EP2254682A2

EP2254682A2 - Gas filter structure having a variable wall thickness

Info

Publication number: EP2254682A2
Application number: EP09721517A
Authority: EP
Inventors: Adrien Vincent; Fabiano Rodrigues; Atanas Chapkov; David Lechevalier; Vignesh Rajamani
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2008-03-11
Filing date: 2009-03-10
Publication date: 2010-12-01
Also published as: US20110030357A1; FR2928562B1; KR20100138913A; FR2928562A1; JP2011513059A; WO2009115753A2; WO2009115753A3

Abstract

The invention relates to a structure for filtering gases laden with particulates, of the honeycomb type and comprising a set of longitudinal adjacent channels of mutually parallel axes separated by porous filtering walls, said channels being alternately blocked off at one or other of the ends of the structure so as to define entry channels and exit channels for the gas to be filtered, and so as to force said gas to pass through the porous walls separating the entry and exit channels, said structure being characterized in that the entry and exit channels share between them at least one wall having an average thickness d which is constant over the entire length of the filter structure, in that the entry or exit channels share between them at least one wall having an average thickness e which is constant over the entire length of the filter structure and in that the ratio e/d is strictly greater than 1.

Description

FILTRATION STRUCTURE OF A GAS WITH VARIABLE WALL THICKNESS

The invention relates to the field of filter structures possibly comprising a catalytic component, for example used in an exhaust line of a diesel type internal combustion engine. Filters for the treatment of gases and the removal of soot typically from a diesel engine are well known in the prior art. These structures all most often have a honeycomb structure, one of the faces of the structure allowing the admission of the exhaust gas to be treated and the other side the evacuation of the treated exhaust gas. The structure comprises, between the intake and discharge faces, a set of adjacent ducts or channels, most often of square section, axes parallel to each other separated by porous walls. The ducts are closed at one or the other of their ends to delimit inlet chambers opening on the inlet face and outlet chambers opening along the discharge face. The channels are alternately closed in an order such that the exhaust gases, during the crossing of the honeycomb body, are forced to pass through the sidewalls of the inlet channels to join the outlet channels. In this way, the particles or soot are deposited and accumulate on the porous walls of the filter body.

At the present time, porous ceramic filters, for example cordierite, alumina, in particular aluminum titanate, mullite silicon nitride, are used for the filtration of gases. silicon / silicon carbide or silicon carbide mixture.

In known manner, during its implementation, the particulate filter is subjected to a succession of filtration phases (accumulation of soot) and regeneration

(removal of soot). During the filtration phases, the soot particles emitted by the engine are retained and are deposited inside the filter. During the regeneration phases, the soot particles are burned inside the filter, in order to restore its filtration properties. The porous structure is then subjected to intense radial and tangential thermomechanical stresses, which can lead to micro-cracking likely over time to cause a severe loss of filtration capacity of the unit, or even its complete deactivation. This phenomenon is particularly observed on monolithic filters of large diameter.

To solve these problems and increase the life of the filters, it has been proposed more recently filtration structures associating several blocks or monolithic honeycomb unit elements. The elements are most often assembled together by gluing by means of a glue or cement of a ceramic nature, hereinafter called seal cement. Examples of such filter structures are for example described in patent applications EP 816,065, EP 1 142 619, EP 1 455 923, WO 2004/090294 or WO 2005/063462. In order to ensure optimal relaxation of the stresses in such an assembled structure, it is known that the coefficients of thermal expansion of the different parts of the structure (filter elements, coating cement, joint cement) must be of substantially the same order. Therefore, said parts are advantageously synthesized on the basis of a same material, most often silicon carbide SiC or cordierite. This choice also makes it possible to homogenize the distribution of heat during the regeneration of the filter. In order to obtain the best performance of thermomechanical resistance and pressure drop, the assembled filters currently marketed for light vehicles typically comprise approximately 10 to 20 unit elements having, in a cross section, a square or rectangular section and whose surface elemental section is between about 13 cm ² and about 25 cm ² . These elements consist of a plurality of channels of usually square section. To further reduce the mass of the filter without reducing its performance in terms of pressure drop and soot storage, an obvious solution could be to reduce the number of unit elements in the assembly by increasing their individual size. Such an increase, however, is not currently possible, particularly with SiC filters, without unacceptably reducing the thermomechanical strength of the filter.

