U.S. patent application number 10/534893 was filed with the patent office on 2007-06-21 for pollution control device and mat for mounting a pollution control element.
Invention is credited to Muneki Miyasaka, Toshiyuki Watanabe.
Application Number | 20070140929 10/534893 |
Document ID | / |
Family ID | 32708293 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070140929 |
Kind Code |
A1 |
Watanabe; Toshiyuki ; et
al. |
June 21, 2007 |
Pollution control device and mat for mounting a pollution control
element
Abstract
A mat for mounting a pollution control element (e.g., a
catalytic converter and diesel particulate filter, etc.) that
maintains support holding strength without impairing elasticity
even when exposed to high temperatures in excess of 800.degree. C.
for long periods of time, and a pollution control device that
includes such a mat. The mat comprises at least two layers, an
alumina fiber layer and a ceramic fiber layer, that are formed into
a single sheet without the use of an auxiliary bonding means.
Inventors: |
Watanabe; Toshiyuki;
(Atsugi, JP) ; Miyasaka; Muneki; (Sagamihara,
JP) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
32708293 |
Appl. No.: |
10/534893 |
Filed: |
November 17, 2003 |
PCT Filed: |
November 17, 2003 |
PCT NO: |
PCT/US03/36478 |
371 Date: |
October 6, 2006 |
Current U.S.
Class: |
422/179 |
Current CPC
Class: |
C04B 2111/00793
20130101; C04B 2111/00612 20130101; B01D 53/9454 20130101; B01D
2265/06 20130101; B28B 1/008 20130101; F01N 2330/06 20130101; F01N
2330/02 20130101; B01D 2279/30 20130101; F01N 3/0211 20130101; Y02T
10/12 20130101; B28B 1/527 20130101; Y02A 50/20 20180101; D04H
1/4209 20130101; F01N 3/2864 20130101; D04H 1/732 20130101; F01N
3/2853 20130101; B01D 53/88 20130101; D04H 1/4374 20130101; C04B
30/02 20130101; C04B 30/02 20130101; C04B 14/46 20130101; C04B
14/4625 20130101; C04B 40/00 20130101; C04B 40/006 20130101; C04B
40/0259 20130101; C04B 40/0263 20130101 |
Class at
Publication: |
422/179 |
International
Class: |
F01N 3/28 20060101
F01N003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2002 |
JP |
2002-377557 |
Claims
1. A mat for mounting a pollution control element in a pollution
control device, said mat comprising at least an alumina fiber layer
and a ceramic fiber layer, wherein the weight ratio of said alumina
fiber layer to said ceramic fiber layer is 3:11-11:3 and said mat
maintains holding strength even when exposed to high temperatures
in excess of 800.degree. C. for long periods of time.
2. The mat according to claim 1, wherein said alumina fiber layer
and said ceramic fiber layer form a single sheet without the use of
an auxiliary bonding means.
3. The mat according to claim 1, wherein the ceramic fibers that
compose the ceramic fiber layer are annealed at a temperature of
700-1200.degree. C.
4. The mat according to claim 1, wherein the alumina fiber layer
contains crystalline alumina fibers formed from a mixture
containing alumina and silica, and the alumina content of that
fiber is 50 wt % or more.
5. The mat according to claim 1, wherein the ceramic fiber layer
contains ceramic fibers formed from a mixture containing alumina
and silica, and the silica content of that fiber is 45 wt % or
more.
6. The mat according to claim 1, wherein the alumina fiber layer
and ceramic fiber layer are formed into a single sheet by preparing
a slurry containing alumina fibers and a slurry containing ceramic
fibers, adhering either of the slurries to a permeable substrate
and partially dehydrating the adhered slurry to form a first layer,
and then adhering the other slurry to the first layer and partially
dehydrating that slurry to form a second layer.
7. The mat according to claim 1, wherein said mat is for mounting a
catalyst support in a catalytic converter.
8. The mat according to claim 1, wherein neither said layer
includes an expanding material.
9. The mat according to claim 1, wherein said mat maintains its
holding strength even when exposed to high temperatures in excess
of 800.degree. C. for 10 years as determined by extrapolation.
10. A pollution control device comprising: a housing; a pollution
control element mounted in said housing; and a mat disposed between
said housing and said pollution control element so as to mount said
pollution control element in said housing, said mat comprising at
least two layers, an alumina fiber layer and a ceramic fiber layer,
wherein the weight ratio of said alumina fiber layer to said
ceramic fiber layer is 3:11-11:3 and said mat maintains holding
strength even when exposed to high temperatures in excess of
800.degree. C. for long periods of time.
