JP2008246295A - Manufacturing method of hydrogen separation membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of hydrogen separation membrane capable of forming a silica separation membrane having high hydrogen selective permeability by a CVD (chemical vapor deposition) method. <P>SOLUTION: The manufacturing method of hydrogen separation membrane includes steps of: supplying a silica source mixed gas of a silica forming substance evaporated on one surface side of a porous substrate and an inert gas; supplying the inert gas being reactive species to the other surface side of the porous substrate to perform opposite diffusion for a prescribed time; thereafter performing one-side supply of the silica source mixed gas; performing such opposite diffusion and one-side supply at several times to deposit silica in pores in the vicinity of the surface of the porous substrate by chemical vapor deposition; and forming a silica membrane to manufacture the hydrogen separation membrane. The one-side supply of the silica source mixed gas is performed by vacuuming and sucking the inert gas-supplied surface side for a prescribed time in a state of continuously supplying the mixed gas or in a state of remaining the mixed gas in a reactor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a hydrogen separation membrane. More specifically, the present invention relates to a method for producing a hydrogen separation membrane having higher hydrogen permselectivity.

  Recently, hydrogen as a clean energy is attracting attention. However, in order for hydrogen to be actually used in a wide range of fields including fuel cells, it is necessary to develop a method for obtaining hydrogen in a large amount and with high efficiency. A typical method for producing hydrogen is a steam reforming method of methane. However, since the reforming reaction is generally performed under a high temperature condition of 800 ° C. or more and is in two steps of hydrogen generation and purification, further improvement in thermal efficiency and simplification of the steps are required.

  On the other hand, if a membrane reformer for hydrogen production that integrates the hydrogen production process and the separation process can be applied to the steam reforming reaction of methane, the reaction temperature will be as low as 500 ° C and the efficiency will be improved by simplifying the process. Can be expected. However, in order to realize this, a hydrogen separation membrane that can be used at high temperatures is indispensable. Since porous ceramics have high chemical and thermal stability, they are expected to be used as separation membranes or supports for processes where organic separation membranes cannot be applied.

Among them, a porous amorphous silica membrane as a hydrogen separation membrane has attracted attention in recent years because it has low raw material costs and exhibits excellent performance in terms of hydrogen selectivity and permeability. In particular, a silica film showing high hydrogen permeability by the CVD method is attracting attention.
Membrane 30 vol.5 275-281 (2005)

The CVD method is a film forming method in which a silica raw material such as an alkoxysilane compound is supplied in a gas phase, and chemical vapor deposition is performed in pores near the surface of the porous substrate. There are two types of counter diffusion methods.
Membrane, Vol. 31, No. 5, pp. 263-266 (2006)

On the other hand, the supply method is a method in which the silica raw material is supplied from one side of the porous substrate, and in some cases, the opposite side of the membrane is sucked and vapor-deposited in the substrate pores. In contrast, the counter diffusion method is a method in which the silica source material is supplied from one side of the substrate, and reactive species such as O ₂ and O ₃ are supplied from the opposite side of the substrate. It has the feature that it can be controlled. In any of these methods, in order to obtain a silica membrane having high hydrogen selectivity by chemically vapor-depositing silica in the pores near the surface of the porous substrate, there are only pores having a pore size suitable for hydrogen separation, It is important to form a film so that there are no defects such as cracks and pinholes. However, the relationship between the film forming conditions and the hydrogen selectivity still remains unclear, and there is a need for film forming conditions for obtaining a film having even higher hydrogen selective permeability.

Actually, the non-patent document 2 discloses that a hydrogen permeation rate of 10 ⁻⁸ to 10 ⁻⁶ mol / m ² · sec for a hydrogen separation membrane made of silica separation membrane-forming porous alumina obtained by various membrane forming methods. Although the value of the separation factor (H ₂ / N ₂ ) under the Pa condition is shown in the figure, the value is only in the order of 10 ² to 10 ³ .

  An object of the present invention is to provide a method for producing a hydrogen separation membrane in which a silica separation membrane having high hydrogen selective permeability is formed by a CVD method.

  An object of the present invention is to supply a silica source mixed gas of a silica-forming substance and an inert gas vaporized on one surface side of a porous substrate, and a reactive species on the other surface side of the porous substrate. After supplying the active gas to be diffused counter-facing for a certain period of time, one supply of the silica source mixed gas is performed, and by performing such counter-diffusion and one-supply multiple times, the pores in the vicinity of the porous substrate surface This is achieved by a method in which silica is chemically vapor-deposited to form a silica membrane to produce a hydrogen separation membrane. One-side supply of the silica source mixed gas is performed by sucking the active gas-supplied surface side under reduced pressure for a certain period of time in a state where the supply of the mixed gas is continued or in a state where the mixed gas remains in the reactor. .

The hydrogen separation membrane obtained by the method of the present invention has a hydrogen selective permeability represented by a separation factor (H ₂ / N ₂ ) of one digit or more even when a silica membrane having an equivalent hydrogen permeability is formed. It can be increased by two orders of magnitude.

