JP2007254222A - Porous ceramic film, ceramic filter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous film which solves so called fouling problems of the existing ceramic filter that uses a titania as the aggregate, suppresses the generation of fouling, and has practical strength and corrosion resistance. <P>SOLUTION: The porous ceramic film is one whose aggregate particles that constitute its surface are a zirconia (ZrO<SB>2</SB>) and whose surface roughness Ra is 1 μm or smaller, or one whose aggregate particles that constitute its surface are a zirconia (ZrO<SB>2</SB>) and whose ζ potential of the film surface is from -40 to 40 mV at pH 7. The ceramic filter is one which is obtained by forming the porous ceramic film on the surface of a porous base material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ceramic porous membrane and a ceramic filter with improved fouling properties.

  A ceramic filter in which a porous film with a smaller pore diameter is formed on the surface of a ceramic porous substrate is superior in physical strength and durability compared to a polymer film, etc., so it has high reliability and corrosion resistance. Since it is high, it is useful as a filter for solid-liquid separation in that it is less deteriorated even when washing with an acid alkali or the like, and furthermore, it is possible to precisely control the pore diameter that determines the filtration ability.

  Such a ceramic filter is obtained by forming a separation layer that governs the pore size of the filter on the surface of a base material made of a ceramic porous body or the surface of an intermediate layer formed on the base material. In a wide range of fields such as gas treatment, exhaust gas treatment and medicine / food, it is widely used to remove suspended substances, bacteria, dust, etc. in liquids and gases.

  As an example of such a ceramic filter, alumina particles having a particle size of 12 μm are bonded to a cordierite support (base material) with glass frit, and further alumina particles having a particle size of 1.5 μm are bonded with glass frit. It is known that alumina particles having a particle size of 0.3 μm are subjected to a self-sintering reaction at 1179 ° C. after firing at 1 ° C. (Patent Document 1).

  Further, there is a patent document describing an example of a filter in which a titania separation layer having a thickness of 25 μm and a pore diameter of 0.2 μm is formed on a support (base material) (Patent Document 2).

  In such a ceramic filter, especially for a ceramic filter used for filtration, the performance and formation method of the porous ceramic membrane that determines the filtration capability are technical points. Usually, the ceramic porous film can be obtained by forming a slurry containing ceramic particles on the surface of the base material, firing at a high temperature of 1300 ° C. or higher, and solid-phase sintering the ceramic particles (Patent Document 3). .

  Further, a porous film in which a slurry in which an inorganic sol such as alumina sol or silica sol is added to ceramic particles as an aggregate is formed on the surface of a base material before firing (so-called raw base material) and then co-fired at 1200 ° C. A manufacturing method is disclosed (Patent Document 4).

  Furthermore, there are provided a ceramic porous film, a ceramic porous body, and a method for producing the same, wherein the ceramic particles are fixed by heat treatment at 300 ° C. or lower in a water vapor atmosphere or at 300 to 700 ° C. in an air atmosphere. A ceramic base material is a mixture in which ceramic sol particles having an average particle size of 1/5 or less of the ceramic particles are added and mixed so that the solid content of the ceramic sol is 1 to 30% by weight of the solid content of the ceramic. A method for producing a porous film is disclosed in which a ceramic porous film is formed on a substrate surface by heat treatment at 300 ° C. or lower in a water vapor atmosphere or at 300 to 700 ° C. in an air atmosphere. (Patent Document 5).

  In addition, the manufacturing method of the porous film which forms a ceramic porous film on the base-material surface by heat-processing at 300 degrees C or less under water vapor atmosphere or 300-700 degreeC in air | atmosphere atmosphere using titania as a binder is disclosed. (Patent Document 6).

  Furthermore, ceramics having a titania separation layer with an average pore size of 0.08 to 1 μm and a film thickness of 5 to 20 μm as a ceramic filter that is excellent in both fouling and sterilization properties and can be suitably used for water purification treatment, etc. A filter is disclosed (Patent Document 7).

