JPH0925184A - Ceramic porous film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare an inexpensive ceramic porous film excellent in corrosion resistance and heat resistance, free from the change of film pore diameter by external pressure and having high filtration accuracy. SOLUTION: This ceramic porous film is composed mainly of mullite crystal, has 68/32 to 78/22 in the weight ratio of Al2 O3 /SiO2 , >=98wt.% in total of Al2 O3 and SiO2 , 0.3-3μm in average crystal diameter, 0.03-1.0μm in each of mode diameter and 50% diameter of film pore diameter and has 10-50m<3> /m<2> in the flow rate of pure water permeation per day.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a porous ceramic membrane formed on the surface of an inorganic porous body and a method for producing the same.

[0002]

2. Description of the Related Art Porous membranes are used to purify wastewater and clean water,
Widely used for filtration and separation of food and gas. As such a porous film, a film mainly made of a metal, an organic polymer, a composite of these and ceramics, or porous glass is used. However,
Compared to ceramics, metals and organic polymers have higher heat resistance,
It has a problem that it is inferior in corrosion resistance and the pore diameter of the porous film is likely to change due to hydraulic pressure. Therefore, the development of the ceramic porous film is being actively promoted.

Conventionally, an alumina-based sintered body has been mainly used as a ceramic porous membrane, but it is difficult to control the membrane pore diameter and the membrane pore diameter distribution, and the alumina pore sintered body is particularly small. As a matter of fact, a fine powder is required as the raw material powder to be used, and there is a problem that the cost becomes high.

As a method for producing an alumina-based porous ceramic membrane, a method for producing a ceramic porous support and a membrane layer from raw materials having different particle sizes, a method for forming a membrane layer on the ceramic porous support, etc. However, the raw material cost is very high in the former method,
There is a disadvantage that mass production is difficult, and the latter method of forming a film layer by coating has an advantage that the cost is lower than the former method and mass production is possible,
Pinholes and cracks are easily generated in the obtained film layer,
As a result, there is a drawback that the filtration accuracy is lowered.

[0005]

SUMMARY OF THE INVENTION The main object of the present invention is to:
Excellent corrosion resistance and heat resistance, no change in membrane pore size due to external pressure,
An object of the present invention is to provide an inexpensive ceramic porous membrane having high filtration accuracy.

[0006]

As a result of intensive studies conducted by the inventor in view of the above situation, the present inventor mainly composed of mullite crystals, and had composition, purity, crystal grain size, membrane pore size and pure water permeation flux. It has been found that the ceramic porous membrane whose value is controlled within a certain range has excellent heat resistance and corrosion resistance, is inexpensive, and has high filtration accuracy and filtration ability, and has completed the present invention.

That is, the present invention provides the following ceramic porous membrane and its manufacturing method.

(I) (1) Mainly composed of mullite crystals, (2) Al ₂ O ₃ / SiO ₂ weight ratio of 68/32 to 7
8/22, the total amount of (3) Al ₂ O ₃ and SiO ₂ is 98
% Or more, (4) average crystal grain size is 0.3 to 3 μm,
(5) The mode diameter and the 50% diameter of the membrane pore diameter are 0.
03-1.0 μm, (6) Pure water permeation flux is 1 per day
A ceramic porous membrane, characterized in that it is 0 to 50 m ³ / m ² .

(II) A mullite-containing slurry obtained by pulverizing and dispersing mullite powder, wherein the solid content in the slurry is Al ₂ O ₃ / SiO ₂ weight ratio of 68/32 to 7
8/22, the total amount of Al ₂ O ₃ and SiO ₂ is 98% by weight or more, the average particle size is about 0.8 to 1.5 μm, and the specific surface area is 6 to 9 m ² / g. The method for producing a ceramic porous membrane as described in (I) above, wherein the slurry is coated on the ceramic porous support, dried, and then baked at 1300 to 1600 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The requirements to be satisfied by the ceramic porous membrane according to the present invention will be described in detail below.

(1) Mainly composed of mullite crystals.

