WO2000039437A1

WO2000039437A1 - A converter for use in the treatment of gases

Info

Publication number: WO2000039437A1
Application number: PCT/US1999/029737
Authority: WO
Inventors: Robert J. Locker; Constance B. Sawyer; Paul S. Schmitt
Original assignee: Corning Incorporated
Priority date: 1998-12-28
Filing date: 1999-12-14
Publication date: 2000-07-06

Abstract

Disclosed is a converter (10) for the treatment of gases including the following: a metal shell or housing (14) having an inlet end (16) and an outlet end (18) through which gases flow, a ceramic substrate (12) exhibiting an aspect ratio of less than about 0.4 and having a longitudinal axis and a ceramic fiber-containing layer (38), located between the metal shell (14) and the ceramic substrate (12) and in contact with and covering at least a portion of said peripheral surface of the substrate (12), for resiliently mounting the substrate (12) within the housing (14). The substrate (12) is resiliently mounted within the housing (14) such that the longitudinal axis of the substrate (12) is at an acute angle with respect to the inlet end (16) and outlet end (18). Furthermore, the substrate (12) has an outer surface and an inlet end face (34) at one end in communication with the inlet (16) of the housing (14) and an outlet end face (36) at its opposite end in communication with the outlet (18) of the housing (14). Lastly, the substrate (12) has a multiplicity of gas passage honeycomb cells (40) that extend along the longitudinal axis and are perpendicular to the inlet and outlet faces (34, 36).

Description

A CONVERTER FOR USE IN THE TREATMENT OF GASES

This application claims the benefit of U.S. Provisional Application No. 60/113,905, filed December 28, 1998, entitled "A Converter for Use in the Treatment of Gases", filed by Locker et al.

BACKGROUND OF THE INVENTION

1. Field of the Invention The invention relates to a converter for treating and reacting gases, and more particularly to a converter exhibiting a thin, low aspect ratio ceramic substrate and positioned in manner such that the longitudinal axis of the substrate is not parallel to the normal axis of flow of the gases.

2. Description of the Related Art

As is well known, the purification of exhaust gases, particularly from internal combustion engines in motor vehicles, is generally achieved by an exhaust gas purification system in which a ceramic element having a honeycomb cell structure acts as a catalyst carrier. More precisely, this honeycomb cell structure is covered with a catalyst that contains a precious metal which functions, in the presence of O₂, to convert noxious components of the exhaust gas, such as HC and CO, to CO₂ and H O.

Conventional catalytic converters typically utilize relatively long cylindrical substrates. For example, U.S. Pat. Nos. 4,093,423, (Neumann) and 4,148,120 (Siebels), FIG. 1 of each of these references illustrate this configuration. Although there have been numerous improvements and variants of the catalytic converters disclosed therein, the general concept of a catalytic converter has remained the same; that of a cylindrical, large aspect ratio ceramic substrate with its inlet and outlet faces substantially perpendicular to the flow channels passing therethrough. The substrate is flexibly wrapped and held in place by a compressed mat located on the cylindrical sides of the ceramic and housed within a gas-tight, sheet metal or cast-metal heat resistant housing or can in a manner such that the inlet and outlet faces of the substrate are perpendicular, and thus the channels of the substrate are parallel to, the inlet and outlet of the housing. Generally, the substrates utilized in this standard system, in the past and presently, have typically exhibited a cylindrical shape having a relatively large aspect ratio ranging between 0.4 to 1.5, i.e., a ratio of substrate length to substrate diameter where the substrate length dimension is significant relative to the diameter dimension.

One variant on this standard system is disclosed in U.S. Pat. No. 5,330, 728 (Foster) which discloses a catalyst coated substrate with an inlet face oriented at an angle less than ninety degrees to the flow of exhaust gas entering the converter and fluid flow channels extending through the substrate from the inlet face to an outlet face and oriented at an angle less than ninety degrees to the inlet face.

Although the catalytic converter disclosed in Foster represents an improved, space efficient, low exhaust flow restriction system, it still, suffers from a shortcoming, common to all systems that use honeycomb substrates having a large aspect ratio, that is the cylindrical honeycomb substrate exhibits non-uniform heating which results in certain areas within the core that are subject to exothermic heating and thus excessively high heat. As a result of this non-uniform heating, and resultant areas of exothermic heating, the catalyst, that has been coated on the surface of the ceramic substrate, is subject to non-uniform, and faster than desired, aging.

