EP1515012B1 - Device for elimination of carbon black particulates from an exhaust gas stream of an internal combustion engine - Google Patents

Abstract

A modular assembly removes soot particles from automotive exhaust gases by oxidation of trapped particles with NO(2). The NO(2) is oxidized by NO exhaust gases in contact with a catalyst in relation to the gas flow speed at a temperature above about 200[deg] C. The module contains one or more layers of open-pored noble metal foam (2).

Description

The invention relates to a device for removing soot particles from an exhaust gas stream of internal combustion engines in a module (1) by oxidation of the temporarily trapped soot particles with nitrogen dioxide (NO ₂ ), wherein the nitrogen dioxide by oxidation of existing in the exhaust nitrogen monoxide (NO) to a catalyst in Depending on the flow rate of the exhaust gas at a temperature above about 200 ° C is formed.

To reduce soot particle emissions, purely motor-side measures to comply with the increasingly stringent emission limit values worldwide, such as EURO IV / EURO V or ULEV / SULEV, for fuel-powered internal combustion engines could only be achieved with economically unreasonable costs. Therefore, today as in the future so-called exhaust aftertreatment systems are used.

Basically, a distinction is made between two methods for exhaust aftertreatment, which focus on the one hand on the minimization of NO _x emissions, which are mentioned here only marginally, such as SCR catalyst systems and NO _x storage catalytic converters, and on the other hand to minimize the soot particle emission.

By using a suitable exhaust aftertreatment system for motor vehicles in combination with engine-side measures, it is therefore possible to comply with the strict regulations regarding soot particle emissions and NO _x emissions.

So today, for example, with classic filter systems, such. As ceramic wall-flow filters, in terms of here particulate matter of interest can already be achieved> 50% separation. However, accumulation of soot particles and ash from the engine oil additives will over time lead to an undesirable increase in engine back pressure, which in turn leads to increased fuel consumption. For this reason, such filter systems are to be completely dismantled and cleaned at regular intervals.

Further developed variants of such filter systems take into account the mentioned disadvantages of the filter systems in use insofar as such systems have a catalytic coating on the filter surface. By such a coating as an active component, the combustion temperature of the soot particles is markedly reduced.

The lowering of the combustion temperature of the soot particles is of great importance in that the exhaust gases emitted from newly developed internal combustion engines are less and less hot. For filter systems without catalytic coating of the filter surface, the combustion temperature of the soot particles is approx. 580 ° C to 600 ° C. However, even with the variants of such filter systems, the particular difficulty of removing the filtered ash remains.

Another approach to remove the accumulated in the filter soot is the thermally induced regeneration. The filter system is, for example, with a burner or electrically brought to the necessary for the oxidation of the soot particles temperature. Of course, such a method is at the expense of the overall energy balance of the internal combustion engine.

Another possibility for the continuous removal of the filtered soot particles is to remove the particles from the filter substrate by injecting an additive which reduces the combustion temperature of the soot particles. Such an approach is also not a particularly suitable solution, because the added additives themselves contribute to the ash formation.

Other approaches in turn deal with the oxidation of the filtered soot particles with NO ₂ .

EP 341832 B1 discloses a process for the exhaust gas aftertreatment of heavy trucks. In the method, the exhaust gas is first passed through a catalyst without filtering action to oxidize the nitrogen monoxide contained in the exhaust gas to nitrogen dioxide. The nitrogen dioxide-containing exhaust gas is then used to burn off the soot particles collected in a downstream filter. The amount of nitrogen oxide is sufficient to allow the combustion of the filtered soot particles below 400 ° C.

Furthermore, EP 835684 A2 discloses a method for the exhaust aftertreatment of vans and passenger cars. According to the specified method, the exhaust gas is passed over two catalysts arranged one behind the other. On the first catalyst, the nitrogen monoxide contained in the exhaust gas is oxidized to nitrogen dioxide. At the second downstream catalyst, which acts as a filter, the collected soot particles are then deposited and oxidized at a temperature of about 250 ° C partly according to equation (1) to carbon dioxide CO ₂ and the nitrogen dioxide NO ₂ reduced to nitrogen:

2NO ₂ + 2C → 2CO ₂ + N ₂ (1)

Thus, in the known method, the filtered soot particles are burned without the use of a burner or electric heating element, i. oxidized. In this case, the first catalyst used consists of a honeycomb flow monolith coated with an oxidation catalyst.