The ceramic porous membrane of the present invention needs to consist mainly of mullite crystals. Mullite has the characteristics of being chemically stable and excellent in corrosion resistance and heat resistance. Furthermore, compared with alumina, mullite has a slower grain growth rate with respect to the firing temperature and is easier to control the film pore size. I have both.

In the present invention, the ceramic porous membrane needs to consist mainly of mullite crystals, but it does not have to be a mullite single phase, and diffraction angles of 20 to 4 by X-ray diffraction.
Mullite (210) plane (M (210)), alumina (113) plane (A (113)), cristobalite (1
The diffraction peak intensity ratio of each of the (01) planes (C (101)) should satisfy the following conditions.

M (210) / (M (210) + A (113) + C (101)) ≧ 0.7 A (113) / (M (210) + A (113) + C (101)) ≦ 0.2 C (101) / (M (210) + A (113) + C (101)) ≦ 0.1 Of the above diffraction peak intensity ratios, A (113) / (M (210) + A (11
When 3) + C (101)) exceeds 0.2, the amount of alumina crystals increases, and due to the difference in thermal expansion between mullite crystals and alumina crystals, microcracks generated at grain boundaries increase, and the pore diameter is It becomes large, which is not preferable. Also, C (101) / (M (210)
When + A (113) + C (101)) exceeds 0.1, the amount of cristobalite in the porous body increases, cracks may occur in the porous film, and corrosion resistance may decrease, which is not preferable. In the present invention, it is more preferable that the following conditions are satisfied.

M (210) / (M (210) + A (113) + C (101)) ≧ 0.8 A (113) / (M (210) + A (113) + C (101)) ≦ 0.15 C (101) / (M (210) + A (113) + C (101)) ≦ 0.05 (2) Al ₂ O ₃ / SiO ₂ weight ratio is 68/32 to 78 /
It should be in the range of 22.

In the present invention, the Al ₂ O ₃ / SiO ₂ weight ratio must be in the range of 68/32 to 78/22, and preferably in the range of 70/30 to 75/25. When the Al ₂ O ₃ / SiO ₂ weight ratio is less than 68/32, that is, when the amount of SiO ₂ is large, there is an advantage that the sinterability is improved, but on the other hand, the permeation amount of the filtered material is decreased, In addition, the amount of glass phase formed by SiO ₂ and impurities such as alkali increases at the crystal grain boundaries, which causes deterioration of corrosion resistance, which is not preferable. On the other hand, Al ₂
When the O ₃ / SiO ₂ weight ratio exceeds 78/22, that is,
If the amount of Al ₂ O ₃ is too large, crystal grains grow easily during firing during film formation, resulting in an increase in film pore size, which is not preferable.

(3) The total amount of Al ₂ O ₃ and SiO ₂ is 9
8% by weight or more.

In the present invention, Al ₂ O ₃ and SiO ₂
It is necessary that the total amount of is 98% by weight or more, and if it is less than 98% by weight, the amount of impurities increases,
As in the case where the amount of SiO ₂ is large, the amount of glass phase in the crystal grain boundaries is large and the amount of permeation of the filtrate is reduced, which is not preferable. The total amount of the alkali metal oxide and the alkaline earth metal oxide contained in the ceramic porous membrane of the present invention is preferably 0.2% by weight or less. Also, Z
Since rO ₂ has an effect as a sintering aid, 0.05
It is preferable to add about 1% by weight.

(4) The average crystal grain size is 0.3 to 3 μm.

In the ceramic porous membrane of the present invention, it is necessary that the average crystal grain size is 0.3 to 3 μm.
It is preferably 3 to 1 μm.

When the average crystal grain size is less than 0.3 μm, although the adhesion strength between the porous membrane and the support can be increased, the membrane pore diameter becomes small and the permeation amount of the filtrate decreases. Not preferable. On the other hand, the average crystal grain size is 3 μm
If it exceeds, the membrane pore size becomes large, and the membrane pore size distribution becomes wide, resulting in deterioration of filtration accuracy, which is not preferable.

