WO1998012424A1

WO1998012424A1 - Catalyst protection filter

Info

Publication number: WO1998012424A1
Application number: PCT/US1997/016165
Authority: WO
Inventors: William C. Pfefferle; Subir Roychoudhury
Original assignee: Precision Combustion Inc.
Priority date: 1996-09-19
Filing date: 1997-09-11
Publication date: 1998-03-26

Abstract

To increase the service life of an automotive catalytic converter, the exhaust system includes a replaceable getter packet (12) to treat the exhaust gases before they pass through the catalytic converter, removing sticky particulates and vaporous contaminants.

Description

CATALYST PROTECTION FILTER

Field of the Invention This invention relates to improved catalytic reaction systems. In one specific aspect the present invention relates to improved catalyst systems for controlling exhaust gas emissions from internal combustion engines. Brief Description of the Prior Art

Automotive emissions are still a major environmental problem in spite of the major advances brought about by the use of catalytic converters. An important factor limiting emissions control is deactivation of the catalyst in use. With ever lower emissions being required and durability requirements extended from 50,000 to 100,000 miles in the U.S., avoidance of catalyst deactivation is of increased importance. With the bulk of present emissions occurring on engine starting before the catalyst reaches its operating temperature, there is also the need to reduce catalyst warm-up time of automotive catalysts. This has led to the need to use high activity fast light-off catalysts or even electrically heated catalysts. Maintaining the activity of such catalysts will be crucial to reducing emissions during the warm-up period. Although catalyst sintering can be a problem without use of advanced design formulations, the main source of activity loss of automotive catalysts is the blocking of active catalyst sites by inorganic deposits. Such deposits include dust which escapes capture by the engine air filter, corrosion products from engine components, and most damaging sticky low melting point inorganic ash and volatiles from combustion of engine oil. Such inorganics consist of compounds having molecular weights greater tha forty. In steady state operation, catalyst deactivation can be allowed for by simply providing extra catalyst to compenstate for that deactivated, as is presently the procedure with present catalytic converters. However, merely increasing the size of a catalytic converter does not negate the increase in light-off time as the front end deactivates. Simply adding additional catalyst to allow for deactivation with conventional monolith structures yields catalysts which have much too high a thermal mass for fast light-off. Further, even though the low thermal mass of the short channel length catalysts of my prior U.S. patent #5,051,241 has been found to allow use of sufficient catalyst to exceed the stringent requirements of the new California Ultra Low Emission Vehicle (ULEV) standards even with deactivated front end catalyst, even lower emissions could be achieved if such deacivation were avoided. The present invention makes possible rugged fast light -off catalytic converters for automotive engine exhaust control which allow long term operation with minimal deactivation.

SUMMARY OF THE INVENTION Definition of Terms

In the present invention the terms "monolith" and "monolith catalyst" refer not only to conventional monolithic structures and catalysts such as employed in conventional catalytic converters but also to short channel length structures of enhanced mass transfer efficiency such as woven screens .

In the present invention the term "minilith" refers to monolith elements having flow channels of less than three millimeters in length and more than forty channels per square centimeter. The term "rigidized fiber mass" for the purposes of this invention means a low density foam or fiber sponge, mass, or assembly of metal or ceramic having a high open area of at least sixty percent and constrained against loss of open area by gas flow compaction of the structure.

The Invention

It has now been found that a multiplicity of high open area, short channel length monoliths or a similar high open area structure can act as an efficient getter to trap engine exhaust gas particulates and contaminant vapors which can otherwise blanket converter catalyst sites without degrading engine performance or impairing catalytic converter fast lightoff. For best performance the thermal mass of the getter must be low to minimize heat loss from the exhaust to the getter, ie less than 100 or more preferably less than 50 grams per liter of engine displacement and preferably be readily replaceable, for example as part of a gasket assembly to attach the exhaust pipe to the exhaust manifold. The getter must also offer minimal resistance to gas flow to avoid degrading engine performance and increasing fuel consumption. Thus getter open area should be at least as high as sixty percent in the direction of gas flow and more preferably at least 70 percent. Further, it is preferred that the getter have a high geometric surface area to maximize traping efficiency. Monoliths or foams should have a high cell density with cell walls no more than 0.127 millimeters (mm) in thickness and preferably no more than 0.08 mm. Fibers or screen wire diameters of the same dimensions are preferred. Use of a getter of the present invention allows achievement of ULEV emission levels for well over 100,000 miles of vehicle operation without the need for excess catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross-sectional side view of a gasket filter packet of the present invention. Figure 2 show a gasket filter packet fitted to an engine exhaust manifold.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention is further described in connection with the drawing. As shown in the sectional view of figure 1, in one preferred embodiment a minilith gasket assembly 10 for a two liter automotive engine consists of gasket 11 attached to minilith packet 12 containing ten hast-x minilith screens 14 having a total mass of less than thirty grams .

Figure 2 shows gasket assembly 20 having a rigidized fiber packet 22 having fibers 0.08 millimeters diameter and 70 percent open area with gasket 21 positioned for attachment with exhaust pipe

25 to manifold 30 of a 2.5 liter engine (not shown) .

Claims

WHAT IS CLAIMED IS:

1. A method of extending the service life of a catalytic converter used to control emissions in the exhaust of an internal combustion engine, which comprises; treating the exhaust before entry into the catalytic converter by passing it through a getter packet having a mass of less than about 100 grams per liter of engine displacement and an open area in the direction of flow of at least sixty percent.

2. The method of claim 1 wherein said packet is replaceable .

3. The method of claim 2 wherein said packet is part of a replaceable exhaust system gasket assembly.

. The method of claim 1 wherein said packet contains at least three monolithic elements.

5. The method of claim 2 wherein said packet comprises catalytic elements.

6. The method of claim 2 wherein said packet contains from five to fifteen minilith monoliths.

7. The method of claim 1 wherein said packet has an open area of at least seventy percent .

8. The method of claim 1 wherein said packet comprises a rigidized fiber mass.

9. The method of claim 1 wherein said packet has a mass of less than fifty grams per liter of engine displacement .

10. In a system for reducing exhaust gas emission from an internal combustion engine, which system comprises a catalytic converter placed in an exhaust conduit; the improvement to prolong service life of the catalytic converter, which comprises; a getter packet positioned in the exhaust conduit ahead of the catalytic converter; said getter packet having a mass of less than about 100 grams per liter of engine displacement and an open area in the direction of exhaust flow of at least sixty percent .

11. The system of claim 10 wherein said getter packet has an open area of at least seventy percent .

12. The system of claim 10 wherein said getter packet is part of a replaceable assembly.

13. The system of claim 12 wherein said getter packet has a mass of less than fifty grams per liter of engine displacement.

14. The system of claim 12 wherein said getter packet comprises a rigidized fiber mass.

15. A replaceable exhaust gas filter to protect a catalytic converter from contamination by inorganic contaminants in internal combustion engine exhaust gases comprising a getter packet having an open area in the direction of gas flow of at least sixty percent and a mass of less than 100 grams per liter of engine displacement .

16. The filter of claim 15 having an open area of at least seventy percent .

17. The filter of claim 15 having a mass of less than fifty grams per liter of engine displacement .

18. The filter of claim 15 wherein the getter packet is composed of minilith elements.

19. The filter of claim 15 wherein the getter packet comprises a rigidized fiber mass.