JPH07163848A - Production of inorganic porous membrane - Google Patents

Abstract

PURPOSE:To provide an inorg. porous membrane suitable as an ultrafiltration membrane having no pinhole or crack. CONSTITUTION:A suspension containing inorg. particles is applied to at least one surface of a porous support to form a membrane which is, in turn, dried and baked to support an inorg. porous membrane with an average pore size of 0.05-0.005mum used as an ultrafiltration membrane. As the suspension, a hydrosol with pH 1-4 using water as a dispersing medium is employed. The suspension is applied so that the supporting thickness per one time of the porous membrane becomes below 100 times the average particle size of the primary particles of the inorg. particles.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an inorganic porous membrane used as an ultrafiltration membrane.

[0002]

2. Description of the Related Art As one type of inorganic porous membrane, a suspension containing inorganic particles is coated on at least one side surface of one or more layers of a porous support to form a thin film, which is then dried and baked. There is an inorganic porous film supporting a porous thin film. Such an inorganic porous membrane is used as various filtration membranes. In the inorganic porous film used for this kind of application, it is important that there are no pinholes, cracks or the like in the porous thin film, and that there are pinholes, cracks or the like in the porous film. , Of course, the filtration accuracy is reduced, pinholes and cracks are increased by acid, alkali cleaning, steam cleaning for the purpose of sterilization when the filtration performance is deteriorated due to clogging of the porous thin film during use, etc. , And the filtration accuracy is further reduced due to expansion, and the corrosion resistance is greatly impaired. In particular, in an ultrafiltration membrane, since an inorganic porous membrane having a porous thin film with an ultrafine pore having an average pore size of 0.05 μm to 0.005 μm is used, an ultrafine pinhole is present in the porous thin film. If cracks are slightly present, they have a great influence on filtration accuracy.

A number of techniques relating to the above-mentioned inorganic porous membrane having a multilayer structure have already been disclosed, and JP-A-60-156510 can be cited as a publication disclosing such a technique. In this publication, a method for producing an inorganic semipermeable membrane that does not cause cracks, specifically, a porous support made of a sintered inorganic oxide is coated with a suspension (sol solution) of an inorganic film-forming coating material. A manufacturing method comprising heating is disclosed. According to the manufacturing method,
An ultrafiltration membrane in which a porous thin film made of γ-alumina is coated on a porous support is obtained. Therefore, the publication describes that the accuracy of the porous support is determined by the pore size (average pore size) of the support, and a preferable average pore size is 0.10 μm to 0.50 μm. There is. Further, it is described that the thickness of the porous thin film is 20 μm or less, and that the concentration of the dispersed phase in the medium is 0.01% by weight to 25% by weight for the coating sol liquid.

[0004]

By the way, in the inorganic porous film, one of the causes of the occurrence of pinholes, cracks, etc. in the porous thin film is one of the causes of the thin film in the drying process and the firing process during manufacturing. There is contraction. In such an inorganic porous film, the present inventors have adopted an appropriate suspension as a suspension for coating, and also, a supported film thickness per time of a porous thin film and inorganic particles forming the thin film. It has been found that the pinholes, cracks, etc. that affect the function of the ultrafiltration membrane can be prevented by precisely defining the relationship.

Therefore, an object of the present invention is to prepare a suspension for coating and an inorganic particle that forms a thin film of the porous thin film at the same time as a supporting film thickness for producing the inorganic porous film. The object of the present invention is to provide a method for producing an inorganic porous membrane in which pinholes, cracks, etc. that may affect the function of the ultrafiltration membrane are not generated by precisely defining the above relationship.

