JP2002537965A - Monolith catalyst / filter device - Google Patents

Abstract

(57) Abstract: A device for controlling gaseous and particulate emissions from a gas stream containing particulate matter or a gas stream containing no particulate matter. The apparatus comprises a plurality of cells having inlets and outlets and walls (260, 265, 270, 275, 280, 285) of a material permeable to a gas flow. The cells are oriented (210, 220, 230, 240) for gas flow from the inlet to the outlet, with each cell having a first end adjacent to the inlet of the device and a second end adjacent to the outlet of the device. Has two ends. The walls are coated with a catalyst. Barriers (200, 201) are applied to the second end of some, but not all, cells, the barrier comprising a material that does not permit passage of a gas stream.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to monolithic catalysts. More particularly, the present invention relates to monolithic catalysts that perform both filtration and catalysis functions for treating gas streams containing particulate matter.

[0002] Government emission standards and the desire to prevent environmental pollution have resulted in a number of technological developments that promote the oxidation of unburned hydrocarbons and the removal of other harmful species found in the exhaust gases of internal combustion engines. . These unburned hydrocarbons, along with carbon monoxide and nitrogen oxides, are often treated in catalytic converters provided in the exhaust gas system. A typical catalyst bed may comprise one or more platinum metal supported on alumina. Of course, other catalyst metals are known.

[0003] Other pollutants are also common in combustion engine systems, especially in diesel exhaust systems. In addition to the pollutants described above, particulate matter containing soot is generated during combustion. Such particulate matter is also harmful to the environment, and it is desirable to remove these components before releasing the exhaust stream to the atmosphere.

[0004] Soot is essentially a carbonaceous material that, when generated during combustion of diesel fuel in the cylinders of a diesel engine, produces a soluble organic fraction (SOF) that surrounds the soot.
) Leave layer on engine. This soot covered with SOF is one type of particulate matter in question.

[0005] Technologies have been developed to address particulate emissions. One example is the technical subject of US Patent No. 4,902,487 to Cooper et al. This technique, which diesel exhaust gas to remove through the filter particulate material, wherein, in which particulate matter is combusted in the presence of NO _2. NO ₂ can be obtained by oxidation of NO upstream of the filter. Such a device is very good at converting diesel exhaust particles. However, when the engine is malfunctioning and excess particulate matter (i.e., the amount of particles in excess of that produced during normal engine operation)
, There is a possible problem with such a system.

[0006] Excess particulate matter can block the filter. Filter blockage begins with increasing pressure drop in the filter and results in an insurmountable blockage that can damage the engine and other parts of the system.

Another method of treating an exhaust stream containing particulate matter is to use only an oxidation catalyst. In such a case, the conversion of SOF is relatively low. This is because no filters are used, but occlusions and the associated problems (the problems associated with the use of filters as described above) do not usually occur.

[0008] The improved filter / catalyst device provides effective filtration and catalysis while preventing the deleterious effects on the system associated with plugging by particulate matter that may be present in the exhaust stream.

The present invention provides an apparatus for controlling gaseous and particulate emissions from a gas stream containing particulate matter with carbonaceous combustible inclusions. The present invention is particularly applicable to diesel exhaust streams, but applies to any stream containing harmful or undesirable gases. The invention is particularly applicable to streams containing both harmful or undesirable gases and particulate matter. The device comprises an inlet side and an outlet side and a plurality of passages, ie cells. The inner wall separating the cells is made of a material permeable to gas flow. The cell is oriented such that a gas stream flows from the inlet to the outlet of the device,
The cells each have a first end adjacent to an inlet of the device and a second end adjacent to an outlet of the device. The cell walls are coated with a catalyst. There are barriers at the second end of some, but not all, cells. The barrier may be one that does not allow the passage of the gas stream, or may comprise a material that allows the passage of gas but does not allow the passage of particulate matter. Thus, the cells, as a group, are partially blocked so that the exhaust stream can pass freely through some, but not all, cells.

