Honeycomb filter body and particulate filter comprising honeycomb filter body

Abstract

A honeycomb filter body comprising: a clean filter pressure drop (P1) and a clean filter efficiency (FE1); a porous ceramic honeycomb body comprising a first end, a second end, and a plurality of walls having wall surfaces defining a plurality of internal channels, the porous ceramic honeycomb body comprising a base clean filter pressure drop (P0) and a base clean filtration efficiency (FE0); and a porous inorganic layer disposed on one or more wall surfaces of the porous ceramic honeycomb body.

Description

[0001] This invention patent application is a divisional application of the invention patent application with international application number PCT / US2020 / 030899, international application date May 1, 2020, application number 202080034444.0 entering the Chinese national phase, and invention name "Honeycomb filter body and particulate filter comprising a honeycomb filter body".

[0002] background

[0003] This application claims the benefit of priority under 35 U.S.C. §119 to U.S. Provisional Application No. 62 / 845,070, filed on May 8, 2019, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0004] The present specification relates to a honeycomb filter body, a particulate filter including the honeycomb filter body, and methods of making the honeycomb filter body and the particulate filter. Background Art

[0005] Wall-flow ceramic filters are used to remove particulates from fluid emission streams, for example, from internal combustion engine exhaust. Examples include ceramic soot filters for removing particulates from diesel engine exhaust, and gasoline particulate filters (GPFs) for removing particulates from gasoline engine exhaust. With a wall-flow filter, the exhaust gas to be filtered enters the inlet pores and passes through the pore walls to exit the filter via an outlet channel, wherein the particulates are captured on or within the inlet pore walls as the gas passes through and then exits the filter. The particulates may comprise soot and / or ash. After prolonged exposure to engine exhaust, an accumulation of soot and / or ash may typically occur within the filter.

[0006] There is a continuing need to improve particulate filters for engine exhaust systems, such as gasoline particulate filters, and to achieve lower pressure drops. Summary of the Invention

[0007] In one aspect, a honeycomb filter body comprises: a clean filter pressure drop (P1) and a clean filter efficiency (FE1); a porous ceramic honeycomb body comprising a first end, a second end, and a plurality of walls, the plurality of walls having wall surfaces defining a plurality of internal channels, the porous ceramic honeycomb body comprising a base clean filter pressure drop (P0) and a base clean filter efficiency (FE0); and a porous inorganic layer disposed on one or more wall surfaces of the porous ceramic honeycomb body; wherein an overall performance parameter of the honeycomb filter body is defined as "X", which is defined according to formula (I):

[0008]

[0009] The filter performance is defined as "F", which is defined according to formula (II):

[0010] and

[0011] X is greater than or equal to 1.75, and F is greater than or equal to 0.25.

[0012] In another aspect, a honeycomb filter comprises: a porous ceramic honeycomb body comprising a first end, a second end, and a plurality of walls, the plurality of walls having wall surfaces defining a plurality of internal channels; a porous inorganic layer disposed on one or more wall surfaces of the porous ceramic honeycomb body, the porous inorganic layer comprising an average porosity (ε), an average particle size in microns (d p ), and thickness t m ; wherein the morphology parameter of the porous inorganic layer is defined as "Y", which is defined according to formula (IV):

[0013] and

[0014] Y is greater than or equal to 0.02.

[0015] Additional aspects include methods for applying inorganic materials to honeycomb filter bodies.

[0016] Additional features and advantages are set forth in the following detailed description, some of which will be apparent to those skilled in the art from that description or may be learned by practicing the embodiments described herein, including the following detailed description, claims, and accompanying drawings.

[0017] It should be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overall overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein and, together with the description, serve to explain the principles and operation of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 According to the embodiments disclosed and described herein, a honeycomb filter body is schematically depicted;

[0019] Figure 2 According to the embodiments disclosed and described herein, a honeycomb filter body with soot loading is schematically depicted;

[0020] Figure 3 According to the embodiments disclosed and described herein, a particulate filter is schematically depicted;

[0021] Figure 4 yes Figure 4 a cross-sectional view of the particulate filter shown;

[0022] Figure 5 is a schematic diagram illustrating an experimental setup for testing a particulate filter according to one or more embodiments;

[0023] Figure 6-7 is a graph showing the relationship between filtration efficiency and pressure drop increase for an embodiment;

[0024] Figure 8-9 is a graph of parameter "X" versus pressure drop increase for an embodiment;

[0025] Figure 10 is a graph of parameter "X" versus increasing parameter "Y" for an embodiment; and

[0026] Figure 11-12 Graph showing the relationship between filtration efficiency and pressure drop increase according to an embodiment. DETAILED DESCRIPTION

[0027] Embodiments of honeycomb filter bodies comprising a porous honeycomb body and having a porous inorganic layer on the porous honeycomb body will now be discussed in detail, and their embodiments are illustrated in the accompanying drawings. Whenever possible, the same reference numerals are used in the drawings to represent the same or similar parts. In some embodiments, the honeycomb filter body comprises a porous ceramic honeycomb body comprising a first end, a second end, and a plurality of walls having wall surfaces defining a plurality of internal channels; and a porous inorganic layer disposed on one or more wall surfaces of the honeycomb body. The honeycomb filter body has a clean filter pressure drop (P1) and a clean filter efficiency (FE1). The porous ceramic honeycomb body not including the porous inorganic layer has a basic clean filter pressure drop (P0) and a basic clean filter efficiency (FE0). The porous inorganic layer comprises an average porosity (ε), an average particle size in microns (d p ) and thickness (t m ). The "clean" pressure drop and "clean" filtration efficiency referred to herein refer to analyses performed on the corresponding honeycomb filter body or porous ceramic honeycomb body without any soot or exhaust particulates trapped in the honeycomb filter body or porous ceramic honeycomb body.

[0028] The honeycomb filter of this article has one or more of the following parameters or a combination of parameters:

[0029] The overall performance parameter of the honeycomb filter, defined as "X", is defined according to formula (I):

[0030]

[0031] Wherein, X is greater than or equal to 1.75;

[0032] The filtration performance of the honeycomb filter, defined as "F", is defined according to formula (II):

[0033]

[0034] Where, F is greater than or equal to 0.25;

[0035] The pressure drop performance, defined as "P", is defined according to formula (III):

[0036]

[0037] Wherein, P is less than or equal to 0.25; and

[0038] The morphology parameter of the porous inorganic layer, defined as "Y", is defined according to formula (IV):

[0039]

[0040] Wherein, Y is greater than or equal to 0.02.

[0041] In various embodiments, a cordierite honeycomb monolith structure can be used for a GPF. An artificial membrane or an inorganic porous layer can be applied to the wall of the cordierite honeycomb monolith structure. The layer prevents soot from penetrating into the wall, thereby eliminating or reducing the increase in pressure drop caused by deep bed soot penetration. The layer improves the filtration efficiency performance of the filter by making it act as an effective filter medium. However, these layers can increase the pressure drop across the filter due to a reduction in the hydraulic diameter of the channel and / or due to a reduction in the effective length of the filter (due to a blockage formed at the rear end of the inlet channel by part of the membrane layer). Preferably, the layer increases the filtration efficiency performance with a small increase in the pressure drop loss caused by the layer. In some embodiments, these layers only partially cover the channel length. The honeycomb filter bodies herein exhibit high filtration efficiency (especially when clean or with very low soot or ash loading), as well as low pressure drop at this high filtration efficiency.

[0042] Various embodiments of honeycomb filter bodies and methods of making the same will be described herein with particular reference to the accompanying drawings. In some embodiments, a particulate filter is provided, comprising a honeycomb body comprising a plugged porous ceramic honeycomb structure comprising a plurality of intersecting porous walls, the porous walls comprising porous wall surfaces defining a plurality of channels extending from an inlet end to an outlet end of the structure, the plurality of channels comprising inlet channels sealed at or near the outlet end and having a surface area, and outlet channels sealed at or near the inlet end and having a surface area, the inlet channels and outlet channels defining a filtration region, wherein the one or more porous wall surfaces defining the inlet channels comprise a base wall portion and a filter material deposit disposed on the base wall portion, wherein the filter material deposit is disposed on the base wall portion.

