JP2009241054A - Method for manufacturing of ceramic filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing of a ceramic filter of high separation ability in which the membrane thickness of a ceramic porous membrane which is formed on the surface of a porous base material is thin, uniform and has little peeling of membrane. <P>SOLUTION: On the porous base material 4 in which a UF membrane which has a small average fine pore diameter on an MF membrane is provided, a ceramic sol 21 in which a ceramic ingredient concentration, water concentration and solid ingredient are properly managed is used, and the number of times of calcination is reduced. Thereby, a ceramic filter of a high separation ability whose frequency of the peeling of membrane of the ceramic porous membrane is low is manufactured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a ceramic filter having a ceramic porous film formed thereon, and more particularly, to a method for manufacturing a ceramic filter that forms a uniform ceramic porous film with few defects and a thin film thickness.

  Conventionally, various methods are known for forming a ceramic porous film on a porous substrate. For example, a hot coat method is known (see Non-Patent Document 1). This method is a method for forming a porous film on the outer surface of a heated tube base material by rubbing and applying the cloth containing the ceramic sol to the tube base material.

  A method of forming a porous film on the inner surface of a tube-shaped or cylindrical lotus-shaped monolithic porous substrate by a filtration film-forming method is also known (see Patent Documents 1 and 2). This method is a method of forming a porous film on the inner surface of the porous substrate by keeping the outer surface side lower than the inner surface side with which the sol solution of the porous substrate contacts.

JP-A-3-267129 JP-A 61-238315 Journal of Membrane Science, 149 (1988), 127-135.

  However, the hot coating method has a problem that the entire surface of the tube base material cannot be uniformly formed, and only the outer surface of the tube base material can be formed. Further, it cannot be applied to a monolith type substrate. On the other hand, in the filtration film formation method, the solvent present in the pores of the porous base material may flow out to the film side during drying after film formation, resulting in film peeling. There is a problem that defects occur in the porous film formed on the inner surface of the material. The dip coating method can be applied to a monolithic substrate, but the number of film formation is large.

  An object of the present invention is to provide a method for producing a ceramic filter having a uniform ceramic porous film that is formed with a small number of times of adhesion of a ceramic sol to a porous substrate, has few defects, is thin, and has a uniform thickness. is there. In particular, the present invention provides a method for producing a ceramic filter in which a ceramic porous membrane having an average pore diameter of 1 nm or less is formed.

  In order to solve the above-described problems, according to the present invention, a ceramic sol with an optimized ceramic component concentration, moisture concentration, and solid component is attached on a porous substrate, and the ceramic sol is dried by blowing, and then It discovered that the said subject could be solved by baking and forming a ceramic porous membrane. That is, according to this invention, the manufacturing method of the ceramic filter in which the following ceramic porous membranes were formed is provided.

  [1] A ceramic sol having a ceramic component concentration of 0.05 to 0.7% by mass is applied onto the surface of the porous substrate, and a portion of the ceramic sol falls due to its own weight and the surface of the porous substrate The remaining ceramic sol that is removed from above and not removed is attached onto the surface of the porous base material, and then the ceramic sol attached to the porous base material is blown and dried, followed by firing to perform ceramics A method for producing a ceramic filter for forming a porous membrane.

  [2] The method for producing a ceramic filter according to [1], wherein the solvent of the ceramic sol is ethanol.

  [3] The method for producing a ceramic filter according to [1] or [2], wherein the moisture concentration of the ceramic sol is 0.03 to 3% by mass.

  [4] The method for producing a ceramic filter according to any one of [1] to [3], wherein the ceramic sol that can pass through a sieve having an opening of 10 μm is used.

  [5] The ceramic according to any one of [1] to [4], wherein the ceramic sol is fired after a plurality of steps of attaching the ceramic sol to the surface of the porous substrate and performing air drying. A method for manufacturing a filter.

  [6] The method for producing a ceramic filter according to any one of [1] to [5], wherein the ceramic component is silica, titania, or zirconia.

