JP5928047B2 - 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, in order to further improve the hydrogen separation material, the present inventors have made extensive studies on the silica-based porous support in particular. As a result, the present inventors have gas permeability suitable as a hydrogen separation material, that is, a high porosity. Silica-based porous materials have low impact resistance and have been found to be frequently damaged by external impact during the distribution process.

  Therefore, the present invention aims to provide a silica-based porous body that can be suitably used as a support for a hydrogen separation material, and in particular, a glass tube with improved impact resistance while having good gas permeation performance. The purpose is to provide.

The present inventors have devised the deposition and sintering conditions in the glass tube manufacturing process by the CVD method described in the above-mentioned prior application, thereby improving the impact resistance while having good gas permeation performance. As a result, the present invention has been completed.
That is, the glass tube of the present invention is a glass tube made of porous silica, having an average porosity of 40% or more and 70% or less, and at least a porosity in a cross section perpendicular to the axial direction of a part of the longitudinal direction. While having an inclination from the inner peripheral side toward the outer peripheral side, the innermost layer porosity is higher than the outermost layer porosity.

Further, the method for producing a glass tube of the present invention for producing the above glass tube comprises depositing a plurality of layers of glass fine particles around the rod, and pulling out the rod after the glass fine particles are deposited, thereby providing a porous support as a support for the hydrogen separation material. A method for manufacturing a glass tube made of glass,
By increasing the deposition temperature when depositing the glass fine particles by the CVD method from the rod side toward the outer peripheral direction, the average porosity of the glass tube is set to 40% or more and 70% or less, and at least one longitudinal direction of the glass tube is set. The glass so that the porosity in the cross section perpendicular to the axial direction of the portion has an inclination from the inner peripheral side toward the outer peripheral side, and the innermost layer porosity in the deposited layer of the glass fine particles is higher than the outermost layer porosity. Control the porosity of the tube,
One end portion of the central hole of the glass tube is closed with the deposited layer formed by the CVD method .

  Another preferred embodiment of the method for manufacturing a glass tube of the present invention is characterized in that the deposition temperature of the innermost layer is set to 1200 ° C. or lower, and then the deposition temperature is raised.

Another preferred embodiment of the method for producing a glass tube of the present invention is characterized in that a thermal expansion coefficient of the rod is 4 × 10 ⁻⁷ / K or more and 5 × 10 ⁻⁶ / K or less.

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

The glass tube of the present invention has a low porosity in the vicinity of the outer surface of the glass tube so as to obtain impact resistance in at least a part of the cross section perpendicular to the axial direction in the longitudinal direction. In order to maintain gas permeability, the innermost layer has a relatively high porosity. Therefore, according to the present invention, it is possible to provide a glass tube that can be suitably used as a support for a hydrogen separation material that has good gas permeation performance and improved impact resistance.
The method for manufacturing the glass tube of the present invention also has manufacturing advantages. In the manufacturing process of glass tubes for hydrogen separation materials, unlike the manufacturing process of glass tubes for optical fiber applications, it is necessary to adjust the porosity to be lower than the deposition process in order to control gas permeability. The deposition temperature of the fine particles is higher than the deposition temperature in manufacturing a glass tube for other applications. In the manufacture of glass tubes for optical fiber applications, for example, carbon or nitride is applied to the surface of the rod in advance for the purpose of facilitating the pulling of the rod. In the manufacturing method of the glass tube for material use, since the coating material such as carbon previously applied around the rod burns, the effect of the coating material cannot be obtained, and depending on the material of the rod, the rod and the glass There may be a fusion between the two. Further, depending on the material of the rod, the rod may be broken. In contrast, the glass tube manufacturing method of the present invention increases the deposition temperature during deposition of glass particles from the rod side toward the outer peripheral direction, and allows the deposition temperature near the outer surface of the glass to have impact resistance. In order to reduce the deposition temperature of the glass fine particles deposited in the vicinity of the rod, the fusion between the glass deposit and the rod and the cracking of the rod are suppressed. The rod pull-out operation becomes significantly easier.

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 figure which shows an example of the porosity distribution in the cross section of the longitudinal direction center part of the glass tube of this invention. The thickness of the deposited layer in each of the deposition steps of Examples 1 to 3 and Comparative Example 1 (herein, “the thickness of the deposited layer” is the distance from the end of the innermost layer on the glass tube center hole side) Is a temperature profile showing the deposition temperature.

  Hereinafter, the glass tube of the present invention and the manufacturing method thereof will be described in detail with reference to the drawings.