The larger section filters, currently used in particular for "truck" -type applications, are made by assembling with a grouting cement of elements of a size similar to those constituting the filters intended for light vehicles. The number of unit elements of truck filter type is then very high and can have up to 30 or even 80 elements. Such filters then have an overall mass and a loss of charge that is too high.

In general, therefore, there is currently a need to jointly increase the overall filtration performance and lifetime of current filters. More specifically, the improvement of the filters can be directly measured by the comparison of the properties which follow, the best possible compromise between these properties being sought according to the invention, for equivalent engine speeds. In particular, the object of the present invention is a filter or a filter element having all at once:

a low pressure loss caused by the filtering structure in operation, that is to say typically when it is in an exhaust line of an internal combustion engine, both when said structure is free of particles of soot (initial pressure drop) than when it is loaded with particles, - an increase in the pressure drop of the filter during said reasonable operation, ie an increase in the pressure drop measured as a function of time of use or, more exactly, depending on the level of soot loading of the filter, - a high specific filtration area, a mass of the monolithic element adapted to ensure a thermal mass sufficient to minimize the maximum regeneration temperature and the gradients caused by the filter, which can themselves cause cracks on the element,

a large soot storage volume, in particular at constant pressure drop, so as to reduce the frequency of regeneration,

a strong thermomechanical resistance, that is to say allowing a prolonged life of the filter,

- a larger residue storage volume.

In order to improve one or the other of the properties described above, it has already been proposed in the prior art to modify the shape of the channels of the filtering structure in various ways: For example, in order to increase the filtration area of said filter to constant filter volume, it has been proposed in the patent application WO 05/016491 that filter elements whose shape and the internal volume of the inlet and outlet channels are output are different. In such structures, the wall elements follow one another, in cross section and following a horizontal row and / or vertical channels, to define a sinusoidal shape or wave (wavy in English). Wall elements typically wave a half sinusoidal period across the width of a channel. Such channel configurations provide a low pressure drop and a large soot storage volume. This type of structure, however, has a high loading slope soot and filters made with this type of channel configuration therefore do not meet all the needs defined above.

According to another solution described to obtain improved filter structures, EP 1495791 discloses structures whose input channels have a generally octagonal cross-sectional cross-section, the outlet channels being of square section. However, the tests carried out by the applicant have shown that such structures present a substantially deteriorated compromise between the thermomechanical resistance and the pressure drop generated by such a filter on the exhaust line.

If each of the configurations of the prior art makes it possible to improve at least one of the desired properties, none of the solutions described thus provides an acceptable compromise between all the properties sought, as previously described. In general, it may be noted that, for each of the configurations of the prior art, the improvement obtained for one of the properties The filter is accompanied by the joint deterioration of another, so that the improvement finally obtained is generally minor in view of the disadvantages induced. The present invention thus aims to provide a filter structure having the best compromise between the induced pressure drop, the mass, the total filtration area, the storage volume of soot and residues and the thermomechanical resistance, as previously described. .

In its most general form, the present invention relates to a filtration structure of particles-loaded gases of the honeycomb type and comprising a set of longitudinal adjacent channels of mutually parallel axes separated by porous filtering walls. said channels being alternately plugged at one or other end of the structure so as to define inlet channels and outlet channels for the gas to be filtered, and to force said gas to pass through the walls porous separating the inlet and outlet channels, said structure being characterized in that: the inlet and outlet channels share with each other at least one wall of constant average thickness over the entire length of the filtration structure, the inlet or outlet channels share with each other at least one wall of constant average thickness over the entire length of the filtration structure, the ratio e / d is strictly greater than ur to 1.

Preferably, the filtering structure is such that: - each outlet channel consists of at least three walls of substantially identical width, so as to form a channel whose section has a substantially regular shape, each output channel has a common wall with several input channels, each common wall constituting one side of said output channel, at least two input channels share a common wall of width b and of average thickness e.

In one possible mode, the input and output channels are hexagonal.