[0043] In some embodiments, the filter material deposits are preferably mechanically stable, e.g., resistant to displacement or rearrangement, e.g., due to high gas flow through the clogged honeycomb structure of the particulate filter, and / or due to mechanical vibrations. In one or more embodiments, the transition material deposits are stable when exposed to water, so that the deposits maintain their position or location on the pore walls. In other words, according to some embodiments, the filter material deposits are bonded to the porous ceramic substrate walls. In some embodiments, the deposits are chemically bonded, rather than just bonded by physical bonding. For example, in some embodiments, the flame pyrolysis filter material deposits are fused or sintered to the porous ceramic substrate walls. Furthermore, in some embodiments, the flame pyrolysis filter material deposits are fused or sintered to each other to form a porous inorganic material layer.

[0044] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include embodiments having plural referents unless the context clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and / or" unless the context clearly dictates otherwise.

[0045] As used herein, the words "have," "have," "contain," "include," "includes," and the like are used in their open-ended sense and generally mean "including but not limited to."

[0046] As used herein, "honeycomb" includes a shaped ceramic honeycomb structure or matrix having intersecting walls that form cells that define channels. The ceramic honeycomb structure can be formed, extruded, or molded and can be of any shape or size. For example, the ceramic honeycomb structure can be formed from cordierite or other suitable ceramic materials.

[0047] A honeycomb body as referred to herein may also refer to a shaped ceramic honeycomb structure having a surface treatment, such as at least one layer, applied to the wall surfaces of the honeycomb structure and configured to filter particulate matter from a gas stream. There may be more than one layer applied to the same location of the honeycomb structure. The surface treatment (e.g., layer) may be inorganic or organic, or both. For example, in one or more embodiments, a honeycomb body may be formed of cordierite or other ceramic material and have a porous inorganic layer applied to the surface of the cordierite honeycomb structure. The layer may be a "filter material" that is used to provide enhanced filtration efficiency both locally through the walls and at the walls and through the entire honeycomb body. The filter material is not considered to be catalytically active because it does not react with components in the gaseous mixture of the exhaust stream.

[0048] As used herein, "green" or "green ceramic" are used interchangeably and refer to unsintered material unless otherwise specified.

[0049] The honeycomb body of one or more embodiments may include a honeycomb structure and a layer disposed on one or more walls of the honeycomb structure. In some embodiments, the layer is applied to a wall surface present within the honeycomb structure, wherein the wall has a surface defining a plurality of internal channels. When present, the internal channels may have a variety of cross-sectional shapes, such as circular, oval, triangular, square, pentagonal, hexagonal, or a checkerboard combination of any of these, and may be arranged, for example, in any suitable geometric configuration. When present, the internal channels may be discrete or intersecting and may extend from a first end of the honeycomb body through the honeycomb body to a second end of the honeycomb body, the second end being opposite the first end.

[0050] Now refer to Figure 1, which shows a honeycomb body 100 according to one or more embodiments shown and described herein. In an embodiment, the honeycomb body 100 may include a plurality of walls 115 defining a plurality of internal channels 110. The plurality of internal channels 110 and the intersecting channel walls 115 extend between a first end 105 and a second end 135 of the honeycomb body. One or more channels of the honeycomb body may be plugged at one or both of the first end 105 and the second end 135. The pattern of plugged channels of the honeycomb body is not limited. In some embodiments, the pattern of plugged and unplugged channels at one end of the honeycomb body can be, for example, a checkerboard pattern, wherein alternating channels at one end of the honeycomb body are plugged. In some embodiments, a plugged channel at one end of the honeycomb body has a corresponding unplugged channel at the other end, and an unplugged channel at one end of the honeycomb body has a corresponding plugged channel at the other end. Thus, in some embodiments, a particulate filter, such as a gasoline particulate filter (GPF), comprises a honeycomb structure formed by an array of parallel channels bounded and separated by porous cell walls, wherein a portion of the channels are blocked or plugged, for example, some channels are blocked at the filter inlet, while the remaining channels are blocked at the filter outlet. Exhaust gas to be filtered thus enters the unblocked inlet channels and passes through the channel walls to exit the filter via the unblocked outlet channels, wherein particulates are trapped on or within the inlet channel walls as the gas passes through the filter.

[0051] In one or more embodiments, the honeycomb body may be formed from cordierite, aluminum titanate, enstatite, mullite, forsterite, corundum (SiC), spinel, sapphire, and periclase. In general, cordierite is a crystalline solid having a carbon structure according to the formula (Mg,Fe)2Al3(Si5AlO 18 ). In some embodiments, the pore size of the ceramic material can be controlled, the porosity of the ceramic material can be controlled, and the pore size distribution of the ceramic material can be controlled, for example, by varying the particle size of the ceramic raw material. Furthermore, a pore former can be included in the ceramic batch material used to form the honeycomb body.

[0052] In some embodiments, the average thickness of the walls of the honeycomb body may be greater than or equal to 25 μm and less than or equal to 250 μm, such as greater than or equal to 45 μm and less than or equal to 230 μm, greater than or equal to 65 μm and less than or equal to 210 μm, greater than or equal to 65 μm and less than or equal to 190 μm, or greater than or equal to 85 μm and less than or equal to 170 μm. The walls of the honeycomb body may be described as having a base wall portion (also referred to herein as the body) comprising a body portion and a surface portion (also referred to herein as the surface). The surface portion of the wall extends into the wall from the surface of the wall of the honeycomb body toward the body portion of the honeycomb body. The surface portion may extend from 0 (zero) into the base wall portion of the wall of the honeycomb body and extend to a depth of about 10 μm. In some embodiments, the surface portion may extend into the base wall portion of the wall to about 5 μm, about 7 μm, or about 9 μm (i.e., to a depth of 0 (zero)) of the wall. The body portion of the honeycomb body constitutes the thickness of the wall minus the surface portion. Thus, the body portion of the honeycomb body may be determined by the following formula:

[0053] t 总 –2t 表面

[0054] Among them, t 总 is the total thickness of the wall, and t 表面 is the thickness of the wall surface.

[0055] In one or more embodiments, the body of the honeycomb body has a body average pore size that is greater than or equal to 7 μm and less than or equal to 25 μm, for example, greater than or equal to 12 μm and less than or equal to 22 μm, or greater than or equal to 12 μm and less than or equal to 18 μm. For example, in some embodiments, the body average pore size of the honeycomb body can be about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, about 15 μm, about 16 μm, about 17 μm, about 18 μm, about 19 μm, or about 20 μm. In general, the pore sizes of any given material exist as a statistical distribution. Therefore, the term "average pore size" or "D" may refer to a material having a body average pore size. 50 ” means that 50% of the pores have a pore size less than or equal to this value, and the remaining 50% of the pores have a pore size greater than this value, based on the statistical distribution of all pores. The pores in the ceramic body can be produced based on at least one of the following: (1) inorganic batch material particle size and particle size distribution; (2) furnace / heat treatment firing time and temperature schedule; (3) furnace atmosphere (e.g., low or high oxygen and / or water content), and (4) pore formers, such as polymers and polymer particles, starch, wood flour, hollow inorganic particles, and / or graphite / carbon particles.

[0056] In some embodiments, the honeycomb body can have a bulk porosity (excluding coatings) greater than or equal to 50% to less than or equal to 70%, as measured by mercury porosimetry. Methods for measuring surface porosity include scanning electron microscopy (SEM), which is particularly useful for measuring surface porosity and bulk porosity independently of each other. In one or more embodiments, the honeycomb body can have a bulk porosity of, for example, less than 70%, less than 65%, 60%, less than 58%, less than 56%, less than 54%, or less than 52%.

[0057] In one or more embodiments, the surface median pore size of the surface portion of the honeycomb body is greater than or equal to 7 μm and less than or equal to 20 μm, for example, greater than or equal to 8 μm and less than or equal to 15 μm, or greater than or equal to 10 μm and less than or equal to 14 μm. For example, in some embodiments, the surface median pore size of the honeycomb body surface can be about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm.

[0058] In some embodiments, the surface porosity of the honeycomb body surface prior to application of the layer may be greater than or equal to 35% to less than or equal to 50%, as measured by SEM. In one or more embodiments, the surface porosity of the honeycomb body may be, for example, less than 65%, such as less than 60%, less than 55%, less than 50%, less than 48%, less than 46%, less than 44%, less than 42%, less than 40%, less than 48%, or less than 36%.

