JP2009011921A - Diesel exhaust gas purifying filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diesel exhaust gas purifying filter which reduces the pressure drop and is excellent in durability in a filter to remove a particulate suspended matter in a diesel exhaust gas. <P>SOLUTION: In the diesel exhaust gas purifying filter which has a cross-sectional honeycomb structure formed by laminating a nonwoven fabric made of metal molded into a cross-section corrugated form and a plate-like nonwoven fabric made of metal fiber or piling up both to wind and of which the end portion of one of the passages is encapsulated and the other end portion of the passage neighboring one of the passage is encapsulated, it is characterized in that the cell density is 80-150 CPSI and further characterized by using the nonwoven fabric constituting the filter with the thickness of 0.3-0.9 mm, the average fiber diameter of 10-50 μm and the porosity of 60-75%. Thus, the particle collection efficiency of the filter falls within the proper range of 50-80%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a filter for removing particulate suspended matter contained in exhaust gas discharged from a diesel engine.

  In exhaust gas treatment from a diesel engine, in addition to decomposition treatment of gaseous substances such as NOx, it is necessary to remove solid or liquid particulate suspended matters. The particulate suspended matter is mainly composed of solid carbon particles, solid or liquid incombustible hydrocarbon fuel particles, and sulfide derived from sulfur in the fuel. This particulate suspended matter has a problem that it is easy to float in the atmosphere because it has a very small particle size and is easily taken into the human body, and effective removal is required from recent interest in environmental problems.

For removal of particulate suspended matter from diesel exhaust gas, collection by a filter is common, and many filters have been reported conventionally. As a conventional diesel exhaust gas treatment filter, for example, Patent Document 1 describes a tubular filter having a honeycomb structure made of ceramic such as cordierite. This filter seals the end of some channels with plugging material, while plugging the end on the opposite side of the remaining channels and allows exhaust gas to pass through the walls between the channels. The particles are collected by the fine pores of the ceramic.
JP-A-9-29022

  However, although the conventional filter has a very high particle collection rate of 95% or more, the pressure loss tends to increase accordingly. In particular, when the wall surface becomes clogged with use, the pressure loss becomes extremely large, and there is a concern about the destruction of the filter and the adverse effect on the engine.

  Further, the exhaust gas purification filter is regenerated and used by performing a heat treatment for burning the soot collected after being used for a predetermined period. However, since ceramic has a low thermal conductivity, heat spots are likely to occur during reproduction, and may be damaged due to melting, cracking, etc., and there is a problem from the viewpoint of durability.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a filter that removes particulate suspended matter in diesel engine exhaust gas with reduced pressure loss and excellent durability.

  The inventors of the present invention have intensively studied to improve the above-described filter, and firstly examined an appropriate range of the particle collection rate. In conventional filters, the higher the particle collection rate, the better. However, due to recent improvements in the diesel engine itself, the amount of particles generated has decreased, and it is not optimal to simply increase the collection rate alone. Moreover, even if the particles are not completely collected (even if the collection rate is not 100%), the particles passed through the filter are burned by placing the catalyst behind the filter. Can be suppressed. Rather, it can be said that such a configuration is preferable in consideration of the burden on the entire exhaust system and the purification efficiency. In consideration of such a background, the present inventors assumed 50 to 80% as an optimum particle collection rate. If it is less than 50%, the original function of the filter cannot be exhibited, while a collection rate exceeding 80% is unnecessary.

  Then, the present inventors have further studied and found out that a filter using a metal non-woven fabric as a constituent material can be used as a filter capable of bringing the particle collection rate within the above appropriate range, and has arrived at the present invention.

  That is, the present invention has a cross-sectional honeycomb structure by laminating a metal fiber non-woven fabric and a flat metal fiber non-woven fabric formed into a corrugated cross section, or by superimposing and winding both, A diesel exhaust gas purification filter in which an end of a road is sealed and the other end of a flow path adjacent to the one flow path is sealed, and has a cell density of 80 to 150 CPSI, and the metal fiber The non-woven fabric is a diesel exhaust gas purification filter having a particle collection rate of 50 to 80% by setting a thickness of 0.3 to 0.9 mm, an average fiber diameter of 10 to 50 μm, and a porosity of 60 to 75%. The filter according to the present invention applies a metal nonwoven fabric having predetermined physical properties as a constituent material while allowing the exhaust gas to pass through the wall surfaces between the flow paths (cells) as the structure. The combination of this structure and the constituent material realizes a soot collection rate in a suitable range.