As such there remains a need for, and it is thus an objective of this invention to provide, for a converter system that exhibits a honeycomb substrate that is subject to uniform heating and exhibits increased resistance to catalyst aging in the applications where the honeycomb substrate is coated with a catalyst. SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to disclose a converter configuration that overcomes the problems and shortcomings of the prior art converters. Specifically, the disclosed herein is a converter system, relatively simple in design, that contains a converter substrate having a low aspect ratio substrate, and is not subject to areas of excessive heating and exhibits the potential for increased resistance to catalytic aging.

The invention is directed at a converter for the treatment of gases comprising the following: a metal shell having an inlet and an outlet end through which gases flow, a ceramic substrate exhibiting an aspect ratio of less than about 0.4 and having a longitudinal axis. The converter further includes a ceramic fiber layer, in contact with and covering at least a portion of the peripheral surface of the substrate, for resiliently mounting the substrate within the metal shell. The substrate is resiliently mounted within the shell such that the longitudinal axis of the substrate is at an angle, preferably acute, with respect to the inlet and outlet end. Furthermore, the substrate has an inlet end face at one end in communication with the inlet of the housing and an outlet end face at its opposite end in communication with the outlet of the housing. Lastly, the substrate has a multiplicity of gas passage honeycomb cells that extend along the longitudinal axis and are normal to the inlet and outlet faces.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded perspective view, of a converter according to the invention described herein;

FIG. 2 is sectional view of the converter of FIG. 1 taken along line 2-2; FIG. 3 is an end view, with a section broken away, of the converter of FIG. 1 ; FIG. 4 is a cross sectional view of another embodiment of the converter according to the invention described herein; FIG. 5 is a cross sectional view of another embodiment of the converter according to the invention described herein; FIG. 6 is a cross sectional view, noted by IV in FIG. 2, of the converter and the preferred embodiment of the supporting mat configuration.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-3 illustrate a first embodiment of a converter designated generally as 10 for use in the treatment of gases. In the converter illustrated in FIGS. 1-3, the thin substrate 12 exhibiting a low aspect ratio of about less than 0.4 is resiliently mounted within a rigid metal shell 14 having an inlet 16 and an outlet 18. Each of the inlet and outlet defines a flow axis, (Aj and Ao, respectively) that approximate the direction of the flow of the gas entering and exiting the converter.

Suitable materials for the metal shell 14 comprise any material which is capable of resisting under-car salt, temperature and corrosion; ferritic stainless steels including grades SS-409, SS-439, and more recently SS-441 are however, generally preferred. The choice of material depends on the type of gas, the maximum temperature and the like. In the embodiments illustrated above, a "clam-shell' type canister is constructed of upper and lower portions, 20, 22, which are stamped in a desired configuration and subsequently joined during assembly along abutting flanges 24, 26 to define an inlet chamber 28, a housing portion 30 and an outlet chamber 32. The clam-shell method of construction is preferred in that it offers substantial flexibility in converter configuration.

The substrate 12 is flexibly mounted within the substrate housing portion 30 of the metal shell 14, with substrate 12 having a channel axis (Ac) and inlet and outlet faces 34 and 36. The substrate 12 is resiliently mounted within the housing portion by providing a ceramic fiber layer 38 between substrate and metal shell, that is in contact with and covers, at a minimum, at least a portion of the peripheral surface of the substrate 12. The substrate 12 is positioned by in a manner such that an angle α, that is between 0 and ninety degrees (90°) is formed between the channel axis (Ac) and the inlet axis (Ai). The substrate is formed to have a multiplicity of gas passage honeycomb cells 40 that extend along the channel axis (A_c) and extend between, and are normal to, the inlet face 34 and the outlet face 36. As described above, the converter substrate utilized herein should exhibit a thin, disc-shaped configuration, specifically a substrate having a lower aspect ratio than is currently utilized in standard catalytic converters. The aspect ratio of the substrate for use in this ceramic converter substrate should be less than about 0.4, and more preferably between about 0.10 to 0.15.

