WO2009144261A1 - Filter device for removing particles from a gas stream - Google Patents

Abstract

The invention relates to a filter device for removing particles from a gas stream, especially of particles from an exhaust gas stream of an internal combustion engine, comprising a filter element, said filter element consisting of an aluminum titanate to which a mineral phase is added. Said mineral phase consists of alkali feldspars and mullite and/or spinels and/or zirconium titanate.

Description

 description

Filter device for removing particles from a gas stream

Technical area

The invention generally relates to a filter device for the removal of

Particles from a gas stream. In particular, the invention relates to a

Such filter device for removing soot particles from a Ab¬

Gas flow of an internal combustion engine. More specifically, the invention relates

Such a filter device based on aluminum titanate.

Such filters are for example in the exhaust aftertreatment

self-igniting internal combustion engines, especially in die¬

self-propelled motor vehicles used. Usually, such Fil¬

made of a ceramic material, for example cordierite or silicon

Carbide manufactured. Cordierite ceramic bodies are used in

a variety of high-temperature applications, such as kata-

lytic converters, NO _x adsorbers, electrically heated catalysts,

chemical process substrates and diesel particle filters.

In the filtration of diesel exhaust was cordierite as cost

Material that auf¬ a low thermal expansion coefficient

shows, long the material of choice. Porous cordierite ceramic filters were used

in the form of Wandflussfiltern since the early 80s for removal

used by particles in the exhaust stream of diesel engines. Wandflussfilter usually have a cylindrical shape with two end faces and a lateral surface and are traversed by the first end face to the second end face of a plurality of lying substantially parallel to the cylinder axis flow channels for the exhaust gases of diesel engines. The cross-sectional shape of the wall flow filter depends on the installation requirements of the motor vehicle. Widely used are filter bodies with a round, elliptical or triangular cross-section. The flow channels usually have a square or hexagonal cross section and are arranged in a narrow grid over the entire cross section of the filter body.

A diesel particulate filter (DPF) ideally combines a low coefficient of thermal expansion, low pressure drop, high strength, and low cost. Problems that may arise with the use of cordierite include both low volumetric heat capacity and low thermal conductivity, which can result in unacceptably high temperatures or temperature peaks during operation, as well as low thermal stability. Furthermore, inorganic particulates present in the diesel exhaust may react with the cordierite and cause filter failures.

An alternative material to cordierite in the manufacture of diesel particulate filters is silicon carbide (SiC). Although this material has both a high volumetric heat capacity and a high thermal conductivity has ability, it has, as a result of a relatively high heat Aus¬

Elongation and a high modulus of elasticity also a bad Tempe¬

raturwechselbeständigkeit. This makes it necessary to segregate SiC filters

to prevent failures during use. Also resultie¬

the processing requirements (i.e., high temperatures, inertness)

atmosphere and segmentation) in high production costs.

[0007] Ceramic filter elements based on aluminum have recently been used.

umtitanat become known, the appropriate properties for use

at high temperatures, e.g. Vehicle exhaust control and Diesel¬

exhaust aftertreatment systems such as DPFs have. aluminum titanate

is the stoichiometric mixed phase of alumina and titania.

It is characterized by a low thermal conductivity, a very

low coefficient of thermal expansion and related

very high thermal shock resistance.

State of the art

From DE 602 17 084 T2 is a honeycomb structure having a plurality of Wa¬

bensegmenten known, which are connected to a unitary body. The

Main component of each of the honeycomb segments comprises at least one of

Silicon carbide, silicon nitride, cordierite, alumina, molybdenum, zirconium di¬

oxide, zirconium phosphate, aluminum titanate, titanium dioxide and Kombinatio¬

of it. DE 10 2006 040 739 A1 discloses a filter for removing particles from a gas stream, in particular soot particles from an exhaust stream of an internal combustion engine, with a filter body of a ceramic filter substrate, wherein the filter substrate is coated with a porous protective layer of a coating material , The coating material is selected from the group consisting of aluminum oxides, aluminum hydroxide, titanium dioxide, silicon dioxide, zirconium oxide, cerium oxide, aluminum silicates, magnesium aluminum silicates, cordierite, mullite, silicon carbide, aluminum titanate, zeolites, quartz, glasses, mixtures and mixed oxides thereof.