  A metal nonwoven fabric is manufactured by laminating and sintering metal fibers. As for the physical properties of the metal nonwoven fabric, the thickness and the porosity are adjusted by the fiber diameter of the metal fibers to be formed and the correlation between the amount of metal fibers used and the sintering conditions. In the present invention, the collection rate is set to an appropriate range by applying a metal nonwoven fabric having a thickness of 0.3 to 0.9 mm and a porosity of 60 to 75% using metal fibers having an average fiber diameter of 10 to 50 μm. Can do. In these physical properties, a more preferable range is a non-woven fabric having a thickness of 0.4 to 0.6 mm and a porosity of 65 to 75% using metal fibers having an average fiber diameter of 20 to 40 μm. Regardless, the collection rate can be 50 to 80%.

  Moreover, since a metal nonwoven fabric has favorable heat conductivity, a heat spot is not produced also in the regeneration process (heat treatment) after collection of soot. In addition, since it has good heat resistance because it is a metal, it is excellent in durability and can be used for a long time even if it is subjected to repeated cycles of use and regeneration. As the metal constituting the metal nonwoven fabric, stainless steel, nickel-base alloy and the like are preferable.

  On the other hand, the structural surface of the filter of the present invention is of a type (wall flow) in which the flow path is partially sealed at both end faces and exhaust gas is allowed to pass through the flow path wall surface. This is the same as the conventional filter. However, in the present invention, in order to set the collection rate within an appropriate range, the cell density, which is the density of the flow path, is set to 80 to 150 CPSI. As for the cell density, increasing this tends to increase the collection rate. In this invention, since it is necessary to avoid an excessively high collection rate, the upper limit is set to 150 CPSI. In addition, since it will become low even if the physical property of a metal nonwoven fabric is prepared if it is less than 80 CPSI, 80 CPSI is made into a minimum.

  For sealing the flow path, a predetermined flow path end may be filled with a sealing material. Preferably, crests and troughs near both ends of the metal fiber nonwoven fabric having a corrugated cross section constituting the filter are crushed from both sides. By doing in this way, a sealing part can be formed easily.

  The filter according to the present invention is preferably one in which a catalyst is supported on a metal nonwoven fabric. By providing the catalyst, the particulate suspended matter collected during the regeneration of the filter can be burned efficiently. The catalyst is not particularly limited as long as the particulate suspended matter can be combusted. For example, a noble metal catalyst containing a noble metal such as silver, gold, platinum, palladium, iridium, ruthenium, and rhodium, or Noble metal alloy catalysts are known, and those having platinum and iridium as main components are particularly preferred.

  When the catalyst is supported, in order to disperse the noble metal particles as the catalyst, the catalyst powder in which the noble metal is supported on a porous oxide containing at least one oxide such as alumina, silica, ceria, zirconia, etc. is filtered. It is preferable to carry it. In addition, these porous oxides may be preliminarily applied to the filter as a base layer (often referred to as a wash coat), and then a noble metal may be supported.

  When the catalyst is loaded, the amount of the catalyst loaded is 0.1 to 6 g / L of the total weight of the catalyst (total weight when different catalysts are used) based on the filter capacity in terms of noble metal. Is preferable, and it is more preferable to set it as 1-3 g / L. Moreover, when using a porous oxide, it is preferable that the usage-amount of a porous oxide shall be 5-150 g / L. The catalyst loading at this time is preferably 0.1 to 60%, more preferably 1 to 40%, based on the weight of the porous oxide.

  The exhaust gas purifying filter according to the present invention can be manufactured by first processing a metal nonwoven fabric so as to have a cross-sectional waveform, and sequentially laminating the metal nonwoven fabric on a flat plate. The metal nonwoven fabric can be molded easily by rolling with a roll with gears.

  In addition, the channel is preferably sealed by crushing the crests and troughs at both ends of the metal nonwoven fabric, but this processing is preferably performed by mold pressing, roller pressurization, or the like on the processing site.

  When laminating a metal nonwoven fabric, a predetermined mold is prepared to fix each layer, and a corrugated metal nonwoven fabric and a flat metal nonwoven fabric are laminated in order, and the contact portions of the laminated metal nonwoven fabric are welded and secured. You may do it. Moreover, what laminated | stacked the corrugated metal nonwoven fabric and the flat metal nonwoven fabric may be wound, and the terminal part may be joined.

  When the catalyst is supported on the filter, the catalyst is prepared by immersing the porous oxide in a precious metal salt solution, drying and firing the catalyst powder in advance, and immersing the filter in a slurry. Supported. Alternatively, the catalyst can be supported by immersing or coating the formed filter in a sol of a porous oxide, further immersing in a metal salt solution containing a catalyst metal, and drying and firing.