The average crystal grain size in the ceramic porous membrane of the present invention was observed by scanning electron microscopy and photographed the surface of the membrane at a magnification such that 100 or more crystals were present in the visual field, and 10 points were obtained from the photographed photograph by the intercept method. It is a value obtained by calculating the average and using the following formula.

D = 1.5 × n / L (D: average crystal grain size,
(n: number of crystals per length L) (5) The mode diameter and 50% diameter of the membrane pore diameter are 0.
It should be from 03 to 1.0 μm.

In the present invention, the membrane pore diameter of the ceramic porous membrane is measured by the bubble point method based on ASTM F316-86 using FC-43 (perfluorocarbon) as a medium. In the mercury porosimetry, which is a conventional method of measuring the pore size of the membrane, since it measures not only open pores but also closed pores, it is not suitable for the measurement of the pore diameter of the ceramic porous membrane of the present invention. In the present invention, the membrane pore size is measured by the bubble point method, which can measure the open pore size that allows filtration.

The 50% diameter of the membrane pore diameter thus obtained is the pore diameter whose cumulative value shows 50% in the pore diameter cumulative distribution curve, and the mode diameter is the fine diameter obtained from the pore diameter cumulative distribution curve. It is the pore size with the highest frequency in the pore size histogram.

In the present invention, the mode diameter of the membrane pore diameter and 50%
It is necessary that the diameter is 0.03 to 1.0 μm, and preferably 0.05 to 0.5 μm.
If the mode diameter and the 50% diameter are less than 0.03 μm, the permeation amount of the filtered material decreases, which is not preferable. Also, 1.
When it exceeds 0 μm, it is not preferable because it leads to deterioration of filtration accuracy. Further, if either the mode diameter or the 50% diameter is out of the range of 0.03 to 1.0 μm, it means that the membrane pore size distribution is wide, and in this case, the filtration accuracy is lowered, which is not preferable.

Further, in the ceramic porous membrane of the present invention,
If the maximum membrane pore size is too large, the permeation amount of the filtrate does not decrease, but the filtration accuracy will deteriorate.
In the pore size distribution measured by the bubble point method, the maximum pore size is preferably 2 μm or less, and 1
More preferably, it is less than or equal to μm.

(6) Pure water permeation flux is 10 to 5 per day
Must be 0 m ³ / m ² .

In the present invention, the pure water permeation flux is formed by forming a ceramics porous membrane on a ceramic porous support having a larger pure water permeation flux than the ceramics porous membrane to be measured, and performing ion exchange. From the permeation amount of water and the area of the ceramic porous membrane (area through which water permeates) per hour when a liquid pressure of 1 kgf / cm ² is applied using water, about 1 m ² of the ceramic porous membrane per day Calculated as the amount of water permeation.

As a specific measuring method, the pure ceramics porous support has a pure water permeation flux of 20 to 60 m ³ / m ² per day when baked at a baking temperature for forming a ceramics porous film. The method for producing a ceramic film described below on a porous support, wherein the pure water permeation flux before forming the porous film on the support is larger than the pure water permeation flux after forming the porous film. After forming a ceramics porous membrane in the same manner as described above, 1 kgf / cm ² with ion-exchanged water
The permeation amount of water when liquid pressure is applied is measured, and the permeation amount of water per 1 m ² of the ceramic porous membrane per day may be determined from this permeation amount. The porous support used at this time is preferably a sintered body composed of alumina crystals, mullite crystals, or a mixed crystal thereof, in consideration of the adhesion to the ceramics porous membrane and the like, and the average pore diameter is 0.1 to 0.1. 3μ
It is preferably about m.

In the ceramic porous membrane of the present invention, the pure water permeation flux measured by the above method is 10 to 5 per day.
It is necessary to be 0 m ³ / m ² , and 20 to 35 m ³ /
m ² is preferred. If the pure water permeation flux is less than 10 m ³ / m ² per day, the permeated amount of the filtrate will be small, which is not preferable, while if it exceeds 50 m ³ / m ² , the strength of the porous membrane will be unsatisfactory. It is not preferable because it becomes sufficient.