FIG. 1 is a schematic view showing an example of the glass tube of the present invention. 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 glass tube 10 has an average porosity of 40% or more and 70% or less, and at least in a cross section perpendicular to the axial direction of a part of the longitudinal direction (preferably the entire longitudinal direction), the porosity is from the inner peripheral side to the outer peripheral side. The outermost layer L _I has a slope (innermost layer porosity) higher than that of the outermost layer L 2 _O and has a slope toward the side.
The innermost layer L _I and the outermost layer L _O described here are also described in a method for manufacturing the glass tube 10 described later. During the deposition of the glass particles, the burner 21 that supplies the glass particles is traversed in the axial direction of the rod 20. Or the “deposition layer deposited in one traverse” in the case where the rod 20 is traversed in the axial direction while fixing the burner 21 for supplying glass particles, The layer is the innermost layer L _I , and the deposited layer farthest from the rod 20 is the outermost layer L 2 _O.
Further, the “porosity” can be calculated as a ratio occupied by the air volume per unit volume, and its distribution changes in the longitudinal direction in one deposition layer depending on the deposition condition. “Average porosity” is the ratio of the air volume to the total volume of the manufactured glass tube, “innermost layer porosity” and “outermost layer porosity” are the volume of air in the innermost layer L _I and outermost layer L _O respectively. It can be calculated as a ratio occupied by. The porosity of the layers can be relatively compared by taking a cross-sectional X-ray CT image of the glass tube. More specifically, it can be obtained by taking an SEM image at an appropriate magnification with respect to a cross section of a glass tube filled with a hole with resin and binarizing the image. Appropriate magnification means that when all the cross sections in the radial direction are divided into a plurality of locations and the local porosity at each part is obtained by the above method, the average value of the porosity and the average porosity are 2%. The magnification is within. In order to evaluate the local porosity with high accuracy, it is preferable to use a cross section polisher or the like to increase the flatness of the cross section as much as possible.
Hereinafter, an example of an embodiment of a method for manufacturing the glass tube 10 will be described.

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. As the material of the rod 20, alumina, glass, refractory ceramics, carbon or the like can be used. 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. By varying the type of feedstock and the gas supply amount for each number of traverses, the innermost layer pores have an inclination of the porosity from the inner peripheral side to the outer peripheral side in an arbitrary cross section orthogonal to the axial direction. It becomes possible to adjust the porosity of the outermost layer lower than the rate. Thereby, the glass fine particles deposited on the outer periphery of the rod 20 have a predetermined porosity and composition distribution in the radial direction. Further, by depositing glass particles on the tip of the rod 20, a glass tube having a closed tip can be obtained.

The glass tube 10 may be sintered and densified by heat-sintering the silica glass fine particles so that the average porosity of the glass tube 10 is in the range of 40% or more and 70% or less after the silica glass fine particles are deposited. It is difficult to control the rate distribution. Therefore, the production method of the present invention employs a method of controlling the porosity while adjusting the temperature at which the silica glass fine particles are deposited. With this method, the porosity distribution can be controlled with high accuracy by increasing the deposition temperature of the silica glass fine particles from the innermost layer L _I toward the outermost layer L _O.
In this case, the deposition temperature of the innermost layer _{L I} is 1200 ° C. or less, the layer of the outer peripheral side of the innermost layer _{L I} is preferably adjusted within a temperature range of 1700 ° C. 1200 ° C. or higher. When the deposition temperature exceeds 1700 ° C., the porosity becomes too small, and gas permeability that can be applied as a hydrogen separation material may not be obtained.

The glass tube 10 obtained by the above method has a configuration in which the innermost layer porosity is larger than the outermost layer porosity. With this configuration, it is possible to improve the impact resistance of the outermost layer L 2 _O most affected by external impact, while the average porosity is in the range of 40% to 70% and suitable for gas permeability. Moreover, the glass tube 10 can adjust an average porosity by making innermost layer porosity small. Thus, between the innermost layer L _I and the outermost layer L _O , the porosity is inclined in the thickness direction, so that both gas permeability and impact resistance can be achieved.

In the present invention, the porosity distribution from the innermost layer L _I to the outermost layer L _O in an arbitrary cross section perpendicular to the axial direction of the glass tube 10 (the porosity in one layer is averaged and distributed for each layer) ones) is the outermost layer porosity sufficient if the slope between and outermost L _O innermost layer L _I lower than the innermost layer porosity. For example, as shown in FIG. 3, it may be linear (see (a)) or curved (see (b)), and some of the inner layer porosity is smaller than the outermost layer porosity. The inner layer porosity of the portion may be larger than the innermost layer porosity (see (c)).

  Next, the drawing process after the deposition process will be described with reference to FIG. In FIG. 2 (c), the rod 20 is pulled out from the deposited and sintered glass tube 10. 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).

