JP5906863B2 - Glass tube and manufacturing method thereof - Google Patents

Description

  The present invention relates to a glass tube and a manufacturing method thereof, and more particularly to a glass tube suitable as a support for a hydrogen separation material for separating hydrogen with high purity from a mixed gas containing hydrogen generated by fuel reforming and the like, and its manufacturing Regarding the method.

  In order to realize a hydrogen energy society, research and development on hydrogen production technology and hydrogen utilization infrastructure are underway. Fuel cells for automobiles, stationary fuel cells for home use, hydrogen stations, and large chemical plants in the future High-purity hydrogen used in Japan is expected to be in great demand in the future, and its production is required to have higher efficiency.

Currently, hydrogen is produced by steam reforming a hydrocarbon fuel at a temperature of about 700 ° C. (CH ₄ + H ₂ O → CO + 3H ₂ ), and then CO conversion at a few hundred degrees (CO + H ₂ O → CO ₂ + H ₂ ). This method is widely used in terms of price competitiveness. Gas components obtained through these reactions include carbon dioxide, carbon monoxide, unreacted hydrocarbons and water in addition to hydrogen. In recent years, in polymer electrolyte fuel cell systems that have become popular in the home, the purity of hydrogen is not increased in order to reduce costs, and a mixed gas with a hydrogen concentration of about 60% is directly used as the fuel electrode of the fuel cell. However, the carbon monoxide poisoning the fuel electrode catalyst is oxidized to carbon dioxide (CO + 1 / 2O ₂ → CO ₂ ) before supply, and the concentration thereof is removed to less than 10 ppm. However, since a fuel cell using a mixed gas has lower power generation efficiency than a pure hydrogen fuel cell, there is a need for a technique for producing hydrogen with higher purity at a low cost in a space-saving manner. Further, in addition to the limitation of the CO concentration, it is necessary to supply 99.99% or more of hydrogen to the automobile fuel cell, and a technique for producing a large amount of inexpensive high-purity hydrogen is required.

  Examples of methods for extracting high-purity hydrogen from a mixed gas containing hydrogen include an absorption method, a cryogenic separation method, an adsorption method, and a membrane separation method. The feature of the membrane separation method is high efficiency and easy miniaturization. have. In addition, by configuring a membrane reactor in which a hydrogen separation membrane is inserted into a reaction vessel that performs steam reforming, hydrogen generated by the reforming reaction is continuously extracted from the reaction atmosphere, and the reforming reaction is performed even at a temperature of about 500 ° C. And CO shift reaction can be promoted at the same time, and high-purity hydrogen can be produced efficiently. Furthermore, an expensive noble metal catalyst such as platinum used for CO conversion is not required in the membrane reactor, and the cost can be reduced and the equipment can be downsized. The purity of the hydrogen gas that has passed through the hydrogen separation membrane depends on the performance of the hydrogen separation membrane, but even if CO removal or high purity is required depending on the application, the load on these steps should be reduced. Is possible.

  As described above, several hydrogen separation membranes have been proposed against the background of the advantages of hydrogen production using hydrogen separation membranes. For example, Non-Patent Document 1 describes a hydrogen separation membrane in which a palladium alloy membrane is supported by a zirconia porous substrate. In this hydrogen separation membrane, hydrogen is dissolved as atoms in the palladium alloy, and is separated by a method of diffusing with the concentration gradient and allowing only pure hydrogen to permeate, so that high purity hydrogen can be obtained in principle. . Non-Patent Document 2 describes a hydrogen separation membrane in which a silica glass membrane is supported by an alumina porous substrate. This hydrogen separation membrane utilizes the fact that the silica glass membrane has pores with a size (0.3 nm) that allows only hydrogen molecules to pass through, and separates hydrogen by a molecular sieving function that selectively permeates hydrogen molecules. Is.

