing into the vaporizer 52, and the gas was allowed to flow directly into the external gas passage 30a, thereby replacing the atmosphere in the external gas passage 30a with pure N ₂ gas ( Step S40).
This N ₂ gas replacement was performed at a supply rate (flow rate) of 200 mL / min for 5 minutes. The supply of O ₂ gas to the internal gas passage 30b was continuously performed at a supply rate of 200 mL / min.

Then, the _{N 2} supply is stopped to the gas of the external gas passages 30a, _{O 2} pure _{O 2} gas from the gas supply source 56 is supplied to the outer gas passages 30a and also _{O 2} gas to the inside gas passage 30b By supplying O ₂ gas from the supply source 42, the silica film 21 formed on the γ-alumina film 12 was stabilized (step S50).
The silica membrane 21 is stabilized by the temperature in the reaction tube 30 of 600 ° C., the supply rate of O ₂ gas to the external gas passage 30a is 200 mL / min, and the supply rate of O ₂ gas to the internal gas passage 30b is 200 mL. The supply time of these O ₂ gases was 5 minutes per minute.
Through the above steps, a single pipe hydrogen gas separator was obtained.

About the obtained hydrogen gas separation material, hydrogen (H ₂ ) gas permeability and nitrogen (N ₂ ) gas permeability were measured, and the permeability coefficient ratio (H ₂ gas to N ₂ gas) (H ₂ / N ₂ ) was calculated. 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. That is, the inside of the reaction tube 30 is adjusted to a measured temperature of 600 ° C. by operating the heater 36 as necessary, 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 (not shown) 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 between 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.
Further, the permeation test was performed to measure the H ₂ gas permeability in a plurality of temperature conditions. The Arrhenius plot of the _{H 2} gas permeability was determined the activation energy of the _{H 2} gas permeability [kJ / mol].

Furthermore, the hydrogen gas separator is a gas mixture of 75% H ₂ O (water vapor) and 25% N _{2 in} a molar ratio of 500 ° C., a total pressure of 0.1 MPa, a flow rate of 200 mL / min for 20 hours. A steam resistance test was performed by performing the treatment.
The H ₂ gas permeability and permeability coefficient ratio (H ₂ / N ₂ ) in the hydrogen gas separation material after this water vapor resistance test were determined by the same method as described above.

  The main part of the result obtained as described above is shown in Table 1 together with the configuration of the hydrogen gas separation material 1 and the outline of the manufacturing method.

<Comparative Example 1>
Next, in this example, the hydrogen gas separation material was manufactured without performing the membrane stabilization process performed in Example 1. The other points are the same as in the first embodiment. Moreover, it evaluated similarly to Example 1. FIG. The main parts of the obtained results are shown in Table 1 together with the configuration of the hydrogen gas separation material and the outline of the production method.

<Comparative example 2>
Next, in this example, the hydrogen gas separation material was manufactured without performing the membrane stabilization process performed in Example 1. The difference from Example 1 is that the film stabilization process is not performed and the film formation time (film formation time) is changed from 5 minutes to 30 minutes at the time of forming the silica film. Otherwise, the hydrogen gas separator according to Comparative Example 2 was produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The main parts of the obtained results are shown in Table 1 together with the configuration of the hydrogen gas separation material and the outline of the production method.

As shown in Table 1, the hydrogen gas separator according to Example 1 has an H ₂ gas permeability at 600 ° C. of 4.7 × 10 ⁻⁷ [mol / m ² · s · Pa], a permeability coefficient ratio ( H ₂ / N ₂ ) was 5.7 × 10 ² , and the H ₂ transmittance and the transmission coefficient ratio were realized at a high level with good balance. Further, the activation energy of the _{H 2} permeation 9.1 [kJ / mol] and small, were those capable of exhibiting high _{H 2} permeability.
On the other hand, as shown in Comparative Example 1, unless the membrane stabilization step was performed, the H ₂ separation performance (permeability coefficient ratio) particularly after the steam treatment was significantly reduced. As shown in Comparative Example 2, when the silica source was formed for a long time without performing the membrane stabilization step to form a silica membrane, the H ₂ separation performance was improved. However, the H ₂ permeation performance (H ₂ transmissivity) decreased.
As described above, by performing the membrane stabilization process, a hydrogen gas separation material capable of realizing a high level of balance between H ₂ permeation performance and H ₂ separation performance in a short time (5 minutes) is required. I understood that I could do it.

