US20080078171A1

US20080078171A1 - Chemically functionalized filter system

Info

Publication number: US20080078171A1
Application number: US11/529,507
Authority: US
Inventors: Herbert F.M. DaCosta; Craig F. Habeger
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2006-09-29
Filing date: 2006-09-29
Publication date: 2008-04-03

Abstract

A filter for engine exhaust gases includes a filter media having an internal and external surface. A plurality of molecules of a fluid catalyst are attached to at least the internal and external surface of the filter media. The molecules of the fluid catalyst are configured to donate an oxygen atom to soot particles to activate the soot particles for regeneration.

Description

TECHNICAL FIELD

The present disclosure relates generally to a chemically functionalized filter system, and more particularly to a chemically functionalized filter system having regeneration capabilities.

BACKGROUND

Internal combustion engines exhaust a complex mixture of chemical species. These chemical species may include gaseous and solid materials, including particulate matter, nitrogen oxides (“NOx”), and sulfur compounds.
Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent over the years. The amount of chemical species emitted from an engine may be regulated depending on the type, size, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove these species from the exhaust flow of an engine with filters. These filters may include filter media to capture and oxidize the particulate matter pollutants contained in the exhaust.
Most filters with filter media operate by a similar process of forcing engine exhaust through the filter media which blocks the particulate matter in the exhaust on the inflow side of the media. Using these filters for extended periods of time may cause the particulate matter to buildup in the filter media, impeding the flow of gas through it, resulting in increased engine back pressure and reduced engine efficiency.
Filter regeneration is one way to remove the particulate build up within the filter media. Regeneration is the process of increasing the temperature of the exhaust system until the organic components of the particulate matter such as the soot and the soluble organic fraction (SOF) that accumulates in the filter burn off. If the engine exhaust does not reach the temperature required for regeneration within the filter, an additional component is necessary to raise the temperature within the filter. In some systems this component is an outside heat source that heats the filter media or the engine exhaust before it reaches the filter. A catalyst is sometimes used to lower the temperature necessary to burn the soot and the SOF. A solid catalyst may be coated on the filter media, or a liquid catalyst may be supplied along with the fuel. In this disclosure a coating refers to a solid layer which substantially covers the surface of an object. Both precious and base metals have been used as catalysts in filters.
U.S. Patent Publication No. US 2006/0057046 A1 (the '046 publication) to Punke et al., describes a catalyzed soot filter with its internal walls coated with different catalyst compositions. The filter of the '046 publication consists of a ceramic wall flow filter media of a honeycomb structure, with a layer of catalyst coated on its internal walls. The catalyst of the '046 publication may be made of a platinum group metal or a rare earth metal oxide. Since a higher proportion of particulate matter is deposited on the downstream side of a filter, the downstream side of the filter will experience a higher temperature during regeneration than the upstream side. Therefore, the durability of the catalyst coating on the downstream side will limit the useful life of the filter. The '046 publication seeks to increase the durability of the filter by selectively increasing the catalyst concentrations of the coating on the downstream side. Thus, the '046 publication seeks to increase durability of the filter media while decreasing cost by increasing the concentration of the catalyst only where it is needed most.
Solid catalyst coatings on the filter media, such as that described in the '046 publication, have the potential of increasing the pressure drop of exhaust gas within the filter. This pressure drop decreases engine efficiency by increasing the resistance to exhaust flow through the filter. Precious metal catalysts also increase the cost of the filter. The present disclosure is directed to solving one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In accordance with one aspect, the present disclosure is directed towards a filter for engine exhaust gases. The filter includes a filter media having an internal and external surface. A plurality of molecules of a fluid catalyst are attached to at least the internal and external surface of the filter media. The molecules of the fluid catalyst are configured to donate an oxygen atom to soot particles to activate the soot particles for regeneration.
According to another aspect, the present disclosure is directed toward a method of regenerating a filter. The method includes chemically functionalizing a filter media of the filter with molecules of a fluid catalyst. The method further includes flowing the exhaust gases through the filter and accumulating the soot particles in the filter media. The method also includes activating the accumulated soot particles by donating oxygen atoms from the catalyst to at least some of the accumulated soot particles, and regenerating the activated soot particles by reacting with oxygen in the exhaust gases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an engine system having a filter system according to an exemplary embodiment of the present disclosure;

FIG. 2 is a cross-sectional illustration of the filter in FIG. 1 showing an exemplary embodiment of the filter media.

