Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1999-11-12
2003-07-08
Caldarola, Glenn (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S177000, C422S180000, C252S062000, C252S06230Q, C252S06230Q, C252S06230C, C501S055000, C501S094000, C501S095100
Reexamination Certificate
active
06589488
ABSTRACT:
TECHNICAL FIELD
The invention relates to a molding for supporting a monolith in a catalytic converter, and to the production and use thereof.
BACKGROUND ART
A catalytic converter, required to be installed, for example, in motor vehicles, consists of a ceramic monolith carrying a catalytically active component on its porous surface, a catalytic converter casing, and a molding which supports and immobilizes the monolith in the casing in a gentle manner.
The moldings used for supporting and immobilizing ceramic monoliths in catalytic converter casings in this gentle manner are usually “swell mats”. These consist of about 55% by weight of unexpanded vermiculite, 35% by weight of ceramic fibers and 10% by weight of binders. The job of the swell mat two fold: first, is to enclose the monolith in such a way that the latter is held immobilized during accelerations; and second, during operation, to compensate for the gap between the monolith and the converter casing, which ordinarily increases after startup owing to the thermal expansion of the outer skin. These objects have been achieved, first, with the aid of very high closing forces during assembly of the catalytic converter, i.e. during sealing of the converter casing, and second, by the presence of unexpanded vermiculite in the swell mat. The vermiculite expands at a temperature of about 400° C. and thus causes an increase in volume of the swell mat, which, in the normal case under the inclusion conditions, ensures adequate immobilization and sealing of the monolith. In swell mats, the increase in the volume of the expanded/swollen parts thus compensates for the different dimensions of the gap between the monolith and the converter casing.
A disadvantage of prior art swell mats is the high closing force during assembly of the catalytic converter, which can easily result in damage to the filigree ceramic monolith and thus irreversibly damage the catalytic converter. In addition, conventional swell mats are regarded as a health risk owing to their content of ceramic fibers. There is thus a demand for a ceramic-fiber-free molding for supporting and immobilizing monoliths in a catalytic converter casing. A known molding which satisfies this condition consists of knitted metal fabrics, but these require a two-layer internal structure. For economic and technical reasons, such moldings are therefore rarely used.
The ever more compact design of vehicles and the increasing exhaust temperatures require swell mats which are distinguished by good thermal insulation and thus make secondary or additional thermal-insulation measures, such as heat shields, either unnecessary or operate to reduce these requirements.
DISCLOSURE OF INVENTION
The object of the invention is to provide a microporous molding for supporting and immobilizing monoliths in catalytic converter casings which does not have the above disadvantages of swell mats, has good thermal insulation properties and in addition is simple and inexpensive to produce.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a microporous molding which comprises
60-95% by weight of finely divided metal oxide,
0.5-10% by weight of fibers which do not represent a health risk,
0-35% by weight of opacifiers,
0-10% by weight of organic fibers, and
0-30% by weight of refractory material which expands at a temperature above 300° C.,
and has a density of 100-240 kg/m
3
, without taking into account the refractory material, and has a compression to 96% of its original thickness or less (thinner), measured during compression or immediately after compression by a pressure of 1 bar applied for a period of 5 minutes, wherein this compression has recovered to more than 70% of its initial value one minute after removal of the pressure. The molding according to the invention preferably exhibits a compression to at least 93% of its original thickness immediately after removal of a pressure of 1 bar applied for a period of 5 minutes. The compression has preferably recovered to more than 80% of its initial value 1 minute after removal of the pressure. In other words, the moldings of the present invention display both a high compressibility as well as a rapid recovery of thickness following compression.
Microporous moldings are usually not designed for elasticity. To the contrary, pressure-resistant sheets are generally desired, which is why such moldings may pass through a hardening step during production. Known microporous moldings are therefore not suitable for supporting and immobilizing a monolith in a catalytic converter casing, since the elasticity of this molding is too low to immobilize the monolith.
Only the molding according to the invention has a sufficiently high elasticity to immobilize the monolith in the converter casing in the long term and at the high temperatures which prevail in the catalytic converter under operating conditions. The elasticity is furthermore advantageous for immobilizing the monolith because the highly effective thermal insulation of the inventive moldings minimize thermal expansion of the converter casing in the hot state. Only a slight increase in the gap between the converter casing and the monolith therefore occurs. Both the elasticity and the thermal insulation of the molding according to the invention thus have an advantageous effect in immobilizing the monolith. Unlike the prior art, therefore, a molding for supporting monoliths according to the invention can be produced even without swellable substances.
The molding according to the invention offers the following advantages over known moldings for supporting monoliths in catalytic converters:
adequate elasticity, even in operation, for sufficient immobilizing the monolith;
free from ceramic fibers and other harmful substances;
installability to insulation/sheet with lower pressures/forces than hitherto, additionally allowing the use of longer monoliths, since the risk of fracture is considerably reduced;
maximum thermal insulation, reducing the external temperature of the catalytic converter, making additional secondary heat-protection measures unnecessary;
good installation behavior during assembly; and
low weight.
The finely divided metal oxide is preferably selected from the group consisting of pyrogenic silicas, arc silicas, low-alkali precipitated silicas, silicon dioxide aerogels, aluminum oxides of analogous preparation, and mixtures thereof. The finely divided metal oxide is more preferably selected from the group consisting of pyrogenic silica, aluminum oxide and mixtures thereof. The finely divided metal oxide preferably has a specific BET surface area of from 50 to 700 m
2
/g, in particular from 70 to 400 m
2
/g.
The molding according to the invention may additionally comprise components selected from the group consisting of opacifiers, inorganic fibers, organic fibers, and refractory materials which expand at temperatures above 300° C.
The molding according to the invention preferably comprises the following components:
70-90% by weight of finely divided metal oxide,
1-5% by weight of fibers which do not represent a health risk,
5-25% by weight of opacifiers,
0-5% by weight of organic fibers, and
0-25% by weight of refractory material which expands at a temperature above 300° C.
The molding according to the invention most preferably is limited to substantially the foregoing components.
The opacifier is preferably selected from the group consisting of ilmenite, titanium dioxide, iron(II)/iron(III) mixed oxides, chromium dioxide, zirconium oxide, manganese dioxide, iron oxide, rutile, zirconium silicate, silicon carbide, and mixtures thereof. Owing to its low density and its absorption behavior in the infra-red region, silicon carbide is particularly preferred as an opacifier. The opacifier preferably has a particle size in the range from 0.1 to 10 &mgr;m.
The fibers which do not represent a health risk are preferably inorganic fibers without respirable components or fibers which do not represent a health risk owing to their chemical composition. Examples of inorganic fibers without respir
Brooks & Kushman P.C.
Caldarola Glenn
Rudnick Douglas W.
Wacker-Chemie GmbH
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