JP3358282B2 - Manufacturing method of thin film laminated porous ceramic hollow fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film laminated porous ceramic hollow fiber. More specifically, the present invention relates to a method for producing a porous ceramic hollow fiber which is effectively used as a gas separation membrane, a separation membrane for a membrane reactor or the like by laminating a thin film on an outer wall surface.

[0002]

2. Description of the Related Art When a gas is separated using a porous membrane, for example, when separating H ₂ and CO and H ₂ and N ₂ , the pore diameter of the porous membrane is controlled so as to be governed by Knudsen diffusion. Number 10
It is necessary to use one adjusted to about several hundred square meters.

[0003] As a specific gas separation membrane, about
An inorganic porous Vycor glass having a pore size of 40 ° has been conventionally known. Since this Vycor glass is a high silicate, it has the characteristic of being excellent in heat resistance and corrosion resistance, but its thickness is about 0.5 m in terms of strength.
Since it is difficult to reduce the diameter to less than m, there is a disadvantage that the gas permeation rate per unit area is small.

Therefore, in order to produce a separation membrane having a high gas permeation rate, it is desirable to adjust the pore diameter of the porous membrane so as to be governed by Knudsen diffusion and to reduce the thickness, but this is not desirable in terms of mechanical strength. Since the film thickness cannot be extremely thin, a so-called multi-layer structure, in which a thin gas separation layer is coated on a porous support having a film thickness of about 1 mm and a relatively large pore diameter and reinforced, is adopted. ing.

[0005] The thin-film laminated porous structure used here is usually used in the form of a hollow tube in terms of handling or strength, and its production is generally carried out by powder metallurgy or sintering. First, a porous hollow tube having a thickness of about 1 mm is manufactured, and a thin film having micropores is laminated thereon by various methods.

As a method of laminating such a thin film, a thickness of 1 μm
There are vacuum deposition method and sputtering method for forming an extremely thin film to the extent that these methods are not practical because of the difficulty in controlling the uniform pore size and the limitation of the apparatus volume, and therefore, it is usually not practical. A method of attaching powder to a thickness of several tens of μm is used.

[0007] Such a method of forming a fine powder layer includes a dry method and a wet method. However, the dry method has poor fluidity of powder particles and is extremely difficult to form a layer having a uniform thickness. The wet method is the mainstream.

In the wet method, a porous hollow tube is rotated, a fine powder slurry is supplied to the inside of the hollow tube, and the powder is adhered by centrifugal force. Electrophoresis using the surface potential of the slurry is carried out. There are an electrophoresis method of attaching a slurry to a porous hollow tube, and a commonly used coating method. In these methods, water or an organic solvent such as alcohol or acetone is added to a fine powder and used as a slurry. Therefore, it has a feature that it has good fluidity and a layer having a uniform thickness can be easily formed.

As described above, a uniform thin film can be formed by the wet method, but the pore diameter which can be easily formed is several thousand mm or more. When an ultrafine powder of 1000 ° or less is used, there is a disadvantage that cracks are easily generated when the liquid is evaporated and dried after the formation of the slurry adhesion layer. There is also a method of adding a binder to the slurry in order to prevent the generation of cracks, but it is difficult to remove the binder later to obtain fine pores.

[0010] One of the methods for obtaining micropores is as follows.
There is also a method of producing a porous substance by filling fine particles in a coarse porous substrate by an immersion method, but this method has a disadvantage that the fine particles are filled in the entire coarse porous substrate.

Therefore, the present inventor has previously found that it is difficult to control such various drawbacks found in the prior art, namely, to control the uniform pore size, to make the pore size smaller, to make the film thinner, and to reduce the occurrence of cracks and peel strength. In order to overcome any problems such as low temperature, a method has been proposed in which a silica sol is flowed into and contacted with a porous alumina hollow fiber, and then dried and fired to produce a thin-film laminated porous alumina hollow fiber (Japanese Patent Laid-Open No. Hei 5 (1994)). -132,822 publication).

Although the thin-film laminated porous alumina hollow fiber produced by the proposed method achieves the intended purpose, for example, the H ₂ / N ₂ separation coefficient has a lower H ₂ permeation rate. Further improvement in performance as a gas separation membrane was required.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to further improve the gas separation membrane performance of a thin film laminated porous ceramic hollow fiber obtained by flowing silica sol into a porous ceramic hollow fiber, drying and firing the silica sol. It is an object of the present invention to provide a method for manufacturing a product.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
The porous ceramic hollow fiber base material obtained by flowing the silica sol into the porous ceramic hollow fiber, contacting, drying and firing is immersed in the silica sol, pulled up, dried and fired to obtain a thin film laminated porous material. Achieved by manufacturing ceramic hollow fibers. Here, the porous ceramic hollow fiber substrate is manufactured according to the method described in the above-mentioned patent publication.

As the porous ceramic hollow fiber, Al ₂ O ₃ hollow fiber is generally used, but other than this, Y ₂ O ₃ , Mg
Hollow fibers such as O, SiO ₂ , Si ₃ N ₄ and ZrO ₂ can also be used. The silica sol that flows into these hollow fibers having an average pore diameter of about 0.1 to 10 μm, preferably about 0.1 to 2 μm is obtained by hydrolyzing tetraalkoxysilane such as tetraethoxysilane in an aqueous solution using an inorganic acid such as nitric acid. It is prepared by The silica sol thus prepared flows into the hollow fiber and comes into contact with the hollow fiber from one end side of the hollow fiber using a liquid feed pump such as a roller pump for about 1 to 30 seconds. Thereafter, if necessary, for example, a drying process of about 70 to 75 hours under a constant temperature and humidity condition of 40 ° C. and 90% RH, followed by drying at about 100 to 200 ° C. for about 0.5 to 2 hours, and then about It is fired at 400-500 ° C for about 1-10 hours. Such an operation is generally performed a plurality of times.