FIG. 3 is an enlarged cross-sectional illustration of a section the filter media of FIG. 2.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.
FIG. 1 illustrates an internal combustion engine system 100, having an engine 10, and an exemplary embodiment of a filter system 50 containing a filter 20. Engine 10 may include an exhaust outlet 12 connecting an exhaust flow 14 of engine 10 with an inlet 16 of the filter 20. The engine 10 may be a diesel engine, a gasoline engine, a gaseous fuel driven engine, or any other type of engine that produces exhaust gases. Engine system 100 may also include a turbine of a turbocharger or an exhaust gas recirculation valve, and/or any other known device connected to the exhaust outlet 12. In such an embodiment, inlet 16 of the filter 20 may be connected upstream or downstream of an outlet of the turbine, the EGR valve, or the other known device.
The filter 20 illustrated in FIG. 1 may be any general type of exhaust filter known in the art and may include a cylindrical housing 22 with tapered ends 24. It is understood that other filter housing shapes could be used in association with this disclosure.
FIG. 2 shows a cross section of the filter 20 of FIG. 1 showing a filter media 26 contained within the filter 20. The filter media 26 can be of any type known in the art, such as, for example, a ceramic foam, ceramic, sintered metal, metal foam, or silicon carbide, or silicon carbide foam type filter. It is also contemplated that filter media 26 can be a flow-through or a wall-through filter. The filter media 26 assists in removing particulate matter like soot, soluble organic fraction (SOF), and other pollutants from engine exhaust flow 14. The filter media 26 may contain heating elements capable of heating the filter media 26 and the exhaust during a regeneration process. The filter media 26 may be situated horizontally, vertically, radially, or in any other configuration allowing for proper filtration. The filter media 26 may also be of a honeycomb, mesh, mat, or any other configuration that provides an appropriate surface area available for filtering of particulate matter. The filter media 26 may also contain pores, cavities or spaces of a size that allows exhaust gas to flow through while substantially restricting the passage of particulate matter. The flow of exhaust through the pores of the filter media 26 is illustrated by the arrows 28 in FIG. 2.
In an exemplary embodiment, the filter media 26 may define a plurality of filter passages 30. The filter passages 30 may be arranged in any configuration known in the art. For example, the filter passages 30 may be substantially parallel channels extending in an axial direction. The filter passages 30 may be, for example, flat, cylindrical, square tube-shaped, or any other shape known in the art. The filter passages 30 may also be configured to allow exhaust gas to pass between adjacent filter passages 30 while substantially restricting the passage of particulate matter. The flow of exhaust through the filter passages 30 is illustrated by arrows 32 in FIG. 2.
In an exemplary embodiment, a plurality of filter passages 30 may be substantially blocked or closed proximate the inlet 16 of the filter 20 such that gas may not enter certain filter passage 30 at the inlet blocked end 33, but rather be directed to particular inflow surfaces of the filter media 26. A plurality of filter passages 30 may also be substantially blocked or closed proximate the outlet 34 of the filter 20 such that gas may not exit the filter passage 30 at the outlet blocked end 36, but rather be directed to other portions of the filter media 26.
FIG. 3 shows an enlarged view of the filter media 26 of filter 20. Although FIG. 3 depicts the filter media 26 as a porous ceramic made of ceramic particles 52 with embedded pores 54, it is understood that any type of filter media 26 can be used with this disclosure. The filter media 26 may include an external surface 38 and an internal surface 42. External surface 38 may be the surface of the filter media 26 facing the filter passages 30, and the internal surface 42 may be the surface of the filter media within the pores, cavities or spaces of the filter media 26. The filter media 26 may include particles of a chemical species 40 embedded or attached on the filter media 26. The chemical species 40 may be attached on the external surface 38 and/or the internal surface 42 of the filter media 26. The particles of the chemical species 40 may include molecules of the chemical species 40 and may serve the purpose of chemically functionalizing the filter media 26. The chemical species 40 may facilitate soot regeneration by acting as a catalyst. The chemical species 40 may donate an oxygen atom to a soot particle that gets accumulated on the filter media 26. By donating the oxygen atom to the soot particle, the chemical species 40 may change in chemical composition. The chemical species 40 then accepts an oxygen atom from the engine exhaust 14, and regain the original chemical composition.
Any fluid (liquid or gas) that will donate an oxygen atom may be used as the chemical species 40. For example, nitrogen dioxide (NO₂) gas may used as the chemical species 40. The NO₂molecules may donate an oxygen atom to soot and undergo a change in composition to nitrous oxide (NO). The NO may then take an oxygen atom from the oxygen in the exhaust flow to convert back to NO₂.
Any process known in the art may be used to attach the chemical species 40 on the filter media 26. The molecules of the chemical species 40 may be attached to the filter media by adsorption. Adsorption is a phenomenon whereby molecules of the chemical species 40 stick to the external and internal surfaces 38, 42 of the filter media 26 due to the attractive force (Van der Waals force) between the surfaces and the molecules of the chemical species 40. In some cases, there may also be some chemical bonding between molecules of the chemical species 40 and the molecules of the filter media 26. For adsorption to occur, the filter media 26 may be soaked in an atmosphere containing the chemical species material 40. In the case of a gaseous chemical species 40, the filter media 26 may be soaked in the gaseous material for adsorption to occur. In the case of a liquid chemical species 40, the filter media 26 may be immersed in the liquid chemical species 40 or in a solution containing the chemical species 40. Droplets of the liquid chemical species 40 may get attached to the external surface 38 or entrapped in pores 54 of the filter media 26. The temperature and pressure of the atmosphere may be controlled or varied to facilitate the attachment of the chemical species 40 on the filter media 26. In some cases other energy sources, such as a high pulse laser, may be used to facilitate attachment.