11. The pollution control device according to claim 10, wherein
said alumina fiber layer and said ceramic fiber layer form a single
sheet without the use of an auxiliary bonding means.
12. The pollution control device according to claim 10, wherein the
ceramic fibers that compose the ceramic fiber layer are annealed at
a temperature of 700-1200.degree. C.
13. The pollution control device according to claim 10, wherein the
alumina fiber layer contains crystalline alumina fibers formed from
a mixture containing alumina and silica, and the alumina content of
that fiber is 50 wt % or more.
14. The pollution control device according to claim 10, wherein the
ceramic fiber layer contains ceramic fibers formed from a mixture
containing alumina and silica, and the silica content of that fiber
is 45 wt % or more.
15. The pollution control device according to claim 10, wherein the
alumina fiber layer and ceramic fiber layer are formed into a
single sheet by preparing a slurry containing alumina fibers and a
slurry containing ceramic fibers, adhering either of the slurries
to a permeable substrate and partially dehydrating the adhered
slurry to form a first layer, and then adhering the other slurry to
the first layer and partially dehydrating that slurry to form a
second layer.
16. The pollution control device according to claim 10, wherein
neither said layer includes an expanding material.
17. The pollution control device according to claim 10, wherein
said mat maintains its holding strength even when exposed to high
temperatures in excess of 800.degree. C. for 10 years as determined
by extrapolation.
18. The pollution control device according to claim 10, wherein
said pollution control device is a catalytic converter.
19. The pollution control device according to claim 10 in
combination with an engine exhaust.
20. The pollution control device according to claim 10 in
combination with an engine.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to pollution control devices
(e.g., catalytic converters, diesel particulate filters, etc.), to
mats for mounting pollution control elements in such devices and,
in particular, to catalytic converters used in exhaust gas
purification devices and, more particularly, to a mat for mounting
a catalyst support in a catalytic converter housing.
BACKGROUND
[0002] Catalytic converters used in the exhaust gas purification
devices of automobile and diesel engines normally contain a
catalyst support composed of a monolith having a so-called
"honeycomb structure" in which through holes are arranged in the
shape of honeycombs, in a metal housing. This monolith is loaded
with a catalyst such as a precious metal, and purifies exhaust gas
by oxidizing carbon monoxide and hydrocarbons and reducing nitrogen
oxides. This monolith catalyst support is formed from a metal or
ceramic material. In order to receive the catalyst support in a
metal housing, a mat for mounting the catalyst support (catalyst
support mounting material) composed of alumina-silica-based fibers
or other ceramic fibers is arranged between the metal housing and
catalyst support, and the catalyst support is held and protected
from damage.
[0003] However, the coefficient of thermal expansion of ceramic
catalyst support is typically nearly a power of ten smaller than
the coefficient of thermal expansion of the metal housing. Although
catalytic converters are normally exposed to high temperatures of
several hundred degrees, under such high temperatures, the thermal
expansion of the metal housing exceeds the thermal expansion of the
ceramic catalyst support due to the difference in the coefficients
of thermal expansion between the metal housing and ceramic catalyst
support. As a result, gaps expand between the metal housing and
catalyst support resulting in a decrease in the holding strength of
the catalyst support, leading to problems such as the occurrence of
rattling in the catalyst support.
[0004] Therefore, it has been proposed to prevent a decrease of the
holding strength of the catalyst support when gaps expand between
the metal housing and catalyst support by containing an expanding
agent in the mat for mounting the catalyst support. See, for
example, Japanese Unexamined Patent Publication No. 2002-514283
(page 2, pages 16-18). Namely, in this Patent Publication, a single
sheet formed from a flexible expanding layer and a flexible
expanding layer containing an expanding material is arranged
between a metal housing and a catalyst support.
SUMMARY OF THE INVENTION
[0005] In recent years however, due to the requirements for
improved automobile fuel consumption and increasingly strict
emissions controls, the catalytic devices used in automobiles are
being exposed to even higher temperatures due to higher
temperatures of the exhaust gas itself from the engine, and due to
the use of a system in which exhaust gas is treated at as high a
temperature as possible by locating the catalytic device
immediately behind the engine in order to improve purification
performance. For example, it is known to be not uncommon for the
temperature of exhaust gas to exceed 1000.degree. C. under certain
driving conditions in vehicles using a gasoline engine.