  Further, even if the filter has a titania separation layer, a filter having an average pore diameter of less than 0.08 μm or a film thickness of more than 20 μm has poor fouling properties. In particular, in the water purification treatment, when the turbidity of the raw water is high, fouling is remarkable when dead end filtration is adopted as a filtration method (see Patent Document 7).

  Furthermore, although the porous film manufactured by the method of Patent Document 7 has been temporarily taken with respect to fouling properties, it is considered that it adheres electrostatically as described later because of the surface potential of the titania film. The effect is limited to the filing substances, particularly humic acid.

  In other words, in the ceramic filter for water purification by the filtration membrane-forming method using the current titania as an aggregate, there is generally a so-called fouling problem that substances in river water adhere to the membrane surface.

  Here, fouling is generally understood to mean a phenomenon in which hardly soluble components and high molecular solutes, colloids, fine solids, and the like contained in raw water are deposited on the membrane to reduce the permeation flow rate. When deposition occurs in the membrane, it is said to be clogged. Fouling proceeds with the time of membrane filtration. It is understood that the degree to which fouling can be recovered by cleaning the film surface varies greatly depending on the fouling material, the film, and the cleaning method.

  For example, it is not clear what the fouling substance is when the river water is filtered, but it is thought to be caused by the minute organic matter components of humic acid, sugar, and protein sugar in the river water.

  A part of the substance adhering to the membrane surface is thinly removed by a regular backwash operation during operation. However, the components that remain without being removed gradually clog the membrane, making it impossible to perform the filtration operation. Therefore, it was necessary to remove the filter, clean the medicine, and regenerate it.

  However, with respect to the fouling mechanism of humin, as schematically shown in FIG. 3, humin has a nano-scale size and enters the pores of the filter. Since humic is adsorbed in the pores of the filter, it does not peel off easily even if it is removed. The leakage of humic to the secondary side was 70 to 80%, and since it was gradually pushed out and deposited, there was a problem that backwashing became ineffective.

Japanese Examined Patent Publication No. 6-67460 Japanese Patent No. 2670967 Japanese Patent Laid-Open No. 2001-300922 JP 63-274407 A JP-A-10-235172 Japanese Patent Laid-Open No. 10-236887 JP 2003-230823 A

  The present invention has been made in view of the above-mentioned problems of fouling, the purpose of which is to suppress the occurrence of fouling, thereby reducing the frequency of removing the filter, cleaning the medicine, and regenerating, It is to provide a porous film having practical strength and corrosion resistance.

As a result of diligent research, the present inventors have considered that the fouling substance has a charge and is adsorbed electrostatically on the film, and thus zirconia having a film surface potential lower than that of conventional titania (TiO ₂ ). It has been found that changing the aggregate particles to (ZrO ₂ ) or forming a zirconia (ZrO ₂ ) film on the conventional titania (TiO ₂ ) has the effect of reducing the adhesion of fouling substances. Reached.

  In addition, as a result of further earnest research, the present inventors consider that the fouling substance is firmly attached to the unevenness of the film surface by the anchor effect, and by forming a smoother film surface than conventional, fouling It has been found that there is an effect of reducing the adhesion of substances, and the present invention has been achieved.

  That is, according to the present invention, there is provided a ceramic porous membrane characterized in that the aggregate particles constituting the surface are zirconia and the surface roughness Ra is 1 μm or less.

Further, according to the present invention, there is provided a ceramic porous membrane characterized in that the aggregate particles constituting the surface are zirconia (ZrO ₂ ), and the membrane surface zeta potential is −40 mV to 40 mV at pH 7. Is done.
Furthermore, according to the present invention, there is provided a ceramic filter characterized in that the ceramic porous film is formed on the surface of a porous substrate.

  The ceramic porous membrane and the ceramic filter of the present invention suppress the occurrence of fouling, have practical strength and corrosion resistance, and have a particularly excellent fouling suppression effect compared to those using known titania. Have. As a result, since the differential pressure rise is small, the frequency of removing the filter, cleaning it with chemicals and regenerating it is reduced, and the cost is reduced. Furthermore, since the differential pressure rise is small, it can be operated with a high water permeability, and the membrane area can be reduced, and the cost is reduced. In addition, the pressure rise is small, so that the load on the apparatus can be reduced. .