[0059] Now refer to Figure 3 and 4 , which schematically depicts a honeycomb body in the form of a particulate filter 300. The particulate filter 300 can be used as a wall-flow filter to filter particulate matter from an exhaust stream 350, such as an exhaust stream emitted from a gasoline engine (in this case, the particulate filter 300 is a gasoline particulate filter). The particulate filter 300 generally includes a honeycomb body having a length L extending between an inlet end 302 and an outlet end 404 and defining an overall length L. a The particulate filter 300 includes a plurality of channels 301 or pores. The channels 301 of the particulate filter 300 are formed by, and at least partially defined by, a plurality of intersecting channel walls 306 extending from an inlet end 302 to an outlet end 304. The particulate filter 300 may also include a skin layer 305 surrounding the plurality of channels 301. The skin layer 305 may be extruded during the formation of the channel walls 306, or formed as a post-applied skin layer during subsequent processing, for example, by applying a skinning adhesive to the outer peripheral portions of the channels.

[0060] Figure 4 Shown Figure 3308 and outlet channels 310. In some embodiments, certain channels are designated as inlet channels 308 and certain other channels are designated as outlet channels 310. In some embodiments of the particulate filter 300, at least a first set of channels may be plugged with plugs 312. Generally, the plugs 312 are arranged near the ends (i.e., the inlet end or the outlet end) of the channels 301. The plugs are generally arranged in a predetermined pattern, for example, Figure 3 The checkerboard pattern arrangement shown, wherein every other channel is blocked at the end. Inlet channel 308 can be blocked at or near outlet end 304, while outlet channel 310 can be blocked at or near inlet end 302 on a channel that does not correspond to an inlet channel, as shown. Figure 3 Thus, each cell may be blocked at or near only one end of the particulate filter.

[0061] Although Figure 3 A checkerboard plugging pattern is generally depicted, but it should be understood that alternative plugging patterns may be used in porous ceramic honeycomb articles. In the embodiments described herein, a particulate filter 300 may be formed having a channel density of up to about 600 channels per square inch (cpsi). For example, in some embodiments, the channel density of the particulate filter 100 may be in the range of about 100 cpsi to about 600 cpsi. In other embodiments, the channel density of the particulate filter 100 may be in the range of about 100 cpsi to about 400 cpsi, or even in the range of about 200 cpsi to about 300 cpsi.

[0062] In the embodiments described herein, the channel walls 306 of the particulate filter 300 may have a thickness greater than about 4 mils (101.6 microns). For example, in some embodiments, the channel walls 306 may have a thickness in a range from about 4 mils up to about 30 mils (762 microns). In other embodiments, the channel walls 306 may have a thickness in a range from about 7 mils (177.8 microns) to about 20 mils (508 microns).

[0063] In various embodiments, the honeycomb is configured to filter particulate matter from a gas stream. Therefore, the median pore size, porosity, geometry, and other design aspects of the honeycomb body and surface are selected with these filtration requirements in mind. As an example, Figure 2As shown in the embodiment of FIG. 2 , the wall 210 of the honeycomb body 200 has a layer 220 disposed thereon, preferably sintered or bonded by heat treatment. The layer 220 includes particles 225 that are deposited on the wall 210 of the honeycomb body 200 and help prevent particulate matter (e.g., soot and ash) from exiting the honeycomb body with the gas flow 230, as well as helping to prevent particulate matter from blocking the base wall portion of the wall 210 of the honeycomb body 200. In this manner, depending on the embodiment, the layer 220 can serve as the primary filtering component, while the base wall portion of the honeycomb body can be configured to minimize pressure drop, for example, compared to a conventional honeycomb body without such a layer. As used herein, pressure drop is measured using a differential pressure sensor to measure the pressure drop across the axial length of the filter. Because the pore size of the layer 220 is smaller than the pore size of the base wall portion, the layer will filter most smaller particulate matter, but it is expected that the base wall portion of the honeycomb filter wall can effectively filter some larger particulate matter. As will be described in further detail herein, honeycombs can be formed by suitable methods, such as flame deposition, which allow for the formation of a thin, highly porous layer on at least some of the surfaces of the walls of the honeycomb.

[0064] In one or more embodiments, the layer disposed on the wall of the honeycomb body has a porosity, as measured by SEM, greater than or equal to 50%, such as greater than 55%, such as greater than 60%, such as greater than 65%, such as greater than 70%, such as greater than 75%, such as greater than 80%, such as greater than 90%. In other embodiments, the layer disposed on the wall of the honeycomb body has a porosity greater than or equal to 92%, such as greater than or equal to 93%, or greater than or equal to 94%. In other embodiments, the layer disposed on the wall of the honeycomb body has a porosity greater than or equal to 95%, such as greater than or equal to 96%, or greater than or equal to 97%. In various embodiments, the layer disposed on the wall of the honeycomb body has a porosity less than or equal to 99%, such as less than or equal to 97%, less than or equal to 95%, less than or equal to 94%, or less than or equal to 93%, less than or equal to 90%, less than or equal to 85%, less than or equal to 80%, or less than or equal to 75%. The porosity of the layer disposed on the wall of the honeycomb body allows the layer to be applied to the honeycomb body without significantly affecting the pressure drop of the honeycomb body compared to the pressure drop of an identical honeycomb body not including the layer thereon. SEM and X-ray tomography are used to independently measure surface porosity and bulk porosity. Porosity is obtained by density calculation, which involves measuring the weight of the inorganic layer and its thickness to obtain the layer density, and calculating the layer porosity according to the following equation: Layer porosity = 1 - layer density / inorganic material density. As an example, for a layer comprising mullite, the "inorganic material density" is the density of the mullite.

[0065] As described above, the layer on the honeycomb wall is very thin compared to the thickness of the base wall portion of the honeycomb wall, and the layer also has porosity and permeability. As discussed in further detail below, the layer on the honeycomb body can be formed by a method that allows the layer to be applied to the honeycomb wall surface in the form of an extremely thin layer. In embodiments, the layer on the base wall portion of the honeycomb wall has an average thickness of greater than or equal to 0.5 μm and less than or equal to 30 μm, such as greater than or equal to 0.5 μm and less than or equal to 20 μm, greater than or equal to 0.5 μm and less than or equal to 10 μm, such as greater than or equal to 0.5 μm and less than or equal to 5 μm, greater than or equal to 1 μm and less than or equal to 4.5 μm, greater than or equal to 1.5 μm and less than or equal to 4 μm, or greater than or equal to 2 μm and less than or equal to 3.5 μm.

[0066] As described above, the layer can be applied to the wall of the honeycomb by a process that allows the inorganic layer to have a small median pore size. This small median pore size allows the layer to filter a high percentage of particulates and prevent the particulates from penetrating the honeycomb and settling into the pores of the honeycomb, as described above with reference to Figure 2 According to the embodiment, the small median pore size of the layer increases the filtration efficiency of the honeycomb body. In one or more embodiments, the median pore size of the layer on the wall of the honeycomb body is greater than or equal to 0.1 μm to less than or equal to 5 μm, for example, greater than or equal to 0.5 μm to less than or equal to 4 μm, or greater than or equal to 0.6 μm to less than or equal to 3 μm. For example, in some embodiments, the median pore size of the layer on the wall of the honeycomb body can be about 0.5 μm, about 0.6 μm, about 0.7 μm, about 0.8 μm, about 0.9 μm, about 1 μm, about 2 μm, about 3 μm, or about 4 μm.

[0067] While the layer on the walls of the honeycomb body can, in some embodiments, cover substantially 100% of the surface of the walls defining the interior channels of the honeycomb body, in other embodiments, the layer on the walls of the honeycomb body covers substantially less than 100% of the surface of the walls defining the interior channels of the honeycomb body. For example, in one or more embodiments, the layer on the walls of the honeycomb body covers at least 70% of the surface of the walls defining the interior channels of the honeycomb body, covers at least 75% of the surface of the walls defining the interior channels of the honeycomb body, covers at least 80% of the surface of the walls defining the interior channels of the honeycomb body, covers at least 85% of the surface of the walls defining the interior channels of the honeycomb body, covers at least 90% of the surface of the walls defining the interior channels of the honeycomb body, or covers at least 85% of the surface of the walls defining the interior channels of the honeycomb body.