[0006] However, expanding materials such as the vermiculite,
expanding graphite or expanding sodium silicate and so forth used
in Japanese Unexamined Patent Publication No. 2002-514283
deteriorate when exposed to temperatures of 800-1000.degree. C.,
and under a significant decrease in strength. In addition to the
thermal deterioration, a mechanical shock such as decreases the
holding strength of the catalyst support. In this Patent
Publication, although the use of an expanding material is able to
effectively accommodate changes in the gap between the metal
housing and catalyst support, there is no discussion of the
durability at high temperatures in excess of 800.degree. C.
[0007] According to the present invention, a mat for mounting a
pollution control element, like a catalyst support, can be provided
that maintains support holding strength without impairing
elasticity even when exposed to temperatures in excess of
800.degree. C. for long periods of time.
[0008] In order to solve one or more of the above problems, the
present invention can provide a mat for mounting a pollution
control element (e.g., a catalyst support, diesel particulate
filter, etc.), and the pollution control device containing such a
mat, where the mat comprises at least two layers, an alumina fiber
layer and a ceramic fiber layer. These layers can be provided in
the form a single sheet without the use of an auxiliary bonding
means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an exploded perspective view of a catalytic
purification device.
[0010] FIG. 2 is a cross-sectional view showing the constitution of
a mat for mounting a catalyst support of the present invention.
[0011] FIG. 3 is a graph showing the changes over time in the
bearing pressure of the mat for mounting a catalyst support of
Sample 3.
[0012] FIG. 4 is a graph showing the extrapolated values of bearing
pressure after 10 years of samples of Examples 1 and 2 and
Comparative Example 1.
DETAILED DESCRIPTION
[0013] The following provides an explanation of the present
invention with reference to the drawings. FIG. 1 is an exploded
perspective view of a typical catalytic converter. Catalytic
converter 10 contains catalyst support 20, composed of a monolith
having a so-called "honeycomb structure" in which through holes are
arranged in the shape of honeycombs, in a metal housing 11. This
monolith is loaded with a catalyst that purifies exhaust gas by
oxidizing carbon dioxide and hydrocarbons and reducing nitrogen
oxides. Catalyst support 20 is normally formed from a ceramic
material, and is frequently extremely brittle. Consequently, a mat
3 for mounting a catalyst support is arranged between metal housing
11 and catalyst support 20 to protect catalyst support 20 from
damage.
[0014] As shown in FIG. 2, mat 30 for mounting a catalyst support
of the present invention contains at least two layers consisting of
an alumina fiber layer 31 and a ceramic fiber layer 32, and these
layers form a single sheet without the use of an auxiliary bonding
means.
[0015] Alumina fiber layer 31 is formed from alumina fibers
prepared by a precursor fibering process and ceramic fiber layer 32
is formed from ceramic fibers prepared by melting a mixture of
alumina (Al.sub.2O.sub.3), silica (SiO.sub.2) and other oxides
followed by melt blowing or melt spanning. These fibers are formed
from 80-95 wt % of fibers and 5-20 wt % of binder.
[0016] Here, in the present specification, the alumina fibers that
compose alumina fiber layer 31 are crystalline fibers that contain
50 wt % or more, and preferably 70 wt % or more, of alumina. On the
other hand, the ceramic fibers that compose ceramic fiber layer 32
are RCF (Refractory Ceramic Fiber) that contain 45 wt % or more of
silica. Examples of other oxides besides alumina and silica include
zirconia (ZrO.sub.2), magnesia (MgO), calcia (CaO), chromium oxide
(Cr.sub.2O.sub.3), yttrium oxide (Y.sub.2O.sub.3) and lanthanum
oxide (La.sub.2O.sub.3).
[0017] The ceramic fibers that compose ceramic fiber layer 32 are
preferably annealed. Annealing improved elasticity and improves the
holding strength and durability of the mat. This annealing is
carried out at a temperature of 700-1200.degree. C., and preferably
950-1100.degree. C., and the annealing time is preferably 0.5-2
hours.
[0018] Acrylic resin, styrene-butadiene, vinyl pyridine,
acrylonitrile, vinyl chloride or polyurethane and so forth is used
for the binder. In addition, an inorganic binder (e.g., glass
particles, calcium carbonate, mica or magnesium hydroxide) or
flexible thermosetting resin (e.g., unsaturated polyester, epoxy
resin or polyvinyl ester) may also be contained in addition to the
alumina fibers or ceramic fibers and binder.