  In the method for producing a ceramic filter of the present invention, a ceramic sol having a ceramic component concentration of 0.05 to 0.7% by mass is deposited on the surface of a porous substrate, the ceramic sol is dried by blowing, and then fired. . In the method for producing the ceramic filter, the porous ceramic membrane becomes dense and the average pore diameter can be reduced. Thereby, a ceramic porous membrane with little membrane peeling is formed, and a high-separability ceramic filter can be manufactured. In addition, in the method of attaching the ceramic sol to the porous base material, even if the porous base material becomes long, the difference in the amount of ceramic sol attached to the top and bottom of the porous base material is unlikely to occur. A film that is homogeneous in direction can be obtained. Furthermore, after performing the process of attaching the ceramic sol to the surface of the porous substrate and performing blow drying for a plurality of times, firing is performed, whereby the number of firings is reduced and the thermal history of the ceramic porous film is reduced. Thereby, a ceramic filter having high hydrophilicity and high permeation amount can be manufactured.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

  The ceramic porous membrane will be described in detail. The ceramic porous membrane is used, for example, in the form of a ceramic filter in which a thin film is formed on the surface of a ceramic porous substrate, and is a portion that forms the center of the filtering function of the filter. FIG. 1 shows an embodiment of a ceramic porous membrane 1 and a porous substrate 4 formed by the method for producing a ceramic filter of the present invention. Here, as one embodiment of the method for producing a ceramic filter of the present invention, a porous UF membrane 2 that is an ultrafiltration membrane having an average pore diameter of 0.5 to 20 nm is formed on a microfiltration membrane (MF membrane) 3. A description will be given using the base material 4. As the UF film 2, for example, titania can be adopted. In the present case, the formation of the ceramic porous membrane 1 refers to the formation of the entire layer 1 denoted by reference numerals 1a to 1d in FIG. Adhesion refers to fixing the required amount by bringing the ceramic sol into contact with the porous substrate 4 or the surface of the ceramic porous film formed in the previous step in order to form the layers 1a to 1d. .

  Next, an embodiment of the ceramic filter 11 in which a ceramic porous film is formed by the method for producing a ceramic filter of the present invention will be described with reference to FIG. A ceramic filter 11 having a ceramic porous film formed by the method for manufacturing a ceramic filter of the present invention has a monolith shape having a plurality of cells 13 defined by partition walls 12 and forming axial fluid passages. . In the present embodiment, the cell 13 has a circular cross section, and the ceramic porous membrane 1 as shown in FIG. 1 is formed on the inner wall surface thereof. The cell 13 may be formed to have a hexagonal cross section or a square cross section. According to such a structure, for example, when a mixture (for example, water and acetic acid) is introduced into the cell 13 from the inlet side end face 14, one of the mixture is formed on the ceramic formed on the inner wall surface of the cell 13. Since it is separated in the porous membrane, passes through the porous partition wall 12 and is discharged from the outermost wall of the ceramic filter 11, the mixture can be separated. That is, the ceramic porous membrane formed on the ceramic filter 11 can be used as a separation membrane, and has, for example, high separation characteristics for water and alcohol or water and acetic acid.

  Since the ceramic porous membrane 1 of the present invention is formed on the inner peripheral surface (inner wall surface) of the porous substrate 4, it is a relatively long cylindrical porous substrate having a length of 50 cm or more. Alternatively, a lotus root-shaped porous substrate can be suitably used.

  The porous substrate 4 will be described. The porous substrate 4 is formed as a cylindrical monolith filter element made of a porous material by extrusion molding or the like. As the porous material, for example, alumina can be used from the viewpoint that the change in the average pore diameter of the filtration part due to the corrosion resistance and the temperature change is small and sufficient strength can be obtained, but other than alumina, cordierite, mullite can be used. Ceramic materials such as silicon carbide can also be used. The porous substrate 4 has an average pore diameter of the surface (outermost surface layer) on which the ceramic porous film 1 is formed, preferably 0.5 to 20 nm, more preferably 0.5 to 10 nm. It may be a porous body having a small number of pores (in the embodiment of FIG. 1, the UF membrane 2 forms the outermost surface layer in the above range).

  The UF membrane 2 that is an ultrafiltration membrane having an average pore diameter of 0.5 to 20 nm formed on the surface of the porous substrate 4 will be described. The UF film 2 has a feature that the surface has less irregularities than the MF film 3. Therefore, when the ceramic porous membrane 1 is formed on the UF membrane 2, the ceramic porous membrane 1 can be a thin and uniform membrane with a smooth membrane surface and few defects. That is, it is possible to produce a ceramic filter with high resolution, high transmission speed, and low cost. On the other hand, when the ceramic porous film 1 is formed directly on the MF film 3, as shown in FIGS. 3A to 3E, the entire surface of the MF film 3 with many irregularities is covered with the ceramic porous film 1. Therefore, it is necessary to form a thick ceramic layer, and the ceramic porous membrane 1 has a low permeation rate. In order to prevent the occurrence of cracks, it is necessary to thinly adhere the ceramic sol to the porous substrate at a time. Therefore, as shown in FIG. 3E, the porous base material having the MF film 3 that requires the formation of a thick ceramic layer as the outermost surface layer increases the number of ceramic sol adhesion steps, resulting in high cost. In addition, as shown in FIG. 3E, the ceramic porous membrane 1 is thin at the convex portion 6 on the surface of the MF membrane 3 and the ceramic porous membrane 1 is thick at the concave portion 5 on the surface of the MF membrane 3. Be filmed. Therefore, the irregularities on the surface of the MF film 3 cause defects such as inhomogeneities and cracks in the ceramic porous film 1. From the above, it is desirable that the ceramic porous membrane 1 be formed with the surface of the UF membrane 2 as the outermost surface layer of the porous substrate.

