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  Zone catalyzed soot filterUSPTO Application #: 20080020922Title: Zone catalyzed soot filter Abstract: A catalyzed soot filter is comprised of a monolithic ceramic honeycomb body that has a catalyzed inlet zone that has a catalyst within the walls of the ceramic honeycomb inlet end to at most about 45% of the length of the catalyzed soot filter. The catalyzed inlet zone has a porosity that is at least ⅓ the porosity of a wall of the ceramic honeycomb that does not have a catalyst in the wall. (end of abstract) Agent: The Dow Chemical Company - Midland, MI, US Inventors: Cheng G. Li, Fuhe Mao USPTO Applicaton #: 20080020922 - Class: 502 73 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080020922. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application claims the benefit of U.S. Provisional Application No. 60/832,580, filed Jul. 21, 2006. FIELD OF THE INVENTION [0002]The present invention relates to an improved catalyzed particulate filter. In particular the invention relates to catalyzed soot filters that have one or more zones of catalysts. BACKGROUND OF THE INVENTION [0003]Diesel engines, because of the way they operate, emit soot particles or very fine droplets of condensate or a conglomerate of the two (particulates) as well as typical harmful gasoline engine exhausts (i.e., HC and CO). These "particulates" (herein Diesel soot), are rich in condensed, polynuclear hydrocarbons, some of which may be carcinogenic. [0004]As the awareness of the danger Diesel soot presents to health collides with the need for greater fuel efficiency that Diesel engines provide, regulations have been enacted curbing the amount of Diesel soot permitted to be emitted. To meet these challenges, soot filters have been used. The filters have had many configurations as exemplified by GB 1,014,498 and U.S. Pat. No. 4,828,807. The most common and useful filters have tended to be porous ceramic honeycombs that have plugged channels such that the exhaust gas must enter a channel and pass through the wall of the channel as exemplified by U.S. Pat. Nos. 4,329,162 and 4,857,089. [0005]To more effectively catalyze the combustion of soot and mediate polluting combustion gases such as NOx, CO and unburnt hydrocarbons, catalysts have been used. Catalysts have been employed on filter elements in series where the gas passes through one filter with a catalyst thereon and then passes through another having a different catalyst such as described by GB 1,014,498 and U.S. Pat. No. 4,828,807. In addition, catalyst have been placed on a flow through substrate honeycomb (three way catalyst converter in one's car) separately in front of a filter such as in U.S. Pat. No. 4,902,487. In a variation, of this approach, a catalyst has been placed partially in the channels of a honeycomb filter on the inlet channels walls effectively creating a flow though catalyst on the front portion of the inlet channels as shown by U.S. Pat. Nos. 6,294,141 and 6,753,294. Each of these suffers from reducing the total effective filter area and excessive thermal stresses due to exaggerated different combustion along the length of the filter. [0006]What is needed is a Diesel particulate filter that avoids one or more problems of the prior art such as one of the aforementioned problems. In particular, it would be desirable to provide a catalyzed Diesel particulate filter that maximizes the effective filtration area while smoothing out temperature differences within the catalyst due to combustion of differing species along the length of the filter. SUMMARY OF THE INVENTION [0007]We have discovered an improved catalyzed soot filter that maximizes the effective filtration area while still providing gaseous pollutant abatement. The filter is also able to mitigate temperature differences due to differing species being combusted preferentially along the filter, which surprisingly allows the catalyzed filter to have improved soot combustion and thermal shock resistance than catalyzed filters without zones or with zones where the first zone does not also filter and combust the soot. [0008]A first aspect of this invention is a catalyzed soot filter comprising a porous monolithic ceramic honeycomb body having an inlet end and outlet end connected by adjacent inlet and outlet channels that extend from the inlet end to the outlet end of the ceramic body, the inlet and outlet channels being defined by a plurality of interlaced thin gas filtering porous partition walls between the inlet and outlet channels and by ceramic plugs, such that the inlet channel has an inlet ceramic plug at the outlet end of the ceramic body and the outlet channel has an outlet ceramic plug at the inlet end of the ceramic body such that a fluid when entering the inlet end must pass through partition walls to exit the outlet end, wherein the ceramic honeycomb body has an inlet end catalyzed zone comprising at least one filtering porous partition wall having a catalyst within the pores of the wall from the inlet end to at most about 45% of the length of the ceramic honeycomb wall-flow filter said inlet catalyzed zone having a porosity no less than about 1/3 of the porosity of a partition wall without catalyst. [0009]Surprisingly, the catalyzed filter of the invention preferentially captures finer soot particles due to the reduced gas flow through the inlet catalyzed zone while still allowing gaseous pollutant abatement (e.g., HC combustion and CO conversion). The preferential collection of finer soot particles within the inlet end tends to allow for reduced temperature differences during regeneration of the filter (i.e., burnout of the soot), because the entire length of the filter tends to contain a more uniform distribution of soot. In addition, it is believed that the soot in the second zone tends to be comprised of solid particulate soot as opposed to liquid (soot containing hydrocarbon fractions). [0010]The catalyzed soot filter may be used in any applications in which soot needs to be removed from a gaseous stream such as an automobile, train, truck or stationary power plant exhaust. The catalyzed soot filter is particularly useful to remove soot from Diesel engine exhausts. BRIEF DESCRIPTION OF THE DRAWINGS [0011]FIG. 1 is a view of the catalyzed soot filter looking down at the inlet end of the filter. [0012]FIG. 2 is a cut away view of the length of an illustrative embodiment of the catalyzed soot filter and a blown up portion of the catalyzed inlet zone of the catalyzed soot filter. [0013]FIG. 3 is a blow up of a length of a channel's partition wall of an embodiment of the invention. [0014]FIG. 4 is a blow up of a length of a channel's partition wall of another embodiment of the invention DETAILED DESCRIPTION OF THE INVENTION [0015]Referring to the Figures as an illustration, the invention is a catalyzed soot filter 10. The catalyzed soot filter is comprised of a porous ceramic honeycomb 20 having an inlet end 30 and outlet end 40. The honeycomb 20 is comprised of interlaced porous partition walls 50 with inlet plugs 60 and outlet plugs 65, which define inlet channels 70 and outlet channels 80. Along the length 90 of the honeycomb 20 there is an inlet catalyzed zone 100 and an outlet zone 110. In the inlet catalyzed zone 100 there is catalyst 120 within the pores 55 of the partition wall 50 essentially from the inlet end 30 to at most about 45% of the length 90 of the honeycomb 20. Essentially from the inlet end 30 means that the catalyst 120 is within a plug length 130 from the inlet end 30. [0016]Even though the length of the catalyzed inlet zone 100 may be up to 45% of the length 90 of the honeycomb 20, it is generally not necessary for the zone to be that long. The length of the catalyzed inlet zone 100 in rising preference is at most about 40%, 35%, 30%, ff25%, 20%, 15%, and 10% to generally at least about 2% of the length 90 of the honeycomb 20. [0017]The amount of catalyst 120 within partition wall 50 of the inlet catalyzed zone 100 is an amount that reduces the porosity of the partition wall 50 to a porosity no less than about 1/3 the porosity of the partition wall 50 without catalyst. For example if the porosity of the partition wall 50 is 75% porous, the partition wall 50 with catalyst would be no less than 25% porous. The porosity of the partition wall 50 within the inlet catalyzed zone 100 in rising preference, is no less than about , no less than about 1/2, no less than about 3/5, no less than about 3/4, no less than 7/8 and no less than 15/16 of the porosity of the partition wall 50 without catalyst. Of course since there is a catalyst present in the pores 55 of the partition wall 50 of the inlet catalyst zone 100, the porosity is less than a partition wall 50 without catalyst and generally the amount of porosity on the partition wall 50 of the inlet catalyzed zone is no more than 31/32 of the porosity of partition wall 50 without a catalyst. [0018]The catalyst 120 within partition wall 50 of the inlet catalyze zone 100 means that the catalyst 120 does not substantially bridge the pores 55 within or at the surface 150 of the partition wall 50. "Does not substantially bridge the pores 55" means that the pressure drop due to gas 160 flowing through the partition wall 50 of the inlet catalyzed zone 100 is no more than about 10 times greater than the pressure drop of partition wall 50 without catalyst. In rising preference, the pressure drop across partition wall 50 in the inlet catalyzed zone 100 is no more than about 9 times, 8 times, 7 times, 6 times 5 times, 4 times 3 times, 2 times, 1.8 times, 1.6 times, 1.5 times, 1.4 times 1.3 times 1.2 times greater than the pressure drop across partition wall 50 without catalyst, but generally is at least about 1.1 times greater than partition wall 50 without catalyst. The pressure drop is measured at typical operating conditions of diesel engines using any suitable technique such as those known in the art. For example, a gas flow rate of about 30 thousand to 70 thousand space velocity (1/hour) may be used. The space velocity is the total amount of gas flowing in 1 hour through a DPF having a given geometric volume. Continue reading... Full patent description for Zone catalyzed soot filter Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Zone catalyzed soot filter patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Zone catalyzed soot filter or other areas of interest. ### Previous Patent Application: Modified ceramic formulations and procedures for the manufacture of ceramic parts with metallic effects and ceramic parts produced Next Patent Application: Multilayered nanostructured films Industry Class: Catalyst, solid sorbent, or support therefor: product or process of making ### FreshPatents.com Support Thank you for viewing the Zone catalyzed soot filter patent info. 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