[0006]

According to the present invention, a suspension containing inorganic particles is coated on at least one side of a porous support having one or a plurality of layers to form a thin film, which is then dried and calcined for averaging. Pore diameter is 0.05μm-0.005μ
A method for producing an inorganic porous membrane, which is used as an ultrafiltration membrane, in which a porous thin film of m is supported, wherein the suspension is sol particles having water as a dispersion medium and a concentration of a dispersed phase. The molar ratio of the medium is 1/40 to 1/3000 and the pH is 1
1 to 4 of the above-mentioned porous thin film using a hydrosol of
It is characterized in that the suspension is coated such that the supported film thickness per time is less than 100 times the average particle diameter of the primary particles in the inorganic particles.

In the present invention, the porous support is an oxide, carbide, etc. of aluminum, zirconium, titanium, etc.
Ceramics such as nitride, glass such as borosilicate glass,
It is made of a metal such as nickel and has a single-layer or multi-layer structure of an appropriate shape such as a pipe shape, a flat plate shape, a honeycomb shape, and a monolith shape, and its thickness is 0.5 mm to 2 mm. Regarding the average pore size of the porous support, when the support is a single layer, it is 0.05 μm to 3 μm, when it is a multilayer, the main layer is 0.1 μm to 30 μm, and the sublayer (intermediate layer). ) Is 1 μm or less, and the thickness of the intermediate layer is 10 μm to
It is 150 μm.

In the present invention, the porous thin film is made of an inorganic substance such as titanium, zirconium oxide, carbide or nitride, and has an average pore diameter of 0.05 μm to 0.005 μm. When the porous support has a multilayer structure, the porous thin film is formed on at least one side surface of the intermediate layer.
Incidentally, at least one side surface of the porous support means, for example, an inner peripheral surface, an outer peripheral surface, an inner peripheral surface when the support has a pipe shape, and one side surface, both sides when it has a flat plate shape. In the case of a honeycomb shape and a monolith shape, it means an outer peripheral surface, a part or front portion of the inner peripheral surface of a large number of inner holes, and both inner and outer peripheral surfaces thereof. In the present invention, the thin film means a film formed on a porous support by coating before being dried and baked, and the porous thin film means a film obtained by drying and baking the above thin film. Further, the thickness of the porous thin film is referred to as a supported film thickness, and the supported film thickness per one time is measured by, for example, a scanning electron microscope.

In the present invention, the suspension used for forming the thin film is a hydrosol solution containing water as a dispersion medium, and is a hydrolytic suspension of a compound such as an alkoxide, an acylate or a xylate, or a hydrolytic suspension of a metal salt. Liquids, colloidal suspensions of metal hydroxides and fine metal oxides, and the like are adopted. Further, the suspension has a pH of 1 to 4. The porous support is dipped in the suspension for a predetermined time to form a thin film on at least one side surface thereof. Then, the thin film is dried and baked. As a result, the thin film is supported on the porous support as a porous thin film. Incidentally, in order to obtain a predetermined supported film thickness in the porous thin film, the thin film is formed several times and dried and fired each time the thin film is formed. In the present invention, the supported film thickness per time needs to be less than 100 times the average pore size of the inorganic particles dispersed in the suspension. The average particle diameter means a weight average particle diameter, and the average particle diameter is an average particle diameter in a state where innumerable particles exist independently without coagulating with each other, that is, in a state of primary particles.

The supported film thickness per one time is adjusted by the characteristics of the suspension and the coating conditions of the suspension on the porous support. The characteristics of the suspension depend on the type of inorganic particles, the particle size and the suspension. It depends on the concentration, clay, etc., and the coating conditions include the immersion time of the porous support in the suspension and the pulling rate. In adopting the production method of the present invention, the relationship between the supported film thickness per operation, the characteristics of the suspension, and the coating conditions is clarified in advance, and the supported film thickness per operation is determined based on this relationship. adjust.

[0011]

In the inorganic porous membrane obtained by the production method of the present invention, since the supported film thickness of the porous thin film per time is less than 100 times the average particle diameter of the inorganic particles, There are no pinholes or cracks in the thin film supported on the quality support during the drying process and the firing process. Pinholes and cracks also occur in the porous thin film obtained by drying and firing the thin film. There is no such thing.

