JPH0139974B2 - - Google Patents

Description

[Detailed description of the invention] The present invention uses borosilicate glass hollow fiber as a material,
The present invention relates to a method for manufacturing a porous glass hollow fiber in which a thin layer surface having countless pores is formed on the inner or outer surface.

Porous hollow glass fibers are generally manufactured by phase-separating hollow fibers made of borosilicate glass and then eluting the parts rich in B ₂ O ₃ and Na ₂ O with acid, but elution treatment is performed from one side. Regarding the structure of the fiber obtained through aging,
Recent research has revealed that it has a porous structure as shown in FIG.
The figure is a conceptual diagram, showing the glass main body (SiO ₂ rich part) 1, glass transmission passage (eluted part)
2, and micropores (SiO ₂ present in the eluted phase)
If we apply this to gas separation and let the mixed gas flow along side A, each gas molecule making up the mixed gas will hit this micropore 3. The gas enters and is emitted to the B side through the gas permeation passage 2. At this time, the degree of penetration of the small-diameter molecules into the micropores 3 is higher than that of the large-diameter molecules, and the small-diameter molecule gas is concentrated in accordance with the difference in the degree of penetration. However, the thickness of the microporous part 3 depends on the degree of phase separation (SiO ₂ content in the B ₂ O ₃ and Na ₂ O-rich part).
It is quite thick and has a considerably high gas permeation resistance, although it varies depending on the elution conditions and elution conditions. Therefore, in order to increase the total amount of gas permeation, the differential pressure between the A side and the B side must be increased, which imposes various operational constraints.

The present invention has been made in view of these circumstances, and has been developed to provide a porous hollow glass fiber that can reduce gas permeation resistance as much as possible and improve the gas concentration and gas separation efficiency described above. It is intended for the purpose of providing. Therefore, the present invention allows B ₂ O ₃ and
Na ₂ O is extracted to form a thin layer surface with countless pores, then phase separation is performed by heat treatment to form a phase rich in B ₂ O ₃ and Na ₂ O in the remaining part, and the phase The key point lies in the fact that it is almost completely eluted with acid.

First, the present inventors conducted sufficient phase separation to reduce the amount of SiO ₂ deposit after elution treatment as much as possible, and strengthened the elution conditions to elute a large amount of SiO ₂ and reduce the deposit thickness. However, we thought that the former method had poor reproducibility, and that if the conditions were incorrectly controlled with the latter method, the deposit would disappear and the purpose of gas separation could not be achieved, so we decided to use another method. As we proceeded with the investigation, we found that the surface of the glass fiber was
Direct extraction of B ₂ O ₃ and Na ₂ O (hereinafter referred to as extraction)
Then, B ₂ O ₃ and Na ₂ O, which are almost uniformly dispersed in the borosilicate glass fiber, are removed from the fiber surface, forming a thin layer with countless pores over the entire surface, and this forms a thin layer in the micropores. In addition, after this treatment, phase separation is performed according to the conventional method, and
When the parts rich in B ₂ O ₃ and Na ₂ O are almost completely eluted and removed with acid, a gas permeation passage without micropores is formed at the bottom of the thin layer, and the pores formed in the thin layer are removed. As a result of the communication between the gas passage and the permeation passage, the gas passage resistance mentioned above is significantly reduced, and the entire surface of the glass fiber can be used as an effective separation surface, allowing efficient concentration and separation of micro-diameter gas components in the mixed gas. It was confirmed that this was the case, and the guideline for the present invention was obtained.

That is, in the present invention, before the borosilicate glass hollow fiber is subjected to phase separation treatment, B is extracted from the inner or outer surface of the hollow fiber (the case where the treatment is performed from the outer surface will be explained below, but the same applies when the treatment is performed from the inner surface). ₂ O ₃ and
Extract Na ₂ O. Then, B ₂ O ₃ and Na ₂ O, which are uniformly dispersed in the hollow fibers, are extracted and removed from the entire surface layer, forming countless pores, and the second
A thin layer 4 having micropores is formed as shown in the figure. Next, this hollow fiber is heat-treated to perform phase separation, and when B ₂ O ₃ and Na ₂ O are almost completely eluted and removed from the B side, a gas permeation passage is formed under the thin layer 4 as shown in Figure 3. 2 are formed, and a state in which the micropores 3 are substantially absent is obtained. The pores formed in the thin layer 4 have approximately the same diameter (10 Å or less) as the pores formed in the conventional microporous part 3, and
They intertwine in every direction within the world. Therefore, since each pore communicates with one of the gas permeation passages 2, the entire surface of the thin layer acts as an effective separation surface, and the B ₂ O ₃ and
Since the removal of Na ₂ O only progresses at the outermost surface of the fiber, it is extremely thin compared to conventional micropores, and gas permeation resistance is significantly reduced.

