JP2017213518A - Honeycomb filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb filter which can achieve both low pressure loss and high collection efficiency.SOLUTION: A honeycomb filter 100 includes: a columnar and porous honeycomb structure which forms a plurality of first flow channels and a plurality of second flow channels; a plurality of first sealing parts which close the respective first flow channels on one end side of the honeycomb structure; and a plurality of second sealing parts which close the respective second flow channels on the other end side of the honeycomb structure. The first sealing parts and the second sealing parts satisfy all of the following conditions. (a) A length in a direction along the flow channel is 0.3-1.8 mm. (b) Porosity is 60-70%. (c) A pore diameter D90 is 30 μm or less. In regard to the pore diameter, 90% of an entire pore volume of the sealing parts have a pore diameter smaller than the pore diameter D90.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a honeycomb filter.

  Conventionally, attempts have been made to make the sealing portion porous and thin so that the sealing portion of the honeycomb filter can be used as a filter.

JP 2003-3823 A Japanese Utility Model Publication No. 6-47616

  However, in the conventional honeycomb filter, it is difficult to achieve both low pressure loss and high collection efficiency.

  The present invention has been made in view of the above problems, and an object thereof is to provide a honeycomb filter capable of achieving both low pressure loss and high collection efficiency.

The honeycomb filter according to the present invention includes a columnar and porous honeycomb structure that forms a plurality of first channels and a plurality of second channels, and closes each of the first channels on one end side of the honeycomb structure. A plurality of first sealing portions, and a plurality of second sealing portions that close the second flow paths on the other end side of the honeycomb structure. And the said 1st sealing part or the said 2nd sealing part satisfy | fills all the following conditions (a)-(c).
(A) The length in the direction along the flow path is 0.3 to 1.8 mm.
(B) The porosity is 60 to 70%.
(C) The pore diameter D90 is 30 μm or less.
However, the pore diameter D90 is a pore diameter in which 90% of the total pore volume of the sealing portion has a smaller pore diameter.

  Here, the said 1st sealing part and the said 2nd sealing part can satisfy | fill all the conditions of said (a)-(c).

  In addition, the honeycomb structure may have a porosity of 60 to 70%, and the honeycomb structure may have a pore diameter D′ 90 of 30 μm or less. However, the pore diameter D'90 is a pore diameter in which 90% of the total pore volume of the honeycomb structure has a smaller pore diameter.

  The partition wall between the first channel and the second channel of the honeycomb structure may have a thickness of 0.15 to 0.25 mm.

  Further, the first sealing portion satisfies all of the above conditions (a) to (c), the length of the first sealing portion is 1.0 to 1.8 mm, and the second flow path is a gas inlet. It can be a flow path.

  ADVANTAGE OF THE INVENTION According to this invention, the honeycomb filter which can make low pressure loss and high collection efficiency compatible is provided.

FIG. 1 is a cross-sectional view along the axis of a honeycomb filter according to an embodiment of the present invention. FIG. 2 is a cross-sectional view perpendicular to the axis of the honeycomb filter according to one embodiment of the present invention. FIG. 3 is a cross-sectional view perpendicular to the axis of a honeycomb filter according to another embodiment of the present invention.

(Honeycomb filter)
A honeycomb filter 100 according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the honeycomb filter 100 includes a honeycomb structure 120, a plurality of inlet sealing portions (a plurality of first sealing portions) 130a, and a plurality of outlet sealing portions (a plurality of second sealing portions) 130b. Have

(Honeycomb structure)
The honeycomb structure 120 has a columnar shape, and has an inlet end face (one end) 100a and an outlet end face (the other end) 100b at both ends in the axial direction. The honeycomb structure 120 is an aggregate of porous partition walls W, and extends in the axial direction of the honeycomb structure, a plurality of inlet channels (a plurality of second channels: through holes) 110a, and a plurality of It has an outlet channel (a plurality of first channels: through holes) 110b. A plug-type outlet sealing part (second sealing part) 130b is provided at the end of the inlet channel 110a on the outlet end surface 100b side, while the inlet end surface 100a of the inlet channel 110a is opened. A plug-type inlet sealing portion (first sealing portion) 130a is provided at the end of the outlet channel 110b on the inlet end surface 100a side, while the outlet end surface 100b of the outlet channel 110b is opened.

