Catalytic Reactor With Monolithic Element

Abstract

A catalytic converter adapter for use in the exhaust systems of internal combustion engines comprises a tubular shell having a differentially hardened fibrous lining to resiliently support, insulate, and secure a monolithic type catalyst element.

Description

BRIEF SUMMARY OF THE INVENTION

It is the basic purpose of this invention to provide an improved type mounting for a monolithic type or honeycomb catalyst element which is suitable for mass manufacture and for use in exhaust systems of automotive internal combustion engines.

The invention accomplishes this purpose by use of a nonmetallic fibrous sleeve to mount the monolithic catalyst element on a metal tube or shell which forms a part of the converter reactor structure. The fibrous sleeve is impregnated with a suitable binder, rigidizer, and adhesive which is differentially deposited on drying to bind, bond, and seal the sleeve without destroying its resiliency and thermal and shock insulating properties.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side elevation partially broken away and partly in section of an internal combustion engine exhaust system incorporating the invention;

FIG. 2 is an enlarged section of the honeycomb catalyst element of FIG. 1;

FIG. 3 is an enlarged cross section along the line 3--3 of FIG. 1;

FIG. 4 is a perspective view of another form of the fibrous wrap, and;

FIG. 5 is a perspective view of a third form of fibrous wrap.

DESCRIPTION OF THE INVENTION

An internal combustion engine 1 has an exhaust manifold 3 that discharges exhaust gases into an exhaust system 5 that includes an enlarged exhaust pipe section 7 that carries gases to a sound attenuating exhaust gas muffler 9 of a suitable construction which in turn discharges gases into a tailpipe 11 that has an outlet opening 13 through which gases flow to the atmosphere. In accordance with this invention, and as a specific embodiment of the broad concept of the invention, honeycomb catalyst means are mounted within the metal exhaust pipe 7 which, therefore, serves as a housing or outer shell for the catalyst means. Honeycomb monolithic catalyst elements for use in elminating undesired constituents in the exhaust gas stream of an internal combustion engine are known in the art, and one type is described in detail in U. S. Pat. No. 3,441,381. Generally speaking, the refractory supports 15 are manufactured so as to have channels or passages 17 that enable gas to pass from the inlet face 19 to the outlet face 21. The desired catalytic material is deposited by a suitable process on the walls of the cells of passages 17 so that the exhaust gas is in contact with the catalyst as it passes through the body 15. The refractory support 15 is relatively brittle and has a different coefficient of expansion than the metallic housing 7, thereby creating a serious danger of damage during the manufacture, assembly, and use of the catalytic unit. The present invention provides a shock resistant means for mounting the frangible refractory element 15 in a metal housing which serves also to protect it during handling prior to operation of the vehicle.

The refractory support member 15 is a part of a mounting and support arrangement 23 wherein a nonmetallic resilient fibrous ring 29 encircles the outer circumference of the support body 15 and serves as the means for resiliently mounting the body 15 inside of a metal shell, such as that illustrated by the exhaust pipe 7. In the unit of FIGS. 1, 2, and 3 the ring 29 is continuous or integral, whereas the ring 29a of FIG. 4 is shown as an overlapped blanket or wrap of fibrous material 5, and the element 29b is indicated as a spirally wound member of layers which can be paper thin and sufficient in number to build up the desired thickness of the ring. Preferably, the fibrous ring is press fitted over the honeycomb body 15 and into the shell 7 so that the natural resiliency of the fibrous material 29 exerts radial pressure on the outside of the body 15 and the inside of the shell 7. In a typical assembly the element 15 might be 4 - 5 inches in diameter and the thickness of ring 29 about 1/4 inch before compression and about 3/16 inch after radial compression in assembly with the element 15 and housing 7. Ordinarily, the outer surface of the body 15 is uneven and irregular and the radially compressed fibrous layer 29 conforms itself to these irregularities and prevents bypassing along the length of the outside face of the body 15.