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be specifically described. However, the present invention is not limited to the following embodiment, and is within the scope of the gist of the present invention. Based on this knowledge, it should be understood that design changes, improvements, etc. can be made as appropriate.

First, the ceramic porous membrane of the present invention will be described in detail. In the following description, “pore diameter” and “particle diameter” both mean “average pore diameter” and “average particle diameter”.
Usually, the ceramic porous film refers to a thin film having a thickness of about 0.5 to 500 μm made of a ceramic porous body. For example, it is used in the form of a ceramic filter in which a thin film is formed on the surface of a ceramic porous substrate, and becomes a central part of the filter function of the filter.

In the ceramic porous membrane of the present invention (hereinafter referred to as a porous membrane), at least the aggregate particles constituting the surface are made of zirconia (ZrO ₂ ), and the zirconia (ZrO ₂ ) particles are formed by solid phase sintering on the surface. Take a combined structure. In the portion excluding the surface, the aggregate particles are not necessarily zirconia particles. As described above, since the surface is made of zirconia having high corrosion resistance, it is usually possible to form a porous film having high corrosion resistance even at a bonding portion sensitive to corrosion.

  The zirconia aggregate particles in the present invention are ceramic particles that form the skeleton of the porous membrane, and the pore size of the porous membrane, that is, the filter function, is determined by the particle size of the aggregate particles. In other words, a porous membrane having a desired pore size can be obtained by appropriately selecting the particle size of the aggregate particles. The object of the present invention is to form a porous membrane having a pore diameter of about 0.05 to 1 μm using aggregate particles having a relatively small particle diameter of 0.1 to 3 μm.

The material of the aggregate particles constituting the portion excluding the surface of the porous film is not particularly limited as long as it is ceramics. For example, alumina (Al ₂ O ₃ ), titania, mullite (Al ₂ O ₃ .SiO ₂ ) ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), spinel (MgO · Al ₂ O ₃ ), or a mixture thereof can be used. From the viewpoint of being stable, alumina, titania and zirconia are preferred.

In the porous membrane according to the present invention, at least the aggregate particles constituting the surface are made of zirconia (ZrO ₂ ), the surface roughness is 1 μm or less in Ra, and / or the membrane surface zeta potential is Its characteristic is that it is -40 mV to 40 mV at pH 7.
In the porous membrane according to the present invention, when the surface roughness is 1 μm or less in Ra, adhesion of the fouling substance is greatly reduced. Moreover, when the membrane surface zeta potential of the porous membrane according to the present invention is -40 mV to 40 mV at pH 7, there is an effect that adhesion of fouling substances is also greatly reduced.

  Next, the ceramic filter of the present invention will be described. The ceramic filter of the present invention (hereinafter referred to as filter) is formed by forming the above-described porous film of the present invention on the surface of a porous substrate.

  The porous base material (hereinafter referred to as the base material) in the present invention is a porous body made of ceramics and refers to a member constituting the outer shape of the filter. However, since the porous film formed exclusively on the surface of the substrate fulfills the filter function, a porous body having a pore size of 1 to 50 μm and a relatively large pore size can be used for the substrate itself.

  The material of the base material is not particularly limited as long as it is ceramics. For example, alumina, titania, mullite, zirconia, or a mixture thereof can be suitably used. Moreover, you may use what the ceramic layer has already coat | covered the ceramic base material surface as a base material. A porous film is formed on the surface of such a substrate using a manufacturing method described later to obtain a filter.

  Finally, a method for producing the ceramic filter of the present invention will be described. In this production method, a slurry containing zirconia, which is aggregate particles, is formed on the surface of a porous substrate to form a film-formed body, and then the film-formed body is subjected to an atmosphere at 900 to 1100 ° C. A porous film is formed on the substrate surface by heat treatment. As a method of forming the slurry on the substrate, a known filtration method can be used, but in order to obtain a smooth surface, for example, a dip coating method (dip coating method) is particularly preferable.

