CA1176822A

CA1176822A - Bifunctional filter for the treatment of exhaust gases

Info

Publication number: CA1176822A
Application number: CA000394114A
Authority: CA
Inventors: Wilhelm Wolsing
Original assignee: Engelhard Kali Chemie Autocat GmbH
Current assignee: Engelhard Kali Chemie Autocat GmbH
Priority date: 1981-01-15
Filing date: 1982-01-14
Publication date: 1984-10-30
Also published as: JPS57136922A; EP0056584B1; EP0056584A1; DE3260741D1; DE3101026A1

Abstract

ABSTRACT OF THE DISCLOSURE

Disclosed is a bifunctional filter for the treatment of an exhaust gas comprising a plurality of inlet chambers wherein the exhaust gas is introduced, a plurality of outlet chambers from which the exhaust gas is released, and a wall separating each of the inlet and outlet chambers, wherein the wall comprises a ceramic material permeable to gas but impermeable to particles and wherein the wall further comprises a coating of a catalytically-active substance on the side of the wall adjacent to each of the outlet chambers.
Also disclosed is a process for treating exhaust gases by means of the bifunctional filter and the use of the filter in diesel engines exhaust systems.

Description

1~76~Z2 BIFUNCTIONAL FILTER FOR THE TREATMENT OF EX~AUST GASES

BACKGROIJND OF T~E INVENTION

The present invention relates to a bifunctional ilter for the treatment of exhaust gases.
5 More especially the present invention relates to a bifunctional filter for the purification of exhaust gases by ~iltration of the solid particles and cataly-tic treatment of the gaseous contaminants. The present invention also provides an improved process for the 10 treatment of exhaust gases. In another aspect, the present invention discloses a use of the bifunctional ~; filter in the treatment of exhaust gases from diesel engines.
According to the present invention, particle ~; 15 filters are provided to reduce particle emissions in combustion processes. The filters function to filter the solid particles, consisting essentially of soot, from the flow of exhaust gas. Simultaneously, a :

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1~71~22 catalytic after-treament of gaseous contaminants, such as for example, hydrocarbons, carbon monoxide, sulfur compounds and nitrogen oxides, may be effected by means of a catalyst applied to the filter.
S Thus, uncoated or catalytically-active filters may be used in the flow of exhaust gases of combustion processes, in particular in the flow of exhaust gases from diesel engines, to reduce the emission of particles and contaminants.
The ceramic filter systems without catalysts used heretofore have the disadvantage that they are limited to particle emission only. In the case of a catalytic coating of the filters, initially sulfate particles are additionally formed on the catalyst by the reaction of the sulfur oxides contained in the exhaust gas. These are precipitated onto the filter, together with the solid particles which consist essen-tially of soot. With the increasing precipitation of solid particles, pressure and temperature in the filter increase, until the ignition temperature of the soot particles is reached and the filter is regenerated by burning. It is not possible, however, to obtain complete regeneration since the codeposited sulfate particles cannot be removed by burning. Depending on Z5 the sulfur content of the exhaust gases, a more or less rapid clogging of the filter pores by the sulfate particles takes place, until the filter becomes useless.
An arrangement is known from European Patent P~Jb/~c~2 f /CJ~ ,rO .
Application ~c. 0,020,766 whereby the exhaust gas of - 3 - 1176~322 diesel engines is treated by filtration and a subsequent catalytic stage. For this purpose, a sponge-like catalyst in a helical form is placed into a hollow cylinder comprised of a metal filter fabric.
S ~owever, such an arrangement has other aggravating disadvantages. For example, to resenerate the filter, which in this embodiment is no longer self--regenerating, the difference in pressure between the inlet and outlet side of the filter must be constantly monitored in order to determine the point in time when regeneration is necessary, and in order to effect this regeneration of the filter, hot air must be passed onto the filter by means of a supplemental burner.