  The cross-sectional shapes of the inlet channel 110a and the outlet channel 110b can be, for example, a circle, an ellipse, a quadrangle, a hexagon, and an octagon. In the honeycomb structure 120, each inlet channel 110 a is adjacent to at least one outlet channel 110 b via a partition wall W.

  The arrangement of the inlet channel 110a and the outlet channel 110b in the honeycomb structure is not particularly limited. The inlet channel 110a may be adjacent to at least one outlet channel 110b via the partition wall W. The inlet channel 110a may be adjacent to another inlet channel via the partition wall W, or the outlet channel 110b. May be adjacent to another outlet channel via a partition wall W. Each partition W is porous and allows gas to pass between the flow paths.

  Specifically, for example, as shown in FIG. 2, the cross-sectional shapes of the inlet channel 110a and the outlet channel 110b are hexagonal, and one inlet channel 110a is adjacent to three other inlet channels 110a. In addition, the inlet channel 110a and the outlet channel 110b can be regularly arranged so as to be adjacent to the three outlet channels 110b. In this case, one outlet channel 110b is adjacent to the six inlet channels 110a, and is not adjacent to the other outlet channels 110b. Each flow path is adjacent to a total of 6 other flow paths through partition walls W. The aggregate of the partition walls W constitutes the honeycomb structure 120.

  Further, as shown in FIG. 3, the inlet channel 110a and the outlet channel are arranged so that one inlet channel 110a is adjacent to the four other inlet channels 110a and adjacent to the two outlet channels 110b. 110b may be regularly arranged. One outlet channel 110b is adjacent to the six inlet channels 110a, and is not adjacent to the other outlet channels 110b. Thus, each channel is adjacent to a total of six other channels.

  The thickness of each partition wall W can be, for example, 6 to 10 mil, that is, 0.15 to 0.25 mm. When W exceeds 0.25 mm, the pressure loss tends to increase. Moreover, when W is less than 0.15 mm, the strength of the honeycomb structure tends to decrease.

  The cell density, that is, the density of the flow path (cell) in the cross section orthogonal to the axis of the honeycomb structure can be set to, for example, 150 to 400 cpsi (cell per square inch). “Cpsi” represents the number of flow paths (cells) per square inch. The circle equivalent diameter of each flow path can be set to 1.5 to 2.0 mm, for example.

  The honeycomb structure 120 is formed from a porous ceramic material. Examples of the ceramic material are aluminum titanate ceramics, cordierite ceramics, and silicon carbide ceramics.

In the present embodiment, in the pore size distribution of the honeycomb structure 120, the pore size D′ 90 is preferably 30 μm or less, more preferably 25 μm or less, and further preferably 20 μm or less. The lower limit of the pore diameter D′ 90 can be 10 μm.
Here, the pore diameter D′ 90 is a pore diameter in which 90% of the total pore volume of the honeycomb structure 120 has a pore diameter smaller than that. If the pore diameter D′ 90 is more than 30 μm, the filtration efficiency tends to decrease.

  Filtration efficiency can be measured by the following method. First, one open end of the honeycomb structure is connected to a carbon generator (manufactured by DNP-2000 PALAS: average particle diameter of carbon particles (soot) 60 nm), and a leakage test is performed. After carbon particles generated from the carbon generator began to pass through the flow path of the honeycomb structure using a diluter (MD-19-1E, manufactured by Matter) and a measuring instrument (EEPS-3000, manufactured by TSI). The number concentration of carbon particles after 180 seconds is measured. In addition, it has shown that the filtration performance as a particulate filter is so high that the number density | concentration of the carbon particle after passing a honeycomb structure is low.