Finally, WO 2005/046840 discloses a ceramic body for use as a DPF having a composition comprising: 8 (Al ₂ O ₃ TiO ₂ ) + b (CaO Al ₂ O ₃ -2SiO ₂ ) + c (SrO Al ₂ O ₃ -2SiO ₂ ) + d (BaO Al ₂ O ₃ -2SiO ₂ ) + e (3Al ₂ O ₃ -2SiO ₂ ) + f (Al ₂ O ₃ ) + g (SiO ₂ ) + In (Fe ₂ O ₃ TiO ₂ ) + i (MgO-2TiO ₂ ), where a, b, c, d, e, f, g, h, and i represent weight fractions of each component such that (a + b + c + d + e + f + g + h + i) = 1, and the following conditions are satisfied 0.5 <a <0.95; 0 ≤ b ≤ 0.5; 0 <c <0.5; 0 <d <0.5; 0 <e <0.5; 0 <f <0.5; 0 <g <0.1; 0 <h <0.3; 0 <i <0.3; b + d> 0.01. This is a mixture of aluminum titanate and a glass phase in an amount of> 5 wt .-%, wherein the glasses are those of alkaline earths, alkalis, silica, alumina, alkali and alkaline earth glasses. Furthermore the mixture contains a mineral phase, such as barium, calcium and

Strontium feldspars and optional mullite. Disadvantages of barium, calcium

and strontium feldspars lie in the high sintering temperature and the

difficult processability. Calcium and in particular Bariumverbin¬

compounds are very irritating, strontium compounds are weak radioak¬

tively.

The invention is based on the object, a filter for the removal of

Particles from a gas stream, in particular a diesel particulate filter on

the base of aluminum titanate to provide that at higher Tempe¬

can be used, and in which a better influence of Mate¬

rialeigenschaften is possible and the structural properties well adjustable

are. Further tasks are to provide a higher mecha¬

niche strength and lower thermal expansion.

Disclosure of the invention

The present invention solves this problem by providing a

Filters for removing particles from a gas stream, in particular

of particles from an exhaust gas stream of an internal combustion engine,

the filter consisting of aluminum titanate, to which a mineral phase zu¬

and the mineral phase of alkali feldspar and mullite

and / or spinels and / or zirconium titanate. Optionally, the Fil¬

In addition, a glass phase of

Contain <5 wt .-%. Brief description of the drawings

The single FIGURE shows a schematic representation of a Verbren¬

combustion engine with a filter device according to the invention.

Embodiment (s) of the invention

The figure shows a schematic representation of a Verbrennungskraft¬

Machine with a filter device according to the invention. The burners

combustion engine 10 is connected via an exhaust pipe 12, in which the

Filter device 14 according to the invention is arranged. With the filter inlet

Direction 14 soot particles from the flowing in the exhaust pipe 12

Exhaust filtered out. This is especially in diesel engines er¬

necessary to comply with legal requirements. It is hin¬

assign that the filter device according to the invention not on Ver¬

is limited as DPF, but quite generally as Heißgasfil¬

ter, for example. In industrial plants, can be used.

The filter device 14 includes in the embodiment shown a zy¬

cylindrical housing 16, in which, for example, a rotationally symmetric, insge¬

including cylindrical filter element 18 is arranged. Other Ge

housing forms are also possible. The filter element 18 consists of A-

aluminum titanate to which a mineral phase is added consisting of alkali metal

late and / or spinels.