Next, the method for producing the ceramic porous film of the present invention will be described.

First, mullite powder is used as a raw material, and the mullite powder is wet pulverized and dispersed using a pulverizer such as a ball mill or an attrition mill to obtain a coating slurry. As the raw material mullite powder, it is desirable to use mullite powder synthesized by a liquid phase method or the like. Upon pulverization and dispersion, a molecular weight of 50,000 to 100,0
It is preferable to add a polycarboxylic acid salt of about 00 as an aqueous solution. The polycarboxylic acid salt not only improves the dispersibility of the slurry, but also imparts an appropriate thixotropy to the slurry, and serves to make the coated film thickness uniform when coating the ceramic porous support, Further, it has an effect of suppressing generation of pores and cracks. Examples of polycarboxylic acid salts that can be used include sodium salts and ammonium salts. The addition amount of the polycarboxylic acid salt is mullite powder 1 used as a raw material.
The amount is preferably about 2 to 10 parts by weight, more preferably about 4 to 10 parts by weight, based on 00 parts by weight. Furthermore, if necessary, polyvinyl alcohol (PVA), wax emulsion, carboxymethyl cellulose (CMC), etc. can be added as a binder, which provides good adhesion between the slurry and the ceramic porous support during coating. Can be The amount of the binder compounded is preferably about 1 to 4 parts by weight with respect to 100 parts by weight of the mullite powder used as a raw material.

In the coating slurry obtained by pulverizing and dispersing, the solid content in the slurry is Al ₂ O ₃ / S.
iO ₂ weight ratio is in the range of 68/32 to 78/22,
The total amount of Al ₂ O ₃ and SiO ₂ is 98% by weight or more, the average particle size is about 0.8 to 1.5 μm, and the specific surface area is 6 to 9 m.
It is necessary to be in the range of ² / g, and pulverization and dispersion are carried out so as to obtain a slurry satisfying such conditions.
The coating slurry preferably has a solid content concentration of 50 to 80% by weight.

The slurry thus obtained is coated on a ceramic porous support so as to have a film thickness of 5 to 30 μm, dried and then calcined at 1300 to 1600 ° C. The porous ceramic membrane of the present invention can be formed on a porous support. As a method for coating the slurry, methods such as spraying, screen printing and dipping can be adopted.

In the present invention, as the ceramic porous support for forming the ceramic porous membrane, pure water permeation before forming the porous membrane is carried out so as not to impair the filtration performance of the porous membrane. A porous body having a larger flux than the pure water permeation flux after the formation of the porous membrane is used. As such a porous support, good corrosion resistance, good compatibility with the coefficient of thermal expansion of the porous coating of the present invention, from the crystal phase of alumina crystals, mullite crystals or mixed crystals thereof The sintered body is preferably a mixed crystal of alumina crystals and mullite crystals, from the viewpoint of good adhesion to the porous film. The pure water permeation flux of the porous support is preferably ²⁰ to 60 m ³ / m ² per day. Pure water permeation flux is 20m ³ per day
If it is less than / m ² , the diffusion resistance of the solution or gas to be filtered cannot be ignored even if the liquid pressure or the gas pressure is increased, and the permeation amount of the filtered material decreases, which is not preferable. On the other hand, when the pure water permeation flux exceeds 60 m ³ / m ² per day, the porosity of the porous support becomes high, so that the adhesion strength with the porous membrane decreases and the cause of the peeling of the porous membrane is Therefore, it is not preferable.
The average pore size of the porous support is preferably 0.1 to 3 μm when measured by the bubble point method described above. If the average pore diameter deviates from the range of 0.1 to 3 μm, the adhesion strength with the porous membrane decreases, which causes peeling, which is not preferable. When the firing temperature of the porous support is lower than the firing temperature at the time of forming the porous film, the average pore diameter when firing the inorganic porous support at the same temperature as the temperature at which the film is formed is measured. To do.