  The slurry concentration depends on the film thickness to be formed, but is usually 100% by weight or less. When the slurry concentration is higher than 100% by weight, aggregation of aggregate particles occurs and defects in the film are likely to occur. Note that an organic binder such as PVA may be added to the slurry to improve the film formability, and a pH adjuster, a surfactant, and the like may be added to improve the dispersibility.

  Next, after the slurry is formed, heat treatment is performed in an air atmosphere, and the heat treatment is performed under a temperature condition of 900 to 1100 ° C. When the temperature is lower than 700 ° C., a strong joint cannot be formed between the aggregate particles, and when the temperature is higher than 1100 ° C., cracks and the like are generated.

  Moreover, when manufacturing a filter, the slurry may be formed on the surface of a porous substrate made of ceramics to form a film-formed body, and then the above heat treatment may be performed. The film forming method is not particularly limited, and for example, a method of forming a film by directly applying slurry to the surface of the porous substrate can be used.

1 (a) to 1 (c) show an example of a film forming method on the surface of a porous substrate by a dip coating method. First, as shown in FIG. 1 (a), a lotus root-like porous substrate is used. The material 1 is set on a jig 2 provided with a tank 3 so that the flow path (cell) direction is vertical. Next, as shown in FIG. 1 (b), a slurry 4 containing a binding material made of zirconia (ZrO ₂ ) is introduced into the tank 3, and a cell (flow passage) of the porous substrate 1 from above the porous substrate 1. 5 is passed through in a downward direction, and a slurry film 6 formed on the inner surface of the cell 5 of the porous substrate 1 as shown in FIG. 1C is obtained. The obtained porous substrate 1 is then dried and fired to produce a ceramic filter having a ceramic porous film formed on the surface.

  Hereinafter, the present invention will be described in detail with reference to examples in which a porous film is formed on the surface of a porous substrate to form a filter, but the present invention is not limited to these examples.

(Example 1)
A zirconia powder (trade name: TZ8Y, specific surface area: BET 16 ± 2 m ² / g) manufactured by Tosoh Corporation was added at 60 wt% with respect to water, and dispersed with a 2 mmφ zirconia ball for 7 hr in a pot mill to obtain a zirconia raw material. This was added so that it might become solid content 10wt% with respect to water. Furthermore, 3-5 wt% of a dispersant (trade name: A-6114) manufactured by Toagosei Chemical Co., Ltd. was added to the zirconia powder to finally obtain a zirconia slurry having a solid content of 10 wt%. A monolithic product (lotus-like base material) of 30 mmφ (pore diameter) × 1 m (length) manufactured by Nippon Choshi Co., Ltd. having a pore diameter of 0.18 μm was used as the base material, and this was installed vertically, and the above-mentioned zirconia was installed from the top. The slurry was passed through a monolith cell. This was calcined at 950 ° C. for 3 hours to obtain Sample 1. The surface roughness (Ra) of the porous film formed on the surface of Sample 1 was 0.9 μm. The membrane surface zeta potential was −30 mV at pH 7.

(Example 2)
Sample 2 was obtained in the same manner as in Example 1 except that it was fired at 1100 ° C. for 3 hours. The surface roughness (Ra) of the porous film formed on the surface of Sample 2 was 0.8 μm. The membrane surface zeta potential was −30 mV at pH 7.

Example 3
Example 1 except that Tosoh zirconia powder (trade name: TZ8Y) was used instead of Tosoh zirconia powder (trade name: TZ8YS, specific surface area: BET 7 ± 2 m ² / g). Thus, sample 3 was obtained. The surface roughness (Ra) of the porous film formed on the surface of Sample 3 was 1.0 μm. The membrane surface zeta potential was −35 mV at pH 7.

(Comparative example)
A sample of a comparative example was obtained in the same manner as in Example 1 except that titania aggregate was used instead of zirconia powder manufactured by Tosoh Corporation. The surface roughness (Ra) of the porous film formed on the surface of this sample was 3.4 μm. The membrane surface zeta potential was −50 mV at pH 7.