[0010] The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to convention, the various features of the drawings are not to be defined. On the contrary, the dimensions of the various features are arbitrarily enlarged or reduced for clarity. The drawings include the accompanying figures.

The present invention provides an apparatus for controlling gaseous and particulate emissions from a gas stream containing particulate matter with carbonaceous combustible inclusions. The invention is particularly applicable to diesel exhaust streams. The apparatus comprises an inlet side and an outlet side and a plurality of cells. The walls of the cell consist of a substance that is permeable to gas flow but not to particulate matter.

FIG. 1 shows a schematic diagram of the device of the present invention. The cell 100 is contained in a part of the device having one inlet and one outlet and is indicated by arrows indicating gas flow. As the exhaust gas enters the device, it passes through the cell and eventually exits from the other side, where the gas stream is released to the atmosphere or further processed. Typical devices are installed directly in the exhaust system. A typical device size is about 15c in length for a vehicle using a 6 liter diesel engine.
m (6 inches), and may be about 20-25 cm (8-10 inches) in diameter.

FIG. 2 shows a schematic sectional view of a part of the device of the invention. The cells are oriented such that a gas flow flows from the inlet to the outlet of the device, the cells each having a first end adjacent to the inlet of the device and a second end adjacent to the outlet of the device. The walls of the cell are coated with or otherwise contain the catalyst. The barrier is at the second end of some, but not all, cells. The barrier is made of a material that does not allow passage of the gas stream. Thus, the cells, as a group, are partially blocked so that the exhaust stream can pass freely through some, but not all, cells. In a preferred embodiment, the cells are alternately plugged. That is, the cells are periodically closed. That is, as schematically shown in both FIGS. 1 and 2, one is closed, one is empty, one is closed, and so on.

In FIG. 2, arrows indicate the gas flow of the exhaust stream through the cell. Barrier 200
And 201 are in every other cell. In the example shown in the figures, the cells are linear cells, but need not be linear. Open cells 210, 220 and 230 easily allow the passage of the gas flow. Closed cells 240 and 250 do not readily allow the passage of gas streams because barriers 200 and 201 are at their ends.

[0015] Walls 260, 265, 270, 275, 280, and 285 are all permeable to gas flow, but substantially not to particulate matter present in the gas flow. The cells 210, 220 and 230 all allow the passage of a gas stream containing freely passing particles, as indicated by the arrows in FIG. However, there is no such free flow in cells 240 and 250 due to the presence of barriers 200 and 201. In cells 240 and 250, gas is forced through the semi-permeable walls into cells 210, 220 and 230, as indicated by the arrows in FIG. This wall does not allow the passage of most particulate matter (some particulate matter may travel through the wall, but most of it will be trapped at the surface of the wall), so that Conceivable.

In this way, as the gas flow passes through the wall, the particulate matter is
Surface of wall 265 exposed to cell 240, surface of wall 270 exposed to cell 240, wall 275 exposed to cell 250, and wall 2 exposed to cell 250
80 is captured on the surface.

Due to the pressure generated in the closed cell, gas is forced through the wall from the closed cell to the open cell. However, further effects on this physical arrangement have been identified. One advantage is that the open cell functions as an editor.
As gas flows through the walls that are exposed to the open cells, the reduction in pressure at the surface of these walls increases the wall pressure loss and gas escapes effectively through the walls.

As the particulate matter accumulates on the surface of the wall, it is typically catalyzed and burns along or on the coated wall. Unburned, inorganic ash or other non-combustible material will spontaneously fall out of the system due to vibrations resulting from forced gas flow, its own weight and / or engine operation and other movements of the device. However, even if the particulate matter does not fall spontaneously, blockage of the device by particulate accumulation will never occur because some cells are open for flow. Similarly, in the event of an engine malfunction, such as excessive particulate matter entering the system, no blockage occurs. Thus, while solutions exist where particulate matter is trapped and the exhaust components are catalytically reacted to form more harmless components, the system is never clogged and does not cause engine damage. The overall effect is to reduce harmful particulate and gaseous emissions and to prevent blockages that would cause engine damage.