Summary of FY2008 Fuel Cell and Hydrogen Technology Development Symposium “Development of Highly Durable Membrane LP Gas Reformer” New Energy and Industrial Technology Development Organization “Development of High-Efficiency High-Temperature Hydrogen Separation Membrane” (Ex-post Evaluation) Minutes of Subcommittee Meeting (July 30, 2007)

  By the way, the present inventors have proposed a hydrogen separation material using a silica-based porous material as a support in PCT / JP2010 / 072201 (filed on Dec. 10, 2010). Such a hydrogen separation material has a silica glass membrane functioning as a hydrogen separation membrane, and a silica-based porous body having a thermal expansion coefficient close to that of the silica glass membrane is used as a support, thereby being resistant to thermal shock and providing hydrogen separation characteristics. An excellent hydrogen separation membrane has been realized. Moreover, in the said prior application, the manufacture example by CVD method is described as an example of the manufacturing method of a silica type porous support body. In such a production method, glass fine particles are deposited around the rod by the CVD method, sintered to such an extent that the gas permeation performance is excellent (that is, to have a high porosity), and then the rod is pulled out to obtain a silica-based porous material. The quality support is configured as a cylindrical glass tube.

  However, the present inventors have been intensively studying a glass tube composed of a silica-based porous material in order to further improve the hydrogen separation material, and the rod used in the production process has been repeated a few times. It came to know that it was damaged only by using. This is because, unlike the glass tube manufacturing process for optical fiber applications, it is necessary to adjust the porosity to be lower than that during the deposition process in order to control gas permeability in the glass tube manufacturing process for hydrogen separation materials. This is due to the fact that the deposition temperature of the glass particles becomes higher than the deposition temperature in the production of glass tubes for other applications. Furthermore, through various studies, it has been found that when the deposition temperature is increased in order to achieve a low porosity, some rod materials are damaged during deposition.

  Accordingly, an object of the present invention is to provide a production method capable of stably producing a glass tube that can be suitably used as a support for a hydrogen separation material.

The present invention made in view of the above problems is as follows.
That is, in the method for producing a glass tube of the present invention, a glass particle is deposited around a rod by a CVD method, and after the glass particle is deposited, the rod is pulled out to form a wall thickness of a porous glass having a porosity of 20% to 70%. a method of manufacturing a following glass tube 5mm above 0.2 mm, the thermal expansion coefficient of the rod Ri der 4 × ^{10 -7} / K or 5 × ^{10 -6} / K or less, the distal end of the rod also said to deposit a glass fine particles, it characterized that you produce the glass tube tip is closed.

  Another preferred embodiment of the method for producing a glass tube of the present invention is characterized in that the rod is non-oxide.

  Another preferred embodiment of the method for producing a glass tube of the present invention is characterized in that the rod is silicon nitride.

  Another preferred embodiment of the method for producing a glass tube of the present invention is characterized in that the rod has a tapered shape.

  According to the method for manufacturing a glass tube of the present invention, it is possible to suppress the breakage of the rod during the deposition for depositing the glass fine particles and to repeatedly use the rod with an excellent service life.

It is a schematic diagram which shows one Embodiment of the glass tube of this invention. It is a figure explaining the deposition process (a) and (b) which are one Embodiment of the manufacturing method of the glass tube of this invention, and a drawing process (c). It is a temperature profile which showed the deposition temperature with respect to the thickness of a deposition layer in the case of each deposition process of Examples 1-2.

  Hereinafter, an example of an embodiment of a glass tube manufacturing method of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view showing an example of a glass tube 10 produced by the method for producing a glass tube of the present invention, and has a form suitably used as a porous silica support for a hydrogen separation material.
The glass tube 10 has a substantially cylindrical shape, and has a central hole 11 having a substantially circular cross section extending in the longitudinal direction at the center thereof.
The outer diameter T of the glass tube 10 is 2 mm to 50 mm, the inner diameter (diameter of the center hole 11) P is 1.6 mm to 48 mm, and the length L is about 200 mm to 400 mm. It is desirable that one end 11a of the center hole 11 is closed. Further, in order to increase the surface area of the tube, the outer diameter T and the inner diameter P may be periodically changed in the longitudinal direction, and the thickness can be partially changed to reinforce the mechanical strength. The thickness of the glass tube 10 is, for example, 0.2 to 5 mm, and more preferably 0.5 to 3 mm.

  The porosity of the glass tube 10 is not particularly limited, but is preferably 20% or more and 70% or less from the balance of mechanical strength and gas permeability. The “porosity” can be calculated as the ratio of the air volume per unit volume.

  FIG. 2 is a schematic diagram showing an example of an embodiment of a method for manufacturing the glass tube 10, (a) and (b) are diagrams for explaining a deposition process according to the method for manufacturing the glass tube 10, and (c). These are figures explaining the drawing process of a rod. FIGS. 2 (a) and 2 (b) show the deposition process and are schematic diagrams for explaining the deposition process ((a) → (b)).