INDUSTRIAL APPLICABILITY

The disclosed filter system 50 comprising a filter 20 and a filter media 26 with a chemical species 40 attached to its external and/or internal surfaces 38, 42, may be used with any type of engine system 100 that exhausts pollutants including diesel engines, gasoline engines, or gaseous fuel driven engines. The operation of an engine system 100 having a filter media 26 chemically functionalized with a gaseous chemical species 40 of NO₂will now be explained.
The engine system 100 may be a part of any mobile or stationary machine that generates exhaust containing various regulated species like soot, soluble organic fraction (SOF), sulphates, and ash. The engine exhaust is passed through the filter 20 comprising the filter media 26 with chemical species 40 of NO₂molecules attached to its external and/or internal surfaces 38, 42. As the exhaust flows through the filter media 26, particulate matter including soot and SOF gets accumulated on or within the filter media 26. The collected particulate matter increases the resistance to exhaust flow through the filter 20, thereby increasing the pressure drop within the filter 20. When the filter pressure drop exceeds a set value, regeneration of the filter 20 is carried out.
Regeneration is the process by which the collected solid particulate matter in the filter 20 is burned to form gaseous and liquid products, which are carried along with the gases exiting the filter 20. As soot particles gets accumulated on the external and internal surface 38, 42 of the filter media 26, a soot particle may receive an oxygen atom from the molecules of NO₂attached to the external and internal surface 38, 42 of the filter media 26. This gain of an oxygen atom by the soot particles activates the soot particle for combustion using oxygen in the exhaust flow 14. Activation of the soot particle allows it to undergo combustion at a lower temperature. Thus, the NO₂chemical species 40 may function as a catalyst by reducing the regeneration temperature of the filter. In some cases, the regeneration temperature may be reduced to below 600° C.
Filter regeneration temperature is the temperature at which combustion of the soot occurs. Reduced regeneration temperatures may increase the durability of the filter 20. For regeneration to occur, the temperature of the soot collected on the filter media 26 should exceed the regeneration temperature. The temperature of the filter media 26 can be increased by enriching the air to fuel mixture, or actively heating the filter media 26, or by any other technique used in the art. This filter temperature may be increased periodically to periodically regenerate the filter 20 when the pressure drop within the filter 20 exceeds a preset limit, or by the occurrence of any other triggering event. Using NO₂ chemical species 40 to activate the soot may decrease the regeneration temperature sufficiently for regeneration to occur at the normal operating temperature of the filter 20, thereby enabling continuous regeneration. Continuous regeneration is the process whereby the combustion of soot occurs continuously.
After donating an oxygen atom, the molecule of NO₂which is bonded to the solid surface, may undergo a change in chemical composition to NO. This surface-bonded molecule of NO then regains its original composition (NO₂) by taking an oxygen atom from oxygen in the exhaust flow 14. The NO₂attached to the filter media 26 may thus be replenished by the oxygen in the exhaust flow 14. This cycle, where the NO₂changes to NO by donating an oxygen atom to a soot particle and changes back to NO₂by taking an oxygen atom from the exhaust flow 14, may continue indefinitely.
Rather than a solid catalyst coating, the chemically functionalized filter media 26 uses particles of a fluid chemical species 40 attached to the external and internal surfaces 38, 42 of a filter media 26 as the catalyst for soot regeneration. Unlike a solid catalyst coating, the particles of the chemically functionalized species 40 will not restrict exhaust flow nor significantly increase the pressure drop within the filter 20, thereby improving engine efficiency. In addition to improving efficiency, the operating cost of the engine 100 may also be reduced by use of the chemically functionalized filter system. Since the chemical species 40 replenishes itself taking oxygen from the exhaust flow 14, the useful lifetime of the filter media 26 is also extended. In addition, since the catalyst of the present disclosure is not made of expensive noble materials, the original cost of the filter 20 may also be reduced.
It will be apparent to those skilled in the art that various modifications and variations can be made to the shape and size of the chemical species 40, the deposited pattern of these particles 40 on the filter media 14, and the process used to deposit them. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed chemically functionalized filter system. It is intended that the specification and examples be considered as exemplary only, with the true scope being indicated by the following claims and their equivalents.