[0068] As above reference Figure 1As described, the honeycomb body may have a first end and a second end. The first end and the second end are separated by an axial length. In some embodiments, the layer on the wall of the honeycomb body may extend the entire axial length of the honeycomb body (i.e., extend along 100% of the axial length). However, in other embodiments, the layer on the wall of the honeycomb body extends along at least 60% of the axial length, for example, along at least 65% of the axial length, along at least 70% of the axial length, along at least 75% of the axial length, along at least 80% of the axial length, along at least 85% of the axial length, along at least 90% of the axial length, or along at least 95% of the axial length.

[0069] In an embodiment, the layer on the wall of the honeycomb body extends from the first end of the honeycomb body to the second end of the honeycomb body. In some embodiments, the layer on the wall of the honeycomb body extends the entire distance from the first surface of the honeycomb body to the second surface of the honeycomb body (i.e., extends along 100% of the distance from the first surface of the honeycomb body to the second surface of the honeycomb body). However, in one or more embodiments, the layer on the wall of the honeycomb body extends along 60% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, for example, along 65% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, along 70% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, along 75% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, along 80% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, along 85% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, along 90% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body, or along 95% of the distance between the first surface of the honeycomb body and the second surface of the honeycomb body.

[0070] In one or more embodiments, the layer on the wall of the honeycomb body is disposed as a continuous coating on the wall surface. As used herein, a "continuous coating" is an area in which no portion of the area is substantially bare or free of layer material. In one or more embodiments, at least 50% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, for example, at least 60% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 70% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 80% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 90% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 92% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 94% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, at least 96% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body, or at least 98% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body. In other embodiments, 100% of the layer is disposed as a continuous layer on the wall surface of the honeycomb body.

[0071] In one or more embodiments, the layer on the wall of the honeycomb body is disposed on the wall surface as a surface treatment of discrete deposits or discontinuous coatings. The discontinuous coating can be discrete sections of bare wall without the layer therein. In general, the discontinuous coating can provide a total coverage of greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, greater than or equal to 97.5%, or greater than or equal to 99% on the wall, based on the total coverage by each discrete section.

[0072] As described above, and without being bound by any particular theory, it is believed that the low pressure drop achieved by the honeycomb bodies of the embodiments is achieved because the layer on the honeycomb body is the primary filtering component of the honeycomb body, which allows for greater flexibility in the design of the honeycomb body. According to embodiments, the selection of a honeycomb body having a low pressure drop, combined with the low thickness and porosity of the layer on the honeycomb body, results in the honeycomb bodies of the embodiments having a low pressure drop when compared to conventional honeycombs. In embodiments, the layer is present in an amount of 0.1 to 30 g / L on the honeycomb body. In embodiments, the layer may be present in the following ranges: 0.2 to 20 g / L, 0.3 to 25 g / L, 0.4 to 20 g / L, or 1 to 10 g / L. In some embodiments, the pressure drop across the honeycomb body (i.e., the clean pressure drop without soot or ash) is less than or equal to 10%, e.g., less than or equal to 9%, or less than or equal to 8%, compared to a honeycomb body without the porous inorganic thin layer. In other embodiments, the pressure drop across the honeycomb body is less than or equal to 7%, e.g., less than or equal to 6%. In other embodiments, the pressure drop across the honeycomb body is less than or equal to 5%, eg, less than or equal to 4%, or less than or equal to 3%.

[0073] As described above and without being bound by any particular theory, the small pore size of the layer on the wall of the honeycomb allows the honeycomb to have excellent filtration efficiency, even before soot or ash accumulation occurs in the honeycomb. The filtration efficiency of the honeycomb is measured herein using the protocol outlined in Tandon et al., 65 Chemical Engineering Science 4751-60 (2010). As used herein, the initial filtration efficiency of a honeycomb refers to a clean honeycomb that does not include any measurable soot or ash loading, such as a new or regenerated honeycomb. In embodiments, the initial filtration efficiency (i.e., clean filtration efficiency) of the honeycomb is greater than or equal to 70%, for example, greater than or equal to 80%, or greater than or equal to 85%. In other embodiments, the initial filtration efficiency of the honeycomb is greater than 90%, for example, greater than or equal to 93%, or greater than or equal to 95%, or greater than or equal to 98%.

[0074] The layer on the wall of the honeycomb according to embodiments is thin and porous, and in some embodiments, the layer on the wall of the honeycomb also has excellent chemical durability and physical stability. This is particularly true if the layer material is cured, sintered, or otherwise bonded to the surface of the honeycomb after being applied to the wall of the honeycomb, as discussed in more detail below. In embodiments, the chemical durability and physical stability of the layer on the honeycomb can be determined by subjecting the honeycomb to a test cycle including a combustion cycle and an aging test, and measuring the initial filtration efficiency before and after the test cycle. For example, an exemplary method for measuring the chemical durability and physical stability of a honeycomb includes: measuring the initial filtration efficiency of the honeycomb; loading soot onto the honeycomb under simulated operating conditions; burning the accumulated soot at approximately 650°C; subjecting the honeycomb to an aging test at 1050°C and 10% humidity for 12 hours; and measuring the filtration efficiency of the honeycomb. Multiple soot accumulation and combustion cycles can be performed. A small change in filtration efficiency (ΔFE) from before to after the test cycle indicates better chemical durability and physical stability of the layer on the honeycomb body. In some embodiments, the ΔFE is less than or equal to 5%, for example, less than or equal to 4%, or less than or equal to 3%. In other embodiments, the ΔFE is less than or equal to 2%, or less than or equal to 1%.

[0075] In some embodiments, the layers on the walls of the honeycomb can include one or a mixture of ceramic components, for example, a ceramic component selected from the group consisting of SiO2, Al2O3, MgO, ZrO2, CaO, TiO2, CeO2, Na2O, Pt, Pd, Ag, Cu, Fe, Ni, and mixtures thereof. Thus, the layers on the walls of the honeycomb can include oxide ceramics or aluminum silicates. As described in more detail below, depending on the embodiment, the method of forming the layers on the honeycomb can allow the composition of the layers to be tailored for a given application. This can be beneficial because the ceramic components can be combined to match the physical properties of the honeycomb, such as, for example, the coefficient of thermal expansion (CTE) and Young's modulus, which can improve the physical stability of the honeycomb. In some embodiments, the layers on the walls of the honeycomb can include cordierite, aluminum titanate, enstatite, mullite, forsterite, corundum (SiC), spinel, sapphire, and periclase. In some embodiments, cordierite, aluminum titanate, enstatite, mullite, forsterite, corundum (SiC), spinel, sapphire and / or periclase are synthetic. In one or more embodiments, the inorganic layer includes synthetic mullite. Mullite is a rare aluminum silicate mineral and can form two stoichiometric forms: 3Al2O3·2SiO2 or 2Al2O3·SiO2 according to the general structure xAl2O3●ySiO2. The preparation of synthetic mullite includes process control to achieve a target of 1.5≤x / y≤2, or to achieve a target of an Al / Si mass ratio in the range of 2.9 to 3.8.

[0076] In some embodiments, the composition of the layer on the wall of the honeycomb is the same as the composition of the honeycomb. However, in other embodiments, the composition of the layer is different from the composition of the honeycomb.

[0077] According to one or more embodiments, the layer has ≥10 -15 m 2 In some embodiments, the layer has a permeability of ≥10 -14 m 2 The permeability, for example, ≥10 -13 m 2 , or ≥10 -12 m 2 .

[0078] In some embodiments, the layer comprises mullite and has an average particle size greater than or equal to 5 nm and less than or equal to 3 μm. In such embodiments, the thickness and porosity of the layer can be a thickness determined by the desired properties of the honeycomb.

[0079] In some embodiments, the layer comprises aluminum oxide and has an average particle size of greater than or equal to 10 nm and less than or equal to 3 μm. In some embodiments, the average particle size is greater than or equal to 100 nm and less than or equal to 3 μm, for example, greater than or equal to 500 nm and less than or equal to 3 μm, or greater than or equal to 500 nm and less than or equal to 2 μm. In such embodiments, the thickness and porosity of the layer on the honeycomb body can be a thickness determined by the desired properties of the honeycomb body.