Examples of preferable ceramic porous supports for forming the ceramic porous membrane of the present invention include those satisfying the following conditions.

(1) The crystal phase is composed of alumina crystals, mullite crystals or mixed crystals thereof, and (2) Al ₂ O ₃ / S.
iO ₂ weight ratio is in the range of 60/40 to 98/2,
(3) The total amount of Al ₂ O ₃ and SiO ₂ is 95% by weight or more, (4) the average pore diameter is 0.1 to 3 μm,
(5) An inorganic porous support comprising a sintered body having a pure water permeation flux of 20 to 60 m ³ / m ² per day.

When a porous support which satisfies the above conditions is used and the ceramic porous membrane of the present invention is formed on it, in particular, the corrosion resistance and heat resistance are good, and the filtration ability is high. A high ceramic porous body can be obtained.

The above-mentioned inorganic porous support can be appropriately produced by a conventional method. An example of the production method is as follows.

First, Al ₂ O ₃ , kaolin or the like is used as a raw material, and this is blended so as to have a predetermined Al ₂ O ₃ / SiO ₂ weight ratio, and a binder, a dispersant, etc. are added, and water or ethyl alcohol is added. In a solvent such as, for example, a pulverizer such as a ball mill or an attrition mill is used to pulverize, mix, and disperse so that the pulverized particle size is about 3 to 50 μm. As the binder and the dispersant, those used in the production of ordinary sintered bodies can be used, and specific examples of the binder include polyvinyl alcohol (PVA), wax emulsion, carboxymethyl cellulose (CMC) and the like. Specific examples of the dispersant include ammonium sulfonate, sodium pyrophosphate, and the like. The amount of binder and dispersant added depends on the molding method, etc.
It may be appropriately determined so that the desired inorganic porous support is formed.

The powder thus obtained is press-molded,
Molded into a predetermined shape by cast molding, extrusion molding, etc., 6
About 0 to 1600 ° C, preferably 700 to 1550 ° C
By calcining for about 2 to 5 hours, an inorganic porous support satisfying the above conditions can be obtained.

As described above, the ceramic porous membrane of the present invention formed on various ceramic porous supports has excellent corrosion resistance and heat resistance, does not change the membrane pore diameter due to external pressure, and has high filtration accuracy. However, it has the feature of being inexpensive. Therefore, it can be particularly effectively used for purification of wastewater, purification of clean water and clean water.

[0044]

The following examples are provided to further clarify the features of the present invention.

Example 1 The weight ratio of Al ₂ O ₃ / SiO ₂ is 65/35 to 78/2.
2, the total amount of Al ₂ O ₃ and SiO ₂ is 95 to 99.5% by weight, the average particle diameter is 2 to 10 μm, and the specific surface area is 3 to
Mullite powder synthesized by the sol-gel method at 9 m ² / g was added with polycarboxylic acid sodium salt as mullite powder 100.
0 to 8 parts by weight with respect to 100 parts by weight of polyvinyl alcohol as a binder, and 100 parts by weight of mullite powder.
Parts was added, made of Al ₂ O ₃ ball mill and made of Al ₂ O ₃ or triturated with ZrO ₂ balls, and dispersed to prepare a coating slurry. Table 1 shows the characteristics of each coating slurry. In Table 1, Al ₂ O ₃ / SiO
_{The 2} weight ratio, Al ₂ O ₃ + SiO ₂ weight%, and ZrO ₂ weight% are based on the solid content in the obtained slurry, and the addition amount of polycarboxylic acid sodium salt was used as a raw material. It is parts by weight based on 100 parts by weight of mullite powder.