The particle size of the inorganic particles has a great influence on the shrinkage of the thin film during drying and firing, and in order to prevent the occurrence of pinholes and cracks due to the shrinkage within the thin film, the thin film during shrinkage should be used. It is necessary to reduce the stress in the film thickness direction. Therefore, in the case of a thin film having a large shrinkage ratio, it is preferable to make the film thickness as small as possible,
Regarding the relationship between (supported film thickness / average particle diameter) of the porous thin film, when the shrinkage ratio of the thin film in the film thickness direction is 20% or less, the range does not exceed 100 times, and the shrinkage ratio exceeds 20%. In this case, a range not exceeding 50 times is preferable.

The suspension is a hydrosol solution using water as a dispersion medium, and in the case of an organosol, the surface tension is small and it easily penetrates into the pores of the porous support, and at the same time, the dispersion medium. Has a high vapor pressure and is quick-drying, which is not preferable in terms of generation of pinholes and cracks. Further, the pH of the suspension is preferably in the range of 1 to 4, and when the suspension is on the acidic side, the dispersed particles easily become a linear polymer and penetrate into the pores of the porous support. It is difficult to do so, and it is easy to form a thin film having a uniform thickness. Therefore,
Generation of pinholes and cracks due to shrinkage in the drying process and baking process of such a thin film is further prevented. For this reason, the pH of the suspension used is an important factor in an inorganic porous membrane used as an ultrafiltration membrane that is greatly affected by ultrafine pinholes and cracks. Also,
The concentration of the dispersed phase of the suspension (sol particle / medium molar ratio) is 1
/ 40 to 1/3000 is preferable, and the viscosity is preferably 1 to 50 cp.

[0014]

【Example】

(Example 1) (1) Porous support As a porous support, an alumina-based porous support having a multilayer structure having an intermediate layer on the inner circumference of a pipe-shaped main layer was adopted. In producing this porous support, an inorganic binder and an organic binder were first added to fused alumina having a uniform particle size to prepare a mixed clay, which was used as a raw material by an extrusion molding method to obtain an outer diameter of 10 mm. , Inner diameter 7 mm, length 150
mm pipes are formed, dried and calcined at 1500 ° C. for 3 hours to obtain a pipe-shaped main layer having an average pore diameter of 3.0 μm.
The inner peripheral surface of this main layer is coated with a fine powder of α-alumina, which is dried and fired in the same manner as the main layer to obtain a film thickness of 30 μm.
An intermediate layer having an average pore size of 0.2 μm is carried.

(2) Porous thin film A predetermined amount of titanium isopropoxide is added little by little to distilled water heated in advance to 70 ° C., and the mixture is heated and stirred for 30 minutes or more to scatter and remove isopropyl alcohol to complete hydrolysis. . Nitric acid was added to the obtained titanium hydroxide suspension as an inorganic peptizer to adjust the pH to 1, and the average particle size was 0.04 μm and 0.008 μm.
To obtain a titania hydrosol solution (first solution). Then
Distilled water is added to these first liquids to adjust the molar ratio of titania and water to 1/40 to 1/3000
A liquid was obtained. Further, distilled water, polyvinyl alcohol as an organic binder, and optyl alcohol as an antifoaming agent are added to these second liquids to give a third coating liquid.
A liquid was prepared. The third liquid was coated on the inner peripheral surface of the porous support by a dynamic pressure vacuum method to form a thin film.

The coated thin film is dried together with the porous support, and after drying, it is baked for 3 hours at 800 ° C. for an average particle size of 0.04 μm and 450 for an average particle size of 0.008 μm. The porous thin film was supported on the inner peripheral surface of the porous support by firing at 3 ° C. for 3 hours.