[0080] The properties of the layer, and thus the properties of the entire honeycomb, can be attributed to the ability to apply thin porous layers having a small median pore size relative to the honeycomb.

[0081] According to some embodiments disclosed and described herein, a method for manufacturing a honeycomb body includes: atomizing, vaporizing or spraying a layer precursor so that the layer precursor can be carried by a gaseous carrier fluid; depositing the atomized, vaporized or sprayed layer precursor on a ceramic honeycomb structure; and bonding the atomized, vaporized or sprayed layer precursor to the ceramic honeycomb structure to form a layer on the ceramic honeycomb structure. In an embodiment, the gaseous carrier fluid can be, for example, air, oxygen or nitrogen. In some embodiments, before the layer precursor is atomized, vaporized or sprayed, the layer precursor can be combined with a solvent, for example, selected from the group consisting of methoxyethanol, ethanol, water and mixtures thereof. In one or more embodiments, the layer precursor is blown into the inner channel of the ceramic honeycomb structure. After the layer precursor has been deposited on the ceramic honeycomb structure, the layer precursor particles can be bonded to the ceramic honeycomb structure by a suitable method, including applying moisture (e.g., steam or moisture), heat, or radiation (e.g., microwaves) to the layer precursor.

[0082] A method for making a honeycomb according to some embodiments disclosed and described herein includes: depositing a layer flame pyrolysis onto a ceramic honeycomb structure, which provides for the deposition of extremely thin layers having porosity and a small median pore size. In an embodiment, the method for making a honeycomb includes: vaporizing a layer precursor by contacting the layer precursor with a vaporizing gas to form a vaporized layer precursor (the layer precursor may include a precursor material and a solvent); decomposing the vaporized layer precursor by contacting the vaporized layer precursor with a flame; depositing the vaporized layer precursor on the ceramic honeycomb structure; and sintering the vaporized layer precursor to form a honeycomb body, wherein the honeycomb body includes walls coating at least a portion of the ceramic honeycomb structure. In one or more embodiments, the layer precursor is selected from the group consisting of CaO, Ca(OH)2, CaCO3, MgO, Mg(OH)2, MgCO3, SiO2, Al2O3, Al(OH)3, calcium aluminate, magnesium aluminate, and mixtures thereof.

[0083] In some embodiments, a method of forming a honeycomb body includes forming or obtaining a layer precursor comprising a ceramic precursor material and a solvent. The ceramic precursor material of the layer precursor includes conventional ceramic raw materials used as a source of, for example, SiO2, Al2O3, TiO2, MgO, ZrO2, CaO, CeO2, Na2O, Pt, Pd, Ag, Cu, Fe, Ni, etc. For example, in some embodiments, the ceramic precursor material is selected from the group consisting of tetraethyl orthosilicate, magnesium ethoxide and aluminum (III) tri-sec-butoxide, trimethylaluminum, AlCl3, SiCl4, Al(NO3)3, aluminum isopropoxide, octamethylpicrocyclotetrasiloxane, and mixtures thereof. The solvent used for the layer precursor is not particularly limited, as long as it can maintain the ceramic precursor material in suspension in the solvent and the solvent can be vaporized at a temperature of less than 200°C. In embodiments, the solvent is selected from the group consisting of methoxyethanol, ethanol, water, xylene, methanol, ethyl acetate, benzene, and mixtures thereof.

[0084] In some embodiments, the layer precursor is vaporized to form a vaporized layer precursor by contacting the layer precursor with a vaporized fluid. In one or more embodiments, the vaporized fluid is selected from the group consisting of oxygen (O2), water (water vapor, H2O), nitrogen (N2), and mixtures thereof. The vaporized fluid flows at a higher flow rate relative to the flow rate of the layer precursor, so that when the vaporized fluid contacts the layer precursor, the layer precursor is vaporized to a molecular level by the vaporized fluid. For example, in an embodiment, the vaporized fluid is a gas flowing at a flow rate of 3 L / min (L / minute) to less than or equal to 100 L / min, for example, a flow rate greater than or equal to 4 L / min to less than or equal to 6.5 L / min, or greater than or equal to 25 L / min to less than or equal to 35 L / min. In other embodiments, the vaporized gas flows at a flow rate greater than or equal to 60 L / min to less than or equal to 70 L / min.

[0085] In embodiments, the flow rate of the gaseous vaporizing fluid is greater than the flow rate of the layer precursor. For example, in one or more embodiments, the layer precursor flows at a flow rate of greater than or equal to 1.0 mL / min to less than or equal to 50 mL / min, such as greater than or equal to 3 mL / min to less than or equal to 5 mL / min, or greater than or equal to 25 mL / min to less than or equal to 35 mL / min. The flow rates of the vaporizing fluid and the layer precursor can be controlled such that the layer precursor is vaporized upon contact with the vaporizing fluid.

[0086] According to some embodiments, once the layer precursor contacts the vaporized fluid to form a vaporized layer precursor, the vaporized layer precursor is decomposed by contacting the vaporized layer precursor with a flame. The flame can be formed by burning a suitable combustion gas, such as oxygen, methane, ethane, propane, butane, natural gas, or a mixture thereof. Once the vaporized layer precursor contacts the flame, the energy from the flame causes the vaporized layer precursor to decompose into atomic-level components, and the solvent burns into gases, such as hydrogen (H2), carbon dioxide (CO2), and carbon monoxide (CO). This combustion provides the elemental components of the ceramic precursor material that are well dispersed in the gas. In one or more embodiments, the flame temperature is greater than or equal to 800K and less than or equal to 2500K. This allows the vaporized layer precursor to be easily guided and deposited on the honeycomb body. It should be understood that in embodiments, a single flame can be used to decompose the layer precursor; however, in other embodiments, two or more flames can be used to decompose the layer precursor. In other embodiments, the vaporized layer precursor is not decomposed by the flame.

[0087] In one or more embodiments, a vaporized layer precursor that is well dispersed in a fluid is directed to the honeycomb, for example, by using a scoop or differential pressure to direct the vaporized layer precursor to the honeycomb. Thereby, the vaporized layer precursor is deposited on the honeycomb. In some embodiments, during the deposition of the vaporized layer precursor on the honeycomb, one or more channels of the honeycomb may be blocked at one end, for example, at the first end 105 of the honeycomb. In some embodiments, the blocked channels may be removed after the layer precursor is deposited. However, in other embodiments, the channels may remain blocked even after the layer precursor is deposited. The pattern of blocked channels of the honeycomb is not limited, and in some embodiments, all channels of the honeycomb may be blocked at one end. In other embodiments, only a portion of the channels of the honeycomb may be blocked at one end. In such embodiments, the pattern of blocked and unblocked channels at one end of the honeycomb is not limited, for example, it may be a checkerboard pattern in which alternating channels at one end of the honeycomb are blocked. By plugging all or a portion of the channels at one end of the honeycomb body during deposition of the vaporized layer precursor, the vaporized layer precursor may be evenly distributed within the channels 110 of the honeycomb body 100 .

[0088] In some embodiments, the vaporized layer precursor is deposited on the honeycomb as an amorphous phase. For example, as described above, the ceramic precursor material can be decomposed into elemental levels in the decomposed layer precursor. The elemental components can be mixed together at the elemental level when deposited on the honeycomb. The particles are dispersed in the amorphous phase on the honeycomb at the elemental level. In the amorphous phase, the decomposed layer precursor that has been deposited on the honeycomb has a porosity greater than or equal to 95%, for example, greater than or equal to 96%, or greater than or equal to 97%, calculated based on the relationship between the layer density and the inorganic material density of the layer. In other embodiments, the decomposed layer precursor in the amorphous phase has a porosity greater than or equal to 98%, or greater than or equal to 99%.