[0019] The mat for mounting a catalyst support of the present
invention is formed by forming a single sheet without the use of an
auxiliary bonding means, such as by simultaneously forming a
ceramic fiber layer on the upper surface of an alumina fiber layer.
This "auxiliary bonding means" refers to an externally used
adhesive means such as resin, adhesive, adhesive tape, stitches or
staples.
[0020] Mats for mounting a catalyst support of the prior art that
are composed of a multi-layered laminate were formed by first
individually forming each layer followed by mutually adhering the
layers using adhesive, adhesive film, stitches or staples. However,
multi-layered mats in which the individual layers were adhered with
adhesive or adhesive film may typically produce undesirable smoke
or odor when used in a catalytic converter. In addition, this
adhesive or adhesive film has an effect on the heat resistance of
the mat. Moreover, the production costs of such a mat increase due
to the cost of mutually adhering each layer as well as the cost of
the adhesive or adhesive film used. On the other hand, in the case
of mats in which the layers were adhered mechanically with stitches
and so forth, the mechanical strength of the mat decreases at those
sites where the stitches penetrate the mat, and there are problems
with costs of the additional steps and materials required.
[0021] The present invention eliminates the above problems since a
single sheet is formed from an alumina fiber layer and ceramic
fiber layer without the use of such auxiliary bonding means.
[0022] More specifically, the mat for mounting a catalyst support
of the present invention is formed by preparing a slurry containing
alumina fibers and a slurry containing ceramic fibers (the solid
portion of these slurries are preferably 5 wt % or less), adhering
the first slurry to a screen or wire and so forth of a rolling
machine, forming a lower layer by partially dehydrating this first
slurry by gravity and/or vacuum, adhering the second slurry to the
above partially dehydrated lower layer, forming an upper layer by
similarly partially dehydrating, and then pressing using a pressing
roller to increase the densities of both layers followed by drying
completely with a heated roller. Although either the alumina fiber
layer or ceramic fiber layer may be initially formed as the lower
layer, it is preferable during drying that the thickest layer be
the lower layer that is formed first.
[0023] In this manner, due to the step of adhering a second slurry
onto a layer formed by partially dehydrating a first slurry
followed by dehydration of the second slurry, the both components
are partially mixed particularly at the interface between the two
layers. As a result, the two layers are permanently and effectively
adhered without the use of an auxiliary bonding means such as an
adhesive, allowing the formation of an integrated sheet.
[0024] In the mat for mounting a catalyst support of the present
invention, the weight ratio between the alumina fiber layer and the
ceramic fiber layer is preferably 3:11-11:3. In addition to the
two-layer structure composed of these alumina fiber and ceramic
fiber layers, the mat for mounting a catalyst support of the
present invention may employ a structure of three or more layers
that include other layers composed of these materials or other
materials. In this case, however, at least one of the outermost
layers must be an alumina fiber layer.
[0025] As shown in FIG. 1, a catalytic purification device can be
completed by wrapping the mat for mounting a catalyst support
obtained in this manner around a catalyst support to that an
alumina fiber layer is in contact with the catalyst support, and
then containing it in a metal housing.
EXAMPLES
Example 1
[0026] 92 wt % of alumina fibers, composed of 72 wt % of alumina
and 28 wt % of silica, were mixed with 8 wt % of binder (acrylic
latex, Nippon Zeon: Nippore LX-816) followed by the addition of
water to prepare a first slurry. In addition, 92 wt % of silica
fibers (Shinnikka Thermal Ceramics: SC-1260D1), formed by melting
and composed of 46 wt % of alumina and 53 wt % of silica, were
mixed with 8 wt % of the above binder followed by the addition of
water to prepare a second slurry. Samples 1 through 5 of mats for
mounting a catalyst support having the weighing capacity ratios
between the alumina fiber layer and ceramic fiber layer shown in
Table 1 were obtained by the above ordinary rolling method using
these slurries.
Example 2
[0027] With the exception of using ceramic fibers that were
annealed for 60 minutes at a temperature of 1000.degree. C.,
samples 6 through 8 of mats for mounting a catalyst support shown
in Table 2 were obtained in the same manner as Example 1.
Comparative Example 1
[0028] With the exception of forming the ceramic fiber layer from
41 wt % of vermiculite, 47 wt % of ceramic fibers and 12 wt % of
binder, samples 9 through 13 of mats for mounting a catalyst
support shown in Table 3 were obtained in the same manner as
Example 1.