Another, somewhat relevant advantage has been identified when the gas flowing through an open cell exhibits a laminar flow profile. Where the gas flow is thin, there is less contact between the gas flow and the catalyst on the wall surface as compared to turbulence. By utilizing the device according to the present invention, wall flow discharge from closed cells to open cells causes disruptions in laminar flow flowing through open cells, thereby
Enhance mass transfer to the catalyst surface and increase catalytic activity.

The amount of cells in a given device can vary depending on the particular application. For example, for an average 6 liter diesel engine, about 15.5 cells per square cm cross section (100 cells per square inch) (cpsi) would probably be sufficient. Of course, special operating conditions and environments will affect this design parameter. For example, different engine designs, exhaust system designs and even fuels may require different cell sizes. The device according to the invention can have a cell size of up to about 31 cells per square cm (200 cpsi) and beyond, depending on the required wall thickness. Besides design choices, manufacturing limitations can also limit cell density. Conventionally, half of the cells are provided with a barrier.

The wall can be composed of a suitable material that meets the needs described above. For example, the wall may be made of woven or braided wire mesh, or porous metal, or a suitable ceramic material. The preferred wall material is cordierite (a crystalline mineral comprising aluminum and magnesium silicates), but silicon carbide and stainless steel mesh may also be used. Because the particulate emissions vary from engine to engine, the walls can be designed appropriately for each engine application.

The catalyst coated on the wall may also be any suitable catalyst for the desired purpose. For example, it can be any catalyst that effectively converts NO to NO ₂ (NO ₂ is an effective oxidant, and therefore the presence of NO ₂ is desirable for the subsequent oxidation of particulate matter) ). It may also be a high platinum loaded catalyst supported on a ceramic or metal honeycomb catalyst support separate from the wall material itself. Alternatively, the wall itself may be the support. The catalyst layer may also be a washcoat based on alumina impregnated with a platinum group metal (ie, platinum, palladium, ruthenium, rhodium, osmium, iridium, etc.). The catalyst may be a base metal with or without any white metal. The base metal may be alone in the base metal washcoat or may be present in combination with the alumina. Typical base metals are manganese, copper, iron,
Includes nickel, cobalt and oxides of these metals. In addition, the rare earth element can comprise a base metal. Such rare earth base metals include cerium, lanthanum, praseodymium, neodymium and the like (atomic numbers 57-71) and oxides of these elements. Of course, combinations of these metals and their oxides can also be used. Many other catalysts and catalyst configurations may be utilized in connection with the present invention, and those skilled in the art will be able to select based on their respective circumstances and the desired catalytic activity.

When applying the catalyst to the wall, care is taken not to block the pores that allow the gas flow to flow through the wall. This plugging problem can be avoided by appropriate methods of applying the catalyst, known to those skilled in the art.

FIGS. 3 and 4 show the results of opacity tests of exhaust streams from different processing equipment.
Opacity is defined as the fraction of light transmitted from the source that is prevented from reaching the observer (observer) or instrument receiver (receiver) and is expressed as a percentage. For example, one with 100% opacity is completely opaque, and one with 0% opacity is completely transparent. For the purpose of generating the comparative data shown in FIGS. 3 and 4, opacity measurements were taken as the exhaust stream exited the test chamber.
This was done by traversing the exhaust stream. In FIG. 3, this number was recorded when the exhaust stream exited only the monolith catalyst chamber. In FIG. 4, the values were recorded as the exhaust stream exited the device of the present invention.

