JP2018034091A - Porous Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology of making a thickness of a porous film uniform.SOLUTION: A porous filter includes a porous support body which has two end surfaces and has a flow passage passing from the one end surface to the other end surface, a first porous film formed on the porous support body, and a second porous film formed on a side where the first porous film does not face to the porous support body. The first porous film includes particles of different particle sizes formed of a same material, has a first local maximum value and a second local maximum value with 5% or more frequencies respectively when viewing particle size frequency distribution of the particles. A first particle size of the first local maximum value is larger than a second particle size of the second local maximum value. The first particle size is 2-7 times of the second particle size. The first particle size is 1-10 μm, and the second particle size is less than 1 μm.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a porous filter.

  Conventionally, a porous filter in which a porous membrane is formed as a separation membrane on a porous support formed of a porous body is known (for example, Patent Document 1). As a method of forming a porous film with a uniform thickness, Patent Document 1 describes a method of adding an organic polymer to a porous film.

Japanese Patent No. 3625682 JP 2002-253915 A JP 2007-229564 A

  However, when the method described in Patent Document 1 is used, cracks may occur in the porous film due to thermal contraction of the organic polymer. For this reason, other techniques have been desired as a technique for forming a porous film having a uniform thickness.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a porous filter is provided. This porous filter has two end faces, a porous support having a flow path penetrating from one end face to the other end face, and a first porous formed in the porous support. A porous filter comprising a membrane and a second porous membrane formed on a side of the first porous membrane not facing the porous support, wherein the first porous membrane is Including particles having different particle diameters formed from the same material, and having a first maximum value and a second maximum value, each of which has a frequency of 5% or more when viewing the particle size frequency distribution of the particles, The first particle size of the first maximum value is larger than the second particle size of the second maximum value, and the first particle size is 2 to 7 times the second particle size, The particle size is 1 μm or more and 10 μm or less, and the second particle size is less than 1 μm. According to the porous filter of this aspect, the first porous membrane is provided with particles having the second particle size, so that the slurry for forming the first porous membrane is uniformly attached to the porous support during production. As a result, the film thickness of the first porous film becomes uniform.

(2) In the porous filter of the above aspect, both the frequency of the first maximum value and the frequency of the second maximum value may be 10% or more. According to the porous filter of this form, the film thickness of the first porous film becomes more uniform.

(3) In the porous filter of the above aspect, the first particle size may be 2 μm or more and 5 μm or less, and the second particle size may be 0.5 μm or more and less than 1 μm. According to the porous filter of this form, the film thickness of the first porous film becomes more uniform.

(4) In the porous filter of the above aspect, the first porous film may be formed on a surface constituting the flow path. According to this form of the porous filter, the thickness of the first porous film is uniform.

  In addition, this invention is not restricted to the form as a porous filter mentioned above, It is possible to implement | achieve in various forms. The present invention can be realized, for example, in an aspect of a method for producing a porous filter.

Explanatory drawing of the porous filter 10 of this embodiment. 2 is a schematic cross-sectional view of a porous membrane 110. FIG. FIG. 5 is a process diagram showing a method for manufacturing the porous filter 10. The schematic diagram for demonstrating the filtration film-forming method. The figure which shows the particle size frequency distribution of the 1st porous film of an Example and a comparative example. The figure which shows typically the image acquired with the scanning electron microscope. The figure which shows the result of having measured the thickness of the 1st porous film 111. FIG. The schematic diagram explaining a measurement place. The cross-sectional schematic diagram which shows the particle | grains which form the 1st porous film 111 of an Example and a comparative example. The cross-sectional schematic diagram which shows the mode of formation of the 1st porous film 111 in an Example.

A. Embodiment:
A1. Porous filter configuration:
FIG. 1 is an explanatory diagram of the porous filter 10 of the present embodiment. FIG. 1 shows a state in which the porous filter 10 is cut along the axis CX direction of the porous filter 10. The porous filter 10 of the present embodiment is used as, for example, a gas or liquid filter. As shown in FIG. 1, the porous filter 10 includes a porous support 100 and a porous membrane 110.