  The porous substrate is usually composed of two layers: a porous support substrate having a pore size of about 0.05 to 5 μm and a porous intermediate having a pore size of about 1 to 10 nm formed on the surface thereof. The material of the supporting substrate is not particularly limited as long as it is an inorganic material, and examples thereof include sintered bodies such as alumina, zirconia, mullite, cordierite, spinel, silicon carbide, silicon nitride, silica, or a mixture thereof. In particular, alumina and zirconia are preferably used. Examples of the shape of the support substrate include a hollow fiber membrane shape, a tube shape, a monolith shape, a honeycomb shape, a flat plate shape, and the like. Preferably, a hollow tubular shape such as a hollow fiber membrane shape or a tube shape is used. The thickness of the support member is about 0.1 to 10 mm because high gas permeability and practical strength are required for the support member.

  The intermediate is formed as a porous layer having nano-order pores by applying a raw material solution obtained by a sol-gel method on the surface of a supporting substrate by a dipping method, drying, and firing. Examples of the material constituting the intermediate include alumina, zirconia, titania, silica, and a mixture thereof. Alumina composed of γ-type crystals is preferable. When γ-alumina is used, the α-alumina porous body is usually coated with a γ-alumina layer. The thickness is about 1 to 10 μm because the intermediate is required to have high gas permeability and no defects such as pinholes and cracks.

  The porous base material constituted in this way is put in a metal cylindrical reactor and hermetically fixed with an O-ring or the like. At this time, the surface outside the film forming range of the porous substrate is hermetically sealed with glass or the like. The reactor is equipped with a heater, the temperature during film formation can be controlled, and the temperature in the reactor during chemical vapor deposition is set to about 500-800 ° C, preferably about 550-650 ° C Is done.

To the intermediate layer side of the porous substrate in the reactor, a silica source mixed gas of a silica-forming substance and an inert gas which is vaporized by heating to a temperature which is preferably vaporized, preferably vaporized, is supplied. The silica source gas mixture is formed by bubbling a constant flow of inert gas through a liquefied silica forming material at a constant temperature. As the inert gas, any gas can be used, but generally nitrogen is used. Examples of the silica-forming substance include various alkoxysilane compounds. Tetra lower alkoxysilanes such as tetraethoxysilane and tetramethoxysilane are preferably used. An active gas is supplied to the support substrate side of the porous substrate. As the active gas, O ₂ , O ₃ or the like is used, and preferably O ₂ is used.

  The flow rates of the silica source mixed gas and the active gas supplied by counter diffusion cannot be specified because they differ depending on the area of film formation, but are generally about 0.1 to 2 L / min in terms of atmospheric pressure. . Also, the supply time varies depending on the area to be formed and cannot be specified in general, but is about 5 to 60 minutes, preferably about 10 to 20 minutes per cycle.

  In the one supply performed after the counter diffusion, the supply of the active gas on the support substrate side of the porous substrate is interrupted, the vacuum suction or the like is performed by a vacuum pump or the like, and the exhaust is exhausted. The one-side supply of the silica source mixed gas is performed by sucking the surface side to which the active gas is supplied under reduced pressure for a certain time while the supply of the mixed gas is continued. Alternatively, the supply of the active gas is stopped, but with the stop of the supply of the active gas, the supply of the inert gas constituting the mixed gas is also stopped, that is, the new supply of the mixed gas is stopped and remains in the reactor. One supply of the silica source mixed gas is also performed by suctioning the surface side to which the active gas is supplied for a certain period of time in a state where the mixed gas exists.

  The internal pressure at the time of evacuation cannot be generally specified because it varies depending on the displacement of the vacuum pump or the like, the film forming area, the formation state of the silica film chemically deposited in the pores near the surface of the porous substrate, etc. In general, the pressure is about 1 to 3000 Pa, and the evacuation time is about 1 to 60 minutes, preferably about 2 to 10 minutes per cycle.

The number of cycles (number of cycles) in which such counter-diffusion and one-side supply are alternately performed is not particularly specified, but the hydrogen permeation rate (hydrogen permeation rate) at 600 ° C. is 1 × 10 ⁻⁷ mol / m ² · sec · Pa. And until the separation factor (H ₂ / N ₂ ), which is the ratio of the permeation rate of hydrogen and nitrogen, reaches 10 ⁴ or more, which is generally achieved in about 10 cycles or more.

  Next, the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an apparatus used in the method of the present invention. Reference numeral 1 is a porous substrate, 1a is a supporting substrate side, 1b is an intermediate layer side, 2 is a film forming part, and 3 is a reaction. 4 is a heater, 5 is a nitrogen cylinder, 6 is an oxygen cylinder, 7 is a pressure regulator, 8 is an open / close valve, 9 is a mass flow controller, 10 is a bubbler, 11 is a cooling trap, 12 is a pressure gauge, and 13 is a vacuum pump. The counter diffusion and the one-side supply as described above are alternately performed by using such an apparatus.

  Next, the present invention will be described with reference to examples.