EP 1 065 352 A discloses two mutually adjacent metal foams. The upstream metal foam oxidizes NO to NOZ for soot oxidation in the downstream particulate filter.

From DE 3407172 C2, a device for exhaust gas aftertreatment of diesel engines is known, which contains in a housing a number of filter elements with different distances from each other. At least one filter element A has a coating which reduces the combustion temperature of soot. Furthermore, at least one filter element B is present which contains a catalyst which promotes the combustion of harmful gaseous substances.

JP 09079024 A discloses a series connection of a plurality of metal foams operating as particle filters, wherein the metal foams are partially spaced apart and the downstream metal foam filter has an oxidation catalyst coating to oxidize NO to NOZ.

From WO 99/09307 a method for the reduction of soot emission from heavy trucks is known. In the specified method, the exhaust gas for the oxidation of nitrogen monoxide to nitrogen dioxide is passed over a catalyst and then, as usual, for the oxidation of the soot collected in a soot filter. New in the specified method is that a portion of the purified exhaust gas is then passed through a radiator and mixed with the intake air of the diesel engine.

The known methods for the exhaust gas aftertreatment of exhaust gases produced by internal combustion engines still have the disadvantage that in each case filter devices are used which, despite all further auxiliary measures provided, entail the risk of clogging at some point.

The object of the present invention is to be seen in an operated as a permanently open system device for To provide exhaust aftertreatment of exhaust gas produced by internal combustion engine, which is constantly open as itself "on-board" regenerating system and operates essentially without the usual filter devices and thus prevents clogging of the exhaust aftertreatment system and at the same time achieves effective post-treatment of the evolved exhaust gas, especially with regard to the removal of the soot particles from the exhaust-gas engine to be treated.

According to the invention, the object is achieved in a generic device by the features of independent claim 1. Further advantageous embodiments of the invention are specified in the subclaims.

It has proved to be particularly advantageous that the soot particles present in the combustion engine exhaust gases are initially captured temporarily using a FeCr alloy based open-pore uncoated or coated metal foam. The soot particles are then oxidized via the so-called gas catalysis according to equations (2) and (3) with the nitrogen dioxide NO ₂ produced on an upstream noble metal-coated and open-pore metal foam, ie burned:

NO ₂ + C → CO + NO (2)

2CO + O ₂ → 2CO ₂ (3)

The nitrogen monoxide NO produced in accordance with equation (2) reacts again on at least one further noble metal-coated open-pored metal foam lying against the first uncoated or coated metal foam to form nitrogen dioxide NO ₂ , which is an adjoining at least one further coated or uncoated metal foam for the oxidation of soot particles is available so that one can speak of a multiple use of nitrogen monoxide, which causes a sustained increase of the nitrogen dioxide NO ₂ required for the reduction of soot particles and produced on the upstream and the other precious metal coated metal foam.

The metal foam is characterized by high thermal oxidation resistance, high thermal shock resistance, high corrosion resistance, especially against dilute sulfuric acid, and mechanical strength.

Here, the noble metal-coated metal foam is coated at least with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals.

Furthermore, the coated or uncoated metal foam is advantageously coated with a compound which reduces the combustion temperature of the soot particles, with cerium orthovanadate (CeVO ₄ ) preferably being used.

It has also proved to be particularly advantageous that the coated metal foams are also not inhibited by the ash from the motor oil additives, since such ashes can pass through the metal foams and be blown out, so that the preferred device remains constantly open as a self-regenerating module.