Claims

1. A filter for engine exhaust gases, comprising;

a filter media having an internal and external surface; and

a plurality of molecules of a fluid catalyst attached to the filter media, wherein the molecules of the fluid catalyst are

attached to at least the internal and external surface of the filter media, and

configured to donate an oxygen atom to soot particles to activate the soot particles for regeneration.

2. The filter of claim 1, wherein the molecules of the fluid catalyst are configured to regain an original chemical composition by taking an oxygen atom from oxygen in the exhaust gases.

3. The filter of claim 1, wherein the fluid catalyst is a gas.

4. The filter of claim 3, wherein the gas includes nitrogen dioxide (NO₂).

5. The filter of claim 4, wherein the nitrogen dioxide (NO₂) is configured to change to nitrous oxide (NO) after donating an oxygen atom to a soot particle contained in the engine exhaust gases.

6. The filter of claim 5, wherein the nitrous oxide (NO) is configured to change back to nitrogen dioxide (NO₂) after taking an oxygen atom from oxygen in the engine exhaust gases.

7. The filter of claim 1, wherein the molecules of the fluid catalyst are attached to the filter media by adsorption.

8. The filter of claim 1, wherein the filter media includes at least one of ceramic cordierite, woven fiber cartridges, knitted silica fiber coils, ceramic foam, wire mesh, and sintered metal substrates.

9. The filter of claim 1, wherein the external surface of the filter media include at least two opposing surface portions of the filter media, and the internal surface of the filter media includes at least the surface portions inside pores of the filter media.

10. A method of regenerating a filter comprising;

chemically functionalizing a filter media of the filter with molecules of a fluid catalyst;

flowing the exhaust gases through the filter;

accumulating the soot particles in the filter media;

activating the accumulated soot particles by donating oxygen atoms from the catalyst to at least some of the accumulated soot particles; and

regenerating the filter by burning the activated soot particles.

11. The method of claim 10, wherein activating the accumulated soot particles includes changing the chemical composition of the catalyst after donation of the oxygen atoms.

12. The method of claim 11, wherein activating the accumulated soot particles further include regaining the chemical composition of the catalyst by taking oxygen atoms from oxygen in the engine exhaust.

13. The method of claim 10, wherein chemical functionalization includes functionalizing the filter media with molecules of a gaseous catalyst.

14. The method of claim 10, wherein chemical functionalization includes functionalizing the filter media with molecules of nitrogen dioxide (NO₂).

15. The method of claim 14, wherein activating the accumulated soot particles includes changing the nitrogen dioxide (NO₂) to nitrous oxide (NO) after donating an oxygen atoms.

16. The method of claim 15, wherein activating the accumulated soot particles further includes changing the nitrous oxide (NO) to nitrogen dioxide (NO₂) by taking oxygen atoms from oxygen in the engine exhaust.

17. The method of claim 10, wherein chemical functionalization includes adsorption of the fluid catalyst on the filter media.

18. The method of claim 10, wherein regeneration of the filter occurs at a temperature below 600° C.

19. The method of operating an internal combustion engine comprising;

exhausting from the engine exhaust gas containing soot particles;

flowing the exhaust gas through a filter having a filter media chemically functionalized with a gaseous catalyst;

collecting soot particles on the filter media;

activating the collected soot particles by donating oxygen atoms from the gaseous catalyst to at least some of the collected soot particles;

replenishing the gaseous catalyst by taking oxygen atoms from oxygen contained in the exhaust gas; and

regenerating the filter by burning the activated soot particles.

20. The method of claim 19, wherein the regeneration of the filter occurs at a temperature below 600° C.