2 (a) and 2 (b), the rod 20 is arranged vertically with the tip portion facing down. Moreover, it is good also as a form which arranges an axial direction horizontally.
The rod 20 has a thermal expansion coefficient of 4 × 10 ⁻⁷ / K or more and 5 × 10 ⁻⁶ / K or less. When the coefficient of thermal expansion of the rod 20 is outside this range, thermal strain occurs between the rod 20 and the glass tube 10 every time the burner 21 approaches during the deposition process, and the glass tube 10 may be damaged. Further, by making the coefficient of thermal expansion within the above range, damage to the rod 20 due to thermal shock can be prevented, and the rod 20 can be used repeatedly with an excellent number of service life. As a material having such a coefficient of thermal expansion, for example, glass, refractory ceramics, carbon, and the like can be used, but it is preferable that the material is formed of a non-oxide such as silicon nitride having low affinity with glass. .

  The rod 20 is fixed and then rotated about the central axis. Then, glass particles are deposited on the outer periphery of the rod 20 by the burner 21 disposed on the side of the rod 20 by an external CVD method (OVD method). Depending on the desired mechanical properties and water vapor resistance, rare earth elements, group 4B elements, Al, Ga, or a combination of two or more of these elements can be added to the glass fine particles. For example, when the glass tube 10 is used for steam reforming of a hydrocarbon fuel as a support for a hydrogen separation material, it necessarily comes into contact with steam at 500 ° C. or higher. Can be improved.

  During the deposition of the glass fine particles, the burner 21 is traversed in the axial direction of the rod 20. In addition, although the form which traversed the burner 21 to the axial direction of the rod 20 is shown in FIG. 2, the method of traversing the rod 20 to the axial direction by fixing the burner 21 may be used. The type of feedstock and the amount of gas supply can be varied for each number of traverses. Thereby, the glass particulates deposited on the outer periphery of the rod 20 have a predetermined porosity and composition distribution in the radial direction. Moreover, the glass tube 10 with the closed tip is produced by depositing glass particles on the tip of the rod 20.

The glass tube 10 may be sintered and densified by heat-sintering the silica glass fine particles so that the porosity thereof is in the range of 20 to 70% after the silica glass fine particles are deposited. May be adjusted to control the porosity. The temperature for heating and sintering after deposition is not particularly limited, but is preferably 1000 ° C to 1400 ° C. If it is less than 1000 ° C., sintering may not proceed sufficiently, and if it exceeds 1400 ° C., the porosity may be too small.
Also, when the porosity is adjusted by the deposition temperature, the temperature is not particularly limited, but is preferably about 1000 ° C. to 1700 ° C., for example. If the deposition temperature is too low, the sintering of the silica glass fine particles may not proceed sufficiently. If the deposition temperature exceeds 1700 ° C., the porosity will be too small, and gas permeability sufficient to be applied as a hydrogen separation material will be obtained. It may not be possible. Moreover, it is preferable that the deposition temperature of the silica glass fine particles in the outermost layer is kept high. If the deposition temperature in the outermost layer is less than 1300 ° C., the sintering of the silica glass particles does not proceed sufficiently, and the desired impact resistance may not be obtained in the outermost layer.

  On the other hand, the deposition temperature of the initial silica glass fine particles deposited in the vicinity of the rod 20 is preferably a relatively low temperature of 1200 ° C. or less. By lowering the initial deposition temperature, the rod itself can be prevented from cracking, and the rod 20 and the glass tube 10 can be made less likely to be fused, so that the rod 20 can be pulled out after the deposition process. You can make sure that there are no obstacles. Further, by drawing carbon, nitride or the like on the surface of the rod 20 in advance, drawing becomes easy.

  After the deposition step, the rod 20 is pulled out from the deposited and sintered glass tube 10 as shown in FIG. The central hole 11 formed by drawing does not penetrate, the lower end side (tip end side) 11a is closed, and only the upper end side is open (see FIG. 1).

  Further, although it is not always necessary if a rod satisfying the above-described thermal expansion coefficient is used, it is more preferable if the rod 20 is tapered from the viewpoint of facilitating the drawing process. For example, the outer diameter gradient is preferably 0.2 to 2.0 mm / 1000 mm, and more preferably 0.5 to 1.5 mm / 1000 mm.