The metal foam used according to the invention, whose geometry can be chosen almost freely, can be produced by two different methods. One method is based on the impregnation of a PU foam precursor with a so-called slurry, which contains spherical metal particles with a precisely defined particle size distribution, and a subsequent sintering process. The other method is a conventional precision casting process.

A particular advantage of the open-pore metal foam used in contrast to wall-flow filters is particularly in the disordered Zellgedmetrie that allows within shortest distances a 3D mixing, ie a turbulent mixing of the exhaust gas. This will increases the efficiency of the catalyst device and prevents clogging.

Preferably, the metal foam is formed with a relative density in the range of 2 to 20%, wherein the metal foam is electrically conductive.

Furthermore, the metal foam is preferably provided with a certain number of pores ranging from 3 to 80 pores per inch (pores per linear inch) or in abbreviation (ppi).

The noble metal coating on the metal foam is preferably used directly or by impregnation of a washcoat with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals in a concentration of 1.0 g to 2.5 g Precious metal applied per liter of metal foam. A catalyst formed in this way is an oxidation catalyst which, depending on the flow rate, of course also oxidizes hydrocarbons (HC), including the heavy hydrocarbons (SOF), above about 200 ° C. and carbon monoxide (CO) above about 150 ° C.

Furthermore, metal foams with a Ce (III) VO ₄ (cerium orthovanadate) coating are preferably provided in the device, a catalytically active compound which reduces the combustion temperature of the soot particles, a so-called oxygen storage compound. Such a catalyst reduces the combustion temperature of the soot particles to about 360 ° C in direct contact, so that one speaks of a so-called solid-phase catalysis.

In this case, the metal foam is advantageously reduced to the combustion temperature of the soot particles Compound Cer orthovanadate by a plasma method, a wash-coat method or a sol-gel method in a concentration of 1.0 g to 25 g CeVO _{4 applied} per liter of metal foam.

The arrangement of the noble metal-coated and the coated or uncoated metal foams in the catalyst module is such that at least two noble metal-coated open-cell metal foams are provided, which are each preceded by an uncoated or coated metal foam. However, the device should preferably consist at least of a metal foam coated with a noble metal. By varying the number of pores and / or the relative density of the metal foam, it is advantageously possible to achieve a continuous regeneration of the exhaust gas to be treated over the length of the catalyst module.

The number of pores of the metal foams in the direction of the exhaust gas flow is variable. However, the number of pores of the metal foams preferably increases downstream. There is no gap between the individual or all metal foams, they are arranged adjacent to one another.

In addition, the metal foams can be introduced particularly advantageously cohesively into a metallic housing, preferably by soldering, since it is the metal foams used, as already mentioned, is a metallic compound. As a result, it is possible to dispense with the use of toxicologically extremely questionable swelling mats when using a cohesive connection, which are used as standard in ceramic filters, for example.

A particular embodiment of the device according to the invention is that the metal foams are introduced with a bearing mat in the metallic module.

Furthermore, a module can be constructed in an advantageous manner, which is composed of a plurality of identically designed modules or modules of different design. The modules are preferably arranged parallel to the exhaust gas flow, depending on the requirements of two identical or different modules or three identical or different modules and the like.

• Fig. 1 eine schematische Darstellung in verkleinertem Maßstab eines Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;
• Fig. 2, nicht Gegenstand der Erfindung, eine schematische Darstellung in verkleinertem Maßstab eines weiteren Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;
• Fig. 3 eine schematische Darstellung in verkleinertem Maßstab eines anderen Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;
• Fig. 4 eine schematische Darstellung in verkleinertem Maßstab einer Ausführung aus zwei parallel angeordneten Modulen gemäß dem Ausführungsbeispiel nach Fig. 1 einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung und
• Fig. 5 einen Querschnitt in verkleinertem Maßstab entlang dem Schnitt A-B entsprechend der Fig. 4.