The fibrous body is formed from materials that will withstand the relatively high temperatures to which the catalytic elements are subjected in use, thus, asbestos and ceramic fibers may be used. These can be vacuum ring formed as an integral part 29, wet formed from a blanket as the ring 29a, or wrapped from thin paper layers as the element 29b. The materials known under the trademarks "Fiberfrax", "Kaowool", "Cerafiber", and "Amosite" are typical of materials that contain fibers of the type desired. "Cera Paper", "Fiberfrax" ceramic paper, and asbestos paper can be used to form the spiral wound element 29b.

In addition to the frictional connection provided by the ring 29 which serves to hold the unit 23 in place, it is preferred that the fiber layer 29 be impregnated with a suitable adhesive, binder, and rigidizer which, upon hardening, will adhere the fibrous material to the metal shell 7 as well as to the refractory honeycomb 15. The adhesive can be applied in various ways as by brushing, dipping, rolling, spraying, etc. and the amount and composition of the adhesive are controlled so that it is insufficient to cause deposition on the walls of cells 17 and the desired differential binder concentration or density and hardness is achieved. The liquid adhesive also serves as a means to seal the fibrous layer and the interfaces and to prevent bypassing of gas.

The adhesive is preferably a refractory cement that resists the high temperature of operation (up to 2,300.degree. F). The preferred fibers are ceramic and for these applications an adhesive and rigidizer such as a colloidal solution of silica is preferably used to provide surface hardening, bonding, and resistance to gas flow erosion. By varying the amount of solutions applied to the fibrous layer 29, 29a, or 29b, the surface hardness can be controlled without sacrificing the resiliency needed in the center of the fibrous layer during handling of the element and operation of the vehicle. When the adhesive is dried out (as by application of suitable heat) the colloidal material (such as silica) tends to preferentially migrate, concentrate, and settle, due to vaporization of the liquid vehicle, at the exposed ends and faces where, upon hardening, it serves to provide a gas impervious barrier to prevent bypassing or gas flow through the fiber layer along the interfaces, or out of broken cell walls in the outer surface of honeycomb element 15.

In use, exhaust gas leaving manifold 3 and entering pipe 7 flows through the honeycomb element 23 where it is treated to remove undesired constituents such as nitrogen oxides, carbon monoxide, and unburned hydrocarbons. It then passes through the muffler means 9 where it is acoustically treated to remove undesired sound, after which it passes to atmosphere through outlet 13. Gas is prevented from bypassing the element 15 by the hardened binder in the layer 29.

The features described have many advantages. The sleeves 29, 29a, and 29b provide a resilient interface between the element 15 and the shell 7 that gives a high degree of mechanical shock resistance and eliminate the need for stringent dimensional tolerances. The high temperature withstanding fibers (such as alumina silica refractory fibers) of the sleeves are stable up to the usual maximum operating temperatures of about 2,300.degree. F so that the reactors are safely positioned and insulated at all normally encountered temperatures. The thermal insulating properties of the layers 29 minimize the temperature of shell 7 to protect the surrounding environment, provide for faster warm-up and better heat retention in the catalyst, minimum cross sectional thermal gradients due to conductive heat loss into the shell, and enable a better selection of metals for use in the shell 7 because of metal isolation from very high temperatures, for example, low grade, low expansion stainless steel might be used. Substantially stress-free relative movement between the elements 15 and shell 7 is provided by layers 29 to accomodate different rates of thermal expansion and contraction. The simple construction of the unit 23 enables the thickness of layers 29 to be readily varied in accordance with the degree of thermal and shock insulation desired. Effective positive sealing against leakage around the outside of elements 15 is obtained, in spite of the usual rough and broken exteriors thereon, and there is no need for a special coating on the outsides of the elements. The differentially hardened nature of the sleeves due to migration of the colloidal material (e. g., silica) to the surfaces where vehicle vaporization occurs provides a positive gas impervious barrier that prevents gas entry into or flow out of the fibrous layer as well as sealing and bonding along the interfaces with shell 7 and element 15 while retaining resiliency in the center of the sleeve. In unit 23 there is no possible abrasion of element 15 by contact with metal.