The porous ceramic hollow fiber base material thus obtained has a silica thin film formed on its outer wall surface with a thickness of about 1 μm.
Since it is formed by growing into the pores of the porous hollow fiber with a thickness of about 1 to 5 μm, cracks and peeling are unlikely to occur in the silica thin film layer having separation performance.

Further, the silica sol solution is rich in fluidity, and once the silica layer is formed, the water permeability is lost. Therefore, the silica sol selectively moves to the portion where the silica layer is not formed by repeating the inflow and the contact of the silica sol. However, since a new silica layer is formed there, uniform thinning is easy.

In the present invention, the porous ceramic hollow fiber substrate is further immersed in silica sol, pulled up, dried and fired. At this time, both ends of the hollow fiber base material are temporarily sealed with an epoxy adhesive or the like to prevent silica sol from flowing into the hollow fiber tube before use. Immersion and pulling are performed using a low-speed motor such as a stepping motor, and the immersion speed is about 3 mm / sec or more, preferably about 5 to 20 mm / sec, and the pulling rate is about 1.
It is performed at a setting of 5 mm / sec or more, preferably about 1.6 to 3 mm / sec. Subsequent drying and baking are performed under the same conditions as described above, and such a series of steps is generally performed a plurality of times to form a silica thin film layer having a thickness of about 0.1 to 5 μm on the outer surface. .

[0019]

According to the present invention, a porous ceramic hollow fiber base material whose surface pores are closed by a silica layer is immersed in silica sol, and a silica thin film layer is further formed on the outer surface layer while preventing silica sol from entering the pores. By forming and growing, it is possible to achieve a laminated thin film in which peeling of the silica layer and generation of cracks are sufficiently prevented. As a result, improvement in gas separation performance, such as thin film multilayer porous ceramic hollow fiber obtained was when used as a gas separation membrane, it is possible to suppress the reduction of the H ₂ permeation rate for H ₂ / N ₂ separation factor It is planned.

[0020]

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

EXAMPLE 25 g of tetraethoxysilane, 37.6 g of ethanol, 35% hydrochloric acid
0.3 g and 23.5 g of water were stirred at room temperature for 2 hours and hydrolyzed to prepare a silica sol. This silica sol is
Porous alumina hollow fiber (average pore diameter 1 μm, porosity 35%,
(Inner diameter 1.5 mm, outer diameter 2.0 mm, length 300 mm) using a liquid feed pump for 5 seconds, after contact and then drying at 40 ° C, 90% RH for 72 hours. Done, then 200
Firing was performed at 2 hours at 500 ° C and 5 hours at 500 ° C. Such a series of operations was performed twice to obtain a porous ceramic hollow fiber substrate.

After sealing both ends of the obtained porous ceramic hollow fiber substrate having a length of 300 mm with an epoxy adhesive,
Using a stepping motor, immersion speed 5 mm / sec in silica sol prepared as described above, pulling speed 1.6 mm /
Dipping and pulling were performed in seconds. After that, 40 ° C, 90% RH
2 hours under constant temperature and humidity conditions, then
Firing was performed at 00 ° C. for 2 hours and at 500 ° C. for 5 hours. A series of operations on such a porous ceramic hollow fiber substrate were performed a predetermined number of times to obtain a separation membrane having a silica thin film layer having the following film thickness formed on the outer surface.

With respect to each of the separation membranes thus obtained, the H ₂ permeation rate and the H ₂ / N ratio were determined under the conditions of 523 K and 0.5 × 10 ⁵ Pa.
_{2 The} separation coefficient was measured, and the following results were obtained. Number of operations Film thickness (μm) H ₂ permeation rate (mol ・ m ^-2・ s ^-1・ Pa ^-1 ) H ₂ / N ₂ separation coefficient 2 0.2 1.32 × 10 ^-7 4.59 3 0.5 1.07 × 10 ^-7 6.70 4 0.9 1.75 × 10 ^-7 8.53 7 3.0 4.12 × 10 ^-8 10.31

The relationship between the H ₂ permeation rate and the H ₂ / N ₂ separation coefficient is indicated by a black circle in the graph of FIG.

Comparative Example In the examples, a series of operations for obtaining a porous ceramic hollow fiber substrate was performed a predetermined number of times, and the H ₂ permeation rate and H ₂ / N ₂
The separation coefficient was measured, and the relationship between the two was also indicated by a circle in the graph of FIG.

[Brief description of the drawings]

FIG. 1 shows H ₂ permeation rate and H ₂ in Examples and Comparative Examples.
6 is a graph showing a relationship with a / N ₂ separation coefficient.

Claims (2)

(57) [Claims] 1. A porous ceramic hollow fiber substrate obtained by flowing silica gel sol into a porous ceramic hollow fiber, contacting, drying and firing, immersing the porous ceramic hollow fiber substrate in the silica sol, pulling up, drying and firing. A method for producing a hollow fiber thin film laminated with porous ceramics, characterized in that: 2. A gas separation membrane comprising a thin film-laminated porous ceramic hollow fiber produced by the method of claim 1.