  The filter formed as described above can be used for exhaust gas purification by inserting the filter into a cylindrical case and attaching electrodes, sensors, and the like for energization heating and temperature management as necessary.

  As described above, according to the present invention, particulate suspended matters in diesel engine exhaust gas can be efficiently removed. The filter according to the present invention can be purified without increasing the pressure loss of the exhaust gas, can prevent damage to the engine, and has excellent durability without fear of damage during regeneration.

  Hereinafter, preferred embodiments of the present invention will be described together with comparative examples.

  FIG. 1 illustrates a manufacturing process of a filter in the present embodiment. A metal nonwoven fabric was formed into a corrugated cross section by a geared roll. Next, it shape | molds and crushes the peak part of one edge part of a metal fiber nonwoven fabric, and crushes the trough part of the other edge part from the back surface, and formed the sealing part of the flow path.

  Then, the processed metal nonwoven fabric and the flat metal nonwoven fabric were inserted into a cylindrical case and sequentially laminated to obtain a columnar exhaust gas purification filter having a honeycomb structure (dimension φ 144 mm × 150 mm).

  Next, the alumina powder is immersed in a dinitrodiamine platinum solution, dried and calcined to prepare a 5% platinum catalyst, and this is slurried. Then, the filter produced above is immersed to support the catalyst, and the catalyst is attached. Filter was produced (catalyst loading 2 g / L). FIG. 2 shows the appearance of the filter.

Comparative example : A commercially available honeycomb structure made of cordierite (dimensions: diameter 144 × 150 mm, cell density 200 cpsi), half of the flow paths are sealed at one end, and the flow path at the other end is sealed The prepared filter was prepared and immersed in the same catalyst slurry as in the present embodiment to produce an exhaust gas purifying filter (catalyst loading 2 g / L).

Based on the above manufacturing method, a plurality of exhaust gas purification filters were manufactured using metal nonwoven fabrics having different fiber diameters and thicknesses. And about those, the evaluation test using a diesel engine was done, and the purification performance of particulate matter was compared and examined. In this evaluation test, the produced purification filter was attached to a diesel engine with a displacement of 2771 cc, and continuously operated in the D13 mode, and the collection rate of particulate suspended matters was measured with a microtunnel. The results are shown in Table 1.

  Further, in the above evaluation test, the change with time in pressure loss is also evaluated. This pressure loss was measured by a differential pressure gauge attached before and after the filter. FIG. 3 shows the result.

  In the above evaluation test, the ceramic filter of the comparative example has a high trapping rate of particulate suspended matter of 95% (Table 1), but the pressure loss tends to be high and the rate of increase is also high (FIG. 3). On the other hand, the pressure loss is reduced in the filter which consists of an Example and a reference example metal nonwoven fabric (FIG. 3). However, it can be seen that unless the cell density and the configuration of the metal nonwoven fabric (fiber diameter, etc.) are appropriate, the collection rate is too low to achieve a sufficient effect (Table 1).

  Considering the suitable range of the collection rate, when using a filter with a collection rate exceeding 90% as in the comparative example, it will be from long-term use such as particulate suspended matter and calcium contained in engine lubricating oil, etc. It is thought that filter clogging occurs due to accumulation of ash. Moreover, although the evaluation test performed in the present embodiment is the engine operation mode D13 mode, in a higher load operation, the pressure loss becomes a limit in a short time and there is a possibility of engine stop.

The figure explaining the manufacturing process of the filter concerning this embodiment. Appearance of the filter according to this embodiment. The figure which shows the time change of the pressure loss of each Example.

Claims (3)

Laminated metal fiber non-woven fabric and flat metal fiber non-woven fabric formed into a corrugated cross-section, or have a cross-sectional honeycomb structure by wrapping and winding both together,
A diesel exhaust gas purification filter in which an end of one flow path is sealed and the other end of the flow path adjacent to the one flow path is sealed,
The cell density is 80-150 CPSI;
The metal fiber nonwoven fabric has a thickness of 0.3 to 0.9 mm, an average fiber diameter of 10 to 50 μm, and a porosity of 60 to 75%, so that the particle collection rate is 50 to 80%. . 2. A clogged flow path is formed by crushing a crest at one end of a nonwoven fabric made of metal fibers formed into a corrugated cross section and crushing a trough at the other end from the back surface. The diesel exhaust gas purification filter as described. The diesel exhaust gas purification according to claim 1 or 2, wherein a catalyst is supported on the metal fiber non-woven fabric, and the catalyst is a noble metal catalyst or a noble metal alloy catalyst containing silver, gold, platinum, palladium, iridium, ruthenium, and rhodium. Filter.

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