  Next, a method for preparing a ceramic sol will be described below with a specific example of an embodiment in which silica is used as the ceramic component of the ceramic sol. However, ceramic sol containing titania or zirconia as a ceramic component can be used instead of silica.

  First, the silica component concentration of the silica sol will be described. A silica sol for forming a porous silica film is prepared. The silica sol is hydrolyzed at 5 to 100 ° C. for 1 to 12 hours in the presence of nitric acid together with a metal alkoxide to form a sol, and the sol is diluted with ethanol. The ethanol concentration of the silica sol after ethanol dilution is preferably 96% by mass. Although it is possible to dilute with water instead of diluting with ethanol, diluting with ethanol can adhere to the surface of the porous substrate more thinly, and make a porous membrane with a high permeation rate. Can do. When the silica component concentration in the silica sol is adjusted to 0.05 to 0.7% by mass, preferably 0.1 to 0.4% by mass, defects such as separation of the porous silica membrane and UF membrane Therefore, it is possible to form a thin porous silica film having a high resolution.

  Subsequently, the solid component in the silica sol will be described. When the silica sol is passed through a sieve having an aperture of 10 μm or less and then attached to the porous substrate, the silica sol has few defects such as separation of the porous silica membrane and UF membrane, and a highly porous silica porous membrane is formed. it can. In addition, many porous silica films formed by the conventional method without passing through the sieving process exist in such a manner that silica agglomerates having a particle size of about 50 μm are buried on the surface of the porous silica film and inside the film. In the porous silica membrane in which the silica agglomerates are frequently observed, membrane peeling tends to occur frequently.

  Next, the moisture concentration of the silica sol will be described. The silica sol is preferably used at a water concentration of 0.03 to 3% by mass, more preferably a water concentration of 0.03 to 1.5% by mass, particularly preferably a water concentration of 0.03 to 1.0%. When the content is% by mass, there are few defects such as exfoliation of the porous silica membrane and UF membrane, and it is possible to form a thin, uniform, high-separation silica porous membrane. In preparing a silica sol having a moisture concentration of less than 1.0% by mass, the silica sol is preferably dehydrated before adhering to the porous substrate. For example, the silica sol is dehydrated with various desiccants (molecular sieves, silica gel, etc.). Preferably, a desiccant by hydrate formation such as calcium sulfate, which is free from the fear of adsorbing silica sol, is used.

  Next, adhesion of the ceramic sol to the porous substrate in the method for producing a ceramic filter of the present invention will be described. As shown in FIG. 4A, in the present invention, the ceramic sol adheres to the porous substrate by applying the ceramic sol 21 onto the surface of the porous substrate 4 and a part of the ceramic sol 21 falls due to its own weight. The remaining portion of the ceramic sol 21 that has been removed from the surface of the porous substrate 4 and not removed is adhered to the surface of the porous substrate 4. The method of bringing the ceramic sol 21 into contact by applying it from the upper side of the porous substrate 4 is also preferable for the following reason. According to the above method, since no water pressure is applied to the film formation surface of the porous substrate 4, the penetration of the ceramic sol 21 into the MF film is suppressed by the capillary force, so that the penetration of the ceramic sol 21 into the MF film is suppressed. It is done. In addition, even when the porous substrate 4 becomes longer, a difference in the amount of the ceramic sol 21 attached between the upper and lower portions of the porous substrate 4 is difficult to occur, and a uniform film in the length direction is formed. Obtainable. In addition, regarding the method of attaching the ceramic sol on the surface of the porous substrate, the applicant applied the above-described method of attaching the ceramic sol on the porous substrate, which is higher than the dip coating method. Has already been filed (see Japanese Patent Application No. 2006-284400).