<Example 2>
In this example, the oxygen-containing gas 4 supplied in the membrane stabilization step is changed from pure O ₂ gas to air in both the external gas passage 30a and the internal gas passage 30b, and the air supply time is changed from 5 minutes to 30 minutes. Extended to minutes. In the silica film forming apparatus 100 shown in FIG. 4, the O ₂ gas supply sources 42 and 56 are changed to air supply sources in order to implement the present embodiment. The hydrogen gas separator according to Example 2 was manufactured in the same manner as Example 1 with respect to other points.
The obtained hydrogen gas separator was evaluated in the same manner as in Example 1. Table 2 shows the main part of the evaluation result together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

<Comparative Example 3>
In this example, the time for supplying the oxygen-containing gas (air) in the film stabilization process was changed from 30 minutes to 5 minutes. Otherwise, the hydrogen gas separator according to Comparative Example 3 was produced in the same manner as in Example 2, and this was evaluated in the same manner as in Example 1. Table 2 shows the main part of the evaluation result together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

As shown in Table 2, the hydrogen gas separators according to Example 2 and Comparative Example 3 had the same H ₂ permeability and permeability coefficient ratio as those of the hydrogen gas separator according to Example 1. . Moreover, the activation energy in Example 2 and Comparative Example 3 was also lower than that in Example 1. Therefore, it was found that the oxygen-containing gas that stabilizes the silica film may have an oxygen content of about 20 mol%, such as air. However, from Comparative Example 3, it was found that when the air supply time was short, the H ₂ separation performance (permeability coefficient ratio) after the steam treatment could be lowered. As a result, it was found that even if the oxygen content was low, a hydrogen gas separation material having sufficiently high H ₂ permeability and separation could be obtained by extending the supply time accordingly. In Example 2, the permeability coefficient ratio after the steam treatment was 4.5 × 10 ^2, which was lower than that in Example 1. However, with this value, the H ₂ separation performance is sufficiently high even in a high-temperature steam atmosphere. I can say that.

<Example 3>
In this example, the internal gas passage 30b was opened to atmospheric pressure (1.01 × 10 ⁵ Pa) in the membrane stabilization step. The oxygen-containing gas 4 supplied to the external gas passage 30a is supplied as pure O ₂ gas, and the O ₂ gas is supplied at a flow rate of 200 mL / min so that the gas pressure in the passage 30a is increased by 0.1 MPa from the atmospheric pressure. (That is, the gas pressure in the external gas passage 30a is about 0.2 MPa). The hydrogen gas separator according to Example 3 was manufactured in the same manner as Example 1 with respect to other points.
The obtained hydrogen gas separator was evaluated in the same manner as in Example 1. Table 3 shows an outline of the structure of the hydrogen gas separation material and an outline of the manufacturing method for the main part of the evaluation results.

As shown in Table 3, in the hydrogen gas separation material according to Example 3, the H ₂ permeability and the hydrogen gas separation material according to Example 1 are approximately the same, and the permeability coefficient ratio is the hydrogen according to Example 1. Improved than gas separator. In addition, both the H ₂ permeability and the permeability coefficient ratio after the steam treatment exceeded the hydrogen gas separation material according to Example 1, and in particular, the hydrogen separation performance (permeability coefficient ratio) was improved by 1.5 times or more. The activation energy for H ₂ permeation was also as low as in Example 1. Thus, it has been found that pressurizing the side on which the silica film is formed so as to generate a differential pressure more effectively than the other side is effective in improving the film performance.

<Example 4>
In this example, a single tube (porous structure 10 in FIG. 1) having an outer diameter of 10 mm, an inner diameter of 7 mm, and a length of 400 mm is produced, and one end in the axial direction thereof is sealed with a sealing plug 11 (see FIG. 5). A sealed “single-end sealed single tube” was used. A silica film forming apparatus 110 shown in FIG. 5 was used for forming the silica film. The film formation time was 120 minutes. The supply rate of O ₂ gas supplied to the hollow portion 10b of the porous structure 10 through the O ₂ supply pipe 45 during film formation was set to 100 mL / min. The film area of the formed silica film was 7.5 × 10 ⁻³ [m ² ].
Further, in the membrane stabilization step, the supply rate of pure O ₂ gas supplied to the external gas passage 30a is set to 1000 mL / min, and the supply rate of pure O ₂ gas supplied to the hollow portion 10b is set to 100 mL / min. _Two gases were supplied.
The hydrogen gas separation material according to Example 4 was manufactured in the same manner as Example 1 for the other points. The obtained hydrogen gas separator was evaluated in the same manner as in Example 1. The essential parts of the evaluation results are shown in Table 4 together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