The porosity of the honeycomb structure 120 is preferably 60 to 70%, more preferably 65% to 70%. If it is less than 60%, the pressure loss tends to increase, and if it exceeds 70%, the filtration efficiency tends to decrease.
The pressure loss can be measured by the following method. First, the open end of the flow path is connected to an instrument air supply source via a pressure reducing valve or a metering regulator. Then, a difference between the pressure value and the atmospheric pressure value (differential pressure: ΔP (kPa)) when instrumented air (pressure value: 1 MPa) is flowed into the test piece at a constant flow rate value is obtained with a manometer.

  The pore size distribution and the porosity of the honeycomb structure 120 can be measured by the mercury intrusion method as follows. First, a small piece of about 2 mm square is cut out from the honeycomb structure and dried in an air at 120 ° C. for 4 hours using an electric furnace. Then, the pore diameter is measured in the range of 0.005 to 200.0 μm by the mercury intrusion method to determine the cumulative pore volume (ml / g) and the average pore diameter (μm). As the measuring device, “Autopore III9420” manufactured by Micromeritics can be used.

(Sealing part)
In the present embodiment, at least one inlet sealing part (first sealing part) 130a or at least one outlet sealing part (second sealing part) 130b satisfies all of the following three conditions (a) to (c). .

(A) The length L in the direction along the flow path, that is, the axial length of the sealing portion is 0.3 to 1.8 mm.
(B) The porosity is 60 to 70%.
(C) The pore diameter D90 is 30 μm or less.
However, the pore diameter D90 is a pore diameter in which 90% of the total pore volume of the sealing portion has a smaller pore diameter. D90 can be 10 μm or more.

  When both the inlet sealing portion 130a and the outlet sealing portion 130b are plug-type sealing portions as in the present embodiment, at least one inlet sealing portion (first sealing portion) 130a and at least one The outlet sealing part (second sealing part) 130b can satisfy all the above three conditions (a) to (c).

  Here, it is preferable that 50% or more of the inlet sealing portions 130a and 50% or more of the outlet sealing portions 130b with respect to the total number of the inlet sealing portions 130a satisfy the above three conditions. It is preferable that 70% or more of the inlet sealing portions 130a and 70% or more of the outlet sealing portions 130b with respect to the total number of the sealing portions 130a satisfy the above three conditions. It is more preferable that 90% or more of the inlet sealing portions 130a and the outlet sealing portions 130b of 90% or more with respect to the total number satisfy the above three conditions.

  The length L of the inlet sealing portion 130a that satisfies the above three conditions is preferably 1.0 to 1.8 mm. In this case, the erosion of the inlet sealing portion caused by particles in the gas colliding with the inlet sealing portion can be suppressed.

  The pore size distribution and the pore size of the inlet sealing portion 130a and the outlet sealing portion 130b can be measured by a mercury intrusion method.

  The porosity and the pore diameter D90 of the inlet sealing portion 130a and the outlet sealing portion 130b are preferably within a range of ± 10% with respect to the porosity and the pore diameter D90 of the honeycomb structure 120, and are within ± 5%. A range is more preferable. Further, the porosity and the pore diameter D90 of the honeycomb structure 120 are preferably within ± 10% of the porosity and the pore diameter D90 of the inlet sealing portion 130a and the outlet sealing portion 130b, respectively, and ± 5% More preferably, it is within the range. By making the porosity and the pore diameter substantially the same between the sealing portion and the honeycomb structure, it is easy to enhance the effect of the invention. The porosity of the inlet sealing part 130a and the outlet sealing part 130b is 60 to 70%, more preferably 65 to 70%. The pore diameter D90 of the inlet sealing portion 130a and the outlet sealing portion 130b is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. The lower limit of the pore diameter D90 of the inlet sealing portion 130a and the outlet sealing portion 130b can be 10 μm.

  The inlet sealing portion 130a and the outlet sealing portion 130b are formed from a ceramic material. An example of the ceramic material is the same as that of the honeycomb structure 120. The material of the sealing portion 130 is preferably the same material as the honeycomb structure 120.