  A method for attaching the ceramic sol 21 by applying the ceramic sol 21 from above the porous substrate 4 will be described in detail. As shown in FIG. 4A, the outer peripheral surface of the porous substrate 4 is masked with a masking tape 22. For example, the porous substrate 4 is fixed to the lower end of the wide-mouth funnel (not shown), and the ceramic sol 21 is poured from the upper portion of the porous substrate 4 to pass through the cell 13. In other words, the ceramic sol 21 is deposited on the surface of the cell 13. After this, it is more preferable that the porous substrate 4 is shaken by hand several times to remove excess ceramic sol 21 and removed.

  A method for drying the ceramic sol 21 attached on the porous substrate 4 will be described. As shown in FIG. 4B, the ceramic sol 21 adhered on the porous substrate 4 is dried by sending air into the cell 13 with a dryer or the like. The temperature of the wind is preferably 10 to 80 ° C. When air having a temperature lower than 10 ° C. is passed, the drying of the ceramic sol 21 adhering to the surface of the cell 13 does not progress, so that a dense film cannot be obtained and the film has a large average pore diameter. Moreover, if warm air is passed at a temperature higher than 80 ° C., cracks are likely to occur on the film surface, which is not preferable. The speed at which the wind for drying passes through the cell 13 may be 0.1 to 100 m / sec. If the speed at which the wind passes through the cell 13 is 0.1 m / second or less, the time required for drying becomes too long, and if the speed at which the wind passes through the cell 13 is 100 m / second or more, the film surface Cracks are likely to occur, which is not preferable. Thus, it can be set as the structure where a ceramic porous membrane turns into a film | membrane densely to a UF membrane by drying by ventilation. Since it is considered important that the solvent is dried from the film surface, evaporation of the solvent contained in the ceramic sol 21 from the porous substrate 4 side may be prevented by masking the outer peripheral surface.

  The ceramic porous film is formed by continuously drying the ceramic sol 21 after the ceramic sol 21 is deposited on the surface of the porous substrate 4.

  In the formation of the ceramic porous film, the number of times of adhesion depends on the ceramic component concentration of the ceramic sol 21. When the ceramic component concentration of the ceramic sol 21 is 0.5 to 0.7 mass%, 3 to 5 times, and when the ceramic sol 21 is 0.3 to 0.5 mass%, 6 to 8 times, 0.05 to 0.3 When mass%, the ceramic sol is attached 9 to 13 times.

  Thereafter, the temperature is raised at 100 ° C./hr, held at 500 ° C. for 1 hour, and then lowered at 100 ° C./hr (hereinafter, this operation is referred to as firing).

  The conventional method of forming a ceramic porous membrane is performed in a sequence of steps of adhesion of ceramic sol to the porous substrate, drying, and firing. With regard to the above process, the number of times of firing can be reduced by firing after a plurality of times of attaching the ceramic sol to the surface of the porous substrate and drying the ceramic sol. When firing after performing the adhesion and drying steps a plurality of times, the ceramic porous membrane with suppressed defects such as peeling of the ceramic porous membrane and UF membrane as compared with the case of the conventional method step Film formation is realized, and a ceramic filter with high resolution can be manufactured. In the case of firing after the adhesion and drying steps are performed three times, the ceramic porous film is peeled off from the surface of the porous base material rather than firing after the adhesion and drying steps are performed twice. This is preferable because defects can be reduced and a ceramic filter with high resolution can be manufactured. In addition, since the number of firings is reduced and the thermal history of the ceramic porous membrane is reduced, a ceramic filter having high hydrophilicity and high permeation amount can be produced.

  In summary, (a) by optimizing the ceramic component concentration of the ceramic sol to be adhered to the porous substrate, a thin, uniform and porous ceramic porous membrane with little membrane peeling is formed, and a high-separation ceramic A filter can be manufactured. Furthermore, in addition to the above (a), when (b) reducing the moisture concentration in the ceramic sol, (c) removing aggregated particles in the ceramic sol, and (d) reducing the number of firings, A ceramic porous membrane that is thin, uniform, has less membrane peeling, and has a high permeation amount can be formed, and a ceramic filter with a high resolution can be manufactured. Regarding the combination of (a) to (e), among the (a) to (e), the ceramic filter by the manufacturing method using all three rather than two than three is more preferable. Has higher resolution.

  EXAMPLES Hereinafter, although the manufacturing method of this invention is demonstrated in detail by an Example, this invention is not limited by these Examples. First, the porous substrate, the ceramic sol, and the film forming method used in this example will be described.

Example 1
(1) Porous substrate A porous substrate having a monolith shape (outer diameter 30 mm, cell inner diameter 3 mm × 37 cells, length 80 mm) on which a UF membrane 2 having an average pore diameter of 0.5 to 20 nm is formed is used. It was. Both ends of the porous substrate were sealed with glass.