Both FIGS. 3 and 4 show a reduction in the percentage of opacity (ie, transmission through the exhaust flow as it exits the device, as compared to before the exhaust flow enters the device). Percent change in the percentage of light emitted). Thus, a greater decrease in the percentage of opacity means that more particulate matter has been removed.
FIG. 3 shows the reduction in opacity using only a monolithic catalyst having no alternately plugged / unplugged cells according to the present invention. Data was generated using a 6 liter diesel engine and collected over a period of about 5 months. Four measurements were taken for each indicated day and averaged. In each figure, two sets of data are shown for each measurement date. One set was measured from the exhaust leaving the system while the engine was running and the rpm rose to 750-2300 rpm within 4 seconds.
Similarly, the second set of data indicates that the engine has been running
m from the exhaust gas exiting the system while rising to m. As can be seen in FIG. 3, the reduction in opacity when all cells are open is in most cases between about 10% and 20%.

FIG. 4 shows the reduction in opacity when the device is configured according to the present invention, ie, as shown schematically in FIG. Here, the range of opacity reduction is between about 30% and 50%. As in FIG. 3, data was collected using a 6 liter diesel engine over the same approximately 5 months. Two sets of data are shown for each measurement date. One set was measured from exhaust leaving the system while the engine was running and rose to 750-2300 rpm within 4 seconds. Similarly, the second set of data was measured from exhaust exiting the system while the engine was running and rose to 1500-2300 rpm within 4 seconds. In addition, four data values were created for each day under each operating condition, and then averaged to create numerical values on the graph.

As can be seen through the data shown, the opacity reduction is increasing when the device of the present invention is utilized. Therefore, the use of the apparatus of the present invention resulted in an increase in the amount of particulate matter totally removed as compared with the case of using only the monolith catalyst. The present invention enhances particle removal and promotes the required catalytic activity, while at the same time the system can become blocked (and subsequently damaged) by excessive particulate matter accumulation that may result from engine malfunctions. Provide a system to remove the

As noted above, even in the absence of particulate matter in the gas stream, the present invention provides a superior system with enhanced catalytic activity. By blocking some channels and allowing free flow through other channels, the enhanced turbulence created by wall flow discharge increases the catalytic effect. Enhanced mass transfer within the system improves overall oxidation and associated combustion processes and chemical reactions.

While illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown.
Rather, various modifications may be made in the details within the scope and scope of the appended claims and without departing from the spirit of the invention.

[Brief description of the drawings]

FIG. 1 shows a schematic view of an apparatus according to the invention.

FIG. 2 shows a schematic sectional view of the device according to the invention.

FIG. 3 is a plot showing opacity reduction where only a monolith catalyst is used.

FIG. 4 is a plot showing the decrease in opacity where the device of the present invention is used.

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Claims (6)

[Claims] 1. An apparatus for controlling gaseous and particulate emissions from a gas stream containing particulate matter, comprising a plurality of cells having an inlet and an outlet, and a wall of material permeable to the gas stream. A cell oriented to flow the gas flow from the inlet to the outlet; a first end adjacent to the inlet of the device, and a second end adjacent to the outlet of the device, respectively. Wherein the second end of some, but not all, of the cells is provided with a barrier, the barrier comprising: A material which does not allow the passage of a gas stream, or which allows the passage of gas but does not allow the passage of particulate matter, and wherein the remaining cells are not restricted to said gas stream. Flow It features to supply apparatus. 2. The apparatus of claim 1, wherein every other cell has the barrier. 3. The device of claim 1, wherein there are up to about 31 cells per square cm of the device (200 cells per square inch). 4. The catalyst comprises a washcoat based on a metal oxide impregnated with one or more metals selected from the group consisting of platinum, palladium, ruthenium, rhodium, osmium, iridium and compounds thereof. Claims 1-3
An apparatus according to any one of the preceding claims. 5. The apparatus according to claim 1, wherein the catalyst comprises a base metal. 6. The device according to claim 1, wherein the wall comprises cordierite.