Patent Application
20080105613
The present invention relates to a ceramic filter for use in separation of various mixtures.
From viewpoints of environment and energy saving, development of a separation membrane for filtering and separating a specific gas or the like from a mixture of various gases or the like has been advanced. As such a separation membrane, a polymer film such as a polysulfone film, a silicon film, a polyamide film or a polyimide film or the like is known, but there are problems of thermal resistance and chemical resistance, for example, a problem that when the mixture includes an organic solvent, the film is degraded and deteriorated.
On the other hand, examples of the separation membrane having excellent thermal resistance and chemical stability include a carbon membrane, and a separation membrane including the carbon membrane formed on a porous base material is known. For example, Patent Document 1 discloses a molecular sieve carbon membrane in which a coating layer is formed on the surface of a ceramic porous body to form the carbon membrane so that the carbon membrane comes in close contact with the surface of the coating layer. Since a large number of pores having pore diameters of 1 nm or less are present in this molecular sieve carbon membrane, only components having a specific molecule diameter can be separated and refined from various mixed gases having different molecule diameters.
Patent Document 1: Japanese Patent No. 3647985
However, in a case where a carbon membrane is formed on a porous base material, since a carbon membrane precursor is dipped in the base material, it is difficult to form a uniform film. Therefore, the film is not uniformly formed, and hence selectivity for separating a mixture deteriorates. When the precursor is dipped to form the carbon membrane, the carbon membrane tends to be formed to be thick, and flux (transmission flux) deteriorates. Furthermore, in a method in which the surface of the porous base material is impregnated with a silica sol to form the carbon membrane on the surface as in Patent Document 1, pore diameters of the carbon membrane increase owing to the formation of the sol layer, and hence a separation performance improves with respect to a part of gases, for example, C3H8/C3H6 or the like having molecule diameters of 0.43 nm or more and a comparatively large molecular weight. However, in another industrially useful mixture having a comparatively small molecular weight, for example, CO2/CH4, N2/O2, water/EtOH or the like, the selectivity deteriorates, the flux also lowers owing to an influence of pressure loss due to the silica sol, and the separation performance remains to be low as compared with a method of directly forming the carbon membrane on the porous base material.
An objective of the present invention is to provide a ceramic filter formed on a porous base material and having satisfactory transmission amount and selectivity.
To achieve the above objective, according to the present invention, there is provided a ceramic filter provided with a base material main body consisting of a ceramic porous body, at least one or more ceramic surface deposited layers formed on the surface of the base material main body and consisting of a ceramic porous body having an average particle diameter smaller than that of the ceramic porous body constituting the base material main body, and a carbon membrane layer formed as a molecular sieve carbon membrane on an outermost surface of the ceramic surface deposited layer.
More specifically, it can be constituted that an average particle diameter of ceramic particles constituting the base material main body consisting of the ceramic porous body is 10 μm or more. It can also be constituted that an average particle diameter of the ceramic surface deposited layer is 0.03 μm or more and 10 μm or less.
Moreover, to achieve the above objective, according to the present invention, there is provided the ceramic filter provided with a heterogeneous surface deposited layer formed on the surface of the ceramic surface deposited layer and having an average particle diameter smaller than that of the ceramic porous body of the ceramic surface deposited layer, and the carbon membrane layer formed on the heterogeneous surface deposited layer.
Specifically, the heterogeneous surface deposited layer may be formed of a titania sol. It may be constituted that an average pore diameter of the heterogeneous surface deposited layer is 0.3 nm or more and 20 nm or less.
Further specifically, it may be constituted that an average pore diameter of the ceramic surface deposited layer is 0.01 μm or more and 3 μm or less. Furthermore, it may be constituted that the ceramic surface deposited layer includes a plurality of layers having different average pore diameters.
Moreover, the base material main body may be constituted of a porous body of alumina, silica, titania, zirconia or the like. The ceramic surface deposited layer may be constituted of a porous body of alumina, silica, titania, zirconia or the like.
The ceramic filter of the present invention has a separating function of separating water and ethanol.
In the ceramic filter of the present invention, since the ceramic surface deposited layer consisting of the ceramic porous body having the average particle diameter smaller than that of the ceramic porous body constituting the base material main body is formed on the surface of the base material main body consisting of the ceramic porous body and the carbon membrane layer is formed on the ceramic surface deposited layer, increase of pressure loss at a base material portion can be prevented, and a transmission amount of a target to be separated can be improved. Moreover, since the carbon membrane layer is formed on the ceramic surface deposited layer or the heterogeneous surface deposited layer having a small average particle diameter, penetration of a film precursor resin constituting the carbon membrane layer to a base material can be inhibited. Therefore, an amount of a film precursor resin solution to be used decreases, and the carbon membrane layer can thinly and uniformly be formed on the base material.