In another mode, the input channels are triangular and the output channels are hexagonal.

According to a third possible mode, the input channels are octagonal and the output channels are square.

For triangular, square, hexagonal or octagonal form, it is understood in the sense of the present invention that the channels have, in a cross section, a general shape that can be respectively in a polygon with 3, 4, 6 or 8 sides.

Preferably, the ratio of the thicknesses e / d is greater than 1 and less than or equal to 10, preferably greater than or equal to 1.05 and less than or equal to 4, and very preferably greater than or equal to 1.1 and less than or equal to 2 and even more preferably greater than or equal to 1.1 and less than or equal to 1.5. According to a possible mode, the walls constituting the input and output channels are planar.

According to an alternative mode, the walls constituting the inlet and / or outlet channels are corrugated, that is to say that they have, in cross-section and with respect to the center of a channel, at least one concavity or a convexity.

For example, the output channels have walls convex relative to the center of said output channels.

Without departing from the invention, the output channels may have concave walls with respect to the center of said output channels. The maximum distance, in a cross-section, between an end point of the concave or convex wall or walls and the line segment connecting the two ends of said wall, is typically greater than 0 and less than 0.5 a.

Preferably, the thickness d is constant over the entire width at common walls between the inlet and outlet channels and / or the thickness e is constant over the entire width b of the common walls between the inlet channels. These thicknesses d or / and e may also have, in cross-section, a variable thickness, it being understood that the ratio of the average thicknesses d and e remains strictly greater than 1. More precisely, it is possible, without departing from the scope of the According to the invention, the ratio e / d is not always greater than 1 in the entire volume of the filter, provided that said ratio e / d remains overall greater than 1 when it is integrated over the widths a and b of the corresponding walls.

Advantageously, the channels, preferably those of exit, may have rounded corners so as to further reduce the pressure drop and improve the mechanical and thermomechanical strength of the structure according to the invention.

In the filtration structures according to the invention, the density of channels is typically between about 1 and 280 cm ² channels and preferably between 15 and 65 channels per cm ² .

In the filtration structures according to the invention, the average wall thickness is typically between 100 and 1000 microns, and preferably between 100 and 700 microns.

In general the width has output channels is between 0.05 and 4.00mm, and preferably between 0.10mm and 2.50mm, and very preferably between 0.20mm and 2.00mm. In general, the width b of the inlet channels is between 0.05 and about 4 mm, and preferably between 0.10 mm and 2.50 mm, and very preferably between 0.20 mm and 2.00 mm. According to one embodiment, the walls are based on silicon carbide, and / or aluminum titanate and / or cordierite and / or mullite and / or silicon nitride and / or sintered metals.

The invention relates in particular to an assembled filter comprising a plurality of filtering structures as previously described, said structures being bonded together by a cement, preferably of ceramic and refractory nature.

The invention further relates to the use of a filter structure or an assembled filter as previously described as a device on an exhaust line of a Diesel engine or Gasoline preferably Diesel.

Figures 1 to 5 illustrate 5 non-limiting embodiments of a filter structure having a configuration of the channels according to the invention.

Figure 6 illustrates an embodiment not according to the invention, in which the thickness of all the walls is constant. More precisely: FIG. 1 is a front view in elevation of the front face of a filter according to a first embodiment according to the invention, comprising six-wall inlet and outlet channels and in which said walls are flat and of constant thickness. FIG. 2 is a front view in elevation of the front face of a filter according to a second embodiment according to the invention, comprising six-wall inlet and outlet channels and in which said walls are corrugated, the channels of outlet being made of convex walls relative to the center of an exit channel. Figure 2a illustrates a more detailed view of Figure 2.

FIG. 3 is a front view in elevation of the front face of a filter according to a third embodiment according to the invention, comprising three-walled inlet channels and six-wall outlet channels and in which said walls are corrugated, the outlet channels being concave walls relative to the center of an outlet channel. Figure 3a illustrates a more detailed view of Figure 3.

FIG. 4 is a front view in elevation of the front face of a filter according to a fourth embodiment in which the walls common to the input channels have a variable thickness, in particular a maximum thickness e2 and a minimum thickness e1.