The third liquid prepared in the same manner as described above was used except that the titania hydrosol solution having an average particle size of 0.04 μm was prepared by appropriately changing the pH. The peripheral surface was coated in the same manner as described above, dried and baked to support a porous thin film having an average pore diameter of 0.04 μm. However, the water concentration of the coating liquid is 95 wt. %, The supported film pressure was 2.0 μm, and the film thickness / (average particle size) was 50.

(3) Discussion The film thickness of each porous thin film and the presence or absence of pinholes and cracks in the film were measured by a scanning electron microscope, and the results shown in Tables 1 and 2 below were obtained. As is clear from Table 1, when the supported film thickness is less than 100 times the average particle size (N
O. 3 to NO. 5, NO. 8, NO. In 9), there is no pin pole or crack in the porous thin film. On the other hand, when the supported film thickness exceeds 100 times the average particle size (NO. 1, NO. 2, NO. 6), pinholes and cracks may be present in the porous thin film. It is confirmed. NO. In the porous thin film of No. 6, no pinholes or cracks were confirmed at the end of drying, and it was confirmed that pinholes or cracks were generated during the firing process.

In the case of a porous thin film having an extremely small average pore diameter of 0.008 μm, even if the supported film thickness is 100 times the average particle diameter (NO. 7), some pinholes, The presence of cracks was confirmed. Therefore, when the average particle diameter of the inorganic particles is extremely small, the supported film thickness is less than 100 times, preferably less than 50 times the average particle diameter.

On the other hand, as is clear from Table 2, it is confirmed that the pH of the coating solution greatly affects the occurrence of pinholes and cracks in the porous thin film. The results in the table are for the case where the coating solution prepared under the same conditions was used as the coating solution except that only the pH was changed. However, when the coating solution having a pH of 1 to 4 and an acidic side was adopted (NO. 1 to NO. 4) does not have pinholes and cracks, when pH exceeds 4 (NO. 5 and NO. 6), the existence of pinholes and cracks is confirmed and the pH increases. As a result, it was confirmed that the number of pinholes and cracks increased.

[0021]

[Table 1]

[0022]

[Table 2]

Example 2 (1) Cross-Flow Filtration Test Using each inorganic porous membrane shown in Table 1, a cross-flow filtration test was conducted under the following conditions. A buffer containing 100 ppm of γ-globulin (average molecular weight 156000) was used as a marker, the flow rate was 2.5 m / sec, and the inlet pressure was 3 kg /
The inhibition rate was measured by circulating the inside of the porous thin film at cm ² and analyzing the marker concentration in the filtrate. The results are shown in Table 3.
Shown in.

[0024]

[Table 3]

(2) Consideration As is apparent from Table 3, the inorganic porous film (NO. 3 to No. 3) having no pinholes or cracks in the porous thin film is shown.
NO. 5, NO. 8, NO. 9) shows a high inhibition rate of γ-globulin of 95% or more. Each of these inorganic porous membranes was treated with 90 ° C. HCl aqueous solution (pH = 0), Na
It was immersed in an OH aqueous solution (pH = 14) for 168 hours, and the presence or absence of pinholes and cracks after the immersion was observed, but it was not confirmed. In addition, the above-mentioned cross-flow filtration test was performed on the inorganic porous membranes after these treatments, but no reduction in the γ-globulin inhibition rate was observed, and high corrosion resistance was confirmed.

Claims (1)

[Claims] 1. A thin film is formed by coating a suspension containing inorganic particles on at least one side surface of one or more layers of a porous support, followed by drying and firing to obtain an average pore diameter of 0.
A method for producing an inorganic porous membrane, which is used as an ultrafiltration membrane, in which a porous thin film having a thickness of 05 μm to 0.005 μm is supported, wherein the suspension contains water as a dispersion medium and p
A hydrosol in which H is 1 to 4 is adopted, and the supported film thickness of the porous thin film per time is 1 in the inorganic particles.
A method for producing an inorganic porous membrane, which comprises coating the suspension so that the average particle diameter of the secondary particles is less than 100 times.