Utilization of substrates of this lowered aspect ratio that have been coated with a catalyst and used in catalytic converter applications is contemplated to result in reduced aging of the catalyst coated on the substrate as a result of the increased radiation heat transfer due to the larger diameter face of the substrate utilized herein. Furthermore, it is contemplated that a thin low-aspect ratio converter configuration as used herein will experience a faster heat-up time than is typical for standard high aspect ratio, commercially available, ceramic substrates.

In a preferred embodiment the substrate should exhibit a high frontal surface area for the gas to flow through, specifically a substrate exhibiting a cell density of greater than 600 cells per square inch, preferably 1000 cells per square inch, and more preferably on the order of about 1600 cells per square inch.

Referring now to FIG. 4, illustrated therein is another embodiment of the converter according to the invention described herein. The major difference between the embodiment depicted here and that of FIG. 2 is that the inlet chamber 28 is configured so that it exhibits a decreasing cross-sectional flow area in the direction of gas flow. The cross-sectional flow area is the area of the plane normal to the gas flow direction and extending from the inlet surface of the substrate 34 to the edge of the inlet chamber 28. Put differently, the cross-sectional flow area should be such that it decreases in relative proportion to the remaining cross-sectional flow area remaining in the inlet surface 34 of the converter substrate 12. This decreasing cross-sectional flow area is accomplished through designing the shape of the inlet chamber 28 such that it is inclined at an angle with respect to the inlet surface 34 of the substrate; that angle is designated as θ. Specifically, the inclined inlet chamber 28 design resulting in the decreasing cross-sectional flow area, described herein, is intended to result in substantially uniform distribution of the gas flow to the frontal area of the converter substrate. It is contemplated that the actual angle at which the inlet chamber is inclined should be empirically determined for each catalytic converter system, based on a number of design factors, including, for example, gas velocity and substrate surface dimensions (area). This angled inlet chamber 28, or decreasing cross-sectional flow area, being the only additional feature, like parts as detailed above for the FIG. 2 embodiment are identified in this embodiment with the same reference numerals used for the parts of the catalytic converter 10. Although the embodiment of FIG. 4 shows an outlet chamber 30 of the same inclined configuration, this is not an essential feature of the invention. However, it is contemplated that the shape of the outlet chamber would likely be the same as that of the inlet chamber for both manufacturing simplicity and space efficiency purposes.

Ceramic honeycomb substrate suitable for use in the present invention may be formed from any ceramic material conventionally used for this purpose such as is disclosed, for example in U.S. Pat. No. 3,885,977 or U.S. Pat. No. Reissue No. 27,747. Preferably, an extruded cordierite ceramic substrate having a high mechanical integrity, low resistance to gas flow and a high geometric surface area is utilized as the substrate.

One important parameter for the ceramic substrate is its mechanical integrity, in particular it's radial strength. Typical cordierite honeycomb substrates are capable of easily withstanding more than 4826.5 kPa (700 psi) of radial pressure before noticeable damage to the honeycomb occurs. Ceramic honeycomb typically comprises square cells, although the cells of the honeycomb may have shapes other than square, including triangular, rectangular and the like. Regarding the formation of the thin low-aspect ratio substrate, it can be formed by forming standard high aspect ratio substrates through the utilization of standard extrusion techniques, and thereafter slicing the so- formed high aspect ratio substrate to the required dimension thereby resulting in the formation of a low aspect ratio substrate.

As described above the resilient mounting of the converter substrate is provided by including a ceramic fiber-containing layer between the substrate and the metal shell housing portion that is in contact with and covers at least a portion of the peripheral surface of the substrate. Ceramic fiber-containing materials suitable for use in the present invention comprise a formed ceramic fiber material, a simple non-expanding ceramic material. Acceptable non-expanding ceramic fiber material include ceramic materials such as those sold under the trademarks "NEXTEL" and S AFFIL" by the "3M" Company, Minneapolis, MN or those sold under the trademarks "CC-MAX" and "FD3ERMAX" by the Unifrax Co., Niagara Falls, NY.