FIG. 5 is a front elevational view of the front face of a filter according to a fifth embodiment according to the invention, comprising four-walled output channels on the one hand and eight-walled input channels. FIG. 6 is a front view in elevation of the front face of a filter not according to the invention, in which, unlike the filter described in relation with FIG. 2, the thickness e of the walls common to the channels of FIG. The input is identical to the thickness of common walls between the input and output channels. FIG. 6a illustrates a more detailed view of FIG. 6. FIG. 1 shows an elevational view of the gas inlet face of a piece of the monolithic filtration unit 1. The present unit input channels 3 and output channels 2. The output channels are conventionally clogged on the gas inlet face by plugs. The inlet channels are also plugged but on the opposite (rear) face of the filter, so that the gases to be purified are forced to pass through the porous walls common to the inlet and outlet channels. exit. According to this first mode, the filtering structure is characterized by the presence of an outlet channel 2 whose cross section has a hexagonal and regular shape, that is to say that the six sides of the hexagon are of one substantially identical length and that two adjacent sides form an angle close to 120 °. A regular outlet channel 2, thus formed by six walls of identical width arranged at 120 °, is in contact with 6 input channels 3 of a general shape also hexagonal but irregular, that is to say formed by adjacent walls of which at least two have a different width, in a cross section.

As shown in FIG. 1, two adjacent inlet channels 3 also have a common wall of width b.

According to the invention, the thickness e of the walls 10 common to the input channels is greater than the thickness of the walls 5 common between the input and output channels. More particularly, the structures are characterized in that the ratio e / d is greater than 1 and preferably less than or equal to 10, or even less than or equal to 4.

As shown in Figures 1 to 6 attached, in a front view (or a cross section) of the filter structure, the distances a and b are defined according to the invention as the distances connecting the two vertices S1 and S2. of the wall considered, said vertices S1 and S2 are inscribed on the central core 6 of said wall (see Figure 1 and following). In this way we obtain values of a and of b independent of the thickness of the walls.

FIG. 2 represents the arrangement of a set of outlet and inlet channels 2 of the gases in an elevational view of the inlet face of the gases to be purified in a honeycomb structure according to the invention whose walls are corrugated. Within this structure and as shown in FIG. 2a, the maximum distance c, in a cross section, is defined as the distance between the end point 7 on the central core 6 of a corrugated wall and the right segment. 8 connecting the two ends Sl and S2 of the wall. According to the invention, the thickness e of the walls common to the input channels is greater than the thickness of common walls between the input and output channels.

FIG. 3 is a front view in elevation of the front face of a filter according to a third embodiment according to the invention, comprising three-walled inlet channels and six-wall outlet channels and in which the walls of the input and output channels are wavy, the output channels being concave walls with respect to the center of an output channel. Again and according to the invention, the thickness e of the walls common to the input channels is greater than the thickness of common walls between the input and output channels. Figure 3a illustrates a more detailed view of Figure 3.

In Figures 3 and 3a and following, the same numbers were used to designate elements identical or similar to those already described in Figures 1, 2 and 2a. The definitions of the parameters a, b and c are also the same as previously explained, in relation to FIGS. 1, 2 and 2a.

FIG. 4 is a front view in elevation of the front face of a filter according to a fourth embodiment according to an embodiment of the invention similar to that already described in relation to FIG. 2, but the walls common to the channels; input 3 present this variable thickness, in particular a maximum thickness e2 at the ends of said wall 10 and a minimum thickness el in the middle of said wall 10. According to the invention, the average thickness e _m of said wall 10 is, however, greater than the average thickness. d of the wall 5, even if the thickness el, taken in the middle of the wall 10, is locally smaller than the thickness d, as represented in FIG.

Figure 5 is a front elevational view of the front face of a filter according to a fifth embodiment of the invention, comprising four-walled output channels on the one hand and eight-walled input channels. The input 3 and output 2 channels have four common walls which delimit said output channels, the walls of the input and output channels being flat. The walls common to the inlet channels 10 form an angle close to 45 ° with the common walls 5 between the inlet and outlet channels. As for the previous examples, the thickness e of the walls common to the input channels is greater than the thickness of common walls 5 between the input and output channels.

