JP5821438B2 - Method for producing porous glass tube - Google Patents

Description

  The present invention relates to a method for producing a porous glass tube used as a fluid separation material or the like for separating hydrogen or the like from a mixed gas containing hydrogen or the like produced by fuel reforming or the like with high purity.

  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 converting CO at a few hundred degrees (CO + H ₂ O → CO ₂ + H ₂ ) is widely used from the viewpoint 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 advantage of the hydrogen production method using the hydrogen separation membrane. 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.

  In addition, as a hydrogen separation apparatus including a hydrogen separation cylinder having a hydrogen permeable membrane formed on the outside, a hydrogen separation cylinder in the shape of a test tube closed at one end, and a cylindrical shape in which an open end side of the hydrogen separation cylinder is inserted The thing provided with the attachment metal fitting is known (for example, refer to patent documents 1). In Patent Document 1, a mixed material in which nickel oxide, zirconia, and graphite powder are mixed is extruded to form a bottomed cylindrical tube, which is fired to produce a porous support tube, and a barrier that covers the periphery thereof. It describes that a hydrogen separation cylinder is manufactured by forming a hydrogen permeable membrane made of a metal thin film so as to cover the layer. The end of the open end side of the hydrogen separation cylinder is fitted to the mounting bracket together with the seal member, and is fixed by screwing the fixing bracket and the mounting bracket into the hydrogen separator.

JP 2009-234798 A

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 made PCT / JP2010 / 072201 (Heisei 22) a hydrogen separation material having a silica glass membrane functioning as a hydrogen separation membrane and a porous body having a thermal expansion coefficient close to that of the silica glass membrane as its support. Filed on Dec. 10, 2000). According to this configuration, it is possible to realize a hydrogen separation material that is resistant to thermal shock, has good adhesion between the hydrogen separation membrane and the support, and has excellent hydrogen separation characteristics. 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, as described above, the glass fine particle powder adheres to the surface of the glass tube produced by depositing the glass fine particles around the rod. For this reason, there exists a possibility that the surface glass fine particle powder may fall out at the time of conveyance of the produced glass tube, or the following process. In order to suppress the dropout of the glass fine particle powder, it is necessary to remove the glass fine particle powder by performing a complicated removal process such as suction, surface cleaning, or wiping. In addition, when a glass tube is made by depositing glass particles in multiple layers, there is a risk that several layers of the surface layer may be peeled off and dropped when vibration or impact is applied by cutting with a diamond cutter in the next process. is there. Even if the deposition temperature is increased when the glass particles are deposited on the surface layer of the glass tube, the surface layer immediately after deposition is in a soft state (the outer layer is not deposited, so it is not blown by a flame) Therefore, it was insufficient to improve the adhesion between the layers and prevent the glass fine particles from falling off.

  The objective of this invention is providing the manufacturing method of the porous glass tube which can suppress the drop-off | omission of the glass fine particle powder from a surface layer, or a deposition layer.

In the method for producing a porous glass tube of the present invention capable of solving the above-mentioned problems, a glass fine particle deposit is produced by depositing glass fine particles around a rod by a CVD method, and the rod is removed from the glass fine particle deposit. A method for producing a porous glass tube that is drawn out to produce a cylindrical porous glass tube,
After the production of the glass fine particle deposit, a heat treatment is performed in which the surface of the glass fine particle deposit is heated by a flame not containing a glass fine particle raw material.

  In the method for producing a porous glass tube of the present invention, it is preferable that heating is performed so that the porosity on the surface of the glass fine particle deposit is 20% or more and 70% or less during the heat treatment.

According to the present invention, the surface of the glass fine particle deposit can be heat-treated to heat the surface of the glass fine particle deposit and a certain depth from the surface. Thereby, the glass fine particle powder on the surface of the glass fine particle deposit can be fixed to each other, or excess glass fine particle powder can be blown off by a flame. Furthermore, the adhesion between the deposited layers of glass particles in the vicinity of the surface layer of the glass particle deposit can be improved.
Accordingly, it is possible to prevent the glass fine particle powder from dropping off from the surface layer part and the depositing layer from falling off during transportation or processing in the next process.

It is a schematic diagram which shows the porous glass tube manufactured by the manufacturing method of this invention. It is a figure explaining each process of one Embodiment of the manufacturing method of the porous glass tube of this invention, Comprising: (a)-(c) is sectional drawing in each process.