An embodiment of the present invention will hereinafter be described with reference to the drawings. The present invention is not limited to the following embodiment, and may be altered, modified or improved without departing from the scope of the present invention.
One embodiment of a ceramic filter according to the present invention will specifically be described. As shown in
Next, the respective layers shown in
Next, the first surface dense layer 3 and the second surface dense layer 4 will be described. The first surface dense layer 3 and the second surface dense layer 4 are formed by a filtering film formation process using various ceramic materials such as alumina particles in the same manner as in the porous base material 2. As alumina particles to form the first surface dense layer 3, there are used particles having an average particle diameter smaller than that of the alumina particles to form the porous base material 2. As alumina particles to form the second surface dense layer 4, there are used particles having an average particle diameter smaller than that of the alumina particles to form the first surface dense layer 3. In such a constitution, the average pore diameter of the surface deposited layer decreases in stages, thereby obtaining a porous surface structure in which the carbon membrane is easily formed with little pressure loss.
A method of forming the first surface dense layer 3 and the second surface dense layer 4 will be described. As shown in
The alumina particles having an average particle diameter of 0.03 to 1 μl are deposited on the first surface dense layer 3 by a similar filtering film formation process and fired, to form the second surface dense layer 4 having an average particle diameter of 0.03 to 1 μm and an average pore diameter of 0.01 to 0.5 μm. In consequence, the ceramic surface deposited layer is formed. It is to be noted that in the ceramic surface deposited layer, the same type of ceramic as that of the base material main body may be used, or a different type of ceramic may be used. The first surface dense layer 3 and the second surface dense layer 4 are formed as layers having different average pore diameters, but the layers may be formed so that the average pore diameter continuously changes (the average pore diameter decreases in a surface direction). Furthermore, three or more surface dense layers may be formed.
Furthermore, titania sol particles having an average particle diameter of 1 to 50 nm and including titanium oxide are deposited on the second surface dense layer 4 by a similar filtering film formation process and fired, to form the third surface dense layer 5 having an average pore diameter of 0.3 to 20 nm. Instead of titania, alumina, silica, zirconia or the like may be used.
After forming the second surface dense layer 4 or the third surface dense layer 5, the carbon membrane is formed on the second surface dense layer 4 or the third surface dense layer 5 by dipping, spin coating, spray coating or the like using a precursor solution forming the carbon membrane, and carbonized in nitrogen at 700° C. to form the carbon membrane layer 6 on the surface of the second surface dense layer 4 or the third surface dense layer 5. It is to be noted that the precursor solution for forming the carbon membrane is formed by mixing or dissolving a thermosetting resin such as a phenol resin, a melamine resin, a urea resin, a furan resin, a polyimide resin or an epoxy resin, a thermoplastic resin such as polyethylene, a cellulose-based resin, or a precursor substance of such resin with an organic solvent such as methanol, acetone, tetrahydrofuran, NMP or toluene, water or the like. During film formation, the mixture or the solution may be subjected to an appropriate thermal treatment in accordance with a type of the resin. The carbonization may be performed in a reduction atmosphere of vacuum, argon, helium or the like instead of the nitrogen atmosphere. In general, when the carbonization is performed at 400° C. or less, the resin is not sufficiently carbonized, and selectivity and transmission speed of the molecular sieve film deteriorate. On the other hand, when the resin is carbonized at 1000° C. or more, the pore diameters contract to reduce the transmission speed.
As described above, the surface deposited layer is formed so that the average pore diameter decreases in stages, so that pressure loss of the base material itself can be suppressed, penetration of the carbon membrane precursor solution to a porous member side and formation of a composite layer are inhibited, and a film structure having a uniform thickness and only little pressure loss can be obtained. In consequence, while decrease of flux is prevented, a high separation factor can be obtained.
The present invention will hereinafter be described in more detail based on examples, but the present invention is not limited to these examples.
As described later, there were formed a base material A having a monolith shape and consisting of an alumina porous base material, a base material B constituting a first surface dense layer formed on the base material A, a base material C constituting a second surface dense layer formed on the base material B, and a base material D constituting a third surface dense layer formed on the base material C. Furthermore, a base material E similar to the base material D was formed as a cylindrical alumina porous base material. These base materials A to E were used, and carbon membrane layers were formed on the surfaces of the base materials A to E.