  An object of the present invention is to optimize the conditions of the ceramic sol to be attached to the surface of the porous substrate and the steps of attaching, drying and firing the ceramic sol in the formation of the ceramic porous film. It should be noted that the embodiment in which the UF film with few irregularities is the outermost surface layer of the porous substrate can eliminate as much as possible the influence of variations in the properties of the porous substrate on the film formation of the ceramic porous film. Adopted.

(2) Ceramic sol In Example 1, the ceramic sol was silica sol. The silica sol was obtained by hydrolysis with metal alkoxide in the presence of nitric acid at 5-100 ° C. for 1-12 hours. The obtained silica sol was diluted with ethanol to prepare a silica component concentration of 0.7% by mass. Note that the water concentration of the silica sol immediately after preparation was 1% by mass (the water concentration was measured by the Karl Fischer method). A titania sol (see Example 22 and Comparative Example 3) and a zirconia sol (see Example 23 and Comparative Example 4) were also prepared in the same manner as described above.

(3) Adhesion of silica sol to porous substrate As shown in FIG. 4A, the outer peripheral side surface of the sample (porous substrate 4) was sealed with a masking tape 22. The porous substrate 4 was fixed to the lower end of the wide-mouth funnel, and 60 ml of silica sol 21 was poured from the top of the porous substrate 4 and allowed to pass through the cell 13. It was confirmed that the silica sol 21 adhered to the entire inner wall.

(4) Drying As shown in FIG. 4B, drying was performed for 1 hour using a dryer so that air at room temperature passed through the cells 13 of the porous substrate 4 into which the silica sol had been poured.

(5) Firing The sample was heated at 100 ° C./hr, held at 500 ° C. for 1 hour, and then cooled at 100 ° C./hr. Said (3)-(5) was performed 4 times and Example 1 was obtained. In (3), the same silica sol 21 was used repeatedly. The water concentration of the residual silica sol 21 after completion of the fourth (3) was 5% by mass.

(Examples 2 and 3)
In the ceramic filter manufacturing method of Example 1, Example 2 performed (3)-(5) 8 times using the silica sol 21 whose silica component density | concentration is 0.35 mass%. In Example 3, in the ceramic filter manufacturing method of Example 1, (3) to (5) were performed 13 times using silica sol 21 having a silica component concentration of 0.05 mass%. In (3), the same silica sol 21 was used repeatedly. In both Examples 2 and 3, the moisture concentration of the residual silica sol 21 after the completion of the eighth (3) was 5% by mass.

(Examples 4 to 6)
In the ceramic filter manufacturing method of Example 1, each time (3) before, the silica sol 21 was passed through a sieve having an opening of 50 μm, and Example 4 was obtained by using the silica sol 21 that passed through the sieve in (3). Example 5 was obtained using a sieve having an aperture of 10 μm and Example 6 using an aperture of 1 μm in the same manner as in the method for producing a ceramic filter of Example 4. Examples 4 to 6 are the same as Example 1 except for the sieving process. In all of Examples 4 to 6, the water concentration of the residual silica sol 21 after the completion of the fourth (3) was 5% by mass.

(Example 7)
In the ceramic filter manufacturing method of Example 1, the moisture concentration of the residual silica sol 21 was measured after the end of (3) each time. In the above measurement, when the water concentration exceeded 3 mass%, silica sol 21 was newly prepared and used in the following (3) to obtain Example 7. Other steps are the same as those in the first embodiment.

(Example 8)
In the ceramic filter manufacturing method of Example 1, Example 8 was obtained by using the newly prepared silica sol 21 having a water concentration of 1% by mass for (3) each time. Other steps are the same as those in the first embodiment.

Example 9
In the method for producing a ceramic filter of Example 1, Example 9 was obtained by using silica sol 21 newly prepared and dehydrated with calcium sulfate and having a water concentration of 0.03 mass% for each time (3). Other steps are the same as those in the first embodiment.

(Examples 10 to 13)
In the method for producing a ceramic filter of Example 8, Example 10 was obtained by using the newly prepared silica sol 21 having a water concentration of 1% by mass through a sieve having an opening of 1 μm and using (3). Other steps are the same as those in Example 8. In the ceramic filter manufacturing method according to Example 10, Example 11 uses silica sol 21 having a silica component concentration of 0.35 mass%, and (3) to (5) are performed 8 times, and Example 12 has a silica component concentration of 0. (3) to (5) were performed 8 times using 14% by mass of silica sol 21, and Example 13 was performed 13 times to (3) to (5) using silica sol 21 having a silica component concentration of 0.05% by mass. , Got to go.