Hereinafter, an example of an embodiment of a method for producing a porous glass tube according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, a porous glass tube 11 manufactured by the method for manufacturing a porous glass tube according to the present embodiment has a substantially cylindrical shape, and a central hole 12 having a substantially circular cross section extending in the longitudinal direction at the center thereof. Have The porous glass tube 11 has a glass particulate deposit 13 as a tube wall on the outer periphery of the center hole 12.

  The glass fine particle deposit 13 has an outer diameter T of 2 mm to 50 mm, an inner diameter (diameter of the center hole 12) P of 1.6 mm to 48 mm, and a length L of about 200 mm to 400 mm. It is desirable that one end 12a of the center hole 12 is closed. Moreover, in order to increase the surface area of the porous glass tube 11, the outer diameter T and the inner diameter P may be periodically changed in the longitudinal direction, and the thickness is partially changed to reinforce the mechanical strength. You can also. The average porosity of the porous glass tube 11 is 40 to 70%, for example. The porosity can be calculated as a ratio occupied by the air volume per unit volume.

  The porous glass tube 11 is used as a fluid separation material, for example. When the porous glass tube 11 is used as a hydrogen separation material that is a fluid separation material, a silica glass separation membrane layer is formed on the outer periphery of the porous glass tube 11 so as to have a pore diameter of about 0.3 nm. The And this silica glass separation membrane layer is used as a hydrogen permeable membrane, without causing membrane deterioration due to hydrogen embrittlement or reaction with raw material impurities. The thickness of the silica glass separation membrane layer is, for example, preferably 0.01 μm to 50 μm, more preferably 0.02 μm to 10 μm, and still more preferably 0.03 μm to 5 μm. If the thickness is less than 0.01 μm, the hydrogen purity of the permeate gas becomes too low, and if it exceeds 50 μm, the hydrogen permeation rate becomes too low, and it may be difficult to obtain practically sufficient hydrogen separation performance. Moreover, it is applicable also as what isolate | separates gas or liquids other than hydrogen by changing the hole diameter etc. of a silica glass separation membrane layer.

  By making the support of the silica glass separation membrane layer the glass fine particle deposit 13, the thin film can be supported without interfering with hydrogen permeation through the silica glass separation membrane layer. The porosity of the external layer of the glass particulate deposit 13 is not particularly limited, but is 20 to 70% larger than the silica glass separation membrane layer from the balance of mechanical strength and gas permeability. Is preferred.

Further, the linear thermal expansion coefficient of the glass fine particle deposit 13 is 2 × 10 ⁻⁶ / K or less. When the linear thermal expansion coefficient exceeds 2 × 10 ⁻⁶ / K, the generated thermal stress increases, and the desired thermal shock resistance may not be obtained. The material for forming the glass fine particle deposit 13 is preferably a material having a linear thermal expansion coefficient approximate to that of a silica glass separation membrane from the viewpoint of thermal shock resistance, and more preferably porous silica glass.
The thickness of the glass fine particle deposit 13 is not particularly limited, but is preferably 0.2 to 5 mm, and preferably 0.5 to 3 mm from the balance of mechanical strength and gas permeability. More preferred.

  From the viewpoint of thermal shock resistance, the glass fine particle deposit 13 is preferably selected from those having a linear thermal expansion coefficient approximate to that of the silica glass separation membrane layer. Further, in the glass fine particle deposit 13 of the present embodiment, it is preferable to add rare earth elements, group 4B elements, Al, Ga, or a combination of two or more of these elements to the porous silica glass. This is because desired mechanical properties, water vapor resistance, and the like can be obtained by adjusting the components of the porous silica glass constituting the glass fine particle deposit 13. For example, when the porous glass tube 11 is used for steam reforming of hydrocarbon fuel, it necessarily comes into contact with steam at 500 ° C. or higher, so that the introduction of other components can improve the steam resistance performance. preferable.

Next, an embodiment of a method for producing a porous glass tube will be described with reference to the drawings.
As an example of a method for manufacturing the porous glass tube 11, glass particles are deposited around a rod to form a glass particle deposit 13 (deposit body preparation step), and then the surface of the glass particle deposit 13 is subjected to heat treatment. (Heat treatment process) and the method of pulling out this rod (drawing process) can be mentioned. An embodiment of the method will be described below with reference to FIG.