The porous support body 100 has two end surfaces, and a flow path C penetrating from one end surface D1 to the other end surface D2 is formed. In the present embodiment, a plurality of flow paths C are formed, but one may be used. The porous support 100 has a large number of communicating pores, and is formed so that fluid (gas or liquid) can pass in any direction. In the present embodiment, the porous support 100 is cylindrical, and the flow path C extends in the direction along the axis CX direction of the porous support 100. As a material of the porous support 100, for example, various oxides such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), cordierite, mullite, or a mixture thereof can be used. .

  FIG. 2 is a schematic cross-sectional view of the porous membrane 110. As shown in FIG. 2, the porous membrane 110 is formed on the surface constituting the flow path C of the porous support 100. The porous membrane 110 is formed of two membranes, and the first porous membrane 111 and the second porous membrane 113 are laminated in this order in the flow path C of the porous support 100. That is, in the present embodiment, the first porous film 111 is formed on the porous support 100, and the second porous film 113 does not face the porous support 100 of the first porous film 111. Formed on the side.

The first porous film 111 is a porous film including particles having different particle diameters formed from the same material. In the present embodiment, alumina (Al ₂ O ₃ ) is used as the same material. The characteristics of the first porous film 111 will be described in detail later.

The second porous film 113 is a film formed on the first porous film 111. The second porous film 113 is a porous film and is formed by firing alumina (Al ₂ O ₃ ) particles in the present embodiment. The second porous membrane 113 contains many particles having an average particle size smaller than the particle size (PS1) of the particles forming the first porous membrane 111. By doing so, the pore size of the second porous membrane 113 can be made smaller than the pore size of the first porous membrane 111.

A2. Method for producing porous filter 10:
FIG. 3 is a process diagram showing a method for manufacturing the porous filter 10. The manufacturer of the porous filter 10 first produces the porous support 100 in the process P100. Process P100 is also referred to as a porous support manufacturing process.

In this embodiment, first, a manufacturer produces a clay by mixing and kneading an alumina (Al ₂ O ₃ ) powder having an average particle diameter of 8 μm, methylcellulose, and water with a mixer. Next, the manufacturer forms the clay using an extruder equipped with a molding die having an outer diameter of about 30 mm in which a plurality of channels having a diameter of about 3 mm are formed. In the present embodiment, the total length is about 1200 mm. Thereafter, the manufacturer produces porous support 100 having a total length of about 1000 mm by firing the clay.

  After the porous support manufacturing process (process P100), the manufacturer forms the first porous film 111 on the porous support 100 in process P110. Specifically, the manufacturer forms the first porous film 111 on the surface constituting the flow path C of the porous support 100. Process P110 is also referred to as a first porous film forming process.

In this embodiment, first, the manufacturer prepares a slurry containing alumina (Al ₂ O ₃ ) powder having an average particle diameter of 3 μm and alumina (Al ₂ O ₃ ) powder having an average particle diameter of 0.7 μm. . Next, the manufacturer forms the first porous film 111 on the porous support 100 by a filtration film forming method. Here, the filtration film formation method is an existing technique, and is described in, for example, Japanese Patent No. 3625682. Therefore, in this specification, the filtration film formation method will be briefly described below.

  FIG. 4 is a schematic diagram for explaining the filtration film forming method. First, the manufacturer places the porous support 100 in the vacuum chamber 200, and then fixes the two end faces D1 and D2 of the porous support 100 with the flange 210 via an O-ring (not shown). Thereafter, the manufacturer uses the pump P in a state where the inside of the vacuum chamber 200 is depressurized to supply about 10 slurry 220 to the flow path C (see FIG. 1) formed in the pipe 230 and the porous support 100. Circulate for minutes. Then, the manufacturer stops the circulation of the slurry 220 and removes the slurry 220 in the pipe 230. Next, the manufacturer (i) after drying the porous support 100 in the vacuum chamber 200 under a reduced pressure environment, (ii) moving the porous support 100 to a warm air dryer, The first porous film 111 is formed by further drying with wind and finally (iii) firing.

  After the first porous film forming process (process P110 (see FIG. 3)), the manufacturer forms the second porous film 113 on the first porous film 111 in the process P120. Process P120 is also referred to as a second porous film forming process.