[0089] In some embodiments, the porosity and pore size of the amorphous phase of the vaporized layer precursor and ultimately the layer on the honeycomb body can be modified by the average particle size of the vaporized layer. The average particle size of the vaporized layer can be controlled by the flow rate of the layer precursor. For example, the average particle size of the vaporized layer precursor increases as the flow rate of the layer precursor increases. The elements of the decomposed layer precursor mix at the atomic level and form a homogeneous phase having a particle size that varies depending on the flow rate of the layer precursor. However, in an embodiment, the average particle size of the vaporized layer precursor is greater than or equal to 5 nm and less than or equal to 3 μm, for example, greater than or equal to 100 nm and less than or equal to 3 μm, or greater than or equal to 200 nm and less than or equal to 1 μm. In other embodiments, the average particle size of the vaporized layer precursor is greater than or equal to 15 nm and less than or equal to 500 nm, for example, greater than or equal to 20 nm and less than or equal to 200 nm, or greater than or equal to 25 nm and less than or equal to 100 nm.

[0090] As described above, according to some embodiments disclosed and described herein, chemical durability and physical stability can be imparted to the layer on the wall of the honeycomb. To improve these properties, in one or more embodiments, after being deposited on the honeycomb, the vaporized layer precursor can be sintered or otherwise bonded to the honeycomb to form a layer coating at least a portion of the honeycomb as a crystalline phase. According to an embodiment, sintering the vaporized layer precursor includes heating the vaporized layer precursor to a temperature of greater than or equal to 950°C and less than or equal to 1150°C, for example, greater than or equal to 1000°C and less than or equal to 1100°C, greater than or equal to 1025°C and less than or equal to 1075°C, or about 1050°C after the vaporized layer precursor is deposited on the honeycomb. In some embodiments, the duration of sintering is greater than or equal to 20 minutes and less than or equal to 2.0 hours, for example, greater than or equal to 30 minutes and less than or equal to 1.5 hours, or greater than or equal to 45 minutes and less than or equal to 1.0 hour. After sintering the vaporized layer precursor to form the honeycomb body, the layer is in a crystalline phase. According to an embodiment, the sintered crystalline phase layer has a porosity of 90% as measured by SEM, for example, a porosity greater than or equal to 91%, or greater than or equal to 92%. In other embodiments, the sintered crystalline phase layer has a porosity greater than or equal to 93%, for example, greater than or equal to 94%, or greater than or equal to 95%. In other embodiments, the sintered crystalline phase layer has a porosity greater than or equal to 96%, for example, greater than or equal to 97%, or greater than or equal to 98%.

[0091] According to one or more embodiments of the present disclosure, a particulate filter is characterized by its filtration efficiency, which represents the ability of the particulate filter to remove a certain fraction of particles from an incoming airstream. Particles can be characterized by their mass concentration or their count concentration. The two values ​​are generally closely related. Using a general concentration C 微粒 , and the unit is particle mass / unit volume or particle number / unit volume. The filtration efficiency FE is usually obtained by the following equation:

[0092] Equation (1):

[0093]

[0094] Experimental measurements of filtration efficiency have different meanings. Figure 5 A schematic diagram of a common laboratory setup is shown. The common laboratory setup includes: a gas supply (e.g., air) regulated to a defined flow rate; a particle generator, e.g., one that generates soot particles at a certain rate and concentration; a filter sample to be tested; and two particle analyzers at the inlet and outlet of the filter sample.

[0095] The experiment is carried out at a controlled temperature (e.g., room temperature). As used herein, "room temperature" refers to a temperature of 20°C-. During the experiment, the air flow is adjusted to a constant flow rate. Particles are then added to the gas. Passing through the filter sample, a portion of the particles is removed by filtration, and this portion of the particles is measured as the difference between the inlet particle concentration and the outlet particle concentration. In the example, the particles are soot particles generated on a soot generator. The test is carried out at room temperature and atmospheric pressure. The relationship between the filtration efficiency and the experimental time is calculated from the inlet and outlet concentrations according to equation (1). At time t=0s, the dosing of the particles begins and the filtration efficiency is recorded. Different filtration efficiency values ​​are observed for different filter samples.

[0096] Filtration efficiency increases over time. This is because the accumulated particles themselves (in this case, soot) act as a filter medium, thereby increasing overall efficiency. To more effectively demonstrate this, it is helpful to plot filtration as a function of accumulated soot mass rather than time. Soot mass is obtained as the difference between the mass of soot entering the filter and the mass of soot leaving the filter, integrated over time.

[0097] The filtration efficiency at the beginning, when time equals t=0s or 0g / L soot load, is usually called the "clean" or "fresh" filtration efficiency and is determined solely by the characteristics of the filter sample. Based on filtration theory, the filtration process occurs based on different mechanisms, mainly depending on the size of the particles. A common model for describing filter media is the concept of a unit collector assembly. For the soot generated by the soot generator of the above experiment, the main filtration mechanism is based on the Brownian motion of small soot particles. The collection efficiency η of the unit collector based on the Brownian motion mechanism is BM It can be described by the following formula:

[0098] Equation (2)

[0099] η BM =4·(A s 1 / 3 Pe i 2 / 3 )·(1-ε) 2 / 3

[0100] A s is a parameter that depends mainly on the porosity ε, and Pe i is the Peclet number. The Peclet number is related to the fluid velocity u in the pore space. w / ε and collector diameter d c Diffusion coefficient D of Brownian motion BM The ratio between them is proportional.

[0101] Equation (3)

[0102]

[0103] The Brownian diffusion coefficient D BM ~(T / d s 2 ) The granularity of this collection mechanism is introduced s Dependence on temperature T. All parameters that depend on the microstructure of the filter medium are combined into a single variable K 微结构 , equation (2) can be rewritten as equation (4):

[0104] Equation (4)

[0105] Fluid velocity u w It is determined by dividing the volumetric flow rate by the cross-sectional area or filtration area. Therefore, in addition to the microstructural properties, the filtration performance at a given flow rate and particle size is proportional to the filtration area of ​​the filter. Therefore, to compare materials with different microstructures, the filtration efficiency is normalized by the filtration area. For wall-flow honeycomb filters with alternating blocked channels, the m 2 The estimated filtration surface area FSA can be obtained according to equation (5):

[0106] Equation (5):

[0107]

[0108] In equation (5), GSA is the geometric surface area per filter volume, and V 过滤器 is the volume of the filter sample. The factor 1 / 2 comes from the fact that only half of the channels represent the inlet channels through which the gas enters and then flows through the porous filter wall. The filtration area (or total filtration) will be the total inlet channel area + the total outlet channel area = the total area. In other words, in equation (5), if the total inlet channel area = the total outlet channel area, then the total inlet channel area can be calculated by dividing the total area by 2. However, if the total inlet channel area is not equal to the total outlet channel area, the denominator in the equation needs to be changed to reflect this.

[0109] In addition to filtration performance, filters are often characterized by their flow resistance, which typically refers to the pressure drop across a sample at a given volumetric gas flow rate. Generally, higher filtration performance corresponds to increased pressure drop or flow resistance. From an application perspective, the lowest possible pressure drop is generally desirable, as this often translates to pumping losses. In motor vehicle applications, this results in reduced power available to propel the vehicle or decreased fuel efficiency.

[0110] The pressure drop properties of a filter sample are typically assessed by measuring the pressure difference upstream and downstream of the filter sample at a given volumetric flow rate. In laboratory measurements, this can be performed at room temperature and at varying flow rates.

[0111] According to one or more embodiments, particulate filters prepared according to the embodiments described herein advantageously exhibit high filtration efficiency normalized to the inlet channel filtration area. Thus, according to one or more embodiments, the particulate filters described herein provide high filtration efficiency in a fresh (new) state immediately after installation in a vehicle at an automaker's factory. In some embodiments, this high filtration efficiency is coupled with a low pressure drop.

[0112] While the present disclosure is not intended to be limited by any particular theory, it is believed that the pressure drop across a particulate filter is comprised of five primary factors: airflow contraction and expansion at the filter's inlet and outlet, frictional losses along the inlet and outlet channels, and pressure drop across the porous channel walls.

[0113] In general, the pressure drop across a filter is influenced by macroscopic geometric parameters, such as component diameter, length, hydraulic diameter of the channels, and open frontal area, as well as the permeability of the porous filter wall. Permeability is a unique material property and is defined by the microstructure, such as porosity, effective pore size, and pore connectivity. Because airflow through the pores is laminar, frictional losses across the wall are determined by the entire path through the porous wall.