(1) Deposit body preparation process As shown to Fig.2 (a), the rod 20 is arrange | positioned perpendicularly | vertically so that a front-end | tip part may turn down. Moreover, it is good also as a form arrange | positioned 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 the OVD method. The burner 21 ejects glass raw material gas, combustible gas, and auxiliary combustible gas, and sprays glass fine particles generated by a flame hydrolysis reaction generated in an oxyhydrogen flame onto the rod 20. By adding a gas of a desired component to the glass raw material gas supplied to the burner 21, the generated glass fine particles have a rare earth element, a group 4B element, Al, Ga, depending on desired mechanical properties and water vapor resistance. Or a combination of two or more of these elements. That is, according to this manufacturing method, the components can be easily adjusted.

  When depositing the glass fine particles, the burner 21 is traversed in the axial direction of the rod 20, or the burner 21 is fixed and the rod 20 is traversed in the axial direction. The type of feedstock and gas supply amount to the burner 21 can be varied for each number of traverses. Thereby, the glass microparticles deposited on the outer periphery of the rod 20 have a predetermined bulk density and distribution of composition in the radial direction. Further, by depositing glass particles on the tip of the rod 20, a tubular glass particle deposit 13 having a closed tip is produced.

  The glass fine particle deposit 13 may be manufactured not only by the OVD method but also by other CVD methods such as the VAD method and the MMD method (multi-burner multi-layering method).

(2) Heat treatment step After the glass fine particles are deposited, the glass fine particle deposit 13 is subjected to a heat treatment. In this heat treatment, by stopping the supply of the glass raw material gas to the burner 21, only the oxyhydrogen flame that does not contain the raw material of glass fine particles is ejected from the burner 21 to traverse, and the surface of the glass fine particle deposit 13 is heated. To do. Thereby, the glass fine particle deposit 13 is heated to a certain depth from the surface. Then, the glass fine particle powder on the surface of the glass fine particle deposit 13 is fixed to each other. Further, the deposition layer of the glass particulates in the vicinity of the surface layer of the glass particulate deposit 13 is densified, and the adhesion between the deposition layers is improved. The fine glass powder may be blown away by a flame in addition to being fixed. In this heat treatment, when the porous glass tube 11 is used as a fluid separation material, the porosity of the surface of the glass fine particle deposit 13 is controlled to be 20% or more so as not to lose fluid permeability. In this heat treatment, it is preferable to control the porosity of the glass fine particle deposit 13 to be in the range of 20% to 70% at any part.

  In this heat treatment, a flame may be generated by supplying oxygen and hydrogen to the burner 21 under the same conditions as when the glass fine particles are generated. However, the amount of the glass fine particle powder adhering to the surface of the glass fine particle deposit 13 It is preferable to adjust the flame strength (temperature and size) of the burner 21 in accordance with the surface state of the glass particulate deposit 13. When adjusting the flame strength of the burner 21, the surface state of the glass particulate deposit 13 is predicted to some extent, the flame strength of the burner 21 is adjusted, and the heat treatment is performed continuously with the production of the glass particulate deposit 13. You can go. In order to set the flame conditions in the heat treatment, the glass fine particle deposit 13 may be temporarily removed from the apparatus, and the adhesion degree and surface state of the glass fine particle powder of the glass fine particle deposit 13 may be observed.

Although the temperature of heat processing is not specifically limited, For example, it is preferable to set it as 900 to 1400 degreeC. If the temperature is lower than 900 ° C., the surface may not be sufficiently stabilized. If the temperature exceeds 1400 ° C., the porosity may be too small. Also, when the porosity is adjusted by the heating temperature, the temperature is not particularly limited, but for example, it is preferably about 1250 ° C. It should be noted that the heating temperature is closely related to the traverse speed. If the traverse speed is slow even at the same heating temperature, the heating time becomes longer, and the porosity may be rapidly reduced. Conversely, when the traverse speed increases, surface stabilization does not advance.
The amount of gas supplied to the burner 21 is adjusted to the flow rates of oxygen and hydrogen so as to achieve the above heating temperature. For example, oxygen is set to 20 to 30 liters / minute and hydrogen is set to 1 to 10 liters / minute. The traverse speed of 21 is preferably 5 to 500 m / second, the rotational speed of the glass fine particle deposit 13 is 50 to 500 rpm, and the traverse number of the burner 21 is preferably 1 to 10 times. Note that the traverse of the burner 21 in the heat treatment may be a one-way traverse or a reciprocating traverse.