  A coating agent layer can be provided on the surface of the inlet end surface 100 a of the honeycomb filter 100 formed by the sealing portion 130 and the honeycomb structure 120. As the coating agent, for example, an aqueous ceramic solution such as alumina, titania or silica can be used.

  This honeycomb filter can be used, for example, as an exhaust gas filter for a diesel engine and an exhaust gas filter for a gasoline engine. This honeycomb filter can realize high filtration efficiency without increasing pressure loss so much. The reason for this is not clear, but by reducing the axial length of the sealing portion sufficiently, increasing the porosity of the sealing portion 130, and reducing the pore diameter D90 of the sealing portion 130, the arrow G in FIG. As described above, gas efficiently flows not only in the partition wall W but also in the sealing portion 130, and the sealing portion 130 functions effectively as a filter, and the generation of turbulence at the end surface is suppressed, and low pressure loss and high It is considered that both filtration efficiencies can be achieved.

(Honeycomb filter manufacturing method)
First, ceramic raw material powder, a binder, a pore former, a solvent, and additives that are added as necessary are mixed, and the mixture is molded to obtain a honeycomb molded body having a large number of through holes.

  The ceramic raw material powder can be appropriately selected according to the target ceramic. For example, aluminum titanate includes a titanium source such as titania and an aluminum source such as alumina. Cordierite includes a magnesium source such as magnesia, an aluminum source such as alumina, and a silicon source such as silica. If it is silicon carbide, a carbon source and a silicon source are included.

  The amount of each component is appropriately adjusted so as to obtain a desired ceramic. The particle size D50 of the ceramic raw material powder may be 1.0 to 10.0 μm. The particle size D50 can be obtained based on a volume-based particle size distribution by a laser diffraction particle size distribution meter.

  The binder can be an organic binder, examples of which are celluloses such as methylcellulose, carboxymethylcellulose, hydroxyalkylmethylcellulose, sodium carboxymethylcellulose; alcohols such as polyvinyl alcohol; lignin sulfonate.

  Examples of the additive include a lubricant, a plasticizer, and a dispersant.

  The pore former is a powder and is removed from the honeycomb formed body by decomposition / combustion / evaporation / sublimation or the like during firing to give a porous structure to the honeycomb structure. Examples of such pore formers are organic powder, carbon powder, and dry ice powder. Examples of organic powders are starch (potato starch, corn starch, wheat starch, pea starch), wheat flour, and resin powder. Examples of the resin powder are polyethylene powder and expandable resin powder (for example, polyethylene, polystyrene, acrylic, epoxy resin, etc.). An example of carbon powder is carbon black. The pore size distribution can be controlled by the amount and particle size of the pore former.

  Examples of the solvent are water and alcohol.

  After the honeycomb formed body is obtained, a sealing material is filled into one end of the through hole and plugged. The material of the sealing material can be the same as that of the honeycomb formed body. Thereafter, by firing the sealed honeycomb formed body, a honeycomb filter having the above-described sealing portion can be obtained. The length L of the sealing portion can be set to a desired value by adjusting the filling amount of the sealing material in each flow path. Moreover, the porosity and pore diameter D90 of a sealing part can satisfy | fill the said conditions by adjusting the quantity of the pore former in a sealing material, and the particle size of a pore former. For example, in order to increase the porosity, the amount of the pore former may be increased. Moreover, what is necessary is just to make the particle size of a pore making material small in order to make a pore diameter small.

  The temperature of baking can be 1300-1500 degreeC, for example. When the pore former is organic powder or carbon powder, firing is preferably performed in an oxygen-containing atmosphere, and is preferably performed in an air atmosphere.