[0114] The inlet and outlet contributions to the pressure drop can be described by:

[0115] Equation (7):

[0116]

[0117] Where Δp is the pressure drop, ρ g is the gas density, Q is the volume flow rate, V 过滤器 is the filter volume, L is the filter length, OFA is the open frontal area of ​​the filter, and ζ 进 and ζ 出 are the empirical coefficients of contraction and expansion, respectively.

[0118] For the pressure drop across the filter, equation (26) from SAE Technical Paper 2003-01-0842 can be used, which is expressed in this article as equation (8).

[0119] Equation (8):

[0120]

[0121] Among them, the new variable μ is the dynamic viscosity, Q 有效is the effective volume flow rate, d h is the hydraulic diameter of the channel, t w is the wall thickness, F is the friction factor (for a square channel, F = 28.45), and κ 有效 is the effective permeability of the wall. The difference between the effective volume flow rate and the total flow rate is that the velocity distribution along the inlet and outlet channels is taken into account. It is empirically found that Q 有效 =1.32*Q better describes the experimental results.

[0122] The total pressure drop as measured in the experiment will be the sum of the contributions described by Equations (7) and (8). In Equations (7) and (8), all parameters except the effective permeability of the wall material are known and easily determined.

[0123] Effective permeability κ 有效 It can be extracted from the experimental data using equations (7) and (8). To do this, the pressure drop contribution due to inlet contraction and outlet expansion is subtracted from the experimental pressure drop value, equation (7), and provides equation (9)

[0124] Equation (9): Δp (2,3,4) =Δp 实验 –Δp (1,5)

[0125] Combining Equation (9) with Equation (8), we obtain the effective wall permeability κ 有效 Solution:

[0126] Equation (10):

[0127]

[0128] The permeability κ0 of the porous wall of an extruded honeycomb can usually be determined by the porosity ε and the effective median pore diameter D 50 The product of the squares of divided by 66.7 can reasonably describe the porosity ε and the effective median pore diameter D 50 All are determined by mercury porosimetry:

[0129] Equation (11):

[0130]

[0131] If a coating or other modification is applied to the base wall portion of the "as extruded" porous wall having a permeability κ0, the permeability becomes the new effective permeability value κ 有效 , which can be determined from experimental pressure drop values ​​using, for example, equation (10). This change in permeability relative to the base wall portion of the honeycomb wall as extruded can also be described by a "normalized permeability value (NPV)" which depicts the ratio of the effective permeability to the permeability of the original, unmodified microstructure:

[0132] Equation (12) NPV = κ 有效 / (εD 50 2 / 66.7) 裸

[0133] For determination of Δp of filter samples 实验 The experimental pressure drop value can be estimated by measuring the pressure difference upstream and downstream of the filter sample at a given volume flow rate. In laboratory measurements, this can be performed at room temperature and different flow rates.

[0134] As mentioned above, particulate filters are characterized by their filtration efficiency, which represents the ability of the particulate filter to remove a certain fraction of the particles from the incoming airstream. Particles can be characterized by either their mass concentration or their count concentration. The two values ​​are usually closely related. Using the common concentration C 微粒 , and the unit is particle mass / unit volume or particle number / unit volume. The filtration efficiency FE is usually obtained according to the above equation (1).

[0135] use Figure 5 A schematic diagram of a common laboratory setup is shown. A particulate filter is tested at room temperature and a constant flow rate. Particulates are then added to the gas. As the sample passes through the filter, a fraction of the particles is removed by filtration, which is measured as the difference between the inlet and outlet particle concentrations.

[0136] As mentioned above, the filtration efficiency at the beginning, at time equal to t = 0s or at a soot load of 0 g / L, is usually referred to as the "clean" or "fresh" filtration efficiency and is determined solely by the characteristics of the filter sample. Based on filtration theory, the filtration process occurs based on different mechanisms, mainly depending on the size of the particles. A common model for describing filter media is the concept of a unit collector assembly. For the soot generated by the soot generator of the above experiment, the main filtration mechanism is based on the Brownian motion of small soot particles. The collection efficiency η of the unit collector based on the Brownian motion mechanism is BM It can be described by equation (2). As mentioned above, the Peclet number is related to the fluid velocity u in the pore space. w / ε and collector diameter d c Diffusion coefficient D of Brownian motion BM The ratio between them is proportional to each other, as shown in equation (3) above.

[0137] SAE Technical Paper 2012-01-0363 explains that for uncoated extruded filters with a “random” porous microstructure, clean filtration efficiency can be related to the filtration characteristic parameter A. 过滤 Related, the filtering feature parameter A 过滤Proportional to the microstructure and macro filter properties, Equation (13):

[0138] Equation (13)

[0139] As a new variable, equation (13) has CPSI as the pore density of the filter structure. The clean filtration efficiency can be related to the filtration characteristic parameter (A 过滤 ) are plotted on a graph where the clean filtration efficiency is on the Y axis and the filtration characteristic parameter (A 过滤 ) on the X-axis.

[0140] The contributions of the microstructural parameters, porosity and median pore size can be combined into an effective microstructure factor EMF. For materials with unknown effective porosity and median pore size, this new parameter can be used to characterize the effective properties of the microstructure. This variable also allows to take into account that in real microstructures, filtration does not necessarily occur along the entire length of the pores on the filter wall, but rather occurs to a greater extent locally at locations that are conducive to particle collection and deposition, such as channels with narrow openings ("pore necks"). Once some particles have collected, they further narrow the pore neck, which further accelerates the filtration process. Thus, the new parameter allows to take into account microstructures that are not uniform and do not have a random pore design.

[0141] Analogously to what has been done for the pressure drop, it is also useful to consider not only the new microstructural parameter EMF but also to normalize the pressure drop for the properties of the substrate microstructure of the substrate wall portion of the extruded filter body with a random microstructure. For the latter, the EMF is taken as the porosity ε 0.43 Divide by the median pore diameter D 50 By this normalization, a new normalized microstructure filtering value, NMFV, is obtained, which describes the filtering characteristics of the microstructure as follows: Equation (14): NMFV = EMF / (ε 0.43 / D 50 5 / 3 ) 基底壁性质 .

[0142] According to one or more embodiments, a particulate filter is provided that achieves a favorable (e.g., high) normalized permeability value (NPV) while increasing the normalized microstructure filtration value (NMFV), e.g., a material that provides a combination of low (variable) pressure drop and increased clean filtration.

[0143] The filtration efficiency and pressure drop performance described above were tested on a variety of filter samples and were tested for a number of samples made according to the present disclosure, wherein the composite microstructure of the porous wall surface defines an inlet channel, i.e., the inlet channel includes a filter material deposit as described in accordance with one or more embodiments herein. For filtration, the initial or clean filtration efficiency in % is considered to be at a flow rate of 21 m / s. 3 / h. At room temperature and 357m 3 The pressure drop was evaluated at the highest flow rate of / h.

[0144] Honeycomb bodies and methods of making honeycomb bodies have been described herein. In embodiments, the honeycomb body includes a layer on at least one surface of the honeycomb body. In embodiments, the layer has a crystalline structure, porosity, for example, greater than or equal to 50% porosity, and is applied as a thin layer, for example, having a thickness greater than or equal to 0.5 μm to less than or equal to 10 μm. It should be understood that in various embodiments described above, the "honeycomb body" can be a ceramic "honeycomb body" and the "layer" can be a ceramic "layer."

[0145] Limited embodiments as disclosed and described herein are now provided.

[0146] Example

[0147] The implementation is further described through the following examples.