Modifications in the specific details described may be made without departing from the spirit and scope of the invention.

Claims

I claim:

1. A catalytic reactor for use in exhaust systems of internal combustion engines comprising a porous refractory catalyst element, a tubular metal shell containing said element, and an annular nonmetallic resilient fibrous layer located between the element and shell, said layer being impregnated with a dried out colloidal adhesive, fiber binding and rigidizing solution wherein the colloidal material has been preferentially deposited out adjacent the outermost faces of the layer.

2. A reactor as set forth in claim 1 wherein said dried out solution serves to seal the outer surface of the porous element and to bond the element and shell to the layer.

3. A reactor as set forth in claim 2 wherein the layer is in a state of radial compression between said element and shell.

4. A catalytic exhaust reactor comprising a tubular metal shell, a cylindrical fluid pervious frangible catalyst element inside said shell, said shell having an inner surface and said element having an outer surface spaced from said inner surface to provide an annular space between said surfaces, an annular resilient nonmetallic fibrous insulating member in said annular space and in contact with each of said surfaces and serving to mount said element in said shell, and an adhesive binder and rigidizer material dispersed through said fibrous member in heavy concentrations at the outside surfaces thereof to fluid seal the exposed surfaces of the member and to bond the member to the shell and element surfaces, the center portion of said member being resilient and relatively free of said material to maintain resilient support of the element in the shell.

5. A device as set forth in claim 4 wherein said material is colloidal silica.

6. A catalytic reactor comprising a tubular metal shell, a gas pervious refractory catalyst element inside said shell and arranged so that flow through the element is substantially axial with respect to the axis of the shell, means resiliently mounting said element inside said shell so that the outer surface of the element is spaced from the inner surface of the shell, said means comprising a nonmetallic resilient fibrous insulating layer in the space between said surfaces, said fibrous layer containing a differentially dispersed solid material deposited on the fibers in heavy concentrations adjacent the exposed surfaces of the layer and adjacent the outer layer surfaces in juxtaposition to said element and shell surfaces and in materially less concentration in the center portion of the layer whereby said center portion is resilient, said deposited material serving to harden and seal said exposed and outer layer surfaces and to bond the outer layer surfaces to said element and shell.

7. A reactor as set forth in claim 6 wherein said fibrous layer is in contact with and bonded to said shell surface and said element surface and in compression between them and serves to seal the outside of said element.

8. A reactor as set forth in claim 6 wherein said layer comprises a fibrous sleeve fitted over the element.

9. A reactor as set forth in claim 6 wherein said layer comprises an overlapped fibrous blanket around the element.

10. A reactor as set forth in claim 6 wherein said layer comprises spirally wrapped fibrous paper around the element.

11. A reactor as set forth in claim 6 wherein said layer, element, and shell are positioned and arranged so that said element is at all times out of contact with relatively moving metal parts of said reactor.

12. A reactor as set forth in claim 11 wherein said fibrous layer is in contact with and bonded to said shell surface and to said element surface and in compression between them and serves to seal the outer surface of the element.

13. A reactor as set forth in claim 6 wherein said material comprises a dried out colloidal adhesive fiber binding and rigidizing solution wherein the colloidal material has been preferentially deposited out adjacent the outermost faces of the layer.

14. A reactor as set forth in claim 13 wherein said material is colloidal silica.

15. A catalytic reactor comprising a metal shell, a gas pervious refractory catalyst element having an outer surface, and means mounting said element in said shell so that said outer surface is spaced from the shell, said means comprising a resilient layer of high temperature resistant nonmetallic insulating fibers having one side in contact with said outer surface and the other side in contact with said shell, said layer containing dried adhesive material dispersed therein and serving as a fiber binder and rigidizer and to bond the layer to the outer surface and to the shell, said adhesive material being of variable concentration in said layer and being of lower concentration at the inner core of the layer and of higher concentration adjacent the outer surfaces of the layer.