<Comparative example 4>
In this example, the film stabilization process was not performed. Otherwise, the hydrogen gas separation material according to Comparative Example 4 was produced in the same manner as in Example 4, and this was evaluated in the same manner as in Example 1. The essential parts of the evaluation results are shown in Table 4 together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

As shown in Table 4, the hydrogen gas separator according to Example 4 had cracks in the silica membrane, although the H ₂ permeability and permeability coefficient were lower than those of the hydrogen gas separator according to Example 1. And sufficient H ₂ permeation performance and separation performance. The activation energy for H ₂ permeation was about twice as high as that in Example 1, but it can be said to be a sufficiently low value. On the other hand, when H ₂ gas and N ₂ gas were supplied to the hydrogen gas separation material according to Comparative Example 4, cracks occurred in the silica film, and the N ₂ gas permeability was comparable to the H ₂ gas permeability. The H ₂ separation performance was not shown. From the above results, by introducing the membrane stabilization process, even if the membrane area is expanded by 7 times or more than the hydrogen gas separation material according to Example 1, there is no generation of cracks and the membrane performance is good. It has been found that hydrogen gas separators can be produced.
Further, in the prior art, it was possible to form a silica film on a single tube, but it was often difficult to use a multi-tube module. The cause of this is “increase in membrane area” and “structure of the multi-tube module” (that is, the single pipe is configured so that the supply gas passes from one end to the other, but the multi-tube module is sealed at one end. A single-end sealed single tube assembly). According to Example 4 and Comparative Example 4, it was determined that the cause was “increase in film area”.

<Example 5>
In the present embodiment, a multi-tube module 70 having a configuration as shown in FIGS. 6 and 7 was used. Six single tubes (porous structure 10 in FIG. 1) having an outer diameter of 10 mm, an inner diameter of 7 mm, and a length of 400 mm were produced, and the six were accommodated in the reaction vessel 71. A silica film was formed in a total area of 40 × 10 ⁻³ [m ² ] (film area) of the outer peripheral surface of these six single tubes. For forming the silica film, a silica film forming apparatus 110 shown in FIG. 5 was used. The film formation time was 120 minutes. Further, the supply rate of O ₂ gas flowing through the O ₂ supply pipe 72 and the single pipe during film formation was set to 100 mL / min. The reaction vessel 71 of the multi-tube module 70 has a larger volume than the reaction tube 30, and it takes about 10 minutes for the silica source concentration to be appropriate. For this reason, before supplying the O ₂ gas, N ₂ gas was supplied for about 10 minutes.
Furthermore, in the membrane stabilization step, the supply rate of the pure O ₂ gas supplied to the outer peripheral surface side of the single tube is 1000 mL / min, and the pure O ₂ gas supplied to the hollow portion (inner peripheral surface side) of the single tube Each O ₂ gas was supplied at a supply rate of 100 mL / min.
The hydrogen gas separation material according to Example 5 was manufactured in the same manner as Example 1 for the other points. The obtained hydrogen gas separator was evaluated in the same manner as in Example 1. The essential parts of the obtained results are shown in Table 5 together with the configuration of the hydrogen gas separator and the outline of the production method.

<Comparative Example 5>
In this example, the film stabilization process was not performed. Other than that, the hydrogen gas separation material according to Comparative Example 5 was produced in the same manner as in Example 5, and this was evaluated in the same manner as in Example 1. Table 5 shows the main part of the evaluation results together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

As shown in Table 5, in the hydrogen gas separation material according to Example 5, the H ₂ permeability decreased compared to the hydrogen gas separation material according to Example 1, but the permeability coefficient of Example 5 was higher. It was much higher, and showed the same high value as the hydrogen gas separator according to Example 1 even after the steam treatment. On the other hand, when H ₂ gas and N ₂ gas were supplied to the hydrogen gas separation material according to Comparative Example 5, cracks were generated in the silica film, and the N ₂ gas permeability was approximately the same as the N ₂ gas permeability. The H ₂ separation performance was not shown. From the above results, by introducing the membrane stabilization process, even when the area of the silica membrane is increased using a multi-tubular module (40 times that of Example 1), sufficient H ₂ permeation performance is obtained without causing cracks. It was found that a hydrogen gas separation material having a separation performance and capable of withstanding a high-temperature steam atmosphere can be produced. The activation energy for H ₂ permeation in Example 5 was about twice as high as that in Example 1, but it can be said that it is sufficiently low that H ₂ can permeate the silica film.