[0148] Example 1

[0149] Characteristics of porous inorganic layers in particulate filters that achieve high filtration efficiency and low pressure drop are presented. Define P0 and FE0 as the clean pressure drop and clean filtration efficiency of the underlying porous ceramic honeycomb body (without the porous inorganic layer); and P1 and FE1 as the clean pressure drop and clean filtration efficiency of a clean honeycomb filter comprising the porous ceramic honeycomb body and the porous inorganic layer. The effect of the layer on filter performance is characterized by the parameter X = (FE - FE0)P0 / (P - P0) / FE0. When defining the parameter X, the clean state of the particulate filter represents a state with near-zero soot loading. In some embodiments, the performance of the particulate filter with the layer is described as X>2. In other embodiments, the performance of the particulate filter with the layer is described as X>3. In other embodiments, the performance of the particulate filter with the layer is described as X>4. In other embodiments, the performance of the particulate filter with the layer is described as X>5. In some embodiments, the increase in the pressure drop of the particulate filter due to the layer is less than 25%. In other embodiments, the increase in the pressure drop of the particulate filter due to the layer is less than 20%. In other embodiments, the increase in the particulate filter pressure drop due to the layer is less than 10%. Defining the porous inorganic layer morphology parameter Y as Y = (layer porosity ^ (6.5 / Sqrt (layer particle size))) * (1 - layer porosity) / Sqrt (layer particle size) shows a good correlation between the layer morphology parameter Y and the particulate filter having the layer performance parameter X. Based on these results, in some embodiments, the layer morphology parameter Y is greater than 0.03. In other embodiments, the layer morphology parameter Y is greater than 0.04. In other embodiments, the layer morphology parameter Y is greater than 0.05.

[0150] Table 1 lists the embodiments analyzed by modeling. The embodiments in Table 1 represent gasoline particulate filters with different combinations of porosity, pore size, and layer thickness. These embodiments are for a gasoline particulate filter with a diameter of 5.66 inches and a length of 6 inches, a CPSI of 200, a wall thickness of 8.5 microns, a wall porosity of 56%, and a wall average pore size of 13 microns. Filtration efficiency and pressure drop performance were evaluated at an exhaust flow rate of 100 kg / hr and 450°C.

[0151] Table 1

[0152]

[0153]

[0154] exist Figure 6-7 , a graph of filtration efficiency versus pressure drop increase for the embodiments of Table 1 is provided. Figure 7 Shown Figure 6 The pressure drop increases by up to 50%.

[0155] Figure 8-9 is a graph of the parameter "X" versus pressure drop for the embodiments of Table 1. The performance of a particulate filter having a membrane is characterized by a performance parameter X defined as X=(FE-FE0)*P0 / FE0 / (P-P0). Figure 9 Shown Figure 8 The pressure drop increases by up to 50%.

[0156] Figure 10 is the correlation between the membrane morphology parameter Y = (membrane porosity^(6.5 / Sqrt(membrane particle size)))*(1-membrane porosity) / Sqrt(membrane particle size) and the particulate filter performance parameter X = (FE1-FE0)*P0 / FE0 / (P1-P0) of the embodiment of Table 1.

[0157] Example 2

[0158] Characterization of a porous inorganic layer in a particulate filter is presented, which partially covers the filter channels and achieves high filtration efficiency and low pressure drop. Define P0 and FEO as the clean pressure drop and filtration efficiency performance of the underlying porous ceramic honeycomb body (absent the porous inorganic layer); and P1 and FEO as the clean pressure drop and filtration efficiency performance of a clean honeycomb filter comprising the porous ceramic honeycomb body and the porous inorganic layer. The effect of the layer on particulate filter performance is characterized by the parameter X = (FE - FEO) P0 / (P - P0) / FEO. When defining the parameter X, the clean state of the particulate filter represents a state with near-zero soot loading. In some embodiments, the performance of the particulate filter with the layer is described as X > 1.7. In other embodiments, the performance of the particulate filter with the layer is described as X > 2. In other embodiments, the performance of the particulate filter with the layer is described as X > 3. In other embodiments, the performance of the particulate filter with the layer is described as X > 4. In some embodiments, the increase in pressure drop of the particulate filter due to the layer is less than 25%. In other embodiments, the increase in the particulate filter pressure drop due to the layer is less than 20%. In other embodiments, the increase in the particulate filter pressure drop due to the layer is less than 10%. In some embodiments, the coverage of the channel wall by the porous inorganic layer is greater than 70%. In other embodiments, the coverage of the channel wall by the porous inorganic layer is greater than 80%. In other embodiments, the coverage of the channel wall by the porous inorganic layer is greater than 90%.

[0159] Table 2 lists the embodiments analyzed by modeling. The embodiments in Table 2 represent gasoline particulate filters with different combinations of layer coverage, porosity, pore size, and layer thickness. These embodiments are for a gasoline particulate filter with a diameter of 5.66 inches and a length of 6 inches, a CPSI of 200, a wall thickness of 8.5 microns, a wall porosity of 56%, and a wall average pore size of 13 microns. Filtration efficiency and pressure drop performance were evaluated at an exhaust flow rate of 100 kg / hr and 450°C.

[0160] exist Figure 11-12 , a graph of filtration efficiency versus pressure drop increase for the embodiments of Table 2 is provided. Figure 12 Shown Figure 11 The pressure drop increases by up to 50%.

[0161] Table 2

[0162]

[0163]

[0164]

[0165]

[0166] It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Therefore, this specification is intended to cover modifications and variations of the various embodiments described herein as long as these modifications and variations are within the scope of the appended claims and their equivalents.

Claims

1. A honeycomb filter comprising: Clean filter pressure drop (P1) and clean filter efficiency (FE1); A porous ceramic honeycomb body comprising a first end, a second end, and a plurality of walls having wall surfaces defining a plurality of internal channels, the porous ceramic honeycomb body comprising a base clean filter pressure drop (PO) and a base clean filtration efficiency (FE0); a porous inorganic layer disposed on one or more wall surfaces of a porous ceramic honeycomb body, the porous inorganic layer comprising an average porosity (ε) greater than or equal to 80%, a thickness tm greater than or equal to 0.5 micrometers and less than or equal to 4 micrometers, and a median pore diameter greater than or equal to 0.5 μm and less than or equal to 3 μm; An overall performance parameter X greater than or equal to 1.75, where X is defined by the following equation: A filtration performance parameter F greater than or equal to 0.25, where F is defined by the following equation: and The morphology parameter Y of the porous inorganic layer is equal to or greater than 0.02, wherein Y is defined by the following equation: and Here, dp represents the average particle size of particles constituting the porous inorganic layer.

2. The honeycomb filter according to claim 1, wherein The axial distance of the honeycomb filter body extends from the first end to the second end of the honeycomb filter body, and the porous inorganic layer covers the wall surface greater than or equal to 70% of the axial distance.

3. The honeycomb filter according to claim 2, wherein The porous inorganic layer covers greater than or equal to 80% of the axial distance of the wall surface.

4. The honeycomb filter according to claim 2, wherein The porous inorganic layer covers greater than or equal to 90% of the axial distance of the wall surface.

5. The honeycomb filter according to claim 2, wherein The porous inorganic layer covers greater than or equal to 95% of the axial distance of the wall surface. The honeycomb filter according to claim 1 , wherein: The average thickness of the walls of the porous ceramic honeycomb body is from 25 μm to 250 μm.

7. The honeycomb filter according to claim 1, wherein The porous ceramic honeycomb body has a bulk porosity of 50% to 70% as measured by mercury porosimetry.

8. The honeycomb filter according to claim 1, wherein The average pore diameter of the pores of the porous ceramic honeycomb body is greater than or equal to 7 μm and less than or equal to 25 μm. 9 . The honeycomb filter according to claim 1 , wherein X is greater than or equal to 2. 10 . The honeycomb filter according to claim 1 , wherein X is greater than or equal to 3. The honeycomb filter according to claim 1 , wherein X is greater than or equal to 4. The honeycomb filter according to claim 1 , wherein X is greater than or equal to 5.

13. The honeycomb filter according to claim 1, wherein F is greater than or equal to 0.

5. The honeycomb filter according to claim 1 , wherein F is greater than or equal to 0.

75. The honeycomb filter according to claim 1 , wherein F is greater than or equal to 1.

0. The honeycomb filter according to claim 1 , wherein F is greater than or equal to 1.

25. The honeycomb filter according to claim 1 , wherein Y is greater than or equal to 0.

03. The honeycomb filter according to claim 1 , wherein Y is greater than or equal to 0.

04. The honeycomb filter according to claim 1 , wherein Y is greater than or equal to 0.

05.

20. The honeycomb filter according to claim 1, wherein The porous inorganic layer includes a density of 0.1 g / liter of the porous ceramic honeycomb to 30 g / liter of the porous ceramic honeycomb.

Images