(Discussion)
The electron micrographs shown in FIGS. 2A and 2B show the porous film of Sample 1 (Example 1), and the electron micrographs shown in FIGS. 2C and 2D show the porous film of the comparative example. Show. The porous membrane of sample 1 (Example 1) has an average pore diameter of 0.1 μm and a surface roughness of 0.9 μm, and the porous membrane of the comparative example has an average pore diameter of 0.18 μm and a surface roughness. Was 3.4 μm. It is clear that the porous membrane of the present invention is smoother than the comparative example.

Next, the fouling property was evaluated.
FIG. 3 shows an outline of the fouling model experiment. The aqueous solution of humic acid was passed through various membranes (Sample 1-3 and Comparative Example) to evaluate the differential pressure on the membrane surface. Each membrane-coated porous substrate 11 was placed in a casing 10 having a structure in which an outer wall and an inner wall were separated, and river water was subjected to constant flow filtration. The humic acid aqueous solution was adjusted to pH 7 by adding 1 ppm of humic acid to river water, and was sent from the raw water tank 12 via the liquid feed pump 13. The filtration direction is from the inner wall side to the outer wall side, and the filtration method is dead-end filtration. The filtration flow rate is a constant flow rate of 5 m / day. When filtration is performed, dirt accumulates on the inner wall surface and the pressure rises. In order to prevent the increase, 5 kg / cm ² of high-pressure water was flowed from the back wall to the inner wall side from the outer wall side every 30 minutes to wash the film deposits. Under these conditions, the operation was continued for about 24 hours and the change in pressure was observed. The behavior of the pressure increases with the operation time and decreases after the cleaning, but even after the cleaning, the initial pressure is not recovered and the pressure gradually increases. The pressure difference at the end of the operation with respect to the pressure in the initial operation was obtained and graphed with Samples 1 to 3 (Examples 1 to 3) and Comparative Example. Here, a film having a low pressure increase rate is a film that is not easily soiled and has excellent fouling properties (fouling resistance).

  4A and 4B show the results of the fouling experiment. FIG. 4A shows a change in the differential pressure over time. Samples 1, 2 and 3 (Examples 1, 2 and 3) do not increase the differential pressure and show excellent fouling properties, but the comparative example shows that the differential pressure increases after 12 hours. Recognize. FIG. 4B is an enlarged view of data from 8 hours to 12 hours. Thus, it can be seen that backwashing is not effective in the comparative example.

  The ceramic porous membrane and the ceramic filter of the present invention have practical strength and corrosion resistance, and have an excellent effect of suppressing fouling generation, so that they can be operated with a high water permeability, and the membrane area can be reduced. In addition to cost reduction, since the pressure rise is small, the load on the apparatus is small, which is extremely useful as a filter for solid-liquid separation.

(A)-(c) is a schematic diagram which shows an example of the film-forming method to the porous base material surface by a dip coating method. (A) and (b) are the electron micrographs which show the porous membrane of sample 1 (Example 1), (c) and (d) are the electron micrographs which show the porous membrane of a comparative example. It is explanatory drawing which shows the outline | summary of a fouling model experiment. (A) (b) is a graph which shows the result of the fouling test of Example 1, 2, 3 and a comparative example.

Explanation of symbols

1: porous substrate, 2: jig, 3: tank, 4: slurry, 5: cell, 6: slurry film, 10: housing, 11: porous substrate with film, 12: raw water tank, 13: Liquid feed pump, 14: backwash tank.

Claims (3)

A ceramic porous membrane characterized in that aggregate particles constituting the surface are zirconia (ZrO ₂ ), and the surface roughness Ra is 1 μm or less. A porous ceramic membrane characterized in that aggregate particles constituting the surface are zirconia (ZrO ₂ ), and the membrane surface zeta potential is −40 mV to 40 mV at pH 7.   A ceramic filter comprising the porous ceramic substrate according to claim 1 or 2 formed on a surface of a porous substrate.