[0046]

[Table 1]

Then, the Al ₂ O ₃ / SiO ₂ weight ratio is 66.
/ 34 so as to, blended with Al ₂ O ₃ and kaolin raw materials, further, the addition of pyrophosphate salt as a wax emulsion and dispersing agent as a binder, using a ball mill and ball milled particle size using water as a solvent A slurry was obtained by pulverizing and mixing so as to have a particle size of 3 to 50 μm. The obtained slurry was dried and adjusted to have a water content of 20% to obtain kneaded clay. The blending amounts of the binder and the dispersant were appropriately adjusted so that appropriate plasticity was obtained during molding. Using this kneaded clay, extrusion molding is performed so that the size after firing will be a pipe shape with an outer diameter of 10 mm, an inner diameter of 7 mm, and a length of 50 mm, and after drying, the temperature is 1100 ° C.
It was calcined for 2 hours to obtain a mullite porous support. The obtained porous support has an average pore diameter of 0.1 to 3 μm.
The pure water permeation flux was 25 to 35 m ³ / m ² per day.

Both ends of this ceramic porous support are sealed and immersed in the above-mentioned coating slurry,
Dry at 100 ° C, calcine at 1200-1700 ° C,
A ceramic porous film having a thickness of 20 μm was formed.

The crystal phase of the obtained ceramic porous film,
The mode diameter and 50% diameter of the membrane pore diameter, the average crystal grain diameter, the membrane state, the pure water permeation flux and the membrane surface state are shown in Table 2 below.
Al ₂ O ₃ / S in the obtained ceramic porous film
Regarding the iO ₂ weight ratio and the Al ₂ O ₃ + SiO ₂ weight,
The amounts were the same as those in the solid content of the slurry shown in Table 1, respectively. The surface condition of the film is observed with an optical microscope or a scanning electron microscope, and those having no abnormality are indicated by a circle.

[0050]

[Table 2]

In Table 2, the ceramic porous membranes of Sample Nos. 1 to 7 satisfy the requirements of the present invention, and the pure water permeation flux per day is in the range of 10 to 50 m ³ / m ² . , The filtration material has a large amount of permeation, and has excellent filtration accuracy,
The adhesion of the film was good. On the other hand, sample No.8-
The ceramic porous membrane of No. 12 does not satisfy at least one of the conditions of the present invention and has a pure water permeation flux of 10
It is less than m ³ / m ² or more than 50 m ³ / m ² , and it is not possible to simultaneously satisfy both the performance of the filtration material permeation amount and the filtration accuracy. Further, in the ceramic porous membranes of Sample Nos. 11 and 12, cracks or pinholes were formed after the membrane was formed, and it could not be used as a ceramic porous membrane for filtration.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Ozaki 1-47 Shikitsu East, Naniwa-ku, Osaka City, Osaka Prefecture Kubota Co., Ltd. (72) Inventor Koji Onishi 3 Ensato Ono-cho, Sakai City, Osaka Prefecture No. 2-24 In Nikkato Co., Ltd. (72) Inventor Ichidai 3 3 Tosato Onocho, Sakai City, Osaka Prefecture No. 2-24 In Nikkato Co., Ltd. (72) Toshio Kawanami 3 Tonosato Onocho, Sakai City, Osaka Prefecture Ding 2-24 In Nikkato Co., Ltd.

Claims (2)

[Claims] (1) Mainly composed of mullite crystals,
(2) Al ₂ O ₃ / SiO ₂ weight ratio is 68/32 to 78 /
22, (3) the total amount of Al ₂ O ₃ and SiO ₂ is 98% by weight or more, (4) the average crystal grain size is 0.3 to 3 μm, (5)
The mode diameter and the 50% diameter of the membrane pore diameter are 0.03 to
1.0 μm, (6) Pure water permeation flux is 10-5 per day
A ceramic porous membrane, characterized in that it is 0 m ³ / m ² . 2. A mullite-containing slurry obtained by pulverizing and dispersing mullite powder, wherein the solid content in the slurry has an Al ₂ O ₃ / SiO ₂ weight ratio of 68/32 to 78 /.
22 and the total amount of Al ₂ O ₃ and SiO ₂ is 9
A ceramic porous support was coated with a slurry having a content of 8% by weight or more, an average particle size of 0.8 to 1.5 μm, and a specific surface area of 6 to 9 m ² / g.
The method for producing a ceramic porous membrane according to claim 1, wherein the firing is performed at 1600C.