The method for producing porous hollow glass fibers as shown in FIG. 3 will be explained in detail below.

First, the thin layer 4 is formed by extracting and removing B ₂ O ₃ and Na ₂ O from the surface of the borosilicate glass hollow fiber (mixed gas supply side). Extraction removal methods include steam treatment, heat treatment under vacuum,
Acid treatment, hot water treatment, etc. can be applied. The thin layer 4 formed in the present invention is preferably an extremely thin layer of about 1000 Å, and since the desired purpose can be achieved even with a thin layer, the extraction process can be performed in a relatively short time. It is sufficient. In this process
Since the extraction is performed while B ₂ O ₃ and Na ₂ O are uniformly dispersed, a uniform thin pore layer 4 is formed over the entire surface. That is, in the present invention, the extraction process performed as the first step before phase separation is extremely important. The extraction processing conditions performed at this stage are not particularly limited, but for steam extraction, the temperature is 100 to 900℃.
for 5 to 50 hours, 10 to 300 mHg for vacuum heating extraction,
1 to 50 hours at 300 to 650°C; for acid extraction, for example, in the case of sulfuric acid, use a 0.5 to 3N aqueous solution at room temperature to 95°C.
For hot water extraction, hot water at 80 to 100°C can be used for 1 to 50 hours, and a treatment time of 1 to 50 hours can sufficiently achieve the purpose. Acid extraction can also be performed using hydrochloric acid, acetic acid, or the like.

Next, in the second step, the hollow fibers with the thin layer 4 formed thereon are heat-treated to perform phase separation. The upper limit of phase separation temperature is
Although the temperature must be below the softening point of the original glass, it is usually carried out at a temperature of about 500 to 650°C. As a result of this heat treatment, the thin layer 4 was dispersed throughout the inner pipe wall.
B ₂ O ₃ and Na ₂ O undergo phase separation to form a concentrated region, but there is no longer any concentration in the thin layer formed in the first step.
Since B ₂ O ₃ and Na ₂ O are hardly included, phase separation does not occur here.

When the phase separation is completed, B ₂ O ₃ and Na ₂ O are then eluted and removed from the phase separation section. As the elution method, all of the elution methods exemplified above can be applied, but the acid treatment method is the most effective in consideration of practicality, especially elution efficiency. That is, in this step, it is necessary to form a gas permeation passage 2 that penetrates the pipe wall (normal thickness is 10 to 500 μm) except for the thin layer 4.
Since it is necessary to perform almost complete elution to prevent the formation of SiO ₂ deposits, methods with low elution efficiency require a long time for elution processing. However, if the acid elution method is employed, the purpose can be achieved in a relatively short time. Although sulfuric acid is the most common acid used in this process, it is also possible to use other acids such as hydrochloric acid and nitric acid, or mixtures thereof, and these can be used in the form of a 0.5-3N aqueous solution. It is used at temperatures ranging from room temperature to 100°C. The elution time should be appropriately determined depending on the type of acid, concentration, treatment temperature, etc., but elution is almost complete in 10 to 50 hours.

As for elution conditions that do not leave SiO ₂ deposits, it is preferable to apply a relatively large amount of acid to the phase-separated glass, such as 1N sulfuric acid (90%
For example, in the case of elution in a 25-hour treatment using 0.1 °C), it is desirable to use a liquid amount of 0.1/g (glass fiber) or more. However, it goes without saying that the amount of liquid should be adjusted depending on the type and concentration of acid, treatment temperature, and treatment time.

There are three possible elution directions in this step: from the side on which the thin layer 4 is formed (side A in Figure 3), from the opposite side (side B in Figure 3), and from both sides. The most preferred method is elution from the opposite side of the thin layer 4. However, the B ₂ O ₃ to be eluted is eluted from the side where the thin layer 4 is formed.
, Na ₂ O, etc. have to pass through the pores of the thin layer 4, and their elution is suppressed in this part. On the other hand, when elution is carried out from the opposite side, relatively large particles are formed sequentially on the back side. Since the eluted components are quickly removed along the large diameter (50 Å or more) gas permeation passage 2, the elution can be completed in a short time. Furthermore, the porous thin layer 4 is relatively fragile and may cause cracks due to resistance to passage of eluted components, but if elution is performed from the back side, there is no risk of such problems. However, if the above-mentioned cracks are prevented from occurring by allowing sufficient elution time and adjusting the acid concentration and treatment temperature, or by using an acid aqueous solution containing boric acid or silicic acid, elution can be carried out from the side on which the thin layer is formed. Alternatively, elution may be performed from both sides, and these are also included in the scope of the present invention.