Evaluation Method
[0029] The high-temperature holding strength (bearing pressure) and
durability of the samples were evaluated in the manner described
below. Namely, each sample was cut to a diameter of 45 mm, and each
cut sample was then clamped between two plates above and below of a
compression tester so that the alumina fiber layer was on the
high-temperature (900.degree. C.) side. The samples were compressed
and the pressure was adjusted to 130 kPa after 5 minutes. Next, the
two upper and lower plates were heated and the times when the
plates reached 900.degree. C. and 700.degree. C., respectively,
were taken to be time 0. The changes in bearing pressure were then
recorded every hour for 20 hours. The results for sample 3 are
shown in FIG. 3. The formula Y=aX.sup.b can be determined from this
graph as an approximation of changes in bearing pressure. Bearing
pressure extrapolated values were then determined using this
approximation formula, and are shown in Tables 1 through 3.
TABLE-US-00001 TABLE 1 1st layer Ceramic 2nd layer Alumina Approx.
formula Bearing pressure fibers (92%), fibers (92%), for changes in
extrapolated value binder (8%) binder (8%) bearing pressure after
10 years (kPa) Sample 1 Weighing capacity (g/m2) 300 1100 Y =
85.933.times..sup.-0.0566 45.1 Weighing capacity ratio 3 11 Sample
2 Weighing capacity (g/m2) 500 900 Y = 68.21.times..sup.-0.0589
34.9 Weighing capacity ratio 5 9 Sample 3 Weighing capacity (g/m2)
700 700 Y = 65.13.times..sup.-0.082 25.6 Weighing capacity ratio 7
7 Sample 4 Weighing capacity (g/m2) 900 500 Y =
48.132.times..sup.-0.0724 21.1 Weighing capacity ratio 9 5 Sample 5
Weighing capacity (g/m2) 1100 300 Y = 43.803.times..sup.-0.1343 9.5
Weighing capacity ratio 11 3
[0030] TABLE-US-00002 TABLE 2 1st layer Ceramic 2nd layer Alumina
Approx. formula Bearing pressure fibers (92%), fibers (92%), for
changes in extrapolated value binder (8%) binder (8%) bearing
pressure after 10 years (kPa) Sample 6 Weighing capacity (g/m2) 300
1100 Y = 103.57.times..sup.-0.0493 59.1 Weighing capacity ratio 3
11 Sample 7 Weighing capacity (g/m2) 700 700 Y =
94.206.times..sup.-0.0446 55.5 Weighing capacity ratio 7 7 Sample 8
Weighing capacity (g/m2) 1100 300 Y = 90.317.times..sup.-0.0538 49
Weighing capacity ratio 7 7
[0031] TABLE-US-00003 TABLE 3 1st layer Vermiculite 2nd layer
Alumina Approx. formula Bearing pressure (41%), ceramic fibers
fibers (92%), for changes in extrapolated value (47%), binder (12%)
binder (8%) bearing pressure after 10 years (kPa) Sample 9 Weighing
capacity (g/m2) 300 1100 Y = 150.42.times..sup.-0.1143 41 Weighing
capacity ratio 3 11 Sample 10 Weighing capacity (g/m2) 500 900 Y =
196.79.times..sup.-0.01574 32.8 Weighing capacity ratio 5 9 Sample
11 Weighing capacity (g/m2) 700 700 Y = 234.08.times..sup.-0.2256
18 Weighing capacity ratio 7 7 Sample 12 Weighing capacity (g/m2)
900 500 Y = 311.91.times..sup.-0.02828 12.5 Weighing capacity ratio
9 5 Sample 13 Weighing capacity (g/m2) 1100 300 Y =
344.19.times..sup.-0.4101 3.24 Weighing capacity ratio 11 3
[0032] A graph containing a plot of extrapolated bearing pressure
values after ten years is shown in FIG. 4. As is clear from FIG. 4,
the high-temperature holding strength after 10 years of the mat for
mounting a catalyst support of the present invention is improved by
about 40% over a mat containing an expanding agent of the prior art
at alumina fiber layer to ceramic fiber layer ratios of 7:7-3:1.
Moreover, when annealed ceramic fibers are used, high-temperature
holding strength after 10 years was improved by about 4-5 times at
an alumina fiber layer to ceramic fiber layer ratio of 3:11, and by
about two times at an alumina fiber layer to ceramic fiber layer
ratio of 7:7.
[0033] The mat for mounting a catalyst support of the present
invention maintains support holding strength without impairing
elasticity even if exposed to high temperatures in excess of
800.degree. C. for long periods of time.
* * * * *