Given the unique shape of the converter substrate utilized in the instant invention, a disc shaped converter having an aspect ratio of less than 0.4, resiliently mounting the ceramic substrate by providing a compressed ceramic fiber-containing layer which covers only the peripheral surface of the substrate may not be sufficient depending upon the conditions. Referring now to FIG. 6, illustrated therein is a preferred configuration for resiliently mounting the substrate. In addition to the peripheral compressed ceramic fiber-containing layer 42, the mounting configuration further includes a second 44 and third 46 fiber-containing layer, each of which is in contact with and covers at least a portion of the inlet and outlet faces 34,36, respectively of the converter substrate 12. In a preferred embodiment, inclusion of these additional layers of ceramic fiber-containing material on the inlet and outlet surfaces necessitates a configuration wherein the cells of the substrate that are covered by the second and third ceramic fiber-containing layers are plugged. The plugging of the mat-covered cells ensures that the mat material, upon compression will not be forced into the cells. Various ceramic fiber containing material layer configurations can be utilized including the following: (1) all ceramic fiber-containing layers, first, second and third comprising an intumescent material exhibiting the same mat weight basis; (2) a first fiber- containing layer comprising an intumescent material and the second and third fiber- containing layers each comprising a first portion in contact with the substrate comprising a non-intumescent mat and a second portion covering the first portion that comprises an intumescent material; (3) the first ceramic fiber-containing layer comprising an intumescent material of a first mat weight basis and the second and third ceramic fiber-containing layers comprising an intumescent material exhibiting a second, larger mat weight basis.

A suitable converter has been designed and produced having the following features: (1) a cordierite substrate having 0.5 inch thickness and 9.5 inch diameter dimensions and a cell density of 1600 cells/in² resiliently mounted such that the aforementioned angle α is 70°; (2) a 0.075 in. thick metal shell comprised of ferritic type SS409 stainless, and configured so that the inlet chamber forms the angle θ of 20°; (3) supporting mat, a first, second and third ceramic layer (second and third layers covering 0.4" of the inlet and outlet surfaces) all exhibiting the equivalent mat weight basis of 6200 g/m² and canned to result in a mat density of approximately 1.07 g/cc. A primary utility of the converter as described herein includes the use as a catalytic converter in the internal combustion engines of vehicles such as cars and motorcycles. Although the invention is particularly advantageous for use in these type of vehicles, the claimed converters can also be used as a catalytic converters in the chemical processing industry. Furthermore, it is contemplated that this converter can be used as a catalyzed reactor substrate for reaction gas applications in the chemical processing industry. Lastly the configuration is suitable for use in dieselfilter applications.

Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and intended scope which is defined by the following claims.

Claims

We claim:

1. A converter for the treatment of gases comprising: a metal shell having an inlet and an outlet, each having a flow axis along which gases flow; a ceramic substrate having an aspect ratio of less than about 0.4, a peripheral surface, an inlet end face at one end in communication with the inlet of the housing, an outlet end face at its opposite end in communication with the outlet of the housing, and a channel axis normal to the inlet and outlet end faces, the substrate resiliently mounted within the metal shell with the channel axis of the substrate at an angle with respect to the inlet and outlet end flow axis; a compressed ceramic fiber-containing layer positioned between the ceramic and the metal shell for resiliently mounting the substrate within the metal shell, the ceramic fiber layer in contact with and covering at least a portion of the peripheral surface of the substrate.

2. The converter of claim 1 wherein the ceramic substrate exhibits an aspect ratio of less than 0.15.

3. The converter of claim 1 wherein the ceramic substrate exhibits an aspect ratio of between about 0.10 to 0.15.

4. The converter of claim 1 wherein the angle formed between the channel axis and inlet flow axis is between 45 and 90 degrees.

5. The converter of claim 1 wherein the angle formed between the channel axis and the inlet flow axis is about 70 degrees.

6. The converter of claim 1 further including a second and third fiber-containing layer, for resiliently mounting the substrate within the metal shell, each of which is in contact with and covers at least a portion of the inlet and outlet faces, respectively.

7. The converter of claim 6 wherein the second and third fiber-containing layers comprises a first portion in contact with the inlet and outlet faces that comprises a non- intumescent material and a second portion covering the first portion that comprises an intumescent material.