In this embodiment, the manufacturer first prepares a slurry containing alumina (Al ₂ O ₃ ) powder having an average particle size of 0.3 μm. Next, the manufacturer forms the second porous film 113 on the first porous film 111 by the filtration film forming method similar to the first porous film forming process (process P110). In other words, the manufacturer circulates the slurry prepared in this step on the porous support 100 on which the first porous membrane 111 is formed, and then performs drying and firing, thereby performing the first porous membrane 111. A second porous film 113 is formed thereon. Through these steps, the porous filter 10 is completed.

  The first porous membrane 111 of the porous filter 10 in the present embodiment has a uniform thickness. This effect will be described below using the results of the evaluation test.

A3. Evaluation test:
In the evaluation test, an example and a comparative example were used. An example is the porous filter 10 produced by the above-mentioned manufacturing method. On the other hand, in the first comparative example, the comparative example added only alumina powder having an average particle size of 3 μm in the first porous film forming step (process P120 (see FIG. 3)), and the average particle size was 0.7 μm. This is different except that no alumina powder is added.

  FIG. 5 is a view showing the particle size frequency distribution of the first porous membranes of Examples and Comparative Examples. In FIG. 5, the vertical axis represents frequency (%), the horizontal axis represents particle size (μm), the results of Examples are indicated by solid lines, and the results of Comparative Examples are indicated by broken lines.

In this specification, the particle size frequency distribution was created in the following order.
1. The number of classes is calculated using the Sturges formula.
2. The class interval of each particle diameter in the histogram is a value obtained by subtracting the smallest value from the largest value among the measured values and dividing the result by the number of classes.
3. The first class starts from the minimum value minus one half of the unit of measurement.
4). The class interval is sequentially added to the starting point value, and the boundary line to the class including the maximum value is determined.
5. The particle size frequency distribution is created using the central value of each class as the class value of that class.

  Here, the measuring method of the particle diameter in this specification is demonstrated. First, the measurer cut the porous membrane 110 from the porous support 100 after breaking the porous filter 10 along the direction of the axis CX (see FIG. 1). Thereafter, the measurer uses a scanning electron microscope (SEM) to scan the surface of the porous film 110 that has been in contact with the porous support 100 because the surface of the porous film 110 is the surface of the first porous film 111. Used to obtain an image magnified 3000 times.

  FIG. 6 is a diagram schematically showing an image acquired by a scanning electron microscope. In this image, the measurer draws two diagonal lines DL1 and DL2 connecting the opposite corners. The measurer measures the longest portion of the particles that intersect with these diagonal lines DL1 and DL2. Here, the longest part means the longest part among the parts appearing in the observed image. For example, as shown in FIG. 6, G1 which is one of the particles intersecting with the diagonal line DL1 has a particle size of S1, and G2 which is one of the particles which intersect with the diagonal line DL2 has a particle size of Is S2. In this evaluation test, the tester prepared two images of different portions for each of the example and the comparative example, and in the example, measured the particle size of any 90 particles from one image. In the comparative example, the particle size of arbitrary 50 particles was measured from one image. Thereafter, the tester determined the average value calculated for each of the examples and comparative examples as the average particle diameter.

As shown in FIG. 5, when looking at the particle size frequency distribution of the first porous membrane 111 of the example, the first porous membrane 111 has the following characteristics.
1. A first maximum value MV1 and a second maximum value MV2 each having a frequency of 5% or more are included.
2. The particle size of the first maximum value MV1 (referred to as “first particle size PS1”) is larger than the particle size of the second maximum value MV2 (referred to as “second particle size PS2”).
3. The first particle size PS1 is 2 to 7 times the second particle size PS2.
4). The first particle size PS1 is 1 μm or less and 10 μm or less, and the second particle size PS2 is less than 1 μm.

  As shown in FIG. 5, in the embodiment, the first particle size PS1 is about 0.7 μm, and the second particle size PS2 is about 3 μm. Therefore, the first particle size PS1 is about 4 times the second particle size PS2. On the other hand, the comparative example has the first maximum value MV1 having a frequency of 5% or more, but does not have the second maximum value MV2. The reason why the comparative example does not have the second maximum value MV2 is that alumina powder having an average particle diameter of 0.7 μm is not added in the first porous film forming step (step P120 (see FIG. 3)). It is done.