(Example 14)
In the method for producing a ceramic filter of Example 10, after performing (3) and (4) twice, the step of performing (5) was performed twice to obtain Example 14.

(Examples 15 and 16)
In the method for producing a ceramic filter of Example 14, the silica component concentration of the silica sol 21 was 0.14% by mass, and the step of performing (5) after performing (3) and (4) twice was performed four times. Got. In the ceramic filter manufacturing method of Example 14, the concentration was 0.05% by mass, and after performing (3) and (4) twice, the step (5) was performed five times to obtain Example 16.

(Example 17)
In the ceramic filter manufacturing method of Example 11, after performing (3) and (4) three times, performing the step of performing (5) twice, and then performing (3) and (4) twice (5 Example 17 was obtained.

(Example 18)
In the ceramic filter manufacturing method of Example 15, Example 18 was obtained by performing the process of (5) three times after performing (3) and (4) three times.

Example 19
In the ceramic filter manufacturing method of Example 16, after performing (3) and (4) three times, the step of performing (5) was performed four times to obtain Example 19.

(Example 20)
In the method for producing a ceramic filter of Example 18, Example 20 was obtained by a method excluding the step of sieving the silica sol 21 used in (3).

(Example 21)
In the ceramic filter manufacturing method of Example 18, Example 21 was obtained by repeatedly using the same silica sol 21 in (3).

(Examples 22 and 23)
In the ceramic filter manufacturing method of Example 18, Example 22 was obtained using the titania sol 21, and Example 23 was obtained using the zirconia sol 21.

(Comparative Examples 1 and 2)
In the method for producing a ceramic filter of Example 1, Comparative Example 1 was obtained by using the silica sol 21 having a silica component concentration of 1.0% by mass, and the concentration was 0.8% by mass.

(Comparative Examples 3 and 4)
In the ceramic filter manufacturing method of Comparative Example 1, Comparative Example 3 was obtained using titania sol 21, and Comparative Example 4 was obtained using zirconia sol 21.

  For Examples 1 to 23 and Comparative Examples 1 to 4, ethanol at 70 ° C. and 90% by mass is circulated in the monolith cell at a liquid flow rate of 10 L / min, and the outside of the monolith is evacuated to a range of 2 to 10 Pa. The pervaporation test was conducted for 2 hours, and sampling was performed 4 times every 30 minutes. Table 1 shows an overview of the steps of Examples 1 to 23 and Comparative Examples 1 to 4, and Table 2 shows separation coefficient values and permeation amounts (Flux). The permeation amount was calculated by the method described below.

[Flux (kg / m ² · h)]: In the pervaporation separation test, the permeate from the side surface of the substrate was collected by a liquid nitrogen trap, and the mass of the collected permeate was measured for sampling time and membrane area 0. The transmission coefficient was calculated by dividing by 028 m ² .

  As shown in Table 2, (a) By improving the ceramic component concentration of the ceramic sol (Group 1 to Group 8), the separation coefficient value is improved as compared with Comparative Examples 1 to 4 of the conventional method. Further, in addition to (a) above, (b) removal of aggregated particles from the ceramic sol by sieving (group 2, groups 4 to 6, group 7 (only Example 21), group 8), (c) It is higher by using together the management of the moisture concentration of the ceramic sol (Groups 3 to 6, Group 7 (Example 20 only), Group 8), and (D) Reduction in the number of firings (Groups 5 to 8). A ceramic filter exhibiting a separation factor value can be manufactured. Moreover, the ceramic filter which shows a higher separation factor value can be manufactured by using the said (A)-(D) together with two, three, and four.

  In Examples 1 to 3 (Group 1), the silica component concentration of the silica sol was verified as 0.7% by mass or less. Examples 1 to 3 showed a separation factor value 2 to 3 times that of Comparative Examples 1 and 2. Example 3 having a silica component concentration of 0.05% by mass showed a lower separation coefficient value than Example 2 having the concentration of 0.35% by mass. As a result of observing the surface of the porous silica membrane of each sample of Examples 1 to 3 with an electron microscope, the membrane surfaces obtained from Examples 1 to 3 were smoother than the membrane surfaces obtained in Comparative Examples 1 and 2. It was found that there was little film peeling. On the other hand, in Comparative Examples 1 and 2, peeling of the UF film having a width of 10 to 100 μm was confirmed. From elemental qualitative analysis of the film surface with an electron probe X-ray microanalyzer (EPMA), silica segregation around the peeling site of the UF film on the film surface was observed.