In this way, in the present invention, B ₂ O ₃ and
In principle, Na ₂ O extraction is performed to form a porous thin layer 4, followed by phase separation and acid elution, but as a simple method, the first stage extraction and phase separation may be performed simultaneously. is also possible. That is, the time required for the heat treatment required for phase separation is usually about 1 to 3 days, whereas the time required for the first stage extraction is generally several hours. Therefore, even when phase separation and extraction are performed simultaneously, the first stage extraction proceeds quickly and forms a porous thin layer 4.
is formed, so there is almost no difference between extraction and phase separation performed separately and sequentially, and the effect is that the time required for the first stage extraction can be saved.

By the way, it has been confirmed that the surface of borosilicate glass changes when left in the atmosphere for a long time, causing _{various problems} .
There are also reports that this is due to the volatilization of Na ₂ O. For example, when an old borosilicate glass molded product is subjected to phase separation and acid elution treatment, the elution efficiency is reduced due to a degraded layer on the surface that inhibits elution, or the degraded layer collapses and the quality deteriorates. It has been confirmed that even when new borosilicate glass molded products are used, surface deterioration occurs during the heat treatment process for phase separation, causing the same problems as described above. Conventionally, in order to prevent problems associated with this alteration, new borosilicate glass molded products were used immediately after molding, and heat treatment was performed in the presence of boric acid vapor during the heat treatment process for phase separation. , studies were being conducted to prevent surface deterioration.

In contrast, the present invention focuses on the fact that the above-mentioned altered layer is a porous layer having countless extremely fine pores, and uses this porous layer as an effective separation surface by actively forming the porous layer. . In other words, the present invention has achieved its purpose by actively utilizing a phenomenon that has been pointed out as a serious defect in the conventional example and for which prevention measures have been difficult. The resulting effects cannot be predicted from conventional wisdom in this field.

A typical example of the porous glass in the present invention has a composition of _SiO2 : 22 to 75% by weight, Na2O: ₂ to 16% by weight.
Borosilicate glass containing _{B2O3 :} 18-67% by weight, _Al2O3 : 0-5% by weight, _ZrO2 : 0-5 _% by weight, and _TiO2 : 0-5% by weight is used as the raw material glass. Examples include high silicate porous glass.

The porous glass obtained in this way is
It is a porous body with a pore diameter of 3000 Å and a nitrogen adsorption area of 200 to 500 m ² /g. In addition, the fiber outer diameter in the present invention is 10 to 3000 μm, and the (inner diameter/outer diameter) of the hollow fiber
The ratio is 0.2-0.8.

The present invention is roughly constructed as described above, and the entire surface of the porous glass hollow fiber can be made into an extremely thin layer of effective separation surface, and gas permeation resistance can be significantly reduced. The amount of gas permeation was increased. In addition, its production is simple, as it only requires a relatively short extraction process prior to the conventional phase separation and elution processes. In particular, if the first stage extraction is carried out in parallel at the beginning of the heat treatment (phase separation) step, which takes a relatively long time, it is possible to obtain high-performance porous glass hollow fibers in the same amount of time as in the conventional method.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram showing the vertical cross-sectional structure of porous glass hollow fiber obtained by the conventional method, and Fig. 2 is a conceptual diagram showing the longitudinal cross-sectional structure of the porous glass hollow fiber obtained by the conventional method.
FIG. 3 is a conceptual diagram illustrating the longitudinal cross-sectional structure of the porous glass hollow fiber obtained in the present invention. 1...Glass main body, 2...Gas permeation passage, 3
... Microporous part, 4... Porous thin layer.

Claims (1)

[Claims] 1 From the inner or outer surface of the borosilicate glass hollow fiber,
B ₂ O ₃ and Na ₂ O are extracted to form a thin layer surface with countless pores, and then heat treatment is applied to phase separate the remaining portion, and B ₂ O ₃ and Na are extracted from the phase separated portion. ₂ O
A method for producing porous glass hollow fibers, characterized by almost completely eluting a phase rich in ions with an acid.