The invention and its advantages over previously known structures will be better understood on reading the nonlimiting examples which follow.

Example 1 (comparative):

It has been synthesized according to the techniques of the art, for example described in patents EP 816065, EP 1 142 619, EP 1 455

923 or WO 2004/090294, a first population of monolithic elements or monoliths in the form of honeycomb and silicon carbide.

To do this, according to the techniques described in particular in EP 1 142 619, 70% by weight of the mixture is mixed initially. of an SiC powder whose grains have a median diameter d ₅ o of 10 microns, with a second SiC powder whose grains have a median diameter d ₅ o of 0.5 microns. For the purposes of the present description, the median pore diameter d ₅ o denotes the diameter of the particles such that respectively 50% of the total population of the grains has a size less than this diameter. To this mixture is added a porogen of the polyethylene type in a proportion equal to 5% by weight of the total weight of the SiC grains and a methylcellulose type shaping additive in a proportion equal to 10% by weight of the total weight of the SiC grains. .

Water is added and kneaded to obtain a homogeneous paste whose plasticity allows extrusion, the die being configured to obtain monolithic blocks by an octagonal arrangement of the internal inlet channels.

(often called an octosquare structure in the domain) as shown in Figure 6b of the EP application

1,495,791. The green monoliths obtained are dried by microwave for a time sufficient to bring the water content not chemically bound to less than 1% by weight.

The channels of each face of the monolith are alternately blocked according to well-known techniques, for example described in application WO 2004/065088.

The monoliths (elements) are then baked under Argon according to a rise in temperature of 20 ° C / hour until reaching a maximum temperature of 2200 ^° C. which is maintained for 6 hours. The porous material obtained has an open porosity of 47% and a median pore distribution diameter of about 15 microns. The dimensional characteristics of the elements thus obtained are given in Table 1 below, the structure having a periodicity, that is to say a distance between two adjacent channels, equal to 2.02 mm. The arrangement of the channels is characterized by the following values according to the preceding description: a = 1.66mm b = 0.52mm d = e = 0.39mm

An assembled filter was then formed from the monoliths. Sixteen elements from the same mixture were assembled together according to conventional techniques by bonding using a cement of the following chemical composition: 72% by weight of SiC, 15% by weight of Al ₂ O 3, 11% by weight of SiO ₂ , the remainder consisting of impurities mainly Fe2O3 and alkali and alkaline earth metal oxides. The average thickness of the joint between two adjacent blocks is of the order of 1 to 2 mm. The assembly is then machined in order to form assembled filters of cylindrical shape of about 14.4 cm in diameter.

EXAMPLE 2 (Comparative) The technique for synthesizing the monoliths described above is also identical, but this time the die is adapted so as to produce monolithic blocks having a greater wall thickness such that: e = 0.41 mm

Example 3 (according to the invention):

The technique for synthesizing the monoliths previously described is also identical, but this time the die is adapted so as to produce monolithic blocks characterized by an octagonal arrangement of the internal input channels as previously but in which the The thickness of the walls common to the inlet channels is greater than the thickness of common walls between the inlet and outlet channels. As illustrated in Figure 5. The dimensional characteristics of the elements thus obtained are given in Table 1 below the structure having a periodicity that is to say a distance between two adjacent channels of 2.02mm.

The arrangement of the channels is characterized by the following values according to the preceding description: a = 1, 66mm b = 0, 52mm d = 0, 390mm e = 0, 544mm

Example 4 (comparative):

The technique for synthesizing the monoliths previously described is also identical, but this time the die is adapted so as to produce monolithic blocks characterized by an arrangement of the internal channels according to the invention and in accordance with the given representation. in Figure 6, that is to say with corrugated walls and convex relative to the center of a regular outlet channel. The arrangement of the channels is characterized by the following values: a = 1.40 mm b = 0.84 mm c = 0.23 mm d = e = 0.30 mm

Example 5 (comparative):

The technique for synthesizing the monoliths described above is also identical, but this time the die is adapted so as to produce monolithic blocks having a greater wall thickness such that: d = e = 0.348 mm Example 6 (according to the invention):