<Example 6>
In this example, HMDS (hexamethyldisiloxane) was used instead of TMOS as the silica source. Also, the silica film formation time was changed to 15 minutes. Otherwise, the hydrogen gas separation material according to Example 6 was produced in the same manner as in Example 5, and this was evaluated in the same manner as in Example 1. Table 6 shows the main part of the evaluation result together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

<Comparative Example 6>
In this example, the film stabilization process was not performed. Otherwise, the hydrogen gas separation material according to Comparative Example 6 was produced in the same manner as in Example 6, and this was evaluated in the same manner as in Example 1. Table 6 shows the main part of the evaluation result together with the configuration of the hydrogen gas separation material and the outline of the manufacturing method.

As shown in Table 6, in Example 6, it was found that even when HMDS was used as the silica source, a hydrogen gas separation material having a silica membrane having a good balance between H ₂ permeation performance and separation performance could be produced. In addition, the activation energy for H ₂ permeation was lower than that in Example 1. On the other hand, in Comparative Example 6, it was possible to form a silica film using HMDS, but when H ₂ gas and N ₂ gas were circulated, cracks thought to be caused by H ₂ gas permeation occurred. The permeation rate of the _two gases increased rapidly and no longer showed H ₂ separation performance. From the above results, by introducing a membrane stabilization step, a hydrogen gas separation material having good H ₂ permeation performance and separation performance can be produced without causing cracks even when a silica source other than TMOS is used. I understood.

  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.

In a preferred embodiment of the present invention, it is a diagram illustrating a process of forming a silica film on a porous substrate, and is a schematic 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 a flowchart which shows the outline of the manufacturing method of the hydrogen gas separation material which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrogen gas separation material 2 Silica source containing gas 2a Silica source 3 Oxygen containing gas supplied in a silica membrane formation process 3a Gas molecule which consists of oxygen atoms 4 Oxygen containing gas supplied in a membrane stabilization process 10 Porous structure 10a Peripheral surface side 10b Hollow part 12 Porous substrate (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 (7)

A method for producing a hydrogen gas separator 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 a carrier 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
Wherein the side hand silica source is vaporized in the silica film forming process a side of is supplied silica film formed substrate, an oxygen-containing gas is supplied in place of the silica source containing gas, A film stabilization step for stabilizing the silica film;
A method for producing a hydrogen gas separator.   The said film stabilization process is a manufacturing method of Claim 1 performed on the temperature conditions of 300 to 1000 degreeC.   The production method according to claim 1 or 2, wherein the oxygen-containing gas used in the film stabilization step is a pure oxygen gas or a mixed gas containing 20 vol% or more of oxygen. In the film stabilization step, the flow rate of the oxygen-containing gas supplied in place of the silica source-containing gas is adjusted to be higher than the flow rate of the oxygen-containing gas on the other surface side at a gas pressure difference of at least 0.01 MPa. The manufacturing method as described in any one of Claims 1-3. In the membrane stabilization step, an oxygen-containing gas is supplied instead of the silica source-containing gas on one surface side of the porous substrate and the side on which the silica source vaporized in the silica membrane formation step is supplied and, and, the porous other oxygen-containing gas to a surface side by the silica film forming step of fibrous base material is supplied side stops the supply of the oxygen-containing gas, at both sides of the porous substrate The manufacturing method according to any one of claims 1 to 3, wherein the pressure on the other side is reduced so as to generate a gas pressure difference of at least 0.01 MPa.   A step of replacing the gas supplied to one surface side of the porous base material with the inert gas from the silica source-containing gas between the silica film forming step and the membrane stabilization step, The gas supplied to one surface side of the porous substrate is replaced with an oxygen-containing gas from an inert gas in the film stabilization step after being replaced with an active gas. The manufacturing method as described in one.   The porous substrate is formed as a porous film having an average pore diameter or a peak value of pore diameter distribution of 2 nm to 20 nm on a porous support having an average pore diameter or a peak value of pore diameter distribution of 4 nm to 1000 nm. The manufacturing method as described in any one of Claims 1-6.

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