  FIG. 7 is a diagram showing the results of measuring the thickness of the first porous membrane 111. FIG. 7 shows the film thickness (μm) of the first porous membrane 111 of the example and the comparative example at each measurement location. In FIG. 7, the thickness of the first porous membrane 111 is compared at five measurement locations. In FIG. 7, the result of the example is indicated by a solid line, and the result of the comparative example is indicated by a broken line. Here, the measurement location will be described below.

  FIG. 8 is a schematic diagram for explaining a measurement place. The first measurement location is the first porous membrane 111 formed in the channel C (also referred to as “central channel CC”) passing through the axis CX, and the other four measurement locations are all porous. This is the first porous film 111 formed in the outermost channel C (also referred to as “outermost channel CT”) of the support 100. The measurer measured the thickness of the first porous membrane 111 of the outermost peripheral channel CT in four places. Specifically, the measurer (i) places C1 on the upstream side when viewed from the end face D1, (ii) place C2 on the axis CX side, and (iii) shows the position when viewed from the end face D1. The film thickness of the first porous membrane 111 was measured after dividing it into a place C3 on the downstream side and (iv) a place C4 on the outer peripheral side. The measurer performs measurement at each of the six measurement locations, and the average value is shown in FIG. Note that a scanning electron microscope was used for the measurement.

  As shown in FIG. 7, in the comparative example, the film thickness of the first porous film 111 formed in the central flow path CC is smaller than the film thickness of the first porous film 111 formed in the outermost peripheral flow path CT. . Further, the thickness of the first porous film 111 formed in the outermost peripheral channel CT in the comparative example is smaller as it is closer to the axis CX, and is larger as it is farther from the axis CX. That is, the film thickness of the first porous film 111 formed in the outermost peripheral channel CT in the comparative example is the smallest (i) at the location C2 on the axis CX side, and (ii) clockwise when viewed from the end face D1. It is the same at the upstream location C1 and the downstream location C3, and (iii) is the largest at the outer peripheral location C4. The reason is considered to be the pressure applied to the slurry 220 (see FIG. 4) during the filtration film formation, which is the formation of the first porous film 111. That is, the pressure applied to the slurry 220 is smaller in the portion away from the axis CX than in the portion close to the axis CX. For this reason, the amount of the slurry 220 deposited on the surface of the flow path C of the porous support 100 is larger in the portion away from the axis CX than in the portion close to the axis CX. As a result, it is considered that the thickness of the first porous film 111 is smaller as it is closer to the axis CX and is larger as it is farther from the axis CX.

  On the other hand, as shown in FIG. 7, in the example, the difference in the thickness of the first porous film 111 depending on the location is small compared to the comparative example, and the thickness of the first porous film 111 is uniform. I understand. The reason why the thickness of the first porous film 111 of the example is uniform will be described below.

  FIG. 9 is a schematic cross-sectional view showing particles forming the first porous film 111 of the example and the comparative example. Examples and comparative examples are the same as those used in the evaluation test.

  In general, when the number of flow paths C of the porous support 100 is one, particles on the slurry supply side of the flow paths C tend to deposit more easily than the slurry discharge side. In addition, when the porous support 100 has a plurality of flow paths C, generally, the flow path C far from the axis CX of the porous support 100 is compared with the flow path C close to the axis CX. When forming 111, the particles for forming the first porous film 111 tend to stay. As described above, the thickness of the porous film formed in the channel C may vary depending on the location where the channel C is formed and the position of the channel C.

  On the other hand, as in the example, the above-described first particle size PS1 and the above-described second particle size PS2 having a particle size smaller than the first particle size PS1 are added to the slurry for forming the porous film 110. In this case, the particles having the second particle size PS2 cause clogging of the pores of the porous support 100 when the slurry is circulated.