The technique for synthesizing the monoliths previously described is also identical, but this time the die is adapted so as to produce monolithic blocks characterized by an arrangement of the internal channels according to the invention and in accordance with the given representation. in Figure 2, that is to say with corrugated walls and convex relative to the center of a regular outlet channel. The arrangement of the channels is characterized by the following values: a = 1.40 mm b = 0.84 mm c = 0.23 mm d = 0.30 mm e = 0.397 mm

The main structural characteristics of the elements obtained according to Examples 1 to 4 are reported in Table 1 below. The technique of assembling and obtaining filters is the same for all the examples and as described in Example 1.

NA = not applicable

Table 1

The samples obtained were evaluated and characterized according to the following procedures:

A- Measurement of loss of charge in the state not loaded with soot:

By pressure loss is meant within the meaning of the present invention the differential pressure existing between the upstream and downstream of the filter. The pressure drop was measured according to the techniques of the art, for a gas flow rate of 250 kg / h and a temperature of 250 ^° C., on the new filters.

B- Measurement of the thermomechanical resistance:

The filters are mounted on an exhaust line of a direct injection diesel 2.0 L engine running at full power (4000 rpm) for 30 minutes and then disassembled and weighed to determine their initial mass. The filters are then reassembled on the engine bench with a speed of 3000 rpm and a torque of 50 Nm for different times to obtain a soot loads of 8 g / liter (by volume of the filter). The filters thus loaded are reassembled on the line to undergo a severe regeneration thus defined: after stabilization at an engine speed of 1700 revolutions / minute for a torque of 95 Nm for 2 minutes, a post-injection is performed with 70 ° phasing for a post-injection flow rate of 18mm ³ / stroke. Once the soot combustion initiated, more precisely when the pressure drop decreases for at least 4 seconds, the engine speed is lowered to 1050 revolutions / minute for a torque of 40 Nm for 5 minutes to accelerate the combustion of soot . The filter is then run at 4000 rpm for 30 minutes to remove the remaining soot. The regenerated filters are inspected after cutting to reveal the possible presence of cracks visible to the naked eye. The thermomechanical resistance of the filter is appreciated in view of the number of cracks, a small number of cracks reflecting a thermomechanical resistance acceptable for use as a particulate filter.

As reported in Table 2, the following scores were assigned to each of the filters:

+++: presence of numerous fissures, ++: presence of numerous cracks, +: presence of some cracks,

: no cracks or rare cracks.

The storage volume was determined according to the usual techniques well known in the art.

C- evaluation of the geometric properties:

The open front area (OFA) is obtained by calculating the percentage ratio of the area covered by the sum of the cross sections of the input channels of the front face of the monolithic unitary elements ( except the walls and plugs) on the total area of the corresponding cross section of said unitary elements. The amount of storage of residues is greater the higher the percentage.

The WALL is the ratio, in cross-section and in percentage, between the area occupied by all the walls of a monolithic unitary element (except plugs) and the total area of said cross-section.

The specific filtering surface of the filter (monolithic or assembled) corresponds to the internal surface of all the walls of the filter inlet channels expressed in m ² , relative to the volume in m ³ of filter, integrating if necessary its external coating. The soot storage volume is all the higher as the specific surface thus defined is large. The loading slope is even lower than the specific filtration surface is large.

The results obtained in the tests for all of Examples 1 to 6 are summarized in Table 2 which follows:

NA = not applicable

Table 2

Results analysis:

The results reported in Table 2 show that the filters according to Examples 3 and 6 according to the invention have the best compromise between the different properties sought in an application as a particulate filter in an automobile exhaust line. More particularly, the results show that the filters according to the invention have, for an identical WALL factor, a significantly lower pressure drop, while nevertheless maintaining a filtration surface and an OFA (representative of the soot storage volume) while acceptable. The results in Table 2 also show that the filters according to the invention have improved thermomechanical resistance compared to comparative filters having an identical internal wall thickness. The filter according to Example 6 additionally exhibits the lowest fresh state pressure drop at the same time as the highest filtration area of the examples provided.