SUMMARY OF T~E INVENTION

It is therefore an object of the present invention to eliminate the disadvantages of the state of the art and, in particular, to provide a bifunc-tional ceramic filter, wherein clogging by sulfate particles may be avoided and regeneration occurs automatically.
Another object of the present invention is to provide an improved filter for removing both solid particles and contaminants.
Yet another object of the present invention is the provision of an improved bifunctional filter which finds particular application in diesel engines.
In accomplishing the foregoing objects of the present invention, there has been provided in accordance with one aspect of the present invention a _ 4 1176~3Z2 bifunctional filter for the treatment of an exhaust gas comprising a plurality of inlet chambers wherein the exhaust gas is introduced, a plurality of outlet chambers from which the exhaust gas is released, and a wall separating each of the inlet and outlet chambers wherein the wall comprises a ceramic material permeable to gas but impermeable to particles and wherein 'he wall further comprises a coating of a catalytically-active substance on the side of the wall adjacent to each of the outlet chambers.
In a preferred embodiment of the invention, each of the inlet chambers is connected to at least one of the outlet chambers to form a system of unilaterally closed pipes, and more preferably, these inlet and outlet chambers are arranged adjacently, most preferably parallel, to each other and are connected by the wall comprising the gas-permeable material.
In a further preferred embodiment, the filter further comprises a gas-impermeable closure means attached both to the end of each of the outlet chambers initially contacted by the exhaust gas ~upstream end) and to the opposite end ~downstream end) of each of the inlet chambers.
In accordance with another aspect of the present invention, there is provided a process for treating an exhaust gas comprising the steps of providing an exhaust gas to an inlet chamber, passing the exhaust gas from the inlet chamber through a wall comprising a gas-permeable ceramic material to remove solid particles therefrom, thus forming an essentially particle-free exhaust gas, passing the essentially ~ 5 ~ 117~2 particle-free exhaust gas through a coating on the wall comprising a catalytically active substance to remove gas contaminants from the exhaust gas, and removing the exhaust gas by means of an outlet chamber.
Finally, in accordance with yet another aspect of the present invention, there is provided a bifunctional filter for treating exhaust gas for use in diesel engines.
An advantageous result of the above-discussed aspects of the present invention is the provision for high exhaust gas flows when the inlet and outlet chambers are adjacent to each other.
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments which follows, when considered in light of the attached figureq of drawing.

BRIEF DESC~IPTION OF T~E DRAWINGS

In the drawings:
Figure 1 is an end view of the inlet side of the filter according to the invention:
Figure 2 is a schematic longitudinal sectional view through the filter according to the invention: and Figure 3 is an expanded partial view of the portion "A~ of the longitudinal sectional view of Figure 2.

- 6 - 117~822 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides for the purification of exhaust gases from a combustion process by an initial filtration of solid particles and a subsequent catalytic treatment of gas contaminants.
As seen in Figure 1 or 2 of the drawings, the filter comprises a plurality of pipes 1 essentially parallel to each other having an essentially square cross-section. The partitions 2 between the pipes 1 consist, except for the outer peripheries, of casing surfaces common to adjacent pipes and are made of a ceramic material permeable to gas but not permeable to particulate material contained in such exhaust gases.
Bodies of this general type are known in the area of catalysis, particularly under the designation monolithic catalyst bodies.
Each pipe 1 is closed at one end by a gas-impermeable ceramic stopper 3, wherein, in the case of the filter with square tubular cross-sections, adjacent pipes are closed at their opposing ends. The end view of the inlet (and/or outlet) side of the filter then shows the checker-board pattern illustrated in Figure 1.
Instead of bodies having square cross-sections, tubes with polygonal, e.g., hexagonal orround cross-sections are also within the scope of the present invention. These adjacent tubular layers are closed at their opposing ends in a manner similar to the square cross-sections discussed above.