  Hereinafter, the present invention will be described in more detail with reference to examples according to the present invention. The present invention is not limited to these examples.

(Example 1)
The deposition temperature on the surface of a silicon nitride rod having a maximum outer diameter of 17 mm (outer diameter gradient: 1.0 mm / 1000 mm) and a linear thermal expansion coefficient of 2.6 × 10 ⁻⁶ / ° C. by the external CVD method is as shown in FIG. After the silica glass porous body was deposited while being changed, the rod was pulled out to seal one end with an outer diameter of 19.5 to 19.8 mm, a wall thickness of 1.5 mm, a length of 250 mm, and an average porosity of 46%. A porous silica glass tube was prepared.
In addition, the porous silica glass tube was repeatedly produced from the same silicon nitride rod by repeating the above process. It was possible.

(Example 2)
By the external CVD method, the deposition temperature is as shown in FIG. 3 on the surface of a silica glass rod having a maximum outer diameter of 16 mm (outer diameter gradient of 1.5 mm / 1000 mm) and a linear thermal expansion coefficient of 5.7 × 10 ⁻⁷ / ° C. After the silica glass porous body was deposited while changing the diameter, the rod was pulled out to seal one end with an outer diameter of 18.0 to 18.4 mm, a wall thickness of 1.5 mm, a length of 250 mm, and an average porosity of 63%. A porous silica glass tube was prepared. The above process was repeated to produce 30 porous silica glass tubes from the same silica glass rod.

(Comparative Example 1)
The same conditions (deposition) as in Example 1 were applied to the surface of an alumina rod having a maximum outer diameter of 16 mm (outer diameter gradient: 1.5 mm / 1000 mm) and a linear thermal expansion coefficient of 7.2 × 10 ⁻⁶ / ° C. by the external CVD method. At that temperature, an attempt was made to deposit a porous silica glass, but the alumina rod broke immediately after heating with an oxyhydrogen flame.

(Comparative Example 2)
The same conditions (deposition) as in Example 2 were applied to the surface of an alumina rod having a maximum outer diameter of 16 mm (outer diameter gradient: 1.5 mm / 1000 mm) and a linear thermal expansion coefficient of 7.2 × 10 −6 / ° C. by an external CVD method. After the silica glass porous body is deposited at the temperature), the rod is pulled out to end-close sealed pores having an outer diameter of 18.0 to 18.4 mm, a wall thickness of 1.5 mm, a length of 250 mm, and an average porosity of 63%. A silica glass tube was produced. The above steps were repeated to produce four porous silica glass tubes from the same alumina rod, but the alumina rod broke during the fifth production.

Since the porous silica glass tube obtained in Examples 1 and 2 has a good average porosity excellent in gas permeation performance, it can be applied to a hydrogen separation material.
Moreover, according to the manufacturing method of Example 1 and 2, the rod was not damaged by the thermal shock. Moreover, the service life was also excellent, and in Example 2, even if it produced 30 silica glass tubes, it was not damaged, and it was found that Example 1 was unlimited.
On the other hand, in the manufacturing method of Comparative Example 1, since an alumina rod having a high thermal expansion coefficient was used, the silica glass fine particles were damaged by thermal shock during the deposition process. Further, in the manufacturing method of Comparative Example 2, although the deposition temperature of the silica glass fine particles deposited in the vicinity of the rod was lowered, the rod was not damaged by the thermal shock during the first deposition, but the service life was small. became.

10: Glass tube, 20: Rod, 21: Burner, 11: Center hole, 11a: Lower end side (tip side) of center hole 11, P: Inner diameter, T: Outer diameter

Claims (4)

A glass tube having a wall thickness of 0.2 mm or more and 5 mm or less made of porous glass having a porosity of 20% or more and 70% or less is manufactured by depositing glass particles around the rod by a CVD method and pulling the rod after the glass particles are deposited. A method,
The thermal expansion coefficient of the rod is 4 × 10 ⁻⁷ / K or more and 5 × 10 ⁻⁶ / K or less, and the glass microparticles are deposited also on the tip of the rod, whereby the glass tube with the closed tip is closed. A method for producing a glass tube, comprising producing the glass tube.   The method of manufacturing a glass tube according to claim 1, wherein the rod is a non-oxide.   The method of manufacturing a glass tube according to claim 2, wherein the rod is silicon nitride.   The method of manufacturing a glass tube according to claim 1, wherein the rod is tapered.

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