In other words, the results reported in Table 2 indicate that the filter structures obtained according to the invention have the best compromise, in particular between the two essential characteristics necessary for an application as a particulate filter in an exhaust line. that is to say the thermomechanical resistance and the pressure drop. Such an improvement results in greater potential lifetimes of the filters, in particular in an automotive application, where the residues resulting from the successive combustion of the soot, during the phases of regeneration, tend to accumulate until finally make the filter unusable.

More particularly, because of this better compromise, it becomes possible according to the invention to synthesize structures assembled from monolithic elements of larger size than before, while ensuring a longer life.

Claims

1. Filtration structure of particles-loaded gases of the honeycomb type and comprising a set of adjacent longitudinal channels of axes parallel to each other separated by porous filtering walls, said channels being alternately plugged to one or the other. other ends of the structure so as to define inlet channels and outlet channels for the gas to be filtered, and so as to force said gas to pass through the porous walls separating the inlet and outlet channels, said structure characterized in that: the inlet and outlet channels share at least one wall of constant average thickness over the entire length of the filtration structure, the inlet or outlet channels share with each other at the same time. less than a wall of average thickness e constant over the entire length of the filtration structure, the ratio e / d is strictly greater than 1.

The gas filtration structure according to claim 1, wherein:

each outlet channel consists of at least three walls of substantially identical width, so as to form a channel whose section has a substantially regular shape, each outlet channel has a common wall with several inlet channels, each common wall constituting one side of said outlet channel, at least two input channels share a common wall of width b and of average thickness e.

The gas filtration structure of claim 1 or 2, wherein the inlet and outlet channels are hexagonal in shape.

4. gas filtration structure according to one of claims 1 or 2, wherein the inlet channels are of triangular shape and the outlet channels are hexagonal shape.

5. gas filtration structure according to one of claims 1 or 2, wherein the input channels are octagonal and the output channels are square.

6. Filtration structure according to one of the preceding claims, wherein the ratio of the average wall thicknesses e / d is greater than 1 and less than or equal to 10, preferably greater than or equal to 1.05 and less than or equal to 5, and very preferably greater than or equal to 1.1 and less than or equal to 2 and even more preferably greater than or equal to 1.1 and less than or equal to 1.5.

7. Filtration structure according to one of the preceding claims, wherein the walls constituting the inlet and outlet channels are planar.

8. Filtration structure according to one of the preceding claims wherein the walls constituting the inlet and outlet channels are corrugated, that is to say they have, in cross section and relative to the center of a channel, at least one concavity or at least one convexity.

9. Filtration structure according to the preceding claim, wherein the outlet channels have walls convex relative to the center of said channels.

10. Filter structure according to claim 8, wherein the outlet channels have concave walls relative to the center of said channels.

Filtering structure according to one of claims 8 to 10, wherein the maximum distance, in a cross section, between a point of the concave or convex wall or walls and the line segment connecting the two ends of said wall is greater than 0 and less than 0.5 a.

12. Filtering structure according to one of the preceding claims, wherein the density of the channels is between about 1 and about 280 channels per cm ² and preferably between 15 and 65 channels per cm ² .

13. Filtering structure according to one of the preceding claims, wherein the average wall thickness is preferably between 100 and 1000 microns, preferably from 100 to 700 microns.

14. Filtering structure according to one of the preceding claims, wherein the width has outlet channels is between about 0.05mm and about 4.00mm, and preferably between about 0.20mm and about 2.00mm.

15. Filtering structure according to one of the preceding claims, wherein the width b of the common wall between two inlet channels is between about 0.05mm and about 4.00mm, and preferably between about 0.20mm and about 2.00mm.

16. Structure according to one of the preceding claims, wherein the walls are based on silicon carbide SiC and / or aluminum Titanate and / or Cordierite and / or Mullite and / or silicon nitride and / or or sintered metals

17. An assembled filter comprising a plurality of filter structures according to one of the preceding claims, said structures being bonded together by a cement of a ceramic nature and preferably refractory.

18. Use of a filter structure or an assembled filter according to one of the preceding claims as a depollution device on an exhaust line of a diesel engine or gasoline preferably diesel.