  FIG. 10 is a schematic cross-sectional view showing how the first porous film 111 is formed in the example. In FIG. 10, the pressure applied to the slurry 220 is indicated by a white arrow, and the larger the force, the greater the arrow. Immediately after the start of the filtration film formation of the first porous membrane 111, as shown in the upper part of FIG. 10, the pressure applied to the slurry 220 is smaller in the portion away from the axis CX than in the portion close to the axis CX. . For this reason, the amount of the slurry 220 deposited on the surface of the flow path C of the porous support 100 is larger in the portion away from the axis CX than in the portion close to the axis CX.

  However, the second particle size PS2 contained in the slurry 220 causes clogging of the pores of the porous support 100 when the slurry 220 is circulated. For this reason, the slurry 220 is preferentially deposited on the surface of the flow path C where clogging does not occur. As a result, it is considered that the slurry 220 is uniformly deposited in the flow path C as shown in the lower part of FIG.

  Here, in order to uniformly form the film thickness of the first porous film 111 while effectively causing clogging, (i) the frequency of the first maximum value MV1 and the second maximum value MV2 (see FIG. 5). Are preferably 10% or more, (ii) the first particle size PS1 is preferably 2 μm or more and 5 μm or less, and (iii) the second particle size PS2 is 0.5 μm or more and 1 μm or less. preferable.

B. Variations:
B1. Modification 1:
In the above-described embodiment, the porous film 110 includes the first porous film 111 and the second porous film 113. However, the present invention is not limited to this. The porous film 110 may include three or more layers.

B2. Modification 2:
In the above-described embodiment, the porous membrane 110 of the porous filter 10 is formed in the flow path of the porous support 100. However, the present invention is not limited to this. For example, the porous membrane 110 may be formed on the outer periphery of the porous filter 10. For example, the flow path C of the porous support body 100 is one, and the aspect which formed the porous film | membrane 110 in the outer peripheral surface which is a surface of the porous support body 100 other than end surface D1, D2 is mentioned.

B3. Modification 3:
In the embodiment described above, the frequencies of the first maximum value MV1 and the second maximum value MV2 are both 10% or more (see FIG. 5), but at least one of the frequencies of the first maximum value MV1 and the second maximum value MV2 is used. May be 5% or more and less than 10%. Further, there may be further local maximum values other than the first local maximum value MV1 and the second local maximum value MV2 and having a frequency of 5% or more.

B4. Modification 4:
In the above-described embodiment, the first particle size PS1 is 2 μm or more and 5 μm or less, but may be 1 μm or more and less than 2 μm, or may be greater than 5 μm and 10 μm or less. Similarly, the second particle size PS2 is 0.5 μm or more and less than 1 μm, but may be less than 1 μm.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and the modifications corresponding to the technical features in each form described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Porous filter 100 ... Porous support body 110 ... Porous membrane 111 ... 1st porous membrane 113 ... 2nd porous membrane 200 ... Vacuum chamber 210 ... Flange 220 ... Slurry 230 ... Pipe C ... Channel CC ... Center Channel CT ... Outermost channel CX ... Axis D1 ... End face D2 ... End face DL1 ... Diagonal line DL2 ... Diagonal line MV1 ... First maximum value MV2 ... Second maximum value P ... Pump PS1 ... First particle size PS2 ... Second particle size

Claims (4)

A porous support having two end faces and having a flow path penetrating from one end face to the other end face;
A first porous film formed on the porous support; and a second porous film formed on a side of the first porous film not facing the porous support. A filter,
The first porous membrane includes particles formed of the same material and having different particle sizes,
When the particle size frequency distribution of the particles is viewed, the frequency has a first maximum value and a second maximum value that are each 5% or more,
The first particle size of the first maximum value is larger than the second particle size of the second maximum value,
The first particle size is 2 to 7 times the second particle size,
The porous filter according to claim 1, wherein the first particle size is 1 μm or more and 10 μm or less, and the second particle size is less than 1 μm. The porous filter according to claim 1,
The frequency of the first maximum value and the frequency of the second maximum value are both 10% or more. The porous filter according to claim 1 or 2,
The porous filter, wherein the first particle size is 2 μm or more and 5 μm or less, and the second particle size is 0.5 μm or more and less than 1 μm. The porous filter according to any one of claims 1 to 3,
The porous filter, wherein the first porous membrane is formed on a surface constituting the flow path.

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