Furthermore, the base materials A to E will be described in detail. The base material A is a monolith type alumina porous base material having an average particle diameter of 10 to 100 μm and an average pore diameter of 1 to 30 μm. With regard to the base material B, alumina particles having an average particle diameter of 0.3 to 10 μm were deposited on the base material A by filtering film formation, and fired to form the first surface dense layer having a thickness of 10 to 1000 μm and an average pore diameter of 0.1 to 3 μm. With regard to the base material C, alumina particles having an average particle diameter of 0.03 to 1 μm were further deposited on the surface dense layer of the base material B by the filtering film formation, and fired to form the second surface dense layer having a thickness of 1 to 100 μm and an average pore diameter of 0.01 to 0.5 μm. With regard to the base material D, titania sol particles having an average particle diameter of 1 to 50 nm were further deposited on the base material C by the filtering film formation, and fired to form the third surface dense layer having a thickness of 0.1 to 5 μm and an average pore diameter of 0.3 to 20 nm. The base material E was a cylindrical alumina porous base material prepared by a method similar to that of the base material C.
These base materials A to E were used, a precursor solution of a carbon membrane was formed into a film by a dipping process, the film was carbonized in nitrogen at 700° C., and the carbon membranes formed on the surfaces of the base materials were obtained (Comparative Example 1, Examples 1 to 4). These carbon membranes were evaluated by a water-ethanol pervaporation (test conditions: water/EtOH=10/90 wt %, a supply liquid temperature of 75° C.). An amount of the precursor solution consumed at a time when the carbon membrane was formed on each base material and a pervaporation performance are shown in Table 1. An electronic microscope photograph indicating a sectional shape of a ceramic filter of Example 3 is shown in
It is to be noted that in the present invention, a value of an average pore diameter D (μm) of the base material measured by a mercury porosimetry process, a gas adsorption process or the like was used. As an average particle diameter d (μm) of ceramic particles, there was used a value of a 50% particle diameter measured by Stokes liquid layer sedimentation process, an X-ray transmission system particle size distribution measurement device (e.g., Sedigraph model, 5000-02 manufactured by Shimadzu Corporation or the like) which performs detection by an X-ray transmission process, a dynamic photo scattering process or the like.
A cylindrical alumina porous base material having an average pore diameter of 1 μm was dipped in a silica sol solution, and dried to obtain a base material F having the surface impregnated with a silica sol (Comparative Examples 2 and 3). In the same manner as in Examples 1 to 4, carbon membranes were formed on the surfaces of Comparative Examples 2 and 3, and the comparative examples were evaluated by a water-ethanol pervaporation (test conditions: a supply liquid composition, water/EtOH=10/90 wt %, a supply liquid temperature of 75° C.). Results are shown in Table 1.
In Comparative Example 1 in which any dense layer was not formed on the surface, a separation performance was scarcely obtained, and the carbon membrane was hardly formed on the surface of the base material. In Example 1 in which the first surface dense layer having an average pore diameter of 0.1 to 3 μm, the separation performance was obtained, but a separation factor was low. In Examples 2 and 4 in which the second surface dense layer having an average pore diameter of 0.01 to 0.5 μm was formed and Example 3 in which the third surface dense layer having an average pore diameter of 0.3 to 20 nm was formed, a high separation factor was obtained.
On the other hand, in Comparative Example 2 in which the surface of the alumina porous base material having an average pore diameter of 1 μm was impregnated with a silica sol, when dipping was performed once, a sufficient separation factor was not obtained, and further the flux was low. In Comparative Example 3 in which the dipping was performed three times, a comparatively high separation factor was obtained, but the flux largely lowered. In Example 2 having a monolith shape, the flux per volume improved as much as about four times that of Example 4 having a cylindrical shape.
The consumption of the precursor solution decreased, as the surface deposited layer became dense. In Comparative Example 1, it was confirmed that a large amount of the precursor solution of the carbon membrane was immersed into the base material. It has been presumed that since this immersion amount was excessively large, an amount of a precursor left on the surface of the base material to contribute to the film formation was insufficient, and this was a cause for a fact that any carbon membrane was not formed at a part of the surface and that a separation performance deteriorated. In Example 2, slight immersion was seen, but the carbon membrane having a film thickness of about 1 to 2 μm was uniformly formed along the base material surface layer. In Example 3, any immersion was not seen. When the dipping was performed once (with a precursor solution use amount of ⅓), a film similar to that of Example 2 was formed.
As described above, according to a deposited structure in which the alumina particles having a small average pore diameter are deposited on the base material main body, increase of pressure loss at the base material and a surface portion of the material can be reduced, so that a transmission amount can be increased. Since the dense surface layer is formed, penetration of the film precursor resin to the base material can be inhibited. Therefore, the amount of the precursor solution to be used can be reduced, and the transmission amount and selectivity can be improved. Furthermore, since the monolith shape is formed, the film area per volume can be increased, and miniaturization of a device can be realized by improvement of the flux per volume.
A ceramic filter of the present invention can broadly be used in an application of separation of a mixed liquid and a mixed gas.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-198250 | Jul 2006 | JP | national |
| 2006-298552 | Nov 2006 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2007/063938 | Jul 2007 | US |
| Child | 11966122 | Dec 2007 | US |