8. The converter of claim 6 wherein the first ceramic fiber containing layer exhibits first mat weight basis and the second and third ceramic fiber layers exhibits a second, larger mat weight basis.

9. The converter of claim 6 wherein the cells of the ceramic substrate that are covered by the second and third ceramic fiber-containing layers are plugged.

10. The converter of claim 1 comprising a high surface area ceramic substrate having a cell density of greater than about 600 cells per in².

11. The converter of claim 1 comprising a high surface area ceramic substrate having a cell density of greater than about 1000 cells per in².

12. The converter of claim 1 comprising a high surface area ceramic substrate having a cell density of about 1600 cells per in².

13. The converter of claim 1 wherein the converter is a catalytic converter and the ceramic is coated with a catalyst.

14. A converter for the treatment of gases comprising: a metal shell having an inlet in communication with an inlet chamber, a housing portion and an outlet in communication with an outlet chamber, each of the inlet and the outlet axis including a flow axis along which gases flow; a ceramic substrate having an aspect ratio of less than about 0.4, a peripheral surface, an inlet end face at one end in communication with the inlet of the housing, an outlet end face at its opposite end in communication with the outlet of the housing, and a channel axis normal to the inlet and outlet end faces, the substrate resiliently mounted within the metal shell with the channel axis of the substrate at an angle with respect to the inlet and outlet end flow axis; a compressed ceramic fiber-containing layer located between the metal shell and the housing for resiliently mounting the substrate within the housing, the ceramic fiber layer in contact with and covering at least a portion of the peripheral surface of the substrate.

15. The converter of claim 14 wherein the inlet chamber possesses a decreased cross- sectional flow area in the direction of normal to gas flow.

16. The converter of claim 14 wherein the ceramic substrate exhibits an aspect ratio of less than 0.15.

17. The converter of claim 14 wherein the ceramic substrate exhibits an aspect ratio of between about 0.10 to 0.15.

18. The converter of claim 14 wherein the angle formed between the channel axis and the inlet flow axis is between 45 and 90 degrees.

19. The converter of claim 14 wherein the angle formed between the longitudinal axis and the inlet flow axis is about 70 degrees.

20. The converter of claim 14 further including second and third ceramic fiber- containing layers, for resiliently mounting the substrate within the housing, that are in contact with and cover at least a portion of the inlet and outlet faces, respectively.

21. The converter of claim 20 wherein the second and third ceramic fiber-containing layers each comprises a first portion in contact with the inlet and outlet faces that comprises a non-intumescent material and a second portion covering the first portion that comprises an intumescent material.

22. The converter of claim 20 wherein the first ceramic fiber-containing layer exhibits first mat weight basis and the second and third ceramic fiber layers each exhibits a second, larger mat weight basis.

23. The converter of claim 20 wherein the cells of the substrate that are covered by the second and third ceramic fiber layers are plugged.

24. The converter of claim 14 comprising a high surface area ceramic substrate having a cell density of greater than about 600 cells per in².

25. The converter of claim 14 comprising a high surface area ceramic substrate having a cell density of greater than about 1000 cells per in².

26. The converter of claim 14 comprising a high surface area ceramic substrate having a cell density of about 1600 cells per in².

27. The converter of claim 14 wherein the converter is a catalytic converter and the catalyst is coated with a catalyst.

28. A dieselfilter for the treatment of gases comprising: a metal shell having an inlet and an outlet, each having a flow axis along which gases flow; a ceramic substrate having an aspect ratio of less than about 0.4, a peripheral surface, an inlet end face at one end in communication with the inlet of the housing, an outlet end face at its opposite end in communication with the outlet of the housing, and a channel axis normal to the inlet and outlet end faces, the substrate resiliently mounted within the metal shell with the channel axis of the substrate at an angle with respect to the inlet and outlet end flow axis; a compressed ceramic fiber-containing layer positioned between the ceramic and the metal shell for resiliently mounting the substrate within the metal shell, the ceramic fiber layer in contact with and covering at least a portion of the peripheral surface of the substrate.

29. The converter of claim 28 wherein the ceramic substrate exhibits an aspect ratio of less than 0.15.

30. The converter of claim 28 wherein the ceramic substrate exhibits an aspect ratio of between about 0.10 to 0.15.