  In the deposition step, particularly when a rod having a high thermal expansion coefficient is used, the deposition temperature of the silica glass fine particles in the vicinity of the rod 20 is preferably 1200 ° C. or lower. In a rod having a high thermal expansion coefficient, if the deposition temperature is 1200 ° C. or higher, the rod may be broken. Further, by setting the temperature at this temperature, almost no fusion between the rod 20 and the glass tube 10 occurs, so that the rod 20 can be drawn easily after the deposition step. Further, by drawing carbon, nitride or the like on the surface of the rod 20 in advance, drawing becomes easy.

  Further, although it is not necessary if it can be adjusted to the above-described deposition temperature, 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.

Further, although it is not necessary if it can be adjusted to the above-described deposition temperature, it is more preferable if the rod 20 is made of a material having a coefficient of thermal expansion 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. Moreover, the damage of the rod 20 by a thermal shock can be prevented by making a thermal expansion coefficient into the said range.
Furthermore, the rod 20 is preferably a rod made of a non-oxide such as silicon nitride having a low affinity with glass, for example.

  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 is as shown in FIG. 4 on the surface of a silica glass rod having a maximum outer diameter of 16 mm (outer diameter gradient: 1.5 mm / 1000 mm) and a linear thermal expansion coefficient of 5.7 × 10 ⁻⁷ / ° C. by the external CVD method. 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. It was confirmed that the innermost layer porosity at the central portion in the longitudinal direction of the porous silica glass tube was larger than the outermost layer porosity.

(Example 2)
By the external CVD method, the deposition temperature is as shown in FIG. 4 on the surface of an alumina 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 7.2 × 10 ⁻⁶ / ° C. After depositing the porous silica glass while being changed, the rod is pulled out to close the end-sealed porous material having an outer diameter of 18.0 to 18.4 mm, a wall thickness of 1.4 mm, a length of 250 mm, and an average porosity of 65%. A silica glass tube was produced. It was confirmed that the innermost layer porosity at the central portion in the longitudinal direction of the porous silica glass tube was larger than the outermost layer porosity.

(Example 3)
By the external CVD method, the deposition temperature is as shown in FIG. 4 on the surface of a silicon nitride rod having a linear thermal expansion coefficient of 2.6 × 10 ⁻⁶ / ° C. with a maximum outer diameter of 17 mm (outer diameter gradient of 1.0 mm / 1000 mm). 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. It was confirmed that the innermost layer porosity at the central portion in the longitudinal direction of the porous silica glass tube was larger than the outermost layer porosity.

(Comparative Example 1)
FIG. 4 shows the deposition temperature 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. by the external CVD method. After the silica glass porous body was deposited while being changed to 1, the rod was pulled out to seal one end of an outer diameter of 18.0 to 18.4 mm, a wall thickness of 1.4 mm, a length of 250 mm, and an average porosity of 65%. Although an attempt was made to produce a porous silica glass tube, the rod and the porous silica glass tube were fused and could not be pulled out. It was confirmed that the innermost layer porosity at the center portion in the longitudinal direction of the porous silica glass tube was smaller than the outermost layer porosity.

The innermost layer porosity in the longitudinal central portion of the porous silica glass tubes obtained in Examples 1 to 3 is larger than the outermost layer porosity, and the porosity in the vicinity of the outer surface of the porous silica glass tube is Since it is low, it is clear that the impact resistance is improved. In addition, since it has a good average porosity with excellent gas permeation performance, it can be applied to a hydrogen separation material.
On the other hand, the porous silica glass tube that was attempted to be manufactured in Comparative Example 1 was presumed to have no problem with gas permeability, but could not be manufactured because the rod and the glass tube were fused. .

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, L _O : outermost layer, L _I : outermost layer Inner layer

Claims (4)

  A method of manufacturing a glass tube made of porous glass as a support for a hydrogen separation material by depositing a plurality of glass particles around a rod and pulling out the rod after the glass particles are deposited,
  By increasing the deposition temperature when depositing the glass fine particles by the CVD method from the rod side toward the outer peripheral direction, the average porosity of the glass tube is set to 40% or more and 70% or less, and at least one longitudinal direction of the glass tube is set. The glass so that the porosity in the cross section perpendicular to the axial direction of the portion has an inclination from the inner peripheral side toward the outer peripheral side, and the innermost layer porosity in the deposited layer of the glass fine particles is higher than the outermost layer porosity. Control the porosity of the tube,
  A method for producing a glass tube, wherein one end of a central hole of the glass tube is closed with the deposited layer formed by the CVD method. The method for producing a glass tube according to claim 1, wherein the deposition temperature of the innermost layer is set to 1200 ° C or lower, and then the deposition temperature is increased. The thermal expansion coefficient of the rod is 4 × 10 ^-7 / K or more 5 × 10 ^-6 The method for producing a glass tube according to claim 1 or 2, wherein the glass tube is / K or less. The method of manufacturing a glass tube according to any one of claims 1 to 3, wherein the rod is tapered.

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