(3) Drawing process As shown in Drawing 2 (c), rod 20 is pulled out from glass particulate deposition object 13 in the drawing process after a heat treatment process. The central hole 12 formed by drawing does not penetrate, the lower end side (front end side) 12a is closed, and only the upper end side is open. In order to facilitate drawing, it is preferable to apply carbon, nitride, or the like to the surface of the rod 20 in advance. Similarly, from the viewpoint of facilitating pulling, the rod 20 preferably has a tapered shape, and for example, the outer diameter gradient can be set to 0.2 to 2.0 mm / 1000 mm. Furthermore, the rod 20 preferably has a thermal expansion coefficient of 5 × 10 ⁻⁶ / K or less. This is because, when the thermal expansion coefficient of the rod 20 is high, the rod 20 expands and contracts every time the burner 21 approaches in the deposit body preparation process, and the glass particulate deposit 13 may be damaged. Moreover, the damage by the thermal shock of rod 20 itself 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.

  Thus, according to the manufacturing method of the porous glass tube which concerns on the said embodiment, the surface of the glass particulate deposition body 13 is heat-processed using the oxyhydrogen flame which does not contain the glass raw material gas of the burner 20, and glass particulate deposition The surface of the body 13 and a certain depth from the surface are heated. Thereby, the glass fine particle powder existing on the surface of the glass fine particle deposit 13 can be fixed to each other, or excess glass fine particle powder can be blown off by a flame. Furthermore, the adhesion between the deposited layers of glass particles in the vicinity of the surface layer of the glass particle deposit 13 can be improved. Therefore, it is possible to suppress the glass fine particle powder from dropping off from the surface layer portion of the porous glass tube 11 or the surface layer deposited layer from falling off during transportation or processing in the next step.

  When the porous glass tube 11 manufactured as described above is used as a hydrogen separation material, a silica glass separation membrane layer used as a hydrogen permeable membrane is formed on the surface of the porous glass tube 11. The silica glass separation membrane layer can be formed by a sol-gel method, a CVD method, a method for modifying the surface of porous silica glass, or the like. “Surface modification” means that a portion to be a surface film, for example, the vicinity of the surface of the porous silica glass constituting the porous glass tube 11 is densified to some extent in order to produce a hydrogen permeable membrane portion. To form a dense silica glass layer. One method is by heating. Specifically, for example, a method of irradiating a CO2 laser, a plasma arc, an oxyhydrogen burner or the like alone or in combination. According to the formation method by surface modification, the bonding strength between the membrane and the support is increased as compared with the production method in which the porous silica glass and the silica glass separation membrane layer constituting the porous glass tube 11 are separately produced and laminated. In addition, the thickness of the silica glass separation membrane layer and the size of the pores can be easily controlled by the degree of densification. The degree of densification of the silica glass separation membrane layer is set by the molecular size of the fluid to be separated. From the viewpoint of hydrogen permeation, it is desirable that the silica glass separation membrane layer be densified so that the pore diameter is about 0.3 nm.

  At this time, in the porous glass tube 11 manufactured by the manufacturing method of the present embodiment, in the formation process of the silica glass separation membrane layer, which is the next process, the glass particulate powder falls off from the surface layer portion or the deposited layer of the glass particulate surface layer. Can be processed smoothly.

(Investigation of defective rate)
A glass fine particle deposit was prepared by the deposit preparation step, followed by heat treatment in the heat treatment step, and a rod was drawn in the drawing step to produce a plurality of porous glass tubes having a length of 300 mm and an outer diameter of 9 mm. The defective rate of the produced porous glass tube was investigated.

(Conditions for heat treatment)
Heating temperature 1250 ° C
Gas supply rate to burner Oxygen 24 liters / minute, hydrogen 6 liters / minute Traverse speed 100 m / minute Traverse number of times 4 times Glass particle deposit speed 100 rpm

(Investigation result)
By performing the heat treatment process after the deposit body preparation process, the defect rate of the porous glass tube due to the drop of the glass fine particle powder from the surface layer part of the porous glass tube or the drop off of the deposited layer of the surface layer can be determined by the conventional method. It was possible to reduce from 23% in the case of 6 to 6%.

11: Porous glass tube, 13: Glass particulate deposit, 20: Rod, 21: Burner

Claims (1)

A method for producing a porous glass tube in which glass fine particles are deposited around a rod by a CVD method to produce a glass fine particle deposit, and the rod is pulled out of the glass fine particle deposit to produce a cylindrical porous glass tube. There,
After preparation of the glass particles deposit, the surface of the glass particles deposit had line heat treatment of heating by a flame that does not contain raw material of glass particles,
A method for producing a porous glass tube , wherein, during the heat treatment, heating is performed so that a porosity of the surface of the glass fine particle deposit is 20% or more and 70% or less .

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