Further advantages of the invention are explained below with reference to exemplary embodiments illustrated in the drawing. Show it:

• Fig. 1 is a schematic representation on a smaller scale of an embodiment of an apparatus for removing combustion engine generated soot particles according to the invention;
• Fig. 2, not the subject of the invention, a schematic representation on a smaller scale of a further embodiment of an apparatus for removing combustion engine generated soot particles according to the invention;
• Fig. 3 is a schematic representation on a smaller scale of another embodiment of a device for removing combustion engine generated soot particles according to the invention;
• Fig. 4 is a schematic representation on a reduced scale of an embodiment of two parallel modules according to the embodiment of FIG. 1 of a device for removing combustion engine generated soot particles according to the invention and
• 5 shows a cross section on a reduced scale along the section AB according to FIG. 4.

In Fig. 1, a flowed through by the exhaust module 1 is shown, are arranged in the metal foams 2, 3 alternately one behind the other. The metal foams are alternately coated or uncoated with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals. The coated metal foams 2 are each arranged upstream of the uncoated metal foams 3 in the exhaust gas flow, which capture each of the soot particles temporarily.

Another arrangement of the metal foams 2, 3, i. the insertion of the uncoated metal foams 3 in each case upstream of the coated metal foams 2 in the exhaust gas flow is not the subject of the invention.

Fig. 2, not the subject of the invention, shows the module 1, are arranged in the only coated with precious metal foams 2, which capture even soot particles temporarily.

The embodiment of FIG. 3 shows the module 1, in which metal foams coated alternately with precious metal 2 and with a metal foams 4 coated with the combustion temperature of soot particles are arranged. In this case, the respective noble metal-coated metal foams 2 upstream of the coated with a combustion temperature of soot particles reducing compound metal foams 4 are mounted in the exhaust gas flow, each capture the soot particles temporarily.

Another arrangement of the metal foams 2, 4, ie, the insertion of the metal foams 4 coated with a compound which reduces the combustion temperature of soot particles, upstream of the respective ones noble metal coated metal foams 2 in exhaust gas flow is not the subject of the invention.

In the embodiment thus formed, the trapped soot is additionally oxidized by direct contact with the superficially applied coating acting as a catalyst. The applied coating consists of an oxygen storage compound, such as cerium orthovanadate Ce (III) VO ₄ .

FIG. 4 shows a further exemplary embodiment with an overall module 5, which is constructed from two parallel modules 1 'according to the exemplary embodiment according to FIG. 1, but in which the conically tapered inlet region for the exhaust gas and the conically tapered outlet region for the exhaust gas In such an embodiment, the exhaust gas flows through the modules 1 'arranged in parallel, as indicated in connection with FIG. 1. The metal foams 2, 3 are alternately coated or uncoated with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals. Advantageously, the coated metal foams 2 are each arranged upstream of the uncoated metal foams 3 in exhaust gas flow.

Another arrangement of the metal foams 2, 3, i. the insertion of the uncoated metal foams 3 in each case upstream of the coated metal foams 2 in the exhaust gas flow is not the subject of the invention.

Furthermore, not only two parallel modules 1 'in the entire module 5 are provided, but in accordance with the requirements are also several modules 1' in the overall module 5 to increase the efficiency to accommodate in an advantageous manner.

5 shows a cross section through the total module 5 shown in FIG. 4 along the section line A-B, wherein in each case a module 1 'is arranged parallel to the exhaust gas flow and flows through the exhaust gas.

The parallel arrangement and the number of modules 1 'in the overall module 5 can be adapted almost arbitrarily to the respective engine power. In this case, the required efficiency with regard to the removal of soot particles from the combustion engine generated exhaust gas flow advantageously be taken into account, by the type of precious metal coating or precious metal loading, the geometric surface of the metal foam and the number of coated metal foams.

For example, emissions reductions for soot particles of approx. 85% to 90% could be achieved without exceeding the required permissible nitrogen dioxide limit values.

In addition, the efficiency for the reduction of the soot particle emission by a thermally induced regeneration can be further increased, as can be achieved for example with a burner or an electrical energy input by a resistance heating.

The thermally induced regeneration can also take place by oxidation of late injected into the internal combustion engine fuel, a so-called post-injection, through which the exhaust gas temperature can first be raised from about 150 to 200 ° C to about 400 ° C.