Example 1
(1) A porous α-alumina capillary (length 350 mm, diameter 2.9 mm, film thickness 0.3 mm, average pore diameter about 0.1 μm) is used as a supporting base material, and glass paste is applied to both ends of each 60 mm length. Was applied, dried, and fired to hermetically seal the portions other than the film forming portion. Next, a γ-alumina sol layer was formed on the film forming part having a center of 230 mm by a dipping method, dried, and then fired at 600 ° C. Such a series of steps of dipping-firing was performed twice. This γ-alumina intermediate layer had a thickness of about 3 mm, and its pore size distribution was measured with a nanopalm porosimeter (manufactured by Seika Sangyo Co., Ltd.). The average pore size was 4 nm.
(2) A porous α-alumina capillary support base material in which this γ-alumina intermediate layer is formed in the film forming part is placed in a metal cylindrical reactor, O-rings are fitted to both ends of the base material, After hermetically fixing with a flange, the reactor was heated with a heater, and the temperature was controlled at 600 ° C. Next, nitrogen bubbling in tetramethoxysilane at 45 ° C. was flowed at a flow rate of 200 ml / min to form a silica source mixed gas, which was supplied to the intermediate layer side in the reactor, while supporting substrate tube Oxygen was supplied to the inside at a flow rate of 200 ml / min. Counter diffusion with these gases was continued for 15 minutes, then the supply of nitrogen and oxygen was stopped, and the inside of the supporting base tube was vacuumed for 5 minutes (internal pressure 2000 Pa or less) ). Such counter-diffusion supply and one-side supply (vacuum suction) were made into one cycle, and a total of 12 cycles were performed, and silica was chemically vapor-deposited in the pores near the surface of the porous substrate to form a silica film.

Example 2
In Example 1 (2), the supply of only oxygen after counter-diffusion was stopped, the counter-diffusion supply and the one supply were made one cycle, and a total of eight cycles were performed to form a silica film.

Comparative Example 1
In Example 1 (2), only the opposing diffusion supply was performed for 120 minutes to form a silica film.

Comparative Example 2
In Example 1 (2), only the supply of the silica source mixed gas to the intermediate layer side and the suction under reduced pressure inside the support base material tube were performed for 120 minutes to form a silica film.

The hydrogen selective permeability of the silica film-forming porous α-alumina capillary obtained in each of the above Examples and Comparative Examples was measured. Measurement is performed by flowing normal-pressure hydrogen to the silica membrane formed at 600 ° C, sucking the inside of the supporting base tube under reduced pressure, and closing the valve between the vacuum lines when the degree of pressure reduction inside the tube becomes constant. The suction was stopped, and the hydrogen permeation rate was calculated by measuring the change over time in the pressure difference between the outer surface side of the supporting substrate and the inner side of the tube, that is, both sides through the silica membrane. Further, nitrogen was allowed to flow on the outer surface side of the supporting substrate, and the nitrogen permeability was calculated by the same method, and the ratio (H ₂ / N ₂ ) with the hydrogen permeability was taken as the separation factor.

The results obtained are shown in the following table.
table
Example Hydrogen permeability (mol / m ² ・ sec ・ Pa) Separation factor (H ₂ / N ₂ )
Example 1 1.1 × 10 ⁻⁷ 23000
Example 2 1.3 × 10 ⁻⁷ 16200
Comparative Example 1 1.8 × 10 ⁻⁷ 2100
Comparative Example 2 0.9 × 10 ⁻⁸ 160

It is a schematic diagram of the apparatus used for the method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous base material 1a Support base material side 1b Intermediate body layer side 2 Film-forming part 3 Reactor 4 Heater 5 Nitrogen cylinder 6 Oxygen cylinder 13 Vacuum pump

Claims (5)

  Supplying a silica source mixed gas of a silica-forming substance and an inert gas vaporized to one surface side of the porous substrate, supplying an active gas as a reactive species to the other surface side of the porous substrate, After the counter diffusion for a certain time, one supply of the silica source mixed gas is performed, and by performing such counter diffusion and one supply multiple times, the silica is chemically vapor-deposited in the pores near the porous substrate surface, A method for producing a hydrogen separation membrane, comprising forming a silica membrane.   The method for producing a hydrogen separation membrane according to claim 1, wherein the one-side supply of the silica source mixed gas is performed by sucking the surface side to which the active gas is supplied for a predetermined time under reduced pressure while the supply of the mixed gas is continued.   One-side supply of the silica source mixed gas is performed by stopping the new supply of the mixed gas and suctioning the surface side to which the active gas is supplied under reduced pressure for a certain time in a state where the mixed gas remaining in the reactor exists. The method for producing a hydrogen separation membrane according to claim 1.   The method for producing a hydrogen separation membrane according to claim 2 or 3, wherein the silica source mixed gas is supplied to the intermediate layer side of the porous substrate.   2. The method for producing a hydrogen separation membrane according to claim 1, wherein the supply of the active gas is performed on the support substrate side of the porous substrate.

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