So far, diesel particulate filters based on aluminum titanate have been used

Finally, calcium, barium and strontium feldspars as additional

Phases and a glass phase in an amount of> 5 wt .-% used. The feldspars used according to the invention offer more suitable material properties with regard to the thermal expansion behavior and the service life of the filter. At the same time, only very small amounts of glass phase are present in the microstructure (<5% by weight), which leads to a significantly improved thermal expansion behavior. The heat capacity can be influenced by this combination of raw materials. From the feldspars used, it is possible to generate different mineral phases, which is not possible with the conventional barium, calcium and strontium feldspars. These are supplied as individual components (barium, calcium, strontium compounds, Al 2 O 3 and SiO 2 or other Al 2 O 3 or SiO 2 -containing compounds), usually as oxides or carbonates, and then react during sintering to the feldspars. In the case of the lithium, sodium and potassium feldspars according to the invention, this reaction does not take place from the individual components. It is possible to use feldspars directly or to use individual components which are sintered via the intermediate step of a glass phase to the required mineral phases. This variant offers the possibility of selectively adjusting microstructures and material properties, since the ratio glass phase; resulting mineral phase, as well as mineral, mineral composition and thus properties such as thermal expansion in a range of 0-2 x 10 " ⁶ Km" ¹ or the heat capacity can be changed. Spinels improve the mechanical properties especially of the strength. Aluminum titanate spinel materials are suitable for use at very high temperatures. In addition, specific structural properties can be influenced. Spinels have a high mechanical strength as materials. By suitable sintering conditions, the spinel can increase the strength in other materials as an additive. This is done by adjusting the sintering conditions, which generates the growth of crystal needles. This in turn leads to a felting of the structure, which can increase the strength.

In a first embodiment, the filter element has the following composition: 35-90% by weight of aluminum titanate; 1-60 wt .-% mineral phase The mineral phase consists of one or more of the following substances in the indicated proportions: 10-80% by weight of MuMt; 0-80% by weight of zirconium titanate; 0-50 wt% alkali feldspars and 0-80 wt% spinels.

In a second embodiment, the filter element may additionally have a glass phase in an amount of <5 wt .-%

The feldspars present invention are selected from the group consisting of lithium, sodium, potassium feldspar. In addition, the filter element may contain zirconium titanate.

The microstructure may also contain two or more mineral phases. In this case, can be dispensed with the glass phase. Are mineral used, which stabilize the entire ATi microstructure and at the same time have low thermal expansion, it can be completely dispensed with the glass phase, as this would be a disadvantage for the structure due to higher thermal expansion. The filter device according to the invention consists of a temperature-resistant material and is therefore suitable for use as a diesel particulate filter. By selecting the mineral phase according to the invention, the material properties can be better influenced and the microstructural properties adjusted better. The filter device according to the invention shows a good thermal shock resistance and a low thermal expansion.

Claims

claims 1. Filter device (14) for removing particles from a gas stream, in particular of particles from an exhaust gas stream of an internal combustion engine, with a filter element (18), wherein the filter element consists of aluminum tantate, to which a mineral phase is added, characterized in that the Mineral phase consists of Alkalifeldspäten and MuIMt and / or spinels and / or zirconium titanate. 2. Filter device according to claim 1, characterized in that the filter element additionally contains a glass phase. 3. Filter device according to claim 2, characterized in that the glass phase in an amount of <5 wt .-% is present. 4. Filter device according to one of claims 1 to 3, characterized in that the Alkalifeldspäte are selected from the group consisting of lithium, sodium, potassium feldspar. 5. Filter device according to one of claims 1 to 3, characterized in that the filter element contains zirconium titanate. 6. Filter device according to claim 1, characterized in that the filter element contains two or more mineral phases. 7. Filter device according to claim 1, characterized in that the filter element has the following composition: 35-90 wt .-% Aluminiumtita- Nat; 1-60 wt .-% mineral phase. 8. Filter device according to claim 7, characterized in that the mineral phase consists of one or more of the following substances: 10-80 wt .-% MuMt; 0-80% by weight of zirconium titanate; 0-50 wt% alkali feldspars and 0-80 wt% spinels. 9. diesel particulate filter, consisting of a honeycomb-shaped filter element (18) with mutually closed flow channels, characterized in that the filter element consists of aluminum titanate to which a mineral phase is added and that the mineral phase consists of Alkalifeldspäten and / or spinels. 10. Diesel particulate filter according to claim 9, characterized in that the filter element (18) has a composition according to one of claims 1 to 8.