  Examples 4 to 6 (group 2) were verified by adding (i) sieving treatment of silica sol to (a) controlling the silica component concentration of silica sol. Examples 4 to 6 have separation factor values of 2.2 to 2.8 times that of Comparative Examples 1 and 2, and 1.1 to 1.4 times that of Example 1 having the same silica component concentration. Indicated. As a result of observing the surface of the porous silica membrane of each sample of Examples 4 to 6 with an electron microscope, the membrane surfaces obtained in Examples 5 and 6 were compared with the membrane surface obtained in Example 1. It was found that there was little peeling. In the silica porous membrane 1 obtained in Example 1, silica agglomerated particles having a particle size of about 50 μm were embedded in the layer of the silica porous membrane, and silica segregation and film peeling were observed at the periphery.

  Examples 7 to 9 (Group 3) were verified by adding (c) the water concentration of silica sol to (a) managing the silica component concentration of silica sol. Examples 7 to 9 have separation factor values of 2.4 to 2.8 times that of Comparative Examples 1 and 2, and 1.2 to 1.4 times that of Example 1 having the same silica component concentration. Indicated. As a result of observing the surface of the porous silica membrane of each sample of Examples 7 to 9 with an electron microscope, the membrane surface obtained in Examples 7 to 9 was compared with the membrane surface obtained in Example 1. It was found that there was little film peeling. The frequency of silica segregation on the surface of the porous silica membrane decreased as the water concentration of the silica sol decreased.

  Examples 10 to 13 (group 4) verified the effects of the combined use of (a) silica component concentration and (c) moisture concentration of silica sol, and (b) sieving treatment. Examples 10 to 13 showed a separation factor value 3 to 4 times that of Comparative Examples 1 and 2. Example 10 in which the numerical values are the same in Example 10 and Example 10 in which the silica component concentration of silica sol was 0.7% by mass and the moisture concentration was 1% and the sieve treatment was performed with an opening of 1 μm. The separation coefficient values of are compared and verified. Example 10 is (a) 1.5 times that of Example 1 in which only the control of the silica component concentration was performed, and (a) Example 6 in which the control of the silica component concentration and (b) the sieving treatment were performed. The separation coefficient value was 1.07 times higher than that of Example 8 in which (a) the silica component concentration and (c) the moisture concentration were controlled. As a result of observing the surface of the porous silica membrane of each sample of Examples 10 to 13 with an electron microscope, the membrane surfaces obtained in Examples 10 to 13 were compared with the membrane surfaces obtained in Examples 1 to 9. It was found that there was little film peeling.

  In Examples 14 to 19 (groups 5 and 6), (a) silica component concentration, (b) sieving treatment, and (c) moisture concentration management of silica sol are combined with (e) a decrease in the number of firings. Verified. Examples 14 to 16 (5 groups) were fired after the adhesion and drying steps were performed twice, and Examples 17 to 19 were fired after the adhesion and drying steps were performed three times. Therefore, the number of firings is further reduced in the sixth group of examples than in the fifth group of examples. Examples 14-16 showed the separation factor value of 3.0-3.6 times compared with the comparative examples 1 and 2. FIG. Examples 17 to 19 showed separation factor values 4.0 to 7.0 times that of Comparative Examples 1 and 2. In particular, Example 18 showed the highest separation coefficient value in this example. As a result of observing the surface of the porous silica membrane of each sample of Examples 14 to 19 with an electron microscope, the membrane surfaces obtained in Examples 14 to 19 were compared with the membrane surfaces obtained in Examples 10 to 13. It was found that there was little film peeling. Examples 10 to 13 (4 groups) that were fired for each silica sol deposition, Examples 14 to 16 (5 groups) that were fired after the adhesion and drying steps were performed twice, and adhesion and drying steps 3 The permeation amount values of Examples 17 to 19 (sixth group) that were fired after repeated firing were compared and verified. Examples 14-16 showed the transmission amount of 1.4 to 2.2 times compared with Examples 10-13. Moreover, Examples 17-19 showed the transmission amount of 1.8 to 2.2 times compared with Examples 10-13.

  Examples 20 and 21 (7 groups) were verified from the conditions of Example 18 except that (i) sieving was performed in Example 20, and (21) excluding optimization of the water concentration of silica sol. . Examples 20 and 21 showed lower separation coefficient values than Example 18. As a result of observing the surface of the porous silica film of each sample with an electron microscope, the film surfaces obtained in Examples 20 and 21 were observed to have more film peeling than the film surface obtained in Example 18. It was. For this reason, in the production of ceramic filters, (i) sieving treatment and (c) managing the water concentration of silica sol are both required to improve the separation coefficient value.