The sealing of the adjacent pipes 1 at their opposing ends creates the inlet chambers 4 and the out-let chambers 5, which communicate with each other through the casing surfaces 2 in a manner permeable to gas but im-permeable to particles. As indicated in Figure 3 the en-larged section "III" of Figure 2, a catalytically active layer 6 is applied to the casing surface of the tubes 1 facing the outlet chambers 5- The catalytic treatment may be effected by means of all known catalysts applicable to exhaust gas treatments- According to the invention, this treatment takes place after the filtration stage- T~e catalyst is applied as a coating to the side facing the outlet chamber of the gas permeable partition. The con-cept of an "application" of catalytic to the carrier is intended to include all conventional technical processes, such as for example, coating with the catalyst or with catalyqt containing masses, impregnation of the surface layers of the partition, etc.
The exhaust gas follows the path indicated by the arrows in Figure 1 when flowing through the filter and is freed initially of particles at the partition 2 and is treated in the catalytically active layer 6 after flowing through the partitions.
Example. Bifunctional filter A porous filter of the cellular ceramic honey-comb type is used as a substrate for a bifunctional fil-ter. Such porous filters are commercially available*) and described in detail in SAE Technical Paper Series 810114, 1981 (Editor: Society of Automotive Engineers, Inc.).
Of these filters the type EX-47 is best suited.
Such a filter is dipped into an aqueous solution of plati-niumtetraminehydroxide, the concentration of which had *) manufacturer:Corning Glass Works .. ~ .

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1176~2Z

been adjusted in such a way, that the finished bi-functional filter contained 0,075 % by weight of platinium. Prior to dipping the side of the substrate which is to become the inlet side of the bifunctional filter was sealed airtight by means of a cuff surround-ing said inlet side. Then the substrate is dipped into said solution- After dipping, the cuff is removed and the filter is shaken to remove excess solution. The bifunctional filter is dried at 120C and tempered at 10 800C.
Other dipping solutions with which good results have been attained are disclosed in DE-PS 23 04 831.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A bifunctional filter for the treatment of an exhaust gas to remove particulate material by filtration and gaseous contaminants by catalytic treatment, comprising:
a plurality of inlet chambers wherein the exhaust gas is introduced;
a plurality of outlet chambers from which the exhaust gas is released; and a wall separating each of said inlet and outlet chambers, wherein said wall comprises a ceramic material permeable to gas but impermeable to particulate material contained in the exhaust gas and wherein said wall further comprises a coating of a catalytically-active substance on the side of said wall adjacent to each of said outlet chambers.

2. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 1, wherein each of said inlet and outlet chambers comprises a pipe closed at one end and each inlet chamber is connected to at least one of said outlet chambers.

3. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 2, wherein said inlet and outlet chambers are arranged adjacently to each other and are connected by said wall comprising said gas-permeable material.

4. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 3, wherein the longitudinal axes of said inlet and outlet chambers are arranged essentially parallel to each other.

5. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 2, 3, or 4 further comprising a gas-impermeable closure means attached to the end of each of said outlet chambers initially contacted by the exhaust gas and to the opposite end of each of said inlet chambers.

6. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 2, 3, or 4 further comprising a gas-impermeable closure means comprising a ceramic stopper attached to the end of each of said outlet chambers initially contacted by the exhaust gas and to the opposite end of each of said inlet chambers.

7. A bifunctional filter for the treatment of an exhaust gas as defined in Claim 1, wherein each of said inlet and outlet chambers comprises a square, cross-section.

8. A process for treating an exhaust gas from a combustion process, comprising the steps of:
providing an exhaust gas comprising gaseous contaminants and solid particles;
introducing the exhaust gas into an inlet chamber;
passing said exhaust gas from said inlet chamber through a wall comprising a gas-permeable ceramic material having sufficient porosity to remove said solid particles, thereby forming an essentially particle-free exhaust gas;
passing said essentially particle-free exhaust gas through a coating on said wall comprising a catalytically active substance to remove said gaseous contaminants from said exhaust gas; and removing said exhaust gas by means of an outlet chamber.

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9. A diesel motor system, comprising:
a diesel motor;
an exhaust system associated with said diesel motor for withdrawing exhaust gases from said motor; and a filter associated with said exhaust system for the treatment of the exhaust gases to remove particulate material by filtration and gaseous contaminants by catalytic treatment, said filter comprising the filter as defined by Claim 1.