In addition, it is possible by oxidation of engine-sustainably produced hydrocarbons (CH) on the noble metal-coated metal foam or oxidation catalyst to increase the temperature in the module by about 200 ° C to finally the required for soot particle temperature of about 600 ° C.

Claims (18)

1. An apparatus for removing soot particles from an exhaust gas stream of an internal combustion engine in a module (1) by oxidation of the soot particles with nitrogen dioxide NO₂, said carbon particles being temporarily trapped in an uncoated metal foam (3) or coated metal foam (4), wherein the nitrogen dioxide is generated by oxidation of the nitrogen oxide NO available in the exhaust gas on an upstream noble-metal-coated and open-pored metal foam (2) in relation to the flow velocity of the exhaust gas at a temperature of greater than approx. 200° C, characterized in that at least two noble-metal-coated, open-pored metal foams (2) are provided, which are respectively disposed upstream of an uncoated metal foam (3) or respectively disposed upstream of a coated metal foam (4), with the metal foams (2, 3, 4) being arranged adjacent to one another.
2. The device according to claim 1, characterized in that the metal foams (2, 3, 4) are comprised of an FeCr alloy.
3. The device according to claim 1 or 2, characterized in that the noble-metal-coated open-pored metal foam (2) is coated at least with a noble metal of the group Ru, Rh, Pd, Os, Ir, Pt, or a mixture of such noble metals.
4. The device according to one of claims 1 to 3, characterized in that the coated metal foam (4) is coated with a compound that reduces the combustion temperature of the soot particles.
5. The device according to claim 4, characterized in that the coated metal foam (4) is coated with a compound comprising cerium orthovanadate (CeVO₄), which reduces the combustion temperature of soot particles.
6. The device according to one of claims 1 to 5, characterized in that the module (1) is embodied as open, self-regenerating module.
7. The device according to one of claims 1 to 6, characterized in that the metal foams (2, 3, 4) are produced by a powder sintering process or a precision casting process.
8. The device according to one of claims 1 to 7, characterized in that the metal foams (2, 3, 4) are embodied with an irregular cell geometry which causes a 3D through-flow and has a mixing function.
9. The device according to one of claims 1 to 8, characterized in that the metal foams (2, 3, 4) are embodied with a relative density in the range of from 2 to 20 %.
10. The device according to one of claims 1 to 9, characterized in that the metal foams (2, 3, 4) are embodied with a pore count in the range of from 3 to 80 ppi.
11. The device according to one of claims 1 to 10, characterized in that noble-metal-coated open-pored metal foam (2) is coated directly, or by impregnation of a wash-coat, with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt, or a mixture of these noble metals, in a concentration of 1.0 g - 2.5 g noble metal per liter of metal foam.
12. The device according to claim 5, characterized in that the compound cerium orthovanadate, which reduces the combustion temperature of the soot particles, is applied on the coated metal foam (4) via a plasma process, a wash-coat process or a sol-gel process in a concentration of 1.0 g - 25 g CeVO₄ per liter of metal foam.
13. The device according to one of claims 1 to 12, characterized in that the number of pores of the metal foams (2, 3, 4) varies in the direction of the exhaust gas stream.
14. The device according to claim 13, characterized in that the number of pores of the metal foams (2, 3, 4) increases in the direction of the exhaust gas flow.
15. The device according to one of claims 1 to 14, characterized in that the metal foams (2, 3, 4) are firmly embedded into the metallic module (1) via a soldering process.
16. The device according to one of claims 1 to 15, characterized in that the metal foams (2, 3, 4) are embedded with a support mat into the metallic module (1).
17. The device according to claim 1, characterized in that a modular assembly (5) is comprised of a plurality of modules (1) of similar type or a plurality of modules of different type.
18. The device according to claim 17, characterized in that the plurality of modules (1) of similar type or the plurality of modules of different type are disposed in the modular assembly (5) parallel to the exhaust gas stream.

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