  In Examples 22 and 23 (group 8), for titania sol and zirconia sol, respectively, (a) ceramic sol component concentration, (b) sieving treatment, and (c) moisture concentration management, And verified. Examples 22 and 23 showed a separation factor value of about 6 times that of Comparative Examples 3 and 4. As a result of observing the surface of the ceramic porous membrane 1 of each sample of Examples 22 and 23 with an electron microscope, the membrane surfaces obtained in Examples 22 and 23 were compared with the membrane surfaces obtained in Comparative Examples 3 and 4. Thus, it was found that there was little film peeling. In addition, Examples 22 and 23 showed a permeation amount approximately 1.75 times that of Comparative Examples 3 and 4.

  Summarizing the above examples, in the method for producing a ceramic filter in which a ceramic porous film is formed, (a) the optimization of the ceramic component concentration of the ceramic sol suppresses the occurrence of peeling of the ceramic porous film, Suitable for the production of separable ceramic filters. Furthermore, in addition to the above (a), when (b) removing aggregated particles from the ceramic sol by sieving, (c) managing the water concentration of the ceramic sol, and (d) reducing the number of firings, The effect of suppressing the occurrence of exfoliation of the ceramic porous membrane is improved as compared with the case of (a) alone, and a ceramic filter with higher separation and high permeability can be produced. In particular, the method for producing a ceramic filter using all of (A) to (D) is the optimum condition, and the high-separation and high-permeability ceramic filter in which peeling of the porous ceramic membrane is suppressed preferentially The production of was realized.

  According to the present invention, in the formation of the ceramic porous film, the ceramic component concentration of the ceramic sol attached to the porous substrate is optimized, the solid component having a large particle size in the ceramic sol is removed, the ceramic sol By controlling the moisture concentration and reducing the number of firings, it becomes possible to stably produce a ceramic filter having a smooth, high-separation and high-permeability ceramic filter surface.

It is sectional drawing which shows one Embodiment of a ceramic filter. It is a perspective view showing one embodiment of a ceramic filter. It is a figure explaining a UF membrane. It is explanatory drawing at the time of making ceramic sol adhere once on the surface of a UF membrane. It is explanatory drawing at the time of making ceramic sol adhere twice on the surface of a UF membrane. It is explanatory drawing at the time of making ceramic sol adhere on the surface of a UF membrane 3 times. It is explanatory drawing at the time of making ceramic sol adhere on the surface of a UF membrane 4 times. It is the schematic which shows roughly an example of the method of attaching ceramic sol to a porous base material. It is the schematic which shows roughly an example of the method of drying the ceramic sol adhering to the porous base material.

Explanation of symbols

1: Ceramic porous membrane, 1a: First adhesion layer, 1b: Second adhesion layer, 1c: Third adhesion layer, 1d: Fourth adhesion layer, 2: UF membrane, 3: MF membrane, 4 : Porous substrate (UF membrane + MF membrane), 5: concave portion on the surface of MF membrane, 6: convex portion on the surface of MF membrane, 11: ceramic filter, 12: partition wall, 13: cell, 14: end surface on the inlet side 21: Ceramic sol (silica sol), 22: Masking tape.

Claims (6)

A ceramic sol having a ceramic component concentration of 0.05 to 0.7% by mass is applied on the surface of the porous substrate,
After a part of the ceramic sol falls by its own weight and is removed from the surface of the porous substrate, and the remaining ceramic sol that is not removed is deposited on the surface of the porous substrate,
A method for producing a ceramic filter, wherein the ceramic sol attached to the porous substrate is blown and dried, and then fired to form a ceramic porous film.   The method for producing a ceramic filter according to claim 1, wherein a solvent of the ceramic sol is ethanol.   The method for producing a ceramic filter according to claim 1 or 2, wherein the ceramic sol has a water concentration of 0.03 to 3 mass%.   The method for producing a ceramic filter according to any one of claims 1 to 3, wherein the ceramic sol capable of passing through a sieve having an opening of 10 µm is used.   The method for producing a ceramic filter according to any one of claims 1 to 4, wherein the ceramic sol is fired after a plurality of steps of attaching the ceramic sol to the surface of the porous substrate and performing air drying. .   The method for producing a ceramic filter according to claim 1, wherein the ceramic component is silica, titania, or zirconia.

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