  The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above-described embodiment, both the inlet channel 110a and the outlet channel 110b are closed by the plugged sealing part 130, but either one of the channels is sealed by the plugged sealing part. Any one of the flow paths may be sealed with a sealing portion other than the plugging type. An example of a sealing part other than the plugging type is that the cross-sectional area of one of the flow paths is enlarged toward the end face of the honeycomb filter in the partition wall at the end of the porous honeycomb molded body, and It is a sealing part obtained by deforming so that the cross-sectional area is reduced to zero and then firing. In this case, it is only necessary that at least one plug-type sealing portion satisfies all the three conditions (a) to (c). Also in this case, it is preferable that 55% or more of the sealing parts with respect to the total number of plugging type sealing parts satisfy the three conditions, more preferably 70% or more of the sealing parts satisfy the three conditions, and 90% or more. It is even more preferable that the sealing portion satisfies the three conditions.

  A numerical model of the honeycomb filter was created, and the pressure loss of the honeycomb filter was calculated by the following method.

Specifically, by calculating the three-dimensional pressure distribution of the honeycomb filter by solving the following Navier-Stokes equations for compressible isothermal Newtonian fluid, and subtracting the pressure downstream of the honeycomb filter from the pressure upstream of the honeycomb filter The pressure loss of the honeycomb filter was obtained.

Here, ∂ is partial differential, ρ is density, t is time, p is pressure, μ is viscosity, u is velocity, x is coordinates, and _Si is a pressure loss during porous permeation described later. Subscripts i and j represent the direction of the Cartesian coordinate system. δ _ij is the Kronecker delta. The expressions (C1) and (C2) are Einstein's sum rules. As the physical properties, air values of 800 ° C. were used.

ここで、μ_ｔは乱流粘性、kは乱流エネルギーを表す。式の記法は（Ｃ１）式及び（Ｃ２）式と同様とする。 The parentheses in the last term of the formula (C2) are Reynolds stresses defined by eddy viscosity approximation as shown in the formula (C3).

Here, μ _t represents turbulent viscosity, and k represents turbulent energy. The notation of the formula is the same as the formula (C1) and formula (C2).

  Equation (C3) can be suitably modeled by a known turbulent model, and equations (C1) and (C2) can be obtained numerically using a computer by a known method.

ここでαは透過率であり、AthanasiosG. Konstandopoulos，John H. Johnson著，「Wall-Flow Diesel Particulate Filters - Their Pressure Drop andCollection Efficiency」，SAE Technical Paper 890405，1989年，doi:10.4271/890405に記載の方法に従って算出した。なお、入口側流路、出口側流路、ハニカム構造体、封口部を含むハニカムフィルタの内部において、μ_ｔはゼロであるとし、新たな乱流の生成は生じないものとした。 In this calculation example, it is difficult from the viewpoint of calculation load to directly determine the pressure loss of the honeycomb structure and the sealing portion of the honeycomb filter from the molecules and the turbulent viscosity. Therefore, this factor was modeled separately and given by the additional term S _i . That, S _i in the honeycomb structure and the sealing unit, represents the pressure loss that occurs when passing through the honeycomb structure and the sealing portion of the porous. Specifically, S _i was given by the following equation.

Where α is the transmittance, as described in AthanasiosG. Konstandopoulos, John H. Johnson, “Wall-Flow Diesel Particulate Filters-Their Pressure Drop and Collection Efficiency”, SAE Technical Paper 890405, 1989, doi: 10.4271 / 890405 Calculated according to the method. Incidentally, inlet passage, outlet passage, a honeycomb structure, inside the honeycomb filter including a sealing portion, the mu _t and is zero, and shall not cause generation of new turbulence.

Further, the filtration efficiency of the honeycomb structure was calculated by the following method with respect to the above numerical model. Specifically, it was calculated from SAE Technical Paper 890405 and SAE Lecture Proceedings SAE 2000-01-1016 by the following formula.

ここで、η_Ｄ：ブラウン拡散による単一捕集効率、η_Ｒ：遮りによる単一捕集効率とした。η_Ｄは次式で算出した。

Here, E: collection efficiency, η: single collection efficiency, ε: porosity, w _S : wall thickness, d _c : single sphere diameter. η was calculated by the following formula.

Here, η _D : single collection efficiency by Brown diffusion, η _R : single collection efficiency by blocking. η _D was calculated by the following formula.

Where g _S : shape function, Pe: Peclet number, U _i : gas pore velocity, D _p : particle diffusion coefficient, u _W : gas superficial velocity, V: gas volume flow rate, TFA: total filtration area, k _B : Boltzmann constant, T: gas temperature, μ: gas viscosity coefficient, d _p : particle diameter (= 90 nm), Kn _p : particle Knudsen number, λ: gas mean free path, ρ: gas density, MW: gas Molecular weight, R: Gas constant. η _R was calculated by the following formula. N _R is a blocking parameter.

ここで、d_poreは平均気孔径とした。 d _c was calculated by the following equation.

Here, d _pore was an average pore diameter.

(Calculation Example 1)
The honeycomb structure has a porosity of 70%, the honeycomb structure has a pore diameter D′ 90 value of 25 μm, the honeycomb filter has a diameter of 118.4 mm, and a length of 50.8 mm. The cross-sectional shape was square, the cell density was 300 cpsi, and the partition wall thickness was 0.20 mm. Furthermore, the sealing part was arrange | positioned at the edge part on the opposite side between adjacent cells, and the sealing part length was 0.5 mm. Moreover, the porosity of the sealing part was 68%, and the pore diameter D90 value of the sealing part was 25 μm. The pressure loss of the honeycomb filter and the filtration efficiency of the honeycomb structure were calculated by the above method.

(Calculation Example 2, Comparative Calculation Examples 1 to 4)
As shown in Table 1, Calculation Example 2 and Comparative Calculation Example 1 were obtained in the same manner as Calculation Example 1 except that the length of the sealing portion was changed.
Comparative Calculation Example 2 was obtained in the same manner as Calculation Example 2, except that the value of the pore diameter D90 of the sealing portion and D′ 90 of the honeycomb structure were changed.
Comparative calculation example 3 was obtained in the same manner as calculation example 1 except that the porosity of the sealing portion and the porosity of the honeycomb structure were changed.
Comparative Calculation Example 4 was obtained in the same manner as in Calculation Example 1 except that the porosity of the sealing portion, D90 of the sealing portion, and the porosity of the honeycomb structure and D′ 90 of the honeycomb structure were changed.

  DESCRIPTION OF SYMBOLS 100 ... Honeycomb filter, 120 ... Honeycomb structure, 110a ... Inlet flow path (2nd flow path), 110b ... Outlet flow path (1st flow path), 130a ... Inlet sealing part (1st sealing part), 130b ... Outlet Sealing part (second sealing part).

Claims (5)

A columnar and porous honeycomb structure forming a plurality of first flow paths and a plurality of second flow paths;
A plurality of first sealing portions for closing the first flow paths on one end side of the honeycomb structure;
A plurality of second sealing portions that close the second flow paths on the other end side of the honeycomb structure, and
The honeycomb filter in which the first sealing portion or the second sealing portion satisfies all of the following conditions (a) to (c).
(A) The length in the direction along the flow path is 0.3 to 1.8 mm.
(B) The porosity is 60 to 70%.
(C) The pore diameter D90 is 30 μm or less.
However, the pore diameter D90 is a pore diameter in which 90% of the total pore volume of the sealing portion has a smaller pore diameter.   The honeycomb filter according to claim 1, wherein the first sealing portion and the second sealing portion satisfy all of the conditions (a) to (c). The honeycomb filter according to claim 1 or 2, wherein a porosity of the honeycomb structure is 60 to 70%, and a pore diameter D'90 of the honeycomb structure is 30 µm or less.
However, the pore diameter D′ 90 is a pore diameter in which 90% of the total pore volume of the honeycomb structure has a smaller pore diameter.   The honeycomb filter according to any one of claims 1 to 3, wherein a thickness of a partition wall between the first flow path and the second flow path of the honeycomb structure is 0.15 to 0.25 mm. The first sealing portion satisfies all the conditions (a) to (c), the length of the first sealing portion is 1.0 to 1.8 mm, and the second flow path is a gas inlet flow path. The honeycomb filter according to any one of claims 1 to 4, wherein

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